Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pi...Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pillar design. This work presents a dissipative particle dynamics(DPD) model to simulate a problem of flow across periodic arrays of circular micropillar and investigates the permeability of two types of micropillar arrays.The flow fields including horizontal and vertical velocity fields, the number density field,and the streamline of the flow are analyzed. The predicted solid volumes by the presented DPD simulation of both types of arrays are quite close to the actual counterparts. These quantitative agreements show usefulness and effectiveness of the DPD model in simulating arrays of micropillar. By comparing two types of micropillar arrangement patterns, we find that the arrangement pattern of micropillar does not have significant influence on the permeability of the array.展开更多
We calculate current correlation functions(CCFs) of dissipative particle dynamics(DPD) and compare them with results of molecular dynamics(MD) and solutions of linearized hydrodynamic equations. In particular, we cons...We calculate current correlation functions(CCFs) of dissipative particle dynamics(DPD) and compare them with results of molecular dynamics(MD) and solutions of linearized hydrodynamic equations. In particular, we consider three versions of DPD,the empirical/classical DPD, coarse-grained(CG) DPD with radial-direction interactions only and full(radial, transversal, and rotational) interactions between particles. To facilitate quantitative discussions, we consider specifically a star-polymer melt system at a moderate density. For bonded molecules, it is straightforward to define the CG variables and to further derive CG force fields for DPD within the framework of the Mori-Zwanzig formalism. For both transversal and longitudinal current correlation functions(TCCFs and LCCFs), we observe that results of MD, DPD, and hydrodynamic solutions agree with each other at the continuum limit. Below the continuum limit to certain length scales, results of MD deviate significantly from hydrodynamic solutions, whereas results of both empirical and CG DPD resemble those of MD. This indicates that the DPD method with Markovian force laws possibly has a larger applicability than the continuum description of a Newtonian fluid. This is worth being explored further to represent generalized hydrodynamics.展开更多
The implementation of solid-fluid boundary condition has been a major challenge for dissipative particle dynamics(DPD)method.Current implementations of boundary conditions usually try to approach a uniform density dis...The implementation of solid-fluid boundary condition has been a major challenge for dissipative particle dynamics(DPD)method.Current implementations of boundary conditions usually try to approach a uniform density distribution and a velocity profile close to analytical solution.The density oscillations and slip velocity are intentionally eliminated,and different wall properties disappear in the same analytical solution.This paper develops a new wall model that combines image and frozen particles and a new strategy to emphasize different wall properties especially wettabilities.The strategy first studies the realistic wall-fluid system by molecular dynamics(MD)simulation depending on physical parameters.Then,a DPD simulation is used to match the density and velocity profiles with the new wall model.The obtained DPD parameters can simulate the systems with the same wall and fluid materials.With this method,a simulation of the Poiseuille flow of liquid argon with copper walls is presented.Other walls with super-hydrophilic,hydrophilic,and hydrophobic wettabilities are also simulated.The limitations of the analytical solution and the effect of the wall-fluid interaction are discussed.The results show that the method suggested in this paper can simulate the mesoscale behavior of the microchannel flow related to realistic systems.展开更多
Metal-enriched minerals have been widely observed near hydrothermal vent fields.However,the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained.Here,radioactive 234Th in both dis...Metal-enriched minerals have been widely observed near hydrothermal vent fields.However,the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained.Here,radioactive 234Th in both dissolved and particulate phases were used to examine the kinetics of particle-reactive metal adsorption,removal,and residence in a newly found hydrothermal plume over the Southwest Indian Ridge.The results showed a relatively low value on ^(234)Th/^(238)U ratios(i.e.,0.73-0.88)compared to the deep oceans,indicating an enhanced adsorption of particle-reactive metals onto particulate matter in the plume.Based on the 234Th-238U disequilibria,the adsorption and sinking rate constants of 234Th averaged(0.009±0.001)d^(-1) and(0.113±0.024)d^(-1) in the hydrothermal plume,corresponding to the residence times of(115±19)d and(16±5)d for dissolved and particulate 234Th,respectively.This timescale allows vent-discharged particle-reactive metals to disperse hundreds to thousands of miles away.Thus,hydrothermal activities might influence the metal distribution in deep ocean over a very large scope.Also,a high sinking flux of(36.2±5.4)B q/(m^(2)·d)for 234Th was observed for the plume,suggesting an enrichment of metal in particles deposited close to the vent.The enhancement of particle sinking could also benefit the transport of organic carbon and nitrogen and fuel the benthic ecosystems under the plume regimes.Thus,hydrothermal plumes may have an impact on both the elemental geochemistry and/or ecosystem to the deep oceans interior than previous expectation.展开更多
