Desde o início do uso de ferramentas computacionais na química, pesquisadores notaram a necessidade de um adequado tratamento da correlação eletrônica para a acurada descrição da estrutura eletrônica. Algum tempo depois, perceberam que, além da correlação, haviam ainda deficiências nos resultados obtidos, as quais estavam relacionadas com efeitos relativísticos, principalmente quando tentavam tratar moléculas com átomos pesados. Um terceiro aspecto a ser levado em consideração nestes estudos diz respeito ao uso de um conjunto acurado de funções de base. No caso específico de cálculos relativísticos, se possível, tais conjuntos ainda precisam garantir a eliminação do prolapso variacional, um problema que está relacionado com uma descrição deficiente da região mais próxima dos núcleos. Com esse propósito, o conjunto RPF-4Z foi desenvolvido recentemente. Sendo assim, este projeto foi voltado para a análise comparativa da qualidade do conjunto RPF-4Z. Desta forma, foram avaliadas propriedades fundamentais das moléculas como, por exemplo, geometrias, momentos de dipolo e constantes espectroscópicas. Simultaneamente, uma propriedade desafiadora, o gradiente de campo elétrico na posição de núcleos de xenônio, também foi considerada. Os resultados obtidos até agora reforçam a eficiência do conjunto RPF-4Z, que é capaz de fornecer valores comparáveis àqueles dados por conjuntos de base de mesma qualidade, mas com menor demanda por recursos computacionais. / Early in the application of computational framework in chemistry, researchers noticed the need for an adequate electronic correlation treatment in order to accurately describe electronic structures. Some years later they realized that, besides correlation, there were also deficiencies in the results, which were related to relativistic effects, especially when dealing with molecules containing heavy atoms. A third aspect to be taken into account is related to the use of an accurate basis set. Specifically for relativistic calculations, these basis sets must also ensure the elimination of variational prolapse if possible, which is a problem related to a poor description of the innermost region close to the nuclei. Thus, the RPF-4Z basis set was recently developed for this aim. This project is focused on a comparative analysis regarding the RPF-4Z basis set\'s quality. Thereby, fundamental properties of molecules were evaluated, such as geometries, dipole moments and spectroscopic constants. At the same time, a challenging property, the electric field gradient at the xenon nuclei, was considered as well. The results obtained so far reinforce the efficiency of the RPF-4Z basis set, which is capable of providing comparable values to those obtained by same quality basis sets but with a lower demand for computational resources.

Orientador: Luiz Guimarães Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T00:36:47Z (GMT). No. of bitstreams: 1 Pinho_MariaGloriadeOliveira_M.pdf: 832379 bytes, checksum: 05244cdafb054c3e2fffdc0bd34cdc3a (MD5) Previous issue date: 2007 / Resumo: Apresentamos neste trabalho o estudo da fotoionização, incluindo os efeitos relativísticos, de elétrons das camadas-s mais externas dos átomos de Sódio, Potássio, Rubídio e Césio. Tratamos do processo onde um átomo não polarizado é fotoionizado por luz incidente linearmente polarizada, utilizando o Estado de Transição de meia ocupação, sob a ótica da aproximação de dipolo elétrico e da Aproximação da Densidade Local (LDA). Em nosso procedimento fazemos uso das equações de Dirac para o cálculo das funções de onda relativísticas, utilizadas para a obtenção das seções de choque totais de fotoionização e dos parâmetros de assimetria. Mostramos as vantagens da utilização do Estado de Transção de meia ocupação e sua precisão numérica nos cálculos de grandezas físicas como o Potencial de Ionização dos átomos. Através dos resultados obtidos, observamos a influência que os mínimos das seções de choque, chamados Mínimos de Cooper, exercem sobre os parâmetros de assimetria. Estes dados sâo comparados com cálculos efetuados através de outras formulações por outros autores e também com resultados experimentais encontrados na literatura / Abstract: In this work we present photoionization results for the valence s-electrons of Sodium, Potassium, Rubidium and Cesium atoms including relativistic effects. In our calculations we consider the photoionization of a non-polarized atom by linearly polarized light, using half occupation transition states, within the electric dipole approximation and the Local Density Approximation. Our total photoionization cross sections and asymmetry parameters were calculated using relativistic wave functions obtained from Dirac¿s equations. We show that the use of half occupation transition states improves the results, producing many advantages, such as numeric precision in the evaluation of the Ionization Potentials. We have also studied the in uence of the cross section minimum (Cooper Minimum) on the asymmetry parameters. We compare our results with experimental data and with other calculations from the literature / Mestrado / Física Atômica e Molecular / Mestre em Física

No description available.

