3,386 research outputs found
Direct photon production from hadronic sources in high-energy heavy-ion collisions
The low direct photon production from a variety of the hadronic sources
is studied within the microscopic HSD transport approach for p+C, p+Pb and
Pb+Pb collisions at 160 A GeV. The direct photon emission from elementary
hadronic scatterings as well as meson-meson bremsstrahlung are incorporated.
The influence of in-medium effects such as a collisional broadening of the
vector-meson spectral functions on the photon emission rate is found to be
hardly observable in the final spectra which are dominated by bremsstrahlung
type processes. The uncertainties in the subtraction of the 'background' from
the photon decay of hadronic resonances inside the hot and dense fireball is
investigated, additionally. Our findings are relevant for the interpretation
and extraction of experimental data on direct photon production at low .Comment: 25 pages, 10 figures, to be published in Phys. Rev.
Global well-posedness for a slightly supercritical surface quasi-geostrophic equation
We use a nonlocal maximum principle to prove the global existence of smooth
solutions for a slightly supercritical surface quasi-geostrophic equation. By
this we mean that the velocity field is obtained from the active scalar
by a Fourier multiplier with symbol , where
is a smooth increasing function that grows slower than as
.Comment: 11 pages, second version with slightly stronger resul
Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles
We present a first principles study of an unusual heterostructure, an
atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the
two bulk constituent materials, BiFeO3 and BiMnO3. The "nanocheckerboard" is
found to have a multiferroic ground state with the desired properties of each
constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively.
The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3
system is studied. The checkerboard geometry is seen to give rise to a a novel
magnetostructural effect that is neither present in the bulk constituent
materials, nor in the layered BiFeO3-BiMnO3 superlattice.Comment: 15 pages, 14 figure
Scalar and vector Keldysh models in the time domain
The exactly solvable Keldysh model of disordered electron system in a random
scattering field with extremely long correlation length is converted to the
time-dependent model with extremely long relaxation. The dynamical problem is
solved for the ensemble of two-level systems (TLS) with fluctuating well depths
having the discrete Z_2 symmetry. It is shown also that the symmetric TLS with
fluctuating barrier transparency may be described in terms of the planar
Keldysh model with dime-dependent random planar rotations in xy plane having
continuous SO(2) symmetry. The case of simultaneous fluctuations of the well
depth and barrier transparency is subject to non-abelian algebra. Application
of this model to description of dynamic fluctuations in quantum dots and
optical lattices is discussed.Comment: 6 pages, 5 eps figures. Extended version of the paper to be published
in JETP Lett 89 (2009
Gravitational lensing due to dark matter modelled by vector field
The specified constant 4-vector field reproducing the spherically symmetric
stationary metric of cold dark matter halo in the region of flat rotation
curves results in a constant angle of light deflection at small impact
distances. The effective deflecting mass is factor greater than the
dark matter mass. The perturbation of deflection picture due to the halo edge
is evaluated.Comment: 17 pages, LaTeX iopart class, 10 eps figures; explanaitions and
discussion are extended and improved, reference added; version to appear in
Classical and Quantum Gravit
Influence of Parent–Child Interaction on Socio-emotional Development of Children With Perinatal Risks
The article is devoted to the study of the influence of peculiarities of child–parent interaction on the early socio-emotional development of children with perinatal risks. This is a relevant area since, first of all, there is an increasing number of children with such risks (especially, with the risk of autism spectrum disorders (ASD) andattention deficit hyperactivity disorder (ADHD)). Moreover, it is parents who can be most instrumental in the successful development, adaptation and socialization of children. The article examines Russian and foreign approaches to the definition of socio-emotional development, stages, and levels of its development. It also analyses the data obtained in the course of research of peculiarities of parent–child interaction with the help of video observation (PCI) that was conducted using the coding scales (SocialinteractionratingScale). In order to assess cognitive, speech, socio-emotional development, and adaptive behavior, «Bayley Scales of Infant Development Third Edition» were used. The data of eight children of the control group (average age 5–8months) and eight children of the experimental group with family risk of atypical development (older sibling or parent have a confirmed diagnosis of ASD and/or ADHD) (average age 2–66 months) were analyzed. Two-way analysis of variance showed that nondirective behavior of parents can lead to a more successful developmentof socio-emotional skills of children with the family risk of ASD and ADHD, namely, the skill ‘social setting’. The study is a pilot but demonstrates a potential for further research in this area.
