Analysis of bistability in molecular J aggregates under their resonant optical excitation taking into account multiparticle effects

Using a model of a homogeneous chain of molecules, we have analyzed bistability in resonantly excited J aggregates taking into account three-particle contributions to the exciton-exciton annihilation. These contributions, which have an interference nature, have previously been calculated in a work by B.N. Levinsky, L.A. Nesterov, B.D. Fainberg, and N.N. Rosanov (Opt. Spectrosc. 115 (3), 406 (2013)) in the course of derivation of equations of motion for J aggregates from first principles. Factorization of expectation values that correspond to these contributions leads to a closed system of equations in which not only pair, but also triple, interactions between molecules of the chain are taken into account. Numerical calculations have been performed, and their results have been compared with those obtained in calculations without taking into account three-particle contributions. We have shown that, on the whole, the inclusion of three-particle interference contributions in equations of motion leads to a restriction of the domain of existence of hysteresis. This, in turn, makes it possible to more reliably single out a real range of parameters in which nonlinear optical effects can considerably manifest themselves.     

Modulation instability of homogeneous resonant excitation regimes of molecular J aggregates

We have performed a linear analysis of the stability of stationary states of homogeneous resonant excitation regimes of molecular J aggregates with coherent sustaining radiation. In the analysis, we have taken into account not only two-particle but also three-particle interactions of molecules, which are related to the exciton-exciton annihilation mechanism. Our detailed investigation of the stability of stationary states has allowed us to determine stability and instability regions and correlate them with the existence of bistability boundaries.     

Non-Markovian solutions for probability amplitudes and dipole-moment expectation values in the case of spontaneous Lyman-α emission

Summary By taking into account the counter-rotating terms, equations of motion for probability amplitudes are derived in the case of spontaneous Lyman-α emission. From these equations non-Markovian solutions for probability amplitudes as well as for dipole-moment expectation values are obtained. All the results are provided with accurate error estimates which are absolutely necessary in a rigorous mathematical treatment.     

Influence of dipole-dipole correlations on the stability of the biaxial nematic phase in the model bent-core liquid crystal

A molecular theory of biaxial nematic ordering in the system of bent-core molecules has been developed in the two-particle cluster approximation which enables one to take into account short-range polar correlations determined by both electrostatic dipole-dipole interaction and polar molecular shape. All orientational order parameters and short-range correlation functions are calculated numerically as functions of temperature in the uniaxial and in the biaxial nematic phases, and the results are compared with the ones obtained in the mean-field approximation and in the cluster approximation but without taking into consideration the dipole-dipole interaction. It is shown that short-range polar correlations and, in particular, the dipole-dipole correlations dramatically increase the temperature of the transition into the biaxial nematic phase and enhancing its stability range. The results are also very sensitive to the value of the opening angle of a model bent-core molecule.     

分子聚集体中激子-激子湮灭过程

分子的激发能量转移和电荷转移是提高光伏电池和发光二极管效率的关键问题,其中分子聚集体中的激子-激子湮灭过程是影响分子激发能量转移的重要方面,细致研究激子-激子湮灭的动力学过程并与相关的瞬间吸收谱信号对比对相关的理论和实验都有重要意义.本文在分子间弱耦合近似下,用经典的率方程,应用方酸分子的基本参数对激子-激子湮灭过程做了微观描述,通过改变相关参数,研究了外场激发强度、聚集体的偶极矩位形、分子内的衰变率等因素对激子-激子湮灭过程的影响,分析了激子在第一激发态和高阶激发态的驰豫时间、电荷转移相干时间、激子融合和湮灭时间之间的关系,得到的结论适用于高阶激发态能级能量约为第一激发态能级能量的2倍的分子组成的分子聚集体.研究发现,J型聚集体由于相干能量转移时间较短,比H型聚集体有更高的湮灭率.激发场强越强,激子-激子湮灭的效率越高.分子高阶激发态的衰变率是激子-激子湮灭过程的关键因素.     