Heat and mass transfer during the process of liquid droplet dynamic behaviors has attracted much attention in decades.At mesoscopic scale,numerical simulations of liquid droplets motion,such as impacting,sliding,and c...Heat and mass transfer during the process of liquid droplet dynamic behaviors has attracted much attention in decades.At mesoscopic scale,numerical simulations of liquid droplets motion,such as impacting,sliding,and coalescence,have been widely studied by using the particle-based method named many-body dissipative particle dynamics(MDPD).However,the detailed information on heat transfer needs further description.This paper develops a modified MDPD with energy conservation(MDPDE)by introducing a temperature-dependent long-term attractive interaction.By fitting or deriving the expressions of the strength of the attractive force,the exponent of the weight function in the dissipative force,and the mesoscopic heat friction coefficient about temperature,we calculate the viscosity,self-diffusivity,thermal conductivity,and surface tension,and obtain the Schmidt number Sc,the Prandtl number P r,and the Ohnesorge number Oh for 273 K to 373 K.The simulation data of MDPDE coincide well with the experimental data of water,indicating that our model can be used to simulate the dynamic behaviors of liquid water.Furthermore,we compare the equilibrium contact angle of droplets wetting on solid surfaces with that calculated from three interfacial tensions by MDPDE simulations.The coincident results not only stand for the validation of Young’s equation at mesoscale,but manifest the reliability of our MDPDE model and applicability to the cases with free surfaces.Our model can be extended to study the multiphase flow withcomplex heat and mass transfer.展开更多
We investigate the behavior of dissipative particle dynamics(DPD) within different scaling regimes by numerical simulations. The paper extends earlier analytical findings of Ripoll, M., Ernst, M. H., and Espa?nol, P.(...We investigate the behavior of dissipative particle dynamics(DPD) within different scaling regimes by numerical simulations. The paper extends earlier analytical findings of Ripoll, M., Ernst, M. H., and Espa?nol, P.(Large scale and mesoscopic hydrodynamics for dissipative particle dynamics. Journal of Chemical Physics, 115(15),7271–7281(2001)) by evaluation of numerical data for the particle and collective scaling regimes and the four different subregimes. DPD simulations are performed for a range of dynamic overlapping parameters. Based on analyses of the current auto-correlation functions(CACFs), we demonstrate that within the particle regime at scales smaller than its force cut-off radius, DPD follows Langevin dynamics. For the collective regime,we show that the small-scale behavior of DPD differs from Langevin dynamics. For the wavenumber-dependent effective shear viscosity, universal scaling regimes are observed in the microscopic and mesoscopic wavenumber ranges over the considered range of dynamic overlapping parameters.展开更多
Smoothed dissipative particle dynamics(SDPD) is a mesoscopic particle method that allows to select the level of resolution at which a fluid is simulated. The numerical integration of its equations of motion still suff...Smoothed dissipative particle dynamics(SDPD) is a mesoscopic particle method that allows to select the level of resolution at which a fluid is simulated. The numerical integration of its equations of motion still suffers from the lack of numerical schemes satisfying all the desired properties such as energy conservation and stability.Similarities between SDPD and dissipative particle dynamics with energy(DPDE) conservation, which is another coarse-grained model, enable adaptation of recent numerical schemes developed for DPDE to the SDPD setting. In this article, a Metropolis step in the integration of the fluctuation/dissipation part of SDPD is introduced to improve its stability.展开更多
Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that t...Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that the distribution of^(210)Po and^(210)Po/^(210)Pb activity ratio in the upper water is mainly affected by biological absorption or particle adsorption.An abnormal excess of^(210)Po relative to^(210)Pb was observed in the surface water at stations P1-2 and P2-2,which is likely to be the horizontal transport of water mass with high DPo/DPb)_(A.R.)and TPo/TPb)_(A.R.).In this study,the removal of particulate^(210)Po is mainly controlled by the scavenging of dissolved^(210)Po and the two have a linear positive correlation with the salinity,a negative linear correlation with the content of dissolved oxygen and a reciprocal relationship with the content of POC.The export flux of POC at 100 m is estimated to be 1.8-4.4 mmol·m^(−2)·d^(−1)(avg.2.9 mmol·m^(−2)·d^(−1))based on^(210)Po/^(210)Pb disequilibria,with the highest value in the shelf,which is consistent with the distribution of biological productivity.展开更多
A simulation study was carried out by using dissipative particle dynamics(DPD) method to explore the effects of properties of coating chains, such as length, density, rigidity of polymer chains, as well as the distanc...A simulation study was carried out by using dissipative particle dynamics(DPD) method to explore the effects of properties of coating chains, such as length, density, rigidity of polymer chains, as well as the distance between nanoparticles on bonding reaction of coating chains grafted onto nanoparticles. The results show that bonding ratios of coated chains strongly depend on the length and density of coating chains. For nanoparticles with different coating densities, the optimum chain length for bonding reaction are varied. The rigidity of coating chains exhibits vigorous effects on bonding reaction that highly depends on chain lengths. DPD simulation can be used to study the bonding reaction between coated nanoparticles, which may help experimental synthesis of nanocomposites with excellent properties.展开更多
Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors.We investigate the ultrafast quasiparticle(QP)dynamics of an inte...Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors.We investigate the ultrafast quasiparticle(QP)dynamics of an intercalated superconductor(Li1-xFex)OHFe1-ySe,which is a bulk crystal but shares a similar electronic structure with single-layer FeSe on SrTiO3.We obtain the electron-phonon coupling(EPC)constant(0.22±0.04),which well bridges that of bulk FeSe crystal and single-layer FeSe on SrTiO3.Significantly,we find that such a positive correlation betweenλA1 g and superconducting Tc holds among all known FeSe-based superconductors,even in line with reported FeAs-based superconductors.Our observation indicates possible universal role of EPC in the superconductivity of all known categories of iron-based superconductors,which is a critical step towards achieving a unified superconducting mechanism for all iron-based superconductors.展开更多
