Browsing by Subject "Science"

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    Analytical perspectives on localized solutions of the phi-4 theory
    (2023) Dika, Alain; Barashenkov, Igor Vladilenovich; Alexeeva Nora
    We investigate the topological and non-topological solitons—kink and breather—in the φ4 model. Our first objective is to explain the chaotic motion of the resonantly driven kink. To this end, we consider the evolution of the kink's wobbling and rocking modes and their coupling. To improve the asymptotic expansion of the wobbling and rocking amplitudes, we introduce a slowly varying width of the kink. The analysis of the wobbling and rocking modes produces three-dimensional systems of equations, while their coupling results in five-dimensional systems for the amplitude of the wobbling, rocking, and the kink's velocity. Although these equations predict hysteretic transitions in the wobbling and rocking amplitudes (a conclusion verified by numerical simulations of the full partial differential equation), the asymptotic approach does not capture the chaotic behaviour of the kink. Numerical simulations indicate that the chaotic motion of the kink is associated with the spontaneous emission of a small-amplitude breather. This observation motivates our subsequent analysis of the kink-breather interaction. To study the kink-breather interaction, we use the variational method. We start with the development of the variational approach to a stand-alone breather. For the quiescent breather, we show that the resulting variational equations have continuous families of periodic orbits for each value of the breather width. For the moving breather, we compare two sets of Ansatze. The first set of trial functions is built by including a translation degree of freedom into the quiescent breather Ansatz. These trial functions turn out to be inconsistent with the conservation of momentum. To correct this inconsistency, we add one more collective coordinate to the previous Ansatze, which leads to two distinct and consistent trial functions for the moving breather. Having developed a variational approach to a stand-alone breather, we apply it to the kink- breather bound state. In our investigation, we implement two distinct Ansatze: the first trial function involves the amplitude of the breather and its distance from the kink, while the second trial function considers the breather's phase and the distance between the two objects. Local minima of the potential energy from both Ansatze are surrounded by families of closed level curves. The kink interacts with the breather when the initial conditions are chosen to be close enough to a local minimum. We observe that breathers with small amplitudes are trapped by the kink, while those with an amplitude greater than a critical value escape. The Ansatz based on the distance between the two objects and the breather's amplitude shows that when the trapping occurs, the kink and the breather move at the same speed. Finally, we test the robustness of the finite-dimensional model by allowing the kink's width to change. This results in a 6-dimensional phase space. The potential energy shows local minima surrounded by families of closed level surfaces. By selecting initial conditions that lie on the energy shell, the resulting trajectory will remain inside that level surface.
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    The birth of modern astronomy
    (2013) Wolfe, David
    by Emeritus Professor David Wolfe, University of New Mexico and visiting lecturer, Physics Department, UCT. Professor Wolfe explores the foundations of astronomy, beginning with the ancient Egyptians, Greeks and Babylonians, to the early modern period and the works of Brahe, Kepler, Copernicus and Newton in condifying the mathematical and theoretical models that underpin modern astronomy.
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    Building the next generation of South African scientists
    (2006) Lutjeharms, Johann R E
    A recent issue carried a most interesting suite of articles, demonstrating the success of the Royal Society/National Research Foundation programme in helping to build a new generation of South African scientists, ‘as ageing researchers retire and retention and new blood become increasingly important’. The NRF’s overview of the programme (‘Reaching out to the world’1 ) correctly points out that ‘South Africa needs excellent science and far more scientists, drawing on the research potential of the entire population.’
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    Computational and modelling aspects of marine riser analysis
    (1987) Phaal, Robert
    [page 119, 132 missing] In recent years much interest has been shown iri the design of offshore structures. Flexible members such as marine risers and mooring cables are critical components in such structures. These systems are characterised by nonlinear geometry and loading. In the formulation of an algorithm to model such systems, simplifying assumptions must often be made. This thesis attempts firstly to give an overview of the literature available in this field. The testing of a riser model is important to ensure that it may be used with confidence. There are several sources of error inherent in a model of this nature. Modelling errors are those caused by the simplifying assumptions made in developing the mathematical statement of the model. Numerical errors include those due to the approximation method and the finite accuracy of the computing machine. Finally, there is a level of randomness in the design parameters, which results in a lack of confidence and an uncertainty in the response obtained from a deterministic model. This thesis attempts to qualify, if not quantify, the sources of error innate to the modelling of flexible offshore structures; in particular, marine risers. Extensive use has been made of a sophisticated, commercially available finite element program, ABAQUS. Three commonly occuring riser configurations have been modelled successfully with ABAQUS. These are the standard, the catenary, and the hanging riser configurations (see figure 1.1). A geometrically linearised finite element riser model has also been developed and tested. The linearised model is shown to be applicable to problems where the maximum model deflection is less than approximately 10% of the riser length. A Probabilistic Finite Element Method (PFEM) has been implemented in order to investigate one source of uncertainty in the problem: that of the hydrodynamic loading. The method is shown to have limitations expressed by coefficient of variation bounds for the random parameters. The C data available in the literature is within these bounds, d while the C data is not. These bounds are shown to be a problem dependent, and the PFEM to be more applicable to the modeiling of the uncertainties associated with the analysis of drag dominated problems such as mooring cables.
