302 research outputs found
First-principles calculation of intrinsic defect formation volumes in silicon
We present an extensive first-principles study of the pressure dependence of
the formation enthalpies of all the know vacancy and self-interstitial
configurations in silicon, in each charge state from -2 through +2. The neutral
vacancy is found to have a formation volume that varies markedly with pressure,
leading to a remarkably large negative value (-0.68 atomic volumes) for the
zero-pressure formation volume of a Frenkel pair (V + I). The interaction of
volume and charge was examined, leading to pressure--Fermi level stability
diagrams of the defects. Finally, we quantify the anisotropic nature of the
lattice relaxation around the neutral defects.Comment: 9 pages, 9 figure
ARFGAP1 promotes the formation of COPI vesicles, suggesting function as a component of the coat
The role of GTPase-activating protein (GAP) that deactivates ADP-ribosylation factor 1 (ARF1) during the formation of coat protein I (COPI) vesicles has been unclear. GAP is originally thought to antagonize vesicle formation by triggering uncoating, but later studies suggest that GAP promotes cargo sorting, a process that occurs during vesicle formation. Recent models have attempted to reconcile these seemingly contradictory roles by suggesting that cargo proteins suppress GAP activity during vesicle formation, but whether GAP truly antagonizes coat recruitment in this process has not been assessed directly. We have reconstituted the formation of COPI vesicles by incubating Golgi membrane with purified soluble components, and find that ARFGAP1 in the presence of GTP promotes vesicle formation and cargo sorting. Moreover, the presence of GTPγS not only blocks vesicle uncoating but also vesicle formation by preventing the proper recruitment of GAP to nascent vesicles. Elucidating how GAP functions in vesicle formation, we find that the level of GAP on the reconstituted vesicles is at least as abundant as COPI and that GAP binds directly to the dilysine motif of cargo proteins. Collectively, these findings suggest that ARFGAP1 promotes vesicle formation by functioning as a component of the COPI coat
Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range
We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.Comment: 10 pages, 7 figures, some typos correcte
Probing quantum and classical turbulence analogy through global bifurcations in a von K\'arm\'an liquid Helium experiment
We report measurements of the dissipation in the Superfluid Helium high
REynold number von Karman flow (SHREK) experiment for different forcing
conditions, through a regime of global hysteretic bifurcation. Our
macroscopical measurements indicate no noticeable difference between the
classical fluid and the superfluid regimes, thereby providing evidence of the
same dissipative anomaly and response to asymmetry in fluid and superfluid
regime. %In the latter case, A detailed study of the variations of the
hysteretic cycle with Reynolds number supports the idea that (i) the stability
of the bifurcated states of classical turbulence in this closed flow is partly
governed by the dissipative scales and (ii) the normal and the superfluid
component at these temperatures (1.6K) are locked down to the dissipative
length scale.Comment: 5 pages, 5 figure
Path lengths in turbulence
By tracking tracer particles at high speeds and for long times, we study the
geometric statistics of Lagrangian trajectories in an intensely turbulent
laboratory flow. In particular, we consider the distinction between the
displacement of particles from their initial positions and the total distance
they travel. The difference of these two quantities shows power-law scaling in
the inertial range. By comparing them with simulations of a chaotic but
non-turbulent flow and a Lagrangian Stochastic model, we suggest that our
results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic
Increasing resilience to droughts in Viet Nam: The role of forests, agroforestry, and climate smart agriculture
Single Crystalline Cadmium Sulfide Nanowires with Branched Structure
In this article, we report the synthesis of branched single crystal CdS nanowires. This branched CdS nanostructure is prepared by a simple surfactant-directing method, which is of particular interest as it uses readily available reagents and provides a convenient route to high-yield single crystal nanowires but with branched shape. These branched nanowires have an average diameter of about 40 nm and length up to several micrometers. A possible mechanism has been proposed and the addition of surfactant dodecylthiol into the two mixed-solvents would play an importance effect on the structure of the product. Based on the mechanism, by controlling the synthesis conditions, such as the ratios between the surfactant, inorganic solvent, and organic solvent, other kinds of nanostructures based on CdS nanowires were also prepared. Photoluminescence (PL) measurement reveals that the branched CdS nanowires have a strong emission at about 700 nm which might be due to its special structure
The window layers effect on the hardness improvement of space solar cells exposed to the 1 MeV electron irradiations
Sequential updating of a new dynamic pharmacokinetic model for caffeine in premature neonates
International audienceCaffeine treatment is widely used in nursing care to reduce the risk of apnoea in premature neonates. To check the therapeutic efficacy of the treatment against apnoea, caffeine concentration in blood is an important indicator. The present study was aimed at building a pharmacokinetic model as a basis for a medical decision support tool. In the proposed model, time dependence of physiological parameters is introduced to describe rapid growth of neonates. To take into account the large variability in the population, the Pharmacokinetic model is embedded in a population structure. The whole model is inferred within a Bayesian framework. To update caffeine concentration predictions as data of an incoming patient are collected, we propose a fast method that can be used in a medical context. This involves the sequential updating of model parameters (at individual and population levels) via a stochastic particle algorithm. Our model provides better predictions than the ones obtained with models previously published. We show, through an example, that sequential updating improves predictions of caffeine concentration in blood (reduce bias and length of credibility intervals). The update of the pharmacokinetic model using body mass and caffeine concentration data is studied. It shows how informative caffeine concentration data are in contrast to body mass data. This study provides the methodological basis to predict caffeine concentration in blood, after a given treatment if data are collected on the treated neonate
Consensus on circulatory shock and hemodynamic monitoring. Task force of the European Society of Intensive Care Medicine.
OBJECTIVE: Circulatory shock is a life-threatening syndrome resulting in multiorgan failure and a high mortality rate. The aim of this consensus is to provide support to the bedside clinician regarding the diagnosis, management and monitoring of shock.
METHODS: The European Society of Intensive Care Medicine invited 12 experts to form a Task Force to update a previous consensus (Antonelli et al.: Intensive Care Med 33:575-590, 2007). The same five questions addressed in the earlier consensus were used as the outline for the literature search and review, with the aim of the Task Force to produce statements based on the available literature and evidence. These questions were: (1) What are the epidemiologic and pathophysiologic features of shock in the intensive care unit ? (2) Should we monitor preload and fluid responsiveness in shock ? (3) How and when should we monitor stroke volume or cardiac output in shock ? (4) What markers of the regional and microcirculation can be monitored, and how can cellular function be assessed in shock ? (5) What is the evidence for using hemodynamic monitoring to direct therapy in shock ? Four types of statements were used: definition, recommendation, best practice and statement of fact.
RESULTS: Forty-four statements were made. The main new statements include: (1) statements on individualizing blood pressure targets; (2) statements on the assessment and prediction of fluid responsiveness; (3) statements on the use of echocardiography and hemodynamic monitoring.
CONCLUSIONS: This consensus provides 44 statements that can be used at the bedside to diagnose, treat and monitor patients with shock
- …