Thesis (Ed.D.)--Boise State University, 2009. / Includes abstract. Includes bibliographical references (leaves 133-144).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Jan. 15, 2009). PDF text: ix, 257 p. ; 3 Mb. UMI publication number: AAT 3315319. Includes bibliographical references. Also available in microfilm and microfiche formats.

It is widely recognised that digitalisation has a significant impact on the organisational environment, triggering challenges on all levels of organisations irrespective of the industry. Despite the fact that digitalisation also brings forth opportunities, ultimately, companies are required to transform their businesses to stay competitive. Although leadership plays a crucial role in this digital transformation process, there is only little research on the link between leadership theory and digitalisation as well as a lack of understanding of what effective leaders in the digital age should encompass. Hence, the purpose of this paper is to add to the discussion of effective leadership in the digital age by investigating employees’ perception of leadership. Therefore, we conduct a qualitative study with twelve semi-structured interviews. Following an abductive research approach, we interpret the empirical findings with the prior established theoretical framework and further literature to fulfil the purpose of research. The study reveals that effective leadership in digitalisation as perceived by employees consists of an interplay between seven leadership skills and respective leadership behaviours that are also partly reflected in specific leadership styles.

General relativity describes gravity in terms of an interacting massless spin-2 field - the graviton. This 100-year-old theory has been spectacularly successful in explaining observations. However, theoretical exploration and the cosmological constant problem motivate the study of alternative theories of gravity. Recently, there has been great progress in understanding theories that give the graviton a mass. This thesis considers several aspects of these massive spin-2 effective field theories and related theories. These theories are first studied from the perspective of scattering amplitudes. The most general 2 → 2 scattering amplitude is constructed for theories containing a single massive graviton or vector. These amplitudes are then used to find the highest strong coupling scales in such theories, assuming a particular scaling of fields and momenta. Generalisations to include additional fields and self-interactions for massive higher-spin fields are also discussed. Constraints that arise from the existence of an ultraviolet completion are then studied. It is shown using dispersion relation arguments that the pseudo-linear massive spin-2 theory cannot admit an analytic, Lorentz-invariant, and unitary ultraviolet completion, but that such completions are not ruled out for massive vector theories. The behaviour of massive spin-2 theories under dimensional reduction is also explored. Stability conditions and the lower-dimensional spectrum are derived for the Kaluza-Klein dimensional reduction of a partially massless graviton and a massive graviton on an Einstein product manifold. Additionally, the nonlinear dimensional reduction of the zero modes in dRGT massive gravity is shown to produce a mass-varying massive gravity theory. Lastly, attempts to construct a version of unimodular gravity containing a massive graviton are discussed. A candidate theory is proposed and is shown to have pathologies. Dimensional reduction is then used to generate massive spin-2 theories with noncanonical kinetic terms and auxiliary fields. These theories are shown to be equivalent to the Fierz-Pauli theory, which provides further evidence for the uniqueness of the kinetic term used in dRGT massive gravity.

Measuring transport properties of rock samples under stress is essential to understanding and predicting the migration of fluids within the Earth's crust. Mudrocks play an essential role in petroleum systems as they are often the source rock and may act as a seal due to their low permeability. With increasing production from unconventional reservoirs where the mudrock is source, reservoir and seal, there is now even greater demand to understand the permeability and storativity of mudstones and tight sandstones. When hydraulic fracture treatment is used to enhance production, flow of hydrocarbons into the fractures will be ultimately controlled by the matrix permeability. Knowledge of the fluid transport properties of mudstones is currently hindered by a scarcity of published experimental data. In this thesis, a combination of permeability and ultrasonic velocity measurements allied with image analysis is used to distinguish the primary microstructural controls on effective stress dependent permeability. Permeabilities of cylindrical samples of Whitby Mudstone and Eagle Ford Shale have been measured using the oscillating pore pressure method at confining pressures ranging between 30-95 MPa and pore pressures ranging between 1-80 MPa. The results show that samples must be pressure cycled in order to obtain a reproducible behaviour, after which the relationship between permeability and effective stress can be described by an exponential law. The permeability of the Whitby Mudstone samples ranges between 7 ×10-21 m2 and 2 ×10-19 m2 (7 nd to 188 nd) and decreases by ~1 order of magnitude across the applied effective stress range. The permeability of the Eagle Ford Shale samples is slightly higher ranging between 2 ×10-18 m2 and 42 ×10-18 m2 (2 μd to 42 μd) and decreases by half an order of magnitude across the applied effective stress range. Permeability is shown to be more sensitive to changes in pore pressure