A TWO PARTICLE CLUSTER THEORY FOR UNIAXIAL NEMATIC LIQUID CRYSTALS FORMED BY BIAXIAL MOLECULES

A two-particle cluster theory is presented to study uniaxial nematic liquid crystals formed by biaxial molecules, which interact with each other via dispersion forces. The equation for the molecular orientational distribution functions in two-particle cluster approximation is obtained and is solved by an terativemethod. The temperature dependences of the order parameter and of the internal energy per particle are calculated, and the values of the relevant quantities at the nematic isotropic phase transition are given. The present theory, by taking into account the short range correlations between molecules , yields improved results compared with the mean field theory.     

多粒子玻色关联对夸克胶子等离子体颗粒源的检测

对由空间离散分布的夸克－胶子等离子体热滴发射的玻色子，本文进行了多粒子玻色关联的蒙特卡罗模拟研究．与两粒子玻色关联相比，多粒子玻色关联能够更敏感地检测玻色子发射源的颗粒性．通过对多粒子可观测量的分析，能够获得夸克－胶子等离子体和强子气体混合相存在的检测信号．     

Multiparticle Bose Correlations: Probes for Granular Source of Quark-Glunon-Plasma Droplets

The multiparticle Bose correlations of bosons emitted from dispersed thermal droplets of quark-gluon plasma are simulated by Monte Carlo.Multiparticle Bose correlations can offer more sensitivity to probe the granularity of the Bosonemitting source than two-particle Bose correlations.A promising signal of the existence of a mixed phase of quark-gluon plasma and hadronic gas can be obtained from multiparticle observables.     

Intermittency and correlations in hadronic Z^0 decays

A multidimensional study of local multiplicity fluctuations and multiparticle correlations of hadrons produced in Z decays is performed. The study is based on the data sample of more than events recorded with the OPAL detector at LEP. The fluctuations and correlations are analysed in terms of the normalized scaled factorial moments and cumulants up to the fifth order. The moments are observed to have intermittency-like behaviour, which is found to be more pronounced with increasing dimension. The large data sample allows for the first time a study of the factorial cumulants in annihilation. The analysis of the cumulants shows the existence of genuine multiparticle correlations with a strong intermittency rise up to higher orders. These correlations are found to be stronger in higher dimensions. The decomposition of the factorial moments into lower-order correlations shows that the dynamical fluctuations have important contributions from genuine many-particle correlations. The Monte Carlo models Jetset 7.4 and Herwig 5.9 are found to reproduce the trend of the measured moments and cumulants but they underestimate the magnitudes. The results are found to be consistent with QCD jet formation dynamics, although additional contributions from other mechanisms cannot be excluded. Received: 8 February 1999 / Published online: 8 September 1999     

Foundations of the fluctuation theory of adsorption on microcrystalline particles

Fundamentals of the equilibrium fluctuation theory of adsorption of molecules on microcrystalline particles taking into account the atomic structure of nonuniform surfaces were developed. The importance of taking into account the discrete character of adsorption centers in constructing adsorption isotherm equations was demonstrated. This changes the type of the mathematical apparatus in the search for a maximum distribution function term in a grand canonical ensemble: instead of differential derivatives, symmetrized difference derivatives should be used. The fluctuation theory of adsorption was generalized to ideal multicomponent mixtures of molecules. Adsorption isotherm equations for multicomponent mixtures on uniform and nonuniform surfaces taking into account limited sizes of the surface of various microcrystal faces and fluctuation contributions were obtained. The equations describe the influence of equilibrium fluctuations on adsorption isotherms for adsorbent particles of all sizes, from nanometric to macroscopic. An analysis of the equations showed that the influence of fluctuations was strongest at low coverages for each microcrystal face. The simplest case of taking fluctuations into account in the presence of contributions of lateral interactions in the mean field approximation was discussed.     

One-particle and two-particle inclusive deep-inelastic electron-positron annihilation in a massive quark model

A massive quark model is reviewed and elaborated upon. The model is applied to deep-inelastic electron-positron annihilation into hadrons. Definite predictions are given for one-particle inclusive and two-particle inclusive annihilations. Predictions for multiplicities, angular distributions, transverse momentum distribution in two-particle inclusive reactions, correlations, and threshold behavior are given. Exclusive annihilation into two mesons is also calculated.     

