纯铜[0 1 1]倾侧型非共格∑3晶界结构稳定性分子动力学模拟研究

有研究表明, 非共格∑₃晶界的行为在中低层错能面心立方金属晶界 特征分布演化中发挥着重要作用. 为了掌握不同界面匹配的非共格∑₃晶界的特性, 本文利用分子动力学(MD)模拟方法首先研究了纯铜的[0 1 1]倾侧型 非共格∑₃晶界在700–1100 K温度范围内和常压下的结构稳定性. MD模拟采用原子间相互作用长程经验多体势, 步长为5×10^-15 s. 模拟结果表明: 所研究的五个非共格∑₃晶界, 其结构稳定性存在很大差异, 其一般规律是, 与(1 1 1)/(1 1 1)共格孪晶界之间的夹角(Φ角)越小, 晶界匹配值越大, 则非共格∑₃晶界越稳定; 反之亦然. Φ角最小的 (2 5 5)/(2 1 1)非共格∑₃晶界较稳定, 在退火过程中几乎不发生变化. 随着Φ角的增大, 非共格∑₃晶界不再稳定, 这类晶界会通过Miller指数较高一侧晶体每三层原子面合并为一层原子面 (或Miller指数较低一侧晶体每一层原子面分解为三层原子面)的机理 转变为亚稳的“台阶”状晶界, 台阶面部分地处于精确的能量极低 的{111}/{111}共格孪晶界上; 当提高温度退火时, 这种“台阶”状晶界最终会全部转变成稳定平直的{111}/{111}共格孪晶界. 关键词： 纯铜 ∑₃晶界')" href="#">非共格∑₃晶界 分子动力学模拟     

The convex hull of two core capacitated network design problems

The network loading problem (NLP) is a specialized capacitated network design problem in which prescribed point-to-point demand between various pairs of nodes of a network must be met by installing (loading) a capacitated facility. We can load any number of units of the facility on each of the arcs at a specified arc dependent cost. The problem is to determine the number of facilities to be loaded on the arcs that will satisfy the given demand at minimum cost.This paper studies two core subproblems of the NLP. The first problem, motivated by a Lagrangian relaxation approach for solving the problem, considers a multiple commodity, single arc capacitated network design problem. The second problem is a three node network; this specialized network arises in larger networks if we aggregate nodes. In both cases, we develop families of facets and completely characterize the convex hull of feasible solutions to the integer programming formulation of the problems. These results in turn strengthen the formulation of the NLP.Research of this author was supported in part by a Faculty Grant from the Katz Graduate School of Business, University of Pittsburgh.     

The Interaction of Polyphenol Flavonoids with β-lactoglobulin: Molecular Docking and Molecular Dynamics Simulation Studies

The interaction of quercetin, quercitrin, and rutin, as natural polyphenolic compounds, with β-lactoglobulin (BLG) using molecular docking and molecular dynamics simulation methods was examined. Molecular docking studies showed that quercetin and quercitrin were bounded to the internal cavity of protein, while rutin was bounded to the entrance of the cavity because of its large structural volume. It was found that there were one-, three-, and four-hydrogen bond interactions between BLG and quercetin, quercitrin, and rutin respectively. This showed that with an increase in the number of OH groups in the flavonoid structure, there was an increase in the number of hydrogen bond interactions. The binding constants for the binding of quercetin, quercitrin, and rutin to BLG were 1.2 × 10⁶, 1.9 × 10⁶, and 7.4 × 10⁴ M^?1 respectively. The results of molecular dynamics simulation showed that the root mean square deviation (RMSD) of non-liganded BLG and BLG–ligand complexes reached equilibration after 3500 ps. The study of the radius of gyration revealed that BLG and BLG–ligand complexes were stabilized around 2500 ps, and unlike the two other complexes, there was no conformational change for BLG–quercetin. Finally, analyzing the RMS fluctuations suggested that the structure of the ligand binding site remained approximately rigid during simulation.     

