1,801 research outputs found
The FGK formalism for black p-branes in d dimensions
We present a generalization to an arbitrary number of spacetime (d) and
worldvolume (p+1) dimensions of the formalism proposed by Ferrara, Gibbons and
Kallosh to study black holes (p=0) in d=4 dimensions. We include the special
cases in which there can be dyonic and self- or anti-self-dual black branes.
Most of the results valid for 4-dimensional black holes (relations between
temperature, entropy and non-extremality parameter, and between entropy and
black-hole potential on the horizon) are straightforwardly generalized.
We apply the formalism to the case of black strings in N=2,d=5 supergravity
coupled to vector multiplets, in which the black-string potential can be
expressed in terms of the dual central charge and work out an explicit example
with one vector multiplet, determining supersymmetric and non-supersymmetric
attractors and constructing the non-extremal black-string solutions that
interpolate between them.Comment: 28 pages no figures; v2: some references adde
Rectification of electronic heat current by a hybrid thermal diode
We report the realization of an ultra-efficient low-temperature hybrid heat
current rectifier, thermal counterpart of the well-known electric diode. Our
design is based on a tunnel junction between two different elements: a normal
metal and a superconducting island. Electronic heat current asymmetry in the
structure arises from large mismatch between the thermal properties of these
two. We demonstrate experimentally temperature differences exceeding mK
between the forward and reverse thermal bias configurations. Our device offers
a remarkably large heat rectification ratio up to and allows its
prompt implementation in true solid-state thermal nanocircuits and
general-purpose electronic applications requiring energy harvesting or thermal
management and isolation at the nanoscale.Comment: 8 pages, 6 color figure
Black holes and black strings of N=2, d=5 supergravity in the H-FGK formalism
We study general classes and properties of extremal and non-extremal static
black-hole solutions of N=2, d=5 supergravity coupled to vector multiplets
using the recently proposed H-FGK formalism, which we also extend to static
black strings. We explain how to determine the integration constants and
physical parameters of the black-hole and black-string solutions. We derive
some model-independent statements, including the transformation of non-extremal
flow equations to the form of those for the extremal flow. We apply our methods
to the construction of example solutions (among others a new extremal string
solution of heterotic string theory on K_3 \times S^1). In the cases where we
have calculated it explicitly, the product of areas of the inner and outer
horizon of a non-extremal solution coincides with the square of the
moduli-independent area of the horizon of the extremal solution with the same
charges.Comment: 33 pages. Revised version: references added. No other change
Z-extremization and F-theorem in Chern-Simons matter theories
The three dimensional exact R symmetry of N=2 SCFTs extremizes the partition
function localized on a three sphere. Here we verify this statement at weak
coupling. We give a detailed analysis for two classes of models. The first one
is an SU(N)_k gauge theory at large k with both fundamental and adjoint matter
fields, while the second is a flavored version of the ABJ theory, where the CS
levels are large but they do not necessarily sum up to zero. We study in both
cases superpotential deformations and compute the R charges at different fixed
points. When these fixed points are connected by an RG flow we explicitly
verify that the free energy decreases at the endpoints of the flow between the
fixed points, corroborating the conjecture of an F-theorem in three dimensions.Comment: 28 pages, 3 figures, JHEP.cls, minor corrections, references adde
Approximation Strategies for Incomplete MaxSAT
Incomplete MaxSAT solving aims to quickly find a solution
that attempts to minimize the sum of the weights of the unsati
sfied soft
clauses without providing any optimality guarantees. In th
is paper, we
propose two approximation strategies for improving incomp
lete MaxSAT
solving. In one of the strategies, we cluster the weights and
approximate
them with a representative weight. In another strategy, we b
reak up
the problem of minimizing the sum of weights of unsatisfiable
clauses
into multiple minimization subproblems. Experimental res
ults show that
approximation strategies can be used to find better solution
s than the
best incomplete solvers in the MaxSAT Evaluation 2017
Results of a combined monolithic crystal and an array of ASICs controlled SiPMs
[EN] In this work we present the energy and spatial resolutions we have obtained for a γ ray detector based
on a monolithic LYSO crystal coupled to an array of 256 SiPMs. Two crystal configurations of the same
trapezoidal shape have been tried. In one approach all surfaces were black painted but the exit one facing
the photosensor array which was polished. The other approach included a retroreflector (RR) layer
coupled to the entrance face of the crystal powering the amount of transmitted light to the photosensors.
