N-formylation of amines,a class of synthetically important reactions,is typically conducted using metal catalysts that are relatively expensive or not readily available and usually needs harsh conditions to increase t...N-formylation of amines,a class of synthetically important reactions,is typically conducted using metal catalysts that are relatively expensive or not readily available and usually needs harsh conditions to increase the reaction efficiency.Here,an efficient continuous microflow strategy was developed for the gas-liquid visible-light photocatalytic N-formylation of piperidine,which achieved a reaction yield of 82.97%and a selectivity of>99%at 12 min using cheap organic dye photocatalyst under mild reaction conditions.The influence of essential parameters,including light intensity,temperature and equivalents of the gas,additive and photocatalyst,on the reaction yield was systematically studied.Furthermore,kinetic investigations were conducted,exhibiting the dependence of reaction rate and equilibrium yield of N-formylpiperidine on light intensity,temperature and photocatalyst equivalent.The microflow photocatalytic approach established in this work,which realized a markedly higher space-time yield than the conventional batch method(37.9 vs.0.212 mmol h-1 L-1),paves the way for the continuous,green and efficient synthesis of N-formamides.展开更多
Micro-flow channel is basic functional component of microfluidic chip,and every step-forward of its construction technique has been receiving concern all over the world.This article presents a not-complicated but flex...Micro-flow channel is basic functional component of microfluidic chip,and every step-forward of its construction technique has been receiving concern all over the world.This article presents a not-complicated but flexible method for fabrication of micro-flow channels.This method mainly utilizes the conventional molding capability of polydimethylsiloxane(PDMS) and widespread commercial microwires as templates.We have fabricated out some conventional types of microchannels with different topological shapes,as examples for the demonstration of this flexible fabrication route which was not dependent on the stringent demands of photolithographical or microelectromechanical system(MEMS) techniques.The smooth surface,high-intensity,and high flexibility of the wires made it possible to create many types of topological structures of the two-dimensional or three-dimensional microchannel or channel array.The geometric shape of the cross-section of thus forming microchannel in PDMS was the negative of that of embedded-in microwire,in high-fidelity if suitable measures were taken.More-over,such a microchannel fabrication process can easily integrate the conductivity and low resistivity of the metal wire to create micro-flow devices that are suitable for the electromagnetic control of liquid or the temperature regulation in the microchannel.Furthermore some preliminary optical analysis was provided for the observation of thus forming rounded microchannel.Based on this molding strategy,we even made some prototypes for functional microflow application,such as microsolenoids chip and temperature control gadgets.And an experiment of forming a droplet in the cross channel further confirmed the feasibility and applicability of this flexible microchannel forming technique.展开更多
Due to the rapid advances inmicro-electro-mechanical systems(MEMS),the study of microflows becomes increasingly important.Currently,the molecular-based simulation techniques are the most reliable methods for rarefied ...Due to the rapid advances inmicro-electro-mechanical systems(MEMS),the study of microflows becomes increasingly important.Currently,the molecular-based simulation techniques are the most reliable methods for rarefied flow computation,even though these methods face statistical scattering problem in the low speed limit.With discretized particle velocity space,a unified gas-kinetic scheme(UGKS)for entire Knudsen number flow has been constructed recently for flow computation.Contrary to the particle-based direct simulation Monte Carlo(DSMC)method,the unified scheme is a partial differential equation-based modeling method,where the statistical noise is totally removed.But,the common point between the DSMC and UGKS is that both methods are constructed through direct modeling in the discretized space.Due to the multiscale modeling in the unified method,i.e.,the update of both macroscopic flow variables and microscopic gas distribution function,the conventional constraint of time step being less than the particle collision time inmany direct Boltzmann solvers is released here.The numerical tests show that the unified scheme