1,050 research outputs found
Parametric tests of a traction drive retrofitted to an automotive gas turbine
The results of a test program to retrofit a high performance fixed ratio Nasvytis Multiroller Traction Drive in place of a helical gear set to a gas turbine engine are presented. Parametric tests up to a maximum engine power turbine speed of 45,500 rpm and to a power level of 11 kW were conducted. Comparisons were made to similar drives that were parametrically tested on a back-to-back test stand. The drive showed good compatibility with the gas turbine engine. Specific fuel consumption of the engine with the traction drive speed reducer installed was comparable to the original helical gearset equipped engine
Neutral Gas Properties and Ly Escape in Extreme Green Pea Galaxies
Mechanisms regulating the escape of Ly photons and ionizing radiation
remain poorly understood. To study these processes we analyze VLA 21cm
observations of one Green Pea (GP), J160810+352809 (hereafter J1608), and HST
COS spectra of 17 GP galaxies at . All are highly ionized: J1608 has the
highest [O III] /[O II] for star-forming galaxies in
SDSS, and the 17 GPs have [O III]/[O II] . We set an upper limit on
J1608's HI mass of , near or below average compared to
similar mass dwarf galaxies. In the COS sample, eight GPs show Ly
absorption components, six of which also have Ly emission. The HI
column densities derived from Ly absorption are high, cm, well above the LyC optically thick limit. Using
low-ionization absorption lines, we measure covering fractions
(f_{\mbox{cov}}) of , and find that f_{\mbox{cov}} strongly
anti-correlates with Ly escape fraction. Low covering fractions may
facilitate Ly and LyC escape through dense neutral regions. GPs with
f_{\mbox{cov}}\sim1 all have low neutral gas velocities, while GPs with lower
f_{\mbox{cov}}=0.2-0.6 have a larger range of velocities. Conventional
mechanical feedback may help establish low f_{\mbox{cov}} in some cases,
whereas other processes may be important for GPs with low velocities. Finally,
we compare f_{\mbox{cov}} with proposed indicators of LyC escape. Ionizing
photon escape likely depends on a combination of neutral gas geometry and
kinematics, complicating the use of emission-line diagnostics for identifying
LyC emitters.Comment: 21 pages, 11 figures, accepted for publication in Ap
Detection of a Substantial Molecular Gas Reservoir in a brightest cluster galaxy at z = 1.7
We report the detection of CO(2-1) emission coincident with the brightest
cluster galaxy (BCG) of the high-redshift galaxy cluster SpARCS1049+56, with
the Redshift Search Receiver (RSR) on the Large Millimetre Telescope (LMT). We
confirm a spectroscopic redshift for the gas of z = 1.7091+/-0.0004, which is
consistent with the systemic redshift of the cluster galaxies of z = 1.709. The
line is well-fit by a single component Gaussian with a RSR resolution-corrected
FWHM of 569+/-63 km/s. We see no evidence for multiple velocity components in
the gas, as might be expected from the multiple image components seen in
near-infrared imaging with the Hubble Space Telescope. We measure the
integrated flux of the line to be 3.6+/-0.3 Jy km/s and, using alpha_CO = 0.8
Msun (K km s^-1 pc^2)^-1 we estimate a total molecular gas mass of
1.1+/-0.1x10^11 Msun and a M_H2/M_star ~ 0.4. This is the largest gas reservoir
detected in a BCG above z > 1 to date. Given the infrared-estimated star
formation rate of 860+/-130 Msun/yr, this corresponds to a gas depletion
timescale of ~0.1Gyr. We discuss several possible mechanisms for depositing
such a large gas reservoir to the cluster center -- e.g., a cooling flow, a
major galaxy-galaxy merger or the stripping of gas from several galaxies -- but
conclude that these LMT data are not sufficient to differentiate between them.Comment: accepted for publication in ApJ Letter
Measurement of ambient aerosol hydration state at Great Smoky Mountains National Park in the southeastern United States
We present results from two field deployments of a unique tandem differential mobility analyzer (TDMA) configuration with two primary capabilities: identifying alternative stable or meta-stable ambient aerosol hydration states associated with hysteresis in aerosol hydration behavior and determining the actual Ambient hydration State (AS-TDMA). This data set is the first to fully classify the ambient hydration state of aerosols despite recognition that hydration state significantly impacts the roles of aerosols in climate, visibility and heterogeneous chemistry. The AS-TDMA was installed at a site in eastern Tennessee on the border of Great Smoky Mountains National Park for projects during the summer of 2006 and winter of 2007–2008. During the summer, 12% of the aerosols sampled in continuous AS-TDMA measurements were found to posses two possible hydration states under ambient conditions. In every case, the more hydrated of the possible states was occupied. The remaining 88% did not posses multiple possible states. In continuous measurements during the winter, 49% of the aerosols sampled possessed two possible ambient hydration states; the remainder possessed only one. Of those aerosols with multiple possible ambient hydration states, 65% occupied the more hydrated state; 35% occupied the less hydrated state. This seasonal contrast is supported by differences in the fine particulate (PM<sub>2.5</sub>) composition and ambient RH as measured during the two study periods. In addition to seasonal summaries, this work includes case studies depicting the variation of hydration state with changing atmospheric conditions
Optical Morphologies of Millijansky Radio Galaxies Observed by HST and in the VLA FIRST Survey
We report on a statistical study of the 51 radio galaxies at the millijansky
flux level from the Faint Images of the Radio Sky at Twenty centimeters,
including their optical morphologies and structure obtained with the Hubble
Space Telescope. Our optical imaging is significantly deeper (~2 mag) than
previous studies with the superior angular resolution of space-based imaging.
