The ever increasing demand for a clean and renewable energy source has stimulated research for alternatives for the use of fossil fuels, which contribute significantly to global warming. The SO2 oxidation reaction was studied for production of hydrogen as a clean and renewable energy carrier. This reaction occurs at a lower standard electrode potential (0.158 V vs. SHE) than normal water electrolysis (1.23 V vs. SHE). This is a theoretical indication that the SO2 oxidation reaction has possible potential when compared to normal water electrolysis, since hydrogen production may occur at lower potentials and therefore lower cost. Rh was compared with Pt for the SO2 oxidation reaction since little research has been done on this catalyst and many studies exist in which Pt was used as catalyst. The oxygen reduction reaction and ethanol oxidation reaction were also included in this study to create a foundation for the catalysts studied, since the SO2 oxidation reaction is complicated by different adsorbed species that can form according to various mechanisms. The electrochemical techniques employed in this study to characterize the catalysts included cyclic voltammetry from which onset potentials and limiting current densities were determined, as well as from which some qualitative analysis was done. Linear polarization experiments were used during rotating disk electrode studies from which Levich and Koutecky-Levich analyses were done and the number of electrons transferred calculated and compared between the two catalysts. From the Koutecky-Levich analysis the kinetic current density was also obtained for use in Tafel analysis for further comparison between catalysts. It was found that Rh showed good behaviour for the oxygen reduction reaction when compared to Pt with similar onset potentials and limiting current densities. From Levich analysis it was concluded that both catalysts achieved diffusion limitation at high overpotentials. However, from the calculated number of electrons transferred it was evident that a difference in mechanism existed between catalysts and that the mechanism for both changed in the potential range studied, which is confirmed by the Tafel slopes. For the ethanol oxidation reaction it was shown that Rh exhibited very low catalytic activity in comparison with Pt. However, it was concluded from cyclic voltammetry and rotating disk electrode studies that more adsorbed species were present on the surface of Rh than on Pt. These results confirmed the possibility of using Rh as a co-catalyst together with Pt since it was shown from rotating disk electrode studies that low adsorption of ethanol and its oxidation products caused species to be transported away from the surface of the electrode during rotation. For the SO2 oxidation reaction it was found that Rh exhibited very poor catalytic activity together with being very susceptible to poisoning by adsorbed species. Pt showed very good behaviour, which corresponded well with what had been observed in literature. Levich analysis revealed that Pt did not exhibit diffusion limitation and Koutecky-Levich analysis revealed that a 2 electron reaction occurred on Pt, which corresponds with the SO2 oxidation reaction during which 2 electrons are transferred. It was, therefore, shown that Rh could exhibit good behaviour and act as a suitable catalyst in certain circumstances. However, for the SO2 oxidation reaction, which was the main focus of this study it was shown that Rh is not a suitable catalyst, either alone or as co-catalyst. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

We present new measures of the rotation curves of disc galaxies from z~0.2 to z~1.7, using deep exposures from both DEIMOS and LRIS spectrographs on the Keck telescopes in combination with multi-band imaging from the Hubble Space Telescope. We do this with a new modelling code, curvation, which has been optimised to extract the rotation velocity measurements from galaxies at intermediate and high redshift. To this end, we conduct a bulge-to-disc de-composition to allow us to de-project observed velocities to extract a model of the intrinsic rotation curve. We demonstrate the improved accuracy and precision of these measurements via a number of tests, but primarily in recovering an intrinsic scatter of the high redshift Tully-Fisher relation which is similar to that found locally. We show for the first time that the stellar mass Tully-Fisher relation is tightly in place at z~1, the normalisation of which has evolved less than 0.02±0.02 dex in stellar mass from z~1.7 to z~0.2. We do however see evidence for evolution in classic B-band Tully-Fisher relation, which is brighter at z~1 by 0.85±0.28 magnitudes than that at z~0.3. This trend is consistent with what was previously known about the evolving star-formation rates of disc galaxies. We then explore the potential drivers of these trends in the Tully-Fisher relation by estimating the baryonic and dark matter content of our galaxies. We also discover a surprising trend in the bulgeless disc galaxies at high redshift, which may be evolving differently from other rotationally supported galaxies. In the context of work which has been conducted at z~2, we discuss our results of a stellar mass Tully-Fisher relation which is strikingly similar over two-thirds of the age of the Universe.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The ultra high capacity disk-based data recorders now entering service offer not just a convenient and inexpensive alternative to conventional tape systems for applications like Telemetry and Flight Test but also a unique opportunity to rethink the classical models for data capture, analysis and storage. Based on ‘open architecture’ interface standards- typically SCSI-this new generation of products represents an entirely new approach to the way data is handled. But the techniques they employ are equally applicable to any SCSI storage device. This Paper discusses a range of practical scenarios illustrating how it is now possible to `mix-and-match’ recording technologies at will-disk-array, DLT, DTF, ExaByte, JAZ, ZIP, DVD, etc.- to produce an almost infinite combination of readily scaleable plug-and-play data capture, analysis and archiving solutions. The cost and reliability benefits arising from the use of standard mass-produced storage sub-systems are also considered

