15,434 research outputs found
Decorrelating a compressible turbulent flow: an experiment
Floating particles that are initially distributed uniformly on the surface of
a turbulent fluid, subsequently coagulate, until finally a steady state is
reached. This being so, they manifestly form a compressible system. In this
experiment, the information dimension D_1, and the Lyapunov exponents of the
coagulated floaters, are measured. The trajectories and the velocity fields of
the particles are captured in a sequence of rapidly acquired images. Then the
velocity sequence is randomly shuffled in time to generate new trajectories.
This analysis mimics the Kraichnan ensemble and yields properties of a velocity
correlation function that is delta-correlated in time (but not in space). The
measurements are compared with theoretical expectations and with simulations of
Boffetta et al., that closely mimic the laboratory experiment reported here.Comment: 6 pages, 5 figure
The mass distribution of the Fornax dSph: constraints from its globular cluster distribution
Uniquely among the dwarf spheroidal (dSph) satellite galaxies of the Milky
Way, Fornax hosts globular clusters. It remains a puzzle as to why dynamical
friction has not yet dragged any of Fornax's five globular clusters to the
centre, and also why there is no evidence that any similar star cluster has
been in the past (for Fornax or any other dSph). We set up a suite of 2800
N-body simulations that sample the full range of globular-cluster orbits and
mass models consistent with all existing observational constraints for Fornax.
In agreement with previous work, we find that if Fornax has a large dark-matter
core then its globular clusters remain close to their currently observed
locations for long times. Furthermore, we find previously unreported behaviour
for clusters that start inside the core region. These are pushed out of the
core and gain orbital energy, a process we call 'dynamical buoyancy'. Thus a
cored mass distribution in Fornax will naturally lead to a shell-like globular
cluster distribution near the core radius, independent of the initial
conditions. By contrast, CDM-type cusped mass distributions lead to the rapid
infall of at least one cluster within \Delta t = 1-2Gyr, except when picking
unlikely initial conditions for the cluster orbits (\sim 2% probability), and
almost all clusters within \Delta t = 10Gyr. Alternatively, if Fornax has only
a weakly cusped mass distribution, dynamical friction is much reduced. While
over \Delta t = 10Gyr this still leads to the infall of 1-4 clusters from their
present orbits, the infall of any cluster within \Delta t = 1-2Gyr is much less
likely (with probability 0-70%, depending on \Delta t and the strength of the
cusp). Such a solution to the timing problem requires that in the past the
globular clusters were somewhat further from Fornax than today; they most
likely did not form within Fornax, but were accreted.Comment: 12 pages, 8 figures, 3 tables, submitted to MNRA
Properties of dense strange hadronic matter with quark degrees of freedom
The properties of strange hadronic matter are studied in the context of the modified quark-meson coupling model using two substantially di erent sets of hyperon-hyperon (Y Y ) interactions. The first set is based on the Nijmegen hard core potential model D with slightly attractive Y Y interactions. The second potential set is based on the recent SU(3) extension of the Nijmegen soft-core potential NSC97 with strongly attractive Y Y interactions which may allow for deeply bound hypernuclear matter. The results show that, for the first potential set, the hyperon does not appear at all in the bulk at any baryon density and for all strangeness fractions. The binding energy curves of the resulting N system vary smoothly with density and the system is stable (or metastable if we include the weak force). However, the situation is drastically changed when using the second set where the hyperons appear in the system at large baryon densities above a critical strangeness fraction. We find strange hadronic matter undergoes a first order phase transition from a N system to a N for strangeness fractions fS > 1.2 and baryonic densities exceeding twice ordinary nuclear matter density. Furthermore, it is found that the system built of N is deeply bound. This phase transition a ects significantly the equation of state which becomes much softer and a substantial drop in energy density and pressure are detected as the phase transition takes place. PACS:21.65.+f, 24.85.+p, 12.39B
Transverse Meissner Physics of Planar Superconductors with Columnar Pins
The statistical mechanics of thermally excited vortex lines with columnar
defects can be mapped onto the physics of interacting quantum particles with
quenched random disorder in one less dimension. The destruction of the Bose
glass phase in Type II superconductors, when the external magnetic field is
tilted sufficiently far from the column direction, is described by a poorly
understood non-Hermitian quantum phase transition. We present here exact
results for this transition in (1+1)-dimensions, obtained by mapping the
problem in the hard core limit onto one-dimensional fermions described by a
non-Hermitian tight binding model. Both site randomness and the relatively
