4,177 research outputs found
Landau degeneracy and black hole entropy
We consider the supergravity solution describing a configuration of
intersecting D-4-branes with non-vanishing worldvolume gauge fields. The
entropy of such a black hole is calculated in terms of the D-branes quantised
charges. The non-extreme solution is also considered and the corresponding
thermodynamical quantities are calculated in terms of a D-brane/anti-D-brane
system. To perform the quantum mechanical D-brane analysis we study
open-strings with their ends on branes with a magnetic condensate. Applying the
results to our D-brane system we managed to have a perfect agreement between
the D-brane entropy counting and the corresponding semi-classical result. The
Landau degeneracy of the open string states describing the excitations of the
D-brane system enters in a crucial way. We also derive the near-extreme results
which agree with the semi-classical calculations.Comment: 30 pages, 1 figure, latex. Minor corrections, version to appear in
Nuclear Physics
Analytical study of tunneling times in flat histogram Monte Carlo
We present a model for the dynamics in energy space of multicanonical
simulation methods that lends itself to a rather complete analytic
characterization. The dynamics is completely determined by the density of
states. In the \pm J 2D spin glass the transitions between the ground state
level and the first excited one control the long time dynamics. We are able to
calculate the distribution of tunneling times and relate it to the
equilibration time of a starting probability distribution. In this model, and
possibly in any model in which entering and exiting regions with low density of
states are the slowest processes in the simulations, tunneling time can be much
larger (by a factor of O(N)) than the equilibration time of the probability
distribution. We find that these features also hold for the energy projection
of single spin flip dynamics.Comment: 7 pages, 4 figures, published in Europhysics Letters (2005
AdS black disk model for small-x DIS
Using the approximate conformal invariance of QCD at high energies we
consider a simple AdS black disk model to describe saturation in DIS. Deep
inside saturation the structure functions have the same power law scaling, F_T
~ F_L ~ 1/x^w, where w is related to the expansion rate of the black disk with
energy. Furthermore, the ratio F_L /F_T is given by the universal value
(1+w)/(3+w), independently of the target. For virtual photon-photon scattering
at high energies we obtain explicit expressions and ratios for the total cross
sections of transverse and longitudinal photons in terms of the single
parameter w.Comment: 5 pages. Minor correction
A multidimensional scaling analysis of musical sounds based on pseudo phase plane
This paper studies musical opus from the point of view of three mathematical tools: entropy, pseudo phase plane (PPP), and multidimensional scaling (MDS). The experiments analyze ten sets of different musical styles. First, for each musical composition, the PPP is produced using the time series lags captured by the average mutual information. Second, to unravel hidden relationships between the musical styles the MDS technique is used. The MDS is calculated based on two alternative metrics obtained from the PPP, namely, the average mutual information and the fractal dimension. The results reveal significant differences in the musical styles, demonstrating the feasibility of the proposed strategy and motivating further developments towards a dynamical analysis of musical sounds
Coleman meets Schwinger
It is well known that spherical D-branes are nucleated in the presence of an
external RR electric field. Using the description of D-branes as solitons of
the tachyon field on non-BPS D-branes, we show that the brane nucleation
process can be seen as the decay of the tachyon false vacuum. This process can
describe the decay of flux-branes in string theory or the decay of quintessence
potentials arising in flux compactifications.Comment: 5 pages, 2 figure
A Piezoelectric Device for Measurement and Power Harvesting Applications
Com o apoio RAADRI.With the fast growth of wireless communications between nodes/sensor units, devices installed in remote places require power energy supply solutions to assure their functionally and data communication capabilities. For these applications energy harvesting takes place as a good solution, to increase the availability of energy, in opposition to the conventional systems of energy supply. Regenerative energy sources like thermoelectric, magnetic, piezoelectric, and/or renewable sources such as photovoltaic, wind, among others, allowed the development of different powering solutions for sensor units. The purpose of this work is to characterize a piezoelectric device to measure and capture mechanical vibrations from equipments, structures and piping vibrations, as well as from other sources. The study is carried out taking into account the power supply capabilities of piezoelectric devices as a function of the amplitude and frequency of the vibration stimulus, as well as, the electrical characteristics of the load circuit
Kaluza-Klein electrically charged black branes in M-theory
We present a class of Kaluza-Klein electrically charged black p-brane
solutions of ten-dimensional, type IIA superstring theory. Uplifting to eleven
dimensions these solutions are studied in the context of M-theory. They can be
interpreted either as a p+1 extended object trapped around the eleventh
dimension along which momentum is flowing or as a boost of the following
backgrounds: the Schwarzschild black (p+1)-brane or the product of the
(10-p)-dimensional Euclidean Schwarzschild manifold with the (p+1)-dimensional
Minkowski spacetime.Comment: 16 pages, uses latex and epsf macro, figures include
MILP approach for then design of vertical vapor-liquid separation vessels-comparison with heuristics
In this article we compare results from different heuristics approaches for the design of VLE separation vessels. In addition, we present an MILP approach that embeds the aforementioned heuristics and considers the discrete nature of the geometric variables. We show that different heuristics render different results and, while results from heuristics and MILP often coincide, significant departures occur.Fil: Fischer, Carlos Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad TecnolĂłgica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; ArgentinaFil: Costa, AndrĂ© Hemerly L.. Universidade do Estado de Rio do Janeiro; BrasilFil: Bagajewicz, Miguel J.. Oklahoma State University; Estados Unido
Provision of academic data for research: a step for academic success
One of the most widely researched issue on higher education relates to exposed paths that lead to academic success. Nowadays information systems represent an essential part of the education sector in many universities. In particular, the increasing of the number of students in higher education in Portugal leads to the progressive increase of student’s data contained in institutional information systems. This article aims to include the use of student data contained in the Fénix information system of a Portuguese higher educational institution, turning their information in an internal tool, to assist analysis and studies of internal academic success. Providing relevant data for queries can offer a clearer explanation of the paths to success in higher education. It can also help the identification of problems and failures aiming to support a more effective intervention of institutions and researchers to improve the academic success.info:eu-repo/semantics/acceptedVersio
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