Browsing Faculty of Natural Sciences by Title
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Tucker, William D. (ACM, 2004)[more][less]
Abstract: Connecting people across the Digital Divide is as much a social effort as a technological one. We are developing a community-centered approach to learn how interaction techniques can compensate for poor communication across the Digital Divide. Preliminary trials have yielded interfaces that deal with poor quality by adapting Instant Messaging techniques for multiple modalities, providing improved semi-synchronous communication. Lessons learned suggest new ways to design user interfaces specifically for the developing world. URI: http://hdl.handle.net/10566/591 Files in this item: 1
Tucker-CHI2004.pdf (81.56Kb) -
Raji, Ismaila; Mugabo, Pierre; Obikeze, Kenechukwu (BioMed Central, 2013)[more][less]
Abstract: Background: Tulbaghia violacea Harv. (Alliaceae) is used to treat various ailments, including hypertension (HTN) in South Africa. This study aims to evaluate the contributions of muscarinic receptors and changes in plasma aldosterone levels to its anti-hypertensive effect. Methods: In the acute experiments, methanol leaf extracts (MLE) of T. violacea (30–120 mg/kg), muscarine (0.16 -10 μg/kg), and atropine (0.02 - 20.48 mg/kg), and/or the vehicle (dimethylsulfoxide (DMSO) and normal saline (NS)) were respectively and randomly administered intravenously in a group of spontaneously hypertensive (SHR) weighing 300 to 350 g and aged less than 5 months. Subsequently, T. violacea (60 mg/kg) or muscarine (2.5 μg/kg) was infused into eight SHRs, 20 min after atropine (5.12 mg/kg) pre-treatment. In the chronic (21 days) experiments, the SHRs were randomly divided into three groups, and given the vehicle (0.2 ml/day of DMSO and NS), T. violacea (60 mg/kg/day) and captopril (10 mg/kg/day) respectively into the peritoneum, to investigate their effects on blood pressure (BP), heart rate (HR), and plasma aldosterone levels. Systolic BP and HR were measured using tail-cuff plethysmography during the intervention. BP and HR were measured via a pressure transducer connecting the femoral artery and the Powerlab at the end of each intervention in the acute experiment; and on day 22 in the chronic experiment. Results: In the acute experiments, T. violacea, muscarine, and atropine significantly (p < 0.05) reduced BP dose-dependently. T. violacea and muscarine produced dose-dependent decreases in HR, while the effect of atropine on HR varied. After atropine pre-treatment, dose-dependent increases in BP and HR were observed with T. violacea; while the BP and HR effects of muscarine were nullified. In the chronic experiments, the T. violaceatreated and captropril-treated groups had signicantly lower levels of aldosterone in plasma when compared to vehicle-treated group. Compared to the vehicle-treated group, significant reduction in BP was only seen in the captopril-treated group; while no difference in HR was observed among the groups. Conclusion: The results obtained in this study suggest that stimulation of the muscarinic receptors and a reduction in plasma aldosterone levels contribute to the anti-hypertesive effect of T. violacea. URI: http://hdl.handle.net/10566/600 Files in this item: 1
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Chetty, Marshini; Tucker, William D.; Blake, Edwin H. (SAICSIT, in assocation with ACM, 2004)[more][less]
Abstract: The digital divide between rural and urban areas within developing countries is vast. We investigate how to address this divide by introducing Information and Communication Technologies (ICTs) into remote rural areas. Our aim is to discover how to create locally relevant software applications with appropriate content for these areas. We use a user centred design approach and a modified software development lifecycle that is participatory, iterative and cyclical. This process is based on principles from Participatory Design and Action Research. This paper presents our initial experience of developing a telemedicine application for a rural village in the Eastern Cape Province of South Africa using this process. We present an overview of the methodology, describe the software application we have developed and cite several challenges we have faced. Finally we conclude that an inter-organisational and inter-disciplinary approach is needed to develop software for remote areas. URI: http://hdl.handle.net/10566/532 Files in this item: 1
ChettyTuckerBlakeICT2004.pdf (386.9Kb) -
Ah Tow, Lemese; Cowan, Donald A. (Springer Verlag, 2005)[more][less]
