Critical anomaly and finite size scaling of the self-diffusion coefficient for Lennard Jones fluids by non-equilibrium molecular dynamic simulation

We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.

Molecular dynamics simulation of self-diffusion coefficients for liquid metals

The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics meth ods based on the embedded-atom-method （EAM） potential function. The simulated results show that a good inverse linear relation exists between the natural logarithm of self-diffusion coefficients and temperature, though the results in the litera ture vary somewhat, due to the employment of different potential functions. The estimated activation energy of liquid metals obtained by fitting the Arrhenius formula is close to the experimental data. The temperature-dependent shear-viscosities obtained from the Stokes-Einstein relation in conjunction with the results of molecular dynamics simulation are generally consistent with other values in the literature.

Dramatic change of the self-diffusions of colloidal ellipsoids by hydrodynamic interactions in narrow channels

The self-diffusion problem of Brownian particles under the constraint of quasi-one-dimensional(q1 D) channel has raised wide concern.The hydrodynamic interaction(HI) plays an important role in many practical problems and two-body interactions remain dominant under q1D constraint.We measure the diffusion coefficient of individual ellipsoid when two ellipsoidal particles are close to each other by video-microscopy measurement.Meanwhile, we obtain the numerical simulation results of diffusion coefficient using finite element software.We find that the self-diffusion coefficient of the ellipsoid decreases exponentially with the decrease of their mutual distance X when X < X0, where X0 is the maximum distance of the ellipsoids to maintain their mutual influence, X0 and the variation rate are related to the aspect ratio p = a/b.The mean squared displacement(MSD) of the ellipsoids indicates that the self-diffusion appears as a crossover region, in which the diffusion coefficient increases as the time increases in the intermediate time regime, which is proven to be caused by the spatial variations affected by the hydrodynamic interactions.These findings indicate that hydrodynamic interaction can significantly affect the self-diffusion behavior of adjacent particles and has important implications to the research of microfluidic problems in blood vessels and bones, drug delivery, and lab-on-chip.

OXYGEN SELF-DIFFUSION AND INTERACTIONS BETWEEN DEFECTS IN Fe_3O_4

New experimental results on the self diffesion of oxygen in Fe3O4 obtained with a high precision SIMS at 1079K allow to conclude the eristence of oxygen vacancies and of oxygen iron vacancy pairs coexisting selectively with different kinds of iron defects.The possibility of measuring the isotopic effect of the two tracers O17 and O18 is also examined.

Enhancement of water self-diffusion at super-hydrophilic surface with ordered water

It has been well acknowledged that molecular water structures at the interface play an important role in the surface properties, such as wetting behavior or surface frictions. Using molecular dynamics simulation, we show that the water self-diffusion on the top of the first ordered water layer can be enhanced near a super-hydrophilic solid surface. This is attributed to the fewer number of hydrogen bonds between the first ordered water layer and water molecules above this layer, where the ordered water structures induce much slower relaxation behavior of water dipole and longer lifetime of hydrogen bonds formed within the first layer.

Anisotropic self-diffusion of fluorinated poly(methacrylate) in metal-organic frameworks assessed with molecular dynamics simulation

Utilizing the periodically structured metal-organic framework （MOF） as the reaction vessel is a promising technique to achieve the aligned polymer molecular chains, where the diffusion procedure of the polymer monomer inside MOF is one of the key mechanisms. To investigate the diffusion mechanism of fluorinated polymer monomers in MOFs, in this paper the molecular dynamics simulations combined with the density functional theory and the Monte Carlo method are used and the all-atom models of TFMA （trifluoroethyl methacrylate） monomer and two types of MOFs,[Zn2（BDC）2（TED）]n and[Zn2（BPDC）2（TED）]n, are established. The diffusion behaviors of TFMA monomer in these two MOFs are simulated and the main influencing factors are analyzed. The obtained results are as follows. First, the electrostatic interactions between TFMA monomers and MOFs cause the monomers to concentrate in the MOF channel, which slows down the monomer diffusion. Second, the anisotropic shape of the one-dimensional MOF channel leads to different diffusion speeds of monomers in different directions. Third, MOF with a larger pore diameter due to a longer organic ligand,[Zn2（BPDC）2（TED）]n in this paper, facilitates the diffusion of monomers in the MOF channel. Finally, as the number of monomers increases, the self-diffusion coefficient is reduced by the steric effect.

