SOFC电化学性能的伸缩式投影Adams多尺度模拟

目前对SOFC的研究主要通过数值分析方法,由于传统宏观模型不能准确描述其内在机理,而细微尺度模拟则面临计算机内存开销巨大,CPU耗时过长的问题。因此本文提出一种用于模拟SOFC电化学性能的伸缩式投影Adams多尺度模拟方法,建立SOFC的系统模型,首次以多尺度的观点从介观尺度出发对SOFC电化学性能进行模拟。研究其各电化学性能参数之间的关系以及入口燃料/空气成分含量、SOFC工作温度、压力对电化学性能的影响,论证了该方法的有效性。     

纳米尺度物质的生物效应和安全性

纳米尺度的物质包括碳纳米管、纳米二氧化碳、纳米三氧化铁和四氧化三铁等，它们与包括氨基酸在内的生物分子和细胞以及动物整体的相互作用受到广泛关注和研究．结果表明这些纳米材料都能和这些生物成分和生物体相互作用，具有明显的生物效应，能够影响生物分子的结构或构象、细胞的生长，且它们的毒性都较小．但从我们获得的资料看，有些纳米物质对生物的整体特性和人的健康有较重的影响．这是我们应该引起严重注意的．     

纳米尺度物质的生物效应和安全性

纳米尺度的物质包括碳纳米管、纳米二氧化碳、纳米三氧化铁和四氧化三铁等,它们与包括氨基酸在内的生物分子和细胞以及动物整体的相互作用受到广泛关注和研究.结果表明这些纳米材料都能和这些生物成分和生物体相互作用,具有明显的生物效应,能够影响生物分子的结构或构象、细胞的生长,且它们的毒性都较小.但从我们获得的资料看,有些纳米物质对生物的整体特性和人的健康有较重的影响.这是我们应该引起严重注意的.     

纳米接触行为的三维多尺度数值模拟

应用分子动力学与有限元耦合的桥域多尺度算法,模拟三维刚性球形压头与光滑基体表面的纳米尺度接触行为,并与全原子分子模拟结果比较.考察在一定载荷下的系统弛豫行为、两种模型桥接区位移和应力的连续性、法向力和接触面积随压头位移变化等,结果表明:一定外载荷下,桥域多尺度算法能较快达到平衡状态,且压头的振荡幅度更小,系统初始温度为0 K时该算法的相对误差最小.在准静态加载过程中,该算法能够将原子区的位移、应力等连续的过渡到连续介质区,具有较好的耦合效果;法向力-压头位移和接触半径-压头位移曲线几乎与分子模拟结果重合,表明算法具有较高的计算精度.     

生物大分子的共振光散射光谱

共振光散射技术是一项在普通荧光分光光度计上可实现分析领域中应用的新技术。本文阐述了共振光散射的基本原理 ,分类介绍了在生物大分子研究和测定方面的应用 ,分析了共振散射体系的新发展。     

拉曼光谱检测生物大分子损伤的研究进展

拉曼光谱是基于拉曼散射效应而发展起来的一种光谱分析技术,体现的是分子的振动或转动信息。由于拉曼光谱技术与常规化学分析技术相比,具有对样品无损、样品制备简单和所需样品量少等特点,广泛用于生物大分子结构变化的研究。拉曼光谱不仅可以用于蛋白质、核酸和脂类等生物大分子损伤的快速检测,而且可以用于癌症的诊断与手术治疗。通过对比正常组织与癌变组织的拉曼光谱,可以找到两种组织特征吸收峰的差异,从而为癌症的最终确诊和确定肿瘤切除范围提供重要信息。文章综述了拉曼光谱检测生物大分子损伤的研究进展,介绍了利用表面增强拉曼光谱、傅里叶变换拉曼光谱和紫外共振拉曼光谱等技术在检测蛋白质二级结构、膜脂及DNA损伤中的应用,并展望了未来拉曼光谱技术的发展前景。     

基于多层感知机和多尺度特征提取的肝脏分割网络

肝脏精准分割对于肝癌的定位与治疗至关重要,针对肝脏形状尺寸不一以及边缘和病灶区域分割难度较大等问题,提出了一个基于多层感知机和多尺度特征提取的肝脏分割网络(M2U-Net)。该网络分为卷积阶段和多层感知机阶段。在卷积阶段的编码器部分加入挤压激励模块,突出特定的肝脏分割任务,抑制无关背景区域;在多层感知机阶段加入标记化多层感知机模块,减小模型复杂度。过渡层增加了多尺度特征提取模块,适应不同尺度肝脏的分割以及细节区域的分割;在LiTS数据集和东方肝胆医院提供的数据集上的实验结果表明,此分割网络在三个评价指标上结果均优于U-Net、U-Net++和CE-Net等分割网络。     

