1,736 research outputs found
Microscopic study of neutrino trapping in hyperon stars
Employing the most recent parametrization of the baryon-baryon interaction of
the Nijmegen group, we investigate, in the framework of the
Brueckner--Bethe--Goldstone many-body theory at zero temperature, the influence
of neutrino trapping on the composition, equation of state, and structure of
neutron stars, relevant to describe the physical conditions of a neutron star
immediately after birth (protoneutron star). We find that the presence of
neutrinos changes significantly the composition of matter delaying the
appearance of hyperons and making the equation of state stiffer. We explore the
consequences of neutrino trapping on the early evolution of a neutron star and
on the nature of the final compact remnant left by the supernova explosion.Comment: Astronomy & Astrophysics, 399, 687-693 (2003
HLA-G: expression in human keratinocytes in vitro and in human skin in vivo
Classical, polymorphic major histocompatibility complex class I molecules are
expressed on most nucleated cells.They present peptides at the cell surface and,
thus, enable the immune system to scan peptides for their antigenicity. The
function of the other, nonclassical class I molecules in man is controversial.
HLA-G which has been shown by transfection experiments to be expressed at the
cell surface, is only transcribed in placental tissue and in the fetal eye.Therefore, a
role of HLA-G in the control of rejection of the allogeneic fetus has been
discussed. We found that HLA-G expression is induced in keratinocytes by
culture in vitro. Three different alternative splicing products of HLA-G can be
detected: a full length transcript, an mRNA lacking exon 3 and a transcript devoid
of exon 3 and 4. Reverse transcription followed by polymerase chain reaction also
revealed the presence of HLA-G mRNA in vivo in biopsies of either diseased or
healthy skin
IRFM T_eff calibrations for cluster and field giants in the Vilnius, Geneva, RI(C) and DDO photometric systems
Based on a large sample of disk and halo giant stars, for which accurate
effective temperatures derived through the InfraRed Flux Method (IRFM) exist, a
calibration of the temperature scale in the Vilnius, Geneva, RI(C) and DDO
photometric systems is performed. We provide calibration formulae for the
metallicity dependent T_eff vs color relations as well as grids of intrinsic
colors and compare them with other calibrations. Photometry, atmospheric
parameters and reddening corrections for the stars of the sample have been
updated with respect to the original sources in order to reduce the dispersion
of the fits. Application of our results to Arcturus leads to an effective
temperature in excellent agreement with the value derived from its angular
diameter and integrated flux. The effects of gravity on these T_eff vs color
relations are also explored by taking into account our previous results for
dwarf stars.Comment: Accepted for publication in A&
A List of Bright Interferometric Calibrators measured at the ESO VLTI
In a previous publication (Richichi & Percheron 2005) we described a program
of observations of candidate calibrator stars at the ESO Very Large Telescope
Interferometer (VLTI), and presented the main results from a statistical point
of view. In the present paper, we concentrate on establishing a new homogeneous
group of bright interferometric calibrators, based entirely on publicly
available K-band VLTI observations carried out with the VINCI instrument up to
July 2004. For this, we have defined a number of selection criteria for the
quality and volume of the observations, and we have accordingly selected a list
of 17 primary and 47 secondary calibrators. We have developed an approach to a
robust global fit for the angular diameters using the whole volume of
quality-controlled data, largely independent of a priori assumptions. Our
results have been compared with direct measurements, and indirect estimates
based on spectrophotometric methods, and general agreement is found within the
combined uncertainties. The stars in our list cover the range K=-2.9 to +3.0
mag in brightness, and 1.3 to 20.5 milliarcseconds in uniform-disk diameter.
The relative accuracy of the angular diameter values is on average 0.4% and 2%
for the primary and secondary calibrators respectively. Our calibrators are
well suited for interferometric observations in the near-infrared on baselines
between ~20m and ~200m, and their accuracy is superior, at least for the
primary calibrators, to other similar catalogues. Therefore, the present list
of calibrators has the potential to lead to significantly improved
interferometric scientific results
First High Contrast Imaging Using a Gaussian Aperture Pupil Mask
Placing a pupil mask with a gaussian aperture into the optical train of
current telescopes represents a way to attain high contrast imaging that
potentially improves contrast by orders of magnitude compared to current
techniques. We present here the first observations ever using a gaussian
aperture pupil mask (GAPM) on the Penn State near-IR Imager and Spectrograph
(PIRIS) at the Mt. Wilson 100 telescope. Two nearby stars were
observed, Eridani and Her A. A faint companion was detected
around Her A, confirming it as a proper motion companion. Furthermore,
the observed H and K magnitudes of the companion were used to constrain its
nature. No companions or faint structure were observed for Eridani.
