Browsing Faculty of Natural Sciences by Title
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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) -
Fielding, Burtram C.; Mnabisa, Amanda; Gouws, Pieter A.; Morris, Thureyah (Termedia Publishing House, 2012)[more][less]
Abstract: Sub-therapeutic doses of antimicrobial agents are administered routinely to poultry to aid growth and to prevent disease, with prolonged exposure often resulting in bacterial resistance. Crossover of antibiotic resistant bacteria from poultry to humans poses a risk to human health. In this study, 17 chicken samples collected from a vendor operating in an informal settlement in the Cape Town Metropolitan area, South Africa were screened for antimicrobial-resistant Gram-negative bacilli using the Kirby Bauer disk diffusion assay. In total, six antibiotics were screened: ampicillin, ciprofloxacin, gentamicin, nalidixic acid, tetracycline and trimethoprim. Surprisingly, Klebsiella ozaenae was identified in 96 and K. rhinoscleromatis in 6 (n = 102) of the samples tested. Interestingly, ~40% of the isolated Klebsiella spp. showed multiple resistance to at least three of the six antibiotics tested. Klebsiella ozaenae and K. rhinoscleromatis cause clinical chronic rhinitis and are almost exclusively associated with people living in areas of poor hygiene. URI: http://hdl.handle.net/10566/743 Files in this item: 1
FieldingKlebsiellaSpecies2012.pdf (68.76Kb) -
Xianfeng, Sun; Jovanovic, Nebo Z.; Kapangaziwiri, Evison; Brendonck, Luc; Bugan, Richard Domain Hunter (Water Research Commission, 2013)[more][less]
Abstract: Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in western South Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and water level fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for the purpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previous RIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales, namely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approach in 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallow unconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfall and observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods, demonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long time series. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated to explore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showed that the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accurate representative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two cases can be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available in similar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissiv - ity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needs to be further explored. URI: http://hdl.handle.net/10566/815 Files in this item: 1
SunApplication2013.pdf (1.155Mb) -
Kanyerere, Thokozani; Levy, Jonathan; Xu, Yongxin; Saka, John (Water Research Commission, 2012)[more][less]
Abstract: In rural Africa, scientific evidence is often lacking to guide the scaling-up of groundwater as the safest source of potable water. An investigation was conducted in the Upper Limphasa Catchment in northern Malawi to determine the safety of groundwater sources and to explore factors influencing water quality. Water samples from 17 boreholes, 6 hand-dug wells and 90 households were analysed for selected parameters. Portable incubators, multi-parameter probe and colorimetric standard methods were used for field measurements, and standard methods were used for laboratory water analysis. Results were compared to specified guidelines of the World Health Organization and Malawi Bureau of Standards to establish the potability of water. Statistical results using non-parametric t-tests indicated that the wells were more contaminated with E. coli bacteria than boreholes (p=6.2x10-6), suggesting non-consideration of local hydrogeologic factors in groundwater development. Water from boreholes that tested negative for pathogens at source tested positive at some households (total coliform: p=0.0042 and E. coli p=7.8x10-7) suggesting the effect of handling practices. Water from wells that was not treated with chlorine showed higher levels of E. coli than treated water from the same sources, confirming the effectiveness of chlorine in reducing pathogenic bacteria in households’ stored drinking-water, reinforcing the scientific basis for scaling up chlorine as effective disinfectant. However, this study demonstrated that chlorine failed to effectively eliminate all pathogens in drinking water. As a case study in tropical rural environments in Africa, these findings on the suitability of using chlorine as disinfectant and on factors explaining groundwater contamination, though provisional, provide a scientific basis for assessing cost-effectiveness and sustainability of scaling-up the use of chlorine as a curative remedy and of systematically investigating local hydrogeologic factors in order to implement measures to protect groundwater quality in poverty-prone rural communities. URI: http://hdl.handle.net/10566/710 Files in this item: 1
KanyerereAssessment2012.pdf (2.600Mb) -
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) -
Xu, Yongxin (Springer Verlag, 2011)[more][less]
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Xu, Yongxin (Springer Verlag, 2012)[more][less]
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Xu, Yongxin; van Tonder, Gerrit J.; van Wyk, B.; van Wyk, E.; Aleobua, B. (Water Research Commission, 1997)[more][less]
