风对光束控制系统内热效应的抑制作用

 用光强沿x轴方向呈线性变化的方形环状光束模拟高功率激光，利用自编四维仿真程序对高功率激光在光束控制系统中的传输作了详细的数值计算研究。结果表明：热效应使远场光束的峰值光强和可聚焦能力下降。入射光强的非均匀分布进一步降低峰值光强和可聚焦能力，导致远场光束重心和峰值光强位置移动，并产生像散。光束的非均匀程度越高，远场光束质量越差。横向风和轴向风对热效应均有抑制作用。然而，轴向风不会引起远场光束重心偏移和像散，但是轴向风比横向风建立稳态所用时间更长。     

有限区域风场分解方法及其在台风SAOMEI研究中的应用

介绍了有限区域水平风场分解的调和-余弦计算方法,该方法把函数分成两部分之和.第一部分是Laplace方程在给定边界条件下的解,由于Laplace方程的解是调和函数,这个部分可称为调和部分,又因为其与区域内部值无关,也称外部部分.第二部分是原始函数与调和部分之差,这个函数是齐次边条件下Poisson方程的解,只与区域内部的涡度或散度有关,故称为内部部分,可以展开成双傅氏的余旋函数系列.调和-余弦计算方法的求导都是用谱系数进行,计算精度比常用的差分方法高两阶以上.而且,由于外部部分对应的边界条件物理意义清楚,边界光滑,成功克服了有限区域流函数和速度势迭代求解出现的计算不稳定、原始风场无法还原、边界上的系统缺失等问题,可以准确分解和重建有限区域的风场.利用NCEP/NCAR 1°×1°的实时分析资料和日本气象厅区域谱模式(RSM)20km分辨率的再分析资料,利用调和-余弦算法得到的无辐散风分量和无旋风分量,对2006年的8号超强台风“桑美"(SAOMEI)进行风场结构的比较分析.结果发现,低层无辐散风比原始风场与台风中心的对应关系更好;同时,无旋风分量能更好地显示原始风场上并不明显的低层辐合高层辐散的特征,大尺度无辐散风分量可以更清晰地显示出台风的水汽输送通道.从与台风中心的对应关系看,台风在海上发展阶段,SAOMEI台风的旋转中心与辐合中心并不是时时重合,这个特点只能通过风场分解才能得到.此外,SAOMEI登陆以后,南部洋面上发展起来的对流活动从水汽和能量补充方面都不利于SAOMEI的维持.可见,分解后的无辐散风场和无旋风场能更清楚地体现出SAOMEI的风场结构,在台风结构分析中有重要的推广应用价值. 关键词： 台风 水平风场分解 调和-余弦算法     

Global existence of generalized solutions of the spherically symmetric Einstein-scalar equations in the large

In this paper we study the global initial value problem for the spherically symmetric Einstein-scalar field equations in the large. We introduce the concept of a generalized solution of our problem, and, taking as initial hypersurface a future light cone with vertex at the center of symmetry, we prove, without any restriction on the size of the initial data, the global, in retarded time, existence of generalized solutions.Research supported in part by National Science Foundation grants MCS-8201599 to the Courant Institute and PHY-8318350 to Syracuse University     

Analytical Description of Electron Motion in a Three-Dimensional Undulator Field

The motion of relativistic electrons in an ideal three-dimensional magnetic undulator field satisfying the stationary Maxwell equation is considered. The system of nonlinear differential equations of the electron motion is solved analytically using perturbation theory rather than the method for averaging fast oscillations of the electron trajectory (the focusing approximation), as was done in a series of previous studies. The obtained analytical expressions for the trajectories describe the behavior of particles in a three-dimensional magnetic undulator field much more accurately than the formulas obtained within the framework of the focusing approximation. The analysis of these expressions shows that the behavior of electrons in a three-dimensional undulator field is much more complicated than that described by equations obtained using the averaging method. In particular, it turns out that the electron trajectories in the undulator have a cross dependence; in this case, variations in the initial trajectory parameters in the vertical plane cause changes in the horizontal trajectory components, and vice versa. The results of calculations of the trajectories carried out using analytical expressions are close to those of numerical calculations using the Runge-Kutta method.     

A comparison of the results of a numerical simulation and an approximate calculation of the statistical characteristics of radio waves in a layer with random inhomogeneities of dielectric permittivity

We consider the formation algorithm for a random inhomogeneity field of dielectric permittivity of a medium that is used in simulations of the statistical characteristics of a wave that has propagated through a randomly inhomogeneous layer. We carry out a comparison of the statistical characteristics of a geometrical-optics wave, obtained via a numerical simulation, with the results of calculations of these characteristics by approximate formulae obtained using perturbation theory. It is pointed out that the applicability limits of the perturbation method, when solving geometrical-optics equations in a randomly inhomogeneous medium, depend on the formulation (one- or two-point) of the trajectory problem. It is shown that a calculation of the spatial correlation function of the field can be carried out using the perturbation method, even in the case of relatively strong fluctuations of dielectric permittivity. This is due to the fact that, in the region where this function differs markedly from zero, the correlation function of the eikonal obtained by the perturbation method is sufficiently accurate, and amplitude fluctuations are small.     

