3,515 research outputs found
Anomalous pressure dependence of the atomic displacements in the relaxor ferroelectric PbMgTaO
The crystal structure of the PbMgTaO (PMT) relaxor
ferroelectric was studied under hydrostatic pressure up to GPa by
means of powder neutron diffraction. We find a drastic pressure-induced
decrease of the lead displacement from the inversion centre which correlates
with an increase by 50 % of the anisotropy of the oxygen temperature
factor. The vibrations of the Mg/Ta are, in contrast, rather pressure
insensitive. We attribute these changes being responsible for the previously
reported pressure-induced suppression of the anomalous dielectric permittivity
and diffuse scattering in relaxor ferroelectrics
The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry
Context: Stars on the asymptotic giant branch (AGB) show broad evidence of
inhomogeneous atmospheres and circumstellar envelopes. These have been studied
by a variety of methods on various angular scales. In this paper we explore the
envelope of the well-studied carbon star TX Psc by the technique of
spectro-astrometry. Aims: We explore the potential of this method for detecting
asymmetries around AGB stars. Methods:We obtained CRIRES observations of
several CO v=1 lines near 4.6 m and HCN lines near 3 m in
2010 and 2013. These were then searched for spectro-astrometric signatures. For
the interpretation of the results, we used simple simulated observations.
Results: Several lines show significant photocentre shifts with a clear
dependence on position angle. In all cases, tilde-shaped signatures are found
where the positive and negative shifts (at PA 0deg) are associated with blue
and weaker red components of the lines. The shifts can be modelled with a
bright blob 70 mas to 210 mas south of the star with a flux of several percent
of the photospheric flux. We estimate a lower limit of the blob temperature of
1000 K. The blob may be related to a mass ejection as found for AGB stars or
red supergiants. We also consider the scenario of a companion object.
Conclusions: Although there is clear spectro-astrometric evidence of a rather
prominent structure near TX Psc, it does not seem to relate to the other
evidence of asymmetries, so no definite explanation can be given. Our data thus
underline the very complex structure of the environment of this star, but
further observations that sample the angular scales out to a few hundred
milli-arcseconds are needed to get a clearer picture
Catching the fish - Constraining stellar parameters for TX Psc using spectro-interferometric observations
Stellar parameter determination is a challenging task when dealing with
galactic giant stars. The combination of different investigation techniques has
proven to be a promising approach. We analyse archive spectra obtained with the
Short-Wavelength-Spectrometer (SWS) onboard of ISO, and new interferometric
observations from the Very Large Telescope MID-infrared Interferometric
instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The
aim of this work is to determine stellar parameters using spectroscopy and
interferometry. The observations are used to constrain the model atmosphere,
and eventually the stellar evolutionary model in the region where the tracks
map the beginning of the carbon star sequence. Two different approaches are
used to determine stellar parameters: (i) the 'classic' interferometric
approach where the effective temperature is fixed by using the angular diameter
in the N-band (from interferometry) and the apparent bolometric magnitude; (ii)
parameters are obtained by fitting a grid of state-of-the-art hydrostatic
models to spectroscopic and interferometric observations. We find a good
agreement between the parameters of the two methods. The effective temperature
and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the
H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star
just recently, which means that the star is still in a 'quiet' phase compared
to the subsequent strong-wind regime. This is in agreement with the C/O ratio
being only slightly larger than 1.Comment: 11 pages, 9 figures, 5 table
COMPETITIVE GRANTS AND THE FUNDING OF AGRICULTURAL RESEARCH IN THE U.S.
To increase the efficiency of the public agricultural R&D system, expanded use of competitive grants to fund state institutions has been advocated. This paper characterizes different funding instruments and empirically assesses the effects of changes in mechanism use. Factors associated with greater levels of competitive grants are modeled.Research and Development/Tech Change/Emerging Technologies,
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Start-Ed: A Model for Commercial Clinical Legal Education
This article outlines a pro bono student law clinic project focusing on providing legal assistance to startup businesses in central London. Serving more than 500 clients over this period, the clinic adapted to a number of problems by modifying its format with an emphasis on flexibility and informality. Additionally, the clinic implemented a survey in order to streamline the delivery of its advice. Data was collected from over 460 startups over a two year period between 2013 and 2015 regarding the nature of their business as well as the type of legal challenges they faced. The study revealed the primary need for basic legal advice on a few select matters including most notably company structure. In addition to collecting data on startups in London, the clinic project is presented as both a model for successful clinical education and example of how the university sector can act to boost innovation and the entrepreneurial economy
Detection of a very bright optical flare from a gamma-ray burst at redshift 6.29
In this letter we discuss the flux and the behavior of the bright optical
flare emission detected by the 25 cm TAROT robotic telescope during the prompt
high-energy emission and the early afterglow. We combine our data with
simultaneous observations performed in X-rays and we analyze the broad-band
spectrum. These observations lead us to emphasize the similarity of GRB 050904
with GRB 990123, a remarkable gamma-ray burst whose optical emission reached
9th magnitude. While GRB 990123 was, until now, considered as a unique event,
this observation suggests the existence of a population of GRBs which have very
large isotropic equivalent energies and extremely bright optical counterparts.
The luminosity of these GRBs is such that they are easily detectable through
the entire universe. Since we can detect them to very high redshift even with
small aperture telescopes like TAROT, they will constitute powerful tools for
the exploration of the high-redshift Universe and might be used to probe the
first generation of stars.Comment: 9 pages, 3 figures. Accepted in ApJ
Expression signatures of cisplatin- and trametinib-treated early-stage medaka melanomas
Small aquarium fish models provide useful systems not only for a better understanding of the molecular basis of many human diseases, but also for first-line screening to identify new drug candidates. For testing new chemical substances, current strategies mostly rely on easy to perform and efficient embryonic screens. Cancer, however, is a disease that develops mainly during juvenile and adult stage. Long-term treatment and the challenge to monitor changes in tumor phenotype make testing of large chemical libraries in juvenile and adult animals cost prohibitive. We hypothesized that changes in the gene expression profile should occur early during anti-tumor treatment, and the disease-associated transcriptional change should provide a reliable readout that can be utilized to evaluate drug-induced effects. For the current study, we used a previously established medaka melanoma model. As proof of principle, we showed that exposure of melanoma developing fish to the drugs cisplatin or trametinib, known cancer therapies, for a period of seven days is sufficient to detect treatment-induced changes in gene expression. By examining whole body transcriptome responses we provide a novel route toward gene panels that recapitulate anti-tumor outcomes thus allowing a screening of thousands of drugs using a whole-body vertebrate model. Our results suggest that using disease-associated transcriptional change to screen therapeutic molecules in small fish model is viable and may be applied to pre-clinical research and development stages in new drug discovery
Continuous optical monitoring during the prompt emission of GRB 060111B
We present the time-resolved optical emission of GRB 060111B during its
prompt phase, measured with the TAROT robotic observatory. This is the first
time that the optical emission from a gamma-ray burst has been continuously
monitored with a temporal resolution of a few seconds during the prompt
gamma-ray phase. The temporal evolution of the prompt optical emission at the
level of several seconds is used to provide a clue to the origin of this
emission. The optical emission was found to decay steadily from our first
measure, 28s after the trigger, in contrast to the gamma-ray emission, which
exhibits strong variability at the same time. This behaviour strongly suggests
that the optical emission is due to the reverse shock
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