Magnetic properties of molecular systems: A nonlocal spin density functional study

A new class of molecular magnets based on aniline and aminonaphthalene sulfonic acid was previously reported. In the present work, a nonlocal density functional theory study was performed on simple molecular models, to determine the mechanism that stabilizes the parallel alignment of the spin component. The role played by transition metals on the magnetic properties of this kind of systems was also studied within this approximation. The results obtained show a high sensitivity of the magnetic coupling on the molecular geometry as well as on the nature and oxidation state of the metallic atom.     

Exploring the interparticle electron transfer process in the photocatalytic oxidation of 4-chlorophenol

This work aimed to investigate the interparticle electron transfer (IPET) process within the coupled-photocatalyst systems on the basis of the degradation of 4-chlorophenol (4-CP). TiO(2), ZnO and SnO(2) are used as the model photocatalysts owing to their increasing energy levels which correspond to the IPET concept. In the single-photocatalyst tests, ZnO tests are associated with the highest degradation rate constants (0.347+/-0.083 h(-1) at pH 7 and 0.453+/-0.011 h(-1) at pH 11) and a better DOC reduction than in other single catalyst tests under given conditions. ZnO/SnO(2) coupled tests have constants of 0.612+/-0.068 and 0.948+/-0.069 h(-1) at pH 7 and 11, respectively. Additionally, the 4-CP prefers the breakdown of chloride group in TiO(2) system while proceeding hydroxylation reaction in ZnO systems. Meanwhile, a phenomenonlogical model coupled with the IPET effect was developed to explore the separation of photo-electrons and photo-holes within catalysts. Based on the model parameters, the recombination rate of photo-electrons and photo-holes in TiO(2)/SnO(2) and ZnO/SnO(2) systems is 20-45% lower than that obtained by a respective single catalyst. Thus, coupled-photocatalyst tests, TiO(2)/SnO(2) and ZnO/SnO(2) efficiently suppress the recombination, particularly for ZnO/SnO(2) tests at pH 11.     

First-principles simulation of vitreous systems

Recent developments in the field of first-principles simulation applied to vitreous systems are reviewed. Starting from first-principles molecular dynamics as a basic tool for the generation of structural models, this paper describes how, in recent years, the scope of first-principles methods has extended to the interpretation of vibrational spectra of glasses.     

Ar-Kr低温界面传热过程分子动力学模拟

运用非平衡分子动力学原理和LJ势函数仿真研究氩(Ar)与氪(Kr)之间的界面层传热问题,模拟其界面传热的能量变化过程.仿真结果表明,即使界面粗糙度为0,低温固体界面热阻仍然存在.平均温度为40 K,粗糙度为0时,氩(Ar)与氪(Kr)之间界面热阻为0.15～0.18 Wm2/K,相对误差小于17%.     

Dual-resolution molecular dynamics simulation of antimicrobials in biomembranes

Triclocarban and triclosan, two potent antibacterial molecules present in many consumer products, have been subject to growing debate on a number of issues, particularly in relation to their possible role in causing microbial resistance. In this computational study, we present molecular-level insights into the interaction between these antimicrobial agents and hydrated phospholipid bilayers (taken as a simple model for the cell membrane). Simulations are conducted by a novel ‘dual-resolution’ molecular dynamics approach which combines accuracy with efficiency: the antimicrobials, modelled atomistically, are mixed with simplified (coarse-grain) models of lipids and water. A first set of calculations is run to study the antimicrobials'' transfer free energies and orientations as a function of depth inside the membrane. Both molecules are predicted to preferentially accumulate in the lipid headgroup–glycerol region; this finding, which reproduces corresponding experimental data, is also discussed in terms of a general relation between solute partitioning and the intramembrane distribution of pressure. A second set of runs involves membranes incorporated with different molar concentrations of antimicrobial molecules (up to one antimicrobial per two lipids). We study the effects induced on fundamental membrane properties, such as the electron density, lateral pressure and electrical potential profiles. In particular, the analysis of the spontaneous curvature indicates that increasing antimicrobial concentrations promote a ‘destabilizing’ tendency towards non-bilayer phases, as observed experimentally. The antimicrobials'' influence on the self-assembly process is also investigated. The significance of our results in the context of current theories of antimicrobial action is discussed.     

Effect of end group of amorphous perfluoro-polymer electrets on electron trapping

Charge trap in amorphous perfluoro-polymer electret is studied, focusing on electron trap site and trap energy. Low-energy inverse photoelectron spectroscopy is adopted to measure solid-state electron affinity (EA) of cyclic transparent optical polymer (CYTOP). EA of CYTOP CTL-S is discovered by compensating the unwanted charge-up effect. Negatively-charged electret materials (polyethylene, ethylene-tetra-fluoro-ethylene, poly-tetra-fluoro-ethylene, and CYTOP) are analyzed by quantum mechanical calculation. Density functional theory with long-range correction is adopted to analyze orbital energies of single molecular systems. Intramolecular distribution of trapped electron and EA are investigated. Calculated electron affinities of CYTOP polymers with different end group are qualitatively in accordance with trapped charge stability measured with thermal stimulated discharge, signifying that electron affinities obtained with the present simulation can be used as an index of amorphous polymer electret.     

