Head-on collisions of kink and antikink solitons are investigated numerically in the classical onedimensional h(4'-1 )2 model. It is shown that whether a kink-antikink interaction settles to a bound state or a two-soliton solution depends "fractally" on the impact velocity. We discuss the results using the framework of perturbation theory which helps to clarify the nature of the fractal structure in terms of resonances with the internal shape mode oscillations. We also review the technique of collective coordinates used to reduce the infinite-dimensional system to one with just two degrees of freedom. Although we do not expect exact agreement by using such a simplification, we show that the reduced system bears a striking qualitative resemblance to the full infinite-dimensional system, reproducing the fractal structure. The maximum Lyapunov exponents are computed for the bound-state oscillations and found to be -0.3 for both the full and reduced systems, demonstrating the chaotic nature of the bound state.
We describe three numerical approaches to the construction of three-dimensional initial data for the collision of two black holes. The first of our approaches involves finite differencing the 3 + 1 Hamiltonian constraint equation on a Cadei coordinate grid. The difference equations are then solved via the multigrid algorithm. The second approach also uses finite-difference techniques, but this time on a regular Cartesian coordinate grid. A Cartesian grid has the advantage of having no coordinate singularities. However, constant coordinate lines are not coincident with the throats of the black holes and, therefore, special treatment of the difference equations at these boundaries is required. The resulting equations are solved using a variant of line-successive overrelaxation. The third and final approach we use is a global, spectral-like method known as the multiquadric approximation scheme. In this case functions are approximated by a finite sum of weighted quadric basis functions which are continuously differentiable. We discuss particular advantages and disadvantages of each method and compare their performances on a set of test problems.
The static and stationary C-metric are revisited in a generic framework and their interpretations studied in some detail. Specially those with two event horizons, one for the black hole and another for the acceleration. We found that: i) The spacetime of an accelerated static black hole is plagued by either conical singularities or lack of smoothness and compactness of the black hole horizon; ii) By using standard black hole thermodynamics we show that accelerated black holes have higher Hawking temperature than Unruh temperature of the accelerated frame; iii) The usual upper bound on the product of the mass and acceleration parameters (< 1/ √ 27) is just a coordinate artifact. The main results are extended to accelerated rotating black holes with no significant changes.
Solutions to the Einstein equation that represent the superposition of static isolated bodies with axially symmetry are presented. The equations nonlinearity yields singular structures ( strut and membranes ) to equilibrate the bodies. The force on the strut like singularities is computed for a variety of situations. The superposition of a ring and a particle is studied in some detail.
Objetivou-se caracterizar os acidentes de trabalho com material biológico em trabalhadores de serviços de saúde. Estudo retrospectivo, quantitativo, realizado em um hospital secundário referência para o atendimento de acidentes com material biológico, localizado no norte do Paraná. Os dados foram coletados de dezembro de 2013 a junho de 2014, em 1.061 prontuários de trabalhadores da saúde e nas fichas de registro no Sistema de Informação de Agravos de Notificação, analisados por meio de estatística descritiva. Dentre os 1.061 acidentes de trabalho com material biológico, 58,1% ocorreram com auxiliares e técnicos de enfermagem, dos quais 82,7% eram do sexo feminino. O principal material orgânico presente em 86,1% dos acidentes foi o sangue, 88,2% ocorreram por meio de exposição percutânea, 66,1% envolveram a utilização de agulhas com lúmen e 21,9% foram decorrentes do descarte inadequado de material perfurocortante. Faz-se necessário implementar medidas preventivas, direcionadas à equipe de enfermagem.
SUMMARY OBJECTIVE We aimed to present a review of renal changes in patients with COVID-19. METHODS We performed a systematic review of the literature to identify original articles regarding clinical, laboratory, and anatomopathological kidney changes in patients infected with SARS-CoV-2 published until May 7, 2020. The search was carried out across PubMed, Scopus, and Embase using the keywords “COVID-19”, “coronavirus”, “SARS-CoV-2”, “kidney injury” and “kidney disease”. Fifteen studies presented clinical and laboratory renal changes in patients with COVID-19, and three addressed anatomopathological changes. DISCUSSION Acute kidney injury (AKI) was a relevant finding in patients with COVID-19. There were also significant changes in laboratory tests that indicated kidney injury, such as increased serum creatinine and blood urea nitrogen (BUN), proteinuria, and hematuria. The presence of laboratory abnormalities and AKI were significant in severely ill patients. There was a considerable prevalence of AKI among groups of patients who died of COVID-19. Histopathological analysis of the kidney tissue of patients infected with SARS-CoV-2 suggested that the virus may directly affect the kidneys. CONCLUSION Although COVID-19 affects mainly the lungs, it can also impact the kidneys. Increased serum creatinine and BUN, hematuria, proteinuria, and AKI were frequent findings in patients with severe COVID-19 and were related to an increased mortality rate. Further studies focusing on renal changes and their implications for the clinical condition of patients infected with the novel coronavirus are needed.
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