TEDE Communidade:
http://www.bdtd.uerj.br/handle/1/3685
2024-10-10T14:37:51ZEstudo da criticalidade quântica no sistema de onda de densidade de carga Lu(Pt1−xPdx)2In
http://www.bdtd.uerj.br/handle/1/22330
Título: Estudo da criticalidade quântica no sistema de onda de densidade de carga Lu(Pt1−xPdx)2In
Autor: Carneiro, Fellipe Baptista
Primeiro orientador: López Giménez, Ada Petronila
Abstract: Quantum phase transitions have been intensively studied in condensed matter physics. Over the recent years, many systems were shown to present an ordered state that can be suppressed by external parameters leading to a quantum critical point (QCP). Investigations on systems with charge ordered QCP’s are, however, still scarce. In this work we study the 3D charge density wave (CDW)/superconducting material Lu(Pt1-xPdx)2In. This compound has a quantum critical point close to xc ~ 0:58 of Pd content, where the CDW state vanishes and superconductivity is enhanced (GRUNER et al., 2017). In this work we describe the synthesis process and the primary physical properties characterization such as electrical resistivity and heat capacity measurements of three compounds with Pd concentrations approaching the critical value xc (x=0.3,0.4,0.5). The compounds were growth by using an arc-melting furnace and using synchrotron x-ray powder diffraction we investigate the CDW superlattice peak as function of temperature and Pd content. We observe the presence of quantum fluctuations effects over the classical CDW phase transition by mapping the charge order parameter critical exponent (b) near the QCP. The critical exponent starts at value expected for 3-dimensional materials and monotonically grows and approaches the value predicted by mean-field theory near the QCP. This might be related with a dimensional crossover that occur due to the competition between the energy scales of quantum and classical fluctuations at relatively high temperatures, indicating the presence of a quantum critical point.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2020-05-20T00:00:00ZBuracos negros carregados: soluções exatas e simulações numéricas
http://www.bdtd.uerj.br/handle/1/22323
Título: Buracos negros carregados: soluções exatas e simulações numéricas
Autor: Oliveira, Felipe Medeiros de
Primeiro orientador: Oliveira, Henrique Pereira de
Abstract: In this present work, we generalized the results found in (Dennison; Baumgarte,
2014) and (Baumgarte; Naculich, 2007) for the Reissner-Nordström black hole, finding
analytical solutions that describe the numerical results in (Duncan, 1985). For this we
explained the concept of dividing the spacetime in spacelike hypersurfaces parameterized
by the time, showing the deduction of the ADM formulation of the general relativity and
from this we showed the deduction of the BSSN formulation in spherical symmetry. We
showed the deduction of the trumpet foliation for black holes and more specifically for the
charged one, finding the generalized solutions of Dennison-Baumgarte and BaumgarteNaculich, where the last one preserves de maximum volume of the hypersurfaces. We explained the 3+1 decomposition of the electromagnetism and showed how the electric field behaves in each case. We validated our results showing that the analytical solutions founded describes a stable foliation for the charged black hole in the BSSN formulation.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2024-03-12T00:00:00ZFusão de informação com o NeuralRinger do Trigger do ATLAS para classificação de elétrons Boosted
http://www.bdtd.uerj.br/handle/1/22292
Título: Fusão de informação com o NeuralRinger do Trigger do ATLAS para classificação de elétrons Boosted
Autor: Assis, Victor Almeida de
Primeiro orientador: Begalli, Marcia
Abstract: Online filtering systems typically have high speed design requirements and limited memory use, making difficult to develop new improvements to the systems. Moreover, it is essential to have no statistical trends, as there will be the irrecoverable disposal of events. In high energy physics experiments, online particle identification is crucial for any new discovery or data analysis. In particular, the calorimeters are essential for this task in different experiments, as they measure the energies of the incident particles and also reveal their nature from the energy profile they leave in the detector. Thus, in the ATLAS experiment, at the LHC (Large Hadron Collider), the calorimetry system plays a fundamental role in online selection of by products resulting from collisions, which occur every 25 nanoseconds. Based on calorimetry information, an ensemble of 30 neural networks (NeuralRinger) is currently used for the selection of electrons, which are messengers of important Physics processes of interest in the LHC. In this work, we evaluated the use of the fusion of information in the detection of boosted electrons, combining the original information of NeuralRinger (concentric energy deposition rings, built around an estimate of baricenter from the particle shower produced by the incident particle) with other calorimetry variables, recognized for their power of electron discrimination. Finally, we evaluate the relevance of these variables for the construction of the new online filter.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2024-02-29T00:00:00ZEstudo do efeito magnetocalórico em amorfos
http://www.bdtd.uerj.br/handle/1/22291
Título: Estudo do efeito magnetocalórico em amorfos
Autor: Freitas, Vagner Luiz Oliveira de
Primeiro orientador: Nóbrega, Eduardo Pilad
Abstract: The development of theoretical models to adequately describe the magnetocaloric eﬀects (MCE) is important both for explaining the experimental responses presented so far and for predicting new and unexpected trends. Among the various materials, the class of amorphous materials presents characteristics that enhance the MCE, such as high refrigeration capacity. In this thesis, a theoretical description of the magnetocaloric eﬀect in amorphous systems will be presented, considering the nature of magnetic interactions and the distribution of magnetic moments through the Handrish-Kobe approximation for systems with isotropic magnetization and the HPZ approximation for anisotropic ones. These models were applied to three distinct families: the ﬁrst with only one magneticnet work, the second with two networks with isotropic magnetization, and the third with two networks with high anisotropy. Thus, in the amorphous compounds of the Gd1−xNixseries, the inﬂuence of magnetic interactions and the amorphization term on the magnetocaloric eﬀect was analyzed. For the materials of the Gd55FexAl45−xseries, the inﬂuence of the Fe/Al ratio, the magnetocaloric interaction, and the amorphization terms on the respective arrangements were veriﬁed. Finally, for the amorphous ErxFe1−x, the inﬂuence of anisotropy and the competition between it and the magnetic interactions were analyzed through a systematic study. Therefore, a methodology for obtaining the magnetization of amorphous systems was presented, allowing for the study of the anisotropic magneto-caloric eﬀect of ferromagnetic and ferrimagnetic nature.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Tese2024-03-20T00:00:00Z