complex World - Forschungsverbund Berlin

Transcription

ALMANAC 2016
verbundjournal
Science in a
complex
The perfect crystal
for the new kilogram �� 24
World
Knut’s mysterious death
finally solved ��28
Quantum dots with
single-atom precision��38
2 SCIENCE COMPACT
Editorial
verbundjournal
Almanac 2016
Content
SCIENCE COMPACT
Dear Reader,
More than a quarter of a century ago,
the Wall that had divided Germany
into two states fell. In the wake of the
Unification Treaty of 1990, the Academy of Sciences of the German Democratic Republic was wound down, and
the 59 individual institutes that belonged to it were evaluated. It was a
“politically sensitive task that was often onerous for both sides, considering
personal aspects,” as Professor Dieter
Simon, Chairman of the German Council of Science and Humanities at the
time, later wrote self-critically. Western
structures were “imposed” on the institutes from the East under intense
pressure to take action. Even so, only
six GDR institutes were closed down
following the evaluation; the rest, for
the most part, were integrated into the
Fraunhofer-Gesellschaft and the Leibniz Association.
The Forschungsverbund Berlin was a
completely new concept that many regarded with misgivings, reminisced Jürgen Schlegel, who was General Secretary of the Bund-Länder Commission
for Educational Planning and Research
Promotion from 1990 to 2007. Eight
scientifically independent institutes
joined forces at the end of 1991 in a bid
to work more efficiently from 1992 under the umbrella of a Joint Administration. The experiment was a success – in
2017 we will be celebrating the 25th
anniversary of Forschungsverbund Berlin e.V. Today, scientists from our institutes are among the best in the world.
We are pleased to present their work in
this edition of the “Verbundjournal” in
English for the first time.
We hope you enjoy reading our “Almanac 2016”!
Best wishes,
Gesine Wiemer and Karl-Heinz Karisch
Newsflash�� 3
Directors’ column: Excellence cannot simply be dictated
by Prof. Klement Tockner�� 6
COMMENTS
“Citizen Science has the potential
to strengthen research on a
sustainable basis,” says
Prof. Johanna Wanka. Page 7 »
Guest commentary by Prof. Johanna Wanka, German Federal Minister of
Education and Research: Citizen Science – a passion for research�� 7
Guest commentary by Prof. Matthias Kleiner, President of the
Leibniz Association: The big pieces in science are symphonies�� 8
SCIENCE IN FOCUS
"In structural biology in particular, the equipment
available plays a crucial role in enabling scientific
breakthroughs,” says Prof. Volker Haucke,
Managing Director of the FMP. Page 9 »
That's excellent: Institutes of FVB belong to the
world’s top league of science�� 9
Ferdinand-Braun-Institut, Leibniz-Institut fuer
Hoechstfrequenztechnik (FBH)
How general is the General Theory of Relativity? �� 11
Using clever tricks to get the perfect crystal �� 12
Fast switching – thanks to HiPoSwitch�� 14
Leibniz-Institut für Molekulare Pharmakologie (FMP)
Pressure relief valve in cellular membrane identified�� 16
A synaptic governess �� 18
Magnetic resonance imaging in colour�� 19
Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB)
Loss of the night�� 20
International master program educates fish experts�� 21
Joining forces to help prehistoric giants �� 22
European freshwaters at a click�� 23
verbundjournal
Almanac 2016
Leibniz Institute for Crystal Growth (IKZ)
The perfect crystal for the new kilogram �� 24
Among crystal spheres�� 25
Electron microscope helps grow perfect crystals �� 26
Leibniz Institute for Zoo and Wildlife Research (IZW)
Mystery of polar bear Knut’s disease finally solved �� 28
Bats versus wind turbines �� 30
Tracking wild animals with GPS�� 31
Max Born Institute for Nonlinear Optics and
Short Pulse Spectroscopy (MBI)
Einstein and the Electron �� 32
Clocking the motions of water on the surface of the DNA double helix�� 34
The world’s first photos of electron clouds �� 35
A new approach towards solving mysteries of the interstellar medium�� 36
Paul-Drude-Institut für Festkörperelektronik (PDI)
Quantum dots with single-atom precision�� 38
A molecule transistor for the quantum world�� 39
Watching crystals grow�� 40
Weierstrass Institute for Applied Analysis and Stochastics (WIAS)
Bose gave Einstein an idea�� 42
Realistic and fictional worlds on the computer �� 44
Many cooks improve the broth�� 45
My PhD thesis
MBI: Preventing the disaster in high-power lasers�� 46
IGB: Deceptive manoeuvres in mate choice�� 48
INSIGHT FORSCHUNGSVERBUND
"The Forschungsverbund can be a great deal
more than simply an administration.
We would like to use it as a strategic instrument,"
says Prof. Marc Vrakking. Page 50 »
Interview with Prof. Marc Vrakking, Chair FVB Board of Directors:
“Our institutes conduct research at a very high level”�� 50
Tailored technologies�� 52
Long Night of the Sciences �� 55
PDI initiates Berlin’s new science and art festival�� 56
Karl Weierstrass and the Golden Age of Mathematics�� 57
Welcome to Germany�� 58
News from the Leibniz Association�� 59
Neighbourly relations: TRUMPF�� 59
SCIENCE COMPACT 3
4 SCIENCE COMPACT
verbundjournal
Almanac 2016
Newsflash
Two precision experiments in
space with lasers from Berlin
Fiber-coupled
r ubidium module
for FOKUS experiment in space.
The Ferdinand-Braun-Institut (FBH) and
the Humboldt Universität zu Berlin (HU)
test modern laser technologies within
the framework of the projects KALEXUS
and FOKUS. The projects
were successfully
carried out on
board the German Aerospace
Center’s sounding
rocket TEXUS-53 in
microgravity, on January 23, 2016. The
demanding technology
demonstrators lay the foundations for the precision
tests of the equivalence
principle with so-called potassium and rubidium atom
interferometers as well as for further
experiments aiming at tests of Einstein’s
theory of relativity. The centrepiece of
the KALEXUS project consists of two micro integrated semiconductor laser modules developed by FBH. The wavelength
of these laser modules is matched to an
atomic transition of potassium. During
the six-minute period of microgravity the
experiment automatically stabilizes the
wavelength of both lasers. Another laser
module designed by FBH and assembled
by HU took part in the FOKUS campaign. The laser system was stabilized
to an atomic transition of rubidium and
also allows for clock comparisons. Here,
the frequency of an “optical oscillator”,
the laser, is compared to the frequency
of a quartz oscillator that “ticks” in the
radio frequency range, like a modern
Accumulation of integrin (red), an important component of
muscles, in vesicles (green) from cells without MTM1 (right images including magnified view) or from control cells (left images
including magnified view).
wristwatch. Both laser experiments use
different types of lasers from the FBH.
This allows a comparison of the different
laser technologies for the application
scenario. (see also page 11)
IGB
Collective intelligence helps to
improve breast cancer diagnosis
FMP
Muscle weakness: Berlin
scientists unravel defects in rare
hereditary disease
Researchers have discovered why cells
from patients suffering from the muscular
disease myotubular myopathy cannot
function properly. The study shows how
a dynamic cellular process essential to
muscle development and function is
regulated by means of minute changes
of certain membrane lipids. Children with
myotubular myopathy, the most severe
form of centronuclear myopathies (also
called XLCNM), might not survive their
first months of life. The research group
led by Prof. Volker Haucke from the Leibniz-Institut für Molekulare Pharmakologie
(FMP) has found out what goes wrong
in this disease at the molecular level.
Phosphates are used by the cell to tag its
compartments and to regulate the transport of substances. If a phosphate group
tags a certain position, it is clear that a
transport container is supposed to be
transported into the interior of the cell; if
the phosphate tag is different, it migrates
to the outer cell membrane, docks there
and unloads its freight to the outside.
This kind of transport comes to a halt in
XLCNM patients. The cause is a defect
in the gene MTM1. In XLCNM patients,
some of the transport containers that were
originally supposed to convey proteins to
the cell surface get stranded inside the cell.
In muscles, this may mean that proteins
necessary for their formation, integrity and
function do not get to the right place in
the cell. In cell culture experiments, FMP
researchers could restart the transport
with a certain active substance. It might
be a starting point for the development of
drugs for treating this severe and currently
incurable hereditary disease.
Nature (2016); DOI: 10.1038/nature16516
Breast cancer is the most frequent type
of cancer in women. Wide-ranging
mammography screening programs
have been set up for early diagnosis.
However, even if two physicians assess
the x-rays, which is the usual procedure
in Europe, this often leads to wrong decisions. A new study shows that swarm
intelligence can help to considerably
improve cancer diagnosis. “Already five
independent assessments of physicians
lead to better results,” says Dr Max Wolf
from the Leibniz Institute of Freshwater
Ecology and Inland Fisheries (IGB),
leader of the study. The behavioural
biologist, together with his interdisciplinary research team, wanted to find
out whether collective intelligence can
be employed to improve breast cancer
screening. Therefore, one of the largest
international mammography datasets
was used. It includes a large number
of mammograms and for each of them
the independent assessment of about
one hundred radiologists as well as the
actual health status (cancer yes or no)
of all patients. The result: already five
independent assessments can be used
to outperform the diagnostic accuracy
of even the best physician within that
group. The procedure is very simple and
could easily be automated and integrated into the screening program. “When it
comes to improving diagnostic accuracy,
the first impulse is often to improve
technology. We believe, however, that a
collective intelligence approach has the
potential to improve diagnostic accuracy
in a wide range of medical decision making contexts,“ concludes Max Wolf.
PLOS ONE 10 (2015); DOI: 10.1371/
journal.pone.0134269
Pictures: FBH/P. Immerz; Image: Katharina Ketel/FMP; Rainer Sturm/pixelio.de
FBH
verbundjournal
IZW
Fewer tiger subspecies – better
protection?
New scientific research could help to
protect tigers (Panthera tigris) from
extinction. A study led by scientists at
the Leibniz Institute for Zoo and Wildlife
Research (IZW), suggests that instead
of nine subspecies of tiger, there are
only two. The new classification will
have a significant impact on species
conservation as from now management
efforts and breeding programmes can be
organised in a more effective way. The
research group investigated differences
between six living and three extinct tiger
subspecies. They compared the morphology of more than 200 skulls and the
colouration and stripe patterns of more
than 100 skins with molecular genetic
data and ecological and life history traits.
The conclusion: Most of these subspecies were much more similar to each
other than previously known. Only two
subspecies could be clearly distinguished:
The “Sunda tiger” (P. tigris sondaica),
formerly from Sumatra, Java and Bali and
the “Continental tiger” (P. tigris tigris,
Amur tiger) from mainland Asia.
“A classification into too many subspecies – with weak or even no scientific
support – reduces the scope of action for
breeding or rehabilitation programmes,”
explained Dr Andreas Wilting from IZW.
The new study provides the scientific
basis for practical and effective tiger
conservation.
Science Advances 1 (2015); DOI:
10.1126/sciadv.1400175
Picture: P. Christansen; Images: MBI/B. Schütte; PDI
SCIENCE COMPACT 5
Almanac 2016
MBI
Energy exchange in highly
ionized nanoparticles
Excited atoms often decay via the emission of radiation, a process that is known
as fluorescence. A different scenario
can emerge when an excited atom is
surrounded by other excited atoms, ions
and electrons. Such a situation is achieved
when an intense laser pulse interacts
with a nanoscale object. In this case, an
excited atom can decay by transferring
its excess energy to another particle in
the environment. Researchers from the
Max-Born-Institut in Berlin, the University of Rostock, and the University of
Heidelberg found evidence for such an
energy exchange involving electrons that
are trapped within a nanocluster. They
observed a so far unidentified peak in the
electron spectrum following the ionization
of a nanocluster by a near-infrared (NIR)
laser pulse. The researchers attributed this
signal to the relaxation of one electron
from an excited Rydberg atom and the
simultaneous transfer of the excess energy to a second electron that can escape
from the cluster. The obtained results are
of universal nature and are expected to
play an important role in other nanoscale
systems including biomolecules.
Nature Communications 6 (2015); DOI:
10.1038/ncomms9596
PDI
A viable route towards the
large-scale fabrication of bilayer
graphene nanostructures
Scaling graphene down to nanoribbons
is the most promising route for implementing this material in devices. Bilayer
graphene nanoribbons (GNRs) are of
special interest, as they are expected to
combine the structurally and dimensionally dependent electronic properties of a
GNR (for example
quantum confinement of charge
carriers), with the
unusual features of
bilayer graphene,
such as its elecAtomic force
tric-ﬁeld-tunable
microscopy phase
band gap. Hence,
contrast image
direct synthesis of
taken from a
bilayer GNRs on an
sample containing
insulating template, 320 nm wide
by a method that
bilayer graphene
allows control of
nanoribbons.
dimensions and
edge structures, would be extremely
advantageous not only for fundamental
investigations of the pristine properties of these nanostructures but also
for applications. A research team from
the Paul-Drude-Institut für Festkörper
elektronik (PDI) demonstrated a novel
approach for the fabrication of isolated
bilayer GNRs on silicon carbide surfaces
(SiC (0001)). It is based on the precise
control of the layer-by-layer growth of
graphene via Si surface sublimation and
a simple annealing step in air. With this
method, the researchers are able to prepare μm-long bilayer GNRs exclusively
over step edge regions of a SiC surface.
The lateral width of the nanoribbons can
be varied by changing either the temperature or time during growth. The present
results open a new perspective on the
tailored fabrication of bilayer graphene
nanostructures for different applications
in nanoelectronics.
Nature Communications 6 (2015); DOI:
10.1038/ncomms8632
6 SCIENCE COMPACT
verbundjournal
Almanac 2016
Directors’ column
Excellence cannot simply be dictated
The Leibniz Institutes that make up the Forschungsverbund Berlin (FVB) consider scientific excellence the primary criterion that justifies public funding. Excellence means that an institute is among the top research facilities worldwide
in its domain. While scientific excellence can be assessed by a combination of
peer evaluation and quantitative indicators (i.e., third-party income, number
of doctoral candidates, and especially bibliometrics), relevance has to be based
on argument.
Excellence and innovation, however, cannot be dictated. What are the key elements for the sustained success of a research institute? It is evident that
highly talented employees, adequate resources, a professional administration
and a participatory organisational structure are prerequisites for success. Furthermore, there are four fundamental attributes that most successful research
institutes have: (i) robust and flexible governance structures are established,
(ii) a continuous quality management strategy is in place, (iii) resources are
shared and synergies are fully exploited, and (iv) the institute has a clear international focus. These attributes are key in creating and retaining excellence.
The scientific landscape undergoes constant reshaping. Greater support will
be given to individuals rather than projects and institutions in the future; innovative cooperation models that transcend disciplinary, institutional, and political boundaries are required, and professional outreach activities will become
more and more relevant because research institutions must demonstrate their
societal relevance as well as scientific excellence. The FVB’s institutes are already excellently positioned in many fields – as such, they are capable, and
willing, to set standards in research and application, and to experience innovative and alternative ways of research collaboration.
Professor Klement Tockner
Director of the Leibniz Institute of
Freshwater Ecology and Inland Fisheries (IGB)
WIAS
Mathematics meets Materials
Science
The MIMESIS-Project has been started
at the Weierstrass Institute for Applied
Analysis and Stochastics (WIAS, Germany). It is a European Industrial Doctorate
project and part of Marie Skłodowska
Curie Actions within the Horizon 2020
programme. The research is focussed on
three major topics – induction heating,
phase transformations in steel alloys, and
gas stirring in a steelmaking ladle.
A successful treatment of the projects requires an understanding of the behaviour
of the materials from a materials science
and phase transformations perspective.
Improved and optimized process control
necessitates quantitative mathematical
modelling, simulation and optimization of the complex thermal cycles and
thermal gradients experienced by the
processed material.
“With MIMESIS we connect not only the
disciplines of mathematics and material
sciences, but also different countries and
as well science and industry,” says project coordinator Prof. Dietmar Hömberg
from WIAS.
For further information please visit:
www.mimesis-eid.eu (MIMESIS:
“Mathematics and Materials Science for
Steel Production and Manufacturing”)
Surface hardening of steel:
these processes can be simulated on
computers.
Pictures: Andy Küchenmeister; IWT Bremen
Science and research underpin
our prosperity. Indeed, science is
a large, complex network consisting of institutions, people, infrastructure, knowledge and outputs, with an increasing shift of
innovation centres towards East
and South Asia. Science is a
global enterprise. Investments in
research and development are
increasing at an annual rate of
more than 5 per cent, amounting
to US$ 1.5 trillion in 2013, which
corresponds roughly to the global military expenditure. Seven
million scientists publish about
two million research articles in
more than 30,000 journals each
year, creating the need to evaluate science in order to separate
the wheat from the chaff.
verbundjournal
COMMENTS 7
Almanac 2016
GUEST ART ICLE
Citizen Science – a passion
for research
BY
PROF ESSOR JOHANNA WANKA ,
th e Germ an Federal Minister of Education and Research
Picture: Steffen Kugler / The Federal Government
T
housands of people are involved: in Germany, ever more
ordinary citizens are actively supporting the work of scientists. All
over the country people collect
mosquitoes and send them to researchers who are preparing a
mosquito atlas ("Mückenatlas"),
for example. Astronomy aficionados observe the night sky and classify celestial bodies. And other volunteers keep an eye out for wild
boar, foxes and hedgehogs when
they are out walking in and around
Berlin. If they see any animals they
report the sightings to the Leibniz
Institute for Zoo and Wildlife Research. People who generate
knowledge in this way are becoming ever more important to researchers. The trend towards
greater participation is a major opportunity for science – and a bonus for many volunteers as
well. Citizen Science has the potential to strengthen research on a sustainable basis. Depending on the precise
question being addressed in a research project, citizens
can more or less easily provide important data. Without
their support, researchers would not be able to access the
information so directly.
There is another point I consider important as well: Citizen Science integrates people with an interest in science
into research in a particularly intensive and active way.
There is a growing need in society to join the dialogue on
science and research, or to participate in other ways. The
aim of science communication has long ceased to be simple public understanding of complex themes. Rather, if
communication between science and the public is to succeed, it is now imperative to hold a seriously meant and
seriously taken conversation between scientists and citizens. And Citizen Science is a particularly active form of
participation. People do not just talk about research; they
are involved in concrete projects. Citizen scientists can satisfy their curiosity and hone their grasp of scientific issues.
In many Citizen Science projects volunteers not only collect data, they also receive feedback from the scientists
and can follow the progress of the project. In this way, citi-
zens move closer to science, and
through Citizen Science, science itself takes its place at the heart of
society – which is precisely where
we want it to be.
Contingent on the type of research, participation can be more
extensive. Depending on the question being examined people can be
motivated to share their thoughts
and ideas. It is fascinating to consider to what extent interested
amateurs can participate and
whether it is possible to develop
projects involving citizens with
greater thematic breadth. At present, most projects deal with nature
and the environment. However,
similar initiatives in other thematic areas are also conceivable and
some are already being implemented – take, for example, the
preparation of a language atlas or research for a dictionary
of dialects.
In order to drive Citizen Science in Germany these opportunities to become actively involved in research projects need to be publicised to reach an even larger audience. The Federal Ministry of Education and Research
(BMBF) therefore funded the development and launch of
an online platform as a central contact point for Citizen
Science in Germany. In 2014, the Berlin Natural History
Museum and Wissenschaft im Dialog, an initiative of Germany’s scientific community have implemented the proposal. Whether citizen or scientist – anyone who is interested should be able to receive information on Citizen
Science projects via the portal.
Moreover, we want to support citizens’ research by
strengthening networking amongst all those involved. A
dedicated project with the aim of achieving yet greater understanding of Citizen Science is already under construction. The programme is expected to generate guidelines
defining quality standards for research projects involving
members of the public. We also hope to find new answers
to the question as to how far participation in this field can
be taken. I am very much looking forward to further developments.
8 COMMENTS
verbundjournal
Almanac 2016
GUEST ART ICLE
The big pieces in science
are symphonies
BY
PROFE SSOR M ATTHI AS KLE I NE R
Science – like music – can produce truly breathtaking masterpieces in unison and harmony – in a symphony of many voices. We need soloists to begin a piece, but it is equally
important in science for the orchestra to strike up at just the right moment, to play along,
pose counterpoints and carry sound far across the borders of disciplines and institutional walls.
he Leibniz Association currently unites 88 independent
scientific institutes of different
specialisations and complementary fields of expertise throughout
Germany. It is unique in this
diversity. The broad spectrum of
scientific disciplines unites in the
commitment to pure scientific

knowledge, the inspiration of application, and the imparting of
knowledge and insights from their
research for and in society. These
three aspects are played out at the
Leibniz Institutes, each in its own
way – and I find that wonderful.
If we consider the major future
topics of our society, for example
demographic change, education,
health and, not least important,
our energy supply: All these subjects require a look over the fence
from one scientific discipline to another, and they require
a view beyond the boundaries of science as a whole.
The Leibniz Association is predestined for this comprehensive overview.
The Leibniz Research Alliances address such thematic
areas as “Biodiversity”, “Healthy Ageing”, “Nanosafety” and
“Educational Potentials”. Research can continually regroup
into temporary relationships according to topic and issue,
and in doing so, achieve impressive results.
In many places, partners within the academic system –
such as universities – are an important complement to the
perspectives of the Leibniz Institutes. To promote this synergy of university and non-university research, there are
currently twelve regional partnerships addressing urgent and fundamental matters of research:
these are the Leibniz Science
Campi.
In the Leibniz Association, we
pursue science for the benefit of
humanity. Accordingly, transfer
and explanation of scientific
knowledge takes an important role
in our work. This significant task is
naturally in the character of the
Leibniz research museums. They
equally conduct and reveal their
research to visitors. This transfer
also takes place in a more targeted
sense in exchange not only with
economical companies, but also in
politics, where scientific insights
from all different disciplines often
act as guidelines and motivators.
Science with society for society
leads to an understanding within multiple perspectives.
Science looks around and conducts benefits for all surrounding parties. At the same time, it has to grant transparency within and to its beneficiaries. The public can
even help to conduct science, as our Citizen Science projects already show.
We would therefore do well to “play” together, and to
understand science as a symphony – especially when it
comes to the masterpieces of science and thus of society.
Professor Matthias Kleiner is President of the Leibniz Association, to which the institutes of the Forschungsverbund Berlin e.V. also belong.
Picture: Oliver Lang
T
verbundjournal
SCIENCE IN FOCUS 9
Almanac 2016
KARL-HEIN Z KARISCH AND GESINE WIEMER
That's excellent
Several things must come together before cutting-edge research can occur: excellent
scientists, a good infrastructure and the best equipment. The eight institutes that make
up Forschungsverbund Berlin e.V. belong to the world’s top league of science, as evaluations in recent years and the multitude of publications in international high-impact
journals show.
