Full Issue - Pertanika Journal of Scholarly Research Reviews

Transcription

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PJSRR(2015) 1(1): 1-7
© Universiti Putra Malaysia Press
Pertanika Journal of Scholarly Research Reviews
http://www.pjsrr.edu.my/
Internet and Facebook Use among University Students
Susan PHUAa,b,*& Su Luan WONGa
a
Faculty of Educational Studies, Universiti Putra Malaysia, 43400 UPMSerdang.
b
UniversitiTunku Abdul Rahman, Jalan Sungai Long, Bandar Sungai Long, Cheras, 43000, Kajang,
Selangor.
*[email protected]
Abstract – The Malaysian government continues to invest heavily in computing and Internet
resources in the belief that the Internet can improve the academic performance of students, offer elearning for undergraduates, and provide the flexibility of distance learning for adult students. The use
of the Internet and Facebook for educational purposes has been a topic of high interest among
researchers in recent years. In Malaysia, Internet access is relatively easy, fast, and affordable. It is
also a valuable source of information. Research shows that online consumers in Malaysia, Thailand
and the Philippines are the most likely to have engaged on social media sites such as Facebook. For
this very reason, students must be well-equipped with the requisite skills to exploit to the full the
benefits of the Internet and Facebook by the time they graduate. Such skills would certainly help to
enhance their employability in the competitive labour market. This study seeks to examine relevant
literature regarding the extent of Internet and Facebook use among university students. The literature
review will also explore how the use of the Internet and Facebook has impacted the academic
performance of university students.
Keywords: Facebook use, internet use, university students
Introduction
The widely held belief that students' academic achievement is impacted, either positively or
negatively, by their use of the Internet as well as Facebook (Irwin, Ball & Desbrow, 2012) has led to
much discussion among researchers. In a study by Sapari (2008), it was reported that the majority
(64.5%) of Malaysian university students from various science and social science faculties use the
Internet mostly for communication and information. This is not surprising as university students are
encouraged to use the Internet to broaden their knowledge by accessing vital information and also
communicating online with the academic community through Facebook (Boach, 2009). Several
studies relating to Malaysian university students’ purpose of Internet usage had been conducted by
researchers such as Luan, Fung, Nawawi, and Hong (2005), Sam, Othman, and Nordin (2005), Sapari
(2008) and Muniandy (2010), and their findings suggested that Malaysian university students used the
Internet for similar reasons as their counterparts in more developed countries. With regard to social
networking, it can be a healthy form of communication if the user does not indulge in it excessively.
Hamat, Embi, and Abu Hassan (2012) reported from their survey that university students made use of
social networking sites for informal learning and exchanging information of mutual interest. Selwyn
(2007) also found that students’ use of social networking sites had an impact on informal education.
Purpose of the Study
Encouragement by lecturers and tutors to exploit Information and Communication Technology (ICT)
has led to more time being spent on the Internet by university students. A recent study by Newsweek
Japan (as cited in Calderon, 2012) reported high Facebook usage amongst university students in
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Malaysia, especially among females. Hence there is a need to investigate the extent to which the use
of the Internet and Facebook impacts the academic performance of university students.
Method
A comprehensive search of the literature (magazines, dissertations, journals, and conference papers)
through the early 1990sto 2012 was carried out to collect relevant information and data. The main
objective of this article is to carry out a comparative literature review of studies on the use of the
Internet and Facebook amongst university students in various parts of the world.
Literature Review
Malaysia was ranked 30th on the Global Networked Readiness Index (Global Information Technology
Report, 2014). The most networked ready country was Finland, followed by Singapore in second
position, and Sweden in third position. The last country on the list of 148 listed was Chad. Being one
of the top 30 countries with network readiness meant that Malaysians used the Internet and were
engaged on Facebook more than many other countries. According to official figures, Internet
penetration in Malaysia by mid-2011 was among the highest in Asia, reaching as high as 17.5 million
users or 60 percent of the population. The figure was further increased after the implementation of
Kuala Lumpur Municipality’s new policy which required food and beverage businesses to provide
free or low cost WiFi service at their outlets (Choong, 2012). Malaysia's Communications and
Multimedia Commission (MCMC) (2014) also reported that the high Internet penetration in Malaysia
in the second Quarter of 2014 was concentrated in Wilayah Persekutuan Putrajaya (98.9%), followed
by Wilayah Persekutuan Labuan (86.7%), and Wilayah Persekutuan Kuala Lumpur (81.7%).
Malaysia was dubbed the country with the most social network friends in 2010 and Facebook
accounted for 77% of social network users (as cited in Calderon, 2012). Malaysia experienced a
26.4% growth in Facebook penetration within 12 months, with male users comprising 53% of
Facebook accounts. By early 2012, Facebook was among the top five most visited websites, and
Malaysians over the age of 15 spent approximately one-third of their time on social-networking
services (ComScore, 2010). Facebook’s popularity will likely continue to soar with more people
gaining access to the mobile web through the convenience of their smartphones.
Internet users go online for various reasons. The Internet is used for both work and pleasure (Hills &
Argyle, 2003). Besides providing entertainment and education materials for young and old (Madell &
Muncer, 2004), it is also a platform for buying and selling products (Kraut, Lundmark, Kiesler,
Mukhopadhyay, & Scherlis, 1997). As a result, the Internet has quickly become a natural part of
everyday life (Bargh& McKenna, 2004). Nielsen, a leading global information and analytics provider,
revealed in its survey that 1,321 Malaysian digital consumers who were surveyed spent close to 20
hours online each week ("Surging Internet Usage", 2011). According to the same survey, 53% of
those surveyed accessed the Internet daily, 5% accessed it once or twice a month while the rest were
less often Internet users. The report by Nielsen concluded that Malaysians were among the top users
of the Internet in Southeast Asia.
A recent summary of studies on Internet use in various countries was carried out by Wong, Bakar,
Ayub, Sapari, Moses, and Khambari (2012). Their findings, which included the purpose of Internet
use in various countries, reviewed a total of nine related studies. Table 1 depicts how undergraduate
students used the Internet for various academic and non-academic activities.
As can be seen in Table 1, Malaysian students generally used the Internet to perform four major and
similar activities, namely information gathering, e-mailing, downloading software, and reading online
newspaper. Other uses of the Internet included social networking, online banking, online shopping,
online games, video watching and downloading music. Wong et al. (2012) concluded that Malaysian
students used the Internet no differently from their counterparts in countries where Internet access was
more readily available.
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Table 1: Summary of Studies for Internet Use in Various Countries
Authors
Design
Sample/Location
Age (yrs)
Size
Purpose of Internet use
Study 1:
Weiser (2000)
Survey
University
students/Texas, USA
Exact age 506
range is
not stated
Entertainment, e-mail;
educational & academic
assistance; interpersonal
communication; course
information; research
Study 2:
Palesh,
Saltzman
&Koopman
(2004)
Survey
University
students/Moscow,
Russia
Exact age 198
range is
not stated
School-related activities; email; entertainment; chat &
pornographic materials
Study 3:
Jones, JohnsonYale,
Millermaier&
Pérez (2008)
Survey
College
students/USA
Age
range:
18-24
7421
Information, e-mail, instant
messaging, wikis & chat
Study 4:
Okon (2010)
Survey
University
students/Nigeria
Not
stated
536
Research; admission
registration & tuition fees
payment; e-mail; scholarship
application; online
newspaper
Study 5:
Tutgun, Deniz,
& Moon (2011)
Survey
University
students/Korea &
Turkey
Age
range:
17-37
595
Study 6:
Luan, Fung,
Nawawi and
Hong (2005)
Survey
University
students/Malaysia
Mean
age:
22.63
310
Friendship; games; chat;
develop websites & blogs;
shopping, pornographic
materials; gambling; games
Information; e-mail;
download software; online
newspaper; games;
shopping; e-banking
Study 7:
Sam, Othman
and Nordin
(2005)
Survey
University
students/Malaysia
Mean
age:
23.8
148
newspaper; games;
shopping;
Study 8:
Sapari (2008)
Survey
University
students/Malaysia
Age
range:
21-26
361
newspaper; games;
shopping; e-banking; &
pornographic materials
Study 9:
Muniandy
(2010)
Survey
University
students/Malaysia
Age
range:
20–34
92
download software; upload
files
Adapted from “Malaysian Students’ Internet Use: Some Research Evidence” by S.L. Wong, A. R. Bakar, A. F.
M.Ayub, N. A., Sapari, P., Moses, & M. N. M. Khambari, 2012, In Chang, B. et al. (Eds). Workshop
proceedings of the 20th International Conference on Computers in Education, p. 102.Copyright 2012 by the
Asia Pacific Society of Computers in Education.
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PJSRR(2015) 1(1): 1-7
Generally, 84% of students who used the Internet for academic purposes believed that the Internet had
positively impacted their academic performance (Jones, Johnson-Yale, Millermaire & Perez,
2008).Today, most university libraries offer free access to hundreds of electronic databases and
thousands of peer-reviewed journals, books and other online resources. The Internet has enabled
education to be borderless and limitless. It is a just a matter of whether students know how to exploit
these resources for their educational advancement (Wang & Artero, 2005).
The Internet is clearly recognised as a powerful technological tool with various academic benefits,
including access to abundant sources of news and information. Universities have begun to use
management systems such as Blackboard and portals that connect them to online university resources
and services. In fact, 94% of students reportedly used the Internet as a source of information when
conducting research for their courses (O’Brien, 2011). Results of a research regarding the use of the
Internet for academic communication purposes revealed that 84% of students used the Internet to
communicate with their professors; they also agreed that using the email helped them express
thoughts that they otherwise would not have shared in a classroom (Jones et al., 2008). The email is
also extremely useful for student-instructor communication as queries on assignments, progression
checks, feedback, and administrative matters can be conveyed with ease. Group projects are also
made easy via email. One considerable advantage of the email is its ease of communication. One can
write and receive emails anytime and anywhere if network connections are available.
Online voice mail and video conferencing have emerged as technologies that can enhance long
distance learning and online courses. Student interactions and student-lecturer interactions are made
easy by these emerging technologies which are supported by the Internet (Carr-Chellman &
Duchastel, 2000). The Internet allows lecturers and students to exchange thoughts, engage in
intellectual discourse, brainstorm ideas, and share knowledge; lecturers can also offer their students
emotional support (Baker, 2000).
However, not everyone shares the view that the Internet and Facebook positively impact academic
performance. Nie, Hillygus, and Erbring (2002) assert that time spent on the Internet displaces time
for other activities while Franzen (2000) suggests that the Internet enables its users to increase
efficiency and save time. Eberhardt (2007) reiterates that more research is needed to determine
whether time spent on social network sites diminishes time spent on schoolwork or studying. It is
unsure whether blame should be placed on the Internet and social networking sites as students already
had the habit of procrastination long before the Internet and Facebook came into being (Wesley,
1994).
A study by Kuh and Hu (2001) showed a positive relationship between the use of the Internet and
engagement in effective educational practices. Communale, Sexton, and Voss (2002) found evidence
to suggest that higher course grades were related to more frequent website use whilst a study
conducted in a university in Sarawak revealed that in general, students had positive attitudes towards
learning using the Internet regardless of their scholastic ability. It was found that students from the
Faculty of Information Technology, Faculty of Engineering, and Faculty of Resource Sciences and
Technology had more positive attitudes compared to students from other faculties. This could be
because the students in these faculties were more exposed to the Internet for course related activities.
These students had basic skills in using the Internet and were able to supplement their learning with
the assistance of the Internet to improve their studies (Hong, Ridzuan & Kuek, 2003).
A large majority of undergraduates have benefitted from the use of the Internet to do research and to
communicate with their faculty and classmates (Jones et al., 2008). Facebook too, has been
incorporated into classroom activities in universities globally. It helps university students better
understand their assignments by enhancing their classroom experiences. It offers students a chance to
break out of the traditional education norms. Facebook can create a school climate that is beneficial to
both learning and growing (Olabanji, 2011).
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Boogart (2006) observed that students who were frequent Facebook users reported a closer
connectedness to their university than those who accessed it less frequently. It has also been reported
that engaging on Facebook also helps build and maintain relationship among students. However, the
same study reported a correlation between heavy Facebook engagement and lower GPAs. Another
highly publicised report by Kirschner and Karpinski (2010) suggests that a relationship exists between
the use of Facebook and low grades.
Hamatet al. (2012) observe that the surge of interest to incorporate social media tools into education is
due to their characteristics which allow interactivity and collaboration. Learning, according to
advocates of socio-cultural theories of learning (Selwyn, 2007), becomes more effective in a social
setting.Students and lecturers can communicate with one another because Facebook is an interactive
website where messages and chats can be shared instantaneously. It can be used as a tool to enhance
the academic integration of students (Madge, Meek, Wellens, & Hooley, 2009). Many students use
Facebook to schedule group meetings and exchange information about assignments and deadlines.
Lecturers post class announcements and offer reviews and academic support online. Facebook has the
potential to be used as a technology that enhances classroom engagement. From the student’s
perspective, education becomes more meaningful, and this will help to improve his or her academic
performance (Olabanji, 2011). Facebook is considered as an extension of the classroom where
different kinds of connection take place (Schwartz, 2009).
In contrast, studies on the relationship of Internet use and academic performance by Chou and Hsiao
(2000), Kubey, Lavin, and Barrows (2001) and Niemz, Griffins and Banyard (2005) revealed a
negative association between Internet use and perceived impact on academic performances. However,
a study by Gulek and Demitras (2005) found that after a year in a laptop immersion program, students
showed significantly higher achievement in overall grade point average (Gulek & Demitras, 2005).
Conclusion
Rather than alienating the space between the home and university, educators should understand that
the present generation of students is exposed to ICT at a very young age outside the classroom. By
implementing the use of the Internet and Facebook engagement in the syllabi, students would benefit
from making a meaningful connection between their personal lives and their academic lives. The most
effective way to determine whether the Internet and Facebook have been properly integrated into the
education of students is to observe the academic progress of the students who have used the
technology (Hayes, 2006). Over-dependence on technology can be avoided if students are taught,
prior to the integration of technology in the classroom, that they are not to rely solely on the Internet
and Facebook but rather to use it as a tool to access and share ideas and information.
Lastly, the authors of this paper acknowledge that the review was limited to studies carried out
between the early 1990s and 2012. By and large, the Internet and social media technologies available
to students during that period of time maybe different from the ones students have today. As the
Internet and Facebook have become ubiquitous now, the authors feel itis important to provide a
glimpse of students' Internet and Facebook use to understand what they do online and what the
implications of their use maybe for other university students.
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Deep Mixing Columns
a
Shahram POURAKBARa*
Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang,
Selangor Darul Ehsan, Malaysia
a*
[email protected]
Abstract - The deep mixing columns (DMCs) is a stabilisation technique that uses cement and lime as
stabilisation agents to improve the ultimate bearing capacity of soils. This method has numerous
applications, such as foundation engineering, providing supporting wall for excavation, liquefaction
mitigation, hydraulic cut-off wall, and environmental remediation. This current paper presents a brief
history and a review of this promising technique for the purpose of ground improvement. Moreover,
several previous works related to the ultimate bearing capacity of DMCs ground are reviewed which
includes analytical analyses, laboratory works (small scale), and full scaled field tests. Finally the
paper suggests further study and development topics and proposes steps forward to enhance the
potential of alternatives for cement and lime replacement in this promising technique.
Keywords: Deep mixing columns, soil stabilisation, ultimate bearing capacity
Introduction
A variety of soil stabilization techniques have been applied to improve the bearing capacity of soft
ground, such as granular and prefabricated vertical drains, vacuum consolidation, granular column
reinforcement (sand compaction piles, vibrated stone columns), and stabilising techniques (deep
mixing, pre‐mixing and lightweight treated soil) (Kirsch & Bell, 2012; Sabih, Shafique, & Hussain,
2011). Of the soil stabilising techniques, deep mixing columns (DMCs) is becoming well established
in an increasing number of countries because it is a cost-effective approach with numerous technical
and environmental advantages including speedy implementation, elimination of off-site disposal, high
ground strength, and impeding of biodegradation (Fang, Chung, Yu, & Chen, 2001; Saitoh, Suzuki, &
Shirai, 1985).
In a broad perspective, deep stabilisation of soils is an in situ soil modification technique using a
stabilizing agent not only to improve bearing capacity but also to reduce settlement, preventing shear
deformation of soils, and treating contaminated soils (Porbaha, 1998; Topolnicki, 2004). According to
the literature, this method has several advantages (Kitazume, 2002; Kitazume & Terashi, 2013): (1)
speed of construction, (2) strength calibration, (3) reliability, (4) variety of applications, and (5)
effective use of resources.
This method has numerous applications, such as foundation engineering, providing supporting wall for
excavation, liquefaction mitigation, hydraulic cut-off wall, and environmental remediation
(Hashizume, Okochi, Dong, Horii, Toyosawa, & Tamate, 1998; Okumura, 1996; Terashi, 2005).
For instance, this method was successfully used to develop soft soil areas such as the Rawang-Ipoh
Rail Double Tracking Project in Malaysia (Raju, Abdullah, & Arulrajah, 2003), and the Carriageway
Trasa Zielona in Poland (Topolnicki, 2004). Several road and rail embankment stabilization projects
have been completed in China, France, United Kingdom and Italy using this method (Massarsch &
Topolnicki, 2005; Liu, Yi, & Zhu, 2008). Besides, the method has widely been used in the United
Kingdom to treat the contaminate soil and encapsulation of contaminated soils, including cut‐off walls
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PJSRR (2015) 1(1): 8-17
and reactive barriers (Al Tabbaa & Evans, 2003). In addition, Japan extensively uses this promising
method for different applications, one of which was the construction of about 15 km long Trans-Tokyo
Bay Highway; whereby the soft clayey foundation soil was improved using a cement mixture to
safeguard the tunnel (Kitazume, 2002). Elsewhere, this method was used for stabilizing failed levees
and flood walls along Orleans Avenue Canal in New Orleans, USA (McGuire, Templeton, & Filz,
2012).
In DMCs, the chemical agents, which are either slurry (wet mixing) or powder (dry mixing), are
mixed into the soft ground to form columns of soil binders. For this purpose, a rotary mixing auger is
drilled to the treatment depth. The drill's rotation direction is then reversed and retrieved whilst binders
are pumped through the auger drill bit and the soil and binders are mixed (Bruce, 2001).
Due to their robustness, easy adoptability, and economic value, cement and lime are employed as
stabilizing agents in DMCs to produce stronger and firmer ground, namely soil–cement/lime columns
(Kawasaki, Suzuki, & Suzuki, 1981; Prusinski & Bhattacharja, 1999; Saitoh, 1988). Although these
traditional cementitious binders can improve many engineering properties of soils, they have several
shortcomings, especially when viewed from an environmental perspective.
This current paper presents a brief history and a review of this promising technique for the purpose of
ground improvement. Moreover, several previous works related to the bearing capacity of DMCs
ground are reviewed which includes analytical analyses, laboratory works (small scale), and full scaled
field tests. Finally the paper suggests further study and development topics and proposes steps forward
to enhance the potential of alternatives for cement and lime replacement in this promising technique.
Deep mixing installation pattern
Specially designed machines are used to construct in situ columns of soil-binder in various patterns.
Several configurations of this method have been applied in the field, including: group, grid, wall, and
block (Kitazume, 2002; Kitazume & Terashi, 2013).
In the group column type improvement, treated soil columns or elements are installed in rows with
either rectangular or triangular arrangements in a ground. The execution needs a relatively short curing
period, and the volume of improvement is quite small (Figure 1 (a)). The group column type has been
constructed to support small structures especially on land (Kitazume & Terashi, 2013).
In the wall type improvement, as shown in (Figure 1 (b)), the long walls of treated soil with or without
short walls oriented perpendicular to the centreline of superstructures are produced by overlapping
adjacent columns (Kitazume & Terashi, 2013). The expected function of long wall is to bear the
weight of superstructure and other external loads, and transfer them to the deeper stiff layer.
The grid type improvement is an intermediate type between the block type improvement and the wall
type improvement. The stabilized soils columns are installed by overlapping execution so that grid
shaped improved masses are produced in the ground (Figure 1 (c)). This pattern is highly stable next to
the block type improvement and its cost ranges between the block type and wall type improvements
(Bruce, 2001; Kitazume & Terashi, 2013).
In the block type improvement, a huge improved soil mass is formed in a field by overlapping all the
stabilized soil columns (Figure 1 (d)). This type of improvement is normally applied to heavy and
permanent structures such as breakwater and sea revetment in port, and harbour structures (Kitazume
& Terashi, 2013).
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PJSRR (2015) 1(1): 8-17
Figure 1: Several configurations of deep mixing have been applied in the field including (a) Group
column type improvement, (b) Wall type improvement, (c) Grid type improvement, and (d) Block
type improvement
From economical and construction considerations, the group columns type is desirable due to the
small amount of improvement area and ease of installation as the treated columns are constructed
without any overlapping (Kitazume & Terashi, 2013; Terashi, 1981).
The deep mixing columns (DMCs) technique has some features in common with other ground
improvement techniques such as the stone column technique. Both methods are employed to improve
bearing resistance and control settlement in soft ground condition (Terashi, 2005). In addition, the
design used in both cases depends on the area replacement area ratio. However, important differences
are the material and installation technique used. The stone columns require granular material of
suitable grading to be available and the vibrations generated during installation can cause problems.
Deep mixing design
The DMCs are designed to precisely address the needs of any particular situation, either by adjusting
one or a combination of the following variables: columns diameter, replacement area ratio, mixing
definitions, binder quantity, and binder type (Porbaha, Shibuya, & Kishida, 2000).
In DMCs, the diameter of the columns ranges from 0.5 to 1.75 m, the spacing is generally 1.0 to 1.5 m
centre to centre and the length usually varies from 10 to 30 m in normal practice for land applications.
In some circumstances especially for harbour structures, 60 m long cement columns have been used
(Bruce, 2001).
The replacement area ratio, α, is the ratio between the total sectional area of the columns to the area of
the ground occupied by the columns. According to Bruce (2001), in the common treatments applied in
the Scandinavia and the United States, α, varies between 10 to 30%. In some situations, for preventing
a sliding failure and lateral deformation due to seismic conditions, an α value of 30 to 50% has been
applied (Bergado, Anderson, Miura, & Balasubramaniam, 1996). Those authors suggested that the
total width of improved ground should be more than half of the thickness of the soft ground if a low α
value is used.
In DMCs, the stabiliser agent is injected at a pressure of up to 280 Bar into the hole by using a
pumping system and a nozzle to mix the soil with the stabiliser agents either in the form of slurry
(wet) or powder (dry) (Druss, 2002; Porbaha, 1998). After mixing process, there is a chemical
reaction between the stabilising agent and soil that produces a composite material.
This composite material is often compacted to a relatively high density so that its properties become
similar to soft rock. The shear strength and modulus of elasticity of this material could be typically 10
to 20% of plain concrete (Jo, Hafez, & Norbaya, 2011) and hence they can be considered as an
engineered low strength concrete columns. In such a condition, a substantial improvement in the soil
bearing capacity is achieved which in turn reduces the overall foundation cost by allowing the
structures to be built on shallow footing rather than pile foundation. It has been documented that the
degree of this substantial improvement in the soil bearing capacity can be related to quantity of binder,
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PJSRR (2015) 1(1): 8-17
binder type, and curing time (Chew, Kamruzzaman, & Lee, 2004; Kawasaki et al., 1981; Kitazume &
Terashi, 2013; Terashi, 1981).
