1,928 research outputs found
Transport and Helfand moments in the Lennard-Jones fluid. II. Thermal Conductivity
The thermal conductivity is calculated with the Helfand-moment method in the
Lennard-Jones fluid near the triple point. The Helfand moment of thermal
conductivity is here derived for molecular dynamics with periodic boundary
conditions. Thermal conductivity is given by a generalized Einstein relation
with this Helfand moment. We compute thermal conductivity by this new method
and compare it with our own values obtained by the standard Green-Kubo method.
The agreement is excellent.Comment: Submitted to the Journal of Chemical Physic
Defect chemistry and transport properties of BaxCe0.85M0.15O3-d
The site-incorporation mechanism of M3+ dopants into A2+B4+O3 perovskites controls the overall defect chemistry and thus their transport properties. For charge-balance reasons, incorporation onto the A2+-site would require the creation of negatively charged point defects (such as cation vacancies), whereas incorporation onto the B4+-site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen-vacancy content, in turn, is relevant to proton-conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites. We propose here, on the basis of x-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, and alternating current impedance spectroscopy, that nominally B-site doped barium cerate can exhibit dopant partitioning as a consequence of barium evaporation at elevated temperatures. Such partitioning and the presence of significant dopant concentrations on the A-site negatively impact proton conductivity. Specific materials examined are BaxCe0.85M0.15O3-d (x = 0.85 - 1.20; M = Nd, Gd, Yb). The compositional limits for the maximum A-site incorporation are experimentally determined to be: (Ba0.919Nd0.081)(Ce0.919Nd0.081)O3, (Ba0.974Gd0.026)(Ce0.872Gd0.128)O2.875, and Ba(Ce0.85Yb0.15)O2.925. As a consequence of the greater ability of larger cations to exist on the Ba site, the H2O adsorption and proton conductivities of large-cation doped barium cerates are lower than those of small-cation doped analogs
Transport and Helfand moments in the Lennard-Jones fluid. I. Shear viscosity
We propose a new method, the Helfand-moment method, to compute the shear
viscosity by equilibrium molecular dynamics in periodic systems. In this
method, the shear viscosity is written as an Einstein-like relation in terms of
the variance of the so-called Helfand moment. This quantity, is modified in
order to satisfy systems with periodic boundary conditions usually considered
in molecular dynamics. We calculate the shear viscosity in the Lennard-Jones
fluid near the triple point thanks to this new technique. We show that the
results of the Helfand-moment method are in excellent agreement with the
results of the standard Green-Kubo method.Comment: Submitted to the Journal of Chemical Physic
Composite nanostructured solid-acid fuel-cell electrodes via electrospray deposition
Stable, porous, nanostructured composite electrodes were successfully fabricated via the inexpensive and scalable method of electrospray deposition, in which a dissolved solute is deposited onto a substrate using an electric field to drive droplet migration. The desirable characteristics of high porosity and high surface area were obtained under conditions that favored complete solvent evaporation from the electrospray droplets prior to contact with the substrate. Solid acid (CsH_2PO_4) feature sizes of 100 nm were obtained from electrosprayed waterâmethanol solutions with 10 g L^(â1) CsH_2PO_4 and 5 g L^(â1) Pt catalyst particles suspended using polyvinylpyrrolidone (PVP). Alternative additives such as Pt on carbon and carbon-nanotubes (CNTs) were also successfully incorporated by this route, and in all cases the PVP could be removed from the electrode by oxygen plasma treatment without damage to the structure. In the absence of additives (Pt, Pt/C and CNTs), the feature sizes were larger, 300 nm, and the structure morphologically unstable, with significant coarsening evident after exposure to ambient conditions for just two days. Electrochemical impedance spectroscopy under humidified hydrogen at 240 °C indicated an interfacial impedance of ~1.5 Ω cm^2 for the Pt/CsH_2PO_4 composite electrodes with a total Pt loading of 0.3 ± 0.2 mg cm^(â2). This result corresponds to a 30-fold decrease in Pt loading relative to mechanically milled electrodes with comparable activity, but further increases in activity and Pt utilization are required if solid acid fuel cells are to attain widespread commercial adoption
Prevalence and assessment of factors contributing to adverse drug reactions in wards of a tertiary care hospital, India
BACKGROUND: Adverse drug reactions account for the highest proportion among the causes of morbidity and mortality in clinical wards and are posing a considerable challenge. Hence, the objective of this study was to find out the prevalence of adverse drug reactions and the factors which contribute to their prevalence. METHODS: A prospective patient record review was carried out at a tertiary care hospital in North India from August 2010- May 2011. A total of 1033 subjects admitted to hospital for any kind of treatment were included while patients admitted in the ward because of adverse drug reactions were excluded. The ward where we collected the data includes multispecialty and cardiovascular wards. The causality, severity, and preventability of adverse drug reactions were assessed using Naranjo, modified Hartwig, and Schumock and Thornton criteria, respectively. KolmogorovâSmyrnov, chi âsquare and multiple logistic regression tests were used to determine adverse drug reactions ascribed to drugs.RESULTS: Out of 1033 patients whose records were assessed, 