Fractal structures and multiparticle effects in soliton scattering.

We study in detail the interaction of composite solitary waves and consider, as an example, the breather collisions in a weakly discrete sine-Gordon equation. We reveal a physical mechanism of fractal soliton scattering associated with multiparticle effects, and demonstrate chaotic interaction of two breathers with incommensurable frequencies.

Periodic metastable structures in the discrete straight phi4 model.

For the discrete straight phi(4) model a class of metastable periodic solutions is given in the form of Fourier series. From the symmetry consideration, we eliminate the harmonics with zero amplitudes and thus, reduce the number of degrees of freedom. For the rest of harmonics we establish the hierarchy of their significance. For solutions with a small period we give the exact expression of energy density in terms of amplitudes of harmonics. Conditions of existence and stability of the solutions are discussed. For some limiting cases the approximate solutions of different kinds are given. The analytical results are compared with the results of numerical study. We also discuss a mechanism of transition from a metastable periodic structure into the ground state and apply the results to the lock-in transition in dielectric crystals supporting incommensurate phase.

Kink-breather solution in the weakly discrete Frenkel-Kontorova model

The discrete Frenkel-Kontorova model, having the sine-Gordon equation as the continuous analog, was investigated numerically at a small degree of discreteness. Interaction between a kink and a breather in a discrete system was compared with the exact three-soliton solution to the continuous sine-Gordon equation. Nontrivial effects of discreteness were found numerically. One is that a kink and a breather in the discrete system are mutually attractive quasiparticles, so they can be regarded as a three-soliton oscillatory system. The other is the energy exchange between a kink and a breather when their collision takes place in a vicinity of a separatrix solution to the continuous sine-Gordon equation. We have estimated numerically the kink-breather binding energy EB and the maximum possible exchange energy EE for different breather frequencies omega. The results suggest that there is a threshold breather frequency for the "spontaneous" breaking up of the three-soliton oscillatory system into a kink and a breather moving in opposite directions.

Comments on the characteristics of incommensurate modulation in quartz: discussion about a neutron scattering experiment.

From analysis of the elastic neutron scattering data of Dolino et al. [J. Phys. (Paris) (1984), 45, 361-371], it is shown that, besides the well identified components u(x) and u(y) of the acoustic displacements in the incommensurate (IC) phase of quartz, there also exists a strong component of the u(z) vector of the modulation. The existence of the large u(z) is not consistent with the currently accepted model for the IC transition in quartz, since the long-period IC modulation observed in quartz cannot induce any noticeable acoustic component u(z). The need for a new model is keenly felt in order to understand the origin of the IC modulation in quartz.

[Technical aids for children with cerebral palsy].

A variety of Technical Aids have been developed and adapted for children with cerebral palsy. The most important objects of Technical Aids are positioning, locomotion and communication. Essencially, Technical Aids are based on assistive technologies, and must be applied to the activities of daily living and to habilitation for children with cerebral palsy by themselves, their family and the professional staff in institutions. It is necessary not only to develop new Technical Aids, but also to extend each adaptive measures and applied technologies for all local areas.

Superfluorescent laser action at 404.7 nm from the transition of a mercury atom produced by photodissociation of HgBr(2) by an ArF laser.

Strong fluorescence with high directionality was observed for the first time to our knowledge from the mercury atomic transition 7(3)S(1)-6(3)P(0) at 404.7 nm by the photodissociation of HgBr(2). Superfluorescence could be obtained only in a limited temperature region (130-160 degrees C) when HgBr(2) was excited by an ArF (193-nm) laser above a certain threshold power. Mechanisms for the formation of the excited mercury atom and for the quenching of the lower metastable state 6(3)P(0) are briefly discussed.