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

This thesis describes and develops two planarization algorithms for geographic routing and a geographic routing protocol for mobile ad hoc and sensor networks. As all nodes are mobile and there is no fixed infrastructure, the design of routing protocols is one of the most challenging issues in mobile ad hoc and sensor networks. In recent years, greedyface- greedy (GFG) geographic routing protocols have been widely used, which need nodes to construct planar graphs as the underlying graphs for face routing. Two kinds of planarization algorithms have been developed, idealized and realistic planarization algorithms, respectively. The idealized planarization algorithms make the ideal assumption that the original network graph is a unit-disk graph (UDG). On the other hand, the realistic planarization algorithms do not need the original network to be a UDG. We propose an idealized planarization algorithm, which constructs an Edge Constrained Localized Delaunay graph (ECLDel). Compared to the existing planarized localized Delaunay graph [42], the construction of an ECLDel graph is far simpler, which reduces the communication cost and saves the network bandwidth. We propose a Pre-Processed Cross Link Detection Protocol (PPCLDP), which generates a planar spanning subgraph of the original network graph in realistic environments with obstacles. The proposed PPCLDP outperforms the existing Cross Link Detection Protocol [32] with much lower communication cost and better convergence time. In GFG routing protocols, greedy routing may fail at concave nodes, in which case, face routing is applied to recover from the greedy routing failure. This may cause extra hops in routing in networks containing voids. We propose a Hill-Area-Restricted (HAR) routing protocol, which avoids the extra hops taken in the original GFG routing. Compared to the existing Node Elevation Ad hoc Routing [4], the proposed HAR guarantees the packet delivery and decreases the communication cost greatly.

<p>Two state of the art finite element reduction techniquespreviously validated against the direct finite element method,one based on classical modal analysis and another based oncomponent mode synthesis, are applied for efficient mistunedfree vibration and forced response analysis of several bladeddisk geometries. The methods are first applied to two testcases in order to demonstrate the differences in computationalefficiency as well as to validate the methods againstexperimental data. As previous studies have indicated, nonoticeable differences in accuracy are detected for the currentapplications, while the method based on classical modalanalysis is significantly more efficient. Experimental data(mistuned frequencies and mode shapes) available for one of thetwo test cases are compared with numerical predictions, and agood match is obtained, which adds to the previous validationof the methods (against the direct finite element method).</p><p>The influence of blade-to-blade coupling and rotation speedon the sensitivity of bladed disks to mistuning is thenstudied. A transonic fan is considered with part span shroudsand without shrouds, respectively, constituting a high and alow blade-to-blade coupling case. For both cases, computationsare performed at rest as well as at various rotation speeds.Mistuning sensitivity is modelled as the dependence ofamplitude magnification on the standard deviation of bladestiffnesses. The finite element reduction technique based onclassical modal analysis is employed for the structuralanalysis. This reduced order model is solved for sets of randomblade stiffnesses with various standard deviations, i.e. MonteCarlo simulations. In order to reduce the sample size, thestatistical data is fitted to a Weibull (type III) parametermodel. Three different parameter estimation techniques areapplied and compared. The key role of blade-to-blade coupling,as well as the ratio of mistuning to coupling, is demonstratedfor the two cases. It is observed that mistuning sensitivityvaries significantly with rotation speed for both fans due toan associated variation in blade-to-blade coupling strength.Focusing on the effect of one specific engine order on themistuned response of the first bending modes, it is observedthat the mistuning sensitivity behaviour of the fan withoutshrouds is unaffected by rotation at its resonant condition,due to insignificant changes in coupling strength at thisspeed. The fan with shrouds, on the other hand, shows asignificantly different behaviour at rest and resonant speed,due to increased coupling under rotation. Comparing the twocases at resonant rotor speeds, the fan without shrouds is lessor equally sensitive to mistuning than the fan with shrouds inthe entire range of mistuning strengths considered.</p><p>This thesis’scientific contribution centres on themistuning sensitivity study, where the effects of shrouds androtation speed are quantified for realistic bladed diskgeometries. However, also the validation of two finite elementreduction techniques against experimental measurementsconstitutes an important contribution.</p>

