基于结构保持的增广型各向异性PDE滤波

基于偏微分方程模型的图像恢复框架,从各向异性扩散的角度,提出了一种基于结构保持的增广型PDE图像滤波算法.首先定义了一种新的扩散权函数,采用差曲率代替传统的梯度算子作为边缘判别器,以克服后者对噪声敏感的不足.并根据图像结构张量信息分别设计了梯度和切线2个不同方向的扩散系数,在图像平坦区域,梯度和切线2个方向具有同等扩散,而在图像边缘处只沿着切线方向扩散.同时,引入数据保真项,有利于在滤波时保持图像细节.实验结果表明,无论对灰度图像还是医学图像,该算法可比现有其他几种扩散模型取得更好的主观视觉效果和客观性能评价指标.     

自旋——未来的科技明星

 磁与电宛如一对孪生兄弟,难以分离,原子是物质的基本单元,原子核以及组成原子核的基本粒子都具有磁矩,但其中中子、微中子等具有磁矩却没有电荷,从此角度考虑,磁比电更具有普适性,然而,人们对电的了解更胜于磁,追其原因,人们的日常生活离不开电,如：电话、电灯、电视、电脑、电动机等,人们没有进一步思考电流是如何产生的,最基本的原理是磁通量的变化产生电流,反之,电流产生磁场,因此,通常磁与电是相互关联的。磁的基本单元是自旋磁矩,电荷与自旋都是电子的本征特性,以往人类社会的发展,从物理的观点看来主要利用电子具有电荷的特性,如电工学奠定了第二次产业革命（电气化）的基础;电子学与微电子学奠定了第三次产业革命（信息化）的基础,而自旋的作用仅体现在磁性材料及其器件中,例如电气化中的发电机、电动机、变压器等离不开磁性材料,同样,信息化中储存信息离不开磁盘、磁带等。在电工学、电子学与微电子学中主要研究电场调控下的电子电荷的运动,没有涉及到电子的自旋。人们不禁要问：为什么同样是电子本征特性的自旋在电子输运过程中不呈现呢？     

考虑再生粗骨料随机分布的混凝土氯离子扩散细观数值模拟

考虑粗骨料分布的随机性及氯离子结合的非线性对氯离子扩散性的影响,对再生混凝土中氯离子扩散进行数值建模与细观仿真分析,并将数值模拟结果与已有试验数据进行对比;通过改变老硬化砂浆扩散系数、新硬化砂浆扩散系数、老界面过渡区扩散系数及浸泡时间,对比研究了不同情况下再生混凝土中氯离子的扩散特性.结果表明:数值模拟结果与试验结果接近;再生混凝土中氯离子沿扩散深度方向呈波浪式下降;随着扩散系数的增大及浸泡时间的增长,氯离子扩散速度加快;随着再生粗骨料取代率的增加,氯离子扩散速度也增加;相同扩散深度处,不同随机骨料模型中氯离子含量最大值接近,说明所采用的随机骨料模型模拟结果具有较好的稳定性.     

基于跳-扩散过程的振动系统的模态识别方法(英文)

本文提出了Lévy激励下LTI系统的一种时域模态识别方法.系统响应可看做是一个跳-扩散过程.基于二次变差和多幂次变差的性质,跳-扩散过程被分解成扩散过程和纯跳激励的过程,二者都具有和原系统相同的未知参数.最后通过扩散过程的极大似然估计方法来估计Lévy激励下LTI系统的参数.数值结果表明该方法估计精度高.     

