Structure of the fronts of strong collisional shock waves in an ideal two-temperature electron-ion plasma with ions of arbitrary charge

Solutions in the form of plane running waves are investigated numerically in the framework of a two-temperature hydrodynamic model of a fully ionized ideal plasma with ions of arbitrary charge number Z₀. Most simulations were carried out for simple boundary conditions corresponding to a cold immobile plasma at the front of a running wave. All the solutions obtained have a discontinuity in the form of an isoelectronic-thermal jump, whose parameters relax to their steady-state values in the course of calculation. The problem of finding numerical solutions in which all the quantities at infinity take on finite (equilibrium) values actually reduces to the problem of the front structure of a strong shock wave. For a plasma with singly changed ions (Z₀ = 1), numerical solutions were found to coincide with the previously known solution. For a plasma with arbitrarily charged ions (Z₀ > 1), numerical solutions were obtained for the first time on the basis of justified formulas for the electron thermal conductivity.     

植被层内能量与水分交换的显式解的推导

本文发展了一个求解植被－大气相互作用的稳态分层模式。它结合了Ｎｏｒｍａｎ提出的植被层内辐射能传输模型和Ｗａｓｓｏｎｅｒ及Ｒｅｉｆｓｎｙｄｅｒ提出的求解通量的电路类比模型,推导了来自空中及地表面辐射能在植被层内传递的显式解,还推导了一套通用的联立方程组,把植被层内显热及潜热通量、空气的温度及水汽压等表示为只是叶温的函数。结果避免了以往一些模型不必要迭代．减少了计算机工作量。     

Development of an Exactly Solvable Model of Resonance Tunneling of Electromagnetic Waves through Gradient Barriers in a Nonuniform Magnetoactive Plasma

An exactly solvable one-dimensional model describing resonance tunneling (reflectionless transmission) of a transverse electromagnetic wave through wide layers of magnetoactive plasma is developed on the basis of the Helmholtz equation. The plasma layers include a set of spatially localized density structures the amplitudes and thicknesses of which are such that approximate methods are inapplicable for their analysis. The profiles of the plasma density structures strongly depend on the choice of the free parameters of the problem that determine the amplitudes of plasma density modulation, characteristic scale lengths of the density structures, their number, and the total thickness of the nonuniform plasma layer. The plasma layers can also include a set of random inhomogeneities. The propagation of electromagnetic waves through such complicated plasma inhomogeneities is analyzed numerically within the proposed exactly solvable model. According to calculations, there are a wide set of inhomogeneous structures for which an electromagnetic wave incident from vacuum can propagate through the plasma layer without reflection, i.e., the complete tunneling of thick plasma barriers takes place. The model also allows one to exactly solve a one-dimensional problem on the nonlinear transillumination of a nonuniform plasma layer in the presence of cubic nonlinearity. It is important that, due to nonlinearity, the thicknesses of the evanescent plasma regions can decrease substantially and, at a sufficiently strong nonlinearity, such regions will disappear completely. The problem of resonance tunneling of electromagnetic radiation through gradient wave barriers is of interest for various applications, such as efficient heating of dense plasma by electromagnetic radiation and transmission of electromagnetic signals from a source located in the near-Earth plasma or deep in the plasma of an astrophysical object through the surrounding evanescent regions.     

Mathematical modeling of gas-dynamic and radiative processes in experiments with the use of laser and heavy-ion beams

Results are presented from theoretical and experimental studies of gas-dynamic and radiative processes in the plasma that is planned to be used in future experiments on the stopping of fast heavy-ion beams. These experiments are aimed at measuring the enhanced (as compared to cold substance) plasma stopping power. To reliably interpret the experimental results, it is necessary to create a hydrodynamically stable homogeneous plasma with a uniform temperature and a lifetime exceeding the transit time of the heavy-ion beam (3–5 ns). The method for calculating plasma gas-dynamic characteristics with allowance for radiative heat transfer is described. The specific features of the so-called ion model of plasma, which is used to calculate plasma radiative characteristics, are discussed. The emission spectrum formed as a result of conversion of laser radiation into X-rays and the subsequent passing through a triacetate cellulose (C₁₂H₁₆O₈) target is calculated. The simulated spectrum of transmitted radiation satisfactorily agrees with experimental data.     

