时间相关外场中量子系统时间演化的辛格式

对显含时间的可分线性哈密顿系统构造了2阶模方守恒-辛格式和显式辛格式,并计算了1维有限宽无限深势阱中的电子与模拟激光场的相互作用,结果与理论分析一致。为数值研究时间相关外场中的量子系统,特别是强激光与原子相互作用提供了合理和有效的方法。     

量子系统保结构计算新进展

本文主要介绍量子系统保结构计算最新进展情况,分以下几部分内容:哈密顿系统的辛算法、适合于量子系统的哈密顿量显含时间的辛算法、A2B模型分子和双原子分子系统的经典轨迹辛算法计算、双原子分子CO在激光场中的经典轨迹的辛算法计算及其振动和解离、定态Schr dinger方程的辛形式及求解定态Schr dinger方程本征值问题的辛 打靶法、含时Schr dinger方程的保结构算法及其在激光原子物理中的应用、伪分立态模型、强激光与原子相互作用的渐近边界条件、"非齐线性正则方程"的辛算法及其在计算强激光场中一维原子的多光子电离和高次谐波发射中的应用以及Heisenberg方程的保结构计算等等。     

量子系统保结构计算新进展

本文主要介绍量子系统保结构计算最新进展情况,分以下几部分内容:哈密顿系统的辛算法、适合于量子系统的哈密顿量显含时间的辛算法、A2B模型分子和双原子分子系统的经典轨迹辛算法计算、双原子分子CO在激光场中的经典轨迹的辛算法计算及其振动和解离、定态Schr dinger方程的辛形式及求解定态Schr dinger方程本征值问题的辛 打靶法、含时Schr dinger方程的保结构算法及其在激光原子物理中的应用、伪分立态模型、强激光与原子相互作用的渐近边界条件、"非齐线性正则方程"的辛算法及其在计算强激光场中一维原子的多光子电离和高次谐波发射中的应用以及Heisenberg方程的保结构计算等等。     

弱场条件下两囚禁离子质心量子态运动

用微扰的方法计算了一个外加周期驱动激光场所组成的,两离子系统质心量子态跃迁几率的解析表达式.以两Ca+作为囚禁离子,模拟出了在弱场的作用下声子态跃迁几率随激光束频偏和相互作用时间变化的分布图形.结果表明:随着外加周期驱动激光场的频率和相互作用时间的调节,系统质心量子态随时间周期性的坍塌与复原;在频偏范围0.85×107...     

原子光激发过程中的选择性和相干性

通过求解含时Ｓｃｈｒｏｄｉｎｓｅｒ方程，对于原子在激光场的共振和非共振驱动下向各个态的跃迁几率进行了计算和分析，探讨了跃迁几率的时间特性以及随激光参数的变化规律，揭示了光场与原子系统相互作用的相干性和选择性。计算并验证由解析解所预测的激发态粒子数布居的峰值和实现粒子数反转所应满足的条件。     

用牛顿力学方法和分析力学方法分析机械能守恒条件时遇到的一些问题

本文认为，由于存在着不稳定力场（或力），有必要区别有势力和保守力的概念，进而较全面地阐明了机械能守恒的条件． 本文还结合实例指出了哈密顿函数和坐标变换方程中是否显含时间才依赖于广义坐标的选取，不能单从系统是否稳定来判断；说明了哈密顿函数具有与系统机械能不同的特性；并得出了用分析力学方法分析机械能守恒问题的有关结论．     

用激光-二能级原子系统实现一位通用量子逻辑门

使用代数动力学方法，对激光-二能级原子系统的含时薛定谔方程进行求解.该系统哈密顿量具有SU(2)代数结构，得到了严格解.基于严格解，适当调节单模激光场的频率和振幅以及短脉冲激光与二能级原子的二阶虚光子作用强度，可实现一位通用量子逻辑门. 关键词： 代数动力学 激光-二能级原子系统 一位量子逻辑门     

MnFe2O4晶体的基态能级和零场分裂参量

由不可约张量理论构成一个3d4/3d6离子三角(C3V)对称的晶体场和自旋-轨道相互作用哈密顿矩阵,由这个晶体场和自旋-轨道相互作用哈密顿矩阵被完全对角化后能够求出MnFe2O4晶体中的Fe2+离子的电子顺磁共振零场分裂参量D和F-a,计算了低自旋态(3L态)对电子顺磁共振零场分裂参量(D,F-a)的贡献.结果显示低自旋3L态对电子顺磁共振的零场分裂参量的贡献是较强的.理论计算的结果与实验值是相符的.     