Picture: Uwe Bellhäuser
T
here are areas in which better-quality equipment results in a scientific lead,” stated Professor Thomas
Elsässer, Managing Director of Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin,
Germany. In physics, for example, it would not be possible
to conduct certain experiments without the necessary devices. Examples mentioned by Elsässer include the
free-electron laser at Stanford and the X-ray laser European XFEL, which is being created in Hamburg. Both of these
devices are, of course, unique to the world. MBI constructed the photocathode laser for Hamburg’s free-electron lasers FLASH and XFEL, which are monitored and controlled
from Berlin.
“Beyond large-scale facilities used on the international
arena, unique laboratory-bound equipment plays a key role
at MBI. It goes without saying that a cooperation strategy is
pursued when it comes to the use of the equipment, particularly involving university groups,” reported Elsässer.
“However, we make sure that we secure the scientific priority.” In time-resolved X-ray diffraction, where MBI plays a
leading role internationally, there are cooperative activities
with scientists seeking to investigate structural dynamics.
MBI also cooperates with researchers at major research facilities by sharing beam times. Negotiations are underway
with the photon source BESSY II in Berlin-Adlershof for the
delivery of lasers for a new generation of accelerators.
“In structural biology in particular, the equipment
available plays a crucial role in enabling scientific breakthroughs,” agreed Professor Volker Haucke, Managing Director of the Leibniz-Institut für Molekulare Pharmakologie (FMP) in Berlin-Buch. At FMP, researchers identify and
create new kinds of active substances for medicine, such
as in the treatment of cancer or viral infections. The scientists are also involved in developing so-called mimetics,
which bind to the same receptors as substances produced
by the body, such as hormones.
10 SCIENCE IN FOCUS
verbundjournal
Almanac 2016
With a combination of modern imaging technologies, the biophysicists at the FMP (Leibniz-Institut für Molekulare Pharmakologie) zoom down to atomic details. The elucidation of key
structures of pathogenic microbes generates starting points for
new therapeutics. Adam Lange, researcher of FMP, has analysed
thin filaments on the surface of E. coli bacteria. The visualisation
is a cartoon representation of the structure of a pilus. Shown are
six pilus building blocks viewed from top.
Translation: Teresa Gehrs
Dynamic leap
At the end of the German game show called “Dalli Dalli”,
the audience chose their favourite act. Presenter Hans
Rosenthal leapt up into the air calling: “Das ist Spitze”
(That’s excellent). The 1970s classic hit has made it back to
the TV channel ARD-Das Erste. The show is produced at the
Studio Berlin in Adlershof. It was there, in the vicinity of the
Forschungsverbund Administration, that German Chancellor
Angela Merkel and her contender Peer Steinbrück held their
televised debate. Once again, the electorate decided in favour of a Grand Coalition of Christian Democrats (CDU/
CSU) and Social Democrats (SPD). The first time round,
when Merkel became Chancellor in 2005, special emphasis
was placed on investing in science and research. Since then,
expenditure in this field has increased by around 85 per cent.
With an expenditure of some € 90 billion, Germany managed as early as in 2012 to achieve its goal of spending at
least three per cent of its gross domestic product on research
and development. “That’s excellent,” Research Minister Professor Johanna Wanka could therefore also proclaim. She
stated in the Bundestag that Germany’s innovative capacity
enables it to export the most high-tech products in the world
– more than the USA and more than China. “This is rooted
in research and development and in education.”
Image: Adam Lange/ FMP
»
Scientists are able to gain such insight using cellular and
animal models, nuclear magnetic resonance spectroscopy
(NMR), crystallography and innovative chemistry. “This
means that the structural information we obtain leads to
target structures for pharmacologically active substances.
We want to know how such an active substance binds to
its target protein,” Haucke explained. “An institute such as
FMP is not only a technological pioneer – it also attracts
to our location companies that want to collaborate with
us.”
The Leibniz-Institut für Molekulare Pharmakologie is
one of the largest centres in Europe that conducts NMR
spectroscopic structural research, primarily using biological samples. In particular, FMP specialises in analysing
what are known as solid samples of biological material.
“NMR is a highly complicated method, because biological
molecules are so amazingly large,” reSuch equipment is not ported Haucke. “As a result, they
available off the shelf; demonstrate extremely complicated
spectra.” Images and interpretations
it is planned in of these spectra depend crucially on
cooperation with the how high-frequency the available
manufacturer.« magnetic field is. It is now possible to
construct devices with a performance
of a gigahertz or more, enabling researchers to access
complicated structures. “After all, we are not only interested in individual protein molecules; often we are concerned
with molecular complexes or molecular machines that we
attempt to influence pharmacologically,” Haucke continued.
In the solid state field, FMP is currently regarded as being one of a handful of national NMR centres. To ensure
that it retains its leading position, the researchers require
a more powerful 1.1 gigahertz NMR. Such equipment is
not available off the shelf; it has to be planned and constructed in cooperation with the manufacturer. FMP
gained backing for its plans from the Scientific Advisory
Board as well as from external assessors, who evaluated
the institute very positively. The NMR was defined as the
central investment for the next few years. “The significance of installing this equipment would have an impact
on research well beyond Berlin and Germany,” Haucke
stressed. “We are discussing whether this device can be financed and, if so, from which coffers.”
These experiences are similar to those at the
Paul-Drude-Institut für Festkörperelektronik (PDI) in Berlin: “Some of the equipment we need to conduct our research is not even available for purchase,” stated Professor
Henning Riechert, Director at PDI. “In that case, we look
for a manufacturer who is able to join forces with us to develop the new technology.” In fact, virtually no piece of
equipment at PDI remains unaltered after delivery by the
manufacturer. “We continually refine the technology and
add further components.” PDI’s measuring station at
BESSY, which enables scientists to observe epitaxial
growth at the boundary of materials in real time, was developed by PDI in cooperation with various companies. It
took ten years to develop. “This device enables our researchers to gain unparalleled insight into basic research.
Only a handful of research teams in the world are capable
of doing this,” Riechert stressed. “But this high standard is
due equally to the expertise of our scientists. There is
nothing to be gained from purchasing expensive equipment if it cannot be used properly.”
verbundjournal
FBH · SCIENCE IN FOCUS 11
Almanac 2016
CATARINA PIET SCHMANN
How general is the
General Theory of Relativity?
Be it feathers, apples or bricks: In a vacuum, when there is no more friction and the only
acting force is gravity, all bodies fall at the same rate, or to be more precise, accelerate at
the same rate. Einstein’s General Theory of Relativity, and more specifically the equivalence principle, predicts this, and this rule corresponds to the prevailing worldview of
physics. And yet, there are doubts as to whether it still applies at physical extremes. Experiments using quantum sensors in space should clear this up one day.
Picture: ZARM – University Bremen
O
n a galactic scale, the laws of gravity do not explain
why the universe has turned out the way we know it,”
says Dr Andreas Wicht, Head of the Joint Lab Laser Metrology at the Ferdinand-Braun-Institut, Leibniz-Institut fuer
Hoechstfrequenztechnik (FBH) in Berlin. “And for the microscopic scale, below a hundred micrometres, we have –
up to now – no way of experimentally confirming the law
of gravity applies as we know it.”
Testing the validity of the equivalence principle at the
atomic scale is the aim of the joint project QUANTUS, involving the Universities of Hannover, Hamburg, Ulm,
Mainz, Darmstadt and Bremen as well as HU Berlin and
FBH. “Specifically, we want to know: Do rubidium atoms
fall just as fast as potassium atoms?” Andreas Wicht and
his group at FBH are developing the laser technology platform for a quantum sensor: a so-called atom interferometer, eventually to be used in space.
Free-fall experiments with atoms have been routinely
performed at the laboratory scale since the late 1980s. Yet
the hypothetical differences in the rates of acceleration are
so tiny – in the best case to the tenth decimal place – that
very long measuring times are required to reach the required sensitivity. Such long times can only be achieved in
space. The trouble is, the 2 x 2 metre experimental platforms are too cumbersome to use up there. The German
Aerospace Center (Deutsches Zentrum für Luft- und
Raumfahrt, DLR) has therefore been funding other experiments and related technologies since the mid-1990s. Experiments have been conducted, for example, at the Bremen drop tower, which allows for about four seconds of
free fall in a vacuum tube from a height of a good 100 metres. “Here, it has been demonstrated that the experiment
works in principle. But the measurement duration is still
far too short.”
How does the free-fall experiment work? “The atoms
effectively act as sensors,” Wicht explains. While the atoms
and the overall system are in free fall together, they are in
quasi zero gravity. First, light pulses of a certain frequency
are used to slow down the thermal atomic motion of the
two types of atom, cooling them down towards absolute
zero until they come to a virtual hold. More laser pulses
then manipulate the atoms into states that can only be de-
scribed in quantum physical terms, hence the term “quantum optical sensor”. The effect of the laser pulses, and consequently the measurement carried out with the quantum
optical sensor, depends very sensitively on the frequency
and phase of the light pulses. Were the two types of atom
now to accelerate at different rates, then the frequency
and phase of the light pulses would have to be tuned differently in order to compensate for the different Doppler
shifts of both types of atoms. “This difference, if it exists, is
what we would be measuring,” Wicht summarises.
As a first step, part of the technology required for operation of a space-based atom interferometer has already
been tested in April 2015 onboard of a sounding rocket
(TEXUS 51). A micro-integrated laser module developed by FBH was actively
frequency-stabilized to the
rubidium D2 transition at
780 nm. The frequency of the
laser system was then compared to the frequency of a
stable 10 MHz radio frequency clock by means of a frequency comb. Laser system
and spectroscopy setup were
successfully operated even
during take-off and demonstrated the suitability of the
technologies developed for
application to quantum sensors in space.
Translation: Peter Gregg
The Bremen drop tower at
the Center of Applied Space
Technology and Microgravity
(ZARM) is where zero-gravity
experiments are performed –
albeit for only four seconds at
a time.
12 SCIENCE IN FOCUS · FBH
verbundjournal
Almanac 2016
Gallium nitride
single crystal
produced by
the method of
hydride vapour
phase epitaxy
K ARL-HEINZ K ARISCH
Using clever tricks to get
the perfect crystal
P
rofessor Markus Weyers explains the requirements
for such a crystal: “We need a substrate that, on the
one hand, is transparent to the light I want to generate. On
the other hand, the lattice parameters have to be just right
for my active structure to grow on it without developing
any crystal defects.” The substrate should only have very
few dislocations in the lattice. As Weyers says, “too many
dislocations are luminescence killers.”
Classical crystal growing methods won’t achieve this.
So the FBH scientists opted for the method that yielded
the first blue-emitting laser diodes for Blu-ray players: hydride vapour phase epitaxy (HVPE). It is used to produce
industrial gallium nitride crystals. Unfortunately, the wafers are still limited to maximum 10 centimetres in diameter. Silicon wafers can be much larger, for example, but to
the crystal researchers’ frustration, these are no good as
Picture: FBH/schurian.com
UV-B diode lasers would have important uses in medicine, microelectronics and printing
technology. We say “would have” because they do not exist yet. Researchers have known
for a long time how such diode lasers would have to look like. However, to actually make
it, an important part is missing – the perfect crystal substrate to grow the UV laser
diodes on. Scientists at the Ferdinand-Braun-Institut (FBH) have now presented the first
aluminium gallium nitride crystals for this application.
verbundjournal
Almanac 2016
the aluminium now reacts with the chlorine as intended.
He already has the first precious AlGaN crystal wafers in
the lab, but they still need to be made much thicker for an
industrial production process. With this goal in mind,
Richter is currently experimenting with micropatterned
sapphire wafers. “We start by growing our aluminium gallium nitride crystal along thin ridges on the sapphire surface,” he explains. After the crystal has grown
for a certain amount of time, the structures
Too many
combine into a complete crystal wafer, which
dislocations are
can then be detached more easily from the
luminescence
sapphire substrate. “Using this growth methkillers.«
od, we have managed to substantially reduce
the dislocation density and the cracks,” Richter reports. The ultimate aim is to produce layers that are
thick enough to be polished. No one in the world has succeeded in doing this so far, but it will happen one day, the
FBH researcher is confident.
The easy-to-use UV-B LEDs or laser diodes would be
highly versatile in their application, Markus Weyers is
convinced.
In medicine, for example, they could be used to treat
psoriasis. “Another important application is curing UV-
reactive printing inks and varnishes,” he says. The UV lamps
currently used are so big and hot that they prevent many
applications that would otherwise be possible. Richter also
sees major potential in UV disinfection, for example: “One
could use them to kill off bacteria in operating rooms, at the
dentist’s or in swimming pools.” They could harden plastics
in the tooth or in repaired pipelines. They would even allow
for stimulation of plant growth, say, in order to improve the
taste and nutritive value of plants in a natural way, or to
produce vaccines without involving animals.
Picture: FBH/P. Immerz
»
substrates. The lattice constants of the substrate and crystal must perfectly match, otherwise cracks and dislocations are generated.
For the very short wavelength UV range, light-emitting
or laser diodes can be grown on aluminium nitride substrates, as produced for example at the Leibniz Institute
for Crystal Growth. The atomic distances of the substrate
and the device structure match well for this range. How
ever, for UV-B range, at the wavelengths of interest from
280 to 315 nanometres, the substrate has to be a ternary
aluminium gallium nitride (AlGaN) crystal.
No such substrate exists, so the researchers start the
HVPE process with a sapphire crystal whose structure is a
reasonably close fit and deposit the desired AlGaN crystal
layers onto that. After detaching and polishing, these AlGaN layers would in turn become the substrate for the
light-emitting or laser diodes. In the HVPE reactor, at several hundred degrees Celsius, gallium and aluminium react with hydrogen chloride, the gas of hydrochloric acid, to
form gallium and aluminium chloride. By adding ammonia, these are converted into nitrides, which grow onto the
substrate, building up a crystalline layer of aluminium gallium nitride.
Dr Eberhard Richter stands in the lab and carefully
opens the HVPE reactor while it is still hot. Behind thick
insulation material, the quartz cylinder comes into view, in
which the components react and crystal deposition takes
place. “Aluminium has a number of unexpected bizarre
properties,” Richter says. “As soon as it melts at 670 degrees Celsius, it climbs up even vertical surfaces and destroys the quartz glass of the reaction vessel.” Using a refined setup, the FBH scientist has solved this problem and
HVPE reactor for
growing crystal
substrates (HVPE
= hydride vapour
phase epitaxy).
14 SCIENCE IN FOCUS · FBH
verbundjournal
Almanac 2016
Fast switching – thanks to
HiPoSwitch
The EU joint project HiPoSwitch has culminated in the successful development of
high-efficiency, lightning-fast gallium nitride power switches. These are the basis for
energy-saving, compact, lightweight power converters that make electrical energy

usable. The market potential is enormous, given that converters are found in almost
every electrical device.
E
lectricity comes out of the wall socket. So far so good.
However not every device, by a long way, can withstand the normal mains voltage. Computers, smartphones
and halogen or LED lights, for example, require only a fraction of the mains output. For each application, we need to
convert and step down 240 volts of alternating current
into, say, 2 or 12 volts of direct current. This used to be
done with transformers, but their efficiency was poor.
Presently, we use so-called switched mode power supplies
to do the job: These “chop up” the mains voltage and then
piece it back together again as needed. Yet our modern
world needs active semiconductors that can make these
power adapters even more efficient and lightning fast.
98 % conversion efficiency
In the EU joint project HiPoSwitch, researchers of the Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik (FBH) led by Dr Joachim Würfl have successfully built tiny gallium nitride (GaN) based transistors
that considerably reduce the energy conversion loss compared to silicon transistors – by as much as 50 per cent.
This raises conversion efficiency from 96 to 98 per cent.
Only two per cent higher efficiency? That may not sound
like much. But things look very different if we consider
the big picture: “Europe generates about 3000 terawatt
hours of electricity every year,” Würfl explains (one terawatt is one trillion watts). “If we convert one quarter of
this to a new level while increasing efficiency by two per
cent points, then we can save about two coal-fired power
stations.”
In the HiPoSwitch project, coordinated at the FBH, the
Berlin researchers and eight European partners from
research and industry spent three years developing

normally-off GaN power transistors to prototype stage.
Most power adapters and chargers on the market still
use silicon transistors. But silicon technology has already
reached its limits. What is the problem? “An efficient switch
ideally has to produce a short circuit as soon as it is
switched on. In reality, however, there is always a certain
residual resistance. It results in a power loss, which reduces
the efficiency,” Würfl explains. This loss is in the form of
heat, which can be easily felt even on extremely energy-
saving LED lamps after long use.
The loss is far lower with gallium nitride based transistors. The semiconductor material unites optimal physical
parameters. “GaN components therefore make highly efficient and very fast power switches. That is because of their
Picture: FBH/P. Immerz
Basis for energy-efficient and
compact power converters: gallium
nitride switching transistors on
silicon substrate developed within
the HiPoSwitch project.
verbundjournal
Almanac 2016
Eight European institutional and industrial project partners
led by the Ferdinand-Braun-Institut, Leibniz-Institut fuer
Hoechstfrequenztechnik (FBH) have successfully developed
prototype power transistors that use gallium nitride (GaN) in
enhancement mode. The EU group-project called HiPoSwitch
was completed in 2015.
low switching resistance, with no significant switching
loss,” Würfl stresses. A higher switching frequency in turn
means the passive elements of the energy converter, i.e.
coils and capacitors, can be built much smaller – a major
improvement for the end system.
Hand in hand: from high-performance
material to industrial production
Image: HiPoSwitch
GaN has already long been used for microwave transistors,
in most cases deposited as ultrafine layers onto silicon carbide (SiC) substrates. This technology, developed at the
FBH, works well but is too expensive for the mass market.
“The lattice constant of GaN makes it fit well onto SiC, but
not perfectly. So the basic technologies were developed on
SiC substrates and then, in cooperation with the project
partners, ultimately transferred to low-cost but technologically more challenging silicon substrates. Now, the wafers
can be produced on a process line for silicon power transistors,” Würfl explains.
With a few tricks, they managed to deposit gallium nitride onto silicon carbide and silicon without the ultrathin
layers changing during the process, ultimately allowing for
virtually ideally functioning components. The expertise of
another partner helped at this stage – the University of
Padua. “Specialists there characterised our test transistors
and studied drift and degradation effects,” Würfl relates.
“These results then flowed back into our research and
helped us successively improve the process.” The transition from silicon carbide to silicon was done by Belgian
partner EpiGaN, specialist for GaN epitaxy on silicon wafers. This all may lower the costs of the substrate by more
than a factor of ten compared to SiC.
Until now, the wafer with the transistors measured four
inches. To be admitted into low-cost industrial production,
however, it has to be larger – six or better still eight inches
– which was also the task of EpiGaN. German manufacturer of epitaxy systems Aixtron developed the suitable concepts for stepwise expansion to 8-inch wafers. The chip
manufacturer Infineon in Villach, Austria, finally adapted
the newly developed GaN technology to a silicon process
line for industrial production of power semiconductors.
Parts of the project had a decidedly “explorative character”, as Würfl describes it, taking a look at entirely new, untested techniques and processes for creating GaN power
transistors. Together with colleagues from TU Wien and
the Bratislava Academy of Sciences, they tested promising
concepts for future semiconductor generations.
Joachim Würfl places the original wafer prototype on
the table: an extremely thin gold-plated wafer, resting on
which are hundreds of tiny transistors of various designs.
It was created in 14 lithography steps in the FBH cleanroom – so finely structured, that the details are hardly discernible to the naked eye. The transistor chips are cut out
of the wafer using a turbo saw and then, at Infineon in Malaysia, mounted into low-inductive housings, called ThinPAKs. The single transistor therein measures only 4.5 x 2.5
millimetres, is optimised to switch 600 volts, has a switching resistance of 75 milliohms and delivers a maximum
current of 120 amperes. At the end of the value chain is the
last HiPoSwitch partner, Artesyn Austria GmbH & Co. KG.
They used the new GaN transistors to build an energy-saving voltage converter for mobile communication base stations, a three kW telecom rectifier that converts alternating current to direct current.
Space-worthy and being resistant to
radiation
The market for energy-saving power converters is giant.
There is hardly a technical device in the world for which
they couldn’t replace an inefficient “predecessor”: computers, mobile communication base stations, chargers for
modern energy stores, solar converters, and electric and
hybrid vehicles. The product is even space-worthy, being
resistant to radiation. Applications in space are not a large
market, “but they are a critical one, since European aerospace is strongly dependent on the USA in this respect,”
Würfl emphasises. FBH researchers already have a contract with the German Aerospace Center (DLR) for a closer
study of these transistors’ resistance to radiation. Energy
efficiency, compactness and low weight are other top priorities for devices destined for space.
16 SCIENCE IN FOCUS · FMP
verbundjournal
Almanac 2016
Pressure relief valve in cellular
membrane identified
Regulation of cell volume is critical for the body’s cells: for example during cellular exposure to fluids of varying salt concentrations, in cell division and cell growth, as well as in
diseases such as cancer, stroke and heart attack. A certain chloride channel, a membrane
protein that allows the passage of the chloride ion, is of crucial importance in volume
regulation. It is activated by the swelling of the cell, and then releases chloride ions and
organic matter (“osmolytes”) from the cell. A research team led by Professor Thomas J.
Jentsch have managed to shed light on the molecular identity of this volume-regulated
anion channel (VRAC).
cientists from the Leibniz-Institut für Molekulare Pharmakologie (FMP) and the Max Delbrück Center for Molecular Medicine (MDC), Berlin-Buch, have identified a
molecule of the VRAC called LRRC8A. When assembled
with related proteins (LRRC8B to E), this molecule can
form a channel with probably six subunits. The group also
managed to show for the first time that these chloride
channels are also permeable to small organic molecules
such as taurine and amino acids. Research groups around
the world had been attempting to shed light on the molecular structure of the VRAC for over 20 years. It took
Jentsch’s team almost four years to achieve this breakthrough. The results of the study were finally published in
the renowned journal Science in 2014.
The regulation of cell volume is important for many
functions in the organism. The VRAC, which Thomas
Components of
the volume-regulated anion
channel (VRAC)
in the plasma
membrane of the
cell: the LRRC8A
protein (coloured
red) together with
at least one of the
five other family
members (here:
LRRC8E, coloured
green, present
in yellow as a
complex).
Jentsch and his co-workers Felizia Voss and Tobias Stauber have now deciphered at the molecular level, is expressed in all vertebrate cells. If a particular cell volume
is exceeded, the channel opens and permits the outflow
of osmolytes such as chloride ions as well as organic ions
such as taurine and amino acids. By contrast, cations
such as potassium and sodium cannot permeate the
channels.
Ion transport is a passive process. Due to its electrochemical properties, the channel only allows anions and
certain organic compounds to pass. Thus, the cell reduces
the concentration of its osmolytically active constituents
to that of the surrounding fluid (or even less). At the same
time, the water content of the cell decreases as water molecules flow out via aquaporins in the cell membrane. The
volume of the cell decreases again.
Image: Tobias Stauber, Labor Jentsch/MDC, FMP
S
verbundjournal
MDC’s Bioinformatics Group helped
evaluate the statistical data
LRRC8A was discovered as a component of the VRAC using genome-wide RNA interference in collaboration with
Katina Lazarow and Jens von Kries from the FMP Screening Unit. It was discovered using small, synthetic RNA
molecules that lead to the enzymatic degradation of messenger RNA in the cell, which matches its RNA sequence.
