Effects of temperature,mechanical motion and source positional jitter on the resolving power of beamline 02B at the SSRF

A detailed analysis of the effects of temperature excursions, instrumental mechanical motion and source position jitter on the energy‐resolving power of beamline 02B at the Shanghai Synchrotron Radiation Facility (SSRF) is presented in this study. This beamline uses a bending‐magnet‐based source and includes a variable‐line‐spacing grating monochromator with additional optics. Expressions are derived for the monochromator output photon energy shifts for each of the performance challenges considered. The calculated results indicate that measured temperature excursions of ±1 K produce an energy shift of less than 11% of the system's energy resolution. Mechanical displacements and vibrations measured at amplitudes of less than 0.5 µm produce changes of less than 5%, while measured source location jitter results in a change of less than 10%. Spectroscopic test experiments at 250 and 400 eV provide energy resolutions of over 10⁴. This analysis, combined with the measured results, confirms the operational stability of the beamline, indicating that it meets the performance requirements for experimental use.     

Polarization Mode Dispersion Probability Distribution for Arbitrary Mode Coupling

The probability distribution of the differential group delay for arbitrary mode coupling is simulated with Monte-Carlo method. Fitting the simulation results, we obtain probability distribution function for arbitrary mode coupling.     

Explicit Time Marching Methods for the Time-Dependent Euler Computations

Four explicit type time marching methods, including one proposed by the authors, are examined. The TVD conditions of this method are analyzed with the linear conservation law as the model equation. Performance of these methods when applied to the Euler equations are numerically tested. Seven examples are tested, the main concern is the performance of the methods when discontinuities with different strengths are encountered. When the discontinuity is getting stronger, spurious oscillation shows up for three existing methods, while the method proposed by the authors always gives the results with satisfaction. The effect of the limiter is also investigated. To put these methods in the same basis for the comparison the same spatial discretization is used. Roe's solver is used to evaluate the fluxes at the cell interface; spatially second-order accuracy is achieved by the MUSCL reconstruction.     

基于波形构型分析的脉冲电路设计方法研究

在脉冲电路设计中,需要根据实际应用的波形要求和负载特性选择、设计其电路构型。工程设计中常用的时域波形叠加和参数扫描等波形构型设计方法存在较大局限性,难以形成对脉冲波形构型的物理本质、脉冲电路结构对负载的适应性等方面的系统认识。从分析影响脉冲波形构型的基本要素入手,从时域和频域角度对脉冲波形构型及其电路实现方法进行系统的分析和归纳,给出时域和频域的电路构型设计方法及相应的电路参数解算方法,使设计人员可采用解析分析方法判断电路中元器件参数的调整方向,同时推动电路设计创新。     

Low-energy surface collision induced dissociation of Ge and Sn cluster ions

Fragmentation of germanium and tin cluster ions in the low-energy collisions with a Si surface has been investigated by means of a tandem time-of-flight mass spectrometer. At low incident energies, smaller clusters fragmented by an atom loss process, whereas larger clusters decayed by fission. The favored fragmentation paths for both cluster ions were similar to those for Si cluster ions. The results support the structural similarities among Si, Ge, and Sn clusters in the present size range. For tin cluster ions, low-energy fragmentation patterns were compared with those obtained from theoretical calculations using generalized gradient approximation (GGA) and the B3PW91 exchange-correlation functional. It has been found that the B3PW91 hybrid functional results are consistent with the experimental observations.     

采用动态核特征及贝叶斯最大后验估计的语音转换方法

针对小样本情况下,使用混合概率线性回归(Mixture of Probabilistic Linear Regressions,MPLR)模型进行语音转换容易出现过拟合的问题,提出利用动态核特征替代源说话人语音谱特征后,对转换函数参数进行贝叶斯最大后验估计(Maximum a Posterior,MAP)求解的方法。首先采用核函数将源说话人的语音谱特征转化为动态核特征,再引入转换函数参数的先验知识,最后根据对误差的不同假设,提出两种求解转换函数参数的方法。客观评测实验结果表明,所提出方法的平均谱失真值相对于MPLR模型转换方法平均降低了4.25%。主观评测实验结果表明,所提出的方法在转换语音的相似度和自然度方面的得分均高于MPLR方法。实验结果证明,所提出方法有效地改善了语音转换中的过拟合问题。     

Nonlinear gain and dispersion in the four-level Λ-type system

The nonlinear gain and dispersion spectra of a four-level Λ-type system, which driven by a weak probe field and coupling field, is investigated. Using the perturbation method, third-order perturbation iterative solutions of the steady density matrix equations are obtained. We find that effect of the SGC on the nonlinear gain and dispersion are negligible. At the resonant coupling, nonlinear dispersion spectra of the two transition paths are symmetrical about a line, but the nonlinear absorption spectra are symmetrical about a point. The degeneration of the two lower states greatly modifies the nonlinear gain and dispersion spectra.     

Phase Separation in Poly(Methyl Methacrylate)-Epoxy Blend

Diglycidyl ether of bisphenol A (DGEBA) epoxy resin was modified with high molecular weight poly(methyl methacrylate) (PMMA). Morphological variations of a 2 wt% PMMA-modified epoxy mixture were studied by optical microscopy and scanning electron microscopy (SEM). A PMMA-epoxy blend cured at 100°C revealed that a secondary phase morphology was observed in both epoxy and PMMA phases from the early stages of the phase separation process. A morphology consisting of a rough striated continuous phase along with large smooth regions was observed by SEM, confirming the secondary phase separation. The dynamic mechanical thermal analysis showed that the PMMA modification of epoxy at such a low PMMA concentration of 2 wt% has no major influence on the glass transition temperature of the epoxy-rich phase. The PMMA-epoxy blend showed a slight increase in the flexural properties and the fracture toughness.     

Effects of Quantum Interference on the Profile of Excitation Spectra in the Atomic Sodium D_1

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30MeV/u 40Ar+112,124Sn反应中的同位素产额比与核温度

系统研究了30MeV/u^40Ar ^112,124Sn反应中的轻粒子同位素产额比随角度和初始激发能的变化关系,对于两个反应体系,均观察到3He/^4He和^6Ni/^7Li的产额比随角度的增加而增加,^6He/^4He和^8Li/^7Li随角度的增加而减少,统计发射的运动学效应不能完全符合实验结果,各种单同位素产额比与靶核的N／Z比有关,表现出同位旋效应,而由双同位素比提取的核温度几乎没有靶核相关性。