376 research outputs found
Quantum phase slips in a confined geometry
We consider tunneling of vortices across a superconducting film that is both
narrow and short (and connected to bulk superconducting leads at the ends). We
find that in the superconducting state the resistance, at low values of the
temperature (T) and current, does not follow the power-law dependence on T
characteristic of longer samples but is exponential in 1/T. The coefficient of
1/T in the exponent depends on the length or, equivalently, the total
normal-state resistance of the sample. These conclusions persist in the
one-dimensional limit, which is similar to the problem of quantum phase slips
in an ultra-narrow short wire.Comment: 14 pages, 1 figure; published in Phys. Rev.
Mathematical modelling of the spatial network of bone implants obtained by 3D-prototyping
In this paper, the mathematical model suitable for bone implants 3D-prototyping is proposed. The composite material with the spatial configuration of reinforcement with matrix of hydroxyapatite and titanium alloys fibers is considered. An octahedral cell is chosen as an elementary volume. The distribution of reinforcing fibers is described by textural parameters. Textural parameters are integrated characteristics that summarize information on the direction of reinforcing fibers and their volume fractions. Textural parameters, properties of matrix and reinforcing fibers allow calculating effective physical and mechanical properties of the composite material. The impact of height and width of the octahedral reinforcement cells on textural parameters of the composite material is investigated in this work. The impact of radius of fibers is also analyzed. It is shown that the composite becomes quasi-isotropic under certain geometrical parameters of cell. © 2016 Author(s)
International students academic mobility automatization in higher education establishments
The research is dedicated to the question of international studentsтacademic mobility automatization due to engineering and design of the special information system. This system should minimize the role of an expert at each stage of mobility support. Some features of such system are considered in the paper.В докладе рассматривается вопрос автоматизации международной студенческой академической мобильности за счёт разработки и внедрения информационной системы, минимизирующей участие эксперта в процессе сопровождения мобильности. Выдвинуты идеи относительно составных модулей такой системы
Quantum Dew
We consider phase separation in nonequilibrium Bose gas with an attractive
interaction between the particles. Using numerical integrations on a lattice,
we show that the system evolves into a state that contains drops of
Bose-Einstein condensate suspended in uncondensed gas. When the initial gas is
sufficiently rarefied, the rate of formation of this quantum dew scales with
the initial density as expected for a process governed by two-particle
collisions.Comment: 4 pages, revtex, 5 figure
Tunneling in a uniform one-dimensional superfluid: emergence of a complex instanton
In a uniform ring-shaped one-dimensional superfluid, quantum fluctuations
that unwind the order parameter need to transfer momentum to quasiparticles
(phonons). We present a detailed calculation of the leading exponential factor
governing the rate of such phonon-assisted tunneling in a weakly-coupled Bose
gas at a low temperature . We also estimate the preexponent. We find that
for small superfluid velocities the -dependence of the rate is given mainly
by , where is the momentum transfer, and is the
phonon speed. At low , this represents a strong suppression of the rate,
compared to the non-uniform case. As a part of our calculation, we identify a
complex instanton, whose analytical continuation to suitable real-time segments
is real and describes formation and decay of coherent quasiparticle states with
nonzero total momenta.Comment: 15 pages, 3 figures; to be published in Phys. Rev.
Cosmic microwave background and parametric resonance in reheating
The variation of the perturbative 3-curvature parameter, \zeta, is
investigated in the period of reheating after inflation. The two-field model
used has the inflaton, with an extra scalar field coupled to it, and non-linear
effects of both fields are included as well as a slow decay mechanism into the
hydrodynamic fluid of the radiation era. Changes in \zeta occur and persist
into the succeeding cosmic eras to influence the generation of the cosmic
microwave background fluctuations.Comment: 21 pages, 6 figures.Corrects misprinted formula and 2 number
Preheating of the nonminimally coupled inflaton field
We investigate preheating of an inflaton field coupled nonminimally to
a spacetime curvature. In the case of a self-coupling inflaton potential
, the dynamics of preheating changes by the effect of
the negative . We find that the nonminimal coupling works in two ways.
First, since the initial value of inflaton field for reheating becomes
smaller with the increase of , the evolution of the inflaton quanta is
delayed for fixed . Second, the oscillation of the inflaton field is
modified and the nonadiabatic change around occurs significantly. That
makes the resonant band of the fluctuation field wider. Especially for strong
coupling regimes , the growth of the inflaton flutuation is
dominated by the resonance due to the nonminimal coupling, which leads to the
significant enhancement of low momentum modes. Although the final variance of
the inflaton fluctuation does notchange significantly compared with the
minimally coupled case, we have found that the energy transfer from the
homogeneous inflaton to created particles efficiently occurs for .Comment: 13pages, 11figure
Post-Inflationary Reheating
We study a model for reheating that has been much investigated for parametric
resonance, having a quartic interaction of the scalar inflaton with another
scalar field. Attention is particularly on the quantum excitations of the
inflaton field and the metric perturbation with a smooth transition from
quantum to classical stochastic states, followed through from a specific
inflation model to a state including a relativistic fluid. The scalar fields
enter non-perturbatively but the metric enters perturbatively, and the validity
of this latter is assessed. In this model our work seems to point the large
scale curvature parameter changing.Comment: 25 pages, 6 figures. Coding error(misprint) corrected:figures and
some conclusions change
Preheating in Supersymmetric Hybrid Inflation
We study preheating in a general class of supersymmetric hybrid inflation
model. Supersymmetry leads to only one coupling constant in the potential and
thus only one natural frequency of oscillation for the homogeneous fields,
whose classical evolution consequently differs from that of a general
(non-supersymmetric) hybrid model. We emphasise the importance of mixing
effects in these models which can significantly change the rate of production
of particles. We perform a general study of the rate of production of the
particles associated with the homogeneous fields, and show how preheating is
efficient in producing these quanta. Preheating of other particle species will
be model dependent, and in order to investigate this we consider a realistic
working model of supersymmetric hybrid inflation which solves the strong-CP
problem via an approximate Peccei-Quinn symmetry, which was proposed by us
previously. We study axion production in this model and show that properly
taking into account the mixing between the fields suppresses the axion
production, yet enhances the production of other particles. Finally we
demonstrate the importance of backreaction effects in this model which have the
effect of shutting off axion production, leaving the axion safely within
experimental bounds.Comment: 37 pages, Latex, 11 eps figures, 14 ps (colour) figure
Leptogenesis with Left-Right domain walls
The presence of domain walls separating regions of unbroken and
is shown to provide necessary conditions for leptogenesis which
converts later to the observed Baryon aymmetry. The strength of lepton number
violation is related to the majorana neutrino mass and hence related to current
bounds on light neutrino masses. Thus the observed neutrino masses and the
Baryon asymmetry can be used to constrain the scale of Left-Right symmetry
breaking.Comment: References added, To appear in Praman
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