Role of t-channel meson exchanges in S-wave πN and KN scatterings

The low-energy S-wave πN and KN scatterings are studied by using the K-matrix approach within the meson exchange framework. The t-channel meson exchanges, especially ρ and σ exchanges, are found to play a very important role in these two processes. The t-channel ρ exchange determines the isospin structure of the scattering amplitudes, it gives attractive force in the low isospin state but repulsive force in the high isospin state. The t-channel σ exchange gives a very large contribution in these two processes, while it is negligible in meson-meson S-wave scatterings.     

Improved Electric Transport Properties of a Multi—wall carbon Nanotube

Up to now quantized conductance of the carbon nanotube has only been observed by replacing the tip of a scanning probe microscope with the tube and putting the other end of the tube in a liquid metal [Science 280 (1998) 1744]. Probably cleaning the tube by the liquid metal has improved its quality and gives rise to the quantized conductance. We report on a new method to improve the electric transport properties of a single multi-wall carbon nanotube by Joule heating. Our experiment indicates that the conductance of the tube can be greatly improved just by repeated scanning the bias voltage in vacuum.     

Hyperbolic Bending of Vortex Lines with Finite Number and Length in Rotating Trapped Bose-Einstein Condensates

The minimal energy configurations of hyperbolic bending vortex lines in the rotating trapped Bose-Einstein condensates are investigated by using a variational ansatz and numerical simulation. The theoretical calculation of the energy of the vortex lines as a function of the rotation frequency gives self-consistently vortex number, curvature and configuration. The numerical results show that bending is more stable than straight vortex line along the z-axis, and the vortex configuration in the xy-plane has a little expansion by increasing z.     

Electromagnetically Induced Transparency in an Atom-Molecule Bose-Einstein Condensate

We propose a new measurement scheme for the atom-molecule dark state by using electromagnetically induced transparency （FIT） technique. Based on a density-matrix formalism, we calculate the absorption coefficient numerically. The appearance of the EIT dip in the spectra profile gives clear evidence for the creation of the dark state in the atom-molecule Bose--Einstein condensate.     

重离子辐射植物的诱变效应研究及应用

重离子生物技术已引起人们的广泛关注, 植物育种是重离子生物技术研究和应用的热点之一。 简要介绍了重离子的基本特征和在育种应用中的优势, 综述了重离子辐射对植物分子、 细胞、 个体3个水平的诱变效应研究及重离子辐射育种取得的进展。 Heavy ion biotechnology has received much attention since the mid 1980s, when the first mutagenic effect of heavy ion beams was found in rice. Since then, plant breeding is one of the focuses in heavy ion biotechnology. In this paper we outlined the recent developments in plant breeding by heavy ion beams. We introduced briefly the essential characteristics and superiority of heavy ion beams applied in plant breeding, and reviewed further the mutagenic research in three levels(e.g., molecular, cell and individual) of plants. At last, we summarized artificial mutants obtained in plants irradiated by heavy ion beams.     

Activation of silicon quantum dots and coupling between the active centre and the defect state of the photonic crystal in a nanolaser

A new nanolaser concept using silicon quantum dots (QDs) is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional (2D) photonic crystal can be used to select the model in the nanolaser.     

THEORETICAL ANALYSIS OF SCATTERING OF ULTRASONIC PULSES BY RIBBON-TYPE CRACKS IN SOLID——GENERAL SOLUTION

Scattering of elastic waves by obstacles of various shapes,especially those having sharp edges,is an important problem in NDE.The problem of scattering of a plane longitudinal or SV ultrasonicpulse in a solid,by a crack of finite width with free faces,is investigated in this paper by applyingdouble Laplace transforms and the generalized Wiener-Hopf technque.A solution in the Laplacedomain is obtained.An approximate form of this solution is then formulated neglecting the higher-order multiple scatterings,which can be inverted by the Cagniard-de Hoop method.The approximatesolution in the time-space domain gives the major features of scattering in the early time and henceof the near field.The result is readily shown in pictorial form. We have experimentally studied the corresponding scattered field in glass by the use of the photo-elastic visualizing technique,but the results are not included here,except for one photoelastic picturefor illustration.     

CALCULATIONS FOR THE FIELD OF PLANE SOUND WAVES IN A REALISTIC ATMOSPHERE

The general theoretical results concerning the reflection and refraction of plane sound wavesin a moving stratified medium obtained in a previous work have been applied to calculate thesound field in a realistic atmosphere.Two distinct approaches,the analytic and the graphic method,have been suggested to estimate the sound field in a multi-layered atmosphere where the gradientsof both temperature and wind velocity are present. The analytic method gives series expressions for the WKB approximation of the field as wellas successive modifications to it.All these expressions may be used as a basis for obtaining specificresults by some further elementary calculations devoted to the profiles of the realistic atmospheremodel. The graphic method gives a clear illustration of the field in a specific example which can beregarded as a standard atmosphere.Both a approaches enable us to simplify considerably the cal-culations referring to the usual multi-layer approaches.     

Metric of Rotating Charged Spherical Mass in Vacuum for Vector Graviton Metric Theory of Gravitation

Based on the vector graviton metric theory of gravitation （VGM） suggested by one of the authors of this article, using the method of null tetrad and analytic continuation, this paper gives the metric of the rotating charged spherical mass in VGM. The result shows once again that a replacement of G by G＊= G（1 - G M / 2r ） in general relativity will yield the corresponding result in VGM for the metric in vacuum.     

