It is well known that the optical properties of multi-level atomic and molecular system can be controlled and manipulated efficiently using quantum coherence and interference, which has led to many new effects in quantum optics for e.g. lasing action without population inversion, ultraslow light, high resolution nonlinear spectroscopy etc. Recent experimental and theoretical studies have also provided support for the hypothesis that biological systems uses quantum coherence. Nearly perfect excitation energy transfer in photosynthesis is an excellent example of this. In this dissertation we studied quantum coherence and interference effects in the transient and the continuous-wave regimes. This study led to (i) the first experimental demonstration of carrier-envelope phase effects on bound-bound atomic excitation in multi-cycle regime (~15 cycles), (ii) a unique possibility for standoff detection of trace gases using their rotational and vibrational spectroscopic signals and from herein called Coherent Raman Umklappscattering, (iii) several possibilities for frequency up-conversion and generation of short-wavelength radiation using quantum coherence (iv) the measurement of spontaneous emission noise intensity in Yoked-superfluorescence scheme. Applications of the obtained results are development of XUV (X-Ray) lasers, con- trolled superfluorescent (superradiant) emission, carrier-envelope phase effects, coherent Raman scattering in the backward direction, enhancement of efficiency for generating radiation in XUV and X-Ray regime using quantum coherence with and without population inversion and to extend XUV and X-Ray lasing to ~4.023 nm in Helium-like carbon.

A (convex) polytope P is said to be 2-level if every hyperplane H that is facet-defining for P has a parallel hyperplane H' that contains all the vertices of P which are not contained in H.Two level polytopes appear in different areas of mathematics, in particular in contexts related to discrete geometry and optimization. We study the problem of enumerating all combinatorial types of 2-level polytopes of a fixed dimension d. We describe the first algorithm to achieve this. We ran it to produce the complete database for d <= 8. Our results show that the number of combinatorial types of 2-level d-polytopes is surprisingly small for low dimensions d.We provide an upper bound for the number of combinatorially inequivalent 2-level d-polytopes. We phrase this counting problem in terms of counting some objects called 2-level configurations, that capture the class of "maximal" rank d 0/1-matrices, including (maximal) slack matrices of 2-level cones and 2-level polytopes. We provide a proof that the number of d-dimensional 2-level configurations coming from cones and polytopes, up to linear equivalence, is at most 2^{O(d^2 log d)}.Finally, we prove that the extension complexity of every stable set polytope of a bipartite graph with n nodes is O(n^2 log n) and that there exists an infinite class of bipartite graphs such that, for every n-node graph in this class, its stable set polytope has extension complexity equal to Omega(n log n). / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Dans cette thèse, nous étudions des systèmes nano-électro-mécaniques (NEMS) en conditions cryogéniques (de 30 mK à 30 K) sensibles à des conditions de fluctuations ou de désordre. Les phénomènes fondamentaux étudiés sont omniprésents dans la physique des NEMS, et pour certains vont même au-delà avec des analogies vers d’autres disciplines de la physique, comme les transitions de phase ou la RMN.Dans la première partie de cette thèse, nous nous intéressons ainsi au bruit d'amplitude du NEMS, fournissant un exemple de mouvement Brownien dans un potentiel de confinement. Du fait de la non-linéarité géométrique intrinsèque au système, l'anharmonicité du potentiel transduit le mouvement Brownien de chaque mode mécanique en fluctuations des fréquences propres de résonance. Ainsi, nous observons expérimentalement un phénomène de diffusion spectrale, se traduisant par un élargissement et un décalage de la raie de résonance non-triviaux rendant compte de la compétition entre la diffusion de la phase de la réponse du mode due à la transduction, et les mécanismes de relaxation du mode fluctuant. Une approche par intégrale de chemin de la diffusion capture l'effet analytiquement. Un tel mécanisme altère la résonance d'un mode mécanique sans influer sur les échanges d'énergie avec le bain thermodynamique du mode. En outre, l'introduction d'une forte excitation sinusoïdale agit