分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2024-05-24
摘要: The electron-diffraction patterns with 5-fold rotational symmetry of the experimental Al-Mn alloy phase reported by Shechtman et al. are assumed to be produced by a periodic structure. A three-dimensional periodic structure is presented based on two kind polyhedrons. The structure can be used as an atomic model to describe the alloy phase. The Fourier-transform patterns of the model are simulated along six “symmetry directions”. The chemical composition of the model is similar to that of the Al-Mn alloy phase. Details of the motivations and approaches that lead to these models are discussed. This study suggests that non classical periodic structures are also well candidates to describe quasicrystals
分类: 数学 >> 应用数学 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2023-07-04
摘要: 伪随机数发生器(PRNG)广泛应用于许多领域,尤其是在密码应用中。设计欠佳的PRNG生成的序列将导致其密钥较弱从而可能泄漏被隐藏的信息。基于Golomb对理想伪随机序列的假设和FIPS 140-2随机性检验准则,本文首次提出了一种改进伪随机序列伪随机性能的新方法。其次,用广义同步定理、Henon映射、logistic映射和tube射构造了一个新的8维混沌广义同步系统(8DCGSS)。然后使用8DCGSS设计了一个混沌PRNG(CPRNG)。CPRNG的密钥空间大于2^{1117}。用FIPS 140-2随机性测试规范和广义FIPS 140-2随机性测试规范分别检测了CPRNG、Matlab PRNG、RC4算法和m序列分别生成的1000条20 000比特长的密钥流的通过率,应用广义FIPS 140-2随机性测试规范分别评估了改进的密钥流流的通过率(伪随机性)。用FIPS 140-2和广义FIPS 140-2伪随机性测试规范分别评估了4个PRNG产生的1000条100 000比特长的密钥流和1000条1 000 000比特长的密钥流和改进的密钥流的通过率。结果表明,本文的方法能够显著提高四个PRNGs生成的密钥流的伪随机性。m序列伪随机数发生器生成的长度小于100 000比特的密钥流的伪随机性能不佳。