CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / O cristal dipeptÃdeo L-Alanil-L-alanina (Ala-Ala) foi estudado atravÃs da tÃcnica de espalhamento Raman polarizado submetido a deformaÃÃes homogÃneas. Os cristais foram crescidos pela tÃcnica de evaporaÃÃo lenta a partir de uma soluÃÃo aquosa supersaturada do pà do cristal. Medidas de raios-x foram realizadas para confirmar a estrutura cristalina do cristal. Foram realizadas medidas de espalhamento Raman polarizado a temperatura ambiente, bem como anÃlise da teoria de grupos para o grupo fator C4 juntamente com uma classificaÃÃo exploratÃria dos modos normais de vibraÃÃo do cristal. As medidas de espalhamento Raman foram realizadas em baixas temperaturas, entre 300 K e 11 K e 11 K e 300 K, e altas temperaturas, entre 300 K e 520 K e 520 K e 300 K, na regiÃo espectral de 50 a 3300 cm-1. Da anÃlise dos resultados das medidas de baixas temperaturas foi possÃvel concluir que o cristal exibe uma transiÃÃo de fase de segunda ordem, entre 80 e 60 K, passando continuamente da estrutura tetragonal com grupo fator C4 para uma estrutura monoclÃnica com grupo fator C2 mantendo o mesmo nÃmero de molÃculas na cÃlula primitiva. O mecanismo proposto para explicar a transiÃÃo de fase à a ocupaÃÃo de sÃtios de simetria C1 nÃo equivalentes pelos Ãons moleculares CH3 numa estrutura monoclÃnica pertencente ao grupo fator C2. O cristal manteve-se estÃvel em todo o intervalo de alta temperatura estudado. Nestas experiÃncias foram observadas apenas mudanÃas quantitativas nas frequÃncias e larguras de linha dos modos Raman estudados, que à normal para qualquer material submetido a variaÃÃes de temperaturas da ordem de 220 K. Medidas de espalhamento polarizado no cristal de Ala â Ala no intervalo de pressÃo entre 0,1 GPa e 6,3 GPa, na compressÃo, e de 6,3 GPa e 0,1 GPa, na descompressÃo, na regiÃo espectral de 100 cm-1 a 3400 cm-1 mostraram dois intervalos de pressÃo em que ocorrem diversas mudanÃas qualitativas; o primeiro entre 1,7 GPa e 2,3 GPa e o segundo entre 4,5 GPa e 4,9 GPa. Entre 1,7 GPa e 2,3 GPa foram observadas mudanÃas qualitativas significantes na regiÃo dos modos externos, tais como, o desaparecimento de um modo da rede em torno de 130 cm-1 e o comportamento anÃmalo de outro modo da rede em torno de 110 cm-1 para pressÃo de 1,7 GPa. Estas mudanÃas qualitativas sugerem que o cristal exibe uma transiÃÃo de fase estrutural de segunda ordem. As outras regiÃes do espectro Raman do cristal apresentaram diversas mudanÃas qualitativas continuas no comportamento dos modos Raman das unidades que participam diretamente das pontes de hidrogÃnio, indicando que o cristal apresenta reorientaÃÃes espaciais dos grupos moleculares CO2, CH3 e NH3. Estas mudanÃas qualitativas caracterizam uma transiÃÃo de fase estrutural de segunda ordem. As principais mudanÃas qualitativas observadas entre 4,5 GPa e 5,2 GPa sÃo o desaparecimento dos modos externos e, quantitativamente, um grande aumento na largura de linha dos modos Raman indicando que o cristal exibe uma desordem na estrutura cristalina durante a transiÃÃo de fase de altas pressÃes, possivelmente uma amorfizaÃÃo. Na descompressÃo da amostra os espectros Raman sÃo quase que totalmente recuperados na sua forma inicial indicando que o cristal apresenta transiÃÃes de fase reversÃveis. / The dipeptide L-Alanyl â L-Alanine crystal was studied through polarized Raman scattering submitted to homogeneous deformations. The crystals were grown by slow evaporation technique from an aqueous supersaturated solution of the crystal powder. Rays-x diffractions measurements were realized to confirm a crystalline structure of the crystal. Polarized Raman scattering measurements were performed at room temperature, as well as the analysis of the group theory to the C4 factor group and a tentative assignment of the vibrational modes of crystal. Raman scattering measurements in the crystals as a function of temperature were realized between two intervals of temperature: first, at low temperature between 300 K and 11 K e 11 K and 300 K, and second, at high temperature between 300 K e 520 K and 520 K e 300 K, in the spectral range of 50 cm-1 to 3400 cm-1. From the results of low temperature measurements, it was possible to conclude that the crystal undergoes a second-order phase transition between 80 K and 60 K, from a tetragonal structure with C4 factor group