The study and characterisation of plasma microfluidic devices

Controlling the behaviour of atmospheric pressure plasmas and their interaction with polymeric materials is of major interest for surface modification applications across multidisciplinary fields intersecting biomedical engineering, bio-nanoengineering, clinical/medical science, material science and microelectronics. The aim of the present work is to investigate the behaviour of atmospheric pressure dielectric barrier discharges in closed systems (microfluidic devices) and open systems (glass capillary devices) and their polymer-surface interactions. Atmospheric pressure microplasma jets operating in helium gas have been used to modify locally the surface energy of polystyrene (PS) and to interact directly with the surface of analytes using a novel plasma assisted desorption ionisation (PADI) method causing desorption and ionization to occur. Although atmospheric pressure micro-jets are now widely studied for the treatment of materials there is still a lack of understanding of the fundamental plasma-surface processes. A number of recent studies using plasma micro-jets for the surface modification of polymerics have used systems in which the emerging plume impinges directly the substrate head-on. Here, by placing the micro-jet side-on to the substrate we can observe how different flow regions of the jet affect the sample, allowing individual effects to be seen. In addition, this configuration may prove an efficient way of treating samples with reduced or no surface damage. These conclusions are considered to be an important contribution to the study of complex mechanisms underpinning the behaviour of radicals and reactive species in surface modification processes of polymeric materials. The study of the behavioural mechanism involved in the plasma was done using various diagnostic techniques such as electrical measurements, optical emission spectroscopy (OES), Time-averaged and time-resolved ICCD Optical Imaging and Schlieren Photography. The filamentary discharge mode was observed in bonded microchannels using metallic and liquid-patterned electrodes. The treated surfaces were characterised using various techniques such as X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM), Optical profiling measurements and Water Contact Angle (WCA) measurements. Schlieren photography has been used to indentify regions of laminar (pre-onset of visual instability) and turbulent flows (post-onset of visual instability) in the exiting gas stream and the nature of their interaction with the substrate surface. The length of both regions varies depending on operating parameters such as frequency, applied voltage and flow rate. WCA results from treated polystyrene (PS) samples exposed directly facing the microjet reveals a change from hydrophobic (high contact angle) to a hydrophilic (low contact angle) surface with substantial reductions in WCA (~ 50 to 60 °) occurring in downstream regions where the turbulent gas mixed with air impinges the substrate surface. In contrast, only small changes in WCA (~ 10 to 20 °) occur in regions where the gas flow is laminar. AFM imaging of treated PS samples reveal holes and ripple like effect with a much larger area than that of the capillary seen on treated samples positioned “head-on” and directly facing the sample but this was not seen using the side-on configuration. The results indicate that excited air species (either mixed or entrained in the He gas flow) which exist only in regions of turbulence are the main agents causing surface covalent bond breaking leading to surface modification. This thesis reports on atmospheric pressure microdischarges and their applications, a brief summary of work done so far including major results, using new and existing technologies including those under development in terms of design, properties and working conditions

Investigation of the contribution of the multi-joint arm stiffness to the motor control deficit experienced in ataxia

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 20).Prior research has shown that the control response of the limbs is affected by the mechanical properties of the limb and the feedback properties of the CNS. Cerebellar ataxia describes a situation in which damage to the cerebellum results in compromised motor control. It is characterized by such things as a clumsy or disturbed gait, a lack of balance and coordination, and unsteady speech patterns; for severe cases of ataxia, gross muscle coordination can degenerate to the point where successful, coordinated movements are not possible. In order to better understand the control deficit experienced by ataxic persons, estimates of the feedback properties of the CNS and the limb-muscle mechanical properties and will be necessary. Specifically, this investigation hopes to determine to what extent ataxia is cause by abnormal effective stiffness. Because ataxic patients do not exhibit deficits in strength or postural maintenance, we hypothesize a priori that the measured stiffness of ataxic subjects will be normal. We test this by conducting postural stiffness study on an ataxic subject, and measuring stiffness for two degrees of subject co-activation - minimal subject co-activation and maximal subject co-activation - and for different equilibrium postures.(cont.) Because the observed kinematic trajectory following neuromuscular activation, as well as the ability of the limb to maintain a given posture in an external force field will be a result of the CNS reflex responses as well as the mechanical properties of the limb-muscle system, we expect all measurements of stiffness to be affected by CNS reflex responses. These reflex responses tend to be noticed between 20 msec (spinal reflexes) and 150 msec (long-loop reflexes) after an environmental disturbance, and because measurements of muscle stiffness require that we wait at least that long after external force application, we expect their contribution to the stiffness measurements to be represented. Our findings show the postural stiffness measured at six static positions in a 0.23 meter by 0.23 meter horizontal workspace and centered 0.45 m in front of the ataxic subject were within (something %) of those measured for a normal subject, and within the range reported by MussaIvaldi. As expected, however, the kinematics of cross-body hand movements were significantly different for the ataxic and normal subject. These results indicate an intact postural regulation for the ataxic subject but a deficit in dynamic control when compared to the normal subject.by Olumuyiwa A. Oni.S.B