The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequencing has shown a broad application prospect and attracted vast re...The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequencing has shown a broad application prospect and attracted vast research interests since it was proposed. In the present study, the dynamics of the electric-driven translocation of a homopolymer through a nanopore is investigated by the dissipative particle dynamics(DPD), in which the homopolymer is modeled as a worm-like chain(WLC). The DPD simulations show that the polymer chain undergoes conformation changes during the translocation process. The different structures of the polymer in the translocation process, i.e., single-file, double folded, and partially folded, and the induced current blockades are analyzed. It is found that the current blockades have different magnitudes due to the polymer molecules traversing the pore with different folding conformations. The nanoscale vortices caused by the concentration polarization layers(CPLs) in the vicinity of the sheet are also studied. The results indicate that the translocation of the polymer has the effect of eliminating the vortices in the polyelectrolyte solution. These findings are expected to provide the theoretical guide for improving the nanopore sequencing technique.展开更多
To clarify the preparation mechanisms of uorinated ordered mesoporous carbon materials (FOMCs), the dissipative par- ticle dynamics method was used to simulate the self-assembly process of the amphiphilic triblock pol...To clarify the preparation mechanisms of uorinated ordered mesoporous carbon materials (FOMCs), the dissipative par- ticle dynamics method was used to simulate the self-assembly process of the amphiphilic triblock poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide) copolymer Pluronic F127 in the aqueous system. The self-assembly mechanisms in aqueous phase and the formation mechanisms of micropores and mesopores were investigated. It was found that the mesoporous structure of the FOMCs was formed by the hydrophobic segments of F127, while the pore wall was formed by both the hydrophilic segments and the carbon precursor in the system. The microporous structure on the pore wall was con- structed by the carbon source in the hydrophilic segments’ spaces after the template was removed. Our ndings could provide understanding and knowledge for the synthesis of mesoporous carbon by the self-assembly method on the mesoscopic scale.展开更多
A two-dimensional non-selfsimilar initial value problem for adhesion particle dynamics with two pieces of constant states separated by a circular ring is considered. By using the generalized characteristic method and ...A two-dimensional non-selfsimilar initial value problem for adhesion particle dynamics with two pieces of constant states separated by a circular ring is considered. By using the generalized characteristic method and the generalized Rankine-Hugoniot relation,which is a system of ordinary equations,the global solution which includes delta-shock waves and vacuum is constructed.展开更多
The phase behaviours of a lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics.We consider a wide range of nanorod concentrations,where the nanorods each...The phase behaviours of a lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics.We consider a wide range of nanorod concentrations,where the nanorods each have a preferential affinity to one of the blocks.Our results suggest that shear not only aligns the orientations of the diblock copolymer templates and nanorods towards flow direction,but also regulates the distribution of the nanorods within the polymer matrix.Meanwhile,the shear-induced reorientation and morphology transitions of the systems also significantly depend on the nanorod concentration.At certain nanorod concentrations,the competitions between shearinduced polymer thinning and nanorods dispersion behaviours determine the phase behaviours of the composites.For high nanorod concentrations,no morphology transition is observed,but reorientation is present,in which the sheared nanorods are arranged into hexagonal packing arrays.Additionally,the orientation behaviour of nanorods is determined directly by the applied shear,also interfered with by the shear-stretched copolymer molecules.展开更多
The Van Allen radiation belts consist of megaelectron volt particles trapped in the Earth’s magnetic field mainly with protons at low altitude</span></span><span style="font-family:Verdana;"&...The Van Allen radiation belts consist of megaelectron volt particles trapped in the Earth’s magnetic field mainly with protons at low altitude</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> and electrons at high altitude</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. These concentric, donut-shaped radiation belts are constantly changing due to a variety of physical processes caused by specific types of heliospheric structure. The radiation poses risks for astronauts and spacecraft systems. The understanding of these processes that operate across the universe can help with designs of future space missions as well as the understanding of the universe. The data gathered from the last three months of the Radiation Belt Storm Probes mission (RBSP mission) is examined for patterns and trends in the dynamics of the radiation belts and their relationships with solar activities. From the data, it is shown that the patterns of the high-energy particle dynamics in the belts follow the changes in solar activity. When the Sun’s magnetic field weakens, cosmic rays from deep space are able to carry an increased flux of energetic particles into the solar system. The outer belt exhibits a pattern of electron energization during cycles lasting an average of 27 days, corresponding to the time taken for one solar rotation. The sudden outward shift of the belts on July 19th, 2019 was most likely caused by the shutdown of one of the two Van Allen probes, as the relative position of the probe to the belts changed. Two solar wind streams that arrived from August 27th to the 28th caused the “dropout” event on August 28th, as the contact between the solar wind streams and magnetosphere pushed the magnetosphere’s boundary and enabled the particles outside the shifted boundary to escape into space. A positive polarity coronal hole high speed stream (CH HSS) contributed to the intense September electron re-energization process in the radiation belts starting on September 1st.展开更多
