227 research outputs found
Probing Multiple Sight Lines through the SN 1006 Remnant by UV Absorption Spectroscopy
Absorption-line spectroscopy is an effective probe for cold ejecta within an
SNR, provided that suitable background UV sources can be identified. For the SN
1006 remnant we have identified four such sources, in addition to the
much-studied Schweitzer-Middleditch (SM) star. We have used STIS on HST to
obtain UV spectra of all four sources, to study "core samples" of the SN 1006
interior. The line of sight closest to the center of the SNR shell, passing
only 2.0 arcmin away, is to a V = 19.5 QSO at z = 1.026. Its spectrum shows
broad Fe II absorption lines, asymmetric with red wings broader than blue. The
similarity of these profiles to those seen in the SM star, which is 2.8 arcmin
from the center in the opposite direction, confirms the existence of a bulge on
the far side of SN 1006. The Fe II equivalent widths in the QSO spectrum are ~
50% greater than in the SM star, suggesting that somewhat more iron may be
present within SN 1006 than studies of the SM star alone have indicated, but
this is still far short of what most SNIa models require. The absorption
spectrum against a brighter z = 0.337 QSO seen at 57% of the shell radius shows
broad silicon absorption lines but no iron other than narrow, probably
interstellar lines. The cold iron expanding in this direction must be confined
within v <~ 5200 km/s, also consistent with a high-velocity bulge on the far
side only. The broad silicon lines indicate that the silicon layer has expanded
beyond this point, and that it has probably been heated by a reverse shock.
Finally, the spectra of two ~ A0V stars near the southern shell rim show no
broad or unusually strong absorption lines, suggesting that the low-ionization
ejecta are confined within 83% of the shell radius, at least at the azimuths of
these background sources.Comment: 26 pages, 8 postscript figure
Identification of a Small Molecule Inhibitor of Importin β Mediated Nuclear Import by Confocal On-Bead Screening of Tagged One-Bead One-Compound Libraries
In eukaryotic cells, proteins and RNAs are transported between the nucleus and the cytoplasm by nuclear import and export receptors. Over the past decade, small molecules that inhibit the nuclear export receptor CRM1 have been identified, most notably,leptomycin B. However, up to now no small molecule inhibitors of nuclear import have been described. Here we have used our automated confocal nanoscanning and bead picking method (CONA) for on-bead screening of a one-bead one-compound library to identify the first such import inhibitor, karyostatin 1A. Karyostatin 1A binds importin beta with high nanomolar affinity and specifically inhibits importin alpha/beta mediated nuclear import at low micromolar concentrations in vitro and in living cells, without perturbing transportin mediated nuclear import or CRM1 mediated nuclear export. Surface plasmon resonance binding-experiments suggest that karyostatin 1A acts by disrupting the interaction between importin p and the OPase Ran. As a selective inhibitor of the importin alpha/beta import pathway, karyostatin 1A will provide a valuable tool for future studies of nucleocytoplasmic trafficking.</p
Time Evolution of the Reverse Shock in SN 1006
The Schweizer-Middleditch star, located behind the SN 1006 remnant and near
its center in projection, provides the opportunity to study cold, expanding
ejecta within the SN 1006 shell through UV absorption. Especially notable is an
extremely sharp red edge to the Si II 1260 Angstrom feature, which stems from
the fastest moving ejecta on the far side of the SN 1006 shell--material that
is just encountering the reverse shock. Comparing HST far-UV spectra obtained
with COS in 2010 and with STIS in 1999, we have measured the change in this
feature over the intervening 10.5-year baseline. We find that the sharp red
edge of the Si II feature has shifted blueward by 0.19 +/- 0.05 Angstroms,
which means that the material hitting the reverse shock in 2010 was moving
slower by 44 +/- 11 km/s than the material that was hitting it in 1999, a
change corresponding to - 4.2 +/- 1.0 km/s/yr. This is the first observational
confirmation of a long-predicted dynamic effect for a reverse shock: that the
shock will work its way inward through expanding supernova ejecta and encounter
ever slower material as it proceeds. We also find that the column density of
shocked Si II (material that has passed through the reverse shock) has
decreased by 7 +/- 2% over the ten-year period. The decrease could indicate
that in this direction the reverse shock has been ploughing through a dense
clump of Si,leading to pressure and density transients.Comment: 8 pages, includes 5 figure
Transcriptome analyses of the Giardia lamblia life cycle
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Molecular and Biochemical Parasitology 174 (2010): 62-65, doi:10.1016/j.molbiopara.2010.05.010.We quantified mRNA abundance from 10 stages in the Giardia lamblia life cycle in vitro using
Serial Analysis of Gene Expression (SAGE). 163 abundant transcripts were expressed
constitutively. 71 transcripts were upregulated specifically during excystation and 42 during
encystation. Nonetheless, the transcriptomes of cysts and trophozoites showed major
differences. SAGE detected co-expressed clusters of 284 transcripts differentially expressed in
cysts and excyzoites and 287 transcripts in vegetative trophozoites and encysting cells. All
clusters included known genes and pathways as well as proteins unique to Giardia or
diplomonads. SAGE analysis of the Giardia life cycle identified a number of kinases,
phosphatases, and DNA replication proteins involved in excystation and encystation, which
could be important for examining the roles of cell signaling in giardial differentiation. Overall,
these data pave the way for directed gene discovery and a better understanding of the biology
of Giardia lamblia.BJD, DSR, and FDG were supported by NIH grants AI42488, GM61896, DK35108, and
AI051687. DP and SGS were supported by grants from the Swedish Natural Science Research
Council, the Swedish Medical Research Council, and the Karolinska Institutet. AGM, SRB,
SPP, and MJC were supported by NIH grant AI51089 and by the Marine Biological Laboratory’s
Program in Global Infectious Diseases, funded by the Ellison Medical Foundation
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Cosmological parameter estimation and the inflationary cosmology
We consider approaches to cosmological parameter estimation in the
inflationary cosmology, focussing on the required accuracy of the initial power
spectra. Parametrizing the spectra, for example by power-laws, is well suited
to testing the inflationary paradigm but will only correctly estimate
cosmological parameters if the parametrization is sufficiently accurate, and we
investigate conditions under which this is achieved both for present data and
for upcoming satellite data. If inflation is favoured, reliable estimation of
its physical parameters requires an alternative approach adopting its detailed
predictions. For slow-roll inflation, we investigate the accuracy of the
predicted spectra at first and second order in the slow-roll expansion
(presenting the complete second-order corrections for the tensors for the first
time). We find that within the presently-allowed parameter space, there are
regions where it will be necessary to include second-order corrections to reach
the accuracy requirements of MAP and Planck satellite data. We end by proposing
a data analysis pipeline appropriate for testing inflation and for cosmological
parameter estimation from high-precision data.Comment: 15 pages RevTeX file with figures incorporated. Slow-roll inflation
module for use with the CAMB program can be found at
http://astronomy.cpes.susx.ac.uk/~sleach/inflation/ This version corrects a
typo in the definition of z_S (after Eq.1) and supersedes the journal versio
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
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