2,526 research outputs found
Circumbinary Ring, Circumstellar disks and accretion in the binary system UY Aurigae
Recent exo-planetary surveys reveal that planets can orbit and survive around
binary stars. This suggests that some fraction of young binary systems which
possess massive circumbinary disks (CB) may be in the midst of planet
formation. However, there are very few CB disks detected. We revisit one of the
known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO
5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new
results confirm the existence of the CB disk. In addition, the circumstellar
(CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral
indices between the wavelengths of 0.85 mm and 6 cm are found to be
surprisingly low, being 1.6 for both CS disks. The deprojected separation of
the binary is 1.26" based on our 1.4 mm continuum data. This is 0.07" (10 AU)
larger than in earlier studies. Combining the fact of the variation of UY Aur B
in band, we propose that the CS disk of an undetected companion UY Aur Bb
obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is
observed due to a mixing of Keplerian rotation of the CB disk, the infall and
outflow gas. The streaming gas accreting from the CB ring toward the CS disks
and possible outflows are also identified and resolved. The SO emission is
found to be at the bases of the streaming shocks. Our results suggest that the
UY Aur system is undergoing an active accretion phase from the CB disk to the
CS disks. The UY Aur B might also be a binary system, making the UY Aur a
triple system.Comment: 14 pages, 11 figures; accepted for publication in Ap
Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell
The high pressure and high temperature phase diagram of Ta has been studied
in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements
up to 52 GPa and 3800 K. The melting was observed at nine different pressures,
being the melting temperature in good agreement with previous laser-heated DAC
experiments, but in contradiction with several theoretical calculations and
previous piston-cylinder apparatus experiments. A small slope for the melting
curve of Ta is estimated (dTm/dP = 24 K/GPa at 1 bar) and a possible
explanation for this behaviour is given. Finally, a P-V-T equation of states is
obtained, being the temperature dependence of the thermal expansion coefficient
and the bulk modulus estimated.Comment: 31 pages, 8 figures, to appear in J.Phys.:Cond.Matte
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Melting of Xenon to 80 GPa, p-d hybridization, and an ISRO liquid
Measurements made in a laser heated diamond-anvil cell are reported that extend the melting curve of Xe to 80 GPa and 3350 K. The steep lowering of the melting slope (dT/dP) that occurs near 17 GPa and 2750 K results from the hybridization of the p-like valence and d-like conduction states with the formation of clusters in the liquid having Icosahedral Short-Range Order (ISRO)
Impact of preoperative right-ventricular function and platelet transfusion on outcome after lung transplantation
Objective: Lung transplantation has become an established treatment option for end-stage pulmonary diseases. However, outcome depends on preoperative condition and co-morbidity. Furthermore, perioperative blood-product use is known to be associated with worse outcome even in transplant surgery. We investigated the impact of poor preoperative right-ventricular function and blood-product use on outcome after lung transplantation. Methods: The medical records of 169 lung-transplant recipients from 1996 to 2006 were examined. Duration of hospital stay, hours on mechanical ventilation, duration of stay in the intensive care unit, perioperative complications, death during hospital stay, and long-term survival were recorded. These outcome parameters were analyzed regarding coherence with right-ventricular function and the perioperative administration of crystalloids, colloids, allogeneic red blood cells, fresh frozen plasma, and platelets. Results: Patients with poor preoperative right-ventricular function had a significant increase in postoperative hours on ventilation (p=0.005), intensive care stay (p=0.003), and in-hospital death (p=0.012). The hours on ventilation increased also with high intra-operative fluid administration (p=0.026). Blood-product use was associated with prolonged mechanical ventilation and intensive care stay. After multivariate analysis, transfusion of platelets (p=0.022) was an independent prognostic factor for in-hospital death. Hours of mechanical ventilation was the only independent prognostic factor for long-term mortality (p=0.014). Conclusions: Perioperative transfusion of platelets is an independent prognostic factor for perioperative mortality. Furthermore, the study indicated that poor preoperative right-ventricular function might worsen perioperatively after lung transplantation. Therefore, pre-transplant treatment of pulmonary hypertension to protract right-ventricular failure and a restrictive use of allogeneic blood products may be options to improve outcom
Structure and Dynamics of Liquid Iron under Earth's Core Conditions
First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.Comment: 13 pages, 8 figure
Psychological response and quality of life after transplantation: a comparison between heart, lung, liver and kidney recipients
PRINCIPLES: Various non-specific questionnaires were used to measure quality of life and psychological wellbeing of patients after organ transplantation. At present cross-organ studies dealing specifically with the psychological response to a transplanted organ are non-existent in German-speaking countries. METHODS: The Transplant Effects Questionnaire TxEQ-D and the SF-36 Quality of Life Questionnaire were used to examine the psychological response and quality of life of 370 patients after heart, lung, liver or kidney transplantation. The organ groups were compared with regard to psychosocial parameters. RESULTS: 72% of patients develop a feeling of responsibility for the received organ and its function. This feeling is even stronger towards the patient's key relationships i.e. family, friends, the treatment team and the donor. 11.6% worry about the transplanted organ. Heart and lung patients report significantly fewer concerns than liver and kidney patients. Overall, only a minority of patients report feelings of guilt towards the donor (2.7%), problems in disclosing their transplant to others (2.4%), or difficulties in complying with medical orders (3.5%). Lung transplant patients show significantly better adherence. CONCLUSIONS: A feeling of responsibility towards those one is close to and towards the donor is a common psychological phenomenon after transplantation of an organ. Conscious feelings of guilt and shame are harboured by only a minority of patients. The fact that heart and lung patients worry less about their transplant might have primarily to do with the greater medical and psychosocial support in this group
Hexagonal Si-Ge Class of Semiconducting Alloys Prepared Using Pressure and Temperature
Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500â1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery atambient pressure of hexagonal Ge-Si solid solutions (P6/mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be preparedfor all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Sisolid solution family, and is of interest for optoelectronic applications
Two-band second moment model and an interatomic potential for caesium
A semi-empirical formalism is presented for deriving interatomic potentials
for materials such as caesium or cerium which exhibit volume collapse phase
transitions. It is based on the Finnis-Sinclair second moment tight binding
approach, but incorporates two independent bands on each atom. The potential is
cast in a form suitable for large-scale molecular dynamics, the computational
cost being the evaluation of short ranged pair potentials. Parameters for a
model potential for caesium are derived and tested
Millimeter Gap Contrast as a Probe for Turbulence Level in Protoplanetary Disks
Turbulent motions are believed to regulate angular momentum transport and
influence dust evolution in protoplanetary disks. Measuring the strength of
turbulence is challenging through gas line observations because of the
requirement for high spatial and spectral resolution data, and an exquisite
determination of the temperature. In this work, taking the well-known HD 163296
disk as an example, we investigated the contrast of gaps identified in high
angular resolution continuum images as a probe for the level of turbulence.
With self-consistent radiative transfer models, we simultaneously analyzed the
radial brightness profiles along the disk major and minor axes, and the
azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap
contrasts measured from these profiles, we constrained the gas-to-dust scale
height ratio to be , and
for the D48, B67 and B100 regions, respectively. The varying
gas-to-dust scale height ratios indicate that the degree of dust settling
changes with radius. The inferred values for translate into a
turbulence level of in the D48 and
B100 regions, which is consistent with previous upper limits set by gas line
observations. However, turbulent motions in the B67 ring are strong with
. Due to the degeneracy
between and the depth of dust surface density drops, the turbulence
strength in the D86 gap region is not constrained.Comment: 13 pages, 7 figures, accepted for publication in Science China
Physics, Mechanics & Astronom
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