磁性量子元胞自动机逻辑电路的转换特性研究

本文研究了磁性量子元胞自动机反相器和择多逻辑门等基本逻辑电路在不同纳磁体厚度和间距下的转换特性.采用单畴近似LLG方程对纳磁体以及电路进行了建模和仿真,结果表明更厚的纳磁体需要更大的转换磁脉冲,大厚度纳磁体逻辑电路表现出较慢的转换;相同厚度和间距下,择多逻辑门比反相器的转换时间略长.此外,模拟结果还表明纳磁体间距对反相器的转换过程影响明显,而对择多逻辑门则影响较小. 关键词： 磁性量子元胞自动机 转换特性 厚度和间距 逻辑电路     

磁性量子元胞自动机功能阵列的实验研究

采用电子束光刻、热蒸镀和剥离工艺在室温下制备了多组磁性量子元胞自动机器件功能阵列. 实验研究了曝光剂量和曝光时间对三个不同间距参数磁性量子元胞自动机阵列图案的影响, 发现100 pA电子束束流和0.38 μs曝光时间可获得理想的阵列图案. 对制备的反相器阵列结构进行了磁力显微测试, 结果显示了正确的逻辑功能, 成功实现了不同间距参数功能阵列的实验制备. 此外, 实验还发现纳磁体阵列制备中容易出现缺陷, 模拟结果表明丢失纳磁体缺陷导致了信号传递反相.     

元胞自动机和复杂性研究

元胞自动机是建立复杂系统的离散模型，深入了解其动力学相互作用与时空演化过程的实验数学方法，它开创了基础科学研究与复杂性探索的新途径，是一类获得迅速发展的新的并行计算机，又是计算机、信息和智能应用高科技的热点之一。     

一维元胞自动机随机交通流模型的理论分析与计算机实验

在一维局部作用元胞自动机(CA)交通流模型中，引入刹车噪声与产生、消失概率，得到一个完全随机的CA交通流模型．利用平衡自旋理论对该模型的研究表明，当P_in＝P_out≠0时，初始密度分布不影响系统的最终状态，求得ρ_ｔ＝0.5；当满足条件P_in＋P_b＝1与P_in＝P_out时，得到简单的“线性”模型，该模型在条件｜1－2P_in｜＝1下，表现出长程相关，导致严重交通“阻塞”的出现．理论结果与计算机实验一致． 关键词：     

二维伊辛模型相变临界现象的元胞自动机模拟

用元胞自动机模型模拟二维伊辛模型的相变临界现象,得出了相变图和时空演化图;当不存在外场时,数值模拟得到的临界温度与理论值精确吻合。     

公交车停靠诱发交通瓶颈的元胞自动机模拟

利用双车道元胞自动机模型,研究公交车停靠对道路混合交通流的影响.针对港湾式和非港湾式两种不同公交车站设置,在开放边界下模拟了公交车停靠所产生的交通瓶颈问题,给出了车辆入流概率-公交车比例相平面上的相图,区分了自由流相和拥挤相,研究了相图各区中公交车站附近的平均密度和速度分布图,比较了两种公交车站情况下的道路交通流的动力学特征.研究发现,当公交车比例较小时,与非港湾式车站相比,港湾式车站可以显著改善车站处的交通状况. 关键词： 元胞自动机 混合交通流 交通瓶颈 公交车站     

基于心脏腔式结构的心电图元胞自动机建模

建立了包含心房肌、心室肌、房室腔、室间隔并考虑心室肌分层结构的心电图元胞自动机模型.利用所建立的模型,仿真了电信号在心脏中的传导,计算了正常和缺血情况下的场点电势走势.数值结果表明:正常情况下,模拟所得的场点电势呈现与标准心电图一致的P波、QRS波群、T波和J波;在心内膜下肌细胞缺血情况下,出现T波倒置的现象;在心外膜下肌细胞缺血情况下,T波变得高耸;在透壁缺血情况下,T波提前形成,QT间期缩短.将正常和异常情况下的场点电势走势与临床结果进行了对比,并分析了其形成与持续机制.研究结果可为准确阐明心电图与心肌细胞电活动之间的关系、探讨心电图的产生与持续机制提供参考.     