to a monoclinic structure with C2 factor group, maintaining the same number of the molecules per primitive cell. The suggested mechanism to explain the phase transition is the occupation of non-equivalent sites by CH3 molecular groups present at Ala-Ala molecule. On the other hand, the crystal remained stable in the high temperature range studied, and the changes observed in the Raman spectra showed no evidence that the Ala-Ala crystal undergone phase transition or changes in molecule conformation. In those experiments were observed only quantitative changes in frequency and widths of the Raman modes, which are normal for any material subjected to variations in temperatures around 220 K. Raman scattering measurements in the crystals as a function of pressure in the pressure range between 0,1 GPa and 6,3 GPa, in compression and of 6,3 GPa and 0,1 GPa, in decompression, in the spectral region between 100 cm-1 and 3400 cm-1 showed two ranges where several qualitative changes occurred; the first, in low pressure interval between 1.7 GPa and 2.3 GPa and the second, at high pressure interval, between 4.5 GPa and 4.9 GPa. Between 1.7 GPa and 2.3 GPa, it was observed qualitative changes as well as the disappearance of an external mode around of 130 cm-1 and the anomalous behavior of other external mode around of 110 cm-1 for pressures of the order of 1,7 GPa. These qualitative changes suggest that the crystal exhibits a second order structural phase transition. Qualitative changes also were observed in others regions of the Raman spectrum through of special reorientation of the molecular groups CO2, CH3 and NH3. These qualitative changes characterize a structural second order phase transition. The mains qualitative changes observed between 4,5 GPa and 5,2 GPa were the disappearance of the external modes and the an large increasing of the width of the Raman modes, suggesting that the crystal exhibits a structural disorder in the crystalline structure when undergoes a phase transition for high pressures, possibly a amorphization. When performing decompression of the sample, the Raman spectrum returns to its initial form relative to pressure of 0,1 GPa indicating reversibility of phase transitions.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Neste trabalho, apresentamos um estudo de espalhamento Raman em cristais de DL-valina (C5H11NO2) à temperatura ambiente e sob condiÃÃes de altas pressÃes hidrostÃticas, no intervalo espectral de 40 cm-1 a 3200 cm-1. Baseando-se em estudos anteriores sobre espectroscopia Raman em cristais de DL-valina e de outros aminoÃcidos, tais como, L-valina, L-isoleucina e L-asparagina, propusemos uma classificaÃÃo das bandas em diversos modos de vibraÃÃo. Os espectros obtidos, por espectroscopia Raman, em funÃÃo da pressÃo sugerem que a DL-valina sofreu duas transiÃÃes de fase estruturais atà 19,4 GPa. A primeira transiÃÃo de fase entre 1,4 GPa e 1,8 GPa onde foi observado o desaparecimento de trÃs modos, um modo de rede e dois modos internos classificados como rocking do NH3+, r(NH3+), e estiramento simÃtrico do CH3, vs (CH3). A segunda transiÃÃo de fase entre 7,8 GPa e 8,8 GPa, onde foi observado o desdobramento de um modo de rede, o desaparecimento de um modo interno associado a uma deformaÃÃo do esqueleto da molÃcula, d(esq) e a divisÃo de um modo designado como estiramento do CH2, v(CH2). / In this work, we present a study of the Raman scattering of DL-valine crystals (C5H11NO2) at room temperature under high hydrostatic pressures conditions using the spectral range of 40-3200 cm-1. Based on previous studies using Raman spectroscopy on crystals of DL-valine and other amino acids such as L-valine, L-isoleucine and L- asparagine, we proposed the classification of the bands in different vibration modes. The Raman spectrum obtained as function of pressure suggests that DL-valine suffered two structural phase transitions by 19,4 GPa. The first transition phase of between 1,4 GPa and 1,8 GPa where we observed the disappearance of three modes, one network mode and two internal modes classified as rocking of NH3+ and symmetric stretching of CH3, vs (CH3). The second phase transition of between 7,8 GPa and 8,8 GPa, where we observe the unfolding of a network mode, the disappearance of the internal mode associated with skeletal deformation, d(esk) and the splitting designated as CH2, v(CH2).

