De très nombreux dispositifs de communication sans fil fonctionnant dans des bandes de fréquences différentes sont déployés dans le monde du ferroviaire afin de répondre à la multitude des usages et des besoins, des applications de contrôle-commande mettant en jeu la sécurité aux applications non vitales (Information voyageur, vidéo surveillance, télévision embarquée, etc..). Ces applications sont associées à des exigences de Qualité de service qui nécessitent des techniques d’estimation et de synchronisation performantes. Ces systèmes de communications s'appuient sur des standards qui reposent aujourd'hui sur deux technologies clefs: l'OFDM (Orthogonal Frequency-division Multiplexing) et le MIMO (Multiple-Input Multiple-Output). La combinaison MIMO-OFDM permet d'allier les avantages des deux méthodes. Cependant, l'orthogonalité entre les sous-porteuses du système MIMO-OFDM est mise à mal par les interférences entre porteuses provoquées par l'effet Doppler et l'offset de fréquence et le bruit de phase variant entre les oscillateurs à l'émission et à la réception. Ainsi, les techniques classiquement utilisées pour l'estimation de canal ou l'égalisation dans un environnement statique, fonctionnent de manière très dégradée en présence d'interférences entre sous-porteuses.L'objet de cette thèse vise à développer de nouvelles méthodes et des algorithmes d'estimation et de synchronisation du canal très sélectif en temps et en fréquence afin de permettre l'évolution des systèmes de communication vers des standards mieux adaptés aux liaisons mobiles à grande vitesse. Il convient de distinguer le cas où le canal de propagation ne varie pas pendant la durée d'un symbole OFDM et celui où il varie. Dans ce travail de thèse, nous nous sommes focalisés sur le deuxième cas. Nous avons d'abord développé un algorithme basé sur le filtre de Kalman étendu et la décomposition QR pour les transmissions MIMO-OFDM. Nous faisons d'abord une approximation du modèle d'expansion de base (BEM) pour les variations temporelles des gains complexes. Notre algorithme modélise l'évolution des coefficients de BEM à l'intérieur d'un symbole OFDM par un modèle auto régressif (AR). Puis, nous présentons un offset de fréquence normalisé appelé CFO normalisé dans la transmission du système OFDM qui introduit les interférences entre porteuse (IEP). Cet offset de fréquence est également modélisé par un modèle AR. La faculté du filtre de Kalman étendu nous permet d’estimer de manière conjointe ce CFO et les coefficients BEM. L'algorithme utilise un détecteur QR pour estimer les symboles de données. Cet algorithme a montré de bonnes performances pour des récepteurs à vitesses très élevées.Notre deuxième contribution consiste en un algorithme qui s'appuie sur le premier algorithme pour résoudre l'IEP dû au bruit de phase existant dans l'oscillateur du récepteur, ainsi que l'IEP dû à l'effet Doppler, mais en se limitant au cadre SISO. Ici, nous considérons que le bruit de phase présente une grande variance à l'intérieur d'un symbole OFDM et également entre les deux symboles OFDM suivants. Le bruit de phase est modélisé par un processus Brownien. Ensuite, le filtre de Kalman étendu estime le vecteur des coefficients de BEM et le vecteur du bruit de phase dans les symboles OFDM. Cet algorithme est très performant et présente un BER remarquable dans les cas où la connaissance du canal et du bruit de phase est mauvaise voire inexistante. / Numerous wireless communication devices operating in different frequency bands are deployed in the railway domain to answer the multitude of uses and needs, from control and command applications involving safety to non-critical applications (passenger information, video surveillance, on board TV, etc.). These applications are associated with quality of service (QOS) requirements that need estimation techniques and synchronization performance.These communications systems are based on standards that rely on two key technologies: OFDM (Orthogonal Frequency-Division Multiplexing) and MIMO (Multiple-Input Multiple-Output). The combination of MIMO and OFDM permits to benefit from the advantages of both methods. However, the orthogonality between subcarriers of OFDM-MIMO system is destroyed by inter-carrier interference caused by the Doppler effect and frequency offset and phase noise varying between oscillators at transmission and at reception. Thus, the performances of the techniques conventionally used for channel estimation and equalization in a static environment are considerably destroyed in the presence of interference between subcarriers.The purpose of this thesis is to develop new methods and algorithms for estimation and synchronization in very selective channel in time and frequency to allow the evolution of communication systems towards standards that will match better with high speed vehicular communications. It is important to distinguish the case where the propagation channel does not vary during the OFDM symbol duration and when it varies. In this thesis, we focused on the latter.We first developed an algorithm based on the Extended Kalman Filter and the QR decomposition for MIMO-OFDM transmissions. We first approximate the Expansion Model as a basis for temporal variations in complex gains. Our algorithm models the evolution of BEM coefficients within an OFDM symbol by an auto regressive model (AR). Then, we present a normalized frequency offset called normalized CFO in OFDM transmission system that introduces interference between carriers (IEP). This frequency offset is modeled by an AR model. Properties of Extended Kalman filter allow us to estimate simultaneously the two unknown variables, a vector of coefficients, the other BEM normalized frequency offset. The QR algorithm uses a detector to estimate the data symbols. This algorithm presented good performance for receivers at very high speeds. Our second contribution consists of an algorithm that uses the first algorithm to solve the IEP due to phase noise existing in the oscillator of the receiver, and the IEP due to the Doppler effect, but limited to SISO case. Here, we consider that the phase noise has a large variance within one OFDM symbol and also between the two following OFDM symbols. The phase noise is modeled by a Brownian process. Then, the Extended Kalman filter estimates the vector of coefficients of BEM and the vector of phase noise in OFDM symbols. This algorithm is very effective and has a remarkable BER performance when knowledge of the channel and phase noise is poor or nonexistent.

