7,515 research outputs found
Black hole entropy arising from massless scalar field with Lorentz violation induced by the coupling to Einstein tensor
We have investigated quantum entropy of a static black hole arising from the
massless scalar field with Lorentz violation induced by the coupling to
Einstein tensor. Our results show that the coupled massless scalar field
contributes to the classical Bekenstein-Hawking term in the black hole entropy.
The corrected classical Bekenstein-Hawking entropy is not one quarter of the
event horizon area of the original background black hole, but of a
corresponding effective metric related to the coupling. It means that the
classical Bekenstein-Hawking entropy depends not only on the black hole
parameter, but also on the coupling which reduces Lorentz violation.Comment: 5 pages, no figure. Accepted by PLB for publicatio
Measuring quality, reputation and trust in online communities
In the Internet era the information overload and the challenge to detect
quality content has raised the issue of how to rank both resources and users in
online communities. In this paper we develop a general ranking method that can
simultaneously evaluate users' reputation and objects' quality in an iterative
procedure, and that exploits the trust relationships and social acquaintances
of users as an additional source of information. We test our method on two real
online communities, the EconoPhysics forum and the Last.fm music catalogue, and
determine how different variants of the algorithm influence the resultant
ranking. We show the benefits of considering trust relationships, and define
the form of the algorithm better apt to common situations
Ageing and Temperature Influence on Polarization/Depolarization Current Behaviour of Paper Immersed in Natural Ester
Transformers play an important role in providing a reliable and efficient electricity supply and are one of the most critical equipments in electric power transmission and distribution systems. The most commonly used liquid in power transformers is mineral oil due to its low price and good properties. However the performance of mineral oil starts to be limited due to environmental consideration [1]. Natural ester insulating fluid offers fire safety, environment and insulation aging advantages over mineral oil and are found to be suitable for the use in transformer insulation system [1]. However, transformer owners require to assess the status of the cellulose insulation in transformer non-destructively. Polarization/depolarization Current (PDC) measurement [2] is one of the non-destructive techniques which have been used to achieve this aim. At the present, there are few publications about the PDC behaviour of natural ester-paper insulation, though the natural ester becomes more widely used in transformers. In this paper, the influence of ageing and temperature on the PDC behaviour of the paper immersed in natural ester and mineral oil were compared. Results show PDC technique can be used to assess the aging condition of the natural-ester paper insulation. The ageing and temperature have similar influence on the PDC behaviour of the paper immersed in natural ester and in mineral oil. The depolarization current of paper immersed in natural ester is lower than that immersed in mineral oil at the same test temperature. The depolarization current of the paper immersed in natural ester and mineral oil increase with the aging time increased. Therefore, the depolarization current can be used to indicate the aging status of natural ester-paper insulation
Effect of thermally aged oil on space charge dynamics in oil/paper insulation system
The formation of space charge in oil/paper insulation system can lead to material degradation in the high electrical field region and affect system reliability. Therefore, it is important to understand factors that affect space charge formation in oil/paper insulation system. In the present study the effect of thermally aged oil on space charge dynamics in oil/paper insulation system has been investigated using the pulsed electroacoustic (PEA) technique under different dc electrical fields at room temperature. The condition of oil was characterised. The ultraviolet/visible (UV/Vis) spectrum of oil shifts to visible wavelength and the oil acidity increased as the ageing time increased. It has been found that oil property has a significant effect on the space charge distribution of oil/paper insulation system. The more the deterioration of the oil and the higher the applied voltage, the larger the amount of negative charge injected into the paper near to the cathode and the positive charge accumulated at the paperpaper interface near to the cathode. The maximum electric field strength for oil/paper sample with seriously aged oil under 4kV and 6kV is more than 20% higher than its average electric field strength
Absorption cross section and Hawking radiation of the electromagnetic field with Weyl corrections
We have investigated the absorption cross section and the Hawking radiation
of electromagnetic field with Weyl correction in the background of a
four-dimensional Schwarzschild black hole spacetime. Our results show that the
properties of the absorption cross section and the Hawking radiation depend not
only on the Weyl correction parameter, but also on the parity of the
electromagnetic field, which is quite different from those of the usual
electromagnetic field without Weyl correction in the four-dimensional
spacetime. With increase of Weyl correction parameter, the absorption
probability, the absorption cross section, the power emission spectra and the
luminosity of Hawking radiation decreases with Weyl correction parameter for
the odd-parity electromagnetic field and increases with the event-parity
electromagnetic field.Comment: 10 pages, 8 figures. Accepted for publication in Physics Letters
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