2,393 research outputs found
Concentration of atomic hydrogen diffused into silicon in the temperature range 900–1300 °C
Boron-doped Czochralski silicon samples with [B]~1017 cm−3 have been heated at various temperatures in the range 800–1300 °C in an atmosphere of hydrogen and then quenched. The concentration of [H-B] pairs was measured by infrared localized vibrational mode spectroscopy. It was concluded that the solubility of atomic hydrogen is greater than [Hs] = 5.6 × 1018 exp( − 0.95 eV/kT)cm−3 at the temperatures investigated
A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies
The relation between X-ray luminosity (L_X) and ambient gas temperature (T)
among massive galactic systems is an important cornerstone of both
observational cosmology and galaxy-evolution modeling. In the most massive
galaxy clusters, the relation is determined primarily by cosmological structure
formation. In less massive systems, it primarily reflects the feedback response
to radiative cooling of circumgalactic gas. Here we present a simple but
powerful model for the L_X-T relation as a function of physical aperture R
within which those measurements are made. The model is based on the
precipitation framework for AGN feedback and assumes that the circumgalactic
medium is precipitation-regulated at small radii and limited by cosmological
structure formation at large radii. We compare this model with many different
data sets and show that it successfully reproduces the slope and upper envelope
of the L_X-T-R relation over the temperature range from ~0.2 keV through >10
keV. Our findings strongly suggest that the feedback mechanisms responsible for
regulating star formation in individual massive galaxies have much in common
with the precipitation-triggered feedback that appears to regulate
galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos
The Chandra X-Ray Point-Source Catalog in The Deep2 Galaxy Redshift Survey Fields
We present the X-ray point-source catalog produced from the Chandra Advanced CCD Imaging Spectrometer (ACIS-I) observations of the combined \sim3.2 deg2 DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1 deg2 fields. The combined total exposures across all four XDEEP2 fields range from ~10ks-1.1Ms. We detect X-ray point-sources in both the individual ACIS-I observations and the overlapping regions in the merged (stacked) images. We find a total of 2976 unique X-ray sources within the survey area with an expected false-source contamination of ~30 sources (~1%). We present the combined logN-logS distribution of sources detected across the XDEEP2 survey fields and find good agreement with the Extended Chandra Deep Field and Chandra-COSMOS fields to f_{X,0.5-2keV}\sim2x10^{-16} erg/cm^2/s. Given the large survey area of XDEEP2, we additionally place relatively strong constraints on the logN-logS distribution at high fluxes (f_{X,0.5-2keV}\sim3x10^{-14} erg/cm^2/s), and find a small systematic offset (a factor ~1.5) towards lower source numbers in this regime, when compared to smaller area surveys. The number counts observed in XDEEP2 are in close agreement with those predicted by X-ray background synthesis models. Additionally, we present a Bayesian-style method for associating the X-ray sources with optical photometric counterparts in the DEEP2 catalog (complete to R_AB \u3c 25.2) and find that 2126 (~71.4\pm2.8%) of the 2976 X-ray sources presented here have a secure optical counterpart with a \u3c6% contamination fraction. We provide the DEEP2 optical source properties (e.g., magnitude, redshift) as part of the X-ray-optical counterpart catalog
Tracing the Evolution of Active Galactic Nuclei Host Galaxies Over The Last 9 Gyr of Cosmic Time
We present the results of a combined galaxy population analysis for the host galaxies of active galactic nuclei (AGN) identified at 0 \u3c z \u3c 1.4 within the Sloan Digital Sky Survey, Boötes, and DEEP2 surveys. We identified AGN in a uniform and unbiased manner at X-ray, infrared, and radio wavelengths. Supermassive black holes undergoing radiatively efficient accretion (detected as X-ray and/or infrared AGN) appear to be hosted in a separate and distinct galaxy population than AGN undergoing powerful mechanically dominated accretion (radio AGN). Consistent with some previous studies, radiatively efficient AGN appear to be preferentially hosted in modest star-forming galaxies, with little dependence on AGN or galaxy luminosity. AGN exhibiting radio-emitting jets due to mechanically dominated accretion are almost exclusively observed in massive, passive galaxies. Crucially, we now provide strong evidence that the observed host-galaxy trends are independent of redshift. In particular, these different accretion-mode AGN have remained as separate galaxy populations throughout the last 9 Gyr. Furthermore, it appears that galaxies hosting AGN have evolved along the same path as galaxies that are not hosting AGN with little evidence for distinctly separate evolution
Parallel transport modeling of linear divertor simulators with fundamental ion cyclotron heating
The Material Plasma Exposure eXperiment (MPEX) is a steady state linear
device with the goal to perform plasma material interaction (PMI) studies at
future fusion reactor relevant conditions. A prototype of MPEX referred as
Porto-MPEX is designed to carry out research and development related to source,
heating and transport concepts on the planned full MPEX device. The auxiliary
heating schemes in MPEX are based on cyclotron resonance heating with radio
frequency (RF) waves. Ion cyclotron heating (ICH) and electron cyclotron
heating (ECH) in MPEX are used to independently heat the ions and electrons and
provide fusion divertor conditions ranging from sheath-limited to fully
detached divertor regimes at a material target. A Hybrid Particle-In-Cell code-
PICOS++ is developed and applied to understand the plasma parallel transport
during ICH heating in MPEX Proto-MPEX to the target. With this tool, evolution
of the distribution function of MPEX/Proto-MPEX ions is modeled in the presence
of (1) Coulomb collisions, (2) volumetric particle sources and (3) quasi-linear
RF-based ICH. The code is benchmarked against experimental data from Proto-MPEX
and simulation data from B2.5 EIRENE. The experimental observation of
density-drop near the target in Proto-MPEX and MPEX during ICH heating is
demonstrated and explained via physics-based arguments using PICOS++ modeling.
