Separations of mixtures in fixed-bed adsorbers are influenced by factors such as(1)selectivity of adsorption,Sads,(2)diffusional time constants,Đi/rc 2,and(3)diffusion selectivity,Đ1/Đ2.In synergistic separations,intr...Separations of mixtures in fixed-bed adsorbers are influenced by factors such as(1)selectivity of adsorption,Sads,(2)diffusional time constants,Đi/rc 2,and(3)diffusion selectivity,Đ1/Đ2.In synergistic separations,intracrystalline diffusion of guest molecules serves to enhance the selectivities dictated by thermodynamics of mixture adsorption.In antisynergistic separations,intracrystalline diffusion serves to reverse the hierarchy of selectivities dictated by adsorption equilibrium.For both scenarios,the productivities of the desired product in fixed-bed operations are crucially dependent on diffusional time constants,Đi/rc 2;these need to be sufficiently low in order for diffusional influences to be effective.Also,the ratioĐ1/Đ2 should be large enough for manifestation of synergistic or antisynergistic influence.Both synergistic and antisynergistic separations have two common,distinguishing characteristics.Firstly,for transient uptake within crystals,the more mobile component attains supraequilibrium loadings during the initial stages of the transience.Such overshoots,signifying uphill diffusion,are engendered by the cross-coefficientsΓij(i≠j)of thermodynamic correction factors.Secondly,the component molar loadings,plotted in composition space,follow serpentine equilibration paths.If cross-coefficients are neglected,no overshoots in the loadings of the more mobile component are experienced,and the component loadings follow monotonous equilibration paths.The important takeaway message is that the modeling of mixture separations in fixed-bed adsorbers requires the use of the Maxwell−Stefan equations describing mixture diffusion employing chemical potential gradients as driving forces.展开更多
Transient liquid phase bonding of two dissimilar alloys Al 2024 and Ti?6Al?4V using Cu?22%Zn interlayer was carried out at 510 °C under vacuum of 0.01 Pa for various bonding time. In order to characterize the mic...Transient liquid phase bonding of two dissimilar alloys Al 2024 and Ti?6Al?4V using Cu?22%Zn interlayer was carried out at 510 °C under vacuum of 0.01 Pa for various bonding time. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied. The results show that joint formation is attributed to the solid-state diffusion of Cu and Zn into Ti?6Al?4V and Al 2024 alloys followed by eutectic formation and isothermal solidification along the Cu?Zn/Al 2024 interface. The hardness of the joints at the interface increases with an increase in bonding time which can be attributed to formation of intermetallic compounds such as Al2Cu, TiCu3, Al4.2Cu3.2Zn0.7, Al0.71Zn0.29, Ti2Cu, TiAl3 and TiZn16 in the joint zone. Moreover, shear strength of the joint reaches the highest value of 37 MPa at bonding time of 60 min.展开更多
We study the nonlinear coupled evolution equations which model the transient MHD natural convection and mass transfer flow of viscous, incompressible and electrically conducting fluid between two infinite vertical pla...We study the nonlinear coupled evolution equations which model the transient MHD natural convection and mass transfer flow of viscous, incompressible and electrically conducting fluid between two infinite vertical plates in the presence of the transversal magnetic field, thermal radiation, thermal diffusion and diffusion-thermo effects. Both analytical and numerical methods are used for this study.展开更多
This paper investigates the airflow patterns connected to different cough conditions, the effects of these arrangements on the regions of droplet fallout and dilution time of virus diffusion of coughed gas. We focus o...This paper investigates the airflow patterns connected to different cough conditions, the effects of these arrangements on the regions of droplet fallout and dilution time of virus diffusion of coughed gas. We focus on some of the physical processes that occur in a double bed hospital isolation room, investigating the effect of the ventilation system on the spread of particles in air. A cough model was carried out and used for the numerical simulation of virus diffusion inside an existent isolation room. Transient simulations of air pattern diffusion and air velocity field, provided by the existing typical HVAC primary air system designed for infectious patients, were performed using CFD. A multiphysics approach, combined Convection-Conduction, Incompressible Navier-Stokes models on non-isothermal air flow and Convection-Diffusion, was used. Simulations results highlighted that the flow field and velocity distribution induced by the high turbulence air inlet diffuser combined with the air return diffusers produce wide recirculation zones near the wall and partial stagnation areas near the ceiling and between the two beds, but lower particle concentration in the room and their shorter spreading distance. This type of analysis is certainly cost effective to identify all the air recirculation zones which can harbour lingering pathogens.展开更多
