2,244 research outputs found
A stochastic model of turbulent mixing with chemical reaction: Nitric oxide formulation in a plug-flow burner
A stochastic model of turbulent mixing was developed for a reactor in which mixing is represented by n-body fluid particle interactions. The model was used to justify the assumption (made in previous investigations of the role of turbulent mixing on burner generated thermal nitric oxide and carbon monoxide emissions) that for a simple plug flow reactor, composition nonuniformities can be described by a Gaussian distribution function in the local fuel:air equivalence ratio. Recent extensions of this stochastic model to include the combined effects of turbulent mixing and secondary air entrainment on thermal generation of nitric oxide in gas turbine combustors are discussed. Finally, rate limited upper and lower bounds of the nitric oxide produced by thermal fixation of molecular nitrogen and oxidation of organically bound fuel nitrogen are estimated on the basis of the stochastic model for a plug flow burner; these are compared with experimental measurements obtained using a laboratory burner operated over a wide range of test conditions; good agreement is obtained
Ventricular Tachycardia in the Absence of Structural Heart Disease
In up to 10% of patients who present with ventricular tachycardia (VT), obvious structural heart disease is not identified. In such patients, causes of ventricular arrhythmia include right ventricular outflow tract (RVOT) VT, extrasystoles, idiopathic left ventricular tachycardia (ILVT), idiopathic propranolol-sensitive VT (IPVT), catecholaminergic polymorphic VT (CPVT), Brugada syndrome, and long QT syndrome (LQTS). RVOT VT, ILVT, and IPVT are referred to as idiopathic VT and generally do not have a familial basis. RVOT VT and ILVT are monomorphic, whereas IPVT may be monomorphic or polymorphic. The idiopathic VTs are classified by the ventricle of origin, the response to pharmacologic agents, catecholamine dependence, and the specific morphologic features of the arrhythmia. CPVT, Brugada syndrome, and LQTS are inherited ion channelopathies. CPVT may present as bidirectional VT, polymorphic VT, or catecholaminergic ventricular fibrillation. Syncope and sudden death in Brugada syndrome are usually due to polymorphic VT. The characteristic arrhythmia of LQTS is torsades de pointes. Overall, patients with idiopathic VT have a better prognosis than do patients with ventricular arrhythmias and structural heart disease. Initial treatment approach is pharmacologic and radiofrequency ablation is curative in most patients. However, radiofrequency ablation is not useful in the management of inherited ion channelopathies. Prognosis for patients with VT secondary to ion channelopathies is variable. High-risk patients (recurrent syncope and sudden cardiac death survivors) with inherited ion channelopathies benefit from implantable cardioverter-defibrillator placement. This paper reviews the mechanism, clinical presentation, and management of VT in the absence of structural heart disease
COLA. III. Radio Detection of Active Galactic Nucleus in Compact Moderate Luminosity Infrared Galaxies
We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L_(IR) = 10^(11.01) L_â) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (~10^(21) W Hz^(â1)) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity
Kinematic Masses of Super Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy
Using high-resolution (R~22,000) near-infrared (1.51 -- 1.75 microns) spectra
from Keck Observatory, we measure the kinematic masses of two super star
clusters in M82. Cross-correlation of the spectra with template spectra of cool
evolved stars gives stellar velocity dispersions of sigma_r=15.9 +/- 0.8 km/s
for MGG-9 and sigma_r=11.4 +/- 0.8 km/s for MGG-11. The cluster spectra are
dominated by the light of red supergiants, and correlate most closely with
template supergiants of spectral types M0 and M4.5. We fit King models to the
observed profiles of the clusters in archival HST/NICMOS images to measure the
half-light radii. Applying the virial theorem, we determine masses of 1.5 +/-
0.3 x 10^6 M_sun for MGG-9 and 3.5 +/- 0.7 x 10^5 M_sun for MGG-11. Population
synthesis modelling suggests that MGG-9 is consistent with a standard initial
mass function, whereas MGG-11 appears to be deficient in low-mass stars
relative to a standard IMF. There is, however, evidence of mass segregation in
the clusters, in which case the virial mass estimates would represent lower
limits.Comment: 16 pages, 8 figures; ApJ, in pres
Star Formation Across the Taffy Bridge: UGC 12914/15
We present BIMA two-field mosaic CO(1-0) images of the Taffy galaxies (UGC
12914/15), which show the distinct taffy-like radio continuum emission bridging
the two spiral disks. Large amounts of molecular gas (1.4 x 10^{10} Msun, using
the standard Galactic CO-to-H conversion applicable to Galactic disk giant
molecular clouds [GMCs]) were clearly detected throughout the taffy bridge
between the two galaxies, which, as in the more extreme case of HI, presumably
results from a head-on collision between the two galaxies. The highest CO
concentration between the two galaxies corresponds to the H_alpha source in the
taffy bridge near the intruder galaxy UGC 12915. This HII region is also
associated with the strongest source of radio continuum in the bridge, and
shows both morphological and kinematic connections to UGC 12915. The overall CO
distribution of the entire system agrees well with that of the radio continuum
emission, particularly in the taffy bridge. This argues for the star formation
origin of a significant portion of the radio continuum emission. Compared to
the HI morphology and kinematics, which are strongly distorted owing to the
high-speed collision, CO better defines the orbital geometry and impact