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-06-14T13:27:03Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Hugo_Andrade_Doutorado.pdf: 3065927 bytes, checksum: 2eeb9c1ecb93e60c146992117b01cbb6 (MD5) / Made available in DSpace on 2016-06-14T13:27:03Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Hugo_Andrade_Doutorado.pdf: 3065927 bytes, checksum: 2eeb9c1ecb93e60c146992117b01cbb6 (MD5) Previous issue date: 2013-02-07 / CNPq / Nesta Dissertac¸ ˜ao estudamos a dinˆamica energ´etica das buscas aleat ´orias aplicadas ao problema de foraging, em que animais buscam por comida ou parceiros em ambientes escassos. Discutiremos, inicialmente, um modelo estat´ıstico de caminhadas aleat ´orias utilizando as distribuic¸ ˜oes de L´evy para os tamanhos dos passos de busca, as quais tˆem sido reportadas na literatura como estrat´egias de eficiˆencia ´otima para o problema. Em seguida vamos incluir no modelo ganhos e perdas de energia na caminhada aleat ´ oria de busca, e abordaremos a dinˆamica energ´etica do processo de busca unidimensional com extremos absorventes. Vamos discutir a transic¸ ˜ao de fase que o buscador experimenta de um estado ativo (“vivo”), t´ıpico de ambientes com abundˆancia de recursos, para um estado est´atico absorvente (“morto”), onde a busca ´e encerrada pela falta de energia oriunda do encontro de recursos. Obteremos os expoentes cr´ıticos relativos a essa transic¸ ˜ao atrav´es de abordagens te ´ oricas, tais como o m´etodo de primeira passagem para o estado de energia nula, e num´ericas, baseadas na hip´otese de escala. Mostraremos a independˆencia destes expoentes com a forma funcional da func¸ ˜ao gasto de energia. Por fim, faremos uma breve revis˜ao da literatura sobre a equac¸ ˜ao de Fokker-Planck canˆonica e tamb´em sobre as suas vers˜oes utilizando derivadas fracion´arias, numa prepararac¸ ˜ao para uma futura abordagem, durante o programa de Doutorado, do problema da busca aleat´oria envolvendo difus˜oes anˆomalas (por exemplo, superdifus˜ao) via equac¸ ˜oes diferenciais. / In this work we study the energy dynamics of random searches applied to the foraging problem, in which animals search for food or mates in scarce environments. Firstly, we discuss a statistical model of random search walks using the L´evy distribution of step lengths, which has been reported in the literature as an optimal solution to the problem. In the sequence we include in the model energy gains and losses during the search walk, and discuss the energy dynamics of the search process in a one dimensional space with absorbing boundaries. We discuss the phase transition that the searcher experiences from an active (“alive”) state, typical of environments abundant in resources, to a static absorbed (“dead”) one, in which the search is terminated due to the lack of energy obtained from the encounters.We obtain the critical exponents for this transition through both theoretical (such as the first-passage method to the state of zero energy) and numerical approaches, based on the scale hypothesis.We show the independence of the exponents with the functional form of the energy cost. Finally, we provide a brief review of the literature on the canonical Fokker-Planck equation and also on its version using fractional derivatives, in a preparation for a future approach of the random search problem involving anomalous diffusion (e.g., superdiffusion) through differential equations during the Ph.D. program.

