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Item Exact solution of a mathematical model for human muscular motion(Elsevier, 2024-09-29) Molati, MotlatsiAn ordinary differential equation (ODE) which models human muscular movement is considered. A functional form of the model parameter is specified through the Lie symmetry approach, yielding a different expression from the one derived in the previous study (Kosugi et al., 2019). The Lie point symmetries corresponding to the model parameter are employed for derivation of exact solution.Item Bile acids as specific faecal pollution indicators in water and sediments(European Scientific Journal, 2013-04) Obuseng, Veronica; Moshoeshoe, Mohau; Nareetsile, FlorenceMicrobiological indicators such as Escherichia coli (E. coli) have been extensively applied to monitor sewage contamination in waters and sediments. However, it has been accomplished by many researchers that microorganism indicators of faecal pollution in aquatic environments have limited applicability, owing to their lack of specificity and variable life span induced by environmental factors such as sunlight and chlorination. This review highlights the use of chemical indicators for faecal or sewage pollution monitoring. It highlights that the differences in bile acid distributions in animal faeces could be utilized to differentiate inputs in an environment. Furthermore, the high resistance to degradation by some of the bile acids would make them better suited for long standing pollution compared to coprostanol, as it is more readily degraded. Bile acid data could be used in conjunction with other available evidence, be it ethnographic or as part of a multi-biomarker approach, employing 5 -stanols and bacterial indicators, such as C. perfringens, to distinguish amongst the different environmental inputs.Item Simultaneous determination of Nitrate, nitrite and Phosphate in environmental samples by high performance liquid Chromatography with UV detection(South African Chemical Institute, 2018-06-15) Moshoeshoe, Mohau N; Obuseng, VeronicaAn HPLC method using an UV detector was developed for the simultaneous determination of nitrites, nitrates and phosphates in environmental samples. Chromatographic separation was achieved isocratically on a Phenomenex Synergi Polar-RP LC column using acetonitrile and acidified water (pH 2.7) at 60:40 v/v as mobile phase. Baseline resolution of all the three analytes was achieved within 3 min. The developed method was applied to water samples obtained from the wastewater treatment plant in Gaborone, Botswana. The use of HPLC technique in this study demonstrated its ability to carry out a simultaneous determination of NO 2 – , NO 3 – and PO 4 3– in water samples. The treatment plant was found to be functioning within expectations, removing 97.6 % NO 2 – , 88.0 % NO 3 – and 90.9 % PO 4 3– from the received wastewater. Results of the developed method were comparable with those of the traditional ion chromatography method, showing accuracy values between 95.22 % and 98.04 %. The precision of the method for the determination of all analytes was determined by RSD values, all of which were lower than 5 %. The method is of low cost, fast, has an easy procedure and avoids the use of many reagents – some of which may be hazardous.Item Group classification, symmetry reductions and exact solutions of a generalized Korteweg-de Vries-Burgers equation(Natural Sciences Publishing, 2015-01-01) Molati, M.; Khaliqu, C. M.; Adem, A.R.Lie group classification is performed on the generalized Korteweg-de Vries-Burgers equationut+δuxxx+g(u)ux−νuxx+γu=f(x), which occurs in many applications of physical phenomena. We show that the equation admits a four-dimensional equivalenceLie algebra. It is also shown that the principal Lie algebra consists of a single translation symmetry. Several possibleextensions of theprincipal Lie algebra are computed and their associated symmetry reductions and exact solutions are obtained. Also, one-dimensionaloptimal system of subalgebras is obtained for the case when the principal Lie algebra is extended by two symmetries.Item Direct approach to a group classification problem: Fisher equation with time-dependent coefficients(World Scientific Publishing, 2016) Molati, M.; Khalique, C. M.We perform Lie symmetry analysis of a time-variable coefficient Fisher equation which models reaction–diffusion–convection phenomena in biological, chemical and physical systems. These time-dependent coefficients (model parameters or arbitrary elements) are specified via the direct integration of the classifying relations.Item Exact solutions of nonlinear diffusion-convection-reaction equation: A Lie symmetry analysis approach(Elsevier, 2019) Molati, M.; Murakawa, H.We derive some exact solutions of a nonlinear diffusion-convection-reaction