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    Drivers and uncertainties of future global marine primary production in marine ecosystem models
    (2015) Laufkötter, C; Vogt, M; Gruber, N; Aita-Noguchi, M; Aumont, O; Bopp, L; Buitenhuis, E; Doney, S C; Dunne, J; Hashioka, T; Hauck, J; Hirata, T; John, J; Le Quéré, C; Lima, D I; Nakano, H; Seferian, R; Totterdell, I; Vichi, M; Völker, C
    Past model studies have projected a global decrease in marine net primary production (NPP) over the 21st century, but these studies focused on the multi-model mean and mostly ignored the large inter-model differences. Here, we analyze model simulated changes of NPP for the 21st century under IPCC's high emission scenario RCP8.5 using a suite of nine coupled carbon–climate Earth System Models with embedded marine ecosystem models with a focus on the spread between the different models and the underlying reasons. Globally, five out of the nine models show a decrease in NPP over the course of the 21st century, while three show no significant trend and one even simulates an increase. The largest model spread occurs in the low latitudes (between 30° S and 30° N), with individual models simulating relative changes between −25 and +40%. In this region, the inter-quartile range of the differences between the 2012–2031 average and the 2081–2100 average is up to 3 mol C m-2 yr-1. These large differences in future change mirror large differences in present day NPP. Of the seven models diagnosing a net decrease in NPP in the low latitudes, only three simulate this to be a consequence of the classical interpretation, i.e., a stronger nutrient limitation due to increased stratification and reduced upwelling. In the other four, warming-induced increases in phytoplankton growth outbalance the stronger nutrient limitation. However, temperature-driven increases in grazing and other loss processes cause a net decrease in phytoplankton biomass and reduces NPP despite higher growth rates. One model projects a strong increase in NPP in the low latitudes, caused by an intensification of the microbial loop, while the remaining model simulates changes of less than 0.5%. While there is more consistency in the modeled increase in NPP in the Southern Ocean, the regional inter-model range is also very substantial. In most models, this increase in NPP is driven by temperature, but is also modulated by changes in light, macronutrients and iron as well as grazing. Overall, current projections of future changes in global marine NPP are subject to large uncertainties and necessitate a dedicated and sustained effort to improve the models and the concepts and data that guide their development.
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    Electronic and solvent effects on monosaccharide conformations
    (2007) Barnett_CB; Professor Kevin J. Naidoo
    The hydroxymethyl group rotational preferences of the monosaccharides glucose and galactose are different from each other and non-intuitive (from a steric point of view) in their preferences for gauche conformers. These molecules exhibit very different biological and thermodynamic properties in, for example their binding to glycosides or their liquid crystalline phases in glycolipids. The preference for gauche conformations has been attributed to solvent effects, stereoelectronic effects and hydrogen bonding; yet the experimentally obtained hydroxymethyl rotational populations have not yet been fully rationalised. In this dissertation, I have used a range of ab initio, Molecular Dynamics (MD), Quantum Mechanics/Molecular Mechanics (QM/MM) and free energy computational methods to resolve and explain this observation. The hydroxymethyl free energy surface was calculated using the Potential of Mean Force (PMF), umbrella sampling and Weighted Histogram Analysis Methods (WHAM). The PMF calculations were performed in the canonical (NVT) ensemble in the gaseous and aqueous phase where each monosaccharide was modelled with Parameter Model 3 for Carbohydrates (PM3CARB-I). Density Functional Theory (OFT) calculations were also carried out and Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) analyses were applied. Gaseous phase simulation results for both glucose and galactose gave hydroxymethyl rotational preferences of gg>tg>gt and gt>gg>tg respectively. These confrontational preferences can be rationalised in terms of an intrinsic stereoelectronic effect (found from NBO calculations) and strong intramolecular hydrogen bonding (found in the tg conformer of glucose and the gg conformer of galactose using AIM) in the gaseous phase. The addition of solvent (water) was found to disrupt the intramolecular hydrogen bonding present in the gaseous phase. Hydroxymethyl rotational preferences in the solution phase were gg>gt>tg for glucose and gt>tg>gg for galactose. The population distributions in solution were also calculated for glucose as gg:gt:tg = 59.21 :34.88:0.83 and for galactose as gg:gt:tg = 3.32:79.60: 1 0.15. These populations agree favourably with experimental NMR populations. The solvent conformational preference is dominated by the intrinsic stereoeIectronic effect and steric interactions. The gauche effect in monosaccharides has been successfully rationalised.
