656 research outputs found
Molecular Line Profile Fitting with Analytic Radiative Transfer Models
We present a study of analytic models of starless cores whose line profiles
have ``infall asymmetry,'' or blue-skewed shapes indicative of contracting
motions. We compare the ability of two types of analytical radiative transfer
models to reproduce the line profiles and infall speeds of centrally condensed
starless cores whose infall speeds are spatially constant and range between 0
and 0.2 km s-1. The model line profiles of HCO+ (J=1-0) and HCO+ (J=3-2) are
produced by a self-consistent Monte Carlo radiative transfer code. The analytic
models assume that the excitation temperature in the front of the cloud is
either constant (``two-layer'' model) or increases inward as a linear function
of optical depth (``hill'' model). Each analytic model is matched to the line
profile by rapid least-squares fitting.
The blue-asymmetric line profiles with two peaks, or with a blue shifted peak
and a red shifted shoulder, can be well fit by the ``HILL5'' model (a five
parameter version of the hill model), with an RMS error of 0.02 km s-1. A peak
signal to noise ratio of at least 30 in the molecular line observations is
required for performing these analytic radiative transfer fits to the line
profiles.Comment: 48 pages, 20 figures, accepted for publication in Ap
Star Formation in Bright Rimmed Clouds. I. Millimeter and Submillimeter Molecular Line Surveys
We present the results of the first detailed millimeter and submillimeter
molecular line survey of bright rimmed clouds, observed at FCRAO in the CO
(J=1-0), C18O (J=1-0), HCO+ (J=1-0), H13CO+ (J=1-0), and N2H+ (J=1-0)
transitions, and at the HHT in the CO (J=2-1), HCO+ (J=3-2), HCO+ (J=4-3),
H13CO+ (J=3-2), and H13CO+ (J=4-3) molecular line transitions. The source list
is composed of a selection of bright rimmed clouds from the catalog of such
objects compiled by Sugitani et al. (1991). We also present observations of
three Bok globules done for comparison with the bright rimmed clouds. We find
that the appearance of the millimeter CO and HCO+ emission is dominated by the
morphology of the shock front in the bright rimmed clouds. The HCO+ (J=1-0)
emission tends to trace the swept up gas ridge and overdense regions which may
be triggered to collapse as a result of sequential star formation. Five of the
seven bright rimmed clouds we observe seem to have an outflow, however only one
shows the spectral line blue-asymmetric signature that is indicative of infall,
in the optically thick HCO+ emission. We also present evidence that in bright
rimmed clouds the nearby shock front may heat the core from outside-in thereby
washing out the normally observed line infall signatures seen in isolated star
forming regions. We find that the derived core masses of these bright rimmed
clouds are similar to other low and intermediate mass star forming regions.Comment: 67 pages, including 35 figures and 6 tables. Accepted for publication
in ApJ. Version with embedded full-resolution figures available at
http://www.astro.umass.edu/~devries/brc1
A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging
We provide a quantitative description and statistical interpretation of the
optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS)
has obtained repeated imaging in five UV-to-IR photometric bands for 33,881
spectroscopically confirmed quasars. About 10,000 quasars have an average of 60
observations in each band obtained over a decade along Stripe 82 (S82), whereas
the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed
time lags span the range from a day to almost 10 years, and constrain quasar
variability at rest-frame time lags of up to 4 years, and at rest-frame
wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of
quasars from the SDSS Data Release 7 that have been observed at least twice in
SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it
to analyze the ensemble properties of quasar variability. Based on a damped
random walk (DRW) model defined by a characteristic time scale and an
asymptotic variability amplitude that scale with the luminosity, black hole
mass, and rest wavelength for individual quasars calibrated in S82, we can
fully explain the ensemble variability statistics of the non-S82 quasars such
as the exponential distribution of large magnitude changes. All available data
are consistent with the DRW model as a viable description of the optical
continuum variability of quasars on time scales of ~5-2000 days in the rest
frame. We use these models to predict the incidence of quasar contamination in
transient surveys such as those from PTF and LSST.Comment: 33 pages, 19 figures, replaced with accepted version. Catalog is
available at http://www.astro.washington.edu/users/ivezic/macleod/qso_dr7
The Spitzer c2d Survey of Nearby Dense Cores: VI. The Protostars of Lynds Dark Nebula 1221
Observations of Lynds Dark Nebula 1221 from the Spitzer Space Telescope are
presented. These data show three candidate protostars towards L1221, only two
of which were previously known. The infrared observations also show signatures
of outflowing material, an interpretation which is also supported by radio
observations with the Very Large Array. In addition, molecular line maps from
the Five College Radio Astronomy Observatory are shown.
One-dimensional dust continuum modelling of two of these protostars, IRS1 and
IRS3, is described. These models show two distinctly different protostars
forming in very similar environments. IRS1 shows a higher luminosity and larger
inner radius of the envelope than IRS3. The disparity could be caused by a
difference in age or mass, orientation of outflow cavities, or the impact of a
binary in the IRS1 core.Comment: accepted for publication in Ap
Sequence-complementarity dependent co-assembly of phosphodiester-linked aromatic donor-acceptor trimers.
