17,463 research outputs found
Orbital Eccentricity Distribution of Solar-Neighbour Halo Stars
We present theoretical calculations for the differential distribution of
stellar orbital eccentricity for a sample of solar-neighbour halo stars. Two
types of static, spherical gravitational potentials are adopted to define the
eccentricity e for given energy E and angular momentum L, such as an isochrone
potential and a Navarro-Frenk-White potential that can serve as two extreme
ends covering in-between any realistic potential of the Milky Way halo. The
solar-neighbour eccentricity distribution \Delta N(e) is then formulated, based
on a static distribution function of the form f(E,L) in which the velocity
anisotropy parameter \beta monotonically increases in the radial direction away
from the galaxy center, such that beta is below unity (near isotropic velocity
dispersion) in the central region and asymptotically approaches \sim 1
(radially anisotropic velocity dispersion) in the far distant region of the
halo. We find that \Delta N(e) sensitively depends upon the radial profile of
\beta, and this sensitivity is used to constrain such profile in comparison
with some observational properties of \Delta N_{obs}(e) recently reported by
Carollo et al. (2010). Especially, the linear e-distribution and the fraction
of higher-e stars for their sample of solar-neighbour inner-halo stars rule out
a constant profile of \beta, contrary to the opposite claim by Bond et al.
(2010). Our constraint of \beta \lesssim 0.5 at the galaxy center indicates
that the violent relaxation that has acted on the inner halo is effective
within a scale radius of \sim 10 kpc from the galaxy center. We discuss that
our result would help understand the formation and evolution of the Milky Way
halo.Comment: 13 pages, 6 figures, accepted for publication in MNRA
Characterizing Entanglement Sources
We discuss how to characterize entanglement sources with finite sets of
measurements. The measurements do not have to be tomographically complete, and
may consist of POVMs rather than von Neumann measurements. Our method yields a
probability that the source generates an entangled state as well as estimates
of any desired calculable entanglement measures, including their error bars. We
apply two criteria, namely Akaike's information criterion and the Bayesian
information criterion, to compare and assess different models (with different
numbers of parameters) describing entanglement-generating devices. We discuss
differences between standard entanglement-verificaton methods and our present
method of characterizing an entanglement source.Comment: This submission, together with the next one, supersedes
arXiv:0806.416
The Anisotropic Distribution of M 31 Satellite Galaxies: A Polar Great Plane of Early-Type Companions
The highly anisotropic distribution and apparent alignment of the Galactic
satellites in polar great planes begs the question how common such
distributions are. The satellite system of M31 is the only nearby system for
which we currently have sufficiently accurate distances to study the
three-dimensional satellite distribution. We present the spatial distribution
of the 15 presently known M31 companions in a coordinate system centered on M31
and aligned with its disk. Through a detailed statistical analysis we show that
the full satellite sample describes a plane that is inclined by -56 deg with
respect to the poles of M31 and that has an r.m.s. height of 100 kpc. With 88%
the statistical significance of this plane is low and it is unlikely to have a
physical meaning. The great stellar stream found near Andromeda is inclined to
this plane by 7 deg. There is little evidence for a Holmberg effect. If we
confine our analysis to early-type dwarfs, we find a best-fit polar plane
within 5 deg to 7 deg from the pole of M31. This polar great plane has a
statistical significance of 99.3% and includes all dSphs (except for And II),
M32, NGC 147, and PegDIG. The r.m.s. distance of these galaxies from the polar
plane is 16 kpc. The nearby spiral M33 has a distance of only about 3 kpc from
this plane, which points toward the M81 group. We discuss the anisotropic
distribution of M31's early-type companions in the framework of three
scenarios, namely as remnants of the break-up of a larger progenitor, as tracer
of a prolate dark matter halo, and as tracer of collapse along large-scale
filaments. (Abridged)Comment: 14 pages, 5 figures, accepted for publication in the Astronomical
Journa
The relation between Hardy's non-locality and violation of Bell inequality
We give a analytic quantitative relation between Hardy's non-locality and
Bell operator. We find that Hardy's non-locality is a sufficient condition for
violation of Bell inequality, the upper bound of Hardy's non-locality allowed
by information causality just correspond to Tsirelson bound of Bell inequality,
and the upper bound of Hardy's non-locality allowed by the principle of
no-signaling just correspond to the algebraic maximum of Bell operator. Then we
study the Cabello's argument of Hardy's non-locality (a generalization of
Hardy's argument) and find a similar relation between it and violation of Bell
inequality. Finally, we give a simple derivation of the bound of Hardy's
non-locality under the constraint of information causality with the aid of
above derived relation between Hardy's non-locality and Bell operator, this
bound is the main result of a recent work of Ahanj \emph{et al.} [Phys. Rev. A
{\bf81}, 032103(2010)].Comment: 4 pages, no figure, minor chang
Critical jamming of frictional grains in the generalized isostaticity picture
While frictionless spheres at jamming are isostatic, frictional spheres at
jamming are not. As a result, frictional spheres near jamming do not
necessarily exhibit an excess of soft modes. However, a generalized form of
isostaticity can be introduced if fully mobilized contacts at the Coulomb
friction threshold are considered as slipping contacts. We show here that, in
this framework, the vibrational density of states (DOS) of frictional discs
exhibits a plateau when the generalized isostaticity line is approached. The
crossover frequency to elastic behavior scales linearly with the distance from
this line. Moreover, we show that the frictionless limit, which appears
singular when fully mobilized contacts are treated elastically, becomes smooth
when fully mobilized contacts are allowed to slip.Comment: 4 pages, 4 figures, submitted to PR
Assessing the usefulness of acute physiological responses following resistance exercise: sensitivity, magnitude of change and time course of measures