is more efficient than the particle-basedmethods in the low speed rarefied flow computation.Themain purpose of the current study is to validate the accuracy of the unified scheme in the capturing of non-equilibrium flow phenomena.In the continuum and free molecular limits,the gas distribution function used in the unified scheme for the flux evaluation at a cell interface goes to the corresponding Navier-Stokes and free molecular solutions.In the transition regime,the DSMC solution will be used for the validation of UGKS results.This study shows that the unified scheme is indeed a reliable and accurate flow solver for low speed non-equilibrium flows.It not only recovers the DSMC results whenever available,but also provides high resolution results in cases where the DSMC can hardly afford the computational cost.In thermal creep flow simulation,surprising solution,such as the gas flowing from hot to cold展开更多
The alterations of mean arterial pressure, pancreatic microflow, serum amylase and lipase,and pancreatic histology were studied in 42 rats in acute necrotizing pancreatitis induced by various concentrations of sodium ...The alterations of mean arterial pressure, pancreatic microflow, serum amylase and lipase,and pancreatic histology were studied in 42 rats in acute necrotizing pancreatitis induced by various concentrations of sodium taurocholate. The results showed that disturbance of pancreatic microflow which was shown by diminished pancreatic microflow occurred dramatically in the early stage of acute pancreatitis (AP) when mean arterial pressure remained stable, as concentration of the inducer increased,levels of serum amylase and lipase increased, pancreatic pathology worsened, and disturbance of pancreatic microflow further evolved. It is suggested that disturbance of pancreatic microflow might occur in the early stage of AP; disturbance of pancreatic microflow might be coincident with the pancreatic enzymes which were directly released into the blood stream during pancreatitis and with the severity of pancreatitis.展开更多
Objective\ The relationship between graft blood flow, epicardial microflow, mean arterial pressure and hemorheologic changes was studied during intraoperative heart failure. Methods\ These parameters were done to ...Objective\ The relationship between graft blood flow, epicardial microflow, mean arterial pressure and hemorheologic changes was studied during intraoperative heart failure. Methods\ These parameters were done to evaluate the use of repeated cardiopulmonary bypass support for the intraoperative heart failure following aorto coronary bypass surgery. Included in this study were 10 patients with a mean age of 70 and unstable angina undergoing coronary bypass grafting and suffering from intraoperative heart failure. The epicardiai microflow, graft flow, mean arterial pressure and blood cell filterability were measured. Resluts\ During heart failure, the mean arterial pressure fell by 41%(P<0.01), graft flow by 67%(P<0.01) and epicardialmicroflow by 64%(P<0.01). After 15 to 56 min of assisted cardiopulmonary bypass support, the epicardial microflow and graft flow were partially restored, while red cell and white cell filterability was reduced by 31% and 64% respectively (P<0.01). There were significant correlations between graft flow, epicardial microflow, blood cell filterability and cardiopulmonary bypass time. All patients recovered and were discharged from the hospital.Conclusion\ It is concluded that the use of temporary assisted CPB support to treat intrapoperative heart failure allows the recovery of the myocardium and thereby restores the mean arterial pressure. The recovery of graft flow and epicardial flow occurred to a lesser extent. The CPB support seemed to be suitable for about 60 min probably because of increasing disturbance to the blood cell filterability, graft flow and the epicardial microcirculation.\;展开更多
Geometric inversion is applied to two-dimensional Stokes flow in view to find new Stokes flow solutions. The principle of this method and the relations between the reference and inverse fluid velocity fields are prese...Geometric inversion is applied to two-dimensional Stokes flow in view to find new Stokes flow solutions. The principle of this method and the relations between the reference and inverse fluid velocity fields are presented. They are followed by applications to the flow between two parallel plates induced by a rotating or a translating cylinder. Thus hydrodynamic characteristics of flow around circular bodies obtained by inversion of the plates are thus deduced. Typically fluid flow patterns around two circular cylinders in contact placed in the centre of a rotating or a translating circular cylinder are illustrated.展开更多