电子强关联对LaMnO_3电子结构的影响

本文利用密度泛函对LaMnO3的电子结构进行了计算。结果表明,LaMnO3反铁磁绝缘基态的形成主要依赖于Jahn-Teller畸变而不是电子强关联,但电子强关联效应对LaMnO3电子结构的影响巨大。为了获得正确的结果,本文计算时考虑了适当的电子强关联修正。通过分析比较,表明在位的库仑能U取3.5eV是一个合理的选择。     

Unusually strong lateral interaction in the CO overlayer in phosphorene-based systems

By means of vibrational spectroscopy and density functional theory (DFT), we investigate CO adsorption on phosphorene-based systems. We find stable CO adsorption at room temperature on both phosphorene and bulk black phosphorus. The adsorption energy and vibrational spectrum are calculated for several possible configurations of the CO overlayer. We find that the vibrational spectrum is characterized by two different C–O stretching energies. The experimental data are in good agreement with the prediction of the DFT model and reveal the unusual C–O vibrational band at 165–180 meV, activated by the lateral interactions in the CO overlayer.

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Ni2 MnGa合金的价电子结构研究

用“固体与分子经验电子理论”研究了Ni2MnGa合金的价电子结构,研究结果表明,在Ni2MnGa中,Ni的杂化状态为A'种杂化第2阶;Mn的杂化状态为B种杂化第9阶,Ga为A种第9阶杂化。Ni的原子磁矩计算值为3.8666μB十分接近。最强的共价键是Ni-Mn键,其上的共价电子对数为0．577,其次为Ni-Ga键,其价电子对数为0．542,其它键上的共价电子对数小于0．2。     

Activated-ion electron transfer dissociation improves the ability of electron transfer dissociation to identify peptides in a complex mixture

Using a modified electron transfer dissociation (ETD)-enabled quadrupole linear ion trap (QLT) mass spectrometer, we demonstrate the utility of IR activation concomitant with ETD ion-ion reactions (activated-ion ETD, AI-ETD). Analyzing 12 strong cation exchanged (SCX) fractions of a LysC digest of human cell protein extract using ETD, collision-activated dissociation (CAD), and AI-ETD, we find that AI-ETD generates 13?405 peptide spectral matches (PSMs) at a 1% false-discovery rate (1% FDR), surpassing both ETD (7?968) and CAD (10?904). We also analyze 12 SCX fractions of a tryptic digest of human cell protein extract and find that ETD produces 6?234 PSMs, AI-ETD 9?130 PSMs, and CAD 15?209 PSMs. Compared to ETD with supplemental collisional activation (ETcaD), AI-ETD generates ～80% more PSMs for the whole cell lysate digested with trypsin and ～50% more PSMs for the whole cell lysate digested with LysC.     

Load transfer of graphene/carbon nanotube/polyethylene hybrid nanocomposite by molecular dynamics simulation

Load transfer of the graphene/carbon nanotube (CNT)/polyethylene hybrid nanocomposite is studied here from molecular dynamics (MD) simulations. Simulations of this composite material under uniaxial tension were conducted by varying CNT’s position and diameter in the polymer matrix. The obtained results show that: (1) The peak strength of stress and strain evolution in the polymer matrix is lower than the peak strength of the graphene/graphene and graphene/polymer interfaces. Hence, the damage zone is always located in the polymer matrix. (2) Agglomerated two-layer graphenes do not possess an increased value in the peak strength compared with single-layer graphene-reinforced polymer nanocomposite (PNC), while two separate layers of graphene show slightly higher peak strength. (3) The largest peak strength is observed before CNT moves to the center of the polymer matrix. The damage location moves from the upper to the lower part of CNT when the CNT is located at the centre of polymer matrix. (4) The influence of the CNT diameter on the peak strength is not obvious, while the damage location and shape in the polymer matrix changes with respect to varying CNT diameters. In addition, the damage zone always falls outside the interphase zone.     

System approach to metrology of quantum multiparticle systems

Features of the metrology of quantum multiparticle systems in connection with general system theory and representational theory are considered. Quantitative characteristics of the periodic system of elements (PSE) are introduced and studied, including property correlation, and also system hierarchies are considered leading to its analysis and possible application of nanosystems and quantum computers. __________ Translated from Izmeritel’naya Tekhnika, No. 4. pp. 3–7, April, 2008.     

Numerical simulation of molding-defect formation during resin transfer molding

The present study investigated a numerical simulation of molding-defect formation during resin transfer molding using boundary element method and line dynamics. The proposed method enables to simulate small molding defects by increasing the node for required position during time evolution; thereby, the method computes high-resolution flow front without being affected by the initial mesh geometry. The method was applied to the radial injection RTM with single inlet, and it was confirmed by comparison with theoretical value based on Darcy’s law that the flow advancement was computed with high accuracy. In addition, the method was also applied to the flow advancement for inclusion problem with cylinder, and four-point injection problem. The simulated flow behavior, void formation, and shrinkage agreed with the results in references. Finally, the method was compared with experiments using two-point injection problem. The computed configuration of the flow front and weld line agreed well with the experimental results.     

