This article investigates the near-field dynamics in a particle-laden round turbulent jet in a large-eddy simulation （LES）. A point-force two-way coupling model is adopted in the simulation to reveal the particle mo...This article investigates the near-field dynamics in a particle-laden round turbulent jet in a large-eddy simulation （LES）. A point-force two-way coupling model is adopted in the simulation to reveal the particle modulation of turbulence. The particles mainly excite the initial instability of the jet and bring about the earlier breakup of vortex rings in the near-field. The flow fluc- tuating intensity either in the axial or in the radial directions is hence increased by particles. The article also describes the mean velocity modulated by particles. The changing statistical velocity induced by particle modulation implies the effects of modulation of the local flow structures. This study is expected to be useful to the control of two-phase turbulent jets.展开更多
The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, wit...The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.展开更多
Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles ...Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.展开更多
The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography...The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained.And the charring-layer was analyzed by using SEM and energy spectrum.The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1st second since the motor starting,but increases rapidly in 1 to 2.5 s,while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1st second;the ablation rate at the section eroded intensively by particle flow increases at first,then decreases,and goes to stabilization after 4.5 s;the higher speed and concentration particle flow are,the deeper particles get into charring layer,which lead to more thermal increment and thinner charring layer.展开更多
The effect of inertial particles with different specific heat on heat transfer in particle-laden turbulent channel flows is studied using the direct numerical simulation（DNS） and the Lagrangian particle tracking met...The effect of inertial particles with different specific heat on heat transfer in particle-laden turbulent channel flows is studied using the direct numerical simulation（DNS） and the Lagrangian particle tracking method. The simulation uses a two-way coupling model to consider the momentum and thermal interactions between the particles and turbulence. The study shows that the temperature fields display differences between the particle-laden flow with different specific heat particles and the particle-free flow,indicating that the particle specific heat is an important factor that affects the heat transfer process in a particle-laden flow. It is found that the heat transfer capacity of the particle-laden flow gradually increases with the increase of the particle specific heat. This is due to the positive contribution of the particle increase to the heat transfer. In addition,the Nusselt number of a particle-laden flow is compared with that of a particle-free flow.It is found that particles with a large specific heat strengthen heat transfer of turbulent flow, while those with small specific heat weaken heat transfer of turbulent flow.展开更多
The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow wi...The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction.展开更多
The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, res...The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are cal- culated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theo- retical estimations in large Reynolds number （isotropic） tur- bulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian inte- gral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian inte- gral macro-time scales increase in near-wall regions but de- crease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measure- ments and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.展开更多
More than being a victory of good against evil,media commentator Cheng Yi says the killing of Osama bin Laden has opened the way for retaliatory attacks from the terror group Al Qaeda who wilt no doubt use their leade...More than being a victory of good against evil,media commentator Cheng Yi says the killing of Osama bin Laden has opened the way for retaliatory attacks from the terror group Al Qaeda who wilt no doubt use their leader’s death as a renewed call to arms.He argues that the irresponsible and unilateral way in which the United States went about the operation has stirred up further chaos and instabil-展开更多
At advanced phases of atherosclerosis,the rupture and thrombogenesis of vulnerable plaques emerge as primary triggers for acute cardiovascular events and fatalities.Pathogenic infection such as periodontitis-associate...At advanced phases of atherosclerosis,the rupture and thrombogenesis of vulnerable plaques emerge as primary triggers for acute cardiovascular events and fatalities.Pathogenic infection such as periodontitis-associated Porphyromonas gingivalis(Pg)has been suspected of increasing the risks of atherosclerotic cardiovascular disease,but its relationship with atherosclerotic plaque destabilization remains elusive.Here we demonstrated that the level of Pg-positive clusters positively correlated with the ratio of necrotic core area to total atherosclerotic plaque area in human clinical samples,which indicates plaque instability.In rabbits and Apoe^(-/-)mice,Pg promoted atherosclerotic plaque necrosis and aggravated plaque instability by triggering oxidative stress,which led to macrophage necroptosis.This process was accompanied by the decreased protein level of forkhead box O3(FOXO3)in macrophages.The mechanistic dissection showed that Pg lipopolysaccharide(LPS)evoked macrophage oxidative stress via the TLR4 signaling pathway,which subsequently activated MAPK/ERK-mediated FOXO3 phosphorylation and following degradation.While the gingipains,a class of proteases produced by Pg,could effectively hydrolyze FOxO3 in the cytoplasm of macrophages.Both of them decreased the nuclear level of FOXO3,followed by the release of histone deacetylase 2(HDAC2)from the macrophage scavenger receptor 1(Msr1)promoter,thus promoting Msr1 transcription.This enhanced MsR1-mediated lipid uptake further amplified oxidative stress-induced necroptosis in lipid-laden macrophages.In summary,Pg exacerbates macrophage oxidative stress-dependent necroptosis,thus enlarges the atherosclerotic plaque necrotic core and ultimately promotes plaque destabilization.展开更多
