A study is made of the importance of the random field when the conductivity of a disordered semiconductor is determined by the derealization of some of the bound carriers. The random field weakens the voltage dependence of the current.
Show AbstractThe production of an electron - temperature superlattice in a hot-electron semiconductor is considered in the linear approximation for the case where the absorption coefficient for the heating light is dependent on the electron temperature. The distribution of the electron temperature under static conditions has been derived, and also for free convection in the electron gas. The electromagnetic-field distribution has also been derived for the latter case. The critical light intensity at which the superlattice arises has been calculated.
Show AbstractTheoretical and experimental studies are presented on a coaxial cavity with an external focusing mirror and an internal grating of cylindrical or conical shape. Expressions are derived for the amplitudes of the incident wave and of the spatial harmonics. Patterns have been derived for the distributions of radially propagating modes with various numbers of half-waves along the zaxis. Measurements have been made on the slow-wave properties of a cylindrical diffraction grating in the cavity.
Show AbstractThe capacitive and other linear transducers that are known provide us with information on the instantaneous coordinate of the mechanical oscillator. The quantum theory of measurements predicts a precision limit of continuous measurement of the coordinate. When the transducer is working in the pulse mode, the instantaneous coordinate of the oscillator can be measured for the time t$_m$ ≪ 1/ ω$_M$ with an error √(ω $_M$t$_m$)times better than for the continuous mode. Consequently, the gravitational detector sensitivity increases. The outer effect on the antenna in this case can be found by measuring the instantaneous coordinate after a time multiple to the period of the antenna oscillations(2π/ ω$_M$).
Show AbstractA calculation is performed on the induced birefringence in a cylindrical garnet rod having a parabolic temperature distribution. An estimate is made of the effects of the induced anisotropy on the lasing performance and on the gain for linearly polarized radiation in a cavity containing a component in which the birefringence varies over the cross - section. The theoretical results are compared with experiment. The effects of residual stresses have been determined.
Show AbstractA theoretical discussion is presented of the parametric excitation of spin waves in ferrite single crystals with high crystallographic anisotropy; it is shown that there are regions of sharp change in the spectrum and in the threshold fields that are related to the effects of the ellipticity and the overlap between the characteristic regions in the anisotropic spectrum for the thermal spin waves; the phenomena are analyzed for Ni -ferrite.
Show AbstractA polarization scheme for four-photon spectrscopy of two - quantum transitions in isotropic media and cubic crystals is presented; a new way of measuring the scattering cross section in two-photon absorption is demonstrated. Irreducible tensor groups are used in averaging the components of the tensor for the molecular resonant hyperpolarizability, and arelationship is established for the invariants of the molecular tensor for two-photon polarizability and the nonzero components of the tensor for the third-order macroscopic susceptibility. Theoretical estimates and experimental results are presented for the polarization dispersion of the signal in various organic liquids. Similar estimates have been made for GaF and ZnSe crystals.
Show AbstractExpressions for the minimal error of measurement of low (≤ 1K) temperature are found; the value of the error is found for the optimal amount of the outer effect. The optimal amount of the outer effect is determined with allowance for two competitive factors: on the one hand, it is desirable to reduce the noise effect (of the sample or the measuring device) on the precision of measurements; on the other, it is also desirable to considerably reduce heating of the sample during measurement. Prom this point of view, several types of low-temperature thermometers were tested: molecular and nuclear paramagnets, NMR-thermometers and thermoresistive thermometers.
Show AbstractFormulas derived in fundamental studies by A.A. Sokolov and I.M. Ternov on synchrotron radiation are used for the probabilities of induced transition, wave functions, and the electron energy spectrum in a magnetic field. The expression for the electron energy is used in derivinga formula for the radiation frequency, which is considerably higher than the nonrelativistic cyclotron frequency in the ultrarelativistic case. Products of matrix elements in the Dirac matrices are derived, and a formula is derived for the probabilities of induced emission and absorption on the assumption that the incident electromagnetic wave is linearly polarized. The values are substituted into the formula for the power in the stimulated transitions to derive an expression for the power in the induced emission for a relativistic rotatin gelectron. The formula implies that relativistic electrons can be used to generate high-power electromagnetic radiation in the submillimeter and infrared wavelength ranges.
Show AbstractStandard equations for the kinetics of the concentrations of free and trapped charges have been used to obtain explicit expressions for the radioluminescence intensity and the concentration of induced absorption centers in ruby with a low chromium concentration. It is assumed that such a ruby corresponds to a band model containing one hole level and two electron levels. The calculations are performed for the approximation of arbitrary trap filling. It is shown that: 1) the increase in the recombination cross section at the radioluminescence centers on reducing the temperature reduces the intensity of the induced absorption and 2) the more rapid rise in the performance of the recombination chann e l at the blue-emission centers reduces the proportion of recombinations that lead to emission of the R lines.
