Simulation of the superlinearity of dose characteristics of thermoluminescence of anion-defective aluminum oxide

The specific features revealed in the superlinearity of dose dependences of thermoluminescence of anion-defective aluminum oxide single crystals have been considered theoretically in terms of the model of an interactive trap system. The model explains the decrease in the degree of superlinearity at a low heating rate, as well as with an increase in the dose increment, the occupancy of deep traps, and the sensitivity of the crystals to radiation due to the increase in the concentration of luminescence centers. The obtained results indicate a widening of the possibilities of the model for interpreting experimental data in the investigation of the dose characteristics of thermoluminescence of the studied crystals.     

Heat of formation of solid solution of alkali halides

Based on a semicontinuum model, the electrostatic, the polarisation, and the repulsive energy change of a lattice is calculated numerically, as a function of the relaxation of the nearest neighbouring ions of a substitutional impurity in an alkali halide crystal. It is found that for a particular displacement, the total energy change of the lattice is a minimum. Thus the heat of formation of a dilute solid solution is obtained. Here, we report calculations on the heat of formation of the following systems-Na⁺ in LiCl, Li⁺ in NaCl, K⁺ in NaCl, Na⁺ in KCl, Rb⁺ in NaCl, Na⁺ in RbCl, F^? in NaCl, Cl^? in NaF. Br^? in NaCl and Cl^? in NaBr.     

Model calculation of the density of states of dilute alloys

We show that the single pole dominance approximation in the theory of localized spin fluctuations gives the structure in the spectral density associated with the formation of localized magnetic moments in metals and with the Kondo effect, that is a triply peaked spectral density, in agreement with experiment.     

Kinetics of Macrolocalization Patterns of Plastic Flow of Metals

The features of the macroscopic inhomogeneity of plastic deformation in the form of autowaves with a pulsating amplitude are analyzed, and data on the localization of sources of acoustic emission at different stages of plastic flow in the stretching of fcc mono- and polycrystals are presented. The relationship between the local components of the plastic distortion tensor in the strain localization zone is traced. The role of acoustic phenomena accompanying the localization of plastic strain in the development of the process of plastic deformation is considered.     

Influence of angles of incidence of laser radiation on the generation of fast ions

It was established experimentally that the number and energy of fast ions in laser plasma increased with increasing angle of focusing laser radiation onto a flat target. Numerical calculations showed that the increase in angle of focusing brought the mean angle of incidence of laser radiation closer to the optimal angle corresponding to the maximal efficiency of the resonance absorption mechanism and, as a result, increased the fraction of absorbed laser energy in the energy of fast electrons and increased the number of fast electrons. In turn, the increase in the energy and number of fast electrons resulted in an increase in the number of fast electrons involved in the formation of a self-consistent electric field at the target edge and led to the growth of the field strength, which, eventually, was the reason for the increase in the number and energy of fast ions.     

Cathodoluminescence of ruby as a function of angle of incidence

The effect is explained in terms of an increase in efficiency with angle of incidence. Inclined excitation is proposed as a method of preventing charging of the surface.We are indebted to Professor V. L. Levshin for discussions, to A. G. Dvchinnikov for assistance in making the attachment, and to Yu. V. Khrushchev for assistance in the experiments.     

Influence of the Concentration of Aqueous Solutions of Sulfuric Acid on the Reflection Spectra of Pine Needles

The effect of solutions of sulfuric acid of different concentrations on the optical characteristics of pine needles was investigated. It is found that an increase in the acid concentration results in a decrease in the content of pigments in pine needles and in their reflectance in the visible region. An analysis of experimental data by using the LIBERTY model has shown that the decrease in the pine needle reflectance with decrease in the pigment content depends on the change in the refractive index at the cell wall–binding medium interface.     

Photoconductivity of thin films of modifications of zinc sulfide

Fine structure in the spectral response in the 300–340 nm range is reported for polycrystalline films at 90 ° and 293 ° K. The response spectrum is compared with the absorption and reflection spectra; peaks in absorption correspond to minima in the photocurrent. The detailed spectrum is dependent on the modification and on the structure defects.     

Current status of equation of state of nuclear matter

The equation of state (EOS) of symmetric nuclear matter (SNM) is a very important ingredient in the study of various phenomena of interest in nuclear physics and astrophysics. Accurate assessment of the value of the SNM incompressibility coefficient, K, which is directly related to the curvature of the EOS, is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K as determined from experimental data on compression modes in nuclei using the mean-field-based random-phase approximation. The text was submitted by the authors in English.     