Engineered microstructures that mimic in vivo tissues have demonstrated great potential for applications in regenerative medicine,drug screening,and cell behavior exploration.However,current methods for engineering mi...Engineered microstructures that mimic in vivo tissues have demonstrated great potential for applications in regenerative medicine,drug screening,and cell behavior exploration.However,current methods for engineering microstructures that mimic the multi-extracellular matrix and multicellular features of natural tissues to realize tissue-mimicking microstructures in vitro remain insufficient.Here,we propose a versatile method for constructing tissue-mimicking heterogeneous microstructures by orderly integration of macroscopic hydrogel exchange,microscopic cell manipulation,and encapsulation modulation.First,various cell-laden hydrogel droplets are manipulated at the millimeter scale using electrowetting on dielectric to achieve efficient hydrogel exchange.Second,the cells are manipulated at the micrometer scale using dielectrophoresis to adjust their density and arrangement within the hydrogel droplets.Third,the photopolymerization of these hydrogel droplets is triggered in designated regions by dynamically modulating the shape and position of the excitation ultraviolet beam.Thus,heterogeneous microstructures with different extracellular matrix geometries and components were constructed,including specific cell densities and patterns.The resulting heterogeneous microstructure supported long-term culture of hepatocytes and fibroblasts with high cell viability(over 90%).Moreover,the density and distribution of the 2 cell types had significant effects on the cell proliferation and urea secretion.We propose that our method can lead to the construction of additional biomimetic heterogeneous microstructures with unprecedented potential for use in future tissue engineering applications.展开更多
The stability of Bickley jet with particle laden flow is investigated numerically. The stability characteristics are calculated for various Stokes numbers and particle concentrations. The results confirm the author＇s...The stability of Bickley jet with particle laden flow is investigated numerically. The stability characteristics are calculated for various Stokes numbers and particle concentrations. The results confirm the author＇s early calculations, which also shows that the numerical program is reliable. It is further shown that there is a critical value for the effect of Stokes number, which is about 2. The most damped mode occurs when Stokes number is of order of 10 for different particle concentrations and depends weakly on the wave number. The difference in the eigenfunctions and its derivatives between the particle-laden flow and the clean gas flow is insignificant for fine particles, while the difference for coarse particles is significant.展开更多
Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The ...Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The conventional methods for calculating the Minimum Water Demand for River Ecosystem (MWDRE) are not appropriate for rivers with high sediment concentration. This paper studied the MWDRE in wet season, dry season and the whole year under different water-and-sediment conditions in the Lower Yellow River, which is regarded as a typical river with sediment-laden flows. The characteristics of MWDRE in the river are analyzed. Firstly, the water demand for sediment transport (WDST) is much larger than the demands for other riverine functions, the WDST accounts for the absolute majority of the MWDRE. Secondly, in wet season when the WDST is satisfied, not only most of the annual incoming sediment can be transported downstream, but also the water demands for other river functions can be satisfied automatically, so that the MWDRE in wet season is identical to the WDST. Thirdly, in dry season, when the WDST is satisfied, the water demands for other river functions can also be satisfied, but the low sediment transport efficiency results in significant waste of water resources. According to these characteristics and aiming at decreasing sediment deposition in the riverbed and improving the utilization efficiency of water resources, hydrological engineering works can be used to regulate or control flow and sediment so that the sediment incoming in dry season can be accumulated and be transported downstream intensively and thus efficiently in wet season.展开更多
基金National Natural Science Foundation of China (50706021)Ph.D.Programs Foundation of Ministry of Education of China (20070003018)TNList Cross-discipline Foundation
文摘This article investigates the near-field dynamics in a particle-laden round turbulent jet in a large-eddy simulation （LES）. A point-force two-way coupling model is adopted in the simulation to reveal the particle modulation of turbulence. The particles mainly excite the initial instability of the jet and bring about the earlier breakup of vortex rings in the near-field. The flow fluc- tuating intensity either in the axial or in the radial directions is hence increased by particles. The article also describes the mean velocity modulated by particles. The changing statistical velocity induced by particle modulation implies the effects of modulation of the local flow structures. This study is expected to be useful to the control of two-phase turbulent jets.