Evidence for a second,local contact condition for a planar electric double layer containing size and valency asymmetric ions

A generalised form of a local contact condition for the charge profile in a primitive model planar double layer [Bhuiyan, Outhwaite, and Henderson, Mol. Phys. 107, 343 (2009)] at low electrode charge is examined for completely asymmetric, binary electrolytes. The cation and anion sizes are taken to be different from each other with the valencies being 2⁺:1^? or 1⁺:2^?, while the electrode surface charge density is varied from being negative through zero to being positive. Monte Carlo simulation data obtained for such double layer systems at varying ionic radius ratios and electrolyte concentrations suggest the generalised contact relation to be valid at low charge on the electrode.     

含磁控和荷控两种忆阻器的混沌电路设计与仿真

利用惠普实验室荷控和磁控两种忆阻器模型设计了一个五阶混沌电路. 数值仿真结果表明该电路在参数变化情况下能产生Hopf分岔和反倍周期分岔两种分岔行为,并能产生双涡卷、单涡卷、周期态等不同相轨道. 为了验证电路的混沌行为,利用基本元器件设计了惠普实验室荷控和磁控忆阻器模拟器,并将其应用到对所设计电路中进行Pspice仿真,电路仿真结果验证了理论分析的正确性. 关键词： 混沌电路 HP忆阻器 模拟器 Pspice仿真     

用概率断裂力学方法预测管状接头的疲劳寿命

本文研究了Ｔ型管状接头在面内和面外弯曲循环载荷作用下的疲劳强度问题，通过将材料常数和初始裂纹尺寸作为随机变量，采用ＭｏｎＣａｒｌｏ模拟方法对疲劳寿命进行了统计分析．同时，对计算结果进行了线性回归，并与实验结果作了比较。     

Structure and stability of Σ3 grain boundaries in face centered cubic metals

Σ3 grain boundaries form as a result of either growth twinning or deformation twinning in face centered cubic (fcc) metals and play a crucial role in determining the mechanical and electrical properties and microstructural stability. We studied the structure and stability of Σ3 grain boundaries (GBs) in fcc metals by using topological analysis and atomistic simulations. Atomistic simulations were performed for Cu and Al with empirical interatomic potentials to reveal the influence of stacking fault energy on the morphology of the twinned grains. Three sets of tilt Σ3 GBs were studied with respect to the tilt axis parallel to ?111?, ?112?, and ?110?, respectively. We showed that Σ3{111} and Σ3{112} GBs are thermodynamically stable and the others will dissociate into terraced interfaces regardless of the stacking fault energy. The morphology of the nano-twinned grains in Cu is predicted from the above analysis and found to match with experiments.     

Performance characteristics of single photon pulse ranging system using Monte Carlo simulation

Single photon pulse ranging system with extremely high sensitivity has been widely used in distance measurement and 3D imaging. To analyze the factors that affect the measurement precision and accuracy will help to improve system performance. According to system structure and principle, we mainly discussed the following factors: laser intensity, pulse width, detection efficiency and time jitter. A simulation model based on Monte Carlo stochastic method was constructed in this paper, and we get the specific influence of factors on measurement precision and accuracy by simulation. Finally, we set up laboratory experiment system and took effective experiments on ranging precision and accuracy.     

A note on stability of some parametrically excited structural elastic systems

An analogue simulation study for the stability investigations of nonlinear parametrically excited structural systems, exhibiting hard and soft spring characteristics is undertaken as a feasible alternative to current asymptotic and other analytic methods. It is shown that this technique locates the position of an unstable limit cycle, identifying the point of change of equilibrium states, which is ordinarily obscured in using the other existing schemes.     

多孔介质两相流的局部守恒有限元分析

用局部守恒有限元法研究多孔介质两相渗流问题.详细阐述局部守恒有限元法的基本原理,推导两相渗流问题的局部守恒有限元计算格式并编制相应的计算程序.通过一维Buckley-Leverett两相渗流算例验证该方法的正确性.应用局部守恒有限元法和混合有限元法分别对2个模型进行分析对比.计算结果表明局部守恒有限元法具有良好的鲁棒性及适用性,相较于混合有限元法,处理过程简单,计算时间缩短,为标准有限元法应用于复杂渗流问题提供了一种途径.