No protein can be translated from this messenger RNA
due to specific degradation. Protein production is discontinued, which is why synthetic RNA is called a “silencer”,
or siRNA, in English. Using a one-by-one approach in a
large-scale cell culture experiment, the Berlin group silenced the products of all 20,000 or so human genes by
means of complex pipetting robots and high-speed measurement systems. In an automated screening process,
they investigated which of the genes are responsible for
the swelling-activated chloride flux across the cell membrane. When it came to the statistical analysis of approximately 130,000 time-dependent ion flux measurements,
Jentsch’s team was supported by Nancy Mah and Miguel
Andrade-Navarro from the Bioinformatics Group of the
MDC.
Once the needle (the LRRC8A gene) in the haystack of
20,000 human genes had been found, it took another year
of intensive work before the data could be published. This
work also involved a thorough electrophysiological analysis by PhD students Florian Ullrich and Jonas Münch. Using relatively new CRISPR/Cas technology, which allows
specific genes on the chromosomes to be disrupted completely and permanently, the scientists initially confirmed
Picture: FMP · Image: FMP/MDC
FMP · SCIENCE IN FOCUS 17
Almanac 2016
that LRRC8A is essential for the channel. Unlike in the partial suppression
of swelling-activated chloride fluxes
by siRNAs, these vanished completely
after the gene had been fully disrupt- It took Professor Thomas J. Jentsch and
ed. By reinitiating the flux after rein- his team at FMP four years to decipher
sertion of the LRRC8A “messenger the chloride channel.
RNA”, the group provided formal
proof that LRRC8A is an essential component of the channel. However, this protein alone does not suffice, because
the channel fluxes did not increase following its overproduction. The Berlin researchers therefore assumed that
the structurally related proteins LRRC8B to E are also involved in the channel alongside LRRC8A. While the disruption of each of these four genes did not suppress the flux,
the simultaneous elimination of these four genes also led
to the complete loss of ion transport. Combinations of two
proteins, however, sufficed. For example, the combination
of the essential A isoform with C, D, or E forms led to fluxes
which, interestingly, had slightly different properties. “This
allows us to explain the behaviour of the channel in different tissues, which had so far eluded us,” explained Thomas
Jentsch. With the assumed structure featuring six s ubunits,
a large number of channels with different details can form
with the combination of five different isoforms.
Information about the molecular
structure of the chloride channel may
enhance medical treatments
“Cells can swell or, in the worst case, even burst. For this
reason, water transport and content must be closely monitored,” explained Thomas Jentsch. In this connection, water transport is always driven by the osmotic gradient.
Cells take up chloride from their surroundings, whereas
organic substances such as taurine and amino acids are
produced within the cells.
Deciphering the molecular structure of this chloride
channel is also important, because it will pave the way for
better medical treatments, such as following a stroke. “In
the case of damage in the brain, cells swell and release glutamate, which acts upon receptors on nerve cells. The subsequent inflow of calcium raises the intracellular concentration of this ion to toxic levels,” stated Jentsch. With the
onset of programmed cell death (apoptosis) during cancer
chemotherapy, however, there is a strong reduction in cell
volume. The volume-regulated chloride channel also appears to be involved in this process.
Science 9 (2014); DOI: 10.1126/science.1252826
The chloride channel is activated by the swelling of the cell.
18 SCIENCE IN FOCUS · FMP
verbundjournal
Almanac 2016
BIRGIT HERDEN
A synaptic governess
The adaptor protein AP180 makes sure that synaptobrevin2
(Syb2) is sorted into fissioning clathrin-coated vesicles. AP180
therefore ensures that the resulting synaptic vesicles contain
sufficient Syb2, which is an essential prerequisite for efficient
neurotransmission in the brain.
P
»
rofessor Volker Haucke likens protein transport at
synapses to a high-speed express coach: with screeching tyres, the harried driver halts abruptly at the stops,
and those needing a ride have to jump on quickly before
the coach sets off again. In order to minimise the number
of passengers left stranded at the stop, unable to
Nerve cells keep up with the rapid pace, attentive assistants
must function stand by to help slower passengers onto the
coach with a quick shove. Two studies conductfor decades.« ed at the Leibniz-Institut für Molekulare Pharmakologie (FMP) have demonstrated just how
important these assistants are for the well-being of the entire organism, and how they even influence complex behavioural patterns.
The two groups headed by Prof. Haucke and Dr Tanja
Maritzen have presented a knockout mouse variant in the
journal Neuron. These mice lack the AP180 protein. Due to
the lack of this protein, the rodents are hyperactive and experience epileptic seizures, which in some cases are fatal.
They also exhibit reckless behaviour, which is completely
atypical for mice.
What is happening here inside the nerve cells? At first
glance, electrical signals continue to be transmitted at the
synapses even in the absence of AP180. However, closer
analysis reveals that the capacity to transmit signals weakens in the event of higher neuronal activity. As a result, inhibitory nerve cells that are often continuously active become particularly impaired, upsetting the balance between
the gas pedal and the brakes in the brain. As the groups
headed by Haucke and Maritzen have shown in numerous
experiments, AP180 ensures the rapid transport of the
vesicle protein synaptobrevin2 (Syb2) at synapses.
Syb2 is one of the three components of the so-called
SNARE protein complex, which causes the fusion of vesicles with the outer membrane in response to incident
nerve impulses. This is how the nerve cell releases neurotransmitters into the synaptic cleft, transporting the electrical signal from one cell to the next. Syb2 must then be
brought back from the nerve cell membrane to the interior
of the cell, where it is needed for new vesicle fusion events.
To this end, the cell membrane becomes locally concave
during the process of endocytosis, enclosing and drawing
vesicle proteins into the cell. The scientists were able to
show that, in this process, the AP180 adaptor protein acts
like a boarding attendant for an express coach. “Syb2 will
still be transported back into the cell’s interior without
AP180, but at much lower efficiency level. Only about half
the normal number of Syb2 molecules return to the synaptic vesicles of the inhibitory nerve cells,” stated Tanja Maritzen. The adaptor protein that links Syb2 to the endocytotic machinery of the cell acts like an attentive governess
specialising in certain passenger types.
Nerve cells fire up to 1,000 times per second during sensory perception. “The system must react quickly, but also
with extreme precision and reliability,” explained Haucke.
“After all, nerve cells are usually irreplaceable – they portray our memories and identity, and must function for decades.“ There are indications that changes to the gene for
AP180 in humans may play a role in the development of
psychotic bipolar disorders and in autism. Detailed understanding of the processes at synapses could therefore also
prove to be a key to understanding neuronal diseases.
Neuron 88 (2015); DOI: 10.1016/j.neuron.2015.08.034
Nat. Commun. 6 (2015), 8392; DOI: 10.1038/ncomms9392
Image: Claudia Knorr
Autism and psychotic bipolar disorders are caused or influenced by a number of genetic
factors. However, the identity and mode of action of these genetic factors are still largely
unknown. It could be the case that the protein AP180 plays a key role in this process.
During high neuronal activity, this protein ensures the efficient recycling of a synaptic
vesicle protein. Animal experiments have shown that the absence of the AP180 protein
has a negative effect on behaviour and lifespan.
verbundjournal
FMP · SCIENCE IN FOCUS 19
Almanac 2016
BIRGIT HERDEN
Magnetic resonance imaging
in colour
Scientists from Berlin have managed for the first time to generate two-colour images using new, highly sensitive contrast agents in magnetic resonance imaging (MRI) scanners.
This method offers new perspectives for clinical application – it may be possible to characterise tumours more precisely, for example, paving the way for individual therapies.
I
t is a matter of course in light microscopy: various stains
are used to colour samples, revealing different cell
structures or enabling a differentiation to be made between healthy and diseased tissue. However, since light
rays are unable to penetrate deeply into tissue, doctors use
radio waves to take X-ray images of their patients using an
MRI scanner. There is a drawback, however: MRI scans
usually only show the distribution of tissue water; doctors
are unable to determine specific target structures, such as
small amounts of tumour cells, in black-and-white images.
This could change if the new technique of xenon magnetic resonance imaging, currently being developed by research groups around the world, becomes established. The
group led by Dr Leif Schröder at the Leibniz-Institut für
Molekulare Pharmakologie (FMP) has now made an important breakthrough in cooperation with Professor Christian
Freund from the Freie Universität Berlin. For the first time,
the scientists have managed to mark different cell types so
that they emit radio waves at different frequencies. Akin to
light microscopy, therefore, they generate images in which
some cells are illuminated red, and others green.
Image: Barth-Jan van Rossum/FMP
Newly developed technique uses the
inert gas xenon
MRI images are generated when atomic nuclei interact
with a strong outer magnetic field – to achieve this, the patient is placed inside the scanner, which contains powerful
magnets. In this state, some atomic nuclei resonate with radio waves, i.e. they emit radio waves themselves. By generating layer by layer of images, a three-dimensional image is
created – hence the name “magnetic resonance tomography”, or MRT for short. In the process, conventional MRI
scanners measure the nuclei of hydrogen atoms, which are
present throughout the human body, but emit only very
weak signals. In contrast, the new technique developed by
Leif Schröder uses the inert gas xenon, which emits much
stronger signals if its atomic nuclei are “hyperpolarised”
beforehand using laser beams. The gas, otherwise known
for its use in car headlights, is harmless and completely
non-toxic. In clinical applications, patients would be able to
inhale the gas, enabling it to spread throughout the body.
In order to generate truly interesting images, however,
doctors would have to be able to mark specific target
structures – such as degenerated cells or deposits in the
arteries – using the inert gas. To this end, the research
group have developed various molecular “containers” that
not only catch the xenon, but can also be inserted easily
into the human body as probes. If such a contrast agent adheres to cells being sought in the body, it immediately
catches xenon atoms from the surrounding area, which
then emit radio waves at a certain frequency. In a further
research study, the Berlin researchers inserted two different containers simultaneously. The xenon subsequently
emitted radio waves at different frequencies – making
some of the cells appear green, and others red.
A multitude of future possibilities for application are
conceivable. For example, cells transplanted into the body
could be tracked, or tumours localised and their cellular
composition portrayed. In this way, the novel MRI images
could help pave the way for personalised therapy.
Leif Schröder’s group recently went one step further:
they managed to pack the molecular probes used in MRI
scanners into tiny biological membrane vesicles (liposomes) and direct them specifically to the type of cells in
the human body that represent the boundary between
blood and cerebral fluid. This enables light to be shed on
this tissue, which is of such neurological importance, visualising damage to the blood-brain barrier.
Nano Letters 14 (2014); DOI: 10.1021/nl502498w
PNAS 111 (2014); Doi: 10.1073/pnas.1406797111
Specific detection of cell surface proteins
by xenon magnetic resonance imaging
(MRI); the image illustrates the use of hyperpolarised xenon gas (purple) in combination with xenon cryptophane cages
(light blue), which are attached to cells via
antibodies. During the MRI experiment, a
unique radio frequency pulse (red) is used
to selectively image and "light up" the
surface of macrophage cells.
20 SCIENCE IN FOCUS · IGB
verbundjournal
Almanac 2016
NADJA NEUMANN AND CHRISTOPHER K YBA
Loss of the night
In the interdisciplinary research project "Loss of the Night" scientists investigate the
reasons for the increasing illumination of the night, its ecological, cultural and socio
economic effects, and the effects on human health. Researchers from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), the Coordinating Institution, have
determined three policy recommendations, which they say could greatly reduce energy
consumption and light pollution – without leaving cities in the dark.
Hölker. Finally the scientists recommend adopting a new
definition for efficiency in urban area lighting. “We need a
more appropriate measure for reporting energy efficiency,
that would allow apple-to-apple comparisons of radically
different lighting delivery systems,” explains physicist Dr
Christopher Kyba, also of the IGB. “For example, suburban
streets with lights that are dimmed after midnight could potentially use less energy in a year than a more efficient lamp
that burns at full power all night.”
A
bright night sky, illuminated by an abundance of
lights – the rapid increase in the quantity and quality
of artificial illumination has fundamentally transformed
our nightscapes in the past few decades. As a result, lighting has become a major source of greenhouse gas emissions, being responsible for an estimated 19 per cent of all
electrical energy use worldwide. Furthermore, the illumination of our nightscapes has potentially important, albeit
almost completely neglected, impacts.
Three steps to sustainable illumination
IGB’s first policy recommendation is a transition to needbased lighting. Dr Franz Hölker of IGB explains: “The idea is
that by directing light more carefully, visibility could actually be improved while saving energy and money. In suburban
and rural locations with little activity after midnight, modern lamps could also be dimmed to 10 per cent of their normal power until morning traffic begins.” In the future, motion sensors could be used to run lamps at full power only
during periods of activity. The second recommendation is
for policymakers like the European Commission that s pecify
minimum requirements for street lighting. The scientists
propose to stipulate conservative maximum illuminances,
because in the US and Europe the amount of light often far
exceeds current standards. “If you use twice as much light
as is needed for a task, then half the energy is wasted,” says
Citizen scientists collect data on light
pollution via smartphone
Within the project, a mobile application was developed
that allows citizen scientists from around the world to
measure sky brightness by determining the number of visible stars in the night sky. “The data from these observations are crucial for our science. We urgently need them to
evaluate how skyglow is changing worldwide,” says Christopher Kyba. This research cannot be done with satellites,
because they measure the light emitted upward, not the
light experienced on the ground by humans and other living creatures. The app is available in 15 languages for free
download for iOS and android. Since 2013, thousands of
observations from 111 countries were sent in. So far, the
data were analysed only by scientists. Christopher Kyba
wanted to change that and put the data and tools to analyse it back into the hands of the public. The web-based
platform “myskyatnight.com” now makes all data available
to the public, and offers tools to visualise and analyse the
measurements. The scientist hopes that the data will eventually feed back into local decisions about outdoor lighting: “In the ideal case, we will find examples of success stories: cities that invest in environmentally friendly lighting
and end up seeing more stars above well-lit sidewalks.”
For further information visit:
www.verlustdernacht.de (Project Loss of the Night/ Verlust
der Nacht)
www.cost-lonne.eu (Loss of the Night Network (LoNNe)
Cost Action)
www.myskyatnight.com (Citizen Science Project)
Picture: ESA/NASA
Brightly lit Northern Europe at night,
seen from the ISS
verbundjournal
IGB · SCIENCE IN FOCUS 21
Almanac 2016
NADJA NEUMANN
International master program
educates fish experts
The Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and the Humboldt Universität zu Berlin (HU) offer an international master program, which enables
students to work in pioneering jobs at the interface of aquatic sciences, sustainable ecosystem management and food production.
T
his master study is exceptional in covering the different fields of knowledge: fish biology and evolution of
fishes, fisheries management and conservation as well as
aquaculture.
The students can take profit from experts in teaching,
science and application: They study at the “University of
Excellence” Humboldt-Universität zu Berlin in a highly motivating and professional learning environment. They are
also part of the scientific community at the IGB as an internationally renowned institution for freshwater sciences.
Prof. Jens Krause is the head of the master program. He
is professor for Fish Ecology at the HU-Berlin and head of
the department “Biology and Ecology of Fishes” at IGB:
“This master program conAquaculture is the siders current issues of sofastest growing cietal relevance. The management of our freshwaters
sector in food is one of the future global
production; experts challenges. Aquaculture is
are needed.« the fastest growing sector
in food production. There
will be a need for experts with a broad range of key qualifications. We have the ambitious goal to educate fish experts
with a strong knowledge in science, practice and nature
conservation. Our lecturers are authorities in their diverse
Picture: Andreas Hartl
»
research fields and are dedicated to offer state-of-the-art
knowledge.”
The students learn about the specificities of habitat
types in lakes and rivers and the effects of human impacts,
and understand how aquatic and terrestrial environments
are ecologically interconnected. But they are also prepared
for all key aspects in aquaculture: rearing concepts, nutrition, evaluation and design of possible farm sites and approaches to improve sustainability and product quality.
This broad educational offering attracts students from
all over the world. Most of them have a high intrinsic motivation for this field of knowledge. Petr Zajicek, for example, came to this study as a passionate hobby angler. He is
currently a PhD student in the department of “Biology and
Ecology of Fishes” at IGB and investigates the impact of
multiple stressors on fish populations of large rivers. “I always wanted to learn more about freshwater ecosystems
and was especially inspired by the large variety of subjects
in the master program. The atmosphere was really familiar and international as almost every student came from
another country,” says Zajicek.
More information on the international M.Sc. Fish Biology,
Fisheries and Aquaculture: www.agrar.hu-berlin.de/de/
lehre/msc/mfs
22 SCIENCE IN FOCUS · IGB
verbundjournal
Almanac 2016
AN GE LINA T IT T MAN AND JÖRN GESSNER
Joining forces to help
prehistoric giants
Sturgeons are among the most threatened fish species worldwide. To ensure that one
day these living fossils will return to our rivers in large numbers, scientists have joined
forces in a Europe-wide network. Seven partner institutions collaborate on research related to the conservation and development of stable sturgeon stocks and therefore pool
their resources. The network has been initiated by the World Sturgeon Conservation Society (WSCS) and the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB),
a pioneer of the sturgeon reintroduction program for almost 20 years.
turgeons migrate between worlds:
They spawn in freshwater and
spend the major part of their lives –
which can last more than a hundred
years – in the sea. Spawning and nursing requirements bring them back to
swiftly running rivers with gravel
sediments. After reproduction, the
adults return from the rivers to marine waters almost immediately. But
the journey of the sturgeons has become increasingly challenging: The
Professor Harald Rosenthal (World largest river fish of the northern latiSturgeon Conservation Society), Professor tudes is stopped by barrages and waKlement Tockner (IGB Berlin) and Profes- terway constructions preventing the
sor Otomar Linhart (University of South sturgeons from reaching their spawnBohemia in České Budějovice) after sign- ing habitats. In addition, pollution ading the Memorandum of Understanding. versely affects the development of
their offspring in many rivers. This,
along with unsustainable harvest practices, lead toward
the extinction of these giants on the European continent.
Transnational collaboration to prevent
the extinction of the sturgeons
Rivers, coasts and sturgeons do not stop at national borders. “The mobility of these animals makes a cross-border
approach essential for effectively restoring the sturgeons.
And this approach can only be successful if we closely coordinate our efforts,” said Dr Jörn Gessner, project coordinator at IGB in Berlin, Germany. In order to better integrate and harmonize research and measures taken in
different countries, scientists have established the European Sturgeon Research Network (ESRN). Their objective is
to pave the way for further co-operations, to stimulate
joint research, to better utilize existing knowledge, and to
support regional networks.
As a start, a Memorandum of Understanding was signed
by the World Sturgeon Conservation Society (WSCS), the
IGB and the University of South Bohemia České Budějovice. Meanwhile, the Danube Delta National Institute in Tul-
cea (Romania), the BOKU Institute of Hydrobiology and
Aquatic Ecosystem Management in Vienna (Austria), the
universities in Belgrade (Serbia) and Padua (Italy) and the
French National Research Institute of Science and Technology for Environment and Agriculture (Irstea) joined
the network.
Partner institutions combine their expertise
Within the WSCS-ESRN the partners share their competences and resources, using this platform for the coordination of individual measures, for the exchange of knowledge as well as for the standardization of methodologies.
The involved scientists expect synergy effects and a better
quality of research results from this close cooperation
while better visualizing to donor agencies the specific research needs. “We also aim at developing harmonized procedures for the realization, documentation and assessment of the measures foreseen," Gessner continued. This is
intended to ensure swift and effective responses to future
challenges.
Besides improving breeding and reproduction for conservation and aquaculture, the scientists want to identify
habitat functions essential for sturgeons and jointly develop approaches for their improvement.
Sturgeon paves the way for other
species to return to our rivers
The successful reestablishment of the sturgeon and the
conservation measures applied for this aim will also help
other species that are equally important for an intact and
resilient ecosystem. Especially the connectivity of the rivers both longitudinally and laterally are essential to allow
migration while functional integrity of habitats is vital for
the completion of the life cycle in many riverine species
like salmon, sea trout, shad or vendace to maintain stable
self-sustaining populations. "It will probably take several
years until we can see the fruits of our efforts,” Gessner
conceded. "The formation of the network is a decisive step
in the right direction.”
Pictures: IGB/Angelina Tittmann
S
verbundjournal
IGB · SCIENCE IN FOCUS 23
Almanac 2016
AN GELINA TITTMAN N AND VANESSA BREMERICH
European freshwaters at a click
Four European research institutions have published an online platform, bringing together information and findings from freshwater ecosystems research. The “Freshwater Information Platform” makes data and maps freely available, offering a unique and comprehensive knowledge base for the sustainable and evidence-based management of our
endangered freshwaters and the resources they provide.
W
e are fundamentally changing how nature works,
most often irreversibly,” stated Professor Klement
Tockner, Director of the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin. These changes not
only endanger the natural systems on which we depend, but
also, ultimately, our survival. Pollution, land use and climate
change are among the factors which are increasingly jeopardising our freshwaters and their biodiversity throughout
Europe. For this reason, numerous research projects have
been conducted in recent years to explore the causes and
consequences of these changes, and renaturation strategies
for rivers, lakes and wetlands have been developed. And yet
it is often difficult for the public, policy-makers, authorities
and water managers to access the information and data collected. In some cases, research data is not published systematically or is embedded in a multitude of different scientific
publications and project websites.
In a bid to change this, IGB joined forces with the University of Natural Resources and Life Sciences in Vienna
(BOKU), the University of Duisburg/Essen (UDE) and the
Royal Belgian Institute of Natural Sciences (RBINS) in
Brussels to develop a new information portal: launched in
2015, the “Freshwater Information Platform” summarises
the findings of completed and ongoing research projects,
and makes them accessible to the public. “With this, we
have created a joint research infrastructure that helps us
track the manifold impacts accelerated environmental
changes have on freshwater ecosystems and their biodiversity,” explained Klement Tockner.
Image: IGB
The portal sheds light on findings and
data from research into European
freshwaters
The platform is composed of several complementary parts
that either facilitate easy access to original data or offer an
easily comprehensible summary of research results. All
sections are continuously updated and further content
keeps getting added.
One focal point covers the spatial aspects of freshwater
research: for example, the integrated “Freshwater Biodiversity Data Portal” offers access to data showing the distribution of freshwater organisms such as fish, insects or mam-
The “Freshwater
Information
Platform” makes
results and data
generated by
a variety of
European research
projects publicly
accessible.
mals in Europe and the whole world. The “Global
Freshwater Biodiversity Atlas” provides a collection of maps
related to biodiversity, stress intensity and climate change.
The “Freshwater Metadatabase” section provides an
overview of numerous data sources related to freshwater
ecosystem research and the management of lakes, rivers
and wetlands. In addition, the “Freshwater Metadata Journal” offers scientists the possibility to publish their data
sets as scientific articles.
The “Freshwater Species Traits” section provides a
summary of relevant information about individual species
that are native to European waters: what do freshwater organisms feed on, in which habitats do they occur, or how
tolerant are they to pollution and environmental change?