Keywords: child–parent interaction, video observation, young children, family risk, socio-emotional developmen
Melting of hexagonal skyrmion states in chiral magnets
Skyrmions are spiral structures observed in thin films of certain magnetic materials (Uchida et al 2006 Science 311 359–61). Of the phases allowed by the crystalline symmetries of these materials (Yi et al 2009 Phys. Rev. B 80 054416), only the hexagonally packed phases (SCh) have been observed. Here the melting of the SCh phase is investigated using Monte Carlo simulations. In addition to the usual measure of skyrmion density, chiral charge, a morphological measure is considered. In doing so it is shown that the low-temperature reduction in chiral charge is associated with a change in skyrmion profiles rather than skyrmion destruction. At higher temperatures, the loss of six-fold symmetry is associated with the appearance of elongated skyrmions that disrupt the hexagonal packing
Coupled multiple-mode theory for pairing mechanism in iron based superconductors
We investigate the interplay between the magnetic and the superconducting
degrees of freedom in unconventional multi-band superconductors such as iron
pnictides. For this purpose a dynamical mode-mode coupling theory is developed
based on the coupled Bethe-Salpeter equations. In order to investigate the
region of the phase diagram not too far from the tetracritical point where the
magnetic spin density wave, (SDW) and superconducting (SC) transition
temperatures coincide, we also construct a Ginzburg - Landau functional
including both SC and SDW fluctuations in a critical region above the
transition temperatures. The fluctuation corrections tend to suppress the
magnetic transition, but in the superconducting channel the intraband and
interband contribution of the fluctuations nearly compensate each other.Comment: 17 pages, 5 figure
Generation of Intrinsic Vibrational Gap Modes in Three-Dimensional Ionic Crystals
The existence of anharmonic localization of lattice vibrations in a perfect
3-D diatomic ionic crystal is established for the rigid-ion model by molecular
dynamics simulations. For a realistic set of NaI potential parameters, an
intrinsic localized gap mode vibrating in the [111] direction is observed for
fcc and zinc blende lattices. An axial elastic distortion is an integral
feature of this mode which forms more readily for the zinc blende than for the
fcc structure. Molecular dynamics simulations verify that in each structure
this localized mode may be stable for at least 200 cycles.Comment: 5 pages, 4 figures, RevTeX, using epsf.sty. To be published in Phys.
Rev. B. Also available at http://www.msc.cornell.edu/~kiselev
Physics of B_c mesons
In the framework of potential models for heavy quarkonium the mass spectrum
for the system () is considered. Spin-dependent splittings, taking
into account a change of a constant for effective coulomb interaction between
the quarks, and widths of radiative transitions between the () levels
are calculated. In the framework of QCD sum rules, masses of the lightest
vector and pseudoscalar states are estimated, scaling relation
for leptonic constants of heavy quarkonia is derived, and the leptonic constant
is evaluated. The decays are considered in the framework of
both the potential models and the QCD sum rules, where the significance of
Coulomb-like corrections is shown. The relations, following from the
approximate spin symmetry for the heavy quarks in the heavy quarkonium, are
analysed for the form factors of the semileptonic weak exclusive decays of
. The lifetime is evaluated with the account of the corrections to
the spectator mechanism of the decay, because of the quark binding into the
meson. The total and differential cross sections of the production in
different interactions are calculated. The analytic expressions for the
fragmentational production cross sections of are derived. The possibility
of the practical search in the current and future experiments at
electron-positron and hadron colliders is analysed.Comment: 81 page, latex, ihep.sty is required and attached in the end of the
file after \end{document}, figures are not availabl
- …