In the present study, a pot experiment was carded out to investigate the effects of a composite soil amendment at different levels (0, 600, 900 and 1 200 mg/kg) on the soil organic matter content, pH, Pb uptake and ...In the present study, a pot experiment was carded out to investigate the effects of a composite soil amendment at different levels (0, 600, 900 and 1 200 mg/kg) on the soil organic matter content, pH, Pb uptake and nutritional quality of pak choi (Brassica rapa L. Chinensis Group) grown in the soils contaminated by four levels (800, 1 200, 1 600 and 2 000 mg/kg) of Pb. The results showed that 900 mg/kg soil amendment increased the soil organic matter content by 24.19%- 60.00%, but had no significant influence on soil pH. Comparing with control (without amendment application), the security and nutritional quality of pak choi were obviously improved by applying the soil amendment. In detail, 900 mg/kg soil amendment improved the content of Vc of pak choi growing in 800, 1 200, 1 600 and 2 000 mg/kg Pb-contaminated soils by 13.27%-69.30%, the content of soluble sugar by 54.17%- 87.50%, the dry matter weight by 28.36%-33.39%, and decreased the content of Pb by 19.11%-35.72% and the content of crude fiber by 20.83%-31.03%, respectively. These data indicated that the composite amendment can be used for the in situ repair of Pb-contaminated soils, and the recommended dosage is 900 mg/kg.展开更多
The slogan of“Combination of medicine and engineering”proposed in“Made in China 2025”has aroused great attention to higher engineering education.However,it is a difficult problem and challenge for schools and educ...The slogan of“Combination of medicine and engineering”proposed in“Made in China 2025”has aroused great attention to higher engineering education.However,it is a difficult problem and challenge for schools and educators to effectively adapt to the economic and social development,train new medical and engineering talents,and explore and cultivate new subject growth points.In order to deal with engineering change and a new round of scientific and technological revolution,facing the challenge of new engineering construction.This paper will combine the reality and characteristics of colleges and universities,analyze the problems existing in the current medical engineering cross-graduate training,and put forward countermeasures and suggestions to promote the progress and development of science and technology in colleges and universities.展开更多
A new vortex identification criterion called W-method is proposed based on the ideas that vorticity overtakes deformation in vortex.The comparison with other vortex identification methods like Q-criterion and λ_2-met...A new vortex identification criterion called W-method is proposed based on the ideas that vorticity overtakes deformation in vortex.The comparison with other vortex identification methods like Q-criterion and λ_2-method is conducted and the advantages of the new method can be summarized as follows:(1) the method is able to capture vortex well and very easy to perform;(2) the physical meaning of W is clear while the interpretations of iso-surface values of Q and λ_2 chosen to visualize vortices are obscure;(3)being different from Q and λ_2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, W is pretty universal and does not need much adjustment in different cases and the iso-surfaces of W=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated;(4) both strong and weak vortices can be captured well simultaneously while improper Q and λ_2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared;(5) W=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate W, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow,the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.展开更多
It is commonly known that riblets with sharper tip generally have better turbulent drag reduction capacity,which,however,poses great challenges for manufacturing and makes the riblets vulnerable to tip erosion.In this...It is commonly known that riblets with sharper tip generally have better turbulent drag reduction capacity,which,however,poses great challenges for manufacturing and makes the riblets vulnerable to tip erosion.In this study,we show that a scalloped riblet which is not as sharp in the tip as corresponding triangular riblet with same height-width ratio,nevertheless has a larger protrusion height,a quantity solely depending on the riblet shape and calculated through a boundary element algorithm in this study,and thus a higher projected drag reduction rate.In addition,it is found that,when subjected to tip rounding,this scalloped riblet performs better in terms of protrusion height than corresponding parabolic riblet,which indicates stronger resilience to riblet tip erosion.With the class of scalloped riblets,designed by smoothly connecting two third-order polynomials and thus the tip sharpness and valley curvature can be well defined,it is revealed that two mechanisms,one for the valley curvature at the viscous limit and one for the tip sharpness at infinite deep limit,determine the protrusion height,and thus the projected drag reduction capacity.Direct numerical simulations are then carried