Browsing Faculty of Natural Sciences by Title
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Jeffries, Michael; Tucker, William D. (Telkom, 2000)[more][less]
Abstract: Current VoIP signaling protocols are interoperable with the PSTN SS7 via H.323-to-SS7 or SIP-to-SS7 gateways. As we move toward the Next Generation Network, the PSTN falls away and we work toward carrier-grade VoIP interoperability between H.323, SIP, and other future VoIP signaling protocols. This paper present a Work in Progress to design and implement a solution based on the Internet Protocol itself. URI: http://hdl.handle.net/10566/425 Files in this item: 1
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Vuza, Xolisa; Tucker, William D. (Telkom, 2004)[more][less]
Abstract: We intend adding video messaging and conferencing to Multimodal Telemedicine Intecommunicator (MuTI), a previous system that has already been in place in the target environment. This is to allow a semi-synchronous communication to occur over the Internet Protocol. Videoconferencing can be used to communicate synchronously and video messaging in a store and forward fashion can be used to communicate asynchronously. MuTI supports store and forward of still images, voicemail and text. The system also supports real time communication by means of audio. The aim of this research is to learn how to bridge the digital divide by building applications that are useful and relevant to the users we build for. We are developing this application together with the users of the application in an iterative fashion where we build the prototypes and show the users at each cycle. The feedback that we get from the users plays an important role in building a prototype for the next cycle. The software will be instrumented to provide statistics about the system usage. We are also going to get data from the users by using questionnaires and compare this data with the statistics about software usage to see how much the system has been used and which features in the system do the users like. We are using a rural South African context in conducting this research. We hope to bring about guidelines and recommendations on how to develop applications to bridge the digital divide in a developing world context. URI: http://hdl.handle.net/10566/435 Files in this item: 1
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Yi, Long; Connan, James (Association for Computing Machinery, 2007)[more][less]
Abstract: Self-tuning has been an elusive goal for operating systems and is becoming a pressing issue for modern operating systems. Well-trained system administrators are able to tune an operating system to achieve better system performance for a specific system class. Unfortunately, the system class can change when the running applications change. Our model for self-tuning operating system is based on a monitor-classify-adjust loop. The idea of this loop is to continuously monitor certain performance metrics, and whenever these change, the system determines the new system class and dynamically adjusts tuning parameters for this new class. This paper describes KernTune, a prototype tool that identifies the system class and improves system performance automatically. A key aspect of KernTune is the notion of Artificial Intelligence (AI) oriented performance tuning. It uses a support vector machine (SVM) to identify the system class, and tunes the operating system for that specific system class. This paper presents design and implementation details for KernTune. It shows how KernTune identifies a system class and tunes the operating system for improved performance. URI: http://hdl.handle.net/10566/53 Files in this item: 1
Yi_KernTune(2007).pdf (262.3Kb) -
Yi, Long; Tucker, William D. (Telkom, 2008)[more][less]
Abstract: This paper describes Kiara, an open source SIPbased communication system that provides the building blocks to enable Deaf relay services. We have implemented a prototype that provides real-time text, voice and video to a variety of end user devices over a variety of networks. The work-in-progress concerns the addition of relay services for the Deaf. URI: http://hdl.handle.net/10566/523 Files in this item: 1
YiTuckerKiara2008.pdf (173.6Kb) -
Babajide, Omotola; Leslie, Petrik; Amigun, Bamikole; Ameer, Farouk (MDPI, 2009)[more][less]
