In the field of quantum gravity, it is widely expected that some form of a minimum length scale, or ultraviolet cutoff, exists in nature. Recently, a new natural ultraviolet cutoff that is fully covariant was proposed. In the literature, most studies of ultraviolet cutoffs are concerned with Lorentz-violating ultraviolet cutoffs. The difficulty in making a minimum length cutoff covariant is rooted in the fact that any given length scale can be further Lorentz contracted. It was shown that this problem is avoided by the proposed covariant cutoff by allowing field modes with arbitrarily small wavelengths to still exist, albeit with exceedingly small, covariantly-determined bandwidths. In other words, the degrees of freedom of sub-Planckian modes in time are highly suppressed. The effects of this covariant ultraviolet cutoff on the kinematics of a scalar quantum field are well understood. There is much to learn, however, about the effects on a field’s dynamics. These effects are of great interest, as their presence may have direct observational consequences in cosmology. As such, this covariant ultraviolet cutoff offers the tantalizing prospect of experimental access to physics at the Planck scale. In cosmology, the energy scales that are probed by measurements of cosmic microwave background (CMB) statistics are the closest that we can get to the Planck scale. In particular, the statistics of the CMB encodes information about the quantum fluctuations of the scalar inflaton field. A measure of the strength of a field’s quantum fluctuations is in turn given by the magnitude of the field’s Feynman propagator. To this end, in this thesis I study how this covariant ultraviolet cutoff modifies the Feynman propagator of a scalar quantum field. In this work, I first calculate the cutoff Feynman propagator for a scalar field in flat spacetime, and then I address the cutoff Feynman propagator of a scalar field in curved spacetime. My studies culminate with an explicit calculation for the case of a power-law Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime. This last calculation is cosmologically significant, as power-law FLRW spacetime is a prototypical and realistic model for early-universe inflation. In preparation for studying the covariant cutoff on curved spacetime, I will review the necessary back- ground material as well as the kinematic influence of the covariant cutoff. I will also discuss several side results that I have obtained on scalar quantum field theories in spacetimes which possess a finite start time.

Cette thèse se focalise sur l'étude des amas de galaxies, via l'effet Sunyaev-Zel'dovich (tSZ), qui consiste en l'interaction de ces même amas avec le fond diffus cosmologique. Pour ce faire j'ai utilisé les données expérimentale de l'instrument HFI du satellite PLANCK. Cette thèse ce découpe en trois parties majeures, (1) L'analyse et le traitement des données en temps, des données brut jusqu'au cartes du ciel, ce focalisant tout particulièrement sur les effets systématiques. (2) Le développement de méthode de séparation de sources, permettant la construction de cartes par émission astrophysique (tout particulièrement l'effet Sunyaev-Zel-dovich) à partir de données multi-fréquences. (3) L'analyse physique des cartes d'effet Sunyaev-Zel'dovich, produit par le gaz d'électron chaud présent dans les amas de galaxies. Ce travail permet la mise en place de contrainte, sur le profile de pression des amas de galaxies, sur la présence de filaments de matière entre des système binaire d'amas de galaxies, ainsi que la mise en évidence du spectre de puissance de l'effet tSZ.

Thesis (Ph.D.); Submitted to the University of California at Berkeley, Berkeley, CA 94720 (US); 1 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56842" Barber IV, John Letherman. USDOE Director. Office of Science. Advanced Scientific Computing Research (US) 12/01/2004. Report is also available in paper and microfiche from NTIS.

