2,589 research outputs found
Transient dynamics and structure of optimal excitations in thermocapillary spreading: Precursor film model
Linearized modal stability theory has shown that the thermocapillary spreading of a liquid film on a homogeneous, completely wetting surface can produce a rivulet instability at the advancing front due to formation of a capillary ridge. Mechanisms that drain fluid from the ridge can stabilize the flow against rivulet formation. Numerical predictions from this analysis for the film speed, shape, and most unstable wavelength agree remarkably well with experimental measurements even though the linearized disturbance operator is non-normal, which allows transient growth of perturbations. Our previous studies using a more generalized nonmodal stability analysis for contact lines models describing partially wetting liquids (i.e., either boundary slip or van der Waals interactions) have shown that the transient amplification is not sufficient to affect the predictions of eigenvalue analysis. In this work we complete examination of the various contact line models by studying the influence of an infinite and flat precursor film, which is the most commonly employed contact line model for completely wetting films. The maximum amplification of arbitrary disturbances and the optimal initial excitations that elicit the maximum growth over a specified time, which quantify the sensitivity of the film to perturbations of different structure, are presented. While the modal results for the three different contact line models are essentially indistinguishable, the transient dynamics and maximum possible amplification differ, which suggests different transient dynamics for completely and partially wetting films. These differences are explained by the structure of the computed optimal excitations, which provides further basis for understanding the agreement between experiment and predictions of conventional modal analysis
Equal Protection and Aesthetic Zoning: A Possible Crack and a Preemptive Repair
In Village of Willowbrook v. Olech, the property owner alleged the Village intentionally demanded a 33-foot easement as a condition of connecting her property to the municipal water supply where the Village required only a 15-foot easement from other similarly situated property owners. The complaint further described the village\u27s demand as irrational and wholly arbitrary. According to the Seventh Circuit, the property owner could allege an equal protection violation by asserting the state\u27s action was motivated solely by a spiteful effort to \u27get\u27 him for reasons wholly unrelated to any legitimate state objective. On appeal, the Supreme Court agreed, holding that [t]hese allegations, quite apart from the Village\u27s subjective motivation, are sufficient to state a claim for relief under traditional equal protection analysis. Although it affirmed the Seventh Circuit\u27s decision, the Court explicitly [did] not reach the alternative theory of \u27subjective ill will\u27 relied on by [the lower] court.
This article considers whether Olech infers that unreasoned zoning decisions violate the Equal Protection Clause, and explores the meaning of similarly situated. The authors further examine what type of evidence might be necessary to ensure that aesthetic regulations pass constitutional muster with respect to the Fourteenth Amendment\u27s Equal Protection Clause
Acute respiratory distress secondary to posterior mediastinal goiter: a case report
Large posterior mediastinal goiters are extremely rare. Progressive enlargement and possible compression of adjacent structures, as well as malignant potential necessitate that these goiters should be surgically excised. A review of mediastinal tumors, specifically intra-thoracic goiters is presented along with a case report of acute respiratory compromise secondary to tracheal compression by a large posterior goiter
Racial Disparities in Intravenous Recombinant Tissue Plasminogen Activator Use Persist at Primary Stroke Centers.
BACKGROUND: Primary stroke centers (PSCs) utilize more recombinant tissue plasminogen activator (rt-PA) than non-PSCs. The impact of PSCs on racial disparities in rt-PA use is unknown.
