Effect of radiation on dust particles in orbital resonances

The effect of electromagnetic radiation on the dynamics of arbitrarily shaped cosmic dust particles is investigated. The paper concentrates on the motion of dust grains near commensurability resonances with a planet—mean-motion resonances—and possible capture of the grains in the resonances. A particle is in resonance with a planet when the ratio of the mean motions of the two objects is a ratio of two small integers.

The most fundamental properties of the orbital evolution of spherical dust particles in the mean-motion resonances are shortly rederived: the solar wind effect is also included and the existing result is improved. The results for spherical particles are compared with the detailed numerical calculations for nonspherical particles. It is shown that the fundamental results valid for spherical grains do not hold, in general, for nonspherical particles. While spherical particles are always characterized by the secular decrease of the semi-major axes near mean-motion resonances, this may not be true for nonspherical particles. Nonspherical grains may exhibit an increase of the semi-major axes before capturing in the mean-motion resonances. This is caused by the effect of electromagnetic radiation on nonspherical dust grains. The eccentricities of spherical particles in the exterior resonances approach a limiting value, but nonspherical grains may not follow this behaviour. The interior resonances are characterized by a systematic decrease of eccentricity for spheres, but various behaviours exist in the case of irregularly shaped particles.

The motion of a nonspherical dust particle under the action of electromagnetic radiation may be characterized by a small change of the semi-major axis during a long-time interval, but the particle is not captured in any mean-motion resonance. This kind of motion does not exist for spherical grains.     

光谱色散匀滑技术对衍射光学器件束匀滑性能的影响

 模拟分析了光谱色散匀滑技术对衍射光学器件束匀滑性能的影响。光谱色散匀滑技术的使用提高了衍射光学器件的抗波前畸变能力，降低了对加工精度的高要求。光谱色散匀滑技术与衍射光学器件的联用有望满足惯性约束聚变对束匀滑性能的高要求。     

基于VPython的天体轨道运动模拟与可视化

运动、力、动量、能量是大学物理教学最基本且重要的内容.在牛顿力学中,如果已知初始条件,对于有序系统可以预测其未来的运动状态,牛顿力学在天文学上的处理是最成功的.本文基于万有引力定律和动量定理,借助计算机软件VPython模拟天体的运动过程,例如卫星、月球绕地球的运动,火星绕太阳的运动,卫星绕双星系统的运动,直观地显示了天体运动轨迹,使天体运动过程实现了可视化.教学实践表明基于VPython的天体轨道运动模拟与可视化,可以使学生更好地理解并灵活运用牛顿运动定律和动量定理,是对经典物理教学内容的有益补充.     

Interplay between orbital and spin motion in heavy nuclei

We investigate the role of orbital and spin motion in shaping the structure of the magnetic dipole and quadrupole spectra in spherical as well as in deformed heavy nuclei.     

Fermi surface nesting and possibility of orbital ordering in FeO

Remarkable inter-band nesting in FeO Fermi surface, hints to examine energy of orbitally ordered states, which turn out to be more stable. We propose this method as a general scheme to check for possibility of orbital ordering in first principle calculations, and demonstrate it for known examples, LiVO₂ and LaMnO₃.     

时域延时多脉冲叠加平滑过程的分析

 为满足惯性约束聚变对ns级可整形激光脉冲的独特要求,提出了一种将多脉冲延迟堆积实现脉冲平滑和灵活整形的方案。这种方案基于多光束耦合器与压电陶瓷结合技术,采用光纤作为传输介质,可以精确控制相邻脉冲延时。详细分析和讨论了时延多脉冲叠加原理和叠加技术,给出了脉冲堆积时满足平滑要求的延迟时间(约为堆积所用高斯脉冲束腰宽度)和相邻脉冲间延时相位差所需的控制精度。     

周期性啁啾脉冲色散衍射实现近场强度匀滑

 对惯性约束聚变（ICF）激光驱动器中的周期性啁啾脉冲光谱色散后的自由空间衍射传输和近场强度匀滑特性进行了理论分析和数值模拟,并计算了色循环数对两者的影响。计算结果表明：远场光斑随色循环数增加而变大,强度调制加剧;近场强度匀滑效果随色循环数和传输距离增加而增强,但空间形状变化加剧。通过匀滑效果对比发现,基于周期性啁啾脉冲的光谱色散平滑系统的近场强度匀滑效果优于传统的正弦调频光束。     

Stabilization and smoothing of pressure in MPS method by Quasi-Compressibility

In this paper, a method to stabilize simulations and suppress the pressure oscillation in Moving Particle Semi-implicit method for an incompressible fluid is presented. To make the pressure smooth in terms of both of space and time, a new representation of the incompressible condition is proposed. The incompressible condition consists of two parts: the Divergence-Free condition and the Particle Number Density condition. The Divergence-Free condition has the effect of making the pressure smooth in terms of both space and time. The Particle Number Density condition is necessary to keep the fluid volume constant. In this work, the Quasi-Compressibility is also introduced for stabilization. A dam break is simulated more stably and the space distribution and the time variation of pressure are evaluated more smoothly than the traditional method. Moreover, surface particles are detected more accurately. Nevertheless the proposed method is computationally cheaper. Some simulations such as a Fluid–Structure Interaction are supposed to be more accurate using this method.     

