2,463 research outputs found
A Universal Temperature Profile for Galaxy Clusters
We investigate the predicted present-day temperature profiles of the hot,
X-ray emitting gas in galaxy clusters for two cosmological models - a current
best-guess LCDM model and standard cold dark matter (SCDM). Our
numerically-simulated "catalogs" of clusters are derived from high-resolution
(15/h kpc) simulations which make use of a sophisticated, Eulerian-based,
Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which
are essential for correctly modelling cluster temperatures. We show that the
temperature structure on Mpc-scales is highly complex and non-isothermal.
However, the temperature profiles of the simulated LCDM and SCDM clusters are
remarkably similar and drop-off as
where and . This decrease
is in good agreement with the observational results of Markevitch et al.(1998)
but diverges, primarily in the innermost regions, from their fit which assumes
a polytropic equation of state. Our result is also in good agreement with a
recent sample of clusters observed by BeppoSAX though there is some indication
of missing physics at small radii (). We discuss the
interpretation of our results and make predictions for new x-ray observations
that will extend to larger radii than previously possible. Finally, we show
that, for , our universal temperature profile is consistent with
our most recent simulations which include both radiative cooling and supernovae
feedback.Comment: 8 pages, 6 figures, accepted for publication in ApJ, full-page
version of Fig. 2 at
http://www.cita.utoronto.ca/+AH4-cloken/PAPERS/UTP/f2.ep
Full density matrix dynamics for large quantum systems: Interactions, Decoherence and Inelastic effects
We develop analytical tools and numerical methods for time evolving the total
density matrix of the finite-size Anderson model. The model is composed of two
finite metal grains, each prepared in canonical states of differing chemical
potential and connected through a single electronic level (quantum dot or
impurity). Coulomb interactions are either excluded all together, or allowed on
the dot only. We extend this basic model to emulate decoherring and inelastic
scattering processes for the dot electrons with the probe technique. Three
methods, originally developed to treat impurity dynamics, are augmented to
yield global system dynamics: the quantum Langevin equation method, the well
known fermionic trace formula, and an iterative path integral approach. The
latter accommodates interactions on the dot in a numerically exact fashion. We
apply the developed techniques to two open topics in nonequilibrium many-body
physics: (i) We explore the role of many-body electron-electron repulsion
effects on the dynamics of the system. Results, obtained using exact path
integral simulations, are compared to mean-field quantum Langevin equation
predictions. (ii) We analyze aspects of quantum equilibration and
thermalization in large quantum systems using the probe technique, mimicking
elastic-dephasing effects and inelastic interactions on the dot. Here, unitary
simulations based on the fermionic trace formula are accompanied by quantum
Langevin equation calculations
A catalog of Nearby Poor Clusters of Galaxies
A catalog of 732 optically selected, nearby poor clusters of galaxies
covering the entire sky north of declination is presented. The
poor clusters, called WBL clusters, were identified as concentrations of 3 or
more galaxies with photographic magnitudes brighter than 15.7, possessing a
galaxy surface overdensity of . These criteria are consistent with
those used in the identification of the original Yerkes poor clusters, and this
new catalog substantially increases the sample size of such objects. These poor
clusters cover the entire range of galaxy associations up to and including
Abell clusters, systematically including poor and rich galaxy systems spanning
over three orders of magnitude in the cluster mass function. As a result, this
new catalog contains a greater diversity of richness and structures than other
group catalogs, such as the Hickson or Yerkes catalogs. The information on
individual galaxies includes redshifts and cross-references to other galaxy
catalogs. The entries for the clusters include redshift (where available) and
cross-references to other group and cluster catalogs.Comment: 27 pages, 7 figures, + one 20-page landscape table, accepted for
publication in A
The X-ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies: A Cosmological Probe
In this letter, we present a new determination of the local (z<0.09) X-ray