Statistical study of the trajectories of the air masses flow in the Alpine area

Summary As a part of our activity in the transboundary transport, this study examines a five years’ trajectory climatology interesting Northern Italy. Our analysis is twofold: firstly we examine the statistics of air masses arriving at an Alpine location (Brenner Pass) separating between rainy only trajectories and all trajectories, and, secondly, we study the climatology of trajectories, going out from the Po Valley. Trajectories are computed by means of a simple three-dimensional trajectory method using the wind data obtained by the analysis of the ECMWF. The distribution of the arrival (or departure) directions of the trajectories is presented and commented. The differences in the travel times for the different directions are presented as well. The vertical distribution of the trajectories is finally computed. The main results are discussed.     

Carrier-envelope phase measurement using plasmonic-field-enhanced high-order harmonic generation of H atom in few-cycle laser pulses

We investigate the plasmonic-field-enhanced high-order harmonic generation (HHG) of H atom driven by few-cycle laser pulses, by solving the time-dependent Schrödinger equation (TDSE). Compared with the homogeneous field, HHG spectra generated by inhomogeneous field exhibit two-plateau structure. We analyze the origin of the two plateaus by using the semiclassical trajectory method. Our results from both classical and TDSE simulations show that the cutoffs of the two plateaus are dramatically affected by the carrier-envelope phase (CEP) of laser pulse in the inhomogeneous field, even for a little longer pulse. Thus, we can determine the CEP of driving laser based on the cutoff position of HHG generated in the inhomogeneous field.     

太赫兹自由电子激光波荡器的设计、测量与优化

波荡器电子轨迹中心偏移和磁场误差对CTFEL装置性能影响很大,通过前期设计和后期测量与优化将其限制在指标要求范围内。在前期设计中尽量避免引入全局性的系统误差：磁结构具有平面反对称结构,保证电子轨迹中心和波荡器磁轴重合;磁结构端部的特殊设计减弱了间隙对出口磁场二次积分的影响;机械系统的大梁和立柱具有良好的刚性,闭环控制系统保证了高的波荡器间隙控制精度,这些措施降低了间隙不一致引入的磁场误差。在后期测量与优化中削弱了磁场的残存全局系统误差和局部随机误差：利用磁场点测台测量了波荡器磁场的纵向和横向分布,通过调节标准单元组件位置对磁场进行了垫补和优化,优化后电子轨迹中心偏移、峰峰值误差、相位误差、好场区及其误差均满足指标要求。     

Basic features of a charged particle dynamics in a laser beam with static axial magnetic field

In this paper, the trajectory and kinetic energy of a charged particle, subjected to interaction from a laser beam containing an additionally applied external static axial magnetic field, have been analyzed. We give the rigorous analytical solutions of the dynamic equations. The obtained analytical solutions have been verified by performing calculations using the derived solutions and the well known Runge-Kutta procedure for solving original dynamic equations. Both methods gave the same results. The simulation results have been obtained and presented in graphical form using the derived solutions. Apart from the laser beam, we show the results for a maser beam. The obtained analytical solutions enabled us to perform a quantitative illustration, in a graphical form of the impact of many parameters on the shape, dimensions and the motion direction along a trajectory. The kinetic energy of electrons has also been studied and the energy oscillations in time with a period equal to the one of a particle rotation have been found. We show the appearance of, so-called, stationary trajectories (hypocycloid or epicycloid) which are the projections of the real trajectory onto the (x, y) plane. Increase in laser or maser beam intensity results in the increase in particle’s trajectory dimension which was found to be proportional to the amplitude of the electric field of the electromagnetic wave. However, external magnetic field increases the results in shrinking of the trajectories. Performed studies show that not only amplitude of the electric field but also the static axial magnetic field plays a crucial role in the acceleration process of a charged particle. At the authors of this paper best knowledge, the precise analytical solutions and theoretical analysis of the trajectories and energy gains by the charged particles accelerated in the laser beam and magnetic field are lacking in up to date publications. The authors have an intention to clarify partly some important aspects connected with this process. The presented theoretical studies apply for arbitrary charged particle and the attached figures-for electrons only.     

Cosmological Implication of the Trace Anomaly

We establish a connection between the trace anomaly and thermal radiation in the standard cosmology. This is done by solving the covariant conservation equation of the stress tensor associated with a conformally invariant quantum scalar field. The solution corresponds to thermal radiation with a temperature which is given in terms of a cut-off time excluding the spacetime regions very close to the initial singularity. We discuss the interrelation between this result and the result obtained in a two-dimensional Schwarzschild spacetime.     

