884 research outputs found
Anti-Unruh Phenomena
We find that a uniformly accelerated particle detector coupled to the vacuum
can cool down as its acceleration increases, due to relativistic effects. We
show that in (1+1)-dimensions, a detector coupled to the scalar field vacuum
for finite timescales (but long enough to satisfy the KMS condition) has a KMS
temperature that decreases with acceleration, in certain regimes. This
contrasts with the heating that one would expect from the Unruh effect.Comment: 6 pages, 5 figures. RevTex 4.1. V2. Typos in the plots labeling
corrected and plot rescaled. New discussion section added. Title change
P-V Criticality in Quasitopological Gravity
We investigate the thermodynamic behaviour of AdS quasitopological black hole
solutions in the context of extended thermodynamic phase space, in which the
cosmological constant induces a pressure with a conjugate volume. We find that
the third order exact quasitopological solution exhibits features consistent
with the third order Lovelock solutions for positive quasitopological coupling,
including multiple reentrant phase transitions and isolated critical points.
For negative coupling we find the first instances of both reentrant phase
transitions and thermodynamic singularities in five dimensions, along with
other modified thermodynamic behaviour compared to Einstein-AdS-Gauss Bonnet
gravity.Comment: 20 pages, 15 figures, REVTeX 4-1; updated to match published versio
Giant Quadrupole Resonances in 208Pb, the nuclear symmetry energy and the neutron skin thickness
Recent improvements in the experimental determination of properties of the
Isovector Giant Quadrupole Resonance (IVGQR), as demonstrated in the A=208 mass
region, may be instrumental for characterizing the isovector channel of the
effective nuclear interaction. We analyze properties of the IVGQR in 208Pb,
using both macroscopic and microscopic approaches. The microscopic method is
based on families of non-relativistic and covariant Energy Density Functionals
(EDF), characterized by a systematic variation of isoscalar and isovector
properties of the corresponding nuclear matter equations of state. The
macroscopic approach yields an explicit dependence of the nuclear symmetry
energy at some subsaturation density, for instance S(\rho=0.1 fm^{-3}), or the
neutron skin thickness \Delta r_{np} of a heavy nucleus, on the excitation
energies of isoscalar and isovector GQRs. Using available data it is found that
S(\rho=0.1 fm{}^{-3})=23.3 +/- 0.6 MeV. Results obtained with the microscopic
framework confirm the correlation of the \Delta r_{np} to the isoscalar and
isovector GQR energies, as predicted by the macroscopic model. By exploiting
this correlation together with the experimental values for the isoscalar and
isovector GQR energies, we estimate \Delta r_{np} = 0.14 +/- 0.03 fm for 208Pb,
and the slope parameter of the symmetry energy: L = 37 +/- 18 MeV
Quasi-topological Reissner-Nordstr\"om Black Holes
We consider Reissner-Nordstrom solutions in quasi-topological gravity,
obtaining exact solutions to the field equations yielding charged
quasi-topological black holes. We study their thermodynamic behaviour over a
range of parameters that yield ghost-free and stable space times. We find that
a sufficiently negative quasi-topological parameter can yield black holes with
2 horizons, even for zero charge. We discuss the thermodynamic stability for
the class of solutions we obtain. We also describe the structure of exact
charged solutions to order quasi-topological gravity.Comment: LaTeX, 16 pages, 9 figures; added references and corrected typo
Nuclear Symmetry Energy: constraints from Giant Quadrupole Resonances and Parity Violating Electron Scattering
Experimental and theoretical efforts are being devoted to the study of
observables that can shed light on the properties of the nuclear symmetry
energy. We present our new results on the excitation energy [X. Roca-Maza et
al., Phys. Rev. C 87, 034301 (2013)] and polarizability of the Isovector Giant
Quadrupole Resonance (IVGQR), which has been the object of new experimental
investigation [S. S. Henshaw et al., Phys. Rev. Lett. 107, 222501 (2011)]. We
also present our theoretical analysis on the parity violating asymmetry at the
kinematics of the Lead Radius Experiment [S. Abrahamyan et al. (PREx
Collaboration), Phys. Rev. Lett. 108, 112502 (2012)] and highlight its relation
with the density dependence of the symmetry energy [X. Roca-Maza et al., Phys.
Rev. Lett. 106, 252501 (2011)].Comment: Proceedings - International Nuclear Physics Conference (INPC),
Firenze 2 - 7 June 201
An estimation model on electricity consumption of new metro stations
Electricity consumption of metro stations increases sharply with expansion of a metro network and this has been a growing cause for concern. Based on relevant historical data from existing metro stations, this paper proposes a support vector regression (SVR) model to estimate daily electricity consumption of a newly constructed metro station. The model considers some major factors influencing the electricity consumption of metro station in terms of both the interior design scheme of a station (e.g., layout of the station and allocation of facilities) and external factors (e.g., passenger volume, air temperature and relative humidity). A genetic algorithm with five-fold cross-validation is used to optimize the hyper-parameters of the SVR model in order to improve its accuracy in estimating the electricity consumption of a metro station (ECMS). With the optimized hyper-parameters, results from case studies on the Beijing Subway showed that the estimating accuracy of the proposed SVR model could reach up to 95% and the correlation coefficient was 0.89. It was demonstrated that the proposed model could outperform the traditional methods which use a back-propagation neural network or multivariate linear regression. The method presented in this paper can be an adequate tool for estimating the ECMS and should further assist in the delivery of new, energy-efficient metro stations
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