Multiround Unconditionally Secure Authentication

Authentication codes are used to protect communication against a malicious adversary. In this paper we investigate unconditionally secure multiround authentication schemes. In a multiround scheme a message is authenticated by passing back and forth several codewords between the sender and receiver. We define a multiround authentication model and show how to calculate the probability of a successful attack for this model. We prove the security for a 3-round scheme and give a construction for the 3-round scheme based on Reed-Solomom codes. This construction has a very small key size for even extremely large messages. Furthermore, a secure scheme for an arbitrary number of rounds is given. We give a new upper bound for the keys size of an n-round scheme.     

Direct measurement of free-volume hole distributions in polymers by using a positronium probe

We have directly measured the free-volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi-isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho-positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc.     

Multifield hyperelasticity: variational theorems for complex bodies

We present some multifield variational principles for complex elastic solids characterized by any material microstructure. Some general constitutive arguments in the context of multifield hyperelasticity are also discussed.     

灵活的应用数学技术

E．E．Daivd指出“当今被称颂的高技术实质上是一种数学技术”，H．Neunzert称“数学是关键技术的关键”．这是人类对数学的新认识一数学既是科学又是技术．数学技术主要是指应用数学技术．它的高难度突出地体现在以解决实际问题为目标的研究上．这就必须灵活地运用数学思想和方法，抓住事物内在最本质的数学结构，提炼其特殊的数学模型，给出精巧的好算法并解决之．本文简述了华罗庚应用数学技术的特色、近期发展及其某些思想与新概念等．     

A relativistic study of the nucleon helicity amplitudes

Abstact: We perform a calculation of the relativistic transition form factors for the electromagnetic excitation of the nucleon resonances. We use as input the 3-quark wave functions obtained in a Constituent Quark Model with three-body forces in the hypercentral approach. With respect to the non relativistic calculations a significant contribution is obtained up to Q ²≃ 2 (GeV/c)². However, the low Q ²-behaviour exhibits a lack of strength, which may be connected with the need of taking into account explicitly further degrees of freedom beyond the three constituent quark ones. Received: 16 April 1998     

第二类窃密信道中的组合数学方法

当信息在第二类窃密信道中传输时,线性码的广义汉明重量谱完全描述的它在该信道中的密码学特征.计算一个线性码的广义汉明重量谱是一个基本问题,首先提出了线性码的“最简基”的概念.在此基础上给出了一般线性码子码的几种计数公式,并给出了它们之间等价性的证明.     

Procyanidin size and composition by thiolysis with cysteamine hydrochloride and chromatography

Summary Cysteamine hydrochloride is shown to be an alternative thiol reagent to toluene-α-thiol for the estimation of structural parameters (mean size, galloylation) of plant polymeric procyanidins. Acid depolymerization in the presence of the thiol yields mixtures which may be directly analysed by RPHPLC. Alternatively, the terminal units of the polymer may be separated from the extension units by cation-exchange chromatography previous to RPHPLC. High reaction-recovery yields (ca. 90% thiolysis and RPHPLC, ca. 69% thiolysis, cation exchange and RPHPLC) are obtained and both procedures are precise.     

CdSxSe1-x半导体微晶掺杂玻璃在抗共振环APM激光器中不能压窄脉

本文对具有较大非线性系数,较快非线性响应和回复时间的CdS_xSe_1-x半导体微晶掺杂玻璃能否在挽共振环(亦称为非谐振环)APM激光器中有效地压缩脉宽等问题做了详尽的理论与实验的切耐与分析。理论计算与实验研究的结果均表明:在抗共振环APM激光器中,应用CdS_xSe_1-x半导体微晶掺杂玻璃不能使超短光脉冲宽度被压窄。     

Effect of the initial phase of the field in ionization by ultrashort laser pulses

We report on observable new features related to ionization of atoms by laser pulses of only few cycles and some intensity. We show that for particular photo-electron energies, the angular distribution becomes asymmetric and that this asymmetry is related to the initial phase of the field. Received: 4 November 1997/Revised: 21 January 1998/Accepted: 23 February 1998     

Palladium-catalysed coupling of terminal alkynes with aryl halides aided by catalytic zinc

The palladium-catalysed coupling of aryl halides with terminal alkynes can be performed using base, zinc chloride and sodium iodide. This protocol represents a convenient method for the generation of nucleophilic acetylides in situ.