哈密顿算符是SU(1,1)和SU(2)算子含时线性组合量子系统的时间演变及厄密不变量

研究了哈密顿算符是SU(1,1)和SU(2)算子线性组合且系数显含时间量子系统的时间演化,我们发现适当选取厄密不变量,不仅可得到统一的量子态时间演化封闭解,而且可得到时间演化幺正算符。用时间演化算符我们讨论了含时双光子压缩态和SU(1,1)相干态以及SU(2)压缩态的压缩性质。     

激光场中电子与氩原子的散射

本文根据实验中的激光脉冲图形,设计了相应的描述脉冲随时间变化的函数形式,分别以多模激光场和调幅模激光场模拟实际激光场,考虑了e-Ar之间的库仑相互作用,采用氩原子的变分波函数,计算了激光场中e-Ar散射的微分数射截面。     

Comparison of nitride-based dual-wavelength light- emitting diodes with an InAlN electron-blocking layer and with p-type doped barriers

The advantages of nitride-based dual-wavelength light-emitting diodes (LEDs) with an InAlN electron blocking layer (EBL) are studied. The emission spectra,carrier concentration in the quantum wells (QWs),energy band and internal quantum efficiency (IQE) are investigated. The simulation results indicate that an LED with an InAlN EBL performs better over a conventional LED with an AlGaN EBL and an LED with p-type-doped QW barriers. All of the advantages are due to the enhancement of carrier confinement and the lower electron leakage current. The simulation results also show that the efficiency droop is markedly improved and the luminous intensity is greatly enhanced when an InAlN EBL is used.     

Complex resonance at periodic excitation of an oscillator

Periodic excitation of an oscillator by an external signal close to an exponential one with a complex frequency at the main part of the period is analyzed. The characteristics of a stabilized excitation regime are determined, as are its features when approaching the complex resonance, when the complex frequency of an external signal at the main part of the period is compared with the complex eigenfrequency of the oscillator. A criterion of closeness to the complex resonance is suggested. Estimations of the allowed level of intensity, when nonlinear distortions of the oscillator response are insignificant, are presented.     

脉冲金属离子等离子体推进器的等离子体生成和传播特性

综述了不同阳极结构脉冲金属离子等离子体推进器的放电特性、等离子体生成及传播特性。首先,讨论了一种带有绝缘套筒的裸阳极推进器结构。对比分析了无、有绝缘套筒的裸阳极推进器的等离子体生成及传播特性的区别。结果表明,绝缘套筒阻碍了阴极近旁带电粒子的径向运动,提高了沿绝缘套筒轴向喷射出去的等离子体的喷射性能。此外,发现采用裸阳极推进器结构放电过程中会有大量带电粒子进入阳极。其次,讨论了一种绝缘阳极推进器结构。结果表明,采用绝缘阳极结构进一步提高了沿绝缘套筒轴向喷射出去的等离子体密度。但是,与裸阳极推进器结构相比,等离子体的生成量减少。再次,讨论了一种微孔绝缘阳极推进器结构。结果表明,与裸阳极推进器结构相比,采用微孔绝缘阳极推进器结构生成的等离子体的密度峰值和传播速度峰值分别提高了12.6倍、3.9倍。最后,分别讨论了一种螺旋阳极推进器结构和一种多阳极推进器结构。结果表明,这两种推进器结构分别利用放电过程中形成的自磁场及电场有效提高了等离子体羽流的定向喷射性能。本研究可以为金属等离子体喷射性能的提高以及脉冲金属离子等离子体推进器的设计提供支持。     

Effective dynamics of an electrically charged string with a current

Equations of motion for an electrically charged string with a current in an external electromagnetic field with regard to the first correction due to the self-action are derived. It is shown that the reparameterization invariance of the free action of the string imposes constraints on the possible form of the current. The effective equations of motion are obtained for an absolutely elastic charged string in the form of a ring (circle). Equations for the external electromagnetic fields that admit stationary states of such a ring are derived. Solutions to the effective equations of motion of an absolutely elastic charged ring in the absence of external fields as well as in an external uniform magnetic field are obtained. In the latter case, the frequency at which one can observe radiation emitted by the ring is evaluated. A model of an absolutely nonstretchable charged string with a current is proposed. The effective equations of motion are derived within this model, and a class of solutions to these equations is found.     

Dynamic viscoelastic effects on sound wave scattering by an eccentric compound circular cylinder

The classical method of separation of variables in conjunction with the translational addition theorem for cylindrical wave functions are employed to obtain an exact solution for two-dimensional interaction of a harmonic plane acoustic wave with an infinitely long (visco)elastic circular cylinder which is eccentrically coated by another (visco)elastic material and is submerged in an ideal unbounded acoustic medium. The novel features of Havriliak-Negami model for dynamic viscoelastic material behaviour are used to take the rheological properties of the coating (and/or core) material into consideration. The analytical results are illustrated with numerical examples in which a steel rod eccentrically coated with (an eccentric steel shell filled with) dissipative materials of distinct viscoelastic properties is insonified by plane sound waves at selected angles of incidence. The effects of incident wave frequency, angle of incidence, core eccentricity and dynamic viscoelastic material properties on the backscattered form function spectra are examined. Limiting cases are considered and fair agreements with available solutions are obtained.     