We found that our observations with the GAPM achieved contrast levels similar
to our coronographic images, without blocking light from the central star. The
mask's performance also nearly reached sensitivities reported for other ground
based adaptive optics coronographs and deep HST images, but did not reach
theoretically predicted contrast levels. We outline ways that could improve the
performance of the GAPM by an order of magnitude or more.Comment: 8 pages, 4 figures, accepted by ApJ letter
Developing, delivering and documenting rehabilitation in a multi-centre randomised controlled surgical trial: experiences from the ProFHER trial
OBJECTIVES: A rigorous approach to developing, delivering and documenting rehabilitation within randomised controlled trials of surgical interventions is required to underpin the generation of reliable and usable evidence. This article describes the key processes used to ensure provision of good quality and comparable rehabilitation to all participants of a multi-centre randomised controlled trial comparing surgery with conservative treatment of proximal humeral fractures in adults. METHODS: These processes included the development of a patient information leaflet on self-care during sling immobilisation, the development of a basic treatment physiotherapy protocol that received input and endorsement by specialist physiotherapists providing patient care, and establishing an expectation for the provision of home exercises. Specially designed forms were also developed to facilitate reliable reporting of the physiotherapy care that patients received. RESULTS: All three initiatives were successfully implemented, alongside the measures to optimise the documentation of physiotherapy. Thus, all participating sites that recruited patients provided the sling immobilisation leaflet, all adhered to the physiotherapy protocol and all provided home exercises. There was exemplary completion of the physiotherapy forms that often reflected a complex patient care pathway. These data demonstrated equal and high access to and implementation of physiotherapy between groups, including the performance of home exercises. CONCLUSION: In order to increase the validity and relevance of the evidence from trials of surgical interventions and meet international reporting standards, careful attention to study design, conduct and reporting of the intrinsic rehabilitation components is required. The involvement of rehabilitation specialists is crucial to achieving this. Cite this article: Bone Joint Res 2014;3:335–40
An uncharged amine in the transition state of the ribosornal peptidyl transfer reaction.
The ribosome has an active site comprised of RNA that catalyzes peptide bond formation. To understand how RNA promotes this reaction requires a detailed understanding of the chemical transition state. Here, we report the Bronsted coefficient of the a-amino nucleophile with a series of puromycin derivatives. Both 50S subunit- and 70S ribosome-catalyzed reactions displayed linear free-energy relationships with slopes close to zero under conditions where chemistry is rate limiting. These results indicate that, at the transition state, the nucleophile is neutral in the ribosome-catalyzed reaction, in contrast to the substantial positive charge reported for typical uncatalyzed aminolysis reactions. This suggests that the ribosomal transition state involves deprotonation to a degree commensurate with nitrogen-carbon bond formation. Such a transition state is significantly different from that of uncatalyzed aminolysis reactions in solution
The Age Of Globular Clusters In Light Of Hipparcos: Resolving the Age Problem?
We review five independent techniques which are used to set the distance
scale to globular clusters, including subdwarf main sequence fitting utilizing
the recent Hipparcos parallax catalogue. These data together all indicate that
globular clusters are farther away than previously believed, implying a
reduction in age estimates. This new distance scale estimate is combined with a
detailed numerical Monte Carlo study designed to assess the uncertainty
associated with the theoretical age-turnoff luminosity relationship in order to
estimate both the absolute age and uncertainty in age of the oldest globular
clusters. Our best estimate for the mean age of the oldest globular clusters is
now Gyr, with a one-sided, 95% confidence level lower limit of
9.5 Gyr. This represents a systematic shift of over 2 compared to our
earlier estimate, due completely to the new distance scale---which we emphasize
is not just due to the Hipparcos data. This now provides a lower limit on the
age of the universe which is consistent with either an open universe, or a
flat, matter dominated universe (the latter requiring H_0 \le 67 \kmsmpc).
Our new study also explicitly quantifies how remaining uncertainties in the
distance scale and stellar evolution models translate into uncertainties in the
derived globular cluster ages. Simple formulae are provided which can be used
to update our age estimate as improved determinations for various quantities
become available.Comment: 41 pages, including 10 eps figs, uses aaspp4.sty and flushrt.sty,
submitted to Ap.J., revised to incorporate FULL Hipparcos catalogue dat
Thermodynamic phase diagram of Fe(Se0.5Te0.5) single crystals in fields up to 28 tesla
International audienceWe report on specific heat Cp , transport, Hall probe, and penetration depth measurements performed on Fe Se0.5Te0.5 single crystals Tc 14 K . The thermodynamic upper critical field Hc2 lines has been deduced from Cp measurements up to 28 T for both H c and H ab, and compared to the lines deduced from transport measurements up to 55 T in pulsed magnetic fields . We show that this thermodynamic Hc2 line presents a very strong downward curvature for T→Tc which is not visible in transport measurements. This temperature dependence associated to an upward curvature of the field dependence of the Sommerfeld coefficient confirms that Hc2 is limited by paramagnetic effects. Surprisingly this paramagnetic limit is visible here up to T/Tc 0.99 for H ab which is the consequence of a very small value of the coherence length c 0 4 Å and ab 0 15 Å , confirming the strong renormalization of the effective mass as compared to DMFT calculations previously observed in ARPES measurements A. Tamai, A. Y. Ganin, E. Rozbicki, J. Bacsa, W. Meevasana, P. D. C. King, M. Caffio, R. Schaub, S. Margadonna, K. Prassides, M. J. Rosseinsky, and F. Baumberger, Phys. Rev. Lett. 104, 097002 2010 . Hc1 measurements lead to ab 0 =430 50 nm and c 0 =1600 200 nm and the corresponding anisotropy is approximatively temperature independent 4 , being close to the anisotropy of Hc2 for T→Tc. The temperature dependence of both T2 and the electronic contribution to the specific heat confirm the nonconventional coupling mechanism in this system
- …