Lymph node targeting is a commonly used strategy for particulate vaccines,particularly for Pickering emulsions.However,extensive research on the internal delivery mechanisms of these emulsions,especially the complex i...Lymph node targeting is a commonly used strategy for particulate vaccines,particularly for Pickering emulsions.However,extensive research on the internal delivery mechanisms of these emulsions,especially the complex intercellular interactions of deformable Pickering emulsions,has been surprisingly sparse.This gap in knowledge holds significant potential for enhancing vaccine efficacy.This study aims to address this by summarizing the process of lymph-node-targeting transport and introducing a dissipative particle dynamics simulation method to evaluate the dynamic processes within cell tissue.The transport of Pickering emulsions in skeletal muscle tissue is specifically investigated as a case study.Various factors impacting the transport process are explored,including local cellular tissue environmental factors and the properties of the Pickering emulsion itself.The simulation results primarily demonstrate that an increase in radial repulsive interaction between emulsion particles can decrease the transport efficiency.Additionally,larger intercellular gaps also diminish the transport efficiency of emulsion droplet particles due to the increased motion complexity within the intricate transport space compared to a single channel.This study sheds light on the nuanced interplay between engineered and biological systems influencing the transport dynamics of Pickering emulsions.Such insights hold valuable potential for optimizing transport processes in practical biomedical applications such as drug delivery.Importantly,the desired transport efficiency varies depending on the specific application.For instance,while a more rapid transport might be crucial for lymph-node-targeted drug delivery,certain applications requiring a slower release of active components could benefit from the reduced transport efficiency observed with increased particle repulsion or larger intercellular gaps.展开更多
The breakage of brittle particulate materials into smaller particles under compressive or impact loads can be modelled as an instantiation of the population balance integro-differential equation.In this paper,the emer...The breakage of brittle particulate materials into smaller particles under compressive or impact loads can be modelled as an instantiation of the population balance integro-differential equation.In this paper,the emerging computational science paradigm of physics-informed neural networks is studied for the first time for solving both linear and nonlinear variants of the governing dynamics.Unlike conventional methods,the proposed neural network provides rapid simulations of arbitrarily high resolution in particle size,predicting values on arbitrarily fine grids without the need for model retraining.The network is assigned a simple multi-head architecture tailored to uphold monotonicity of the modelled cumulative distribution function over particle sizes.The method is theoretically analyzed and validated against analytical results before being applied to real-world data of a batch grinding mill.The agreement between laboratory data and numerical simulation encourages the use of physics-informed neural nets for optimal planning and control of industrial comminution processes.展开更多
Although phase separation is a ubiquitous phenomenon, the interactions between multiple components make it difficult to accurately model and predict. In recent years, machine learning has been widely used in physics s...Although phase separation is a ubiquitous phenomenon, the interactions between multiple components make it difficult to accurately model and predict. In recent years, machine learning has been widely used in physics simulations. Here,we present a physical information-enhanced graph neural network(PIENet) to simulate and predict the evolution of phase separation. The accuracy of our model in predicting particle positions is improved by 40.3% and 51.77% compared with CNN and SVM respectively. Moreover, we design an order parameter based on local density to measure the evolution of phase separation and analyze the systematic changes with different repulsion coefficients and different Schmidt numbers.The results demonstrate that our model can achieve long-term accurate predictions of order parameters without requiring complex handcrafted features. These results prove that graph neural networks can become new tools and methods for predicting the structure and properties of complex physical systems.展开更多
A three-dimensional model for gas-solid flow in a circulating fluidized bed(CFB) riser was developed based on computational particle fluid dynamics(CPFD).The model was used to simulate the gas-solid flow behavior ...A three-dimensional model for gas-solid flow in a circulating fluidized bed(CFB) riser was developed based on computational particle fluid dynamics(CPFD).The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport(DPT) regime and a fast fluidization(FF) regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.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
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
