3,480 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
Non-Markovian Dynamics of Charge Carriers in Quantum Dots
We have investigated the dynamics of bound particles in multilevel
current-carrying quantum dots. We look specifically in the regime of resonant
tunnelling transport, where several channels are available for transport.
Through a non-Markovian formalism under the Born approximation, we investigate
the real-time evolution of the confined particles including transport-induced
decoherence and relaxation. In the case of a coherent superposition between
states with different particle number, we find that a Fock-space coherence may
be preserved even in the presence of tunneling into and out of the dot.
Real-time results are presented for various asymmetries of tunneling rates into
different orbitals.Comment: 9 pages, 3 figures, International Workshop on Physics-Based
Mathematical Models for Low-Dimensional Semiconductor Nanostructures. BIRS,
November 18-23, 200
Quantum general relativity and Hawking radiation
In a previous paper we have set up the Wheeler-DeWitt equation which
describes the quantum general relativistic collapse of a spherical dust cloud.
In the present paper we specialize this equation to the case of matter
perturbations around a black hole, and show that in the WKB approximation, the
wave-functional describes an eternal black hole in equilibrium with a thermal
bath at Hawking temperature.Comment: 13 pages, minor revisions in: (i) para 5 of Introduction, (ii) para
following Eqn. (10). Revised version to appear in Phys. Rev.
Wind tunnel study of coal dust release from train wagons
The paper presents a wind tunnel study to assess the coal dust released due to aeolian erosion from wagons equipped with two different shelter cover systems. A 1:25 scale model was used, and it comprises one locomotive and four train wagons with a 3.55 m maximum length. Several tests were conducted for different train configurations, and two initial load levels, with an undisturbed flow velocity of 13.4 m/s.http://www.sciencedirect.com/science/article/B6V3M-4C7DFX4-2/1/7e5214aa39411c25551eb15955a969a
Entropy from the foam II
A simple model of spacetime foam, made by two different types of wormholes in
a semiclassical approximation, is taken under examination: one type is a
collection of Schwarzschild wormholes, while the other one is made by
Schwarzschild-Anti-de Sitter wormholes. The area quantization related to the
entropy via the Bekenstein-Hawking formula hints a possible selection between
the two configurations. Application to the charged black hole are discussed.Comment: Revtex 3.0, 10 pages, Replaced version with minor changes and one
ref. adde
A simple derivation of the naked singularity in spherical dust collapse
We describe a simple method of determining whether the singularity that forms
in the spherically symmetric collapse of inhomogeneous dust is naked or
covered. This derivation considerably simplifies the analysis given in the
earlier literature, while giving the same results as have been obtained before.Comment: Latex, 9 page
Classical and quantum LTB model for the non-marginal case
We extend the classical and quantum treatment of the Lemaitre-Tolman-Bondi
(LTB) model to the non-marginal case (defined by the fact that the shells of
the dust cloud start with a non-vanishing velocity at infinity). We present the
classical canonical formalism and address with particular care the boundary
terms in the action. We give the general relation between dust time and Killing
time. Employing a lattice regularization, we then derive and discuss for
particular factor orderings exact solutions to all quantum constraints.Comment: 23 pages, no figures, typos correcte
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
Creating shared value in Rock in Rio business model: case study
This discourse will attempt to discuss `Creation of Shared Value' (CSV) through the case study of the music festival "Rock in Rio" (RIR) in order to further understand the company's sustainability program. The main goal is to clearly recognize if RIR uses a genuine practice of CSV to accomplish their social policies. To commence, we started with the State of Art, studying the CSV theory created by Porter and Kramer, as well as the authors that were either in support of, or against, the strategy. Qualitative Research Method was used, thus focusing the enterprise case study, by analysing media interviews given by the managerial staff of RIR. Content analysis was used to process data and deliver results. The main limitation of the study was the lack of institutional information, due to an absence of responses, to the survey in sufficient time by RIR's managers, subsequently a triangulation of the information acquired could not be achieved.info:eu-repo/semantics/acceptedVersio
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