The database contains information about some 20,000 different species.
This offer is supplemented by various tools, guidelines
and information about relevant policy directives, and the
“Freshwater Blog” providing features, interviews and podcasts on the latest developments in freshwater research.
Visit the “Freshwater Information Platform”:
www.freshwaterplatform.eu
24 SCIENCE IN FOCUS · IKZ
verbundjournal
Almanac 2016
GESINE WIEMER
A flawless crystal for the
new kilogram
S
The PTB’s kilogram
project enters its
crucial stage with
the new Si-28 crystal from the Leibniz
Institute for Crystal
Growth.
cientists have therefore been working for many years
on defining the kilogram by a constant of nature instead – similarly to the metre and the second. To serve as a
basis for this definition, the Leibniz Institute for Crystal
Growth (IKZ) has grown a single crystal of silicon. Physicists of the Physikalisch-Technische Bundesanstalt (PTB),
in Germany will cut the IKZ crystal into a one-kilogram silicon sphere and then count the number of atoms within it.
For the IKZ in Berlin, which has internationally sought
after expertise in growing silicon crystals, it was just another day at the lab. Dr Nikolai Abrosimov, physicist at IKZ,
explains: “Natural silicon is composed of three stable isotopes, namely silicon-28, -29 and -30. To redefine the kilogram, we need a silicon-28 crystal of the highest isotopic
purity possible.” Russian partners produced the starting
material for this in a highly elaborate technical feat. They
achieved greater than 99.998 per cent isotopic purity.
Working from this polycrystalline feedstock, the IKZ’s task
in the project was to manufacture a single crystal with a
perfect lattice structure – with no irregularities and with
as good as no foreign atoms.
The IKZ researchers developed new techniques that
are unique in the world specifically for this task. They
grew the crystal using the floating zone method. In this
method, the feedstock does not come into contact with any
other substances, such as a crucible, rather it deposits as a
molten mass from above onto the growing crystal below,
whose atoms align in a perfect crystalline lattice as it sets
from the bottom up. With no crucible, no foreign atoms
are introduced into the crystal.
Another imperative was to produce as little waste as possible – the material is too valuable, being about ten times
the price of gold.
There is no way to completely avoid production-related
waste in the crystal growing process. This is where the
crystal growers got creative, putting the leftovers to good
use in their process: With the help of the Russian specialists, they coated a quartz crucible with isotopically pure silicon dioxide. Inside this, they grew from the leftovers a
much purer crystal, far less contaminated with the “wrong”
Si isotopes, than could be grown in an ordinary crucible.
While this crystal was not pure enough for the kilogram
standard sphere itself, it was good enough to fuse onto the
top of the pure feedstock. Since the floating zone method
always leaves behind a certain amount of unused material
at the top, which cannot become part of the single crystal,
their trick allowed much more of the pure feedstock to be
melted into the crystal than usual. With that, the groundwork was laid for the PTB. There, the physicists’ job is to
work the IKZ crystal into two extremely round spheres in
which they can count the number of atoms. Knowing this
and the exact volume then yields the Avogadro constant.
When the time comes, the annual testing ceremony of
the International Prototype of the Kilogram in Paris will
have run its course, and the platinum–iridium cylinder
will take its worthy place in the museum.
Picture: Physikalisch-Technische Bundesanstalt (PTB)
When it comes to the kilogram, we are still in the 19th century: Since 1889, our original
reference, called the International Prototype of the Kilogram (IPK), has been kept under
lock and key in a vault in Paris. Every year, under tight security, experts take out the platinum-iridium cylinder to re-examine it. What they have observed is that the IPK is continually losing weight, and has already lost several micrograms to date.
verbundjournal
IKZ · SCIENCE IN FOCUS 25
Almanac 2016
KARL-HE INZ K ARISCH
Among crystal spheres
The 2014 Nobel Prize in Physics for the growth of crystals for producing blue LEDs co
incides with an anniversary year. One hundred years ago, the Nobel Prize was awarded
for the proof that crystals have a lattice-like structure. UNESCO, the United Nations Educational, Scientific and Cultural Organisation, accordingly named 2014 the international
year of crystallography. Several institutes of the Forschungsverbund Berlin e.V. are continuing successful research in this field.
Picture: IKZ
C
a laboratory in the USA was desperately
rystals have fascinated people for
searching for a method of growing silithousands of years. A mediaeval
hypothesis was that the earth resided
con single crystals. They found their anat the centre of nine crystalline
swer in Czochralski, whose method the
spheres, but most of our fascination
world can now thank for essentially all
has been with valuable gemstones.
microelectronics.
Today, crystals produced artificially in
At the Leibniz Institute for Crystal
the lab serve entire industries. WithGrowth (IKZ) in Berlin, special crysout them there would be no lasers, no Single-crystal growth at the IKZ, Leibniz
tals are grown in this way for applicacomputers, no electronic devices, no Institute for Crystal Growth in Berlin,
tions such as future mobile telesatellite technology. Many of these Germany.
phones. Exotic crystals that cannot be
crystals don’t even occur in nature;
produced by conventional methods
they have to be grown, sometimes at great scientific effort. are instead grown with the help of molecular beam epiThe German physicist Max von Laue had an ingenious idea taxy: employed at the Ferdinand-Braun-Institut, Leibfor determining the structure of crystals in 1912. He sug- niz-Institut fuer Hoechstfrequenztechnik (FBH) and at the
gested that the X-rays discovered by Wilhelm Conrad Paul Drude Institute for Solid State Electronics (PDI). In
Röntgen had a wavelike character and should therefore ex- this method, extremely thin crystal layers are vapour dehibit interference as they passed through a crystal lattice. posited in a vacuum, one atomic layer at a time.
Biophysicist Walter Friedrich conducted related experiments with doctoral student Paul Knipping in Munich. Us- Translation: Peter Gregg
ing X-rays, the two young researchers were able to demonstrate that crystals have a lattice structure. Max von Laue
delivered the theoretical explanation, for which he reQuasicrystals – projections from hyperspace
ceived the Nobel Prize in 1914.
This discovery was the birth of modern crystallography.
At 2014 the Congress of the International Union of Crystallography (IUCr) in
Since then, X-rays have been used to determine the strucMontréal, Canada, Dan Shechtman gave a talk about his discovery of quasicrystals, for which he won the 2011 Nobel Prize in chemistry. Quasicrystals are structures of nearly all crystallisable materials. One of the hightures that do not follow the rules of translational symmetry, meaning they have a
lights among organic materials were the diffraction experstructure that is ordered but not periodic. Such crystals were regarded as comiments done by Rosalind Franklin. Working from her data,
pletely impossible until Shechtman’s discovery. To his death, twice Nobel laureate
biochemists Francis Crick and James Watson deciphered
Linus Pauling defended the opinion that “there are no quasicrystals, only quathe structure of DNA in 1953. British Nobel laureate Dorosi-scientists”. He was wrong. Today, quasicrystals can already be grown to centithy Crowfoot Hodgkin used X-ray analysis to elucidate the
metre scales. The talks at the IUCr Congress made it clear that quasicrystals and
structures of many important biological molecules, includthe crystallographic theory required to describe them could soon gain major
ing pepsin (1934), penicillin (1944) and insulin (1969).
practical relevance. Quasicrystals couple electric polarisation with magnetic poToday, there are even more powerful radiation sources
larisation, and are conceivable as future data memories with enormous storage
available for structural analysis, including neutron and
density. It has already been mathematically confirmed that quasicrystals are
synchrotron radiation sources.
translationally symmetrical in “hyperspaces” of up to six dimensions. What we
There was another crystalline breakthrough made in
see is accordingly only the projection from hyperspace into our three-dimensionBerlin a hundred years ago. Polish chemist Jan Czochralski
al world. While all this may be difficult to imagine, the mathematics is quite
(1885–1953) was working as head of the AEG laboratory of
manageable. There is now great need for the development of suitable theoretical
metallurgy. Legend has it that he accidentally dipped his founand metrological methods for providing a quantitative description of hyperspace.
tain pen into a crucible full of liquid tin. As he carefully pulled
This means plenty of work for future generations of crystallographers.
the pen out of the melt, it drew a long crystalline thread with
DR DETLEF KLIMM (LEIBNIZ INSTITUTE FOR CRYSTAL GROWTH)
it. While Czochralski immediately published the method, it
wasn’t until 1950 that it was applied in practice. At that time,
26 SCIENCE IN FOCUS · IKZ
verbundjournal
Almanac 2016
Electron microscope helps
grow perfect crystals
The single crystals grown by the Leibniz Institute for Crystal Growth (IKZ) in Berlin-
Adlershof are in great demand amongst scientists and industrial clients around the
world. The institute possesses unrivalled expertise in growing very large crystals, called
bulk crystals. Using electron microscopes, scientists are able to optimise growth conditions for nearly flawless crystals.
D
»
r Martin Albrecht and his team analyse the exact
chemical structure of tiny crystal samples to discover
the correlation between atomic structure and the properties of semiconductor crystals. As early as the 1950s, the
visionary physicist Richard Feynmann theorised that if
there were a microscope with a resolution all the way
down to the atomic level and one knew the position of
each individual atom in the crystal, it would, in principle,
be possible to derive its physical properties. All you would
have to do was to solve the Schrödinger equation...
Easier said than done! “Of course, you can’t solve it for
infinitely large systems,” Martin Albrecht from IKZ concedes
with a laugh. “But that’s okay, because
We are now able to we have made quite a lot of headway
achieve a high degree using density functional theory.” This
theory facilitates fairly accurate comof accuracy at the level puter calculations and simulations of
of 1.2 picometres.« complex structures. But the main
problem was that, for a long time, the
microscopes were not nearly good enough because of major
lens aberrations. This was not remedied until the 1990s.
Some years ago, IKZ had already decided to expand its
structural research and use electron microscopes on a
high methodological level. On the one hand, they wanted
to gain a better understanding of the growth processes of
their “own” crystals – and further optimise them, and on
the other, they wanted to advance materials research. After all, it was not just the colleagues at IKZ, the Ferdinand-Braun-Institut and the Paul Drude Institute who
were very keen to get a closer, atomic-level look at hetero-
Atomic structure of a layer used to reduce
the density of defects that negatively
affect the efficiency of GaN-based LEDs.
The layer consists of an atomic layer in
which Si-atoms and Ga-atoms as well
as defects are lined up periodically. The
monoatomic layer, marked with arrows,
reduces the density of linear defects.
structures created with gas-source or molecular-beam epitaxy, but also industry.
“We have great expertise in studying gallium nitride
semiconductors, which are used in LEDs and power components. This is why we have a lot of joint projects with
OSRAM, one of the world’s leading LED manufacturers,”
says Albrecht. In the past, efforts to improve a product
usually ended up in one great battle of materials. “People
would tweak here and there, all over the parameter field,
trying to find out what would yield the best properties.”
Classic trial and error.
Electron microscopes and theoretical calculations like
density functional theory shorten this process significantly. “This is how we learn what is worth tweaking in the
first place – which makes for drastically shorter development times,” says Albrecht. Using this process, IKZ physicists have managed to solve some of the problems the scientific community had been tackling in vain for the last
twenty years.
For instance: Why do nitride semiconductors become
more efficient if you first run ammonia over the substrate
instead of secreting gallium nitride directly onto sapphire?
It creates a sort of buffer which, to a certain extent, evens
out the ill-matching lattice parameters of sapphire and
GaN. The inventors of blue LED lights used this trick,
which earned them the Nobel Prize in 2014. What remained unclear, however, was why this worked so well.
New development opportunities
for users
“We just discovered that the differing lattice parameters
weren’t actually the point – it was the polarity of the sapphire surface.” The mineral sapphire, or aluminium oxide
(Al2O3) to give it its chemical name, always carries oxygen;
the oxygen atoms are virtually “riding” the mineral. Running ammonia (NH3) over it creates a mixture of aluminium,
oxygen and nitrogen. “That causes a switch in the polarity,
meaning that now the gallium nitride (which is polar) is in
an ideal state to attach itself with its metal side.” This insight
now opens up new development opportunities for users.
“The great thing about electron microscopes is that you
can really see things, not like with X-ray diffraction,”
verbundjournal
lbrecht says. His Ph.D. candidates and postdocs are workA
ing with an HRTEM, a high-resolution transmission electron
microscope. It has a resolution of 0.7 Ångström (10-10 m),
which roughly corresponds to the lattice spacing in a crystal. “We use the phase contrast, which under certain conditions makes the atoms appear in bright colours. What we
see is the density distribution of electrons that are scattered
on the crystal lattice,” Albrecht explains. Since there are always a few water molecules that condense on the samples
from the air and that blur the image to some extent because
they cannot simply be blow-dried away, researchers resort
to a trick: “We don’t just take one image, we take thirty.” Because the electron beams make the intruders fluctuate on
the surface, compiling all the images into one will “mendel
out” the blur, and what is more: “We are now able to achieve
accuracy at the level of 1.2 picometres (10-12 m).”
A question of temperature
Images: IKZ
IKZ · SCIENCE IN FOCUS 27
Almanac 2016
The most exciting moment is when the image of the real
sample is compared to the computer simulation (based on
theoretical calculations). It is astounding when they match
up perfectly – as is the case with gallium nitride that contains 33 per cent of indium. Albrecht turns on the projector and shows both images on the wall. “Here we can see a
perfect monolayer in which every third little ball is an indium atom. Very regular,” Martin Albrecht explains. A layman would expect a more statistical, that is irregular, distribution. “It’s a question of temperature, because there is
a phase transition. If the temperature is low enough, the
ordered phase has less energy. It is therefore the preferred
phase. If the temperature is too high, entropy kicks in, and
the atoms are distributed across the crystal statistically.” A
genuine mixed crystal will only form when indium levels
are as high as they are in this case. Theoreticians at the
Max Planck Institute in Düsseldorf have determined the
exact temperature for the phase transition: 750 degrees
kelvin (477 degrees centigrade).
In addition to nitride semiconductors, IKZ researchers
often place their own oxide semiconductors under the electron beam. This was how they finally solved the mystery of
the colour of zinc oxide monocrystals. “Due to their large
photonic band gap, they ought to be completely colourless
– but they are always orange,” says Albrecht. Heating (annealing) up these crystals in an oxygenic atmosphere
makes the colour vanish. The same happens to coloured
crystals of other oxides. “Many colleagues thought this was
due to oxygen vacancies, that is, defects which act as colour
centres and which are refilled while heating. But we
couldn’t believe that.” In fact, it was zinc particles that were
responsible, atomic crumbs of zinc, two to three nanometres in size. They create resonance, just like old stained
High-resolution image of a boundary layer between a strained
ferroelectric layer (NaNbO3) and the substrate (DyScO3), taken at
IKZ with a scanning transmission electron microscope. In this imaging mode, the intensity of the image increases with the atomic
number of the atom, which makes it possible to derive statements about the chemical composition. The analysis of images
taken in different crystallographic projections (a) [1-10]o and (b)
[001]o led to the conclusion that layer and substrate mingle at
the boundary layer, which affects the electronic properties of the
boundary layer. Atomic models of the structure are superimposed
over the image: blue, purple, red, yellow and green atoms represent Dy, Sc, O, Na and Nb. (c) Intensity profiles perpendicular to
the boundary layer along positions 1 and 2 in Figure b.
glass windows in churches. “They are coloured because the
glassmakers mixed in small amounts of the finest gold or
silver particles with the silicon dioxide before they melted
it.” At the interface between the glass and the tiny spherical
metal objects, electromagnetic waves of light are scattered
elastically – an effect known in physics as Mie scattering.
“Whether it is blue, red or yellow: the size of the particles is
the sole determining factor for colour,” Martin Albrecht explains. When annealing in oxygen, the particles are fully oxidised and defects disappear as if by magic.
Following processes in the electron
microscopes
So far, researchers have only been able
to take “before and after” images of
this, because typically, electron microscopes operate in a high vacuum. However, a tiny gas chamber is now being
installed at the microscope, which will
hold the sample. Under atmospheric
pressure, it will be possible to induce
oxygen or hydrogen and to heat the
chamber to any temperature up to
1000°C. “This way, we can observe the
processes as they happen and gain a
better understanding of their thermodynamics,” Albrecht enthuses.
The electron microscope at IKZ is
housed in a joint lab operated in cooperation with the Humboldt University of
Berlin (HU). “HU mainly uses its device
for chemical-analytical purposes – we
use ours to conduct structural studies,”
Albrecht explains. “This is another collaboration we are planning to expand.”
Translation: Lynda Lich-Knight
IKZ’s scanning transmission electron
microscope FEI Titan 80-300 G2 (STEM
/ TEM) is capable of taking images at a
resolution of 0.07 nanometres.
28 SCIENCE IN FOCUS · IZW
verbundjournal
Almanac 2016
ST EVEN SEET
Mystery of polar bear Knut’s
disease finally solved
Four years after Berlin’s celebrity polar bear Knut died, scientists from Germany have
finally found the cause of Knut’s death: The bear suffered from an autoimmune disease
of the brain. This non-infectious illness is called “anti-NMDA receptor encephalitis”, with
symptoms in human patients similar to those displayed by the polar bear. Knut is the
first animal in which this form of encephalitis has been established.
K
nut, the polar bear of the Berlin Zoological Garden
(Germany), was a favourite with the public across the
world. Hand-raised by a zookeeper, he became a real sensation. In 2011 the bear unexpectedly died at the age of
four: drowned after he suffered epileptic seizures and fell
into the enclosure’s pool. Scientists under the leadership
of the Leibniz Institute for Zoo and Wildlife Research
(IZW) in Berlin intensively investigated the potential causes of Knut’s death and revealed that the seizures were
caused by encephalitis, suspecting an infection by an unknown pathogen. However, the exact cause of the disease
remained a mystery for a long time.
Cooperation of neuroscientists and
wildlife researchers
»
Dr Harald Prüß, researcher at the Berlin site of the German Center for Neurodegenerative Diseases (DZNE) and
a specialist in neurology at the Charité, read the autopsy
report and discovered parallels to his own studies on human brain diseases. The neuroscientist contacted Professor Alex Greenwood – the head of the Department of
Wildlife Diseases of the IZW –
Epileptic seizures, who had led the primary study on
hallucinations and Knut. Could it be that Knut had
suffered from an autoimmune disdementia are among the ease of the brain? The two scienpossible symptoms.« tists quickly agreed to follow up
on this line of research together.
Greenwood had considered there might be a non-infectious cause of disease, but until the collaboration with
Prüß there was no real possibility to test for this class of
diseases in wild animals. The IZW had kept samples of
the polar bear’s brain which could be used for later analysis.
“This study gave us the opportunity to extend and refine our test methods,” says Prüß. Analysis revealed that
the polar bear had developed “anti-NMDA receptor encephalitis”. In the animal’s tissue samples, the scientists
demonstrated the presence of NMDA-receptor antibodies,
the characteristic proteins for this encephalitis.
“Until now, this autoimmune disease has only been known
in humans. In this illness, the body’s immune system overreacts and produces antibodies which damage nerve cells
instead of fighting against pathogens,” Prüß explains. “Epileptic seizures, hallucinations and dementia are among the
possible symptoms.”
Unknown until recently
These diseases were discovered only a few years ago. According to Prüß, until recently, patients with encephalitis
for which viruses or bacteria were not identified as the
causative agent remained undiagnosed, and their origin a
mystery. “In the past few years, the number of unsolved
cases has decreased considerably. Since 2010, we have
known that the majority of patients with encephalitis of
unknown etiology are suffering from anti-NMDA receptor
encephalitis, once infectious causes were ruled out. There
are now standard tests to diagnose the disease,” says the
neuroscientist. “In humans this disease is relatively responsive to medical treatment.”
“We were quite intrigued by this result,” comments
IZW scientist Greenwood on this discovery. “Anti-NMDA
receptor encephalitis has been described only very recently in humans. Clearly it is also of importance for other mammals. We are relieved to have finally solved the
mystery of Knut’s disease, especially as these insights
could have practical applications. If the current therapy
for human patients is also suitable for wild animals,
many cases of fatal encephalitis in zoos may be prevented in future.”
Antibody tests in dementia patients
“Knut’s disease has further implications. It is possible that
autoimmune diseases of the nervous system might be far
more common in humans and other mammals than previously assumed,” says Greenwood.
“We might underdiagnose autoimmune inflammations
in human patients suffering psychoses or memory disturbances, because these patients are not routinely screened
verbundjournal
IZW · SCIENCE IN FOCUS 29
Almanac 2016
Picture: Berlin Zoological Garden
Knut, the famous polar bear from the Berlin Zoo, suffered from an autoimmune disease of the brain. The illness is called “anti-NMDA
receptor encephalitis”, with symptoms that are also seen in human patients. The body’s immune system overreacts and produces
antibodies which damage nerve cells instead of fighting against pathogens.
for associated antibodies. As a result they may not receive
the optimal treatment. Therefore, I believe it is reasonable
to examine patients for associated antibodies, especially if
the cause of a dementia is unknown. These antibodies can
be held in check by pharmaceutical means. There are also
other forms of encephalitis, where errant antibodies
against other receptor molecules are important in disease
development,” comments DZNE researcher Prüß.
“The research results are an important contribution to
understanding autoimmune diseases of the nervous sys-
tems in animals. One can only congratulate the scientists
of the Center for Neurodegenerative Diseases, the Leibniz
Institute for Zoo and Wildlife Research and the Charité –
Universitätsmedizin Berlin. They have made it possible
that in the future, diseases in animals similar to Knut’s
could be diagnosed earlier and treated,” says Dr Andreas
Knieriem, Director of the Berlin Zoological Garden.
Scientific Reports 5, Article number: 12805 (2015);
DOI: 10.1038/srep12805
30 SCIENCE IN FOCUS · IZW
verbundjournal
Almanac 2016
GESINE WIEMER
Bats versus wind turbines
Wind turbines are responsible for the death of many bats. Scientists determined the origin
of these animals: They do not only come from local areas; rather many have already been
on a long migratory journey. Germany therefore bears responsibility for protecting not
only native bat populations, but also the populations of other countries.
ind turbines are an important component of renewable energy policies. The technology is well advanced and wind is available in abundance, particularly in
northern Germany. While there is plenty of discussion
about how to transport the electricity to the power-
demanding southern parts of Germany, and many are
quick to comment on the aesthetics of turbines, there is
another problem: the rotor blades are a deadly danger to
many birds and bats. An estimated 300,000 bats are at
risk of being killed by wind turbines in Germany every
year, unless this risk is reduced by turning off the systems
at night during the main hours of bat activity.
In a 2014 study, a research team led by the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin identified the origin of greater noctules – a migrating bat species that is often in collisions with wind turbines in the
eastern states of Germany. More than one quarter of the
bats studied were not local but were on their way to their
wintering grounds in Germany or southwestern Europe.
They had started their flights in the northeastern range of
their habitat in the Baltic States, Russia, Belarus or Poland.
Wind turbines cause large numbers of
bat fatalities
A surprisingly large proportion of females and young
animals were amongst those killed. This is especially
critical for wildlife populations because, with each
female, their potential offspring is also eliminated.