Finding the shortest paths in a graph has been studied for a long time, and there are many main memory based algorithms dealing with this problem. Among these, Dijkstra's shortest path algorithm is one of the most commonly used efficient algorithms to the non-negative graphs. Even more efficient algorithms have been developed recently for graphs with particular properties such as the weights of edges fall into a range of integer. All of the mentioned algorithms require the graph totally reside in the main memory. Howevery, for very large graphs, such as the digital maps managed by Geographic Information Systems (GIS), the requirement cannot be satisfied in most cases, so the algorithms mentioned above are not appropriate. My objective in this thesis is to design and evaluate the performance of external memory (disk-based) shortest path algorithms and data structures to solve the shortest path problem in very large digital maps. In particular the following questions are studied:What have other researchers done on the shortest path queries in very large digital maps?What could be improved on the previous works? How efficient are our new shortest paths algorithms on the digital maps, and what factors affect the efficiency? What can be done based on the algorithm? In this thesis, we give a disk-based Dijkstra's-like algorithm to answer shortest path queries based on pre-processing information. Experiments based on our Java implementation are given to show what factors affect the running time of our algorithms.

In this thesis I present an investigation into the presence, nature and origin of the thick disk component in late-type galaxies. I use ground-based wide-field observations to study two edge-on low-mass galaxies in the Local Universe: NGC 4244 and NGC 55. The large field-of-view of the ground-based data enables me to inspect the radial and vertical structure of each galaxy. The vertical profiles are studied up to larger distances fromthemid-plane than in any previous study and the presence of a second disk component beyond the thin disk with a larger scale height is revealed for both galaxies. The high-quality data allows me to carry out stellar population and metallicity studies for stars above and below the plane. Furthermore, direct comparisons with two simulated low-mass galaxies provided by the Preston group at the University of Central Lancashire are carried out. By putting the results for NGC 4244 and NGC 55 into context with the thick disk properties from these simulations and from the literature, the most likely thick disk formation scenarios can be pointed out. The bulgeless low-mass systemNGC 4244 lies at a distance of 4.4 Mpc and is studied using V- and I-band wide-field images taken with Suprime-Cam on the Subaru telescope, Hawaii. The extra-planar regions of NGC 4244 show the presence of a large population of Red Giant Branch (RGB) stars and some Asymptotic Giant Branch (AGB) stars. The best strategy to study the presence and structure of a thick disk component is to use the vertical diffuse light profiles in the crowded central regions and RGB star counts in the sparser and sky background dominated outskirts. The profiles show evidence for the presence of a sparsely populated second structural component beyond ∼ 2 kpc above and below the mid-plane. The profiles are fitted with a twodisk model, where each disk is approximated by an isothermal, self-gravitating sheet. A Bayesian model comparison confirms the need for a second disk component in the profile fit. Furthermore, the AGB profiles are inspected and are found to have a lower scale height than the RGB profiles. Metallicity studies of the RGB population in the thick disk component reveal that the metallicity is much lower than the solar metal-licity. Last, the scale length of the thin disk is quantified from the diffuse light radial profiles. At a distance of 1.9 Mpc the Magellanic type low-mass galaxy NGC 55 is studied using V- and I-band images from the VIsible MultiObject Spectrograph (VIMOS) in imaging mode on the Very Large Telescope (VLT, UT3) on Cerro Paranal, Chile. The very central regions of the galaxy are not covered by the VIMOS pointings so I use additional images from the Curtis-Schmidt telescope on Cerro Tololo. As for NGC 4244, I find that the RGB star count profiles extend to larger scale heights than the AGB profiles. The combined diffuse light + RGB profiles show evidence for a very prominent second disk component beyond ∼ 2 kpc above and below the plane. The metallicity studies of the RGB population show, that there is no trend in themetallicity with height above or below the plane. As for NGC 4244 the metallicity is significantly lower than the solar metallicity. Furthermore, the scale length of the thin and thick disk is derived from the radial profiles. The properties of thick disks in galaxies of all masses is studied by compiling the results fromobserved and simulated galaxies in the literature in addition to the results for NGC 4244, NGC 55 and the two simulated low-mass galaxies provided by the Preston group. By studying the similarities, differences and global trends with mass in the thick disk properties it is possible to confront the thick disk formation models. I find that none of the formation scenarios can be ruled out and even a hybrid scenario is possible.

