15,483 research outputs found
Non-linear metric perturbation enhancement of primordial gravitational waves
We present the evolution of the full set of Einstein equations during
preheating after inflation. We study a generic supersymmetric model of hybrid
inflation, integrating fields and metric fluctuations in a 3-dimensional
lattice. We take initial conditions consistent with Eintein's constraint
equations. The induced preheating of the metric fluctuations is not large
enough to backreact onto the fields, but preheating of the scalar modes does
affect the evolution of vector and tensor modes. In particular, they do enhance
the induced stochastic background of gravitational waves during preheating,
giving an energy density in general an order of magnitude larger than that
obtained by evolving the tensors fluctuations in an homogeneous background
metric. This enhancement can improve the expectations for detection by planned
gravitational waves observatories.Comment: 5 pages, 4 eps figures, matches Phys. Rev. Lett. versio
Qubit authentication
Secure communication requires message authentication. In this paper we
address the problem of how to authenticate quantum information sent through a
quantum channel between two communicating parties with the minimum amount of
resources. Specifically, our objective is to determine whether one elementary
quantum message (a qubit) can be authenticated with a key of minimum length. We
show that, unlike the case of classical-message quantum authentication, this is
not possible.Comment: LaTeX, 8 page
Length-weight relationships of coral reef fishes from the Alacran Reef, Yucatan, Mexico
Length-weight relationships were computed for 42 species of coral reef fishes from 14 families from the Alacran Reef (Yucatan, Mexico). A total of 1 892 individuals was used for this purpose. The fish species were caught by different fishing techniques such as fishhooks, harpoons, gill and trawl nets. The sampling period was from March 1998 to January 2000
Evaluation of a Local Fault Detection Algorithm for HVDC Systems
A great increase in the amount of energy generated from clean and renewable sources integrated in the electric power system is expected worldwide in the coming years. High Voltage Direct Current (HVDC) systems are seen as a promising alternative to the traditional Alternating Current (AC) systems for the expansion of the electric power system. However, to achieve this vision, there are some remaining challenges regarding HVDC systems which need to be solved. One of the main challenges is related to fault detection and location in HVDC grids. This paper reviews the main protection algorithms available and presents the evaluation of a local fault detection algorithm for DC faults in a multi-terminal Voltage Source Conversion (VSC) based HVDC grid. The paper analyses the influence of the DC voltage sampling frequency and the cable length in the performance of the algorithm. © 2019, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ).The authors thank the support from the Spanish Ministry of Economy, Industry and Competitiveness (project ENE2016-79145-R AEI/FEDER, UE) and GISEL research group IT1083-16), as well as from the University of the Basque Country UPV/EHU (research group funding PPG17/23)
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