一种极线近似的双目结构光相位立体匹配方法北大核心CSCD

针对双目结构光三维重建中的相位立体匹配效率较低问题,提出了一种极线近似的快速匹配方法。首先依据两相机光心与左像素形成平面与右成像平面交线对极线进行描述;对每行像素中部分区域的对应极线进行近似,结合立体视觉的连续性约束,使得孤立的沿各自极线搜索匹配相位改为区域内沿近似极线连续搜索匹配相位;同时结合双目相机位姿特性,实现全局均匀分区,避免针对每行数据重复分区;计算过程中采用查表法辅助计算。实验结果表明,立体匹配后获得点云平均误差为0.436 mm,属可接受误差范围内,立体匹配计算速度平均提升10.18倍,对640×480尺寸图像可在17 ms内完成立体匹配,可应用于结构光实时三维重建。     

Calculation of solid-state NMR lineshapes using contour analysis

Two new methods for calculating lineshapes in solid-state NMR spectra are described. The first method, which we refer to as semi-analytical, allows the rapid calculation of quadrupolar central-transition lineshapes in both static and magic-angle spinning cases. The second method, which is fully numerical, allows the calculation of lineshapes resulting from any combination of interactions, including quadrupolar, dipolar and chemical shift anisotropy, and is not restricted to cases in which the principal axis systems for the different interactions are aligned. Both methods are derived from consideration of the contour lines on a plot of the resonance frequency against the Euler angles, allowing the intensity of the lineshape to be calculated at each frequency. Consequently, highly accurate lineshapes can be calculated more rapidly than previously possible, since only orientations contributing to each specific frequency are considered. For our semi-analytical method, the intensity of each point in the lineshape can be directly calculated in tens of milliseconds on a standard PC. In contrast, established methods can take several hours to calculate the same lineshape.     

Burton-Miller改进型边界方程的多频计算方法

提出了一种采用Burton-Miller改进型边界积分方程进行多频计算的方法。将Burton-Miller方程中的高奇异积分转化为弱奇异积分形式,获得Burton-Miller改进型边界积分方程;将方程中格林函数进行Taylor级数展开,并把波数从方程中分离出来,从而使随波数变化的计算矩阵表示为波数的矩阵级数形式。数值分析表明,本方法不仅保证了解在全波数范围内的唯一性,并且计算频率点数较多时可以节约大量时间,提高计算效率。      

Polarization of atomic hydrogen lines upon collision with an electron beam

A technique is described for the analytical calculation of the degree of linear polarization of atomic hydrogen lines formed by several radiative transitions with different polarizations upon excitation by an electron impact. The degree of linear polarization of the line L of the hydrogen atom is calculated as an example. The analytical equations used are derived by the Born method. The results of the analytical calculation are compared with experiment and with other calculations. The effective excitation cross sections and the degree of linear polarization of the H_α and H_β lines of the hydrogen atom are calculated analytically for the case of electron-beam excitation. The results of the analytical calculation of the effective excitation cross section of the H_α line are compared with the available experimental and calculated data.     

矩阵理论在半导体激光器耦合中的应用

傍轴近似下的光学矩阵理论,可以简化光束传输计算过程,使光学系统设计更为方便。将ABCD变换矩阵方法引入到耦合光学系统的设计中,运用高斯光束的ABCD法则,详尽地给出了某一耦合方式下的半导体激光器耦合入单模光纤系统的设计;另一方面,对系统的耦合损耗与耦合距离的关系进行了理论计算,并把计算结果与最近的实验报道做了比较,它们基本相吻合,说明此方法是可行的、合理的。从整个设计及理论计算来看,ABCD矩阵方法减少了复杂的计算,从而简化了设计过程,与通常的衍射计算相比,它不失为一种方便、有效的方法,同时它对生产半导体激光耦合器也有实际指导意义。     

红宝石中分子轨道效应和塞曼参数的确定

本文在配位场理论中利用普遍的静电相互作用参数,计算了红宝石吸收线的位置,结果比前人稍有改善。讨论了这些参数与分子轨道的关系,利用了二个共价键参数和自由离子参数,虽然引入的参数很少,但所得结果与上面的计算相近,并定出N_π≌0.92,N_σ≌0.89。计算了推广等效自旋哈密顿中的参数,发现修正项中的g因子是来自四级微扰的贡献,其数量级约为10^-5。得到了红宝石R线的等效哈密顿。     

R值扫描实验中触发效率的测量

介绍了北京正负电子对撞机(BEPC)/北京谱仪(BES)R值扫描实验中触发效率的测量方法,BES触发判选系统触发条件表的设置,给出了R值测量实验期间各触发条件、触发道以及不同类型事例的触发效率.     