Thesis (Ph. D.)--Boston University, 2003. / In this thesis, studies which concern two different subjects related to phase transitions in fluids and crystalline solids are presented. Condensed matter formation, structure, and phase transitions are modeled using molecular dynamics simulations of simple discontinuous potentials with attractive and repulsive interactions. Novel phase diagrams are proposed for quasicrystals, crystals, and liquids. In the first part of the thesis, the formation of a quasicrystal in a two dimensional monodisperse system is investigated using molecular dynamics simulations of hard sphere particles interacting via a two-dimensional square-well potential. It is found that for certain values of the square-well parameters more than one stable crystalline phase can form. By quenching the liquid phase at a very low temperature, an amorphous phase is obtained. When this the amorphous phase is heated, a quasicrystalline structure with five-fold symmetry forms. From estimations of the Helmholtz potentials of the stable crystalline phases and of the quasicrystal, it is concluded that within a specific temperature range, the observed quasicrystal phase can be the stable phase. The second part of the thesis concerns a study of the liquid-liquid phase transition for a single-component system in three dimensions, interacting via an isotropic potential with a repulsive soft-core shoulder at short distance and an attractive well at an intermediate distance. The potential is similar to potentials used to describe [TRUNCATED}

Submitted in fulfilment of the requirements of the Master in Education in the Department of Educational Psychology and Special Education in the Faculty of education at the University of Zululand, 2019. / This study forms part of an ongoing attempt to understand the prevalence and management of stressors experienced by teachers. The main focus for this study is foundation phase teachers in rural Mbombela schools. Quantitative and qualitative measures were used in order to gain more insight into the prevalence and management of stressors experienced by teachers. A questionnaire with open-ended and closed-ended questionnaires was used to collect data. The results of the study indicated a high prevalence of foundation phase teachers experiencing stressors. There was also an indication that the teachers do have the necessary skills to cope with stressors that they experience as a result of their teaching and learning environment. Exercise, spirituality and planning were the main techniques teachers used in the management of stressors. Recommendations were made in order to assist teachers with the management of stressors they experience as a result of their teaching and learning environment. Avenues for further research are also discussed.

abstract: The delivery of construction projects, particularly with respect to design phase or preconstruction efforts, has changed significantly over the past twenty years. As alternative delivery methods such as Construction-Manager-at-Risk (CMAR) and Design-Build models have become more prominent, general contractors, owners, and designers have had the opportunity to take advantage of the collaborative planning opportunities that exist during the preconstruction portion of the project. While much has been written regarding the benefits of more collaborative approaches and the utilization of various tools and practices during preconstruction to mitigate risk and maximize positive outcomes, what is lesser known is how to teach a coursework that exposes students to various tools and practices that are being utilized today. The objective of this research was to create a testable methodology that can be used to analyze a developed approach that answers the question of how to teach preconstruction tools and practices. A coursework was developed and taught as a graduate level class and data was collected from the actual teaching of that class. In addition, feedback was solicited from the construction industry concerning recommended content applicable to such a class. Data was then analyzed to ascertain student retention of the material and topical content of the course. Through these findings and literature review process the methodology and baseline coursework was shown as an effective means to teach preconstruction tools and practices. / Dissertation/Thesis / Masters Thesis Construction Management 2019