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    Inclusion of the insecticide fenitrothion in dimethylated-β-cyclodextrin: unusual guest disorder in the solid state and efficient retardation of the hydrolysis rate of the complexed guest in alkaline solution
    (2013) Cruickshank, Dyanne L; Rougier, Natalia M; Vico, Raquel V; Bourne, Susan A; Buján, Elba I; Caira, Mino R; de Rossi, Rita H
    An anhydrous 1:1 crystalline inclusion complex between the organophosphorus insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl)phosphorothioate] and the host compound heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) was prepared and its structure elucidated by single-crystal X-ray diffraction. This revealed two independent host molecules in the asymmetric unit. In one of these, the cavity is occupied by two disordered guest components (distinguishable as rotamers with respect to the P–OAr bond) while in the other, three distinct guest components with site-occupancies 0.44, 0.29 and 0.27 appear, the last having a reversed orientation relative to all the other components. Kinetic studies of the alkaline hydrolysis of fenitrothion in the presence of DIMEB showed a remarkable reduction of 84% in the rate of this reaction relative to that for the free substrate, a value exceeding those previously attained with the native hosts, β- and γ-cyclodextrin, and fully methylated β-cyclodextrin.
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    An investigation of the molecular biology and genetics of Witches' Broom disease of Protea cynaroides
    (1987) Dorrington, Rosemary Ann; Woods, David R
    An investigation was undertaken into the biology and genetics of Witches' Broom disease on Protea cynaroides. The investigation was approached in two ways: firstly, from a physiological and pathological angle and secondly at the genetic level. As very little is known about the causes of Witches' Broom disease on P. cynaroides, an attempt was made to identify a pathogen which could be held responsible for the disease. A number of plants were studied in the field and from these samples were taken and cultured on culture medium. Healthy P. cynaroides tissue was not established in tissue culture, while more success was obtained with teratoma tissue. Attempts were made to transmit the disease but these were unsuccessful. Four strains of Agrobacterium tumefaciens were unable to induce tumours on P. cynaroides seedlings. Sections of vascular tissue from teratoma and healthy tissue were viewed under the electron microscope but revealed no pathogen.
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    Late Holocene Climatic Change: The little ice age and El Nino from planktonic foraminifera in sediments off walvis bay, South West Africa
    (1986) Herbert, Russel S; Johnson, R
    The variation in abundance of the species G. bulloides and G. pachyderma with depth in a core of diatomaceous sediment off Walvis Bay, South West Africa, seems to correlate with the Little Ice Age that occurred during the late Holocene. Although similar research, using species and oxygen isotope variations has been completed in similar sediment off northern Venezuela and in the Santa Barbara Basin (Kipp and Towner 1975, Dunbar 1983), these are the first downcore foraminiferal species records of the South West African deposit. The abundances of some of the minor species, most notably G. ruber, show very distinctive peaks at apparently random intervals. It is thought that these sudden and short-lived increases could be linked to major El-Nino-type events. In order to measure accurately all the down-core foraminiferal changes, we had to develop a chemical solution which dissolves diatoms and organic material without damaging the foraminiferal skeletons. It consists of K2CO3, CaCl2, NaOH and H202 in particular concentrations. By using this technique, it is possible to prevent biassing of the foraminiferal signal during extraction of foraminifera from diatomaceous mud.
