DSpace Collection:
http://hdl.handle.net/11422/50
2024-06-09T04:10:48ZFotodestruição do benzeno em ambientes interestelares
http://hdl.handle.net/11422/6082
Title: Fotodestruição do benzeno em ambientes interestelares
Author(s)/Inventor(s): Neves, Rosicler da Silva
Advisor: Boechat-Roberty, Heloísa Maria
Abstract: The abundance of interstellar molecules depends on their dissociation and destruction rate, and those depend on the photodissociation cross section which is function of the photon energy. We had experimentally study photoionization and photodissociation processes of the benzene (C6H6), and the deuterated benzene (C6D6). Benzene is an essential intermediate in the formation pathways of polycyclic aromatic hydrocarbons (PAHs), which are thought to be responsible for unidentified infrared bands (UIR), observed in differents astronomical environments. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), using soft X-ray and UV photons. The experimental set-up consists of a high vacuum chamber with a Time-Of-Flight Mass Spectrometer (TOF-MS). Kinetic energy distributions, abundances for each ionic fragment and dissociative and non-dissociative photoionization cross sections were determined by using PhotoElectron PhotoIon Coincidence techniques. We have observed that C6H6 is extremely resistant to UV photons, confirming that PAHs absorb the UV photons and after some internal energetic rearrangements, they can emit in the IR range. However, this molecule is destroyed by soft X-rays photons producing several ionic fragments. We also observed that C6D6 is more resistant than benzene. Stable doubly-charged species were observed. From the photodissociation and cross sections we have determined the photodissociation rate and the half-life of C6H6 and C6D6 in differents astrophysical environments.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2007-04-04T00:00:00ZPerturbações das equações de Einstein-Boltzmann e suas aplicações à radiação cósmica de fundo
http://hdl.handle.net/11422/6070
Title: Perturbações das equações de Einstein-Boltzmann e suas aplicações à radiação cósmica de fundo
Author(s)/Inventor(s): Barros, Gustavo de
Advisor: Calvão, Maurício Ortiz
Abstract: Study aimed at understanding the basics of the new and growing topic of cosmic microwave background (CMB) physics. We present the fundamental concepts, principles and results related with this problem. Since the relevant equations are essentially the Einstein-Boltzmann perturbed equations, a great part of this work is dedicated to these linearized equations, in the conformal Newtonian gauge, with vanishing tri-curvature, for scalar perturbations only. The initial conditions are also touched on. Another part of paramount importance is the application to the description of the power spectrum of temperature anisotropies.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2006-05-08T00:00:00ZHomogeneidades espacial e observacional da distribuição de galáxias
http://hdl.handle.net/11422/5943
Title: Homogeneidades espacial e observacional da distribuição de galáxias
Author(s)/Inventor(s): Lemos, Luis Juracy Rangel
Advisor: Ribeiro, Marcelo Byrro
Abstract: In this work we propose a second way of analysing the homogeneity of the matter distribution in the Universe, called here as observational homogeneity (OH), and which is carried out along the past light cone null type hypersurface. The usual type of homogeneity is given by the Cosmological Principle, called here as spatial homogeneity (SH), and which is defined along space-like hypersurfaces of the spacetime. In this work we adopted the Einstein-de Sitter cosmological model. All discussion regarding homogeneity were done by means of four cosmological distances, namely, the area distance dA, the galaxy area distance dG, the luminosity distance dL and the redshift distance dz. Simulations of various types of counting of cosmological sources were carried out and in the case of an universe model with SH we used the number counting obtained from the Einsteinde Sitter (EdS) model (NEdS), since it assumes the Cosmological Principle. In order to simulate an universe with OH, we adopted the number counts expression advanced by Wertz (1970) and Pietronero (1987) for the galaxy distribution. Starting from two radial density functions defined in Ribeiro (2005), namely the differential density γi and the integral differential density γ ∗ i , we carried out an analysis of spatial and observational homogeneities of the galaxy distribution, were the latter (OH) was defined by the constant value of γ ∗ i . Various plots were presented showing the central role played by the cosmological distance choice. It was also clearly observed that in order to characterize whether or not the large-scale galaxy distribution in the Universe has, or has not, OH, it is necessary to know not only the general mass-energy distribution, which is determined by the count Ni of cosmological sources, but also the geometrical volume which defines the density and, by itself, depends on the cosmological distance.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2006-10-16T00:00:00ZAnálise de observações do diâmetro no contexto da atividade solar
http://hdl.handle.net/11422/5897
Title: Análise de observações do diâmetro no contexto da atividade solar
Author(s)/Inventor(s): Boscardin, Sérgio Calderari
Advisor: Andrei, Alexandre Humberto
Abstract: From 1997 to 2003 the CCD Solar Astrolabe of the Observatório Nacional in Rio de Janeiro made more than 20,000 observations of the Solar Semidiameter. The experimental data from1998 to 2001 had been obtained in two independent previous works, by the corrections of the systematic effects on the raw observational results. In the present work similar corrections for the observational results of 2002 and 2003 were determined. Aiming at the robustness of the corrections, the measurements of each year have been considered separately, as well as the series of observational data as taken at east or west from the local meridian were separately considered. Initially, for each annual series a statistical approach was used, justified by the amount of data. The values to east and west have been corrected in function of their mean quadratic offset to the local trend averages, therefore without modifying the measured variations. Finally, the values have been corrected of the bias, using coefficients obtained from the correlation between the parameters and the observational measures. The series of 16.523 coherent data of the variation of the Solar Semidiameter, between 1998 and 2003, allowed the detailed comparison with series of pointers of the solar activity: Flare Index, Total Irradiance, Integrated Magnetic Field, Sunspot Number and 10.7cm Radio Flux. The hypothesis of variation of the Semidiameter tied to the solar activity, otherwise being its estimator, was examined through the correlations between the different pairs of pointers. The correlations have been calculated at continuous spacing of the series of values, from the data annual division until the monthly division. Strong correlations between some pairs were obtained, and interpreted as strong physical interaction between them. For the pair Solar Semidiameter and Irradiance the mode of the phase for maximum correlation was calculated for two distinct cases: either for the complete series of data, or leaving off the data relative to the epochs of the two summits of the solar activity cycle. The comparison shows that the Solar Semidiameter responds closely to variations of Irradiance in the conditions where the peaks of activity are considered inversely, it precedes the variations of Irradiance, by at least one hundred days, when the peak values are discarded, thus indicating the existence of two distinct regimes. We also studied how the Solar Semidiameter varies throughout its latitudes. It was noted that each band of latitude has a different response, even so there is a global variation in time. It was also determined the solar latitude bands that exhibit small modules for the Solar Semidiameter variation and those bands where the variation modules are much stronger.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2005-12-15T00:00:00Z