Abstract: Biodiesel has attracted increasing interest and has proved to be a good substitute for fossil-based fuels due to its environmental advantages and availability from renewable resources such as refined and waste vegetable oils. Several studies have shown that biodiesel is a better fuel than the fossil-derived diesel in terms of engine performance, emissions reduction, lubricity and environmental benefits. The increasing popularity of biodiesel has generated great demand for its commercial production methods, which in turn calls for the development of technically and economically sound process technologies. This paper explores the applicability of ultrasound in the optimization of low-cost feedstock – in this case waste cooking oil – in the transesterification conversion to biodiesel. It was found that the conversion efficiency of the waste oil using ultrasound was higher than with the mechanical stirring method. The optimized variables of 6:1 methanol/oil ratio at a reaction temperature of 30 °C and a reaction time of 30 min and 0.75% KOH (wt/wt) catalyst concentration was obtained for the transesterification of the waste oil via the use of ultrasound. URI: http://hdl.handle.net/10566/573 Files in this item: 1
BabajideBiodiesel2009.pdf (248.8Kb) -
Cowan, Donald A.; Stafford, William (ASM Press, 2007)[more][less]
URI: http://hdl.handle.net/10566/126 Files in this item: 1
CowanMetagenomicMethods2007.pdf (432.7Kb) -
Cowan, Donald A.; Arslanoglu, A.; Burton, Stephanie; Cameron, Rory A.; Baker, Gillian; Smith, Jacques J.; Meyer, Quinton (Portland Press, 2004)[more][less]
Abstract: With the rapid development of powerful protein evolution and enzyme-screening technologies, there is a growing belief that optimum conditions for biotransformation processes can be established without the constraints of the properties of the biocatalyst. These technologies can then be applied to find the ‘ideal biocatalyst’ for the process. In identifying the ideal biocatalyst, the processes of gene discovery and enzyme evolution play major roles. However, in order to expand the pool genes for in vitro evolution, new technologies, which circumvent the limitations of microbial culturability, must be applied. These technologies, which currently include metagenomic library screening, gene-specific amplification methods and even full metagenomic sequencing, provide access to a volume of ‘sequence space’ that is not addressed by traditional screening. URI: http://hdl.handle.net/10566/142 Files in this item: 1
CowanMetagenomicsGeneDiscovery2004.pdf (575.0Kb) -
Neethling, Simone; Channing, Alan; Gershwin, Lisa-Ann; Gibbons, Mark J. (Cambridge University Press, 2011)[more][less]
Abstract: A new record of Crambionella stuhlmanni is reported from the east coast of South Africa. The material is described using quantitative morphological data, and mitochondrial (CO1) and nuclear (ITS-1) sequence data. The species can be diagnosed by a combination of morphological features including the presence of conical projections on velar lappets, the absence of orbicular appendages among mouthlets and the short length of the terminal club on the oral arm. Mitochondrial sequence data unambiguously delineate C. stuhlmanni as a separate species from C. orsini, and phylogenetic analyses support its placement within the monophyletic genus, Crambionella URI: http://hdl.handle.net/10566/249 Files in this item: 1
Neethling et al 2011.pdf (481.9Kb) -
Mugabo, Pierre; Els, Ilse; Smith, Johan; Rabie, Helena; Smith, Peter; Mirochnick, Mark; Steyn, Wilhelm; Hall, David; Madsen, Richard; Cotton, Mark F (Health & Medical Publishing Group, 2011)[more][less]
Abstract: Background. No pharmacokinetic data exist for premature infants receiving single-dose nevirapine (sd NVP) for prevention of mother-to-child transmission (MTCT) of HIV. Aim. To describe NVP decay pharmacokinetics in two groups of premature infants - those whose mothers either received or did not receive NVP during labour. Methods. Infants less than 37 weeks' gestation were prospectively enrolled. Mothers received sd NVP during labour if time allowed. Infants received sd NVP and zidovudine. Blood was collected on specified days after birth and NVP concentrations were determined by liquid chromatography-mass spectrometry. Results. Data were obtained from 81 infants, 58 born to mothers who received sd NVP during labour (group I) and 23 to mothers who did not receive NVP (group II). Of the infants 29.6% were small for