The problem of a self-gravitating scalar field

In this paper we begin the study of the global initial value problem for Einstein's equations in the spherically symmetric case with a massless scalar field as the material model. We reduce the problem to a single nonlinear evolution equation. Taking as initial hypersurface a future light cone with vertex at the center of symmetry, we prove, the local, in retarded time, existence and global uniqueness of classical solutions. We also prove that if the initial data is sufficiently small there exists a global classical solution which disperses in the infinite future.Research supported in part by National Science Foundation grants MCS-8201599 to the Courant Institute and PHY-8318350 to Syracuse University     

Solution of Maxwell’s equations on a de Sitter background

The Maxwell equations for the electromagnetic potential, supplemented by the Lorenz gauge condition, are decoupled and solved exactly in de Sitter space–time studied in static spherical coordinates. There is no source besides the background. One component of the vector field is expressed, in its radial part, through the solution of a fourth-order ordinary differential equation obeying given initial conditions. The other components of the vector field are then found by acting with lower-order differential operators on the solution of the fourth-order equation (while the transverse part is decoupled and solved exactly from the beginning). The whole four-vector potential is eventually expressed through hypergeometric functions and spherical harmonics. Its radial part is plotted for given choices of initial conditions. We have thus completely succeeded in solving the homogeneous vector wave equation for Maxwell theory in the Lorenz gauge when a de Sitter space–time is considered, which is relevant both for inflationary cosmology and gravitational wave theory. The decoupling technique and analytic formulae and plots are completely original. This is an important step towards solving exactly the tensor wave equation in de Sitter space–time, which has important applications to the theory of gravitational waves about curved backgrounds.     

How Is the Local-scale Gravitational Instability Influenced by the Surrounding Large-scale Structure Formation?

We develop the formalism to investigate therelation between the evolution of the large-scale(quasi) linear structure and that of the small-scalenonlinear structure in Newtonian cosmology within theLagrangian framework. In doing so, we first derive thestandard Friedmann expansion law using the averagingprocedure over the present horizon scale. Then thelarge-scale (quasi) linear flow is defined by averaging the full trajectory field over a large-scaledomain, but much smaller then the horizon scale. Therest of the full trajectory field is supposed todescribe small-scale nonlinear dynamics. We obtain the evolution equations for the large-scale andsmall-scale part of the trajectory field. These arecoupled each other in most general situations. It isshown that if the shear deformation of fluid elements is ignored in the averaged large-scaledynamics, the small-scale dynamics is described byNewtonian dynamics in an effectiveFriedmann-Robertson-Walker (FRW) background with a localscale factor. The local scale factor is defined by the sum of theglobal scale factor and the expansion deformation of theaveraged large-scale displacement field. This means thatthe evolution of small-scale fluctuations is influenced by the surrounding large-scale structurethrough the modification of FRW scale factor. The effectmight play an important role in the structure formationscenario.     

高温二氧化碳气体红外辐射实验研究

主要介绍了依托高频等离子体风洞建立的高温气体辐射测量平台,并在此平台上开展了高温二氧化碳气体红外辐射实验测量。介绍了高频等离子体风洞的运行原理、流场特性及工作介质;介绍了实验测量的条件、装置、标定、数据处理方法和结果分析;通过自建的高温气体发射光谱测量平台实验测量了二氧化碳气体在1 500～3 000 K范围内4个温度点的红外发射光谱;介绍了Abel变换在测量二氧化碳气体红外辐射空间分布中的应用,通过Abel变换获得了高温下二氧化碳气体红外辐射的空间分布结果; 分析了高温二氧化碳气体在4.3 μm附近的红外辐射的强度及其中心波长随温度变化的分布,得到了发射峰中心波长随温度的升高向长波方向展开的结果,并与文献结果进行了对比分析。     

Particle Trajectory Integrator in Guiding Center Phase Space

A trajectory integrator is developed based on a particle's guiding center Hamiltonian.It is verified by a series of benchmarks,which are in good accordance with theoretical prediction.This integrator can be used as the guiding center trajectory integrator of a particle-in-cell simulation platform,such as the newly developed Virt Ex.It can also be used as a stand-alone tool to investigate particle dynamics in a given background field.     