A number of studies have investigated the maximum effective percentage of binders to be mixed with
particular types of soils to gain a considerable increase in the compressive strength and to achieve a
desired improvement ratio (Kitazume & Terashi, 2013). Ahnberg, Ljungkrantz, and Holmqvist (1995)
reported that between 5 to 40% of binder content with respect to the dry weight is usually required to
stabilise soil columns. Meanwhile, 20 to 30% of binder content is typically used in Japan (Okumura,
1996; Yoshizawa, Tanaka, & Shekdar, 2004) and 10 to 50% of binder content is used in the United
States (Bruce, 2001; Porbaha et al., 2000). From the literature, the difference in binder amount is due
to the binder type and different reaction pathways in order to attain structural integrity (Kawasaki et
al., 1981).
Binder type
Traditional cementitious binders
Traditionally, the common binders in soil stabilization are lime, cement, or lime/cement (i.e., a
mixture of lime and cement) (Kawasaki, Saitoh, Suzuki, & Babasaki, 1984; Kawasaki et al., 1981).
Incorporation of these cementitious binders has gained popularity due to their robustness, easy
adaptability, and cost effectiveness (Akpokodje, 1985; Miura, Horpibulsuk, & Nagaraj, 2001;
Prusinski & Bhattacharja, 1999).
In cemented soil, when the pore water of the soil makes contact with cement, hydration of the cement
occurs rapidly and the major hydration (primary cementitious compounds) produces calcium silicate
hydrate (C-S-H), calcium silicate hydrate (C-A-H), and hydrated lime Ca(OH)2 (Janz & Johansson,
2002). In lime-stabilized soil, soil particles become closer and the soil is treated through flocculation
and pozzolanic reactions (Bell, 1996; Kamon & Nontananandh, 1991). Although the type of reaction
in cemented soil is completely different in comparison with lime-stabilized soil, the final products,
based on Si and Ca compounds, are very much alike. In terms of mechanical strength, cement-based
binders usually deliver substantially better results than lime-based binders (Janz & Johansson, 2002).
It should be noticed that the use of cementitious binders (i.e., cement and lime) in soil stabilization and
specifically in DMCs is under discussion, not only for their negative environmental effects during
manufacture but also for their cost.
In the case of cement, this traditional binder generates around 7% of artificial CO2 emissions, because
of carbonate decomposition (Gartner, 2004; Matthews, Gillett, Stott, & Zickfeld, 2009). It is estimated
that every ton of cement produces around one ton of CO2, a major greenhouse gas implicated in global
warming (Kim & Worrell, 2002; Lothenbach, Scrivener, & Hooton, 2011; Taylor, Tam, & Gielen,
2006). In addition to the emission of CO2, another by-product of cement production is NOx. Most of
these nitrogen oxides are produced in cement kilns, which can contribute to the greenhouse effect and
acid rain (Hendriks, Worrell, De Jager, Blok, & Riemer, 1998).
Beyond these problems, the use of cementitious binders in DMCs shows poor tensile and flexural
strength and a brittle behaviour (Correia, Oliveira, & Custódio, 2015; Sukontasukkul & Jamsawang,
2012). For instance, when the cemented soil column is subjected to seismic loads, either lateral earth
pressures (as for deep-mixed soil walls) or horizontal displacements (as in the case of columns
installed under the sides of embankments and in slopes), the stabilized soil tends to fail under tension,
due to its brittleness (Correia et al., 2015; Sukontasukkul & Jamsawang, 2012). Another issue
concerning about cement is associated with the intrinsic characteristics of the material that allow water
and other aggressive elements to enter cemented soil columns, resulting in corrosion and carbonation
problems (Fang et al., 2001). In the case of lime, it is essential to note that this soil binder reacts with
water rapidly and increases the difficulty during deep mixing projects (Bell, 1996; Cong, Longzhu, &
Bing, 2014).
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Pozzolanic materials
Several studies have focused on finding supplementary materials as partial replacements for traditional
cementitious binders. In this respect, the use of pozzolanic materials deserves special attention. These
materials are rich in silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) with little or no
cementitious value. It is a well-documented fact that pozzolanic binders cannot react completely by
themselves during stabilization (Basha, Hashim, Mahmud, & Muntohar, 2005; Chen & Lin, 2009).
However, when certain pozzolanic materials containing silica and alumina are added during the
hydration of cementitious binders, the reaction produces an additional amount of C-S-H and C-A-H
gels, the main cementing components (Dwivedi & Jain, 2014).
A pozzolanic reaction takes place when high amounts of reactive SiO2, Al2O3, and Fe2O3 are mixed in
the presence of water. Usually CaO is added to the mixture as lime or cement in Equation 1, while
SiO2, Al2O3, and Fe2O3 can be presented in the pozzolan to develop further cementation gels including
C-S-H and C-A-H. In this process, as shown in Equation 2, the hydration of the CaO liberates OHions, which causes the pH value to increase up to approximately 12. Under such circumstances, as
shown in Equations 3 and 4, pozzolanic reactions occur: the Si, Al, and Fe combine with the available
Ca, resulting in further cementation gels. Depending on the pozzolanic activity, the contribution of this
reaction is usually developed at later curing stages (Dermatas & Meng, 2003; Pourakbar, Asadi, Huat,
& Fasihnikoutalab, 2015; Seco et al., 2012). Therefore, pozzolanic materials require Ca(OH)2 in order
to form strengthening products, while cementitious materials themselves contain quantities of CaO
and can exhibit a self-cementitious (hydraulic) activity (Papadakis & Tsimas, 2002).
(1)
2(3CaO.SiO2) + 6H2O = 3CaO.2SiO2.3H2O + 3 Ca(OH)2
Hydrolysis:
Ca(OH)2 = Ca ++ + 2(OH)-
(2)
Pozzolanic reactions:
Ca ++ + 2(OH)- + SiO2 (pozzolan rich in silica) = C-S-H
(3)
Ca ++ + 2(OH)- + Al2O3 (pozzolan rich in alumina) = C-A-H
(4)
The use of pozzolanic materials in DMCs is still at the early stage of development and, hence, need
comprehensive research works in order to become technically and economically viable.
Researches on deep mixing
Analytical analyses
Theoretically, a stress concentration on the treated soil columns occurs when the treated columns are
much stiffer than the surrounding soil (Broms, 2003). In such condition, the foundation components
will carry external loads and deform together. Thus, the internal stability of the columns may become
a significant aspect of the design. Consequently the majority of the existing analytical methods for the
determination of ultimate bearing capacity (qult) value of treated soil columns were mainly dependent
on the strength performance of the columns.
In light of the abovementioned explanation, the qult value of the model ground has been determined in
several laboratory and full scale experiments based on two analyses including Broms (2000) and
weighted method as shown in Equations 5 and 6, respectively.
Broms’ method
Weighted method
qult =0.7 quc.α+ λ (1-α).Cus
(5)
qult = Cuc.α+ (1-α). Cus
(6)
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PJSRR (2015) 1(1): 8-17
where Cus and quc are undrained shear strength of the soft ground and the unconfined compressive
strength (UCS) value of the treated columns, respectively, where λ is a dimensionless coefficient,
proposed by Bergado et al. (1996) to equal 5.5. Furthermore, as mentioned earlier, α is the
replacement area ratio.
Lower bound (qmin) and upper bound (qmax) of the qult of treated soil by means of group columns
were established by Boussida and Porbaha (2004), and Bouassida, Jellali, and Porbaha (2009). Those
researchers established lower and upper bounds based on the yield design theory. They assumed that
the treated soil columns and untreated surrounding columns, which are deemed to have the same unit
weight, are purely cohesive materials and that their resistance obeys Tresca’s criterion.
According to the above-mentioned studies, the lower and upper bonds of qult can be computed using
Equations 7 and 8. In addition, Kc indicates the cohesion ration band on Equation 9.
qmin=Cus. [ 4 + 2α (kc-1)]
(7)
qmax= Cus.(2 √2 .√[1 + 𝛼(𝑘𝑐 − 1)][2 + α(kc − 1)])
(8)
Kc= Cuc⁄Cus
(9)
in which Cus and Cuc are undrained shear strength of native soil and treated soil column, respectively,
and α is replacement area ratio.
Laboratory research studies
A study conducted by Terashi (1981), who performed ten physical modelling tests in a laboratory with
a range of improvement of the area ratio from 13 to 32% and the strength ratio that ranged from 11 to
173. That author used cement as a soil binder and the prefabricated soil cement columns were inserted
into consolidated model ground for the column installation process. A rigid plate was used to load the
model ground and the loading was displacement controlled. They reported a clear peak was observed
when a strong column was used (quc = 1040 kPa) which indicates a brittle failure. According to their
test results, progressive failures in the columns occurred so that individual column displacements at
the overall peak load did not coincide.
Other studies were conducted by Kitazume (1996), and Kitazume, Okano, and Miyajima (2000), who
carried out physical modelling tests with an improvement area ratio of 79%, subjected to various
combinations of vertical loads. The strength of the columns, quc, ranged from 213 to 27200 kPa. Sand
was used as a drainage layer at the bottom of the specimen box and the box was then filled with kaolin
slurry. Acrylic pipes with 20 mm inside diameter and 250 mm length were used to fabricate the
cemented columns and extracted after seven days of curing. Further weeks of curing were conducted
under water at room temperature. All the model tests were carried out in an undrained condition. They
reported that the magnitude of the stress increased rapidly with the increase in displacement and the
peak stress occurred at about 0.05 to 0.10 of normalised vertical displacement. Moreover, they found
that the failure mode depends on the column strength (due to presence of cement) and vertical load
component.
Boussida and Porbaha (2004) carried out the research on the qult of ground improved by means of the
group column type. The study focused on an improvement area ratio of 18.8% with varying column
strength. Clay was used to construct the soft ground and sand was used for a drainage layer at the
bottom of the box. Soil cement columns of diameter 20 mm were constructed and cured outside of the
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PJSRR (2015) 1(1): 8-17
soil. The column installation technique was similar to that of Terashi (1981). The model was left in
fully saturated conditions for two days before loading was carried out. According to their test results,
peak load values were observed for all tests at less than 10% of normalised displacement and the
failures were classified as brittle failures.
A study was performed by Yin and Fang (2010), who conducted a physical modelling test on DMCs
with an improvement area ratio, α, of 12.6%. A rigid box with dimensions 900 mm width by 300 mm
length was used to study the qult value of the cemented soil column under a 300 mm wide footing. The
column preparation and installation technique were similar to that of Terashi (1981). According to this
study, a brittle failure was observed from the stress‐normalised displacement curve.
Full scale-field tests
Bergado, Ruenkrairergsa, Taesiri, and Balasubramaniam (1999) conducted a case study on the Bagna‐
Bangkapong Highway in Thailand improved by the DMCs. The purpose of the study was to
investigate the qult and settlement of the DMCs. The column diameter was 0.6 m and the length was
either 14 m or 16 m. The spacing centre to centre between the columns was 1.5 m. A wet mixing
method with 150 kg/m3 of cement was used in order to achieve 600 kPa column strength in the field.
The floating column group was constructed on soft clay having an average shear strength of 12.5 kPa.
Those authors found that the qult was larger than the embankment loading and measurements from
plate bearing tests.
Lin and Wong (1999) conducted a static load test on floating soil cement columns at the Fu‐Xia
Expressway, Fujian Province, China. Two columns were loaded, after being mixed in situ and cured
for 28 days, by jacking against steel beams loaded with sand bags. The diameter of the columns was
0.5 m and the length was 9.6 m for column three and 8.6 m for column four. By considering that the
failure occurred when the settlement reached 25 mm, the qult of columns was 150 kN and 183 kN and
the maximum compression strength was 667 kPa and 832 kPa, respectively. Lin and Wong (1999)
concluded that the failure of columns three and four could be due to either soil or column material
failure. Those authors found that the ultimate unit skin friction was 50% for column three and 70% for
column four of the average shear strength of the soft clay, 15 kPa. Disturbance of the surrounding clay
during column installation could have reduced the skin friction initially. For the column material
failure, they suspected that could have been caused by the heterogeneity of the cement mixing with the
soil in the field. As a result, the strength of the column in the field was lower than the strength
obtained from a laboratory trial mix.
Chai, Liu, and Du (2002) observed the performance of the DMCs at the Lian‐Yun‐Gang section of
the Xu‐Lian Expressway in eastern China. The field vane shear strength ranged from 5 kPa to 25 kPa
over a 10 m depth. A group of cement columns with a diameter of 0.5 m and 10 m long were installed
using the dry mixing method. The columns were arranged in a triangular pattern with 1.1 m to 1.6 m
spacing. In most cases, the amount of cement used was 59 kg/m3 to achieve the strength of 0.8 MPa.
Field loading tests were conducted on a single column and on a composite foundation which covered
either two or three columns. For the single cement column, a square loading plate with an area of 0.25
m2 was used. Chai and his co-workers found that the average compression strength of the column was
0.96 MPa which was close to the value of the laboratory unconfined compression strength (0.8 MPa).
As a result, they concluded that the qult of a single fully penetrated cement column was due to the
failure of the column itself. For the composite foundation, a study was made with different column
spacing (1.1 m, 1.2 m, 1.4 m and 1.6 m) with different areas of loading plate for the three columns
group (3.14 m2, 3.84 m2, 5.25 m2 and 6.65 m2). As a result, different improvement area ratios
underneath the loading plate were tested (8.9%, 11.2%, 15.3% and 18.8%). They concluded that the
qult increased with increasing improvement area ratio, although the conditions in each test were not
exactly the same and a precise comparison is not possible to achieve under field conditions.
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PJSRR (2015) 1(1): 8-17
Summary and conclusions
From the review of the literature available to date, it can be seen that the DMCs provides an alternative
to more traditional methods of soil stabilization. Several configurations of this method have been
applied in the field, including: group, grid, wall, and block. From economical and construction
considerations, the group columns type is desirable due to the small amount of improvement area and
ease of installation as the treated columns are constructed without any overlapping.
The majority of the existing analytical methods for the determination of ultimate bearing capacity
value of DMCs were mainly dependent on the strength performance of the columns. In this respect,
the ultimate bearing capacity value of the model ground has been determined in several laboratory and
full scale experiments based on two analyses including Broms and weighted methods.
According to the laboratory results, the failure mode depends on the column strength (due to the
presence of cement and other cementitious binders) and vertical load component. Moreover, according
to full scale tests, the strength of the column in the field was lower than the strength obtained from a
laboratory trial mix.
Traditionally, the common binders in DMCs are lime, cement, or lime/cement (i.e., a mixture of lime
and cement). Although the type of reaction in cemented soil is completely different in comparison
with lime-stabilized soil, the final products, based on Si and Ca compounds, are very much alike. The
use of cementitious binders (i.e., cement and lime) in DMCs is under discussion, not only for their
negative environmental effects during manufacture but also for their cost. Since the pozzolanic
materials are rich in silica, alumina, and iron oxide with little or no cementitious value, the use of
these materials in DMCs deserve special attentions.
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Olivine for Soil Stabilization
Mohammad Hamed FASIHNIKOUTALABa*
a
Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang,
Selangor Darul Ehsan, Malaysia
*
[email protected]
Abstract-The aim of this paper is to review the potential capability of olivine as a new binder for soil
stabilization. The recent research shows that using environmental friendly materials for soil
stabilization is expanding. The increasing amount of greenhouse gasses (GHG) such as CO2 has also
instigated research into finding environmentally friendly materials for soil stabilization. For quite
some time, cement is one of the well-known binders in soil stabilization, but it releases high amount
of CO2, and energy consumption of cement have caused civil engineers to use some other materials or
by-products to fully or partially replace cement for soil stabilization. Recently, alkaline activation
process in soil stabilization is an interesting option at medium-term to fully eliminate traditional
cementitious binders such as cement and lime. Olivine is a well-known material for CO2
sequestration. Furthermore, the high amount of SiO2, Al2O3 and Fe2O3 in olivine could classify this
mineral as a pozzolanic material in soil stabilization.
Keywords: Carbonation, olivine, soil stabilization, pozzolanic material, dissolution
Introduction
Using cement in civil engineering comes with several significant disadvantages, the most important of
which is the resultant release of carbon dioxide (CO2) into the atmosphere. CO2 is the leading
greenhouse gas which is an outcome from fossil fuels and human activities, and it causes climate
change and global warming. In the 1950s, CO2 doping grew about 0.7 ppm per year. In the last
decade, the CO2 level significantly increased by 2.1 ppm per year (Hanle, Jayaraman, & Smith, 2004;
Ke, Mcneil, Price, & Khanna, 2013). Olivine is a sustainable material that has the potential for use in
treating soils as it can capture CO2 because of the high amount of MgO. The literature indicates the
effect of carbonating reactive magnesia for soil stabilization and the positive role of reactive magnesia
against cement treated soil (Yi, Liska, Unluer, & Al-Tabbaa, 2013; Yi, Liska, Akinyugha, Unluer, &
Al-Tabbaa, 2013).
Soil stabilization
Soil stabilization is one of the oldest and most widespread techniques among the ground improvement
methods because construction on soft ground is a main problem in civil engineering. If the ground is
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PJSRR (2015) 1(1): 18-26
untreated, it is not good enough for the construction, and the bearing capacity or slope failure may
occur because of insufficient soil strength (Lee & Karunaratne, 2007).
Stabilized soil is, in general, a composite material that results from a combination and optimization of
properties in individual constituent materials. Well-established techniques of soil stabilization are
often used to obtain geotechnical materials improved through the addition into soil of such cementing
agents (Basha, Hashim, Mahmud, & Muntohar, 2005). The solution of refining these soils in-situ by
stabilization often becomes handy, as this has the insinuation of natural resource conservation,
reduction in energy usage and carbon dioxide release and increased cost efficiency (Obuzor, Kinuthia,
& Robinson, 2012).
Many binder materials possess hardening applications which could potentially be used for the
stabilization of soils. Soils with high water content stabilized by traditional mixtures have been
commonly used for the construction purpose to enhance bearing capacity, reduce settlement, control
shrinking and swelling, and reduce permeability (Miller & Azad, 2000; Åhnberg & Johansson; 2003,
Basha, Hashim, Mahmud, & Muntohar, 2005). Although such traditionally chemical stabilizers have
been economically attractive, from an environmental point of view, it is more prudent to consider
industrial by-products for soil stabilization that are most cost-effective, and not affecting the
surrounding soil and groundwater ecology upon treatment. Nevertheless, there are some negative
effects of using some of these materials in soil stabilization.
Soil stabilization by cement and lime
Cement is often used as an additive to improve the strength and stiffness of soft clayey soils, and the
increase in strength of soft soil by cement is well recognized. Cement treated soils have been
developed in the field of geotechnical engineering (Uddin, Balasubramaniam, & Bergado, 1997;
Miura, Horpibulsuk, & Nagaraj, 2001; Chew, Kamruzzaman, & Lee, 2004; Horpibulsuk, Rachan, &
Suddeepong, 2011). Cement can be used for both modification and stabilization purposes. The
addition of a few percentages by weight of cement has shown its success to better control the
workability during compaction, and significant cost savings over the removal and replacement of
filled materials in some projects (Sariosseiri & Muhunthan, 2009). The properties of cement-treated
soil can be divided into primary and secondary cementitious materials in the soil cement matrix. The
primary cementitious materials formed by hydration reaction are composed of hydrated calcium
silicates (C2SHx, C3S2Hx), calcium aluminates (C3AHx, C4AHx), and hydrated lime Ca(OH)2. A
secondary pozzolanic reaction between the hydrated lime and the silica and alumina from the clay
minerals leads to the formation of additional calcium silicate hydrates (CSH) and calcium aluminate
hydrates (CAH) (Chew et al., 2004; Kasama, Zen, & Iwataki, 2007). The reduction in plasticity index
(PI) caused by an increasing plastic limit (PL) and soil swelling, and outstanding increase in strength,
modulus of elasticity, and resistance against the effects of moisture can be significantly achieved by
cement stabilization. The addition of cement increased the optimum water content (OWC) but
decreased the maximum dry density (MDD) (Muhunthan & Sariosseiri, 2008; Horpibulsuk et al.,
2011).
Lime, CaO or Ca(OH)2, is the burned byproduct of lime stone (CaCO3), which is one of the oldest
developed construction materials that is still popularly used to improve fine-grained soils. Today, lime
stabilization is extensively used in numerous structures such as highways, railways, airports,
embankments, foundation base, slope protection, canal linings, and others (Muhunthan & Sariosseiri,
2008; Wilkinson, Haque, Kodikara, Adamson, & Christie, 2010; Dash & Hussain, 2011). A
considerable amount of literature has been published on soil stabilization by lime. On a major study
about the chemical stabilization, the researcher investigated the data on the interaction of the clay
from the Mirkovo deposit with lime, and he suggested that under the chosen experimental conditions,
the increase in strength during the first six months is entirely caused by the initially formed and
hardened gelated products of pozzolanic reactions involving mainly the clay minerals (Ref?). A
stabilized soil material is obtained with dry unconfined compressive strength (UCS) of the order of
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PJSRR (2015) 1(1): 18-26
5MPa to 6MPa. The processes causing changes in the phase composition of the calcium hydrosilicates
occur at long storage times (Ninov, Donchev, Lenchev, & Grancharov, 2007).
Lime can change the soil plasticity. First, a decrease in the liquid limit (LL) and an increase in the PL
result in an important reduction in PI. Reduction in PI facilitates higher workability of the treated soil.
Second, a reduction in water content occurs as a result of chemical reaction between soil and lime
(Petry & Little, 2002; Barker, Rogers, & Boardman, 2006). Apart from modifying the plasticity and
swelling characteristics, lime can stabilize the soils through cementation, visible increasing soil
strength and stiffness (Rajasekaran & Narasimha Rao, 2000; Alavéz-Ramírez, Montes-García,
Martínez-Reyes, Altamirano-Juárez, & Gochi-Ponce, 2012). The strength of lime-treated soils is
primarily dependent on the dissolved SiO2 and Al2O3 available for pozzolanic reactions, as well as on
the existing amounts of Ca2+ and OH-. Once the ions Ca2+ and OH- are fully consumed, the pH drops,
and the pozzolanic reactions cease, unless the amounts of Ca2+ and OH- are restored to the soil limewater system (Barker et al., 2006; Consoli, Lopes, Prietto, Festugato, & Cruz, 2011). However, the
lime-treated soil shows a complex behavior that is affected by several factors such as the
physicochemical properties of the soil, porosity, and the lime content at the time of compaction
(Pedarla, Chittoori, Puppala, Hoyos, & Saride, Sireesh, 2010). Cement and lime production involves
CO2 emission. The cement industry produces 5% of global man-made CO2 emissions, of which 40%
and 50% are from burning fuel and chemical process, respectively. The rests are divided between
transport and electricity uses (The Cement Sustainability Initiative, 2002). This emission is a
contributing factor to the significant global warming expected in future decades. For example in 2010,
the China cement output was 1.9 gigatonnes, which accounted for 56% of the world cement
production. The Total CO2 emissions from the Chinese cement production can therefore exceed 1.2
gigatonnes (Ke et al., 2013). CO2 is emitted from the calcination process of limestone, from
combustion of fuels in the kiln, and from power generation. In addition, CO2 is formed by calcination,
which can be expressed by Equation 2.1. According to the equation, 1 kg of CaCO3 can release 0.44
kg of CO2 (Worrell, Price, Martin, Hendriks, & Meida, 2001).
CaCO3 + Heat → CaO + CO2
1kg
(1)
0.56 kg + 0.44 kg
Using magnesium oxide in soil stabilization
Soil stabilization may be a technique introduced several years ago with the main purpose to render the
soils capable of meeting the necessities of the particular engineering projects (Kolias, KasselouriRigopoulou, & Karahalios, 2005). Stabilized soil is a composite material that results from the
combination and optimization of properties in individual constituent materials. Well-established
techniques of soil stabilization are typically used to obtain geotechnical materials that are improved
by adding into soil of such cementing agents as Portland cement, lime, and asphalt. The replacement
of natural soils, aggregates, and cement with solid industrial by-product are extremely captivating
(Basha et al., 2005). Previous studies show the effects of using Mg oxide for soil stabilization, for
example, the use of Mg hydroxide to stabilize the swelling clay. The results concluded that the Mghydroxide is absorbed by swelling clays both on their external and internal surfaces, whereas it is
adsorbed on the external surface by non-swelling clays. The internally adsorbed phase of Mghydroxide forms an ill-defined interlayer of brucite to retard swelling, whereas the external phase
covers the particles drastically to modify their surface properties (Xeidakis, 1996).