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    Perceptual depth cues in support of medical data visualisation
    (2004) Lyness, Caleb A; Blake, Edwin; Marais, Patrick
    This work investigates methods to provide clinically useful visualisations of the data produced by an X-ray /CT scanner. Specifically, it examines the use of perceptual depth cues (PDCs) and perceptual depth cue theory to create effective visualisations. Two visualisation systems are explored: one to display X-ray data and the other to display volumetric data. The systems are enhanced using stereoscopic and motion PDCs. The presented analyses show that these are the only possible enhancements common to both systems. The theoretical and practical aspects of implementing these enhancements are presented. Volume rendering techniques are explored to find an approach which gracefully handles poorly sampled data and provides the interactive rendering needed for motion cues. A low cost real time volume rendering system is developed and a novel stereo volume rendering technique is presented. The developed system uses commodity graphics hardware and Open-GL. To evaluate the visualisation systems a task-based user test is designed and implemented. The test requires the subjects to be observed while they complete a 3D diagnostic task using each system. The speed and accuracy with which the task is performed are used as metrics. The experimental results are used to compare the effectiveness of the augmented perceptual depth cues and to cross-compare the systems. The experiments show that the user performance in the visualisation systems are statistically equivalent. This suggests that the enhanced X-ray visualisation can be used in place of CT data for some tasks. The benefits of this are two fold: a decrease in the patient's exposure to radiation and a reduction in the data acquisition time.
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    Potentiometric and Blood Plasma Simulation Studies of Nickel(II) Complexes of Poly(amino)amido Pentadentate Ligands: Computer Aided Metal-Based Drug Design
    (2014) Odisitse, Sebusi; Jackson, Graham E
    The thermodynamic equilibria of nickel(II) with N,N′-di(aminoethylene)-2,6-pyridinedicarbonylamine (L1), Bis-(N,N-dimethylethyl)-2,6-pyridinedicarboxamide (L2), and N,N′-bis[2(2-pyridyl)-methyl]pyridine-2,6-dicarboxamide (L3) have been studied at 25°C and an ionic strength of 0.15 mol dm−3 by glass electrode potentiometry. The protonation and formation constants added to blood plasma model predict that Cu(II) competes effectively against Ni(II), Zn(II), and Ca(II) for these ligands in vivo.
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    Promoting equality for ethnic minority NHS staff—what works?
    (2015) Priest, Naomi; Esmail, Aneez; Kline, Roger; Rao, Mala; Coghill, Yvonne; Williams, David R
    NHS organisations are now being judged on indicators of ethnic diversity. Naomi Priest and colleagues look at the international evidence on how they should tackle discrimination
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    Science and Religion: friends or foes?
    (2014-08-04) Mall, Anwar
    This three-lecture course will trace the historical relationship between science and religion, explore the ‘conflict hypotheses’ related to them and reflect on the successes of science. In recent decades science and religion seem in conflict, particularly with increasing evidence supporting Darwin’s theory of evolution. Evolutionary biologists have provoked people into considering what evidence for evolution means in relation to religious practice. In response, religious proponents have sprouted intelligent design theories, angrily taking legal action against the teaching of evolution in schools. But there are significant conciliatory positions on both sides of the divide, such as Stephen J. Gould’s theory of non-overlapping magisteria, in which science deals with the ‘how’ of life, and religion its meaning. It is generally agreed that science has contributed enormously to the progress of humanity especially since the 1600s. Despite our comforts derived from technological innovation, there is still little knowledge of and much suspicion about scientific activity, with scientific concepts difficult to grasp, their presentation ‘unfriendly’ and scientists ridiculing religion as an outdated dogma, made obsolete by evolutionary theory. From the perspective of a scientist, this course will explore some of the great ideas of science, some of its failings and its heady relationship with religion. The first lecture will include focus on the biological sciences, the second will deal more specifically with science and its relationship with Christianity and Judaism and the third with the historical status of science in the Muslim world and personal experience of views of science amongst local Muslims. LECTURE TITLES 1. The value of science: its current relationship with religion 2. Science in Christian and Jewish societies 3. Muslims and science: a personal view Recommended reading Coyne, J. 2009. Why Evolution is True. New York: Viking Press. Dawkins, R. 2006. The God Delusion. London: Bantam Press. Feierman, J.R. Ed. 2009. The Biology of Religious Behaviour: The Evolutionary Origins of Faith and Religion. Santa Barbara: Praeger. Haag, J., Peterson, G. & Spezio, M. Eds. 2012. The Routledge Companion to Religion and Science. Oxon: Routledge. * Only podcasts for lecture 1 & 2 are available for this lecture series. This lecture series was part of the 2014 UCT Summer School programme http://www.summerschool.uct.ac.za/
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    SEAmester – South Africa’s first class afloat
    (2016) Dorrington, Rosemary A; Fawcett, Sarah; Gammon, David W; Henry, Tahlia; Hermes, Juliet; Hölscher, Beate; d’Hotman, Jethan; Meiklejohn, Ian; Morris, Tammy; Pinto, Izidine; du Plessis, Marcel; Roman, Raymond; Saunders, Clinton; Shabangu, Fannie W; de Vos, Marc; Walker, David R; Louw, Gavin
    The International Society for Burns Injuries (ISBI) has published guidelines for the management of multiple or mass burns casualties, and recommends that 'each country has or should have a disaster planning system that addresses its own particular needs.' The need for a national burns disaster plan integrated with national and provincial disaster planning was discussed at the South African Burns Society Congress in 2009, but there was no real involvement in the disaster planning prior to the 2010 World Cup; the country would have been poorly prepared had there been a burns disaster during the event. This article identifies some of the lessons learnt and strategies derived from major burns disasters and burns disaster planning from other regions. Members of the South African Burns Society are undertaking an audit of burns care in South Africa to investigate the feasibility of a national burns disaster plan. This audit (which is still under way) also aims to identify weaknesses of burns care in South Africa and implement improvements where necessary.