Random and block copolymers of 2-methoxyethyl vinyl ether(MOVE)and 2-ethoxyethyl vinyl ether(EOVE)were synthesized within 180 s via IBVE-HCl/SnCl_(4) initiating system in the presence of THF in a microflow system.The ...Random and block copolymers of 2-methoxyethyl vinyl ether(MOVE)and 2-ethoxyethyl vinyl ether(EOVE)were synthesized within 180 s via IBVE-HCl/SnCl_(4) initiating system in the presence of THF in a microflow system.The polymers can be produced continuously and efficiently with extremely narrow molecular weight distributions(M_(w)/M_(n)=1.09-1.18)even at the existence of pendant oxyethylene units Polymerization rate can be accelerated by reducing THF to very low concentration([THF]=50 mmol/L),reaching conversions over 60%and 70%in 60 s for EOVE and MOVE,respectively.Random copolymers poly(MOVE_(100x)-r-EOVE(_(100)(1-x)))(x=0.25,0.5,0.75)experienced very sensitive phase separation process,of which phase separation temperature(T_(ps))can be adjusted between 20 and 70℃by controlling monomer composition.On the other hand,thermally induced phase separation of diblock copolymers poly(MOVE_(100)-b-EOVE_(100))was not so sensitive as its random copolymer counterpart.Relatively bigger difference between phase separation temperatures of heating and cooling process(ΔT_(ps))was found for diblock copolymer.展开更多
Fluid flow in the microchannel is limited to the low Reynolds number regime.As a result,mixing of solutions with different concentrations in the microchannel is inherently diffusion dominated,requiring a long mixing c...Fluid flow in the microchannel is limited to the low Reynolds number regime.As a result,mixing of solutions with different concentrations in the microchannel is inherently diffusion dominated,requiring a long mixing channel and retention time to attain a homogeneous solution.In this paper the flow characteristics in the two-dimension closed-end microchannel electroosmotic flow were simulated,and the mixing efficiencies of the closed-end microchannel electroosmotic flow applying different electric field intensities were compared.The results showed that because of existing non-uniform induced back pressure,there were two annular flows in the whole closed-end microchannel,enhancing the convection effect and leading to a shorter mixing time and higher mixing efficiency.展开更多
We develop the dimension-reduced hyperbolic moment method for the Boltzmann equation,to improve solution efficiency using a numerical regularized moment method for problems with low-dimensional macroscopic variables a...We develop the dimension-reduced hyperbolic moment method for the Boltzmann equation,to improve solution efficiency using a numerical regularized moment method for problems with low-dimensional macroscopic variables and highdimensional microscopic variables.In the present work,we deduce the globally hyperbolic moment equations for the dimension-reduced Boltzmann equation based on the Hermite expansion and a globally hyperbolic regularization.The numbers of Maxwell boundary condition required for well-posedness are studied.The numerical scheme is then developed and an improved projection algorithm between two different Hermite expansion spaces is developed.By solving several benchmark problems,we validate the method developed and demonstrate the significant efficiency improvement by dimension-reduction.展开更多
基金the financial support from the National Natural Science Foundation of China(No.21808059)the Fundamental Research Funds for the Central Universities(No.JKA01221712).
文摘N-formylation of amines,a class of synthetically important reactions,is typically conducted using metal catalysts that are relatively expensive or not readily available and usually needs harsh conditions to increase the reaction efficiency.Here,an efficient continuous microflow strategy was developed for the gas-liquid visible-light photocatalytic N-formylation of piperidine,which achieved a reaction yield of 82.97%and a selectivity of>99%at 12 min using cheap organic dye photocatalyst under mild reaction conditions.The influence of essential parameters,including light intensity,temperature and equivalents of the gas,additive and photocatalyst,on the reaction yield was systematically studied.Furthermore,kinetic investigations were conducted,exhibiting the dependence of reaction rate and equilibrium yield of N-formylpiperidine on light intensity,temperature and photocatalyst equivalent.The microflow photocatalytic approach established in this work,which realized a markedly higher space-time yield than the conventional batch method(37.9 vs.0.212 mmol h-1 L-1),paves the way for the continuous,green and efficient synthesis of N-formamides.