parameter of the interaction, as well as the disk properties (e.g., rotation,
orientation) of the progenitor galaxies. Based on the 20cm-to-CO ratio maps, we
conclude that the starburst sites are primarily located in UGC 12915 and the
H_alpha source in the bridge and show that the molecular gas in the taffy
bridge is forming into stars with star formation efficiency comparable to that
of the target galaxy UGC 12914 and similar to that in the Galactic disk.Comment: Minor typo/style corrections to match with the published version (AJ,
Nov. issue). A single .ps.gz file of the entire paper can be downloaded from
http://spider.ipac.caltech.edu/staff/gao/Taffy/all.ps.g
Radio-Luminous Southern Seyfert Galaxies. I. Radio Images and Selected Optical/Near-Infrared Spectroscopy
This is the first of two papers in which a study is made of a sample of 12
southern radio-luminous Seyfert galaxies. Our aim is to investigate possible
correlations between radio morphology and nuclear/circumnuclear emission-line
properties. In this paper we present radio images at 13, 6, and 3 cm taken with
the Australia Telescope Compact Array (ATCA), global far-infrared (FIR)
properties for the whole sample, and optical and near-infrared (NIR)
spectroscopy of an interesting subset. We find a mixture of radio morphologies,
including linear, diffuse and compact sources. When the FIR colors of the
galaxies are considered there is an indication that the compact radio sources
have warmer FIR colors than the diffuse sources, whereas the linear sources
span a wide range of FIR colors. There is a wide variation in radio
spectral-indices, suggesting that free-free absorption is significant in some
systems, particularly IRAS 11249-2859, NGC 4507, and NGC 7213. Detailed
emission-line studies are presented of 4 galaxies IC 3639, NGC 5135, NGC 3393 &
IRAS 11249-2859. In IC 3639 we present evidence of vigorous, compact star
formation enclosed by very extended [OI]6300 emission, suggestive of the
boundary between a diffuse outflow and the surrounding ISM. In another galaxy,
IC 5063, we see evidence for the possible interaction of a highly collimated
outflow and the surrounding rotating inner disk. Of the 5 galaxies which show
compact radio emission, 4 have radio/FIR flux ratios consistent with an
energetically dominant AGN, whereas IC 4995 exhibits evidence for a very
compact starburst.Comment: 42 pages, including 7 tables, latex, 19 jpeg figures, Accepted to
ApJ. Replacement updates coordintes of galaxies in Table
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The Rapid Determination of Chemical Oxygen Demand in Waste Waters and Effluents using Flow Injection Analysis
The Role of a Hot Gas Environment on the Evolution of Galaxies
Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres
Progressive Star Bursts and High Velocities in the Infrared Luminous, Colliding Galaxy Arp 118
In this paper we demonstrate for the first time the connection between the
spatial and temporal progression of star formation and the changing locations
of the very dense regions in the gas of a massive disk galaxy (NGC 1144) in the
aftermath of its collision with a massive elliptical (NGC 1143). These two
galaxies form the combined object Arp 118, a collisional ring galaxy system.
The results of 3D, time-dependent, numerical simulations of the behavior of the
gas, stars, and dark matter of a disk galaxy and the stars and dark matter in
an elliptical during a collision are compared with multiwavelength observations
of Arp 118. The collision that took place approximately 22 Myr ago generated a
strong, non-linear density wave in the stars and gas in the disk of NGC 1144,
causing the gas to became clumped on a large scale. This wave produced a series
of superstarclusters along arcs and rings that emanate from the central point
of impact in the disk. The locations of these star forming regions match those
of the regions of increased gas density predicted the time sequence of models.
The models also predict the large velocity gradients observed across the disk
of NGC 1144. These are due to the rapid radial outflow of gas coupled to large
azimuthal velocities in the expanding ring, caused by the impact of the massive
intruder.Comment: 12 pages in document, and 8 figures (figures are separate from the
document's file); Submitted to Astrophysical Journal Letter
Powerful H Emission and Star Formation on the Interacting Galaxy System Arp 143: Observations with Spitzer and GALEX
We present new mid-infrared (m) and ultraviolet (1539 -- 2316 \AA)
observations of the interacting galaxy system Arp 143 (NGC 2444/2445) from the
Spitzer Space Telescope and GALEX. In this system, the central nucleus of NGC
2445 is surrounded by knots of massive star-formation in a ring-like structure.
We find unusually strong emission from warm H associated with an expanding
shock wave between the nucleus and the western knots. At this ridge, the flux
ratio between H and PAH emission is nearly ten times higher than in the
nucleus. Arp 143 is one of the most extreme cases known in that regard. From
our multi-wavelength data we derive a narrow age range of the star-forming
knots between 2 Myr and 7.5 Myr, suggesting that the ring of knots was formed
almost simultaneously in response to the shock wave traced by the H
emission. However, the knots can be further subdivided in two age groups: those
with an age of 2--4 Myr (knots A, C, E, and F), which are associated with
m emission from PAHs, and those with an age of 7-8 Myr (knots D and G),
which show little or no m emission shells surrounding them. We attribute
this finding to an ageing effect of the massive clusters which, after about 6
Myr, no longer excite the PAHs surrounding the knots.Comment: 19 pages, 11 figures, including tables at the end; accepted by Ap
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