On certain regularities of the response of a medium upon generation of the triple frequency of a few-period laser pulse in the case of its passage through an optically thin nonlinear layer

The response of a medium at the triple frequency under the action of few-period laser pulses is considered within the framework of the thin-optical-layer approximation for the case where the triple frequency is close to the natural frequency of the linear oscillator. It is shown that a bistable dependence of the polarization amplitudes on the external action amplitude simultaneously appears at both the natural frequency and the frequency of the external action. This allows one, in particular, to reveal the presence of bistability of the regime of third harmonic generation in a physical experiment by using the transmitted radiation of the acting pulse. A decrease in the duration of the pulse incident on the medium leads to an increase in the hysteresis loops. The effect of the absolute phase of a short pulse on the spectral composition of the response of the medium is studied. For pulses of medium duration, in addition to the resonant response of the medium, the presence of the dynamic response of the medium at the triple frequency was revealed, despite a detuning of the latter from the resonance. The presence of this frequency in the spectrum of the response of the medium results in the dependence of the resonant response of the medium on the absolute phase even for a sufficiently long pulse containing tens oscillations of the electric field strength under the pulse envelope. To obtain the dynamics of the spectral lines from the results of computer simulation, the Fourier-Gabor method is used, the applicability of which is demonstrated by the comparison of the results obtained on its basis with the corresponding analytical dependences.     

Spatial quasi-periodic oscillations of the refractive index in an optically dense medium with a closed excitation contour

A closed contour of excitation (Δ-scheme) of a three-level atom in an optically dense medium under the action of two optical fields and a microwave field has been studied. It is found that phase relations between exciting fields in this medium play a determining role. It is established that, under certain conditions, in an optically dense Δ-atom medium exhibits a quasi-periodic dependence of the refractive index on the coordinate. The conditions under which this dependence is most pronounced are determined.     

Impact Parameter and Bombarding Energy Dependence of Collective Flow in the Dynamics Process of Intermediate High Energy Heavy Ion Collision

The time processes of collective flow were calculated by use of BUU equation with momentum dependence mean field and nucleonhucleon collisions in medium.It is shown that the momentum dependence mean field effect and the medium effect on the collective flow are obvious and sensitive to impact parameter and bombarding energy.     

Position difference regularity of corresponding R-wave peaks for maternal ECG components from different abdominal points

We collected 343 groups of abdominal electrocardiogram(ECG) data from 78 pregnant women and deleted the channels unable for experts to determine R-wave peaks from them; then, based on these filtered data, the statistics of position difference of corresponding R-wave peaks for different maternal ECG components from different points were studied. The resultant statistics showed the regularity that the position difference of corresponding maternal R-wave peaks between different abdominal points does not exceed the range of 30 ms. The regularity was also proved using the fECG data from MIT–BIH PhysioBank. Additionally, the paper applied the obtained regularity, the range of position differences of the corresponding maternal R-wave peaks, to accomplish the automatic detection of maternal R-wave peaks in the recorded all initial 343 groups of abdominal signals, including the ones with the largest fetal ECG components, and all 55 groups of ECG data from MIT–BIH PhysioBank, achieving the successful separation of the maternal ECGs.     

Simulation of multiple light scattering in a bounded nematic

The multiple-scattering problem is formulated for a single-constant model of a nematic liquid crystal with allowance for the dependence on the orienting external magnetic field. Based on the Bethe-Salpeter equation, an original Monte Carlo procedure in a birefringent medium is developed with allowance for the long-range action of dielectric permittivity fluctuations and backward and forward scatterings are calculated. The dependence of multiple scattering in a nematic on the distance between the incident and scattered rays is quantitatively studied for the first time and a nonmonotonic dependence on the external magnetic field is discovered. We numerically have established that the light-diffusion anisotropy noticeably weakens as compared to the extinction length anisotropy; this is shown to be caused by the weak anisotropy of the transport length.     

Nonlinear wave processes in porous waterlike media containing a system of capillaries partially filled with a viscous liquid

A nonlinear dynamic state equation of waterlike porous material that contains a system of cylindrical capillaries partially filled with viscous liquid was received. It is shown that an acoustic nonlinearity of such media contains the relaxation elastic and inelastic components due to the nonlinear dependence of the capillary and viscous pressure in fluid on the capillary diameter. For the medium, theoretical study of such nonlinear phenomena as generation of the second harmonic and a difference frequency wave, self-demodulation of high-frequency pulses as well as the change in the propagation velocity and absorption coefficient of a test wave being under an action of static loading have been carried out. The frequency dependences of medium nonlinearity parameters for these processes were determined.     

