We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molec...We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molecular dynamics(EMD)simulations.D_(G)and D_(E)are computed for a broad domain of screening length(κ)and coupling parameters(Γ)along with different system sizes.It is observed that both D_(G)and D_(E)decrease linearly with increasing Г in warm liquid states and increase with increasingκ.In cold liquid states,the Einstein relation accurately predicts D_(E)in 2D SC-DPs because diffusion motion is close to normal diffusion,but the G-K relation provides overestimations of D_(G),because VACF indicates anomalous diffusion;thus,D_(G)is not accurate.Our new simulation outcomes reveal that D_(G)and D_(E)remain independent of system sizes.Furthermore,our investigations demonstrate that at higher temperatures,D_(G)and D_(E)converge,suggesting diffusion motion close to normal diffusion,while at lower temperatures,these two values diverge.We find reasonable agreement by comparing current and existing numerical,theoretical and experimental data.Moreover,when normalizing diffusion coefficients by the Einstein frequency and testing against the universal temperature scaling law,D_(G)deviates from theoretical curves at low temperatures and κ,whereas D_(E)only disagrees with theory at very smallκ(■0.10).These findings provide valuable insight into diagnosing dust component parameters within 2D DP systems and contribute to the broader understanding of diffusion processes in DP environments.展开更多
A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chap...A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.展开更多
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 t...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.展开更多
Pulsed field gradient nuclear magnetic resonance （PFG NMR） has been performed to study the diffusion of organic solvents into semicrystalline polyethylene particles. Self-diffusion coefficients in different domains ...Pulsed field gradient nuclear magnetic resonance （PFG NMR） has been performed to study the diffusion of organic solvents into semicrystalline polyethylene particles. Self-diffusion coefficients in different domains of the sample can be extracted through a bi- exponential fit to the echo intensity attenuation, which allows the precise determination of the tortuosity of the polyethylene particles. Further exploration comes from the measurements with branched polyethylene particles and it was found that the diffusion in polymer phase contributed significantly to the slow component of the exponential decay curve. 2007 Jing Dai Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.展开更多
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 g...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.展开更多
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 ...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.展开更多
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 selectivel...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.展开更多
Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantl...Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantly from that in the bulk. Based on the simple quasicrystal model of liquid, analytical expressions of self-diffusion coefficient both in bulk and in slit nanopore are derived from the Stokes–Einstein equation and the modified Eyring's equation for viscosity. The local self-diffusion coefficient in different layers of liquid and the global self-diffusion coefficient in the slit nanopore are deduced from these expressions. The influences of confinement by pore walls,pore widths, liquid density, and temperature on the self-diffusion coefficient are investigated. The results indicate that the self-diffusion coefficient in nanopore increases with the pore width and approaches the bulk value as the pore width is sufficiently large. Similar to that in bulk state, the self-diffusion coefficient in nanopore decreases with the increase of density and the decrease of temperature, but these dependences are weaker than that in bulk state and become even weaker as the pore width decreases. This work provides a simple method to capture the physical behavior and to investigate the dynamic properties of liquid in nanopores.展开更多
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 s...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.展开更多
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 monom...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.展开更多
Self-diffusion coefficients of exponential-six fluids are studied using equilibrium molecular dynamics simulation technique. Mean-square displacements and velocity autocorrelation functions are used to calculate self-...Self-diffusion coefficients of exponential-six fluids are studied using equilibrium molecular dynamics simulation technique. Mean-square displacements and velocity autocorrelation functions are used to calculate self-diffusion coefficients through Einstein equation and Green-Kubo formula. It has been found that simulation results are in good agreement with experimental data for liquid argon which is taken as exponential-six fluid. The effects of density, temperature and steepness factor for repulsive part of exponential-six potential on self-diffusion coefficients are also investigated. The simulation results indicate that the self-diffusion coefficient of exponential-six fluid increases as temperature increases and density decreases. In addition, the larger self-diffusion coefficients are obtained as the steepness factor increases at the same temperature and density condition.展开更多
The grand canonical Monte Carlo (GCMC), the canonical Monte Carlo by using equal probability perturbation, and the molecular dynamics (MD) methods were used to study the capillary phase-transition (capillary condensat...The grand canonical Monte Carlo (GCMC), the canonical Monte Carlo by using equal probability perturbation, and the molecular dynamics (MD) methods were used to study the capillary phase-transition (capillary condensation and evaporation) and self-diffusion for a simple Lennard-Jones model of ethylene confined in slit carbon pores of 2.109 nm at temperatures between 141.26 K and 201.80 K. The critical point of capillary phase-transition was extrapolated by the critical power law and the law of rectilinear diameter from the capillary phase-transition data in the near critical region. The effects of temperature and fluid density on the parallel self-diffusion coefficients of ethylene molecules confined in the slit carbon pores were examined. The results showed that the parallel selfdiffusion coefficients in the capillary phase transition area strongly depended on the fluids local densities in the slit carbon pores.展开更多
