Browsing Faculty of Natural Sciences by Title
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Brierley, Andrew S.; Axelson, Bjorn Erik; Buecher, Emmanuelle; Sparks, Conrad A.J.; Boyer, Helen; Gibbons, Mark J. (Inter-Research, 2001)[more][less]
Abstract: Multi-frequency acoustic data (18, 38 and 120 kHz) were collected in conjunction with pelagic trawl sampling for gelatinous macrozooplankton during a cruise to the Namibian Benguela in September 1999. Sampling focused specifically on the scyphozoan Chrysaora hysoscella and the hydrozoan Aequorea aequorea, both of which occur in large numbers, are probably of major ecological importance, and physically hamper pelagic fishing and diamond extraction activities. C. hysoscella was detected predominantly at an inshore station and A. aequorea was found in greatest abundance further offshore in deeper water. Echo-sounder observations were linked directly to net catches, and relationships between catch density (number of individuals m–3) and nautical area scattering coefficients (sA) at each frequency were determined for both species in order to estimate target strength (TS) using the comparison method. TS for C. hysoscella (mean umbrella diameter 26.8 cm) was –51.5 dB at 18 kHz, –46.6 dB at 38 kHz and –50.1 dB at 120 kHz; for A. aequorea (mean central umbrella diameter 7.4 cm) TS was –68.1 dB at 18 kHz, –66.3 dB at 38 kHz and –68.5 dB at 120 kHz. These TS values compared favourably with previously published estimates for related species. Jellyfish were caught at high numerical densities (maxima 3 C. hysoscella per 100 m3, 168 A. aequorea per 100 m3). These high densities, combined with the not unsubstantial TS at frequencies used for fisheries surveys, imply that jellyfish could potentially bias acoustic estimates of fish abundance. We suggest a simple multifrequency approach that could be used to discriminate between echoes from jellyfish and some commercially important pelagic fish in the northern Benguela ecosystem. URI: http://hdl.handle.net/10566/246 Files in this item: 1
BrierleyAcoustic 2001.pdf (799.2Kb) -
Acrolein in wine: Importance of 3-Hydroxypropionaldehyde and derivatives in production and detectionCowan, Donald A.; Crouch, Andrew; Bauer, Rolene (American Chemical Society, 2010)[more][less]
Abstract: This review highlights the importance of 3-HPA and derivates in the detection of acrolein in wine. The biochemical and environmental conditions leading to 3-HPA production are also reviewed. URI: http://hdl.handle.net/10566/168 Files in this item: 1
BauerAcrolein2010.pdf (123.6Kb) -
Ma, Zhen Yu; Tucker, William D. (Telkom, 2008)[more][less]
Abstract: Deaf people want to communicate remotely with sign language. Sign language requires sufficient video quality to be intelligible. Internet-based real-time video tools do not provide that quality. Our approach is to use asynchronous transmission to maintain video quality. Unfortunately, this entails a corresponding increase in latency. To reduce latency as much as possible, we sought to adapt a synchronous video codec to an asynchronous video application. First we compared several video codecs with subjective and objective metrics. This paper describes the process by which we chose x264 and integrated it into a Deaf telephony video application, and experimented to configure x264 optimally for the asynchronous environment. URI: http://hdl.handle.net/10566/511 Files in this item: 1
MaTuckerDeafVideoTelephony2008.pdf (348.1Kb) -
Cowan, Donald A.; Mamais, A.; Russell, Nick A.; Sheppard, Devon M. (Springer Verlag, 2002)[more][less]
Abstract: We have applied bioluminescent ATP detection methods to microbial enumeration in Antarctic Dry Valley mineral soils, and validated our ATP data by two independent methods. We have demonstrated that ATP measurement is a valid means of determining microbial biomass in such sites, and that the desiccated surface mineral soils of the Antarctic Dry Valleys contain cell numbers over four orders of magnitude higher than previously suggested URI: http://hdl.handle.net/10566/162 Files in this item: 1
CowanAntacticDryValleys2002.pdf (475.3Kb) -
Ma, Zhen Yu; Tucker, William D. (Telkom, 2007)[more][less]
Abstract: The South African Deaf community has very limited telephony options. They prefer to communicate in sign language, a visual medium. Realtime video over Internet Protocol is a promising option, but in reality, the quality is often not enough for the Deaf to be able to understand each other’s sign language. Furthermore, these applications were not design specifically for the Deaf. This paper introduces an asynchronous video chat system to provide better quality video at the expense of increased latency. It determined a codec/transmission protocol combination in the laboratory environment and tested it out with actual Deaf users. This paper will address the results based on comparison between different codecs, transmission protocol on asynchronous video communication for the Deaf. URI: http://hdl.handle.net/10566/486 Files in this item: 1
MaTuckerDeaf2007.pdf (875.1Kb) -
Yi, Long; Tucker, William D. (Telkom, 2009)[more][less]