Orientador: Maurice de Koning / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-13T12:16:33Z (GMT). No. of bitstreams: 1 CarvajalJara_DiegoAlejandro_M.pdf: 4649880 bytes, checksum: d014cd5c835938e4643e478fa70353be (MD5) Previous issue date: 2009 / Resumo: Recentemente tem sido proposta a existência de uma transição líquido-líquido em substâncias puras com o propósito de explicar alguns comportamentos anômalos como os incrementos de funções resposta (compressibilidade isotérmica, coeficiente de expansão térmica, calor específico) ao diminuir a temperatura de um líquido. A existência deste tipo de transição foi demostrada experimentalmente para o fósforo por dispersão de raios X, e através de simulações atomísticas ou de primeiros princípios para a água, o silício, o carbono, etc. A compreensão detalhada deste tipo de transição está intimamente relacionada à questão fundamental de quais fatores físicos controlam as propriedades de um líquido, e portanto o estudo desta é de grande importância para o desenvolvimento de novas tecnologias, a síntese de novos materiais e o controle de suas propriedades. Neste trabalho realizamos simulações atomísticas sobre um sistema de 1152 partículas de Gálio submetidas a um potencial semi-empírico MEAM, com condições periódicas de contorno. Com estas simulações procuramos uma transição líquido-líquido no Gálio através de um processo de eliminação de três teorias. Inicialmente mostramos que o limite de metaestabilidade do líquido super-aquecido tem um comportamento monótono decrescente no plano de fase P-T. Posteriormente nosso sistema apresenta histerese, uma descontinuidade no volume, estruturas locais diferentes, duas fases que fluem, e um calor latente característico de uma transição de fase de primeira ordem. Por todas estas razões concluímos que o sistema simulado apresenta um transição líquido-líquido de primeira ordem. Adicionalmente foram realizadas compressões e expansões isotérmicas para temperaturas diferentes, observando que estes processos também apresentam histerese e que ela diminui com o aumento da temperatura, indicando assim a possível existência de um segundo ponto crítico e a finalização da transição líquido-líquido. Finalizamos o trabalho com a obtenção e a caracterização de uma possível nova fase cristalina do Gálio cuja estrutura ainda não tem sido obtida experimentalmente. Esta fase foi obtida por casualidade durante o estudo da existência de uma transição líquido-líquido no Gálio ao tencionar o Gálio a -1.6GPa. Sua estrutura é do tipo ortorrômbica com uma simetria Cmcm (grupo espacial 63) e sua principal diferença do Gálio-I é a orientação dos dímeros de Gálio, que nesta nova fase estão dispostos paralelamente. Simulações por DFT mostraram que esta nova fase é metaestável a pressão nula e chega a ser estável a pressões negativas abaixo de ~ 1.5GPa. / Abstract: Recently, the existence of a liquid-liquid transition in pure substances has been proposed as an explanation of anomalous behaviors such as the increase of response functions (isothermal compressibility, coefficient of thermal expansion, specific heat) with decreasing temperature displayed by some liquids. The existence of this type of transition has been demonstrated experimentally for phosphorous by X-ray diÿraction, and through atomistic simulations for water, silicon and carbon. The detailed understanding of this type of transition is closely related to the fundamental question of which physical factors control the properties of a