Hemoglobin S Polymerization Effect on Water Self-Diffusion Coefficient

The transversal relaxation time, the effective transversal relaxation time and the water self-diffusion coefficient are evaluated during hemoglobin S polymerization. One homogeneous permanent magnet and one inhomogeneous and portable unilateral magnet with a very strong and constant static magnetic field gradient were utilized. The Carr-Purcell-Meiboom-Gill method was used before and after placing the studied samples 24 hours at 36&deg;C to guarantee the polymerization. The transversal relaxation shows two exponents after polymerization supporting the concept of partially polymerized hemoglobin. The effective transversal relaxation time decreases around 40%, which can be explained by the increase of water self-diffusion coefficient 1.8 times as a main value. This result can be explained considering the effects of the agglutination process on the obstruction and hydration effects in a partially polymerized solution.

The Relation between the Heat of Melting Point, Boiling Point, and the Activation Energy of Self-Diffusion in Accordance with the Concept of Randomized Particles

On the example of typical metals, it’s found that the activation energy of self-diffusion is above of the melting heat and below of vaporization heat. This corresponds to the existence of liquid-mobile particle classification based on the concept of randomized particles. A formula for estimating the activation energy of self-diffusion by which it is approximately half of the heat of evaporation of the substance is recommended. We derive the temperature dependence for a fraction self-diffusion’s particles.

Investigation of Self-Diffusion and Structure in Calcium Aluminosilicate Slags by Molecular Dynamics Simulation

Molecular dynamics simulation is applied to investigate the mechanism and variation of self-diffusion in calcium aluminosilicate slags. The self-diffusion coefficients are calculated for eleven slag compositions with varying Al2O3/SiO2 ratios at a fixed CaO content. In practice, the results of the study are relevant to the significant changes in transport phenomenon caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The cooperative movement between O atoms and network formers is discussed since [AlO4] and [SiO4] tetrahedra are the elementary structural units in the CaO-Al2O3-SiO2 (CAS) slag system. The diffusivities for four atomic types are affected by the degree of polymerization (DOP) of slag network characterized by the proportions of non-bridging oxygen (NBO) and Qn species in the system. On the other hand, a sudden increase in 5-coordinated Al as network modifiers in high alumina regions slightly increases the self-diffusion coefficient for Al. As another structural defect, oxygen tricluster plays an important role in the behavior of self-diffusion for O atoms, while the diffusivity for Ca is deeply influenced by its bonding and coordinating conditions.

Thermodynamic and transport properties of spiro-(1,1')-bipyrrolidinium tetrafluoroborate and acetonitrile mixtures:A molecular dynamics study

Organic salts such as spiro-（1,1’）-bipyrrolidinium tetrafluoroborate（[SBP][BF4]） dissolved in liquid acetonitrile（ACN） are a new kind of organic salt solution,which is expected to be used as an electrolyte in electrical double layer capacitors（EDLCs）.To explore the physicochemical properties of the solution,an all-atom force field is established on the basis of AMBER parameter values and quantum mechanical calculations.Molecular dynamics（MD） simulations are carried out to explore the liquid structure and physicochemical properties of [SBP][BF4] electrolyte at room temperature.The computed thermodynamic and transport properties match the available experimental results very well.The microscopic structures of [SBP][BF4] salt solution are also discussed in detail.The method used in this work provides an efficient way of predicting the properties of organic salt solvent as an electrolyte in EDLCs.

