Influence of dielectric microcavity on the spontaneous emission rate of atom: a perspective on the closed-orbit theory of photons

The formulas of the quantum electrodynamics have been applied to calculate the spontaneous emission rate of excited atom in dielectric microcavity.The results exhibit damping oscillating Patterns which depend sensitively on the scaling parameter and geometrical structure.Compared with the case that the emitting atom is immersed in dielectric,the spontaneous emission rate is depressed obviously and the center or the mean value of the oscillations is intimately related to the real refractive index of the local position where the atom is.In order to explain this phenomenon,we utilize the closed-orbit theory to deal with the classical trajectories of the emitted photon.and extract the corresponding frequencies of the oscillations by Fourier transform.It is found that the oscillations can be represented in terms of the closed-orbits of the photon motion constrained in dielectric microcavity,thus providing another perspective on the spontaneous emission of atom sandwiched by dielectric slabs.     

PHONONS IN POLYACENIC CHAINS

We have theoretically resolved phonon excitations in quasi-two-dimensional organic crystals of polyacenic semiconductor material which may be obtained by the pyrolytic treatment of phenol-formaldehyde resin. A model for studying the dynamical properties using three polyacene chains is proposed with the aim to present the vibrational properties of this structure. It employs the formalism of solid states in two dimensions which admit phonons. A simulation process of the two-dimensional lattice structure shows that elastic waves may explain the existence of vibrational modes in the frequency range 100-400 cm-1. The presence of acoustic and optical like phonons is discussed in terms of the elastic force constants. A hyperfine resonance structure is obtained. It allows the analysis of the dynamical evolution in thin films of polyacene. It is found that the behavior of the phonon density of states exhibits resonance between modes in the structure.     

铁电阴极材料压电系数在电子发射过程中的实验规律

 作为一种新型功能材料，铁电阴极材料的研究日益受人们重视。对铁电材料进行电子发射试验时，偶然观测到材料压电系数随着电子发射次数的增多，其数值大小渐次先由高降低至零，然后又开始反向增大并逐渐稳定于某一绝对值,该绝对值略小于预极化初始值，而在这变化过程中，材料的电子发射电流密度基本恒定。对此进行重复验证以及系统考察发现，压电系数的这种变化规律，为铁电材料电子发射时所普遍遵循，这为铁电电子发射的机理研究探索又提供了一种新的实验现象。     

Dissolved oxygen sensor by using Ru-fluorescence indicator and a U-shaped plastic optical fiber

A dissolved oxygen (DO) sensor based on U-shape plastic optical fiber (POF) and dichlorotris (1, 10- phenanthroline) ruthenium ([Ru(dpp)3]2 ) as an oxygen indicator was described. Fluorescence intensity and lifetime were measured when the sensor was soaked into a water bath blasted with air with varied O2/N2 ratios. The influence of Ru concentration, annealing time and U-shaped POF curve radius on the system sensitivity was also studied. A two-layer model was proposed to analyze the deviation from linear relation described by Stern-Volmer equation, and to explain the deviation and the dependence of the fluorescence on curvature of U-shape POF. By fitting the experimentally measured sub-linear relation ofτ0/τ ratio versus oxygen concentration, the proportion of effectively sensitive layer and the Stern-Volmer coefficient can be evaluated to be f = 0.59 and Ksv = 0.61 typically.     

MORPHOLOGY EVOLUTION OF POLY（St-co-BuA）/SILICA NANOCOMPOSITE PARTICLES SYNTHESIZED BY EMULSION POLYMERIZATION

Poly（St-co-BuA）/silica nanocomposite latexes were synthesized via conventional emulsion polymerization in the presence of 3-（trimethoxysilyl）propyl methacrylate modified colloidal nano-silica. The effects of surface property, particle size and content of colloidal nano-silica as well as the concentrations of monomer and surfactant on the morphology of nanocomposite latex particles were investigated by transmission electron microscope （TEM） and scanning electron microscope （SEM） in detail. Various interesting morphologies such as grape-like, Chinese gooseberry-like, pomegranate-like and normal core-shell structures were observed. Droplet nucleation mechanism competing with micelle nucleation mechanism was proposed to explain the morphological evolution of the nanocomposite particles.     

THE DISTRIBUTION FUNCTION OF RESIDUE-RESIDUE CONTACTS IN PROTEIN MOLECULES

In protein molecules each residue has a different ability to form contacts.In this paper,we calculated the number of contacts per residue and investigated the distribution of residue-residue contacts from 495 globular protein molecules using Contacts of Structural Units(CSU)software.It was found that the probability P(n)of amino acid residues having n pairs of contacts in all contacts fits Gaussian distribution very well.The distribution function of residue-residue contacts can be expressed as:P(n)=P_0+aexp[-b(n-n_c)~2].In our calculation,P_0=-0.06,α=11.4,b=-0.04 and n_c=9.0.According to distribution function,we found that those hydrophobic(H)residues including Leu,Val,Ile,Met,Phe,Tyr,Cys,and Trp residues have large values of the most probable number of contact n_c,and hydrophilic(P)residues including Ala,Gly,Thr, His,Glu,Gln,Asp,Asn,Lys,Ser,Arg,and Pro residues have the small ones.We also compare with Fauchere-Pliska hydrophobicity scale(FPH)and the most probable number of contact n_c for 20 amino acid residues,and find that there exists a linear relationship between Fauchere-Pliska hydrophobicity scale(FPH)and the most probable number of contact n_c, and it is expressed as:n_c=a+b×FPH,here α=8.87,and b=1.15.It is important to further explain protein folding and its stability from residue-residue contacts.     

INFLUENCE OF SAMPLE THICKNESS ON ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYMERS IN A CONFINED VOLUME

Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method. The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated. It was found that there was a critical thickness value. Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value. For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization. When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process. A model was proposed to explain the mechanism of this phenomenon. According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei, and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one. Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model.     

Qualitative Analysis of Bifurcating Solutions in the Lengyel-Epstein Model

One of the most fundamental problems in theoretical biology is to explain the mechanisms by which patterns and forms are created in the＇living world. In his seminal paper ＂The Chemical Basis of Morphogenesis＂, Turing showed that a system of coupled reaction-diffusion equations can be used to describe patterns and forms in biological systems. However, the first experimental evidence to the Turing patterns was observed by De Kepper and her associates（1990） on the CIMA reaction in an open unstirred reactor, almost 40 years after Turing＇s prediction. Lengyel and Epstein characterized this famous experiment using a system of reaction-diffusion equations. The Lengyel-Epstein model is in the form as follows     

对夫兰克-赫兹实验屏流曲线的讨论

夫兰克-赫兹（FH）实验是大学物理实验的重要实验,许多研究性课题从中不断产生.对实验曲线产生的机理与分析常常是实验教学中的难题.本文针对学生在FH实验中,对屏流IP曲线产生机理提出的问题,从汞原子的浓度和电子能量的变化系统研究了IP曲线产生机理,对这些问题给予了解释.