liquid. Therefore, the study of this phenomenon is of great importance for the development of new technologies, the synthesis of new materials and the control of their properties. In this work, we carry out a series of atomistic simulations of a system containing 1152 Gallium atoms described by a semi-empirical Modified Embedded-Atom Model subject to periodic boundary conditions. By means of these simulations we search for a liquid-liquid transition in Gallium by means of a process of elimination of three theories. Initially we show that the limit of metastability of the superheated liquid has a decreasing monotonous behavior in the pressure-temperature phase diagram. Subsequently, our system presents hysteresis, a discontinuity in volume, two phases that have different local atomic structures and display diffusion, and a latent heat, all characteristic of a first-order phase transition. For all these reasons we conclude that the simulated system presents a liquid-liquid phase transition of first-order in the supercooled regime. In addition, we carried out several simulations of isothermal compressions and expansions for different temperatures. These results also show hysteresis although it is found to decrease with increasing temperature, thus indicating the possible existence of a second critical point at which the liquid-liquid transition ends. We finish our studies with the discovery and characterization of a crystalline phase of Gallium whose structure has not been observed experimentally. This phase was obtained by chance during the study of the existence of a liquid-liquid transition in Gallium under tension of -1.6GPa. Its structure is of the orthorhombic type with Cmcm symmetry (space group 63). Its main difference with respect to the Gallium-I phase is that in the new phase the Gallium dimers are disposed in a parallel fashion. Subsequent DFT simulations show that this new phase is metastable at zero pressure and predict it to become stable with respect to Gallium-I arrives at negative pressures below ~1.5GPa. / Mestrado / Física da Matéria Condensada / Mestre em Física

Nesta dissertação estudaremos sistemas de bósons ultrafrios armadilhados em uma rede ótica quadrada bidimensional sem levar em consideração o confinamento harmônico. A dinâmica desses sistemas é bem descrita pelo modelo de Bose-Hubbard, que prevê uma transição de fase quântica de um superfluido para um isolante de Mott a temperaturas baixas, e pode ser induzida variando a profundidade do potencial da rede ótica. Apresentaremos o diagrama de fases dessa transição construído a partir de uma aproximação de campo médio e também com um cálculo numérico usando um algoritmo de Monte Carlo Quântico, denominado algoritmo Worm. Encontramos o ponto crítico para o primeiro lobo de Mott em ambos os casos, concordando com trabalhos anteriores. / This work study the two-dimensional ultracold bosonic atoms loaded in a square optical lattice, without harmonic confinement. The dynamics of this system is described by the Bose-Hubbard model, which predicts a quantum phase transition from a superfluid to a Mott-insulator at low temperatures that can be induced by varying the depth of the optical potential. We present here the phase diagram of this transition built from a mean field approach and from a numerical calculation using a Quantum Monte Carlo algorithm, namely the Worm algorithm. We found the critical transition point for the first Mott lobe in both cases, in agreement with the standard literature.