The study indicated that the principal forces concerned in the process are believed to be physical
adsorption on the external surface, and a few chemical bonding, largely in the inner surface.
Furthermore, cementation occurs because of crystallization and, in the long term, some pozzolanic
reactions occur. Internal adsorption of the Mg-hydroxide is postulated to be in the shape of
completely charged mono- and/or small polymers, and it is chiefly diffusion controlled. Given that
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PJSRR (2015) 1(1): 18-26
Mg-hydroxide is internally adsorbed by swelling clays whereas Ca-hydroxide (lime) is not, and also
the Mg Ca-clay aggregates are more stable than the Ca-clay or the Mg-one, the mixture of the two
hydroxides might provide higher results in soil stabilization than hydroxide alone (Xeidakis, 1996).
Another study showed the effect of a low grade MgO on the stability of contaminated soil. The
investigation showed that the contaminated soil is stabilized with a low grade MgO, independent of
the amount of stabilizer used, and a pH close to 9.2, that is controlled by the solubility of the
Mg(OH)2 (García et al., 2004). In 2010, the investigation about the sustainable material for soil
stabilization indicated that the industrial by-products, specifically GGBS, PFA, and cement kiln dust
(CKD), and innovative materials such as reactive magnesia and zeolite, clearly have various
sustainability benefits over PC in terms of reduced environmental impacts and enhanced technical and
durability performances. The stabilization of gravelly sand and clayey silt with a range of PC-blended
binders using the above materials showed that all these materials can act as partial replacement for PC
in ground improvement applications, which rely on the dosage applied and/or curing time that
provided higher strengths (Jegandan, Al-Tabbaa, Liska, & Osman, 2010).
Another study has looked at the properties of the two kinds of soil with different blends and contents
of GGBS, lime, MgO, and PC. The investigation has focused on the effect of mixed MgO and GGBS
and compared the result by using PC and GGBS-lime mixture on soil stability. The final outcome of
this research concluded that the UCS results showed that GGBS-MgO was more extreme than GGBSlime for soil stabilization with an optimum MgO content in the range of 5% to 20%; also the 28 days
UCS value of MgO-GGBS are up to four times higher than mixed PC (Y. Yi, Liska, & Al-Tabbaa,
2014). The recent study in 2013 mentioned the effect of carbonating magnesia for soil stability. The
study concluded the effect of carbonated reactive magnesia on the soil stability compared with PC
blended in soil. Results showed the treated soil by reactive carbonated magnesia after a few hours has
the same stability of 28 days of soil stabilized by PC. The main products of reactive magnesia
carbonated are nesquehointe and hydromagnesite-dypingite that are responsible in soil stability
(Yaolin, Martin, Cise, & Abir, 2013; Yi, Liska, Unluer, & Al-Tabbaa, 2013).
Olivine characterization
Olivine with the formula (Mg,Fe)2SiO4 is a magnesium iron silicate. It is a prevalent mineral within
the Earth's subsurface and is usually found in mafic to ultramafic igneous rocks. It is found less
commonly in marbles and some alternative metamorphic rock types (Jesa, 2011). The ratio of
magnesium to iron can vary in any proportion from pure Mg2SiO4 (fosterite) through to pure Fe2SiO4
(fayalite). Olivine can exist with colours ranging from yellowish green, olive green, greenish black
and reddish brown with densities from 3.27 to 3.37 and averaging 3.32 g/cm3 (Barthelmy, 2010).
Table 1 shows the nominal chemistry and physical properties of olivine, which, according to chemical
composition, consists of approximately 45% to 49% of MgO.
Table 1: Physical properties of olivine
MgO
48.28%
SiO2
40.32%
Fe2O3
8.9%
Al2O3
1.37%
LOI
1.13%
Olivine worldwide distribution
Olivine is found all over the world: India, Myanmar, Egypt, Pakistan, South Africa, Russia, Norway,
Sweden, Germany, France, Brazil, Mexico, Ethiopia, China, Australia, and the USA. As early as 1500
BC Egyptian pharaohs mined olivine on Zabargad Island in the Red Sea. Olivine can be detected in
the green beaches in Hawaii as well as in meteorites on Mars and Moon(“What is Olivine,” 2013). In
Malaysia, according to its geology, there is a possibility of olivine being mined. According to a study
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PJSRR (2015) 1(1): 18-26
of the Tawau geological heritage area located in the eastern part of Semporna Peninsula in Sabah,
West Malaysia, volcanic rocks of the andesite-dacite association form the major mountainous
backbone in this area. The rocks contain plagioclase, olivine, hornblende phenocrysts, clinopyroxene,
and magnetite microcrystals (Tahir, Musta, & Rahim, 2010). There is every possibility of surface
mining the substantial amount of olivine that exists here. Alternatively in tropical areas, the great
advantage of this is the fast weathering in tropical areas (Schuiling & Praagman, 2011).
Olivine dissolution
Dissolution and hydrolysis are the results of reactions with acids. Hydrolysis occurs as the
transformation of silicate and carbonate minerals into new minerals. In this process, there is total
dissolution of the original rock leaving no solid residue(Kayar, 2011). It can be generally explained
that olivine dissolution happens when-carbonate-saturation-is-attained in the fluid stage, resulting in
the precipitation of magnesite, and summarized as follows (Dufaud, Martinez, & Shilobreeva, 2009):
Mg2SiO4 + 3H2O + 2CO2 → Mg2+ + Mg3Si2O5(OH)4 + 2HCO−(2)
Earlier research findings on the description of the dissolution rate of olivine at low-temperature-canbe-extended-to-higher temperature, which could contain its behaviour as a function-of-pH, in the
presence of CO2, and at pH ≤ 5 (at 120 °C).Dissolution rates have been found to be two times greater
than-those-without-CO2-at the same pH. Citric acid, another ligand previously studied in the
literature, also shows a dissolution improvement effect (Hänchen, Prigiobbe, & Storti, 2006). As a
result, certain scholars have pointed out that-sorption-of-inorganic carbon type to surfaces can affect
dissolution performance for Fe oxides and Ca or Mg silicates. Even at alkaline conditions; silicate
dissolution rates demonstrate only an-insignificant-or-at-best-weak condition on PCO2 when pH is
held constant. For example, the liberation of Ca and Mg from diopside during dissolution decreased
slightly or not at all for PCO2> atmospheric (Brantley, 2008).
Many factors affect the dissolution rate of olivine, and some of the most important factors are: the
grain size, temperature, solution chemistry (pH, concentration of carbonate, magnesium, silica,
organic acids, ionic strength), and the formation of the coating on the grains (Veld, Roskam, & Enk,
2008). Mineral carbonation, that includes the reaction of Mg-rich minerals with CO2 to produce
geologically stable mineral carbonates, has been proposed as a promising CO2capturing technology.
Potential of using olivine for soil stabilization
Regarding the chemical properties of olivine as shown in Table 1, olivine is the major source of
magnesium oxide (MgO) which makes up to between 45% to 49% by weight. Prior research has
demonstrated that magnesium oxide can be successfully utilized for soil stabilization, for example, the
use of Magnesium hydroxide to stabilize swelling clay (Xeidakis, 1996). Another investigation
studied how a low grade MgO affected the stability of contaminated soil, and the results showed that
the contaminated soil was successfully stabilized with the low grade MgO (García et al., 2004). A
significant study conducted in 2010 addressed the use of sustainable materials for soil stabilization.
The study investigated the effect of mixing industrial by-products with innovative materials such as
reactive magnesia and zeolite. These were demonstrated to clearly show a variety of sustainability
benefits over PC in terms of reduced environmental impacts and enhanced technical and durability
performance (Jegandan et al., 2010). A recent study in 2013 investigated the effects of carbonating
magnesia on soil stabilization by comparing it with PC blended in soil. The results showed that soil
treated with reactive carbonated magnesia after a few hours had the same stability of soil stabilized by
PC after 28 days. The main reaction products of carbonated magnesia responsible for the increased
stability were nesquehointe and hydromagnesite-dypingite (Yi, Liska, Unluer, & Al-Tabbaa, 2013).
The formulations below show the main products of reactive carbonated magnesium:
MgO + H2O → Mg(OH)2Brucite (3)
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PJSRR (2015) 1(1): 18-26
Mg(OH)2 + CO2 +2H2O → MgCO3 . 3H2O
Nesquehonite (4)
5Mg(OH)2 + 4CO2 + H2O → (Mg)5(CO3)4(OH)2 . 5H2O
5Mg(OH)2 + 4CO2 → (Mg)5(CO3)4(OH)2 . 4H2O
Dypingite (5)
Hydromagnesite (6)
Conclusion
The aim of this paper is to review the olivine potentials as a new binder for soil stabilization. Olivine is a
sustainable martial to not only can capture CO2 from atmosphere through the high amount of MgO, but
also the chemical composition of olivine will put this mineral as a pozzalanic material for soil stabilization
because of the high amount of SiO2, Al2O3 and Fe2O3. The use of olivine as a new martial for soil
stabilization will be a great opportunity for environmental friendly soil stabilization.
Acknowledgment
This review study is for a related research project entitled “Sustainable soil stabilization by olivine and its
mechanisms” supported by the Fundamental Research Grant Scheme (FRGS) funded by Ministry of
Higher Education in Malaysia (Project ID 93474-135837). Sincere thanks are also due to Prof. Bujang
B.K. Huat, Dr. Afshin Asadi and Dr. Haslinda Nahazanan, Prof. Emeritus Dr. R.D. Schuiling from the
Netherlands, and Ir. Parminder Singh from Malaysia who have contributed ideas to the research.
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blg18827.pdf
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problematic soils by lime slurry pressure injection: Case Study. Journal of Geotechnical and
Geoenvironmental Engineering, 136(10), 1459–1468.
Worrell, E., Price, L., Martin, N., Hendriks, C., & Meida, L. O. (2001). Carbon dioxide emissions
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http://www.pjsrr.upm.edu.my/
Data Envelopment Analysis Models and Software Packages
for Academic Purposes
a
Abdullahi ILIYASU, *a Zainal Abidin MOHAMED,a & Rika TERANO
Department of Agribusiness and Information System, Faculty of Agriculture, Universiti Putra
Malaysia, Selangor Malaysia.
*
[email protected]
Abstract – Data envelopment analysis (DEA) is a popular technique used in measuring the
performance of an industry. DEA has wide applications in agriculture, manufacturing, health care,
transportation, education, energy and environment, as well as banking and finance. However, many
students and academicians are in dilemma in finding the appropriate software to execute a particular
DEA model. In recent years, different DEA software packages have been developed by some
universities and companies for both academic and commercial purposes. The software packages
offered wide varieties of most recent DEA models that could be used in science and technology. Some
of these software packages are free for academic users while others are commercialised. In this study,
nine different DEA software packages were reviewed. Among them, only three are free for academic
purposes while four have been commercialized. One of the former is still in the development stage,
but expected to be available soon.
Keywords: Academic, commercial, data envelopment analysis, review models, software packages
Introduction
Data envelopment analysis (DEA) involves the application of linear programming technique to
estimate the performance of an industry such as agriculture, health care, transportation, education,
manufacturing, power, energy and environment, communication, banking, and finance (Liu et al.,
2013). Table 1 shows the number of articles published in various industries that employed DEA
models in their data analysis. In addition, many empirical research studies that employed DEA models
as tools of analysis have been published in ISI or Scopus journals (see Table 2).
Since the novel works by Charnes et al. (1978), many software packages have been developed to
applied DEA models in various industries. Barr (2004), Hollingsworth (2002), and Herrero and
Pascoe (1997) did a good review of these software packages. However, some of these software
packages are no longer available for empirical analyses while new ones have emerged. Furthermore,
many models that are previously undiscovered are now available. The recent DEA models include
dynamic DEA with network such as a slack-based measure approach (Tone & Tsutsui, 2014), an
alternative approach of a slack-based measure of super-efficiency in DEA, (Fang et al., 2013), a
modified super-efficiency measure based on simultaneous input–output projection in data
envelopment analysis (Chen et al., 2011), super-efficiency in DEA by effectiveness of each unit in
society (Nuara et al., 2011), a slack-based measure of super-efficiency in DEA (Du et al., 2010), an
epsilon-based measure of efficiency in DEA (Tone & Tsutsui, 2010), and variations on the theme of
slacks-based measure of efficiency in DEA (Tone, 2010). Other models include network DEA such as
a slacks-based measure approach (Tone & Tsutsui 2009), models for performance benchmarking
(Cook et al., 2004), Undesirable Measure (Seiford & Zhu, 2002), a slack-based measure of superefficiency in DEA (Tone, 2002), a slack-based measure of efficiency in DEA (Tone, 2001), Network
DEA (Färe & Grosskopf, 2000), and bootstrapping DEA (Simar & Wilson 1998).
27
PJSRR (2015) 1(1): 27-32
Consequently, a need arises to review existing packages to help students and academicians to select
the one that best fits the DEA model of interest. Information on the DEA software packages such as
license price, developers, models, and website are, therefore, of paramount importance. It is against
this backdrop that this review study is conducted.
Table 1: DEA applications in industries
Industries
Total no. of papers
Banking
323
Health care
271
Agriculture
258
Transportation
249
Education
184
Power
156
Manufacturing
146
Energy
109
Communication
70
Finance
51
(%)
17.8
14.9
14.2
13.7
10.1
8.6
8
6
3.9
2.8
2005–2009
147
107
140
131
75
87
75
75
28
33
Source: Liu et al. (2013)
Commercial DEA software packages
In this study, five commercialized DEA software packages are discussed in details. Three out of these
five packages (DEA Solver, Frontier analyst, and MaxDEA) were developed by commercial
companies. The other two (PIM-DEA and DEA Frontier) were developed by universities/polytechnics
(see Table 3).
Table 2: Commercial and academic DEA software
Software
Developer
DEA-Solver
Frontier Analyst
PIM-DEA
DEAFrontier
MaxDEA
FEAR
DEAP
EMS
SAITECH, Inc, USA
Bonxia Software Ltd, Uk
Emrouznejad A. and Thanassoulis E.
Joe Zhu
Beijing Res. & Con. Com. Ltd China
Paul W. Wilson
Tim Coelli
Holger Scheel
License price (single CPU)
Academic
Commercial
$800
$1,600
£395-£3995
£395-£3995
£245-£966
£490-£1932
$699
$2,889
$890
&2000
Free
$180
Free
Free
Free
Free
DEA Solver Pro version
The DEA Solver Pro version is developed by SAITECH Inc., New Jersey, USA and runs within
Microsoft Excel. The latest release is Version 10.0, which has additional features not available in the
previous versions. The lists of comprehensive models in this package are shown in Appendix A. The
license price for single central processing unit (CPU) is $800 (academic purposes) and $1600
(commercial purposes) as illustrated in Table 3. However, a temporary license is also available at a
price of $200, $250 and $350 for classes comprising up to 20, 30, and 40 students, respectively. The
software package can be purchased from the developer’s website (http://www.saitech-inc.com).
Alternatively, a potential user may buy a textbook (Cooper et al., 2006) to use the student trial version
packaged with the book. The student trial version is, however, limited to only 50 Decision Making
Units (DMUs).
28
PJSRR (2015) 1(1): 27-32
Frontier Analyst
Frontier Analyst is developed by Bonxia Software Limited, UK. The strongest feature of this software
is its ability to display a variety of results. These include graphs of technical efficiency scores,
distribution of efficiency tables, frontier plots, pie charts, reference set frequency, X-Y plots, and
efficiency plots. Appendix A displays different DEA models available in this software package.
However, unlike most of the DEA software packages reviewed, there is no difference between the
license prices for academic or commercial users for Frontier Analyst. The license price escalates as
the number of DMUs increases from £395 (75 DMUs only) to about £3995 (20000 plus). Furthermore,
the cost for a single CPU and a three-month trial version with a maximum of 500 DMUs is £295. The
annual maintenance and upgrading of the software costs about £289 per CPU but it is optional.
Therefore, Frontier Analysis is the most expensive among all the commercial DEA software packages
based on this review. This software package can be bought online through the developer’s website
(www.bonxia.com).
Performance Improvement Management Software (PIM-DEA)
PIM-DEA Version 3 is developed by A. Emrouznejad and E. Thanassoulis at Aston Business School,
Aston University Birmingham, England. This software can handle large data sets, which can be
directly imported from Microsoft Excel. Similarly, outputs can be easily exported to Microsoft Excel
including different types of graphs for presenting results. Additionally, it allows computation of
different DEA models as showed in Appendix A.
PIM-DEA, same as Frontier Analyst, has a variety of prices depending on the license type (academic
or commercial), validity type (permanent or temporally), number of DMUs, additional packages,
maintenance duration and postal methods. For instance, the permanent license price for academic
purposes is £245 (100 DMUs) to £966 (5000 DMUs) whereas £490 (100 DMUs) to £1932 (5000
DMUs) for commercial users. PIM-DEA is the second most expensive DEA software package based
on this review. For further information on PIM-DEA, visit the developer’s website
(www.deasoftware.co.uk).
DEA Frontier
DEA Frontier is written by Joe Zhu of Operations and Industrial Engineering, School of Business,
Worcester Polytechnic Institute, USA. The software solves different DEA models (Appendix A) using
Microsoft Excel solver and with no limitation in the number of DMUs, inputs or outputs. However,
unlike most DEA software, well-illustrated tutorials are available online on how to use the software to
solve various DEA models. Although the software is commercialized, it has a free download trial
version, but the trial version can only handle 20 DMUs and has very limited DEA models. The
developer advised potential users to try the trial version before purchasing the licensed version. The
license prices for single CPUs are $699 and $2889 for academic and commercial purposes,
respectively. This license includes one month free technical support for using the software package
only. The pricing and order information is available on the developer’s website (www.deafronier.net).
MaxDEA
MaxDEA is developed by Beijing Real World Research and Consultation Company Limited. This
software is easy to use because it comes in a folder and as such requires no installation. Multiple DEA
models can be run at the same time and results can be displayed in Microsoft Excel. The software is
of two types, basic and professional. The former allows free download, but it also has a limited
number of DEA models that can be executed. On the other hand, the latter is strictly commercialized
but deals with comprehensive DEA models as shown in Appendix A. The license price varies
depending on the validity type (permanent or temporal) and usage purpose (commercial or academic).
The one year license price per single CPU is $360 and $800 for academic and commercial purposes,
respectively. On the other hand, the perpetual license price for a single user is $890 and $2000 for
academic and commercial users. However, the prices of the license escalate as the number of DMUs
increases. Further information on the software can be obtained from the developer’s website
(www.maxdea.cn).
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PJSRR (2015) 1(1): 27-32
Free DEA software packages (academic purposes only)
Unlike commercial DEA software, the free downloadable packages are developed by universities.
Although Frontier Efficiency Analysis in R (FEAR) is free for academic purposes, a license fee needs
to be paid for commercial usages.
Frontier Efficiency Analysis in R (FEAR)
FEAR is developed by Paul W. Wilson of Department of Economics and School of Computing,
Clemson University, USA. Unlike most DEA software, FEAR works in General Purpose Statistical
Package called R, which can be freely downloaded from the website. However, in order to use FEAR,
R needs to be downloaded first in the CPU. The FEAR library is then linked to R for various DEA
computations. The FEAR package is free for academic purposes, but users must cite Wilson (2008) in
all reports, papers, and publications. On the other hand, the FEAR package is not free for commercial
users, but costs only $180 (single CPU license). The user guide and FEAR packages are available at
the following website: www.clemson.edu/economics/faculty/Wilson/software/FEAR.
Data Envelopment Analysis Program (DEAP)
DEAP is a DOS programme developed by Tim Coelli of Centre for Efficiency and Productivity
Analysis (CEPA), School of Economics, University of Queensland, Australia. This software can be
downloaded freely from the website (www.uq.au/economics/cepa/deap.php) in zip form, which
contains user guide (Coelli, 1996), read me, and many short examples. Three text files are normally
used when conducting an analysis using DEAP. These include data file, instruction file and output file,
and all can be edited according to the user analysis. Three analysis options are available in DEAP,
standard CRS and VRS DEA models, cost and allocative efficiencies, and Malmquist DEA approach
(Appendix A). DEAP is the most popular DEA software package especially among students and
academicians perhaps because it is user friendly.
Efficiency Measurement System (EMS)
EMS Version 1.3 is developed by Holger Scheel at University of Dortmund, Germany. The software
is free for download for academic purposes. EMS accepts data files from Microsoft Excel or text
format, and it operates in Window 9x/NT. There is no limitation in the number of inputs, outputs, and
DMUs in using the software. The EMS is distributed in zip file together with the user guide from the
website (www.holger-scheel.de/ems/).
Data Envelopment Analysis using Stata (DEAS)
DEAS is not yet available for academic and commercial purposes because it is still in the developing
stage. According to the developers, the package was registered with Source Forge.net on January 3,
2013. However, the main aim of developing DEAS is to replace the existing DEASTATA that was
proposed for management performance analysis. According to the developers, DEAS models will
include CCR, BCC, slack-based measure of efficiency, super-efficiency, allocative efficiency,
revenue efficiency, profit efficiency, cost efficiency, free disposal efficiency, additive model, virtual
price model, and Malmquist productivity index among others.
Conclusion
The study reviewed nine different DEA software packages for executing various analysis models.
Three of these software packages are free for academic purposes while the remaining five need to be
purchased accordingly. The other one is still in the developing stage, and expected to be available
soon. The major shortcoming of all these software packages reviewed is that none of them performs
all the DEA analysis. In addition, the free software packages have limited number of DEA models
when compared with the commercial versions. The licensed software is very expensive and hence not
affordable by many students and academicians especially in developing countries. Effort should be
geared towards producing a single software that computes all the DEA models and at a cheaper price
or free of charge to enable wider applications.
30
PJSRR (2015) 1(1): 27-32
References
Barr, R. S. (2004). DEA software tools and technology. Handbook on Data Envelopment Analysis,
Boston: Kluwer Academic Publishers.
Charnes, A., Cooper, W. W., & Rhodes, E. (1978). Measuring the efficiency of decision making units.
European Journal of Operational Research, 2(6), 429-444.
Chen, J.-X., Deng, M., & Gingras, S. (2011). A modified super-efficiency measure based on
simultaneous input–output projection in data envelopment analysis. Computers & Operations
Research, 38(2), 496-504.
Coelli, T. J. (1996). A guide to FRONTIER version 4.1: A computer program for stochastic frontier
production and cost function estimation: CEPA Working papers.
Cook, W. D., Seiford, L. M., & Zhu, J. (2004). Models for performance benchmarking: measuring the
effect of e-business activities on banking performance. Omega, 32(4), 313-322.
Cooper, W. W., Lawrence M. S., & Kaoru Tone (2006). Data Envelopment Analysis: A
comprehensive text with models, applications, references and DEA-Solver Software.
Second Edition. New York: Springer.
Du, J., Liang, L., & Zhu, J. (2010). A slacks-based measure of super-efficiency in data envelopment
analysis: a comment. European Journal of Operational Research, 204(3), 694-697.
Fang, H.-H., Lee, H.-S., Hwang, S.-N., & Chung, C.-C. (2012). A slacks-based measure of superefficiency in data envelopment analysis: An alternative approach. Omega - The International
Journal of Management Science, 41(4): 731–734.Färe, R., & Grosskopf, S. (2000). Network
dea. Socio-economic planning sciences, 34(1), 35-49.
Herrero, I., & Pascoe, S. (2002). Estimation of technical efficiency: a review of some of the stochastic
frontier and DEA software. Computers in Higher Education Economics Review, 15(1), 38-43.
