List of Titles

Unitarity constraints on the ratio of shear viscosity to entropy density in higher derivative gravity

Authors: Brustein, R , Medved, A J M
Date: 2011
Language: English
Type: text , Article
Identifier: vital:6815 , http://hdl.handle.net/10962/d1004325
Description: We discuss corrections to the ratio of shear viscosity to entropy density η/s in higher-derivative gravity theories. Generically, these theories contain ghost modes with Planck-scale masses. Motivated by general considerations about unitarity, we propose new boundary conditions for the equations of motion of the graviton perturbations that force the amplitude of the ghosts modes to vanish. We analyze explicitly four-derivative perturbative corrections to Einstein gravity which generically lead to four-derivative equations of motion, compare our choice of boundary conditions to previous proposals and show that, with our new prescription, the ratio η/s remains at the Einstein-gravity value of 1/4π to leading order in the corrections. It is argued that, when the new boundary conditions are imposed on six and higher-derivative equations of motion, η/s can only increase from the Einstein-gravity value. We also recall some general arguments that support the validity of our results to all orders in the strength of the corrections to Einstein gravity. We then discuss the particular case of Gauss-Bonnet gravity, for which the equations of motion are only of two-derivative order and the value of η/s can decrease below 1/4π when treated in a nonperturbative way. Our findings provide further evidence for the validity of the KSS bound for theories that can be viewed as perturbative corrections to Einstein gravity.
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Date Issued: 2011

A comparison of two sampling methods for surveying mammalian herbivore impacts on beetle communities in the canopy of Acacia drepanolobium in Kenya

- Kuria, Simon K, Villet, Martin H, Palmer, T, Stanton, M

Authors: Kuria, Simon K , Villet, Martin H , Palmer, T , Stanton, M
Date: 2010
Language: English
Type: Article
Identifier: vital:6860 , http://hdl.handle.net/10962/d1011150
Description: Even though several methods are used to sample and monitor canopy arthropods, there are no studies to indicate which of these methods is more effective.We compared the efficacy of the beating and canopy fogging methods in collecting beetles that inhabit Acacia drepanolobium (Harms) tree canopies at Mpala Research Centre in Laikipia district, Kenya. These trees grow naturally on the black cotton soils of the Laikipia ecosystem, accounting for more than 98%of the overstorey at the study site, and are important for local cattle and wildlife production. The ultimate objective of this study was to determine the effect of differential grazing and browsing pressure from large mammalian herbivores on the beetle communities of A. drepanolobium. Seven hundred and twenty trees 1.0–2.5 m tall were sampled using each method, making a total of 1440 trees. Sampling using the two methods was done concurrently and repeated quarterly over a period of 14 months. In total, 4320 individuals were collected, 1456 by beating and 2864 by fogging. The methods jointly yielded beetle specimens from 13 families and 55 morphospecies. Fogging collected significantly more beetle morphospecies than beating, and there was a significant interaction effect between method and sampling date. We found that numerically Anthicidae and Curculionidae responded positively to the presence of cattle.We also found that Anthicidae sp. A and Myllocerus sp. A numbers significantly increased in plots where livestock were grazed.
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Date Issued: 2010

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A decade later: follow-up review of South African research on the consequences of and contributory factors in teen-aged pregnancy

- Macleod, Catriona I, Tracey, Tiffany

Authors: Macleod, Catriona I , Tracey, Tiffany
Date: 2010
Language: English
Type: Article
Identifier: vital:6276 , http://hdl.handle.net/10962/d1008276 , http://journals.sagepub.com/doi/abs/10.1177/008124631004000103
Description: In this paper, we review South African research conducted in the last 10 years on the consequences of and contributory factors in teen-aged pregnancy. We discuss research into the rates of teen-aged pregnancy, the intentionality and wantedness of pregnancy, the disruption of schooling, health issues, consequences for the children, welfare concerns, knowledge and use of contraception, timing of sexual debut, age of partner, coercive sexual relations, cultural factors and health service provision. We compare this discussion to the reviews on the same topic appearing in the South African Journal of Psychology a decade ago. We find that there are several changes in focus in the research on pregnancy amongst young women. We conclude that, in general, there has been an improvement in the breadth of data available, mostly as a result of representative national and local surveys. A better teasing out of nuances around particular issues and a grappling with theoretical issues are also evident in recent research.
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Date Issued: 2010

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An in-service development programme for potential information services staff in the Rhodes Library

