Les propriétés physiques d'un système de particules homogène à l'équilibre thermodynamique sont caractérisées par son équation d'état : une relation entre différentes grandeurs thermodynamiques. Le gaz de Bose bi-dimensionnel est un système particulier de ce point de vue car son équation d'état est invariante par changement d'échelle en présence d'interactions atomiques répulsives faibles. Une autre caractéristique remarquable du gaz de Bose 2D est l'existence d'une transition de phase vers un état superfluide à basse température. Dans ce manuscrit de thèse, je présente une mesure de l'équation d'état du gaz de Bose homogène pour trois grandeurs thermodynamiques : la pression réduite, la densité dans l'espace des phases et l'entropie par particule. Je présente également une mesure de l'énergie d'interaction d'un gaz 2D piégé dans un potentiel harmonique. Cette mesure a permis de mettre en évidence l'existence d'une phase précédant la phase superfluide où les fluctuations de densité sont fortement réduites. Cette phase constitue une étape essentielle dans l'établissement de la transition superfluide. Enfin, je décris l'observation de signatures de vortex dans des gaz de Bose 2D. Ces vortex constituent l'ingrédient clé du mécanisme microscopique de la transition superfluide à deux dimensions.

Pictorial cues, together with motion and stereoscopic depth fields, can be used for perception and constitute ‘three kinds’ of vision. Edges in images are important features and can be created in either of these attributes. Are local edge and global shape detection processes attribute-specific? Three visual phenomena, believed to be due to low-level visual processes, were used as probes to address these issues. (1) Tilt illusions (misperceived orientation of a bar caused by an inducing grating) were used to investigate possible binding of edges across attributes. Double dissociation of tilt repulsion illusions (obtained with small orientation differences between inducer and bar) and attraction illusions (obtained with large orientation differences) suggest different mechanisms for their origins. Repulsion effects are believed to be due to processes in striate cortex and attraction because of higher level processing. The double dissociation was reproduced irrespective of the attributes used to create the inducing grating and the test-bar, suggesting that the detection and binding of edges across attributes take place in striate cortex. (2) Luminance-based illusory contour perception is another phenomenon believed to be mediated by processes in early visual cortical areas. Illusory contours can be cued by other attributes as well. Detection facilitation of a near-threshold luminous line occurred when it was superimposed on illusory contours irrespective of the attributes used as inducers. The result suggests attribute-independent activation of edge detectors, responding to real as well as illusory contours. (3) The performance in detecting snake-like shapes composed of aligned oriented elements embedded in randomly oriented noise elements was similar irrespective of the attributes used to create the elements. Performance when the attributes alternated along the path was superior to that predicted with an independent channel model. These results are discussed in terms of binding across attributes by feed-forward activation of orientation selective attribute-invariant cells (conjunction cells) in early stages of processing and contextual modulation and binding across visual space mediated by lateral and/or feedback signals from higher areas (dynamic binding).

Transmitting quantum information across quantum channels is an important task. However quantum information is delicate, and is easily corrupted. We address the task of protecting quantum information from an information theoretic perspective -- we encode some message qudits into a quantum code, send the encoded quantum information across the noisy quantum channel, then recover the message qudits by decoding. In this dissertation, we discuss the coding problem from several perspectives.} The noisy quantum channel is one of the central aspects of the quantum coding problem, and hence quantifying the noisy quantum channel from the physical model is an important problem. We work with an explicit physical model -- a pair of initially decoupled quantum harmonic oscillators interacting with a spring-like coupling, where the bath oscillator is initially in a thermal-like state. In particular, we treat the completely positive and trace preserving map on the system as a quantum channel, and study the truncation of the channel by truncating its Kraus set. We thereby derive the matrix elements of the Choi-Jamiolkowski operator of the corresponding truncated channel, which are truncated transition amplitudes. Finally, we give a computable approximation for these truncated transition amplitudes with explicit error bounds, and perform a case study of the oscillators in the off-resonant and weakly-coupled regime numerically. In the context of truncated noisy channels, we revisit the notion of approximate error correction of finite dimension codes. We derive a computationally simple lower bound on the worst case entanglement fidelity of a quantum code, when the truncated recovery map of Leung et. al. is rescaled. As an application, we apply our bound to construct a family of multi-error correcting amplitude damping codes that are permutation-invariant. This demonstrates an explicit example where the specific structure of the noisy channel allows code design out of the stabilizer formalism via purely algebraic means. We study lower bounds on the quantum capacity of adversarial channels, where we restrict the selection of quantum codes to the set of concatenated quantum codes. The adversarial channel is a quantum channel where an adversary corrupts a fixed fraction of qudits sent across a quantum channel in the most malicious way possible. The best known rates of communicating over adversarial channels are given by the quantum Gilbert-Varshamov (GV) bound, that is known to be attainable with random quantum codes. We generalize the classical result of Thommesen to the quantum case, thereby demonstrating the existence of concatenated quantum codes that can asymptotically attain the quantum GV bound. The outer codes are quantum generalized Reed-Solomon codes, and the inner codes are random independently chosen stabilizer codes, where the rates of the inner and outer codes lie in a specified feasible region. We next study upper bounds on the quantum capacity of some low dimension quantum channels. The quantum capacity of a quantum channel is the maximum rate at which quantum information can be transmitted reliably across it, given arbitrarily many uses of it. While it is known that random quantum codes can be used to attain the quantum capacity, the quantum capacity of many classes of channels is undetermined, even for channels of low input and output dimension. For example, depolarizing channels are important quantum channels, but do not have tight numerical bounds. We obtain upper bounds on the quantum capacity of some unital and non-unital channels -- two-qubit Pauli channels, two-qubit depolarizing channels, two-qubit locally symmetric channels, shifted qubit depolarizing channels, and shifted two-qubit Pauli channels -- using the coherent information of some degradable channels. We use the notion of twirling quantum channels, and Smith and Smolin's method of constructing degradable extensions of quantum channels extensively. The degradable channels we introduce, study and use are two-qubit amplitude damping channels. Exploiting the notion of covariant quantum channels, we give sufficient conditions for the quantum capacity of a degradable channel to be the optimal value of a concave program with linear constraints, and show that our two-qubit degradable amplitude damping channels have this property.