Abstract: One way for Deaf people to communicate with hearing people over the telephone is to use a voice relay. The service is often provided with a human relay operator that relays text into voice, and vice versa, on behalf of the Deaf and hearing users. In developed countries, voice relay is frequently subsidised by governments or service providers. There is no such service in South Africa. We have built several automatic voice relay systems for a disadvantaged Deaf community in Cape Town. This paper describes how we augmented a general-purpose communication system for voice relay. Kiara is a fully open source Instant Messaging, voice and video over Internet Protocol communication system based on the Session Initiation Protocol. We integrated automatic speech recognition and text-to-speech technologies into Kiara to provide real-time automatic voice relay for relayed communication. As it stands, Kiara can also be used for standard voice and video relay with a human operator. URI: http://hdl.handle.net/10566/619 Files in this item: 1
YiTucker-SATNAC2009.pdf (257.6Kb) -
Bustard, Mark T.; Whiting, Samantha; Cowan, Donald A.; Wright, Phillip C. (Springer Verlag, 2002)[more][less]
Abstract: The aerobic biodegradation of high-concentration, to 24 g l –1 , 2-propanol (IPA) by a thermophilic isolate ST3, identified as Bacillus pallidus , was successfully carried out for the first time. This solvent-tolerant B. pallidus utilized IPA as the sole carbon source within a minimal salts medium. Cultivation was carried out in 100-ml shake flasks at 60°C and compared with cultivation within a 1-l stirred tank reactor (STR). Specific growth rate () was about 0.2 h–1 for both systems, with a maximum cell density of 2.4 x 10 8 cells ml–1 obtained with STR cultivation. During exponential growth and stationary phase, IPA biodegradation rates were found to be 0.14 and 0.02 g l –1h–1, respectively, in shake-flask experiments, whereas corresponding values of 0.09 and 0.018 g l –1h–1 were achievable in the STR. Generation of acetone, the major intermediate in aerobic IPA biodegradation, was also monitored as an indicator of microbial IPA utilization. Acetone levels reached a maximum of 2.2–2.3 g l–1 after 72 and 58 h for 100-ml and 1-l systems, respectively. Both IPA and acetone were completely removed from the medium following 160 and 175 h, respectively, during STR growth, although this was not demonstrated within shake-flask reactions. Growth of B. pallidus on acetone or IPA alone demonstrated that the maximum growth rate () obtainable was 0.247 h–1 at 4 g l–1 acetone and 0.202 h–1 at 8 g l–1 IPA within shake-flask cultivation. These results indicate the potential of the solvent-tolerant thermophile B. pallidus ST3 in the bioremediation of hot solvent-containing industrial waste streams. URI: http://hdl.handle.net/10566/154 Files in this item: 1
BustardBiodegradation2002.pdf (453.9Kb) -
Blake, Edwin H.; Tucker, William D. (CTIT, 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. We have incorporated the lessons learnt regarding Social Intelligence Design in an (abstract) device called the SoftBridge. The device allows information to flow from endpoints through adapters (getting converted if necessary), and out to destination endpoints. Field trials are underway with two communities in South Africa, disadvantaged deaf users and an isolated rural community. First lessons learned show that we have to design user interfaces that allow users to understand and cope with delay (latency) as a necessary consequence of our approach. URI: http://hdl.handle.net/10566/617 Files in this item: 1
BlakeTucker-SID2004.pdf (158.2Kb) -
Wang, Yuan Yuan; Tucker, William D. (Telkom, 2009)[more][less]
Abstract: This paper describes work in progress to to provide browser-based sign language communication for Deaf users. The paper introduces the communication requirements for a disadvantaged Deaf community in Cape Town, describes related work of generic open source browser-based video and video systems targeted specifically to Deaf users. We posit an experimental design to test if Adobe Flash can help provide an acceptable video system for Deaf users. We wish to learn if the transport and video quality of browser-based Adobe Flash video can provide an effective platform for sign language communication. URI: http://hdl.handle.net/10566/622 Files in this item: 1
WangTucker-SATNAC2009.pdf (141.2Kb) -
Zulu, Docas Dudu; Tucker, William D. (Telkom, 2010)[more][less]
Abstract: This paper describes work in progress on call capacity optimization for voice over Internet Protocol on wireless mesh networks. In a developing country such as South Africa, evidence has shown that rural inhabitants find it difficult to afford the voice services offered by cellular networks. Voice over Internet Protocol is known for its affordability relative to cellular voice services, therefore deploying such services for rural communities will not only benefit rural inhabitants but also offer economic advantages to service providers. We are interested in the provision of voice services with rural wireless mesh networks. Unfortunately voice on mesh networks can experience packet loss and delays that cause reduction in voice quality. Transmission of small voice packets over wireless mesh networks imposes high overhead that leads to a tremendous decrease in call capacity. Therefore, we aim to study the performance of voice over 802.11 wireless mesh networks and evaluate packet aggregation mechanisms that merge small voice packets into a single large packet, in order to preserve voice quality with more calls. We will implement and evaluate packet aggregations mechanisms on a 'mesh potato' network with iterative cycles of laboratory experiments using a network simulator to collect data for performance evaluation. URI: http://hdl.handle.net/10566/618 Files in this item: 1