gestational age (SGA). Median (range) maximum concentration (Cmax), time to reach maximum concentration (Tmax), area under the plasma concentration-time curve (AUC) and halflife (T) were 1 438 (350-3 832) ng/ml, 25h50 (9h40-83h45), 174 134 (22 308-546 408) ng×h/ml and 59.0 (15.4-532.6) hours for group I and 1 535 (635-4 218) ng/ml, 17h35 (7h40-29h), 168 576 (20 268-476 712) ng×h/ml and 69.0 (22.12-172.3) hours for group II. For group II, the median (range) volume of distribution (Vd) and body clearance (Cl) were 1 702.6 (623.7-6 189.8) ml and 34.9 (6.2-163.8) ml/h. The AUC was higher (p=0.006) and Cl lower (p<0.0001) in SGA infants. Plasma concentrations exceeding 100 ng/ml were achieved over 8 days in 78% infants in group I and 70.0% in group II. The MTCT rate was 4.8%. Conclusion. Women in preterm labour often deliver with little advance warning. Our study suggests that NVP dosing of preterm infants as soon as possible after birth without maternal intrapartum dosing may be as effective as combined maternal and infant dosing. URI: http://hdl.handle.net/10566/405 Files in this item: 1
MugaboPrematureMTCT.pdf (503.0Kb) -
Buecher, Emmanuelle; Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 2003)[more][less]
Abstract: Diel vertical migration (DVM) of six common species of hydromedusae was investigated during two drogue studies conducted in St Helena Bay on the west coast of South Africa in February 1995. Clytia spp., Obelia spp. and Bougainvillia macloviana, were largely confined to surface waters and did not appear to display any DVM. By contrast, Leuckartiara octona and Euphysa aurata displayed clear DVM and, like Proboscidactyla menoni, were found at greater depths than the other species. The depth distribution and amplitude of migration varied between surveys for most species, so definitive interpretations of patterns could not be made. URI: http://hdl.handle.net/10566/377 Files in this item: 1
BuecherDielVerticalMigration2003.pdf (121.3Kb) -
Clarke, Dylan T.; Paterson, Gordon L. J.; Florence, Wayne K.; Gibbons, Mark J. (Iziko Museums of Cape Town, 2010)[more][less]
Abstract: A new species of Magelonidae, Magelona debeerei sp. nov., is described and illustrated from grab-samples collected at <100moff the southwest coast of Africa. Magelona debeerei sp. nov. has previously been identified from the region as M. papillicornis (Müller, 1858) by Day (1955, 1961, 1967) but differs from M. papillicornis sensu stricto by possessing dorsal medial lobes on chaetigers 4–8 and lateral pouches (Σ configuration) between chaetigers 10 and 11. Three species of Magelona have now been recorded from southern Africa (M. capensis Day, 1961, M. cincta Ehlers, 1908 and M. debeerei sp. nov.), and a key to Magelona from this region is provided. URI: http://hdl.handle.net/10566/245 Files in this item: 1
Clarke et al 2010.pdf (455.5Kb) -
Ah Tow, Lemese; Cowan, Donald A. (Society for General Microbiology, 2003)[more][less]
Abstract: Our results allow us to conclude that there appears to be significant conservation between the tuf genes of Planococcus, Planomicrobium and Staphylococcus spp., and that although the primer set TstaG422/TStag765 has been shown to possess high specificity, its use for the definitive identification of Staphylococcus spp. must be treated with some caution. Description: Published as a "Microbiology Comment": this provides a platform for readers of Microbiology to communicate their personal observations and opinions in a more informal way than through the submission of papers. URI: http://hdl.handle.net/10566/143 Files in this item: 1
AhTow&Cowan2003.PDF (251.5Kb) -
Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 1995)[more][less]
Abstract: A total of 24 species of euphausiid was collected during a survey along the South African south coast during January 1992. Communities over the Agulhas Bank were of low diversity and abundance and were dominated by Nycliphanes capensis. Those at the shelf-edge were of high diversity and abundance and were dominated by Euphausia recurI'll and Thysalloessa gregaria. Such high diversity may be maintained by vertical scgregation at night. Few species displayed obvious diel vertical migration, although N. capen sis may be able to maintain itself on the shelf by means of this behaviour. E. recurl'Cl appeared to feed on phytoplankton throughout the water column at night, reflecting the distribution of food. URI: http://hdl.handle.net/10566/374 Files in this item: 1