en retour sur les fluctuations hors équilibre via la non-linéarité, ralentissant la dynamique du système et comprimant ses fluctuations pour certains points critiques de l'espace des paramètres, près du ou dans le régime de la réponse bistable permise par la non-linéarité. Enfin, des expériences-modèles ont été réalisées afin de comprendre en détail la décohérence mécanique classique à l’aide d’un bruit en fréquence extrinsèque, réalisé à l’aide d’une grille couplée au NEMS.La deuxième partie de cette thèse explore plus en détail certains mécanismes microscopiques de relaxation d'énergie ou du bruit en fréquence interne d’un mode mécanique, encore partiellement incompris pour les NEMS. Nous considérons d’abord le cas d’une contribution extérieure, mais universelle, qui a pour origine le transfert d’impulsion entre le NEMS et le gaz présent dans la cellule expérimentale, ici l’hélium 4. Dans la limite des faibles densités, la théorie cinétique décrit la dissipation dans le gaz ballistique. De façon inattendue, nous observons aux plus basses pressions atteignables une déviation à la théorie. Nous montrons pour plusieurs températures et plusieurs échantillons que cette déviation s’échelonne avec le rapport entre le libre parcours moyen des atomes dans le gaz et la hauteur du NEMS vis-à-vis du fond de l’échantillon. Ce résultat est justifié par un modèle phénoménologique prenant en compte la réflexion diffusive des atomes du gaz sur le mur du fond, qui présente à petite échelle une structure désordonnée. Cette réflexion résulte en une déviation à la Maxwellienne près du fond, et donc en l’établissement d’un gradient de densité du gaz sur une longueur de l’ordre du libre parcours moyen, qui renormalise le taux de relaxation d’énergie mécanique. Ainsi, le NEMS agit comme une sonde non-invasive d’un milieu hors équilibre du fait de ses très petites dimensions transverses. Enfin, nous mesurons la dissipation intrinsèque du NEMS jusqu’à 30 milliKelvin. Nous mettons en évidence le rôle des excitations de basse énergie couplées à la déformation du NEMS dans la relaxation d’énergie mécanique. Ces excitations, permises par la structure désordonnée des matériaux constitutifs du NEMS, sont modélisées comme des atomes se déplaçant par effet tunnel entre deux positions équivalentes du réseau atomique (TLS). Nous obtenons également le bruit en fréquence intrinsèque en développant une nouvelle technique de mesure utilisant la non-linéarité du NEMS. L’étude poussée nous permet de lier phénoménologiquement les deux phénomènes. / In this thesis we address cryogenic nano-electro-mechanical systems (NEMS) from 30 mK to 30 K sensitive to conditions involving fluctuations or disorder. The fundamental aspects studied are ubiquitous in NEMS physics, and for some of them go beyond, with possible analogies with phase transitions or NMR.In the first part of this work we focus on the NEMS position noise, which is a good example of Brownian motion within a confinement potential. Owing to the system’s intrinsic geometric nonlinearity, the potential anharmonicity translates each mode’s Brownian motion into fluctuations of the structure’s resonance eigenfrequencies. As a result we observe experimentally a spectral diffusion phenomenon that manifests through a linewidth broadening and a frequency shift of the resonance line: they account non-trivially for the competition between the probed mode’s response’s phase diffusion due to the transduction mechanism and the fluctuating modes relaxation mechanisms. A path integral approach to diffusion encompasses analytically the effect. Such a mechanism alters a mechanical mode’s resonance without changing energy transfers to the mode’s thermal bath. Furthermore, adding a strong sinusoidal excitation acts back on the out-of-equilibrium fluctuations through the nonlinearity: the system dynamics is slowed down, with its fluctuations squeezed, in peculiar points of the parameters space, near or within the non-linearity induced bistable regime. Finally, model experiments are realized so as to understand classical mechanical decoherence, through the use of an extrinsic frequency noise, artificially crafted thanks to a gate electrode coupled to the NEMS.In a second part, some microscopic mechanisms leading to mechanical damping and internal frequency noise of a mechanical mode are investigated, as they are still elusive to date for NEMS. We first consider the case of an external but universal source of damping, which originates from the momentum transfer between the NEMS and the gas flowing in the