Investigation of Ion-Acoustic Solitons in Magnetosphere and Tokamak Warm Plasma with Two-Temperature Electrons

The properties of oblique propagation of small amplitude ion-acoustic soliton are investigated in a plasma containing weakly relativistic ions and two-temperature electrons (cold and hot electrons). The reductive perturbation method is used to derive the Korteweg?de Vries equation for the present plasma model. It is found that the parameters determining the nature of soliton are different for compressive or rarefactive structures. Moreover, the effects of weakly relativistic ions, the temperature ratio, and the density ratio of hot-to-cold electron species on soliton characters are studied. The theory is applied on the case of relativistic ions observed in the magnetosphere and in the case of nonrelativistic ions observed in tokamaks.     

Charging of a rodlike grain in a plasma flow

The charging of a chain of spherical dust grains in a two-temperature plasma flow is analyzed numerically by the particle method. The cases of dielectric and metal grains are considered.     

Two-dimensional MHD simulations of a plasma focus with allowance for the acceleration mechanism for neutron generation

The problem is formulated and a numerical model is developed for calculating MHD flows in plasma-focus (PF) devices. An implicit (with respect to the magnetic field) difference scheme and a method for its numerical implementation are proposed. The scheme allows one to describe plasma flows with drastically different densities and, therefore, to take into account the presence of a vacuum region behind the PF current sheath. Taking into account this region is important to numerically simulate the focusing process and adequately describe the acceleration mechanism for the generation of fast ions and fusion neutrons. The results of calculations are compared with the experimental data on the plasma dynamics in two different types of PF device. A model of accelerated ions is proposed to estimate the contribution of the acceleration mechanism to the total neutron yield. The neutron yield calculated in the framework of this model for three different geometries of the PF chamber at currents of 0.5–1.5 MA differs from the measured values by less than a factor of 2.     

Transport processes in plasma with an admixture of several heavy impurities

A two-temperature magnetohydrodynamic model of an ideal, fully ionized magnetized plasma consisting of electrons and several types of ions is developed for the case in which the mass of ions of the first type is much lower than that of jth-type ions, where j = 2,3,…, m ₁ ? m _j, while the densities of heavy ions are so low that collisions between them can be neglected. The ion component is assigned a common velocity, common temperature, and common density, while its composition can vary in time and space.     

Model of control of diurnal melatonin secretion by the solar radiation

The mathematical model of the control process of diurnal melatonin secretion under the influence of solar radiation on retina photoreceptors is proposed. Invariant relations for calculating melatonin secretion rate and its concentration in blood plasma are obtained. Spectral, time and energy characteristics of solar radiation synchronizing diurnal melatonin secretion and circadian rhythms in human are defined. A possibility of using the relations obtained is shown for arbitrary combination of calendar dates, local time of any time zone and geographical coordinates of a calculated point on earth surface. The adequacy of model is confirmed by coincidence of the calculation data with the results of independent experimental studies on diurnal secretion of melatonin and circadian rhythm in human. The model proposed can be used during investigation of diurnal secretion of melatonin and circadian rhythm in human.     

Calculation of transport coefficients with allowance for the chemical composition of a low-temperature high-density metal plasma

The model proposed by Ichimaru for calculating transport coefficients is generalized to describe a plasma containing neutral atoms and ions with different charges. Ichimaru's model was developed for a fully ionized two-component (electrons and a single ion species) plasma with a temperature above 10⁵ K. Taking into account several species of positive ions and neutral atoms makes it possible to extend Ichimaru's model to a partially ionized plasma. Transport coefficients calculated from different models are compared with the experimental data.     

Scattering of an ultrashort electromagnetic pulse in a plasma

An analytic approach is developed to describing how ultrashort electromagnetic pulses with a duration of one period or less at the carrier frequency are scattered in a plasma. Formulas are derived to calculate and analyze the angular and spectral probabilities of radiation scattering via two possible mechanisms-Compton and transition radiation channels-throughout the entire pulse. Numerical simulations were carried out for a Gaussian pulse. The effect of the phase of the carrier frequency relative to the pulse envelope on the scattering parameters is investigated.     

Three-dimensional simulations of anomalous absorption of laser radiation by plasma with supercritical density

A three-dimensional (3D) model of the interaction of laser radiation with plasma in the framework of Maxwell-Vlasov equations has been used to calculate the anomalous optical absorption in plasma of supercritical density. The results of calculations confirmed the development of anomalous absorption that was previously revealed by 2D models, which were insufficient for comparison to the experiment. Calculations were performed for a system containing about 10⁶ macroparticles that allowed the absorption coefficient and other characteristics of anomalous absorption in plasma with an inhomogeneous surface to be determined as functions of various parameters of the incident radiation and plasma target. Results are analyzed and estimations are obtained for the contributions of ionization processes and pair collisions of electrons, which show that these factors were quite reasonably ignored in the model. All quantitative results are obtained for the third harmonic of neodymium laser (λ = 0.351 μm) at a tenfold excess of the substance density over a critical value for this radiation.     