than changes in confining pressure yielding values of alpha between 1.1-2.1 for Whitby Mudstone and 1.6-4.6 for Eagle Ford Shale. Gas slippage (Klinkenberg) effects are restricted to pore pressures below 10 MPa in the Whitby Mudstone and therefore do not affect the results presented. The permeability-effective stress relationship is thus empirically described using a modified effective stress law in terms of confining pressure, pore pressure and a Klinkenberg effect. Use of a simple reservoir model demonstrates that if pressure dependent permeability is not taken into account, substantial overestimation of gas flow rate and original gas in place will be made from well tests. Changes in ultrasonic velocity and pore volume were related to the observed loss of permeability with increasing effective stress, providing further insight into the nature of the permeability-controlling pore network. Combining the petrophysical data with pore conductivity modelling and microstructural analysis shows that at low effective stresses, permeability is controlled by a network of long, thin crack-like pores associated with grain boundaries. At high effective stresses, these cracks are closed and fluid is restricted to flowing through a less permeable network of higher aspect ratio, stiffer, nm-scale pores in the clay matrix. Applying the methods developed in the present work to different mudstones with a range of compositions and textures will help to refine understanding of the variability in fluid-conducting pore networks, thereby advancing the interpretation of data from well logs and well tests used for reservoir evaluation.

La majeure partie des études menées pour comprendre les aspects fonctionnels du cerveau se concentre sur la notion de spécialisation fonctionnelle c’est-à-dire qu’elles visent à identifier les « rôles » des différentes structures cérébrales et les ensembles de structures qui s’activent lors d’une tâche donnée. Partant de l’hypothèse que pour comprendre comment le cerveau génère les fonctions, l’architecture du réseau de structures est tout aussi important que l’identification des structures activées, nous avons choisi d’utiliser une approche basée sur l’étude de la connectivité intracérébrale afin d’appréhender la complexité des processus cognitifs en général et des systèmes de mémoire en particulier. Pour ce faire, nous avons caractérisé la connectivité intracérébrale induite lors de tâches de mémoire spatiale (« emplacement » et « indice ») et décrit son évolution au cours de l’apprentissage et à la suite d’une lésion de l’hippocampe. La comparaison de la connectivité fonctionnelle induite par chacune des deux stratégies a permis de mettre en évidence qu’alors que la stratégie « emplacement » induit la convergence de la connectivité vers l’hippocampe, l’utilisation de la stratégie « indice » coïncide avec la convergence de la connectivité des mêmes structures vers l’amygdale. Ces résultats nous mènent à penser qu’il serait possible d’établir des dissociations entre les systèmes de mémoire en se basant sur l’étude de leurs connectivités. Dans une deuxième partie, nous avons montré que la maîtrise de la tâche « emplacement » s’accompagnait d’une modification de la connectivité fonctionnelle. En effet, au cours de l’acquisition, l’hippocampe semble se désengager du réseau sous-tendant la procédure au profit du striatum. Enfin, la dernière partie de notre travail visait à caractériser la réorganisation du réseau neuronal associée aux phénomènes compensatoires post-lésionnels. Cette étude s’est appuyée sur des techniques d’analyses statistiques multivariées. Nous avons montré que la récupération comportementale observée suite à la lésion de l’hippocampe était couplée à l’établissement d’un nouveau réseau composé des cortex entorhinal, périrhinal, rétrosplénial, prélimbique, cingulaire, piriforme, visuel et somatosensoriel ainsi que du subiculum. L’ensemble de ces résultats suggère que les processus cognitifs reposent sur la formation de clusters fonctionnels dynamiques, décrits par des schémas de connectivité entre des structures cérébrales spécialisées. / In order to understand the processes underlying memory systems, the first part of my PhD has concerned the way common cerebral structures differentially interact to sustain two different strategies tested in a spatial memory task, the water cross maze. The functional connectivity among these structures has been evaluated by using the matrices of correlation among the structure activities (revealed by counting the number of Zif 268 immunoreactive cells). We have observed a rearrangement of the functional connectivity according to the learning condition, what suggests that the activation of a memory system should be described as the focusing of functional connectivity toward the central structure of the system. My second aim has been to study the effect of brain injuries on the network supporting memory retrieval test inducing bilateral dorso-hippocampal lesions to mice. Though impaired during the first three days, lesioned-mice had the same level of performance than the sham-mice on the last day of behavioural training. Our recent studies have shown that structural equation modeling can accurately be used on low sample sizes. Therefore, we applied this method on imaging data to describe how the pattern of effective connectivity induced by learning is changed face to the lesion of the hippocampus. In other words we have shown that behavioural recuperation is coupled with a change in the pattern of connectivity. Although, this change in connectivity may be due to the use of a different strategy, this study gives an insight into understanding how decreasing cognitive resources due to age (or pathology) may be compensated.