Structural Transformation and Capital Formation in Nigeria: An ARDL Analysis

The study tests the proposition that structural transformation drives capital formation which in turn underlies development through the expansion of gross domestic product (GDP). Relevant data consistent with extant literature were obtained from the World Development Indicators between 1980 to 2017 and checked for integration and mean reversion properties. Having obtained satisfactory results from the pre-regression tests, the autoregressive distributed lag (ARDL) regression was chosen to fit the series. Post-regression evaluations check about the assumptions of normality, serial correlation, and homoskedasticity were all satisfactory to enable us to draw valid inference. Our results find no long-run evidence of structural transformation as a process of fixed capital formation in Nigeria. The correlation between the two is strongly negative. The GDP provides the most powerful and significant drive for fixed capital formation as well as the volume of domestic credit to the private sector, gross domestic saving, and the real rate of interest. The pattern of structural transformation observed showed an industrial structure comprising weak and low-capital intensive industries. The study recommends an industrial road map focused on both the industrialisation of agriculture and the creation of capital-intensive industries to drive sustained fixed capital accumulation. Keywords: structural transformation, capital formation, agriculture, modern sectors, Nigeria DOI: 10.7176/JESD/10-8-13 Publication date: April 30th 201

Vowel assimilation in Èkìtì dialects of Yorùbá language

Abstract - Vowel assimilation is a common phonological process in Yorùbá language and its numerous dialects.  However, the occurrence of this process differs in the language and its dialects. It is against this backdrop that this study investigates vowel assimilation in Èkìti dialects of Yorùbá. The paper, which is basically descriptive, makes a careful comparison of the phonological process in the dialects and Standard Yorùbá language. The paper shows that unlike Standard Yorùbá, vowel assimilation is confined to certain constructions in Èkìtì dialects. The paper also posits that unlike Standard Yorùbá which employs two assimilation rules, Èkìtì dialects employ one assimilation rule. The rule is however, blocked when there need to maintain contrast

On paired decoupled quasi-linearization methods for solving nonlinear systems of differential equations that model boundary layer fluid flow problems.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Two numerical methods, namely the spectral quasilinearization method (SQLM) and the spectral local linearization method (SLLM), have been found to be highly efficient methods for solving boundary layer flow problems that are modeled using systems of differential equations. Conclusions have been drawn that the SLLM gives highly accurate results but requires more iterations than the SQLM to converge to a consistent solution. This leads to the problem of figuring out how to improve on the rate of convergence of the SLLM while maintaining its high accuracy. The objective of this thesis is to introduce a method that makes use of quasilinearization in pairs of equations to decouple large systems of differential equations. This numerical method, hereinafter called the paired quasilinearization method (PQLM) seeks to break down a large coupled nonlinear system of differential equations into smaller linearized pairs of equations. We describe the numerical algorithm for general systems of both ordinary and partial differential equations. We also describe the implementation of spectral methods to our respective numerical algorithms. We use MATHEMATICA to carry out the numerical analysis of the PQLM throughout the thesis and MATLAB for investigating the influence of various parameters on the flow profiles in Chapters 4, 5 and 6. We begin the thesis by defining the various terminologies, processes and methods that are applied throughout the course of the study. We apply the proposed paired methods to systems of ordinary and partial differential equations that model boundary layer flow problems. A comparative study is carried out on the different possible combinations made for each example in order to determine the most suitable pairing needed to generate the most accurate solutions. We test convergence speed using the infinity norm of solution error. We also test their accuracies by using the infinity norm of the residual errors. We also compare our method to the SLLM to investigate if we have successfully improved the convergence of the SLLM while maintaining its accuracy level. Influence of various parameters on fluid flow is also investigated and the results obtained show that the paired quasilinearization method (PQLM) is an efficient and accurate method for solving boundary layer flow problems. It is also observed that a small number of grid-points are needed to produce convergent numerical solutions using the PQLM when compared to methods like the finite difference method, finite element method and finite volume method, among others. The key finding is that the PQLM improves on the rate of convergence of the SLLM in general. It is also discovered that the pairings with the most nonlinearities give the best rate of convergence and accuracy