The theoretical calculation of transition probabilities for some excited p-d transitions in atomic nitrogen

The atomic transition probabilities are calculated for individual lines between some quartet terms of 3p↦4d and 3p↦5d transition arrays using weakest bound electron potential model theory (WBEPMT). In the determination of relevant parameters which are needed for calculation of transition probabilities, we employed numerical non-relativistic Hartree-Fock wave functions for expectation values of radius in both ground and excited states unlike to NCA method used on traditional WBEPMT procedure. We have obtained very good agreement between our results and the accepted values taken from NIST.     

Improved algorithms and coupled neutron-photon transport for auto-importance sampling method

The Auto-Importance Sampling(AIS) method is a Monte Carlo variance reduction technique proposed for deep penetration problems, which can significantly improve computational efficiency without pre-calculations for importance distribution. However, the AIS method is only validated with several simple examples, and cannot be used for coupled neutron-photon transport. This paper presents improved algorithms for the AIS method, including particle transport, fictitious particle creation and adjustment, fictitious surface geometry, random number allocation and calculation of the estimated relative error. These improvements allow the AIS method to be applied to complicated deep penetration problems with complex geometry and multiple materials. A Completely coupled Neutron-Photon Auto-Importance Sampling(CNP-AIS) method is proposed to solve the deep penetration problems of coupled neutron-photon transport using the improved algorithms. The NUREG/CR-6115 PWR benchmark was calculated by using the methods of CNP-AIS, geometry splitting with Russian roulette and analog Monte Carlo, respectively. The calculation results of CNP-AIS are in good agreement with those of geometry splitting with Russian roulette and the benchmark solutions. The computational efficiency of CNP-AIS for both neutron and photon is much better than that of geometry splitting with Russian roulette in most cases, and increased by several orders of magnitude compared with that of the analog Monte Carlo.     

Reduced adiabatic hyperspherical basis in the Coulomb three-body bound state problem

A new version of the adiabatic hyperspherical approach (AHSA) is suggested which has significant advantages for the calculation of three-body states with total angular momentumJ> 0. The binding energies of all bound states of mesic molecules with normal parity are calculated by the suggested method. Comparison with results of variational calculations and the fast convergence of the method confirm its high efficiency.     

Optimal conditions of the acousto-optic interaction in crystals with gyrotropy

The conditions of the acousto-optic interaction in the crystals with gyrotropy are considered. The optimal length of the acousto-optic interaction and the diffraction efficiency in the gyrotropic direction are calculated. The diffraction efficiency is determined by the coupled wave method which allows calculation of the field interaction in the gyrotropic crystal [1]. It is theoretically shown and experimentally confirmed that the diffraction efficiency in the gyrotropic direction is independent of incident light polarization, when the polarization plane rotates by 45° along the interaction length.     

Opposite-parity orthonormal function expansion for efficient full-vectorial modeling of holey optical fibers

An improved full-vectorial method exploiting the opposite-parity property of eigenmodes based on orthonormal-functions expansion is proposed to solve the wave equation for holey optical fibers. By use of the parity property of eigenmodes in symmetric structures, the number of orthonormal function integrals involved in the calculation is reduced, and the computation efficiency is greatly enhanced. The coupling between the two transverse field components is considered, and both dominant and minor field components can be calculated for the accurate modeling of fiber modes. This method is useful for efficiently modeling holey fibers, especially those with large air holes, in which the coupling effect that is due to refractive-index discontinuities is strong.     

Calculation of line parameters of the ν<Subscript>3</Subscript> band of monodeuterated methane: Nitrogen broadening

Halfwidths and shifts of CH₃D lines are calculated for the case of nitrogen broadening. The calculations are performed for room temperature (296 K) for vibrational–rotational lines in the ν₃ parallel band, with the rotational quantum numbers varying in the ranges of 0 ≤ J ≤ 70 and 0 ≤ K ≤ 20. For each line, the temperature-dependence characteristics are calculated in the range of 200–400 K recommended for the HITRAN database. The calculations are carried out using a semiempirical method with a correction factor the parameters of which are adjusted on a number of experimental values.     