Objective:In this study,we try to establish an initial electron beam model by combining Monte Carlo simulation method with particle dynamic calculation(TRSV)for the single 6 MV X-ray accelerating waveguide of BJ-6 med...Objective:In this study,we try to establish an initial electron beam model by combining Monte Carlo simulation method with particle dynamic calculation(TRSV)for the single 6 MV X-ray accelerating waveguide of BJ-6 medical linac.Methods and Materials:1.We adapted the treatment head configuration of BJ-6 medical linac made by Beijing Medical Equipment Institute(BMEI)as the radiation system for this study.2.Use particle dynamics calculation code called TRSV to drive out the initial electron beam parameters of the energy spectrum,the spatial intensity distribution,and the beam incidence angle.3.Analyze the 6 MV X-ray beam characteristics of PDDc,OARc in a water phantom by using Monte Carlo simulation(BEAMnrc,DOSXYZnrc)for a preset of the initial electron beam parameters which have been determined by TRSV,do the comparisons of the measured results of PDDm,OARm in a real water phantom,and then use the deviations of calculated and measured results to slightly modify the initial electron beam model back and forth until the deviations meet the error less than 2%.Results:The deviations between the Monte Carlo simulation results of percentage depth doses at PDDc and off-axis ratios OARc and the measured results of PDDm and OARm in a water phantom were within 2%.Conclusion:When doing the Monte Carlo simulation to determine the parameters of an initial electron beam for a particular medical linac like BJ-6,modifying some parameters based on the particle dynamics calculation code would give some more reasonable and more acceptable results.展开更多
We derive an effective Hamiltonian for a spin-1/2 particle confined within a curved thin layer with non-uniform thickness using the confining potential approach.Our analysis reveals the presence of a pseudo-magnetic f...We derive an effective Hamiltonian for a spin-1/2 particle confined within a curved thin layer with non-uniform thickness using the confining potential approach.Our analysis reveals the presence of a pseudo-magnetic field and effective spin–orbit interaction(SOI)arising from the curvature,as well as an effective scalar potential resulting from variations in thickness.Importantly,we demonstrate that the physical effect of additional SOI from thickness fluctuations vanishes in low-dimensional systems,thus guaranteeing the robustness of spin interference measurements to thickness imperfection.Furthermore,we establish the applicability of the effective Hamiltonian in both symmetric and asymmetric confinement scenarios,which is crucial for its utilization in one-side etching systems.展开更多
Improving the energy conversion efficiency in metallic fuel(e.g.,Al)combustion is always desirable but challenging,which often involves redox reactions of aluminum(Al)with various mixed oxidizing environments.For inst...Improving the energy conversion efficiency in metallic fuel(e.g.,Al)combustion is always desirable but challenging,which often involves redox reactions of aluminum(Al)with various mixed oxidizing environments.For instance,Al-O reaction is the most common pathway to release limited energy while Al-F reaction has received much attentions to enhance Al combustion efficiency.However,microscopic understanding of the Al-O/Al-F reaction dynamics remains unsolved,which is fundamentally necessary to further improve Al combustion efficiency.In this work,for the first time,Al-O/Al-F reaction dynamic effects on the combustion of aluminum nanoparticles(n-Al)in oxygen/fluorine containing environments have been revealed via reactive molecular dynamics(RMD)simulations meshing together combustion experiments.Three RMD simulation systems of Al core/O_(2)/HF,n-Al/O_(2)/HF,and n-Al/O_(2)/CF4 with oxygen percentage ranging from 0%to 100%have been performed.The n-Al combustion in mixed O_(2)/CF_4 environments have been conducted by constant volume combustion experiments.RMD results show that Al-O reaction exhibits kinetic benefits while Al-F reaction owns thermodynamic benefits for n-Al combustion.In n-Al/O_(2)/HF,Al-O reaction gives faster energy release rate than Al-F reaction(1.1 times).The optimal energy release efficiency can be achieved with suitable oxygen percentage of 10%and 50%for n-Al/O_(2)/HF and n-Al/O_(2)/CF_4,respectively.In combustion experiments,90%of oxygen percentage can optimally enhance the peak pressure,pressurization rate and combustion heat.Importantly,Al-O reaction prefers to occur on the surface regions while Al-F reaction prefers to proceed in the interior regions of n-Al,confirming the kinetic/thermodynamic benefits of Al-O/Al-F reactions.The synergistic effect of Al-O/Al-F reaction for greatly enhancing n-Al combustion efficiency is demonstrated at atomicscale,which is beneficial for optimizing the combustion performance of metallic fuel.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.31370953,10942004,and 91230203)
文摘Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pillar design. This work presents a dissipative particle dynamics(DPD) model to simulate a problem of flow across periodic arrays of circular micropillar and investigates the permeability of two types of micropillar arrays.The flow fields including horizontal and vertical velocity fields, the number density field,and the streamline of the flow are analyzed. The predicted solid volumes by the presented DPD simulation of both types of arrays are quite close to the actual counterparts. These quantitative agreements show usefulness and effectiveness of the DPD model in simulating arrays of micropillar. By comparing two types of micropillar arrangement patterns, we find that the arrangement pattern of micropillar does not have significant influence on the permeability of the array.