Hollingsworth, B. (1997). A review of data envelopment analysis software. Economic Journal,
107(443): 1268-1270.
Liu, J. S., Lu, L. Y., Lu, W.-M., & Lin, B. J. (2013). A survey of DEA applications. Omega, 41(5),
893-902.
Kaoru Tone, M. T. (2014). Dynamic DEA with network structure: A slacks-based measure approach.
Omega, 42(1), 124-131.
Noura, A., Hosseinzadeh Lotfi, F., Jahanshahloo, G. R., & Fanati Rashidi, S. (2011). Super-efficiency
in DEA by effectiveness of each unit in society. Applied Mathematics Letters, 24(5), 623-626.
Seiford, L. M., & Zhu, J. (2002). Modeling undesirable factors in efficiency evaluation. European
Journal of Operational Research, 142(1), 16-20.
Simar, L., & Wilson, P. W. (1998). Sensitivity analysis of efficiency scores: How to bootstrap in
nonparametric frontier models. Management science, 44(1), 49-61.
Tone, K. (2001). A slacks-based measure of efficiency in data envelopment analysis. European
Tone, K. (2002). A slacks-based measure of super-efficiency in data envelpoment analysis. European
Journal of Operational Research, 143, 32-41.
Tone, K. (2010). Variations on the theme of slacks-based measure of efficiency in DEA. European
Tone, K., & Tsutsui, M. (2009). Network DEA: a slacks-based measure approach. European Journal
of Operational Research, 197(1), 243-252.
Tone, K., & Tsutsui, M. (2010). An epsilon-based measure of efficiency in DEA–a third pole of
technical efficiency. European Journal of Operational Research, 207(3), 1554-1563.
Wilson, P. W. (2008). FEAR: A software package for frontier efficiency analysis with R. SocioEconomic Planning Sciences, 42(4), 247-254.
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Appendix A: DEA Software
Models
Models
DEASolver
CCR/CRS
y
BCC/VRS
y
NIRS,NDRS,GRS
y
Additive/Slack-Based
Method
y
Malmquist
y
Non-convex
y
Non-radial
y
Preference-structure
n
Undesirable-measure
n
Context-dependent
n
Free-disposal hull (FDH)
y
Order m efficiency
n
Allocative efficiency
n
Cost efficiency
y
Revenue efficiency
y
Profit, revenue/cost
efficiency
y
Variable-benchmark
n
Fixed-benchmark
n
Minimum-efficiency
n
Weak disposability
n
Congestion
y
Super Efficiency
n
Scale elasticity
y
Slack-Based Super
Efficiency
n
Bootstrapping
n
Network
n
Dynamic
n
Cross Efficiency
n
Epsilon-Based Measure
(EBM)
n
Restricted multiplier
n
y = available; n = not available
Frontier
Analyst
DEA
MaxDEA
Frontier
Pro
PIMDEA
FEAR DEAP EMS
Y
Y
N
y
y
y
y
y
y
y
y
y
y
y
y
y
y
n
y
y
y
N
y
n
n
n
n
n
n
n
n
n
n
y
y
y
y
y
y
y
y
n
n
y
y
y
y
n
y
y
y
y
y
n
n
y
y
n
y
n
n
n
n
n
n
n
y
y
n
n
y
n
n
n
n
n
y
y
n
y
y
n
y
n
n
n
n
n
n
n
n
y
n
y
y
y
n
n
n
n
y
n
n
n
n
n
n
n
n
n
n
n
n
y
y
y
y
y
y
y
n
y
y
y
y
y
n
y
n
n
n
n
n
n
n
n
y
y
n
n
n
n
n
n
n
n
n
n
n
n
n
n
y
n
n
n
n
n
n
n
n
n
n
n
n
n
y
y
n
n
y
n
y
y
y
y
n
y
n
n
n
n
y
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
y
y
y
n
n
n
n
n
n
n
n
32
PJSRR (2015) 1(1): 33-39
Renewable Energy Policy Status and Challenges of POME-Biogas Industry in
Malaysia
Wong, SIEW YIEN,aAmir, HAMZAH SHARAAI,b*Faradiella, MOHD KUSIN,a
& Mohd, MANSOR ISMAIL,c
a
Department of Environmental Sciences, Faculty of Environmental Studies, Universiti Putra
Malaysia, 43400 UPM Serdang, Selangor, Malaysia
b
Department of Environmental Management, Faculty of Environmental Studies, Universiti Putra
Malaysia, 43400 UPM Serdang, Selangor, Malaysia
c
Institute of Agricultural and Food Policy Studies, Unirversiti Putra Malaysia, 43400 UPM Serdang,
Selangor, Malaysia
*
[email protected]
Abstract – Palm oil can be considered as a mainstay in the regional development and economic
growth of Malaysia. It is an important raw material for local industries and as an export product. Most
recently, palm oil has been referred to as a promising feedstock for the production of biofuel which
could lead Malaysia towards a low carbon society. With the growing concern towards the increase of
energy demand and global warming, the conversion of palm biomass to biogas for power generation
has then been recognized as a feasible option in response to the mentioned problems. Nevertheless,
various constraints have come in the way to slow down the biofuel production. Therefore, this paper
presents an overview on the existing renewable energy (RE) policy and its current programme status,
as well as to identify the challenges facing the Malaysian palm oil mill effluent (POME) and biogas
industry in order to propose appropriate measures for further improvement of the programme.
Keywords: Biogas, energy demand, energy policy, palm biomass, renewable energy
Introduction
Global warming has become one of the prominent global issues and its impacts towards human health
and environment have always captured the attention of people around the world. Global warming can
be ascribed by a substantial emission of greenhouse gas (GHG) into the atmosphere through fossil fuel
combustion. In addition to the rapid growth of population and urbanization in the country, the GHG
emission rate has become higher as this significant development in the country would require a greater
amount of energy consumption for power generation. This condition is more obvious in the United
States and China, as both countries have been identified to be the world’s largest and second largest
energy user, respectively (IEA, 2010). In comparison, Malaysia is reported to be the third largest
energy consumer in ASEAN countries and it is anticipated that the per capita power consumption will
further escalate as the country becomes more developed (IEA, 2013).
Since 1990, every nation has started to do some negotiations regarding the carbon emission issue and
has promised to reduce more carbon content into the atmosphere by maximizing the RE utilization.
However, this is merely a blatter rather than a promise as the global carbon emissions at the moment
have increased to 65% compared to that in 1990 (Global Carbon Project, 2014). In the current trend of
370 hundred million tons of carbon emissions, it is predicted that the global carbon emissions will hit
432 hundred million tons by 2019, of which 127 hundred million tons of the carbon emissions will be
mostly contributed by China (Global Carbon Project, 2014). The rapid increment rate of carbon
33
PJSRR (2015) 1(1): 33-39
emissions should has struck the nations’ senses back to reality and it should have served as a vital
reminder for all parties to play their parts in response to the concerned global problem.
In fact, many countries have implemented various regulations or incentives in favour of RE
particularly bioenergy derived from biomass resources such as POME biogas. The intention is
obvious, which is to alleviate the carbon emission rate and the dependency on the main fossil energy
resources such as natural gas, coal and oil in electricity generation, as well as to achieve the goals of
environmental protection and economic advancement. Nevertheless, the result is not very promising as
many challenges have been found in the RE industry. Therefore, this review on the existing RE policy
and current programme status could be feasible in identifying challenges and loopholes confronted by
the industry so that appropriate alternatives could be developed to ensure a sustainable RE
development. This paper focuses on the POME-biogas aspect of bioenergy and challenges for the
POME-biogas development in Malaysia.
Government policies related to RE and POME-biogas production
Overview of Malaysian RE Plans
Energy policies and relevant programmes have been adopted in Malaysia since 1949, but virtually,
they were executed actively only after and up to 2000. Within the period of 2001 to 2010, the Third
Outline Perspective Plan (OPP3) under Vision 2020 emphasised on managing both non-renewable
and RE resources to accommodate the demands for a rapid economic growth and minimizing
pollution and waste generation on the environment was established. Along the same line, the Eighth
Malaysian Plan (8-MP) (2001-2005) focused on the initial phase of OPP3 by introducing RE
especially biomass as the fifth fuel into the existing energy sources so that 5.5% of the country’s
electricity derived from RE can be achieved by 2020 (EPU, 2010). Then, the Ninth Malaysian Plan
(9-MP) (2006-2010) continued the efforts built up during 8-MP in strengthening the initiatives for
energy efficiency (EE) and RE with a variety of fiscal and monetary incentives (Jalal & Bodger,
2009). Subsequently, the Tenth Malaysian Plan (10-MP) (2011-2015) and National Green Technology
Policy (2009) emphasised the creation of new opportunities and stronger incentives for investments in
RE projects to boost the growth of green economy and sustainable energy supply (EPU, 2010). As for
the recently announced Eleventh Malaysian Plan (11-MP) (2016-2020), the country will emphasize
“green growth” in society, which aims to ensure that the environment is facing the least impact whilst
conserving natural resources through the aspects of energy-efficient lifestyle and stressing more on
3Rs (i.e. Reduce, Reuse and Recycle) in households and the industrial sector, and improving the
current educational systems (EPU, 2015).
Undeniably, these implemented Malaysian Plans would have opened up many opportunities to the
industry to further explore the RE development notably on palm biomass and POME biogas-derived
energy where the biomass resources are generally recognized to be highly abundant in the country.
Furthermore, it is projected that the country’s policies and regulation in terms of environmental
governance will get improved in line with the execution of the mentioned Plans. However, these Plans
do not seem to go far enough and there is no specific explanation or declaration on how the
environmental legal framework and principles (in RE context) can be further reinforced which
commonly found in most of the relevant environmental policies and regulations. The Plans are more
likely to be a little over generalisation and this has led to a poor and unclear comprehension among
the nations and RE players towards the country’s current and future environmental governance issues
which the Plans do not portend well as a foundation for action. Nevertheless, relevant authorities
should not remain overly passive but they need to take initiatives while conserving the environment.
Meantime, the policy makers should really be urged to develop more concrete and specific strategies
that could attain the environmental objectives targeted in the Plans.
POME-biogas development and National Key Economic Area
Since the Malaysian palm oil industry is considered as one of the biggest contributors to the national
economy because it has reportedly contributed RM53 billion in the country’s Gross National Income
(GNI) (NKEA, 2013), its activities are then being further advocated to a certain extent. Up to 2015,
34
PJSRR (2015) 1(1): 33-39
443 palm oil mills are in operation at present compared to 439 palm oil mills in 2014 (MPOB, 2015).
As the development of palm oil mills are in line with the increase of economic growth, eight core
Entry Point Projects (EPPs) have been implemented by the Palm Oil National Key Economic Area
(NKEA) programme to boost a higher economic status in the country by 2020. As stated in the EPP 5
under the eight core EPPs, the government aimed to achieve the biogas facility installation in all palm
oil mills in Malaysia by 2020 (MPOB, 2012). However, based on the data documented by MPOB in
2014, only 67 out of 439 palm oil mills were recorded to have involved in biogas activities in
Malaysia (Loh et al., 2014). With less than 20% of the palm oil biogas plants installed in Malaysia, a
question on the practicality of EPP 5 is asked. However, it is optimistic that the number of biogas
plants will increase in the near future as the generation of palm biomass is anticipated to increase from
80 million dry tonnes in 2010 to 110 million dry tonnes by 2020, and this will definitely initiate more
new wealth creations in the industry, if the National Biomass Strategy 2020 is comprehensively
executed. Therefore, the implementation of biogas plants should be imposed but under a strict and
comprehensive control of environmental management strategy as this implementation could bring a
win-win situation to both the country and environment such as 1) reduce cost of production by using
in-house energy production, 2) mitigate GHG emissions (carbon credits), and 3) extension of biofuel
market by upgrading biogas to a practical transport fuel on roads.
POME-biogas development, Clean Development Mechanism and Small Renewable Energy Program
Apart from NKEA, a scheme namely Clean Development Mechanism (CDM) under Kyoto Protocol
has also been established which aims to facilitate developing countries to achieve sustainable
development through the sales of certified emission reductions (CERs). In 2002, Malaysian
government has ratified Kyoto Protocol, and biogas projects are eligible for this CDM programme.
With the establishment of CDM, more investment opportunities for the public are created to involve
in the GHG emission reduction projects. It is also beneficial to palm oil industry by capturing biogas
to earn CER revenue as well as to prepare the industry to meet an increasingly stringent sustainability
requirement in future.
In order to ensure the sustainability of environmental and energy supply in Malaysia, the government
also launched a programme known as Small Renewable Energy Power (SREP) on 11th May 2001 to
encourage a wider use of RE resources in power generation where the generated electricity is
suggested to be connected to a power grid whenever possible (Anuar et al., 2005). In 2002, another
project namely BIOGEN Project funded by the Malaysian government, United Nation Development
Program (UNDP), Global Environment Facility (GEF) and private sectors was introduced as a
compliment to SREP programmes (PTM, 2001). This project plays a role primarily in reducing the
GHG emissions from fossil fuel combustion, and it exploits biomass as a highly potential source for
energy generation. Under the SREP, it is suggested that all the small power plants are encouraged to
sell the electricity produced to Utility through the Distributed Grid System where the biomass and
biogas plant operators can enjoy the RM 0.3184/kWh through the Feed-in Tariff (FiT) system (SEDA,
2014). However, the achievement is rather disappointing because less than 4% of the electricity
generated from RE resources is being captured. This limit of grid connection of biogas plants can be
ascribed by a limit set by the FiT system under the Renewable Energy Act 2011, of which the FiT
system is only applicable in Sabah and Peninsular Malaysia but not in Sarawak due to the presence of
the state’s own legislation and regulations governing exclusively on their electricity supply (RE Act
2011). Moreover as in the palm oil industry, palm oil mills which have enough power generated from
the combustion of their own biomass resources especially fibre and shell, the millers found that this
would not be a big deal to the mills even if the electricity produced from the biogas plants is not
connected to grid.
Challenges for POME-biogas plant development
Although the development of POME-biogas plants in Malaysia has come a long way through the
years, a few significant challenges have been found to have hampered its development, for example,
high costs of investment including plant construction, and lack of required knowledge and technical
expertise.
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PJSRR (2015) 1(1): 33-39
Financial constraint
The financial barrier can be considered the main stumbling block in implementing a biomass power
plant and POME-biogas plant in Malaysia. At present, majority of the biomass industry players are
still facing difficulty in getting feedstock from biomass producers who are mostly private plantations.
Thus, when they try to apply for a commercial loan, they have to present the field supply agreement
on a long term basis and this is apparently not possible for them to secure. Compared to the biomass
industry players, POME-biogas industry players are more concerned with the investment cost of the
POME treatment system in the mill, and the construction cost of closed anaerobic digestion tank is
found to be comparatively higher than the conventional way of POME treatment in the mill known as
anaerobic ponding system. From this point of view, both cases have shown that these biomass and
biogas industry players are indeed struggling on solving the financial problems. The POME-biogas
systems currently in use in Peninsular Malaysia are found to be more developed compared to those
located in East Malaysia (especially in Sarawak) in terms of infrastructure developments, legal
implications and tariff deliberations. The lack of infrastructures for feed-in capability into power grids,
gridlines availability issue and the long distance between the location of palm oil mills and power
grids in the State are the significant factors that resulted in a low possibility of biogas implementation.
In other words, the biogas industry players in East Malaysia would require greater efforts and funding
to invest the biogas facilities in their mills.
Besides, the lack of support from the government and the relevant authorities on the related RE
technology adoption at the current market has resulted in a slower growth of biogas plant
development in Malaysia. The relevant stakeholders believe that these projects could have high risk
when the new RE technology of POME-biogas is adopted. Moreover, a long payback period has also
bothered the stakeholders to finance the projects, and it gradually makes the RE technology not
commercially viable in Malaysia. In addition, when a high capital is needed, smallholders will
definitely find it unattractive to make such an investment. This is where the government should come
in with more viable financing schemes. Therefore, the cooperation among the government, private
sectors and institutions is important in developing such projects because the financial assistance from
each authority can support a high initial cost and enough capital to adopt appropriate RE technology
in plants. With respect to this economic issue, the understanding and trust among the financiers and
investors are vital because any misunderstanding and lack of communication related to RE among the
groups will lead to a low participation of national financiers.
Availability of technical expertise
Advanced technologies are required to ensure the biogas digesters and maintenance activities going
all well and to reduce extra expenses on repairing the machines as time passes. Hence, personnel with
good skills are most needed to monitor the related technologies under a careful supervision. However,
what makes it difficult is that Malaysia is facing a shortage of professional technicians in the country.
Therefore, maintenance activities to address technological monitoring are difficult. Furthermore, some
of the local conversion technologies available in local universities are still at the lab level, and this
situation has indirectly affected the development of the biogas power plant as many entrepreneurs are
not fully confident to use local technologies. Unlike Malaysia, many western countries have
technologies that are always developed and commercialized up to industrial practice. Their
technologies can even developed to the extent of proposing policy implementations of certain related
models. When the Malaysian government is taking the initiative to implement and rely on the western
technology in Malaysia, it might not be reliable due to differences found in management and required
knowledge which demanded highly skilled personnel and careful maintenance. Furthermore, the
capital-intensive initiative requiring huge costs to cover such imported technologies to the country is
unsustainable. Thus, an overview on the existing biogas systems in Malaysia will enhance the wastes
management measure as well as to be served as a reference in providing basic guiding principles for
policy makers and researchers. Nevertheless, the information on biogas production system in
Malaysia is rather limited due to the lack of systematic analysis and outdated periodic documentation,
and this again has slowed down the research progress.
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PJSRR (2015) 1(1): 33-39
Termination of CDM and inefficient environmental tool application
As aforementioned, the CDM programme could further facilitate the biogas development through the
sales of CERs where the profits could actually be used to recover part of the operating cost. However,
after the announcement of its termination at the end of 2012, only those CDM developers whose
projects were accepted before 31st December 2012, were allowed to sell their CERs to the Europe’s
Emissions Trading Scheme until the mid of 2015 (CDM, 2014). This also means that CDM projects
that were accepted after 2012 have a difficulty in financial support to run the biogas system in the
mills as they cannot sell their CERs. Correspondingly, the termination of the programme would also
denote that the improvement of the present anaerobic digestion technology is prompted to stop
moving forward as there will be no enforcement on the current increasingly stringent sustainability
requirement which is supposed to be adopted in the plants to manage the wastes. Moreover, there are
no rigorous restrictions and/or standard technology in treating POME in the country and this situation
has resulted in an establishment of an unclear biogas development schedule among the majority of
palm oil companies. This trend is believed to be the main driving force of an uncontrollable of GHG
emissions in the atmosphere. Therefore, it is suggested that the continuity of the CDM programme
should be taken into consideration by the government so that the POME-biogas players are
incentivized and thus attracting them to invest in the initiative.
However, under certain circumstances where no subsidy is provided by the government, biogas
industry players might confront a bigger financial issue. Therefore, the efficient use of environmental
tools in the companies could be a feasible solution to them. Environmental tools such as Life Cycle
Assessment (LCA) and Environmental Life Cycle Costing (ELCC) could be employed in the relevant
palm oil mills to evaluate the performance of their mills and plants from the environment and
economic aspects, in terms of their life cycle perspective (raw materials extraction to end-of-life
process). With the employment of these tools, palm/biogas industry players can determine the
possible environmental impacts that could arise throughout the entire life cycle of biogas production
system (by using LCA) while evaluating the efficiency of their financial management of which each
unit process of the biogas production system should be allocated with appropriate amount of capital
(by using ELCC). Consequently, palm/biogas industry players could avoid unnecessary expenses on
environmental remediation by referring to the results computed from the assessments. This selfgovernance system could possibly reduce their high operating and environmental costs while attaining
a sustainable environment in their mills and plants. Nonetheless, the majority of the palm companies
are not familiar and have no experience on using the mentioned approaches in their mills and plants.
Therefore, the relevant authorities should train their employees on the related course which will
definitely be a credit to the companies and environment in the near future.
Debate on loss of biodiversity and climate change
The rapid emerging of palm biomass industry in the country for economic advancement has caused an
active clearance of land for oil palm plantations to boost a higher yield of productions. This has
gained attention from environmental groups such as Greenpeace and Friends of the Earth who
strongly criticized that the related projects have triggered a severe threat on biodiversity loss
especially those involved endangered species including the orangutans, Sumatran tigers and elephants
(Buckland, 2005). Moreover, many other environmentalists also claimed that the deforestation for
palm oil cultivations has caused a significant production of CO2 emission (Karousakis, 2007; Stern,
2006). Nevertheless, a study reported by Tan et al. (2009) stated that an oil palm plantation can
actually assimilated a number of 64.5 t ha-1y-1 of CO2 whereas only 42.2 tha-1y-1 of CO2 is assimilated
by a rainforest. Hence, if the oil palm plantation could qualify as planted forests, this agri-industrybased activity can actually contribute towards biodiversity conservation efforts as well as facilitating
carbon sequestration (carbon sink) and GHG reduction. This is because most of the oil palms planted
in the country are on forest peripheries, of which majority of the palm oil developers have starting to
commit or have already committed themselves in implementing good agricultural practices in the
fields.
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PJSRR (2015) 1(1): 33-39
Conclusion
Most policies would give a general picture on the status of RE management in Malaysia and the
necessity to provide detailed information, realistic and conducive regulatory frameworks on RE
management and energy recovery is commonly been treated carelessly. Hence, despite a huge number
of current RE policies and frameworks that have been strongly promoted to attract developers and
investors to get involved in the field, the current biogas development in Malaysia is still considered
very discouraging compared to other countries such as Germany, Denmark and China as many of the
palm oil mills in the country are having difficulty in financial acquisition. The limiting factors such as
high investment cost, new technology, skilled personnel and termination of CDM programme are
forcing oil palm companies to adjust their RE strategy. Consequently, this has led to an increment of
reluctance level among the millers to venture into higher efficiency technologies in the mills.
However, it is believed that a comprehensive RE Policy, effectively application of relevant
environmental tools and a long term commitment associated with an effective cooperation from the
government and related stakeholders can lead to a rapid growth of RE development and to create a
sustainable biogas market in the country.
References
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oil palm biomass energy. Sixth National Seminar on the Utilisation of Oil Palm Tree. Organized
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E. R. A., Mohd Faris, M. R., Lim, W. S. & Choo, Y. M. (2014). Biogas capture and utilisation
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39
PJSRR(2015) 1(1): 40-49
Comparing Asynchronous and Synchronous Interaction
Using Online Technology
Yolanda Lee Lee HIEW* & Bee Hoon TAN
Department of English, Faculty of Modern Languages and Communication,
Universiti Putra Malaysia
* [email protected]
Abstract – The move from traditional face-to-face classroom learning to the use of information and
communication technology (ICT) has been implemented by universities in Malaysia and abroad
vigorously with computer-mediated communication (CMC) systems. These technologies promote
interaction among tertiary level students in collaboration where they can have discussions with peers
for collaborative tasks by means of posting messages (asynchronous) and instant messaging
(synchronous). This review paper focused on comparative studies of asynchronous and synchronous
interaction among university students using online tools. The quantitative and qualitative research
studies were reviewed preliminarily based on the types of CMC used, looking at the theories,
methods, respondents, and findings. This paper also discusses the online tools used for interaction
such as Wiki and Skype, and concludes with an understanding of students’ experience of different
online systems and tools in their communication that may affect their learning.
Keywords: Asynchronous, computer-mediated communication, interaction, Skype, synchronous,
Wiki
Introduction
A number of universities in Malaysia and other countries are actively implementing online learning,
through learning management system (LMS) and virtual learning environment (VLE) at
undergraduate and postgraduate levels (Embi, 2011; Goi & Ng, 2009; Hussain, 2004; Kirkwood,
2009). Computer-mediated communication (CMC) systems facilitate asynchronous or synchronous
interaction among individuals in an online environment. In addition, educational technologies such as
WebCT, Moodle or Blackboard are widely used in collaborative learning (Alavi, Yoo & Vogel, 1997;
Williams, Duray & Reddy, 2006). Thus, asynchronous and synchronous interaction using online
tools, and Wiki and Skype are reviewed in this paper.