Show AbstractДано описание методики и аппаратуры для физического моделирования процессов энергообмена в двухслойной жидкости.Исследования проводились в прямоугольном аэрогидроканале, заполненном пресной и соленой водой с резкой границей раздела между ними. Под действием воздушного потока возникала сложная структура течений и происходила турбулизация верхнего слоя воды. Экспериментально определены скорости вовлечения нетурбулизированной жидкости в перемешанный слой в зависимости от внешних параметров. Рассчитана доля,энергии ветра, расходуемая на процесс вовлечения (0,2%). Выделены характерные частоты, соответствующие выбросам соленой воды в перемешанный слой. Для объяснения существования на границе раздела периодических выбросов была привлечена гипотеза вязкого колеблющегося подслоя Эйнштейна и Ли, получено удовлетворительное согласование экспериментальных результатов с расчетами.
Show AbstractA study is made of the perturbed motion of a solid satellite about its center of mass; it is assumed that the satellite moves in a circular orbit in the central field of a planet.
Show AbstractBogolyubov's method has been used in numerical estimation of the correlation contributions to the free energy and specific heat of a crystal. The correlations improve the agreement between the ory and experiment for the specific heat. The correction terms in the free energy increase as the atomic weights decrease for crystals of the inert gases.
Show AbstractResults are reported for a pulsed laser employing yttrium-aluminum garnet in a nonstationary cavity. Kinetic synchronization of the axial modes occurs in such a laser when the rate of change of cavity length exceeds 2 cm/sec; the establishment of kinematic synchronization is examined. It is found that the ultrashort pulses arising in such a laser have parameters closely reproducible from burst to burst. The length of the ultrashort pulses and the shift in the center of the lasing spectrum are examined in relation to the rate of change of cavity length.
Show AbstractA Hamiltonian formulation is given for the equations of hydrodynamics for a compressible liquid in a uniformly rotating frame of reference; it is shown that the liquid is stratified, while the motion in general is of vortex type. A Clebsch representation is used for the momentum density. It is shown that this formalism can be applied to solve wave problems in media of hydrodynamic type.
Show AbstractThe finite-element method has been used in a program for numerical solution of the equations describing laser self-focussing in the isotropic phase for nematic liquid crystals. It is shown that the spatial dispersion in the nonlinear susceptibility arising from the thermal and orientation mechanisms stabilizes the time envelope of the laser pulse, while sharpening the leading edge and reducing the characteristic selff ocussing length.
Show AbstractCollinear acoustooptic filtration in a long crystal is considered, where the acoustic power density varies on account of damping and divergence. An estimate is made of the limiting passband for such a filter in the visiblerange. It is shown for a quartz crystal that a length of about 20 cm may be taken as optimal, while the realistically attainable passband is 0.1 nm.
Show AbstractThe hypertine structure of the Mossbauer spectrum of FeMn$_2$Al has been calculated, and it is shown that the ion atoms in this structure of β—Mn type are in different electronic states. The ordering of the iron atoms in the β—Mn structure has been determined by experiment.
Show AbstractDirect measurements have been made of the differential heats of adsorption of oxygen on atomically clean surfaces of germanium, silicon, and lead sulfide; which have been produced by crushing the initial single crystals under ultrahigh vacuum. The high heats of adsorption for Ge and Si (115 ± 10 and 210 ± 30 kcal/mol, respectively) are associated with the formation of double bonds. The interaction of an atomically clean surface of Ge with oxygen is dependent on the presence of minute traces of water. No such relationship is observed for silicon.
Show AbstractResults are presented on a gadolinium molybdate crystal examined in spontaneous parametric scattering at polaritons; the frequency-angle spectra indicate the dispersion of the ordinary refractive index In the range 350-5000 cm$^{-1}$. The frequencies of the type B$_1$ lattice modes have been determined. Two-particle state bands are observed, which determine the absorption of the crystal in the region around ~1800 cm$^{-1}$.
Show AbstractПриведены оценки потока рентгеновских и гамма-гравитонов на поверхности детектора (приемной антенны). Предлагается один из возможных путей регистрации высокочастотных гравитонов с использованием избирательного (резонансного) детектирования на мёссбауэровских Ƴ-переходах. Электромагнитное излучение, происходящее от взрыва сверхновых звезд, содержит линии спектра ионов железа, поэтому эксперименты по поиску гамма-гравитонов наиболее перспективны для распространенного мёссбауэровского изотопа железа $^{57}$Fe. Приведена оценка скорости счета, которая равна 10$^{-3}_{\text{квант}}* c^{-1}$ см$^{-2}$.
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