基金funding support of the U.S.Army Research Laboratory with Cooperative Agreement No.W911NF-12-2-0023
文摘We calculate current correlation functions(CCFs) of dissipative particle dynamics(DPD) and compare them with results of molecular dynamics(MD) and solutions of linearized hydrodynamic equations. In particular, we consider three versions of DPD,the empirical/classical DPD, coarse-grained(CG) DPD with radial-direction interactions only and full(radial, transversal, and rotational) interactions between particles. To facilitate quantitative discussions, we consider specifically a star-polymer melt system at a moderate density. For bonded molecules, it is straightforward to define the CG variables and to further derive CG force fields for DPD within the framework of the Mori-Zwanzig formalism. For both transversal and longitudinal current correlation functions(TCCFs and LCCFs), we observe that results of MD, DPD, and hydrodynamic solutions agree with each other at the continuum limit. Below the continuum limit to certain length scales, results of MD deviate significantly from hydrodynamic solutions, whereas results of both empirical and CG DPD resemble those of MD. This indicates that the DPD method with Markovian force laws possibly has a larger applicability than the continuum description of a Newtonian fluid. This is worth being explored further to represent generalized hydrodynamics.
文摘The implementation of solid-fluid boundary condition has been a major challenge for dissipative particle dynamics(DPD)method.Current implementations of boundary conditions usually try to approach a uniform density distribution and a velocity profile close to analytical solution.The density oscillations and slip velocity are intentionally eliminated,and different wall properties disappear in the same analytical solution.This paper develops a new wall model that combines image and frozen particles and a new strategy to emphasize different wall properties especially wettabilities.The strategy first studies the realistic wall-fluid system by molecular dynamics(MD)simulation depending on physical parameters.Then,a DPD simulation is used to match the density and velocity profiles with the new wall model.The obtained DPD parameters can simulate the systems with the same wall and fluid materials.With this method,a simulation of the Poiseuille flow of liquid argon with copper walls is presented.Other walls with super-hydrophilic,hydrophilic,and hydrophobic wettabilities are also simulated.The limitations of the analytical solution and the effect of the wall-fluid interaction are discussed.The results show that the method suggested in this paper can simulate the mesoscale behavior of the microchannel flow related to realistic systems.
基金The National Natural Science Foundation of China under contract Nos 41721005,41476061China Ocean Mineral Resources R&D Association Programs under contract Nos DY135-E2-2-03,DY125-22-QY-17the Fundamental Research Funds for the Central Universities under contract No.20720190102。
文摘Metal-enriched minerals have been widely observed near hydrothermal vent fields.However,the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained.Here,radioactive 234Th in both dissolved and particulate phases were used to examine the kinetics of particle-reactive metal adsorption,removal,and residence in a newly found hydrothermal plume over the Southwest Indian Ridge.The results showed a relatively low value on ^(234)Th/^(238)U ratios(i.e.,0.73-0.88)compared to the deep oceans,indicating an enhanced adsorption of particle-reactive metals onto particulate matter in the plume.Based on the 234Th-238U disequilibria,the adsorption and sinking rate constants of 234Th averaged(0.009±0.001)d^(-1) and(0.113±0.024)d^(-1) in the hydrothermal plume,corresponding to the residence times of(115±19)d and(16±5)d for dissolved and particulate 234Th,respectively.This timescale allows vent-discharged particle-reactive metals to disperse hundreds to thousands of miles away.Thus,hydrothermal activities might influence the metal distribution in deep ocean over a very large scope.Also,a high sinking flux of(36.2±5.4)B q/(m^(2)·d)for 234Th was observed for the plume,suggesting an enrichment of metal in particles deposited close to the vent.The enhancement of particle sinking could also benefit the transport of organic carbon and nitrogen and fuel the benthic ecosystems under the plume regimes.Thus,hydrothermal plumes may have an impact on both the elemental geochemistry and/or ecosystem to the deep oceans interior than previous expectation.
