• Understanding Fivefold Symmetry in Electron-Diffraction Patterns

    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 

  • A New Approach for Improving Pseudorandomness of Pseudorandom Sequences with Applications

    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。