In recent years, there has been increased awareness that stochasticity in chemical reactions and diffusion of molecules can have significant effects on the outcomes of intracellular processes, particularly given the low copy numbers of many proteins and mRNAs present in a cell. For such molecular species, the number and locations of molecules can provide a more accurate and detailed description than local concentration. In addition to diffusion, drift in the movements of molecules can play a key role in the dynamics of intracellular processes, and can often be modeled as arising from potential fields. Examples of sources of drift include active transport, variations in chemical potential, material heterogeneities in the cytoplasm, and local interactions with subcellular structures. This dissertation presents a new numerical method for simulating the stochastically varying numbers and locations of molecular species undergoing chemical reactions and drift-diffusion. The method combines elements of the First-Passage Kinetic Monte Carlo (FPKMC) method for reaction-diffusion systems and the Wang—Peskin—Elston lattice discretization of the Fokker—Planck equation that describes drift-diffusion processes in which the drift arises from potential fields. In the FPKMC method, each molecule is enclosed within a "protective domain," either by itself or with a small number of other molecules. To sample when a molecule leaves its protective domain or a reaction occurs, the original FPKMC method relies on analytic solutions of one- and two-body diffusion equations within the protective domains, and therefore cannot be used in situations with non-constant drift. To allow for such drift in our new method (hereafter Dynamic Lattice FPKMC or DL-FPKMC), each molecule undergoes a continuous-time random walk on a lattice within its protective domain, and the lattices change adaptively over time. One of the most commonly used spatial models for stochastic reaction-diffusion systems is the Smoluchowski diffusion-limited reaction (SDLR) model. The DL-FPKMC method generates convergent realizations of an extension of the SDLR model that includes drift from potentials. We present detailed numerical results demonstrating the convergence and accuracy of our method for various types of potentials (smooth, discontinuous, and constant). We also present several illustrative applications of DL-FPKMC, including examples motivated by cell biology.

The subject of the thesis is the derivation of non-local diffusion equations from kinetic models with heavy-tailed equilibrium in velocity. We are particularly interested in confining the kinetic equations and developing methods that allow us, from the confined kinetic models, to derive confined versions of non-local diffusion equations.

Made available in DSpace on 2014-06-11T19:22:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-01Bitstream added on 2014-06-13T18:49:54Z : No. of bitstreams: 1 araujo_mt_me_sjrp.pdf: 1105011 bytes, checksum: 8882d04f0f922d97e919cd8dd4e66abb (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho versa sobre difusão anômala, especificamente a proposição e solução exata e aproximada de um conjunto de equações não lineares de difusão. Primeiramente é apresentada a solução de dois sistemas sujeitos a difusão normal para explicitar a restrição que há em métodos de solução para a equação de difusão não linear. Em seguida, focamos o trabalho em processos anômalos mostrando, inicialmente a solução estacionária que maximiza a entropia de Tsallis. Sua solução exata é uma gaussiana generalizada que unifica o comportamento tipo lei de potência e exponencial alongada. Para um dos casos solucionados é incluído na equação um termo de fonte dependente da parte temporal da probabilidade. As soluções analíticas encontradas são analisadas para diferentes valores de não linearidade, caracterizando processos sub ou super difusivos, embora ao se considerar uma equação não linear, uma escolha conveniente na dependência temporal dos coeficientes também conduz a esses processos. Neste caso, equações não lineares com solução não gaussiana podem conduzir à difusão usual, da mesma forma que surgem anomalias em processos descritos por equações lineares e solução gaussiana. Por fim, a equação do tipo Fokker- Planck não linear é solucionada através do emprego de método numérico visando uma forma alternativa para analisar sistemas que não permitem obter uma solução exata da equação / This work describes anomalous diffusion, specifically the proposition and exact and approximate solution of a set of nonlinear equations of diffusion. First is shown the solution solve of two systems subject to normal diffusion to exhibit the restriction that exist in solution methods for nonlinear diffusion equation. After, we focus on the work showing anomalous processes, initially stationary solution which maximizes the entropy purpose of Tsallis. Its exact solution is a generalized Gaussian that unifies behavior power law and stretched exponential. For one of the solved cases is included in the equation a source term dependent on the temporal part of probability. The analytical solutions found are analyzed for different values of nonlinearity characterizing diffusion processes under or over, although when considering a nonlinear equation, a convenient choice in the time dependence of the coefficients also leads to these processes. In this case, nonlinear equations with non-Gaussian solution can lead to the usual diffusion, similar anomalies that arise in processes described by linear equations and Gaussian solution. Finally, the equation of nonlinear Fokker-Planck is solved by employing numerical method seeking an alternative way to analyze systems that do not achieve an exact solution of the equation