^(231)Pa and ^(230)Th are two crucial isotopes in the ongoing GEOTRACES Project.However,the controversy on ^(231)Pa/^(230)Th proxy pertaining to archiving ocean circulation or recording paleoproductivity,is still unre...^(231)Pa and ^(230)Th are two crucial isotopes in the ongoing GEOTRACES Project.However,the controversy on ^(231)Pa/^(230)Th proxy pertaining to archiving ocean circulation or recording paleoproductivity,is still unresolved,partly owing to the unclear understanding of fractionation between ^(231)Pa and ^(230)Th during adsorption.In this study,controlled experiments were conducted to examine the adsorption of ^(234)Th and ^(233)Pa onto biogenic particles(SiO_(2) and CaCO_(3)),authigenic minerals(MnO_(2) and Fe_(2)O_(3)),and lithogenic minerals(kaolinite,attapulgite,montmorillonite,and aluminum oxyhydroxides),and the role of organic compounds in regulating the adsorption of ^(234)Th and ^(233)Pa in natural seawater was evaluated.The distribution coefficients(K d,presented as logK_(d))varied from 3.56 to 6.05 and from 3.27 to 5.82 for ^(234)Th and ^(233)Pa,respectively.Fe_(2)O_(3) is the strongest sorbent for both ^(234)Th and ^(233)Pa.Most of the particles showed comparable logK_(d) values for either ^(234)Th(~4.8)or ^(233)Pa(~3.9)in the presence of dextran,indicating that the adsorption of Th and Pa is likely controlled by organic coating on particle surfaces.The fractionation factors(F Th/Pa)of SiO_(2)(3±1)and CaCO_(3)(33±1)suggest in situ observed preferential scavenging of ^(230)Th to ^(231)Pa in the surface water of low-to mid-latitude regions and the nearly equal removal in the Antarctic Ocean where biogenic silica dominates the particle regime.The F Th/Pa values of the lithogenic and biogenic particles indicate that ^(230)Th is scavenged prior to ^(231)Pa in the particle-scarce ocean interior.The equal scavenging of ^(230)Th and ^(231)Pa at the ocean margins and the ridge crests is dominated by high particle fl uxes instead of particle composition control.These results imply that ^(230)Th/^(231)Pa can be used as different proxies in different oceanic settings.展开更多
Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry (PIV) and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred...Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry (PIV) and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics (CFD), using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.展开更多
The hydrodynamics and mixing during the nonaxisymmetry impingement of a micro-droplet and a sessile droplet of the same fluid are investigated by many-body dissipative particle dynamics(MDPD) simulation.In this work,t...The hydrodynamics and mixing during the nonaxisymmetry impingement of a micro-droplet and a sessile droplet of the same fluid are investigated by many-body dissipative particle dynamics(MDPD) simulation.In this work,the range of the impingement angle(θ_(i)) between the impinging droplet and the sessile droplet is 0°-60° and the contact angle is set as 45° or 124°.The droplets impingement and mixing behavior is analyzed based on the droplet internal flow field,the concentration distribution and the time scale of the decay of the kinetic energy of the impinging droplet.The dimensionless total mixing time(τ_(m)) is calculated by a modified mixing function.With the Weber number(We) ranging from 5.65 to22.7 and the Ohnesorge number(Oh) ranging from 0.136 to 0.214,we find rm hardly changes with We and Oh.Whereas,θ_(i)and surface wettability are found to have a significant effect on τ_(m).We find that θ_(i)has no clear effect on τ_(m)on a hydrophobic surface,while on the hydrophilic surface,τ_(m)increase with the θ_(i).Thus,reducing the impinging angle is a valid method to shorten the τ_(m).展开更多
We calculate current correlation functions (CCFs) of dissipative particle dy- namics (DPD) and compare them with results of molecular dynamics (MD) and solutions of linearized hydrodynamic equations. In particul...We calculate current correlation functions (CCFs) of dissipative particle dy- namics (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 fa- cilitate 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 gen- eralized 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
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 ea...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 eopolymer 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
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
The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequenc- ing has shown a broad application prospect and attracted vast ...The DNA sequencing technology has achieved a leapfrog development in recent years. As a new generation of the DNA sequencing technology, nanopore sequenc- ing 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 dynam- ics (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 block- ades 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 tech- nique.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 Espafiol, ...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 Espafiol, P. (Large scale and mesoscopic hy- drodynamics 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
Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and sy...Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration (RMSGR) and end-end distance (RMSED) increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.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
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 s...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) con- servation, 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
Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace ...Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.展开更多
基金supported by the National Natural Science Foundation of China(22373104 and 22293024)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(21821005)+1 种基金supported by the National Key Research and Development Program of China(2021YFE020527)support by the Distinguished Young Scholars of the National Natural Science Foundation of China(T2222022).