- Shepherd, Eileen

Authors: Shepherd, Eileen
Date: 2010
Language: English
Type: Article
Identifier: vital:6986 , http://hdl.handle.net/10962/d1011602
Description: This paper discusses the need for continuing professional development for librarians in academic libraries in general and at Rhodes University Library, South Africa in particular. It describes the planning, design, implementation and evaluation of a staff-development and training pilot programme for professional librarians at Rhodes Library. A group of 15 librarians, drawn from the library staff complement, participated in an 8-session training course developed by Information Services librarians. The course, which covered basic information-finding skills using a variety of research databases and offered an introduction to concepts in 21st century academic librarianship, was presented using course management software in a face-to-face environment and required homework exercises and the completion of a 2-hour final test. The results of the project demonstrated the urgent need for such development programmes for professional library staff. 80% of the participants completed the course. The final test results indicated below average database search skills and an inability to think laterally. An unexpected finding was a lack of IT competencies. Important lessons were learned with regard to course-construction, content and timing.
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Date Issued: 2010

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Analytical methods for the quantitative determination of oxytocin

- Chaibva, Faith A, Walker, Roderick B

Authors: Chaibva, Faith A , Walker, Roderick B
Date: 2010
Language: English
Type: Article
Identifier: vital:6353 , http://hdl.handle.net/10962/d1006037
Description: Oxytocin is a clinically important nonapeptide that is used for the induction and/or augmentation of labor and is normally administered as a slow intravenous infusion diluted with normal saline or Ringer’s lactate solution. Oxytocin is also indicated for use in the prevention and treatment of post partum hemorrhage and may be administered via either the intramuscular or intravenous routes in order to increase uterine tone and/or reduce bleeding. The analysis of oxytocin in different media has evolved over the past 30 years with the result that more sophisticated, selective and sensitive techniques are used for the determination of the compound. A variety of techniques have been applied to the determination of oxytocin in different matrices ranging from simple paper chromatography to hyphenated liquid chromatographic such as liquid chromatography coupled with mass-spectrometry. Additionally enzyme linked immuno-sorbent assays (ELISA) and radio immuno-assays (RIA) are used for the determination of low concentrations of oxytocin in biological matrices. This manuscript provides a systematic survey of the analytical methods that have been reported for isolation and quantitation of oxytocin in different matrices.
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Date Issued: 2010

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Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

- Pineda, Jesus, Porri, Francesca, Starczak, Victroria, Blythe, Jonathan

Authors: Pineda, Jesus , Porri, Francesca , Starczak, Victroria , Blythe, Jonathan
Date: 2010
Language: English
Type: Article
Identifier: vital:6869 , http://hdl.handle.net/10962/d1011501
Description: Marine broadcast spawners have two-phase life cycles, with pelagic larvae and benthic adults. Larval supply and settlement link these two phases and are crucial for the persistence of marine populations. Mainly due to the complexity in sampling larval supply accurately, many researchers use settlement as a proxy for larval supply. Larval supply is a constraining variable for settlement because, without larval supply, there is no settlement. Larval supply and settlement may not be well correlated, however, and settlement may not consistently estimate larval supply. This paper explores the argument that larval supply (i.e., larval abundance near settlement sites) may not relate linearly to settlement. We review the relationship between larval supply and settlement, from estimates and biases in larval supply sampling, to non-behavioral and behavioral components, including small-scale hydrodynamics, competency, gregarious behavior, intensification of settlement, lunar periodicity, predation and cannibalism. Physical and structural processes coupled with behavior, such as small-scale hydrodynamics and intensification of settlement, sometimes result in under- or overestimation of larval supply, where it is predicted from a linear relationship with settlement. Although settlement is a function of larval supply, spatial and temporal processes interact with larval behavior to distort the relationship between larval supply and settlement, and when these distortions act consistently in time and space, they cause biased estimates of larval supply from settlement data. Most of the examples discussed here suggest that behavior is the main source of the decoupling between larval supply and settlement because larval behavior affects the vertical distribution of larvae, the response of larvae to hydrodynamics, intensification of settlement, gregariousness, predation and cannibalism. Thus, larval behavior seems to limit broad generalizations on the regulation of settlement by larval supply. Knowledge of the relationship is further hindered by the lack of a well founded theoretical relationship between the two variables. The larval supply–settlement transition may have strong general consequences for population connectivity, since larval supply is a result of larval transport, and settlement constrains recruitment. Thus, measuring larval supply and settlement effectively allows more accurate quantification and understanding of larval transport, recruitment and population connectivity.
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Date Issued: 2010