Made available in DSpace on 2014-06-12T18:04:23Z (GMT). No. of bitstreams: 2 arquivo7752_1.pdf: 2968182 bytes, checksum: b99b78d01729ac83718a680337a6d7f1 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2006 / Faculdade de Amparo à Ciência e Tecnologia do Estado de Pernambuco / Os resultados apresentados nesta tese podem ser divididos em duas partes. Na primeira estudamos uma classe de ensembles de movimento browniano (EMB) da teoria de matrizes aleatórias, gerados a partir da teoria matricial de processos estocásticos markovianos. Os ensembles são caracterizados por uma equação de Fokker-Planck e estão intimamente relacionados a hamiltonianos de sistemas quânticos do tipo Calogero-Sutherland. Esta conexão leva a um esquema geral de classificação baseada numa recente generalização multidimensional dos polinômios ortogonais clássicos. Mostramos que, sob certas condições, os EMB englobam os ensembles de matrizes de transferência. Desta forma, desenvolvemos um tratamento unificado dos ensembles de polinômios e de matrizes de transferência que, além de servir como um esquema de classificação das diversas classes de simetria, fornece técnicas eficientes de cálculo. Desenvolvemos métodos de Fokker-Planck para o cálculo de médias de observáveis representados por estatísticas lineares, assim como para o cálculo de funções de correlação. Neste contexto, desenvolvemos um método de transformada integral e uma generalização do método das funções biortogonais para o cálculo da função de correlação de n-pontos. Os resultados deduzidos neste contexto geral são aplicados a pontos e fios quânticos. Em particular, apresentamos um estudo numérico de propriedades de transporte em pontos quânticos com simetria quiral. Na segunda parte, estudamos uma cavidade caótica balística acoplada, via barreiras de transparência arbitrária, a dois guias semi-infinitos usando as duas abordagens de teoria de circuito disponíveis na literatura: a escalar e a matricial. Mostramos a equivalência destas teorias através do cálculo dos cumulantes da estatística de contagem. Para isso, determinamos as funções geratrizes fornecidas pelas duas teorias e verificamos a concordância dos 18 primeiros cumulantes usando um programa de computação algébrica. Também estudamos distribuições exatas de corrente de alguns sistemas simples de dois terminais, como um ponto quântico com barreiras simétricas. Estes resultados são importantes, pois fornecem uma grandeza diretamente mensurável em experimentos

Les paquets d'électrons relativistes circulant dans les anneaux de stockage sont des sources de rayonnement VUV, X et THz incontournables. Cependant, ces systèmes sont également connus pour présenter des instabilités dynamiques. Dans cette thèse, nous nous sommes intéressés à l'instabilité dite de microbunching, qui mène à l'apparition de microstructures à l'échelle millimétrique, et à l'émission de bouffées intense de rayonnement THz cohérent. L'objectif de la thèse était d'avancer dans la compréhension de la dynamique non-linéaire de ces structures, en combinant études expérimentales et numériques. Les expériences ont été effectuées au Synchrotron SOLEIL et à UVSOR, et les études numériques ont été principalement basées sur l'équation de Vlasov-Fokker-Planck. Dans un premier temps, la rapidité des échelles de temps impliquées nous a menés à réaliser des études indirectes. Des informations sur la dynamique à l'échelle picoseconde ont ainsi pu être déduites d'enregistrements au moyen de détecteurs possédant des constantes de temps beaucoup plus lentes (la microseconde), et en particulier en étudiant la réponse à des perturbations laser. Ensuite, au moyen de deux techniques nouvelles, nous avons pu réaliser les premières observations directes des structures et de leur dynamique. A UVSOR, nous avons utilisé un détecteur THz à film mince de YBCO supraconducteur. Ensuite, nous avons développé une méthode originale associant l'effet électro-optique et l'étirement temporel, ce qui nous a permis d'atteindre une résolution picoseconde, au Synchrotron SOLEIL. Ces nouvelles observations nous ont immédiatement permis de réaliser des tests extrêmement sévères des modèles théoriques. / Relativistic electron bunches circulating in storage rings are used to produce intense radiation from far-infrared to X-rays. However, above a density threshold value, the interaction between the electron bunch and its own radiation can lead to a spatio-temporal instability called microbunching instability. This instability is characterized by a strong emission of coherent THz radiation (typically 105 times stronger than the classical synchrotron radiation) which is a signature of the presence of microstructures (at mm scale) in the electron bunch. This instability is known to be a fundamental limitation of the operation of synchrotron light sources at high beam current. In this thesis, we have focused on this instability from a nonlinear dynamics point of view by combining experimental studies carried out at the Synchrotron SOLEIL and UVSOR storage rings with numerical studies mainly based on the Vlasov-Fokker-Planck equation. In a first step, due to the very indirect nature of the experimental observations, we have sought to deduce information on the microstructure wavenumber either by looking at the temporal evolution of the THz signal emitted during the instability or by studying the response of the electron bunch to a laser perturbation. In a second step, we have achieved direct, real time observations of the microstructures dynamics through two new, very different, detection techniques: a thin-film superconductor-based detector at UVSOR, and a spectrally-encoded electro-optic detection technique at SOLEIL. These new available experimental observations have allowed severe comparisons with the theoretical models.