“Our study showed that Germany bears responsibility not only for the protection of local bats,
but also for the migrating bats from other
countries owing to its central location as a
transit area,” emphasises Dr Christian Voigt,
biologist and bat researcher at IZW. Germany lies right along the migratory
route of bats that move to warmer regions – such as southern Germany,
Switzerland or southern France – during autumn after leaving their breeding areas in northeastern Europe, where females give birth to their young every
spring. Additional losses of bats at wind farm facilities in
Germany are especially dramatic for these populations
since harsh climatic conditions in their northern breeding
range prevent them from successfully reproducing every
year. If many of these bats die at wind turbines, source populations in northeastern Europe could be significantly
weakened.
The researchers determined the bats’ origins using methods from forensic science. When a cadaver of unknown
origin appears, forensic experts examine the ratio of
heavy hydrogen (deuterium) to light hydrogen in the keratin of hair – a “geographic fingerprint”. This ratio varies
in precipitation water as a factor of continental gradients
in ambient temperature, i.e. precipitation in northern areas is less rich in deuterium than that of southern areas.
Humans and animals assimilate this water directly or
through their food and deposit the isotopes in their body
tissue. Since keratin is biologically inactive, the isotopic
ratio remains constant over several months. Like a geographical fingerprint, this indicates the origin of a human
or an animal. The method is particularly useful because
the scientists can determine the origin of each bat without having to band them, as is the conventional method
in migration studies. That would truly require an immense effort.
Attracted to wind turbines
Unfortunately, wind turbines even attract bats. During
the mating season in autumn, bats swarm at conspicuous
landscape features such as exposed rocks, church towers
or even wind turbines. Christian Voigt is surprised that
only few far-reaching measures have been taken to stop
wind turbines turning into deadly traps. “Bats are protected under both German law and EU law, and migratory species are protected by a UN convention signed by
Germany. Anyone who kills a bat on purpose can be prosecuted for a criminal offence,” he says. There is little emphasis on making operators of wind turbines accountable for these bat accidents because increasing the share
of renewable energy is a political priority. “The protection of climate and species are played off against each
other – but for a comprehensive approach to environmental conservation they should really go hand in hand,”
Voigt says.
Wind turbines and bats could actually get along well
with each other: bats do not like strong wind. They are
only active at wind speeds of up to six to eight metres per
second. At this speed, wind turbines barely produce
enough energy to be economical. If the turbines would
only run at stronger wind speed, collisions could be avoided – as could clashes between the protectors of species
and climate.
PLOS ONE 9 (2014); DOI: 10.1371/journal.pone.0103106
Picture: Bjoern Wylezich – Fotolia
W
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IZW · SCIENCE IN FOCUS 31
Almanac 2016
KARL-HEINZ-K ARISCH
Tracking wild animals with GPS
The natural habitat for wild animals is shrinking. Human settlements, roads and agriculture are making it harder for animals to travel long distances to find food or a mate. Using telemetry collars and the Global Positioning System (GPS), scientists of the Leibniz
Institute for Zoo and Wildlife Research (IZW) have for several years been tracking the
migration of elephants and cheetahs in Africa.
I
ZW Director Prof. Heribert Hofer and his colleague Prof.
Thomas Hildebrandt did their first work with GPS tele
metry collars in 2000, in the border zone between Mozambique and Tanzania. In those days, they tracked the migratory movements of elephants. “GPS has made many
observations much easier,” says Hofer, who was one of the
first researchers to use telemetry in wildlife observation. In
the 1980s, he already had used the first satellite navigation
system, called Transit, to precisely locate his own position
while watching wildlife in the Serengeti. “Back then, we
could only dream of locating animals by GPS,” he recalls.
Yet, unceasing miniaturisation of GPS devices has made it
possible to track even small animals these days. Essentially,
the only limit to this approach is battery power.
But technology is advancing in this respect, too. Measurements can be scheduled flexibly, which saves power.
There are also multiple ways by which to access the GPS
data from the animals’ collars. They can be read very easily over the mobile phone network, for example for sea eagles, via special satellites or from light aircraft.
Dr Bettina Wachter is just returning from a three-day
excursion when our query reaches her at the camp in Namibia. She has headed the IZW Cheetah Research Project
there for over twelve years. Her days in the field were exceptionally successful. “We caught several cheetahs, put
GPS tracking collars on them and released them back into
the wild,” she reports.
There are around 50 cheetahs with a GPS collar at present, 200 animals having been fitted with a collar so far. The
devices record each animal’s position every 15 minutes.
PhD student Jörg Melzheimer on board a Piper aircraft
downloads and then analyses the flood of data. “We can fly
for about six hours and locate six or seven animals per
flight,” Bettina Wachter explains.
Picture: IZW/Bettina Wachter
Involving Namibian farmers in a
carnivore research project
The project has a serious background. The cheetah is a vulnerable species that only exists on Namibia’s commercial
farmland in large populations. Here, local farmers see cheetahs as a potential threat for their cattle. By analysing isotopes of hair and tissue samples, IZW researcher Dr Christian Voigt and the Cheetah research team have proven that
cheetahs only rarely feed on cattle. Bettina Wachter provides
the farmers with further assistance. From the GPS data, Jörg
Melzheimer was able to show distribution patterns of chee-
tahs are variable: “There are areas
where there is high cheetah activity
and there are areas where the predators hardly go at all.” From this, Wachter has put together suggestions for the
farmers on where to keep their cattle
herds during the most vulnerable calving time – far away from the wild cats.
The Namib Desert in the African
Kunene Region is one of the hottest
places on earth. Here, Christian Voigt is
studying the living conditions of the
oryx antelope, also known as the gemsbok. “The animals are popular game
for tourist trophy hunters, and they are
an important source of protein for the
indigenous population,” the IZW researcher reports. The wild animal populations are managed by the local population, meaning the hunting quota is IZW Cheetah Research Project: Taking
determined locally. “But for this,” Voigt blood from a free-ranging cheetah on
continues, “it is important to know Namibian farmland and attaching a GPS
whether the animals do have local hab- collar to the animal.
itats or whether they migrate over
large areas.” Zoologists had previously assumed the oryx antelope migrate over large distances to greener regions. “So,
we put GPS collars on eight animals and recorded where the
animals went over three seasons,” he reports. “Contrary to
what we had assumed, they remained almost exclusively local.” That suggests the animals are very well adapted to the
food availability in the desert habitat.
IZW researchers are helping to reduce human-wildlife
conflicts. In some cases, this has meant having to create
the technical means to do so. Dr Anne Berger and industrial partners have, for example, combined GPS transmitters
with accelerometers and developed algorithms for analysing the activity data. Thus, the IZW researchers are now
able to break down the movements of the animals in three
dimensions. “This is what is truly exciting for us researchers,” says Heribert Hofer. “From such combined data, we
can draw increasingly precise conclusions about the animals’ behaviour.”
PLOS ONE 9 (2014); DOI: 10.1371/journal.pone.0101917
(Editors' Suggestion)
32 SCIENCE IN FOCUS · MBI
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Almanac 2016
CLAUS-PETER SCHULZ, JOCHEN MIKOSCH, JULIA BRÄNZEL, CHRIST IAN KOSCHIT ZKI,
MATTHIAS SCHNÜRER, T HOMAS ELSAESSER
Einstein and the electron –
photoeffect, Theory of Relativity
and ultrashort light pulses
T
he first correct description of the photoeffect was given in a paper entitled “Generation and conversion of
light with regard to a heuristic point of view” (German:
“Über einen die Erzeugung und Verwandlung des Lichtes
betreffenden heuristischen Gesichtspunkt”) which was
later recognised by the Nobel Prize. A second publication
from the same year contains the fundamentals of the special relativity theory. As an example the relativistic motion
of an electron in electric fields is discussed. Important research projects of the Max Born Institute for Nonlinear
Optics and Short Pulse Spectroscopy (MBI) are settled in
these scientific fields.
Ultrashort light pulses and the
photoelectron
Einstein’s interpretation of the photoeffect is based on the
following experimental observation (Fig. 1 top): When a
metal surface is irradiated with single-coloured ultraviolet
light electrons are excited from the metal into free space.
All ejected electrons have the same kinetic energy, which
only depends on the colour of the light and the type of
metal. According to Einstein the kinetic energy of the elec-
Fig. 1: (top) Photoelectric Effect as predicted from Einstein.
(bottom) Irradiation of a metal surface with very intense laser
pulses changes the observed electron spectrum fundamentally.
trons corresponds exactly to the quantum energy of the
photon, which is determined by its wavelength (colour)
minus the work function of the metal surface. Hence, a
stronger light intensity does not lead to higher electron
energy but to more photoelectrons with the same kinetic
energy.
Einstein did not know yet that at very high light intensities also more than one photon can be absorbed at the
same time. This multi-photon absorption first described
by Maria Goeppert-Mayer in 1930 is the first cornerstone
of nonlinear spectroscopy. When a metal surface is illuminated by a very intense laser pulse the energy distribution
of the photo electron shows discrete maxima at multiples
of the photon energy (Fig. 2 bottom). In contrast to Einstein’s photoeffect now the exact energies depend on the
intensity of the light pulse, since the light field accelerates
the electrons additionally, i.e., it creates a so-called ponderomotive potential.
At even higher intensities around 1014 W/cm2 easily
producible with lasers at the MBI the strength of the light
field becomes comparable to the electric field within atoms. The electrical potential of an atom or molecule will
be distorted strongly by such light fields and the weakest
bound electron can tunnel through the remaining energy
barrier into the vacuum, a genuine quantum mechanical
effect. The released electron will subsequently be accelerated strongly and – at certain phases of the light field – return to the atom or molecule where it originates from.
There it can recombine and its total energy is converted
into a photon. Since the period of the driving laser field
amounts to only a few femtoseconds (= 10-15 s) and the
moment of recombination for all released electrons is
about the same, light pulses of about 100 attoseconds
(= 10-16 s) duration can be generated.
Attosecond pulses are an important probe for fast electron motions in molecules. If one manages to manipulate
the electron motion in the time domain from a few hundreds of attoseconds up to a few femtoseconds one would
be able to steer molecular processes with unmatched precision. In the last years attosecond dynamics in molecules
have been studied theoretically in computer simulations
(Fig. 2 top). Recently, experiments in the attosecond labo-
Images: MBI
In 1905 Albert Einstein published several epoch-making papers which strongly influenced the development of modern physics and formed the basis of numerous applications in modern research with light.
verbundjournal
Almanac 2016
MBI · SCIENCE IN FOCUS 33
Fig. 2: (top) Computer simulation of a photo induced electron dynamics. Within a few femtoseconds the excess charge moves from
the left to right end of the molecule. (bottom) The laser induced
charge oscillations in a CO2 molecule is observed in a pump probe
experiment through the variation of the ionization rate.
Relativistic particle acceleration with
High Field Lasers
ratory of the MBI succeeded in making the electron motion visible for the first time. An infrared laser polarizes
molecules and induces an oscillating dipole moment synchronous to the laser field. A phase locked attosecond
pulse train samples this ultrafast dynamics via photoionization of the molecule, i.e. via the photoeffect. Depending
on the phase between the attosecond pulse train and the
synchronous infrared laser the ionization probability varies on an attosecond time scale (Fig. 2 bottom).
Fig. 3: Apparatus for laser driven electron acceleration located at
MBI´s High Field Laser Laboratory. Background: radiation protection, spectrometer housing and laser plasma interaction chamber.
Foreground: Chamber for laser beam steering and focusing.
The inertial mass of a particle increases the more its velocity approaches the speed of light – this pivotal conclusion
of the special relativity theory has far-reaching consequences for particle acceleration. In the strong electric
fields of large accelerator electrons can gain kinetic energies up to giga-electronvolt (GeV) where they move with
99.99 per cent of the speed of light. A completely different
approach is the particle acceleration in plasma, a mixture
of electrons and positively charged atomic cores (ions).
Plasma can be formed by focusing a laser beam into a tiny
volume. The extremely high energy concentration and local field generated in the focus can accelerate particles.
Here, relativistic effects of the light matter interaction are
exploited.
About 30 years ago computer simulations showed that
intense laser pulses can drive a large number of electrons
to giga-electronvolt energy while propagating through
plasma. The principle of this phenomenon – called wake
field acceleration – is simple: A moving object on a water
surface tows a wake wave which travels along with it.
Such propagation is exploited by surfers who get accelerated while riding down a wave. Due to a propagating laser
pulse – which is the analogous object – plasma electrons
can surf on initiated charge waves and are accelerated
close to speed of light. Using femtosecond laser pulses
provided by Terawatt laser systems, such as those at MBI,
it is possible to build a compact laser plasma accelerator.
Such a device covers a few square metres only (cf. Fig. 3,
the driver laser covers about 20 m2) and is able to generate similar electron energies as produced with an electron storage ring of BESSY II type with 240 m circumference. Currently research at the Max
Born Institute is focused on control
and stability of the acceleration process. It is essential to steer the injection of electrons into the wave field.
Thus a high reproducibility can be
achieved and the electrons are
bunched within femtosecond duration in a very narrow beam. Fig. 4 exemplifies how injection can be con- Fig. 4: Electron energy in MeV as a
trolled with a technical trick which function of injection position into plasma
determines the electron energy and wave. The acceleration strength amounts
allows calculating the acceleration to 100 MV/mm.
field strength. This type of basic research is a requirement for development of new facilities
for electron acceleration being used in diverse application
from a broad user community.
verbundjournal
Almanac 2016
THOMAS ELSÄSSER AND TORST EN SIEBERT
Clocking the motions of water
on the surface of the
DNA double helix
Schematic representation of the
DNA surface and
the surrounding
water derived
from the X-ray
crystal structure of
a hydrated DNA
double helix.
S
urfaces of biological macromolecules are complex environments governed by the electric interactions and bonding of polar and charged surface structures with interfacial constituents such
as water, ions as well as other molecular species
in direct proximity. This interplay of a molecular
surface and its environment is crucial for regulating the global structure of proteins, lipid membranes and nucleic acids and plays a central role
in the remarkable biological functions and chemical processes realised by these systems. Despite
this high relevance for biomolecular functionality,
short-range electric interactions at molecular
surfaces – in particular their dynamics – are
not fully understood. While X-ray crystallography can provide static molecular-scale geometries in which these interactions take place,
unraveling the mechanisms with which diverse molecular
participants and surface structures act together to define
the processes taking place at the interface is challenging.
Molecular motions and structural dynamics of these interfacial constituents must be captured on time scales faster
than 1/1012 of a second in an environment extending only a
few molecular layers from the surface.
The DNA double helix with its hydration shell and atmosphere of counterions presents a prominent example of
surface interactions that are central for the global structure and function of this system. By using the vibrational
motions of structural elements in the DNA backbone, local
interactions and electric forces in this environment have
been measured for the first time without disturbing the
natural molecular arrangements at the surface. This is
achieved by monitoring the distortions that fluctuating
electric forces at the interface impose on vibrational motions of the backbone after their excitation with ultrashort
infrared laser pulses. The optical response to these coherent excitations detected as so-called photon echoes reveals the magnitude and time scale of electric interactions
at the interface when vibrational frequencies measured
upon excitation are correlated with those acquired after a
defined waiting period.
Using this approach, fundamental insight to
the properties of the hydration shell surrounding the DNA double-helix has been obtained.
While other charged elements and counterions
are present at the interface, varying the amount
of water molecules in the hydration shell shows
that water dipoles dominate the electric interactions at the DNA surface. From the time scale of
the electric fluctuations, it was further concluded
that water at distances up to several angstroms
form the DNA surface behaves very differently
from pure water in its bulk state. The fluctuating
motions of water molecules are several times
slower and the typical positions that water molecules assume around the helix as well as the
bonding with the DNA surface are preserved for
durations at least an order of magnitude longer
than the making and breaking of the equivalent
bonding network in pure water. This change in the dynamic properties of water exposed to the electric potential of
the DNA surface is synonymous with changes in its fundamental physical properties. Effects such as electric screening from water at the surface and the influence of outer
water layers or species at greater distances can be evaluated correctly with this insight.
The DNA surface not only influences the properties of
water in proximity, the measurements further show that
the inner hydration shell significantly changes the local
coupling between vibrational motions in different structural elements of the DNA backbone. Since the DNA surface and the hydration shell alter the properties of the respective partner as a result of their electric interaction,
neither can be described correctly without the presence of
the other. From this picture of the interface, the first two
water layers of the hydration shell can be seen as an integral part of the double helix structure in its natural state
and not as a separate, independently acting medium surrounding the DNA at the surface.
J. Phys. Chem. B 119 (2015); DOI: 10.1021/acs.jpcb.5b04499
Struct. Dyn. 3 (2016); DOI: 10.1063/1.4936567
Image: MBI
A research team led by the Max Born Institute (MBI) in Berlin have found that water at
the interface with DNA contributes prominently to subpicosecond structure fluctuations, and leaves hydrogen bonds between DNA and water intact.
verbundjournal
Almanac 2016
KARL-HE INZ K ARISCH
The world’s first photos
of electron clouds
The first delicate rings of green, yellow and red on a blue background were an international sensation in the world of physics in 2013. Until then, namely, it had been considered absolutely impossible to take photos of electron clouds around atomic nuclei. It
took the group, led by Professor Marc Vrakking at the Max Born Institute (MBI), around
ten years to capture the orbital structure of hydrogen and helium atoms. By now, the images have not only made it into the first physics textbooks – they are also included in our
“Verbundjournal”.
B
Image: MBI
asic research takes time. “At the beginning, we experimented with xenon atoms,” Vrakking recalled. However, they have a total of 54 electrons, with a lot of mutual interaction. For this reason, the scientist and his research
group put their heads together to design simpler experiments. “As a result, we arrived at the hydrogen atom, which
has just one electron, and later helium, which has two,” the
physicist explained.
In the world of atoms, the special laws of quantum mechanics apply, which always describe states using a wave
function, enabling physicists to characterise the velocity or
the position of an electron. The photos of the orbital clouds,
Vrakking explained, “reflect the respective probability distribution of the electron in different energy states, even
though the photo itself was generated from millions of
electrons.”
In simplified terms, the energy of a laser is adjusted so
that the individual light particles (photons) contain just
enough energy to separate the electron from the atomic
nucleus. Only 0.1 per cent of the energy is emitted to the
released electron in the form of kinetic energy. These socalled photoelectrons are very slow and are directed towards a detector screen using an electric field. Since electrons have a wave nature in addition to a particle nature,
this leads to a number of circular interference rings on the
observation screen. Previous experiments revealed two
different mechanisms for the formation of interference,
during which waves intensify or diminish. In the case of hydrogen, the interference directly reflects the nodal patterns
of the wavefunctions. With larger atoms, additional interference is caused
In the world of atoms,
by the electrons’ different path lengths
the special laws of
to the detector.
quantum
mechanics
In the case of helium, researchers at
apply.«
MBI succeeded in controlling the correlation between the two electrons. When
the correlation is switched off, helium behaves like hydrogen. In contrast, when the correlation is switched on, interaction between the two electrons determines the dynamics
of the ionisation process. “We want to define the properties
of these electrons as precisely as possible, which will enable
us to understand interaction between atoms and electrons,”
states Vrakking. Of course, the colour coding was also chosen with aesthetics in mind. Nonetheless: “The photos of
the electron orbitals are not merely a nice side effect generated by our research – they were our primary aim.”
»
This image, showing the interference
rings of a helium
atom, portrays
the subtleties of
quantum physics
verbundjournal
Almanac 2016
Large amounts of polycyclic aromatic
hydrocarbons are revealed in the spectra of
interstellar clouds in space, as supported by
experiments at the Max Born Institute.
MARC VRAK K ING AND K ARL-HEINZ K ARISCH
A new approach towards solving
mysteries of the interstellar
medium
T
he astronomers have so far discovered some 400 diffuse interstellar bands (DIBs) in light from interstellar
clouds. Until now, however, it was virtually impossible to
assign DIBs precisely to specific compounds. Together
with international partners, Professor Marc Vrakking from
the Max Born Institute for Nonlinear Optics and Short
Pulse Spectroscopy (MBI) has shown that they indeed may
well be the assumed polycyclic aromatic hydrocarbons
(PAHs). The results, published in Nature Communications
in 2015, could have far-reaching consequences. “The larger the number of complex molecules we are able to prove
in space, the more plausible it is that there are common
life forms in the universe,” stated Vrakking.
Image: NASA/JPL-Caltech/T. Pyle (SSC)
For several years, there have been strong indications that, in the early universe, vast
amounts of complex organic compounds formed in interstellar clouds. Support for this
assumption is provided by the Max Born Institute in Berlin.
verbundjournal
By using ultrafast UV lasers, Vrakking and his colleagues
were able to identify the dynamics of highly excited molecular states. PAHs were considered to be one of the most
promising hydrocarbons as carriers of interstellar bands.
The presence of PAH molecules has previously been inferred in many astronomical objects, such as in the interstellar medium of the Milky Way, as well as in ten billionyear-old medium from the early universe. However, some
astronomers doubted these hypotheses, because the lifetimes of these unusual molecular states were unknown.
These doubts have now been dispelled after MBI researchers, in collaboration with scientists from the University of
Lyon, managed to prove that the lifetimes of electronic
states of small to medium-sized PAHs are consistent with
the linewidths observed for DIBs. The work was supported by theoretical input from scientists at the universities
of Leiden, Heidelberg and Hyderabad.
In the experiments, a series of small to medium-sized
PAH molecules (naphthalene, anthracene, pyrene and
tetracene, each containing several condensed aromatic
rings) were ionised by an ultrashort extreme-ultraviolet
(XUV) laser pulse. The absorption of an XUV photon led
not only to the removal of one of the electrons, but also to
electronic excitation of the resulting positively charged
molecular ion. The lifetimes of these excited cationic electronic states were measured using a time-delayed infrared
(IR) laser pulse. Directly after an electron has been removed from the molecule, electronic excitation is at its
highest, meaning that only one or a few infrared photons
are required to remove a second electron. Subsequently,
the ion “relaxes”, and more IR photons are required to remove the second electron. In other words, monitoring the
Image: MBI
Almanac 2016
»
formation of doubly charged ions as a
The larger the number
function of the time delay between
of complex molecules
XUV and IR laser pulses enables the
we
are able to prove in
lifetimes of different states to be
space, the more plausimeasured. These measurements, supported by theoretical high-level calcuble it is that there are
lations, were able to show that the
common life forms in
lifetime of organic PAH ions is in the
the universe.«
order of a few tens of femtoseconds
and well within the range of the diffuse interstellar bands measured from space.
These experiments have implications for the further development of attosecond physics because precise knowledge of charge migration, i.e. the ultrafast motion of an
electron or of a hole through a molecular structure, is of
great interest in the field of chemistry. This motion occurs
within the incredibly short space of attoseconds (a billionth of a billionth of a second) to a few femtoseconds (1015
seconds). Controlled charge migration could offer completely new opportunities for controlling chemical
reactions, a goal that is as old as chemical research itself.