Perovskite ferroelectrics and antiferroelectrics have attracted a lot of attention owing to their potential for device applications including THz sensors, solid state cooling, ultra high density computer memory, and electromechanical actuators to name a few. The discovery of ferroelectricity at the nanoscale provides not only new and exciting possibilities for device miniaturization, but also a way to study the fundamental physics of nanoscale phenomena in these materials. Ferroelectric nanowires show a rich variety of physical characteristics which are advantageous to the design of nanoscale ferroelectric devices such as exotic dipole patterns, a strong dependence of the polarization and phonon frequencies on the electrical and mechanical boundary conditions, as well as a dependence of the transition temperatures on the diameter of the nanowire. Antiferroelectricity also exists at the nanoscale and, due to the proximity in energy of the ferroelectric and antiferroelectric phases, a phase transition from the ferroelectric to the antiferroelectric phase can be facilitated through the application of the appropriate mechanical and electrical boundary conditions. While much progress has been made over the past several decades to understand the nature of ferroelectricity/antiferroelectricity in nanowires, many questions remain unanswered. In particular, little is known about how the truncated dimensions affect the soft mode frequency dynamics or how various electrical and mechanical boundary conditions might change the nature of the phase transitions in these ferroelectric nanowires. Could nanowires offer a distinct advantage for solid state cooling applications? Few studies have been done to elucidate the fundamental physics of antiferroelectric nanowires. How the polarization in ferroelectric nanowires responds to a THz electric field remains relatively underexplored as well. In this work, the aim is to to develop and use computational tools that allow first-principles-based modeling of electric-field-induced phenomena in ferroelectric/antiferroelectric nanowires in order to address the aforementioned questions. The effective Hamiltonian approach is a well validated model which reliably reproduces many static and dynamic properties of perovskite ferroelectric and antiferroelectrics. We begin by developing an effective Hamiltonian for the prototypical ferroelectric potassium niobate, a lead-free material which undergoes multiple structural phase transitions. Density functional theory calculations within the LDA and GGA are used to determine the effective Hamiltonian parameters for KNbO3 . By simulating an annealing within an NPT ensemble, we find that the KNbO3 parameters found from first principles underestimate the experimental transition temperatures. We apply a universal scaling technique to all of the first-principles derived parameters and are thus able to more accurately reproduce the transition temperatures predicted by experiment as well as a number of other static and dynamic properties of potassium niobate. Having determined the parameters of the effective Hamiltonian for KNbO3 , we use this as well as previously determined effective Hamiltonian parameters for PbTiO3 and BaTiO3 to study the electrocaloric effect in nanowires made of these materials. We determined that, in general, the electrocaloric effect in ferroelectric nanowires is diminished due to the reduced correlation length resulting from the finite lateral dimensions. However, certain temperature ranges were identified near ambient temperature where the electrocaloric response is enhanced with respect to bulk. The effective Hamiltonian model was also employed to study the response of the spontaneous polarization and temperature to tailored electric fields. We identified a novel means of reversing the polarization in ferroelectric nanowires which could potentially be used in the design of nanoscale THz sensors of ultra high density ferroelectric memory devices. While the soft mode frequency dynamics of bulk ferroelectrics under various mechanical boundary conditions have been studied extensively, the effects of different mechanical boundary conditions on the soft mode dynamics in ferroelectric nanowires remains relatively under-explored. We conduct a comprehensive study on PbTiO3 nanowires which explores the effects of hydrostatic pressure, applied uniaxial stress, and biaxial strain on the structural properties, transition temperatures, and soft mode dynamics. We found that depending on the particular type of mechanical boundary condition, the nanowire can exhibit either monodomain or polydomain vortex phases, drastically different from what is found for PbTiO3 bulk and originates from the critical role of the depolarizing field. We found a rich variety of dipole patterns, particularly for the polydomain states with the dipoles arranged in single and double polarization vortices depending on the type and strength of the mechanical boundary conditions. The soft mode frequency dynamics are also strongly affected by the mechanical boundary conditions. In particular we find that the frequency of the E mode in the P4mm phase is significantly larger than the A 1 mode which is in contrast with bulk PbTiO3 . This striking finding is attributed to the presence of the depolarizing field along the truncated directions which leads to mode hardening. In the last chapter, we identify the emergence of a ferroelectric state in antiferroelectric PbZrO3 nanowires and describe possible ways to stabilize the ferroelectric phase. Finally, we explore how our findings could potentially be used to improve existing technologies such as energy storage devices and electromechanical actuators as well as future technologies like solid state cooling devices.