Asynchronous Learning Network (ALN) is defined as environments where students use computers to
communicate and work with their peers and instructors (Mayadas, 1999). One of the benefits of
asynchronous interaction is that the participants have more time to think and reflect on the course
content and contribute (Biesenbach-Lucas, 2003). Asynchronous interaction takes place through a
discussion forum in a private webpage where students discuss their task collaboratively. Synchronous
interaction using a CMC tool involves real-time participation among students, such as live chat using
text, audio and video-conferencing (Martin, Parker, & Deale, 2012). Providing synchronous elements
to online courses can enhance meaningful interactions (Repman, Zinskie & Carlson, 2005).
40
PJSRR(2015) 1(1): 40-49
Computer-mediated communication
Computer-mediated communication (CMC) has started since the late 1960s. Murray Turoff was the
first to introduce computer conferencing in 1970 to offer a setting for scholarly community for
exchanging information and effective problem-solving (Hiltz & Turoff, 1978). Some studies on
asynchronous discussion also indicate that using writing to communicate with peers online is easier to
control or take charge. This is because there is no need for immediate feedback in the writing process,
so students have sufficient time to think and validate so as to convey meaning clearly (Koschmann et
al., 1996). However, in a face-to-face team, members may interact through facial expressions, such as
smiling, body language and gestures, and such interaction does not occur in online teams (Macdonald,
2003). Moreover, the process of collaboration becomes more visible when students in an online team
use text messages to communicate, thus, postings among students on discussion boards can be used to
verify both their joint effort and contribution in the procedure. Consequently, the result of the
teamwork can reflect students’ collaboration by means of a written essay or report.
According to Chou (2002), asynchronous interaction is more suitable and sufficient for a course that
needs memorising factual knowledge. However, the author suggests that synchronous interaction is
more appropriate when the course objective is to improve online interaction skills. Thus, synchronous
interaction is as important as asynchronous interaction depending on the context and nature of task,
though some online interaction and collaboration studies have merely used asynchronous system (e.g.
Biesenbach-Lucas, 2003; Elgort, Smith & Toland, 2008). Some universities use the LMS platform
and other social media software that consist of features of live chat and discussion board to facilitate
students’ collaborative learning and writing. There are a handful of comparative studies of
asynchronous and synchronous communication and most of these compared text-conversations and
real-time chat among undergraduates and graduates. Their framework is based on collaborative and
social constructivist theories. These studies have used, inter alia, content analysis, interviews,
observation and survey as the main methods of analysis (e.g. Bonk et al., 1998; Chou, 2002;
Davidson-Shivers et al., 2001; Hrastinski, 2007; Schullo et al., 2005). A few major studies have
indicated considerable differences between asynchronous and synchronous interaction that were
mainly found in qualitative content analysis in smaller groups. Table 1 presents a summary of the
comparative studies.
The findings in these studies indicate that asynchronous discussions promote more complex ideas
(Bonk et al., 1998), more attention on the task (Chou, 2002), more reflective statements (DavidsonShivers et al., 2001), and effective for collaborative writing (Mabrito, 2006). Synchronous
discussions allow students to interact more frequently (Bonk et al., 1998), exchange socio-emotional
interactions (Chou, 2002), teacher-student as well as student-student can communicate effectively
(Haythornthwaite, 2001; Schullo et al., 2005), and the chat sessions are satisfying (Spencer &
Spencer, 2002). However, Ng and Detenber (2005) found that synchronous discussions were viewed
as more useful and influential but this form of discussion has no considerable impact on student’s
participation. Moreover, Schwier and Balbar (2002) found that synchronous interaction was less
efficient in dealing with content, and students spent lesser amount of time on course task in the chat
discussions (Mabrito, 2006). Thus, the studies suggested that asynchronous interaction was more
appropriate for thinking and discussing complicated views (Hrastinski, 2008), while learners favoured
synchronous communication as there were more social communications. Despite the utilisation of
CMC among business corporations and educational communities, the effectiveness of these tools
should be realised, where asynchronous and synchronous systems should also facilitate knowledge
sharing in group interaction and collaboration.
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PJSRR(2015) 1(1): 40-49
Table 1: Comparative Studies of Asynchronous and Synchronous Interaction
Source
Type of CMC
Purpose of Study
Methods
Respondents
Findings
Bonk et al.
(1998)
Text-discussion
board and
chat
Content
analysis
65 pre-service
teachers
Chou (2002)
Text-discussion
board and
chat
To explore how
to use the Web to
foster
collaboration and
interaction
To examine the
patterns of
learner-learner
interaction
Content
analysis
Number of
undergraduates
not indicated
DavidsonShivers et al.
(2001)
Text-discussion
board and
chat
To investigate
how graduates
participated in
online discussion
Content
analysis,
survey
14 graduates
Haythornthwaite (2001)
Text-discussion
board, chat,
e-mail, and
audio
Interviews,
survey
14 graduates
Hrastinski
(2007)
Text-discussion
board and
chat
Content
analysis,
interviews,
surveys
8 graduates
Mabrito
(2006)
Text-discussion
board and
chat
Content
analysis,
survey
16
undergraduates
Ng &
Detenber
(2005)
Text-discussion
board and
chat
Survey
153
Schullo et al.
(2005)
ElluminateLive
(synchronous)
and WebCT
(mainly
asynchronous)
Schwier &
Balbar
(2002)
Text-discussion
board and
chat
Spencer &
Spencer
(2002)
Text-discussion
board and
chat
To explore how
group members
exchange
information
online
To examine how
synchronous chat
complementing
asynchronous
discussion affect
participation
To examine
students’
collaborative
writing in
synchronous and
asynchronous
interaction
To investigate
the effects of two
features of CMC
and students’
perceptions of
online discussion
To investigate
the use of
synchronous
system as a
supplement to
existing courses
To experiment
synchronous and
asynchronous
interaction in a
theory course
To investigate
the effects of
synchronous chat
in supplementing
asynchronous
online courses
Students conveyed more
complicated views in
asynchronous interactions
and engaged frequently in
synchronous discussions
Students concentrated on the
subject in asynchronous
discussions, and exchanged
socio-emotional relations in
Students stated more
reflective comments in the
asynchronous discussions,
and put some remarks in the
Class used discussion board
and chat for communication,
and e-mail for intra-team
communication
undergraduates
Content
70 graduates,
analysis,
5 instructors
interviews,
surveys,
observations
Not
specified
7 Graduates
Content
analysis,
interviews,
survey
133 students
42
Not easy to acquire
asynchronous discussions
initiated with a few students.
Combining asynchronous
and synchronous interaction
enhance participation
Asynchronous interaction
were effective for
collaborative writing.
Students spent less time
focusing on tasks in
synchronous sessions
Synchronous discussions
were observed as more
informative and persuasive
but did not have significant
impacts on students’
intention to participate
Synchronous interaction
allowed instructors to build
connections with and among
students more effectively
Synchronous interaction
contributed to stability and
sense of community but was
less effective in dealing with
content
Students found synchronous
sessions satisfying, various
hypotheses were examined
but few were statistically
significant.
PJSRR(2015) 1(1): 40-49
Interaction through online tools
Distance educators have classified interactions in distance learning in several ways. Although there
are many classifications available, the classification suggested by Moore (1989) has been largely
recognised. According to Moore, there are three types of interaction: (1) interaction between studentstudent, (2) interaction between student-instructor, and (3) interaction between student-content. This
classification has been influential to researchers even in recent studies. For instance, some researchers
agreed that most communications have reflected student-instructor, student-content and studentstudent interactions, thus receiving considerable attention as they believe that such form of interaction
can promote collaboration (e.g. Balaji & Chakrabarti, 2010; Howarth, 2006). However, Hillman et al.
(1994) identified that the interaction between student and interface also plays an important role in the
distance learning environment. Hence, Moore and Kearsley (1996) suggested that the learning
interaction can be categorised into four types: student-content, student-instructor, student-student, and
student-interface. The first three are most frequently used to assess interactions, thus, this review
focused on student-student interaction for collaboration.
Student-student interaction occurs in several modes within the course environment. These interactions
among students take place through email, discussion boards, video- and audio-conferencing, or
chatting, and interaction with peers helps the student to understand the course content (Dewey, 1996).
Garrison (1990) stated that students who interacted on a regular basis with other students were more
motivated and participated actively in their learning. Nonetheless, Freed (2004) reported that
interaction between instructor-student and student-student remained as the major barrier in the online
distance learning environment. It is vital for online distance learning instructors to design and
develop a learning environment to promote student-content, student-instructor, and student-student
interactions (Anderson & Garrison, 1997; Garrison & Cleveland-Innes, 2005). Besides, Olson and
Wisher (2002) observed the difficulties of many students, who lacked high-speed computers and
Internet connections to respond promptly during interaction. In addition, Ko and Rossen (2001)
proposed that if the size of the class was too small, engaging students in interaction became rather
difficult.
McGreal and Elliott (2008) proposed some of the most stimulating technologies and features used in
online instruction, and these multimedia applications offer various opportunities for educators. For
instance, audio chat and web-conferencing on Skype are commonly used for teaching and learning
while mobile technologies are also explored along with wikis, blogs, and other instant messaging in a
virtual world. However, the availability of technology to students and their skill levels in using the
medium can support or hinder collaborative dynamics as the technology can be the cause of either
frustration or motivation (Brindley, Blaschke & Walti, 2009). Asynchronous system hinders the
discussion of complicated problems and conversations that require immediate response, and breaks in
between communication can delay initial postings and responses. Brindley et al. (2009) state that
tools which are more suitable for collaborative learning such as Wiki and Skype are readily obtainable
on the Internet. However, these tools are not necessarily introduced to students or incorporated into
traditional and virtual classroom efficiently. Table 2 illustrates various online interaction tools. Two
categories are relevant to this review: Wiki and Skype.
Wiki is an asynchronous system with free open-sources that permits multiple writers to create and
write on a page in the website. Skype is a synchronous system that consists of voice call, video call
and instant chat that comes free or with very low rates. Apart from personal computers, Skype can be
run steadily on smart phones and tablets across multiple platforms. Besides, both Wiki and Skype can
be used for online interaction among students to carry out their group projects. The former offers
discussion forum with delays in time to response, while the latter provides real-time chat with instant
responses. The use of the Internet in educational settings provides opportunities for interaction and
collaboration between students living at a distance. The similarities between asynchronous and
synchronous systems are that both types of interactions are user-friendly and requiring basic ICT
skills, and they are both time efficient and not costly. This could be the reason why online learning is
gradually becoming popular.
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Name
Blackboard,
WebCT
Elluminate
GoToMeeting,
Zoho
Table 2: Online Interaction Tools (Adapted from Kask, 2009)
Type of
Categories
Comments
Communication
Learning Management System
Message Board
Synchronous and
(LMS) provides a learning
Forum, Chat, Email asynchronous
environment to students though it is
costly.
Application allows voice and video
Whiteboarding,
Synchronous and
communication and costly. Good for
Chat, VoIP, Video
asynchronous
presentation of material.
Web conferencing allows people to
Whiteboarding,
Synchronous and
meet and do presentation and it is
Chat, VoIP, Video
asynchronous
low cost. Suitable for short term use
or long term assignments.
Facebook,
Myspace,
Nexopia
SNS, Chat
Synchronous and
asynchronous
MediaWiki,
Wiki
Wiki discussion
forum
Asynchronous
Moodle
CMS, Forum, Chat
Synchronous and
asynchronous
Messenger
Chat
Synchronous
Google Wave
Email, Chat
Synchronous and
asynchronous
Skype
VoIP, Video, Chat
Synchronous
Web 2.0 technology supports social
participation and it is free to users.
Free open-source allows for multiple
writers and suitable for collaborative
writing tasks.
Free open-source but requires an
existing web server to run on, and
accessible to a SQL database.
Instant messaging with no costs, and
can be functioned as an email.
Application allows groups to share
documents for free, and email is
available to facilitate group tasks.
Accessible in multiple platforms
(Windows, MacOS, Linux, etc.), and
can be run on few mobile devices.
Free for basic features, but at a cost
for other features.
Wiki as a tool for asynchronous interaction
Students working in a group have been a challenge for both instructors and students as they are
frequently dissatisfied with its content and process. While content can be the goal of a course
instruction, the process of learning becomes the roots to understanding of content as part of the goal.
Thus, content exists within the process of acquiring that content, not outside of it (Tobin & Tippins,
1993). The establishment of new technology such as Wiki could possibly offer a solution for
asynchronous interaction (Karasavvidis, 2010).
Wiki discussion forum
Wiki is known as server software that permits users to produce and edit content of a piece of writing,
and it can be used to coordinate a group using any Web browser (Cunningham, 2002). Wiki is an
integrated Web environment that also allows users to simply produce and uphold a Web presence for
their subjects in collaboration with others. There are lists of Wiki software platforms available such
as MediaWiki, WikiMatrix, XWiki, Tiki Wiki, WikiFoundry, and so on. WikiFoundry (previously
known as Wetpaint) is a free website hosting service where anyone can create their own Wiki site.
The system consists of features where students can access from any place at any time through an
Internet connection. Further key features of the system are areas for the group members to post
messages and respond to others postings, create forums or topics for discussion. Members have the
opportunity to reply the messages in a manner that is not time and place dependent, as long as a
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computer connected to the Internet is accessible. Each member can create new threads to the
discussion topics or respond to the comments of other members in the forum. Moreover, all members
have access to the above features and able to view, download, or print out the information.
A Wiki consists of features exist in traditional content management systems (CMS) such as blogs and
discussion forums. A CMS is a computer application that permits creating, deleting, editing,
publishing, modifying content, and also maintenance from a central interface (Boag, 2009). It can
also upload files to share information and download files sent by group members. The opening view
of a forum shows the subject heading for the postings. The group member has the choice of either
reading just the threads of a discussion forum or expanding the thread list to expose all threads or the
responses to these threads. Individual messages can be viewed by clicking on the subject heading and
then proceed through the thread and read each message.
Černá, Poulová and Draessler (2011) conducted a survey via an online questionnaire on social
software applications at a university and the respondents’ satisfaction towards the software. The data
were collected from more than three hundred students at the University of Hradec Králové. The
results show that wikis can be served as platforms for knowledge incorporation and collaboration in
developing common knowledge.
In relation to knowledge incorporation, wikis websites are wholly editable as any user can read, write
or add content to a Wiki site. In a study, Augar, Raitman and Zhou (2004) used Wiki for an icebreaking activity at Deakin University, Australia, to facilitate online interactions among group
members. The findings reveal that Wiki is indeed a useful tool for facilitating online education and
can enhance the process of teaching and learning online. The features in a Wiki Webpage show that it
is an exceptional tool for collaboration in an online environment which is also a valuable system for
teaching and learning.
In another study, Chu and Kennedy (2011) reported the use of Google Docs and MediaWiki as
collaboration tools for co-constructing knowledge in an online group project. Twenty two
undergraduates from the Information Management program at The University of Hong Kong
participated in the study. All students have used MediaWiki for the major project and Google Docs
for their final year project. Questionnaires and telephone interviews were conducted after completion
of the final projects. They found that some of the students had positive experiences from using the
tools where MediaWiki was effective in knowledge management, while Google Docs features were
more user-friendly. However, Judd, Kennedy and Cropper (2010) investigated a learning activity
which involved a large group of 177 undergraduates studying psychology at The University of
Melbourne. There were 30 groups that consisted of 20-30 students and Wiki was used in the
investigation. The authors found that although the features in Wiki are designed to facilitate
collaboration, it does not constantly promote collaborative learning. This is due to little use of Wiki
commenting feature and thus many students’ contribution were superficial.
In another study, Witney and Smallbone (2011) have utilised Wiki to support group assessment for
full-time undergraduate students. They observed the main constraint to the use of online tool was that
student preferred traditional face-to-face teamwork. Elgort, Smith and Toland (2008) examined the
perceptions of students and lecturers using wikis as a platform for group project in two postgraduate
Master’s level courses. The authors highlighted that students’ attitude to group work are mixed and
utilising Wiki is insufficient to improve these attitudes, though on the positive side the students
considered Wiki as useful for sharing knowledge and organising information.
Skype as a tool for synchronous interaction
The synchronous, real-time interactions with free software such as Skype can actually enhance
conventional classroom teaching and learning, and engage students to communicate, share and write
on various projects. Skype is a software program using Voice over Internet Protocol (VoIP)
technology (Fryer, 2014). The software is free for download and users can also make audio calls and
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video conferences over the Internet everywhere in the world without any costs (Tsukamoto, Nuspliger
& Senzaki, 2009).
Skype instant messaging
A Skype network can be used as a real-time interactive chat among group members. Skype provides
services that enable users to communicate with their peers either by voice with a microphone or by
video with a webcam and instant messaging by text over the Internet. The name ‘Skype’ was derived
from ‘sky’ and ‘peer’ where originally it was a hybrid peer-to-peer and client-server system (Bryant,
2006). Its free version is often used among teachers and students to fulfill their educational goals.
For instance, Skype is being used for communication among scholars in completing projects from
different parts of the world as well as locally by real-time chat.
Skype is also used in the classroom implemented by the teacher to facilitate sharing of ideas
synchronously among students which makes the classroom more interactive (Sivula, 2011). It also
enables teachers to collaborate with other teachers around the world for resources and getting to know
the experts in the same field (Eaton, 2010). All synchronous dialogues that emerged in Skype Chat
were automatically archived by date.
In the survey of Černá et al. (2011), the authors found Skype an exclusive social communication
application. Indeed, Skype is an example of a twenty-first century educational tool as it can basically
support the teaching and learning environment, changing from traditional classroom learning to
successful online collaborative learning. For instance, online technologies promise massive
transformation in language learning (Mullen, Appel & Shanklin, 2009), and students are allowed to
talk with an author via Skype (Foote, 2008). However, Sivula (2011) utilises Skype for courses
involved a team in a collaborative project, claiming that problems do occur within the team
interaction while completing the assignment, whether applied traditionally or online.
Team members can share resources and information within their team through real-time meeting at a
chosen time in Skype. Kearsley and Schneiderman (1999) suggested that learning activities should:
(1) take place in a group setting (e.g. collaborative teams); (2) be task-based, and (3) have an external
focus (authentic). Skype facilitates interaction by allowing students to form groups and they can also
use their smartphones, iPads, iPods, tabs and a range of personal computers to interact with team
members using Skype software.
Conclusion
The review suggests that online interaction systems have encouraged collaboration, thus CMC has
become a topic of interest. Indeed, online collaboration offers new opportunities in learning with the
arrival of technological innovations. In tertiary education, students need to generate in-depth
understanding in their learning through managing interaction effectively and utilise online technology
for collaborative tasks. Such management entails students’ interaction with resources, teachers, and
peers. This type of interaction focuses online collaboration and this explains how a course should be
designed to promote student participation and satisfaction. From this review, it is suggested that
asynchronous interaction is good for students to practise and to improve writing skills, while
synchronous is good for developing students’ social interaction or communication skills. In terms of
pedagogical aspect, online collaboration involves learning resources and supports active learning
which enables students to construct knowledge and attain their learning goals. For instance, students
can perform collaborative writing through CMC interaction. In terms of social aspect, constant social
interaction may also encourage students’ readiness to participate in online collaboration. Thus, it is
significant to study further in order to understand more thoroughly concerning the usefulness of CMC
for interaction and collaboration either asynchronous or synchronously in completing collaborative
tasks.
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Active and Passive Compliance Mechanisms
in Legged Robot Locomotion
Shing-Yan LOOa*, S.H. TANGb & Mashohor Syamsiahc
a b
Department of Mechanical and Manufacturing Engineering, cDepartment of Computer and
Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia
*
[email protected]
Abstract – Legged robot locomotion is a challenging field. Problems can occur during locomotion
such as morphology, controller, and ambience factor, to name a few. However, there are always tradeoffs in designing legged robots, for example, speed against stability, number of limbs against
complexity of controller, and mass of the robot against energy consumption of the actuators.
Therefore, the problems can be minimized when the hardware and software complement each other.
Active compliance mechanism describes a closed-loop system which actively sense-and-act according
to the surroundings. Passive compliance mechanism, as its name suggests, is a regulatory mechanism
in which it does not rely on the controller to actively respond in order to achieve adaptability. The
composition materials of a legged robot provide the advantages during locomotion. In this review, we
are going to investigate the differences of the mechanisms and how they can be complemented to
diminish problems during locomotion.
Keywords: Active compliance mechanism, legged robot, locomotion, passive compliance mechanism
Introduction
Legged robots belong to the family of mobile robots. Mobile robots are capable of moving around an
environment by means of discrete foothold, continuous foothold, or hybrid foothold. A legged robot
possesses a number of feet, which provide the maximum number of supporting points. As opposed to
a legged robot, a wheeled robot locomotes around the environment with a continuous foothold. A
hybrid mode combines the advantages of both legged and wheeled robots by producing continuous
support on flat terrain and discrete support on uneven terrain. Mobile robots can be manually
controlled or operate autonomously.
Walking is a sequential mass shifting procedure which comprises a series of actuation of joints in a
systematic manner. Several popular methods to generate a walking motion are zero-moment point
(ZMP) (Vukobratović & Borovac, 2004), inverted pendulum (Kajita et al., 2002), inverse dynamics
(Fujimoto & Atsuo, 1998), central pattern generator (Ijspeert, 2008), tri-pod gait (Cham, Karpick, &
Cutkosky, 2004), to name a few. Therefore, it is a strenuous effort to perform the walking task.
The interaction between a legged robot and the arbitrary surroundings is challenging because of high
uncertainties ahead. Therefore, designing an intelligent controller is the ultimate goal of a legged
robot locomotion. Floating-base inverse dynamics on LittleDog exhibits superior walking
performance on uneven terrain by a precise foothold selection and a variable step length (Buchli,
Kalakrishnan, Mistry, Pastor, & Schaal, 2009). However, a frequent controller activity results in high
energy consumption and relatively low walking speed. Moreover, crashing with the surroundings and
excessive foot impact forces are less desirable.
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In this study, we are going to review two main streams of solving legged robot locomotion problems,
namely, active compliance and passive compliance mechanisms. Active compliance mechanism is a
closed-loop system, which the robot responds to the environment according to the sensory
information. In contrast, passive compliance is an open-loop system, which the robot responds to the
environment based on the body regulatory mechanisms, such as spring-damper mechanism, adjustable
joint, and link stiffness.
In the next section, active compliance and passive compliance mechanisms are equally investigated.
The investigation includes fundamental principles of both mechanisms. Then, the importance of
fusion of active and passive compliance mechanisms is discussed. In the conclusion section, problems
of designing legged robots are summarised.
Active compliance mechanisms
As its name suggested, active compliance mechanisms require sensory information to aid decision
making. The behaviour of the robot is solely reflected from sensory information. Therefore, an
intelligent control paradigm is required in order to produce a walking behaviour.
A legged robot possesses sensors, which are attached around its body to perceive the world. Robot
cognition is a house of storing and retrieving information to aid a decision-making process. Kaplan
(2000) implemented a learning mechanism in which the robot is able to interact with its user in order
to acquire knowledge (object recognition). A cognition process is important because it allows the
robot to understand the world, and acts accordingly. Figure 1 exemplifies three different layers of
constructing a controller for a legged robot locomotion. The highest level is the main command to the
robot, i.e. wandering aimlessly or target-oriented locomotion. Then, based on the start-point and the
end-point, the path is planned. Lastly, according to the prearranged path, the trajectories of the joints
are mapped.
