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.     

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.     

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.     

Experimental study of the prereverberation times in deep-water and surface sound channels

Experimental data on the volume and surface prereverberation are presented. The main prereverberation features and parameters are considered, and the mechanism and theory of the phenomenon are discussed. The range dependences of the prereverberation times are analyzed for different ocean regions and for distances from 180 to 1500 km. Quantitative data on the prereverberation times are presented. The widths of the scattering diagrams are estimated for the underwater and surface sound channels.     

Transaxial mirror with combined static electric and magnetic fields

Combined transaxial mirrors are studied. In the areas of motion of charged particles, the fields of these mirrors are symmetric relative to the axis and mid-plane representing the plane of symmetry for the electric field and the plane of asymmetry for the magnetic one. An image equation is inferred and simple relationships between the linear and angular dispersions with respect to mass and energy are obtained. Aberration properties of the mirrors in the directions parallel to the mid-plane are considered. Expressions for the coefficients of the third-order geometric aberration corresponding to the beam divergence angle in the mid-plane are obtained. These expressions are especially simple when both object and image are located in the principal planes of the mirror. The aforementioned coefficients are expressed via parameters characterizing the mirror under the first-order approximation.     

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.     

亲水性材料固相萃取-紫外导数光谱法检测血中茚满二酮灯抗凝 …

本文报导了血中茚满二酮类抗凝血杀鼠剂敌鼠、氯敌鼠、杀鼠酮的亲水性材料固相萃取－紫外导数光谱检测法。血样用pＨ５缓冲液等体积稀释后加于西雷脱硅藻土柱上,柱用乙酸乙 酯洗脱,将洗脱液挥发干净,剩余物用pＨ１０缓冲液溶解,测定所得溶液的二阶导数光谱进行定性和定量分析。三种杀鼠剂以１０mg／Ｌ的量加于空白血中测得萃取率为８５％以上,血中三种杀鼠剂的检出限低于２ｍｇ／Ｌ。萃取中亲水性硅藻土可用硅胶和氧化铝代替,     

Control of radiation parameters of pulse-periodic tunable diode lasers based on lead salts with double heterostructure

Spectral and power properties of the pulse-periodic tunable diode lasers based on lead salts with double heterostructure grown by MBE are considered. Procedure and criteria of preliminary selection of the laser samples are discussed. Typical characteristics of such lasers are presented. Methods for controlling the spectral and power properties in the pulse mode are considered. General mechanisms of laser wavelength tuning by current and temperature variations are demonstrated on the basis of experimental data. Methods for optimizing these parameters are considered.     

Aerial Video Trackers Review

Target tracking technology that is based on aerial videos is widely used in many fields; however, this technology has challenges, such as image jitter, target blur, high data dimensionality, and large changes in the target scale. In this paper, the research status of aerial video tracking and the characteristics, background complexity and tracking diversity of aerial video targets are summarized. Based on the findings, the key technologies that are related to tracking are elaborated according to the target type, number of targets and applicable scene system. The tracking algorithms are classified according to the type of target, and the target tracking algorithms that are based on deep learning are classified according to the network structure. Commonly used aerial photography datasets are described, and the accuracies of commonly used target tracking methods are evaluated in an aerial photography dataset, namely, UAV123, and a long-video dataset, namely, UAV20L. Potential problems are discussed, and possible future research directions and corresponding development trends in this field are analyzed and summarized.     

Nonlinear squeezed states for SU(1,1) Lie algebra

The nonlinear extensions of the single-mode squeezed vacuum and squeezed coherent states are studied. We have constructed the nonlinear squeezed states (NLSS's) realization of SU(1,1) Lie algebra. Two cases of this realization are considered for unitary and non-unitary deformation operator function. The nonlinear squeezed coherent states (NLSCS's) are defined and special cases of these states are obtained. Some nonclassical properties of these states are discussed. The s-parameterized characteristic function and various moments are calculated. The Glauber second-order coherence function is calculated. The squeezing properties of the NLSCS's are studied. Analytical and numerical results for the quadrature component distributions for the NLSCS's are presented. A generation scheme for NLSCS's using the trapped ions centre-of-mass motion approach is proposed.     

约束对Birkhoff系统Noether对称性和守恒量的影响

研究约束对Birkhoff系统的Noether对称性和守恒量的影响．首先，建立了Birkhoff系统的运动微分方程．其次，给出了系统Noether对称性的判据．然后，讨论了受约束作用后，Birkhoff系统的Noether对称性发生的变化，并给出了系统的Noether对称性以及守恒量保持不变的条件．最后，举例说明结果的应用． 关键词： 分析力学 Birkhoff系统 约束 Noether对称性 守恒量     

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.     

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.     

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     

Spin-Wave Excitations in Anisotropic Kondo Lattice Model

The spin-wave excitations in anisotropic Kondo lattice model are studied using the spin Green's function. Both the ferromagnetic and antiferromagnetic cases are considered. The equations to determine the spectrum of low-energy excitations are given. The anisotropy gaps are obtained, and the long-wavelength and strong-coupling limits are analyzed.     

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.     

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     

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.