A hybrid electronic-density-functional/molecular-dynamics simulation scheme for multiscale simulation of materials on parallel computers: applications to silicon and alumina

In hybrid electronic-density-functional/molecular-dynamics schemes, a total system is partitioned in real space into the quantum-mechanical (QM) region treated by the electronic-density-functional theory and the molecular dynamics (MD) region in which atoms are interacting through the empirical inter-atomic potential. In the former hybrid scheme [Ogata et al. Comput. Phys. Commun. 149 (2002) 30], appropriate selection of QM atoms for seamless coupling between the QM and MD regions is limited in Si systems, and applications of the scheme to other materials are difficult. Novel hybrid scheme that is free from the limitation and applicable to both Si and alumina systems, is presented.     

Effect of exogenous flavins on the microbial corrosion by Geobacter sulfurreducens via iron-to-microbe electron transfer

Microbes can cause or accelerate metal corrosion,leading to huge losses in corrosion damages each year.Geobacter sulfurreducens is a representative electroactive bacterium in many soils,sediments,and wastew-ater systems.It has been confirmed to directly extract electrons from elemental metals.However,little is known about the effect of electron shuttles in G.sulfurreducens corrosion on stainless steel.In this study,we report that exogenous flavins promote iron-to-microbe electron transfer,accelerating micro-bial corrosion.G.sulfurreducens caused 1.3 times deeper pits and increased electron uptake(with 2 times increase of icorr)from stainless steel when riboflavin was added to the culture medium.OmcS-deficient mutant data suggest that G.sulfurreducens utilizes riboflavin as a bound-cofactor in outer membrane c-type cytochromes.The finding that,in the presence of microbes,riboflavin can substantially accelerate corrosion highlights the role of flavin redox cycling for enhanced iron-to-microbe electron transfer by G.sulfurreducens and provides new insights in microbial corrosion.     

A trust region-based approach to optimize triple response systems

This article presents a new computing procedure for the global optimization of the triple response system (TRS) where the response functions are non-convex quadratics and the input factors satisfy a radial constrained region of interest. The TRS arising from response surface modelling can be approximated using a nonlinear mathematical program that considers one primary objective function and two secondary constraint functions. An optimization algorithm named the triple response surface algorithm (TRSALG) is proposed to determine the global optimum for the non-degenerate TRS. In TRSALG, the Lagrange multipliers of the secondary functions are determined using the Hooke–Jeeves search method and the Lagrange multiplier of the radial constraint is located using the trust region method within the global optimality space. The proposed algorithm is illustrated in terms of three examples appearing in the quality-control literature. The results of TRSALG compared to a gradient-based method are also presented.     

A Monte Carlo simulation approach to the availability assessment of multi-state systems with operational dependencies

This paper deals with multi-state systems (MSS), whose performance can settle on different levels, e.g. 100%, 80%, 50% of the nominal capacity, depending on the operative conditions of the constitutive multi-state elements. Examples are manufacturing, production, power generation and gas and oil transportation systems. Often in practice, MSS are such that operational dependencies exist between the system state and the state of its components. For example, in a production line of nodal series structure, with no buffers between the nodes, if one of the nodes throughput changes (e.g. switches from 100% to 50% due to a deterministic or stochastic transition of one of its components), the other nodes must be reconfigured (i.e. their components must deterministically change their states) so as to provide the same throughput.In this paper, we present a Monte Carlo simulation technique which allows modelling the complex dynamics of multi-state components subject to operational dependencies with the system overall state. A correlation method is tailored to model the automatic change of state of the relevant components following a change in one of the system nodes. The proposed technique is verified on a simple case study of literature.     

An approach to Monte Carlo simulation of low-energy electron and photon interactions in air

In this paper we present an approach to an energy deposition model for low energy (10 eV–10 keV) photons and electrons. The model is based on Monte Carlo simulations of the tracks and energy loss resulting from single electron scattering events with the constituent molecules of air, namely N₂ and O₂. The simulation code is based on the Geant4 toolkit. The original physics in Geant4 low-energy processes for photon interactions was used for the incoming photons and secondary X- and gamma-rays, from energies below 1–10 keV. Two new electron interaction processes were developed,and both of them were considered as discrete processes. The new implemented physics is based on experimental cross-sections for elastic and inelastic scattering, complemented with theoretical calculations. Ionization is treated as a subprocess of the inelastic process. The implementation of the new processes in the standard Geant4 frame is considered. Validation tests and comparison with other Monte Carlo results are discussed. The current limitations of this version of the code are also outlined. The code can be of interest in areas where energy deposition at microscopic level is crucial, such as microdosimetry.