experimental cell, here Helium 4. In the rarefied limit, dissipation in a ballistic gas is well described by kinetic theory. Yet, unexpectedly, we observe at our lowest pressures a discrepancy between our measurements and theory. We show for several temperatures and samples that this deviation scales with the ratio between the gas atoms mean free path and the gap between the NEMS and the sample’s bottom trench. This result is modelled phenomenologically as arising from diffusive scattering of gas atoms at the bottom’s wall, which at small lengthscales has a disordered landscape. Diffusive scattering results in a deviation to the Maxwellian distribution, leading to a gas density gradient in the vicinity of the wall, established over a distance comparable with the mean free path, and which renormalizes the mechanical energy relaxation rate. Therefore, the NEMS acts as a non-invasive probe in a nonequilibrium medium due to its small cross-section. Finally, we investigate the NEMS intrinsic dissipation down to 30 milliKelvin. We highlight the role of low-energy excitations coupled to the NEMS deformation in damping mechanisms. These excitations, allowed by the disordered structure of the NEMS constitutive materials, are modelled as atoms tunneling between two equivalent positions of the atomic lattice (also referred to as TLS). Using a new technique which relies on the NEMS non-linearity, we measure the intrinsic frequency noise, and we show that it can be linked phenomenologically to the damping due to the TLS.

Desde o início dos anos 2000, o regionalismo sul-americano vive uma tendência multidimensional, incluindo novas temáticas ao foco das discussões sobre integração, entre elas, a energia. Diante deste cenário, o objetivo central deste trabalho é entender como se dá a formação de preferências do Brasil por um acordo de integração energética. Além dele, foram adotados como objetivos secundários: (i) estudar o histórico da integração energética na América do Sul, especialmente no que tange ao Brasil; (ii) entender o processo de negociação que envolve um acordo, formulando um tipo ideal voltado a integração energética e; (iii) reconhecer os benefícios e as dificuldades que envolvem a opção por um acordo energético de tipo bilateral ou multilateral. A fim de responder a essas perguntas, adotou-se a abordagem de Jogos de Dois Níveis, de Robert Putnam, por sua capacidade em relacionar a dinâmica da política interna com a externa, permitindo a análise do cenário complexo das negociações de um acordo de integração energética. A partir desta pesquisa, viu-se que a morosidade que envolve o processo de integração energética na América do Sul não é resultado apenas da falta de vontade política ou da ausência de um ator que arque com seus custos, mas principalmente da dificuldade em coordenar uma ampla gama de atores, interesses, expectativas e ordenamentos jurídicos, em mais de uma esfera de negociação. Por isso, diante de necessidades pontuais e imediatas, vê-se, por parte do Brasil, a adoção majoritária de acordos bilaterais, sem abandonar, no entanto, paralelamente, as discussões dos foros multilaterais. / Since the early 2000s, the South America regionalism lives a multidimensional trend, including new themes to focus the integration discussions, including energy. In this scenario, the aim of this research is to understand the preferences formation in Brazil for an energy integration agreement. Besides, were adopted as secondary objectives: (i) study the history of energy integration in South America, especially in regard to Brazil; (ii) understand the negotiation process that involves an agreement by formulating an ideal energy integration agreement and; (iii) recognize the benefits and difficulties involving the choice of an energy bilateral or multilateral agreement. In order to answer these questions were adopted the approach of Two-Level Games by Robert Putnam, because of its ability to relate the dynamics of internal politics with the foreign policy, allowing the analysis of the complex scenario of an energy integration agreement negotiations. From this research, it is clear that the length involving the energy integration process in South America is not the result only a political lack or a paymaster absence, but mainly the difficulty in coordinating a wide range of actors, interests, expectations and legal systems, in more than one sphere of negotiation. So, by particular needs, Brazil elects bilateral agreements, without abandoning, however, in parallel, discussions in multilateral forums.

