聚乙烯醇与羟基磷灰石相互作用的理论分析

为了研究聚乙烯醇在羟基磷灰石晶面上形成的相互作用,文中运用分子动力学方法,从分子理论的角度研究了羟基磷灰石(HA)的(001)、(100)、(110)晶面分别与含不同单元体数(40、80、120)聚乙烯醇相互作用后混合体系的结合能,并对(110)晶面径向分布函数和力学性能进行了计算分析和比较。结果表明,3个晶面所对应结合能大小为HA(110)>HA(100)>HA(001),同时结合能的大小和混合体系的力学性能在一定范围内会随着聚乙烯醇所含单体数的增加而增加,但当单体数达到一定值后结合能与力学性能反而会下降,这与单组分间是否形成有效接触有关;其相互作用主要源自PVA中的O原子分别与HA中的H原子形成的氢键以及Oa-Ca之间形成了离子键。     

Li2O·Al2O3·4SiO2-Ta2O5系微晶玻璃分相与析晶机理研究

采用Ta2O5为晶核剂制备Li2O.Al2O3.4SiO2-Ta2O5微晶玻璃,并研究其分相、析晶机理,构建晶化模型.结果表明Ta2O5能有效促进玻璃的体积析晶,获得了晶粒尺寸为50nm的精细组织.非等温动力学计算显示随Ta2O5含量增加,析晶活化能降低,析晶指数增加,析晶动力学参数K(Tp)作为析晶判据更为合理.研究发现,LAST玻璃冷却时因亚稳分解导致互锁分相,形核前期又借助成核生长机制发生微滴分相,晶体生长则在继承亚稳分相形貌基础上发生"他形"析晶.最终构建了LAST微晶玻璃的晶化模型.     

YSZ包覆YDC纳米晶复合固体电解质的制备

研究了YSZ包覆YDC纳米晶复合固体电解质的制备工艺.首先,以分析纯的Ce(NO3)3·6H2O和Y(NO3)3·6H2O为原料,采用沉淀法制备了分散性较好的YDC纳米粉体,然后将其均匀分散于含有分析纯的ZrOCl2·8H2O、Y(NO3)3·6H2O的醇水溶液中,采用溶胶凝胶法制备了ZrO2(Y2O3)包覆CeO2(Y2O3)复合纳米粉体.XRD、TEM、IR分析结果表明经600℃焙烧后的CeO2-Y2O3复合纳米粉体为单一萤石相,晶粒尺寸为15nm左右且分散性良好;成功合成了的YSZ包覆YDC复合纳米粉体,其中反应温度在75℃时粉体的包覆性及其分散性较好.以合成的包覆型纳米粉体为原料,通过常压烧结制备了包覆型YSZ/YDC复合固体电解质.研究表明,在相同保温时间内(2h),随着烧结温度从800℃提高到1350℃,试样相对密度从52%迅速增加95%以上.当烧结条件为从室温升温到1300℃,迅速降温到1250℃保温2h后,烧结体的相对密度可达95%以上,平均晶粒度为100nm左右.     

羟基磷灰石/α-氰基丙烯酸正丁酯相互作用及力学性能的MD模拟

基于羟基磷灰石陶瓷微球人工骨支架的制备工艺,用分子动力学(MD)方法研究了羟基磷灰石(HA)的三个晶面(001)、(100)、(110)分别与生物胶黏剂α-氰基丙烯酸正丁酯(NBCA)相互作用后混合体系的结合能,并计算分析了(110)晶面的力学性能和径向分布函数。结果表明,三晶面所对应结合能关系为HA(110)HA(100)HA(001);HA(110)晶面与NBCA之间粘结强度高于HA(100)和HA(001)晶面;对聚合度为40的NBCA聚合物与HA相互作用的MD计算表明,HA(110)/NBCA混合体系的力学性能比单组份HA体系有所下降,但满足人工骨对力学性能的要求;元素之间的径向分布函数揭示了混合体系HA/NBCA组分之间的相互作用机理,NBCA与HA(110)晶面存在较强的相互作用。其主要原因是,NBCA中的N原子和羰基中的O原子分别与HA中的H原子形成的氢键,进而说明了HA对NBCA的强吸附作用。     