Two coupling media between the scintillator and the SiPM array were used, namely direct coupling by
means of optical grease and coupling through an array of light guides. Since the same operational voltage
was supplied to the entire array, it was needed to equalize their gains before feeding their signals to the
Data Acquisition system. Such a job was performed by means of 4 scalable Application Specific Circuits
(ASICs). An energy resolution of about 24.4% has been achieved for the direct coupling with the RR layer
together with a spatial resolution of approximately 2.9 mm at the detector center. With the light guides
coupling the effects of image compression at the edges are significantly minimized, but worsening the
energy resolution to about 33.1% with a spatial resolution nearing 4 mm at the detector center.
& 2013 Elsevier B.V. All rights reserved.cknowledgments
This work was supported by the Centre for Industrial Technological Development co-funded by FEDER through the Technology
Fund (DREAM Project, IDI-20110718), the Spanish Plan Nacional de
Investigación Científica, Desarrollo e Innovación Tecnológica
(IþDþI) under Grant no. FIS2010-21216-CO2-01 and the Valencian Local Government under Grant PROMETEO 2008/114Conde Castellanos, PE.; González Martínez, AJ.; Hernández Hernández, L.; Bellido, P.; Iborra Carreres, A.; Crespo Navarro, E.; Moliner Martínez, L.... (2014). Results of a combined monolithic crystal and an array of ASICs controlled SiPMs. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 734:132-136. https://doi.org/10.1016/j.nima.2013.08.079S13213673
Direct exfoliation and dispersion of two-dimensional materials in pure water via temperature control
The high-volume synthesis of two-dimensional (2D) materials in the form of platelets is desirable for various applications. While water is considered an ideal dispersion medium, due to its abundance and low cost, the hydrophobicity of platelet surfaces has prohibited its widespread use. Here we exfoliate 2D materials directly in pure water without using any chemicals or surfactants. In order to exfoliate and disperse the materials in water, we elevate the temperature of the sonication bath, and introduce energy via the dissipation of sonic waves. Storage stability greater than one month is achieved through the maintenance of high temperatures, and through atomic and molecular level simulations, we further discover that good solubility in water is maintained due to the presence of platelet surface charges as a result of edge functionalization or intrinsic polarity. Finally, we demonstrate inkjet printing on hard and flexible substrates as a potential application of water-dispersed 2D materials.close1
Updating known distribution models for forecasting climate change impact on endangered species
To plan endangered species conservation and to design adequate management programmes, it is necessary to predict their
distributional response to climate change, especially under the current situation of rapid change. However, these
predictions are customarily done by relating de novo the distribution of the species with climatic conditions with no regard
of previously available knowledge about the factors affecting the species distribution. We propose to take advantage of
known species distribution models, but proceeding to update them with the variables yielded by climatic models before
projecting them to the future. To exemplify our proposal, the availability of suitable habitat across Spain for the endangered
Bonelli’s Eagle (Aquila fasciata) was modelled by updating a pre-existing model based on current climate and topography to
a combination of different general circulation models and Special Report on Emissions Scenarios. Our results suggested that
the main threat for this endangered species would not be climate change, since all forecasting models show that its
distribution will be maintained and increased in mainland Spain for all the XXI century. We remark on the importance of
linking conservation biology with distribution modelling by updating existing models, frequently available for endangered
species, considering all the known factors conditioning the species’ distribution, instead of building new models that are
based on climate change variables only.Ministerio de Ciencia e Innovación and FEDER (project CGL2009-11316/BOS
Intercomparison of the northern hemisphere winter mid-latitude atmospheric variability of the IPCC models
We compare, for the overlapping time frame 1962-2000, the estimate of the
northern hemisphere (NH) mid-latitude winter atmospheric variability within the
XX century simulations of 17 global climate models (GCMs) included in the
IPCC-4AR with the NCEP and ECMWF reanalyses. We compute the Hayashi spectra of
the 500hPa geopotential height fields and introduce an integral measure of the
variability observed in the NH on different spectral sub-domains. Only two
high-resolution GCMs have a good agreement with reanalyses. Large biases, in
most cases larger than 20%, are found between the wave climatologies of most
GCMs and the reanalyses, with a relative span of around 50%. The travelling
baroclinic waves are usually overestimated, while the planetary waves are
usually underestimated, in agreement with previous studies performed on global
weather forecasting models. When comparing the results of various versions of
similar GCMs, it is clear that in some cases the vertical resolution of the
atmosphere and, somewhat unexpectedly, of the adopted ocean model seem to be
critical in determining the agreement with the reanalyses. The GCMs ensemble is
biased with respect to the reanalyses but is comparable to the best 5 GCMs.
This study suggests serious caveats with respect to the ability of most of the
presently available GCMs in representing the statistics of the global scale
atmospheric dynamics of the present climate and, a fortiori, in the perspective
of modelling climate change.Comment: 39 pages, 8 figures, 2 table
- …