Time of flight spectra in thermal desorption of helium

Time of flight spectra are calculated within the cascade model of phonon-mediated desorption for helium desorbing from graphite, sapphire and Nichrome. One and three-dimensional theories are compared. Deviations from Knudsen's cosine law are traced to dynamical effects. The spectra are — as a function of time — narrower than a Maxwellian distribution and their maxima are generally shifted to shorter times indicating that the desorbed molecules are hotter than the solid temperature. Relevant experiments are discussed. Experimental geometries are analysed.     

Radar cross sections of a random medium layer

Analytic expressions are derived for the normalized radar cross sections (NRCS) of a random medium layer. These are calculated from the first-order solutions for diffuse intensities which are based on a multiple-scattering wave theoretical analysis. The permittivity fluctuations are assumed to be small and to obey stationary Gaussian statistics. On studying the expressions for the NRCS, some of their characteristics are pointed out. Three different correlation functions are considered and expressions for the coherent propagation constants are provided. Numerical examples are used to verify theoretical results and highlight some interesting characteristics of NRCS.     

Predicting rogue waves

Observational data regarding anomalously high waves on the sea’s surface (freak or rogue waves) are reviewed. The objectives of the research are identified, and the difficulties encountered are noted. The main physical mechanisms employed in explaining rogue waves are listed, and possible approaches to predicting marine hazards are discussed. Principles for ongoing short-term forecasting of extreme waves (within tens of wave periods or wavelengths) are proposed. Some preliminary results are presented.     

Effect of magnetic field on freely moving superconductors in the audio band

The results of studying the magnetomechanical effects in classical superconductors are analyzed. The energy losses are determined, and a number of macroscopic parameters are calculated using a developed model. The studies of superconductors by the method of rotation of a body suspended without contact are described. The results obtained are analyzed, and the values of some parameters are determined.     

Radar cross sections of a random medium layer

Abstract

Analytic expressions are derived for the normalized radar cross sections (NRCS) of a random medium layer. These are calculated from the first-order solutions for diffuse intensities which are based on a multiple-scattering wave theoretical analysis. The permittivity fluctuations are assumed to be small and to obey stationary Gaussian statistics. On studying the expressions for the NRCS, some of their characteristics are pointed out. Three different correlation functions are considered and expressions for the coherent propagation constants are provided. Numerical examples are used to verify theoretical results and highlight some interesting characteristics of NRCS.     

Parameter design of a liquid-filled sloshing system

<正>The nonlinear governing equations of the liquid sloshing modals in a cylindrical storage tank are established. Through analytical analysis,the analytical expressions of the solutions of this kind of system are obtained.With different parameters,the dynamical behaviors of the solutions are different from the trivial ones.To prevent system instability,two selection principles that the stiffness equations are positive-definite and the nonlinear terms of the system are not regenerative elements are given.Meanwhile,numerical simulations are also given,which confirm the analytical results.     

Parametric excitation of subharmonic oscillations

Subharmonic oscillations of order one-half for a single-degree-of-freedom system with quadratic, cubic, and quartic nonlinearities under parametric excitation are investigated. Two approximate methods (multiple scales and generalized synchronization) are used for comparison. The modulation equations (reduced equations) of the amplitudes and the phases are obtained. Steady-state solutions (periodic solutions) and their stability are determined. Numerical solutions are carried out, and graphical representations of the results are presented and discussed. The results obtained by the two methods are in excellent agreement.     

Faithful quantum secure direct communication protocol against collective noise

An improved quantum secure direct communication (QSDC) protocol is proposed in this paper.Blocks of entangled photon pairs are transmitted in two steps in which secret messages are transmitted directly.The single logical qubits and unitary operations under decoherence free subspaces are presented and the generalized Bell states are constructed which are immune to the collective noise.Two steps of qubit transmission are used in this protocol to guarantee the security of communication.The security of the protocol against various attacks are discussed.     

Semiclassical elementary particle models

Some simple models of elementary particles are discussed; they may be described as semiclassical, quark, shell models. Particles are assumed to be composed of spherical concentric charged shells. Three basic types of shell are allowed, quantum numbers are associated with each type such as to establish a quantum number correspondence between the shell types and the (p, n, ) quarks. Particles are identified through the quantum numbers of their constituent shells (quarks).The basic assumptions underlying the models considered are relationships between the electromagnetic energy associated with elementary particles (quark systems) and particle masses. The electromagnetic energy is represented classically; the models are semiclassical in that the shell radii are related to particle Compton wavelengths.Particle mass and magnetic moment formulas are derived, possible values for quark masses are suggested, and possible connections of the models considered with particle symmetry schemes are discussed.     

离子交换KTP晶体光波导及其各向异性波导性能研究

采用离子交换法制备了Ｒｂ：ＫＴＰ晶体光波导，在不同波长的耦合光下测量了ＴＥ和ＴＭ偏振波导模式的有效折射率，拟合了波导层折射率的余误差函数分布，证明了波导折射率增量的各向异性，给出了其色散关系；最后计算并讨论了Ｒｂ：ＫＴＰ波导的扩散特性。     

Experimental aspects of high energy neutrino physics

Neutrino physics from the viewpoint of the high energy results from Fermilab are discussed. The high energy experiments are described and their results are discussed. The status of both the charged current reactions are reviewed in detail. Also, the important observations of topologies indicating new particle production by neutrinos are covered. Comparisons between results of different experiments are made where relevant.     