纳米流体多相流动的多尺度模拟方法

针对纳米流体多相流动的微观特征,提出一种基于格子Boltzmann的多尺度耦合方法,在速度和悬浮纳米粒子分布变化比较剧烈的区域采用细网格多相模型,在其它区域视纳米流体为均匀混合的单相流体,使用粗网格单相模型.为保证不同尺度区域之间的物理信息(参数)的准确传递,运用质量和动量守恒原理,建立跨区域的边界耦合模型.几个算例表明,该方法既可以反映纳米流体流动的微观特征,又能提高计算效率,与单纯使用多相模型相比,节省大量时间.     

应用多尺度化的基本尺度熵分析心率变异性

本文采用多尺度化的基本尺度熵方法,针对心率变异性信号进行了分析,研究发现多尺度化的基本尺度熵可以区分不同生理病理信号,包括健康人、充血性心力衰竭患者和房颤心律失常患者的心率变异性信号,以及健康人白天黑夜的心率变异性信号.通过对健康人代理数据的分析,发现房颤心律失常患者与代理数据的熵值趋势相似,研究结果表明房颤心律失常患者的心率变异性信号更多的是反映生理信号的线性特征,而对环境变化不能很好的进行自我调节. 关键词： 多尺度化的基本尺度熵 心率变异性 充血性心力衰竭 房颤心律失常     

中子小角散射讲座：第四讲 中子小角散射在聚合物和生物大分子中的应用

三十多年来,研究化学聚合物和生物大分子的空间结构,一般都袭用光或X射线的弹性散射或准弹性散射技术,并已获得了大量的结构信息.但是,由于非晶态化学聚合物的不断出现及其特殊的技术应用价值,而能形成结晶态的生物大分子毕竟有限,再加上聚合物和生物大分子中都含有大量的氢,氢和氘对中子的散射振幅完全不同,使得中子小角散射在化学聚合物和生物大分子科学研究中,显示出独到之处,取得了极有价值的成果,澄清了一些长期有争议的问题,受到有关专家的重视[1,2] 一、在化学聚合物中的应用1.一般原理 化学聚合物是由单体或单分子物质经聚合反应而…     

Modeling hydrogen exchange of proteins by a multiscale method

We proposed a practical way for mapping the results of coarse-grained molecular simulations to the observables in hydrogen change experiments. By combining an atomic-interaction based coarse-grained model with an all-atom structure reconstruction algorithm, we reproduced the experimental hydrogen exchange data with reasonable accuracy using molecular dynamics simulations. We also showed that the coarse-grained model can be further improved by imposing experimental restraints from hydrogen exchange data via an iterative optimization strategy. These results suggest that it is feasible to develop an integrative molecular simulation scheme by incorporating the hydrogen exchange data into the coarse-grained molecular dynamics simulations and therefore help to overcome the accuracy bottleneck of coarse-grained models.     

The non-ideal solvation of NaCl in solvent: a simulation study

The non-ideality of the solvation of NaCl in a family of modified hybrid water solvent environments with varying local structural order is investigated using intensive molecular dynamics simulations. The results show that there are ion clusters of different size in all environments studied. The size distribution of the ion clusters is sensitive to the local structure of the solvent, which is determined by the hydrogen bonding strength. The ions are inclined to be in contact in solvents with high translational order, for competition between structure breaking among solvent molecules and structure formation around hydrated ions.     

Molecular kinetic theory of boundary slip on textured surfaces by molecular dynamics simulations

A theoretical model extended from the Frenkel-Eyring molecular kinetic theory (MKT) was applied to describe the boundary slip on textured surfaces. The concept of the equivalent depth of potential well was adopted to characterize the solid-liquid interactions on the textured surfaces. The slip behaviors on both chemically and topographically textured surfaces were investigated using molecular dynamics (MD) simulations. The extended MKT slip model is validated by our MD simulations under various situations, by constructing different complex surfaces and varying the surface wettability as well as the shear stress exerted on the liquid. This slip model can provide more comprehensive understanding of the liquid flow on atomic scale by considering the influence of the solid-liquid interactions and the applied shear stress on the nano-flow. Moreover, the slip velocity shear-rate dependence can be predicted using this slip model, since the nonlinear increase of the slip velocity under high shear stress can be approximated by a hyperbolic sine function.     