Numerical analysis for smoothing of CW multimode beam transformed by time-varying random phase plate

The numerical analysis of CW multimode laser beam transformed by time-varying random phase plate is presented in this paper. The method is based on diffraction integral formula. The dependence of the intensity distribution on the element size, changing frequency and duty ratio is discussed in detail. The numerical results account for the experimental results satisfactorily.     

Application of iteration and finite element smoothing technique for displacement and strain measurement of digital speckle correlation

In this paper, an improved method for measuring displacement in digital speckle correlation technology, which is based on an iterative and spatial-gradient algorithm, is developed. After obtaining full-field displacement, both finite element method and 2D generalized cross-validation (GCV) algorithm are adopted for smoothing the displacement field, and then the strain field can be obtained from the smoothed displacement field. The method is estimated by simulated speckle patterns and three-point bending experiment. All the results show the improved method can obtain a reasonable estimation of displacement and strain fields in digital speckle correlation method.     

Spin and orbital magnetic moments and spin anisotropy energies of light rare earth atoms embedded in graphene: A first-principles study

The geometries, electronic structures, spin magnetic moments (SMMs), orbital magnetic moments (OMMs) and spin anisotropy energies (SAEs) of light rare earth atoms (La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd) embedded in graphene were studied by using first-principles calculations based on Density Functional Theory (DFT). The spin-orbital coupling effect was taken into account and GGA+U method was adopted to describe the strongly localized and correlated 4f electrons. There is a significant deformation of the graphene plane after doping and optimization. The deformation of Gd doped graphene is the largest, while Eu the smallest. The results show that the valence is +3 for La, Ce, Pr, Nd, Pm, Sm and Gd, and +2 for Eu. Except Eu and Gd, there are obvious OMMs. When the spin is in the Z direction, the OMMs are −0.941 μ_B, −1.663 μ_B, −3.239 μ_B, −3.276 μ_B and −3.337 μ_B for Ce, Pr, Nd, Pm and Sm, respectively, and point the opposite direction of SMMs. All the doped systems except Gd show considerable SAEs. For Ce, Pr, Nd, Pm, Sm, and Eu, the SAEs are −0.928 meV, 20.941 meV, −8.848 meV, 7.855 meV, 75.070 meV and 0.810 meV, respectively. When the spin orientation is different, different orbital angular moments lead to apparent charge density difference of the 4f atoms, which can also explain the origin of SAEs.     

Effects of charging and doping on orbital hybridizations and distributions in TiO2 clusters

Charging and doping are two important strategies used in TiO₂ quantum dots for photocatalysis and photovoltaics. Using small clusters as the prototypes for quantum dots, we have carried out density functional calculations to study the size-specific effects of charging and doping on geometry, electronic structure, frontier orbital distribution, and orbital hybridization. We find that in neutral (TiO₂)_n clusters the charge transfer from Ti to O is almost size independent, while for the anionic (TiO₂)_n clusters the corresponding charge transfer is reduced but it increases with size. When one O atom is substituted with N, the charge transfer is also reduced due to the smaller electron affinity of N. As the cluster size increases, the populations of 3d and 4s orbitals of Ti decrease with size, while the populations of the 4p orbital increase, suggesting size dependence of spd hybridizations. The present study clearly shows that charging and doping are effective ways for tailoring the energy gap, orbital distributions, and hybridizations.     

行星的视运动与圆外旋轮线

用简化模型（行得在同一平面内绕太阳作匀速圆周运动）分析了行星相对于地球的运动（视运动）。给出了视运动的运动方程，证明了行星视运动的轨迹与圆外旋轮线，讨论了行星的顺向运动与逆向运动，给出了关于水星、金星、火星、土星、木星的数值结果。     

Tunable anisotropic anomalous Nernst effect and orbital magnetization in Floquet Weyl semimetals

Weyl semimetals and nodal line semimetals display a host of novel properties. Floquet Weyl semimetals with tunable Weyl points can be obtained from nodal line semimetals under the circularly polarized off-resonant light. Here we theoretically investigate the anomalous Nernst effect and orbital magnetization in Floquet Weyl semimetals. Due to the anisotropy of the band structure in Floquet Weyl semimetals, highly anisotropic Berry phase mediated anomalous Nernst effect and orbital magnetization in the absence of magnetic field are observed, indicating orientation-dependent applications in the design of nanodevices. The amplitude and sign of anomalous Nernst coefficient and orbital magnetization can be tuned by the light direction, amplitude and polarization. The effect of the chemical potential on anomalous Nernst coefficient and orbital magnetization is also discussed. The light-modulated anomalous Nernst effect and orbital magnetization make Floquet Weyl semimetals potential candidates for thermoelectric devices.     