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 inhomogene...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°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.展开更多
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 class...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.展开更多
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 ...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.展开更多
Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow fi...Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow field and temperature field coupling(referred to as self-diffusion flow and heat coupling model)was established based on the previously proposed self-diffusion flow model,while considering the influence of the temperature field change.Then,its calculation result was compared with that of the flow model based on Darcy's law and Knudsen diffusion(referred to as modified Darcy flow model).Based on the self-diffusion flow and heat coupling model,the self-diffusion flow behaviors of deep shale gas under the influence of temperature field change were analyzed,and the influence of bottomhole temperature on the degree of reserve recovery of deep shale gas was discussed.Finally,the self-diffusion flow and heat coupling model was applied to simulate the production of one shale-gas horizontal well in the Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in the Changning Block of the Sichuan Basin.And the following research results were obtained.First,at the same parameters,the shale gas production calculated by the selfdiffusion flow and heat coupling model is higher than the result calculated by the modified Darcy flow model.Second,when temperature field change is taken into consideration,the selfedviffusion coefficient profile presents a peak,the gas density profile presents a valley and the data points corresponding to the peak/valley move synchronously to the internal formation,which indicates that the selfediffusion coefficient influences the gas mass transfer rate,and the influence range of near well low temperature on gas self-diffusion increases continuously as the production continues.Third,when the bottomhole temperature is lower than the formation temperature,the selfediffusion coefficient of the gas near the well decreases and the gas is blocked near the well,which reduces the gas well production.Fourth,the production simulation result of the case well shows that the self-diffusion flow and heat coupling model can predict the production of deep shale gas more accurately if temperature field change is taken into consideration.In conclusion,the self-diffusion flow and heat coupling model established in this paper is of higher reliability and accuracy and can be used for productivity simulation and prediction of deep shale gas wells.The conclusion of this paper has certain guiding significance for deep shale gas production and gas well productivity prediction.展开更多
Potassium metal is regarded as a promising anode material for potassium-ion batteries due to its high theoretical capacity and low redox potential.However,its performance is hindered by rapid capacity fading,primarily...Potassium metal is regarded as a promising anode material for potassium-ion batteries due to its high theoretical capacity and low redox potential.However,its performance is hindered by rapid capacity fading,primarily caused by an unstable solid electrolyte interphase(SEI)and continuous dendrite growth.Herein,by coating liquid metal(LM)alloy(GaInSn)onto copper foil,we prepared a special LM@Cu substrate,significantly improving the deposition/stripping behavior of potassium metal and thus achieving long-cycling K metal battery.The excellent potassiophilicity and electrolyte wettability of LM@Cu effectively reduce the K nucleation overpotential,promote charge transfer kinetics,and enable self-diffusive planar growth mode.Moreover,ex situ scanning electron microscopy and in situ optical microscopy analyses show that the LM coating induces uniform potassium deposition,reduces volume expansion,and achieves a dendrite-free K anode.Additionally,when 3,4,9,10-perylene-tetracarboxylic diimide(PTCDI)is employed as the cathode and K-LM@Cu(LMK)as the anode,the potassium metal battery demonstrates an initial reversible capacity of 124.4 mAh·g^(-1).Even after 4900 cycles at a current density of 500 mA·g^(-1),it maintains a high reversible capacity of 78.2 mAh·g^(-1).The self-diffusive planar growth mechanism enabled by liquid metal offers a promising approach for developing practical and durable potassium metal batteries.展开更多
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 mechan...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.展开更多
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 betw...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,展开更多
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) m...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.展开更多
基金support of the Fundamental Research Funds for the Central Universities of China(Grant No.2019ZDPY16).
文摘We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molecular dynamics(EMD)simulations.D_(G)and D_(E)are computed for a broad domain of screening length(κ)and coupling parameters(Γ)along with different system sizes.It is observed that both D_(G)and D_(E)decrease linearly with increasing Г in warm liquid states and increase with increasingκ.In cold liquid states,the Einstein relation accurately predicts D_(E)in 2D SC-DPs because diffusion motion is close to normal diffusion,but the G-K relation provides overestimations of D_(G),because VACF indicates anomalous diffusion;thus,D_(G)is not accurate.Our new simulation outcomes reveal that D_(G)and D_(E)remain independent of system sizes.Furthermore,our investigations demonstrate that at higher temperatures,D_(G)and D_(E)converge,suggesting diffusion motion close to normal diffusion,while at lower temperatures,these two values diverge.We find reasonable agreement by comparing current and existing numerical,theoretical and experimental data.Moreover,when normalizing diffusion coefficients by the Einstein frequency and testing against the universal temperature scaling law,D_(G)deviates from theoretical curves at low temperatures and κ,whereas D_(E)only disagrees with theory at very smallκ(■0.10).These findings provide valuable insight into diagnosing dust component parameters within 2D DP systems and contribute to the broader understanding of diffusion processes in DP environments.