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    Sea–air CO2 fluxes in the Southern Ocean for the period 1990–2009
    (2013) Laufkötter, C; Hoppema, M; Lovenduski, N S; Matear, R J; McNeil, B I; Metzl, N; Mikaloff Fletcher, S E; Monteiro, P M S; Rödenbeck, C; Sweeney, C; Takahashi, T
    The Southern Ocean (44-75° S) plays a critical role in the global carbon cycle, yet remains one of the most poorly sampled ocean regions. Different approaches have been used to estimate sea-air CO2 fluxes in this region: synthesis of surface ocean observations, ocean biogeochemical models, and atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Southern Ocean sea-air CO2 fluxes between 1990-2009. Using all models and inversions (26), the integrated median annual sea-air CO2 flux of -0.42 ± 0.07 Pg C yr-1 for the 44-75° S region, is consistent with the -0.27 ± 0.13 Pg C yr-1 calculated using surface observations. The circumpolar region south of 58° S has a small net annual flux (model and inversion median: -0.04 ± 0.07 Pg C yr-1 and observations: +0.04 ± 0.02 Pg C yr-1), with most of the net annual flux located in the 44 to 58° S circumpolar band (model and inversion median: -0.36 ± 0.09 Pg C yr-1 and observations: -0.35 ± 0.09 Pg C yr-1). Seasonally, in the 44-58° S region, the median of 5 ocean biogeochemical models captures the observed sea-air CO2 flux seasonal cycle, while the median of 11 atmospheric inversions shows little seasonal change in the net flux. South of 58° S, neither atmospheric inversions nor ocean biogeochemical models reproduce the phase and amplitude of the observed seasonal sea-air CO2 flux, particularly in the Austral Winter. Importantly, no individual atmospheric inversion or ocean biogeochemical model is capable of reproducing both the observed annual mean uptake and the observed seasonal cycle. This raises concerns about projecting future changes in Southern Ocean CO2 fluxes. The median interannual variability from atmospheric inversions and ocean biogeochemical models is substantial in the Southern Ocean; up to 25% of the annual mean flux, with 25% of this interannual variability attributed to the region south of 58° S. Resolving long-term trends is difficult due to the large interannual variability and short time frame (1990-2009) of this study; this is particularly evident from the large spread in trends from inversions and ocean biogeochemical models. Nevertheless, in the period 1990-2009 ocean biogeochemical models do show increasing oceanic uptake consistent with the expected increase of -0.05 Pg C yr-1 decade-1. In contrast, atmospheric inversions suggest little change in the strength of the CO2 sink broadly consistent with the results of Le Quéré et al. (2007).
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    SHOP-Net: Moving from Paper to Mobile
    (2011) Talbot, Michael; Marsden, Gary
    Stock-ordering is one of the challenges that microenterprises face, because shop owners often need to leave their shops to travel to suppliers of goods. Triple Trust Organization (TTO) is a non-profit organization (NGO) that works with microenterprises around Cape Town and addresses this problem. They act as a supplier and fetch stock orders from shops they work with. Their ordering system relied on paper order forms and had a number of inefficiencies. To address these inefficiencies, a mobile-based stock-ordering system was designed with TTO. This system allows orders to be recorded and sent to a server at the TTO office using a mobile phone application where the orders are then processed. This system successfully increased TTO's efficiency in three ways, namely, improved data processing ability, increased order accuracy and increased access to information. The evaluation was done according to their success criteria and the system has been in use for seven months. We argue that evaluations with NGOs should go further than just the management but include all of those affected by the system.