METHODS AND RESULTS: We used data from the Nationwide Inpatient Sample from 2004 to 2010, limited to states that publicly reported hospital identity and race. Hospitals certified as PSCs by The Joint Commission were identified. Adults with a diagnosis of ischemic stroke were analyzed. Rt-PA use was defined by the International Classification of Diseases, 9th Revision procedure code 99.10. Discharges (304 152 patients) from 26 states met eligibility criteria, and of these 71.5% were white, 15.0% black, 7.9% Hispanic, and 5.6% other. Overall, 24.7% of white, 27.4% of black, 16.2% of Hispanic, and 29.8% of other patients presented to PSCs. A higher proportion received rt-PA at PSCs than non-PSCs in all race/ethnic groups (white 7.6% versus 2.6%, black 4.8% versus 2.0%, Hispanic 7.1% versus 2.4%, other 7.2% versus 2.5%, all P
CONCLUSIONS: Racial disparities in intravenous rt-PA use were not reduced by presentation to PSCs. Black patients were less likely to receive thrombolytic treatment than white patients at both non-PSCs and PSCs. Hispanic patients were less likely to be seen at PSCs relative to white patients and were less likely to receive intravenous rt-PA in the fully adjusted model
The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214
We report on X-ray and optical observations of the X-ray burster EXO
1747-214. This source is an X-ray transient, and its only known outburst was
observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data
to derive the source position, column density, and a distance upper limit using
its peak X-ray burst flux. We observed the EXO 1747-214 field in 2003 July with
the Chandra X-ray Observatory to search for the quiescent counterpart. We found
one possible candidate just outside the EXOSAT error circle, but we cannot rule
out the possibility that the source is unrelated to EXO 1747-214. Our
conclusion is that the upper limit on the unabsorbed 0.3-8 keV luminosity is L
< 7E31 erg/s, making EXO 1747-214 one of the faintest neutron star transients
in quiescence. We compare this luminosity upper limit to the quiescent
luminosities of 19 neutron star and 14 black hole systems and discuss the
results in the context of the differences between neutron stars and black
holes. Based on the theory of deep crustal heating by Brown and coworkers, the
luminosity implies an outburst recurrence time of >1300 yr unless some form of
enhanced cooling occurs within the neutron star. The position of the possible
X-ray counterpart is consistent with three blended optical/IR sources with
R-magnitudes between 19.4 and 19.8 and J-magnitudes between 17.2 and 17.6. One
of these sources could be the quiescent optical/IR counterpart of EXO 1747-214.Comment: 7 pages, accepted by the Astrophysical Journa
Spectroscopic Identification of a Proto-Cluster at z=2.300: Environmental Dependence of Galaxy Properties at High Redshift
We have discovered a highly significant over-density of galaxies at
z=2.300+/-0.015 in the course of a redshift survey designed to select
star-forming galaxies in the redshift range z=2.3+/-0.4 in the field of the
bright z=2.72 QSO HS1700+643. The structure has a redshift-space galaxy
over-density of delta_g,z ~= 7 and an estimated matter over-density in real
space of delta_m ~= 1.8, indicating that it will virialize by z~0 with a mass
scale of ~= 1.4x10^15 M_sun, that of a rich galaxy cluster. Detailed modeling
of the spectral energy distribution -- from the rest-far-UV to the rest-near-IR
-- of the 72 spectroscopically confirmed galaxies in this field for which we
have obtained K_s and Spitzer/IRAC photometry, allows for a first direct
comparison of galaxy properties as a function of large-scale environment at
high redshift. We find that galaxies in the proto-cluster environment have mean
stellar masses and inferred ages that are ~2 times larger (at z=2.30) than
identically UV-selected galaxies outside of the structure, and show that this
is consistent with simple theoretical expectations for the acceleration of
structure formation in a region that is over-dense on large scales by the
observed amount. The proto-cluster environment contains a significant number of
galaxies that already appear old, with large stellar masses (>10^11 M_sun), by
z=2.3.Comment: 7 pages including 3 figures. Accepted for publication in ApJ. Typo
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Morphologies of Galaxies in and around a Protocluster at z=2.300
We present results from the first robust investigation of galaxy morphology
as a function of environment at z>1.5. Our study is motivated by the fact that
star-forming galaxies contained within a protocluster at z=2.3 in the HS1700+64
field have significantly older ages and larger stellar masses on average than
those at similar redshifts but more typical environmental densities. In the
analysis of HST/ACS images, we apply non-parametric statistics to characterize
the rest-frame UV morphologies of a sample of 85 UV-selected star-forming
galaxies at z=1.7-2.9, 22 of which are contained in the protocluster. The
remaining 63 control-sample galaxies are not in the protocluster but have a
similar mean redshift of ~2.3. We find no environmental dependence for the
distributions of morphological properties. Combining the measured morphologies
with the results of population synthesis modeling, we find only weak
correlations, if any, between morphological and stellar population properties
such as stellar mass, age, extinction and star-formation rate. Given the
incomplete census of the protocluster galaxy population, and the lack of
correlation between rest-frame UV morphology and star-formation history at z~2
within our sample, the absence of environmental trends in the distribution of
morphological properties is not surprising. Additionally, using a larger sample
of photometric candidates, we compare morphological distributions for 282
UV-selected and 43 near-IR-selected galaxies. While the difference in the
degree of nebulosity between the two samples appears to be a byproduct of the
fainter average rest-frame UV surface brightness of the near-IR-selected
galaxies, we find that, among the lowest surface brightness galaxies, the
near-IR-selected objects have significantly smaller angular sizes (abridged).Comment: 25 pages including 16 figures. Accepted for publication in ApJ.