文摘A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.
基金supported by the National Natural Science Foundation of China (Grant No. 51076128)the National High Technology Research and Development Program of China (Grant No. 2009AA05Z107)
文摘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.
基金This work was supported by the National Natural Science Foundation of China （No. 20490205 and No. 20406017） ； CSC-DAAD （PPP2004） project.
文摘Pulsed field gradient nuclear magnetic resonance （PFG NMR） has been performed to study the diffusion of organic solvents into semicrystalline polyethylene particles. Self-diffusion coefficients in different domains of the sample can be extracted through a bi- exponential fit to the echo intensity attenuation, which allows the precise determination of the tortuosity of the polyethylene particles. Further exploration comes from the measurements with branched polyethylene particles and it was found that the diffusion in polymer phase contributed significantly to the slow component of the exponential decay curve. 2007 Jing Dai Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
基金supported by the National Natural Science Foundation of China(Grant Nos.11032003 and 11221202)the National Basic Research Program of China(Grant No.2010CB731600)
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grants Nos.U1738118 and 11372314)the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(A)(Grant Nos.XDA04020202 and XDA04020406)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB22040301)
文摘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.
文摘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.
基金Supported by Guangdong Science and Technology Project(2012B050600012)
文摘Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantly from that in the bulk. Based on the simple quasicrystal model of liquid, analytical expressions of self-diffusion coefficient both in bulk and in slit nanopore are derived from the Stokes–Einstein equation and the modified Eyring's equation for viscosity. The local self-diffusion coefficient in different layers of liquid and the global self-diffusion coefficient in the slit nanopore are deduced from these expressions. The influences of confinement by pore walls,pore widths, liquid density, and temperature on the self-diffusion coefficient are investigated. The results indicate that the self-diffusion coefficient in nanopore increases with the pore width and approaches the bulk value as the pore width is sufficiently large. Similar to that in bulk state, the self-diffusion coefficient in nanopore decreases with the increase of density and the decrease of temperature, but these dependences are weaker than that in bulk state and become even weaker as the pore width decreases. This work provides a simple method to capture the physical behavior and to investigate the dynamic properties of liquid in nanopores.
基金supported by the National Natural Science Foundation of China(Grant Nos.11290164,11674345,and U1532260)the Key Research Program of Chinese Academy of Sciences(Grant Nos.KJZD-EW-M03 and QYZDJ-SSW-SLH019)+3 种基金the Youth Innovation Promotion Association,Chinese Academy of Sciences,the Shanghai Supercomputer Center of Chinathe Computer Network Information Center of Chinese Academy of Sciencesthe Special Program for Applied Research on Super Computation of the NSFC–Guangdong Joint Fund(the second phase)China
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant No.61575096)
文摘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.
基金Supported by the National Natural Science Foundation of China(No.29736170).
文摘Self-diffusion coefficients of exponential-six fluids are studied using equilibrium molecular dynamics simulation technique. Mean-square displacements and velocity autocorrelation functions are used to calculate self-diffusion coefficients through Einstein equation and Green-Kubo formula. It has been found that simulation results are in good agreement with experimental data for liquid argon which is taken as exponential-six fluid. The effects of density, temperature and steepness factor for repulsive part of exponential-six potential on self-diffusion coefficients are also investigated. The simulation results indicate that the self-diffusion coefficient of exponential-six fluid increases as temperature increases and density decreases. In addition, the larger self-diffusion coefficients are obtained as the steepness factor increases at the same temperature and density condition.
基金the National Science Foundation of China (NSFC) the China Petrochemical Corporation (SINOPEC) (No. 29792077).
文摘The grand canonical Monte Carlo (GCMC), the canonical Monte Carlo by using equal probability perturbation, and the molecular dynamics (MD) methods were used to study the capillary phase-transition (capillary condensation and evaporation) and self-diffusion for a simple Lennard-Jones model of ethylene confined in slit carbon pores of 2.109 nm at temperatures between 141.26 K and 201.80 K. The critical point of capillary phase-transition was extrapolated by the critical power law and the law of rectilinear diameter from the capillary phase-transition data in the near critical region. The effects of temperature and fluid density on the parallel self-diffusion coefficients of ethylene molecules confined in the slit carbon pores were examined. The results showed that the parallel selfdiffusion coefficients in the capillary phase transition area strongly depended on the fluids local densities in the slit carbon pores.