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    Spatial and temporal disaggregation of anthropogenic CO2 emissions from the City of Cape Town
    (2015) Nickless, Alecia; Scholes, Robert J; Filby, Ed
    Abstract This paper describes the methodology used to spatially and temporally disaggregate carbon dioxide emission estimates for the City of Cape Town, to be used for a city-scale atmospheric inversion estimating carbon dioxide fluxes. Fossil fuel emissions were broken down into emissions from road transport, domestic emissions, industrial emissions, and airport and harbour emissions. Using spatially explicit information on vehicle counts, and an hourly scaling factor, vehicle emissions estimates were obtained for the city. Domestic emissions from fossil fuel burning were estimated from household fuel usage information and spatially disaggregated population data from the 2011 national census. Fuel usage data were used to derive industrial emissions from listed activities, which included emissions from power generation, and these were distributed spatially according to the source point locations. The emissions from the Cape Town harbour and the international airport were determined from vessel and aircraft count data, respectively. For each emission type, error estimates were determined through error propagation techniques. The total fossil fuel emission field for the city was obtained by summing the spatial layers for each emission type, accumulated for the period of interest. These results will be used in a city-scale inversion study, and this method implemented in the future for a national atmospheric inversion study.
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    Studies in the genus Eulophia R. Br.
    (1959) Hall, A V; Schelpe, E A C L E
    Detailed variation studies of 23 species of the genus Eulopbia R. Br. (Orchidaceae) indicate that six taxa may be upheld as distinct species, together with two or possibly three intraspecific taxa, whose status can only be assessed on the basis of further field work. It is considered highly likely that the remaining 17 taxa should be relegated to the synonymy of the six species upheld, possibly together with a further eight doubtfully distinct species of which only descriptions were available.
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    Studies of non-adiabatic pulsations in the atmospheres of the roAp stars
    (2002) Medupe, Rodney; Christensen-Dalsgaard, J; Kurtz, D W
    The roAp stars are high overtone pulsators characterised by strong global magnetic fields with effective field strength of between a few hundred to a few thousand Gauss. They also show overabundances in rare-earths and iron peak element. Multi-colour photometry of roAp stars shows that their pulsation amplitudes decrease more rapidly with increasing wavelength compared to other classically pulsating stars (e.g. Medupe & Kurtz 1998). In addition, this thesis shows that the pulsation phase can vary by up to 80° from Johnson U to V filters. In an attempt to explain the amplitude vs wavelength Kurtz & Medupe (1996) derived an analytic formula that indicated that the steep variation of the temperature eigenfunction with depth in the roAp atmospheres is the possible reason the rapid decrease of amplitude with wavelength. Even though Medupe & Kurtz (1998) showed that the analytical formula they derived in 1996 was a special form of a more general formula presented in Watson (1988), they found limitations in both formulae (see also Medupe, Christensen-Dalsgaard & Kurtz 1998 and chapter 3 of this thesis). This motivated me to attempt a numerical solution of the pulsation equations with consistent treatment of radiative transfer to investigate the multi-colour photometric data. In this thesis, we report on the multi-colour pulsation amplitudes and phases for HD 128898, HD 101065, HD 134214 and HD 137949. We also report on the campaign undertaken in 1996 and 1998 to determine whether the HR 3831 amplitude and phase vs wavelength changes with rotation. No variations with rotation are found. We find that the pulsation phase varies by up to about 80° from Johnson U to V in HD 101065 and HR 3831.
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    Successful Deployment of a Wireless Sensor Network for Precision Agriculture in Malawi
    (2013) Mafuta, Million; Zennaro, Marco; Gombachika, Harry; Chadza, Timothy
    This paper demonstrates how an irrigation management system (IMS) can practically be implemented by deploying a wireless sensor network (WSN). Specifically, the paper describes an IMS which was set up in Manja township, city of Blantyre. Deployment of IMS in rural areas of developing countries like Malawi is a challenge as grid power is scarce. For the system to be self-sustained in terms of power, the study used solar photovoltaic and rechargeable batteries to power all electrical devices. The system incorporated a remote monitoring mechanism through a General Packet Radio Service modem to report soil temperature, soil moisture, WSN link performance, and photovoltaic power levels. Irrigation valves were activated to water the field. Preliminary results in this study have revealed a number of engineering weaknesses of deploying such a system. Nevertheless, the paper has highlighted areas of improvement to develop a robust, fully automated, solar-powered, and low-cost IMS to suit the socioeconomic conditions of small scale farmers in developing countries.