3,829 research outputs found
The Quantum Stress-Tensor in Self-Similar Spherical Dust Collapse
We calculate the quantum stress tensor for a massless scalar field in the 2-d
self-similar spherical dust collapse model which admits a naked singularity. We
find that the outgoing radiation flux diverges on the Cauchy horizon. This may
have two consequences. The resultant back reaction may prevent the naked
singularity from forming, thus preserving cosmic censorship through quantum
effects. The divergent flux may lead to an observable signature differentiating
naked singularities from black holes in astrophysical observations.Comment: Latex File, 19 page
Efeito do uso de efluente de esgoto tratado sobre a resistência do solo à penetração em pastagem.
Estudo e implementação de modelo mais preciso para determinação da granulometria do solo por atenuação de raios gama.
bitstream/CNPDIA-2009-09/11030/1/BPD19_2007.pd
Avaliação da disponibilidade de cobre e manganês em amostras de solo tratadas com efluente - comparação entre AAS e SWASV.
Analisador granulométrico: implementação de modelo mais preciso para determinação de frações de areia.
Determinação eletroanalítica do pesticida paration metílico em eletrodo de carbono vítreo.
bitstream/CNPDIA-2009-09/11854/1/DOC26_2006.pd
Avaliação de propriedades físicas de solos arenosos do cerrado sob área nativa, cultivada em coja ou pastagem.
Desenvolvimento de metodologia de análise do íon Cu(II) em solução aquosa e em solução de solo com microeletrodo de irídio recoberto com filme de mercúrio.
On the error of calculation of heat gains through walls by methods using constant decrement factor and time lag values
A transient heat transfer model was developed to numerically predict the thermal behaviour of the external walls of a room under realistic outdoor conditions. The excitation is not simply sinusoidal even though it is considered to have daily periodicity. The numerical model is based on the finite difference method and handles one-dimensional heat conduction through multilayered walls. The boundary condition at the outer surface of the wall is described with the sol-air temperature concept. The temperatures of indoor air and of other internal surfaces in the room are assumed to be equal and constant.
The numerical results were used to calculate values of the decrement factor and time lag of several walls. The calculation followed two methods found in literature, in which these parameters are assumed constant, distinguished by the temperature evolution used: the sol-air or the wall's outer surface. Additionally, the inner surface temperature is used in both methods. The walls investigated range from low to high mass construction, face towards various directions and have light or dark coloured sunlit outer surfaces.
The heat fluxes at the inner surface of the walls predicted by numerical modelling and estimated by the simplified methods are compared in detail to conclude on the validity of these simplified methods. As a by-product it is also possible to conclude on the dependence of the decrement factor and of the time lag on the outer surface colour and on the orientation of different types of walls. The results show that both simplified methods have poor accuracy in a significant number of cases. Also, it was found that the wall's azimuth significantly affects the time lag
Determinação simultânea de Cu, Cd e Pb em água e solo com microeletrodo de irídio recoberto com filme fino de mercúrio.
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