The first study was conducted to evaluate the dietary inclusion of effective microorganisms (EM) on body weight (BW), feed intake, feed conversion ratio (FCR) and mortality of broilers, which had been either challenged or non-challenged with Clostridium perfringens (1mL of 1 x 108 CFU/mL orally). Six hundred and forty day-old Ross 788 broiler chicks were randomly allocated to thirty-two pens in groups of twenty birds per pen, giving a stocking density of ±18 birds per square meter from zero to forty days of age. The facility consisted of two rooms with sixteen pens per room. All the chicks were fed on a commercial maize-soya type diet, including a mash starter and a mash grower/finisher feed. At two weeks of age 320 chicks were inoculated with Clostridium perfringens type A through oral administration. The study had a randomised block design with four replicates and four treatments as: 1) Control-unmedicated; 2) antibiotic growth promoters (AGP) added to feed at 33g/kg; 3) EM added to feed and water at 50g/kg and 50mL/L respectively; and 4) AGP in feed at 33g/kg and EM (50g/kg) in feed and water (50mL/L). The inclusion of EM negatively affected water palatability that resulted in reduced water intake and increased FCR for the non-challenged broilers at 21 days of age. However, because feed intake was not affected, it was suggested that EM should rather be supplemented through the feed rather than through the water. The use of AGP alone or in combination with EM proved (P<0.05) broiler production performance. The cumulative feed intake, BW, FCR, average daily gain (ADG), cumulative water intake and production efficiency factor (PEF) of challenged broilers were not different (P>0.05) at 40 days of age. In this study the incidence of mortality was low (2.2%) and examination of livers and intestines showed only mild necrotic enteritis lesions. In conclusion, the findings of this study showed that EM under the current dosage failed to improve broiler production performance. A second experiment was conducted as a follow-up study to evaluate the effect of EM on broiler performance when supplemented through the feed only. Cloacal swabs were taken from all day-old chicks and a day after inoculation with Clostridium perfringens for laboratory analysis of the microorganisms in the gut. All the chicks were fed on a commercial two-phase maize-soya type diet consisting of a mash starter and a mash grower/finisher feed with additional fishmeal. The chicks from one room were inoculated orally with Clostridium perfringens, while the chicks from the other room remained unchallenged. The challenged group was inoculated orally with 1 mL (1 x 108 CFU/mL) of Clostridium perfringens as a single dose on day 14. The EM was supplemented to the broilers from day one through the feed. The supplementation of EM through the feed showed a poor performance for non-challenged whilst for the challenged showed an improved performance at 3 weeks. Both non-challenged and challenged broilers given EM had a poor performance at 6 weeks of age, and this showed inconsistent results throughout the experiment. However, it was found that the combination of both AGP and EM had a better performance than EM alone. It is noted when the results of broilers nonchallenged versus challenged control groups were compared, the challenged ones showed a better performance. The broilers showed a low mortality of 1.3% and the causes were not related to the incidence of necrotic enteritis. The gross examination of the broilers inoculated orally with Clostridium perfringens showed mild intestinal lesions. Copyright / Dissertation (MSc(Agric))--University of Pretoria, 2010. / Animal and Wildlife Sciences / unrestricted

Cette thèse s’intéresse à la caractérisation de couches diélectriques et magnétiques de structures multicouches par cavité résonante microonde. Les matériaux multicouches ont des propriétés électromagnétiques spécifiques et sont utilisés dans beaucoup de secteurs industriels, par exemple, dans les radiocommunications. La caractérisation électromagnétique reste une priorité pour la compréhension des caractéristiques de propagation des ondes électromagnétiques dans ces milieux. Dans ce travail de thèse nous proposons une nouvelle approche expérimentale pour déterminer les propriétés diélectriques effectives d’une structure multicouches en fonction des propriétés et de l’épaisseur de chacune des couches. En particulier, nous appliquons les expressions de permittivités issues de la méthode des perturbations utilisée en cavité résonante au cas d’un échantillon rectangulaire bicouche. L’analyse théorique établie a montré qu’une expression de simple proportionnalité reliant les propriétés diélectriques moyennes d’un matériau bicouche avec les propriétés diélectriques relatives et les épaisseurs des couches constituantes peut être obtenue. Cette méthode a été appliquée avec succès sur différents matériaux bicouches. En