Made available in DSpace on 2016-08-18T18:19:28Z (GMT). No. of bitstreams: 1 Rafael Mendonca Almeida.pdf: 3974122 bytes, checksum: 09838059334093a825a9917f9ecd4379 (MD5) Previous issue date: 2010-11-26 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this work we have investigated the dielectric and ionic properties of the pure Bi2Sn2O7 (BSO) and manganese doped ceramics in the temperature range from 23°C to 326°C. Amongst the main results of the BSO it is worthwhile to point out the PTCR ef-fect when it was analysed the temperature dependence of the electrical resistance. Furthermore, in both samples, the imaginary electrical modulus relaxational peaks are related to conductive processes, but only the BSO shows an anomaly in the tempera-ture range investigated. This anomaly is expressed with a displacement of the peaks to the region of low frequencies, as the temperature rises from the ambient value until 100°C, and after to the region of high frequencies, when the temperature changes from 100°C to 326°C. This dynamic of the data allowed to estimate the phase transition value as being equal to 121.5°C. It was also observed that this transition is possibly ferroic because the capacitance dependence with temperature shows a Curie like behaviour. By other side, the analysis of the real part of the electrical permittivity with temperature highlighted that the BSO phase transition point is located some-where around 125°C, while the one from BSO:Mn is around 120°C. The conductivity dependence with the reciprocal temperature showed an Arrhenius like behaviour and, from the mathematical adjustment at high temperatures, it was possible to estimate an activation energy of 1.26 eV. It was also found that the manganese doping inhibited the effect observed in the graphs of versus frequency, favored the conduction me-chanism of the system and preclude the PTCR effect. Analyzing the temperature de-pendence of the dielectric loss it was realized that this quantity also presents an ano-maly at around 120°C that can be assigned to the structural phase transition. Studying the real part of the admittance as function of the frequency, one could segregate the contributions from the bulk and grain boundary of the system and observe that the response of the last one exhibits a peak at 120°C, probably due to the transi-tion. Regarding the manganese ion substitution in the BSO structure, two hypotheses are proposed. It is believed that in both, the tin ion occurs with an oxidation state equal to 2+ and, but substituting either in the tin ion site or in the bismuth ion site, and releasing oxygen vacancies. / Nesse trabalho, investigamos as propriedades dielétricas e iônicas das cerâmicas Bi2Sn2O7 pura (BSO) e dopado com manganês (BSO:Mn) no intervalo de temperaturas entre 23°C e 326°C. Dentre os principais resultados do BSO, pode-se destacar o efeito PTCR (do inglês, Resistência com Coeficiente Positivo de Temperatura) quando se anali-sou a dependência da resistência elétrica com a temperatura. Além disso, em ambas as amostras, os picos de relaxação do módulo elétrico imaginário ( ) estão relacionados a processos condutivos, mas apenas o BSO exibe uma anomalia no intervalo de tempe-raturas investigadas. Essa anomalia se expressa como o deslocamento dos picos para a região de baixas frequências à medida que a temperatura aumenta do valor ambiente até 100°C e, depois para a região de altas frequências, quando a temperatura varia de 100°C a 326°C. Essa dinâmica dos dados permitiu estimar o valor da transição de fase como sendo igual a 121,5°C. Observou-se também que essa transição é possi-velmente ferróica, pois a dependência da capacitância com a temperatura mostra um comportamento tipo Curie. Por outro lado, a análise da parte real da permissividade elétrica com a temperatura evidenciou que a temperatura de transição do BSO situa-se em algum ponto próximo de 125°C, enquanto que a do BSO:Mn está por volta de 120°C. A dependência da condutividade com a temperatura recíproca mostrou um comportamento tipo Arrhenius e, a partir do ajuste matemático, em altas temperatu-ras, estimou-se uma energia de ativação