equation which models biological, chemical and physical phenomena. The Lie symmetry classification approach is employed to specify the model parameters and then the symmetries of resulting submodels are utilized for construction of exact solutions.Item Chaos-based Encryption Keys and Neural Key-store for Cloudhosted Data Confidentiality(Technological University Dublin, 2017-09) Mosola, N.N.; Dlamini, M.T.; Blackledge, J.M.; Eloff, J.H.P.; Venter, H.S.Cloud computing brings flexible and cost effective services. However, security concerns plague the cloud. Data confidentiality is one of the concerns inhibiting the adoption of cloud computing. This concern stems from various cyberattacks directed towards gaining unauthorised access to cloud-bound or cloud-hosted data. This paper proposes a client-end encryption and key management system to curb attacks that targets compromising the confidentiality of cloud-hosted data. The proposed system uses chaotic atmospheric noise to generate a fitness function. The fitness function generates random numbers which create encryption keys. The strength of the encryption keys is derived from the chaotic and random nature of the atmospheric noise. The keys are then used for encrypting cloud-bound data using Advanced Encryption Standard (AES-128, 192 and 256), Data Encryption Standard (DES), 3-DES, and our novel cryptosystem named Cryptor, before it can be sent to the cloud. However, encryption bears no significance if the key management is flawed. To address the inherent key management problem, the solution uses a neural network to learn patterns of an encryption key. Once learnt, the key is then discard to thwart possible key attacks. The key is reconstructed by the neural network for decryption purposes.Item The ecology and plant functional composition of the afromontane palustrine wetlands in Lesotho(National University of Lesotho, 2020-02) Chatanga, P; Seleteng-Kose, L.The classification and description of wetland vegetation is important for biodiversity conservation and water resource management as it provides an understanding of the wetland vegetation-environment relationships and information to interpret spatial variation in plant communities. This study characterises the Afromontane palustrine wetlands of Lesotho in terms of plant communities, plant functional types and plant functional composition. Relationships of plant communities and functional traits were also explored. Vegetation, environmental and plant functional trait data were collected using the Braun-Blanquet method and standard methods. The data were analysed mainly by means of clustering, ordination and diversity analysis techniques. Twenty-two communities were produced by the classification of the Afromontane wetland vegetation and seven plant functional types, as well as seven functional communities were obtained from the classification. The wetland plant communities are diverse in terms of species richness. The ordination revealed that the wetland vegetation is mainly influenced by altitude, longitude, slope, soil parent material, landscape, inundation, peat, potassium content, soil texture, total organic carbon, nitrogen, sulphur, electrical conductivity, calcium, soil depth, wetness, magnesium, aspect and latitude. Plant functional traits and functional composition of the communities were found to be broadly influenced by altitude, slope, longitude, soil parent material, landscape and inundation, and more finely by edaphic factors that include electrical conductivity, calcium, sodium, magnesium, nitrogen, organic matter, total organic carbon, clay percentage, pH, sand percentage and potassium. Regarding species composition and diversity, plant communities in the Highlands were more diverse and were distinctively different from those in the Lowlands. Although a few wetlands, particularly in the Highlands are still in their near-pristine condition, many wetlands in the country are showing severe signs of degradation. While some communities are either restricted to the Highlands or Lowlands, others exhibit a wide ecological amplitude and occur in both regions. The study further highlights the possibility of alterations in plant functional traits, types and functional composition in the face of environmental changes, including climate change. The diversity of most of the wetlands, coupled with their restricted habitat and distribution at high altitudes and their role in supplying ecosystem services that include water resources, highlights the high conservation value associated with these wetlands, particularly in the face of climate change and loss of biodiversity.Item Raman spectroscopy and imaging of Bernalstacked bilayer graphene synthesized on copper foil by chemical vapour deposition: growth dependence on temperature(2017) Fabiane, M.; Madito, M. J.; Bello, A.; Manyala, N.We