钛酸钾晶须水热合成多形体TiO2及结构演变

从不同种类的钛酸钾晶须(K2Ti6O13,K2Ti4O9和K2Ti8O17)出发,通过水热条件下转晶得到了多形体TiO2晶粒,其中K2Ti6.O13晶须通过酸性条件下水热反应得到形貌规整的孪晶金红石TiO2.并借助XRI)、SEM和TEM等手段,考察了水热反应过程中的晶体结构演变,证明了前驱物中的弱结合晶面是发生晶体结构转变的关键因素,K2Ti6O13.通过{100}和{201-}晶面上的原子重排,生成孪晶金红石型TiO2.     

锂快离子导体Li3-2x(Al1-xTix)2(PO4)3的合成与表征

NASICON型正磷酸盐LiM2(PO4)3(M=Ti,Ge,Zr,Hf)是近来研究得比较深入的锂快离子导体.LiTi2(PO4)3难于烧结得到致密的LiT2(PO4)3陶瓷,且离子电导率很低,在298K时为8.260×10-8 S/cm,613K时为8.241×10-5 S/cm,而当以三价的Al3 离子经传统的固相烧结反应部分取代LiTi2(PO4)3中四价的Ti4 离子后,通过DSC、DTG、电化学阻抗与SEM测试表明,不仅能获得致密度高稳定的产物,而且烧结后得到的锂快离子导体Li3-x(Al1-xTix)2(PO4)3(X=1.0～0.55)体系在室温下的电导率有了巨大的提高.当X=0.85时,组分Li1.3Al0.3Ti1.7(PO4)3离子电导率最大,298K时为1.792×10-6S/cm和613K时为9.210×10-4S/cm.     

组成对R2O-CaO-ZnO-Al2O3-SiO2系统分相的影响

通过大量的配方实验和OM,TEM观察,系统研究了R2O－CaO-ZnO-Al2O3-SiO2系统分相与组成间的相互关系,研究结果表明,K2O比Na2O更有利于系统的分相,用Na2O等摩尔取代K2O时,分相区向低铝高硅区收缩,此外,系统分相区大小还明显受到ZnO,CaO相对含量的影响,高锌系统具有更为宽广的分相区,Al2O3对R2O－CaO-ZnO-Al2O3-SiO2系统分相影响呈现出明显的反常现象,在ZnO含量为0．55mol的系统中,当R2O由0．10mol K2O 0.10mol Na2O共同引入时,分相区大小和分相结构尺度都呈现出明显的铝反常现象,而R2O仅由0.20mol K2O引入时,仅分相结构尺度呈现出明显的铝反常现象,反常点的Al2O3含量约为6．20mol%,在一定的热处理条件下,适当增加SiO2的含量有利于系统分相,但当SiO2的含量过高时,分相将由连通结构逐渐转变为孤立相分布于连续基质相中的液滴状结构,甚至消失。     

包覆和凝胶注模成型对氮化硅陶瓷性能的影响

利用含 Al (NO3) 3,Y (NO3) 3和尿素的水溶液中无机盐的沉淀再经煅烧在 Si3N4粉料的表面包覆 Y2 O3- Al2 O3层 ,作为氮化硅烧结的助烧剂。包覆层改变了 Si3N4粉料的电动性和胶态特性 ,从而提高了 Si3N4的分散性。研究表明 ,经包覆和凝胶注模成型的方法所制备的氮化硅烧结体较冷等静压方法所获得的烧结体的抗弯强度和 Weibull模数都大大提高     

Al2O3陶瓷制备及性能分析

以纯Al2O3粉、Mg(NO3)2·6H2O、Y(NO3)3·6H2O为原料,于1500℃、1600℃和1700℃常压制备了高纯Al2O3陶瓷,研究了烧结温度和烧结助剂的含量对Al2 O3陶瓷密度、硬度及微观结构的影响.结果表明,添加剂的作用受烧结温度的影响较大,进而影响了烧结体的硬度.     

