1,996 research outputs found
Zero-temperature resistive transition in Josephson-junction arrays at irrational frustration
We use a driven Monte Carlo dynamics in the phase representation to determine
the linear resistivity and current-voltage scaling of a two-dimensional
Josephson-junction array at an irrational flux quantum per plaquette. The
results are consistent with a phase-coherence transition scenario where the
critical temperature vanishes. The linear resistivity is nonzero at any finite
temperatures but nonlinear behavior sets in at a temperature-dependent
crossover current determined by the thermal critical exponent. From a dynamic
scaling analysis we determine this critical exponent and the thermally
activated behavior of the linear resistivity. The results are in agreement with
earlier calculations using the resistively shunted-junction model for the
dynamics of the array. The linear resistivity behavior is consistent with some
experimental results on arrays of superconducting grains but not on wire
networks, which we argue have been obtained in a current regime above the
crossover current.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Fast and Slow solutions in General Relativity: The Initialization Procedure
We apply recent results in the theory of PDE, specifically in problems with
two different time scales, on Einstein's equations near their Newtonian limit.
The results imply a justification to Postnewtonian approximations when
initialization procedures to different orders are made on the initial data. We
determine up to what order initialization is needed in order to detect the
contribution to the quadrupole moment due to the slow motion of a massive body
as distinct from initial data contributions to fast solutions and prove that
such initialization is compatible with the constraint equations. Using the
results mentioned the first Postnewtonian equations and their solutions in
terms of Green functions are presented in order to indicate how to proceed in
calculations with this approach.Comment: 14 pages, Late
Sample-to-sample fluctuations of power spectrum of a random motion in a periodic Sinai model
The Sinai model of a tracer diffusing in a quenched Brownian potential is a
much studied problem exhibiting a logarithmically slow anomalous diffusion due
to the growth of energy barriers with the system size. However, if the
potential is random but periodic, the regime of anomalous diffusion crosses
over to one of normal diffusion once a tracer has diffused over a few periods
of the system. Here we consider a system in which the potential is given by a
Brownian Bridge on a finite interval and then periodically repeated
over the whole real line, and study the power spectrum of the diffusive
process in such a potential. We show that for most of realizations of
in a given realization of the potential, the low-frequency behavior is
, i.e., the same as for standard Brownian motion, and
the amplitude is a disorder-dependent random variable with a finite
support. Focusing on the statistical properties of this random variable, we
determine the moments of of arbitrary, negative or positive order
, and demonstrate that they exhibit a multi-fractal dependence on , and a
rather unusual dependence on the temperature and on the periodicity , which
are supported by atypical realizations of the periodic disorder. We finally
show that the distribution of has a log-normal left tail, and
exhibits an essential singularity close to the right edge of the support, which
is related to the Lifshitz singularity. Our findings are based both on analytic
results and on extensive numerical simulations of the process .Comment: 8 pages, 5 figure
Field-induced superconductor to insulator transition in Josephson-junction ladders
The superconductor to insulator transition is studied in a self-charging
model for a ladder of Josephson-junctions in presence of an external magnetic
field. Path integral Monte Carlo simulations of the equivalent
(1+1)-dimensional classical model are used to study the phase diagram and
critical behavior. In addition to a superconducting (vortex-free) phase, a
vortex phase can also occur for increasing magnetic field and small charging
energy. It is found that an intervening insulating phase separates the
superconducting from the vortex phases. Surprisingly, a finite-size scaling
analysis shows that the field-induced superconducting to insulator transition
is in the KT universality class even tough the external field breaks
time-reversal symmetry.Comment: 5 pages, 7 figures, to appear in Phys. Rev.
Elaboracion y normalizacion de una prueba de habla comprimida en oraciones a un 40% de comprension
51 p.El procesamiento auditivo central (PAC) se entiende como los procesos del sistema nervioso central, para entender el mensaje. Actualmente no existen estudios hispanos y algunos pertenecientes a otros idiomas, que se encuentren validados, en la medición de la(s) habilidad(es) del procesamiento auditivo central; la misma realidad se repite en Chile. Por ello se presenta a continuación el proceso de elaboración y normalización de una prueba de habla comprimida en oraciones a un 40% de compresión, mediante el diseño y aplicación de una prueba que se adapta a la realidad lingüística chilena con el fin de obtener una prueba válida para medir el Procesamiento Auditivo Central en una población de personas jóvenes entre los 18 y 24 años de la Universidad de Talca en la carrera de Fonoaudiología. Además se explica detalladamente la metodología y los estímulos utilizados en la aplicación de la prueba; cómo fueron obtenidos y analizados los datos para su uso y mediante las conclusiones se detallarán los posteriores hallazgos con la finalidad de aportar información necesaria para futuros fines audiológicos en personas con Trastornos en el Procesamiento Auditivo Central (TPAC)
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