de 1,26 eV. Ademais se constatou que a do-pagem do BSO com manganês inibiu o efeito observado nos gráficos de versus fre-qüência, facilitou o mecanismo de condução do sistema e impediu o efeito PTCR. Ana-lisando a dependência com a temperatura da perda dielétrica percebe-se que a mesma apresenta uma anomalia por volta de 120°C que pode ser devido à transição de fase estrutural . Estudando a parte real da admitância em função da frequência pu-deram-se separar as contribuições de contorno de grão e bulk do sistema e, observar que a resposta deste último exibe um pico em 120 °C que se deve possivelmente à transição . Quanto à substituição do íon manganês na estrutura do BSO, duas hipóteses são levantadas. Acredita-se que em ambas o íon Mn ocorra no estado de oxidação 2+, mas substituindo ou no sítio do íon de estanho ou no sítio do íon de bis-muto, e liberando vacâncias de oxigênio.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere. / Science, Faculty of / Chemistry, Department of / Graduate

Staphylococcus aureus est une bactérie Gram positive qui colonise la peau des animaux et des humains sains. Dans certaines conditions, telles que la perturbation du microbiote, S. aureus peut induire différentes maladies en déjouant les fonctions de défenses de la cellule hôte. Récemment, notre équipe a montré que les S. aureus méthiciline-résistant (MRSA) souche MW2 (USA400) étaient capables d’induire un retard de la transition de phase G2/M des cellules HeLa. Dans ce travail, nous avons démontré que cette action est initiée par des composants du surnagent de culture de S. aureus.Différentes fractions de surnagents de culture de MW2 ont été obtenues par la chromatographie d’exclusion et analysées par la spectrométrie de masse. Ces techniques nous ont permis d’identifier les peptides phenol-soluble modulins alpha (PSMa) comme responsables du retard du cycle cellulaire des cellules hôtes. Confirmant l’implication de ces modulines, la souche LAC¿psma déficiente en PSMa 1 – 4, n’a pas affecté la progression normale du cyle cellulaire de cellules epitheliales HeLa. De plus, le traitement de ces cellules avec des PSMa1 et PSMa3 synthétiques a induit un retard de la transition de phase G2/M qui a été associé à la diminution de l’expression de gènes codant des défensines ß. Enfin, nous avons démontré que la souche MW2 diminue le niveau d’optineurine et d’optineurine phosphorylée sur la sérine-177, une protéine hôte qui est impliquée dans la transition de phase G2/M. Ce travail représente une étape importante de la compréhension du mécanisme d’interférence de S. aureus / Staphylococcus aureus is a Gram-positive bacterium that colonizes the skin of healthy animals and humans. In certain conditions, including the disruption of the commensal microbiota, S aureus can cause different diseases by deviating the host defense functions. Recently, our group has shown that the methicillin-resistant S. aureus (MRSA) MW2 (USA400) strain causes delay in the transition of the G2/M phase of HeLa cells. In the present work, we demonstrated that this action is initiated by components of the supernatant of the S. aureus culture. Different supernatant fractions were obtained by size exclusion chromatography and were analyzed by mass spectrometry, which allowed to identify phenol-soluble modulins alpha (PSMa) as responsible for the host cell cycle delay.Confirming the involvement of these modulins in the delay, the MRSA LAC¿psma strain, which is deficient in PSMa1–4, did not affect the normal progression of the cycle in HeLa cells. In addition, the treatment of these cells with synthetic PSMa1 and PSMa3 caused delay in the transition of the G2/M phase associated with the decreased production of host ß-defensins. Lastly, we demonstrated that the MW2 strain, which produce PSMa, decreases the level of optineurin and optineurin phosphorylated at serine 177, a host protein that is involved in the G2/M phase transition. The work conducted in this thesis represents an important achievement in the understanding of how S. aureus interferes with the host cell cycle, revealing a new role for PSMa produced by this bacterium.