Effect of amorphous C films deposited by RF magnetron sputtering on smoothing K9 glass substrate

Soft X-ray multilayer reflectors must be deposited on super-smooth surface such as super-polished silicon wafers or glasses, which are complicate, time-consuming and expensive to produce. To overcome this shortage, C films deposited by RF magnetron sputtering were considered to smooth the K9 glass substrates’ surface in the present paper. The structure of C films was systematically studied by XRD and Raman spectrum. The surface morphology and rms-roughness were obtained by AFM. Then, we calculated the impact of the C layers on the reflectivity curve of Mo/Si soft X-ray multilayer reflector around 13.5 nm. The C films exhibit typical amorphous state. With the increasing of power and thickness, the content of sp3 hybrid bonding decreases while the amount or size of well-organized graphite clusters increases. The surface rms-roughness decreases from 2.4 nm to 0.62 nm after smoothed by an 80 nm thick C layer deposited in 500 W, which is the smoothest C layer surface we have obtained. The calculation results show that the theoretical normal incidence reflectivity of Mo/Si multilayer at 13.5 nm increases from 7% to 63%.     

Semiclassical approach to orbital magnetism of interacting diffusive quantum systems

We study interaction effects on the orbital magnetism of diffusive mesoscopic quantum systems. By combining many-body perturbation theory with semiclassical techniques, we show that the interaction contribution to the ensemble-averaged quantum thermodynamic potential can be reduced to an essentially classical operator. We compute the magnetic response of disordered rings and dots for diffusive classical dynamics. Our semiclassical approach reproduces the results of previous diagrammatic quantum calculations.     

Influence of spectral dispersion parameters on the beam smoothing performance of a diffractive optical element

In this paper, a theoretical model to analyze the beam smoothing performance, realized by the smoothing by spectral dispersion (SSD) and the diffractive optical element (DOE), is set up with the use of the spatial frequency spectra of the far-field intensity distribution. The influences of the parameters of the SSD, for example, the frequency of the electrical field, the integration time and the angular dispersion of the diffraction grating, on the beam smoothing performance of the DOE are numerically analyzed. Furthermore, the phase distortion is considered, and the simulated results show the phase distortion should be changed during the integration time in order to obtain a good performance of beam smoothing.     

Sorting and detecting orbital angular momentum states by using a Dove prism embedded Mach-Zehnder interferometer and amplitude gratings

An experimental system consisting of a Dove prism embedded Mach-Zehnder (M-Z) interferometer and two gratings was built to sort and detect orbital angular momentum (OAM) states of light beams. The helical beams with different OAM states were generated by propagating the fundamental-mode Gaussian beam through a spatial light modulator. The Dove prism embedded M-Z interferometer was used to sort helical beams with odd or even OAM number and two binary amplitude gratings were used to measure the OAM states. Sorting of coaxially-superposed coherent and incoherent helical beams with odd and even OAM states was realized in the experiment.     

注氢纯铝中间隙型位错环一维迁移现象的原位观察

核聚变堆材料在高能粒子辐照过程中会产生大量点缺陷,导致辐照脆性和辐照肿胀等现象.因而,研究点缺陷在辐照过程中的演变过程至关重要.点缺陷团簇的一维迁移现象是这种演变过程的主要研究内容之一.本文采用普通低压(200 kV)透射电镜,在室温条件下对注氢纯铝中的间隙型位错环在电子辐照下的一维迁移现象进行了观察和分析.在200 keV电子辐照下,注氢纯铝中的位错环可多个、同时发生一维迁移运动,也可单个、独立进行一维迁移运动.位错环沿柏氏矢量1/3<111>的方向可进行微米尺度的一维长程迁移,沿柏氏矢量1/2<110>的方向一维迁移也可达数百纳米.电子束辐照时产生的间隙原子浓度梯度是引起位错环一维迁移并决定其迁移方向的原因.位错环发生快速一维迁移时,其后会留下一条运动轨迹;位错环一维迁移的速率越快,运动的轨迹则越长,在完成迁移过后的几十秒内这些运动轨迹会逐渐消失.