文摘Lymph node targeting is a commonly used strategy for particulate vaccines,particularly for Pickering emulsions.However,extensive research on the internal delivery mechanisms of these emulsions,especially the complex intercellular interactions of deformable Pickering emulsions,has been surprisingly sparse.This gap in knowledge holds significant potential for enhancing vaccine efficacy.This study aims to address this by summarizing the process of lymph-node-targeting transport and introducing a dissipative particle dynamics simulation method to evaluate the dynamic processes within cell tissue.The transport of Pickering emulsions in skeletal muscle tissue is specifically investigated as a case study.Various factors impacting the transport process are explored,including local cellular tissue environmental factors and the properties of the Pickering emulsion itself.The simulation results primarily demonstrate that an increase in radial repulsive interaction between emulsion particles can decrease the transport efficiency.Additionally,larger intercellular gaps also diminish the transport efficiency of emulsion droplet particles due to the increased motion complexity within the intricate transport space compared to a single channel.This study sheds light on the nuanced interplay between engineered and biological systems influencing the transport dynamics of Pickering emulsions.Such insights hold valuable potential for optimizing transport processes in practical biomedical applications such as drug delivery.Importantly,the desired transport efficiency varies depending on the specific application.For instance,while a more rapid transport might be crucial for lymph-node-targeted drug delivery,certain applications requiring a slower release of active components could benefit from the reduced transport efficiency observed with increased particle repulsion or larger intercellular gaps.
基金supported in part by the Ramanujan Fellowship from the Science and Engineering Research Board,Government of India(Grant No.RJF/2022/000115)。
文摘The breakage of brittle particulate materials into smaller particles under compressive or impact loads can be modelled as an instantiation of the population balance integro-differential equation.In this paper,the emerging computational science paradigm of physics-informed neural networks is studied for the first time for solving both linear and nonlinear variants of the governing dynamics.Unlike conventional methods,the proposed neural network provides rapid simulations of arbitrarily high resolution in particle size,predicting values on arbitrarily fine grids without the need for model retraining.The network is assigned a simple multi-head architecture tailored to uphold monotonicity of the modelled cumulative distribution function over particle sizes.The method is theoretically analyzed and validated against analytical results before being applied to real-world data of a batch grinding mill.The agreement between laboratory data and numerical simulation encourages the use of physics-informed neural nets for optimal planning and control of industrial comminution processes.
基金Project supported by the National Natural Science Foundation of China(Grant No.11702289)the Key Core Technology and Generic Technology Research and Development Project of Shanxi Province,China(Grant No.2020XXX013)。
文摘Although phase separation is a ubiquitous phenomenon, the interactions between multiple components make it difficult to accurately model and predict. In recent years, machine learning has been widely used in physics simulations. Here,we present a physical information-enhanced graph neural network(PIENet) to simulate and predict the evolution of phase separation. The accuracy of our model in predicting particle positions is improved by 40.3% and 51.77% compared with CNN and SVM respectively. Moreover, we design an order parameter based on local density to measure the evolution of phase separation and analyze the systematic changes with different repulsion coefficients and different Schmidt numbers.The results demonstrate that our model can achieve long-term accurate predictions of order parameters without requiring complex handcrafted features. These results prove that graph neural networks can become new tools and methods for predicting the structure and properties of complex physical systems.
基金support by the National Basic Research Program (Grant No. 2010CB226906,and 2012CB215000)
文摘A three-dimensional model for gas-solid flow in a circulating fluidized bed(CFB) riser was developed based on computational particle fluid dynamics(CPFD).The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport(DPT) regime and a fast fluidization(FF) regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.
