Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.     

The influence of exciton motion on spin-resonance absorption

We use a stochastic model for the exciton motion which comprises both the coherent and the incoherent motion. The incoherent part is taken care of by a stochastic process which allows the local excitation energy and the transition matrix element to fluctuate by means of a Markovian process. The interaction between the spins and their surroundings is described by the usual spin-Hamiltonian which is, however, simplified to a spin 1/2 particle (instead of the triplet state). In the present paper we solve exactly the two limiting cases of completely coherent and incoherent motion (for two molecules). In the incoherent case the influence of the exchange interaction integral is taken into account by perturbation theory. We find expressions which are immediately comparable with ESR-experimental data. This comparison and additional information derived from optical absorption measurements allow us to determine all free parameters of our model uniquely. In particular, the fluctuations of the exchange interaction integral (with strength γ₁) play an important role. From these parameters we may furthermore calculate the correlation time of the proton spin resonance in agreement with experimental data. The results show clearly that at room temperature in anthracene crystals the exciton undergoes a hopping process.     

The combined influence of the Pauli principle and saturation on the effectiveα andα α interactions

The recently developed fish bone optical model with saturation has been applied tonα. andαα scattering. Short ranged nucleon-nucleon correlations, which are responsible for nuclear saturation, have an influence both on the local potential part and on the exchange potential. The local potential becomes less attractive in the inner region and steeper in the surface region; it is better represented by a Woods Saxon shape than by a gaussian. A modification of the exchange potential is caused by the effect of short range correlations on the resonating group norm kernel. It is seen that short ranged nucleonnucleon correlations have no dramatic effect on two-cluster optical potentials. The present calculations rather support conventional phenomenological approaches. Together with older results one may conclude that, in multicluster systems, saturation is predominantly carried by three- and multicluster forces.     

Phase structure of Gross-Neve model, taking the influence of temperature and finite volume into account

A regular procedure (based on the Riemann — Epstein zeta function) is proposed for calculating the effective potential of the Gross — Neve model in the case of a two-dimensional lattice, with various boundary conditions modeling the effects of finite volume and temperature. The effective potential and phase structures of the model are constructed for various boundary conditions. In the two-dimensional case, in contrast to the three-dimensional case, the phase pattern does not depend on the coupling constants. Moscow Institute of Radioengineering, Electronics, and Automation (Technical University). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 29–45, February, 1998.     

On the calculation of mean lifetimes in the preequilibrium exciton model

An explicit and exact calculation method of mean lifetimes in the nuclear exciton model describing preequilibrium decay is presented. A simple algorithm is suggested. Relations of existing approaches with the analytical solution of the time-integrated master equation are discussed.     

The Pauli principle and the spin-dependence of the deuteron-nucleus interaction

It is shown that the effect of the Pauli principle on the propagation of a deuteron in nuclear matter depends strongly on the relative orientation of the momentum and spin of the deuteron. Possible implications for experiments with polarized deuterons discussed.     

Violations of the Pauli principle and the interior of the sun

The consequences of a violation of the Pauli principle for the physics of the solar interior are explored. It is found that a bound state of two protons becomes possible. This leads to an increase in the rate of hydrogen burning in the sun. Because a very large cross section for this reaction is in clear contradiction with the theory of stellar structure when compared with observations of solar luminosity, radius and mechanical oscillations, stringent limits on a violation of the Pauli principle in the two nucleon system can be given. However, a very small violation of the Pauli principle in the two nucléon system might solve the longstanding solar neutrino problem.     

Effect of the Pauli exclusion principle on the potential of nucleus-nucleus interaction

The dependence of the potentials of nucleus-nucleus interaction on taking into account the antisymmetrization of nucleons and the contribution of the nucleon kinetic energy to the potential is studied within approaches based on the energy-density functional, double-folding model, and the two-center shell model. It is shown that the contribution of the nucleon kinetic energy in colliding nuclei leads to the appearance of a significant core at short distances between the nuclei involved.     

Renormalizing Sznajd model on complex networks taking into account the effects of growth mechanisms

We present a renormalization approach to solve the Sznajd opinion formation model on complex networks. For the case of two opinions, we present an expression of the probability of reaching consensus for a given opinion as a function of the initial fraction of agents with that opinion. The calculations reproduce the sharp transition of the model on a fixed network, as well as the recently observed smooth function for the model when simulated on a growing complex networks.     

Pauli principle and renormalization of the pion nucleon interaction in nuclei

We show that the exclusion principle provides an alternative mechanism to the Lorentz-Lorenz effect for the renormalization of the pion-nucleon coupling constant in nuclei. This mechanism proves to be less sensitive to the range of the π - N forces. The implications for pion-nucleus scattering are discussed.     

The quantum and thermodynamical characteristics of fission taking into account adiabatic and nonadiabatic modes of motion

In the framework of the quantum theory of spontaneous and low-energy induced fission, the nature of quantum and thermodynamical properties of a fissioning system is analyzed taking into account adiabatic and nonadiabatic modes of motion for different fission stages. It is shown that, owing to the influence of the Coriolis interaction, the states of the fissile nucleus and of primary fission products are cold and strongly nonequilibrium. The important role of superfluid and pairing nucleon-nucleon correlations for binary and ternary fission is demonstrated. The mechanism of pumping of high values of relative orbital momenta and spins of fission fragments for binary and ternary fission and the nonevaporation mechanism of formation of third particles for ternary fission are investigated. The anisotropies and P-odd, P-even, and T-odd asymmetries for angular distributions of fission products are analyzed. The text was submitted by the author in English.     