Abstract: Continental Antarctic is perceived as a largely pristine environment, although certain localized regions (e.g., parts of the Ross Dependency Dry Valleys) are relatively heavy impacted by human activities. The procedures imposed on Antarctic field parties for the handling and disposal of both solid and liquid wastes are designed to minimise eutrofication and contamination (particularly by human enteric bacteria). However, little consideration has been given to the significance, if any, of less obvious forms of microbial contamination resulting from periodic human activities in Antarctica. The predominant commensal microorganism on human skin, Staphylococcus epidermidis, could be detected by PCR, in Dry Valley mineral soils collected from heavily impacted areas, but could not be detected in Dry Valley mineral soils collected from low impact and pristine areas. Cell viability of this non-enteric human commensal is rapidly lost in Dry Valley mineral soil. However, S. epidermidis can persist for long periods in Dry Valley mineral soil as non-viable cells and/or naked DNA. URI: http://hdl.handle.net/10566/146 Files in this item: 1
AhTowDissemination2005.pdf (393.6Kb) -
Valisi, Andiswa; Maiyalagan, Thandavarayan; Khotseng, Lindiwe; Linkov, Vladimir; Pasupathi, Sivakumar (Springer, 2012)[more][less]
Abstract: This work studies the effect of heat treatment of carbon-dispersed platinum and platinum alloys on its methanol tolerance and catalytic activity as gas diffusion electrodes for oxygen reduction reaction (ORR) in acid medium. The catalyst powders were subjected to heat treatments at three different temperatures for a fixed period at controlled atmospheres. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrochemical characteristics and activity of the electro-catalysts were evaluated for ORR and methanol tolerance using cyclic voltammetry, in the form of gas diffusion electrodes. The optimum heat-treatment temperature is found to be strongly dependent on the individual catalyst. The maximum ORR activity and better methanol tolerance for the oxygen reduction reaction (ORR) was observed in Pt-Fe/C and Pt-Cu/C catalysts subjected to heat treatment at 350 °C.A trend of catalytic activity for oxygen reduction reaction (ORR) was obtained: Pt-Cu/C (350°C)>Pt-Fe/C (350°C) > Pt-Ni/C (350°C) > Pt-Co/C (250°C) > Pt/C (350°C), showing that Pt-Cu/C-type catalysts had a higher catalytic activity with reasonable methanol tolerance. URI: http://hdl.handle.net/10566/343 Files in this item: 1
ValisiHeatTreatment2012.pdf (10.92Mb) -
Mugabo, Pierre; Khan, Fatima; Burger, Andries (Open Access Science Research Publisher, 2012)[more][less]
Abstract: The use the aqueous decoction of Leonotis leonurus (L. leonurus) (Ll) R. Br. (Lamiaceae) in the treatment of hypertension (HPT) in traditional medicine is well documented. The effect of the aqueous extract of LI on the blood pressure (BP) and heart rate (HR) has been investigated in normotensive rats. The aim of this study was to investigate the effect of Ll aqueous extract on the in isolated perfused rat heart (IPRH). Hearts were excised from male Wistar albino rats weighing 250-350g, aged less than 6 months. They were perfused at constant flow using the modified Langendorff perfused model of the heart. Effects of adrenaline on the left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), heart rate (HR), cardiac work (CW) and coronary perfusion pressure (CPP) were compared to that of Ll. Adrenaline (1µM) significantly (p<0.05) increased the LVSP by 40.6%, the LVDP by 43.9%, the HR by 22.5% and the CW by 89.4%. Ll (1.0 mg/ml and 2.0 mg/ml respectively and significantly (p<0.01) increased the LVSP by 25.36 and 14.91, the LVDP by 29.40 and 14.88. Ll (1.0 mg/ml and 2.0 mg/ml) significantly produced a negative chronotropic effect. Both adrenaline and Ll aqueous extract did not have any significant effect on the LVEDP. Adrenaline resulted in positive inotropic and chronotropic effects. At low concentrations Ll produced a positive inotropic and a negative chronotropic effect. At the concentration of 2.0mg/ml Ll decreased all parameters to zero. At higher concentrations higher than 2.0mg/ml, Ll seemed to have toxic effects on the heart. URI: http://hdl.handle.net/10566/400 Files in this item: 1
MugaboLeonotisLeonurus2012.pdf (362.4Kb) -
Wilkinson, Dianne E.; Jaenicke, Thomas; Cowan, Donald A. (Kluwer Academic Publishers, 2002)[more][less]
Abstract: An efficient and simple method for constructing an environmental library using mechanically sheared DNA obtained directly from geothermal sediments is presented. The method is based on blunt-end modification of DNA fragments followed by 3' -adenylation using Vent DNA polymerase and Taq DNA polymerase, respectively. The prepared DNA fragments are then ligated into a TA cloning vector and used in the transformation of Escherichia coli. This method has been successfully applied to the cloning of ORFs derived from uncultivated prokaryotes present in geothermal sediment. URI: http://hdl.handle.net/10566/161 Files in this item: 1