Ce mémoire a pour but d'étudier les propriétés des solutions à l'équation aux valeurs propres de l'opérateur de Laplace sur le disque lorsque les valeurs propres tendent vers l'in ni. En particulier, on s'intéresse au taux de croissance des normes ponctuelle et L1. Soit D le disque unitaire et @D sa frontière (le cercle unitaire). On s'inté- resse aux solutions de l'équation aux valeurs propres f = f avec soit des conditions frontières de Dirichlet (fj@D = 0), soit des conditions frontières de Neumann ( @f @nj@D = 0 ; notons que sur le disque, la dérivée normale est simplement la dérivée par rapport à la variable radiale : @ @n = @ @r ). Les fonctions propres correspondantes sont données par : f (r; ) = fn;m(r; ) = Jn(kn;mr)(Acos(n ) + B sin(n )) (Dirichlet) fN (r; ) = fN n;m(r; ) = Jn(k0 n;mr)(Acos(n ) + B sin(n )) (Neumann) où Jn est la fonction de Bessel de premier type d'ordre n, kn;m est son m- ième zéro et k0 n;m est le m-ième zéro de sa dérivée (ici on dénote les fonctions propres pour le problème de Dirichlet par f et celles pour le problème de Neumann par fN). Dans ce cas, on obtient que le spectre SpD( ) du laplacien sur D, c'est-à-dire l'ensemble de ses valeurs propres, est donné par : SpD( ) = f : f = fg = fk2 n;m : n = 0; 1; 2; : : :m = 1; 2; : : :g (Dirichlet) SpN D( ) = f : fN = fNg = fk0 n;m 2 : n = 0; 1; 2; : : :m = 1; 2; : : :g (Neumann) En n, on impose que nos fonctions propres soient normalisées par rapport à la norme L2 sur D, c'est-à-dire : R D F2 da = 1 (à partir de maintenant on utilise F pour noter les fonctions propres normalisées et f pour les fonctions propres quelconques). Sous ces conditions, on s'intéresse à déterminer le taux de croissance de la norme L1 des fonctions propres normalisées, notée jjF jj1, selon . Il est vi important de mentionner que la norme L1 d'une fonction sur un domaine correspond au maximum de sa valeur absolue sur le domaine. Notons que dépend de deux paramètres, m et n et que la dépendance entre et la norme L1 dépendra du rapport entre leurs taux de croissance. L'étude du comportement de la norme L1 est étroitement liée à l'étude de l'ensemble E(D) qui est l'ensemble des points d'accumulation de log(jjF jj1)= log : Notre principal résultat sera de montrer que [7=36; 1=4] E(B2) [1=18; 1=4]: Le mémoire est organisé comme suit. L'introdution et les résultats principaux sont présentés au chapitre 1. Au chapitre 2, on rappelle quelques faits biens connus concernant les fonctions propres du laplacien sur le disque et sur les fonctions de Bessel. Au chapitre 3, on prouve des résultats concernant la croissance de la norme ponctuelle des fonctions propres. On montre notamment que, si m=n ! 0, alors pour tout point donné (r; ) du disque, la valeur de F (r; ) décroit exponentiellement lorsque ! 1. Au chapitre 4, on montre plusieurs résultats sur la croissance de la norme L1. Le probl ème avec conditions frontières de Neumann est discuté au chapitre 5 et on présente quelques résultats numériques au chapitre 6. Une brève discussion et un sommaire de notre travail se trouve au chapitre 7. / The goal of this master's thesis is to explore the properties of the solutions of the eigenvalue problem for the Laplace operator on a disk as the eigenvalues go to in nity. More speci cally, we study the growth rate of the pointwise and the L1 norms of the eigenfunctions. Let D be the unit disk and @D be its boundary (the unit circle). We study the solutions of the eigenvalue problem f = f with either Dirichlet boundary condition (fj@D = 0) or Neumann boundary condition ( @f @nj@D = 0; note that for the disk the normal derivative is simply the derivative with respect to