Features of the Mechanism of Formation of the Radiation Belt of High-Energy Electrons and Positrons

New results of the PAMELA experiment revealed significant difference in the electron and positrons flux and fraction between trapped particles of the radiation belt and quasitrapped particles. A decrease in the ratio of the electron-to-positron fluxes both with increasing altitude and with decreasing energy was observed for the inner radiation belt, but this does not fit in currently used models. The residual atmosphere density in the trapping region for L ~ 1.15?1.2 is estimated on the basis of calculations of trapped-particle trajectories in the Earth’s magnetosphere. It is shown that processes leading to the energy loss for trapped electrons and positrons in the interactions with residual-atmosphere atoms play an important role in the formation of fluxes of these particles, but these processes cannot cause the reduction of the positron fraction in the total flux at energies below some 100 MeV. The role of the process of δ-electron production in the formation of the belt of trapped electrons and positrons is considered. Allowance for this process makes it possible to explain the above reduction at least partly.     

Change in nature of the conductivity of germanides of rare-earth metals

Conclusions The change in the type of conductivity in REM germanides is due to a change in the energy state of electrons in these compounds.The temperatures at which changes occur in the electrophysical and thermal properties of REM germanides of the compositions MeGe₂, MeGe, and Me₅Ge₃ were determined.The transition temperatures are lowest for phases of the composition MeGe₂ and highest for phases of the composition Me₅Ge₃, and increase in the series of REM germanides with reduction in the atomic radius of the metal.The anomalous behavior of cerium germanides is due to the presence of tetravalent metal ions in addition to the trivalent ions.     

Effect of irradiation on the laws of annealing of impurity hardening of NaCl crystals

Studies were carried out on crystals containing various types of impurity: Ca²⁺, a hole-acceptor impurity, which dissolves well in NaCl; and Pb²⁺, an electronacceptor impurity, which dissolves poorly in NaCl. For the first time when doped crystals were annealed softening was observed to occur as a result of irradiation with soft x-rays prior to the annealing. The microhardness of irradiated doped NaCl crystals drops below the value that corresponds to the unannealed unirradiated sample. This effect is more pronounced in NaCl:Pb. It is postulated that the weakening effect is due to the breakup of impurity complexes. This assumption is supported by the results of studies on the laws governing the annealing of dislocation structures about the imprints of an indenter. These laws are shown to depend on the type of impurity: processes of dislocation polygonization were observed in NaCl:Ca crystals and the dislocation distribution was random in NaCl:Pb crystals. Pre-irradiation of the latter caused dislocations to be built in and polygonization to appear. Evidently, by breaking up impurity complexes in NaCl:Pb crystals x-ray irradiation brings the state of the impurity in them closer to that in NaCl:Ca.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 57–62, August, 1988.     

Solvent-induced acceleration of the rate of activation of a molecular reaction

An increase in the rates of activated processes with the coupling to the solvent has long been predicted through the phenomenological Langevin equation in the weak coupling regime. However, its direct observation in particle-based models has been elusive because the coupling typically places the processes in the spacial-diffusion limited regime wherein rates decrease with increasing friction. In this work, the forward and backward reaction rates of the LiNC<==>LiCN isomerization reaction in a bath of argon atoms at various densities have been calculated directly using molecular dynamics trajectories. The so-called Kramers turnover in the rate with microscopic friction is clearly visible, thus providing direct and unambiguous evidence for the energy-diffusion regime in which rates increase with friction.     

Effect of Long-Period Ordering of the Structure of a Plant on the Initial Stages of Photosynthesis

Using data on the structure of plant leaves, specific features of light propagation in biophotoniccrystal structures have been established by the transfer matrix method. Splitting of the stopband in two bands has been found. The density of photonic states and the electromagnetic field value have been calculated. The occurrence of two photosystems (splitting of the stopband in two bands), the peculiarity of the long-wavelength quantum yield and its enhancement (Emerson effect), and water dissociation in the soft mode due to an increase in the electromagnetic field on the layers are explained.     