Dynamic Analysis of the impact of Capital Structure on Firm Performance in Nigeria

The thesis examines the dynamic impact of capital structure on firm performance in Nigeria. The aims of this thesis are; first, to investigate the impact of capital structure of firms on their performance in a dynamic framework. This is unlike previous studies in the capital structure literature that have used static analysis. Second, to examine the dynamic feedback from performance to capital structure using the two-step system generalized method of moment estimator. Third, to explore the determinants or variables that influence capital structure choice of firms in Nigeria and the rate of adjustment to achieve optimal debt position. Fourth, to assess the possibility of non-monotonicity effect of capital structure on firm performance and non-monotonicity effect of performance on capital structure. The second chapter discusses the theoretical framework and review the empirical literatures on capital structure and firm performance.Also, the chapter review empirical literature on firm performance and capital structure as well as on determinants of capital structure. The study find much evidence in support of the theoretical prediction of the agency cost theory of capital structure. The stuudy observed that there are limited empirical studies on the franchise value and efficiency-risk hypotheses of reverse causality from performance to capital structure.The empirical literatures on determinants of capital structure suggests that both firm specific and country factors are important variables that drive capital structure choice of firms. The thrid chapter examines the methodology of the study. The population, sampling and sampling size, estimation methods were discussed in this chapter. The fourth chapter analysis and described the data employed in the study.Specifically, the results of the dynamic relationship between capital structure and firm performance were presented in this chapter. The results indicate that capital structure has non-monotonic effect on firm performance thereby supports the agency cost theory of capital structure. The fifth chapter provides results on the reverse causality between performance and capital structure. The findings indicate that there is reverse causality between performance and capital structure. This is evidence in the statistically significant negative finding between performance and capital structure. This finding support the franchise value hypothesis. The findings of this study also reveal that non-monotonic relationship exist between performance and capital structure. The sixth chapter provides results on the determinants of capital structure of Nigerian firms. The findings indicate that both firm specific variables (return on equity, risk, profitablity, age, size, tangibility, growth opportunities, dividend, ownership) and country variables (inflation, interest rates, credit to private sector as percentage of gross domestic product, institutional quality) jointly influence capital structure choice of firms in Nigeria. The findings equally indicate that firms in Nigeria adjust to their optimal debt target relatively faster with lower cost of adjustment because of better access to private debt that public debt. Conclusions from the empirical chapters indicate that firm specific and country factors are major determinants of capital structure of firms in Nigeria and that capital structure choice of firms influence their performance. Equally, there is evidence that indicate that there is reverse causality from performance to capital structure of firms. The study therefore contend that the agency cost theory of capital structure and franchise value hypothesis are portable in the Nigerian context. Full portability of these theories in emerging market like Nigeria may require modifications to accommodate specific peculiarities of operating and business environment of Nigeria

Consumption Expenditures as Key Drivers of Economic Growth and Manufacturing Expansion in Nigeria