La miniaturisation toujours plus poussée des composants électroniques génère des contraintes thermiques de plus en plus importantes. Les boucles diphasiques à pompage thermo-capillaire ou LHP suscitent actuellement un intérêt croissant en raison de leurs bonnes performances thermiques, de leur fiabilité et de leur géométrie permettant une grande souplesse d’implantation. Cependant, une meilleure compréhension des phénomènes en jeu dans ces systèmes est essentielle pour optimiser leur conception et prédire leur comportement de manière fiable. Dans ce travail, un modèle analytique est développé qui intègre les paramètres de fonctionnement d’une LHP, afin d’étudier leur influence en fonction des conditions opératoires. Son originalité principale réside dans la détermination précise de la répartition des différents flux thermiques dans l’évaporateur. Une étude de sensibilité est menée pour évaluer les influences de la résistance de contact entre la structure capillaire poreuse et l’enveloppe de l’évaporateur, de la conductivité thermique équivalente du matériau poreux, du coefficient d’accommodation lié aux transferts de chaleur par évaporation et des coefficients de transfert thermique entre la paroi et le milieu ambiant ou la source froide. Cette analyse montre que les paramètres mentionnés ci-dessus peuvent être estimés individuellement, en comparant le modèle à des données expérimentales judicieusement choisies. Un banc expérimental a également été conçu et fabriqué. Partiellement transparent, il permet l’observation de la position des phases liquide et vapeur au cours du fonctionnement. Les influences de la puissance thermique appliquée, de la présence de gaz incondensables et de la température de la source froide sont analysées. Aux puissances thermiques élevées, un régime d’ébullition nucléée est observé dans le réservoir, qui se traduit par une augmentation des flux parasites vers le réservoir donc une dégradation des performances de la LHP. Plusieurs phénomènes oscillatoires sont également observés et corrélés aux observations visuelles des écoulements. Enfin, différents régimes de condensation sont observés et les mécanismes conduisant au détachement des bulles dans le condenseur sont décrits. Un modèle numérique a été développé, afin de simuler le comportement du banc expérimental en se rapprochant au plus près de ses caractéristiques géométriques et thermophysiques. La comparaison entre les prédictions du modèle et les données expérimentales montre les carences des modèles de pertes de charges dans les écoulements diphasiques, pour la configuration étudiée. Les transferts de chaleur et de masse dans l’évaporateur sont analysés, ainsi que l’influence de l’apparition de l’ébullition dans le réservoir et celle de la conductivité thermique de l’enveloppe de l’évaporateur. Les résultats mettent également en évidence l’importance de la conduction thermique longitudinale dans les canalisations dans le cas d’un matériau conducteur. / The increasing development of electronics leads to higher constraints regarding their thermal management. Loop heat pipes (LHP) become more and more attractive because they offer thermal efficiency, reliability and large implementation flexibility. However, a better understanding of the physical phenomena involved within them is required in order to optimise their design and predict accurately their operation. An analytical model is developed to highlight the main parameters of a LHP and their influence depending on the operating conditions. Its main originality lies in a thorough consideration of heat transfer in the evaporator. A sensitivity analysis is conducted to study the influence of the contact thermal resistance between the wick and the body of the evaporator, of the effective thermal conductivity of the wick, of the accommodation coefficient linked to the evaporation heat transfer and of the heat transfer with the ambient and with the heat sink. This analysis shows that these parameters can be individually and separately estimated by comparing the model to a set of well-chosen experimental data. An experimental setup is designed and built. It is partially transparent, to observe the location of the liquid and vapour phases in operating conditions. The effects of the heat input, non-condensable gases and of the heat sink temperature are discussed. Nucleate boiling is observed inside the reservoir for high heat fluxes. This phenomenon increases significantly the parasitic heat flux towards the reservoir and therefore decreases the performance of the LHP. Several oscillating phenomena are also observed and correlated to the flow patterns. Finally, distinct condensation regimes are investigated and the mechanisms leading to the bubble detachment in the condenser are discussed. A numerical model is developed in accordance with the geometrical and thermophysical characteristics of the experimental setup. The model is compared with the experimental data. The comparison shows the lack of accuracy of the two-phase pressure drops models in this configuration. Heat and mass transfer in the evaporator are discussed and the effects of boiling in the reservoir and of the thermal conductivity inside the evaporator casing are investigated. The results highlight the importance of the longitudinal thermal conduction inside the tube in the case of conductive materials.

In this diploma thesis precursors of quantum phase transitions in finite many-body systems are studied. The main attention is paid to the mechanism, how nonanalytic behaviour of the ground state is generated for certain critical values of real control parameters. It is shown that nonanalytic behaviour of energy levels and eigenstates is closely connected with exceptional points of the hamiltonian, which are points in control parameter space extended into a complex domain where at least two eigenvalues and corresponding eigenvectors coincide. Differences in the distribution of exceptional points in the complex plane of control parameter for the first and second order phase transitions and also evolutions of the position of exceptional points with increasing particle number are discussed.