particulier, elle a permis la caractérisation d’une couche de YIG d’épaisseur très mince (19.6 μm) déposée par pulvérisation cathodique sur un substrat d’alumine en connaissant l’épaisseur et les propriétés diélectriques du substrat. La comparaison avec les résultats expérimentaux a révélé un bon accord entre théorie et mesure. L’analyse de l’incertitude associée au calcul de la permittivité par la méthode a montré une bonne sensibilité. Enfin, nous donnons les courbes de variation de la perméabilité effective mesurée pour un empilement bicouche avec une couche mince de YIG / This thesis aimed at characterizing the dielectric and magnetic layers of multilayer structures by using the technique of microwave resonant cavity. Multilayer structures have specific electromagnetic properties and are becoming increasingly important in many industrial domains, such as in radio-communication systems. The electromagnetic characterization remains a priority for understanding the characteristics of electromagnetic wave propagation in such environments. The thesis proposed a new experimental approach to determine the effective dielectric properties in a bilayer structure as a function of the characteristics and thickness of each specific layer. In particular, we apply the expressions of permittivities derived from the perturbations method which are used in resonant cavities in case of a bilayer rectangular sample. The established theoretical analysis leads us to propose a new expression of simple proportionality describing a relationship between the mean dielectric properties of a bilayer material and the relative dielectric properties and thickness of the constituent layers. The presented method has been successfully applied to different bilayer materials. Particularly, it allowed the characterization of a very thin layer (YIG layer) of thickness 19.6 microns deposited by cathodic sputtering on an alumina substrate by knowing the thickness and dielectric properties of this substrate. The comparison with the experimental results revealed good agreement between theory and measurement. The analysis of the uncertainty associated to the calculation of the permittivity by the presented method showed good sensitivity. Finally, we provide the curves of variation of the effective permeability measured for a bilayer stack

Presented in this thesis are extensive theoretical investigations into the causes and effects of carrier localization in InGaN/GaN quantum wells. The results of the calculations agree well with experimental data, where it is available, and provide additional insights into the mechanisms that lead to some of the experimentally observed effects of localization. Firstly, the wave functions of the electrons and holes in InGaN/GaN quantum wells have been calculated by numerical solution of the effective-mass Schrödinger equation. In our calculations we have assumed a random distribution of indium atoms, as suggested by the results of atom probe tomography: this allows us to find the contributions to the carriers' potential energy that arise from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We show that the fluctuations in alloy composition can be sufficient to localize the carriers; our results are in good agreement with the results of experiment and more detailed ab-initio calculations, but we also obtain information about the distribution of localized states which those methods cannot yet provide. We find that the holes are localized on a short scale in randomly-occurring regions of high indium content, whereas the electrons are localized on a longer length scale. We consider the effect of well width fluctuations and find that these contribute to electron localization, but not to hole localization. We also simulate the low-temperature photoluminescence spectrum and find good agreement with experiment for the energy, width and shape of the photoluminescence peak. Secondly, we have used first-order time-dependent perturbation theory to study the diffusion of the carriers between their localized states at non-zero temperatures. The rates for scattering via the interaction with acoustic phonons are calculated using the carrier wave functions, and the resulting master equation for the distribution of the carriers is solved by a Monte Carlo method. We find that, even towards room temperature, the carriers are localized to a small number of states, and that their diffusion lengths are proportional to a combination of the density of localized states and the localization length. The experimentally-observed `S-shape' of the photoluminescence peak energy as a function of temperature is reproduced in our results and is explained by the thermal redistribution of holes among the localized states. A reduction of the depth of this S-shape is found as the excitation power is increased, as has been observed experimentally, and which we attribute to the saturation of the localized states.