Last year, researchers from the University of Milan presented first indications that charge migration on a time scale
from attoseconds to a few femtoseconds can be controlled.
The PAH molecules investigated in experiments at the
Max Born Institute represent the largest molecular species
yet to which ultrafast XUV-IR pump-probe spectroscopy
has been applied.
Nat. Commun. 6 (2015); DOI: 10.1038/ncomms8909
Schematic diagram of the experiment.
(a) Schematic of the XUV-induced dynamics in PAH molecules studied in this paper.
Excited states are created in the valence shell of the cation through one of two
possibilities, namely the formation of a single-hole configuration or the formation
of a 2hole-1particle configuration (involving a shake-up process) (left) (IP stands for
Ionization potential). The cation can be further ionised by the IR probe laser, provided
that non-adiabatic relaxation has not yet taken place (middle). After relaxation, the IR
probe cannot ionise the cation anymore (right).
(b) Two-colour XUV-IR ion signals measured in the case of anthracene, as a function of
the detected mass-to-charge ratio and the XUV-IR delay. XUV-only and IR-only signals
have been subtracted. The XUV pump and IR probe pulses overlap at zero delay (black
dashed line). A red colour corresponds to a signal increase, while a blue colour signifies
depletion. For positive XUV-IR delays, a very fast dynamics is observed for the doubly
charged anthracene ion (A2+, m/q=89). As explained in the text, the measurement
reflects non-adiabatic relaxation in the anthracene cation (A+).
38 SCIENCE IN FOCUS · PDI
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GESINE WIEMER
Quantum dots with
single-atom precision
A research team led by the Paul-Drude-Institut für Festkörperelektronik (PDI) has created quantum dots with identical, deterministic sizes. The perfect reproducibility of these
dots opens the door to quantum dot architectures completely free of uncontrolled variations, an important goal for technologies from nanophotonics to quantum information
processing as well as for fundamental studies.
uantum dots are often dubbed artificial atoms because,
like real atoms, they confine their electrons to quantized states with discrete energies. But the analogy breaks
down quickly because, while real atoms are identical, quantum dots usually comprise hundreds or thousands of atoms – with unavoidable variations in their size and shape
and, consequently, in their properties and behaviour. PDI
physicist Dr Stefan Fölsch, head of the team, explains: “For
applications like quantum computing, for example, we
need to be able to precisely control the size of quantum
dots, and with it their quantum state.” So far it has only
been possible to partially compensate for all the disruptive
influences using tricks such as applying an external electrical voltage. The international group from Berlin, Japan and
the USA has now for the first time achieved the ambitious
goal of producing quantum dots with perfect fidelity.
Quantum dots with perfect fidelity
Creating atomically precise quantum dots requires every
atom to be placed in a precisely defined location without
error. The researchers assembled the quantum dots atom-by-atom on a substrate using “atomic tweezers”. The
substrate was the surface of an indium arsenide semiconductor crystal.
A scanning tunnelling microscope normally serves to
produce images of a surface: Its tip scans the charge distribution of the surface, from which the position of the atoms
can be derived. The PDI physicists used the tip not to scan,
but instead to manipulate individual atoms. Much like using tweezers, they picked up each indium atom with the
tip and placed it in a new location. The team assembled
quantum dots in the form of linear chains comprising six
to 25 indium atoms each.
Steve Erwin, physicist from Washington D.C. and the
team’s theorist, explains: “The ionised indium atoms form a
quantum dot by creating an electrostatic well that confines
electrons normally associated with a surface state of the indium arsenide crystal.” Being spatially confined by the positively charged chain of indium atoms, the electrons become quantised. All this takes place at such miniscule
dimensions that the laws of quantum mechanics dominate.
Because the indium atoms are strictly confined to the
regular lattice of indium vacancy sites, every quantum dot
with N atoms is essentially identical, with no intrinsic variation in size, shape, or position.
For applications in quantum computing, many such quantum dots must be coupled together. The PDI researchers
therefore arranged quantum dots of three chains each with
three-fold symmetry. These become coupled in a known way
and exhibit behaviours like those of real molecules. “With
these precisely defined quantum states, we come a step closer to the quantum computer,” Stefan Fölsch stresses.
This method of atom manipulation was previously only
possible on metallic surfaces. Worldwide, the PDI has
made the greatest progress in growing stable structures
based on semiconductors.
Nature Nanotechnology 9 (2014); DOI: 10.1038/NNANO.2014.129
Image: PDI
Q
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GESINE WIEMER
A molecule transistor for the
quantum world
An international research team led by the Paul-Drude-Institut für Festkörperelektronik
(PDI) in Berlin has successfully built a minute transistor consisting of a single molecule
and a small number of atoms. It measures only one and a half nanometres across and exhibits quantum behaviour. From it, the researchers can gain fundamental physical insights that will bring us closer to electronics in the quantum realm.
T
ransistors, as fundamental components of micro
electronics, are continually shrinking. To make one,
one typically starts with a semiconductor material. Using
two electrodes (source and drain), a voltage can be applied to induce current to flow through the semiconductor, while another control electrode (gate) can be used to
modulate the flow of electrons. This means a transistor
can be used both to switch a current on and off and to
regulate the flow. Several millions of electrons, behaving
as charged particles, flow through the semiconductor in
this system.
One can achieve a similar transistor function on a much
smaller scale, of a few ten to hundred nanometres, using a
so-called quantum dot. This consists of hundreds or thousands of atoms deposited onto a suitable substrate in the
form of a tiny semiconductor crystal. In this kind of transistor, the electrons can only exist at discrete energy levels.
A current then flows when
The molecule does a single electron hops from
not sit still on the the source electrode to the
semiconductor quantum
surface, rather it dot and from there onward
can rotate.« to the drain electrode. This
is known as single electron
tunnelling. Using an additional gate electrode, one can
shift the energy level and thus influence the probability
that electrons will pass through the semiconductor, and
thus regulate the rate of flow. In this realm of quantum
physics, the electrons behave both as a particle and as a
wave.
The trouble is, conventional quantum dots are not perfectly identical since the atoms deposited onto a substrate
are afflicted with all the irregularities of a statistical
growth process. The research team wanted to build a
nanoscale system whose properties they could be certain
of. So they decided to use an organic molecule as their
quantum dot. Such a molecule is chemically precisely defined and always has discrete states analogous to a quantum dot. The tricky part is in applying contacts and a gate
to a molecule only 1.3 nanometres in size.
There are already various approaches, such as the
break junction technique. This is where a thin wire is re-
Image: PDI/Fölsch
»
peatedly bent in precisely the
same place until it breaks. If the
wire is in a liquid full of molecules, then, with a bit of luck,
exactly one molecule can bridge
the break point. As can be imagined, this takes many tries,
after which one still cannot see
with atomic resolution how the
molecule is sitting on the contacts.
The research team led by Dr
Stefan Fölsch of PDI has now
managed to build a molecule
transistor with atomic precision. The physicists deposited
an organic phthalocyanine molecule onto the surface of
an indium arsenide crystal. Using the tip of a scanning
tunnelling electron microscope (STM), they then positioned individual positively ionised indium atoms on the
crystal surface around the molecule. With that, the
mini-transistor was finished: The crystal surface and the
STM tip serve as the electrodes. The control voltage is
regulated by shifting the positions of the indium atoms.
Stefan Fölsch reports: “We know exactly how the contacts
and the gate electrode are arranged, and we can modulate the control voltage with atomic precision.” The physicists in fact also observed a new phenomenon, which
does not occur in a semiconductor quantum dot: Unlike
the atoms of a quantum dot, the molecule does not sit
still on the surface, rather it can rotate. The charge state
and rotation mutually influence each other, leading to a
novel current-voltage characteristic of the transistor.
The researchers are not yet issuing the assembly instructions for a molecular transistor as an electronic component. At this stage, it is about understanding the underlying physical processes that allow single-molecule-based
quantum electronics in the first place.
Nature Phys. 11 (2015); DOI: 10.1038/nphys3385
A single phthalocyanine molecule
deposited onto an
indium arsenide
surface, surrounded by twelve
indium atoms.
The atoms are
electrically ionised
and serve as the
electrostatic gate
of the single-molecule transistor.
40 SCIENCE IN FOCUS · PDI
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GESINE WIEMER
Watching crystals grow
Crystals grown for use in technological applications must have as perfect a lattice structure as possible. To assess whether a growing method meets every need, researchers
typically study the finished crystals. Physicists of the Paul-Drude-Institut für Festkörperelektronik (PDI) have developed a method by which to watch the crystal as it grows.
O
»
nce a crystal has finished growing, there is no way of
knowing certain things. How thin layers build up and
how ordering and disordering phenomena take place can
only be observed on the “live object” as it grows. “Borrowing a term from biology, we call this in vivo,” says Dr Michael Hanke of the PDI.
The PDI physicists grew extremely thin crystal layers
using the method of molecular beam epitaxy (MBE). They
vapour deposited a rare earth oxide
Surprising phenomena onto a silicon substrate one atomic
appear especially in the layer at a time. “Rare earth oxides are
a wonderful model system for studylowest crystal layers.«
ing deformation-driven phenomena
during the growth of ultrathin layers
because the lattice parameter difference with respect to
silicon can be continuously varied,” Hanke explains. Rare
earth oxides are popular above all for their high dielectric
This apparatus is
highly complex:
The heavy-weight
device can be
adjusted to an
angular precision
of less than 0.001
degrees.
constant, which makes them an important material for developing ever smaller components.
In the institute’s PHARAO experiment, the PDI researchers
used high-brilliance synchrotron radiation from the electron storage ring BESSY II in Berlin-Adlershof to analyse
the layers as they grew. The sample studied was placed in
an MBE chamber under ultra-high vacuum conditions,
where the X-rays travel in and out through beryllium windows that are transparent in this wavelength range. The
entire apparatus itself, weighing nearly a tonne, is installed on a diffractometer, with which the diffraction condition can be adjusted to an angular precision of less than
0.001 degrees. In order to guarantee high surface sensitivity, the researchers take advantage of an optical phenomenon: the total internal reflection. This can only occur at the
transition of light rays from an optically denser medium to
a less dense one. The effect can be seen while swimming
Pictures: PDI
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PDI · SCIENCE IN FOCUS 41
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below the surface of the water: At a shallow angle, the underwater world reflects on the water’s surface because the
air is the optically rarer medium. In the PDI X-ray experiment, they used the same effect, where remarkably the
vacuum assumes the role of the optically denser medium
for the very shortwave X-rays compared to the studied
crystal. When the X-rays enter at a very shallow angle (of
about 0.2 degrees), total internal reflection therefore occurs. The wave field only penetrates about 10 to 15 nanometres into the sample during the irradiation. From the
reflections, the physicists can thus discern properties of
the topmost surface, meaning the layer that is just growing
and not the domain beneath it. Indeed, the boundaries are
of most interest to the physicists, since their properties
differ from those inside the body of the crystal.
The PDI researchers studied two different rare earth
oxides: Gadolinium oxide (Gd2O3) and lanthanum oxide
(La2O3). Michael Hanke reports: “With gadolinium oxide,
we discovered an interesting phenomenon during growth:
As we apply the first atomic layers, then at first this happens without any detectable lateral ordering between the
respective layers.” Only starting from the fourth to fifth
atom layer do they snap into place and the crystal starts to
form three-dimensionally.
The physicists were also amazed as they watched the
first layers of lanthanum oxide grow. Two modifications of
the lattice structure are known for massive crystals: one
With lanthanum oxide, to the physicists’ surprise, a cubic lattice structure forms in the first
crystal layers. Only from a certain thickness does the expected hexagonal structure form.
hexagonal and one cubic. The hexagonal variant is thermodynamically more stable than the cubic variant. Also, the
difference from the lattice parameter of silicon is smaller.
Accordingly, one would expect the hexagonal lattice structure to form when grown on silicon – it fits better and is
energetically more favourable. To the researchers’ surprise, however, they discovered that growth begins in cubic form – in defiance of all theory. Only starting from a
certain thickness do layers with a hexagonal structure
form. This observation agrees with transmission electron
microscopic studies, which grant a direct, high-resolution
view of the finished structures. “From this, we have developed a method by which the cubic form of lanthanum oxide can be targetedly produced,” Michael Hanke is pleased
to announce.
The researchers have so far worked with planar layers.
Next, they intend to study the growth of nanowires. In
these tiny structures, the surface-to-volume ratio i ncreases
drastically, whereby the surface plays an increasingly important role.
Applied Physics Letters 105 (2014), DOI:
10.1063/1.4890107
42 SCIENCE IN FOCUS · WIAS
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GESINE WIEMER
Bose gave Einstein an idea
Einstein predicted it in 1924, but its first experimental proof was not to come until 1995
– for which the Nobel Prize in Physics was promptly awarded in 2001. The Bose-Einstein condensate is an extreme state of aggregated particles all in a very strange relationship with one another. To this day, the state has never been fully described mathematically. Professor Wolfgang König of the Weierstrass Institute is working on a proof.
T
he young Indian physicist Satyendranath Bose (1894–
1974) sent Einstein a paper on a new calculation
strategy for quantum statistics of photons. Einstein was
impressed with Bose’s idea and recognised that the theory
could in fact be extended to all indistinguishable particles.
He had thus predicted the existence of the Bose-Einstein
condensate at very low temperatures. There was no way of
proving it experimentally at the time, since the theory
dealt only with the simplest case at absolute zero temperature (zero kelvins, or about -273 degrees Celsius) and
with zero interaction between the particles. This is an idealisation, which is unrealistic. Wolfgang König of the Weierstrass Institute for Applied Analysis and Stochastics
(WIAS) recounts: “Einstein never worked the theory out in
exact detail. Mathematicians came back to the idea from
time to time, but the foundations for a mathematical
theory were always lacking.”
Simulation of the measurements of the 1995
experiment: In a Bose-Einstein condensate, the atoms
do not bustle about entirely independently of one
another, rather the many-particle wave function that
describes all physical properties such as location and
speed is reducible to just one single-particle wave
function. The individual atoms of the condensate
follow the same statistics.
Then in 1995, a group of physicists successfully created
the first Bose-Einstein condensate in an experiment. “It
was a real research thriller, in a race between several
groups. The physicists achieved a temperature of 10–9 kelvins, that is a billionth of a degree above absolute zero,”
König reports. A previous group had achieved 10–6 kelvins
– which was not low enough for the Bose-Einstein condensate to form, but did earn them the Nobel Prize for achieving such an icy temperature.
Creation of the first Bose-Einstein condensate gave
mathematicians new resolve to tackle the problem. The
maths involved is more complex than Einstein’s treatment,
mainly because the interactions between real-world particles cannot be neglected. Its experimental creation awoke
the curiosity of analysts and stochasticians alike.
In a 2011 scientific paper, Wolfgang König and colleagues described a system of particles that merge into
Image: NIST JILA CU-Boulder
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many loops whose behaviour can be treated as Brownian
motion. These loops do not exist in reality. They merely
serve as a means of visualisation. “It is how I imagine my
formulas. It is the image I use to help me do the maths,”
says the mathematician. When the system is not in a
Bose-Einstein condensate only loops of bounded lengths
arise, each comprising just a bounded number of particles.
These loops are distinctly separate from one another;
everything is a big jumble in which only closely neighbouring particles interact. The mathematicians delivered a
complete characterisation of this system in 2011. However, it only represents the situation at relatively high temperatures, far from those at which Bose-Einstein condensation is expected to occur.
The theory also only applies up to a certain saturation
density. As soon as the particle density becomes any higher, the system can no longer keep all the particles in small
loops and instead packs some of them into long loops.
Thus a macroscopic amount of particles enter into a relationship-at-a-distance. “Then you have not only small
loops, but also a considerable number of particles, maybe
a few percent, also forming big loops,” König explains.
Those particles in the long loops represent the Bose-Einstein condensate. So far, the mathematical means to describe them have been lacking. Wolfgang König’s approach
is to describe the Bose-Einstein condensate in terms of
Brownian interlacements.
»
Stochasticians have
It was a real research thriller, in
been studying Brownrace between several groups.«
ian interlacements, a
special construct of
Brownian motion, for about ten years. “We are now establishing the correlation between Brownian interlacements
and the long loops. I am certain we can characterise the
long loops in this way,” König emphasises. And he is highly
optimistic that the long loops make for a correct physical
description of the Bose-Einstein condensate. “We cannot
be one hundred percent sure about this, and that is not
even my field,” König says. “But we have at least a beautiful
phase transition to look at. Most likely it is what we are
searching for, but even if not, we have still developed a
new mathematical theory whose relevance will surely be
established in time.” Wolfgang König thus hopes the latest
advancements in stochastics will help describe an elusive
fundamental effect in physics. For now, our fingers are
crossed that he will solve at least the loop condensate!
a
44 SCIENCE IN FOCUS · WIAS
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GESINE WIEMER
Realistic and fictional worlds
on the computer
We can explore places on the other side of the world via the internet virtually. Animated
films present realistic or fantasy landscapes, and in computer games we move through
complex surroundings using fictitious characters. A great deal of mathematics is required to generate such virtual imagery. A software program developed by the Weierstrass Institute decomposes complex three-dimensional bodies into tetrahedra, enabling them to (seemingly) come to life on the computer.
I
n order to create computer graphics, the objects to be
presented need to be decomposed into simple shapes
that the computer finds easy to calculate. On a plane,
mathematicians find it easiest to deal with triangles; in the
case of three-dimensional space, tetrahedra are the preferred shape. The TetGen software by the Weierstrass Institute for Applied Analysis and Stochastics (WIAS) is a
widely used tool that breaks down three-dimensional objects into tetrahedra. Google uses the program for image
processing; it is also integrated into the Mathematica software package for generating 3D graphics and conducting
calculations in three-dimensional structures. TetGen is integrated into many simulation tools based on partial differential equations.
Breaking down an arbitrary three-dimensional body
into tetrahedra is a highly complex matter: it is akin to a
3D puzzle in which the straight edges of the tetrahedra
have to fill the entire space without overlapping. The individual “parts of the puzzle” have to be as small as possible
so as to portray curved surfaces properly. And yet they
must not be too small, else it would take an excessively
long time for the graphics to be loaded.
First of all, the algorithm decomposes the surface into
triangles – that is the first step; the second step involves
adding points on the inside of the solid figure and connecting them into triangles. Large triangles are not good at illustrating curved surfaces. However, extremely elongated,
thin triangles can fit well into creases and folds. Scientists
call them anisotropic (i.e. “an-isotropic”) triangles, as opposed to isotropic triangles, which are relatively even. Dr
Hang Si from the WIAS research group “Numerical Mathematics and Scientific Computing” stated: “With anisotropic
triangles, we can achieve almost the same precision as
with small triangles, but are able to considerably reduce
the number of triangles required. This will make the program a lot quicker.” After all, what is the point of having
highly realistic animation if the program keeps having to
reload all the time: “there’d be no fun in that,” his colleague
Dr Jürgen Fuhrmann added.
TetGen is integrated into the Houdini 13 software program by the company Side Effects, for example. Game developers use the software to create realistic animations.
Complicated scenarios can also be illustrated with outstanding precision: if, for example, a slimy squid falls down
the steps, you can almost hear the sloshing sound when
viewing the animation. A lot of things get destroyed in films
and games. If a building is blown up virtually, it still looks
real – thanks to mathematics – and costs much less money.
The options available to programmers and users thanks
to these increasingly realistic images are simply inexhaustible. But one thing is for sure: virtual imagery is an
addition, but in no way a replacement for our real world.
ACM Trans. on Mathematical Software 41 (2015); DOI:
10.1145/2629697 (Editors' Suggestion)
Soft objects are not rigid. The software allows for quick recreation of
tetrahedralizations of deforming objects.
Images: WIAS
The triangle mesh
is coarser in the
picture on the
right, meaning that
the computer can
load the image
much more quickly.
Nevertheless, the
WIAS algorithm
illustrates the
curves well, and
the computer
graphic has no
rough edges.
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WIAS · SCIENCE IN FOCUS 45
Almanac 2016
GESINE WIEMER
Many cooks improve the broth
Many modern technologies are unthinkable without semiconductor lasers. They are
used in sectors such as telecommunications, medical technology, materials processing
and sensor technology. To help engineers build ever smaller and more powerful lasers,
mathematicians from the Weierstrass Institute are designing computer models that reduce the need for expensive experiments.
T
he models developed by the Weierstrass Institute for
Applied Analysis and Stochastics (WIAS) are no substitute for real-life experiments, but mathematicians are able
to identify trends indicating which parameters determine
the behaviour of a laser. This helps engineers to decide how
to construct a good laser, obviating the necessity for less
promising experiments. Dr Mindaugas Radziunas from
WIAS says, “Our models are highly complex and multidimensional. And yet, they are just highly simplified versions of reality – otherwise they would be too unwieldy.”
The mathematicians at WIAS worked on high-performing broad-area lasers. “I’m sure the public notion of a
‘broad area’ is a little different from what we mean," Radziunas comments. After all, their devices are only about 1 to
10 millimetres long and no more than one millimetre
wide. “And that is pretty broad for those tiny things,” Radziunas emphasises. “Also, people probably wouldn’t think
of a few watts in terms of ‘high performance’.” But on this
scale, a couple of dozen watts is a lot of power. Semiconductor lasers are used as highly efficient, low-cost pump
sources for fibre lasers, for example, which operate in the
kilowatt range and are used in materials processing.
Image: WIAS
Engineers, physicists and
mathematicians develop lasers
together
For high-precision applications, the laser radiation must be
well-ordered. However, as the light exits the device, it radiates at different angles. The idea is to construct a new generation of lasers to minimise the radiation angle. Timing is
another important factor. Not only does the emitted field
spread at different angles, it also varies over time. The objective therefore is not only to obtain a narrow radiation
angle, but also to achieve optimum field emission that remains constant over time – apart from which, new lasers
should always be more efficient than their predecessors.
The mathematicians at WIAS cooperate closely with
physicists and engineers, often from the Ferdinand-Braun-Institut (FBH). In order to do so, they must
speak each other’s language. Radziunas clarifies, “And by
that we don’t mean German, English or Lithuanian, which
is my mother tongue.” Terminology varies greatly, as well.
“I have picked up some ‘engineerese’ – but I’m still a beginner,” the mathematician grins. An example for such collab-
The theoretical study of angular shaping of the optical field emitted from the broad-area
semiconductor laser with the periodically structured electrical contact. Field intensity
dependence on emission angles for different moments in time (left) and time-averages
of these intensities (right) in conventional (top) and periodically structured (bottom)
broad-area semiconductor lasers.
oration is a study on a semiconductor laser with u
ndesired,
almost periodical jumps in emission wavelength during
bias current changes. The cause was not immediately obvious. The model analysis and simulations at WIAS indicated that strong laser facet reflections, together with
thermic effects, could be causing these jumps. Further
simulations suggested that these jumps in the laser spectrum could be reduced by a proper choice of the design parameter. The engineers now know where it might make
sense to alter their design. Radziunas is currently investigating the angle formation of the optical field in a broad-
area semiconductor amplifier with periodically structured
electrical contact. Together with colleagues from FBH, the
mathematician plans to study the persistence of the simulated effects (see figure) in periodically modulated
broad-area lasers.