Explore the world
Robot’s path planning
Robot’s joints trajectories
Figure 1: Hierarchical classification of active compliance mechanism controller
The controller can be designed to act reactively or deliberatively. A reactive controller is defined as an
action that is caused directly by the controller. A remarkable example is from Kimura, Fukuaka, and
Cohen (2007) in which the robot is programmed with CPG to produce walking behaviour; reflexes
and responses are designed to provide immediate response in order to cope with uncertainties
(Kimura, Fukuoka, & Cohen, 2007). On the other hand, a deliberative controller is meant for prudent
jobs. Tasks such as mine removal cannot afford a single failure, even for a minor case (Kato &
Hirose, 2001). Brooks asserted that the traditional AI is weak to problem solving, because it requires
internal representation of the world to make every decision. Comparatively, he proposed Subsumption
Architecture (SA) of which a hierarchical set of layers is used to represent the behaviours (Brooks,
1991). Next, the robot behaviour is elicited by the mutual inhibition of signals from different layers.
Details of traditional AI and SA are illustrated in Figure 2.
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Figure 2: The principle of traditional AI is explained. The sensory information is required to penetrate
into every single layer before a decision can be made. Therefore, it is time consuming and not
applicable to highly dynamic world. Conversely, SA as shown in the lower figure decomposes the
behaviour into layers with various priorities (Brooks, 1991)
Passive compliance mechanisms
A passive compliance mechanism, on the other hand, is a regulatory mechanism that does not rely on
the controller to actively respond in order to achieve adaptability. The composition materials of a
legged robot provide the advantages during locomotion. As observed in nature, we experience the
flexibility and durability of bone structure, which allows us to perform prominently in sports, recover
from stumbling, and protect the viscera against forces. Several studies have been conducted on tensile
characteristics of human rib cortical bone, adaptability of bone properties to individual’s physical
activities, and biomechanical properties of bone (Natali & Meroi, 1989; Rittweger et al., 2000; Subit,
de Dios, Valazquez-Ameijide, Arreigui-Dalmases, & Crandall, 2011).
There are a number of researches based on improving the material characteristics of the robot. For
example, spring-damper mechanism (Poulakakis, Smith, & Buehler, 2005), variable link stiffness
(Brown & Zeglin, 1998; Bailey, Cham, Cutkosky, & Full, 2000; Takuma, Ikeda, & Masuda, 2010;
Galloway, Clark, Yim, & Koditschek, 2011), and adjustable joint stiffness (Pratt, Williamson, 1995;
Poulakakis, Smith, & Buehler, 2005; Ham, Sugai, Vanderborght, Hollander, & Lefeber, 2009;
Scarfogliero, Stefanini, & Dario, 2009). An experiment done on Scout II (Poulakakis, Smith, &
Buehler, 2005) demonstrated the flexibility of the hip joints facilitate the running gait of the robot
with only one actuator in a leg. The elasticity and flexibility of the materials bestow the capabilities of
the legged robot to confront with various kinds of danger. Nonetheless, passive compliance
mechanisms are still lack of flexibility, because the material properties are not changeable. Unlike
living organisms, robots cannot adapt to the environment psychologically and physiologically.
Energy storage in links and joints are useful to eliminate transient effects of external perturbation on
the robot (Kim, Clark, & Cutkosky, 2006). Because the limbs and torso are interacting in unison, the
chain reaction of the extrinsic disturbances are not negligible. The effect is more distinguishable when
a higher locomotion speed and bouncing gait are required (Poulakakis et al., 2005). The former
indicates the continuous impact between the limbs and terrain results in instability of robot; the latter
illustrates the importance of releasing and storing energies to realize the bouncy movement. Thus,
passive compliance mechanisms deliver the supplementary function to combat against disturbance
from surroundings and to enhance the mobility of the robot.
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Discussion
In the previous section, we have revealed the functions of active compliance and passive compliance
mechanisms. Next, we are going to make a comparative study on robot locomotion and animal
locomotion, especially human. The study is divided into three facets, namely, pure active compliance
mechanism, pure passive compliance mechanism, and combination of active compliance and passive
compliance mechanisms.
Pure active compliance mechanism
Deliberative actions such as path planning, footstep placement on unstructured terrain require massive
amount of signal processing. It emphasizes continuous perception-action cycle to generate the right
behaviour to deal with current situations. The array of sensory information is utilized to determine the
action which is more rewarding.
There is a number of researches to show that emotion affects decision-making in human beings.
(Carver, Sutton, Scheier, 2000; Wood, Quinn, & Kashy, 2002; Baumeister, DeWall, Vohs, & Alquist,
2010) The effect is twofold: emotion causes behaviour (Baumeister, Vohs, DeWall, & Zhang, 2007),
and behaviour pursues emotion (Baumeister, Stillwell, & Heatherton, 1994). The former explains that
an action of an individual is caused by the inner state (such as joy, grief, angry, and thirst), e.g. he is
giving up because the weather is bad. By contrast, the latter denotes an action taken to acquire or
refrain from the inner state, e.g. he is striving to reach the destination because he triumphs for
achievement. It is still difficult to implement an emotional decision-making algorithm on a mobile
robot because of our limited understanding of the brain.
The concept of adaptive control is to control the movements of the joints in order to provide adequate
joint stiffness and proper posture. Gait adaptation can be done by visual input, proprioceptive
responses, force feedback at the feet, to name a few (Weingarten, Lopes, Buehler, Groff, &
Koditschek, 2004; Manjanna & Dudek, 2015). A muscle-like property in the actuator can be realized
by adjusting the parameters of the controller, and the joint position and stiffness can be varied
according to various situations. A PD-controller is used to model a virtual spring-damper mechanism
with the aim of increasing stability (Kimura et al., 2007). Xiong, Worgotter, and Manoonpong (2015)
have created a modular neural network (MNN) controller to automatically tune the leg stiffness,
thereby gaining adaptability on different surfaces.
Pure passive compliance mechanism
When the controller is inactive, a passive compliance mechanism demonstrates the practicality in a
legged robot. A passive walker exemplifies the utilization of gravitational force to walk on slightly
down slope without actuation (McGeer, 1990). The potential energy to kinetic energy conversion
eliminates the power consumption from actuation. Besides, there is a 20% failure rate for a twolegged robot to walk steadily, mostly due to inappropriate initial conditions (Collins, Wisse, & Ruina,
2001).
A morphological design of the robot is an important factor for maximum locomotion efficiency.
Centre of gravity, number of limbs, type of limbs, type of actuators, material, and size are important
components to robot building. For example, the bow leg design by Brown (1998) shows the
possibility of using a string to control the elastic leg for robot locomotion. The leg compressed and
extended during landing and lifting. As a result, it eliminates the knee and ankle actuators to produce
locomotion. Another example of a single rotary actuator to produce forward locomotion is EduBot by
Galloway (2011). In order to increase the passive compliance of the robot on various terrain
conditions, the stiffness of the leg is tuneable. The study also discusses the effect of leg stiffness on
walking speed and terrain conditions.
In Takuma’s (2010) work, a wire is holding a series of elastic discs and a rigid block, and is attached
to a winch. The winch is used to control the flexibility of the spine. As a result, this structure produces
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a unique oscillation according to the degree of viscoelasticity. A simulation study is conducted to
illustrate the effect of rigid spine, unidirectional flexibility spine, and bidirectional flexibility spine on
passive running down on a slope (Kani, Derafshian, Bidgoly, & Ahmadabadi, 2011). The result shows
that the bidirectional flexibility spine is the best in terms of stability and velocity. It is also worth
mentioning that the joints are not controlled by actuators. Thus, the motion is generated by
gravitational force. There are also many studies working on passive walkers. Thus, an energy efficient
walker can be created using the concept of passive walkers with little power actuators to walk on
slopes and flat terrains. In the next section, the combination of active and passive walking
mechanisms is discussed in detail.
Combination of active compliance and passive compliance
Active compliance and passive compliance mechanisms are equally important for legged robot
locomotion. It is recognizable in a complex situation, for instance, walking over uneven terrain,
deformable surface, dynamic obstacles, and high speed locomotion. Because energy storage in the
links and joints depress the external forces and disturbance, it indirectly regulates the behaviour of the
robot. For example, a robot walks on a flat terrain with a fixed behaviour, and it stumbles over the
uneven platform. The passive compliance mechanism is activated to buffer the ground perturbation.
Another example illustrating the importance of combination of active and passive compliance
mechanisms is leg configuration in Figure 3. Usually, a robot with an insect leg configuration has its
legs widely spread and has lower centre of gravity. On the other hand, a mammal leg configuration
has a smaller support polygon and a taller centre of gravity. In this example, it shows that different leg
configurations attribute to different stabilities, walking speeds, energy expenditures, etc. It would be a
long explanation for detailed elaboration for leg configuration alone. Böttcher (2006) explains the
energy expenditure, stability, leg configuration and number of legs in order to get the right
combination in legged robot design. On the other hand, Jones and Hurst (2012) analyse the effect of
leg configuration on running and walking legged robots. In the study of De Santos, Estremera, and
Garcia (2005), the energy requirement of the actuators is reduced by strategically placing the legs
around the robot’s body.
Figure 3: The left figure is a model of an insect-type leg configuration. The right figure is a model of
mammal leg configuration.
In another study, Zhao, Sumioka, and Pfeifer (2011) used two motors to actively control the spine
motion. The spine is constructed using deformable and rigid blocks. By removing deformable blocks
at different positions, it creates a virtual joint. In addition, the flexibility and length of the spine can be
adjusted according to the specification of the robot. A flexible spine is also used in biped robot to
increase the degree of freedom of the torso, and the advantage of flexibility and variability (Mizuuchi,
Inaba, & Inoue, 2001). The flexibility of the torso allows the robot to have various postures and better
impact absorption when the robot falls. A simulation study also shows that a flexible spine increases
travel distance and walking performance (Moore, McGowan, & McKinley, 2015).
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A semi passive walking study is done by Omer, Ghorbani, Lim, and Atsuo Takanishi (2011). A
passive compliance mechanism is added to ankle joint. The ankle has springs built-in to store and
release energy during walking. By adjusting the stiffness of the ankle joint, semi-passive motion can
be realized. When a robot is walking, there are impact and friction losses. In order to continuously
walking on flat surface, actuators can be added to compensate the energy losses during walking.
Passive walker Veronica uses series elastic actuator to control swing phase and stand phase of the
passive walker (Van Ham, Vanderborght, Verrelst, Van Damme, & Lefeber, 2006). A study also
shows that serial elastic actuators have several benefits such as shock tolerance, lower reflected inertia,
more accurate and stable force control, less damage to the environment and energy storage (Hutter,
Remy, Hoepflinger, & Siegwart, 2011; Pratt, 1995).
The difference between living organisms and robots is recoverability. Nevertheless, a true intelligent
robot design emerges from the hardware and software designs. The hardware design fortifies the
manoeuverability with resilient properties; the software design enhances the efficiency of actuation
during locomotion.
Conclusion
This paper highlighted the importance of balanced consideration of morphology and controller of the
robot, i.e. controller provides compliance of robot to the environment; morphology imparts resilient
properties to cope with uncertain surrounding in order to minimize locomotion problems; conscious
and subconscious judgment for decision making process. Nonetheless, there are a few problems to be
solved as follows:
 The paradigm of efficient walker is missing, i.e. morphology, sensors, and controller
requirement for locomotion.
 The optimization of legged robot locomotion in terms of perception, cognition and action.
 Materials usage and combination to alleviate locomotion problems such as stability, speed
and energy expenditure.
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Antioxidant Vitamins, Oxidant Injuries and Diseases
Yusuf ABBAa, Hasliza Abu HASSIMb, Hazilawati HAMZAHa & Mohamed Mustapha NOORDINa*
a
Department of Veterinary Pathology and Microbiology, bDepartment of Veterinary Preclinical
Sciences, Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400 Serdang, Selangor
*[email protected]
Abstract – Over the past few decades antioxidant vitamins have been shown to aid in disease
prophylaxis as well as treatment. Deficiencies of these vitamins in diets have resulted in associated
deficiency syndromes in both humans and animals. Since a handful of disease conditions is associated
with imbalances of antioxidant enzymes such as catalase, superoxide dismutase, glutathione as well as
increases in reactive oxygen species (ROS), nitrogen oxide species (NOS) and lipid per-oxidation
markers such as malondialdehyde, supplementation with antioxidant vitamins has resulted in
amelioration of oxidative damage and ultimately disease recession. Vitamins A, C and E together with
compounds such as carotenoids have been extensively studied for their roles in disease modulation or
exacerbation. However, while Vitamins C and E have been shown to have immense potentials in the
alleviation of several conditions, Vitamin A and especially carotenoids had shown little or no use in
conditions such as cardiovascular disease and cancer prevention. This review highlights the
documented roles of these vitamins in disease prevention over the past few decades and the potentials
that need to be explored further.
Keywords: Antioxidant vitamins, disease, oxidative stress, antioxidant enzymes
Introduction
An antioxidant is any substance that significantly reduces or impairs the oxidation of a substrate once
present in small amounts. The term oxidizable substrate includes every type of molecule found in vivo
(Halliwell, 2001; Niki, 2014). Antioxidant vitamins are readily available in food items; however, most
of them are not available in sufficient quantities to meet the daily recommended amount for humans
or animals. Thus, in order to avert problems associated with chronic deficiencies, supplemental doses
have to be taken to meet up the shortages. Most of the classical deficiency syndromes associated with
these vitamins are not seen in the western countries. However, chronic deficiencies are common and
associated with a lot of complex health problems especially in the elderly (Iqbal et al., 2004; Rao &
Rao, 2007).
Oxidant injuries to cells result from production of reactive oxygen species (ROS) and nitrogen oxides
(NO). Reactive oxygen species such as superoxide (O2- ) and hydrogen peroxide (H2O2) cause
respiratory burst and damage to cells. On the other hand, cellular enzymes such as catalase,
glutathione and superoxide dismutase (SOD) modulate various chemical reactions that prevent
oxidant injury to the cell. For example, while catalase activates the breakdown of hydrogen peroxide
into water and oxygen, SOD catalyzes the dismutation of superoxide radicals to O2- and H2O2 and
glutathione plays a major role in the reduction of oxygen species formed during respiratory burst and
cellular metabolism (Halliwell & Whiteman, 2004). Since various disease processes have been shown
to induce oxidant injury in cells, the use of antioxidant vitamins have been equally shown to modulate
such oxidant injuries and ameliorate its deleterious effects in the body (Blokhina et al., 2003; S. Zaidi
& Banu, 2004; S. M. Zaidi et al., 2005). Thus, this review discusses the various antioxidant vitamins
and their mechanisms of preventing certain illnesses or conditions.
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Antioxidant vitamins
There are three main documented antioxidant vitamins, namely Vitamin A, Vitamin C and Vitamin E
(α-tocopherol). Carotenoids (β-carotene) and selenium are also considered important since they have
been shown to function synergistically with Vitamins A and E, respectively. Carotenoids are
converted to Pro-Vitamin A and thus posses similar antioxidant roles in the physiological system to
Vitamin A. This write-up also discusses the major antioxidant Vitamins A, C and E, as well as
carotenoids and their mechanisms of action.
(a) Trans-retinol
(b) Ascorbic acid
(C) α-tocopherol
(d) β-carotene
Figure 1: Chemical structures of (a) trans-retinol, (b) Ascorbic acid, (c) alpha-tocopherol and (d) βcarotene.
Mechanisms of antioxidant vitamin action
Aerobic microorganisms are shielded from ROS and NOS produced from oxidative stress by a diverse
mechanism involving multiple antioxidants which have different functions and roles (Niki, 2014).
While all antioxidants are either micro or macro molecules such as proteins and enzymes, they all
proffer several defensive strategies against damage caused by oxidant damage (Halliwell & Whiteman,
2004). The first defensive action involves the prevention of ROS/NOS production by catalyzing the
breakdown of hydroperoxidase and hydrogen peroxides to hydroperoxides and water. In the second
defensive action, the antioxidants neutralize ROS/NOS before they induce cellular injury to the cells.
Thirdly, damage caused to membranes and tissues are repaired by these antioxidant compounds or
enzymes. Hence, antioxidants act cooperatively and synergistically in a dynamic defensive network to
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cope with oxidative stress (Niki, 2014). Antioxidant defense against oxidative stress involves both
enzymatic and non-enzymatic activities. While enzymatic defenses require enzymes such as
glutathione peroxidase, catalase and superoxide dismutase, non-enzymatic defenses involve the
presence of antioxidants such as carotenoids, lipoic acid, Vitamin C and Vitamin E. In order to
minimize the effects of ROS, cells produce superoxide dismutase, glutathione peroxidase and catalase.
Superoxide dismutase catalyzes superoxide anions to oxygen and hydrogen peroxide, catalase then
reduces the hydrogen peroxide formed to water. Ascorbate peroxidase and dehydroascobate
peroxidase formed by ascorbic acid in the cell also catalyzes the breakdown of hydrogen peroxide to
water (Blokhina et al., 2003). This is a very important step in the neutralization of the peroxide and in
alleviating oxidative stress in the cell.
Vitamin A and β-carotene in disease prevention
Vitamin A is one of the most essential vitamins of the biological system. It is required for maintaining
the injury of the epithelium, immune function and cellular differentiation. Retinol is the active
compound that is responsible for its numerous functions in the body system. The primary storage of
Vitamin A in the kidneys, liver and adipose tissues is in the form of long chain fatty esters and
provitamins (carotenoids). Its antioxidant action is exhibited through its excellent radical quenching
ability, thus making it more effective in hypoxic state (Harabawy & Mosleh, 2014; Palace et al.,
1999). Vitamin A has not been as efficient as Vitamins C and E in regulating the levels of oxidative
stress enzymes such as glutathione, catalase and superoxide dismutase in stressed cells.
In a study of chickens exposed to carbon tetrachloride, Vitamin A supplementation reduced
glutathione levels in the plasma of chickens. However, while concurrent administration of Vitamin E
was found to reduce plasma levels of SOD and glutathione, Vitamin A was found to attenuate this
effect (Mahmoud & Hijazi, 2007). Similarly, it was earlier observed that retinol administration
resulted in increased levels of SOD, catalase and glutathione peroxidase in rat sertoli cells thereby
modulating oxidative enzyme activities (Dal-Pizzol et al., 2001). Vitamin A supplementation has been
shown to lower the risk of coronary heart disease and ischemic heart disease. In another study,
Vitamin A was observed to reduce injury and scarring following pyelonephritis (Dalirani et al., 2011).
Β-carotene, which is a precursor for retinol and a carotenoid has been shown to have no protective
effects against various conditions. For example in a randomized trial study in 18,314 smokers and
asbestos workers given 30 mg of beta-carotene and 25,000IU of Vitamin A per day, it was observed
that there was no reduction in the incidence of lung cancer, and adverse effects were seen in cancer
development and cardiovascular disease (Omenn et al., 1996). In another randomized trial,
administration of 20mg/day of beta-carotene was reported to be associated with a slight increase in the
incidence of angina pectoris in 29,133 male smokers (Rapola et al., 1996). In a related study, a
metanalysis study on the effect of beta-carotene administration and lung cancer development found an
association between high dose of beta-carotene and risk of cancer (Tanvetyanon & Bepler, 2008).
However, in a 9.4-year randomized trial study testing the effects of supplementation of 50mg of betacarotene given every other day to women, there was no overall effect of the supplementation on the
outcomes of myocardial infarction, stroke, coronary revascularization or cardiovascular disease death
(Cook et al., 2007).
Thus, it can be seen from these numerous studies that the vitamin has very little or no beneficial effect
on the prevention of conditions such as cancer and cardiovascular disease. Earlier studies with
carotenoids reported beneficial and protective effects of carotenoids against ischemic heart disease,
stroke, cancer, aging, immunomodulation, macular degeneration, cataract and photo-protection
(Mayne, 1996; Rao & Rao, 2007). However, the manner at which most of these studies were
conducted such as source of carotenoids, dose and duration of exposure were variable, and in most
cases the studies were irreproducible. Nevertheless, these studies have contributed to the literature of
the compound (Mayne, 1996; Rao & Rao, 2007).
Vitamin C and its prophylactic role in disease
Vitamin C (ascorbic acid) is a commonly available compound that acts effectively as an antioxidant
and reducing agent at physiological pH, thus neutralizing the effect of reactive oxygen species (ROS)
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in the body. This vitamin is required in many other processes such as collagen synthesis, synthesis of
L-carnitine and conversion of dopamine to nor-epinephrine. Most animals can synthesize ascorbic
acid physiologically, but humans, primates and hamsters cannot synthesize this vitamin because of the
deficiency of gulonolactone oxidase. Hence, Vitamin C is unable to meet their daily requirements and
they need daily supplementation in order to avert deficiency syndromes such as scurvy, spontaneous
bleeding and joint and muscle pains (Iqbal et al., 2004; Y. Li & Schellhorn, 2007). As a nonenzymatic antioxidant defense system, ascorbic acid plays a crucial role in the regulation of hydrogen
peroxide levels in oxidative stress. It has been shown to work concurrently with glutathione and
glutathione transferase, thus its presence may boost cellular glutathione levels. Since it does not have
a direct role in lipid peroxidation, it may not significantly alter the level of malondialdehyde in
oxidative stress (Padayatty et al., 2003). In addition, Vitamin C was found to regulate the levels of
SOD, catalase, GST, GSH and MDA in immobilized stressed rats (S. M. Zaidi et al., 2005). This
shows the potential of regulating increased level of MDA and decreased levels of SOD, catalase, GST
and GSH by this vitamin. However, since different factors such as infection, injury and toxicity inflict
oxidative stress via different mechanisms/paths, the amelioration of elevated enzyme levels reported
has been conflicting (Padayatty et al., 2003).
Moreover, Vitamin C via its antioxidant properties have been shown to prevent or alleviate a lot of
conditions including viral diseases. It has been found to alleviate hypoxia-reperfusion induced
apoptosis via the release of Cytochrome C and the activation of Caspases 9 and 3 in human
endothelial cells (Montecinos et al., 2007). In cancer cells and normal endothelial cells, it was found
to alleviate oxidative stress by the uptake of cysteine (Park, 2013). Decreased lung pathology in mice
and prevention/suppression of flu symptoms in man were also observed following ascorbic acid
administration (Gorton & Jarvis, 1999; W. Li et al., 2006). Vitamin C has also been shown to arrest
cancer cell development via both its antioxidant and pro oxidant effects (Y. Li & Schellhorn, 2007).
The supplementation of Vitamin C in exercise-stressed rats was shown to cause reduction in the levels
of previously elevated enzymes such as Copper SOD, magnesium SOD and glutathione (Ryan et al.,
2010).
The in vitro and in vivo anti-viral effects of Vitamin C have been studied in a number of viral
infections. In general, Vitamin C exhibits either a direct effect on the virus by inhibiting its replication
or an indirect one by modulating ROs and NOS production by decreasing bioavailability of
superoxide dismutase (SOD), inhibition of SOD mediated NO activation and by preserving the
normal enzymatic activity of NOS (Brinkevich et al., 2012). In vitro viral inactivation from Vitamin C
administration has been reported in the rabies virus (Madhusudana et al., 2004), cytomegalo virus
(Cinatl et al., 1995), influenza virus (Cheng et al., 2012), herpes virus and paramyxo virus (White et
al., 1986), and herpes simplex virus (Betanzos-Cabrera et al., 2004), just to mention a few.
The in vivo actions of Viatamin C have been reported in HIV, where ROS contributing to viral
replication via the activation of NFK-B was attributed to changes in ascorbic acid, Vitamin E,
carotenoids, selenium, SOD and glutathione. Overall concentrations were observed to decline in
plasma despite an unchanged redox status during the infection course (Baker & Wood, 1992).
Ascorbic acid has also been shown to increase levels of IL2, CD4+, CD8+, IgM+ cells and anti IgG
antibodies in vaccinated chickens challenged with infectious bursal disease virus (Wu et al., 2000).