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Change ringing in eastern Breconshire before the First World War, with especial reference to peal ringing at Glasbury

- Lewis, Colin A

Authors: Lewis, Colin A
Date: 2010
Language: English
Type: Article
Identifier: vital:6191 , http://hdl.handle.net/10962/d1012397 , http://www.brecknocksociety.co.uk/society.htm
Description: This paper discusses the development of change ringing in eastern Breconshire before the start of the First World War in 19 14, with special reference to peal ringing at Glasbury. Since the men who rang peals there, prior to that war, came from other towers as well as from Glasbury, brief mention is made of ringing at those towers and of members of those towers who rang peals at Glasbury. The towers discussed include Talgarth, Bronllys, Brecon, Llanelli (named Llanelly on Ordnance Survey maps) and Builth Wells, which were in the Diocese of St David's at that time, and centres in Herefordshire which were in the Diocese of Hereford. Attention is also paid to the role of the Hereford Diocesan Guild of Bellringers and of the peripatetic instructors employed by that Guild. An excellent introduction toringing is provided by R. J. Johnston's Bell-Ringing; the English Art of Change-Ringing (Viking, 1986), while the web-site of the Central Council of Church Bell Ringers (www.cccbr.org.uk) is also informative. , Colin Lewis was Professor of Geography at Rhodes University, Grahamstown, South Africa from 1989 until his retirement at the end of 2007. In 1990, with the strong support of the incumbent Vice-Chancellor, Dr Derek Henderson, he instigated the Certificate in Change Ringing (Church Bell Ringing) in the Rhodes University Department of Music and Musicology - the first such course to be offered in Africa. Since that date he has lectured in the basic theory, and taught the practice of change ringing. He was the Ringing Master of the Cathedral of St Michael and St George, Grahamstown, South Africa for 20 years.
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Date Issued: 2010

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Connectivity between marine reserves and exploited areas in the philopatric reef fish Chrysoblephus laticeps (Teleostei: Sparidae)

- Teske, Peter R, Forget, Fabian R G, Cowley, Paul D, von der Heyden, S, Beheregaray, Luciano B

Authors: Teske, Peter R , Forget, Fabian R G , Cowley, Paul D , von der Heyden, S , Beheregaray, Luciano B
Date: 2010
Language: English
Type: Article
Identifier: vital:6776 , http://hdl.handle.net/10962/d1008086
Description: "No-take‟ Marine Protected Areas (MPAs) are successful in protecting populations of many exploited fish species, but it is often unclear whether networks of MPAs are adequately spaced to ensure connectivity among reserves, and whether spillover occurs into adjacent exploited areas. Such issues are particularly important in species with low dispersal potential, many of which exist as genetically distinct regional stocks.The roman, Chrysoblephus laticeps, is an overexploited, commercially important fishery species endemic to South Africa. Post-recruits display resident behavior and occupy small home ranges, making C. laticeps a suitable model species to investigate connectivity in marine teleosts with potentially low dispersal ability. We used multilocus data from two types of highly variable genetic markers (mitochondrial DNA control region and microsatellites) to clarify patterns of genetic connectivity and population structure in C. laticeps using samples from two MPAs and several moderately or severely exploited regions. Despite using analytical tools that are sensitive to detect even subtle genetic structure, we found that this species exists as a single, well-mixed stock throughout its core distribution. This finding lends supports to the status of MPAs as an adequate tool for managing overexploited marine teleosts. Even though adult dispersal out of MPAs is limited, the fact that the large adults in these reserves produce exponentially more offspring than their smaller counterparts in exploited areas makes MPAs a rich source of recruits. We nonetheless caution against concluding that the lack of structure identified in C. laticeps and several other southern African teleosts can be considered to be representative of marine teleosts in this region in general. Many such species are represented in more than one marine biogeographic province and may be comprised of regionally-adapted stocks that need to be managed individually.
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Date Issued: 2010

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Control and integrability on SO (3)

- Remsing, C C

Authors: Remsing, C C
Date: 2010
Language: English
Type: Article
Identifier: vital:6787 , http://hdl.handle.net/10962/d1006938
Description: This paper considers control ane left- invariant systems evolving on matrix Lie groups. Such systems have signicant applications in a variety of elds. Any left-invariant optimal control problem (with quadratic cost) can be lifted, via the celebrated Maximum Principle, to a Hamiltonian system on the dual of the Lie algebra of the underlying state space G. The (minus) Lie-Poisson structure on the dual space g is used to describe the (normal) extremal curves. An interesting, and rather typical, single-input con- trol system on the rotation group SO (3) is investi- gated in some detail. The reduced Hamilton equa- tions associated with an extremal curve are derived in a simple and elegant manner. Finally, these equations are explicitly integrated by Jacobi elliptic functions.
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Date Issued: 2010