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The augmented phase portrait, introduced by Sabrina Streipert and Gail Wolkowicz, is used to analyze second order rational discrete maps of the form \begin{align*} x_{n+1} = \frac{\alpha + \beta x_n + \gamma x_{n-1}}{A + Bx_n + C x_{n-1}}, \text{ for } n \in \mathbb{N}_0 =\{0,1,2,\dots, \} \end{align*} with parameters $\alpha, \, \beta, \, \gamma, \, A, \, B, \, C \geq 0$, and initial conditions, $x_{0}, \, x_{-1} > 0$. First we study the special case, \begin{align*} x_{n+1} = \frac{\alpha + \gamma x_{n-1}}{A + Bx_n}, \end{align*} with $\alpha, \, \gamma, \, B > 0$ and $A \geq 0$. Applying the change of variables, $y_n = x_{n-1}$, this equation can be rewritten as a planar system. We provide a new proof to show that oscillatory solutions have semicycles of length one, except possibly the first cycle, and that nonoscillatory solutions must converge monotonically to the equilibrium. This was originally done by Gibbons, Kulenovic, and Ladas. We also show that when the unique positive equilibrium is a saddle point, there exist nontrivial positive solutions that increase and decrease monotonically to the equilibrium, proving Conjecture 5.4.6 from the monograph by Kulenovic and Ladas. In particular, Theorem 1.2 from this monograph defines the tangent vector to the stable manifold at the equilibrium. We show that specific regions defined by the augmented phase portrait have solutions that increase and decrease monotonically to the equilibrium along the stable manifold. While Conjecture 5.4.6 was previously proven in a paper by Hoag and a paper by Sun and Xi, our proof provides a more intuitive and elementary solution. We then consider the case, \begin{equation*} x_{n+1} = \frac{\alpha + \beta (x_n + x_{n-1})}{A + B(x_n + x_{n-1})}, \end{equation*} with $\alpha, \beta, A, B > 0$. Again, using $y_n = x_{n-1}$, this system can be written as a planar system. Thus, applying the augmented phase plane, we prove global asymptotic stability of the positive equilibrium for some cases. In other cases, we show this using other theorems from the monograph by Kulenovic and Ladas as was previously done by Atawna, et al. / Thesis / Master of Science (MSc) / The augmented phase portrait, introduced by Sabrina Streipert and Gail Wolkowicz, is used to analyze second order rational discrete maps with nonnegative parameters and positive initial conditions. Using a change of variable to transform the second order rational discrete maps into planar maps, various properties of solutions were analyzed for various cases. For one case, we provide a new proof to show that oscillatory solutions have semicycles of length one, except possibly the first cycle, and that nonoscillatory solutions must converge monotonically to the equilibrium. This was originally done by Gibbons, Kulenovic, and Ladas. We also prove Conjecture 5.4.6 from the monograph by Kulenovic and Ladas, showing the existence of solutions that increase and decrease monotonically to the equilibrium. While Conjecture 5.4.6 was previously proved in a paper by Hoag and a paper by Sun and Xi, our proof provides a more intuitive and elementary solution. Finally, for another case we prove global asymptotic stability of the positive equilibrium using the augmented phase portrait. Sometimes, we show this using other theorems from the monograph by Kulenovic and Ladas as was previously done by Atawna, et al.

Carotenoids in W. dermatitids were found to be associated with membranes of lipid globules and/or proteins dispersed in the lipids in the yeast-phase of the organism. The lipid globules increase in size and the pigment concentrations increase with age of the cell. Electron micrographs show these organelles to be surrounded by a single unit membrane. The free carotenoids are extractable with ethyl ether from pigmented fractions of osmotically ruptured protoplasts only after the sample has been treated with acetone, indicating the pigment is non-covalently bound, presumably to a protein.

The objective of this study is to observe the correlations between variable operating conditions and power quality parameters for a three-phase to single-phase cycloconverter. The cycloconverter is examined in its most straightforward form without additional output filters or elaborate control methods. Variable operating conditions include input frequency, output frequency, and resistive load size. The power quality parameters of interest are power factor, input current total harmonic distortion (THD), output voltage THD, and efficiency. The scope of the project includes analytical calculations, PSpice simulations, as well as a hardware implementation. The results show that output frequency has minimal effect on power quality. High input frequencies tend to yield less efficiency and larger loads yield higher efficiency. Total harmonic distortion undesirably peaks at a combination of low input frequency and high output frequency. Extrapolations can be made for the cycloconverter operating at different frequencies and loads based on the trends observed within the test matrix.