This study has two goals: first, to investigate the effects of private and government consumption expenditures as well as imports and exports on economic growth in Nigeria. Second, to analyse the implications of these expenditures for manufacturing sector expansion given the special growth-enhancing properties of manufacturing as articulated in the theoretical and empirical literature. Our estimations of the three models specified for the study are based on the Nigeria time-series data from the World Development Indicators database between 1981 and 2019 using Pesaran’s ARDL regression methodology after testing the trend properties of the series. The validity and reliability of regression results were certified by the regression diagnostics.Our findings support significant positive effects of private consumption expenditure and exports on economic growth while government consumption expenditure and imports exert a significant negative impact on growth. These two expenditures that grow the economy neither significantly expand nor decrease manufacturing as the positive impacts of private consumption expenditure and the negative impacts of exports were insignificant. The negative effects on manufacturing of government consumption expenditure and imports were not significant. However, economic growth was found to significantly expand manufacturing activities. We conclude that over two-thirds of Gross Domestic Product expenditures constitute a leakage from the economy being insignificant to drive manufacturing expansion. The resultant loss of the flow of growth-enhancing externalities from manufacturing to other sectors of the economy may constrain future economic growth or cause the economy to grow in an unsustainable manner. Keywords: consumption, government expenditure, economic growth, manufacturing, exports. DOI: 10.7176/DCS/11-1-05 Publication date: January 31st 202

CFD modelling of mono-component and binary gas-solid fluidized beds with application to industrial materials

Fluidized bed technology is employed in a wide range of industrial applications, covering the pharmaceutical, food, chemical and petrochemical industries as well as the mining and power generation industries. However in most industrial applications of fluidization, the suspension consists of non-spherical particles of different diameters and sometimes-different densities. Computational Fluid Dynamics modelling has been recognized by several in academia and industry as an indepensible tool to study multiphase systems including fluidization. CFD models that describe gas solid flow systems can be formulated at different levels of mathematical detail. The use of the Eulerian-Eulerian approach has been considered as the highest possible level of continuum modelling where both the fluid and particle phase are treated as interpenetrating continua and mass and momentum conservation equations are solved for each phase. The Eulerian-Eulerian approach has been successfully used by many researchers for tackling problems relating to the modelling of gas-solid fluidized beds coupled with using the kinetic theory of granular flow for the description of the solid phase as derived from the kinetic theory of gases. However, most of the CFD investigations carried out to date have been limited to the study of the fluidization behaviour of mono-component gas-solid systems of modelling type materials (e.g. Ballotini). The aim of this thesis is to address the computational modelling of mono-component and binary gas-solid fluidized beds with particular focus placed on industrial materials. This work, sponsored by Huntsman Tioxide, is concerned with the titanium refining industry where a bubbling fluidized bed is used for extracting titanium from naturally occurring ore. The refining process begins in a fluidized bed with the chlorination of titanium rich rutile ore which is composed of many constituents. Due to the size and density differences of all the feedstock components used in the process, there are industrial concerns about the pervasiveness of dead zones within the fluidized bed as a result of feed stock segregation. Thus, the objective of the work is to develop a model capable of predicting the degree of mixing and segregation in the fluid bed system. To this end, the following powders, slag, natural and synthetic rutile, belonging to the Geldart Group B classification and used as feedstock in the Huntsman Tioxide chlorination process, were provided for the experimental and computational investigations in this project. This work presents a new hydrodynamic model for the CFD simulations of the mono-component and binary industrial materials using a commercial code (CFX4.4). The modelling development allowed the assessment of suitable governing equations for the description of the internal stress relevant to the solid phase(s), the fluid-particle and particle-particle interphase exchange terms. For the mono-component systems, a new expression for the fluid-particle interaction term has been developed based on the fluid bed elasticity concept originally proposed by Wallis (1969). Consequently, the procedure followed to obtain a stability criterion was re-examined analytically and subsequently numerical simulations were performed to validate the ability of the model to predict the fluidization behavior of the materials investigated. As part of the development, a comparison was conducted between the model proposed in this thesis and the granular kinetic theory model in order to assess the impact of the collisional stresses on the numerical predictions. The new modelling approach was subsequently extended to the modelling of binary systems using the three fluid approach, where a separate momentum equation is solved for the fluid and each solid phase. This part of the study also assessed the effect of the particle- particle drag force on the dynamics of the binary system by comparing three different closures available in literature and catering for this contribution against a reference test case where such contribution was not accounted for. Similar to the approach followed for the mono-component systems, a sensitivity analysis on the effect of the collisional stress on the simulations of the binary systems was also performed. Furthermore, a sensitivity analysis on grid and time step resolution was also carried out. Results of these analyses enabled the qualitative and quantitative numerical investigation into the mixing and segregation behaviour of the binary mixture of the industrial materials provided for this project. In this investigation, three different average compositions, corresponding to the average mass fraction of jetsam particles of 0.25, 0.50, 0.75 in the bed were considered, so that the hydrodynamic behavior of three binary mixtures in all was studied. In addition, a new fluid-particle interaction force closure for well mixed binary systems based on the two-fluid approach, where mixture continuity and momentum equations are employed in the description of the solid phases, was also derived and corresponding CFD simulations are carried out to assess the reliability of the derived mixture models