Dans cette thèse, nous étudions le comportement à longue distance des membranes polymérisées en utilisant une approche de groupe de renormalization non-perturbative (NPRG). Après une présentation du NPRG, nous introduisons les membranes. Dans notre travail, nous nous concentrons sur différents types de membranes polymérisées: homogène, anisotrope et avec du désordre gelé́. De plus, nous avons aussi étudié les points de Lifshitz dans les systèmes magnétiques. Nos résultats, aussi bien pour les membranes que pour Lifshitz, se comparent bien aux résultats perturbatifs dans les différents cas limites: couplages faibles, basse température et large-d (ou large-n pour Lifshitz). Mais, en utilisant le NPRG, nous pouvons aller au de-là̀ de ces cas limites et atteindre les cas qui sont physiquement intéressants. La question de l'ordre de la transition entre la phase froissé et la phase plate dans les membranes homogènes est depuis longtemps sans une réponse définitive. Malgré̀ que nos résultats ne permettent pas encore de lever cette question, ils semblent indiquer que la transition est du premier ordre en accord avec des simulations récentes. Une propriété́ importante des membranes polymérisées est l'existence d'une phase plate à basse température avec un comportement non-trivial. Cette phase décrit correctement le comportement du graphène malgré̀ que les dégrées de liberté́ électroniques ne soient pas pris en compte

The main interest of the present thesis is the constrained control of time-delay system, more specifically taking into consideration the discretization problem (due to, for example, a communication network) and the presence of constraints in the system's trajectories and control inputs. The effects of data-sampling and modeling problem are studied in detail, where an uncertainty is added into the system due to additional effect of the discretization and delay. The delay variation with respect to the sampling instants is characterized by a polytopic supra-approximation of the discretization/delay induced uncertainty. Some stabilizing techniques, based on Lyapunov's theory, are then derived for the unconstrained case. Lyapunov-Krasovskii candidates were also used to obtain LMI conditions for a state feedback, in the ''original" state-space of the system. For the constrained control purposes, the set invariance theory is used intensively, in order to obtain a region where the system is ''well-behaviored", despite the presence of constraints and (time-varying) delay. Due to the high complexity of the maximal delayed state admissible set obtained in the augmented state-space approach, in the present manuscript we proposed the concept of set invariance in the ''original" state-space of the system, called D-invariance. Finally, in the las part of the thesis, the MPC scheme is presented, in order to take into account the constraints and the optimality of the control solution.