We that find 8/51 (16%) of the radio sources have no optically identifiable
counterpart to AB~24 mag. For the remaining 43 sources, only 25 are
sufficiently resolved in the HST images to reliably assign a visual
classification: 15 (60%) are elliptical galaxies, 2 (8%) are late-type spiral
galaxies, 1 (4%) is an S0, 3 (12%) are point-like objects (quasars), and 4
(16%) are merger systems. We find a similar distribution of optical types with
measurements of the Sersic index. The optical magnitude distribution of these
galaxies peaks at I~20.7+-0.5 AB mag, which is ~3 mag brighter than the depth
of our typical HST field and is thus not due to the WFPC2 detection limit. This
supports the luminosity-dependent density evolutionary model, where the
majority of faint radio galaxies typically have L*-optical luminosities and a
median redshift of z~0.8 with a relatively abrupt redshift cut-off at z>~2. We
discuss our results in the context of the evolution of elliptical galaxies and
active galactic nuclei.Comment: 20 pages, 8 figures, 51 galaxy images, and 5 tables. Uses
emulateapj.cls and natbib.sty. Accepted to ApJS. High resolution images are
available upon reques
Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE -- II. Redshift distribution and nature of the submillimetre galaxy population
We report the results of the counterpart identification and a detailed
analysis of the physical properties of the 48 sources discovered in our deep
1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC
instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or
more robust or tentative counterpart candidate is found for 27 and 14 AzTEC
sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC,
and LABOCA 870 micron data. Five of the sources (10%) have two robust
counterparts each, supporting the idea that these galaxies are strongly
clustered and/or heavily confused. Photometric redshifts and star formation
rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The
median redshift of z~2.6 is similar to other earlier estimates, but we show
that 80% of the AzTEC-GOODS sources are at z>2, with a significant high
redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC
sources are extremely diverse, spanning 10 magnitude in the i- and K-band
photometry with median values of i=25.3 and K=22.6 and a broad range of red
colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in
the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x
10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000
solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is
independent of redshift or stellar mass. The resulting specific star formation
rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies
at z=0, and they extend the previously observed rapid rise in the SSFR with
redshift to z=2-5. These galaxies have a SFR high enough to have built up their
entire stellar mass within their Hubble time. We find only marginal evidence
for an AGN contribution to the near-IR and mid-IR SEDs. (abridged)Comment: 31 pages including 14 figures, accepted for publication in the MNRAS.
A higher quality Figure 1 is also included as Figure1.jp
Evaluation of organic markers for chemical mass balance source apportionment at the Fresno Supersite
International audienceSources of PM2.5 at the Fresno Supersite during high PM2.5 episodes occurring from 15 December 2000?3 February 2001 were estimated with the Chemical Mass Balance (CMB) receptor model. The ability of source profiles with organic markers to distinguish motor vehicle, residential wood combustion (RWC), and cooking emissions was evaluated with simulated data. Organics improved the distinction between gasoline and diesel vehicle emissions and allowed a more precise estimate of the cooking source contribution. Sensitivity tests using average ambient concentrations showed that the gasoline vehicle contribution was not resolved without organics. Organics were not required to estimate hardwood contributions. The most important RWC marker was the water-soluble potassium ion. The estimated cooking contribution did not depend on cholesterol because its concentrations were below the detection limit in most samples. Winter time source contributions were estimated by applying the CMB model to individual and average sample concentrations. RWC was the largest source, contributing 29?31% of measured PM2.5. Hardwood and softwood combustion accounted for 16?17% and 12?15%, respectively. Secondary ammonium nitrate and motor vehicle emissions accounted for 31?33% and 9?15%, respectively. The gasoline vehicle contribution (3?10%) was comparable to the diesel vehicle contribution (5?6%). The cooking contribution was 5?19% of PM2.5. Fresno source apportionment results were consistent with those estimated in previous studies
Measuring the Halo Mass of z=3 Damped Ly-alpha Absorbers from the Absorber-Galaxy Cross-correlation
[Abridged] We test the reliability of a method to measure the mean halo mass
of Damped Ly-alpha absorbers (DLAs). The method is based on measuring the ratio
of the cross-correlation between DLAs and galaxies to the auto-correlation of
the galaxies themselves (), which is (in linear theory)
the ratio of their bias factor. This is shown to be true irrespective of the
galaxy redshift distribution, provided that one uses the same galaxies for the
two correlation functions. The method is applicable to all redshifts. Here, we
focus on z=3 DLAs and we demonstrate that the method robustly constrains the
mean DLA halo mass using smoothed particle hydrodynamics (SPH) cosmological
simulations. If we use the bias formalism of Mo & White with the DLA and galaxy
mass distributions of these simulations, we predict a bias ratio of 0.771.
Direct measurement from the simulations of st yields a
ratio of 0.73+/-0.08, in excellent agreement with that prediction.
Equivalently, inverting the measured correlation ratio to infer a mean DLA halo
mass yields (log. averaging, in solar units) =11.13+/-013, in
excellent agreement with the true value in the simulations: 11.16. The cross-
correlation method thus appears to yield a robust estimate of the average host
halo mass even though the DLAs and the galaxies occupy a broad mass spectrum of
halos, and massive halos contain multiple galaxies with DLAs. We show that the
inferred mean DLA halo mass is independent of the galaxy sub-sample used, i.e.
the cross-correlation technique is also reliable. Our results imply that the
cross-correlation length between DLAs and LBGs is predicted to be, at most,
2.85 Mpc. Future observations will soon distinguish models in which DLAs are in
low mass halos from those in which DLAs are in massive halos.Comment: 15 pages, 7 figures, to be published in ApJ 2005 July 20th (Full
resolution of Fig.2 at
http://www.mpe.mpg.de/~nbouche/papers/Xcorr/f2-orig.eps); minor changes to
match the published tex
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