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Developing an ionospheric map for South Africa

- McKinnell, Lee-Anne, Okoh, D I, Cilliers, P J

Authors: McKinnell, Lee-Anne , Okoh, D I , Cilliers, P J
Date: 2010
Language: English
Type: Article
Identifier: vital:6822 , http://hdl.handle.net/10962/d1004438 , http://dx.doi.org/10.5194/angeo-28-1431-2010
Description: The development of a map of the ionosphere over South Africa is presented in this paper. The International Reference Ionosphere (IRI) model, South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were combined within their own limitations to develop an accurate representation of the South African ionosphere. The map is essentially in the form of a computer program that shows spatial and temporal representations of the South African ionosphere for a given set of geophysical parameters. A validation of the map is attempted using a comparison of Total Electron Content (TEC) values derived from the map, from the IRI model, and from Global Positioning System (GPS) measurements. It is foreseen that the final South African ionospheric map will be implemented as a Space Weather product of the African Space Weather Regional Warning Centre.
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Date Issued: 2010

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Development of a stability-indicating high performance liquid chromatographic method for the analysis of topiramate and dissolution rate testing in topiramate tablets

- Mohammadi, Ali, Rezanour, Nasrin, Ansari Dogaheh, M, Walker, Roderick B

Authors: Mohammadi, Ali , Rezanour, Nasrin , Ansari Dogaheh, M , Walker, Roderick B
Date: 2010
Language: English
Type: text , Article
Identifier: vital:6412 , http://hdl.handle.net/10962/d1006507
Description: A stability-indicating high performance liquid chromatographic(HPLC) method was developed and validated for the quantitation and dissolution determination of topiramate in tablet dosage forms. An isocratic separation was achieved using a phenyl column with a flow rate of 1 mL/min using UV detection at 264 nm. Topiramate has low UV absorbtivity and was subjected to derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl). The mobile phase for the separation consisted of acetonitrile: 50 mM sodium dihydrogen phosphate(NaH2PO4) containing 3 % v/v triethylamine (pH 2.8) in a 48:52 v/v ratio. Topiramate was subjected to oxidation, hydrolysis, photolysis and heat for the purposes of stress testing. Separation was achieved for the parent compound and all the degradation products in an overall analytical run time of approximately 15 min with the parent compound topiramate eluting at approximately 9.2 min. The method was linear over the concentration range of 1-100 μg/mL (r = 0.9996) with limits of quantitation and detection of 1 and 0.3 μg/mL, respectively.
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Date Issued: 2010

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Ecological impacts of small dams on South African rivers Part 2: Biotic response – abundance and composition of macroinvertebrate communities

- Mantel, Sukhmani K, Muller, Nikite W J, Hughes, Denis A

Authors: Mantel, Sukhmani K , Muller, Nikite W J , Hughes, Denis A
Date: 2010
Language: English
Type: text , Article
Identifier: vital:7095 , http://hdl.handle.net/10962/d1012437
Description: This paper investigates the cumulative impacts of small dams on invertebrate communities in 2 regions of South Africa – the Western Cape and Mpumalanga. Previous research found reduced discharge, increased total dissolved salts, and a decrease in average score per taxon (ASPT; collected using SASS4 methods) at sites with high density of small dams in their catchment. These changes in ASPT are investigated using the invertebrate abundance data available in the River Health Programme. Multivariate analyses found differences in invertebrate communities in rivers with high densities of small dams in their catchment in foothill-gravel streams (in both Western Cape and Mpumalanga) and in foothill-cobble streams (in Western Cape only). Opportunistic taxa that are tolerant of pollution, and capable of exploiting various habitats, and those that prefer slower currents increased in numbers, while other taxa that are sensitive to pollution and disturbance declined in numbers. Some regional differences were noted possibly reflecting climatic differences between the regions. Since the results of this study are correlative, it highlights the need for a systematic (by sites and seasons) and detailed (at species level) collection of data to verify the results of cumulative effects of small dams. This can further the development of a framework for small-dam construction and management that will limit their impact on river catchments.
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Date Issued: 2010

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Empirically modelled Pc3 activity based on solar wind parameters

