3,483 research outputs found
Electronic and phononic properties of the chalcopyrite CuGaS2
The availability of ab initio electronic calculations and the concomitant
techniques for deriving the corresponding lattice dynamics have been profusely
used for calculating thermodynamic and vibrational properties of
semiconductors, as well as their dependence on isotopic masses. The latter have
been compared with experimental data for elemental and binary semiconductors
with different isotopic compositions. Here we present theoretical and
experimental data for several vibronic and thermodynamic properties of CuGa2, a
canonical ternary semiconductor of the chalcopyrite family. Among these
properties are the lattice parameters, the phonon dispersion relations and
densities of states (projected on the Cu, Ga, and S constituents), the specific
heat and the volume thermal expansion coefficient. The calculations were
performed with the ABINIT and VASP codes within the LDA approximation for
exchange and correlation and the results are compared with data obtained on
samples with the natural isotope composition for Cu, Ga and S, as well as for
isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev
The nature of the continuum limit in the 2D gauge model
The RP(2) gauge model is studied in 2D. We use Monte-Carlo renormalization
techniques for blocking the mean spin-spin interaction, , and the mean gauge
field plaquette, . The presence of the O(3) renormalized trajectory is
verified and is consistent with the known three-loop beta-function. The
first-order `vorticity' transition observed by Solomon et al. is confirmed, and
the location of the terminating critical point is established. New scaling
flows in (,) are observed associated with a large exponent kappa in the
range 4~5. The scaling flows give rise to a strong cross-over effect between
regions of high and low vorticity and are likely to induce an apparent signal
for scaling in the cross-over region which we propose explains the scaling
observed for RP(2), RP(3) and SO(4)-matrix models. The signal for this `pseudo'
scaling will occur for the RP(2) spin model in the cross-over region which is
the region in which computer simulations are done. We find that the RP(2) spin
model is in the same universality class as the O(3) spin model but that it is
likely to require a very large correlation length before the true scaling of
this class sets in. We conjecture that the scaling flows are due either to the
influence of a nearby new renormalized trajectory or to the ghost of the
Kosterlitz-Thouless trajectory in the associated XY model.Comment: 29 pages, LATEX2e, 10 figures, uses styles[epsfig,latexsym
Expansion of epidemic dengue viral infections to Pakistan
Objectives: Antibodies to dengue viruses have occasionally been reported in individuals in Pakistan, but the frequency of occurrence of dengue infection in Pakistan is unclear. The first confirmed dengue hemorrhagic fever outbreak in Pakistan occurred in 1994. In October 1995, the authors investigated an outbreak of a febrile illness among employees of a construction contractor at a power generation plant in Baluchistan, Pakistan, to determine the cause of illness and recommend appropriate preventive measures.Methods: The work site and living arrangements were inspected, a questionnaire was administered, and serum samples were collected from all consenting contractor employees and their families if they lived at the camp. Sera were analyzed for IgM against dengue virus, using an enzyme-linked immunosorbent assay.Results: Interviews were conducted with 76 persons (mean age, 42y); 95% were men. Forty-two persons (55%) reported having experienced fever, headache, or myalgia in the preceding 6 weeks. Fifty-seven subjects (75%) had IgM antibodies against at least one dengue serotype; 45 subjects (59%) had IgM antibodies against dengue serotype 2.CONCLUSION: This was an outbreak of dengue fever due to multiple serotypes of dengue virus. This confirms that epidemic dengue infection was present in southern Pakistan for 2 consecutive years
A cascade of magnetic field induced spin transitions in LaCoO3
We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.Comment: 5 pages + supplementary materials, 5 figure
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