Explanation of the temperature variation of Hall coefficient of doped bismuth

The Hall effect in single crystals of bismuth doped with tin and lead has been measured in the temperature range 80 to 300 K. An attempt has been made here to explain the observed variations of Hall coefficient with temperature by considering the relative variation of the free carrier concentrations with temperature in different bands in alloys of bismuth in addition to variation of other parameters. Calculations have been made to see the effect of the overlap on Hall coefficient for different values of band overlap. The experimental curves are in satisfactory agreement with the theoretical calculations.     

Magnetooptical studies of aggregates of nanoparticles in colloidal solutions of magnetite

The birefringence in a colloidal solution of nanosized magnetite particles in kerosene exposed to constant, alternating, and pulsed magnetic fields is studied. Data on the birefringence kinetics in nonstationary magnetic fields is used to determine the hydrodynamic radius of particle aggregates in solutions. The permanent dipole moment of aggregates and the anisotropy of the magnetic susceptibility are calculated based on the data of magnetooptical experiments. It is shown that the induced dipole moment plays a significant role in an orientation of aggregates of magnetic nanoparticles under the effect of a field.     

Model of stochastization of the oscillatory regime of superradiance

Based on the analysis of the experimental data on the observation of the fluorescence and superradiance of praseodymium ions in a matrix of lanthanum trifluoride, a model of superradiance of three-level radiators with two close upper levels is developed in the mean-field approximation and studied. The uppermost level is coherently pumped by an ultrashort pulse of electromagnetic field, after which the excitation is transferred to the close energy level, from which the superradiance transition occurs to the lower level. In limiting cases, the considered model is reduced to the known models of superradiance and describes the ordinary regimes of monopulse and multipulse (oscillatory) superradiance. However, in a certain region of parameters, the model under discussion describes such a multipulse superradiance signal in which electromagnetic field spikes composing it follow in time with random intervals and amplitudes, so that the regime of regular chaotic dynamics is demonstrated in a single superradiance signal. In a certain time interval, the proposed model can be described by the Lorenz equations with the parameters corresponding to the chaotic dynamics of spikes composing the superradiance signal. The presented results of the numerical simulation of the model equations qualitatively correspond to the picture of stochastic pulsations observed experimentally.     

Evolution of disturbances of the sphericity of a bubble under strong compression

The growth in the amplitude of the small nonsphericity of cavitation bubbles in acetone and water under strong compression is considered. A hydrodynamic model is used in which the compressibility of the liquid, the nonstationary thermal conduction of the vapor and the liquid, and nonequilibrium evaporation–condensation processes, as well as imperfection of the vapor, are considered. It has been shown that the increase in the amplitude of the small nonsphericity of cavitation bubbles in the form of separate spherical harmonics during compression in water is substantially (more than 10 times) higher than during compression in acetone. This indicates that acetone is much more advantageous over water to implement a process of the nearer-to-spherical extreme compression of the medium in the cavitation bubbles.     

Spectral dependence of resolving power of optical method of detection of ultrasonically enhanced agglutination of human blood erythrocytes

The spectral dependence of the resolving power of an acoustooptic method of monitoring agglutination of human blood erythrocytes is studied theoretically and experimentally. It is shown that, in principle, the resolving power of this method can be increased by several dozen times. The results of the work can be used to create instruments for determining the human blood type in the AB0 system and in the Rhesus system.     

Influence of deformations of a polymer matrix on the characteristics of dual fluorescence of 3-hydroxyflavone

The possibility of considerably changing the conditions for the proton transfer reaction in 3-hydroxyflavone molecules in polyvinyl alcohol (PVA) polymer matrices by stretching deformations is demonstrated. Samples of this kind are traditionally used to obtain ensembles of fluorophore molecules oriented along a chosen axis and for polarization measurements. The fluorescence spectrum of 3-hydroxyflavone in PVA has two characteristic bands in the violet and green spectral regions, which indicates excited-state proton transfer. Stretching leads to a strong reduction in the violet band, whose contribution in undeformed samples is comparable to the contribution of green fluorescence. Even twofold stretching of PVA films strongly decreases the violet band intensity, which is more pronounced in the case of sixfold stretching. In the latter case, the fluorescence spectrum behavior is very close to the pattern observed in nonpolar and aprotic solvents, in which the violet fluorescence intensity is very low. The data obtained indicate that mechanical stretching allows one to eliminate the main intermolecular factors that slow down the proton transfer between the active groups in PVA.