921 research outputs found
Interatomic potentials for the vibrational properties of III-V semiconductor nanostructures
We derive interatomic potentials for zinc blende InAs, InP, GaAs and GaP
semiconductors with possible applications in the realm of nanostructures. The
potentials include bond stretching interaction between the nearest and
next-nearest neighbors, a three body term and a long-range Coulomb interaction.
The optimized potential parameters are obtained by (i) fitting to bulk phonon
dispersions and elastic properties and (ii) constraining the parameter space to
deliver well behaved potentials for the structural relaxation and vibrational
properties of nanostructure clusters. The targets are thereby calculated by
density functional theory for clusters of up to 633 atoms. We illustrate the
new capability by the calculation Kleinman and Gr\"uneisen parameters and of
the vibrational properties of nanostructures with 3 to 5.5 nm diameter.Comment: 22 pages, 5 figures; Phys. Rev. B 201
Non-reciprocal light scattering by lattice of magnetic vortices
We report on experimental study of optical properties of two-dimensional
square lattice of triangle Co and CoFe nanoparticles with a vortex
magnetization distribution. We demonstrate that intensity of light scattered in
diffraction maxima depends on the vorticity of the particles magnetization and
it can be manipulated by applying an external magnetic field. The experimental
results can be understood in terms of phenomenological theory.Comment: 10 pages, 4 figure
Considerable enhancement of the critical current in a superconducting film by magnetized magnetic strip
We show that a magnetic strip on top of a superconducting strip magnetized in
a specified direction may considerably enhance the critical current in the
sample. At fixed magnetization of the magnet we observed diode effect - the
value of the critical current depends on the direction of the transport
current. We explain these effects by a influence of the nonuniform magnetic
field induced by the magnet on the current distribution in the superconducting
strip. The experiment on a hybrid Nb/Co structure confirmed the predicted
variation of the critical current with a changing value of magnetization and
direction of the transport current.Comment: 6 pages, 7 figure
Neutrino Geophysics at Baksan I: Possible Detection of Georeactor Antineutrinos
J.M. Herndon in 90-s proposed a natural nuclear fission georeactor at the
center of the Earth with a power output of 3-10 TW as an energy source to
sustain the Earth magnetic field. R.S. Raghavan in 2002 y. pointed out that
under certain condition antineutrinos generated in georeactor can be detected
using massive scintillation detectors. We consider the underground Baksan
Neutrino Observatory (4800 m.w.e.) as a possible site for developments in
Geoneutrino physics. Here the intrinsic background level of less than one
event/year in a liquid scintillation ~1000 target ton detector can be achieved
and the main source of background is the antineutrino flux from power reactors.
We find that this flux is ~10 times lower than at KamLAND detector site and two
times lower than at Gran Sasso laboratory and thus at Baksan the georeactor
hypothesis can be conclusively tested. We also discuss possible search for
composition of georector burning nuclear fuel by analysis of the antineutrino
energy spectrum.Comment: 7 pages in LaTeX, 3 PS figures, Submitted to Physics of Atomic Nucle
Finite size effects on thermal denaturation of globular proteins
Finite size effects on the cooperative thermal denaturation of proteins are
considered. A dimensionless measure of cooperativity, Omega, scales as N^zeta,
where N is the number of amino acids. Surprisingly, we find that zeta is
universal with zeta = 1 + gamma, where the exponent gamma characterizes the
divergence of the susceptibility for a self-avoiding walk. Our lattice model
simulations and experimental data are consistent with the theory. Our finding
rationalizes the marginal stability of proteins and substantiates the earlier
predictions that the efficient folding of two-state proteins requires the
folding transition temperature to be close to the collapse temperature.Comment: 3 figures. Physical Review Letters (in press
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