The conditions for self-focusing and stratification of a laser beam in liquid crystals at a temperature close to the phase-transition point from the isotropic to the liquid-crystal phase are found. It is shown that the spatial dispersion of the nonlinear susceptibility, due to a thermal or orientational mechanism, can ensure self-focusing of intense beams that is stable with respect to stratification. The analysis of the spatial dispersion mechanisms presented shows that liquid crystals are promising materials for forming continuous light beams of high intensity.
Show AbstractThe microscopic theory of the coupling between a particle and a hole with more complex states is developed. Particular attention is given to considering coupling with two-particle - two-hole states. It is shown that particle-hole states plus the low-lying collective state play an important role. As regards the extent to which interaction between the particles is taken into account a comparison is made with the theory of finite Fermi systems. The results obtained using the microscopic theory are compared with the corresponding results obtained using the phenomenological theory. A correspondence is established between the parameters of the model considered. When an appropriate choice of the parameters is made and the formfactors are matched, the matrix elements of the interaction between the nucleon and the core calculated by the two models are practically identical.
Show AbstractIt is shown that algebras of observables in the case of a charge scalar free field (also defined as the gradient-invariant parts of the corresponding field algebras) can be obtained using a simple mathematical operation, namely, finding the second commutant of a denumerable set of generating operators corresponding to the specified region of spacetime.
Show AbstractUsing the Nozieres-de Dominicis-Langreth theory the effect of plasmons on the structure and features of the dynamic formfactor describing the scattering of a fast electron with a transition of an internal electron from an atomic level onto the Permi surface is investigated. Neglecting dispersion of the plasmons an expression is obtained for the dynamic formfactor which explains the features of the spectrum due to plasmons. It is shown that the probability of an (e, e')-process W(q,ω)depends to a large extent on the sign of the exponent of the energy factor a(1). For a(l)< 0 the function W(q,ω) is a decreasing function of ω,which vanishes when ω = ω(n) = ω + а ω(p) + n ω(p), when а(l)> 0 the function W(q,ω) has a singularity of the type (ω—ω(n))^(-α(β)). These features are important when a fairly wide range of the transmitted energy spectrum is being investigated.
Show AbstractFor crystals grown under large temperature gradients from melts with seven different compositions, we study the effect of the conditions of crystallization on the formation of growth layers. We investigate the diffraction of light by the growth layers. It is observed that the variations of the refractive index (the optically observable growth layers) have a complicated nature due to the ferroelectric properties of the material. These cause two anomalies to arise in the temperature dependence of the intensities of the diffraction maxima. The lowtemperature anomaly (at T < 100°C) is explained by the pyroelectric charges on the domain boundaries. The high-temperature anomaly (at temperature close to the Curie point) is explained by the existence of variations in the Curie temperature with amplitudes of up to 1°C, which are synchronous with the variations in the composition of the crystal in the growth layers. As the content of sodium oxides in the melt is decreased, the Curie point of the crystals grown from it decreases from 575 to 542°C. The crystals with zero and 90-degree orientations were grown under conditions which were as similar as possible, but the Curie point for the latter orientation was lower by 10-20°C.
Show AbstractThe field dependences of the short-circuited photomagnetic current when crystals of GaAs with oxygen, chromium, and iron impurity are illuminated with light of different wavelengths are investigated. In GaAs(O) with bipolar Hall mobility 0 « μ*(n)< μ(n) for i$_{pm}$(B) in addition to the usual diffusion component n = i(+), which is linear with respect to the magnetic field B, reverse components n = i(-) are found, the contribution of which increases as the depth of penetration of the light decreases. In the region 50-77°K a maximum of these currents is also observed and a sharp increase in the effective rate of surface recombination. In GaAs(Fe)μ$^*_{n}$= μ$_{n}$ is monopolar for T < 110°K; i$_{pm}$(B) in the temperature range 8-100°K contain explicitly nonlinear n-i(-) (B) and linear p-i(+)(B). A maximum of n-i(-) is also observed at 50-77°K. In GaAs(Cr) μ*(n)= μ(n) is monopolar at room temperature, and in P - i$_{pm}$(B) a contribution that is nonlinear in В n-i(-) is also observed. The results obtained indicate the presence of a layer of p-conductivity ≥ 10$^{-5}$ thick, common for all the crystals, situated under the spacecharge layer. The presence of a layer leads to strong compensation of the photomagnetic current in the case of n-type volume photoconductivity, and can produce an antigate system with a considerable reduction in the effective rate of surface recombination for volume p conductivity.