report on the effect of temperature on the growth of bilayer graphene on a copper foil under atmospheric pressure chemical vapour deposition (AP-CVD). Before characterization of the AP-CVD bilayer graphene, a high-quality graphene flake was obtained from the Kish bulk graphite by micro-mechanical exfoliation and characterized by using Raman spectroscopy and imaging. The Raman data of the exfoliated, high-quality graphene flake show monolayer and bilayer graphenes and were compared with the Raman data of AP-CVD graphene. Raman spectroscopy of AP-CVD graphene shows bilayer films that exhibit predominantly Bernal stacking with an I2D/IG ratio of ~1. At low growth temperature (~780 °C), Raman disorder-related peak intensity in the AP-CVD graphene is high and decreases with an increase in growth temperature to the lowest disorder intensity at ~973 °C. The selected area electron diffraction and atomic force microscopy average step height analysis showed the thickness of the bilayer graphene. The AP-CVD graphene is uniform at low growth temperatures (~780 °C) with a high disorder and becomes nonuniform at high growth temperatures (~867–973 °C) with a very low disorder as bilayer graphene evolves to form islands with an average lateral size of <10 μm. Competition between carbon adatoms supply through dehydrogenation of the CHx species, mobility and desorption rate of the carbon-adatom species for nucleation of the bilayer graphene as a function of temperature is elucidated. This study provides further insight into the growth mechanisms of bilayer graphene by AP-CVD on Cu.Item Synthesis and characterization of Y3+-doped TiO2 nanocomposites for photocatalytic applications(IOP Publishing Ltd, 2009) Macheli, Lebohang; Narayan, Himanshu; Alemu, Hailemichael; Gundu Rao, T. K.; Thakurdesai, MadhaviThe TiO2·[Y2O3]x (x = 0.1–0.4) nanocomposites (NCs) with an average particle size of 74 nm were prepared by the method of chemical co-precipitation followed by hydrolysis (CPH). Their visible light photocatalytic activity was investigated for the degradation of congo red (CR) dye. All NCs showed improved degradation as compared to the polycrystalline samples of similar compositions prepared by the solid-state reaction (SSR) route (average particle size of a few micrometers), as well as to the pure TiO2. The better photocatalytic activity of the NCs was attributed to their smaller particle size. Another comparison of the results with those obtained with Zn2+/Fe3+ ions co-doped TiO2 NCs, under similar experimental conditions, revealed that in the Y3+-doped NCs, particle size might not be the only factor responsible for the improved photocatalytic properties. It was concluded that the Y3+ ion-mediated suppression of the unwanted e−/h+ recombination could be the possible factor leading to additional enhancement.Item Synthesis, characterization and conductivity measurements of polyaniline and polyaniline/fly-ash composites(WILEY-VCH Verlag GmbH & Co., 2006-10-24) Iwuoha, Emmanuel I.; Alemu, Hailemichael; Narayan, HimanshuPolyaniline (PANI) and polyaniline/fly ash (PANI/FA) composites with various concentrations of fly ash (20%, 40% and 50%) were synthesized by the process of in-situ polymerization. The samples were characterized by powder X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. Moreover, the dc conductivity of the samples was measured as a function of temperature in the range 80–290 K and it was found that the addition of FA decreases the conductivity. The temperature dependence of the dc conductivity for PANI and FA/PANI composites has been explained on the basis of the quasi one-dimensional variable hopping model. A very good agreement was found between the experimental data and the theory.Item Swift heavy ion irradiation of MgB2 thin films: a comparison between gold and silver ion irradiations(2007) Narayan, Himanshu; Agrawal, H. M.; Kushwaha, R. P. S.; Kishan, H.; Bhatt, Ravindra K.The effect of 200 MeV Au ion irradiation on the temperature and field dependence of the critical current density, Jc, of MgB2 thin films on sapphire substrates is reported. The results have been presented in comparison with those obtained after 200 MeV Ag ion irradiation of a similar film. After irradiation, the critical temperature Tc decreased for all samples except for the one with a higher dose of gold ions, where it increased marginally. This observation was also confirmed from measurements of magnetization as a function of temperature with a constant applied field of 10−2 T. The critical current density, Jc, was estimated from the widths of magnetization loops using Bean’s critical state model. It has been found that Jc increases after irradiation, the enhancement being more pronounced for the Au ion irradiation. The higher enhancement of Jc by Au ion irradiation