L-丙氨酸掺杂下ZTS晶体法向生长动力学及化学侵蚀研究

通过对L-丙氨酸掺杂下ZTS(100)、(010)及(001)面法向生长速度的研究发现,各晶面法向生长速度随过饱和度的增加而线性增加;随掺杂浓度的增加,(100)面的法向生长速度先增大后减小,而(010)及(001)面的法向生长速度先减小,接着增大,然后又减小。分析表明(100)面以位错生长机制为主,(010)及(001)面以连续生长机制为主。利用光学显微镜在侵蚀后的(100)面观察到矩形位错蚀坑,蚀坑密度为33~308 mm-2;掺杂浓度为1%(摩尔分数)时,蚀坑密度最小。     

Aspiration dynamics of multi-player games in finite populations

On studying strategy update rules in the framework of evolutionary game theory, one can differentiate between imitation processes and aspiration-driven dynamics. In the former case, individuals imitate the strategy of a more successful peer. In the latter case, individuals adjust their strategies based on a comparison of their pay-offs from the evolutionary game to a value they aspire, called the level of aspiration. Unlike imitation processes of pairwise comparison, aspiration-driven updates do not require additional information about the strategic environment and can thus be interpreted as being more spontaneous. Recent work has mainly focused on understanding how aspiration dynamics alter the evolutionary outcome in structured populations. However, the baseline case for understanding strategy selection is the well-mixed population case, which is still lacking sufficient understanding. We explore how aspiration-driven strategy-update dynamics under imperfect rationality influence the average abundance of a strategy in multi-player evolutionary games with two strategies. We analytically derive a condition under which a strategy is more abundant than the other in the weak selection limiting case. This approach has a long-standing history in evolutionary games and is mostly applied for its mathematical approachability. Hence, we also explore strong selection numerically, which shows that our weak selection condition is a robust predictor of the average abundance of a strategy. The condition turns out to differ from that of a wide class of imitation dynamics, as long as the game is not dyadic. Therefore, a strategy favoured under imitation dynamics can be disfavoured under aspiration dynamics. This does not require any population structure, and thus highlights the intrinsic difference between imitation and aspiration dynamics.     

圆弧齿锥齿轮接触动力学分析

运用三角网格方法重构了三维离散的圆弧齿啮合齿面模型。基于多体动力学理论和迟滞接触动力学方法,提出了考虑全齿面动态接触关系的螺旋锥齿轮三维接触动力学模型和动力学分析方法。运用三角网格单元接触的包围盒搜索技术和微分代数方程求解方法,仿真分析了单侧齿面接触、双侧齿面接触、负载扭矩和齿侧侧隙等因素对齿轮啮合传动特性的影响,获得了圆弧齿啮合全齿面接触冲击力,力矩和角速度等齿轮啮合传动的动态响应特性。研究表明：新方法和动力学模型较好地模拟了圆弧齿锥齿轮的承载特性和啮合接触动力学特性,对以动力学特性为目标的圆弧齿锥齿轮设计和齿轮系统动力学研究提供了理论参考。     

Spatial dynamics and genetics of infectious diseases on heterogeneous landscapes.

Explicit spatial analysis of infectious disease processes recognizes that host-pathogen interactions occur in specific locations at specific times and that often the nature, direction, intensity and outcome of these interactions depend upon the particular location and identity of both host and pathogen. Spatial context and geographical landscape contribute to the probability of initial disease establishment, direction and velocity of disease spread, the genetic organization of resistance and susceptibility, and the design of appropriate control and management strategies. In this paper, we review the manner in which the physical organization of the landscape has been shown to influence the population dynamics and spatial genetic structure of host-pathogen interactions, and how we might incorporate landscape architecture into spatially explicit population models of the infectious disease process to increase our ability to predict patterns of disease occurrence and optimally design vaccination and control policies.     