WilkinsonEfficientMolecular2002.pdf (754.4Kb) -
Cowan, Donald A.; Ah Tow, Lemese (Annual Reviews, 2004)[more][less]
Abstract: The Antarctic continent harbors a range of specialized and sometimes highly localized microbial biotopes. These include biotopes associated with desiccated mineral soils, rich ornithogenic soils, glacial and sea ice, ice-covered lakes, translucent rocks, and geothermally heated soils. All are characterized by the imposition of one or more environmental extremes (including low temperature, wide temperature fluctuations, desiccation, hypersalinity, high periodic radiation fluxes, and low nutrient status). As our understanding of the true microbial diversity in these biotopes expands from the application of molecular phylogenetic methods, we come closer to the point where we can make an accurate assessment of the impacts of environmental change, human intervention, and other natural and unnatural impositions. At present, it is possible to make reasonable predictions about the physical effects of local climate change, but only general predictions on possible changes in microbial community structure. The consequences of some direct human impacts, such as physical disruption of microbial soil communities, are obvious if not yet quantitated. Others, such as the dissemination of nonindigenous microorganisms into indigenous microbial communities, are not yet understood. URI: http://hdl.handle.net/10566/145 Files in this item: 1
Endangered Antarctic Environments.docx (12.30Kb) -
Adesina, Ademola O.; Agbele, Kehinde K.; Februarie, Ronald; Abidoye, Ademola P.; Nyongesa, Henry O. (Academy of Science of South Africa, 2011)[more][less]
Abstract: The sensitivity of health-care information and its accessibility via the Internet and mobile technology systems is a cause for concern in these modern times. The privacy, integrity and confidentiality of a patient’s data are key factors to be considered in the transmission of medical information for use by authorised health-care personnel. Mobile communication has enabled medical consultancy, treatment, drug administration and the provision of laboratory results to take place outside the hospital. With the implementation of electronic patient records and the Internet and Intranets, medical information sharing amongst relevant health-care providers was made possible. But the vital issue in this method of information sharing is security: the patient’s privacy, as well as the confidentiality and integrity of the health-care information system, should not be compromised. We examine various ways of ensuring the security and privacy of a patient’s electronic medical information in order to ensure the integrity and confidentiality of the information. URI: http://hdl.handle.net/10566/279 Files in this item: 1
AdesinaSecurity2011.pdf (453.4Kb) -
Hersh, Marion A.; Tucker, William D. (Elsevier, 2005)[more][less]
Abstract: There are a number of pressures on researchers in academia and industry to behave unethically or compromise their ethical standards, for instance in order to obtain funding or publish frequently. In this paper a case study of Deaf telephony is used to discuss the pressures to unethical behaviour in terms of withholding information or misleading participants that can result from mono-disciplinary orthodoxies. The Deaf telephony system attempts to automate multiple aspects of relayed communication between Deaf and hearing users. The study is analysed in terms of consequentialist and deontological ethics, as well as multi-loop action learning. Discussion of a number of examples of bad practice is used to indicate both the compatibility of ethical behaviour and good scientific method and that ethical behaviour is a pre-requisite for obtaining meaningful results. URI: http://hdl.handle.net/10566/466 Files in this item: 1
HershTuckerUnethicalBehaviour2005.pdf (86.66Kb) -
Gibbons, Mark J.; Stuart, V (NISC and Taylor & Francis, 1994)[more][less]