In developing countries, there is a great demand for university education. In order to select students to universities a standardized test score is used. In Turkey, the Student Selection Test (SST) have important role in admission to universities. However, there is very limited knowledge about what SST mathematics sections actually measures. The main purpose of the present study is to evaluate the content of the mathematics subtest of the SST in line with mathematical cognitive skills and eventually provide construct related evidence for dimensionality of the test items. Within this framework, it is aimed to cross validate the mathematics subtest across gender groups, school types and two consecutive years. Also relations among mathematical abilities are investigated. This study is first in investigating what is measured by SST Mathematics sections and analyzing construct validity by testing several nested confirmatory factor models. Comparison of fit indices of five competitive models showed three-factor model has better fit indices in which Basic Computation Ability, Advanced Computation Ability and Geometry Ability is measured. It is concluded that problem solving items are not measuring a different process, but measures some sort of computation ability. There is a problem related to the content of the mathematics subtests of the SST in line with mathematical cognitive skills. Higher order cognitive skills are not measured properly. Three-factor model is tested about the invariance of the factors across gender, school types and years. It is concluded that invariant factor structure indicates that SST mathematics section is operating similarly for subgroups and years. The relations among mathematical abilities on three-factor model are investigated by item mapping and structural equation models. It is seen that Basic Computation Ability is a prerequisite to acquire Geometry Ability and Advanced Computation Ability.

Ce travail est dédié à l'étude de la rupture du manteau neigeux, conduisant<br />aux avalanches de plaques de neige.<br />La détermination expérimentale de la ténacité de la neige, qui caractérise sa résistance à la propagation d'une fissure, nous a donné des résultats originaux que nous interprétons en tenant compte de la structure particulière de ce matériau.<br />Une étude statistique basée sur les données de La Plagne et de Tignes nous a permis de montrer pour la première fois que les distributions des tailles d'avalanches sont invariantes d'échelle. Aucun modèle ne reproduisant correctement ces statistiques de terrain, nous avons créé un automate cellulaire à deux seuils, piloté en contrainte,<br />qui reproduit le comportement statistique des avalanches mais aussi celui d'autres aléas gravitaires naturels à l'aide du réglage d'un unique paramètre reflétant l'anisotropie de cohésion du matériau. Cette approche peut être considérée comme une alternative<br />à la Criticalité Auto Organisée pour les ruptures gravitaires.

Epstein et al.'s Theory of Overlapping Spheres of Influence focuses on the interaction and communication, or partnerships, among families, schools, and the community to bring the three closer together. The theory works in conjunction with Epstein's typology of parental involvement, which focuses on six types of involvement that are instrumental to a child's development and his/her school and educational success. These serve as the framework for the study and support the construct of parent's involvement in children's schooling. The purpose of the current study was to conduct further validation analyses of an inventory designed to measure the construct of parent involvement in their children's schooling through the investigation of measurement invariance to determine if the measurement properties of the inventory varied by race/ethnicity. The study compared the responses of 126 Hispanic parents/guardians with 116 White/non-Hispanic parents/guardians to investigate if these two groups were interpreting the items on the inventory in the same manner. The inventory was administered to a sample of parents/guardians of children in grades 3 through 5 in a local school district. Findings indicated that the measurement model was misspecified for the White/non-Hispanic group and the Hispanic group and further measurement invariance testing was not conducted. Exploratory factor analyses were conducted in order to investigate which models would best fit the data for both groups. Feedback also was obtained from parents/guardians about the clarity of the inventory, which revealed their confusion with the response scale and the wording of particular items. In addition, they supplied issues or aspects of parent involvement that they found important but missing from the inventory. Results from the psychometric analyses and qualitative feedback indicated that the inventory requires modification and further psychometric investigation. In addition, caution should be exercised for anyone who may be considering utilizing the inventory. Results of the study were interpreted in terms of contributions to the parent involvement literature, as well as recommendations for the improvement of the inventory.

