Structural characteristic of cubic GaN nucleation layers on GaAs(001) substrates by MOCVD

The structural characteristic of cubic GaN (C-GaN) nucleation layers on GaAs(0 0 1) substrates by metalorganic chemical vapor deposition was in detail investigated first by X-ray diffraction (XRD) measurements, using a Huber five-circle diffractometer and an intense synchrotron X-ray source. The XRD results indicate that the C-GaN nucleation layers are highly crystallized. Phi scans and pole figures of the (1 1 1) reflections give a convincing proof that the GaN nucleation layers show exactly cubic symmetrical structure. The GaN(1 1 1) reflections at 54.74degrees in chi are a measurable component, however (002) components parallel to the substrate surface are not detected. Possible explanations are suggested. The pole figures of {1 0 (1) over bar 0} reflections from H-GaN inclusions show that the parasitic H-GaN originates from the C-GaN nucleation layers. The coherence lengths along the close-packed [1 1 1] directions estimated from the (1 1 1) peaks are nanometer order of magnitude. (C) 2002 Elsevier Science B.V. All rights reserved.

Investigation of {111}A and {111} planes of c-GaN epilayers grown on GaAs(001) by MOCVD

A determination of {1 1 1}A and {1 1 1}B in cubic GaN(c-GaN) was investigated by X-ray diffraction technique in detail. The c-GaN films are grown on GaAs(0 0 1) substrates by metalorganic chemical vapor deposition(MOCVD). The difference of integrated intensities measured by omega scan for the different order diffractions from {1 1 1}A and {1 1 1}B planes in the four-circle diffractometer gives convincing evidence as to which is the {1 1 1}A and which is the {1 1 1}B planes. The lesser deviation between the ratios of /F-h k l/(2)//F-(h) over bar (k) over bar (l) over bar/(2) and the calculated values after dispersion correction for atomic scattering factor shows that the content of parasitic hexagonal GaN(h-GaN) grown on c-GaN{1 1 1}A planes is higher than that on {1 1 1}B planes. The reciprocal space mappings provide additional proof that the h-GaN inclusions in c-GaN films appear as lamellar structure. (C) 2001 Published by Elsevier Science B.V.

RSA-Based Password-Authenticated Key Exchange, Revisited

The RSA-based Password-Authenticated Key Exchange (PAKE) protocols have been proposed to realize both mutual authentication and generation of secure session keys where a client is sharing his/her password only with a server and the latter should generate its RSA public/private key pair (e, n), (d, n) every time due to the lack of PKI (Public-Key Infrastructures). One of the ways to avoid a special kind of off-line (so called e-residue) attacks in the RSA-based PAKE protocols is to deploy a challenge/response method by which a client verifies the relative primality of e and φ(n) interactively with a server. However, this kind of RSA-based PAKE protocols did not give any proof of the underlying challenge/response method and therefore could not specify the exact complexity of their protocols since there exists another security parameter, needed in the challenge/response method. In this paper, we first present an RSA-based PAKE (RSA-PAKE) protocol that can deploy two different challenge/response methods (denoted by Challenge/Response Method1 and Challenge/Response Method2). The main contributions of this work include: (1) Based on the number theory, we prove that the Challenge/Response Method1 and the Challenge/Response Method2 are secure against e-residue attacks for any odd prime e; (2) With the security parameter for the on-line attacks, we show that the RSA-PAKE protocol is provably secure in the random oracle model where all of the off-line attacks are not more efficient than on-line dictionary attacks; and (3) By considering the Hamming weight of e and its complexity in the RSA-PAKE protocol, we search for primes to be recommended for a practical use. We also compare the RSA-PAKE protocol with the previous ones mainly in terms of computation and communication complexities.