基金Project supported by the National Natural Science Foundation of China(Nos.11872283,12002242,11902188,and 12102218)the Shanghai Science and Technology Talent Program(No.19YF1417400)the China Postdoctoral Science Foundation(No.2020M680525)。
文摘Heat and mass transfer during the process of liquid droplet dynamic behaviors has attracted much attention in decades.At mesoscopic scale,numerical simulations of liquid droplets motion,such as impacting,sliding,and coalescence,have been widely studied by using the particle-based method named many-body dissipative particle dynamics(MDPD).However,the detailed information on heat transfer needs further description.This paper develops a modified MDPD with energy conservation(MDPDE)by introducing a temperature-dependent long-term attractive interaction.By fitting or deriving the expressions of the strength of the attractive force,the exponent of the weight function in the dissipative force,and the mesoscopic heat friction coefficient about temperature,we calculate the viscosity,self-diffusivity,thermal conductivity,and surface tension,and obtain the Schmidt number Sc,the Prandtl number P r,and the Ohnesorge number Oh for 273 K to 373 K.The simulation data of MDPDE coincide well with the experimental data of water,indicating that our model can be used to simulate the dynamic behaviors of liquid water.Furthermore,we compare the equilibrium contact angle of droplets wetting on solid surfaces with that calculated from three interfacial tensions by MDPDE simulations.The coincident results not only stand for the validation of Young’s equation at mesoscale,but manifest the reliability of our MDPDE model and applicability to the cases with free surfaces.Our model can be extended to study the multiphase flow withcomplex heat and mass transfer.
文摘We investigate the behavior of dissipative particle dynamics(DPD) within different scaling regimes by numerical simulations. The paper extends earlier analytical findings of Ripoll, M., Ernst, M. H., and Espa?nol, P.(Large scale and mesoscopic hydrodynamics for dissipative particle dynamics. Journal of Chemical Physics, 115(15),7271–7281(2001)) by evaluation of numerical data for the particle and collective scaling regimes and the four different subregimes. DPD simulations are performed for a range of dynamic overlapping parameters. Based on analyses of the current auto-correlation functions(CACFs), we demonstrate that within the particle regime at scales smaller than its force cut-off radius, DPD follows Langevin dynamics. For the collective regime,we show that the small-scale behavior of DPD differs from Langevin dynamics. For the wavenumber-dependent effective shear viscosity, universal scaling regimes are observed in the microscopic and mesoscopic wavenumber ranges over the considered range of dynamic overlapping parameters.
基金Project supported by the Agence Nationale de la Recherche(No.ANR-14-CE23-0012(COSMOS))the European Research Council under the European Union’s Seventh Framework Programme(FP/2007-2013)/ERC(No.614492)
文摘Smoothed dissipative particle dynamics(SDPD) is a mesoscopic particle method that allows to select the level of resolution at which a fluid is simulated. The numerical integration of its equations of motion still suffers from the lack of numerical schemes satisfying all the desired properties such as energy conservation and stability.Similarities between SDPD and dissipative particle dynamics with energy(DPDE) conservation, which is another coarse-grained model, enable adaptation of recent numerical schemes developed for DPDE to the SDPD setting. In this article, a Metropolis step in the integration of the fluctuation/dissipation part of SDPD is introduced to improve its stability.
基金financially supported by National Polar Special Program “Impact and Response of Antarctic Seas to Climate Change” (Grant nos. IRASCC 01-01-02C, 02-01-01)supported by National Natural Science Foundation of China (Grant no. 41721005)the program funded by China Ocean Mineral Resources R & D Association (Grant no. DY135-13-E2-03)。
文摘Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that the distribution of^(210)Po and^(210)Po/^(210)Pb activity ratio in the upper water is mainly affected by biological absorption or particle adsorption.An abnormal excess of^(210)Po relative to^(210)Pb was observed in the surface water at stations P1-2 and P2-2,which is likely to be the horizontal transport of water mass with high DPo/DPb)_(A.R.)and TPo/TPb)_(A.R.).In this study,the removal of particulate^(210)Po is mainly controlled by the scavenging of dissolved^(210)Po and the two have a linear positive correlation with the salinity,a negative linear correlation with the content of dissolved oxygen and a reciprocal relationship with the content of POC.The export flux of POC at 100 m is estimated to be 1.8-4.4 mmol·m^(−2)·d^(−1)(avg.2.9 mmol·m^(−2)·d^(−1))based on^(210)Po/^(210)Pb disequilibria,with the highest value in the shelf,which is consistent with the distribution of biological productivity.
基金Funded by the National Natural Science Foundation of China(Nos.20974001,21174001,51273001,and 51403001)
文摘A simulation study was carried out by using dissipative particle dynamics(DPD) method to explore the effects of properties of coating chains, such as length, density, rigidity of polymer chains, as well as the distance between nanoparticles on bonding reaction of coating chains grafted onto nanoparticles. The results show that bonding ratios of coated chains strongly depend on the length and density of coating chains. For nanoparticles with different coating densities, the optimum chain length for bonding reaction are varied. The rigidity of coating chains exhibits vigorous effects on bonding reaction that highly depends on chain lengths. DPD simulation can be used to study the bonding reaction between coated nanoparticles, which may help experimental synthesis of nanocomposites with excellent properties.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303603 and 2016YFA0300300)the National Natural Science Foundation of China(Grant Nos.11574383,11774408,and 11574370)+4 种基金the Frontier Program of the Chinese Academy of Sciences(Grant No.QYZDY-SSW-SLH001)the Strategic Priority Research Program of CAS(Grant No.XDB30000000)the Beijing Natural Science Foundation(Grant No.4191003)the International Partnership Program of Chinese Academy of Sciences(Grant No.GJHZ1826)CAS Interdisciplinary Innovation Team。
文摘Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors.We investigate the ultrafast quasiparticle(QP)dynamics of an intercalated superconductor(Li1-xFex)OHFe1-ySe,which is a bulk crystal but shares a similar electronic structure with single-layer FeSe on SrTiO3.We obtain the electron-phonon coupling(EPC)constant(0.22±0.04),which well bridges that of bulk FeSe crystal and single-layer FeSe on SrTiO3.Significantly,we find that such a positive correlation betweenλA1 g and superconducting Tc holds among all known FeSe-based superconductors,even in line with reported FeAs-based superconductors.Our observation indicates possible universal role of EPC in the superconductivity of all known categories of iron-based superconductors,which is a critical step towards achieving a unified superconducting mechanism for all iron-based superconductors.