基金supported by the National Natural Science Foundation of China (Grants 11272198, 11572183)
文摘The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.
基金supported by National Natural Science Foundation of China (Grant No. 51175405)
文摘Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.
基金Sponsored by the National Nature Science Foundation of China(50976095)
文摘The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained.And the charring-layer was analyzed by using SEM and energy spectrum.The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1st second since the motor starting,but increases rapidly in 1 to 2.5 s,while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1st second;the ablation rate at the section eroded intensively by particle flow increases at first,then decreases,and goes to stabilization after 4.5 s;the higher speed and concentration particle flow are,the deeper particles get into charring layer,which lead to more thermal increment and thinner charring layer.
基金Project supported by the National Natural Science Foundation of China(Nos.11272198 and11572183)
文摘The effect of inertial particles with different specific heat on heat transfer in particle-laden turbulent channel flows is studied using the direct numerical simulation（DNS） and the Lagrangian particle tracking method. The simulation uses a two-way coupling model to consider the momentum and thermal interactions between the particles and turbulence. The study shows that the temperature fields display differences between the particle-laden flow with different specific heat particles and the particle-free flow,indicating that the particle specific heat is an important factor that affects the heat transfer process in a particle-laden flow. It is found that the heat transfer capacity of the particle-laden flow gradually increases with the increase of the particle specific heat. This is due to the positive contribution of the particle increase to the heat transfer. In addition,the Nusselt number of a particle-laden flow is compared with that of a particle-free flow.It is found that particles with a large specific heat strengthen heat transfer of turbulent flow, while those with small specific heat weaken heat transfer of turbulent flow.
文摘The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction.
基金supported by the National Natural Science Foundation of China (11132005 and 50706021)
文摘The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are cal- culated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theo- retical estimations in large Reynolds number （isotropic） tur- bulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian inte- gral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian inte- gral macro-time scales increase in near-wall regions but de- crease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measure- ments and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.
文摘More than being a victory of good against evil,media commentator Cheng Yi says the killing of Osama bin Laden has opened the way for retaliatory attacks from the terror group Al Qaeda who wilt no doubt use their leader’s death as a renewed call to arms.He argues that the irresponsible and unilateral way in which the United States went about the operation has stirred up further chaos and instabil-
基金supported by National Natural Science Foundation for Key Program Projects of China(no.82030070,to L.L.C.)the National Science Foundation for Distinguished Young Scholars of China(31725011 to L.L.C.)+1 种基金the National Natural Science Foundation for Young Scientists of China(no.82101025,to M.R.X.)the Youth talents training program of Orthodontic Committee of Chinese Stomatological Association(no.Cos-B2021-01,to M.R.X.).
文摘At advanced phases of atherosclerosis,the rupture and thrombogenesis of vulnerable plaques emerge as primary triggers for acute cardiovascular events and fatalities.Pathogenic infection such as periodontitis-associated Porphyromonas gingivalis(Pg)has been suspected of increasing the risks of atherosclerotic cardiovascular disease,but its relationship with atherosclerotic plaque destabilization remains elusive.Here we demonstrated that the level of Pg-positive clusters positively correlated with the ratio of necrotic core area to total atherosclerotic plaque area in human clinical samples,which indicates plaque instability.In rabbits and Apoe^(-/-)mice,Pg promoted atherosclerotic plaque necrosis and aggravated plaque instability by triggering oxidative stress,which led to macrophage necroptosis.This process was accompanied by the decreased protein level of forkhead box O3(FOXO3)in macrophages.The mechanistic dissection showed that Pg lipopolysaccharide(LPS)evoked macrophage oxidative stress via the TLR4 signaling pathway,which subsequently activated MAPK/ERK-mediated FOXO3 phosphorylation and following degradation.While the gingipains,a class of proteases produced by Pg,could effectively hydrolyze FOxO3 in the cytoplasm of macrophages.Both of them decreased the nuclear level of FOXO3,followed by the release of histone deacetylase 2(HDAC2)from the macrophage scavenger receptor 1(Msr1)promoter,thus promoting Msr1 transcription.This enhanced MsR1-mediated lipid uptake further amplified oxidative stress-induced necroptosis in lipid-laden macrophages.In summary,Pg exacerbates macrophage oxidative stress-dependent necroptosis,thus enlarges the atherosclerotic plaque necrotic core and ultimately promotes plaque destabilization.