Quantized bimolecular auger recombination of excitons in single-walled carbon nanotubes

Auger-like exciton-exciton annihilation in isolated single-walled carbon nanotubes (SWNTs) has been studied by femtosecond transient absorption spectroscopy. We observe a quantization of the Auger recombination process and extract dynamics for 2 and 3 electron-hole pair excited states. We further demonstrate that Auger recombination in SWNTs is a two-particle process involving strongly bound excitons and not a three-particle Auger process involving unbound electrons and holes. We thus provide explicit experimental evidence for one-dimensional discrete excitons in SWNTs.     

液晶胆甾相中的分子短程关联

向列相液晶的二粒子集团理论被推广应用于研究胆甾相二维模型.手征性分子固定在三维简单立方晶格的格点上,而分子取向限制在二维.理论结果表明,平衡态螺旋波矢依赖于温度的变化,且存在胆甾相到向列相相变.通过考虑分子间短程关联,二粒子集团理论的数值结果较平均场理论更接近Monte Carlo模拟结果.     

Compton scattering on a target with degeneracy states

An additional pole term and the contributions to it from intermediate states with the same mass but with different spins is calculated for the Compton scattering amplitude on a two-particle system with zero total angular momentum. It is shown that the decomposition of invariant amplitudes on the generalized polarizabilities of the system does not take place if this term is taken into account.     

Charge distribution and correlation functions near the boundary of a weakly nonideal plasma

We consider the electric double layer formed near the boundary of a weakly nonideal multicomponent classical plasma as a result of interparticle correlations. On the basis of the generalized plasma uncoupling of the equilibrium chain of BBGKY equations, which correctly takes into account correlations of particles at small distances, we find the two-particle and one-particle correlation functions near the surface of the plasma. The asymptotic form of the two-particle correlation function along the boundary of the plasma falls off as the power law 1/r³. The solution obtained here is qualitatively consistent with earlier results, but it takes into account particle correlations at small distances and hence does not have a singularity at the boundary of the plasma. Therefore in a charge-asymmetric plasma there are two correlation radii, the Debye radius D and the radius /tr2D. The thermodynamic functions of the surface layer are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 72–77, March, 1989.     

Atomic ordering in amorphous systems

A theoretical method is proposed for describing the atomic ordering in multicomponent amorphous systems. It accounts for both two-particle and multiparticle correlations between atoms. A configurational Hamiltonian allows for the existence of multiparticle interaction potentials. A crystal with an arbitrary number of various structural defects is assumed to model the amorphous state. These defects are regarded as new kinds of atoms. The present work is based on the multiparticle-entropy method.     

Kinetics of exciton-exciton annihilation in molecular crystals

The theoretical investigation of the time dependence of the concentration of incoherent excitons formed by pulsed pumping is carried out. The basis of this investigation is a system of an infinite number of coupled equations for multiparticle distribution functions. Using the Kirkwood method of uncoupling, this system is reduced to a system of differetial equations for one- and two-particle distribution functions. The algorithm for calculating these equations by means of an electronic computer is developed.A simple phenomenological differential equation for exciton density has been obtained. The solution of this phenomenological equation coincides with good accuracy with the solution obtained by numerical integration of the above-mentioned system of differential equations for one- and two-particle distribution functions.     

The role of two-particle effects in the behavior of refraction of single-component liquids and two-component solutions

The role of irreducible two-particle contributions to the refraction properties of liquids and solutions has been studied. Two-particle contributions to the polarization vector of the system are calculated by electrostatics methods, which can be explained by weak deformations and overlaps of the electron shells of atoms and molecules. It is shown that, when the two-particle effects are taken into account, the constant of molecular refraction for binary solutions becomes a weakly nonadditive function of the constant of refraction of the components. It is shown by the example of aqueous solutions of ethanol and methanol that our values of the refractive indices and constants of refraction of the solutions are in good agreement with the experimental data.     

The influence of final state interaction on two-particle correlations in multiple production of particles and resonances

The structure of pair correlations of interacting particle moving with nearby velocities is analysed. A general formalism of the two-particle space-time density matrix, taking into account the space-time coherence of the production process, is developed. The influence of strong final state interaction on two-particle correlations in the case of the production of a systemresonance+particle is investigated in detail. It is shown that in the limit of small distances between the resonance and particle production points the effect of final state interaction is enhanced due to logarithmic singularity of the triangle diagram. Numerical estimates indicate that, in this limit, the effect of strong final state interaction becomes important even for two-pion correlations.