may be attributed to higher flux-pinning efficiency of the irradiated samples. It has been concluded that, although the flux-line shear (FLS) model satisfactorily explains the silver ion irradiation induced enhancement of Jc, some other mechanisms also seem to play a role in the Jc enhancement by gold ion irradiation.Item Surface smoothing of metallic glasses by swift heavy ion irradiation(Elsevier Ltd., 1999) Narayan, Himanshu; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.Self supporting samples of Metglass 2204 (Ti50Be40Zr10) and substrate bound samples of Metglass 2705M (Co69B12Si12Fe4Mo2Ni1) have been irradiated with 260 MeV 107Ag and 130 MeV 28Si ions, respectively at liquid nitrogen temperature. The surfaces have been examined by Scanning Electron Microscopy prior to and after irradiation. It is found that the surfaces have been smoothened after irradiation in both cases. The heights of the ÔhillsÕ have been decreased and the ÔvalleysÕ have been ®lled, without any detectable mass loss. The observed surface smoothing has been explained on the basis of shear ¯ow mechanism within the framework of the viscoelastic model. Ó 1999 Elsevier Science B.V. All rights reserved.Item Er1−yCayBa2Cu3−x(Fe, Zn)xO7−δ superconductors: a study of microstructure and resistive transitions in a dc magnetic field(IOP Publishing Ltd, 2001-10-15) Chaudhuri, Sukalpa; Gupta, Anurag; Ganesan, V.; Das, I.; Kumar, Anil; Zaleski, A. J; Narayan, Himanshu; Narlikar, A. V.We report an investigation of structure by x-ray diffraction, microstructure by atomic force microscopy (AFM) and broadening of resistive transitions in high dc magnetic fields (0–20 kOe) in Er1−yCayBa2Cu3−x(Fe, Zn)xO7−δ (y = 0.1, 0.2; and 0 x 0.20) ceramic superconductors. The XRD shows that the presence of Ca does not alter the known effect of Fe/Zn substitution on the structure of the pure (y = 0) system. Substitution of both Fe and Zn leads to a decrease in the grain size and micro-hardness. Interesting results were obtained on the influence of various dopants on the broadening of resistive transitions in dc magnetic fields, in general: (1) an increase in Ca content suppresses it; (2) Zn substitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux motion (TAFM), and the effect of various dopants on the properties like pinning barrier and anisotropy.Item Study of microstructural changes in MgB2 thin film superconductors irradiated with 200 MeV 107Ag ions(IOP Publishing Ltd, 2004-06-18) Narayan, Himanshu; Gupta, Anurag; Narlikar, A. V.; Sood, K. N.; Kishore, R.MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evaporation (EBE), have been investigated by scanning electron microscopy (SEM) before and after 200 MeV 107Ag ion irradiation. The severe degradation of superconducting properties in irradiated PLD film and the absence of the same in EBE film correlates with the observed changes in their microstructures. The micrographs of the PLD film show an overall smoothing, flow pattern and reduction in size of the bigger agglomerates after irradiation. On the other hand, the microstructure of the EBE film does not show any significant change after irradiation. The flow pattern observed in the PLD film can be understood on the basis of the viscoelastic model for irradiation induced shear flow in amorphous solids. The observed degradation of the PLD film may thus be attributed primarily to its disordered nature under irradiation, whereas the radiation hardness of the EBE film may be due to its higher crystallinity.Item Study of magnetization and pinning mechanisms in MgB2 thin film superconductors: effect of heavy ion irradiation(IOP Publishing Ltd, 2003) Narayan, Himanshu; Gupta, Anurag; Astill, D.; Kanjilal, D.; Ferdeghini, C.; Paranthaman, M.; Narlikar, A. V.We report magnetization studies on MgB2 superconducting thin films in a temperature range 4.2–40 K and magnetic field range 0–6 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In addition, both films were studied before and after heavy ion irradiation by 200 MeV Ag ions with a dose of 1011 ions cm−2. Variation of sweep rates during the measurement of the magnetization loop reveals the presence of flux creep in both films. The PLD film, after irradiation, shows a severe degradation of Tc, critical current densities (Jc) in low fields and irreversibility line (B∗(T )). In contrast, the EBE film shows a slight enhancement in Tc, and nearly no change in Jc(B) and the position of irreversibility line after irradiation. For both pristine films, the obtained volume pinning forces Fp versus reduced field b = B/B∗ shows a good scaling for T 10 K, which matches well with the theoretical curve based on the flux line shear (FLS) pinning model. These and other results can be interpreted in terms of grain boundaries in MgB2 films acting as FLS channels.Item A