- Heilig, B, Lotz, S I, Verő, J, Sutcliffe, P, Reda, J, Pajunpää, G, Raita, T

Authors: Heilig, B , Lotz, S I , Verő, J , Sutcliffe, P , Reda, J , Pajunpää, G , Raita, T
Date: 2010
Language: English
Type: text , Article
Identifier: vital:6814 , http://hdl.handle.net/10962/d1004324
Description: It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of ground-level Pc3–4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and ground-based magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during low-density events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves.
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Date Issued: 2010

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First oceanographic survey of the entire continental shelf adjacent to the northern Agulhas Current

- Lutjeharms, Johan R E, Durgadoo, Jonathan V, Schapira, Mathilde, McQuaid, Christopher D

Authors: Lutjeharms, Johan R E , Durgadoo, Jonathan V , Schapira, Mathilde , McQuaid, Christopher D
Date: 2010
Language: English
Type: Article
Identifier: vital:6867 , http://hdl.handle.net/10962/d1011499 , http://www.sajs.co.za/index.php/SAJS/article/view/410
Description: [from introduction] The Agulhas Current is by far the largest western boundary current of the southern hemisphere1 and carries about 70 × 106 m3/s of seawater past the eastern shores of South Africa.2 Being more than 2000 m deep, it follows the continental shelf edge quite closely. Its northern part, all the way downstream to Algoa Bay, has a very stable trajectory whereas the southern part meanders widely to either side of a mean geographical location,3 in the process creating shear edge eddies and attendant plumes of warm surface water over the shelf.4 However, the direct influence of the Agulhas Current on the waters and ecosystems of the adjacent shelf of South Africa remains largely unknown.
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Date Issued: 2010

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Framework for local government to implement integrated water resource management linked to water service delivery

- Haigh, Eliria H, Fox, Helen E, Davies-Coleman, Heather D

Authors: Haigh, Eliria H , Fox, Helen E , Davies-Coleman, Heather D
Date: 2010
Language: English
Type: text , Article
Identifier: vital:7097 , http://hdl.handle.net/10962/d1012440
Description: The Water Services Act (No. 8 of 1997) of South Africa states that water service delivery is the responsibility of local government as Water Services Authorities. The principal legal responsibility is to complete a Water Services Development Plan (WSDP) every 5 years with annual review. The WSDP encapsulates all the responsibilities and tasks required in water service delivery. However, it does not spell out local government’s role in water resource protection or its responsibilities as far as integrated water resource management is concerned. It is well known in South Africa that there is a challenging level of inadequate capacity in technical and administrative skills in local government to adequately fulfil water service delivery. This paper highlights the consequences of this incapacity for municipalities and their difficulties in fulfilling their responsibilities as service providers. A framework is provided within which improvements can be brought about, with guidance on how to engage in the practice of integrated water resource management (IWRM) in the context of the legal framework for water services. The additional tasks and changes required to practise IWRM are set in the context of the WSDP. The framework provides a guide for a municipality to first accomplish an adequate WSDP, and then to gradually implement IWRM. A discussion on the skills needed to accomplish, firstly, a comprehensive WSDP, and secondly, IWRM, is included.
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Date Issued: 2010

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In-service training for academic librarians : a pilot programme for staff

- Shepherd, Eileen

Authors: Shepherd, Eileen
Date: 2010
Language: English
Type: Article
Identifier: vital:6992 , http://hdl.handle.net/10962/d1012418 , http://www.emeraldinsight.com/doi/full/10.1108/02640471011065346
Description: This paper discusses the need for continuing professional development for librarians in academic libraries in general and at Rhodes University Library, South Africa in particular. It describes the planning, design, implementation and evaluation of a staff-development and training pilot programme for professional librarians at Rhodes Library. A group of 15 librarians, drawn from the library staff complement, participated in an 8-session training course developed by Information Services librarians. The course, which covered basic information-finding skills using a variety of research databases and offered an introduction to concepts in 21st century academic librarianship, was presented using course management software in a face-to-face environment and required homework exercises and the completion of a 2-hour final test. The results of the project demonstrated the urgent need for such development programmes for professional library staff. 80% of the participants completed the course. The final test results indicated below average database search skills and an inability to think laterally. An unexpected finding was a lack of IT competencies. Important lessons were learned with regard to course-construction, content and timing.
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Date Issued: 2010

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Mechanisms of habitat segregation between an invasive (Mytilus galloprovincialis) and an indigenous (Perna perna) mussel: adult growth and mortality