Le rayonnement fossile, ou CMB, est un sujet d’étude clé pour la cosmologie car il indique l’état de l’univers à une époque primordiale. Le CMB est observable dans le ciel dans la bande de fréquences des micro-ondes. Cependant, il existe des processus astrophysiques, les avant-plans, qui émettent dans les micro-ondes, et rendent indispensable le traitement des données avec des méthodes de séparation de composantes. J'utilisé la méthode aveugle SMICA pour obtenir une estimation directe du spectre de puissance angulaire du CMB. La détermination des petites échelles de ce spectre est limité par les avant-plans comme les galaxies lointaines, et par le biais du bruit. Dans cette analyse, ces deux limitations sont abordées. En ajoutant des hypothèses sur la physique des galaxies lointaines, il est possible de guider l’algorithme pour estimer leur loi d'émission. Un spectre de puissance angulaire obtenu d'une carte du ciel a un biais dû au bruit à petites échelles. Toutefois, les spectres obtenus en croisant différentes cartes n'ont pas ce biais. J'ai donc adapté la méthode SMICA pour qu'elle n'utilise que ces derniers, diminuant l'incertitude due au bruit dans l'estimation du CMB. Cette méthode a été étudiée sur des nombreuses simulations et sur les données Planck 2015, afin d'estimer des paramètres cosmologiques. Les résultats montrent que la contamination résiduelle des avant-plans présente dans le spectre CMB, même si fortement réduite, peut introduire des biais dans l'estimation des paramètres si la forme des résiduels n'est pas bien connue. Dans cette thèse, je montre les résultats obtenus en étudiant un modèle de gravité modifiée. / The Planck satellite observed the whole sky at various frequencies in the microwave range. These data are of high value to cosmology, since they help understanding the primordial universe through the observation of the cosmic microwave background (CMB) signal. To extract the CMB information, astrophysical foreground emissions need to be removed via component separation techniques. In this work I use the blind component separation method SMICA to estimate the CMB angular power spectrum with the aim of using it for the estimation of cosmological parameters. In order to do so, small scales limitations as the residual contamination of unresolved point sources and the noise need to be addressed. In particular, the point sources are modelled as two independent populations with a flat angular power spectrum: by adding this information, the SMICA method is able to recover the joint emission law of point sources. Auto-spectra deriving from one sky map have a noise bias at small scales, while cross-spectra show no such bias. This is particularly true in the case of cross-spectra between data-splits, corresponding to sky maps with the same astrophysical content but different noise properties. I thus adapt SMICA to use data-split cross-spectra only. The obtained CMB spectra from simulations and Planck 2015 data are used to estimate cosmological parameters. Results show that this estimation can be biased if the shape of the (weak) foreground residuals in the angular power spectrum is not well known. In the end, I also present results of the study of a Modified Gravity model called Induced Gravity.

This master’s thesis is specialized on the influence of correct parameters of emissivity, which depends on the temperature, wavelength and ambient environment. The investigation the parameter was taken infrared non-contact thermometer MI3 from company Raytek. To improve the quality of measurement was designed and programmed measuring utility program. The program was developed in the LabView 8.5 programming environment. To obtain the true value of the measured temperature of the target was designed and constructed the touch thermometer with the resistance dependent sensor. The thermometer is connected to the communication box of infrared thermometer and contain the same program. Nowadays are the most advanced IR thermometer with fixed parameters emissivity, which is applicable just to the real body in the vicinity of the parameter emissivity 0,95. For those IR thermometers were designed correction function, which would have temperature measured at a fixed emissivity parameter 0,95 set close to the actual value of the object.