基金supported by the National Natural Science Foundation of China(Nos.11272197 and11372175)the Innovation Program of Shanghai Municipality Education Commission,China(No.14ZZ095)
文摘The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequencing has shown a broad application prospect and attracted vast research interests since it was proposed. In the present study, the dynamics of the electric-driven translocation of a homopolymer through a nanopore is investigated by the dissipative particle dynamics(DPD), in which the homopolymer is modeled as a worm-like chain(WLC). The DPD simulations show that the polymer chain undergoes conformation changes during the translocation process. The different structures of the polymer in the translocation process, i.e., single-file, double folded, and partially folded, and the induced current blockades are analyzed. It is found that the current blockades have different magnitudes due to the polymer molecules traversing the pore with different folding conformations. The nanoscale vortices caused by the concentration polarization layers(CPLs) in the vicinity of the sheet are also studied. The results indicate that the translocation of the polymer has the effect of eliminating the vortices in the polyelectrolyte solution. These findings are expected to provide the theoretical guide for improving the nanopore sequencing technique.
基金supported by the National Natural Science Foundation of China (No. 21104035)
文摘To clarify the preparation mechanisms of uorinated ordered mesoporous carbon materials (FOMCs), the dissipative par- ticle dynamics method was used to simulate the self-assembly process of the amphiphilic triblock poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide) copolymer Pluronic F127 in the aqueous system. The self-assembly mechanisms in aqueous phase and the formation mechanisms of micropores and mesopores were investigated. It was found that the mesoporous structure of the FOMCs was formed by the hydrophobic segments of F127, while the pore wall was formed by both the hydrophilic segments and the carbon precursor in the system. The microporous structure on the pore wall was con- structed by the carbon source in the hydrophilic segments’ spaces after the template was removed. Our ndings could provide understanding and knowledge for the synthesis of mesoporous carbon by the self-assembly method on the mesoscopic scale.
基金the National Natural Science Foundation of China(No.10671120)
文摘A two-dimensional non-selfsimilar initial value problem for adhesion particle dynamics with two pieces of constant states separated by a circular ring is considered. By using the generalized characteristic method and the generalized Rankine-Hugoniot relation,which is a system of ordinary equations,the global solution which includes delta-shock waves and vacuum is constructed.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 21074096 and 21104060)
文摘The phase behaviours of a lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics.We consider a wide range of nanorod concentrations,where the nanorods each have a preferential affinity to one of the blocks.Our results suggest that shear not only aligns the orientations of the diblock copolymer templates and nanorods towards flow direction,but also regulates the distribution of the nanorods within the polymer matrix.Meanwhile,the shear-induced reorientation and morphology transitions of the systems also significantly depend on the nanorod concentration.At certain nanorod concentrations,the competitions between shearinduced polymer thinning and nanorods dispersion behaviours determine the phase behaviours of the composites.For high nanorod concentrations,no morphology transition is observed,but reorientation is present,in which the sheared nanorods are arranged into hexagonal packing arrays.Additionally,the orientation behaviour of nanorods is determined directly by the applied shear,also interfered with by the shear-stretched copolymer molecules.
基金Project supported by the Shanghai Leading Academic Discipline Project(Grant No.S30109)the Research and Development Special Fundation of Excellent Young Teachers of Universities in Shanghai,the Developmental Foundation of Scientific Technology of Shanghai Universitythe Innovation Foundation of Shanghai University
文摘The Van Allen radiation belts consist of megaelectron volt particles trapped in the Earth’s magnetic field mainly with protons at low altitude</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> and electrons at high altitude</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. These concentric, donut-shaped radiation belts are constantly changing due to a variety of physical processes caused by specific types of heliospheric structure. The radiation poses risks for astronauts and spacecraft systems. The understanding of these processes that operate across the universe can help with designs of future space missions as well as the understanding of the universe. The data gathered from the last three months of the Radiation Belt Storm Probes mission (RBSP mission) is examined for patterns and trends in the dynamics of the radiation belts and their relationships with solar activities. From the data, it is shown that the patterns of the high-energy particle dynamics in the belts follow the changes in solar activity. When the Sun’s magnetic field weakens, cosmic rays from deep space are able to carry an increased flux of energetic particles into the solar system. The outer belt exhibits a pattern of electron energization during cycles lasting an average of 27 days, corresponding to the time taken for one solar rotation. The sudden outward shift of the belts on July 19th, 2019 was most likely caused by the shutdown of one of the two Van Allen probes, as the relative position of the probe to the belts changed. Two solar wind streams that arrived from August 27th to the 28th caused the “dropout” event on August 28th, as the contact between the solar wind streams and magnetosphere pushed the magnetosphere’s boundary and enabled the particles outside the shifted boundary to escape into space. A positive polarity coronal hole high speed stream (CH HSS) contributed to the intense September electron re-energization process in the radiation belts starting on September 1st.