Abstract: This paper shows that a borehole dilution experiment using common salt is a useful technique for better understanding of some hydrogeological features of a fractured aquifer. A sense of such tracer experiments was performed in the campus site aquifer, a hydrological experiment site of the Institute for Ground Studies at the University of the Orange Free State in Bloemfontein. It is demonstrated that the model for use in homogeneous aquifers may be adapted in fractured aquifers. Results have revealed valuable information on hydraulic parameters of the fracture system at different scales. Profiles of electrical conductivities monitored in several boreholes can be used to locate horizontal fracture zones in the aquifer. These results may provide an important guide to formulate realistic conceptual models for borehole protection zoning. The experiment can also serve as a reference to future experiments of this kind in Karoo aquifers which cover some 50% of the subcontinent of Southern Africa. URI: http://hdl.handle.net/10566/823 Files in this item: 1
XuBoreholeDilutionExperiment1997.pdf (483.3Kb) -
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, 2010)[more][less]
Abstract: This paper describes the design and evaluation of two browser-based video communication prototypes that support sign language communication between Deaf people. The research explores combinations of technologies, protocols and architectures with the hope to eventually provide a mobile video system that Deaf people would want to use enough to pay for. Technology products, and in particular mobile and web-based video communication systems, are designed for the majority of people in general. These are not necessarily suitable for Deaf people who have very different physiological and cultural needs. We focus on browser-based video transmission because end-users need not fiddle with application installation. Web-browsers are also common on mobile phones. This paper compares two prototypes built with Adobe Flex and the fifth version of the HyperText Markup Language, H.264 and H.263 video codecs, and PC and mobile phone implementations. The paper describes the motivation, related work, methods, prototype design and finally analyses results of user experiments conducted with Deaf users. URI: http://hdl.handle.net/10566/739 Files in this item: 1
WangTucker-SATNAC 2010.pdf (351.2Kb) -
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) -
Xu, Yongxin; van Tonder, Gerrit J. (Water Research Commission, 2002)[more][less]
Abstract: Delineation of capture zones for groundwater source protection is normally performed by using numerical codes which are based on the porous medium flow equation. However, boreholes are often sited in or along permeable dykes or single fracture zones through which aquifers are drained. It is very important to take into account dyke-influenced aquifers. This paper makes use of Linesink to simulate permeable dyke or fractured zones and utilises the pathline distribution to delineate the capture zones. Conditions when the influence of a fractured dyke can be considered negligible are also discussed through comparison with stagnation point in a uniform flow field. The approach may be sufficient to illustrate protection zoning requirements when dyke aquifers are considered. URI: http://hdl.handle.net/10566/811 Files in this item: 1
XuCaptureZone2002.pdf (333.9Kb) -
Muriithi, Grace; Gitari, Wilson; Petrik, Leslie; Ndungu, Patrick (Elsevier, 2011)[more][less]
Abstract: Coal combustion by-products such as fly ash (FA), brine and CO2 from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO2 has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO2 with FA/brine slurry can potentially provide a viable route for CO2 sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20–150 μm size fraction was observed to have the highest CO2 sequestration potential of 71.84 kg of CO2 per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO2 per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues. URI: http://hdl.handle.net/10566/757 Files in this item: 1
MuriithiFlyAsh2011.pdf (5.073Mb) -
Mugabo, Pierre; Obikeze, 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) -
Maneveldt, Gavin; Keats, Derek; Chamberlain, Yvonne (Elsevier, 2008)[more][less]
Abstract: Non-geniculate coralline red algae are common in all of the world’s oceans, where they often occupy close to 100% of the primary rocky substratum. The South African rocky subtidal and intertidal habitats in particular, are rich in diversity and abundance of non-geniculate coralline red algae. Despite their ubiquity, they are a poorly known and poorly understood group of marine organisms. Few scattered records of non-geniculate coralline red algae were published prior to 1993, but these should be treated with caution since many taxa have undergone major taxonomic review since then. Also, generic names such as Lithophyllum and Lithothamnion were loosely used by many authors for a host of different non-geniculate coralline algae. A series of taxonomic studies, based mainly on the Western Cape Province of South Africa, published particularly between 1993 and 2000, has significantly extended our knowledge of these algae from southern Africa. References to these latter papers and the older records are now gathered here and a list of the well delimited families (3), subfamilies (4), genera (17) and species (43) are presented. A catalogue with keys to the various taxonomic categories is also provided. A marked reduction in the number of real taxa has been found largely because many earlier recorded taxa have been reduced to synonymy, or have not been verified, or examined in a modern context and so their placement is considered dubious, particularly because the Corallinales have undergone major taxonomic revisions in recent years. URI: http://hdl.handle.net/10566/656 Files in this item: 1
Maneveldtcataloguewithkeys2008.pdf (182.2Kb) -
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)