Thesis (MSc (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The overall goal of this project is to study neutron star properties and locate the transition density from the core to the crust using fifteen parameter sets of the effective Skyrme nucleon-nucleon interaction within a method called the dynamical method. Although another approach used to describe nucleon-nucleon interactions called the modified Gogny interaction is briefly discussed in this work, along with a second method for locating the transition density called the thermodynamical method, results using this interaction and method were not generated, but lays some foundation for a PhD project to be undertaken and potentially showing the relation between the interactions and results. The importance of results depends on how well other theoretical approaches to the problem can reproduce those results and to what accuracy. For models to be valid there also has to be good agreement between the theoretical results and known observables. In this project some properties of neutron stars, such as the equation of state, saturation density, binding energy, symmetry energy, slope and incompressibility parameters of symmetry energy are studied. The transition density is located using the dynamical method. Results of the fifteen Skyrme parameter sets show excellent agreement with the published values of the properties of neutron stars and are consistent with their empirical values inferred from nuclear laboratory data, thus validating the use of the Skyrme interactions for describing nuclear matter. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie projek is om neutron ster eienskappe te bestudeer en die oorgangsdigtheid vanaf die kors na die kern te vind deur gebruik te maak van vyftien parameter stelle van die effektiewe Skyrme nukleon-nukleon interaksie binne ‘n metode genaamd die dinamiese metode. Alhoewel ‘n ander benadering vir die beskrywing van nukleon-nukleon interaksies, genaamd die gewysigde Gogny interaksie kortliks in hierdie werk beskryf word, asook ‘n tweede metode, genaamd die termodinamiese metode om die oorgangsdigtheid te bepaal, was resultate vir hierdie interaksie en metode nie gegenereer nie, maar l die fondasie vir verdere werk aan ‘n PhD projek wat die verband tussen die twee interaksies en resultate kan wys. Die belangrikheid van resultate hang af van hoe goed ander teoretiese benaderinge tot die problem daardie resultate kan herproduseer en tot watter akkuraatheid. Vir modelle om geldig te wees moet daar ook goeie ooreenkomste wees tussen teoretiese resultate en bekende waarneembare eienskappe. In hierdie projek word sommige eieskappe van neutron sterre, soos die toestandandsvergelyking, versadigingsdigtheid, bindingsenergie, simmetrie-energie, gradiënt en onsaampersbaarheids parameters van die simmetrie-energie bestudeer. Die oorgangsdigtheid word dan gevind deur gebruik te maak van die dinamiese metode. Resultate van die vyftien Skyrme interaksie parameter stelle wys goeie ooreenstemming met die gepubliseerde waardes van die eienskappe van neutron sterre en is konsistent met hulle empiriese waardes afgelei van kern laboratorium data, wat die geldigheid van Skyrme interaksies vir die beskrywing van kernmaterie bevestig.

