Improved Roundoff Error Analysis for Precomputed Twiddle Factors

The accurate precomputation of the twiddle factors is necessary in order to perform discrete trigonometric transforms. This paper presents both worst case and average case analysis of roundoff errors occurring in eight precomputation methods of twiddle factors. We are interested in methods with small roundoff errors, low complexity and using only little computer memory. Numerical tests confirm the theoretical results.     

从刚体的转动角谈地球的自转周期

从刚体转动角的计算入手，结合地球自转和公转运动的几种周期，分析了地球自转的真正周期－恒星日的长度，纠正了某些献和日常生活中关于地球自转周期的错误说法。     

Supertoughness and critical interparticle distance dependence in poly(butylene terephthalate) and poly(ethylene‐co‐glycidyl methacrylate) blends

Supertough poly(butylene terephthalate) (PBT)‐based blends were obtained by the melt blending of PBT with 0–30 wt % poly(ethylene‐co‐glycidyl methacrylate) (EGMA). The reaction between PBT and EGMA was detected by torque measurements. The particle size was almost constant with increasing EGMA content, and this indicated that compatibilization occurred. The minimum EGMA content for achieving supertoughness (i.e., an impact strength 16 times greater than that of PBT) was 20 wt %. The interparticle distance was the parameter controlling toughness in these PBT/EGMA blends. The dependence of the critical interparticle distance (τ_c) on the modulus of the dispersed phase appeared only at low τ_c values, and the primary dependence of τ_c on the ratio of the modulus of the matrix to the modulus of the rubbery dispersed phase was proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2236–2247, 2003     

趋近平均法测量普朗克常量

为解决光电效应实验中的测量误差较大问题,提出了“趋近平均法”对普朗克常量进行测量,可使测量误差由使用拐点法的34%降至13.5%.     

基于中国颜色体系的色差公式分析

CIE均匀颜色空间及利用色差公式对色差进行计算对彩色复制品的评价具有很关键的作用。利用中国颜色体系在视觉上为等色差系统以及色调、彩度和明度可以单独改变的特性,分别从色调、彩度、明度三方面对CIEL*a*b*、CMC(l:c)、CIE94、CIEDE2000色差公式进行了比较分析。结果表明:用各色差公式计算出的平均色差值是不同的,它们的均匀性也不同。需要针对不同的明度、彩度、色调选择使用不同的色差公式。     

Laser peening of aluminum alloy 7050 with fastener holes

The fatigue properties of laser peened aluminum alloy 7050 specimens with fastener holes were investigated.The surface profile and residual stress induced in the shock affected zone were characterized.Then,the fatigue specimens with notch were treated by laser peening(LP),and the fatigue lifes of LP-treated specimens were measured and compared with base materials without LP.The results indicated that LP improved the fatigue lifes of all tested specimens.The average fatigue lifes of specimens treated by LP before hole-drilling were 173% longer than those of untreated samples and had better effects than those specimens treated by LP after hole-drilling.     

Edge-pumped passively Q-switched thin Nd: YAG slab lasers

We report a high-power thin Nd: YAG slab laser with slab dimension of 1×10×60(mm) partially edgepumped by diode laser arrays.Passive Q-switching is achieved with a Cr4 : YAG microchip adopted as the saturable absorber mirror.The pulse duration is around 10ns while the pulse repetition rate is higher than 10kHz.The average output power of 70W is obtained with a slope efficiency of 36%.The diffraction limited beam quality in the thickness direction is obtained by controlling the pump beam diameter inside the slab.The laser head is very compact with size of only 60×74×150(mm).     

Transposition invariant string matching

Given strings A=a₁a₂…a_m and B=b₁b₂…b_n over an alphabet , where is some numerical universe closed under addition and subtraction, and a distance function d(A,B) that gives the score of the best (partial) matching of A and B, the transposition invariant distance is , where A+t=(a₁+t)(a₂+t)…(a_m+t). We study the problem of computing the transposition invariant distance for various distance (and similarity) functions d, including Hamming distance, longest common subsequence (LCS), Levenshtein distance, and their versions where the exact matching condition is replaced by an approximate one. For all these problems we give algorithms whose time complexities are close to the known upper bounds without transposition invariance, and for some we achieve these upper bounds. In particular, we show how sparse dynamic programming can be used to solve transposition invariant problems, and its connection with multidimensional range-minimum search. As a byproduct, we give improved sparse dynamic programming algorithms to compute LCS and Levenshtein distance.     

Consecutive reversible ionization-recombination reactions and ionic charge state distribution of Au plasma

The ionic charge state distribution is an important diagnostics parameter for laser in-ertia confinement fusion (LICF). It is usually obtained by solving Saha equation or using some other models, such as local thermodynamic equilibrium (LTE), corona equilibrium (CE), collision-radiation (CR) and average atom (AA); however, these methods are rather limited for high-Z element plasma. The theory of entropy fluctuation is also a pos-sible method[1]. Lawrence Livermore National Laboratory (…     

Transportation cost inequalities on path and loop groups

Let G be a connected Lie group with the Lie algebra . The action of Cameron-Martin space on the path space P_e(G) introduced by L. Gross (Illinois J. Math. 36 (1992) 447) is free. Using this fact, we define the H-distance on P_e(G), which enables us to establish a transportation cost inequality on P_e(G). This method will be generalized to the path space over the loop group , so that we obtain a transportation cost inequality for heat measures on .