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(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Supported by the National Natural Science Foundation of China(Nos.42076030,41476061)andNational Key Basic Research Special Foundation Program of China(No.2015CB452902)。
文摘^(231)Pa and ^(230)Th are two crucial isotopes in the ongoing GEOTRACES Project.However,the controversy on ^(231)Pa/^(230)Th proxy pertaining to archiving ocean circulation or recording paleoproductivity,is still unresolved,partly owing to the unclear understanding of fractionation between ^(231)Pa and ^(230)Th during adsorption.In this study,controlled experiments were conducted to examine the adsorption of ^(234)Th and ^(233)Pa onto biogenic particles(SiO_(2) and CaCO_(3)),authigenic minerals(MnO_(2) and Fe_(2)O_(3)),and lithogenic minerals(kaolinite,attapulgite,montmorillonite,and aluminum oxyhydroxides),and the role of organic compounds in regulating the adsorption of ^(234)Th and ^(233)Pa in natural seawater was evaluated.The distribution coefficients(K d,presented as logK_(d))varied from 3.56 to 6.05 and from 3.27 to 5.82 for ^(234)Th and ^(233)Pa,respectively.Fe_(2)O_(3) is the strongest sorbent for both ^(234)Th and ^(233)Pa.Most of the particles showed comparable logK_(d) values for either ^(234)Th(~4.8)or ^(233)Pa(~3.9)in the presence of dextran,indicating that the adsorption of Th and Pa is likely controlled by organic coating on particle surfaces.The fractionation factors(F Th/Pa)of SiO_(2)(3±1)and CaCO_(3)(33±1)suggest in situ observed preferential scavenging of ^(230)Th to ^(231)Pa in the surface water of low-to mid-latitude regions and the nearly equal removal in the Antarctic Ocean where biogenic silica dominates the particle regime.The F Th/Pa values of the lithogenic and biogenic particles indicate that ^(230)Th is scavenged prior to ^(231)Pa in the particle-scarce ocean interior.The equal scavenging of ^(230)Th and ^(231)Pa at the ocean margins and the ridge crests is dominated by high particle fl uxes instead of particle composition control.These results imply that ^(230)Th/^(231)Pa can be used as different proxies in different oceanic settings.
基金This project is supported by Provincial Science Technology Committee of Jiangsu China(No.BJ99025).
文摘Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry (PIV) and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics (CFD), using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.
基金financial support from National Natural Science Foundation of China(22078008,22178014)the Fundamental Research Funds for the Central Universities(XK1802-1)。
文摘The hydrodynamics and mixing during the nonaxisymmetry impingement of a micro-droplet and a sessile droplet of the same fluid are investigated by many-body dissipative particle dynamics(MDPD) simulation.In this work,the range of the impingement angle(θ_(i)) between the impinging droplet and the sessile droplet is 0°-60° and the contact angle is set as 45° or 124°.The droplets impingement and mixing behavior is analyzed based on the droplet internal flow field,the concentration distribution and the time scale of the decay of the kinetic energy of the impinging droplet.The dimensionless total mixing time(τ_(m)) is calculated by a modified mixing function.With the Weber number(We) ranging from 5.65 to22.7 and the Ohnesorge number(Oh) ranging from 0.136 to 0.214,we find rm hardly changes with We and Oh.Whereas,θ_(i)and surface wettability are found to have a significant effect on τ_(m).We find that θ_(i)has no clear effect on τ_(m)on a hydrophobic surface,while on the hydrophilic surface,τ_(m)increase with the θ_(i).Thus,reducing the impinging angle is a valid method to shorten the τ_(m).
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 dy- namics (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 fa- cilitate 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 gen- eralized 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 eopolymer 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.
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 sequenc- ing 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 dynam- ics (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 block- ades 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 tech- nique.
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 Espafiol, P. (Large scale and mesoscopic hy- drodynamics 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 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Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration (RMSGR) and end-end distance (RMSED) increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.
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) con- servation, 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supported by the National Outstanding Youth Science Fund Project (Grant No. 12125206)Basic Science Center for “Multiscale Problems in Nonlinear Mechanics”(Grant No. 11988102)+1 种基金General Project of National Natural Science Foundation of China (Grant No. 11972345)CAS Project for Young Scientists in Basic Research (Grant No. YSBR-096)。
文摘Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.