46 SCIENCE IN FOCUS · MY PHD THESIS · MBI
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MART IN HEMPEL
Preventing the disaster in
high-power lasers
Dr Martin Hempel (32) is currently postdoctoral researcher at the Paul-Drude-Institut für Festkörperelektronik
(PDI). He completed his PhD at the Max Born Institute
(MBI) about defects in high-power diode lasers, supervised by Thomas Elsässer, director of MBI and professor
at the Humboldt-University Berlin. Hempel’s PhD thesis
“Defect mechanisms in diode lasers at high optical output
power: The Catastrophic Optical Damage” give rise to numerous scientific publications. For the comprehensible
presentation of his scientific results, Martin Hempel was
awarded the ”Adlershof Dissertation Award“ in 2014.
From 2004 to 2009 he studied physics at the Humboldt
University of Berlin and completed with a diploma.
O
ur telecommunication systems are based on optical
fibres. Data, such as phone calls or the internet, travel
around the world in the form of laser light pulses. Thanks
to lasers, we can watch and burn DVDs and CDs. Moreover,
they enable laser printers, laser scalpels, bar code scanners and range finders. Lasers have become indispensable
in our private life. But they are also an essential research
tool: analysing rock samples far out in space or taking
measurements of ultra-fast processes – laser light is the
measurement probe.
The most important sources of laser light are semiconductor diode lasers. Their success is based on their unique
properties: They are highly efficient, converting up to 70
per cent of the electric energy into light (a light bulb reaches five per cent). They are small – you can put approximately twenty of them on your thumbnail – while being
powerful, emitting about ten times the power of a light
bulb out of one of them. At the same time they are highly
reliable with an operating life of several 10,000 hours. All
these advantages are reflected in the sale volume for semiconductor laser of US$ 4.32 billion in 2013.
If we succeed in making the semiconductor laser even
more efficient, we will open up new fields of application.
An example is the laser driven spark plug for car engines,
making the combustion more efficient. A limit for a further
increase in optical output power is the Catastrophic Optical Damage (COD). In case of COD the following happens: A
part of the laser light is absorbed locally inside the laser
right after it has been generated in a volume of about one
cubic micrometre, that is, a one thousandth of the size of
the light generating region. The light absorption increases
in a semiconductor with increasing temperature. This sets
a feedback loop into action of local heating and increased
absorption.
This one does not become catastrophic as long as the
heat can be dispersed fast enough to the surrounding material. In case of a COD, the local light absorption leads to a
temperature rise of above 1000 °C in a nanosecond, as
shown in my thesis. The device starts to melt at this location and will be completely destroyed after a couple of microseconds. A novel measurement setup based on a thermal imaging microscope camera allowed me to detect and
trace the damage front during these crucial microseconds.
It turns out that the COD moves at approximately 90 km/h
through the diode laser until its energy source (laser light)
vanishes.
This live tracking of the damage is fine; however, how
does it help to improve the laser? In order to improve the
diode laser one has to know where its present bottleneck
is. A model of the defect spread has been developed based
on the analyses of the damage motion. It allows reconstructing the temporal and spatial development starting
from the final defect pattern. It has been demonstrated
that the defect spread is a sensitive indicator for weak
points of a diode laser design. The COD starting point is of
particular interest. An improvement in coating technology
is required if the COD starts where the light leaves the
semiconductor material. Moreover, the analysis shows
how serious the problem is. If there are multiple starting
points, the used coating technique should be questioned
generally. A single starting point requires a deeper investigation to rule out the effects of dirt, inhomogeneities etc.
verbundjournal
Almanac 2016
MY PHD THESIS · MBI · SCIENCE IN FOCUS 47
Catastrophic
Optical Damage in
a diode laser.
Picture & Image: MBI/Martin Hempel
Experiment set-up
A starting point inside the laser often indicates a poor
material quality. This means that the perfect order of the
atoms in the crystal is distorted, e.g., by a missing atom.
Interestingly, the crystal quality can be validated even if
the COD starts at the edge. The COD defect pattern shows
many branches if a lot of crystal defects are present. The
result looks like a leafless tree with its trunk at the COD
starting site and its branches inside the laser.
Another issue, often underestimated by the manufactures of the lasers, are modifications made further away
from the light generating region of the device. For example
the metal strips on top of the laser, used as electrical contacts. The problem: The edges of these metal strips. Their
impact is comparable to a sharp knife edge pressing onto
the semiconductor material. It leads to a local deformation
of the crystal lattice. Such deformations elevate the level of
local light absorption, because the intrinsic properties of a
semiconductor, as transparency, are related to the periodic
arrangement of its constitutional atoms. All these problems can be identified by the newly developed model and
systematically solved afterwards.
The final defect pattern is, as shown above, sufficient to
identify the bottlenecks of the laser. In order to develop
this model, however, the defect motion had to be detected
with high spatial and temporal resolution. We had to produce a COD on demand. Under normal operating conditions COD will start after thousands of hours but ends
after few microseconds. A special aging regime was developed, to reduce the waiting time from these thousands of
hours to microseconds: The diode laser is driven not by a
continuous current anymore, but by short pulses in the
range of one to ten microseconds. The test sequence is
started at a low current which causes no damage. In the
following pulses the current is increased slightly until COD
takes place. The short duration of the pulses allows for a
successful triggering of the data recording.
When changing the aging conditions in such a fundamental way, it was not clear if the defect we provoke is the
same as in a long term test. We compared the defect pattern, energy balances, and microscopic material analyses
of both test regimes. Latter ones revealed comparable
damage structures in the semiconductor crystal which are
indicative for temperatures around 1600 °C, that is, the
melting point of the material. It turned out that the COD is
similar in both cases. In the long term regime the built-in
weak point already increases the temperature locally. The
heat can still be dispersed to the surrounding material.
Therefore the described feedback loop did not lead to COD
at the first moment.
However, such places of local elevated temperature are
popular gathering places for small defects in semiconductors, which are always present in small numbers. They
move slowly through the crystal, but tend to gravitate towards warmer places. If the density of the defects exceeds
a certain value, the absorption becomes critical and COD
will start. In the test regime with short pulses the current is
elevated leading to high light intensities. Therefore the
same percentage absorption triggers COD in microseconds.
The results and developed analysis techniques of my
Ph. D. thesis show a way to efficiently detect bottlenecks in
high-power diode lasers. They pave the way for more powerful devices in the future.
48 SCIENCE IN FOCUS · MY PHD THESIS · IGB
verbundjournal
Almanac 2016
DAVID BIERBACH
Deceptive manoeuvres in
mate choice – lessons from the
Animal Kingdom
When animals live in groups, virtually all of their actions are noticed by their companions. While it is common for animals to live in groups, the impact of group living on key
life processes – such as reproduction – has hardly been explored. In fact, the social environment could provide an explanation for several puzzling phenomena, such as male
homosexuality in the Atlantic molly (Poecilia mexicana) or deceptive mate-swapping
manoeuvres of Arabian sand gazelles (Gazella marica).
T
»
he successful production of offspring is an essential
component of all life. However, males in numerous animal species obviously appear to have no interest in siring
offspring of their own. Male homosexuality is a phenomenon that can be properly described as a “Darwinian puzzle” and even today, it is scarcely un
Too much sexual derstood. My idea was that the social
activity in a potential context in which animals display homosexual behaviour might make a
mate is both a blessing valuable contribution to the underand a curse for the standing of this phenomenon. In this
female.« regard, the Atlantic molly (Poecilia
mexicana) has proven to be a useful
model organism since males in this small live bearing fish
species from the Atlantic coast of Mexico regularly show
same-sex sexual behaviours.
In one experiment, I presented Atlantic molly females
with various video animations. Two films showed molly
males interacting sexually with either a female or another
male. No sexual activity was exhibited by the fish in the
third video. The females found both molly males exhibiting homosexual behaviour and those showing hetero
sexual behaviour to be considerably more attractive than
In Southern Mexico, Atlantic mollies (Poecilia mexicana)
mainly inhabit small mountain streams. However, they
may also be encountered in brackish water. Their natural
distribution ranges along the Atlantic coast of Central and
South America.
males not exhibiting any sexual activity. Consequently,
males can by all means increase their attractiveness to females by exhibiting homosexual behaviour. Of course, in
turn this increases their chances of future heterosexual interactions and, ultimately, of producing offspring of their
own. Viewing homosexuality as a competitive advantage is
a completely new approach for explaining this behaviour.
But why do Atlantic molly females find males exhibiting
homosexual behaviour as attractive as their heterosexual
counterparts? For females, a potential mate’s sexual activity is both a blessing and a curse. Too much attention may
increase their risk of injury during copulation. After all, as
in the case of mammals, Atlantic mollies practice internal
fertilisation involving the transfer of sperm packages from
the male using a penis-like sexual organ. In addition, males
almost constantly try to copulate with females, leaving
them little time to search for food. However, too little sexual activity does not appear to be well received either – after all, it could be an indication of inferior quality or a diseased male.
In addition to the requirement of being duly tactful,
males must always keep a vigilant eye on observant rivals
seeking to snap up the best mates. Atlantic molly males ex-
verbundjournal
MY PHD THESIS · IGB · SCIENCE IN FOCUS 49
Almanac 2016
Dr David Bierbach has been conducting
research as a postdoc at the Leibniz Institute of Freshwater Ecology and Inland
Fisheries since August 2013. David Bierbach was awarded first prize by the
“Vereinigung der Freunde und Förderer
für den Naturwissenschaftlichen Nachwuchs” of the Goethe University of Frankfurt/Main for his PhD thesis.
hibit a general preference for large females, because those
fish produce more eggs. Indeed, copulating with one of
them offers the best prospects for a large number of offspring to sire. If males are observed by a rival during copulation, they reduce their sexual activity and in some cases
they even change their preferences, showing an increased
interest in a previously neglected female. This is an attempt to lure the rival away from their first choice. Such a
deceptive manoeuvre makes perfect sense, because fresher sperm is used more frequently for fertilisation; despite
the fact that females are able to store sperm. True to the
motto “life punishes latecomers”, the longer a duration is
before any further copulation, the more likely it is the first
male will fertilise a majority of the eggs.
Why, then, do Atlantic molly males allow themselves to
be lured away from attractive females by other males? Females in this species do not always have eggs that are
ready for fertilisation. The chances of fertilisation are
greatest shortly after a brood has been born – corresponding to a time frame of roughly one to two days per month.
Males can only evaluate a female’s exact state of receptivity through chemical cues obtained by nipping at the female genital opening with
There’s a rea- the tip of the snout – a very
son for these time-consuming procedure.
Smarter molly males circummate-swapping vent this problem of finding
games.« receptive mates by selecting
females that are preferred
by other males willing to mate. This behaviour is called
“mate choice copying”. Sometimes almost a dozen males
can be observed in a so-called “mating frenzy” trying to
mate with their ideal female either in quick succession or
even simultaneously. That’s bad news for the first male to
discover the receptive female. Unless, of course, he is
tricky and puts his rivals on the wrong track by enticing a
non-preferred female. His preferred female can now escape unchallenged, and the chances that his sperm will
fertilise her eggs increase with every minute she is left
alone.
What is the case in other groups of animals, such as
mammals, with similar reproductive biology? In order to
address this issue, I participated in a cooperative study at
the King Khalid Wildlife Research Center, a gazelle breeding station in Saudi Arabia. My colleagues and I were able
to show that male Arabian sand gazelles (Gazella marica)
Pictures: David Bierbach (2x); Melanie Hauber
»
have very stable preferences for certain females. However,
as soon as a rival male was placed in a separate adjacent
enclosure, they showed little interest in their preferred female. Sometimes they even altered their preferences and
interacted with an initially non-preferred female. This behaviour appears to resemble the deceptive manoeuvre described in the case of Atlantic mollies, though in the course
of our experiments we noticed that this change in preference only lasted for around one hour after which the males
reverted back to their initial preferences. It appears that
the rival lost its threatening effect after an hour because it
became clear that the audience male was unable to reach
the female from his enclosure. In the wild, young males
frequently alternate between different adult shoals. In
such a situation, established males must first learn to assess the newcomer. The young male gazelles initially alter
the established males’ sexual preferences, which is probably because they can prevent giving the intruder information about the high quality females. However, as soon as it
becomes obvious that the new guy cannot catch up with
the established males they revert to their original behaviour and continue to entice their preferred females. It can
therefore be assumed from these observations that such
deceptive manoeuvres are not unusual in the Animal Kingdom. If males succeed in putting their rivals on the wrong
track, they increase their chances to mate with their preferred females, and accordingly their prospects of siring
numerous offspring. However, the extent to which these
strategies can be transferred also to humans remains unclear.
Two Atlantic molly
males (Poecilia
mexicana): the
standard behavioural repertoire
of this species
includes same-sex
sexual behaviour
between males,
enabling them
to increase their
attractiveness to
females.
50 INSIGHT FORSCHUNGSVERUND
verbundjournal
Almanac 2016
GESIN E WIEMER AND K ARL-HEINZ K ARISCH
“Our institutes conduct research
at a very high level”
Professor Marc Vrakking, the new Chair of the Board of Directors, has tasked himself with an
ambitious programme. It includes showing the colours of the Forschungsverbund Berlin e.V.
(FVB) more openly in public; striving for a better financial footing; and achieving a strategic
realignment of the FVB. He explained his plans in an interview with the “Verbundjournal”.
Professor Vrakking, you left the Netherlands to join the
Forschungsverbund Berlin e.V. five years ago. How do you
perceive the association today?
Professor Marc Vrakking: When I was appointed as a new
Director at the Max Born Institute (MBI) in 2010, I was initially unsure of the significance of the Forschungsverbund.
This soon changed, of course. I consider it to be a very interesting organisational structure that has brought great benefits to the eight independent institutes under its umbrella.
As a result, we have access to extensive know-how, such as a
patent or a legal department, that a small institute would
never be able to afford on its own. This provides us with numerous opportunities. I can therefore well understand that
the directors decided to maintain the Joint Administration
shortly after it was founded in 1992. The original intention
was for the eight institutes to have their own individual administration after a transitional period.
Bearing in mind your work as Director of the MBI, what are
the benefits of having a Joint Administration?
When I started out as Director of the MBI, it was fantastic to be able to benefit from the experience of my colleagues on the Board. And, conversely, new directors are
able to contribute the experience they have gained perhaps abroad or in industry. This makes things a lot easier
and helps us to ensure we make the right decisions on behalf of our institutes.
Can you give a few examples of what works particularly well
collaboratively?
Well, we belong to the Leibniz Association, which
brings together 88 research institutions across Germany.
Here, too, we exchange with important discussion partners once or twice a year. But there is closer contact between the ten directors within FVB. This means we have a
very interesting group where we can discuss matters and
think about strategies, not only for our own benefit but
also related to Leibniz. Being the Leibniz Association’s
largest organisation, and being represented in several of
the sections of the Leibniz Association, we can achieve
much more than if we were individual institutes.
How do you think the Leibniz Association is placed within
Germany’s research landscape?
Or course I can’t speak for the other Leibniz institutes,
but if I look at the FVB’s institutes, we conduct research at
a very high level, often even with the world’s best. They
have all developed exceedingly well over the last 23 years.
I am sure that being part of the FVB has given the institutes the incentive to continually become more creative
and achieve better results. Excellence in Germany can often be found within the Max Planck Society, but we too
have a lot of excellence to offer. Our eight institutes set
very high standards.
Thanks to its universities and research institutions, Berlin is
one of Germany’s key science locations. How is FVB placed in
the capital?
We discussed this matter recently in a board meeting.
Shortly after German reunification, the Forschungsverbund evolved from former institutes of the GDR Academy
of Sciences, which inevitably caught the public’s attention.
There has been less attention in recent years, which is also
one of the reasons why the directors want to show their
colours more openly vis-à-vis our politicians, donors and
the general public. I believe we are on the right track. German Federal Minister of Education and Research Johanna
Wanka has already paid a visit to Leibniz-IGB, to be followed shortly by a visit to the Leibniz-IZW. She and the
new Leibniz President Matthias Kleiner have written articles for our “Verbundjournal”; Cornelia Yzer, Berlin’s Senator for Economics, Technology and Research, gave us a
long interview. The event “Wissenschafts-Häppchen”, held
in the Germany Parliamentary Society, also helped to raise
FVB’s profile among members of the Bundestag and in the
Berlin House of Representatives. One problem will, however, remain: when presenting their research results, our
institutes appear in the media as individual entities, meaning that the Forschungsverbund remains in the background. We intend to discuss this in greater detail on the
board. We wish to gain in importance collectively.
The impression made is bound to be important when it
comes to securing resources in the years ahead. What is
your opinion on the situation?
I fear that the support for running costs will no longer
suffice in future. If the forecasts are correct and prices continue to increase as in the past, we will soon have to downsize by one or two per cent year for year. I believe the
Forschungsverbund must take action to prevent this from
verbundjournal
Professor Marc Vrakking at the 2015 symposium “Lasers and
Accelerators for Science and Society” in Liverpool.
happening. Many of our institute buildings were constructed or refurbished some 20 years ago, meaning that we are
faced with considerable maintenance requirements. We
are in urgent need of additional funding for this.
Are there any other key areas that you would like to focus on?
We have already decided on the board that as a regular
feature of our board meetings the individual directors will
explain their institutes’ research strategy in future. By doing this, we hope to inspire each other’s work with new
ideas while enabling us to improve how we are perceived
together externally.
What do your colleagues expect from you as the new Chair
of the Board of Directors?
One of my tasks is to represent the FVB to the outside
Picture: University of Liverpool
INSIGHT FORSCHUNGSVERUND 51
Almanac 2016
Professor Marc Vrakking (born in the Netherlands in 1963)
was appointed the new Chair of the Board of Directors of
the Forschungsverbund Berlin e.V. on 1 May 2015. The FVB
consists of eight research institutes based in Berlin. The term
of office is two years. Professor Klement Tockner (IGB) assumes the role of Vice Chair. Vrakking succeeded Professor
Henning Riechert, Director of the Paul-Drude-Institut (PDI).
Vrakking has been Director of the Max Born Institute for
Nonlinear Optics and Short Pulse Spectroscopy (MBI) since
2010, when he was also appointed a professor in the Department of Physics at Freie Universität Berlin, focusing on
ultrafast physics. He is a pioneer of time-resolved spectroscopy with attosecond pulses. Marc Vrakking studied physics
in Eindhoven (Netherlands). Following a period in Okazaki
(Japan) he then spent seven years in Berkeley at the University of California, where he researched dynamical processes
world: for example, when members of the Bundestag visit
us, which was the case recently with Dr Simone Raatz of
the Social Democratic Party. As a chemist, she is particularly interested in our work. I would also like to intensify
contacts to the Administration, which was agreed on in a
meeting with FVB’s Administrative Director Dr Manuela
Urban. We are more or less neighbours here in Adlershof,
so there is little distance between her and me as the Chair.
I want to make sure that we can tackle the future challenges we face together. For example, there will be a joint procurement programme for the Administration and the institutes, which will bring us all major benefits. As soon as this
process is running smoothly and successfully, further potentials can be exploited. But it must always be voluntary.
The Forschungsverbund can be a great deal more than
simply an administration. We would like to use it as a strategic instrument.
in molecules using frequency-domain spectroscopy. He
started working with short pulse lasers at the National Research Council in Ottawa (Canada), and continued down
this road leading a work group at Amsterdam’s Institute for
Atomic and Molecular Physics (AMOLF). He achieved global
acclaim as the first person to take photos of electron clouds
of hydrogen in different energy states. These photos were
listed in the Top 10 breakthroughs in physics in 2013. Alongside Vrakking, Professor Thomas Elsässer and Professor Stefan Eisebitt are also directors at the MBI. Vrakking attaches
particular importance to promoting young scientists. As
such, he coordinated the Marie Curie Initial Training Network ATTOFEL (Ultrafast Dynamics using Attosecond and
XUV Free Electron Laser Sources) and is a founding member
of MINT Impuls Berlin. Marc Vrakking is married and has
one daughter.
verbundjournal
Almanac 2016
Tailored technologies
The eight Berlin-based institutes that belong to the Forschungsverbund pursue excellence in science. To achieve this, they require instruments that open up entirely new dimensions. Technology is adapted again and again to research needs, and experts continuously refine these instruments.
Electron beam lithography system
The modern electron beam lithography
system (e-beam) by the company VISTEC
is one of the central units for further
development of state-of-the-art devices
at the Ferdinand-Braun-Institut (FBH).
The shaped beam system allows direct
write applications with a minimum feature
size of down to less than 50 nm on up to
eight inch wafers. Thanks to this powerful
system, scientists can, for instance, further
develop the gate technology of gallium
nitride-based high-power transistors
at FBH to dimensions up to 100 nm or
even less – which is crucial for further
increasing the working frequencies of
the components. The e-beam can also
be used to create gratings of high-power
diode lasers with periods of 120 nm and
more. As a result, the laser beam is spectrally stabilised, enabling it to emit light
with the exactly required wavelength.
This ability is one of the key requirements
for numerous applications, from precision
spectroscopy to medical technology.
Direct stochastic optical reconstruction microscopy (dSTORM)
enables individual fluorescent dyes, coupled to specific proteins,
to be precisely localised.
FMP
FMP dSTORM:
a glimpse of the nanoworld
Ernst Abbe (1840-1905) placed microscopy on a scientific footing. Based on the
wave structure of light, he calculated that
light microscopes are unable to display
structures below half the wavelength of
light. Hence 0.2 micrometres (thousandths of a millimetre) would be the
end of the road. However, Abbe put
forward this hypothesis before the arrival
of computer technology, lasers and novel
fluorescence dyes. Dr Jan Schmoranzer
and his team at the Leibniz-Institut für
Molekulare Pharmakologie (FMP) have
constructed super-resolution light microscopes that pave the way for resolution
Pictures: FBH/schurian.com; FMP
FBH
in a range of 20 nanometres (millionths
of a millimetre). This means that nanoscale molecular structures within cells
can be observed at work. To this end,
Schmoranzer developed two new devices
called dSTORM (direct stochastic optical
reconstruction microscopy) and SIM
(structured illumination microscopy), and
cleverly optimised them. In dSTORM,
individual fluorescent dyes coupled to
specific proteins are visualised using
extremely sensitive cameras and localised
precisely down to a few nanometres.
Special lasers can be used to specifically
switch on and off individual molecules.
As a result, not all of the dyes are illuminated at the same time, enabling them
to be detected individually. This increases
the resolution approximately ten-fold.