<p>Plasma-based particle acceleration holds the promise to make the applications that revolve around accelerators more affordable. The central unifying theme of this dissertation is the modeling of certain non-linear and relativistic phenomena in plasma dynamics to devise mechanisms that benefit plasma-accelerators. Plasma acceleration presented here has two distinct flavors depending upon the accelerated particle mass which dictates the acceleration structure velocity and potential. The first deals with ion acceleration, where acceleration structure velocities are a significant fraction of the speed of light, with major applications in medicine. The second focusses on the acceleration of electrons and positrons for light-sources and colliders where the acceleration structures are wakefields with phase-velocities near the speed of light.</p> <p>The increasing Lorentz factor of the laser-driven electron quiver momentum forms the basis of Relativistically Induced Transparency Acceleration (RITA) scheme of ion acceleration. Lighter ions are accelerated by reflecting off a propagating acceleration structure, referred to as a snowplow, formed by the compression of ponderomotively driven critical layer electrons excited in front of a high intensity laser pulse in a fixed-ion plasma. Its velocity is controlled by tailoring the laser pulse rise-time and rising density gradient scale-length. We analytically model its induced transparency driven propagation with a 1-D model based on the linearized dispersion relation. The model is shown to be in good agreement with the weakly non-linear simulations. As the density compression rises into the strongly non-linear regime, the scaling law predictions remain accurate but the model does not exactly predict the RITA velocity or the accelerated ion-energy. Multi-dimensional plasma effects modify the laser radial envelope by self-focussing in the rising density gradient which can be integrated into our model and filamentation which is mitigated by a matched laser focal spot-size. We show that the critical layer motion in RITA compares favorably to the bulk-plasma motion driven by radiation pressure or collision-less shocks.</p> <p>Non-linear mixing of the laser, incident on and reflected off the propagating critical layer modulates its envelope affecting the acceleration structure velocity and potential, in the process setting up a feedback loop. For long pulses the envelope distortion grows with time, disrupting the accelerated ion-beam spectral shape. We model the Chirp Induced Transparency Acceleration (ChITA) mechanism that over- comes this effect by introducing decoherence through a frequency chirp in the laser. </p> <p>In a rising density gradient, the non-linearity of electron trajectories leads to the phase-mixing self-injection of electrons into high phase-velocity plasma wakefields. The onset of trapping depends upon the wake amplitude and the density gradient scale-length. This self-injection mechanism is also applicable to controlling the spuriously accelerated electrons that affect the beam-quality. </p> <p>Non-linear ion dynamics behind a train of asymmetric electron-wake excites a cylindrical ion-soliton similar to the solution of the cylindrical Korteweg-de Vries (cKdV) equation. This non-linear ion-wake establishes an upper limit on the repetition rate of the future plasma colliders. The soliton is excited at the non-linear electron wake radius due to the time-asymmetry of its radial fields. In a non-equilibrium wake heated plasma the radial electron temperature gradient drives the soliton. Its radially outwards propagation leaves behind a partially-filled ion-wake channel. </p> <p>We show positron-beam driven wakefield acceleration in the ion-wake channel. Optimal positron-wakefield acceleration with linear focussing fields is shown to require a matched hollow-plasma channel of a radius that depends upon the beam properties. </p> / Dissertation

Thesis (PhD (Physics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this dissertation we present, for the first time, a relativistic distorted wave impulse approximation formalism to describe quasielastic proton-nucleus scattering. We start from a full many-body description of the transition matrix element and show systematically how to derive the equivalent two-body form. This procedure allows for a clear and unambiguous method to introduce relativistic distorted waves. It is shown that the polarized double differential cross section may be written as the contraction of two tensors namely, the hadronic tensor (describing the projectile and ejectile), and the polarization tensor describing the target nucleus. The basic nucleon-nucleon (NN) interaction is described by the SPVAT or IA1 representation of the NN scattering matrix. Analytical expressions are derived for the polarization tensor using a Fermi gas model for the target nucleus. The nuclear distortion effects on the projectile and ejectile are described using the relativistic eikonal formalism. The expression for the double differential cross section is a nine dimensional oscillatory integral and an efficient procedure is developed to calculate this quantity. Comparison of Gaussian, Monte Carlo and quasi-Monte Carlo numerical integration schemes reveal that for this work, Gaussian quadrature is best suited for this problem. Traditional Gaussian quadrature is used to generate single variable functions whereby these functions are used in combination with modern software such as MATLAB to complete the computation of the full multidimensional integral in a reasonable amount of time. Even though the calculation of the cross section for a single value of the energy transfer is still time consuming, the computational time can be decreased by spreading the calculational burden across a number of nodes in a cluster computing system. A test calculation is performed whereby a proton with incident laboratory energy of 400 MeV is scattered off a 40Ca target nucleus at θcm = 40◦. For this reaction we calculate the unpolarized double differential cross section, as well as a complete set of spin observables namely Ay, Dℓ′,ℓ, Ds′s, Dnn,Ds′ℓ and Dℓ′s. We find that the distortions lead to a reduction of the unpolarized double differential cross section. On the other hand the spin observables are complex entities which show no uniformity in behaviour. However, the differences between the distorted wave spin observables and that of the plane wave observables are minor and we conclude that distortions have little effect on spin observables. / AFRIKAANSE OPSOMMING: Hierdie proefskrif bevat, vir die eerste keer, ’n relatiwistiese vervormdegolf impuls benadering formalisme vir die beskrywing van kwasielastiese proton-kern verstrooiing. Daar word aangetoon hoe om stapsgewys te gaan vanaf ’n veel-deeltjie beskrywing van die oorgangsmatriks element na die ekwivalente twee-deeltjie vorm. Hierdie metode laat toe dat die vervormde golwe op ’n duidelike en ondubbelsinnige manier ingevoer kan word. Daar word aangetoon dat die gepolariseerde dubbele differensiële kansvlak geskryf kan word as die kontraksie van twee tensore naamlik, die hadroniese tensor (wat die projektiel en uitgaande nukleon beskryf), sowel as die polarisasie tensor wat die kern beskryf. Die basiese kern-kern (NN) wisselwerking word beskryf deur gebruik te maak van die SPVAT of IA1 daarstelling van die NN verstrooiingsmatriks. Analitiese uitdrukkings word ook afgelei vir die polarisasie tensor binne die Fermi gas model. Die vervormdegolf beskrywing van die projektiel en uitgaande deeltjie word gedoen deur gebruik te maak van die eikonal vervormdegolf benadering. Die uitdrukking vir die ongepolariseerde dubbele differsieële kansvlak bevat ’n nege dimensioneële ossilatoriese integraal en ’n prakties-effektiewe prosedure is ontwikkel om hierdie waarneembare te bereken. Vegelyking van Gauss, Monte Carlo en kwasi-Monte Carlo numeriese integrasie tegnieke het uitgewys dat die Gauss integrasie tegniek die beste geskik is om die probleem op te los. Die gebruik van Gauss integrasie om funksies te bereken wat afhanklik is van net een veranderlike en dit te kombineer met moderne sagteware programme soos MATLAB laat ons toe om die gepolariseerde dubbele differensieële kansvlak te bekeren in ’n redelike tyd. Alhoewel die berekening van die kansvlak vir een waarde van die energie-oordrag nogsteeds tydrowend is, word dit bespoedig deur die berekeningslas te versprei oor ’n aantal nodusse in ’n rekenaarbondel sisteem. ’n Toets berekening word gedoen waarby ’n proton met inkomende laboratoriese energie van 400 MeV vanaf ’n 40Ca kern verstrooi word teen ’n hoek van θcm = 400. Vir hierdie reaksie word die ongepolariseerde dubbele differensieële kansvlak bereken sowel as ’n volledige stel spin waarneembares naamlik Ay, Dℓ′,ℓ, Ds′s, Dnn, Ds′ℓ en Dℓ′s. Daar word gevind dat die versteurings lei tot ’n afname in die differensieële kansvlak. Die spin waarneembares egter, is komplekse hoeveelhede wat geen univorme gedrag toon nie. Die verskil tussen die vervormde golf spin waarneembares en die van vlak golf waarneembares is minimaal en ons lei daarvan af dat spin waarneembares onsensitief is teen oor versteurings.