一种计算机网络的元胞自动机模型及分析

通过分析一种计算机网络元胞自动机模型,对网络内部结点的整体行为进行了探讨.研究表明,在负载守恒的传输过程中,各网络结点的吞吐量和缓存区的排队长度在空间和时间上均呈现幂率分布,承受系统中局部负载的结点数变化的功率谱呈现1/f噪声的特点,网络结点的整体行为表现出自组织临界现象.排队长度的分布呈现幂率,预示着较大的拥塞以较小的概率发生.吞吐量在时间上的分布呈现幂率,或许为业务量呈现自相似性提供一种合理的解释. 关键词：     

心肌组织机械形变的元胞自动机模拟

采用Greenberg-Hastings元胞自动机模型研究机械形变对心肌组织中螺旋波动力学行为的影响.数值模拟表明：对于规则网格下的稳定螺旋波,在生理性机械形变作用下,螺旋波发生漫游但不破碎;在病理性机械形变作用下,螺旋波会发生持续漫游、漫游后消失和破碎进入螺旋波湍流态三种变化.通过对比发现机械形变的振幅变化率对螺旋波的影响较大,而机械形变的角频率对螺旋波的影响较小.结合数值模拟,对心前区受到猛烈撞击会出现心颤致死及耐力运动员在发生心动过速后比一般人员更容易恢复正常进行解释.     

Periodic behavior of cellular automata

I propose an explanation of the observation of a globally synchronized behavior of deterministic cellular automata and coupled map lattices, together with local fluctuations.     

Annealed and quenched inhomogeneous cellular automata (INCA)

A probabilistic one-dimensional cellular automaton model by Domany and Kinzel is mapped into an inhomogeneous cellular automaton with the Boolean functions XOR and AND as transition rules. Wolfram's classification is recovered by varying the frequency of these two simple rules and by quenching or annealing the inhomogeneity. In particular, class 4 is related to critical behavior in directed percolation. Also, the critical slowing down of second-order phase transitions is related to a stochastic version of the classical halting problem of computation theory.     

量子细胞神经网络的超混沌特性研究

研究了由量子点细胞自动机构成的量子细胞神经网络的非线性动力学特性.以量子点细胞的极化率和量子相位作为状态变量，对3个细胞耦合的量子细胞神经网络进行了理论分析和计 算机仿真研究.结果表明，该网络系统呈现复杂的混沌动力学行为，混沌振荡产生非常容易. 由数值计算得到的两个最大正Lyapunov指数证实了该系统具有超混沌特性. 关键词： 量子点细胞自动机 极化率 量子细胞神经网络 超混沌     

Statistical mechanics of probabilistic cellular automata

We investigate the behavior of discrete-time probabilistic cellular automata (PCA), which are Markov processes on spin configurations on ad-dimensional lattice, from a rigorous statistical mechanics point of view. In particular, we exploit, whenever possible, the correspondence between stationary measures on the space-time histories of PCAs on ^d and translation-invariant Gibbs states for a related Hamiltonian on ( ^d+1). This leads to a simple large-deviation formula for the space-time histories of the PCA and a proof that in a high-temperature regime the stationary states of the PCA are Gibbsian. We also obtain results about entropy, fluctuations, and correlation inequalities, and demonstrate uniqueness of the invariant state and exponential decay of correlations in a high-noise regime. We discuss phase transitions in the low-noise (or low-temperature) regime and review Toom's proof of nonergodicity of a certain class of PCAs.     

Time-series analysis of a collective variable in high-dimensional cellular automata

We perform a maximum-entropy frequency analysis of the occupation-density time series for a recently proposed totalistic cellular automaton rule in five dimensions. This new information complements partial knowledge coming from winding number measurements. We discuss the possible phenomenology of the model in terms of our findings.     

耦合双量子点的磁序与电子结构

耦合双量子点中电子间静电相互作用对电子在系统中隧穿效应具有重要影响.考虑电子隧穿,交换及Hubbard关联作用后,在单态近似下,本文求解了耦合双量子点二电子问题,讨论了铁磁基态及Mott局域化态出现的条件。这里的结果表明电子的隧穿不利于铁磁基态的形成,Hubbard关联越强越有利于Mott局域化态的形成,并且在交换作用下Mott局域化态会转变为铁磁基态. 此外,外场可以诱导磁序相的改变。     

Stochastic cellular automata modeling of excitable systems

A stochastic cellular automaton is developed for modeling waves in excitable media. A scale of key features of excitation waves can be reproduced in the presented framework such as the shape, the propagation velocity, the curvature effect and spontaneous appearance of target patterns. Some well-understood phenomena such as waves originating from a point source, double spiral waves and waves around some obstacles of various geometries are simulated. We point out that unlike the deterministic approaches, the present model captures the curvature effect and the presence of target patterns without permanent excitation. Spontaneous appearance of patterns, which have been observed in a new experimental system and a chemical lens effect, which has been reported recently can also be easily reproduced. In all cases, the presented model results in a fast computer simulation.      

A study of a main—road cellular automata traffic flow model

A main-road cellular automata traffic flow model on two dimensions is presented based on the Biham－Middleton－Levine traffic model. Its evolution equations are given and the self-organization and organization cooperation phenomena in this model are also studied by using computer simulation.