基于分子动力学模拟的主链型液晶聚合物的新模型

在传统的Gay-Berne (GB)/Lennard-Jones (LJ)模型的基础上，发展了一种用于模拟半刚性主链型液晶聚合物(LCP)的分子级模型，命名为Solo-LJ-SP-GB 模型.单一的LJ联合体和非线性弹簧被用于描述LCP分子中的间隔体.用分子动力学模拟半刚性主链型LCP系统(该系统由169条分子链组成，每两个刚性体之间的间隔体个数为6)时，该模型所需的计算时间不到传统的GB/LJ 模型所需时间的十分之一，大大地提高了计算效率.通过采用该模型模拟半刚性主链型LCP的相变问题，观察到了与半刚性主链型LCP分子中间隔体个数相关的热力学的奇偶效应以及从等方相到向列相的相转变过程.这些模拟结果与当前的试验结果相当符合，从而表明了该模型可以较为准确地描述出半刚性主链型LCP的结构特性. 关键词： Solo-LJ-SP-GB模型 液晶聚合物 分子动力学模拟     

Multiscale simulations in face-centered cubic metals: A method coupling quantum mechanics and molecular mechanics

An effective multiscale simulation which concurrently couples the quantum-mechanical and molecular-mechanical calculations based on the position continuity of atoms is presented.By an iterative procedure,the structure of the dislocation core in face-centered cubic metal is obtained by first-principles calculation and the long-range stress is released by molecular dynamics relaxation.Compared to earlier multiscale methods,the present work couples the long-range strain to the local displacements of the dislocation core in a simpler way with the same accuracy.     

Tight-binding simulations for bulk and low dimensional properties of SiC

Based on an orthogonal sp³s^∗${\mathit{sp}}^3{s}^{\ast }$ basis set, we report a tight-binding model and its transferable Si–C, C–C and Si–Si interatomic parameters. Our calculations are performed to study the structural properties of SiC in different configurations, namely, bulk, surface, clusters, and point defects. It is essential to involve the two-center intra-atomic parameters and the local environment dependent on-site atomic energy levels to get more accurate results for bulk and low dimensional configurations of SiC. In addition, the structural and electronic properties of higher-coordinated metallic structures are well described besides to those of lower-coordinated covalent structures. The parametrization of tight-binding model is found by a simultaneous fit to the structural and electronic structures of SiC in various bulk crystal configurations and its transferability to low dimensional systems. In this scheme, the results for surface energies, native formation energies, and stacking fault energies, as well as some medium size clusters are in reasonable accordance with the available experimental and theoretical calculations.     

Classical density functional theory meets Monte-Carlo simulations

ABSTRACT

Typically the quality of an approximate density functional is evaluated by a direct comparison of its predictions in a given test case to exact data obtained by computer simulations. An important example for such an approach is the test of equilibrium structure of a simple fluid as measured by the pair distribution function g(r) or the cavity correlation function y(r). However, the combination of exact density profiles and the analytical structure of density functional theory allows one to determine and potentially improve the quality of a functional in a more sophisticatedway.     

Multiscale dislocation dynamics simulations of shock-induced plasticity in small volumes

Multiscale dislocation dynamics plasticity (MDDP) was used to investigate shock-induced deformation in monocrystalline copper. In order to enhance the numerical simulations, a periodic boundary condition was implemented in the continuum finite element (FE) scale so that the uniaxial compression of shocks could be attained. Additionally, lattice rotation was accounted for by modifying the dislocation dynamics (DD) code to update the dislocations’ slip systems. The dislocation microstructures were examined in detail and a mechanism of microband formation is proposed for single- and multiple-slip deformation. The simulation results show that lattice rotation enhances microband formation in single slip by locally reorienting the slip plane. It is also illustrated that both confined and periodic boundary conditions can be used to achieve uniaxial compression; however, a periodic boundary condition yields a disturbed wave profile due to edge effects. Moreover, the boundary conditions and the loading rise time show no significant effects on shock–dislocations interaction and the resulting microstructures. MDDP results of high strain rate calculations are also compared with the predictions of the Armstrong–Zerilli model of dislocation generation and movement. This work confirms that the effect of resident dislocations on the strain rate can be neglected when a homogeneous nucleation mechanism is included.     

磁流变液动态屈服行为的随机多尺度建模

根据能量保守原理,将微观粒子运动的动能等效成宏观动态屈服的应变能,建立内秉悬浮粒子运动涨落的磁流变液剪切应力的随机多尺度模型.分析表明,悬浮粒子初始随机条件和Brownian运动,以及剪切应变加载过程中,链簇反复断裂、重组的先后次序和数目不均匀,导致系统宏观屈服性态的非线性涨落和随机涨落;同时,微观运动涨落在体积平均过程中被严重弱化,宏观随机涨落相对不明显.拟合Bingham剪变率本构模型则进一步表明,外加场强对宏观屈服性态的变异性有一定程度的影响,磁流变液装置设计中应该考虑物理参数的随机性.