逐线积分气体吸收模型及其在NDIR气体检测中的应用

介绍了一种精确的逐线积分痕量气体吸收模型,模型适用于中红外波段大气环境中痕量气体、污染气体检测的理论研究和工程应用。首先介绍了气体辐射特性的理论计算方法和现有逐线积分大气模 型,比较了各自的优劣性,其次详述了逐线积分计算的理论: 吸收系数是温度、波长、气体浓度和相关吸收线参数的函数,单条谱线的平均吸收系数是积分线强与谱线线型的卷积,在不同的大气条件下选 择不同的线型。最后,详细描述了模型的算法细节,并给出了模型计算的结果与傅里叶变换光谱仪实测数据的对比,举例介绍了吸收模型在NDIR气体探测技术中的实际应用,并使用该模型模拟了NDIR探 测器两个通道的信号强度随尾气中CO₂,CO浓度变化的关系,通过计算确定了NDIR探测器合适的工作范围。所述模型利用HITRAN光谱数据库,考虑了展宽、线翼截断、温度修正、光谱分辨 率变化等情况,可以有效的模拟大气环境中多种气体的红外吸收特征。     

一种计算多导体传输线电磁脉冲响应的时域方法

基于波形松弛技术, 提出一种计算外界电磁脉冲激励下理想大地上无损多导体传输线瞬态响应的时域迭代方法。首先利用波形松弛技术对复频域内多导体传输线的电报方程进行解耦, 其中相邻导线的耦合作用等效为线上的分布源, 从而使电报方程转换为一系列关于独立导线的解耦方程组; 然后将复频域内传输线的解耦方程转换到时域, 根据时域方程建立相应的等效电路; 最后利用电路仿真软件PSCAD计算电磁脉冲激励下多导体传输线的瞬态响应。本文时域方法的计算结果与时域有限差分(FDTD) 法计算的结果进行对比, 证实了该时域方法的有效性和准确性, 这为工程和科研人员快速评估、分析电磁脉冲激励下多导体传输线的瞬态响应问题提供了一种可靠方法。     

基于Geant4的回旋加速器束流动力学计算

针对回旋加速器的束流动力学设计,基于Geant4模拟研究,提供一种可行的数值模拟方法。通过电磁场仿真软件Opera建立相应的电磁场数据导入到Geant4中进行插值计算,利用Geant4自带的电磁场微分方程与微分方程求解器计算粒子的平衡轨道,振荡频率以及加速轨道。其结果表明:对于横向运动而言,Geant4的计算结果与传统数值方法计算结果趋于一致;对于轴向运动而言,由于磁场插值方法的差异性,二者有一定的区别,对于在加速过程中的非平衡粒子,其能量变化围绕平衡粒子振荡。对于束损,通过限制粒子的运动时间,轴向位移加快计算效率,加入电极碰撞的判定使模拟更趋近实际情况。     

基于自吸收量化的激光诱导等离子体表征方法

为了表征激光诱导等离子体的定量特征参数,提出了一种谱线自吸收量化的方法,通过获得分析元素谱线的半高全宽来量化谱线自吸收程度,进而得到等离子体的特征参数,包括电子温度、元素含量比以及辐射物质的绝对数密度.与传统激光诱导击穿光谱定量分析方法相比,新方法由于计算过程与谱线强度弱相关,所以分析结果基本不受自吸收效应的影响,同时也无需额外的光谱效率校准.基于铝锂合金的实验结果表明,该方法能够实现精确的相对定量分析和等离子体的特性诊断.     

Thermodynamics of III–V solutions with n components

A method has been developed for the calculation of phase diagrams of III–V mixtures with more than three components. The equations for the chemical potentials, activity coefficients and the free energy of the mixture and for the liquidus- and iso-solidus-concentration lines are given. The parameters, needed for the calculation, are the temperature of fusion, heats of fusion, and the interaction parameters. The interaction parameters can be fitted to datas of the binary or quasi-binary phase diagrams, or can be calculated using the electronegativities, energies of sublimation and molar volumes of the constituent elements.Two approaches for a mixture with n components are given, which give in the ternary and binary case the known equations. The two possible cases of quaternary III–V solutions are discussed explicitly.     

LBM伪势MRT三维模型GPU并行计算的性能优化

格子Boltzmann方法伪势模型算法中的格点间计算未完全局部化,因此在并行计算时需要更多次的全局内存读写、使用更多数量的寄存器和线程同步操作,从而导致GPU并行计算效率下降.本文针对伪势模型并行计算的局限性,基于三维十五速格子结构的多松弛时间伪势模型,以气液相分离为算例,通过合并访问的方式提高全局内存的读写效率;并提出一种"定向转移"算法,提高格子边界格点获取邻居格点数据的效率;最后探索不同资源分配中各种因素对计算效率的影响,总结最优资源分配的方法.