O presente trabalho se destina a um estudo detalhado da chamada equação de spin, a qual pode ser utilizada para descrever o comportamento de sistemas de dois níveis. Para campos externos dados por funções reais, esta equação pode ser identificada com uma redução da equação de Pauli para o caso 0+1 dimensional. Inicialmente, demonstraremos a relação entre esta equação de spin e várias outras equações relacionadas com diversos problemas em física. Com estas relações, podemos construir novas soluções da equação de spin a partir do conhecimento de soluções exatas destes outros problemas e, por outro lado, estender a aplicação das soluções obtidas. Em seguida, descrevemos a forma geral da solução desta equação, construímos o operador de evolução e resolvemos o problema inverso, i.e., a determinação do campo externo supondo o conhecimento de uma solução. Finalizando, para o importante caso de campos externos reais, desenvolvemos um método de construção de novas soluções a partir de uma solução previamente conhecida, utilizando a chamada transformação de Darboux. Em particular, demonstramos a existência de operadores de entrelaçamento de Darboux, que não violam a estrutura específica dos sistemas de dois níveis, e permitem construir novos campos externos também dados por funções reais. Como resultado destes desenvolvimentos, apresentamos uma série de novas soluções exatas para a equação de spin. / The aim of the present work is to study in detail the so called spin equation, which can be used to describe the behavior of two-level systems. We recall that, for real external fields, this equation can be treated as a reduction of the Pauli equation to the 0+1 dimensional base. Initially, we present the relation between the spin equation and some other equations related to diferent physical problems. With these relations, we construct new solutions to the spin equation from the knowledge of the exact solutions of these other problems and, on the other hand, extend the applicability of the obtained solutions. After that, we describe the general solution of the spin equation, construct the evolution operator and solve the inverse problem, i.e., the construction of the external field from a given supposed solution. Finally, for the important case of real fields, we develop a method to construct new solutions from a previously known one, by the application of the so called Darboux transformation. In particular, we demonstrate the existence of Darboux intertwining operators which do not violate the specific structure of the two-level systems and allow the construction of external fields which are also given by real functions. As a result of all these developments, we present several new sets of exact solutions for the spin equation.

This study explores different actors’ perceptions on how the democratization process is being influenced in Kosovo. It is based upon empirical facts gathered during a field study in Kosovo. The material was mainly gathered through interviews with different representatives from international organizations present in Kosovo and with members of the Kosovar political elite. The theoretical standpoint in the study draws on the theory of polyarchy for defining the concept of democracy, and the two-level game. The interaction between domestic and international actors within the democratization process is highlighted. The conclusions are that different actors are influencing the ongoing democratization process in Kosovo, mainly international external ones acting in several ways and on different levels. This influence is considered by the international community and the domestic political elite to be necessary both for the continued development of democracy and for the preservation of stability. However as the influence has more or less become institutionalized, problems occur when responsibility is handed over to domestic authorities without accountability being made clear.