Molecular Dynamics Simulation of Gas Diffusion in B2O3 and SiC

Molecular dynamics simulation using a universal force field has been employed to determine the diffusion coefficients of O2 and Na2SO4 vapor into B2O3 and SiC from 700 K to 1273 K, respectively. Einstein diffusion was observed in a 250～300 ps simulation.     

转向传动机构间隙对车辆摆振系统动力学行为的影响分析

对考虑转向传动机构间隙的车辆摆振系统动力学行为进行了分析。基于非线性系统动力学相关理论,应用二状态模型描述横拉杆和转向梯形臂之间的间隙副接触状态,建立了考虑转向传动机构间隙的四自由度摆振系统动力学模型。对上述模型进行数值分析,借助相平面、Poincaré映射及分岔特性等分析了间隙对于车辆摆振系统动力学行为的影响,为更好地实现车辆摆振控制提供了理论支持。     

Intrinsic dynamics of the boundary of a two-dimensional uniform vortex

The link between the shape of a two-dimensional, uniform vortex and self-induced velocities on its boundary is investigated through a contour-dynamics approach. The tangent derivative of the velocity along the boundary is written in a complex form, which depends on the analytic continuation of the tangent unit vector outside the vortex boundary. In this way, a classical analysis in terms of Schwarz's function of the boundary, due to Saffman, is extended to vortices of arbitrary shape. Time evolution of intrinsic quantities (tangent unit vector, curvature and Fourier's coefficients for the vortex shape) is also analyzed, showing that it depends on tangent derivatives of the velocities, only. Furthermore, a spectral method is proposed, aimed at investigating the dynamics of nearly-circular vortices in an inviscid, isochoric fluid. Comparisons with direct numerical simulations are also established.     

Synthesis and properties of novel materials at high pressure and temperature—molecular dynamics simulation studies

Molecular dynamics simulations, in combination with lattice dynamics studies, based on semiempirical interatomic potentials, have been very useful in the study of properties of complex novel materials at high temperature and pressure. Various properties such as the equation of state, elastic and thermodynamic properties, phase transitions and melting have been studied. These studies help in understanding the synthesis of important new and novel materials, especially the amorphous materials, compounds with unusually coordinated atoms, (e.g. with five-coordinated silicon atoms), materials with controlled thermal expansion, etc. A few examples will be discussed from our recent studies.     

转子动力学研究的现状及展望

本文分析了转子动力学的某些特点,说明了转子动力学与振动学科中其他分支学科的关系,分析了国际上转子动力学研究的现状与趋势,提出了对一些研究课题的展望,使读者对转子动力学的研究有一概括的了解。     

Uncertainty propagation in a multiscale model of nanocrystalline plasticity

We characterize how uncertainties propagate across spatial and temporal scales in a physics-based model of nanocrystalline plasticity of fcc metals. Our model combines molecular dynamics (MD) simulations to characterize atomic-level processes that govern dislocation-based-plastic deformation with a phase field approach to dislocation dynamics (PFDD) that describes how an ensemble of dislocations evolve and interact to determine the mechanical response of the material. We apply this approach to a nanocrystalline Ni specimen of interest in micro-electromechanical (MEMS) switches. Our approach enables us to quantify how internal stresses that result from the fabrication process affect the properties of dislocations (using MD) and how these properties, in turn, affect the yield stress of the metallic membrane (using the PFMM model). Our predictions show that, for a nanocrystalline sample with small grain size (4 nm), a variation in residual stress of 20 MPa (typical in today's microfabrication techniques) would result in a variation on the critical resolved shear yield stress of approximately 15 MPa, a very small fraction of the nominal value of approximately 9 GPa.     

非线性涡动时裂纹转子的分叉与浑沌特性研究

分析非线性涡动裂纹转子中刚度变化比△K，裂纹角β，不平衡参数U对系统分叉及浑沌行为的影响：在转速区Ω=2Ωe／3附近，当△K较大时，会出现分叉及浑沌现象，β对这些行为有很大影响。在Ω=Ωc／2附近，当△K很大时，无论β为何值，将由拟周期通向浑沌。U作为一种外部因素，将使系统的非线性行为得到激发或抑制。