unexplored case of bond randomness are considered. Analysis near the mobility
edge and near the band center in the latter case is facilitated by a real space
renormalization group procedure used previously for Hermitian quantum problems
with quenched randomness in one dimension.Comment: 23 pages, 22 figure
Hot hypernuclear matter in the modified quark meson coupling model
Hot hypernuclear matter is investigated in an explicit SU(3) quark model based on a mean field description of nonoverlapping baryon bags bound by the self-consistent exchange of scalar sigma, zeta and vector omega,phi mesons. The sigma, omega mean fields are assumed to couple to the u, d-quarks while the zeta ,phi mean fields are coupled to the s-quark. The coupling constants of the mean fields with the quarks are assumed to satisfy SU(6) symmetry. The calculations take into account the medium dependence of the bag parameter on the scalar fields sigma, zeta. We consider only the octet baryons N,Lambda,Sigma, Xi in hypernuclear matter. An ideal gas of the strange mesons K and K is introduced to keep zero net strangeness density. Our results for symmetric hypernuclear matter show that a phase transition takes place at a critical temperature around 180 MeV in which the scalar mean fields sigma, zeta take nonzero values at zero baryon density. Furthermore, the bag contants of the baryons decrease significantly at and above this critical temperature indicating the onset of quark deconfinement. The present results imply that the onset of quark deconfinement in SU(3) hypernuclear matter is much stronger than in SU(2) nuclear matter. PACS:21.65.+f, 24.85.+p, 12.39B
Decoherence and Entanglement Dynamics in Fluctuating Fields
We study pure phase damping of two qubits due to fluctuating fields. As
frequently employed, decoherence is thus described in terms of random unitary
(RU) dynamics, i.e., a convex mixture of unitary transformations. Based on a
separation of the dynamics into an average Hamiltonian and a noise channel, we
are able to analytically determine the evolution of both entanglement and
purity. This enables us to characterize the dynamics in a concurrence-purity
(CP) diagram: we find that RU phase damping dynamics sets constraints on
accessible regions in the CP plane. We show that initial state and dynamics
contribute to final entanglement independently.Comment: 10 pages, 5 figures, added minor changes in order to match published
versio
INTEGRAL observations of V0332+53 in outburst
We present the analysis of a 100ksec Integral(3-100kev) observation of the
transient X-ray pulsar V0332+53 inoutburst. The source is pulsating at
P=4.3751+/-0.0002s with a clear double pulse from 6 kev to 60 kev. The average
flux was ~550mCrab between 20 kev and 60 kev. We modeled the broad band
continuum from 5 kev to 100 kev with a power-law modified by an exponential cut
off. We observe three cyclotron lines: the fundamental line at 24.9+/-0.1 kev,
the first harmonic at 50.5+/-0.1 kev as well as the second harmonic
at71.7+/-0.8 kev, thus confirming the discovery of the harmonic lines by Coburn
et al. (2005) in RXTE data.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letter
Introduction: Second Annual Gallery of Nonlinear Images (Los Angeles, California, 2005)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87886/2/041101_1.pd
SCUBA - A submillimetre camera operating on the James Clerk Maxwell Telescope
The Submillimetre Common-User Bolometer Array (SCUBA) is one of a new
generation of cameras designed to operate in the submillimetre waveband. The
instrument has a wide wavelength range covering all the atmospheric
transmission windows between 300 and 2000 microns. In the heart of the
instrument are two arrays of bolometers optimised for the short (350/450
microns) and long (750/850 microns) wavelength ends of the submillimetre
spectrum. The two arrays can be used simultaneously, giving a unique
dual-wavelength capability, and have a 2.3 arc-minute field of view on the sky.
Background-limited performance is achieved by cooling the arrays to below 100
mK. SCUBA has now been in active service for over a year, and has already made
substantial breakthroughs in many areas of astronomy. In this paper we present
an overview of the performance of SCUBA during the commissioning phase on the
James Clerk Maxwell Telescope (JCMT).Comment: 14 pages, 13 figures (1 JPEG), Proc SPIE vol 335
On how much X-ray and UV radiation processes are coupled in accretion disks: AGN case
Within the standard accretion disk theory for active galactic nuclei (AGN),
the observed X-rays are often modeled by Compton up-scattering of ultraviolet
(UV) disk photons inside a hot disk corona. Here, we point out that for many
AGN, radiation pressure due to the very same UV disk photons can drive a flow
from the disk into the corona and couple the processes producing X-rays and UV
photons. This coupling could lead to quenching of the disk corona because the
regions above the UV disk will be too dense, too opaque, and consequently too
cold. We discuss various consequences of this new type of the X-ray/UV coupling
on the dynamical and radiative properties of AGN.Comment: to appear in ApJ Letter
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