Global Existence of Solutions to the Prey-predator System of Three Species with Cross-diffusion

有跨散开的压力的三种的猎物食肉动物系统被知道与最大的存在时间 T 拥有一个本地答案。由获得 T 的本地答案独立人士的 W12 标准的界限，它被建立答案的全球存在。

Experimental investigation of process parameters during graphitization of catalytic coke

The aim of this project is studying the effect of thermal operation parameters on the graphitization of self-diffused ethane-based catalytic coke.The novelty of this study refers to self-diffused metals that had given unique properties to the catalytic coke and had improved the graphitization degree at low temperatures.The main feature of this research is presenting a remarkable energy saving approach that uses low-cost installations for production of graphitized carbon.The experiments were performed in two steps including preparation of self-diffused ethane-based catalytic coke and then low-temperature graphitization of coke samples below 1500 ℃.Characteristic tests were performed by determination of electrical resistivity and XRD pattern of graphitized samples including graphitization degree,aromaticity,coke rank,number of carbon rings,graphene thickness and length.The results revealed that the blanket atmosphere,final temperature and exposure time had the greatest impact on the aforementioned criteria,while the role of thermal ramp and sulfur content of catalytic coke was negligible.The electrical resistivity tests on the graphitized sample showed how the electrical resistivity of graphitized samples is a function of graphitization degree.

Stability Analysis of Predator-Prey System with Consuming Resource and Disease in Predator Species

The present study is concerned with formulating a predator-prey eco-epidemiological mathematical model assuming that an infection exists in the predator species.The two classes of predator species(susceptible and infected)compete for the same sources available in the environment with the predation option.It is assumed that the disease does not spread vertically.The proposed model is analyzed for the stability of the coexistence of the predators and prey.The fixed points are carried out,and the coexisting fixed point is studied in detail by constructing the Lyapunov function.The movement of species in search of food or protection in their habitat has a significant influence,examined through diffusion.The ecological influences of self-diffusion on the population density of both species are studied.It is theoretically proved that all the under consideration species can coexist in the same environment.The coexistence fixed point is discussed for both diffusive and non-diffusive cases.Moreover,a numerical scheme is constructed for solving time-dependent partial differential equations.The stability of the scheme is given,and it is applied for solving presently modified eco-epidemiological mathematical model with and without diffusion.The comparison of the constructed scheme with two exiting schemes,Backward in Time and Central in Space(BTCS)and Crank Nicolson,is also given in the form of plots.Finally,we run a computer simulation to determine the effectiveness of the proposed numerical scheme.For readers’convenience,a computational code for the proposed discrete model scheme may be made available upon request.

Dynamic Molecular Behavior and Cluster Structure of Octanoic Acid in Its Liquid and CCl₄Solution

Fatty acids such as oleic and stearic acids having a long hydrocarbon chain are known to exist as dimers in their melt and even in a non-polar solvent. In their melt the dimers arrange longitudinally and alternately to form clusters which resemble a smectic liquid crystal. The clusters determine the liquid properties of the fatty acids such as density, viscosity and fluidity. Then, do the dimers of fatty acid having a moderate-length hydrocarbon chain construct such the clusters? In the present study the dynamic molecular behavior and assembly structure of octanoic acid in its melt and also in CCl4 solution have been investigated by the X-ray diffraction, near infrared spectroscopy, 1H-NMR chemical shift, self-diffusion coefficient and 13C-NMR spin-lattice relaxation time measurements. From these results it has been revealed that the clusters of octanoic acid exist in its melt and also in CCl4 and that the clusters in the melt disintegrate with an increase in temperature. The dissociation profile of dimers of octanoic acid into monomers in CCl4 also has been clarified.

Adatom self-diffusion on Pt (100) surface by an ad-dimer migrating

We study the self-diffusion of adatom on Pt(100) surface by molecular dynamics. The metal is modeled by the surface embedded-atom potential. Besides the conventional concerted exchange mechanism, a new exchange mechanism in which an ad-dimer diffuses by a concerted motion of three atoms is observed. The importance is that it could become a dominant diffusion mechanism in some cases.

