24,997 research outputs found
Field dependence of gaseous ion mobility: Test of approximate formulas
The accuracies of three approximate formulas were tested by comparison with special cases for which accurate results could be found. The Wannier free flight theory was found to be superior, and can be extended to yield a formula without further adjustable constants that gives an exact result at low electric fields and good results at medium and high fields. It is applicable for any ion neutral force law and mass ratio
Halo-to-Halo Similarity and Scatter in the Velocity Distribution of Dark Matter
We examine the Velocity Distribution Function (VDF) in dark matter halos from
Milky Way to cluster mass scales. We identify an empirical model for the VDF
with a wider peak and a steeper tail than a Maxwell--Boltzmann distribution,
and discuss physical explanations. We quantify sources of scatter in the VDF of
cosmological halos and their implication for direct detection of dark matter.
Given modern simulations and observations, we find that the most significant
uncertainty in the VDF of the Milky Way arises from the unknown radial position
of the solar system relative to the dark matter halo scale radius.Comment: Accepted to ApJ. Figure 3 and 5 and Section 4 newly added. 6 pages, 6
figures, typeset using emulateap
RHAPSODY-G simulations II - Baryonic growth and metal enrichment in massive galaxy clusters
We study the evolution of the stellar component and the metallicity of both
the intracluster medium and of stars in massive ( M) simulated galaxy clusters from the Rhapsody-G suite in
detail and compare them to observational results. The simulations were
performed with the AMR code RAMSES and include the effect of AGN feedback at
the sub-grid level. AGN feedback is required to produce realistic galaxy and
cluster properties and plays a role in mixing material in the central regions
and regulating star formation in the central galaxy. In both our low and high
resolution runs with fiducial stellar yields, we find that stellar and ICM
metallicities are a factor of two lower than in observations. We find that cool
core clusters exhibit steeper metallicity gradients than non-cool core
clusters, in qualitative agreement with observations. We verify that the ICM
metallicities measured in the simulation can be explained by a simple
"regulator" model in which the metallicity is set by a balance of stellar yield
and gas accretion. It is plausible that a combination of higher resolution and
higher metal yield in AMR simulation would allow the metallicity of simulated
clusters to match observed values; however this hypothesis needs to be tested
with future simulations. Comparison to recent literature highlights that
results concerning the metallicity of clusters and cluster galaxies might
depend sensitively on the scheme chosen to solve the hydrodynamics.Comment: 22 pages, 11 figures, 2 tables. Accepted for publication on MNRA
Rhapsody-G simulations: galaxy clusters as baryonic closed boxes and the covariance between hot gas and galaxies
Within a sufficiently large cosmic volume, conservation of baryons implies a
simple `closed box' view in which the sum of the baryonic components must equal
a constant fraction of the total enclosed mass. We present evidence from
Rhapsody-G hydrodynamic simulations of massive galaxy clusters that the
closed-box expectation may hold to a surprising degree within the interior,
non-linear regions of haloes. At a fixed halo mass, we find a significant
anti-correlation between hot gas mass fraction and galaxy mass fraction (cold
gas + stars), with a rank correlation coefficient of -0.69 within .
Because of this anti-correlation, the total baryon mass serves as a low-scatter
proxy for total cluster mass. The fractional scatter of total baryon fraction
scales approximately as , while the scatter of
either gas mass or stellar mass is larger in magnitude and declines more slowly
with increasing radius. We discuss potential observational tests using cluster
samples selected by optical and hot gas properties; the simulations suggest
that joint selection on stellar and hot gas has potential to achieve 5% scatter
in total halo mass.Comment: 10 pages, 6 figures, 3 tables; replaced to match published versio
The Ah receptor: adaptive metabolism, ligand diversity, and the xenokine model
Author Posting. © American Chemical Society, 2020. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Chemical Research in Toxicology, 33(4), (2020): 860-879, doi:10.1021/acs.chemrestox.9b00476.The Ah receptor (AHR) has been studied for almost five decades. Yet, we still have many important questions about its role in normal physiology and development. Moreover, we still do not fully understand how this protein mediates the adverse effects of a variety of environmental pollutants, such as the polycyclic aromatic hydrocarbons (PAHs), the chlorinated dibenzo-p-dioxins (“dioxins”), and many polyhalogenated biphenyls. To provide a platform for future research, we provide the historical underpinnings of our current state of knowledge about AHR signal transduction, identify a few areas of needed research, and then develop concepts such as adaptive metabolism, ligand structural diversity, and the importance of proligands in receptor activation. We finish with a discussion of the cognate physiological role of the AHR, our perspective on why this receptor is so highly conserved, and how we might think about its cognate ligands in the future.This review is dedicated in memory of the career of Alan Poland, one of the truly great minds in pharmacology and toxicology. This work was supported by the National Institutes of Health Grants R35-ES028377, T32-ES007015, P30-CA014520, P42-ES007381, and U01-ES1026127, The UW SciMed GRS Program, and The Morgridge Foundation. The authors would like to thank Catherine Stanley of UW Media Solutions for her artwork
Bone mineral content after renal transplantation
Forearm bone mineral content (BMC), as evaluated by photonabsorption densitometry, was measured in 28 cadaver kidney donor recipients who entered the study 8 weeks postoperatively and were followed up for 18 months. BMC decreased signifiantly (p<0.05) but marginally in placebo-treated patients (n=14) (initial BMC 1.09±0.25 g/cm; final BMC 1.05±0.24). Fourteen patients were prophylactically given 1,25(OH)2vitamin D3 in a dose which avoided hypercalcemia and hypercalciuria (sim0.25 µg/day); under 1,25(OH)2 vitamin D3 prophylaxis a significant decrease of forearm BMC was observed no longer (initial BMC 0.94±0.21 g/cm; final BMC 0.95±0.21), but the difference between placebo and 1,25(OH)2 vitamin D3 narrowly missed statistical significance (p=0.066).
It is concluded that the decrease of forearm BMC is negligible in transplant recipients with low steroid regimens. The data suggest a trend for prophylaxis with 1,25(OH)2 vitamin D3 to slightly ameliorate forearm (cortical) BMC loss
Ferrite-damped higher-order mode study in the Brookhaven energy-recovery linac cavity
A superconducting energy-recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL) to serve as a test bed for an application to upgrades of the Relativistic Heavy Ion Collider (RHIC). The damping of higher-order modes in the superconducting five-cell cavity is of paramount importance and represents the topic of this paper. Achieving the damping by the exclusive use of two ferrite absorbers and the adoption of a space-saving step instead of the conventional taper are part of the exploratory study. Absorber properties which are portable to simulation programs for the ERL cavity have been obtained by measuring the absorber as a ferrite-loaded pill-box cavity. Measured and simulated results for the lowest dipole modes in the prototype copper cavity with one absorber are discussed. First room-temperature measurements of the fully assembled niobium cavity string are presented which confirm the effective damping of higher-order modes by the ferrite absorbers, and which give credibility to the simulated R over Q's in the ERL.open1
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