As a result of growing attention in cross-cultural research, existing measurement instruments developed in one language are being translated and adapted for use in other languages and cultural contexts. The benefits of having the same instrument across cultures can only be realized if the process of translation and adaptation of the measurement instruments produces measurement operations that function similarly across national and cultural boundaries. Producing invariant measurement instruments that assess educational and psychological constructs provide a way of testing the cross-cultural generality of theories that include these constructs. The major purposes of the study were to translate and adapt the Teaching Perspectives Inventory (Pratt, 1992, 1990) from English to Bahasa Malaysia and compare the psychometric properties of the two versions. The TPI is an instrument developed by Pratt (1992) to ascertain the different conceptions that teachers in higher education have about teaching. The TPI has 45 items, which are divided into five subscales or perspectives referred to as Transmission, Apprenticeship, Developmental, Nurturing, and Social Reform. The first phase of this study translated and adapted the TPI from English into the Malay language of Malaysia or Bahasa Malaysia (BM) using multiple approaches as recommended by the International Test Commission. The approaches used to translate the TPI included forward and back translations, an expert panel review, a pilot study, and cognitive interviews. In the translation process, three initial translators, two back translators, and six expert panel members, including the researcher, came up with a pre-final version of the Malay TPI. During the translation process, two items were found to contain expressions that had no exact equivalent forms in Malay: "virtuoso performers" and "higher ideals." Overall, translating the TPI was a challenging task due to the relatively large number of items in the instrument (45) as well as the complexity and very abstract nature of the constructs. Many of the words and expressions that were brief and concise in the English version became longer and more verbose when translated in Malay. As a result, the translated TPI version appeared longer than the original version. Pilot testing with 25 native speakers of Malay who were faculty members from a number of public universities in Malaysia revealed nine items that needed modification. Cognitive interviewing with five participants from the pilot group revealed one item requiring a change by adding a borrowed word "novis" in brackets next to the Malay expressions, which refers to the original word novice. Due to the confusion with the words referring to `people' in many of the items, additional instructions were added at the beginning of the survey to ensure that the participants responded according to the original intention of the items, which focuses on learners in the faculty's specific classroom context instead of people in the society in general. Following changes to the TPI, this instrument was administered in phase two to a Malaysian sample of 561 faculty. In the second phase, the study assessed the psychometric properties of the original English version of the TPI with 605 faculty in the U. S. and the translated TPI version of the TPI with the Malaysian sample. The overall internal consistency reliability of both the English (α=.88) and the Malay TPI (α=.93) appeared to be adequate. At the subscale level, the internal consistency reliabilities of all the scales were on the lower side considering the large number of items (9) for each subscale (range = .67 to .83 for the U. S. and .59 to .81 for Malaysia). It was found that three out of the five subscales of the U. S. and Malay TPI had similar alpha reliabilities (Apprenticeship, Nurturing, Social Reform). To assess the cross-cultural factorial validity and measurement invariance of the TPI, confirmatory factor analysis (CFA) was carried out for both the original and the Malay TPI. The sample size for the U. S. group was 605 and the Malay group was 561. The fit for both the U. S. and the Malay correlated five-factor models was less than adequate with the Malay model showing a much worse fit. Correlated errors were found between 64 item pairs in the U. S. model and 389 item pairs in the Malay model. The correlations between the five perspectives in the Malay sample were much higher than those in the U. S. sample suggesting that the perspectives had limited discriminant validity. For example, the correlations between the Nurturing and Developmental perspectives and Nurturing and Social Reform perspectives were 1.0. The inadequate fit of the five-factor correlated model in the Malaysian sample and the minimally acceptable fit in the U. S. sample led to the decision to carry out analyses and compare the groups one subscale at a time. Model modifications for each subscale of both samples were carried out to improve the fit by adding one or more parameters (i.e., correlated errors) for each subscale model to obtain acceptable baseline models. The results of the invariance testing for each subscale did not support the existence of measurement invariance. Overall, the results indicate that the Malay version of the TPI is not ready for use and additional translation and adaptation work is recommended. Future efforts could incorporate improvements in the translation process in the form of recruiting a larger number of certified translators who have in-depth knowledge of teaching in higher education as well as a deep knowledge of the philosophy and purposes behind the TPI. Additional cognitive interviews before and after pretesting and pilot testing of the pre-final version are recommended. Finally, adding a large sample of bilingual educators who would complete both the Malay and English versions of the TPI would provide important psychometric data on the equivalence of the TPI items.

Les propriétés physiques d'un système homogène à l'équilibre thermodynamique sont fortement contraintes par sa dimensionnalité. Le gaz de Bose à deux dimensions est un système particulier de ce point de vue : bien que l'établissement d'un ordre à longue portée soit impossible à température non-nulle, il existe néanmoins une transition de phase vers un état superfluide à basse température. De plus, la dimensionalité réduite du système rend son équation d'état invariante par changement d'échalle pour de faibles interactions atomiques répulsives. Dans ce manuscrit de thèse, nous présentons une étude expérimentale du gaz de Bose à deux dimensions. Nous mesurons son équation d'état de deux methodes différentes, et trouvons un résultat en bon accord avec les prédictions analytiques et numériques. Ces résultats ont également permis de confirmer l'invariance d'échelle du système. De plus, l'une des méthodes ne nécessite qu'un seul paramètre ajustable pour la mesure de l'équation d'état. Nous présentons ensuite une mesure locale du caractère superfluide du gaz. À cet effet, nous avons mis en évidence l'absence de dissipation lors de la perturbation du système par un obstacle en mouvement. Enfin, nous effectuons une analyse des fluctuations du gaz de Bose 2D, qui a permis de confirmer la suppression des fluctuations de densité dans la phase superfluide, ainsi que le rôle dominant joué par les phonons dans les fluctuations de phase.