An analytical model was developed to describe Si？As alloy solidification in the whole range of measured interface velocity. It is demonstrated that at low interface velocity, the solidification occurs in the initial ...An analytical model was developed to describe Si？As alloy solidification in the whole range of measured interface velocity. It is demonstrated that at low interface velocity, the solidification occurs in the initial transient regime. The model leads to good comparison with the experimental data taking both local nonequilibrium effects at high interface velocity and steady state effects at low interface velocity into account. The local nonequilibrium diffusion effects shrink the initial transient period and lead to diffusionless solidification at high interface velocity.展开更多
We developed a transient model for actin-based motility.Diffusion of actin monomers was included in the formulation and its influence on the speed of actin-driven cargos was examined in detail.Our results clearly demo...We developed a transient model for actin-based motility.Diffusion of actin monomers was included in the formulation and its influence on the speed of actin-driven cargos was examined in detail.Our results clearly demonstrated how actin polymerization accelerates cargos that are initially stationary,as well as how steady-state is eventually reached.We also found that,due to polymerization and diffusion,actin monomer concentration near the load surface can be significantly lower than that in the rest of the comet tail,suggesting that many previous models may not be very accurate.展开更多
A localized space-time method of fundamental solutions(LSTMFS)is extended for solving three-dimensional transient diffusion problems in this paper.The interval segmentation in temporal direction is developed for the a...A localized space-time method of fundamental solutions(LSTMFS)is extended for solving three-dimensional transient diffusion problems in this paper.The interval segmentation in temporal direction is developed for the accurate simulation of long-time-dependent diffusion problems.In the LSTMFS,the whole space-time domain with nodes arranged i divided into a series of overlapping subdomains with a simple geometry.In each subdomain,the conventional method of fundamental solutions is utilized and the coefficients associated with the considered domain can be explicitly determined.By calculating a combined sparse matrix system,the value at any node inside the space-time domain can be obtained.Numerical experi-ments demonstrate that high accuracy and efficiency can be simultaneously achieved via the LSTMFS,even for the problems defined on a long-time and quite complex computational domain.展开更多
Recent analytical solutions for peridynamic(PD)models of transient diffusion and elastodynamics allow us to revisit convergence of 1D PD models to their classical counterparts.We find and explain the reasons for some ...Recent analytical solutions for peridynamic(PD)models of transient diffusion and elastodynamics allow us to revisit convergence of 1D PD models to their classical counterparts.We find and explain the reasons for some interesting differences between the convergence behavior for transient diffusion and elastodynamics models.Except for very early times,PD models for transient diffusion converge monotonically to the classical one.In contrast,for elastodynamic problems this convergence is more complex,with some periodic/almost-periodic characteristics present.These special features are investigated for sine waves used as initial conditions.The analysis indicates that the convergence behavior of PD solutions to the classical one can be understood in terms of convergence properties for models using the Fourier series expansion terms of a particular initial condition.The results obtained show new connections between PD models and their corresponding classical versions.展开更多