Using a novel two-colour method, Jan
Schmoranzer’s team has already succeeded in resolving the nanostructure of tiny
cytoskeletons and membrane elements of
the cell. In SIM, up to four colours can be
portrayed simultaneously, with a two-fold
higher resolution, in all three dimensions. Thus Jan Schmoranzer was able to
demonstrate that there are many more
zones in a nerve cell (synapse) in which
neurotransmitters can send signals than
previously thought. He also managed to
clearly resolve in 3D the substructures
of a synapse consisting of pre- and
post-synaptic nerve endings, which are
just a few nanometres from each other.
verbundjournal
IGB
The LakeLab: Looking into the
future of our lakes
“We strive to conduct global-change
experiments under environmental
conditions as realistic as possible,” says
Professor Mark Gessner, head of the Experimental Limnology Department at the
Leibniz Institute of Freshwater Ecology
and Inland Fisheries (IGB). This is why
IGB set up the LakeLab in Lake Stechlin
(north-east Germany). The experimental
facility 80 km north of Berlin consists
of 24 enclosures, each 9 m in diameter
and 20 m deep, thus separating water
volumes of about 1250 m3 from the lake.
These dimensions provide a unique opportunity to run experiments simulating
scenarios of future climatic conditions.
For example, experiments in 2014 and
2015 were conducted to determine the
impacts of extreme weather events such
as heavy rainfall and summer storms,
and the experiment in 2016 will be
designed to assess effects of nighttime
light pollution on aquatic organisms,
food-web interactions and biogeochemical cycles. “To take full advantage of
the LakeLab, national and international
partners are welcome to collaborate on
this and future experiments,” emphasises
Mark Gessner. For more information visit
www.lake-lab.de
Aerial view of the LakeLab
in Lake Stechlin
Pictures: M. Oczipka IGB / HTW Dresden; Felix Peschko; Ralf Guenther
Almanac 2016
Monocrystalline silicon rods
(“single-crystal silicon”)
IKZ
vacuum. An ambitious task but, thanks
to its unique technologies, IKZ has been
able to continue pursuing this research in
an alliance with 33 partners within an EU
project since 2013.
Tailor-made crystals for industry
As the basic element of the semiconductor industry, silicon is practically irreplaceable. The condition for use in power
electronics, for instance, is the provision
of crystals containing only very few
defects or faults that can be produced as
cheaply as possible. The Leibniz Institute
for Crystal Growth (IKZ) develops relevant technologies and systems for growing silicon and other semiconductors. In
order to ensure that these technologies
can also be transferred to industry at a
later point in time, the systems must be
more or less on an industrial scale – in
fact, the equipment at IKZ is one of the
reasons for the institute’s numerous
cooperative activities with industry. Research is conducted into semiconductors
on a small scale – nanowhiskers could
be the basis for applications in nanoelectronics and for miniaturised components.
There are also potential applications as
thermoelectrics or for new batteries. A
molecular beam epitaxy system by Dr.
Eberl MBE-Komponenten GmbH was
further developed and adapted for the
purpose of growing nanowhiskers. It is
used to produce crystalline semiconductor layers on a substrate in an ultrahigh
IZW
High performance computed
tomography
The Leibniz Institute for Zoo and
Wildlife Research
(IZW) houses
the world’s most
modern computer
tomography (CT)
scanner in veterinary research since
2015. Applications
The new TOSHIBA research computed
range from evolutomography at IZW
tionary morphology to veterinary medicine and forensics.
This high-power CT scanner is unique for
several reasons: it enables 4D CT scans
to be produced at an entirely new level
of resolution. In a matter of seconds,
the object is virtually cut into “slices” –
without touching or damaging it. Hidden
inner motion sequences can be illustrated
and analysed, such as a beating heart.
The Aquilion ONE by Toshiba is the CT
with the world’s biggest and most powerful X-ray detector in veterinary medicine. 640 sliced images can be created in
one rotation around the (animal) patient:
in other words, a 16 cm section is visually displayed within the space of just
35 milliseconds. The novel dual energy
technology permits quantitative material
analysis of the mineral composition of
the animal patients and other research
objects, thus opening new areas of
scientific research. An innovative funding
model – equipment leasing – enabled
the CT scanner to be acquired. It was the
first time that such large-scale equipment
was made available for science in publicly funded research. The new high-end
instrument replaced its predecessor from
2010. Industrial cooperation has existed
between IZW and TOSHIBA Medical
Systems GmbH since 2009.
verbundjournal
Almanac 2016
The illustrated
PCPA system
O
creates 6 femtosecond pulses.
Generating powerful few-cycle
pulses
Optical parametric amplification (OPA)
allows for amplifying light pulses with
considerably higher bandwidths to
intensities which are higher than from
traditional titanium-sapphire lasers. The
amplified ultra-broadband radiation can
then be compressed to pulses with a few
optical cycles (chirped-pulse amplification, CPA). Researchers at the Max Born
Institute for Nonlinear Optics and Short
Pulse Spectroscopy (MBI) have developed four OPCPA (Optical parametric
chirped pulse amplification) systems for
different parameter ranges. The system
presented in the figure generates pulses
with a duration of six femtoseconds (fs)
at a wavelength of 800 nm. It reaches
a pulse energy of 12.5 μJ at a repetition
rate of 400 kHz. The pulses are used to
investigate ultrafast processes in chemical reactions.
of a millionth of a second) at kilohertz
repetition rates. The X-ray pulses are
synchronized with optical pulses from
the laser system and allow for X-ray
diffraction experiments with very high
time resolution. The femtosecond X-ray
plasma source enables the direct imaging
of transient structures with a 100 fs time
resolution. It acts like a “camera” that
takes an ultrafast sequence of “snapshots” (see image) of the electron density in crystals, making ultrafast atomic
and molecular motions directly visible.
The most important instrument
in mathematics
At the Weierstrass Institute for Applied
Analysis and Stochastics (WIAS), scientists are working on algorithms that will
make efficient use of computing capacity
and render supercomputers unnecessary
for many applications. Among other
things, WIAS algorithms can clearly
identify important details from MRT
(magnetic resonance tomography)
images of the brain, enabling doctors to
recognise structural changes to nerves at
an early stage.
Femtosecond X-ray plasma
source
Together with the company IfG – Institute for Scientific Instruments GmbH
– the Max Born Institute has developed
a laser-driven hard X-ray plasma source.
The compact new device generates –
driven by an amplified femtosecond laser
– extremely short X-ray pulses of 100
fs duration (1 fs = 10-15 s = 1 billionth
WIAS
Works at almost absolute zero: PDI’s
scanning tunnelling microscope.
PDI
Atomic microscope and atomic
tweezers rolled into one
The scanning tunnelling microscope
(STM) at the Paul-Drude-Institut für
Festkörperelektronik (PDI) enables
metal and semiconductor surfaces to be
visualised at atomic resolution. When
conducting STM investigations, the
Pictures: MBI (2x); PDI; Image: WIAS
MBI
samples are under vacuum. As a result,
the highly sensitive surfaces are protected against impurities; in addition, the
temperature can be kept stable. Using an
extremely fine metal tip, the microscope traces the surface charge density,
enabling conclusions to be drawn on the
atoms’ position. The scanning tip can
also be used to move individual atoms
(atom manipulation). In order to achieve
extreme thermal stability, the microscope
and the sample are cooled to five kelvin
(-268 °C). Using liquid helium, the
system is kept at these icy temperatures
for the duration of the experiment –
typically for several weeks.
Fotos: Ralf Günther (5x); Peter Himsel (3x)
verbundjournal
Almanac 2016
The Forschungsverbund Berlin e.V.
presented at
Long Night of the Sciences
(“Lange Nacht der Wissenschaften“)
verbundjournal
Almanac 2016
PDI initiates Berlin’s new science
and art festival
Have aliens landed in Berlin? A creature with a silvery lumpy head inches along cautiously in front of the “Alte Münze” opposite the Red City Hall. Two young women guide
him along, making sure he does not lose his balance. The EYEsect helmet device, featuring two freely pivoting cameras, enables the wearer to see the world from completely
new perspectives. The wearable installation created by the artist collective “The Constitute” was just one of the highlights at the STATE Experience Science Festival. Strikingly
enough: the new creative format blending art and science was initiated by the
Paul-Drude-Institut für Festkörperelektronik (PDI). It led to the foundation of a spin-off
company, STATE Experience Science GmbH.
A
The EYEsect helmet device offers a whole new perspective of the world.
The first festival, which addressed the umbrella theme of
“time”, had plenty of highlights, such as the lecture by British
physicist Julian Barbour, who believes that time exists merely as an illusion. Although this and the others lectures held
at the event were pretty complex stuff, they were so popular
that all of the seats were taken and listeners had to follow
the talks standing up outside the hall. Several hundred people participated in interactive experiments. In addition, art
films inspired by science were screened, and there were live
performances featuring music, dance and visuals.
By establishing the company STATE Experience Science
GmbH in the course of the festival, Rauch and his team
seek to increase their activity in the area of interdisciplinary science communication. In other words, there is a future to the delicate liaison between art and science.
Save the Date: Autumn 2016
For the second time STATE Experience Science Festival will
celebrate scientific ideas and creativity across disciplines.
The STATE Festival will take place from the 2nd to the 6th
November 2016. Again, the location “Alte Münze” in Berlin will host the main event, where most of the program
formats will be shown.
For further information please visit: www.statefestival.org
Picture: STATE Festival
»
tremendous success for founder and organiser, Dr
Christian Rauch from PDI. After all, more than 1,000
visitors attended the first festival, held within the walls of
the former mint in the heart of Berlin. “We succeeded in
generating enthusiasm among the
Science and art seek public for such difficult topics – what
answers to the big a fantastic achievement,” stated the
physicist delightedly. As is usually the
questions of our time.« case, every good idea has an origin.
This idea was no exception. During
the years he spent working as a scientist, he always regretted being unable to truly explore his artistic talents. “And
yet there is a considerable overlap between science and
art, both of which seek answers to the big questions of our
time,” he stated with conviction.
Rauch has been involved in knowledge transfer at PDI
for some two years now. Not only did the institute cause a
stir in this field with the installation of the Science Facade
in 2012; the idea for the festival also took shape there. “We
are on the look-out for new methods of transferring basic
research into society,” he reported. “I want to enable the
public to experience science in a new way.”
The first project he developed was a series of Science
Slams in Helsinki, which he established in the Finnish capital in 2010. However, Finland turned out to be somewhat
on the dark side, so he moved back to Berlin – to the
Paul-Drude-Institut. Together with other organisers, the
culture-loving physicist Rauch brought the “Science Hack
Day” to Berlin. This event enabled budding researchers and
creative minds to spend a whole weekend experimenting
with the development of weird and wonderful devices. For
Christian Rauch, this meant that a critical mass had been
reached. “I wanted to create a platform for this and other
innovative initiatives for science communication. There are
exciting opportunities out there at present, particularly in
collaboration with artists,” he stated. In a bid to exploit
these opportunities, he drew up a concept that became the
starting point for the STATE Experience Science Festival.
verbundjournal
Almanac 2016
GESINE WIEMER
Karl Weierstrass and the
Golden Age of Mathematics
Karl Weierstrass was a school dropout and a late bloomer – but that didn’t stop him
from becoming one of the greats in the history of mathematics. On the 31st of October
2015, the Weierstrass Institute for Applied Analysis and Stochastics (WIAS) celebrated
his 200th birthday. One of the guests was mathematician and German Federal Minister
of Education and Research Johanna Wanka.
Picture: Herschelmann
P
rofessor Johanna Wanka praised Karl Weierstrass’s
contributions to mathematics and his support of Sofja
Kovalevskaja, the first ever female professor of mathematics. In promoting Sofja Kovalevskaja, Weierstrass was a pioneer of equal opportunity in science. This is still a current
issue today: “Offering women and men the same career
opportunities in science is a key priority in the politics of
science, for which my ministry is campaigning very
strongly,” says Federal Minister Wanka.
“As a public administration official, you have a secure
position,” Weierstrass Sr. would likely have told his son. Yet
Karl Weierstrass, born 31 October 1815 in Germany near
Münster, chose instead to pursue mathematics. Thus,
against his father’s will, he stopped his studies of public finances and administration after two years and studied to
become a mathematics teacher.
He first taught at a Gymnasium (secondary school) in
Münster and later in Deutsch-Krone (West Prussia) and in
Braunsberg (East Prussia). On the side, he pursued his
true passion developing his theory of Abelian functions.
When he finally published his first results in the prestigious Crelle’s Journal in 1854, he was nearly 40 years old –
too late to start a scientific career, one might presume
nowadays. Yet Weierstrass became suddenly famous in
mathematical circles. The University of Königsberg in East
Prussia awarded him an honorary doctorate in 1854, and
he received numerous job offers.
Weierstrass was also enticed to work in Berlin. Starting
in 1856, he taught at the Königliches Gewerbeinstitut Berlin, one of the predecessor institutes of today’s Technische
Universität Berlin. Within the same year, he was appointed
associate professor of mathematics at the University of
Berlin (today’s Humboldt-Universität zu Berlin). It took
eight years until he obtained a full professorship. In the
1870s he held a function as the Dean of the Faculty of Philosophy and as the Rector of the University of Berlin.
Weierstrass was always pleased when transcripts of his
lectures were circulated, and supported young talents. In
particular, his support of Sofia Kovalevskaja (1850–1891)
is enshrined in scientific history. Because women were still
denied admission to the university, he taught her privately.
Sofia Kovalevskaja ultimately became a professor in Stockholm and was the first woman to hold her own lectures.
Weierstrass’s counterexamples
were feared by all
One outstanding mathematical achievement of Karl Weierstrass is the precision and rigidity with which he placed
Analysis on a new footing. He pondered very deeply over
how fundamental terms can be precisely understood so
that no contradictions would arise. His colleagues were often not so thorough – and Weierstrass was happy to find
exceptions to disprove them. His counterexamples were
feared by all. One function he construed was indeed called
the “monster function”. Before then, mathematicians had
generally assumed that, apart from a few exceptions, every
continuous function was differentiable everywhere. Weierstrass thereupon constructed a continuous function that
is not differentiable anywhere.
Weierstrass dedicated himself to mathematics and held
lectures to a ripe age. He contributed much during the
“Golden Era” of mathematics in Berlin and was held in
high esteem.
The Weierstrass Institute in Berlin honoured its namesake on his 200th birthday with a ceremony. Eight historical lectures were given, based on the volume “Karl Weierstraß (1815–1897). Aspects of his Life and Work”,
published by Wolfgang König and Jürgen Sprekels, both
from the Weierstrass Institute.
A group portrait
with the bust of
Weierstrass; to his
left: The German
Federal Minister
of Education and
Research (BMBF),
Professor Johanna
Wanka.
verbundjournal
Almanac 2016
GESINE WIEMER
Welcome to Germany
Scientists of many nationalities work at WIAS in Berlin. The picture shows the Research
Group of Professor König, “Interacting Random Systems”.
T
»
he sound of chalk squeaking on a blackboard. In no
time at all, Dr Michiel Renger from the Netherlands
has completely covered the board in formulae. He belongs
to Professor Wolfgang König’s WIAS research group on
“Interacting Random Systems” and is presenting his
thoughts on how chemical reactions can be described in
mathematical terms. He is feeling his way forward, has had
some new ideas and wants to share them with the group.
Such intensive information-sharing between researchers who are all experts in one field but still have different
perspectives is a core element of scientific work. And in
this WIAS group it functions especialThat it has turned into ly well because here, effectively, the
such a ‘pick ‘n’ mix’ whole world is focused on one point:
the 13 members come from nine
just adds to the fun.« countries and five continents, including the Master’s student Astrid Boje
from South Africa. As Wolfgang König notes: “This degree
of international diversity came about by chance. I simply
filled the positions with the best people. That it has turned
into such a ‘pick ‘n’ mix’ just adds to the fun.”
The young mathematicians are used to working in international teams and most of them have already done research in various different countries. “We really benefit
from the international diversity of the group. Because the
researchers are working in highly-specialised fields there
are often only a few experts in any given area. Our group
has contacts all over the world: there is always someone
who knows somebody who knows somebody…,” emphasises Michiel Renger. Every member thus contributes new
connections, new knowledge, new ideas.
Why did these young researchers decide to come to
Berlin? For all of them, the most important reason was the
interesting work being done at WIAS. And Berlin Mathematical School (BMS) also has great international pulling
power. Some of the group studied or conducted research
there before joining WIAS. Not to forget the magnetism of
Berlin itself: “My friends were quite envious when they
heard I had a job in Berlin,” reports Paul Keeler from Australia. “Berlin is considered cool and trendy.” Adrian Gonzalez Casanova from Mexico was also glad to come to Berlin. “In Berlin everyone has opportunities, but it is also a
city full of contradictions.”
In the run-up, some of the group had doubts – Germans
have the reputation of not being especially open to other
cultures. No one had expected a warm welcome. But they
all agree that their prejudice had been groundless. "Germans are very helpful and much more open than a lot of
other nationalities,” says Renato Soares do Santos from
Brazil. And there were not even any problems with the authorities provided that the job – with the relevant financing – was guaranteed.
In most of these young people’s own countries there is
a shortage of junior researchers in STEM subjects (science,
technology, engineering and mathematics). “In Australia,
we have to pay academic fees,” Paul explains, “and although they have been reduced a lot for mathematics,
there still aren’t many students.” In the Netherlands there
were plenty of people interested in going to university,
Michiel reports, but not because of their enthusiasm for
science but because it opened up good career prospects in
business. In India, too, young people tended to choose the
subjects that were likely to lead to good jobs, reports Chiranjib Mukherjee from the Subcontinent. “Mathematics is
not one of them – people go for computer science and engineering.” The young researchers are all agreed that the
only places where mathematics is cool are Russia and
France. Perhaps this is the reason why their passion for
mathematics binds the group even closer together – beyond all cultural differences.
Picture: WIAS
Science is international. Especially in highly-specialised research fields, international
collaboration is essential because there are only a handful of experts scattered around
the world. In one of the research groups at the Weierstrass Institute for Applied Analysis
and Stochastics (WIAS) a particular wealth of nations can be found.
verbundjournal
Almanac 2016
From the Leibniz Association
“the best of all possible worlds“
The Leibniz Association enters 2016 –
the Year of Leibniz – with numerous
events, a new website and its new
magazine “leibniz”. The German
poly
math Gottfried Wilhelm Leibniz
was born 370 years ago in Leipzig and
died 300 years ago in Hannover. The
Leibniz Association is taking this as an occasion for a major thematic year. Under the
title “the best of all possible worlds” – a Leibniz
quote – it is calling attention to the diversity and current relevance of the topics to which the scientists of the 88 Leibniz institutions throughout Germany have dedicated themselves. It
also presents the people behind the research. What drives
them to keep making new discoveries? And how are they helping to solve major social, economic and ecological issues?
The questions of life
At the end of the 17th century, philosopher, mathematician, legal practitioner, diplomat, historian and political adviser Gott
fried Wilhelm Leibniz ponders the fundamental questions of
life. He develops a binary numeral system that will later form
the basis for computer language and tinkers for decades on an
innovative mechanical calculator. He studies languages, builds
up a library and becomes a pioneer of wind energy – even if
his experiments with wind turbines fail. At the
same time, Leibniz counts among the great
Enlightenment philosophers. He muses
on religion and coins the much-debated phrase “the best of all possible
worlds”.
According to Leibniz, reality as a
whole is “the best of all possible
worlds”. It is – as current and dramatic
events show – no perfect world, but rather one in which
both progress and setbacks are possible. Man has the freedom
to observe the world, to understand it – and to bring about improvements. This freedom is also the prerequisite of science.
Looking ahead to the Year of Leibniz
How its scientists use this freedom, the Leibniz Association
shows in events such as the lecture series “Leibniz debattiert”, a
large open-air salon and a joint exhibition of the eight research
museums in the Leibniz Association.
Throughout the year 2016, the Leibniz Association will be
publishing articles from the world of sciences in its newly

designed print magazine “leibniz” and on the website

www.bestewelten.de.
Neighbourly relations: TRUMPF and Ferdinand-Braun-Institut
In close proximity to, and
in close cooperation with,
the Ferdinand-Braun-Institut,
Leibniz-Institut
fuer Hoechstfrequenztechnik (FBH), the laser
manufacturer TRUMPF
opened a new subsidiary
for the advance engineering of laser diodes in Berlin-Adlershof. In terms of power
density and power-to-light conversion rate, diode lasers
from FBH and TRUMPF are currently among the most powerful in the world, and new records are constantly being set
in the laboratories. The Berlin TRUMPF subsidiary will be
driving the development further. The laser diode is a key
module in today’s laser technology, where it is used both as
a pump source and as a direct diode laser. This cooperation
between industry and research is aimed at making laser
Picture: TRUMPF
Imprint
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is published by Forschungsverbund Berlin e.V.
Rudower Chaussee 17 · D-12489 Germany
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systems from TRUMPF even more energy-efficient. “We’re
attempting to look ten years ahead here, and to lay the foundations for future applications,” says Professor Günther
Tränkle, Director of FBH. “The joint venture underlines the
capability of our FBH teams, as well as the desire, even of
major players, to maintain and further extend their market
lead with our assistance,” he stated.
Both partners have already worked together for several
years now on brilliant high-power diode lasers. “Over the
past years our research activities have resulted in numerous patents, enabling further improvements to diode lasers,” says Tränkle. “The demand is there and will continue
to grow, because the market for laser systems that can
process and cut metals is vast.” For some materials, such
as the tempered steel used in the manufacture of monocoque safety cells in automobiles, the laser is virtually unrivaled, and has long since become an indispensable tool
in production.
Chair of the Board of Directors: Professor Marc Vrakking
Administrative Director of the FVB: Dr Manuela Urban
Editorial Office: Karl-Heinz Karisch, Gesine Wiemer,
Susanne Schiller
Copyediting/Proofreading: Dr Sarah Quigley
Cover Pictures: ESA/WIAS/ Berlin Zoological Garden/
Stefan Fölsch
Design: Unicom Werbeagentur GmbH
Printed by: Druckerei Arnold
The magazines “Verbundjournal” are free of charge.
Reproduction allowed with indication of source, copy
of reprint desired.
Editorial deadline: January 31, 2016
Cover Picture:
World record in
space
The FerdinandBraun-Institut in
Berlin supplies a
decisive component – a particularly robust and
capable pump
laser module. In
2014, for the first
time, data have
been successfully
transmitted between a near-earth
and a geostationary satellite over a
distance of 40,000
kilometers through
innovative laser
technology.
www.fv-berlin.de
www.facebook.com/ForschungsverbundBerlin
Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik (FBH) · Leibniz Institute of
Freshwater Ecology and Inland Fisheries (IGB) · Leibniz Institute for Crystal Growth (IKZ) · Leibniz-Institut für Molekulare Pharmakologie (FMP) · Leibniz Institute for Zoo and Wildlife Research ·
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) · Paul-Drude-Institut
für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V. (PDI) · Weierstrass Institute for Applied Analysis and Stochastics (WIAS), Leibniz Institute in Forschungsverbund Berlin e.V.
Computed tomography (CT) of a dead wolf (Canis lupus). The wolf was admitted to the IZW (Leibniz Institute for Zoo and Wildlife Research) as part of their
research and monitoring programme “Wolf-Totfundmonitoring” (post-mortem wolf research and monitoring in Germany). Cause of death: A car accident.
The new generation research CT at IZW is the world’s most advanced state-of-the-art CT in veterinary research.
Image: Guido Fritsch/IZW

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