Condensate formation and vortex generation in Bose gas upon cooling

The mechanism of transition of a Bose gas to the superfluid state via thermal fluctuations under the condition of external cooling at a temperature above the transition point is considered. The probability of formation of such critical fluctuations (instantons) is calculated; it is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part.     

Comments on transitions in bulk tetramethyltin Sn(CH3)4 and as adsorbate on a (0001) graphite plane

In the case of tetramethyltin, whether in bulk form or in the form of an adsorbate on (0001) graphite basal plane, it was found that anomalies in the Mössbauer or X-ray diffraction parameters occur at similar temperatures, viz: 83 K, 95 K, and 125 K. It is therefore suggested that these anomalies can be associated in some way with intramolecular rearrangements and be affected by intramolecular motions.Sponsored by the U.S.-Israel Binational Science Foundation     

Low temperature anharmonicity in Sn(CH3)4 due to methyl group reorientation: A Mössbauer study

The detailed temperature variation of the Mössbauer spectral intensity in Sn(CH₃)₄ displays a pronounced drop of the Debye temperature from _D 96K below the transition temperature (T _t 43K) to _D 76K above it. The transition atT _t is discussed in terms of recent INS and NMR results where increased motion of inequivalent CH₃ groups has been observed around the temperatureT _t .Supported by the U.S.-Israel Binational Science Foundation     

The Schwinger variational principle for the rearrangement collisions

The Lippmann-Schwinger equations were rewritten in the form of Faddeev equations. The number of equations is determined by the number of open channels. On the basis of the Schwinger variational principle the approximate one-dimensional equations for the rearrangement collisions are obtained.Submitted to the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.In conclusion the authors wish to thank V. B. Belyaev for useful discussions and interest in this work.     

Multiple-channel wavelength conversion by use of engineered quasi-phase-matching structures in LiNbO(3) waveguides

We report difference frequency generation-based wavelength converters with multiple phase-matching wavelengths that use engineered quasi-phase-matching structures in LiNbO(3) waveguides. Multiple-channel wavelength conversion is demonstrated within the 1.5-mum band and between the 1.3- and 1.5-mum bands. With simultaneous use of M pump wavelengths, these devices can also be used to perform wavelength broadcasting, in which each of N input signals is converted into M output wavelengths.     

Coarsening kinetics with elastic effects

We discuss the coarsening process of melt inclusions inside a solid phase. Elastic effects lead to an oblate shape of the particles, resulting in a system with strong diffusional and elastic interactions between inclusions. The usual mean-field approximation breaks down and several independent length scales have to be taken into account. In a system of parallel oriented particles we find scaling laws for the coarsening of the different length scales involved. In particular, the lateral size of the particles obeys a nontrivial growth law, R approximately t(5/12).     

Nonlinear Green’s functions in smectics

A solution of the problem of the strain of smectics subjected to a localized force has been proposed. An increase in the force is accompanied by a change from a linear increase in the strain amplitude to a square-root increase.