Decreased lung pathology in mice and prevention/suppression of flu symptoms in man were also
observed following ascorbic acid administration (Gorton & Jarvis, 1999; W. Li et al., 2006).
Vitamin E (α-tocopherol) and disease prevention
There are eight isomers in the Vitamin E family namely α-, β-, γ-, and δ-tocopherols and tocotrienols
(4 Tocopherols and 4 Tocotrienols). Several studies have been conducted on the pharmacological uses
of these isomers since almost a century ago (1922), when the vitamin was first discovered. Vitamin E
is a scavenger for active free radicals through the transportation of hydrogen atom to produce Vitamin
E and radical free product. In some situations, Vitamin E may scavenge free radicals through a
mechanism of electron transfer to yield a Vitamin E cation radical, which subsequently undergoes fast
de-protonation to produce a Vitamin E radical. In other scenarios, Vitamin E scavenges lipid peroxyl
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PJSRR (2015) 1(1): 58-66
radicals and lipid hydroperoxide resulting in the formation of Vitamin E radicals (Niki, 2014).
Although there are conflicting reports on its mode of action as an anti-oxidant, some believe that its
major function is that of peroxyl radical scavenger, which is important for maintaining the integrity of
membranes of cells (Traber & Atkinson, 2007). However, others believe its action are due to its
antioxidant properties (Brigelius-Flohé & Davies, 2007). Since it has been shown that the most
abundant and readily available form of Vitamin E is α-tocopherol, most of the studies were conducted
using this isomer (Paul et al., 2012; Traber & Atkinson, 2007). Interestingly, other researchers argued
that tocotrienols and other tocopherol isomers (δ and λ) are better than α-tocopherol especially in
preventing cancer (Yang et al., 2012). As a potent lipid peroxyl radical, tocopherol has been reported
to reduce the level of lipid peroxidation associated with oxidative stress in highly lipogenic tissues
like the brain. Thus it was found to reduce the level of MDA in the tissues and alleviate tissue damage.
Additionally, it was found to reduce the level of SOD, GST, catalase and glutathione (S. Zaidi &
Banu, 2004). Vitamin E was also found to restore decreased SOD, catalase, GST, GSH and increased
MDA, ALT and AST in rats after immobilization (S. M. Zaidi et al., 2005). In a related study, the
vitamin was found to decrease SOD and GPx activities that were increased following restraintinduced stress (S. M. Zaidi et al., 2005).
Moreover, Vitamin E has been reported to reduce the incidence of cancer, aging, restoration of blood
flow following ischemia and reperfusion injury, arthritis, cataract and platelet hyper-aggregability
(Packer, 1991). Several human and animal trial studies have shown the beneficial roles of Vitamin E
in the prevention of a number of diseases and conditions. However, some findings are contradictory in
the sense that different research groups propose different findings. An example is in the case of
prostate cancer; while some found it to have a preventive role (Klein et al., 2011; Virtamo et al.,
2014), others found it to predispose more to the development of cancer (Albanes et al., 2014;
Lippman et al., 2009). However, Yang et al. (2014) explained that the vitamin can have a double role
in cancer prevention or potentiation due to the absence of other isomers in current therapeutic forms.
In other studies, Vitamin E administration was found to reduce cardiovascular conditions and related
deaths in women by 7% and 24%, respectively (Lee et al., 2005). However in a recent study, the
administration of vitamin E did not show any beneficial effect in the prevention of cardiovascular
disease in human participants (Myung et al., 2013). Other reported uses of the vitamin include the
prevention of pro inflammatory state in calves and the enhancement of passive maternal antibody
transfer (Krueger et al., 2014); prevention of vascular degeneration through reduction in
homocysteine and cholesterol levels in rats (Kirac et al., 2013); reduction in inflammatory stressor;
IL2, C-reactive protein and vascular endothelial growth factor which lead to atherosclerosis due to
heavy and chronic alcohol consumption (Shirpoor et al., 2013); protection against contrast induced
acute kidney injury in chronic kidney disease patients (Tasanarong et al., 2013); the reduction in renal
scarring secondary to pyelonephritis in children (Sobouti et al., 2013); the reduction in the incidence
of angina pectoris in male smokers (Rapola et al., 1996), and the prevention of mono sodium
glutamate induced renal toxicity in rats, among many other preventive functions (Paul et al., 2012).
Synergistic actions of antioxidant vitamins in prophylaxis
Several antioxidant vitamins have been shown to have synergistic effects when combined together.
For instance, Vitamins A, C and E prevented the gastro-esophageal disease, Barret’s esophagus and
esophageal carcinoma (Lukic et al., 2012), while other observed a low incidence of in heavy metal
toxicity following the administration of a combination of Vitamins A, C, E and selenium in fish, as
compared to administration of a single vitamin (Harabawy & Mosleh, 2014). In a 9.4-year
randomized trial study testing the effects of a combination of 600IU of Vitamin E and 500mg of
Vitamin C on women, there were fewer incidences of stroke in participants taking a combination of
the two vitamins as compared to those taking either of the two (Cook et al., 2007). These few
examples show the compatibility these vitamins have in the biological system and they may act better
together than alone, in some instances.
Conclusion
Antioxidant vitamins play important roles in the biological system as they counteract the oxidative
stress and imbalances in the system produced by excess ROS and NOS production. Vitamins E and C
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are most effective in ameliorating decreased levels of SOD, GSH, GPx and catalase, while they were
also found to modulate increased levels of MDA. Vitamin A has so far been shown to be poor in
modulating these enzyme alterations. Therefore, the safety of prolonged usage of this vitamin in
humans and other animals still needs to be evaluated as several reports have shown them to be either
inefficient or even increase mortalities in certain trail cases (Bjelakovic et al., 2012).
Acknowledgements
The authors are grateful for the funding from Universiti Putra Malaysia (Grant No: 9438740) and
Ministry of Higher Education Malaysia (Fundamental Research Grant: 5524641).
Author Contribution
All authors contributed equally to this work and have read and approved the final manuscript.
Conflict of Interest
None to declare
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Quantum Dot-sensitized Solar Cell Based on nano-TiO2 Electrodes
Wardatun Nadrah, MOHD AMIN1, a Zulkarnain, ZAINAL1,2, b *
Zainal Abidin, TALIB3, c Hong Ngee, LIM1, 4, d and Sook Keng, CHANG2,e
1
Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang,
Selangor, Malaysia
2
Material Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti
Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
3
Department of Physic, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor,
Malaysia
4
Functional Device Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400
UPM Serdang, Selangor, Malaysia
a
[email protected], [email protected], [email protected],
d
[email protected]
Abstract - Quantum dots-sensitized solar cell (QDSSC) is one of the third generation solar cell that is
the most promising low cost, easy to manufacture and highly efficient solar cell. Compared to Dyesensitized solar cell (DSSC), quantum dots (QDs) of QDSSC has a narrow bandgap and possess
excellent properties such as tunable band gaps, strong light absorption and high multiple electron
generation. Titanium dioxide or titania (TiO2) is an oxides semiconductor material that is frequently
used as a photoanode in this photovoltaic system due to high stability under visible light illumination.
TiO2 is also known as a good photocatalyst and an excellent choice in environmental purification. The
efficiencies of electron injection and light harvesting in QDSSC are affected by the nature, size
morphology, and quantity of this nanomaterial. In this review, the concept and principles of the
QDSSCs are reviewed. The preparation and fabrication method ofTiO2 electrode in QDSSC are also
discussed. It is worthwhile to know the architecture of TiO2 in order to enhance the efficiency of
QDSSC.
Keywords: Quantum dots-sensitized solar cell, titanium dioxide, quantum dots
Introduction
Sunlight continued to be harvested by technologies up to the early years of the industrial revolution.
Since then, the temperature has risen by 0.6oC because of the global activities which cause the
greenhouse effect whereby the quantity of carbon dioxide increases and eventually causing global
warming (Du, Li, Brown, Peng, & Shuai, 2014; El Chaar, Lamont, & El Zein, 2011; Gong, Liang, &
Sumathy, 2012). In recent years, renewable energy has attracted high interest due to these factors. As
an alternative source of energy, the sun sends high quantities of light energy to the surface of the earth
(Selinsky, Ding, Faber, Wright, & Jin, 2013). It is also completely renewable and definitely an
abundant resource with rapidly declining conversion cost (Jun, Careem, & Arof, 2014). The energy
provided by the sun for our planet is 10,000 times more than world demand whereby 10 % of the
efficiency of the solar cell would fulfil global needs (Kouhnavard et al., 2014). A broad range of solar
cell research is currently underway and they include dye-sensitized solar cell (Abdullah & Rusop,
2014), organic solar cell (Halim, 2012), silicon solar cell (Halim, 2012) and heterojunction solar cell
(Church, Muthuswamy, Zhai, Kauzlarich, & Carter, 2013; Guo, Shen, Wu, & Ma, 2012).
The photovoltaic technology (PV) is a highly potential candidate for an alternative or renewable
source of energy in the current market. PV can be classified into first, second and third generation
solar cell. Solar cells based on silicon wafer, so-called first generation technology solar cell, make up
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the most number of solar cells present in the market and can reach as high a 27% solar cell efficiency
(Green, 2002).Meanwhile solar cell utilized with inorganic film is the second generation solar cell
which is cheaper to produce but has less than 14% solar cell efficiency (Jun, Careem, & Arof, 2013).
Chronologically, the invention of the third-generation solar cell is to decrease cost by significantly
increasing efficiencies as high as above 30% and at the same time maintain the economic and
environmental cost advantage (Conibeer, 2007). Figure 1 shows the PV production per square meter
against the efficiency of solar cell and the cost unit power.
Figure 1: Efficiency and cost projection for first (I), second (II) and third generation (III) (waferbased, thin films, and advanced thin film, respectively)
Dye-sensitized solar cell (DSSCs) is the first third generation which has attracted much attention due
to low fabrication cost and high efficiency, flexibility in colour, shape and transparency
(Golobostanfard & Abdizadeh, 2014). However QDSSCs is the further improvement of dye-sensitized
solar cell (DSSCs) in boosting the overall efficiency by coupling synthesized inorganic quantum dots
(QDs) semiconducting materials as sensitizers (Prabakar, Minkyu, Inyoung, & Heeje, 2010).QDSSC
based on semiconductor nanocrystal has attracted attention as an alternative to DSSCs owing to their
great stability, good absorption over wider wavelength range and multiple exciton generation leading
to the production of power efficiencies (Z) that are much higher than DSSC (Xu, Zou, Yu, & Zhi,
2013; Yang, Chen, Roy, & Chang, 2011). All these unique characteristics of the QDSSC have raised
high interest among researchers in renewable energy research field.
Despite all of these good characteristics of QDSSCs, the power conversion efficiency is still not as
impressive as DSSCs mainly due to several reasons such as bad charges separation, less efficient
photo excited electrons and unsuitable sensitizers (Li, Yu, Liu, & Sun, 2015). The electrode also plays
a critically important role in contributing to the high efficiency of the QDSSC performance. Photo
anode with high strong light scattering, efficient electron transport, high QD loading and quick
electrolyte is of great importance to the QDSSC system (Zhou et al., 2014). The unique textural and
structural characteristic of nanostructured material such as TiO2, SnO2 and ZnO has attracted much
interest in the past decade(Malekshahi Byranvanda, 2013). The unique textural and structural
characteristics are particle size distribution, specific surface area, morphology, crystallinity and
crystal structure (Hu et al., 2014). This review paper is focused on TiO2 as an electrode in QDSSC.
During the past decade, TiO2 has become one of the most popular electrode materials and different
methods apply to photovoltaic application and QDSSC specifically. In addition TiO2 is an ecofriendly commercial product and has been known to be effective and is of great value(Liao et al.,
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2012). TiO2 is a semiconductor with wide band gap known to be n-type. It has three crystalline phases
which are anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic).The most stable phase
is rutile TiO2 whereby anatase and brookite TiO2 are metastable and they can be converted into rutile
phase at high temperature that is, around 750oC (Wang, He, Lai, & Fan, 2014). Single crystal anatase
is reported to be more effective than rutile phase in photovoltaic application (Bet-moushoul,
Mansourpanah, Farhadi, & Tabatabaei, 2016).
Basic principle of QDSSC
QDSSCs have similar configuration with DSSCs and the only difference is that QDSSCs uses
inorganic semiconductor quantum dots (QDs) as light absorbing material instead of molecular dyes,
onto the surface of a thin film of nano-TiO2 electrode that acts as a working electrode (Song et al.,
2014). Similar to DSSCs, in QDSSCs, excitons are formed in quantum dots whereby the charge
separation occurs in the QD molecule layer upon the photoexcitation as electrons are injected from the
QD excited state into the conduction band of the nano-TiO2 and that eventually produces a
photovoltaic effect as shown in figure 2.
Figure 2: Operating principle of QDSSC
QDs is restored through electron donation from the frequently used polysulfide electrolyte, which
consist of (S2-/Sx2-) the redox system. The oxidized QD is then restored (hole is filled with electron)
when it is reduced by S2- from the electrolyte and in turn it is oxidized into Sx2- that diffuses to the
counter electrode.
𝑆 2− + 2ℎ+ → 𝑆
(1)
2−
𝑆 + 𝑆𝑥−1
→ 𝑆𝑥2− (𝑥 = 2 − 5)
(2)
The oxidized group 𝑆𝑥2− are reduced to 𝑆 2− occur on the counter electrode.
2−
𝑆𝑥2− + 2𝑒 − → 𝑆𝑥−1
+ 𝑆 2−
(3)
In the electrolytes, voltage is generated in the Fermi levels between the electron in the photo electrode
and the redox potential of 𝐼 − /𝐼3− .𝐼 − ion reduced to 𝐼3− at the counter electrode whereby platinum and
carbon based materials coated on the substrate (Guo, Shen, Wu, Wang, et al., 2012; Lee & Chang,
69
PJSRR (2015) 1(1): 67-81
2008; Yu, Lia, Qiu, Kuang, & Su, 2011). The efficiency of the solar cell can be determined by the
equation below:
𝜂=
(𝐽𝑆𝐶 ×𝑉𝑂𝐶 ×𝐹𝐹)
,
𝑃𝑖𝑛
(4)
where 𝐽𝑆𝐶 is the short circuit photocurrent density, 𝑉𝑂𝐶 is the open circuit voltage, 𝐹𝐹 is the fill factor
and 𝑃𝑖𝑛 is the power intensity of the incident light. The 𝐽𝑆𝐶 ,𝑉𝑂𝐶 and 𝐹𝐹 values can be calculated from
the direct current density-voltage (J-V) curves.
TiO2 as an electrode
The excellent properties of TiO2such as good chemical stability, low cost production, high corrosion
resistance, non-toxicity, high photocatalytic activities and good charge transport properties play an
important role in the performance of QDSSC (Barbe et al., 1997; Kong, Chang, & Jang, 2014; Ou &
Lo, 2007). TiO2 nanostructure such as nanoparticles(Balis, Dracopoulos, Bourikas, & Lianos, 2013;
Chen, Chappel, Diamant, & Zaban, 2001; Ito et al., 2007; Jung, Kim, Kim, Choi, & Ahn, 2012;
Kongkan, Tvrdy, Takechi, Kuno, & Kamat, 2008; Zaban, Micíc, Gregg, & Nozik, 1998; Zhang et al.,
2009), nanotubes (Chen et al., 2009), nanorods (Gonfa et al., 2014), nanowires (Nikhil, Thomas,
Amulya, Mohan Raj, & Kumaresan, 2014; Sun et al., 2012) and nanoflower (Yu, Li, Liu, Cheng, &
Sun, 2014b) have been widely recognised as excellent photo anodes in QDSSC. The size of the TiO2
building units, apparently in nanometer scale, highly influences the performance of QDSSC (Kavitha,
Gopinathan, & Pandi, 2013). Table 1 shows the example of QDSSC and the solar cell efficiency
performance based on nano- TiO2 as an electrode.
Table 1: Example of QDSSC and the solar cell efficiency performance based on nano-TiO2 as an
electrode.
TiO2
TiO2 nanoparticle
Sensitizer
CuInS2
Counter electrode
Cu2S
Efficiency
1.05%
Reference
(Gong et al., 2012)
TiO2 sol
CdSe
Cu2S/CNT
1.05%
TiO2 nanoparticle
CdSe
Pt
3.65%
TiO2 nanotube
TiO2 beads
TiO2 nanoparticle
TiO2 nanoparticle
CdSexTe1-x
CdS/CdSe
CdSe
CdS
Pt
Cu2S
Pt
Pt
0.588%
4.33%
2.23%
1.15%
Mesoporous
spherical TiO2
powder
TiO2 sol gel
CdS/CdSe
Pt
0.29%/0.34
%
(Golobostanfard &
Abdizadeh, 2014)
(Prabakar et al.,
2010)
(Xu et al., 2013)
(Zhou et al., 2014)
(Song et al., 2014)
(Lee & Chang,
2008)
(Kong et al., 2014)
InP
Pt
-
TiO2 nanoparticle
TNT/TNP
ZnS, CdS, CdSe
CdSe
Pt, CoS, CuS
2.7%
-
TNP
TiO2 nanoparticle
TiO2 nanoparticle
TiO2 nanoparticle
CdS
CISe
CdS/CdSe/ZnS
CdS
Pt
Cu2S
NiS
Cu2S
4.3%
2.97%
2.15%
70
(Zaba, Micíc´,
Gregg, & Nozik,
1998)
(Balis et al., 2013)
(Kongkanand,
Tvrdy, Takechi,
Kuno, & Kamat,
2007)
(Jung et al., 2012)
(Yang et al., 2013)
(Kim et al., 2014)
(Zhou et al., 2013)
PJSRR (2015) 1(1): 67-81
Table 1: Example of QDSSC and the solar cell efficiency performance based on nano-TiO2 as an
electrode (continued).
TiO2
TiO2 nanoparticle
Sensitizer
CdS/CdSe
Efficiency
1.2%
Reference
(Jun, Careem, &
Arof, 2014)
SnSe2
SnS
CdS
Ag2Se
Counter electrode
Pt/Cu2S/Graphite/
Carbon soot/
Reduced Graphene
Oxide (RGO)
Pt
Pt/CuS
Pt
TiO2 nanoparticle
TiO2 nanoparticle
TiO2 nanosheet
TiO2 nanoparticle
0.12%
<0.1%
1.95%
3.6%
TiO2 nanoparticle
CdS
NiS
3.6%
TiO2 nanorod
CdS/PbS
Pt
2.0%
TiO2 nanoparticle
CuInS2
Cu2S
1.85%
TiO2 nanodendrite
array
TiO2 nanoparticle
TiO2 hollow sphere
TiO2 nanowire
CuInS2
Cu2S
1.26%
CdS/CdSe
CdS/N719
PbSe
Brass plate
Pt
-
0.45%
4.66%
-
TiO2 nanoparticle
CdS
CoS2/Pt
2.27%
TiO2 nanotube
CdS0.54Se0.46
Pt
-
TiO2 nanoparticle
Cu1.8/CuS
3.26%
TiO2 nanoparticle
CdSxSe1-x/
Mn-CdS
CdS/CdSe/ZnS
(Yu et al., 2012)
(Miyauchi, 2011)
(Li et al., 2014)
(Tubtimtae, Lee, &
Wang, 2011)
(Li, Yang, Zhang,
Zhang, & Li, 2014)
(Jiao, Zhou, Zhou,
& Wu, 2013)
(Peng, Liu, Shu,
Chen, & Chen,
2013)
(Peng, Liu, Zhao, et
al., 2013)
(Shen et al., 2015)
(Cui et al., 2015)
(Győri, Kónya, &
Kukovecz, 2015)
(Punnoose, Kim,
Srinivasa Rao, &
Pavan Kumar,
2015)
(Gakhar, Smith,
Misra, &
Chidambaram,
2015)
(Li et al., 2015)
NiS
3.03%
TiO2 nanorods arrays
CdSe/Mn-CdS
Cu1.8S/CuS
2.40%
(Gopi, Srinivasa
Rao, Kim,
Punnoose, & Kim,
2015)
(Yu, Li, Liu,
Cheng, & Sun,
2014a)
Preparation of TiO2 as an electrode in QDSSC
In QDSSC, TiO2 nanoparticles (example like commercial P25 nanoparticles) have been extensively
studied as a photoanode due to their special characteristics as mentioned before (Zhou et al.,
2014).Anatase, rutile and brookite are the three crystalline form of TiO2 whereby anatase is the most
preferable in solar energy conversion. This is due to the ability to avoid charge recombination and
71
PJSRR (2015) 1(1): 67-81
efficient electron transport in photoanode (Byranvana, Bazarganb, & Kharat, 2012). In recent years, a
lot of research have gone into preparing TiO2among them are in achieving low cost production and
making them easily reproducible by using a simple method which is eventually imperative for the
industrial manufacture of QDSSC (Zhang et al., 2009).The methods in preparing TiO2 such as the
hydrothermal method (Gopinathan, & Pandi, 2008; Vijayalakshmi & Rajendran, 2012; Wu et al.,
2013), the sol gel method (Behnajady & Eskandarloo, 2013; Guo, Liu, Hong, & Jiang, 2005;
Sabataitytė, Oja, Lenzmann, Volobujeva, & Krunks, 2006) and anodization (Tang et al., 2008) have
been studied extensively in order to produce excellent characteristics of TiO2 as a photoelectrode.
Sol-gel method
The sol-gel method for TiO2 synthesis is a very useful tool for photo-induced molecular reaction due
to the special variables such as particle size, incident light, phase composition and convenient
preparation method (Karami, 2010). Titanium (IV) isopropoxide (TIPP) is usually used as a starting
material in this method(Manoharan & Venkatachalam, 2015; Zeng, Chen, Su, Li, & Feng, 2014). The
mixture will undergo an aging period and it is kept in the oven to obtain the colloidal solution (Zeng
et al., 2014). Next the solution is dried and calcined to get TiO2 nanocrystal powder (Hu, Tang, He,
Lin, & Chen, 2014; Laranjo et al., 2014; Zhu, Zhang, Gao, & Cao, 2000). Figure 3 shows TiO2
nanoparticles prepared by the sol gel method at different levels of concentration.
Figure 3: SEM surface images of three different kinds of TiO2 concentrations of (a) 17 wt.%, (b) 20
wt.%, and (c) 24 wt.% films on the SnO2:F glass after sintering process(Lee et al., 2009).
Hydrothermal method
Hydrothermal method is one of the most popular methods to prepare TiO2 nanostructure. Other than
TiO2 nanoparticle, other nanostructures such as nanotube and nanorod can also be synthesized via the
hyrothermal method (Lee, Lee, Rhee, & Park, 2014). One of the suggested methods is TIPP where it
is mixed and stirred with nitric acid, ethanol and distilled water through the sol-gel method. The
product produced from the sol-gel method will undergo hydrothermal treatment in the teflon-lined
autoclave to produce TiO2 powder and the powder will receive further treatment for calcination to
achieve the desired size and crystallinity (Manoharan & Venkatachalam, 2015). Figure 4 shows SEM
images of TiO2 nanorod arrays formed by the hydrothermal method by optimization of the seed layer.
