Optimization methods for computing global minima of nonconvex potential energy functions

The minimization of potential energy functions plays an important role in the determination of ground states or stable states of certain classes of molecular clusters and proteins. In this paper we introduce some of the most commonly used potential energy functions and discuss different optimization methods used in the minimization of nonconvex potential energy functions. A very complete bibliography is also given.Also a researcher at the Army High Performance Computing Research Center, University of Minnesota, Minneapolis, MN 55415     

Circulation distribution on groups

The problem of expressing a symmetric measure on a countable finitely generated groupG and the corresponding random walkA _gh =({g ^–1 h}),g, hG, in terms of directed circuits is solved. Connections with transient groups are given as well.     

遗传算法及其在化学化工中的应用

本文介绍了遗传算法的基本概念、工作原理和步骤, 综述了它在化学化工领域的应用。     

Mechanism of electrooptic switching time enhancement in ferroelectric liquid crystal/gold nanoparticles dispersion

It is well established that incorporation of nanoparticles (NPs) in the structure of ferroelectric liquid crystals (FLCs) leads to a decrease in their electrooptic response time. Several approaches have been suggested to explain this effect (decrease in rotational viscosity of FLCs, ions enhanced localised electric field, dipole–dipole interaction among NPs and FLC molecules, FLC ordering). In this article, we will report the role of the voltage divider formed by the structural elements of a FLC cell based on ferroelectric liquid crystal/gold nanospheres (FLC/GNSs) dispersion in enhancement of the switching time. Using the impedance spectroscopic measurements, it was demonstrated that the dispersing of GNSs leads to the increase in the voltage drop on FLC/GNSs layer in comparison with the pristine FLC one. Consequently, the electrooptic response time of the FLC/GNSs cell is faster than that of the pristine one. However, the rotational viscosity of the FLC does not depend on the presence of the GNSs.     

Electric and dielectric behavior of copper-chromium layered double hydroxide intercalated with dodecyl sulfate anions using impedance spectroscopy

The Cu₂Cr-DS-LDH hybrid was successfully prepared by the anion exchange method at room temperature. The structure, the chemical composition and the physico-chemical properties of the sample were determined using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and inductively coupled plasma (ICP). In this work, the electrical and dielectric properties investigated are determined using impedance spectroscopy (IS) in a frequency range of 1 Hz to 1 MHz. Indeed, the Nyquist diagram modelized by an electrical equivalent circuit showed three contributions attributed respectively to the polarization of grains, grains boundaries and interface electrode-sample. This modelization allowed us to determine the intrinsic electrical parameters of the hybrid (resistance, pseudo-capacitance and relaxation time). The presence of the non-Debye relaxation phenomena was confirmed by the frequency analysis of impedance. Moreover, the evolution of the alternating current conductivity (σ_ac) studied obeys the double power law of Jonscher. The ionic conduction of this material was generated through a jump movement by translation of the charge carriers. As for the dielectric behavior of the material, the evolution of dielectric constant as a function of frequency shows relatively high values in a frequency range between 10 Hz and 1 KHz. The low values of the loss tangent obtained in this frequency zone can valorize this LDH hybrid.     

Characterization of the Outer Layer Nanostructure in the Electrochemical Response of Stainless Steel in Aqueous Sodium Hydroxide

The outer layer nanostructure of stainless steel’s passive film in 0.1?M NaOH has been studied by electrochemical atomic force microscopy and the role of the outer layer in the electrochemical response of stainless steel has been characterized. The outer layer is mainly composed of nanoscale particles whose average diameter is up to 13.14?±?3.52?nm at the end of the formation period. The formation process is characterized by the nucleation, growth, and contact of oxide particles. Based on the study on the outer layer nanostructure, the gaps/boundaries between particles in the outer layer should be diffusion paths for ions across the layer. The electrochemical impedance spectroscopy analysis revealed that the ion diffusion resistance first increased and then remained stable due to the three-dimensional growth of nanoscale particles.     

Complete Spacelike Submanifolds in de Sitter Space with Parallel Mean Curvature Vector Satisfying H2 = 4(n − 1)/n2

Recently, Montiel [7] proved that an n-dimensional (n 3) complete spacelike hypersurface in de Sitter space S^{1 1 +1}(1) with constant mean curvature H satisfying H² = 4 (n – 1)/n² which is not connected at infinity must be, up to rigidity motion, a certain hyperbolic cylinder. In this paper, we prove that Montiel's result still holds for higher codimensional spacelike submanifolds in de Sitter space Sⁿ _p ^+p(1).     

Decomposing 40 billion integers by four tetrahedral numbers

Based upon a computer search performed on a massively parallel supercomputer, we found that any integer less than billion (B) but greater than can be written as a sum of four or fewer tetrahedral numbers. This result has established a new upper bound for a conjecture compared to an older one, B, obtained a year earlier. It also gives more accurate asymptotic forms for partitioning. All this improvement is a direct result of algorithmic advances in efficient memory and cpu utilizations. The heuristic complexity of the new algorithm is compared with that of the old, .

     

High Selective Determination of Anionic Surfactant Using Its Parallel Catalytic Hydrogen Wave

IntroductionAnionicsurfactants (AS)arewidelyusedinhouse holdorindustrialcleaners ,cosmetics ,researchlaborato ries,textiles ,pharmacies ,etc .,solargeamountofASreleasedintotheenvironmentarecausingpollution .There foreitisnecessarytodevelopafast,simpleandcosteffec tivemethodforthedeterminationofAS .Theofficialmeth odsrecommendedforthedeterminationofASarespec trophotometryandpotentialtitration .SpectrophotometricmethodanditsvariationsarebasedonthemeasurementofthecoloredassociatesofASwithposi…     

Ba12Y4.67Ti8O35的交流阻抗谱和氧浓差电势测量

用高温固体合成法制备了经验分子式为Ba12Y4.67Ti8O35的导电陶瓷.利用交流阻抗谱技术、氧浓差电势测量和热电效应测量等方法表征了材料的导电性能.研究指出, 该材料是一种氧离子/空穴混合导体.在700 ℃下，材料本体的电导约为2×10－3 Ω－1•cm－1，氧离子迁移数为0.35.对700 ℃下空气、O2和N2气氛中的交流阻抗谱数据进行了等效电路拟合.拟合指出，在空气和O2气氛中，氧离子的扩散阻抗谱不能明显地观察到是因为氧离子电导通路被空穴电导短路；而在N2气氛中，阻抗谱在低频段表现出特征的扩散阻抗.