116 research outputs found
Elasticity modules and acoustic properties of metal ceramics on the basis of tungsten monocarbide
The results of measurements of acoustic wave speeds and elasticity modules of metal ceramic alloys on the basis of tungsten monocarbide in temperature range of 100...295 K as well as amplitude dependences of internal friction at temperatures 140...295 K and after ?-irradiation (60Со, 1,25 MeV, 5.103 and 105 Gy) have been given. It was shown that elasticity modules of alloys decrease monotonously at increase of cobalt concentration. Radiation influence stimulates the processes complicating movement of grain boundary dislocations in alloys. Representation of these alloys in the form of isotropic mixes of anisotropic phases describes qualitatively correctly the dependence of elasticity modules on structure. The resulted experimental and calculated values of elasticity modules may be used for estimation of elastic and strength properties of these alloy
Darboux Transformation of the Green Function for the Dirac Equation with the Generalized Potential
We consider the Darboux transformation of the Green functions of the regular
boundary problem of the one-dimensional stationary Dirac equation. We obtained
the Green functions of the transformed Dirac equation with the initial regular
boundary conditions. We also construct the formula for the unabridged trace of
the difference of the transformed and the initial Green functions of the
regular boundary problem of the one-dimensional stationary Dirac equation. We
illustrate our findings by the consideration of the Darboux transformation for
the Green function of the free particle Dirac equation on an interval.Comment: 14 pages,zip. file: Latex, 1 figure. Typos corrected, the figure
replace
Interdependence between integrable cosmological models with minimal and non-minimal coupling
We consider the relation between exact solutions of cosmological models
having minimally and non-minimally coupled scalar fields. This is done for a
particular class of solvable models which, in the Einstein frame, have
potentials depending on hyperbolic functions and in the Jordan frame, where the
non-minimal coupling is conformal, possess a relatively simple dynamics. We
show that a particular model in this class can be generalized to the cases of
closed and open Friedmann universes and still exhibits a simple dynamics.
Further we illustrate the conditions for the existences of bounces in some
sub-classes of the set of integrable models we have considered.Comment: 15 pages, v2: figures and references added, accepted for publication
in CQ
Induced gravity, and minimally and conformally coupled scalar fields in Bianchi-I cosmological models
We study the cosmological evolution and singularity crossing in the Bianchi-I
universe filled with a conformally coupled scalar field and compare them with
those of the Bianchi-I universe filled with a minimally coupled scalar field.
We also write down the solution for the Bianchi-I Universe in the induced
gravity cosmology.Comment: 11 pages, 3 figures, final version, to appear in Physical Review
Integrable cosmological models with non-minimally coupled scalar fields
We obtain general solutions for some flat Friedmann universes filled with a
scalar field in induced gravity models and models including the
Hilbert-Einstein curvature term plus a scalar field conformally coupled to
gravity. As is well known, these models are connected to minimally coupled
models through the combination of a conformal transformation and a
transformation of the scalar field. The explicit forms of the self-interaction
potentials for six exactly solvable models are presented here. We obtain the
general solution for one of the integrable models, namely, the induced gravity
model with a power-law potential for the self-interaction of the scalar field.
We argue that although being mathematically in a one-to-one correspondence with
the solutions in the minimally coupled models, the solutions in the
corresponding non-minimally coupled models are physically different. This is
because the cosmological evolutions seen by an internal observer connected with
the cosmic time can be quite different. The study of a few induced gravity
models with particular potentials gives us an explicit example of such a
difference.Comment: 20 pages, v3: references added, accepted for publication in CQ
Connection between the Green functions of the supersymmetric pair of Dirac Hamiltonians
The Sukumar theorem about the connection between the Green functions of the
supersymmetric pair of the Schr\"odinger Hamiltonians is generalized to the
case of the supersymmetric pair of the Dirac Hamiltonians.Comment: 12 pages,Latex, no figure
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