GibbonsEuphausiid1995.pdf (584.2Kb) -
Gibbons, Mark J.; Buecher, Emmanuelle; Thibault-Botha, Delphine (NISC (Pty) Ltd and Taylor& Francis, 2003)[more][less]
Abstract: The vertical distribution, abundance and size composition of a population of Pleurobrachia pileus was studied during a six-day drogue study conducted off the west coast of South Africa in February 1995. The population was centred in deep water, possibly because of the presence of a potential predator, Beroe sp., at shallower depths. The population of P. pileus failed to display clear patterns of migration, although nocturnal recruitment from deeper water resulted in a deepening of the depth of occupation then. The population was dominated by individuals <4 mm polar diameter, and large animals were confined to the upper water layers. These results are discussed with reference to possible spawning activities. Using published equations relating size to clearance rates, it was estimated that the population could remove up to 27% of integrated mesozooplankton standing stocks, and in excess of 100% (293%) at some depths. URI: http://hdl.handle.net/10566/373 Files in this item: 1
GibbonsPleurobrachia2003.pdf (270.1Kb) -
Barange, M; Macpherson, E; Gibbons, Mark J. (NISC and Taylor & Francis, 1994)[more][less]
Abstract: Information on vertical and horizontal distribution patterns, abundance and morphology of the decapod Pasiphaea semispinosa in the Benguela upwelling system is presented. P. semispinosa is the dominant pelagic decapod in the system, occurring between 19 and 32°S along the mid and inner shelf in concentrations of 10-100•m-2• Although it is more abundant during abated than during active upwelling in the northern Benguela, it would appear to be equally abundant during both upwelling scenarios in the southern Benguela. In the southern Benguela, reproductive females are present during winter and juveniles dominate during active upwelling, but juveniles appear to be more common during abated upwelling in the northern Benguela. The estimates of abundance of P. semispinosa presented in this study are subject to sampling biases attributable to their vertical migratory behaviour and net avoidance capabilities. URI: http://hdl.handle.net/10566/307 Files in this item: 1
GibbonsPasiphaea1994.pdf (692.3Kb) -
Tucker, William D.; Blake, Edwin H.; Marsden, Gary (Telkom, 2004)[more][less]
Abstract: We looked for and found two situations within the South African Digital Divide where constant and severe macro-scale latencies would most likely interfere with the usage of Information and Communication Technology (ICT) solutions. We describe how these systems tend to exhibit both social and technical macro-scale delays. Our experience building bridges for these communities has inspired several innovations with respect to the design, development and measurement of IP communications systems. The main contribution is the Open User Interconnect (OUI) stack, a communications system model that explicitly includes the user in relation to the underlying network. The OUI stack is orthogonal to the Open System Interconnect stack. There are two outcomes from including the user in the model. First, the OUI approach necessitates the adoption of usercentred methods such as Participatory Design and in the case of the South African Digital Divide, the adoption of Action Research principles. The second outcome is a user-centred measurement notion, called Quality of Communication (QoC), that is a macro-scale spin on Quality of Service. QoC explicitly includes the measurement of user behaviour in addition to system metrics. In conclusion, we suggest that these Digital Divide-inspired contributions may be applicable to IP communications system design, development and measurement in general. The paper concludes with a brief dissertation completion plan. URI: http://hdl.handle.net/10566/485 Files in this item: 1
TuckerDigitalDivide2004.pdf (131.4Kb) -
Baker, Gillian; Ah Tow, Lemese; Cowan, Donald A. (Elsevier, 2003)[more][less]