A variety of strategies exist to modulate acute physiological responses following resistance exercise aimed at enhancing recovery and/or adaptation processes. To assess the true impact of these strategies, it is important to know the ability of measures to detect meaningful change. We investigated the sensitivity of measures used to quantify acute physiological responses to resistance exercise and constructed a physiological profile to characterise the magnitude of change and time course of this response. Eight males, accustomed to regular resistance exercise, performed experimental sessions during a ‘control week’, void of an exercise stimulus. Participants repeated this sequence of experimental sessions the following week, termed the ‘exercise week’, except they performed a bout of lower-limb resistance exercise following baseline assessments. Assessments were conducted at baseline, 2, 6, 24, 48, 72 and 96 h post-intervention. Based on the signal-to-noise ratio, the most sensitive measures were maximal voluntary isometric contraction, 20m sprint, countermovement jump peak force, rate of force development (100-200ms), muscle soreness, daily analysis of life demands for athletes Part B, limb girth, matrix metalloproteinase-9, interleukin-6, creatine kinase and high sensitivity C-reactive protein with ratios of >1.5. There were clear changes in these measures following resistance exercise, determined via magnitude-based inferences. These findings highlight measures that can detect real changes in acute physiological responses following resistance exercise in trained individuals. Researchers investigating strategies to manipulate acute physiological responses for recovery and/or adaptation can use these measures, as well as recommended sampling points, to be confident that their interventions are making a worthwhile impact
Time-dependent particle acceleration in supernova remnants in different environments
We simulate time-dependent particle acceleration in the blast wave of a young
supernova remnant (SNR), using a Monte Carlo approach for the diffusion and
acceleration of the particles, coupled to an MHD code. We calculate the
distribution function of the cosmic rays concurrently with the hydrodynamic
evolution of the SNR, and compare the results with those obtained using simple
steady-state models. The surrounding medium into which the supernova remnant
evolves turns out to be of great influence on the maximum energy to which
particles are accelerated. In particular, a shock going through a density profile causes acceleration to typically much higher energies
than a shock going through a medium with a homogeneous density profile. We find
systematic differences between steady-state analytical models and our
time-dependent calculation in terms of spectral slope, maximum energy, and the
shape of the cut-off of the particle spectrum at the highest energies. We also
find that, provided that the magnetic field at the reverse shock is
sufficiently strong to confine particles, cosmic rays can be easily
re-accelerated at the reverse shock.Comment: 19 pages, 20 figures, accepted for publication in MNRA
Effect of hot water immersion on acute physiological responses following resistance exercise
Purpose: Hot water immersion (HWI) is a strategy theorised to enhance exercise recovery. However, the acute physiological responses to HWI following resistance exercise are yet to be determined.
Methods: The effect of HWI on intramuscular temperature (IMT), muscle function, muscle soreness and blood markers of muscle cell disruption and inflammatory processes after resistance exercise was assessed. Sixteen resistance trained males performed resistance exercise, followed by either 10 min HWI at 40°C or 10 min passive recovery (PAS).
Results: Post-intervention, the increase in IMT at all depths was greater for HWI compared to PAS, however this difference had disappeared by 1 h post at depths of 1 and 2 cm, and by 2 h post at a depth of 3 cm. There were no differences between groups for muscle function, muscle soreness or any blood markers.
Conclusion: These results suggest that HWI is a viable means of heat therapy to support a greater IMT following resistance exercise. Recovery of muscle function and muscle soreness is independent of acute changes in IMT associated with HWI
\Lambda-buildings and base change functors
We prove an analog of the base change functor of \Lambda-trees in the setting
of generalized affine buildings. The proof is mainly based on local and global
combinatorics of the associated spherical buildings. As an application we
obtain that the class of generalized affine building is closed under ultracones
and asymptotic cones. Other applications involve a complex of groups
decompositions and fixed point theorems for certain classes of generalized
affine buildings.Comment: revised version, 29 pages, to appear in Geom. Dedicat
The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years
We combine deep UBVRIzJK photometry from the Multiwavelength Survey by
Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a
large-scale study of the rest-frame ultraviolet (UV) properties of 674
high-redshift (0.5<z<1) early-type galaxies, drawn from the Extended Chandra
Deep Field South (E-CDFS). Galaxy morphologies are determined through visual
inspection of Hubble Space Telescope (HST) images taken from the GEMS survey.
We harness the sensitivity of the UV to young (<1 Gyr old) stars to quantify
the recent star formation history of early-type galaxies across a range of
luminosities (-23.5 < M(V) < -18). Comparisons to simple stellar populations
forming at high redshift indicate that only ~1.1 percent of early-types in this
sample are consistent with purely passive ageing since z=2. Parametrising the
recent star formation (RSF) in terms of the mass fraction of stars less than a
Gyr old, we find that the early-type population as a whole shows a typical RSF
between 5 and 13% in the redshift range 0.5<z<1. Early-types on the UV red
sequence show RSF values less than 5% while the reddest early-types are
virtually quiescent with RSF values of ~1%. We find compelling evidence that
early-types of all luminosities form stars over the lifetime of the Universe,
although the bulk of their star formation is already complete at high redshift.
This tail-end of star formation is measurable and not negligible, with luminous
(-23<M(V)<-20.5) early-types potentially forming 10-15% of their mass since
z=1, with their less luminous (M(V)>-20.5) counterparts potentially forming
30-60 percent of their mass in the same redshift range. (abridged)Comment: Submitted to MNRA
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