Abstract: The feeding biology and the vertical migration of Sagitta friderici were examined over 24 h at two stations in the southern Benguela during spring (October) 1987. Together with studies conducted during summer (February 1991) and winter (May 1984), they serve to allow valuable generalizations of the biology and ecology of this abundant chaetognath. Populations migrate vertically and feed nocturnally, although the timing and the extent of migration vary between studies. S.friderici exhibits ontogenetic layering and the cross-shelf distribution of maturity stages differs, suggesting that it is able to take advantage of cross-shelf water movement in order to maintain populations in the nearshore waters of the West Coast. S.friderici prey almost exclusively on copepodg (cannibalism is rare), and there is a positive relationship between the lengths of predator and prey that is influenced by the size structure of the prey environment. This casts doubt on the validity of a chaetognath species-specific relationship between predator and prey size. S. friderici selects its prey on the basis of size, and not species. Daily ration is related linearly to prey density, so reflecting the low density of prey and providing support for theoretical predictions regarding ingestion rates under oceanic conditions. The impact of S. friderici predation on the copepod assemblage is generally less than 3% of the standing stock, although it could be much higher under conditions of low copepod biomass and poor secondary production. URI: http://hdl.handle.net/10566/306 Files in this item: 1
GibbonsFeeding1994.pdf (866.4Kb) -
Chitedze, Zimani; Tucker, William D. (Telkom, 2012)[more][less]
Abstract: This paper shows that mobility management protocols for infrastructure Internet may be used in a wireless mesh network environment. Mesh topology tends to be an unplanned graph and routes change dynamically and in this research Mobile IPv6 and Fast Handover for Hierarchical Mobile IPv6 are successfully implemented in a wireless mesh network environment. Horizontal handover simulation with ns2 involved Mobile IPv6 and Fast Handover for Hierarchical Mobile IPv6 applied to wireless mesh networks. Mobile IPv6 was used as a baseline to compare the performance of the two protocols. The results show that in mesh networks, Fast Handover for Hierarchical Mobile IPv6‘s performance is superior to Mobile IPv6. Fast Handover for Hierarchical Mobile IPv6 generates more throughput and less delay than Mobile IPv6. Furthermore, Fast Handover for Hierarchical Mobile IPv6 drops fewer data packets than Mobile IPv6. Even though MIPv6 and its extensions are for infrastructure networks, they can be used effectively in mesh networks. URI: http://hdl.handle.net/10566/424 Files in this item: 1
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Benjamin, Anita; Tucker, William D. (Telkom, 2003)[more][less]
Abstract: We have built a hybrid voice/text web–board that utilizes floor control for handling resources such as microphone and interface events. The aim of this research is to determine the most appropriate floor control mechanism for a hybrid communication tool that allows conventional text and audio users to communicate with one another using a common interface. Research on floor control mechanisms provides many implementations for arbitration that are application-specific. Myers proposes a categorical explanation of the most widely used mechanisms for providing floor control and discusses these different dimensions with respect to a project called Pebbles. We have chosen to model our arbitration policies along these categories. The application will be implemented as a Java applet and gives users a view of both the text and audio aspects of the exchange. To facilitate the multi-modality of the system we will provide media conversion, using the Nuance system’s Java API. Our hypothesis is that well–known multi-tasking arbitration protocols such as FCFS, Round Robin, Token – based, and many more can be adapted to create a conferencing floor control policy for the interface of a hybrid communication environment so as to facilitate free–flowing multi-modal conversation. Measurements to determine which floor control implementation provides the best arbitration in terms of user interaction with the system will be calculated using RPT, ORT and usage tests based on the Kirkpatrick Model. We hope to show that users benefit more from an implicit arbitration mechanism than they do from an explicit one. URI: http://hdl.handle.net/10566/538 Files in this item: 1
BenjaminTuckerHybridVoice2003.pdf (123.3Kb) -
Tucker, William D.; Keats, Derek (Telkom, 1998)[more][less]
Abstract: Grafting an ATM network onto an existing Ethernet network is a non-trivial exercise in network configuration. The process of mating ATM technology to an Ethernet network without tampering the underlying backbone and network configuration gives rise to a variety of networking issues including addressing, compatibility, security, efficiency, administrative effort, and scalability. Examples of actual situations serve to illustrate these issues. We have designed several scenarios to tackle the topological problems of an ATM graft. A dual IP approach works but suffers from a lack of scalability. We expect an edge routing solution, with subnetting, will be the most elegant and scalable. URI: http://hdl.handle.net/10566/448 Files in this item: 1
