X-ray diffraction pattern of a Gulyaev-Bleustein surface acoustic wave in grazing geometry

The X ray diffraction pattern of a Gulyaev-Bleustein surface acoustic wave (SAW) under grazing angles of incidence in noncoplanar symmetric Laue geometry has been considered. It is supposed that the propagation direction of an SAW makes a small angle with the diffraction vector. It is shown that small deviations from the Bragg angle (～0.01″ induced by the SAW and do not affect the reflection coefficient lead to the formation of diffraction satellites both in the cases of standing and traveling SAWs. It has been established that the recorded diffraction pattern, which is a time-averaged intensity distribution, has characteristic profiles for odd and even satellites.     

Aqueous dispersions of cholesteric liquid crystals and their optical properties

This paper reports on a theoretical and experimental investigation of light transmission by a layer of aqueous suspension of polymer dispersed cholesteric liquid crystals (CLC) with a helical molecular structure. The transmission spectra and the spectral order parameter of the supramolecular texture of CLC confirm the high degree of ordering of CLC molecules in the spherical cells. Cell morphology and the spectral dependences of light transmission by the plane-parallel layer of CLC aqueous dispersion are considered.     

Growth,X-ray structure and optical investigations of epitaxial films of solid solutions of lithium niobate-tantalate

Processes of the liquid phase epitaxy of films of solid solution of lithium niobate-tantalate grown from the limited plane-parallel volume of the liquid phase is considered in the paper. Morphological and structure characterstics of films are investigated. The possibility of the effective use of the obtained structures as active elements of the integrated optics is shown.     

Development of helical cholesteric structure in a nematic liquid crystal due to the dipole-dipole interaction

A nematic liquid crystalline phase is considered whose rod-like non-centrosymmetric molecules possess a permanent dipole moment. This phase is a “liquid ferroelectric” if all the molecules are oriented along the same “preferred” direction. It is shown that a liquid ferroelectric can not exist in a homogeneous nematic state. It is transformed into a more stable helical structure (the vector of the spontaneous polarization of such a structure rotates aroung the helical axis). There is a variety of domain structures for the specific case when the anisotropy coefficient of the polarization is equal to zero. Since each elementary dipole moment is rigidly bound to its molecule, the “preferred” alignment direction of the rod-like molecules as well as the polarization vector rotates with respect to the same axis in a helical manner. Therefore a nematic phase with a nonzero spontaneous polarization has a cholesteric structure. Its helical pitch is determined by the geometric size of the sample, the absolute value of the spontaneous polarization, and the elastic moduli. Apparently, we can consider some cholesteric phases to be liquid ferroelectrics with helical domain structure.     

On the helical domain structure of the liquid ferroelectrics

The case when a nematic liquid crystalline phase is ferroelectric is considered. Such “liquid ferroelectric” is, surely, instable and transforms into a helical cholesteric-type structure which for this case is a variety of the ferroeltric domain structure. One can think that some cholesteric phases are liquid ferroelectrics with the helical domain structure.     

Three-dimensional phase field microelasticity theory of a multivoid multicrack system in an elastically anisotropic body: Model and computer simulations

The phase field microelasticity theory of a three-dimensional, elastically anisotropic system of voids and cracks is proposed. The theory is based on the equation for the strain energy of the continuous elastically homogeneous body presented as a functional of the phase field, which is the effective stress-free strain. It is proved that the stress-free strain minimizing the strain energy of this homogeneous modulus body fully determines the elastic strain and displacement of the body with voids and/or cracks. The proposed phase field integral equation describing the elasticity of an arbitrary system of voids and cracks is exact. The geometry and evolution of multiple voids and/or cracks are described by the phase field, which is the solution of the time-dependent Ginzburg-Landau equation. Other defects, such as dislocations and precipitates, are trivially integrated into this theory. The proposed model does not impose a priori constraints on possible void and crack configurations or their evolution paths. Examples of computations of elastic equilibrium of systems with voids and/or cracks and the evolution of cracks under applied stress are considered.