Abstract: PCR-based technologies are widely employed for the detection of specific microorganisms, and may be applied to the identification of non-indigenous microorganisms in ‘pristine’ environments. For ‘pristine’ environments such as those found on the Antarctic continent, the application of these methods to the assessment of environmental contamination from human activities must be treated with caution. Issues such as the possibility of non-human dispersal of organisms, stability and survival of non-indigenous organisms in vivo, the sensitivity, reproducibility and specificity of the PCR process (and particularly primer design) and the sampling regime employed must all be considered in detail. We conclude that despite these limitations, PCR and related technologies offer enormous scope for assessment of both natural and non-indigenous microbial distributions. URI: http://hdl.handle.net/10566/149 Files in this item: 1
BakerPCRdetection2003.pdf (391.8Kb) -
Naidoo, Vaughn; Tucker, William D. (Telkom, 2001)[more][less]
Abstract: Next Generation Networks use policy-based network management and QoS protocols to provide voice services on IP networks. Large numbers of older equipment still push IP packets. We present several solutions that include legacy equipment into a PBNM and QoS system. A static design uses traffic shaping at the legacy edge. A dynamic solution uses a Quasi-PEP implemented over RSVP and COPS. Preliminary test results are presented for the static solution. Collected data shows that the solution decreases packet loss on the legacy side. URI: http://hdl.handle.net/10566/519 Files in this item: 1
NaidooTuckerNextGenNetworks2001.pdf (59.43Kb) -
Glaser, Meryl; Tucker, William D.; Mashao, Daniel (Telkom, 2004)[more][less]
Abstract: Following on the development of several prototypes, we have built a semi-automated Deaf Telephony prototype on the SoftBridge platform. This prototype relays text and speech between Deaf users on the Internet and hearing users on the telephone system. Previous work with a pilot trial in the laboratory revealed several opportunities for enhancement. We added a Wizard of Oz (WoOz) to replace the poorly performing automatic speech recognition functionality as well as H.323 breakout, more extensive logging and advanced call initiation functionality. In order to trial the current prototype, we initiated an Information and Communication Technology (ICT) training programme with the Deaf Community of Cape Town. Twenty Deaf users participated in the training. In addition to the training, much baseline user data was collected to give an indication of how Deaf users communicate with hearing users as well as how familiar they are with ICT devices and services. The work for the rest of this year requires us to recruit and train a WoOz operator. Subsequent trials will essentially consist of monthly cycles of prototype introduction, training, automated metric and log collection, user feedback and then feature enhancement. Linguistic analyses of the text output of the Deaf users will be analyzed. We hope to refine the SoftBridge prototype to fit the needs of the Deaf and hearing users, from both technical and social viewpoints. We expect that these iterative cycles will continue for some time and will teach us many lessons regarding multi-modal semi-synchronous IP-based communications systems. URI: http://hdl.handle.net/10566/447 Files in this item: 1
GlaserTuckerMashaoDeafTelephony2004.pdf (133.0Kb) -
Cowan, Donald A.; Sayed, Muhammed F.; Tsekoa, Tsepo L.; Cameron, Rory A.; Sewell, B. Trevor (Academy of Science of South Africa (ASSAf), 2004)[more][less]
Abstract: Microbial nitrile hydratases are important industrial enzymes that catalyse the conversion of nitriles to the corresponding amides. Bacillus strain RAPc8 nitrile hydratase has recently been cloned and functionally expressed in E. coli. Here, the purification, crystallization and preliminary X-ray diffraction data of this nitrile hydratase are described. The heterotetrameric enzyme was crystallized using the hanging-drop vapour-diffusion method. Crystals produced in the presence of 30% PEG 400, 0.1 M MES (pH 6.5) and 0.1 M magnesium chloride were selected for X-ray diffraction studies. A data set complete to 2.5 Å was collected under cryoconditions at the in-house X-ray source at the University of the Western Cape. The space group was determined to be primitive tetragonal (P41212) with unit cell dimensions a = 106.61 Å, b = 106.61 Å, c=83.23 Å, = = =90°; with one dimer per asymmetric unit. Solution of the three-dimensional structure via molecular replacement is in progress. URI: http://hdl.handle.net/10566/167 Files in this item: 1
TsekoaPurification2004.pdf (784.0Kb)