TuckerKeatsATM1998.pdf (612.2Kb) -
Julius, Elroy P.; Tucker, William D. (Telkom, 2005)[more][less]
Abstract: This paper presents an empirical solution for guaranteeing the delivery of synchronous and asynchronous messages within a semi-synchronous IPbased communication domain. The communication infrastructure that is needed between Deaf and hearing communities forms the application domain within which the research is situated. SoftBridging is a framework for multi-modal bridging as well as multi-user, multi-modal conversation sessions. An implementation of this concept called SoftBridge for Instant Messaging Bridging Application (SIMBA), is a communication platform that allows a hearing and Deaf person to communicate inside a single uniform space. The system makes use of various web services to do the actual data conversions such as voice to text and text to voice. Publish-subscribe systems are an emerging paradigm for building a range of distributed applications. The architecture of publishsubscribe systems make use of Message Oriented Middleware (MOM) to guarantee reliable delivery of messages within a communication domain. We have incorporated a publish-subscribe system within the overall architecture of SIMBA. We have thus modified the existing architecture of SIMBA to reliably transport semi-synchronous data over a synchronous established session. We have chosen to use the Session Initiation Protocol (SIP) for the establishment of a synchronous session between various users and SIMBA. The system is currently being used as a basis for developing a Deaf telephony application that guarantees the delivery of messages no matter the synchrony. URI: http://hdl.handle.net/10566/509 Files in this item: 1
JuliusTuckerSoftBridging2005.pdf (589.9Kb) -
Julius, Elroy P.; Tucker, William D. (Telkom, 2004)[more][less]
Abstract: This research aims to find an empirical solution for guaranteeing the delivery of synchronous and asynchronous messages within a semi-synchronous IP-based communication domain. The communication infrastructure that is needed between the Deaf and hearing communities forms the application domain within which the research is situated. SoftBridging is a framework for multi-modal bridging as well as multiuser, multi-modal conversation sessions. An implementation of this concept called SoftBridge, is a communication platform that allows a hearing and Deaf person to communicate inside a single uniform space. The system is based on an asynchronous transport mechanism that makes use of various web services to do the actual data conversions such as voice to text and text to voice. Publish-subscribe systems are an emerging paradigm for building a range of distributed applications. The architecture of publish-subscribe systems make use of Message Oriented Middleware (MOM) to guarantee reliable delivery of messages within a communication domain. We will choose one of these systems and incorporate it within the overall architecture of a SoftBridge system. We will modify the existing architecture of a SoftBridge system to reliably transport synchronous as well as asynchronous data over a synchronous established session. We will use the Session Initiation Protocol (SIP) to establish a synchronous session between various users and a SoftBridge system. The system will then be used as a basis for developing a Deaf telephony application that guarantees the delivery of messages no matter the synchrony. URI: http://hdl.handle.net/10566/463 Files in this item: 1
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Adesemowo, A. Kayode; Tucker, William D. (Telkom, 2003)[more][less]
Abstract: As mobile devices and networks become more data-centric, text messaging requires an extension of co-presence capabilities for better interactive discussion between input/output handicapped handheld users and their free form desktop counterparts. Given some degree of co-presence (online presence and awareness) in text-based Instant Messaging, we hope to increase this co-presence on a handheld with fast-track feedback (FF) mechanisms. These are user-defined gestures, such as emoticons, and prioritised messages. We are building a system that facilitates gesture input within an interactive text-based chat over a wireless network running Session Initiation Protocol (SIP). The chat bridges a robust desktop environment and a small number of handhelds. This work in progress looks into the SIP Instant Messaging and Presence Leveraging