Show AbstractWe describe an experimental apparatus and method for measuring the vibrational temperature of nitrogen and the density of particles in a gas-dynamic current of a С02—N2—Не mixture through the use of Raman scattering of light. Raman scattering is excited by the second harmonic of an yttrium aluminum garnet-neodymium laser (λ$_{L}$ = 532 nm) inside a multipass cuvette with the number of light passes ~50. The useful signals of the Stokes and anti-Stokes components of the scattering are discriminated with the aid of narrow-band contrast interference color filters. The degree of suppression of the parasitic signal in the optical system is not less than 10. The apparatus permits determination of the nitrogen density all the way up to applied pressures of about 1000 Pa. The measured values of the vibrational temperature of nitrogen are in the 850-1000°K range.
Show AbstractFor a Stanley model with long-range interactions, we find exact equations for the time dependence of the order parameter within the framework of a unification of the Bogolyubov (Jr.) method of approximate Hamiltonians and the stochastic approach of Glauber.
Show AbstractThe problems of the stimulated electromagnetic radiation of a system of rotating anharmonic oscillators in a resonator is solved. The calculation is carried out using nonlinear dispersion theory. Taking into account the coupling between the complex permittivity and the resonator parameters the amplitude of the steady-state oscillations of the field in the resonator and the power emitted by the system is obtained.
Show AbstractBy analyzing the experimental data obtained by other researchers it is shown that the anomalous molecular-weight dependence of the partial specific volume of macromolecules in dilute solutions cannot be explained using the hypothesis of the "free volume" formed between colliding monomers. Another explanation is proposed in which this anomalous dependence is due to a reduction in the number of bends in the chain when there is an increase in the volume repulsion in the coil. This explanation is in better agreement with the experimental facts.
Show AbstractWe investigate the tensile strength of filiform crystals of ammoniumand potassium dihydrogen phosphate (ADP and KDP) at room temperature and liquid nitrogen temperature as a function of their diameter for the two directions of growth <100> and <011>. It is observed that the filiform crystals, in contrast to macrocrystals of ADP and KDP, not only fail to break up during the low-temperature phase transition, but actually become stronger as the temperature is further decreased. It is shown that the observed strength of the filiform ADP and KDP crystals reaches 20-30% of the theoretical tensile strength.
Show AbstractThe results of work on the modernization of a 120-centimeter cyclotron, which enables the energy of the ions to be increased smoothly, and enables the range of accelerated ions to be extended are presented.
Show AbstractThe possibility of practically complete absorption of the wave energy in semiconductor plates of arbitrary conductivity and thickness is considered. The conditions for which complete matching with a waveguide line occurs are obtained theoretically and confirmed experimentally.
Show AbstractA class of completely unconnected topological spaces for formalizing the representation of discrete space-time is proposed.
Show AbstractEmission images of the (0001) plane of monocrystalline hafnium were observed in the temperature interval l800-2100°K in an electron emission microscope in a 5x10^(-8) mm*Hg vacuum. The transition from the α-phase to the β-phase is preceded by a stable intermediate state of the crystal at T = 2020 ± 5 K. The transition αHf→βHf at T= 2050 ± 5К occurs after a time interval of Δt ~ 2 min. The effective work functions of hafnium were measured in the α-phase as (ϕ(α)= 4,1 ± 0,05 V) and in the β-phase as (ϕ(β)= 3,9±0,5 V).
Show AbstractThe application of the diffraction theory of multiple collisions to the scattering of nuclei at high energies is discussed. Using this theory an approximate method is formulated for calculating the scattering cross sections of nuclei in which part of the virtual excitations of the colliding nuclei is taken into account. Unlike the well-known approximation of "rigid" nuclei the proposed approximation is symmetrical with respect to both nuclei participating in the reaction. Numerical calculations of the total cross sections and differential cross sections of elastic scattering showed considerable difference between the results of the "symmetrical" approximation and those obtained by the unsymmetrical approximations of "rigid" nuclei and the Czyz-Maximon approximation, which do not completely take into account the virtual excitations.
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