- Bownes, Sarah J, McQuaid, Christopher D

Authors: Bownes, Sarah J , McQuaid, Christopher D
Date: 2010
Language: English
Type: Article
Identifier: vital:6868 , http://hdl.handle.net/10962/d1011500
Description: The invasive mussel Mytilus galloprovincialis and the indigenous mussel Perna perna coexist intertidally on the south coast of South Africa through partial vertical habitat segregation: M. galloprovincialis dominates the upper shore and P. perna the lower shore. Recruitment patterns can explain the zonation of P. perna, but not the invasive species. We examined the role of post-recruitment interactions by measuring spatial and temporal differences in adult growth and mortality rates of the two species. Specifically, we tested the hypothesis that interspecific differences in growth and mortality reflect adult distribution patterns. The two study locations, Plettenberg Bay and Tsitsikamma, are 70 km apart with two sites (separated by 300–400 m) per location, each divided into three vertical zones. Growth was measured seasonally using different marking methods in 2001 and 2003. Cumulative adult mortality was measured through summer in 2003/2004. Both species generally grew more slowly upshore, but they showed different effects of season. For P. perna, growth was significantly reduced in winter in the low zone, but unaffected by season in the high zone. For M. galloprovincialis, growth was either unaffected by season or increased in winter, even in the high zone. Thus, growth of P. perna and M. galloprovincialis was reduced under cool winter and warm summer temperatures, respectively; and while growth was more similar between species in summer, M. galloprovincialis grew much faster than P. perna in winter. Mortality of P. perna increased upshore. For M. galloprovincialis, mortality was not zone-dependent and was significantly greater than for P. perna on the low-shore and (generally) across the shore in Tsitsikamma. Both species had higher growth and mortality rates in Plettenberg Bay than in Tsitsikamma. Thus, P. perna seems able to maintain spatial dominance on the low-shore and at certain sites because of higher mortality of M. galloprovincialis. We conclude that seasonality in growth of the two species reflects their biogeographic affinities and that coexistence is possible through pre-recruitment effects that limit the vertical distribution of P. perna and post-recruitment effects that limit M. galloprovincialis.
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Date Issued: 2010

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Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions

- Zagal, José H, Griveau, Sophie J, Silva, Francisco, Nyokong, Tebello, Bedioui, Fethi

Authors: Zagal, José H , Griveau, Sophie J , Silva, Francisco , Nyokong, Tebello , Bedioui, Fethi
Date: 2010
Language: English
Type: text , Article
Identifier: vital:7239 , http://hdl.handle.net/10962/d1019718
Description: Metallophthalocyanines confined on the surface of electrodes are active catalysts for a large variety of electrochemical reactions and electrode surfaces modified by these complexes can be obtained by simple adsorption on graphite and carbon. However, more stable electrodes can be achieved by coating their surfaces with electropolymerized layers of the complexes, that show similar activity than their monomer counterparts. In all cases, fundamental studies carried out with adsorbed layers of these complexes have shown that the redox potential is a very good reactivity index for predicting the catalytic activity of the complexes. Volcano-shaped correlations have been found between the electrocatalytic activity (as log I at constant E) versus the Co(II)/(I) formal potential (E°′) of Co-macrocyclics for the oxidation of several thiols, hydrazine and glucose. For the electroreduction of O2 only linear correlations between the electrocatalytic activity versus the M(III)/M(II) formal potential have been found using Cr, Mn, Fe and Co phthalocyanines but it is likely that these correlations are “incomplete volcano” correlations. The volcano correlations strongly suggest that E°′, the formal potential of the complex needs to be in a rather narrow potential window for achieving maximum activity, probably corresponding to surface coverages of an M-molecule adduct equal to 0.5 and to standard free energies of adsorption of the reacting molecule on the complex active site equal to zero. These results indicate that the catalytic activity of metallophthalocyanines for the oxidation of several molecules can be “tuned” by manipulating the E°′ formal potential, using proper groups on the macrocyclic ligand. This review emphasizes once more that metallophthalocyanines are extremely versatile materials with many applications in electrocatalysis, electroanalysis, just to mention a few, and they provide very good models for testing their catalytic activity for several reactions. Even though the earlier applications of these complexes were focused on providing active materials for electroreduction of O2, for making active cathodes for fuel cells, the main trend in the literature nowadays is to use these complexes for making active electrodes for electrochemical sensors. , Original publication is available at http://dx.doi.org/10.1016/j.ccr.2010.05.001
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Date Issued: 2010

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