A logic for default reasoning

The need to make default assumptions is frequently encountered in reasoning about incompletely specified worlds. Inferences sanctioned by default are best viewed as beliefs which may well be modified or rejected by subsequent observations. It is this property which leads to the non-monotonicity of any logic of defaults. In this paper we propose a logic for default reasoning. We then specialize our treatment to a very large class of commonly occuring defaults. For this class we develop a complete proof theory and show how to interface it with a top down resolution theorem prover. Finally, we provide criteria under which the revision of derived beliefs must be effected.

an improved smart card based password authentication scheme with provable security

Password authentication has been adopted as one of the most commonly used solutions in network environment to protect resources from unauthorized access. Recently, Lee–Kim–Yoo [S.W. Lee, H.S. Kim, K.Y. Yoo, Improvement of Chien et al.'s remote user authentication scheme using smart cards, Computer Standards & Interfaces 27 (2) (2005) 181–183] and Lee-Chiu [N.Y. Lee, Y.C. Chiu, Improved remote authentication scheme with smart card, Computer Standards & Interfaces 27 (2) (2005) 177–180] respectively proposed a smart card based password authentication scheme. We show that these two schemes are both subject to forgery attacks provided that the information stored in the smart card is disclosed by the adversary. We also propose an improved scheme with formal security proof.

共代数中的互模拟证明方法及其应用

本论文主要研究共代数中的互模拟证明方法及其应用两个方面。 代数理论已被证实在计算机科学中具有广泛的应用，其对偶概念——共代数理论是近年来兴起的一个理论，它在描述无穷状态系统方面具有明显的优势。 因此，我们在本文中以共代数作为抽象的研究模型。 因为互模拟判定中的up-to方法能够非常有效地加速判定过程，我们首先将该方法从传统的集合论中 扩展到共代数理论。作为Sangiorgi的可靠函数的扩展，我们引入了一致函数。因此， 为了证明某个二元关系中的进程对都是互模拟等价的，只要证明该关系前进到其在某个一致函数作用下得到的新关系中即可。 另外，我们给出了span-互模拟和ref-互模拟之间的等价转换关系，并且，利用该结果证明了共代数中原有的up-to方法 都能被一致函数所覆盖。 一致函数是为单个函子$F$定义的。但是，当$F$是某种类型的多项式函子时，有可能存在一些 函数，它们与$F$的某些子函子一致却不与整个$F$一致。因此，我们将一致函数进一步扩展，定义 联合一致函数，它是那些只与某些子函子一致的函数在一定条件下的组合。联合一致函数使用起来和一致函数一样，能够用来产生 新的up-to证明方法。另外，我们也相应地给出了传统并发理论中的联合一致函数概念，并且利用它给出了 弱互模拟的up-to方法。 在抽象的共代数模型中给出一般化的up-to方法之后，本文继续研究其在具体的无穷状态系统，即 BPA系统上的应用。Caucal的self-互模拟理论在 BPA系统的互模拟判定算法中起着关键作用，而它恰恰 是运用up-to方法协助互模拟判定的一个典范。 因为一个BPA系统也是一个共代数，我们在共代数理论中利用一致函数证明了该理论。 同时，本文给出了一个tableau算法，用来判定包含normed 与unnormed BPA进程的全BPA系统的互模拟等价问题。该算法非常直接且易于理解。 利用该tableau算法，我们证明了Hans H\"{u}ttel 和 Colin Stirling 为normed BPA进程设计的等式理论对于全BPA系统同样是可靠的与完备的。

on lin-bose problem

This paper study generalized Serre problem proposed by Lin and Bose in multidimensional system theory context [Multidimens. Systems and Signal Process. 10 (1999) 379; Linear Algebra Appl. 338 (2001) 125]. This problem is stated as follows. Let F ∈ Al×m be a full row rank matrix, and d be the greatest common divisor of all the l × l minors of F. Assume that the reduced minors of F generate the unit ideal, where A = K[x 1,...,xn] is the polynomial ring in n variables x 1,...,xn over any coefficient field K. Then there exist matrices G ∈ Al×l and F1 ∈ A l×m such that F = GF1 with det G = d and F 1 is a ZLP matrix. We provide an elementary proof to this problem, and treat non-full rank case.