27,333 research outputs found
Spherical agglomeration of superconducting and normal microparticles with and without applied electric field
It was reported by R. Tao and coworkers that in the presence of a strong
electric field superconducting microparticles assemble into balls of
macroscopic dimensions. Such a finding has potentially important implications
for the understanding of the fundamental physics of superconductors. However,
we report here the results of experimental studies showing that (i) ball
formation also occurs in the absence of an applied electric field, (ii) the
phenomenon also occurs at temperatures above the superconducting transition
temperature, and (iii) it can also occur for non-superconducting materials.
Possible origins of the phenomenon are discussed.Comment: Small changes in response to referee's comments. To be published in
Phys. Rev.
Low-Mass X-Ray Binaries, Millisecond Radio Pulsars, and the Cosmic Star Formation Rate
We report on the implications of the peak in the cosmic star-formation rate
(SFR) at redshift z ~ 1.5 for the resulting population of low-mass X-ray
binaries(LMXB) and for that of their descendants, the millisecond radio pulsars
(MRP). Since the evolutionary timescales of LMXBs, their progenitors, and their
descendants are thought be significant fractions of the time-interval between
the SFR peak and the present epoch, there is a lag in the turn-on of the LMXB
population, with the peak activity occurring at z ~ 0.5 - 1.0. The peak in the
MRP population is delayed further, occurring at z < 0.5. We show that the
discrepancy between the birthrate of LMXBs and MRPs, found under the assumption
of a stead-state SFR, can be resolved for the population as a whole when the
effects of a time-variable SFR are included. A discrepancy may persist for
LMXBs with short orbital periods, although a detailed population synthesis will
be required to confirm this. Further, since the integrated X-ray luminosity
distribution of normal galaxies is dominated by X-ray binaries, it should show
strong luminosity evolution with redshift. In addition to an enhancement near
the peak (z ~ 1.5) of the SFR due to the prompt turn-on of the relatively
short-lived massive X-ray binaries and young supernova remnants, we predict a
second enhancement by a factor ~10 at a redshift between ~ 0.5 and ~ 1 due to
the delayed turn-on of the LMXB population. Deep X-ray observations of galaxies
out to z ~ 1 by AXAF will be able to observe this enhancement, and, by
determining its shape as a function of redshift, will provide an important new
method for constraining evolutionary models of X-ray binaries.Comment: 13 pages, including 1 figure. Accepted for publication in ApJ Letter
Entropy in the Classical and Quantum Polymer Black Hole Models
We investigate the entropy counting for black hole horizons in loop quantum
gravity (LQG). We argue that the space of 3d closed polyhedra is the classical
counterpart of the space of SU(2) intertwiners at the quantum level. Then
computing the entropy for the boundary horizon amounts to calculating the
density of polyhedra or the number of intertwiners at fixed total area.
Following the previous work arXiv:1011.5628, we dub these the classical and
quantum polymer models for isolated horizons in LQG. We provide exact
micro-canonical calculations for both models and we show that the classical
counting of polyhedra accounts for most of the features of the intertwiner
counting (leading order entropy and log-correction), thus providing us with a
simpler model to further investigate correlations and dynamics. To illustrate
this, we also produce an exact formula for the dimension of the intertwiner
space as a density of "almost-closed polyhedra".Comment: 24 page
Enhancing Synchrony in Chaotic Oscillators by Dynamic Relaying
In a chain of mutually coupled oscillators, the coupling threshold for
synchronization between the outermost identical oscillators decreases when a
type of impurity (in terms of parameter mismatch) is introduced in the inner
oscillator(s). The outer oscillators interact indirectly via dynamic relaying,
mediated by the inner oscillator(s). We confirm this enhancing of critical
coupling in the chaotic regimes of R\"ossler system in absence of coupling
delay and in Mackey-Glass system with delay coupling. The enhancing effect is
experimentally verified in electronic circuit of R\"ossler oscillators.Comment: 4 pages, 9 figure
Bosonisation Excercise in Three Dimensions: Gauged Massive Thirring Model
Bosonisation of the massive Thirring model, with a non-minimal and
non-abelian gauging is studied in 2+1-dimensions. The static abelian model is
solved completely in the large fermion mass limit and the spectrum is obtained.
The non-abelian model is solved for a restricted class of gauge fields. In both
cases explicit expressions for bosonic currents corresponding to the fermion
currents are given.Comment: 11 pages, LaTeX, E-mail: [email protected]
Fan Loops Observed by IRIS, EIS and AIA
A comprehensive study of the physical parameters of active region fan loops
is presented using the observations recorded with the Interface Region Imaging
Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS) on-board Hinode and the
Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager
(HMI) on-board the Solar Dynamics Observatory (SDO). The fan loops emerging
from non-flaring AR~11899 (near the disk-center) on 19th November, 2013 are
clearly discernible in AIA 171~{\AA} images and those obtained in \ion{Fe}{8}
and \ion{Si}{7} images using EIS. Our measurements of electron densities reveal
that the footpoints of these loops are approximately at constant pressure with
electron densities of 10.1 cm at
(\ion{O}{4}), and 8.9 cm at
(\ion{Si}{10}). The electron temperature diagnosed across the fan loops by
means of EM-Loci suggest that at the footpoints, there are two temperature
components at and 5.95, which are picked-up by IRIS lines
and EIS lines respectively. At higher heights, the loops are nearly isothermal
at , that remained constant along the loop. The measurement
of Doppler shift using IRIS lines suggests that the plasma at the footpoints of
these loops is predominantly redshifted by 2-3~km~s in \ion{C}{2},
10-15~km~s in \ion{Si}{4} and 15{--}20~km~s in \ion{O}{4},
reflecting the increase in the speed of downflows with increasing temperature
from to 5.15. These observations can be explained by low
frequency nanoflares or impulsive heating, and provide further important
constraints on the modeling of the dynamics of fan loops.Comment: Accepted for publication in The Astrophysical Journal; 8 Figures, 11
page
Solitons in 1+1 Dimensional Gauged Sigma Models
We study soliton solutions in 1+1 dimensional gauged sigma models, obtained
by dimensional reduction from its 2+1 dimensional counterparts. We show that
the Bogomol'nyi bound of these models can be expressed in terms of two
conserved charges in a similar way to that of the BPS dyons in 3+1 dimensions.
Purely magnetic vortices of the 2+1 dimensional completely gauged sigma model
appear as charged solitons in the corresponding 1+1 dimensional theory. The
scale invariance of these solitons is also broken because of the dimensional
reduction. We obtain exact static soliton solutions of these models saturating
the Bogomol'nyi bound.Comment: 21 pages, RevTeX, minor changes, version to appear in Physical Review
Constrained Dynamics of an Anomalous Relativistic Spinning Particle in Electromagnetic Background
In this paper we have considered the dynamics of an anomalous ()
charged relativistic spinning particle in the presence of an external
electromagnetic field. The constraint analysis is done and the complete set of
Dirac brackets are provided that generate the canonical Lorentz algebra and
dynamics through Hamiltonian equations of motion. The spin-induced effective
curvature of spacetime and its possible connection with Analogue Gravity models
are commented upon.Comment: 10 pages Latex, minor corrections and changes in ref., slightly
enlarged version, to appear in EPJ
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