System Requirements Analysis for e-learning systems using grid

Until recent years network-based education and grid technologies were two distinct areas. But e-learning systems have been increasingly addressing learning resources sharing (text, images, video, on-line data, etc.) and reuse, interoperability and other more different modes of interactions. E-learning systems consist of complex activities and most of them have been designed based on client-server or peer to peer, and recently web services architecture. These systems have major drawback because of their limitations in scalability, availability, distribution of computing power and storage systems, as well as sharing information between users that contribute to these systems. In this context the use of grid technology reveals its utility and availability, as scalable, flexible coordinated and secure resource sharing among geographically distributed individuals or institutions, in the perspective of e-learning.networked-based, education, grid technologies, e-learning systems,resouce sharing, interoperability, standardisation.

Weathering and Iron Oxide Mineralogy of Hong Kong Granite

This thesis describes the research work done on the mineralogy and properties of iron oxides in a weathered granite from Hong Kong Island. In general, after the initial introductory chapters, subsequent chapters present studies made using different techniques with one chapter discussing one technique. Chapter 1 gives the Introduction to the research and presents a basis for the study as well as the aim of the research. The methodology used in accomplishing the aims is presented. Chapter 2 reviews the past literature relating to the investigation. The structure of the different iron oxides as proposed by past workers as well as the occurence, properties and characteristics of iron oxides in the soil environment are reviewed. In Chapter 3 descriptions of the soil materials are given in order to provide a framework of reference for the main part of the work. The sampling methods and both the field and laboratory descriptions of the soils used in the study are provided together with a brief geology of the sampling site. The initial sample preparation done prior to testing the soils has been outlined and results of preliminary tests such as particle size analysis and scanning electron microscopy presented. Chapter 4 presents the aspect of the investigation where wet chemistry was used to provide additional information which helped in explaining some of the observation of the main techniques used. The chemical tests perfomed included concentration methods for the iron oxides using the 5 M boiling NaOH and HF methods, selective dissolution using dithionite citrate bicarbonate and acid ammonium oxalate methods, and determination of the chemical contents of the untreated soils and residues obtained from the different treatments. pH and organic content determination of the soils were also performed. Chapter 5 presents the electron microscopy study on the different fractions of the soils. The method has the advantage of allowing direct observation of the particles being studied. The theories explaining the acquisition of images in the transmission electron microscope are included. The experimental methods used for transmission and scanning electron microscopy are also presented. Complementary results of scanning electron microscopy are also given. The clay minerals and iron oxide minerals were identified on the basis of data provided by electron diffraction and lattice images, and the morphology of the different minerals is described. Chapter 6 presents X--- ray diffraction analysis on the samples. The technique complements electron microscopy in the identification of the mineralogy of the various soil components. Furthermore X-ray diffraction made it possible to estimate Al substitution for Fe in the iron oxide structure, a property that helped in explaining the formation and occurence of the iron oxides in the soils. The experimental technique and testing procedures are given and the results presented and discussed. Chapter 7 gives the details of the infrared spectroscopy and differential scanning calorimetery study of the soils. Both methods allowed a study of the mineralogy of the clays and iron oxides in the soils, thereby complementing the work done using electron microscopy and X-ray diffraction. Some additional information on particle size of some of the clay minerals was also obtained. The characteristics of the infrared vibrations and DSC traces of the iron oxides have been explained on the basis of some peculiar properties of the oxides. Chapter 8 presents a general discussion on the basis of the collective results obtained from using the different analytical techniques. The chapter also serves as a summary for some of the results presented earlier in the different chapters. Important conclusions drawn from these results are presented and discussed