合肥同步辐射软X射线显微术研究

合肥国家同步辐射实验室首期建设的光束线之一用于软Ｘ射线显微成像研究。实验站现已装置初型的扫描透射Ｘ射线显微镜，并正在进行亲一代的扫描显微建设，同时还使同步辐射光进行接触软Ｘ射线呈微成像研究，并对选取的一些生物样品进行了成像试验。本文介绍了合肥同步辐射光源上软Ｘ射线显微术实验线站的建设及完成的一些实验结果。     

环形线电荷的电场分布

给出了圆环形线电荷电场分布的理论公式，并利用计算机计算出其具体分布规律。     

Radiation-induced fermion resonance

The Dirac equation is solved for two novel terms which describe the interaction energy between the half-integral spin of a fermion and the classical, circularly polarized, electromagnetic field. A simple experiment is suggested to test the new terms and the existence of radiation-induced fermion resonance.     

Excitation energy transfer between Er3+ and Tm3+ in LiNbO3

Conclusions Nonradiative energy transfer between similar and different rare-earth ions in LiNbO₃ has been evidenced for the first time. The contribution of nonradiative energy transfer to the decay of the¹G₄ and³H₄ levels of thulium and the⁴S_3/2 and⁴I_13/2 levels of erbium is significant for activator concentrations of the order of several thousand ppm in LiNbO₃. The excitation of higher-lying levels of both activators is transferred faster in codoped crystal to the lowest luminescent levels, from which the luminescence in the 1–2-μm spectral region occurs. This accelerated relaxation is advantageous for broadband optical pumping since the contribution of radiative transitions competing with the³F₄−³H₆ laser transition of thulium is reduced. On the other hand, it appears that erbium ions will influence adversely the efficiency of a laser-diode-pumped LiNbO₃∶Er, Tm laser operating near 1.8 μm since the part of the³H₄ excitation transferred to erbium ions is emitted from the long-lived⁴I_11/2 level of Er³⁺. Furthermore, the⁴I_13/2 excitation is not transferred fully to thulium ions and is lost in⁴I_13/2−⁴I_15/2 emission. Lithium niobate singly doped with thulium is more promising since the cross-relaxation process that transfers the excitation from the³H₄ level to the³F₄ level appears to be efficient in this host. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 125–133, September–October, 1995.     

QCD corrections to the forward-backward asymmetries of c and b quarks at the Z pole

Measurements of the forward-backward production asymmetry of heavy quarks in Z decays provide a precise determination of . The asymmetries are sensitive to QCD effects, in particular hard gluon radiation. In this paper QCD corrections for and are discussed. The interplay between the experimental techniques used to measure the asymmetries and the QCD effects is investigated using simulated events. A procedure to estimate the correction needed for experimental measurements is proposed, and some specific examples are given. Received: 26 February 1998 / Published online: 2 June 1998     

Single change covering designs

A single-change covering designSC (v, k, b) on av-setV is a sequence ofb k-sets (blocks) onV which together cover every pair of elements ofV at least once, such that two successive blocks havek–1 elements in common. It is desirable to minimizeb. Some constructions and lower bounds forb are given.     

Mixed block elimination for linear systems with wider borders

The paper is about the stable solution of possibly ill-conditionedbordered linear systems. Given stable solvers for matrix A andfor A^T, we prove that the Govaerts Mixed Block Elimination (BEM)method constitutes a stable solver for the matrix consistingof A or A^T with a border of width 1, and hence by recursionfor a border of any width. We express the algorithm in an efficient,iterative, form. We analyse its operation count, and verifythe theory by extensive numerical experiments. ^*Senior Research Associate of the Belgian National Fund of ScientificResearch NFWO.     

双折射双频激光器偏振特性的分析

用激光原理和晶体光学原理分析了腔内加旋光晶体的激光器输出光的偏振特性，实验和分析表明，激光器输出两束不同频率的垂直线偏振光，激光器两端输出光的偏振面有一夹角ａ，且此夹角与晶轴和传光方向的夹角θ有关。理论计算结果在双折射双频激光器的实验结果符合很好。