基金Supported by the Key Project for International Science and Technology Collaboration of the Ministry of Science & Technology (Grant No. 2005DFA00190)partially supported by "111 Project" (B06023)Chongqing University Post-graduates' Science and Innovation Fund (No.200707A1A0110248)
文摘Micro-flow channel is basic functional component of microfluidic chip,and every step-forward of its construction technique has been receiving concern all over the world.This article presents a not-complicated but flexible method for fabrication of micro-flow channels.This method mainly utilizes the conventional molding capability of polydimethylsiloxane(PDMS) and widespread commercial microwires as templates.We have fabricated out some conventional types of microchannels with different topological shapes,as examples for the demonstration of this flexible fabrication route which was not dependent on the stringent demands of photolithographical or microelectromechanical system(MEMS) techniques.The smooth surface,high-intensity,and high flexibility of the wires made it possible to create many types of topological structures of the two-dimensional or three-dimensional microchannel or channel array.The geometric shape of the cross-section of thus forming microchannel in PDMS was the negative of that of embedded-in microwire,in high-fidelity if suitable measures were taken.More-over,such a microchannel fabrication process can easily integrate the conductivity and low resistivity of the metal wire to create micro-flow devices that are suitable for the electromagnetic control of liquid or the temperature regulation in the microchannel.Furthermore some preliminary optical analysis was provided for the observation of thus forming rounded microchannel.Based on this molding strategy,we even made some prototypes for functional microflow application,such as microsolenoids chip and temperature control gadgets.And an experiment of forming a droplet in the cross channel further confirmed the feasibility and applicability of this flexible microchannel forming technique.
基金Hong Kong Research Grant Council(621709,621011)and grants SRFI11SC05 and RPC10SC11 atHKUST.J.C.Huang was supported by National Science Council of Taiwan through grant No.NSC 100-2221-E-019-048-MY3.
文摘Due to the rapid advances inmicro-electro-mechanical systems(MEMS),the study of microflows becomes increasingly important.Currently,the molecular-based simulation techniques are the most reliable methods for rarefied flow computation,even though these methods face statistical scattering problem in the low speed limit.With discretized particle velocity space,a unified gas-kinetic scheme(UGKS)for entire Knudsen number flow has been constructed recently for flow computation.Contrary to the particle-based direct simulation Monte Carlo(DSMC)method,the unified scheme is a partial differential equation-based modeling method,where the statistical noise is totally removed.But,the common point between the DSMC and UGKS is that both methods are constructed through direct modeling in the discretized space.Due to the multiscale modeling in the unified method,i.e.,the update of both macroscopic flow variables and microscopic gas distribution function,the conventional constraint of time step being less than the particle collision time inmany direct Boltzmann solvers is released here.The numerical tests show that the unified scheme is more efficient than the particle-basedmethods in the low speed rarefied flow computation.Themain purpose of the current study is to validate the accuracy of the unified scheme in the capturing of non-equilibrium flow phenomena.In the continuum and free molecular limits,the gas distribution function used in the unified scheme for the flux evaluation at a cell interface goes to the corresponding Navier-Stokes and free molecular solutions.In the transition regime,the DSMC solution will be used for the validation of UGKS results.This study shows that the unified scheme is indeed a reliable and accurate flow solver for low speed non-equilibrium flows.It not only recovers the DSMC results whenever available,but also provides high resolution results in cases where the DSMC can hardly afford the computational cost.In thermal creep flow simulation,surprising solution,such as the gas flowing from hot to cold
文摘The alterations of mean arterial pressure, pancreatic microflow, serum amylase and lipase,and pancreatic histology were studied in 42 rats in acute necrotizing pancreatitis induced by various concentrations of sodium taurocholate. The results showed that disturbance of pancreatic microflow which was shown by diminished pancreatic microflow occurred dramatically in the early stage of acute pancreatitis (AP) when mean arterial pressure remained stable, as concentration of the inducer increased,levels of serum amylase and lipase increased, pancreatic pathology worsened, and disturbance of pancreatic microflow further evolved. It is suggested that disturbance of pancreatic microflow might occur in the early stage of AP; disturbance of pancreatic microflow might be coincident with the pancreatic enzymes which were directly released into the blood stream during pancreatitis and with the severity of pancreatitis.
