17,799 research outputs found
Negative modes and the thermodynamics of Reissner-Nordstr\"om black holes
We analyse the problem of negative modes of the Euclidean section of the
Reissner-Nordstr\"om black hole in four dimensions. We find analytically that a
negative mode disappears when the specific heat at constant charge becomes
positive. The sector of perturbations analysed here is included in the
canonical partition function of the magnetically charged black hole. The result
obeys the usual rule that the partition function is only well-defined when
there is local thermodynamical equilibrium. We point out the difficulty in
quantising Einstein-Maxwell theory, where the so-called conformal factor
problem is considerably more intricate. Our method, inspired by hep-th/0608001,
allows us to decouple the divergent gauge volume and treat the metric
perturbations sector in a gauge-invariant way.Comment: 24 pages, 1 figure; v2 minor changes to fit published versio
Loading of a Bose-Einstein condensate in the boson-accumulation regime
We study the optical loading of a trapped Bose-Einstein condensate by
spontaneous emission of atoms in excited electronic state in the
Boson-Accumulation Regime. We generalize the previous simplified analysis of
ref. [Phys. Rev. A 53, 2466 (1996)], to a 3D case in which more than one trap
level of the excited state trap is considered. By solving the corresponding
quantum many-body master equation, we demonstrate that also for this general
situation the photon reabsorption can help to increase the condensate fraction.
Such effect could be employed to realize a continuous atom laser, and to
overcome condensate losses.Comment: 7 pages, 5 eps figures, uses epl.st
Atomic quantum gases in Kagom\'e lattices
We demonstrate the possibility of creating and controlling an ideal and
\textit{trimerized} optical Kagom\'e lattice, and study the low temperature
physics of various atomic gases in such lattices. In the trimerized Kagom\'e
lattice, a Bose gas exhibits a Mott transition with fractional filling factors,
whereas a spinless interacting Fermi gas at 2/3 filling behaves as a quantum
magnet on a triangular lattice. Finally, a Fermi-Fermi mixture at half filling
for both components represents a frustrated quantum antiferromagnet with a
resonating-valence-bond ground state and quantum spin liquid behavior dominated
by continuous spectrum of singlet and triplet excitations. We discuss the
method of preparing and observing such quantum spin liquid employing molecular
Bose condensates.Comment: 4 pages, 1 figure. Missing affiliations adde
Android Malware Clustering through Malicious Payload Mining
Clustering has been well studied for desktop malware analysis as an effective
triage method. Conventional similarity-based clustering techniques, however,
cannot be immediately applied to Android malware analysis due to the excessive
use of third-party libraries in Android application development and the
widespread use of repackaging in malware development. We design and implement
an Android malware clustering system through iterative mining of malicious
payload and checking whether malware samples share the same version of
malicious payload. Our system utilizes a hierarchical clustering technique and
an efficient bit-vector format to represent Android apps. Experimental results
demonstrate that our clustering approach achieves precision of 0.90 and recall
of 0.75 for Android Genome malware dataset, and average precision of 0.98 and
recall of 0.96 with respect to manually verified ground-truth.Comment: Proceedings of the 20th International Symposium on Research in
Attacks, Intrusions and Defenses (RAID 2017
Tecnologia para produção orgância de cenoura consorciada com alface em Sergipe.
bitstream/CPATC/19935/1/ct-50.pd
Tecnologia para produção de mudas de hortaliças e plantas medicinais em sistema orgânico.
bitstream/CPATC/19934/1/ct-48.pd
Tecnologia para biodegradação da casca de coco sem gerar outros resíduos.
bitstream/CPATC/19770/1/f_07_2007.pdfExiste o documento impresso
Probing the quantum phase transition in the Dicke model through mechanical vibrations
This paper is concerned with quantum dynamics of a system coupled to a
critical reservoir. In this context, we employ the Dicke model which is known
to exhibit a super radiant quantum phase transition (QPT) and we allow one of
the mirrors to move under a linear restoring force. The electromagnetic field
couples to the movable mirror though radiation pressure just like in typical
optomechanical setups. We show that, in the thermodynamical limit, the
super-radiant phase induces a classical driving force on the mirror without
causing decoherence.Comment: 6 pages, 3 figures, final versio
Tecnologia para biodegradação da casca de coco seco e de outros resíduos do coqueiro.
bitstream/item/158629/1/ct-46.pd
One-Electron Singular Branch Lines of the Hubbard Chain
The momentum and energy dependence of the weight distribution in the vicinity
of the one-electron spectral-function singular branch lines of the 1D Hubbard
model is studied for all values of the electronic density and on-site repulsion
. To achieve this goal we use the recently introduced pseudofermion
dynamical theory. Our predictions agree quantitatively for the whole momentum
and energy bandwidth with the peak dispersions observed by angle-resolved
photoelectron spectroscopy in the quasi-1D organic conductor TTF-TCNQ.Comment: Replaced with shortened version; 4 figure
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