Since social media gains ever increasing popularity, Online Social Networks have become important repositories for information retrieval. The concept of social search, therefore, is gradually being recognized as the next breakthrough in this field, and it is expected to dominate topics in industry. However, retrieving information from OSNs with high Quality of Experience is non-trivial as a result of the prevalence of mobile applications for social networking services. For the sake of shortening user perceived latency Web caching was introduced and has been studied extensively for years. Nevertheless, the previous works seldom focus on the Web caching solutions for social search. In the context of this master’s thesis project, emphasis is given to the design of a Web caching system which is used to cache public data from social media with the objective of improving the user experience in terms of the freshness of data and the perceived service latency. To be more specific, a Web caching strategy named Staleness Bounded LRU algorithm is proposed to limit the term of validity of the cached data. In addition, a Two-Level Web Caching System that adopts the SB-LRU algorithm is proposed in order for shortening the user perceived latency. Results of trace-driven simulations and performance evaluations demonstrate that serving clients with stale data is avoided and the user perceived latencies are significantly shortened when the proposed Web caching system is used in the use case of unauthenticated social search. Besides, the design idea in this project is believed to be helpful to the design of a Web caching system for social search, which is capable of caching user specific data for different clients.

This paper presents a two-level morphological description of Tagalog for use in PC-Kimmo and a mechanism created for updating the results output from PC-Kimmo in order to meet the standards for current database and natural language processing applications. There are two main research tasks presented in this paper which constituted this project. First, a complete morphological engine for Tagalog is presented. Next, a tool is introduced that takes the morphological engine output and stores it in XML format.

<p>Current gasoline blend planning practice is to optimize blend plans via discrete-time multi-period NLP or MINLP models and schedule blends via interactive simulation. Solutions of multi-period models using discrete-time representation typically have different blend recipes for each time period. In this work, the concept of an inventory pinch point is introduced and used it to construct a new decomposition of the multi-period MINLP problems: at the top level nonlinear blending problems for periods delimited by the inventory pinch points are solved to optimize multi-grade blend recipes; at the lower level a fine grid multi-period MILP model that uses optimal recipes from the top level is solved in order to determine how much to blend of each product in each fine grid period, subject to minimum threshold blend size. If MILP is infeasible, corresponding period between the pinch points is subdivided and recipes are re-optimized.</p> <p>Two algorithms at the top level are examined: a) multi-period nonlinear model (MPIP) and b) single-period non-linear model (SPIP). Case studies show that the MPIP algorithm produces solutions that have the same optimal value of the objective function as corresponding MINLP model, while the SPIP algorithm computes solutions that are most often within 0.01% of the solutions by MINLP. Both algorithms require substantially less computational effort than the corresponding MINLP model. Reduced number of blend recipes makes it easier for blend scheduler to create a schedule by interactive simulation.</p> / Master of Applied Science (MASc)

The literature is clear that intentional or unintentional clustering of data elements typically results in the inflation of the estimated standard error of fixed parameter estimates. This study is unique in that it examines the impact of multilevel data structures on subject ability which are random effect predictions known as empirical Bayes estimates in the one-parameter IRT / Rasch model. The literature on the impact of complex survey design on latent trait models is mixed and there is no "best practice" established regarding how to handle this situation. A simulation study was conducted to address two questions related to ability estimation. First, what impacts does design based clustering have with respect to desirable statistical properties when estimating subject ability with the one-parameter IRT / Rasch model? Second, since empirical Bayes estimators have shrinkage properties, what impacts does clustering of first-stage sampling units have on measurement validity-does the first-stage sampling unit impact the ability estimate, and if so, is this desirable and equitable? Two models were fit to a factorial experimental design where the data were simulated over various conditions. The first model Rasch model formulated as a HGLM ignores the sample design (incorrect model) while the second incorporates a first-stage sampling unit (correct model). Study findings generally showed that the two models were comparable with respect to desirable statistical properties under a majority of the replicated conditions-more measurement error in ability estimation is found when the intra-class correlation is high and the item pool is small. In practice this is the exception rather than the norm. However, it was found that the empirical Bayes estimates were dependent upon the first-stage sampling unit raising the issue of equity and fairness in educational decision making. A real-world complex survey design with binary outcome data was also fit with both models. Analysis of the data supported the simulation design results which lead to the conclusion that modeling binary Rasch data may resort to a policy tradeoff between desirable statistical properties and measurement validity. / Ph. D.