the radial variable: @ @n = @ @r ). The corresponding eigenfunctions are given by: f (r; ) = fn;m(r; ) = Jn(kn;mr)(Acos(n ) + B sin(n )) (Dirichlet) fN (r; ) = fN n;m(r; ) = Jn(k0 n;mr)(Acos(n ) + B sin(n )) (Neumann) where Jn is the nth order Bessel function of the rst type, kn;m is its mth zero and k0 n;m is the mth zero of its derivative (here we denote the eigenfunctions for the Dirichlet problem by f and those for the Neumann problem by fN). The spectrum of the Laplacian on D, SpD( ), that is the set of its eigenvalues, is given by: SpD( ) = f : f = fg = fk2 n;m : n = 0; 1; 2; : : :m = 1; 2; : : :g (Dirichlet) SpN D( ) = f : fN = fNg = fk0 n;m 2 : n = 0; 1; 2; : : :m = 1; 2; : : :g (Neumann) Finally, we normalize the L2 norm of the eigenfunctions on D, namely: R D F2 da = 1 (here and further on we use the notation F for the normalized eigenfunctions and f for arbitrary eigenfunctions). Under these conditions, we study the growth rate of the L1 norm of the normalized eigenfunctions, jjF jj1, in relation to . It is important to mention that the L1 norm of a function on a given domain corresponds to the iv maximum of its absolute value on the domain. Note that depends on two parameters, m and n, and the relation between and the L1 norm depends on the regime at which m and n change as goes to in nity. Studying the behavior of the L1 norm is linked to the study of the set E(D) which is the set of accumulation points of log(jjF jj1)= log : One of our main results is that [7=36; 1=4] E(B2) [1=18; 1=4]: The thesis is organized as follows. Introduction and main results are presented in chapter 1. In chapter 2 we review some well-known facts regarding the eigenfunctions of the Laplacian on the disk and the properties of the Bessel functions. In chapter 3 we prove results on pointwise growth of eigenfunctions. In particular, we show that, if m=n ! 0, then, for any xed point (r; ) on D, the value of F (r; ) decreases exponentially as ! 1. In chapter 4 we study the growth of the L1 norm. Eigenfunctions of the Neumann problem are discussed in chapter 5. Some numerical results are presented in chapter 6. A discussion and a summary of our work could be found in chapter 7.

Indexing and processing strings are very important topics in database management. Strings can be database records, DNA sequences, protein sequences, or plain text. Various string operations are required for several application categories, such as bioinformatics and entity resolution. When the string count or sizes become very large, several state-of-the-art techniques for indexing and processing such strings may fail or behave very inefficiently. Modifying an existing technique to overcome these issues is not usually straightforward or even possible. A category of string operations can be facilitated by the suffix tree data structure, which basically indexes a long string to enable efficient finding of any substring of the indexed string, and can be used in other operations as well, such as approximate string matching. In this document, we introduce a novel efficient method to construct the suffix tree index for very long strings using parallel architectures, which is a major challenge in this category. Another category of string operations require clustering similar strings in order to perform application-specific processing on the resulting possibly-overlapping clusters. In this document, based on clustering similar strings, we introduce a novel efficient technique for record linkage and entity resolution, and a novel method for correcting errors in a large number of small strings (read sequences) generated by the DNA sequencing machines.