Extensions as a platform to provide fast-track interactive and co-presence feedback. The aim is to rubberise a hitherto plastic and limited instant messaging conversation. We shall measure co-presence levels between FF and standard IM environments in and without desktop and handhelds by engaging two groups of users in chats session. We expect to demonstrate that there exists high co-presence notion in open (work by Sun Research Awarenex Group and AT&T Hubbubme in similar domain were in closed systems) FF text messaging open environment as we would like to show that this higher presence brings a much more enhanced interactive discourse. The envisaged results are intended to extrapolate to online aware co-presence in the up and coming smart phones on 3G packet networks. URI: http://hdl.handle.net/10566/539 Files in this item: 1
AdesemowoTuckerMobileDevices2003.pdf (180.9Kb) -
Sjoling, Sara; Cowan, Donald A. (Springer Verlag, 2003)[more][less]
Abstract: The microbial diversity in maritime meltwater pond sediments from Bratina Island, Ross Sea, Antarctica was investigated by 16S rDNA-dependent molecular phylogeny. Investigations of the vertical distribution, phylogenetic composition, and spatial variability of Bacteria and Archaea in the sediment were carried out. Results revealed the presence of a highly diverse bacterial population and a significantly depthrelated composition. Assessment of 173 partial 16S rDNA clones analyzed by amplified rDNA restriction analysis (ARDRA) using tetrameric restriction enzymes (HinP1I 5'GVCGC3'and Msp I. 5'CVGG3', BioLabs) revealed 153 different bacterial OTUs (operational taxonomic units). However, only seven archaeal OTUs were detected, indicating low archaeal diversity. Based on ARDRA results, 30 bacterial clones were selected for sequencing and the sequenced clones fell into seven major lineages of the domain Bacteria; the a, c, and d subdivisions of Proteobacteria, the Cytophaga–Flavobacterium– Bacteroides, the Spirochaetaceae, and the Actinobacteria. All of the archaeal clones sequenced belonged to the group Crenarchaeota and phylogenetic analysis revealed close relationships with members of the deep-branching Group 1 Marine Archaea. URI: http://hdl.handle.net/10566/148 Files in this item: 1
Sjoling16SrDNA.pdf (543.4Kb) -
Sparks, Conrad, A.J.; Gibbons, Mark J. (Taylor & Francis and NISC, 2003)[more][less]
Abstract: A total of 242 zooplankton samples from the upper 100 m of the water column was collected discontinuously from March 1997 to January 1999 off the Orange River mouth on the west coast of southern Africa. Six species of hydromedusae were recovered at generally low abundance, of which Euphysa aurata, Leuckartia octona and Proboscidactyla menoni were dominant. E. aurata and L. octona showed evidence of seasonality in abundance. The low diversity of the fauna was remarkable and it is hypothesized that this might be attributable in part to sedimentation from the Orange River, and in part to locally weak circulation and the wide extent of the continental shelf. URI: http://hdl.handle.net/10566/380 Files in this item: 1
SparksHydromedusaeOrangeRiver2003.pdf (57.50Kb) -
Ngara, Rudo; Ndimba, Roya; Borch-Jensen, Jonas; Jensen, Ole Nørregaard; Ndimba, Bongani (Elsevier, 2012)[more][less]
Abstract: Sorghum bicolor, a drought tolerant cereal crop, is not only an important food source in the semi arid/arid regions but also a potential model for studying and gaining a better understanding of the molecular mechanisms of drought and salt stress tolerance in cereals. In this study, seeds of a sweet sorghumvariety, MN1618, were planted and grown on solid MS growth medium with or without 100mM NaCl. Heat shock protein expression immunoblotting assays demonstrated that this salt treatment induced stress within natural physiological parameters for our experimental material. 2D PAGE in combination with MS/MS proteomics techniques were used to separate, visualise and identify salinity stress responsive proteins in young sorghum leaves. Out of 281 Coomassie stainable spots, 118 showed statistically significant responses (p<0.05) to salt stress treatments. Of the 118 spots, 79 were selected for tandem mass spectrometric identification, owing to their good resolution and abundance levels, and of these, 55 were positively identified. Identified proteins were divided into six functional categories including both known and novel/putative stress responsive proteins. Molecular and physiological functions of some of our proteins of interest are currently under investigation via bioinformatic and molecular biology approaches. URI: http://hdl.handle.net/10566/543 Files in this item: 1
NdimbaSweetSorghum2012.pdf (765.8Kb)