基金supported by the National Key Research and Development Program of China under grant 2023YFB4705400the National Natural Science Foundation of China under grant number 62222305,U22A2064+1 种基金the Beijing Natural Science Foundation under grant 4232055the Fundamental Research Program of Shanxi Province 20210302124033.
文摘Engineered microstructures that mimic in vivo tissues have demonstrated great potential for applications in regenerative medicine,drug screening,and cell behavior exploration.However,current methods for engineering microstructures that mimic the multi-extracellular matrix and multicellular features of natural tissues to realize tissue-mimicking microstructures in vitro remain insufficient.Here,we propose a versatile method for constructing tissue-mimicking heterogeneous microstructures by orderly integration of macroscopic hydrogel exchange,microscopic cell manipulation,and encapsulation modulation.First,various cell-laden hydrogel droplets are manipulated at the millimeter scale using electrowetting on dielectric to achieve efficient hydrogel exchange.Second,the cells are manipulated at the micrometer scale using dielectrophoresis to adjust their density and arrangement within the hydrogel droplets.Third,the photopolymerization of these hydrogel droplets is triggered in designated regions by dynamically modulating the shape and position of the excitation ultraviolet beam.Thus,heterogeneous microstructures with different extracellular matrix geometries and components were constructed,including specific cell densities and patterns.The resulting heterogeneous microstructure supported long-term culture of hepatocytes and fibroblasts with high cell viability(over 90%).Moreover,the density and distribution of the 2 cell types had significant effects on the cell proliferation and urea secretion.We propose that our method can lead to the construction of additional biomimetic heterogeneous microstructures with unprecedented potential for use in future tissue engineering applications.
基金supported by the National Natural Science Foundation of China (Grant Nos.50806023,50721005)the Program of Introducing Talents of Discipline to Universities,(111 Program,Grant No.B06019),China
文摘The stability of Bickley jet with particle laden flow is investigated numerically. The stability characteristics are calculated for various Stokes numbers and particle concentrations. The results confirm the author＇s early calculations, which also shows that the numerical program is reliable. It is further shown that there is a critical value for the effect of Stokes number, which is about 2. The most damped mode occurs when Stokes number is of order of 10 for different particle concentrations and depends weakly on the wave number. The difference in the eigenfunctions and its derivatives between the particle-laden flow and the clean gas flow is insignificant for fine particles, while the difference for coarse particles is significant.
文摘Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The conventional methods for calculating the Minimum Water Demand for River Ecosystem (MWDRE) are not appropriate for rivers with high sediment concentration. This paper studied the MWDRE in wet season, dry season and the whole year under different water-and-sediment conditions in the Lower Yellow River, which is regarded as a typical river with sediment-laden flows. The characteristics of MWDRE in the river are analyzed. Firstly, the water demand for sediment transport (WDST) is much larger than the demands for other riverine functions, the WDST accounts for the absolute majority of the MWDRE. Secondly, in wet season when the WDST is satisfied, not only most of the annual incoming sediment can be transported downstream, but also the water demands for other river functions can be satisfied automatically, so that the MWDRE in wet season is identical to the WDST. Thirdly, in dry season, when the WDST is satisfied, the water demands for other river functions can also be satisfied, but the low sediment transport efficiency results in significant waste of water resources. According to these characteristics and aiming at decreasing sediment deposition in the riverbed and improving the utilization efficiency of water resources, hydrological engineering works can be used to regulate or control flow and sediment so that the sediment incoming in dry season can be accumulated and be transported downstream intensively and thus efficiently in wet season.