Version with full resolution figures available at
http://www.astro.princeton.edu/~apeter/LBG/papers/peter2007_fullres.ps.g
The Physical Nature of Rest-UV Galaxy Morphology During the Peak Epoch of Galaxy Formation
Motivated by the irregular and little-understood morphologies of z ~ 2 - 3
galaxies, we use non-parametric coefficents to quantify the morphologies of 216
galaxies which have been spectroscopically confirmed to lie at redshifts z =
1.8 - 3.4 in the GOODS-N field. Using measurements of ultraviolet (UV) and
optical spectral lines, multi-band photometric data, and stellar population
models we statistically assess possible correlations between galaxy morphology
and physical observables such as stellar mass, star formation rate, and the
strength of galaxy-scale outflows. We find evidence that dustier galaxies have
more nebulous UV morphologies and that larger, more luminous galaxies may drive
stronger outflows, but otherwise conclude that UV morphology is either
statistically decoupled from the majority of physical observables or determined
by too complex a combination of physical processes to provide characterizations
with predictive power. Given the absence of strong correlations between UV
morphology and physical parameters such as star formation rates, we are
therefore unable to support the hypothesis that morphologically irregular
galaxies predominantly represent major galaxy mergers. Comparing galaxy
samples, we find that IR-selected BzK galaxies and radio-selected submillimeter
galaxies (SMGs) have UV morphologies similar to the optically selected sample,
while distant red galaxies (DRGs) are more nebulous.Comment: 26 pages. Accepted for publication in the ApJ. Version with full
resolution figures is available at
http://www.astro.caltech.edu/~drlaw/Papers/UVmorph.pd
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De novo formation of an aggregation pheromone precursor by an isoprenyl diphosphate synthase-related terpene synthase in the harlequin bug.
Insects use a diverse array of specialized terpene metabolites as pheromones in intraspecific interactions. In contrast to plants and microbes, which employ enzymes called terpene synthases (TPSs) to synthesize terpene metabolites, limited information from few species is available about the enzymatic mechanisms underlying terpene pheromone biosynthesis in insects. Several stink bugs (Hemiptera: Pentatomidae), among them severe agricultural pests, release 15-carbon sesquiterpenes with a bisabolene skeleton as sex or aggregation pheromones. The harlequin bug, Murgantia histrionica, a specialist pest of crucifers, uses two stereoisomers of 10,11-epoxy-1-bisabolen-3-ol as a male-released aggregation pheromone called murgantiol. We show that MhTPS (MhIDS-1), an enzyme unrelated to plant and microbial TPSs but with similarity to trans-isoprenyl diphosphate synthases (IDS) of the core terpene biosynthetic pathway, catalyzes the formation of (1S,6S,7R)-1,10-bisaboladien-1-ol (sesquipiperitol) as a terpene intermediate in murgantiol biosynthesis. Sesquipiperitol, a so-far-unknown compound in animals, also occurs in plants, indicating convergent evolution in the biosynthesis of this sesquiterpene. RNAi-mediated knockdown of MhTPS mRNA confirmed the role of MhTPS in murgantiol biosynthesis. MhTPS expression is highly specific to tissues lining the cuticle of the abdominal sternites of mature males. Phylogenetic analysis suggests that MhTPS is derived from a trans-IDS progenitor and diverged from bona fide trans-IDS proteins including MhIDS-2, which functions as an (E,E)-farnesyl diphosphate (FPP) synthase. Structure-guided mutagenesis revealed several residues critical to MhTPS and MhFPPS activity. The emergence of an IDS-like protein with TPS activity in M. histrionica demonstrates that de novo terpene biosynthesis evolved in the Hemiptera in an adaptation for intraspecific communication
The Mass-Metallicity Relation at z~2
We use a sample of 87 rest-frame UV-selected star-forming galaxies with mean
spectroscopic redshift z=2.26 to study the correlation between metallicity and
stellar mass at high redshift. Using stellar masses determined from SED fitting
to 0.3-8 micron photometry, we divide the sample into six bins in stellar mass,
and construct six composite H-alpha+[NII] spectra from all of the objects in
each bin. We estimate the mean oxygen abundance in each bin from the
[NII]/H-alpha ratio, and find a monotonic increase in metallicity with
increasing stellar mass, from 12+log(O/H) =
2.7e9 Msun to 12+log(O/H) = 8.6 for galaxies with = 1e11 Msun. We use
the empirical relation between star formation rate density and gas density to
estimate the gas fractions of the galaxies, finding an increase in gas fraction
with decreasing stellar mass. These gas fractions combined with the observed
metallicities allow the estimation of the effective yield y_eff as a function
of stellar mass; in constrast to observations in the local universe which show
a decrease in y_eff with decreasing baryonic mass, we find a slight increase.
Such a variation of metallicity with gas fraction is best fit by a model with
supersolar yield and an outflow rate ~4 times higher than the star formation
rate. We conclude that the mass-metallicity relation at high redshift is driven
by the increase in metallicity as the gas fraction decreases through star
formation, and is likely modulated by metal loss from strong outflows in
galaxies of all masses. There is no evidence for preferential loss of metals
from low mass galaxies as has been suggested in the local universe. [Abridged]Comment: 18 pages, 9 figures, 2 tables; accepted for publication in Ap
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