High—Order Harmonic Generation by Two Non—collinear Coherent Femtosecond

We have studied the high-order harmonic generated by two coherent pulses in argon gas produced by a gas jet. A loop in the relationship of the harmonic intensity versus the absolute values of relative phase difference was observed for non-collinear arrangement. Compared with the collinear arrangement, increase of 10 times of the conversion efficiency for 17th-order harmonic generation at an appropriate relative phase difference was obtained. The calulation of the intensity and phase for the laser field near the focus gives a simple reason for these phenomena.     

Instruments and channels in quantum information theory

While a positive operator valued measure gives the probabilities in a quantum measurement, an instrument gives both the probabilities and the a posteriori states. By interpreting the instrument as a quantum channel and by using the typical inequalities for the quantum and classical relative entropies, many bounds on the classical information extracted in a quantum measurement, of the type of the Holevo bound, are obtained in a unified manner.     

基于遗传算法的PID控制器优化设计

遗传算法是一种模拟自然进化而提出的简单高效的优化组合方法。本文研究了比例-积分-微分(PID)控制器优化设计的性能指标的选择问题，介绍了遗传算法的基本原理，给出了利用遗传算法进行PID控制器优化设计的步骤。同时给出了一个用遗传算法进行单环系统PID控制器优化设计的仿真实例。仿真结果表明了遗传算法应用于PID控制器优化设计的可行性和有效性。遗传算法还克服了其它方法的某些弊端。     

Insulating one house against aircraft noise

A house near Manchester Airport has been insulated against aircraft noise and measurements were made to establish the usefulness of different methods. It was found that domestic quality dual glazing gives an insulation of about 40 dB(A), glass fibre laid in the loft gives an insulation increase of about 4 dB(A) compared with the bare ceiling, and extra boarding in the loft gives no benefit, probably because the existing lath-and-plaster ceiling is fairly heavy and so gives adequate insulation. The insulation can be increased further by installing heavy glazing, but that would normally be prohibitively expensive.     

Blocking probability for a multistage clos connecting network

The blocking probability is computed by assuming a thermodynamic limit when the number of stages increases above a certain value. In this limit we exhibit a set of two algebraic equations which gives the blocking probability as a function of the traffic demand. A comparison with a computer simulation of the system gives an excellent agreement.     

Numerical simulation of cavitation bubble dynamics induced by ultrasound waves in a high frequency reactor

The use of high frequency ultrasound in chemical systems is of major interest to optimize chemical procedures. Characterization of an open air 477 kHz ultrasound reactor shows that, because of the collapse of transient cavitation bubbles and pulsation of stable cavitation bubbles, chemical reactions are enhanced. Numerical modelling is undertaken to determine the spatio-temporal evolution of cavitation bubbles. The calculus of the emergence of cavitation bubbles due to the acoustic driving (by taking into account interactions between the sound field and bubbles' distribution) gives a cartography of bubbles' emergence within the reactor. Computation of their motion induced by the pressure gradients occurring in the reactor show that they migrate to the pressure nodes. Computed bubbles levitation sites gives a cartography of the chemical activity of ultrasound. Modelling of stable cavitation bubbles' motion induced by the motion of the liquid gives some insight on degassing phenomena.     

高功率激光表面大气击穿阈值的波长关系

通过对大气击穿的物理机制、低空大气中的自由电子及其寿命和电离机制进行讨论,给出了高功率激光大气击穿较为明晰的物理图像。并通过理论分析,给出了激光大气击穿阈值的波长关系,对给定波长激光的大气击穿阈值可以作出迅速的估值,是一种较为简捷的方法     

Leptogenesis from spin-gravity coupling following inflation

The energy levels of the left- and the right-handed neutrinos are split in the background of gravitational waves generated during inflation, which, in presence of lepton-number-violating interactions, gives rise to a net lepton asymmetry at equilibrium. Lepton number violation is achieved by the same dimension five operator which gives rise to neutrino masses after electroweak symmetry breaking. A net baryon asymmetry of the same magnitude can be generated from this lepton asymmetry by electroweak sphaleron processes.     

短脉冲高斯光束的时空形式

考虑到腔模光腰尺寸的频率依赖性，得到了一短脉冲高斯光束在自由空间传播的时域解析形式，发现其可由一复时间变量来描述，复时间变量的实部给出了脉冲的传输时间，其与波前曲率有关，虚部给出了空间量值，两者的交叉项称为时空耦合，并对傅里叶变换极限脉冲和啁啾脉冲的时空形式作了分析。     

密封舱室内氧气再生过程的模拟计算

建立了封闭舱室内氧气再生与二氧化碳降浓的数学模型,采用S-系统在对数空间内对模型进行了数值解析,通过计算机模拟计算,讨论了系统中氧气和二氧化碳浓度随时间的变化情况,以及小球藻的液相培植对气相中氧气浓度的影响。计算结果表明通过培植小球藻来再生氧气并减少二氧化碳,维持密封舱内生命生存是可能的。     

Metallic bolometers with temperature dependent thermal impedance

The paper gives the solution of a bolometer with thermal impedance, which is a general function of the temperature. The general solution is applied to a bolometer cooled by radiation for which the appropriate expressions fo the resistance, sensitivity and dynamic resistance are derived and the expression for the maximum sensitivity of this type of bolometers from nickel, platinum and electrolytical platinum is given. The case of a bolometer cooled by conduction through the air and radiation is solved as the case of a bolometer with several ways of cooling. The paper also gives a graphico-numerical method for determining all the important parameters of the bolometer from the measured dependence of the resistance on the electric power RI²; an example of the application of this method is given for a conduction and radiation cooled bolometer. Deviations from the theoretical course are explained by convection of heat caused by the flow of air along the bolometer due to the increase in temperature of the bolometer over that of its surroundings. The paper also gives the maximum attainable sensitivity of this type of bolometer and metallic bolometers in general.