Aggregation of sodium dodecyl sultonate studied by N MR self-diffusion

SURFACTANT-POLYMER flooding has received much attention recently because it is an efficientpetroleum recovery process. The optimum efficiency is due to its ability to improve the charac-teristics of the interface between the solid surface of the micropores of cores, the ground wa-ter, and oil included in the oil reservoirs. Surfactant molecules aggregate in water solution canallow ultra low interfacial tension (IFT) between oil and water to be achieved so that oil pro-duction is favorable. Nuclear magnetic resonance (NMR) measurement provides informationabout Brownian movement of various kinds of molecules in solution of multicomponent,

Calculations of Self-diffusion Activation Energies for Alkaline Metals With Embedded Atom Method

Calculations were performed for the self-diffusion activation energies of monovacancy and both formation and binding energies of divacancies for alkaline metals Li, Na, K, Rb, Cs using the embedded atom method (EAM) model for bcc transition metals developed by the authors recently. The aim of the paper is to extend the application of the new model, to compare the calculated values for self-diffusion with the experimental data and those of previous calculations, and to discuss the intrinsic characteristic of self-diffusion in alkaline metals. The calculated monovacancy migration energies and activation energies are in excellent agreement with experimental data, and the calculated divacancy migration and activation energies are in good agreement with the experimental values available.

Self-aggregation of surfactants in water solution by NMR

Dynamic behavior of surfactant molecules, sodium dodecyl sulfonate （SDSN）, cetyl trimethyl ammoniumbromide （CTAB） and triton X-100, and their micelles in water solution at various concentrations were studied bychemical shift, self diffusion coefficient （D） and nuclear magnetic resonance relaxation （T1 and T2） measurements.Experimental results show that there exist turning points at surfactant concentration （C） nearby the critical micelleconcentration （cmc） for all of the above-mentioned parameters, which approach the constant values when C equals 5to 10 times cmc. T1 and T2 measurements show that when C 【 cmc, Triton X-100 molecules exhibit fast isotropicmotion in water solution. After micellization, the motion of hydrophobic chains is far away from the extreme narrow-ing condition, however, the long hydrophilic oxyethylene chains move relatively freely, although their T1 and T2 be-come shorter in comparison with those of the molecules in mono-molecular state. The behavior of the

Microstructure Evolution in 9Cr Martensitic Steel During Long-Term Creep at 650℃

Standardarized creep and rupture strength tests were conducted for commercial T91 martensitic heat-resistant steel at 650℃and corresponding microstructure was characterized by BSED, TEM and EDS. The martensitic microstructure degenerated seriously during creep exposure, including martensitic substructure recovering, carbides coarsening, dissolving and precipitating. EDS analysis shows that the M23C6 carbides in different morphologies have dissimilar compositions. The rod/sheet like M23 C6 particles within the matrix contain more additions, which might precipitate in situ while fine MX particles were re-solving. The high content of silicon in these rod/sheet like M2aC6 carbides is probably related to self diffusion coefficient increasing for the exposed condition at 650 ~C close to Curie temperature To. For those reasons, martensite substructure becomes unstable, and microstructure evolution is accelerated and leads to creep strength deteriorating severely.

Effect of Graphite Layers on the Conformation and Thermal Conductivity of n-octadecane:A Molecular Dynamics Study

To understand the thermal conductivity improvement of the paraffin and graphite composite PCMs in micro-scale,the conformation characteristics of molecules with rising temperature was studied by molecular dynamics(MD)simulation.And then the structure and dynamics characteristics of the paraffin PCM,including the structural evolution,the self-diffusion coefficient,phase change properties and thermal conductivity,were analyzed.The results indicate that the distribution of the n-octadecane molecules is more regular in the region near the graphite layers,although the temperature is higher than the phase transition point,which means that the graphite layer has a significant absorption influence on the conformation of alkane molecules.Then,the self-diffusion coefficient of n-octadecane molecules increases with the increasing of temperature,which shows great agreement with the literature.Meanwhile,the self-diffusion coefficient of n-octadecane molecules staying far away from the graphite layers is larger than that of the molecules in the region near the graphite layer.In addition,the radial distribution function(RDF)was used to analyze the molecular interaction of the system at different temperatures.The sudden increase of R(ratio of the first peak value to the first valley value of the RDF)within the temperature range from 293 K to 313 K corresponds to the phase transition point,indicating that the solid-liquid phase transition occurs at the temperature range.Besides,the results indicate that the thermal conductivity of amorphous n-octadecane is about 2.5 times lower than that of the crystal n-octadecane with perfect structure.This investigation provides theoretical guidance for the study of the micro-mechanism of n-octadecane doped with graphite composite phase change materials.