109 research outputs found
Composition of powders produced by electrospark dispersion of metal granules in water
The results of experimental studies of metal powders composition produced by electrospark dispersion according to the scheme "metal electrodes - metal granule loading - distilled water" are given in the paper. With a help of X-ray diffraction analysis and other methods, it was found that chemical and phase composition of dispersion products is determined by affinity of metal to oxygen
Dislocation Kinks in Copper: Widths, Barriers, Effective Masses, and Quantum Tunneling
We calculate the widths, migration barriers, effective masses, and quantum
tunneling rates of kinks and jogs in extended screw dislocations in copper,
using an effective medium theory interatomic potential. The energy barriers and
effective masses for moving a unit jog one lattice constant are close to
typical atomic energies and masses: tunneling will be rare. The energy barriers
and effective masses for the motion of kinks are unexpectedly small due to the
spreading of the kinks over a large number of atoms. The effective masses of
the kinks are so small that quantum fluctuations will be important. We discuss
implications for quantum creep, kink--based tunneling centers, and Kondo
resonances
Relativistic recoil corrections to the electron-vacuum-polarization contribution in light muonic atoms
The relativistic recoil contributions to the Uehling corrections are
revisited. We consider a controversy in recent calculations based on different
approaches including Breit-type and Grotch-type calculations. We have found
that calculations of those authors were in fact done in different gauges and in
some of those gauges contributions the retardation and two-photon-exchange
effects were missed. We have evaluated such effects and obtained a consistent
result from those approaches. We present a correct expression for the
Grotch-type approach which produces a correct gauge-invariant result. We also
consider a finite-nuclear-size correction for the Uehling term. The results are
presented for muonic hydrogen and deuterium atoms and for muonic helium-3 and
helium-4 ions.Comment: Submitted to Phys. Rev. A; in v.2 results for muonic helium are
correcte
Breit Hamiltonian and QED Effects for Spinless Particles
We describe a simplified derivation for the relativistic corrections of order
for a bound system consisting of two spinless particles. We devote
special attention to pionium, the bound system of two oppositely charged pions.
The leading quantum electrodynamic (QED) correction to the energy levels is of
the order of and due to electronic vacuum polarization. We analyze
further corrections due to the self-energy of the pions, and due to recoil
effects, and we give a complete result for the scalar-QED leading logarithmic
corrections which are due to virtual loops involving only the scalar
constituent particles (the pions); these corrections are of order for S states.Comment: 12 pages, LaTeX; references added (J. Phys. B, in press
Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell during initial stage of shell expansion
Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell, created under laser heating of nanoparticle in water, were theoretically investigated. Vapor shell expansion leads to decreasing up to one to two orders of magnitude in comparison with initial values of scattering and extinction of the radiation with wavelengths 532 and 633 nm by system while shell radius is increased up to value of about two radii of nanoparticle. Subsequent increasing of shell radius more than two radii of nanoparticle leads to rise of scattering and extinction properties of system over initial values. The significant decrease of radiation scattering and extinction by system of nanoparticle-vapor shell can be used for experimental detection of the energy threshold of vapor shell formation and investigation of the first stages of its expansion
The Boltzmann equation for colourless plasmons in hot QCD plasma. Semiclassical approximation
Within the framework of the semiclassical approximation, we derive the
Boltzmann equation describing the dynamics of colorless plasmons in a hot QCD
plasma. The probability of the plasmon-plasmon scattering at the leading order
in the coupling constant is obtained. This probability is gauge-independent at
least in the class of the covariant and temporal gauges. It is noted that the
structure of the scattering kernel possesses important qualitative difference
from the corresponding one in the Abelian plasma, in spite of the fact that we
focused our study on the colorless soft excitations. It is shown that
four-plasmon decay is suppressed by the power of relative to the process of
nonlinear scattering of plasmons by thermal particles at the soft momentum
scale. It is stated that the former process becomes important in going to the
ultrasoft region of the momentum scale.Comment: 41, LaTeX, minor changes, identical to published versio
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