6,499 research outputs found
Epitaxial strain effects in the spinel ferrites CoFe2O4 and NiFe2O4 from first principles
The inverse spinels CoFe2O4 and NiFe2O4, which have been of particular
interest over the past few years as building blocks of artificial multiferroic
heterostructures and as possible spin-filter materials, are investigated by
means of density functional theory calculations. We address the effect of
epitaxial strain on the magneto-crystalline anisotropy and show that, in
agreement with experimental observations, tensile strain favors perpendicular
anisotropy, whereas compressive strain favors in-plane orientation of the
magnetization. Our calculated magnetostriction constants of
about -220 ppm for CoFe2O4 and -45 ppm for NiFe2O4 agree well with available
experimental data. We analyze the effect of different cation arrangements used
to represent the inverse spinel structure and show that both LSDA+U and GGA+U
allow for a good quantitative description of these materials. Our results open
the way for further computational investigations of spinel ferrites
Superconductivity in epitaxial thin films of NaxCoO2 y D2O
The observation of superconductivity in the layered transition metal oxide
NaxCoO2 y H2O (K. Takada et al., Nature 422, 53 (2003)) has caused a tremendous
upsurge of scientific interest due to its similarities and its differences to
the copper based high-temperature superconductors. Two years after the
discovery, we report the fabrication of single-phase superconducting epitaxial
thin films of Na0.3CoO2 x 1.3 D2O grown by pulsed laser deposition technique.
This opens additional roads for experimental research exploring the
superconducting state and the phase diagram of this unconventional material.Comment: 3 pages, 5 figure
Effects of weightlessness on human baroreflex function
Impaired cardiovascular function, characterized by orthostatic intolerance and reduced exercise capacity, is a result of space travel. We hypothesized that postflight baroreflex dysfunction may contribute. We studied the vagally mediated carotid baroreceptor-cardiac reflex response of 6 astronauts before, during, and after the ten day SLS-l mission. A series of R-waves triggered pressure and suction steps (from 40 to minus 65 mmHg) were delivered to a neck chamber during held expirtation. Resulting R-R interval changes were plotted against carotid distending pressure (systolic - neck pressure), and curve parameters calculated. After an initial rise, the operational point declined consistently during the flight and reached a nadir on landing day, but had recovered to preflight levels by L + 4. Slope and range of the response declined throughout the flight, were slightly recovered by the time measurements were made on landing day, but still were reduced on L + 4. These data indicate that space flight results in a significant impairment of the carotid baroreceptor cardiac reflex response
Environmental Dependence of the Fundamental Plane of Galaxy Clusters
Galaxy clusters approximate a planar (FP) distribution in a three-dimensional
parameter space which can be characterized by optical luminosity, half-light
radius, and X-ray luminosity. Using a high-quality catalog of cluster
redshifts, we find the nearest neighbor cluster for those common to an FP study
and the cluster catalog. Examining scatter about the FP, we find 99.2%
confidence that it is dependent on nearest neighbor distance. Our study of
X-Ray clusters finds that those with high central gas densities are
systematically closer to neighbor clusters. If we combine results here with
those of Fritsch and Buchert, we find an explanation for some of our previous
conclusions: Clusters in close proximity to other clusters are more likely to
have massive cooling flows because they are more relaxed and have higher
central gas densities.Comment: Accepted for publication in Astrophysical Journal Letters. Moderate
revisions, including more statistical analysis and discussion. Latex, 7 page
L-Lactide and ϵ-caprolactone ring opening polymerization by binary catalysts systems that include bis-ligated magnesium complexes
A series of bis-ligated magnesium complexes supported by tridentate ketoiminates containing electron-donating and electron-withdrawing groups were prepared. The complexes were characterized with 1H, 13C, and 19F NMR, absorbance spectroscopy, and x-ray crystallography. The complexes were assessed for their ring opening polymerization activity with L-lactide (L-lac) and ϵ-caprolactone (eCL) in binary catalyst systems with 4-fluorophenol at 100 °C. The magnesium complexes supported by ketoiminates bearing electron-donating groups yielded greater percentage conversions from monomers to polymers than those containing electron-withdrawing groups for both L-lac and eCL. The magnesium complexes were more efficient at polymerizing L-lac than eCL, and di-block copolymers of PCL-PLA were produced by the sequential polymerization of eCL followed by L-lac
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