In fact, the density drops at the target during ICH in Proto-MPEX/MPEX to
conserve the flux and to compensate for the increased flow during ICH.
Furthermore, sensitivity scans of various plasma parameters with respect to ICH
power are performed for MPEX to investigate its role on plasma transport and
particle and energy fluxes at the target. Finally, we discuss the pathway to
model ECH in MPEX using the Hybrid PIC formulation herein presented for kinetic
electrons and fluid ions
Contribution of the Accretion Disk, Hot Corona, and Obscuring Torus to the Luminosity of Seyfert Galaxies: Integral and Spitzer Observations
We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spitzer mid-infrared (MIR) observations of a complete sample of 68 nearby active galactic nuclei (AGNs) from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal-to-noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L 15 μm∝L0.74 ± 0.06 HX. Assuming that the observed MIR emission is radiation from an accretion disk reprocessed in a surrounding dusty torus that subtends a solid angle decreasing with increasing luminosity (as inferred from the declining fraction of obscured AGNs), the intrinsic disk luminosity, L Disk, is approximately proportional to the luminosity of the corona in the 2-300 keV energy band, L Corona, with the L Disk/L Corona ratio varying by a factor of 2.1 around a mean value of 1.6. This ratio is a factor of ~2 smaller than for typical quasars producing the cosmic X-ray background. Therefore, over three orders of magnitude in luminosity, HX radiation carries a large, and roughly comparable, fraction of the bolometric output of AGNs. We estimate the cumulative bolometric luminosity density of local AGNs at ~(1-3) × 1040 erg s–1 Mpc–3. Finally, the Compton temperature ranges between kT c ≈ 2 and ≈6 keV for nearby AGNs, compared to kT c ≈ 2 keV for typical quasars, confirming that radiative heating of interstellar gas can play an important role in regulating SMBH growth
Engineering soil organic matter quality: Biodiesel Co-Product (BCP) stimulates exudation of nitrogenous microbial biopolymers
Biodiesel Co-Product (BCP) is a complex organic material formed during the transesterification of lipids. We investigated the effect of BCP on the extracellular microbial matrix or ‘extracellular polymeric substance’ (EPS) in soil which is suspected to be a highly influential fraction of soil organic matter (SOM). It was hypothesised that more N would be transferred to EPS in soil given BCP compared to soil given glycerol. An arable soil was amended with BCP produced from either 1) waste vegetable oils or 2) pure oilseed rape oil, and compared with soil amended with 99% pure glycerol; all were provided with 15N labelled KNO3. We compared transfer of microbially assimilated 15N into the extracellular amino acid pool, and measured concomitant production of exopolysaccharide. Following incubation, the 15N enrichment of total hydrolysable amino acids (THAAs) indicated that intracellular anabolic products had incorporated the labelled N primarily as glutamine and glutamate. A greater proportion of the amino acids in EPS were found to contain 15N than those in the THAA pool, indicating that the increase in EPS was comprised of bioproducts synthesised de novo. Moreover, BCP had increased the EPS production efficiency of the soil microbial community (μg EPS per unit ATP) up to approximately double that of glycerol, and caused transfer of 21% more 15N from soil solution into EPS-amino acids. Given the suspected value of EPS in agricultural soils, the use of BCP to stimulate exudation is an interesting tool to consider in the theme of delivering sustainable intensification
Megamaser Disks Reveal a Broad Distribution of Black Hole Mass in Spiral Galaxies
We use new precision measurements of black hole masses from water megamaser
disks to investigate scaling relations between macroscopic galaxy properties
and supermassive black hole (BH) mass. The megamaser-derived BH masses span
10^6-10^8 M_sun, while all the galaxy properties that we examine (including
stellar mass, central mass density, central velocity dispersion) lie within a
narrow range. Thus, no galaxy property correlates tightly with M_BH in ~L*
spiral galaxies. Of them all, stellar velocity dispersion provides the tightest
relation, but at fixed sigma* the mean megamaser M_BH are offset by -0.6+/-0.1
dex relative to early-type galaxies. Spiral galaxies with non-maser dynamical
BH masses do not show this offset. At low mass, we do not yet know the full
distribution of BH mass at fixed galaxy property; the non-maser dynamical
measurements may miss the low-mass end of the BH distribution due to inability
to resolve the spheres of influence and/or megamasers may preferentially occur
in lower-mass BHs.Comment: 6 pages, 4 figures, replaced to fix error: NGC 4594 is not a maser
galax
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