Classical Model of Confinement

The confinement mechanism proposed earlier and then applied successfully to meson spectroscopy by one of the authors is interpreted in classical terms. For this aim the unique solution of the Maxwell equations, an analog of the corresponding unique solution of the SU(3)-Yang-Mills equations describing linear confinement in quantum chromodynamics, is used. Motion of a charged particle is studied in the field representing magnetic part of the mentioned solution and it is shown that one deals with the full classical confinement of the charged particle in such a field: under any initial conditions the particle motion is accomplished within a finite region of space so that the particle trajectory is near magnetic field lines while the latter are compact manifolds (circles). An asymptotical expansion for the trajectory form in the strong field limit is adduced. The possible application of the obtained results in thermonuclear plasma physics is also shortly outlined.     

地基气辉成像干涉仪探测高层大气风场的定标研究

我们研制的地基气辉成像干涉仪(ground based airglow imaging interferometer,GBAⅡ)样机成功地探测了地球上空90—100 km的大气风速和温度.为了提高GBAⅡ的探测精度,本文研究GBAⅡ所拍摄的成像干涉条纹的定标:对干涉条纹中心位置定标、电荷耦合器(CCD)暗噪声和平场定标、整个光学系统衰减系数定标、步进步长定标、光程差随入射角变化量定标、仪器响应度定标和零风速相位定标等理论和实验进行了研究.利用最小二乘法对GBAⅡ拍摄的30幅成像干涉图的圆心坐标定标在CCD(123.3,121.1)像素位置;利用632.8 nm激光获得GBAⅡ所用CCD的平场定标系数矩阵,分别得到平场前后的干涉图并检测出CCD的噪声和坏点;利用GBAⅡ获得图像的边缘亮环相位与中心亮斑相位的差值对入射角10.24°时,光程差相对0°入射角时变化了0.356个条纹;拍摄200幅成像干涉图的实验离散点进行正弦拟合后的均方根标准偏差达90.34%,该完整干涉条纹的步进间隔为4.06 nm,对应步进相位为0.0094π;针对正演公式中GBAⅡ的系统衰减系数对所拍摄的原始干涉图利用IDL编程得到光学系统衰减系数的多项式,拟合的均方根标准偏差达99.98%;采用632.8 nm激光作光源,简化了GBAⅡ的响应度表达式,通过实验得其响应度为4.97×10~(-3)counts·(Rayleigh·s)~(-1);针对GBAⅡ室外观测,给出零风速定标的矩阵表达式后,对532.0 nm和632.8 nm激光的对应零风速相位分别为-9.2442°和-68.6353°.本文提供了多种定标方法,并逐一通过实验进行验证,为国内被动遥感探测高层大气风场提供了强有力的实验支持.     

Probability and complex quantum trajectories

It is shown that in the complex trajectory representation of quantum mechanics, the Born’s ΨΨ probability density can be obtained from the imaginary part of the velocity field of particles on the real axis. Extending this probability axiom to the complex plane, we first attempt to find a probability density by solving an appropriate conservation equation. The characteristic curves of this conservation equation are found to be the same as the complex paths of particles in the new representation. The boundary condition in this case is that the extended probability density should agree with the quantum probability rule along the real line. For the simple, time-independent, one-dimensional problems worked out here, we find that a conserved probability density can be derived from the velocity field of particles, except in regions where the trajectories were previously suspected to be nonviable. An alternative method to find this probability density in terms of a trajectory integral, which is easier to implement on a computer and useful for single particle solutions, is also presented. Most importantly, we show, by using the complex extension of Schrodinger equation, that the desired conservation equation can be derived from this definition of probability density.     

The Influence of the Duration of Wind Impact on the Formation of Currents and a Thermal Bar in a Freshwater Reservoir over the Period of Melting of the Ice Cover

The impact of wind of different strengths, directions, and durations on the development of a thermal bar and accompanying currents in reservoirs over the period of ice cover melting was studied using mathematical modeling. It is shown that as the duration of the wind impact on the reservoir increases, the role of energy exchange at the water-air interface in the formation of currents in the reservoir increases. The passage of surface waters through the temperature of maximum density (4°C) leads to the formation of a thermal bar and convective structures to the right and to the left of it. In this case, the increase in the energy exchange as the duration of the wind grows occurs with different degrees of intensity on different sides of the thermal bar. In certain hydrometeorological situations (when the wind is directed offshore) this can increase the intensity of the convective vortex in the deep part of the reservoir and weaken it in the shore part, which will slow the propagation of the thermal bar towards the center of the reservoir.     

The effect of electron initial longitudinal velocity on the non-sequential double ionization process in an elliptically polarized laser field

The effect of initial longitudinal velocity of the tunnelled electron on the non-sequential double ionization(NSDI) process in an elliptically polarized laser field is studied by a semiclassical model.We find that the non-zero initial longitudinal velocity has a suppressing effect on single-return collision(SRC) events in the double ionization process,more specifically,it results in an obvious reduction in the center part of the correlation momentum distributions in the direction of the major polarization axis(z axis) and makes the distribution of single-return collision in the minor polarization axis(x axis) become narrower.