A view on reactions of complete fusion

Complete fusion reactions are analysed within the framework of a theoretical model. Energy density interaction potentials are made use of and are renormalized for the purpose. A large number of heavy ion reactions are studied and the calculated critical angular momenta are compared with experimental data.     

用于高速数据通信的梯度塑料光纤

概述了梯度塑料光纤的开发历史和现状。从应用于高速数据通信的角度 ,介绍了聚甲基丙烯酸甲酯(PMMA)、全氘化和全氟化梯度塑料光纤的损耗、带宽、稳定性和寿命。详细介绍了梯度塑料光纤的损耗光谱和损耗机制 ,介绍了制作梯度塑料光纤的界面凝胶聚合技术和两种扩散法 ,分析了梯度塑料光纤的制作方法同折射率剖面和带宽的关系 ,讨论了梯度塑料光纤的稳定性同掺杂物质的关系。同时介绍了高稳定性梯度塑料光纤的研究进展及今后的发展动向     

过渡金属原子掺杂的锯齿型磷烯纳米带的磁电子学特性

利用基于密度泛函理论的第一性原理方法,研究了掺杂铁、钴和镍原子的锯齿型磷烯纳米带(ZPNR)的磁电子学特性.研究表明,掺杂和未掺杂ZPNR的结构都是稳定的.当处于非磁态时,未掺杂和掺杂钴原子的ZPNR为半导体,而掺杂铁或者镍原子的ZPNR为金属.自旋极化计算表明,未掺杂和掺杂钴原子的ZPNR无磁性,而掺杂铁或者镍原子的ZPNR有磁性,但只能表现出铁磁性.处于铁磁态时,掺杂铁原子的ZPNR为磁性半导体,而掺杂镍原子的ZPNR为磁性半金属.掺杂铁或者镍原子的ZPNR的磁性主要由杂质原子贡献,产生磁性的原因则是在ZPNR中存在未配对电子.掺杂位置对ZPNR的磁电子学特性有一定的影响.该研究对于发展基于磷烯纳米带的纳米电子器件具有重要意义.     

Non-linear algorithms based on SAFT ideas for reconstruction of flaws

The main idea and the assumptions of time domain synthetic aperture focusing technique (SAFT) are discussed. It is underlined that the major SAFT assumption is that the flaw can be represented by a number of single non-interacting scalar point scatterers, which act as point sources after illumination with the incident wavefield. As a result some important classes of flaws are incorrectly reconstructed by means of SAFT. Among them are cracks from which reflected signals are similar to those from mirror-shaped flaws. Different non-linear SAFT algorithms proposed earlier by the author are discussed and compared. Among them are SAFT with non-linear normalization (NSAFT), second order SAFT, and the radial tomography technique. The principles of these algorithms are discussed. Then their advantages and disadvantages are analysed. Unfortunately each algorithm cannot be considered universal as a classical SAFT, but for many important cases these algorithms are useful for solving inverse problems in ultrasonics. The ideas of non-linear SAFT algorithms are illustrated by physical experiments.     

Simulation Study of the Electromagnetic Calorimeter Triggers in BESⅢ

Based on the detector and trigger simulation of beijing spectrometer Ⅲ (besⅢ), schemes of besⅢ emc triggers are studied. neutral triggers, bhabha triggers and charged event triggers are designed to fulfill the requirements of the physics goals. the trigger parameters are optimized and the ability of backgrounds rejection are carefully studied. trigger simulation for some typical physics channels are studied and the expected backgrounds event rates are obtained     

Thermodynamics of electrons in the graphene bilayer

Some problems of the thermodynamics of electrons in a doped graphene bilayer are considered. Analytical expressions are derived for chemical potential and specific heat in the limiting cases of low and high temperatures. The Seebeck and Thomson coefficients are estimated. Landau levels are studied using a semi-classical approach. An expression for thermodynamic potential is obtained and the de Haas-van Alphen oscillations are studied. The oscillations of magnetic entropy and electron temperature in a magnetic field, i.e., the oscillating magnetocaloric effect, are investigated. For all parameters, the cases of graphene bilayer and monolayer are compared.     

Advanced research in millimeter-wave vacuum electronics

Selected basic research efforts currently sponsored by the U.S. Department of Defense (DOD) and the National Science Foundation (NSF) are reviewed. Major achievements are highlighted and remaining obstacles are discussed. Future advances are suggested. Opinions expressed are solely those of the author.     

低压下飞秒激光诱导Cu等离子体的诊断及空间分布实验研究

本文分别利用Gauss、Lorentz和Voigt函数对10Pa背景气压下飞秒激光诱导Cu等离子体光谱进行了拟合分析,结果表明,光谱在150ns内与Lorentz线型符合较好,200ns后与Gauss线型符合较好,Voigt线型与实验谱线一直符合较好。本文还对等离子体的电子密度和温度进行了诊断,并给出了它们随时间的演化;由发射光谱强度的时空演化,推知了等离子体的空间分布;利用时间飞行谱(TOF)得出了等离子体初期沿垂直靶面的膨胀速度。