文摘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°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.
文摘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.
文摘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.
基金Project supported by the Youth Science Foundation Project of National Natural Science Foundation of China“Dynamic Evolution Mechanism of Shale Reservoir Stress Field under Multi-well Interference”(No.5190040058)the General Project of National Natural Science Foundation of China“Research on Hydrodynamic Mechanism of Multi-scale Channels in Tight Reservoir”,(No.51874321)the Scientific Research Foundation of China University of Petroleum(Beijing)for Young Top Talent“Multi-scale Characteristics of Fluid Flow in Complex Fracture Network of Shale Gas Reservoirs”(No.2462018YJRC014).
文摘Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow field and temperature field coupling(referred to as self-diffusion flow and heat coupling model)was established based on the previously proposed self-diffusion flow model,while considering the influence of the temperature field change.Then,its calculation result was compared with that of the flow model based on Darcy's law and Knudsen diffusion(referred to as modified Darcy flow model).Based on the self-diffusion flow and heat coupling model,the self-diffusion flow behaviors of deep shale gas under the influence of temperature field change were analyzed,and the influence of bottomhole temperature on the degree of reserve recovery of deep shale gas was discussed.Finally,the self-diffusion flow and heat coupling model was applied to simulate the production of one shale-gas horizontal well in the Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in the Changning Block of the Sichuan Basin.And the following research results were obtained.First,at the same parameters,the shale gas production calculated by the selfdiffusion flow and heat coupling model is higher than the result calculated by the modified Darcy flow model.Second,when temperature field change is taken into consideration,the selfedviffusion coefficient profile presents a peak,the gas density profile presents a valley and the data points corresponding to the peak/valley move synchronously to the internal formation,which indicates that the selfediffusion coefficient influences the gas mass transfer rate,and the influence range of near well low temperature on gas self-diffusion increases continuously as the production continues.Third,when the bottomhole temperature is lower than the formation temperature,the selfediffusion coefficient of the gas near the well decreases and the gas is blocked near the well,which reduces the gas well production.Fourth,the production simulation result of the case well shows that the self-diffusion flow and heat coupling model can predict the production of deep shale gas more accurately if temperature field change is taken into consideration.In conclusion,the self-diffusion flow and heat coupling model established in this paper is of higher reliability and accuracy and can be used for productivity simulation and prediction of deep shale gas wells.The conclusion of this paper has certain guiding significance for deep shale gas production and gas well productivity prediction.
基金support from the following sources:the National Natural Science Foundation of China(NSFC)(Nos.52171206 and 52271209)the Key Project of Hebei Natural Science Foundation(Nos.F2024201031 and E2020201030)+1 种基金the Science Research Project of Hebei Education Department(No.JCZX2025019)the Interdisciplinary Research Program of Hebei University(No.DXK202401).
文摘Potassium metal is regarded as a promising anode material for potassium-ion batteries due to its high theoretical capacity and low redox potential.However,its performance is hindered by rapid capacity fading,primarily caused by an unstable solid electrolyte interphase(SEI)and continuous dendrite growth.Herein,by coating liquid metal(LM)alloy(GaInSn)onto copper foil,we prepared a special LM@Cu substrate,significantly improving the deposition/stripping behavior of potassium metal and thus achieving long-cycling K metal battery.The excellent potassiophilicity and electrolyte wettability of LM@Cu effectively reduce the K nucleation overpotential,promote charge transfer kinetics,and enable self-diffusive planar growth mode.Moreover,ex situ scanning electron microscopy and in situ optical microscopy analyses show that the LM coating induces uniform potassium deposition,reduces volume expansion,and achieves a dendrite-free K anode.Additionally,when 3,4,9,10-perylene-tetracarboxylic diimide(PTCDI)is employed as the cathode and K-LM@Cu(LMK)as the anode,the potassium metal battery demonstrates an initial reversible capacity of 124.4 mAh·g^(-1).Even after 4900 cycles at a current density of 500 mA·g^(-1),it maintains a high reversible capacity of 78.2 mAh·g^(-1).The self-diffusive planar growth mechanism enabled by liquid metal offers a promising approach for developing practical and durable potassium metal batteries.
文摘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.
文摘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,
基金Project supported by the National Natural Science Foundation of China.
文摘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.
