343 research outputs found
Bis[2-phenyl-1-(phenyliminio)isoindoline] di-μ-chlorido-bis[dichloridopalladate(II)] benzene disolvate
In the title compound, (C20H17N2)2[Pd2Cl6]·2C6H6, the dichloride-bridged [Pd2Cl6]2− anion lies across an inversion center with each PdII ion in a slightly distorted square-planar environment. In the crystal structure, two cations and an anion are connected via N—H⋯Cl hydrogen bonds between the NH groups of the iminioisoindoline cations and terminal Cl atoms of a hexachloridodipalladate(II) anion. The Pd—Cl distance of the terminal chloride engaged in hydrogen bonding is slightly longer than the Pd—Cl distance of the adjacent terminal chloride which is not involved in hydrogen bonding
Gravitational Lensing, Dark Matter and the Optical Gravitational Lens Experiment
After briefly reviewing the history of gravitational lensing, we recall the basic principles of the theory. We then describe and use a simple optical gravitational lens experiment which has the virtue of accounting for all types of image configurations observed so far among the presently known gravitational lens systems. Finally, we briefly present the 4m International Liquid Mirror Telescope project in the context of a photometric monitoring of multiply imaged quasars
(16) Psyche: A mesosiderite-like asteroid?
Asteroid (16) Psyche is the target of the NASA Psyche mission. It is
considered one of the few main-belt bodies that could be an exposed
proto-planetary metallic core and that would thus be related to iron
meteorites. Such an association is however challenged by both its near- and
mid-infrared spectral properties and the reported estimates of its density.
Here, we aim to refine the density of (16) Psyche to set further constraints on
its bulk composition and determine its potential meteoritic analog.
We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large
program (ID 199.C-0074). We used the high angular resolution of these
observations to refine Psyche's three-dimensional (3D) shape model and
subsequently its density when combined with the most recent mass estimates. In
addition, we searched for potential companions around the asteroid. We derived
a bulk density of 3.99\,\,0.26\,gcm for Psyche. While such
density is incompatible at the 3-sigma level with any iron meteorites
(7.8\,gcm), it appears fully consistent with that of
stony-iron meteorites such as mesosiderites (density
4.25\,cm). In addition, we found no satellite in our images
and set an upper limit on the diameter of any non-detected satellite of
1460\,\,200}\,m at 150\,km from Psyche (0.2\%\,\,R, the
Hill radius) and 800\,\,200\,m at 2,000\,km (3\%\,\,).
Considering that the visible and near-infrared spectral properties of
mesosiderites are similar to those of Psyche, there is merit to a
long-published initial hypothesis that Psyche could be a plausible candidate
parent body for mesosiderites.Comment: 16 page
Identification and analysis of hepatitis C virus NS3 helicase inhibitors using nucleic acid binding assays
Typical assays used to discover and analyze small molecules that inhibit the hepatitis C virus (HCV) NS3 helicase yield few hits and are often confounded by compound interference. Oligonucleotide binding assays are examined here as an alternative. After comparing fluorescence polarization (FP), homogeneous time-resolved fluorescence (HTRF®; Cisbio) and AlphaScreen® (Perkin Elmer) assays, an FP-based assay was chosen to screen Sigma’s Library of Pharmacologically Active Compounds (LOPAC) for compounds that inhibit NS3-DNA complex formation. Four LOPAC compounds inhibited the FP-based assay: aurintricarboxylic acid (ATA) (IC50 = 1.4 μM), suramin sodium salt (IC50 = 3.6 μM), NF 023 hydrate (IC50 = 6.2 μM) and tyrphostin AG 538 (IC50 = 3.6 μM). All but AG 538 inhibited helicase-catalyzed strand separation, and all but NF 023 inhibited replication of subgenomic HCV replicons. A counterscreen using Escherichia coli single-stranded DNA binding protein (SSB) revealed that none of the new HCV helicase inhibitors were specific for NS3h. However, when the SSB-based assay was used to analyze derivatives of another non-specific helicase inhibitor, the main component of the dye primuline, it revealed that some primuline derivatives (e.g. PubChem CID50930730) are up to 30-fold more specific for HCV NS3h than similarly potent HCV helicase inhibitors.National Institutes of Health [RO1 AI088001]; Research Growth Initiative Award [101X219] from the University of Wisconsin-Milwaukee Research Foundation; National Institutes of Health Molecular Libraries Initiative [U54 HG005031]. Funding for open access charge: University of Wisconsin-Milwaukee Research Foundation
The fate of the interstellar medium in early-type galaxies I. First direct measurement of the timescale of dust removal
An important aspect of quenching star formation is the removal of the cold
interstellar medium (ISM; non-ionised gas and dust) from a galaxy. In addition,
dust grains can be destroyed in a hot or turbulent medium. The adopted
timescale of dust removal usually relies on uncertain theoretical estimates. It
is tricky to track the dust removal, because usually dust is constantly
replenished by consecutive generations of stars. Our objective is to measure
observationally the timescale of dust removal. We here explore an approach to
select galaxies which do have detectable amounts of dust and cold ISM but
exhibit a low current dust production rate. Any decrease of the dust and gas
content as a function of the age of such galaxies therefore must be attributed
to processes governing the ISM removal. We used a sample of galaxies detected
by Herschel in the far-infrared with visually assigned early-type morphology or
spirals with red colours. We also obtained JCMT/SCUBA-2 observations for five
of them. We discovered an exponential decline of the dust-to-stellar mass ratio
with age, which we interpret as an evolutionary trend of dust removal from
these galaxies. For the first time we directly measure the dust removal
timescale in such galaxies to be tau=(2.5+-0.4) Gyr (the corresponding
half-life time is (1.75+-0.25) Gyr). This quantity may be used in models in
which it must be assumed a priori and cannot be derived. Any process which
removes dust in these galaxies, such as dust grain destruction, cannot happen
on shorter timescales. The timescale is comparable to the quenching timescales
found in simulations for galaxies with similar stellar masses. The dust is
likely of internal, not external origin. It was either formed in the past
directly by supernovae, or from seeds produced by SNe and with grain growth in
the ISM contributing substantially to the dust mass accumulation.Comment: Astronomy & Astrophysics, accepted; 13 pages, 9 figures, 1 tabl
Thermal properties of large main-belt asteroids observed by Herschel PACS
Non-resolved thermal infrared observations enable studies of thermal and
physical properties of asteroid surfaces provided the shape and rotational
properties of the target are well determined via thermo-physical models. We
used calibration-programme Herschel PACS data (70, 100, 160 m) and
state-of-the-art shape models derived from adaptive-optics observations and/or
optical light curves to constrain for the first time the thermal inertia of
twelve large main-belt asteroids. We also modelled previously
well-characterised targets such as (1) Ceres or (4) Vesta as they constitute
important benchmarks. Using the scale as a free parameter, most targets
required a re-scaling 5\% consistent with what would be expected given
the absolute calibration error bars. This constitutes a good cross-validation
of the scaled shape models, although some targets required larger re-scaling to
reproduce the IR data. We obtained low thermal inertias typical of large main
belt asteroids studied before, which continues to give support to the notion
that these surfaces are covered by fine-grained insulating regolith. Although
the wavelengths at which PACS observed are longwards of the emission peak for
main-belt asteroids, they proved to be extremely valuable to constrain size and
thermal inertia and not too sensitive to surface roughness. Finally, we also
propose a graphical approach to help examine how different values of the
exponent used for scaling the thermal inertia as a function of heliocentric
distance (i.e. temperature) affect our interpretation of the results.Comment: Accepted for publication in Astronomy & Astrophysics (preprint
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