文摘Objective\ The relationship between graft blood flow, epicardial microflow, mean arterial pressure and hemorheologic changes was studied during intraoperative heart failure. Methods\ These parameters were done to evaluate the use of repeated cardiopulmonary bypass support for the intraoperative heart failure following aorto coronary bypass surgery. Included in this study were 10 patients with a mean age of 70 and unstable angina undergoing coronary bypass grafting and suffering from intraoperative heart failure. The epicardiai microflow, graft flow, mean arterial pressure and blood cell filterability were measured. Resluts\ During heart failure, the mean arterial pressure fell by 41%(P<0.01), graft flow by 67%(P<0.01) and epicardialmicroflow by 64%(P<0.01). After 15 to 56 min of assisted cardiopulmonary bypass support, the epicardial microflow and graft flow were partially restored, while red cell and white cell filterability was reduced by 31% and 64% respectively (P<0.01). There were significant correlations between graft flow, epicardial microflow, blood cell filterability and cardiopulmonary bypass time. All patients recovered and were discharged from the hospital.Conclusion\ It is concluded that the use of temporary assisted CPB support to treat intrapoperative heart failure allows the recovery of the myocardium and thereby restores the mean arterial pressure. The recovery of graft flow and epicardial flow occurred to a lesser extent. The CPB support seemed to be suitable for about 60 min probably because of increasing disturbance to the blood cell filterability, graft flow and the epicardial microcirculation.\;
文摘Geometric inversion is applied to two-dimensional Stokes flow in view to find new Stokes flow solutions. The principle of this method and the relations between the reference and inverse fluid velocity fields are presented. They are followed by applications to the flow between two parallel plates induced by a rotating or a translating cylinder. Thus hydrodynamic characteristics of flow around circular bodies obtained by inversion of the plates are thus deduced. Typically fluid flow patterns around two circular cylinders in contact placed in the centre of a rotating or a translating circular cylinder are illustrated.
基金financially supported by the National Natural Science Foundation of China(Nos.21422603,U1662120 and 21978152)。
文摘Random and block copolymers of 2-methoxyethyl vinyl ether(MOVE)and 2-ethoxyethyl vinyl ether(EOVE)were synthesized within 180 s via IBVE-HCl/SnCl_(4) initiating system in the presence of THF in a microflow system.The polymers can be produced continuously and efficiently with extremely narrow molecular weight distributions(M_(w)/M_(n)=1.09-1.18)even at the existence of pendant oxyethylene units Polymerization rate can be accelerated by reducing THF to very low concentration([THF]=50 mmol/L),reaching conversions over 60%and 70%in 60 s for EOVE and MOVE,respectively.Random copolymers poly(MOVE_(100x)-r-EOVE(_(100)(1-x)))(x=0.25,0.5,0.75)experienced very sensitive phase separation process,of which phase separation temperature(T_(ps))can be adjusted between 20 and 70℃by controlling monomer composition.On the other hand,thermally induced phase separation of diblock copolymers poly(MOVE_(100)-b-EOVE_(100))was not so sensitive as its random copolymer counterpart.Relatively bigger difference between phase separation temperatures of heating and cooling process(ΔT_(ps))was found for diblock copolymer.
文摘Fluid flow in the microchannel is limited to the low Reynolds number regime.As a result,mixing of solutions with different concentrations in the microchannel is inherently diffusion dominated,requiring a long mixing channel and retention time to attain a homogeneous solution.In this paper the flow characteristics in the two-dimension closed-end microchannel electroosmotic flow were simulated,and the mixing efficiencies of the closed-end microchannel electroosmotic flow applying different electric field intensities were compared.The results showed that because of existing non-uniform induced back pressure,there were two annular flows in the whole closed-end microchannel,enhancing the convection effect and leading to a shorter mixing time and higher mixing efficiency.
基金supported in part by the National Basic Research Program of China(2011CB309704)the National Natural Science Foundation of China(NSFC91330205)+2 种基金supported by the Hong Kong Research Council GRF grant(PolyU 2021/12P)the Hong Kong Polytechnic University grant(A-PL61)supported by the Hong Kong RGC grant PolyU 2017/10P during their visits to the Hong Kong Polytechnic University。
文摘We develop the dimension-reduced hyperbolic moment method for the Boltzmann equation,to improve solution efficiency using a numerical regularized moment method for problems with low-dimensional macroscopic variables and highdimensional microscopic variables.In the present work,we deduce the globally hyperbolic moment equations for the dimension-reduced Boltzmann equation based on the Hermite expansion and a globally hyperbolic regularization.The numbers of Maxwell boundary condition required for well-posedness are studied.The numerical scheme is then developed and an improved projection algorithm between two different Hermite expansion spaces is developed.By solving several benchmark problems,we validate the method developed and demonstrate the significant efficiency improvement by dimension-reduction.