ZuluTucker-SATNAC2010.pdf (138.4Kb) -
Mugabo, Pierre; Obikezea, Kenechukwu; Njagi, Angela; Burger, Andries; Dietrich, Danielle; Green, Ivan (Open Access Science Research Publisher, 2012)[more][less]
Abstract: Crinum macowanii has been used extensively in traditional medicines for treatment of various illnesses such as oedema and ‘heart disease’. Previous studies of the crude bulb extracts on Langendorff perfused isolated rat hearts indicated a positive inotropic effect. The aim of this study was to isolate and characterize compound(s) from C. macowanii with cardiovascular effects similar to that observed with the crude extracts of the plant. The methanol extract of dried bulbs was extracted for alkaloids, and structural elucidation of the isolated alkaloid identified it as hippadine. The cardiovascular effects of hippadine was evaluated in vitro in isolated perfused rat hearts using the “double sided” working heart system. Perfusion with 0.5 μg/ml and 5.0 μg/ml hippadine in Krebs-Hanseleit buffer led to significant decreases in coronary flow, aortic output, cardiac output, systolic pressure, and heart rate, accompanied by increases in diastolic pressure. Hippadine exhibited a negative chronotropic and inotropic effect on the isolated rat heart and is responsible either partly or fully for the cardiovascular effects of C. macowanii. URI: http://hdl.handle.net/10566/401 Files in this item: 1
MugaboHippadine2012.pdf (63.78Kb) -
Gershwin, Lisa-Ann; Gibbons, Mark J. (Magnolia Press, 2009)[more][less]
Abstract: A common and conspicuous member of the medusan fauna of South Africa has been the subject of repeated taxonomic confusion. After having been mistakenly identified by earlier workers as either Carybdea alata or Tamoya haplonema, this large and colourful carybdeid is described herein as Carybdea branchi, sp. nov. It is distinguished from its congeners on numerous characters: body to about 8cm in life, densely scattered with nematocyst warts over the whole body and abaxial keels of the pedalia; a bulge or lateral thorn on the pedalial canal bend; with 2 dendritic velarial canals per octant, highly diverticulated; with a long manubrium; with greatly bushy epaulette-like phacellae, comprising 20 or more roots tightly clustered; with well developed mesenteries; and with conspicuous brownish pigmented areas over the proximal and distal regions of the pedalia and over the phacellae. A comparative table of the primary diagnostic characters of species in the genus Carybdea is given. URI: http://hdl.handle.net/10566/369 Files in this item: 1
GershwinCarybdeida2009.pdf (1.003Mb) -
Mutemwa, Muyowa; Tucker, William D.; Norman, Michael (Telkom, 2009)[more][less]
Abstract: This paper discusses how an Instant Messaging application on a computer can use Bluetooth in order to provide vibration notification on a mobile phone. The initial motivation was to aid Deaf1 office workers to know when events happened on the computer on their desks. Deaf people with access to modern technology have become accustomed to using Instant Messaging, email and video conferencing. However, most of these applications are designed for hearing users and often use audible notification. Cell phone vibration offers a way to convey similar notifications because many Deaf users have a cell phone. The use of SMS has also become widespread among Deaf users because they cannot hear or speak, even though they might be somewhat text illiterate. Vibration notification in addition to aural notification is common on most cell phones and Deaf users can use the former. This paper describes a Bluetooth notification system to notify a Deaf user with vibration on a cell phone whenever a new Instant Message is received on a given computer. A design goal was to provide an application programming interface to the notification system so that it can be used with any form of Web 2.0 desktop communication tool. URI: http://hdl.handle.net/10566/530 Files in this item: 1
MutemwaNormanTuckerBluetooth2009.pdf (343.6Kb) -
Musingarimi, Wicleffe; Tuffin, I. Marla; Cowan, Donald A. (Academy of Science of South Africa, 2010)[more][less]
Abstract: An arsenic resistant Bacillus sp. UWC was isolated from fly ash acid mine drainage (FA-AMD) neutralised solids. A genomic library was prepared and screened in an arsenic sensitive mutant Escherichia coli strain for the presence of arsenic resistance (ars) genes. Sequence analysis of a clone conferring resistance to both sodium arsenite and sodium arsenate revealed homologues to the arsR (regulatory repressor), arsB (membrane located arsenite pump), arsC (arsenate reductase), arsD (second regulatory repressor and a metallochaperone) and arsA (ATPase) genes from known arsenic resistance operons. The Bacillus sp. UWC arsRBCDA genes were shown to be arranged in an unusual manner with the arsDA genes immediately downstream of arsC. URI: http://hdl.handle.net/10566/160 Files in this item: 1
MusingarimiCharacterisation2010.PDF (566.6Kb) -
Sivakumar, Pasupathi; Maiyalagan, Thandavarayan (Trans Tech Publications, 2010)[more][less]
Abstract: Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA. URI: http://hdl.handle.net/10566/166 Files in this item: 1
MaiyalaganPasupathi2010.pdf (1.330Mb) -
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)