Femtosecond time-resolved transient grating technique was adopted to insight into the intra-chain exciton diffusion of MEH-PPV in solution with different polarity. Broadband white-light continuum was introduced as the...Femtosecond time-resolved transient grating technique was adopted to insight into the intra-chain exciton diffusion of MEH-PPV in solution with different polarity. Broadband white-light continuum was introduced as the probe to observe the transient absorption and the femtosecond time-resolved transient grating information simultaneously. The vibrational dephasing behaviors, single exciton relaxation, and population relaxation dynamics of MEH-PPV were systematically investigated. The result shows that the relaxation processes of the sample solution will be accelerated in the solvent with larger polarity.展开更多
文摘Separations of mixtures in fixed-bed adsorbers are influenced by factors such as(1)selectivity of adsorption,Sads,(2)diffusional time constants,Đi/rc 2,and(3)diffusion selectivity,Đ1/Đ2.In synergistic separations,intracrystalline diffusion of guest molecules serves to enhance the selectivities dictated by thermodynamics of mixture adsorption.In antisynergistic separations,intracrystalline diffusion serves to reverse the hierarchy of selectivities dictated by adsorption equilibrium.For both scenarios,the productivities of the desired product in fixed-bed operations are crucially dependent on diffusional time constants,Đi/rc 2;these need to be sufficiently low in order for diffusional influences to be effective.Also,the ratioĐ1/Đ2 should be large enough for manifestation of synergistic or antisynergistic influence.Both synergistic and antisynergistic separations have two common,distinguishing characteristics.Firstly,for transient uptake within crystals,the more mobile component attains supraequilibrium loadings during the initial stages of the transience.Such overshoots,signifying uphill diffusion,are engendered by the cross-coefficientsΓij(i≠j)of thermodynamic correction factors.Secondly,the component molar loadings,plotted in composition space,follow serpentine equilibration paths.If cross-coefficients are neglected,no overshoots in the loadings of the more mobile component are experienced,and the component loadings follow monotonous equilibration paths.The important takeaway message is that the modeling of mixture separations in fixed-bed adsorbers requires the use of the Maxwell−Stefan equations describing mixture diffusion employing chemical potential gradients as driving forces.
文摘Transient liquid phase bonding of two dissimilar alloys Al 2024 and Ti?6Al?4V using Cu?22%Zn interlayer was carried out at 510 °C under vacuum of 0.01 Pa for various bonding time. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied. The results show that joint formation is attributed to the solid-state diffusion of Cu and Zn into Ti?6Al?4V and Al 2024 alloys followed by eutectic formation and isothermal solidification along the Cu?Zn/Al 2024 interface. The hardness of the joints at the interface increases with an increase in bonding time which can be attributed to formation of intermetallic compounds such as Al2Cu, TiCu3, Al4.2Cu3.2Zn0.7, Al0.71Zn0.29, Ti2Cu, TiAl3 and TiZn16 in the joint zone. Moreover, shear strength of the joint reaches the highest value of 37 MPa at bonding time of 60 min.
文摘We study the nonlinear coupled evolution equations which model the transient MHD natural convection and mass transfer flow of viscous, incompressible and electrically conducting fluid between two infinite vertical plates in the presence of the transversal magnetic field, thermal radiation, thermal diffusion and diffusion-thermo effects. Both analytical and numerical methods are used for this study.
文摘This paper investigates the airflow patterns connected to different cough conditions, the effects of these arrangements on the regions of droplet fallout and dilution time of virus diffusion of coughed gas. We focus on some of the physical processes that occur in a double bed hospital isolation room, investigating the effect of the ventilation system on the spread of particles in air. A cough model was carried out and used for the numerical simulation of virus diffusion inside an existent isolation room. Transient simulations of air pattern diffusion and air velocity field, provided by the existing typical HVAC primary air system designed for infectious patients, were performed using CFD. A multiphysics approach, combined Convection-Conduction, Incompressible Navier-Stokes models on non-isothermal air flow and Convection-Diffusion, was used. Simulations results highlighted that the flow field and velocity distribution induced by the high turbulence air inlet diffuser combined with the air return diffusers produce wide recirculation zones near the wall and partial stagnation areas near the ceiling and between the two beds, but lower particle concentration in the room and their shorter spreading distance. This type of analysis is certainly cost effective to identify all the air recirculation zones which can harbour lingering pathogens.