luminosity function (XLF) using a large, statistical sample of 294 Abell
clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have
reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine
our data with previous work in order to explore possible constraints imposed by
the shape of the XLF on cosmological models. A set of currently viable
cosmologies is used to construct theoretical XLFs assuming Lx is proportional
to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the
local X-ray temperature function. We fit these models to our observed XLF and
verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser
1986) disagrees strongly with observations. If we assume that clusters can be
described by the pre-heated, constant core-entropy models of Evrard & Henry
(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the
energy per unit mass in galaxies is roughly equal to the gas energy (ie if
beta=1). (abridged)Comment: 4 pages, 2 figures, accepted for publication in ApJ Letters. uses
emulateapj.st
Redshifts and Optical Properties for a Statistically Complete Sample of Poor Galaxy Clusters
From the poor cluster catalog of White et al. (1996), we define a sample of
71 optically-selected poor galaxy clusters. The surface-density enhance- ment
we require for our clusters falls between that of the loose associations of
Turner and Gott (1976) and the Hickson compact groups (Hickson, 1982). We
review the selection biases and determine the statistical comleteness of the
sample. For this sample, we report new velocity measurements made with the ARC
3.5-m Dual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiber
spectrograph. Combining our own measurements with those from the literature, we
examine the velocity distributions, velocity dispersions, and 1-d velocity
substructure for our poor cluster sample, and compare our results to other poor
cluster samples. We find that approximately half of the sample may have
significant 1-d velocity substructure. The optical morphology, large-scale
environment, and velocity field of many of these clusters is indicative of
young, dynamically evolving systems. In future papers, we will use this sample
to derive the poor cluster X-ray luminosity function and gas mass function (see
astro-ph/9606120), and will examine the optical/X-ray properties of the
clusters in more detail.Comment: 15 pages LaTeX, 3 tables, 5 postscript figures. To appear in the
August 1996 Astronomical Journa
Acute Effects of Barbell Bouncing and External Cueing on Power Output in Bench Press Throw in Resistance-Trained Men.
The aims of this study were to compare power output during a bench press throw (BPT) executed with (BPT(bounce)) and without (BPT) the barbell bounce technique, and examine the effect of cueing different barbell descent velocities on BPT power output in resistance-trained males. In total, 27 males (age 23.1 ± 2.1 years; body mass 79.4 ± 7.4 kg; height 178.8 ± 5.5 cm; and 4.6 ± 1.9 years of resistance training experience) were recruited and attended one familiarization session and two experimental sessions (EXP 1 and EXP 2). The forceâvelocity profile during maximal BPT and BPT(bounce) (randomized order) under different loads (30â60 kg) was established (EXP 1), and the effect of varying external barbell descent velocity cues âslow, medium, and as fast as possibleâ (i.e., âfastâ) on the power output for each technique (BPT and BPT(bounce)) was examined (EXP 2). Comparing two BPT techniques (EXP 1), BPT(bounce) demonstrated 7.9â14.1% greater average power (p †0.001, ES = 0.48â0.90), 6.5â12.1% greater average velocity (p †0.001, ES = 0.48â0.91), and 11.9â31.3% shorter time to peak power (p †0.001â0.05, ES = 0.33â0.83) across the loads 30â60 kg than BPT. The cueing condition âfastâ (EXP 2) resulted in greater power outcomes for both BPT and BPT(bounce) than âslow.â No statistically significant differences in any of the power outcomes were observed between âmediumâ and âslowâ cuing conditions for BPT (p = 0.097â1.000), whereas BPT(bounce) demonstrated increased average power and velocity under the âmediumâ cuing condition, compared to âslowâ (p = 0.006â0.007, ES = 0.25â0.28). No statistically significant differences were observed in barbell throw height comparing BPT and BPT(bounce) under each cuing condition (p = 0.225â1.000). Overall, results indicate that both bouncing the barbell and emphasizing barbell descent velocity be considered to improve upper body power in athlete and non-athlete resistance-training programs
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