Shear and compressional wave speeds in Hertzian granular media

It is shown that the shear wave speed in a granular medium is less than that in an elastic solid of the same shear modulus-to-density ratio. Shear and compressional wave speeds are derived for granular media using a conservation of energy approach. The grains are assumed to be spherical with elastic Hertzian contacts of constant stiffness. The affine approximation is used to determine the relative displacements of grain centers, and it is also assumed that the grains are small compared to a wavelength, consistent with the effective medium approximation. Potential and kinetic energies associated with linear motion are the same as those in an elastic solid, but it is found that shear wave propagation in a granular medium involves additional energies associated with grain rotation. The partition of energies results in a reduction in the shear wave speed, relative to an elastic solid of the same shear modulus-to-density ratio. It is shown that the reduction is an inherent property of granular media, independent of any departure from the affine approximation or fluctuations in coordination number or contact stiffness. The predicted wave speed ratios are consistent with published measurements.     

Analysis of a compliantly suspended acoustic velocity sensor

The dynamics of a compliantly suspended acoustic velocity sensor having a spherical geometry are analyzed using theory and experiment. The analysis starts with a review of the motion associated with an unconstrained solid sphere when subjected to an acoustic plane wave in an unbounded inviscid fluid medium. The theory is then modified to account for the inclusion of an inertial sensor and an external suspension system. Accordingly, the open-circuit receiving response of a geophone-based and accelerometer-based device is derived. Density variations associated with the sphere and the surrounding fluid medium are assessed along with the effects fluid viscosity. Wave effects in the sphere and the suspension system are also analyzed.     

Waves in an active medium guided by a reactive surface with reactance of gain modulation

The characteristics of surface waves (i) in a passive medium supported by a passive surface with reactance modulation and an active surface with the modulation of either the reactance or the negative resistance, and (ii) in an active medium supported by a passive surface with a reactance modulation are investigated with emphasis on the band regions. The periodic variation is sinusoidal and is in the propagation direction. For a passive medium terminated by a passive surface with a reactance modulation, there are stop bands in frequency for the surface waves and the structure of the first two stop bands is analyzed. For a passive medium terminated by an active surface and for an active medium terminated by a reactance-modulated passive surface, the characteristics of the absolute instabilities occurring in the first-order band are examined. The nature of the convective instability taking place in the second-order band for an active medium terminated by a reactance-modulated surface is discussed. Analytical expressions for the frequency shift of the second-order band are deduced. The Floquet theory is used to obtain the exact dispersion relation in the form of a continued fraction which is analyzed by singular expansions.     

On the exact formulation of multi-configuration density-functional theory: electron density versus orbitals occupation

The exact formulation of multi-configuration density-functional theory is discussed in this work. As an alternative to range-separated methods, where electron correlation effects are split in the coordinate space, the combination of configuration interaction methods with orbital occupation functionals is explored at the formal level through the separation of correlation effects in the orbital space. When applied to model Hamiltonians, this approach leads to an exact site-occupation embedding theory (SOET). An adiabatic connection expression is derived for the complementary bath functional and a comparison with density matrix embedding theory is made. Illustrative results are given for the simple two-site Hubbard model. SOET is then applied to a quantum chemical Hamiltonian, thus leading to an exact complete active space site-occupation functional theory (CASSOFT) where active electrons are correlated explicitly within the CAS and the remaining contributions to the correlation energy are described with an orbital occupation functional. The computational implementation of SOET and CASSOFT as well as the development of approximate functionals are left for future work.     

A CO2 laser rangefinder using heterodyne detection and chirp pulse compression

The sensitivities of heterodyne and direct-detection systems at CO₂ laser wavelengths are compared to illuminate the design principles involved. It is shown that destruction of the temporal coherence of scattered radiation is a significant effect when heterodyne systems are used on targets with internal motion. The complete system and the results obtained are then described. The compact optics head contains a waveguide laser, an acousto-optic modulator and SAW chirp devices; it has 45 mm diameter transmit and receive apertures. Whem many returns are integrated, ranges of several kilometres are obtained off natural targets with an accuracy of 10 m. From the Doppler shift off a moving target, radial velocity can be determined simultaneously with the range when an up-chirp/down-chirp technique is used; an accuracy of better than 1 m s^–1 is demonstrated.