Navegando por Autor "ROZAL, Edilberto Oliveira"

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Acesso aberto (Open Access)
Efeitos do manto de intemperismo sobre anomalias “VLF” dos corpos tabulares inclinados
(Universidade Federal do Pará, 1997-03-16) ROZAL, Edilberto Oliveira; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Application of eletromagnetic methods for mineral exploration in tropical regions is complicated due to a presence of a conducting overburden encountered in these regions. In the Amazon region, overburden is well developed and conductive; while in semi-arid regions there may be a fine layer containing salts. Consequently, considerable error is introduced in the interpretation of EM data if the presence of the conducting overburden is ignored. In order to study the overburden effects, on VLF anomalies due inclined tabular bodies in contact with the former (Ohmic - overburden), a number of analog model experiments were conducted for varying response parameters of the overburden and the ore body. Overburden is simulated by an amonium chloride solution (NH4Cl) and the ore body by inclined grafite sheets of different thicknesses. Three overburdens of varying conductance were used to simulate diverse geological situations. Both, tilt-angle and elipsity anomalies decrease in amplitude with the increase in depth of the ore body and the position of the peak in the profile is removed further away from the crossover irrespective of the presence of the overburden or not. There is some increase and tilt-angle anomaly profiles. Eliptisity anomaly increases with the increase in the condutance of the overburden while tilt-angle anomaly decreases a little bit. However, at higher overburden condutances both of then are attenuated. Phase angle are rotated anti-clockwise with the overburden. This rotation is more intense at higher induction number of the conductor. In the presence of the ohmic-overburden and at moderate values of their condutance, the conductor appears (i) at lower depth than the real, due to the increase in the anomaly amplitude, and ii) less conducting due to the anti-clockwise rotation of the Argand diagram.
Acesso aberto (Open Access)
Modelagem canais de comunicações móveis com a utilização de series temporais e geoestatísticas
(Universidade Federal do Pará, 2013-03-12) ROZAL, Edilberto Oliveira; QUEIROZ, Joaquim Carlos Barbosa; http://lattes.cnpq.br/4383935463464893; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362
This work presents the results of propagation channel modeling, based on multivariate time series models using data collected in measurement campaigns and the main characteristics of urbanization in the city of Belem-PA. Transfer function models were used to evaluate effects on the time series of received signal strength (dBm) which was used as the response variable and as explanatory variables of the height of buildings and distances between buildings. As time series models disregard to the possible correlations between neighboring samples, we used a geostatistical model to establish the correctness of this model error. This phase of the work consisted of a set of procedures necessary to geostatistical techniques. Aiming at the analysis on two dimensions for data spatially distributed, with respect to the interpolation of surfaces generated from georeferenced samples obtained from residues of received signal power computed using the model series. The results obtained with the proposed model showed an excellent performance, with mean square error in the order of 0.33 dB compared to the measured signal, considering the data of the eleven routes from the center of the city of Belém/Pa. From the map of the spatial distribution of the received signal strength (dBm), one can easily identify areas below or above dimensional in terms of this variable, that is benefited or damaged compared with the signal reception, which may result in a greater investment of the local operator (concessionaire mobile phone) in those regions where the signal is weak.