文摘Objective:In this study,we try to establish an initial electron beam model by combining Monte Carlo simulation method with particle dynamic calculation(TRSV)for the single 6 MV X-ray accelerating waveguide of BJ-6 medical linac.Methods and Materials:1.We adapted the treatment head configuration of BJ-6 medical linac made by Beijing Medical Equipment Institute(BMEI)as the radiation system for this study.2.Use particle dynamics calculation code called TRSV to drive out the initial electron beam parameters of the energy spectrum,the spatial intensity distribution,and the beam incidence angle.3.Analyze the 6 MV X-ray beam characteristics of PDDc,OARc in a water phantom by using Monte Carlo simulation(BEAMnrc,DOSXYZnrc)for a preset of the initial electron beam parameters which have been determined by TRSV,do the comparisons of the measured results of PDDm,OARm in a real water phantom,and then use the deviations of calculated and measured results to slightly modify the initial electron beam model back and forth until the deviations meet the error less than 2%.Results:The deviations between the Monte Carlo simulation results of percentage depth doses at PDDc and off-axis ratios OARc and the measured results of PDDm and OARm in a water phantom were within 2%.Conclusion:When doing the Monte Carlo simulation to determine the parameters of an initial electron beam for a particular medical linac like BJ-6,modifying some parameters based on the particle dynamics calculation code would give some more reasonable and more acceptable results.
基金This work was supported in part by the National Natural Science Foundation of China(Grant No.12104239)National Natural Science Foundation of Jiangsu Province of China(Grant No.BK20210581)+2 种基金Nanjing University of Posts and Telecommunications Science Foundation(Grant Nos.NY221024 and NY221100)the Science and Technology Program of Guangxi,China(Grant No.2018AD19310)the Jiangxi Provincial Natural Science Foundation(Grant No.20224BAB211020).
文摘We derive an effective Hamiltonian for a spin-1/2 particle confined within a curved thin layer with non-uniform thickness using the confining potential approach.Our analysis reveals the presence of a pseudo-magnetic field and effective spin–orbit interaction(SOI)arising from the curvature,as well as an effective scalar potential resulting from variations in thickness.Importantly,we demonstrate that the physical effect of additional SOI from thickness fluctuations vanishes in low-dimensional systems,thus guaranteeing the robustness of spin interference measurements to thickness imperfection.Furthermore,we establish the applicability of the effective Hamiltonian in both symmetric and asymmetric confinement scenarios,which is crucial for its utilization in one-side etching systems.
基金support by the National Natural Science Foundation of China(NSFC,Grant Nos.12002324,12372341,12172342)。
文摘Improving the energy conversion efficiency in metallic fuel(e.g.,Al)combustion is always desirable but challenging,which often involves redox reactions of aluminum(Al)with various mixed oxidizing environments.For instance,Al-O reaction is the most common pathway to release limited energy while Al-F reaction has received much attentions to enhance Al combustion efficiency.However,microscopic understanding of the Al-O/Al-F reaction dynamics remains unsolved,which is fundamentally necessary to further improve Al combustion efficiency.In this work,for the first time,Al-O/Al-F reaction dynamic effects on the combustion of aluminum nanoparticles(n-Al)in oxygen/fluorine containing environments have been revealed via reactive molecular dynamics(RMD)simulations meshing together combustion experiments.Three RMD simulation systems of Al core/O_(2)/HF,n-Al/O_(2)/HF,and n-Al/O_(2)/CF4 with oxygen percentage ranging from 0%to 100%have been performed.The n-Al combustion in mixed O_(2)/CF_4 environments have been conducted by constant volume combustion experiments.RMD results show that Al-O reaction exhibits kinetic benefits while Al-F reaction owns thermodynamic benefits for n-Al combustion.In n-Al/O_(2)/HF,Al-O reaction gives faster energy release rate than Al-F reaction(1.1 times).The optimal energy release efficiency can be achieved with suitable oxygen percentage of 10%and 50%for n-Al/O_(2)/HF and n-Al/O_(2)/CF_4,respectively.In combustion experiments,90%of oxygen percentage can optimally enhance the peak pressure,pressurization rate and combustion heat.Importantly,Al-O reaction prefers to occur on the surface regions while Al-F reaction prefers to proceed in the interior regions of n-Al,confirming the kinetic/thermodynamic benefits of Al-O/Al-F reactions.The synergistic effect of Al-O/Al-F reaction for greatly enhancing n-Al combustion efficiency is demonstrated at atomicscale,which is beneficial for optimizing the combustion performance of metallic fuel.