Forced oscillations of a magnetic liquid drop

Oscillations of a magnetic liquid drop suspended in a nonmagnetic viscous medium were studied analytically and experimentally. Oscillations occurred under the action of a linearly polarized alternating magnetic field. The frequency dependence of the amplitude and phase of oscillations was determined in the weak field and laminar flow approximation. The influence of the viscosity of the liquid on the natural drop oscillation frequency was studied. The obtained solution was used in experiments on determining interphase surface tension.     

The Properties of Nuclear Collective Flow in the Intermediate and High Energy Heavy-ion Collisions

In this paper the static characteristic of the nuclear matter characterized by the interior pressure and the binding energy as a function of density is studied with different interactions.By taking into account both the momentum dependence potential and the nuclear medium effect,the dependence of the nuclear collective flow on the impact parameters and the bombarding energies is investigated systematically with BUU dynamical calculations.The nuclear equation of state is better understood by comparing the calculation results with the experiments.     

中能重离子碰撞中前平衡核子发射的同位旋效应

利用同位旋相关的输运理论,研究了中能重离子碰撞中丰中子和缺中子碰撞系统在较宽能区范围内前平衡发射核子的同位旋效应.结果表明除低能区外,在100MeV/u以上核子–核子碰撞动力学效应起主要作用的能区,前平衡发射的中子–质子比仍然对介质中核子–核子碰撞截面的同位旋效应不灵敏,然而对于对称势的改变非常灵敏.故从低能量到较高能量的较大能区内,前平衡发射的中子–质子比的理论值与实验值的比较是提取对称势形式和强度的灵敏探针.     

Peculiarities of motion of a ferrofluid drop in a rotating magnetic field

The motion of a ferrofluid drop in a liquid nonmagnetic medium under the action of a rotating magnetic field is analyzed experimentally. A deviation of the falling drop from the vertical direction in the fields exceeding a certain critical value is detected. An extremum of the dependence of the deviation of the drop on the frequency of the rotating field is also observed. The results are analyzed theoretically and the algorithm of the numerical solution of the problem is proposed.     

Diffusionless motion of high-absorptivity domains along the laser beam axis

A new mechanism of motion of high-absorptivity domains under the action of Gaussian beams without allowance for diffusion of the material characteristics along the direction of beam propagation is studied by computer simulation. The essence of this mechanism is the dependence of the absorption factor growth rate on the radiation intensity. As a result, high-absorptivity domains may drift from heavily to weakly irradiated regions of the medium.     

Simulation of radiative heating of snow and ice coating

Numerical simulation of thermal state was performed for semitransparent medium; the thermal state is formed under impact of incident radiation and convective heat transfer to the ambient medium. The model takes into account the heat transfer to the semi-infinite opaque substrate below the layer of semitransparent material. Computation was performed for governing parameters typical of snow and ice coating during winter period. Solving the radiative part of problem uses the modified average flux method. This method takes into account the dependence of optical properties on the wavelength of incident radiation, scattering, and reflective properties of the layer boundaries.     

The temperature dependence of the third-order nonlinear susceptibility χ(3) of CS2 and dodecylbenzene

The dependence of the third-order nonlinear susceptibility ⁽³⁾ of CS₂ and C₁₈H₃₀ (dodecylbenzene) on temperature was measured by the degenerate four-wave mixing method. The empirical formula of this dependence was obtained. An explanation of this relationship was also given through the application of the model of a polar molecular moving in a viscous medium under the action of a laser beam.     

Energy transfer in solid-state dye lasers based on methyl methacrylate co-doped with sulforhodamine B and crystal violet

Laser action in methyl methacrylate(MMA)co-doped with sulforhodamine B and crystal violet dyes was investigated.The dye mixture was incorporated into a solid polymeric matrix and was pumped by a 532-nm Nd:YAG laser.Distributed feedback dye laser(DFDL)action was induced in the dye mixture using a prism arrangement both in the donor and acceptor regions by an energy transfer mechanism.Theoretically,the characteristics of acceptor and donor DFDLs,and the dependence of their pulse widths and output powers on acceptor–donor concentrations and pump power,were studied.Experimentally,the output energy of DFDL was measured at the emission peaks of donor and acceptor dyes for different pump powers and different acceptor–donor concentrations.Tuning of the output wavelength was achieved by varying the period of the gain modulation of the laser medium.The laser wavelength showed continuous tunability from 563 nm to648 nm.     