We have created sequenced phosphoester-linked trimers of aromatic donor/acceptors which participate in charge-transfer interactions. Each sequence displays characteristic self-assembly, and complementary sequences interact with each other to produce new nanostructures and thermochromism. This paves the way towards new functional nanomaterials which make bio-analogous use of sequence to tune structure
Who's Cueing Whom? Mass-elite linkages and the future of European integration
The 2005 French and Dutch referendum campaigns were characterized by an alleged disconnect between pro-European political elites and Eurosceptic masses. Past evidence regarding elite-mass linkages in the context of European integration has been conflicting. Whereas some scholars argue that political elites respond to the changing preferences of their electorates, others suggest that party elites cue the mass public through a process of information and persuasion. We contend that these conflicting results stem from the reciprocal nature of elite-mass linkages and estimate a series of dynamic simultaneous equations models to account for this reverse causation. Using Euro-barometer and expert survey data from 1984-2002, we find evidence of a dual-process model, whereby party elites both respond to and shape the views of their supporters. We also find that the strength of these results is contingent on several factors, including the type of electoral system, intra-party dissent and voter characteristics. Copyright © 2007 Sage Publications
XMM-NEWTON Detection of X-ray Emission from the Compact Steep Spectrum Radio Galaxy 3C303.1
Using XMM we detect faint unresolved X-ray emission from the Compact Steep
Spectrum radio galaxy 3C303.1. We detect a thermal component at kT = 0.8 keV
which seems likely to be produced in the ISM of the host galaxy. There is
evidence for a second component in the spectrum whose nature is currently
ambiguous. Plausible hypotheses for the second component include (1) hot gas
shocked by the expansion of the radio source, and (2) Synchrotron self-Compton
emission from the southern radio lobe if the magnetic field is below the
equipartition value by a factor of about 3.5
Using Real-World Data to Guide Ustekinumab Dosing Strategies for Psoriasis: A Prospective Pharmacokinetic-Pharmacodynamic Study.
Variation in response to biologic therapy for inflammatory diseases, such as psoriasis, is partly driven by variation in drug exposure. Real-world psoriasis data were used to develop a pharmacokinetic/pharmacodynamic (PK/PD) model for the first-line therapeutic antibody ustekinumab. The impact of differing dosing strategies on response was explored. Data were collected from a UK prospective multicenter observational cohort (491 patients on ustekinumab monotherapy, drug levels, and anti-drug antibody measurements on 797 serum samples, 1,590 measurements of Psoriasis Area Severity Index (PASI)). Ustekinumab PKs were described with a linear one-compartment model. A maximum effect (Emax ) model inhibited progression of psoriatic skin lesions in the turnover PD mechanism describing PASI evolution while on treatment. A mixture model on half-maximal effective concentration identified a potential nonresponder group, with simulations suggesting that, in future, the model could be incorporated into a Bayesian therapeutic drug monitoring "dashboard" to individualize dosing and improve treatment outcomes
Early Target Cells of Measles Virus after Aerosol Infection of Non-Human Primates
Measles virus (MV) is highly infectious, and has long been thought to enter the host by infecting epithelial cells of the respiratory tract. However, epithelial cells do not express signaling lymphocyte activation molecule (CD150), which is the high-affinity cellular receptor for wild-type MV strains. We have generated a new recombinant MV strain expressing enhanced green fluorescent protein (EGFP), based on a wild-type genotype B3 virus isolate from Khartoum, Sudan (KS). Cynomolgus macaques were infected with a high dose of rMVKSEGFP by aerosol inhalation to ensure that the virus could reach the full range of potential target cells throughout the entire respiratory tract. Animals were euthanized 2, 3, 4 or 5 days post-infection (d.p.i., n = 3 per time point) and infected (EGFP+) cells were identified at all four time points, albeit at low levels 2 and 3 d.p.i. At these earliest time points, MV-infected cells were exclusively detected in the lungs by fluorescence microscopy, histopathology and/or virus isolation from broncho-alveolar lavage cells. On 2 d.p.i., EGFP+ cells were phenotypically typed as large mononuclear cells present in the alveolar lumen or lining the alveolar epithelium. One to two days later, larger clusters of MV-infected cells were detected in bronchus-associated lymphoid tissue (BALT) and in the tracheo-bronchial lymph nodes. From 4 d.p.i. onward, MV-infected cells were detected in peripheral blood and various lymphoid tissues. In spite of the possibility for the aerosolized virus to infect cells and lymphoid tissues of the upper respiratory tract, MV-infected cells were not detected in either the tonsils or the adenoids until after onset of viremia. These data strongly suggest that in our model MV entered the host at the alveolar level by infecting macrophages or dendritic cells, which traffic the virus to BALT or regional lymph nodes, resulting in local amplification and subsequent systemic dissemination by viremia
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