社交网络中基于贝叶斯和半环代数模型的节点影响力计算机理

本文综合考虑网络结构及节点间的互动等关键因素, 提出了一种节点影响力分布式计算机理. 首先根据节点交互行为在时域上的自相似特性, 运用带折扣因子的贝叶斯模型计算节点间的直接影响力; 然后运用半环模型来分析节点间接影响力的聚合; 最后根据社交网络的小世界性质及传播门限, 综上计算出节点的综合影响力. 仿真结果表明, 本文给出的模型能有效抑制虚假粉丝导致的节点影响力波动, 消除了虚假粉丝的出现对节点影响力计算带来的干扰, 从中选择影响力高的若干节点作为传播源节点, 可以将信息传播到更多数目的节点, 促进了信息在社交网络中的传播. 关键词： 社交网络 影响力 贝叶斯 半环代数     

Thermal conductivity of Cu2Se taking into account the influence of mobile copper ions

Physics of the Solid State - The temperature dependence of the thermal conductivity of nanostructured samples of copper selenide prepared by mechanochemical synthesis from initial pure components...     

Derivation of the equation of motion for resonantly excited molecular J aggregates taking into account multiparticle effects

We have analyzed a model of molecular J aggregates in the form of a chain of three-level molecules. Equations of motion for these chains with taking into account multiparticle contributions caused by different mechanisms by which molecules interact with each other (dipole-dipole interactions, exciton-exciton annihilation, etc.) are presented. These contributions describe not only the interaction of any pair of molecules with each other, but also the interaction of a given molecule simultaneously with two, three, or more number of molecules. In the general case, it is necessary to take into account effects related to correlations between such molecules. To take into account these correlation effects, it is necessary to derive equations of motion from the first principles. As a result, a hierarchy of mutually coupled equations for the expectation values of the products of operators that refer to different molecules of the chain. In this work, we take into account only two-particle correlations between molecules. This, in turn, has led us to the necessity of taking into account equations for the two-particle expectation values with subsequent factorization of higher-order averages to obtain a closed system of equations. Correct taking into account of the mechanism of exciton-exciton annihilation from first principles has made it necessary to introduce multiparticle contributions into equations of motion that describe the relaxation of the system due to this mechanism and that are absent in a purely phenomenological consideration. By this means, we have obtained a set of equations that makes it possible to successively and rigorously take into account two-particle correlations between molecules of J aggregates.     

Exact analytic treatment of the influence of the coupled coherent and incoherent triplet exciton motion on the line shape of ESR

Starting from a stochastic Hamiltonian, describing the coupled coherent and incoherent motion of triplet excitons between two differently oriented molecules, an exact expression for the line shape of ESR is derived. Approximations for the limiting cases of nearly coherent and nearly incoherent exciton motion are given.     

Modelling the length distribution of etched tracks taking into account fragmentation due to partial annealing

Fission track length measurements on apatite minerals are of great interest in thermo-chronology studies. RBS analyses on Durango apatites irradiated by Krypton ions have previously shown the progressive fragmentation of tracks by annealing. This study made for different irradiation energies corresponding to those of uranium fission fragments has been completed by TEM and AFM on etched tracks. In all cases, segmentation figures have been observed, that clearly necessitates to introduce fragmentation of latent tracks to model the length distribution of uranium etched fission tracks. This presentation concerns the case of a homogeneous population of tracks with partial amorphization. The next step will consist in considering multiple sub-populations with different segmentation rates. This algorithm is a new aspect to be included in our model, which already takes into account diffusion and crystallography in the track etching process.     

基于耦合振子模型的摩擦力计算研究

以界面摩擦为研究对象,探讨了基于耦合振子模型(coupled-oscillator model)的滑动摩擦微观机理,分析了滑动过程中的能量耗散问题. 采用Maugis-Dugdal接触模型替代界面摩擦中的Lennard-Jones势能,并将该模型融入耦合振子模型之中,通过计算振子在一个周期内的能量增加值,推导出了界面摩擦力的理论计算公式. 理论分析表明,对于探针-试样接触系统,滑动摩擦力近似随着法向载荷的2/3次方增加,这与纳米摩擦学经典理论是相符的.理论计算结果与超高真空原子力显微镜镀铜探针在Cu(111)晶面扫描实验结果符合良好,表明本文提出的理论和方法可行. 关键词： 耦合振子模型 界面摩擦 摩擦力 法向载荷     

Micro-hot-spot model taking into account the temperature dependence of the laser pulse absorption efficiency factor

An improved model of the laser initiation of the explosive decomposition of energetic materials containing light-absorbing nanoparticles is investigated. The model takes into account how the light absorption efficiency factor changes with an increasing temperature. It is demonstrated that, as the temperature of an aluminum nanoparticle in pentaerythritol tetranitrate increases from 300 to 700 K, the light absorption efficiency factor increases by a factor of over 2. It is also shown that, for each particular nanoparticle radius in the 40–150 nm range, the temperature dependence of the light absorption efficiency factor over the relevant temperature range can be interpolated well by a second-order polynomial. Taking into account the variation of the efficiency of light absorption by the aluminum nanoparticle in the initiation of the explosive decomposition of pentaerythritol tetranitrate by a 12-ns-long neodymium laser pulse reduces the calculated critical energy density by a factor of 2.11 and decreases the optimum nanoparticle radius from 98 to 92 nm.