Absorption optical bistability in semiconductors under the action of an external electric field

The conditions for the realization of absorption optical bistability under the simultaneous action of two (radiative and nonradiative) mechanisms of recombination of free charge carriers are investigated. It is shown that, in the diffusion mechanism of stream of free electrons from the beam axis, the temperature dependence of radiative recombination does not expand the temperature range of the thermostat in which the optical bistability occurs. A scheme is proposed with application of an external transverse electric field, which makes it possible to realize absorption optical bistability at any ambient temperature. An important advantage of this scheme is the conservation of the state of a bistable system after the action of a light pulse and a significant decrease in the energy spent on cooling of the medium.     

A multidimensional pendulum in a nonconservative force field under the presence of linear damping

A nonconservative force field in the dynamics of a multidimensional solid is constructed according to the results from the dynamics of real solids occurring in the force field of the action of the medium. In this case, it becomes possible to generalize the equations of motion of a multidimensional solid in a similarly constructed field of forces and to obtain a complete list of, generally speaking, transcendental first integrals expressed through a finite combination of elementary functions. In the study, the integrability in elementary functions is shown for the simultaneous equations of motion of a dynamically symmetric fixed multidimensional solid under the action of a nonconservative pair of forces in the presence of the linear damping moment (the additional dependence of the force field on the tensor of angular velocity of the solid).     

Analysis of Gain Volume in Random Laser in a Spherical Multiple Scattering Medium

We performed numerical simulation of a random laser in a spherical multiple scattering medium in order to examine the saturation absorption in the excitation process and the resultant increasing process of the gain volume under the random laser action. The size of the gain volume increases with 1/3 power of the excitation pulse energy in the weak excitation region, and then approaches a critical value L_th when the excitation pulse energy is increased above the threshold. The dependence of L_th, as well as the dependence of the threshold excitation pulse energy on the dye concentration, transport mean free path, stimulated emission cross section and excited state lifetime were also examined. These results of the simulation well correspond to the experimental results by a two-beam spatial-correlation method.     

Impact-induced splash and spill in a quasi-confined granular medium

The splash and spill effects caused by the impact of a ball dropped from a height into a granular medium held in a small open container are examined. Different granular media, namely rice, mustard seeds, cream of wheat and plastic beads are used. The quantity of spilled-over granular matter (W, grams) is measured as a function of the ball-drop height and compared for different cases. Digital pictures of the splash process are also recorded. The quantity W is seen to vary approximately linearly with the energy of impact. Interestingly, a distinct upward jump is seen in the spilled quantity at specific impact energy in the case of mustard seeds, which have spherical shape and also exhibit some charging effects. Similar jump was also confirmed for the case of plastic beads with broadly similar properties. Although the parameters such as mass per grain and packing density for the case of mustard seeds are intermediate between those for rice and cream of wheat, the spill quantity for comparable impact energy is considerably higher in the former case. The possible reasons for this non-monotonicity of behavior are discussed in terms of the differences in grain shapes and properties. Experiments are also performed using plastic beads of the same type but with four different sizes to explore the dependence of spilled quantity on bead size. The container size dependence is also examined for various bead types. Interesting systematics are seen, which are discussed qualitatively.     

Seismic emission in technological impact zones

A complex and multistage scenario for generating seismic emission in technogenic destruction zones and individual tectonic elements is proposed and described based on present-day mathematical physics methods. It is shown that the generation mechanism is based on the amplitude instability of seismic envelopes of high-frequency acoustic oscillations of the geoenvironment excited as a result of energetic impact on the medium. The action of the aforesaid mechanisms is illustrated by experimental results of monitoring the process of hydraulic fracturing using seismic tomography.     

Unique effective action in two dimensional induced quantum gravity

The gauge dependence of the effective action in two dimensional induced gravity with non-local action is investigated. The unique effective action in this theory on flat background is also discussed. The configuration-space metric dependence of the unique effective action is studied.On leave from Tomsk Pedagogical Inst., Tomsk, Russia Address after 1.08.92: Dept. of Physics, Hiroshima Univ., Higashi-Hiroshima 724, Japan