Atomistic phenomena in dense fluid shock waves

The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases.     

虚拟技术在实验教学中的应用

介绍了虚拟技术在实验教学改革中的作用与意义，探讨了电子信息系统实验教学改革的新思路与实现措施，并总结了实验教学改革的初步成果．     

Low-energy ion-assisted control of interfacial structures in metallic multilayers

A molecular dynamics method has been used to simulate the argon ion-assisted deposition of Cu/Co/Cu multilayers and to explore ion beam assistance strategies that can be used during or after the growth of each layer to control interfacial structures. A low-argon ion energy of 5–10 eV was found to minimize a combination of interfacial roughness and interlayer mixing (alloying) during the ion-assisted deposition of multilayers. However, complete flattening with simultaneous ion assistance could not be achieved without some mixing between the layers when a constant ion energy approach was used. It was found that multilayers with lower interfacial roughness and intermixing could be grown either by modulating the ion energy during the growth of each metal layer or by utilizing ion assistance only after the completion of each layers deposition. In these latter approaches, relatively high-energy ions could be used since the interface is buried and less susceptible to intermixing. The interlayer mixing dependence upon the thickness of the over layer has been determined as a function of ion energy.     

狭义相对论效应──运动时钟变慢的计算机模拟演示实验

利用精炼的C语言进行程序设计，定量模拟狭义相结论的运动时钟变慢，并对处于两种不同时空观的时钟运行进行对比，使得时间膨胀效应变得直观。     

Numerical Analysis and Simulation Analysis for Space‐Time Data

Spatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Meshless simulation of equilibrium swelling/deswelling of pH‐sensitive hydrogels

Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio‐MEMS devices. In this article, the equilibrium swelling/deswelling of the pH‐stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi‐field coupling model, called multi‐effect‐coupling pH‐stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi‐field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative—meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi‐field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli‐sensitive hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 326–337, 2006     

Molecular dynamics studies on octadecylammonium chloride at the air/liquid interface

Molecular dynamics simulations on surfactant octadecylammonium chloride at the air/liquid interface were performed. It was found that the alkyl chains of octadecylammonium would change to order with increasing the concentration of octadecylammonium at the air/liquid interface. Some functions, such as the concentration distributions, the radial distribution function and the mean squared displacement (MSD) were evaluated to investigate the structural properties of interface. We found that the salts can affect octadecylammonium aggregate at the interface: (1) univalent ions, such as chloride and sodium ions, affect slightly the structure of monolayer and (2) bivalent ions, such as sulfate or calcium ions, affect greatly, especially for the bivalent negative ions.     

Chiral separation of 1,1'-bi-2-naphthol and its analogue on molecular imprinting monolithic columns by HPLC

Two molecular imprinting polymer (MIP) monolithic columns with (S)-(-)-1,1'-bi-2-naphthol and (R)-(+)-5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol as the templating molecules, respectively, have been prepared by in situ polymerization using 4-vinylpyridine and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The columns with good flow-through properties were obtained by changing the molar ratio of the functional monomer and the template molecule. The effects of mobile-phase composition on separation of enantiomers were systematically investigated. The results indicate that hydrophobic interaction in aqueous solution and hydrogen-bonding interaction in ACN between the enantiomers and polymers could play important roles in the retention and resolution. The effects of chromatographic conditions, such as flow rate, column temperature, sample loading, on the enantioseparation were also studied. Further, these two MIP columns show a cross-reactivity.     

Molecular potential-energy surfaces for chemical reaction dynamics

This paper reviews the construction of molecular potential-energy surfaces by an interpolation method which has been developed over the last several years. The method uses ab initio quantum chemistry calculations of the molecular electronic energy in an automated procedure to construct global potential- energy surfaces which can be used to simulate chemical reactions with either classical or quantum dynamics. The methodology is explained and several applications are presented to illustrate the approach. Received: 22 February 2002 / Accepted: 2 May 2002 / Published online: 6 November 2002 Correspondence to: M. A. Collins e-mail: collins@rsc.anu.edu.au Acknowledgements. The methods described in this overview are the result of collaborations with former members of my group, in particular with Josef Ischtwan, Meredith Jordon, Keiran Thompson and Ryan Bettens. I am also indebted for inspiration gained from many discussions with my colleagues Leo Radom and Donghui Zhang (National University of Singapore). This work has been supported by the Supercomputer Facility of the Australian National University and the Australian Partnership for Advanced Computing.     

Molecular determinants in the bioactivation of the dopaminergic neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Summary Nineteen analogs of the dopaminergic neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) have been used as probes to study the structural parameters that influence MAO-catalyzed oxidation. In this study, the efficiency of enzyme-catalyzed substrate oxidation was found to be unrelated to parameters such as the ionization potential, dipole moment, net atomic charge at C5 and the dihedral angle between the phenyl ring and the tetrahydropyridine moiety. Conformational analysis revealed that substitution at the C2 position of MPTP yields atropisomers. It is suggested that one of these atropisomers would be either inactive or substantially less active than the other. Therefore, the relative oxidative efficiency and toxicity of these compounds reported earlier may have been significantly underestimated. Based on the conformational analysis and other data, a rudimentary model of the MAO substrate site has been developed which partially explains the substrate specificities of MAO A and MAO B.Each substrate binding site can be divided into two regions, (a) an amine-binding pocket (for the tetrahydropyridine moiety), and (b) a bulky substituent region (for the phenyl group and its substituents). The length of the substrate binding site (measured along the long axis of MPTP) is approximately 8.5 Å, and the width of the amine-binding pocket is approximately 2.5 Å (from C3 to C5). The bulky substituent region contains a central area for binding the phenyl group of MPTP. This central area is flanked by two hydrophobic pockets, P2 and P3. In MAO A, the pocket P2-A is oriented 45–135° relative to the plane of the tetrahydropyridine moiety, with a radius of 3.1 Å from C2 of the phenyl ring. The radius of a similar but smaller pocket, P2-B, in MAO B, is approximately 2.7 Å. In MAO B, the pocket P3-B (radius 2.36 Å from C3) is larger than a similar pocket P3-A (radius 1.70 Å from C3) in MAO A. The foregoing characterization suggests that differences in the size and topography of both of the substituent pockets play an important role in determining the substrate specificities of these two isozymes.