General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. First, I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry. I show that the shadow of a black hole as well as the shape of a bright and narrow ring surrounding the shadow depend uniquely on its mass, spin, inclination, and the deviation parameter. I argue that the no-hair theorem can be tested with observations of the supermassive black hole Sgr A*. Second, I investigate the potential of quasi-periodic variability observed in both galactic black holes and active galactic nuclei to test the no-hair theorem in two different scenarios. Third, I show that the profiles of relativistically broadened iron lines emitted from the accretion disks of black holes imprint the signatures of deviations from the Kerr metric. In the second part, I devise a method to test the predicted evaporation of black holes in the Randall-Sundrum model of string theory-inspired braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480. I predict the first detection of orbital evolution in a black-hole binary.

No description available.

Rapid progress in ultra-intense laser technology has resulted in intensity levels surpassing 1022 W/cm2, reaching the highest possible density of electromagnetic energy amongst all controlled sources available in the laboratory. During recent decades, fast growth in available intensity has stimulated numerous studies based on the use of high intensity lasers as a unique tool for the initiation of nonlinear behavior in various basic systems: first molecules and atoms, then plasma resulting from the ionization of gases and solids, and, finally, pure vacuum. Apart from their fundamental importance, these studies reveal various mechanisms for the conversion of a laser pulse's energy into other forms, opening up new possibilities for generating beams of energetic particles and radiation with tailored properties. In particular, the cheapness and compactness of laser based sources of energetic protons are expected to make a revolution in medicine and industry.   In this thesis we study nonlinear phenomena in the process of laser radiation interacting with plasmas of ionized targets. We develop advanced numerical tools and use them for the simulation of laser-plasma interactions in various configurations relating to both current and proposed experiments. Phenomenological analysis of numerical results helps us to reveal several new effects, understand the physics behind them and develop related theoretical models capable of making general conclusions and predictions. We develop target designs to use studied effects for charged particle acceleration and for the generation of attosecond pulses of unprecedented intensity. Finally, we analyze prospects for experimental activity at the upcoming international high intensity laser facilities and uncover a basic effect of anomalous radiative trapping, which opens up new possibilities for fundamental science.