167(16.2%) experienced one or more adverse drug reactions. The metabolic systems, which accounted for 49(24.6%) were most frequently affected by adverse drug reactions, followed by gastrointestinal, 45(22.6%); hematological, 28(14.1%) and cutaneous, 21(10.6%) systems. The drug classes most frequently associated with the reactions were antibiotics 40(20.1%), diuretics 35(17.6%) and anticoagulants 30(15.1%). According to the selected preventability scale, 72(36.2%) adverse drug reactions were classified as probably or definitely preventable. About 165(83%) of the reactions were type A, which represents augmentation of the pharmacological action of a drug. Number of drugs, length of hospitalization and number of diagnosis were identified as significant predisposing factors for ADRs.CONCLUSION: The result of this study suggested that adverse drug reactions were significant causes of superimposed health problems that occur following hospitalization. The major risk factors associated with ADR include number of drugs, length of hospitalization and number of diagnosis. Based on the findings a rigorous study is recommended to determine the burden and identify the risk factors of adverse drug reactions to target interventions.KEYWORDS: Adverse drug reactions, Causality assessments, Type A reactions, Predisposing facto
Construction of the Key Lake Tailings Facility
Construction of the Tailings Storage Facility for the Key Lake Project a major uranium mine in northern Saskatchewan, Canada, was completed in June, 1983. Principal design features of the tailings facility are an underseal and underdrainage system over the entire area, systematic deposition of the tailings in thin layers using the sub-aerial technique, and continuous removal and recycling of all surface water and underdrainage outflows to the mill for treatment. These features are designed to achieve a consolidated, drained tailings deposit suitable for immediate decommissioning QD completion of milling, and with a minimal potential of long term seepage. The design has used naturally occurring materials as far as possible, with the underseal constructed by modification of the natural till with imported bentonite. Design requirements, specifications and quality control procedures during construction are described, together with initial deposition of the tailings slurry
Evidence for compact cooperatively rearranging regions in a supercooled liquid
We examine structural relaxation in a supercooled glass-forming liquid
simulated by NVE molecular dynamics. Time correlations of the total kinetic
energy fluctuations are used as a comprehensive measure of the system's
approach to the ergodic equilibrium. We find that, under cooling, the total
structural relaxation becomes delayed as compared with the decay of the
component of the intermediate scattering function corresponding to the main
peak of the structure factor. This observation can be explained by collective
movements of particles preserving many-body structural correlations within
compact 3D cooperatively rearranging regions.Comment: 8 pages, 4 figure
Irreversibility in response to forces acting on graphene sheets
The amount of rippling in graphene sheets is related to the interactions with
the substrate or with the suspending structure. Here, we report on an
irreversibility in the response to forces that act on suspended graphene
sheets. This may explain why one always observes a ripple structure on
suspended graphene. We show that a compression-relaxation mechanism produces
static ripples on graphene sheets and determine a peculiar temperature ,
such that for the free-energy of the rippled graphene is smaller than
that of roughened graphene. We also show that depends on the structural
parameters and increases with increasing sample size.Comment: 4 pages, 4 Figure
Pressure-induced amorphization, crystal-crystal transformations and the memory glass effect in interacting particles in two dimensions
We study a model of interacting particles in two dimensions to address the
relation between crystal-crystal transformations and pressure-induced
amorphization. On increasing pressure at very low temperature, our model
undergoes a martensitic crystal-crystal transformation. The characteristics of
the resulting polycrystalline structure depend on defect density, compression
rate, and nucleation and growth barriers. We find two different limiting cases.
In one of them the martensite crystals, once nucleated, grow easily
perpendicularly to the invariant interface, and the final structure contains
large crystals of the different martensite variants. Upon decompression almost
every atom returns to its original position, and the original crystal is fully
recovered. In the second limiting case, after nucleation the growth of
martensite crystals is inhibited by energetic barriers. The final morphology in
this case is that of a polycrystal with a very small crystal size. This may be
taken to be amorphous if we have only access (as experimentally may be the
case) to the angularly averaged structure factor. However, this `X-ray
amorphous' material is anisotropic, and this shows up upon decompression, when
it recovers the original crystalline structure with an orientation correlated
with the one it had prior to compression. The memory effect of this X-ray
amorphous material is a natural consequence of the memory effect associated to
the underlying martensitic transformation. We suggest that this kind of
mechanism is present in many of the experimental observations of the memory
glass effect, in which a crystal with the original orientation is recovered
from an apparently amorphous sample when pressure is released.Comment: 13 pages, 13 figures, to be published in Phys. Rev.
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