72
PJSRR (2015) 1(1): 67-81
Figure 4: SEM images of TiO2nanorod arrays grown by hydrothermal method on (a) bare FTO,
(b) FTO immersed in 0.05 M TiCl4 solution, (c) FTO immersed in 0.1 M TiCl4 solution,
(d) FTO immersed in0.15 M TiCl4 solution, (e) FTO immersed in 0.2 M TiCl4 solution,
respectively (Wang et al., 2013)
Electrochemical method
The Electrochemical method is an impressive technology to develop the nanotube or nanoporous layer
as an electrode especially in QDSSC. TiO2 nanotube can be formed by an anodization of the titanium
whose capability is strongly influenced by the variation of parameters. The quality and ability of TiO2
nanotubes also depends on their very own properties such as crystallite size, morphology and the
lattice strain. Yulian Zhang et al.,(2015)reported the frequent used of ammonium fluoride (NH4F) as
an electrolyte and indicated that high NH4F concentration is beneficial to the growth of ribs around
the nanotubes. Figure 5 shows the FESEM images of surface morphologies and cross-section of TNTs
obtained in electrolytes with different NH4F concentrations. Meanwhile, Munirathinam, Pydimukkala,
Ramaswamy, & Neelakantan (2015) reported on the development of TiO2 nanotubes by the
anodization process using the two electrode system whereby titanium was used as anode and a
stainless steel plate as a cathode at a specific distance. In this research, two different electrolytes
which are hydrofluoric acid, HF (acidic medium) and sodium sulfate, Na2SO4 (neutral) were used and
then followed by annealing at 450oC for 2h. The result clearly indicated nanotubes formed from the
neutral bath are four times longer than the ones synthesized from the acidic bath.
73
PJSRR (2015) 1(1): 67-81
Figure 5: FESEM images of surface morphologies and cross-section of TNTs obtained in electrolytes
with NH4F concentrations of (a) (d) 0.2 wt%, (b) (e) 0.4 wt%, (c) (f) 0.6 wt%,
respectively (Zhang et al., 2015)
Approach in improving TiO2photoanode in QDSSCs
Although QDSSC raised tremendously high attention among researchers in order to improve solar cell
performance, energy conversion efficiency remains under 10% as reported in figure 1. A lot of work
has been done in the approach to improve QDSSC. One of the important approaches to increase the
energy conversion efficiency yield is the architecture of the photoanodes. This is because photoanode
material like TiO2 has wide band gap (3.20 eV for anatase and 3.02 eV for rutile TiO2) that limit its
usage at UV light region(Maheswari & Venkatachalam, 2015). Other than that, optimal nanoparticle
interconnection and pores size can control the charge carrier transport to ensure an efficient
electrolyte penetration (Yacoubi, Samet, Bennaceur, Lamouchi, & Chtourou, 2015).
Among studies that have been done recently are doping TiO2 electrode with Ni (Maheswari &
Venkatachalam, 2015), Au (Liu et al., 2014), Co (Brigham, Achey, & Meyer, 2014; C. Wang et al.,
2014), Fe (Wang et al., 2014) and Mn (Wang et al., 2014). Doping TiO2 with impurities dopants will
broaden the use of the PV to the visible region and at the same time provide a good surface for the
deposition of QDs (Maheswari & Venkatachalam, 2015; Yacoubi et al., 2015). The dopants also act
as a light harvesting material which means the light will be scattered and trapped in order to increase
the effective path length of incident light of the absorption of the semiconductor (Liu et al., 2014).
Some dopant like Fe have been reported as having the ability to increase charge carrier density of
TiO2 leading to good carrier transportation and separation and relatively long electron lifetime(Wang
et al., 2014).
Beside dopants, surface modification also play an important role in order to avoid or reduce
recombination of excited electron whereby it is a major problem in QDSSC(Kim et al., 2012). TiCl4is
usually applied on the substrate at multiple times of immersion, followed by annealing at 450oC for 30
min before depositing TiO2 paste (Kim et al., 2012). Nevertheless, TiCl4 treatment decreases average
74
PJSRR (2015) 1(1): 67-81
pore size whereby it can lower the recombination and increase the current (Guo et al., 2014).
Recently, a study focused on the treatment of TiO2 hydrolysed by hydrochloric acid (HCl) in
preparation of TiCl4 stock solution has been reported for the synthesis of nanosized crystalline TiO2
(Lee & Yang, 2005). The result from this study showed that the brookite phase was transformed to the
rutile phase with increase reaction time, while through a heat treatment, it was transformed to rutile
via anatase phase (Lee & Yang, 2005).
Previously, there were so many efforts made to optimize TiO2 structures to enhance QDSSC
performance. The first effort made was by creating large pore size distribution of TiO2 to make the
loading process of quantum dots much easier due to the small size of quantum dots (Salant et al.,
2012). Secondly, the surface area of TiO2 was increased in order to increase quantum dots loading.
Moreover, high surface area of photoanaode may improve the quantum dots coverage and retard
unnecessary interface recombination (Song et al., 2012). Thirdly, an additional layer of coating was
also added to improve the electron transport path in order to enhance the QDSSC performance.
However, previous researches reported that an additional layer of TiO2 can hardly balance the
required qualities of TiO2 (Wu et al., 2015). Therefore, further studies on optimization of TiO2 should
be done to meet the demand in QDSSC. For example, Wu et al. (2015) designed a multi-dimension
titanium dioxide made up of mesoporous nanoribbons consisting of oriented aligned nanocrystal. This
impressive development resulted in increased surface area of TiO2 that led to a high photocurrent
efficiency of 4.15%. Meanwhile, in another study an attempt has been done by doping TiO2
nanocrystal with two dimensional graphene in order to improve the photovoltaic performance owing
to the graphene unique characteristics such as good thermal conductivity, good mobility charge
carriers and specific surface area (Chen, Tuo, Rao, & Zhou, 2014). The incorporation of graphene
with TiO2 increase the photocurrent efficiency by 37% compared to the pure TiO2 and eventually
increased the QDSSC performance.
Conclusions and future directions
The review on TiO2 as a working electrode in QDSSC demonstrated high potential inorder to increase
energy conversion efficiency in a novel QDSSC system. The study of photoanode configuration is
critically important because the significance can be of high impact particularly in providing high QD
loading, strong light scattering, quick electrolyte diffusion and efficient electron transport (Zhou et al.,
2014). Different nanocrystal structure such as nanotubes, nanorods and nanowire have been
developed whereby particular control is given to recombination and this eventually improves PV
performance. Currently, a lot of studies are focused on developing low cost high ability nanocrystal
material for PV application and this will no doubt raise its potential when developed and applied in
the academia and industry. The low cost nanocrystal material used make the current price of QDSSC
cheaper than DSSC ($3/Wp–$4/Wp) and silicon solar cell ($3/Wp) (Kalowekamo & Baker, 2009).
Future work should be focused on improving the solar cell efficiency as mentioned in this review
paper. Many modifications on QDSSC have been developed however, they are still in their early
stages and many other new developments can be done in order to improve the efficiency, robustness
and potential of the thin-film-type material. No doubt, as the understanding of the topic continues,
more possible ideas can be conceived to improve QDSSC potential.
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PJSRR (2015) 1(1): 67-81
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Nitric oxide and Its Important Role in Plant Defence
Nurul Najihah, MOHD NASIR,a & Noor Baity, SAIDI,b*
a
Department of Cell and Molecular Biology, Faculty of Biotechnology and Biomolecular Sciences,
Universiti Putra Malaysia, 43400 Serdang, Selangor Darul Ehsan, Malaysia.
E-mail address: [email protected]
b
Department of Cell and Molecular Biology, Faculty of Biotechnology and Biomolecular Sciences,
Universiti Putra Malaysia, 43400 Serdang, Selangor Darul Ehsan, Malaysia.
E-mail address: [email protected]
*
[email protected]
Abstract – Nitric oxide (NO) is a signaling molecule involved in numerous physiological processes
in both animals and plants. The bioactivity of NO is mainly transduced via post-translational
modification of cysteine residues of proteins termed S-nitrosylation. Interestingly, a number of key
regulatory components in plant defense responses have been found to be regulated by S-nitrosylation
making this type of protein modification an important modulator of plant immunity. As a signaling
molecule, NO intimately interact with other important molecules such as reactive oxygen species.
Since the identification of NO in plants, increasing number of papers isbeing published in the area of
NO biology each year. Here, a collection of papers describing the role of NO in plant immunity has
been brought together to provide a bird's-eye view on the focus area.
Keywords: Nitric oxide, plant immunity, S-nitrosylation
__________________________________________________________________________________
Nitric Oxide: General Properties
Nitric oxide (NO) acts as a signaling molecule within species from every biological kingdom.
Because of its unique chemistry, which permits permeability, stability and reactivity, NO and its
derivatives are ideally suited to its cellular signaling function. At room temperature and at
atmospheric pressure, NO is a free radical colourless diatomic gas with lipophilic property. Its small
Stoke’s radius and neutral charge allow rapid membrane diffusion (Kiger et al., 1993) and can play a
part in cell-to-cell signaling over a brief period of time. Due to the presence of unpaired electron and
the free radical nature of NO, it readily reacts with oxygen (O2), superoxide (O2-), transition metals
and thiols, which largely shape its cellular function within the cell (Mur et al., 2006; Neill et al., 2008;
Hong et al, 2008). The reaction of NO with O2 results in the generation of NOx compounds (including
NO2, N2O3, and N2O4), which can either react with cellular amines and thiols, or simply hydrolyze to
form end metabolites of nitrite (NO2-) and nitrate (NO3) (Wendehenne et al., 2001).
Nitric Oxide Production in Animals and Plants
NO is a multifunctional effector involved in numerous mammalian physiological processes, including
neurotransmission, immunological and inflammatory responses, and relaxation of vascular smooth
muscle (Schmidt and Walter, 1994). However, the use of NO is not confined to the animal kingdom
alone. NO is also involved in diverse physiological processes in plants, such as defense response,
metabolism, cellular detoxification, transport, iron homeostasis, signaling, flowering, and lignin
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biosynthesis (He et al., 2004; Bason-Bard et al., 2008; Wendehenne et al., 2014; Yu et al., 2014).
Despite the importance to elucidate the biosynthesis of NO in plants, there is still much uncertainty
after years of research. In animals, NO is synthesized primarily by the enzyme nitric oxide synthase
(NOS), which catalyzes the NADPH-dependent oxidation of L-arginine to L-citrulline and NO
(Stuehr et al., 2004). Three NOS isoforms have been identified (Nathan and Xie, 1994); neuronal
NOS (nNOS), endothelial NOS (eNOS) and inducible NOS in macrophages (iNOS). nNOS and eNOS
are considered as constitutive and both show fast and transient activation. iNOS is induced in
macrophages and many other cell types in response to inflammatory agents and cytokines (Mayer and
Hemmens, 1997; Beck et al., 1999). Compared to constitutive NOSs, iNOS activityis able to be
sustainedlonger, ismore stable and generates more NO, thus exerting cytotoxic and antimicrobial
effects on the immune systems (Beck et al., 1999).
NO synthesis in plants involves both arginine and nitrite-dependent pathways. It is well documented
that potential enzymatic sources of NO in plant cells include nitrate reductase (NR) and NOS-like
activity (Neill et al., 2003; Romero-Puertas et al., 2004; Wang et al., 2006; Medina-Andres et al.,
2015). NR catalyzes the in vitro production of NO through a one-electron reduction of nitrite via the
use of NAD(P)H as an electron donor (Yamasaki and Sakihama, 2000). Despite a few contradictory
evidences that collectively suggest that NR is not likely to be the major generator of the NO
synthesized during pathogen-triggered nitrosative burst (Hong et al., 2008; Yamasaki, 2000), it has
been viewed as a candidate for NO production during plant-pathogen interaction (Neill et al., 2003).
Moreover, recent genetic based approaches using NR-deficient mutants denoted that NO is mainly
produced from NR that probably operates downstream of the L-arginine-dependent pathway (Corpas
et al., 2009; Vitor et al., 2013)
Although there is no obvious homolog of animal NOS in the Arabidopsis genome, several NOS-like
activities have been reported (Cueto et al., 1996; Barroso et al., 1999; Corpas et al., 2006). In addition,
mammalian NOS inhibitors have been shown to effectively abrogate the pathogen-triggered NO
production in plants (Delledone et al., 1998; Neill et al., 2003). Corpas et al. (2009) had elaborately
compared animal and plant NOS and concluded that plants also possess L-arginine-dependent NOS
activity which is different from canonical animal NOS.
A search for the enzyme(s) that catalyze(s) the pathogen-triggered NO production in Arabidopsis led
to the cloning of the Arabidopsis NOS 1 (AtNOS1) gene, which exhibited significant sequence
similarity to a snail gene that encoded a NOS-like activity, but with no homology to mammalian NOS
(Guo et al., 2003). However, it has been difficult to demonstrate reproducibility of typical NOS
activity through recombinant AtNOS1 (Crawford et al., 2006). Instead, AtNOS1 was found to serve as
a chloroplast-targeted GTPase essential for proper ribosome assembly (Flores-Perez et al., 2008) and
therefore renamed Arabidopsis nitric oxide associated 1 (AtNOA1). Several other mutants with altered
NO levels had been found to show increased NO accumulation correlated with concentrations of
putative substrates for NO biosynthesis but none of them was exclusively involved in NO production
(Leitner et al., 2009). The closest evidence to the existence of a plant NOS-like enzyme is the
identification of a functional NOS with 40% similarity to human NOSs in the green alga,
Ostreococcustauri (Foresi et al., 2010).
On the other hand, researchers have reported that NO can also be formed non-enzymatically in a
reaction between nitrogen dioxide and plant metabolites, in nitrous oxide decomposition or as a result
of chemical reduction of NO2- at acidic pH (Wendehenne et al., 2001). This area of research remains
controversial and clearly, it is imperative to determine the key NO generator in plants to improve our
understanding of NO metabolism.
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S-nitrosylation as a Redox-Based Signalling Factor in Plants
NO-related signaling can be attributed to various NO derivatives, collectively referred to as reactive
nitrogen species (RNS), which comprise of not only the NO radical (NO·) and its nitroxyl (NO -) and
nitrosonium (NO+) ions, but also peroxynitrite (ONOO-), S-nitrosothiols (SNO), higher oxides of
nitrogen and dinitrosyl-iron complexes (Leitner et al., 2009). NO and RNS exert their biological
actions through the chemical modification of targets by reacting with different amino acids or
prosthetic groups. They mostly act through the binding oftransition metals of metalloproteins (metal
nitrosylation), the covalent modifications of cysteine (S-nitrosylation) and tyrosine (tyrosine 3nitration). These processes emerge as specific post-translational protein modifications and the best
characterized among these is S-nirosylation which involves the covalent attachment of an NO moiety
to the thiol side chain of cysteine to form SNO.
S-nitrosylated proteins have been identified through a proteome-wide scale analysis in several plants
including Arabidopsis, potato, pea and citrus L. (Lindermayr et al., 2005, Kato et al., 2013, Camejo et
al., 2013, Tanou et al, 2009). In this framework, S-nitrosylation regulates a wide array of proteins
involved in all major cellular activities and the formation of SNO may serve to stabilize and diversify
NO-related signals.
As a regulatory mechanism in plants and animals, S-nitrosylation is a reversible process. Indeed, Snitrosylated proteins can be easily de-nitrosylated as the S-NO bond is labile in a cytoplasm’s
reducing environment, allowing cells to flexibly and precisely modulate protein function in response
to environmental signals. S-nitrosylated proteins are in dynamic equilibrium with de-nitrosylated
proteins largely due to the action of glutathione (GSH) with the subsequent formation of Snitrosoglutathione (GSNO), reconstituting the protein thiol as a consequence. GSNO has the ability to
release NO or function as a transnitrosylationg agent, thus it is considered as a natural reservoir of NO
(Besson-Bard et al., 2008; Leitner et al., 2009).
Two of the enzymes that are known to metabolize GSNO are S-nitrosoglutathione reductase (GSNOR)
and thioredoxin (Feechan et al., 2005; Lamotte et al., 2015). The presence of GSNOR is conserved in
bacteria, animals and plants (Liu et al., 2001) and due to its ubiquitous nature, this enzyme was
suggested to confer protection against nitrosative stress rather than as a cell signaling factor. In
contrast, thioredoxin or thioredoxin reductase denitrosylation reactions seem to be a part of a signal
transduction mechanism (Lindermayr and Durner, 2009). GSNOR controls intracellular levels of
GSNO and limits NO toxicity through NADH-dependent reduction of GSNO to glutathione disulfide
(GSSG) and ammonia (NH3) (Sakamoto et al., 2002). Though highly specific for GSNO, GSNOR
seems to modulate the extent of total cellular SNO formation (Liu et al., 2001; Feechan et al., 2005),
and thus is regarded as the key enzyme responsible for the modulation of NO-mediated signaling
pathways (Cheng et al., 2015).
Important Role of NO and SNO in Plant Disease Resistance
The function of NO in signaling defense responses during plant-pathogen interactions has been well
documented in many experiments conducted years ago. A widespread feature of plant disease
resistance is the programmed hypersensitive response (HR), a programmed execution of plant cells at
sites of attempted infection that serve to limit the pathogen spread (Delledonne et al., 2001; Mur et al.,
2006 ). NO is suggested to play a key signaling role during HR, next to the accumulation of ROS and
salicylic acid (Agurla et al., 2014). In animals, many biological effects of NO including apoptosis are
mediated by the highly toxic molecule, ONOO-, which is relatively non-toxic in plants (Bonfoco et al.,
1995). On the contrary, HR-associated cell death in plants is proposed to be mediated by the relative
levels of NO and H2O2 that areformed by the dismutation of O2- by SOD. In many cases, impairment
of NO production via genetic mutation or treatment with NO inhibitor will negatively affect H 2O2
accumulation, leading to suppressed HR advancement (Rasul et al., 2012; Vitor et al., 2013; Kulik et
al., 2014; Trapet et al., 2014; Qiao et al., 2015). In plants, ONOO- is continuously produced in healthy
cells, exposing them to an environment rich in ONOO-. Therefore, plants have developed some
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PJSRR (2015) 1(1): 82-90
detoxification mechanisms, for example, through the action of peroxiredoxin II E (PrxIIE), a member
of the peroxiredoxin family of antioxidant enzymes responsible for lipidoxidation and tyrosine
nitration (Romero-Puertas et al., 2007). Interestingly, PrxIIE has been found to be S-nitrosylated
during the HR resulting in inhibition of its hydroperoxide-reducing peroxidise activity together with
its ability to detoxify ONOO- and also increasing the amount of tyrosine nitration (Romero-Puertas et
al., 2007). In conclusion, NO regulates the effect of its own reactive species through S-nitrosylation of
crucial components of the antioxidant defence system. NO also controls cell death in plants through
S-nitrosylation of Arabidopsis metacaspase 9 and cytosolic glyceraldehyde 3-phosphate
dehydrogenase, both of which can act as potential executioners of programmed cell death (Belenghi et
al., 2007). The involvement of NO in controlling cell death is further unearthed by the study of one of
the mammalian NADPH oxidase homologs in plants, respiratory burst oxidase homolog (RBOH) D
(Yun et al., 2011). RBOH is involved in the production of reactive oxygen species (ROS), particularly
hydrogen peroxide, which is produced in response to pathogen recognition (Torres et al., 2002). NO
was shown to inhibit AtRBOHD activity through S-nitrosylation at Cys-890, thus influencing the
inherent effect of ROS during HR-associated cell death in plants. Based on the fact that Cys-890 is
evolutionary conserved, it was suggested that S-nitrosylation of this specific residue might regulate
the activity of NADPH oxidase in many other eukaryotes.
NO is not only thought to function during the development of hypersensitive cell death but also in the
establishment of plant disease resistance complementary to and independent of ROS (Wang et al.,
2013; Trapet et al., 2014). Administration of NO donors induced the expression of defense-related
genes encoding phenylalanine ammonia lyase (PAL), the first enzyme of phenylpropanoid
biosynthesis pathway and pathogenesis-related protein 1 (PR-1) (Durner et al., 1998; Vitor et al,
2013). NO action in plants, at least partially, is mediated through the SA-dependent signaling pathway.
NO treatment induces GSH accumulation which is required to elevate endogenous SA accumulation
(Kovac et al., 2015) that results in induction of PR genes (Durner et al., 1998; Kovac et al., 2015).
NPR1, a master regulator of SA-mediated defense genes and a crucial component of disease resistance
and signal cross-talk is known to be redox-regulated (Tada et al., 2008), adding an important clue
towards understanding NO’s signaling functions (Figure 1). Treatment with GSNO induces NPR1dependent defense response in Arabidopsis (Kovac et al., 2015). S-nitrosylation of NPR1 controls its
subcellular localization through oligomer-monomer exchange and thus its transcription co-factor
activity. Mutations at critical cysteine residues in NPR1 increased monomer accumulation,
constitutive nuclear localization and NPR1-mediated gene expression in the absence of a pathogen
(Mou et al., 2003; Tada et al., 2008). Another very interesting example for the regulatory function of
NO is S-nitrosylation of AtSABP3, which may interfere with the signal cross-talk as both carbonic
anhydrase and SA-binding activities of the protein are inhibited (Wang et al., 2009).
85
PJSRR (2015) 1(1): 82-90
Figure 1: Cross-talk of nitric oxide (NO) in plant cells
In addition to the data presented above, the importance of NO and SNO in plant disease resistance
were presented through the analysis of a GSNOR knock-out mutant. Loss-of-function mutation in
Arabidopsis GSNO reductase 1 (AtGSNOR1) resulted in increased cellular levels of SNOs and
compromised all modes of disease resistance (Feechan et al., 2005). GSNO accumulation in the
mutant plant is accompanied by a marked decrease in SA content and increased susceptibility to
various pathogenic microbes. Interestingly, the mutant showed an increase in HR even in the absence
SA and ROS, suggesting that plant cell death mediated by an increase in SNO alone is sufficient to
convey resistance in the absence of associated defence responses (Yun et al., 2011). Conversely,
enhanced AtGSNOR1 activity results in increased protection against ordinarily virulent microbial
pathogens. AtGSNOR1 also positively regulates the signaling network controlled by the plant immune
system activator, SA (Feechan et al., 2005). Subsequently, similar results were obtained by Tada et al.
(2008) through NPR1 studies. Surprisingly, when using antisense strategy, basal resistance has been
reported to increase in atgsnor1 antisense plants, correlating with higher levels of intracellular SNOs
and constitutive activation of PR-1 (Rusterrucci et al., 2007), which is the opposite result to that
obtained by Feechan et al. (2005). Probably the contradictory reactions of the GSNOR modified
plants might be a result of different cellular levels of SNO that change dramatically in atgsnor1
mutants (Feechan et al., 2005) compared to minor changes in the antisense plants (Rusterucci et al.,
2007). Nevertheless, both studies underline the physiological importance of SNO formation and
turnover in regulating multiple modes of plant disease resistance. The work of Feechan et al. (2005) is
supported by a study on the levels of SNO and NO in Arabidopsisthaliana cell suspension cultures
(Frungillo et al., 2014). According to the study, antisense GSNOR transgenic lines displayed higher
levels of SNO and NO under optimal growth conditions; in accordance with the designated role of
GSNOR as a modulator for GSNO. A similar observation was reported in a study with different
organs of healthy pepper plants where tissues with the lowest GSNOR activity presented higher
GSNO and NO contents (Airaki et al., 2011). In the involvement of GSNO, the postulated mobile
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PJSRR (2015) 1(1): 82-90
signal modulation by GSNOR in the systemic defense response was also investigated and GSNO was
shown to act synergistically with classical defense hormones such as SA and JA (Espunya et al., 2012;
Freschi, 2013; Zhou et al., 2015). Collectively, GSNOR would serve as an ideal target for crop
improvement through genetic engineering.
Conclusion and Perspective
Fundamental studies to understand the complexity of S-nitrosylation in the plant biological system
especially during the execution of plant stress responses is undeniably crucial since S-nitrosylation
provides a distinctive platform for NO to exert its impact on various proteins associated with
pathophysiological mechanisms. To date, the number of candidates for S-nitrosylation is increasing
and the physiological relevance of the S-nitrosylation process is becoming more evident.
Notwithstanding the infancy of S-nitrosylation research, we may want to consider the wider
perspective of its application in the real world. Exploring S-nitrosylation in crop plants would shed
light on how S-nitrosylation controls the expression of plant disease resistance. The associated
components could be the target of genetic modifications for the development of durable disease
resistant crops.
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