O advento dos colisores modernos tem proporcionado novas possibilidades de estudo em física de partículas como, por exemplo, a busca por nova física e o estudo de novos estados da matéria hadrônica. Em particular, em colisões de íons pesados em altas energias, acredita-se que um novo estado da matéria seja formado antes da colisão, o chamado condensado de vidros de cor. Tal estado seria a condição inicial de um plasma de quarks e glúons e é caracterizado por altas densidades de pártons (quarks e glúons). De fato, as equações de evolução da Cromodinâmica Quântica predizem que, para virtualidades moderadas e altas energias, os hádrons se tornam sistemas extremamente densos devido ao crescimento das distribuições de glúons nessas condições. Um crescimento indefinido das distribuições de glúons poderia levar à violação do vínculo de unitariedade. Para evitar essa violação, existe um mecanismo chamado de saturação de pártons o qual contém o crescimento das distribuições de quarks e glúons de forma a respeitar o vínculo de unitariedade. Teoricamente, no limite de altas energias, observa-se que os hádrons são populados especialmente por glúons. Experimentalmente, existem indícios da saturação em colisões ep, pp, pA e AA, contudo, isso ainda é uma questão em aberto. Portanto, no limite de altas densidades, espera- se que a física não linear, a qual leva em conta efeitos de recombinações de glúon, passe a se manifestar. Uma alternativa para o estudo da saturação em colisores hadrônicos são os processos foto-induzidos, os quais ocorrem em interações ultraperiféricas. Em uma colisão ultraperiférica entre dois hádrons, o parâmetro de impacto é maior do que a soma dos raios dos hádrons, de forma que interações fortes são suprimidas. Dessa forma os hádrons atuam como fontes de fótons (quase reais) podendo ocorrer interações fóton-hádron e fóton-fóton. Nesse trabalho estudamos a fotoprodução difrativa de mésons vetoriais em energias do LHC para colisões ultraperiféricas próton-próton, próton-núcleo e núcleo-núcleo e a produção dupla de mésons vetoriais em colisões fóton-fóton e devido ao mecanismo de duplo espalhamento fóton-p(A). Mostramos como esses processos podem ser usados para estudar a física de altas energias e os efeitos de saturação. Os efeitos de saturação em nossos cálculos são levados em conta através do formalismo de dipolo de cor, que é uma das ferramentas básicas usadas nessa tese. O tratamento de colisões ultraperiféricas hádron-hádron foi feito com a aproximação de fótons equivalentes que assim como o formalismo de dipolo, foi extensamente usada. Nossos resultados apontam que o estudo fenomenológico e experimental dos tipos de processos citados acima são factíveis e podem ser usados para vincular a dinâmica da QCD em altas energias. / The advent of the modern colliders has provided new possibilities of study in particle physics as, for example, the search for new physics and the study of new states of the hadronic matter. In particular, in high energy heavy ion collisions is expected that a new state can be formed before the collision, the so called Color Glass Condensate. This state would be the initial condition of the Quark Gluon Plasma and is characterized by high parton (quarks and gluons) densities. Indeed, the Quantum Chromodynamics evolution equations predict that, for moderate virtualities and high energies, the hadrons become extremely dense systems due to the growth of the parton distribution in these conditions. An indefinite growth of the parton distributions could lead to the violation of the unitarity bound. To avoid this violation, there is a mechanism called parton saturation which tames the growth of the parton distributions to satisfy the unitarity bound. Theoretically, in the high energy limit, one can see that the hadrons are populated mainly by gluons. Experimentally, there are indications of the saturation in ep, pp, pA and AA collisions, however, this is an open question. So, in the high density limit, we expect that the nonlinear physics, which takes into account gluon recombination effects start to manifest itself. An alternative for the study of the saturation at hadronic colliders are the photon-induced processes, which occurs in ultra-peripheral collisions. In a ultra-peripheral collision between two hadrons the impact parameter is greater than the sum of the radii of the hadrons, so the strong interaction is suppressed. Thus, the hadrons act as sources of (almost real) photons and may occur photon-hadron and photon-photon interactions. In this work we study the diffractive photoproduction of vector mesons at LHC and future colliders energies in ultra-peripheral proton-proton, proton-nucleus and nucleus-nucleus collisions and the double vector meson production in photon-photon collisions and due to the double photon-p(A) scattering mechanism. We show how these processes can be used to study the high energy physics and the saturation effects. These effects are considered in our calculations through the color dipole formalism, which is one of the basic tools used in this thesis. The treatment of the ultra-peripheral hadron-hadron collisions was done through the equivalent photon approximation that just as in the dipole formalism, was widely used. Our results point that the phenomenological and experimental studies of the processes cited above are feasible and can be used to constraint the QCD dynamics in high energies.