水溶液中趋磁微生物体吸附Ni~(2+)的模拟研究

为了探索趋磁微生物体对水溶液中Ni2+的吸附机理,考察微观作用力对吸附过程的影响,本文通过酸碱滴定实验确定了趋磁微生物体具有吸附作用的表面功能基团,建立了由体内磁小体Fe3O4和表面功能基团-PO3H,-OH,-COOH构成的趋磁生物体模型,并通过分子动力学模拟方法从静电作用、分子间作用、热运动等方面研究了磁小体和功能基团对Ni2+的吸附过程的影响规律。模拟结果证明对Ni2+的吸附过程是基团的静电吸引力和范德华力相互作用的综合结果,不同基团的静电引力强弱是有区别的。模拟结果还表明,Ni2+对-PO3H的趋聚倾向最大,对-OH的趋聚倾向次之,而对-COOH和Fe3O4的趋聚作用较弱。采用化学修饰法分别掩蔽菌体表面基团,并做了吸附实验,吸附效果与模拟结果完全吻合。这些结论将对生物磁选的开发应用提供新的理论依据。     

Convergence analysis and performance of the extended artificial physics optimization algorithm

This paper presents extended artificial physics optimization (EAPO), a population-based, stochastic, evolutionary algorithm (EA) for multidimensional search and optimization. EAPO extends the physicomimetics-based Artificial Physics Optimization (APO) algorithm by including each individual’s best fitness history. Including the history improves EAPO’s search capability compared to APO. EAPO and APO invoke a gravitational metaphor in which the force of gravity may be attractive or repulsive, the aggregate effect of which is to move individuals toward local and global optima. A proof of convergence is presented that reveals the conditions under which EAPO is guaranteed to converge. Discrete-time linear system theory is used to develop a second-order difference equation for an individual’s stochastic position vector as a function of time step. Stable solutions require eigenvalues inside the unit circle, leading to explicit convergence criteria relating the run parameters {m_i, w, G}. EAPO is tested against several benchmark functions with excellent results. The algorithm converges more quickly than APO and with better diversity.     

Simulations of thixotropic liquids

In thixotropic liquids the rheological properties depend on the liquid’s deformation history. Clay suspensions (as encountered in oil sands mining) are a prominent example. Activated clay particles form a network. As a consequence of (ionic) transport limitations, the network is not an instantaneous feature; it takes time to build up, and also to break down, the latter as a result of deformation in the liquid. In this paper a procedure for detailed simulations of flow of viscous thixotropic liquids is outlined. The local viscosity of the liquid relates to the level of integrity of the network. The time-dependence of the liquid’s rheology is due to the finite rate with which the network in the liquid builds up or breaks down. This concept has been incorporated in a lattice-Boltzmann discretization of the flow equations. With this methodology the way thixotropic liquids are mobilized in mixing tanks and the drag force experienced by dense assemblies of coarse particles (e.g. sand) in thixotropic liquids have been studied.     

Bending and vibration of an electrostatically actuated circular microplate in presence of Casimir force

The pull-in instability and the vibration for a prestressed circular electrostatically actuated microplate are investigated in consideration of the Casimir force. Based on von Kármán’s nonlinear bending theory of thin plates, the governing equations for the whole analysis are decomposed into two two-point boundary value problems. For static deformation of the plate, the geometric nonlinearity is involved and the pull-in parameters are obtained by using the shooting method through taking the applied voltage or Casimir parameter as an unknown. This algorithm is also used to study the small amplitude free vibration about the predeformed bending configuration following an assumed harmonic time mode, and the variation of the prestress and Casimir parameters dependent fundamental natural frequency with the applied voltage is presented. Several case studies are compared with available published simulations to confirm the proposed method. The influences of various parameters, such as the initial gap-thickness ratio, Casimir effect, prestress on the pull-in instability behavior and the natural frequency are examined.     

管件无模拉伸成形力能参数数学模型研究

对不锈钢管件无模拉伸变形速度场及力能参数进行了理论及实验研究.分析了不锈钢管件无模拉伸的变形模型、速度场以及力能参数的影响因素及影响规律,采用上限法确定了不锈钢管件无模拉伸速度场及力能参数物理模型,填补了国内外关于不锈钢管件无模拉伸变形及力能参数物理模型研究的空白.为不锈钢管件无模拉伸工艺工业化应用奠定基础.     

Fabrication of nanostructured silicon by metal-assisted etching and its effects on matrix-free laser desorption/ionization mass spectrometry

A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300 s then decreases until 600 s for both low resistance (0.001–0.02 Ω cm) and high resistance (1–100 Ω cm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance.     

Influence of physical properties and operating parameters on hydrodynamics in Centrifugal Partition Chromatography

Besides the selection of a suitable biphasic solvent system the separation efficiency in Centrifugal Partition Chromatography (CPC) is mainly influenced by the hydrodynamics in the chambers. The flow pattern, the stationary phase retention and the interfacial area for mass transfer strongly depend on physical properties of the solvent system and operating parameters. In order to measure these parameters we visualized the hydrodynamics in a FCPC-chamber for five different solvent systems with an optical measurement system and calculated the stationary phase retention, interfacial area and the distribution of mobile phase thickness in the chamber. Although inclined chambers were used we found that the Coriolis force always deflected the mobile phase towards the chamber wall reducing the interfacial area. This effect increased for systems with low density difference. We also have shown that the stability of phase systems (stationary phase retention) and its tendency to disperse increased for smaller values of the ratio of interfacial tension and density difference. But also the viscosity ratio and the flow pattern itself had a significant effect on retention and dispersion of the mobile phase. As a result operating parameters should be chosen carefully with respect to physical properties for a CPC system. In order to reduce the effect of the Coriolis force CPC devices with greater rotor radius are desirable.     

Hydration forces between bilayers in the presence of dissolved or surface-linked sugars

We analyse the experimental evidence of the hydration force near phospholipid bilayers when the “solvent” is a solution of carbohydrates. Two cases must be clearly distinguished: when sugar is dissolved, depletion causes a supplementary attractive force, while in the case of sugar linked to the lipid the contact pressure increases by orders of magnitude. Attractive interaction inferred between bilayers is sometimes derived from indirect evidence, i.e. scattering, attraction between layers adsorbed, shape of phase boundary limits, and without the simultaneous determination of the osmotic compressibility. Generally, water molecules in the first hydration shell of sugar compete with water molecules bound (by more than one kT in free energy) to lipid head-groups. A general result is that the decay length of any repulsive effect remains close to 0.2 nm, even in concentrated sugar solutions. A tentative general explanation of this experimental fact is given together with consequences, such as the possibility of several types of critical points appearing in bilayer stacks. Decay length as well as effective contact pressure is considered with respect to carbohydrate activity.     

The missing link between the Hydration Force and interfacial water: Evidence from computer simulations

In this article I briefly review Molecular Dynamics Simulations studies relevant to the understanding of the physical origin of the controversial Hydration Force. The focus of the review is in simulations of realistic models of hydrophilic surfaces. The results reviewed here show a molecular perspective on how this repulsive, stabilizing force comes from interfacial water.