Factors affecting the voxel-based analysis of diffusion tensor imaging

Diffusion tensor imaging （DTI） provides a unique method to reveal the integrity of white matter microstructure noninvasively. Voxel-based analysis （VBA）, which is a highly reproducible and user-independent tech- nique, has been used to analyze DTI data in a number of studies. Fractional anisotropy （FA）, which is derived from DTI, is the most frequently used parameter. The parameter setting during the DTI data preprocessing might affect the FA analysis results. However, there is no reliable evidence on how the parameters affect the results of FA analysis. This study sought to quantitatively investigate the factors that might affect the voxel-based analysis of FA; these include the interpolation during spatial normalization, smoothing kernel and statistical threshold. Because it is difficult to obtain the true information of the lesion in the patients, we simulated lesions on the healthy FA maps. The DTI data were obtained from 20 healthy subjects. The FA maps were calculated using DTIStudio. We randomly divided these FA maps into two groups. One was used as a model patient group, and the other was used as a normal control group. Simulated lesions were added to the model patient group by decreasing the FA intensities in a specified region by 5 %- 50 %. The model patient group and the normal control groupwere compared by two-sample t test statistic analysis voxel- by-voxel to detect the simulated lesions. We evaluated these factors by comparing the difference between the detected lesion through VBA and the simulated lesion. The result showed that the space normalization of FA image should use the trilinear interpolation, and the smoothing kernel should be 2-3 times the voxel size of spatially normalized FA image. For lesions with small intensity change, FWE correction must be cautiously used. This study provided an important reference to the analysis of FA with VBA method.     

Observation of directional change of core field inside flux ropes within one reconnection diffusion region in the Earth’s magnetotail

Two consecutive magnetic flux ropes, separated by less than 30 s （△t 〈 30 s）, are observed within one magnetic reconnection diffusion region without strong guide field in the Earth＇s magnetotail by Cluster multispacecraft. The flux ropes are characterized by bipolar signatures of the south-north magnetic field component Bz accompanied with strong core magnetic field By, intense current J and density depletions inside of them. In spite of the small but non-trivial global scale negative guide field （-By）, there exists a directional change of the core fields of two flux ropes, i.e., -By for the first one, and ＋By for the second one. The directions of the core fields are the same as the ambient cross-tail magnetic field component （By） just outside of flux ropes. Therefore, we suggest that the core field of flux ropes is formed by compression of the local preexisting By and that the directional change of core field is due to the change of local preexisting By. Such a change in ambient By might be caused by some microscale physics.     

基于ARCGIS的河南省分区农业旱灾风险分析

针对以往研究中旱灾发生概率计算精度不高、权重确定不够客观等不足,利用信息扩散理论和农业旱灾风险指数法,从致灾因子、孕灾环境、承灾体和抗旱减灾能力4个方面选取相应的评估指标,基于ARCGIS平台,对河南省农业旱灾风险进行分区分析.结果表明:濮阳和安阳处于致灾因子高危险区;鹤壁和新乡处于孕灾环境高敏感区;焦作和济源处于承灾体高脆弱区;开封、郑州、洛阳处于高抗旱减灾能力区.综合各影响因素的风险指数,安阳、鹤壁和济源处于农业旱灾高风险区.     

一类反应扩散系统的振幅方程及其斑图稳定性分析

分析了Brusselator模型产生斑图的必要条件,求得系统在图灵分岔处的振幅方程,进一步讨论了对应斑图的稳定性.在此基础上,通过数值模拟,验证了理论分析的正确性.     

锦界选煤厂粉尘治理实践

粉尘问题是影响选煤厂高效安全洁净生产的重要问题,本文结合本选煤厂的生产和实际,分析了粉尘来源所产生和扩散的原因,对选煤厂的粉尘治理进行了综合性探讨。综合破碎车间对本选煤厂粉尘治理的情况做以实践分析。     

S盒密码性质的测试与研究

本文介绍了S盒的设计准则和构造方法,并利用程序实现了非线性度、扩散准则、雪崩效应、差分均匀性这几个设计准则。利用上述程序对现代主流的几个分组密码进行了分析和测试,主要就非线性度、差分均匀度、雪崩效应、扩散特性以及可逆性对其中的S盒进行了分析和讨论。此外,在上述基础上,本文采用有限域上的幂函数和逆函数线性组合的方式构造S盒。对得到的S盒的密码性质进行了分析和讨论,并与现代主流密码的S盒进行比较。