基金partially supported by RFBR, research project No. 14-48-03535
文摘An analytical model was developed to describe Si？As alloy solidification in the whole range of measured interface velocity. It is demonstrated that at low interface velocity, the solidification occurs in the initial transient regime. The model leads to good comparison with the experimental data taking both local nonequilibrium effects at high interface velocity and steady state effects at low interface velocity into account. The local nonequilibrium diffusion effects shrink the initial transient period and lead to diffusionless solidification at high interface velocity.
基金supported by the National Natural Science Foundation of China(Grant Nos.A020307 and 11072094)the program for New Century Excellent Talents in University(NCET-10-0445)
文摘We developed a transient model for actin-based motility.Diffusion of actin monomers was included in the formulation and its influence on the speed of actin-driven cargos was examined in detail.Our results clearly demonstrated how actin polymerization accelerates cargos that are initially stationary,as well as how steady-state is eventually reached.We also found that,due to polymerization and diffusion,actin monomer concentration near the load surface can be significantly lower than that in the rest of the comet tail,suggesting that many previous models may not be very accurate.
基金the Fundamental Research Funds for the Central Universities(Grants B200203009 and B200202126)the Natural Science Foundation of Jiangsu Province(Grant BK20190073)+2 种基金the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant SKLA202001)the State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures,Shijiazhuang Tiedao University(Grant KF2020-22)the China Postdoctoral Science Foundation(Grants 2017M611669 and 2018T110430).
文摘A localized space-time method of fundamental solutions(LSTMFS)is extended for solving three-dimensional transient diffusion problems in this paper.The interval segmentation in temporal direction is developed for the accurate simulation of long-time-dependent diffusion problems.In the LSTMFS,the whole space-time domain with nodes arranged i divided into a series of overlapping subdomains with a simple geometry.In each subdomain,the conventional method of fundamental solutions is utilized and the coefficients associated with the considered domain can be explicitly determined.By calculating a combined sparse matrix system,the value at any node inside the space-time domain can be obtained.Numerical experi-ments demonstrate that high accuracy and efficiency can be simultaneously achieved via the LSTMFS,even for the problems defined on a long-time and quite complex computational domain.
基金supported by the Fundamental Research Funds for the Central Universities(HUST:YCJJ202203014 and No.2021GCRC021)the Natural Science Foundation of China(No.11802098).
文摘Recent analytical solutions for peridynamic(PD)models of transient diffusion and elastodynamics allow us to revisit convergence of 1D PD models to their classical counterparts.We find and explain the reasons for some interesting differences between the convergence behavior for transient diffusion and elastodynamics models.Except for very early times,PD models for transient diffusion converge monotonically to the classical one.In contrast,for elastodynamic problems this convergence is more complex,with some periodic/almost-periodic characteristics present.These special features are investigated for sine waves used as initial conditions.The analysis indicates that the convergence behavior of PD solutions to the classical one can be understood in terms of convergence properties for models using the Fourier series expansion terms of a particular initial condition.The results obtained show new connections between PD models and their corresponding classical versions.
基金supported by the National Natural Science Foundation of China(No.61704120)Science & Technology Development Foundation of Tianjin Higher Education Institutions(No.20140904)
文摘Femtosecond time-resolved transient grating technique was adopted to insight into the intra-chain exciton diffusion of MEH-PPV in solution with different polarity. Broadband white-light continuum was introduced as the probe to observe the transient absorption and the femtosecond time-resolved transient grating information simultaneously. The vibrational dephasing behaviors, single exciton relaxation, and population relaxation dynamics of MEH-PPV were systematically investigated. The result shows that the relaxation processes of the sample solution will be accelerated in the solvent with larger polarity.