Simple, Potential-Free Model to Calculate Elastic Constants of Solids at High Temperature(Scientific & Academic Publishing, 2012) Singh, Madan; Narayan, Himanshu; Kumar, MunishA simple method for the determination of temperature dependent second order elastic constants (SOEC) of MgO, CaO, Mg2SiO4 and Grossular garnet[Ca3Al2(SiO4)3] using a potential free model based on thermodynamical relationships, has been proposed. The equations developed here are based on the linear relationship between elastic constants at temperatures higher than the Debye temperature. The extrapolated data for elastic constants at very high temperatures obtained in the present study are useful to understand the thermoelastic properties of given solids. It is found that the calculated values of elastic constants, in general, decrease with temperature. The theoretical predictions incorporating the concept of Debye temperature, reported in this paper, are well supported by the available experimental data. The proposed empirical relationship provides a method to estimate the thermoelastic properties of geophysical minerals and solids at high temperature range.Item SEM, STM/STS and heavy ion irradiation studies on magnesium diboride superconductor(Elsevier Ltd., 2002) Narayan, Himanshu; Samanta, S. B.; Gupta, Anurag; Narlikar, A. V.; Kishore, R.; Sood, K. N.; Kanjilal, D.; Muranaka, T.; Akimitsu, J.We have presented here the results of SEM and STM/STS investigations carried out on MgB2 superconductor. The SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers have been directly observed in atomically resolved STM images. The lattice constants have been determined to be aMg ¼ 3:1 AA, aB ¼ 1:7 AA and c ¼ 3:5 AA. Grain boundaries (GB) of width ranging from 50 to 200 AA have been observed. Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the GB interior as inferred from STS analysis. Irradiation with 200 MeV 107Ag ions gives tracks of about 65 AA in the bulk of the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which is related to possibility of wide practical application of this material.Item An SEM and STM investigation of surface smoothing in 130 MeV Si-irradiated metglass MG2705M(IOP Publishing Ltd, 1999) Narayan, Himanshu; Samanta, S. B.; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.; Narlikar, A. V.Metglass MG2705M foils of about 17 m thickness were irradiated at 90 K by 130 MeV 28Si ions, up to a fluence of 1:154 1016 ions cm−2. The surface modifications induced by irradiation have been examined by scanning electron microscopy (SEM) and scanning tunnelling microscopy (STM). It has been observed that smoothing of the sample surface is evident in both SEM and STM micrographs. The SEM pictures show a decrease in the heights of the ‘hills’ and filling up of the ‘valleys’ on micrometre length scales. The STM pictures, on the other hand, show smoothing of scratchlike surface disorders at nanometre length scales. However, the electronic energy loss Se, of 5:75 keV nm−1, does not lead to detectable track diameters, in agreement with the existing results. The observations have been attributed to a large electronic energy deposition due to high fluence, and a subsequent local shear relaxation of the near surface atoms. The theory of shear flow mechanism has been extended further to explain the results.Item Role of particle size in visible light photocatalysis of Congo Red using TiO2⋅[ZnFe2O4]x nanocomposites(Springer-Verlag, 2009) Narayan, Himanshu; Alemu, Hailemichael; Macheli, Lebohang; Sekota, 'Mantoa; Thakurdesai, Madhavi; Gundu Rao, T. K.TiO2⋅[ZnFe2O4]x (x = 0⋅0–0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by the method of co-precipitation/hydrolysis (CPH). For the comparison of particle-size dependent effects, a set of polycrystalline samples with similar compositions was also prepared by solid state reaction (SSR) route. Average particle size for SSR prepared samples was about 3⋅0 μm. All the samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer, Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Their visible light photocatalytic activity was tested for the degradation of Congo Red dye. Maximum photodegradation was observed for the NC with x = 0⋅1 synthesized by CPH (particle size, 71 nm). Similar composition prepared by SSR method (particle size, 6⋅19 μm) showed lower photoactivity in comparison even with that observed for pure TiO2 (particle size, 4⋅03 μm). It was, therefore, concluded that enhanced photodegradation is directly related to the reduced particle size of the composites, which implies that photosensitization is the process primarily involved. Although, doping of TiO2 with ZnFe2O4 does extend the cut-off wavelength towards visible parts of the spectrum, its contribution in the enhancement is not as significant as that due to the photosensitization.