杉木人工林单叶至冠层光合作用的扩展与模拟研究

根据野外条件下杉木（Ｃｕｎｎｉｎｇｈａｍｉａ ｌａｎｃｅｏｌａｔａ（Ｌａｍｂ．）Ｈｏｏｋ．）针叶光合作用的测定结果。考虑到光合作用对光的非线性响应特性,及其与叶所处的实际冠层环境变量和冠层的空气动力学特性的相关,以筒化的林冠辐射传输模型为基础,结合不同部位和年龄针叶的光响应曲线,实现了叶室测量结果向冠层环境的调整,并进行了冠层光合作用模拟的初步研究。经过调整后的冠层光合作用平均比未经过调整的值高１     

A method for calculating the effective charge of ions decelerated in a hot dense plasma

A method for calculating the effective charge of fast ions decelerated in a hot dense plasma is proposed. The method is based on the known experimental dependence of the effective charge of an ion decelerated in cold matter on its velocity. The ion velocity in this dependence is replaced with the velocity of an ion relative to plasma electrons, averaged over the Fermi-Dirac distribution. Using results of numerical calculations performed in a wide range of plasma parameters (from a Maxwellian plasma to a fully degenerate one), a scale-invariant representation of the effective charge of a decelerating ion as a function of its initial velocity and the plasma temperature and density is obtained. An analytical formula fitting the calculated results to within 5% is derived. The obtained dependences of the effective charge are incorporated in the model describing deceleration of fast ions in plasma. Using this model, the stopping powers of krypton and lead ions in a relatively cold rarefied gas-discharge plasma and hot ICF plasma are calculated. The results of calculations are shown to agree satisfactorily with available experimental data.     

Electron distribution function in a two-temperature plasma with cold ions

By modeling the dynamics of a large ensemble of particles, it is shown that slow electrons in a two-temperature plasma are in equilibrium with the electron component rather than with cold ions. The result of cooling by a cold ion component is that the number of the low-energy electrons only slightly exceeds that in the equilibrium Maxwellian distribution.     

Computational model of chromosome aberration yield induced by high- and low-LET radiation exposures

We present a computational model for calculating the yield of radiation-induced chromosomal aberrations in human cells based on a stochastic Monte Carlo approach and calibrated using the relative frequencies and distributions of chromosomal aberrations reported in the literature. A previously developed DNA-fragmentation model for high- and low-LET radiation called the NASARadiationTrackImage model was enhanced to simulate a stochastic process of the formation of chromosomal aberrations from DNA fragments. The current version of the model gives predictions of the yields and sizes of translocations, dicentrics, rings, and more complex-type aberrations formed in the G(0)/G(1) cell cycle phase during the first cell division after irradiation. As the model can predict smaller-sized deletions and rings (<3 Mbp) that are below the resolution limits of current cytogenetic analysis techniques, we present predictions of hypothesized small deletions that may be produced as a byproduct of properly repaired DNA double-strand breaks (DSB) by nonhomologous end-joining. Additionally, the model was used to scale chromosomal exchanges in two or three chromosomes that were obtained from whole-chromosome FISH painting analysis techniques to whole-genome equivalent values.     

Interaction of electromagnetic waves with plasma in the radiation-dominated regime

A study is made of the main regimes of interaction of relativistically strong electromagnetic waves with plasma under conditions in which the radiation from particles plays a dominant role. The discussion is focused on such issues as the generation of short electromagnetic pulses in the interaction of laser light with clusters and highly efficient ion acceleration in a thin plasma slab under the action of the ponderomotive pressure of the wave. An approach is developed for generating superintense electromagnetic pulses by means of up-to-date laser devices.     

Numerical modeling of the dynamics of a slow Z-pinch

A study is made of the method for numerical modeling of pulsed plasma systems by simultaneously solving two-temperature MHD equations and the equations of ionization kinetics. As an example, the method is applied to simulate a relatively slow moderate-density Z-pinch, whose dynamics is well studied experimentally. A specially devised two-dimensional computer code makes use of a promising technique of parallel modeling.