Speedup estimates for some variants of the parallel implementations of the branch-and-bound method

The efficiency of parallel implementations of the branch-and-bound method in discrete optimization problems is considered. A theoretical analysis and comparison of two parallel implementations of this method is performed. A mathematical model of the computation process is constructed and used to obtain estimates of the maximum possible speedup. Examples of problems in which none of these two parallel implementations can speed up the computations are considered.     

Acoustic properties of the disordered relaxor ferroelectric PbSc1/2Ta1/2O3

The behavior of acoustic phonons in crystals of a relaxor ferroelectric, namely, the lead scandium tantalate PbSc_1/2Ta_1/2O₃ (PST), is studied in the vicinity of the diffuse phase transition. The behavior of longitudinal and transverse acoustic phonons in a PST single crystal is examined using Brillouin scattering. The phonon subsystem is found to behave anomalously in the vicinity of T = 297 K, which can probably be assigned to the existence of a phase transition. Analysis of the results obtained yields the values of the elastic moduli C₁₁, C₁₂, and C₄₄ for the cubic phase of the crystal over a wide temperature range.     

Structural phase transformations and physical properties of intercalation compounds in the Cr0.5Ti(Se1−x Tex)2 system

The atomic structure and magnetic and electric properties of the Cr_0.5TiSe₂-Cr_0.5TiTe₂ system of intercalated phases were studied in detail by gradually replacing selenium by tellurium. It was revealed that this replacement changes the crystalline structure from monoclinic in the initial compounds to hexagonal in the compounds containing various types of chalcogen atoms; this is accompanied by disordering of chromium atoms in the van der Waals gaps. The electrical resistance and magnetic characteristics vary nonmonotonically on replacement of selenium by tellurium, which is associated with a change in the degree of atomic disordering during the transition from Cr_0.5TiSe₂ to Cr_0.5TiTe₂.     

Kinetics of polarization reversal in irradiated thin PZT films

The effect of irradiation with electrons and neutrons and of exposure to synchrotron radiation on cyclic switching of polarization in thin films of lead zirconate titanate Pb(Zr,Ti)O₃ (PZT) was studied. It is shown that variations in the shape of switching currents are due to the generation of a spatially nonuniform bound internal field with account for an increase in the rate of bulk screening caused by irradiation. A correlation between structural variations and the evolution of the switching current measured during and after irradiation is established.     

Spontaneous symmetry breaking in an electromagnetic field-insulator system

Conditions for spontaneous symmetry breaking and generation of quasi-particles in an insulator through which an electromagnetic field propagates are considered. The order parameter of the system is determined. The mass spectrum of the quasi-particles is found in the cases of linear and nonlinear propagation through the medium with and without interfaces.     

Theoretical photoelectronic spectra of molybdenum, tungsten, and rhenium disilicides

Photoelectronic spectra of volume samples of molybdenum, tungsten, and rhenium disilicides are theoretically investigated as functions of the excitation energy (hv = 12–1486 eV) by the method of linearized attached plane waves. The main contribution to the spectrum at low (hv = 12–52 eV) and very high (hv = 1486 eV) excitation energies is given by the metal d-states, while the contribution of the Si p-states is dominant at intermediate excitation energies. An analysis of the calculated results demonstrates that the main peak of the photoelectronic spectra is displaced by 0.2 eV toward the bottom of the valence band when going from MoSi₂ to WSi₂; it is displaced by 0.3 eV when going from WSi₂ to ReSi_1.75. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 75–80, July, 2006.     

Conformational characteristics of polycaproamide in dimethylacetamide containing lithium chloride

The viscosity behavior, index of refraction, and density of dilute polycaproamide solutions in DMAc containing lithium chloride have been studied. On the basis of temperature dependences of the index of refraction and the density of solutions, the θ-condition of polycaproamide solutions in DMAc containing 2.5% lithium chloride is estimated as 21.3°C. From intrinsic viscosity [η] measurements, the coefficients of swelling of a polymer coil, the mean-square distance between chain ends, and other parameters of macromolecules in solution are calculated.     

Recovered-voltage phenomenon and prospects for its use for assessment of the condition of polymers

A general theory of the phenomenon of recovered voltage in polymers was considered on the basis of representation of an actual poling process by a discrete set of Debye relaxators. Examples of numerical solution of the direct and inverse problems are given. A correlation expression between intentionally aged polymer specimens and recovered-voltage curves was proposed for use in the assessment of the material state of a polymer under actual service conditions. It was shown that it is sufficient to restrict consideration to three relaxation processes in analysis of the phenomenon.