out to investigate controlled boundary layer transition with the scalloped riblet of width s+=20 and 5+=60.A 7.8%drag reduction in the turbulent region is found for the smaller riblet with a preferable transition delay,while for the larger riblet transition is promoted and drag is increased in the turbulent region.It is also found that the area fraction of high drag region around the riblet tips is basically the same for the two cases.Surprisingly,even higher drag is found around the tip region for the smaller drag-reducing riblets.On the other hand,a much smaller drag coefficient is found in the valley of the smaller riblet,which results in the reduction of turbulent drag.It is thus inferred that the issue of sharp riblet tip,that hard to manufacture and deteriorate substantially when subjected to tip erosion,could be mitigated by optimization of the riblet geometry.展开更多
The secondary organic aerosol(SOA)formation mechanism and physicochemical properties can highly be influenced by relative humidity(RH)and NOx concentration.In this study,we performed a laboratory investigation of the ...The secondary organic aerosol(SOA)formation mechanism and physicochemical properties can highly be influenced by relative humidity(RH)and NOx concentration.In this study,we performed a laboratory investigation of the SOA formation from toluene/OH photooxidation system in the presence or absence of NOx in dry and wet conditions.The chemical composition of toluene-derived SOA was measured using Aerodyne high-resolution timeof-flight aerosol mass spectrometer(HR-ToF-AMS).It was found that the mass concentration of toluene decreased with increasing RH and NOx concentration.However,the change of SOA chemistry composition(f_(44),O/C)with increased RH was not consistent in the condition with or without NOx.The light absorption and mass absorption coefficient(MAC)of the toluene-derived SOA only increased with RH in the presence of NOx.In contrast,MAC is invariant with RH in the absence of NOx.HR-ToF-AMS results showed that,in the presence of NOx,the increased nitro-aromatic compounds and N/C ratio concurrently caused the increase of SOA light absorption and O/C in wet conditions,respectively.The relative intensity of CHON and CHOxN family to the total nitrogen-containing organic compounds(NOCs)increased with the increasing RH,and be the major components of NOCs in wet condition.This work revealed a synergy effect of NOx and RH on SOA formation from toluene photooxidation.展开更多
In this paper,we propose a new method to study intermittent behaviors of coupled piecewise-expanding map lattices.We show that the successive transition between ordered and disordered phases occurs for almost every or...In this paper,we propose a new method to study intermittent behaviors of coupled piecewise-expanding map lattices.We show that the successive transition between ordered and disordered phases occurs for almost every orbit when the coupling is small.That is,lim inf n→∞∑1≤i,j≤m|x_(i)(n)−x_(j)(n)|=0,lim sup n→∞∑1≤i,j≤m|x_(i)(n)−x_(j)(n)|≥c_(0)>0,where xi(n)correspond to the coordinates of m nodes at the iterative step n.Moreover,when the uncoupled system is generated by the tent map and the lattice consists of two nodes,we prove a phase transition occurs between synchronization and intermittent behaviors.That is,limn→∞|x_(1)(n)−x_(2)(n)|=0 for c−1/2<1/4 and intermittent behaviors occur for|c−1/2|>1/4,where 0≤c≤1 is the coupling.展开更多
Experimental and numerical investigations have suggested the existence of a strong correlation between the passage of coherent structures and events of bursting and intermittency. However, a detailed cause-and-effect ...Experimental and numerical investigations have suggested the existence of a strong correlation between the passage of coherent structures and events of bursting and intermittency. However, a detailed cause-and-effect study on the subject is rarely found in the literature due to the complexity and the nonlinear multiscale nature of turbulent flows. The primary goal of this research is to explore the motion and evolution of coherent structures during late transition, whose structure is much more ordered than that of fully developed turbulence, and their relationship with events of bursting and intermittency based on a verified high-order direct numerical simulation(DNS). The computation was carried out on a flat plate at Reynolds number 1000(based on the inflow displacement thickness) with an inflow Mach number 0.5. It is concluded that bursting and intermittency detected by stationary sensors in a transitional boundary layer actually result from the passage and development of vortical structures, and it would be more rational to design transitional turbulence models based on modelling the moving vortical structures rather than the statistical features and experimental experiences.展开更多
基金Supported by the Fund of Beijing Leafy Vegetables Innovation Team of Modren Agroindustry Technology Research System(BAIC07-2016)the Fund of Beijing Municipal Commission of Rural Affairs(20120129)~~
文摘In the present study, a pot experiment was carded out to investigate the effects of a composite soil amendment at different levels (0, 600, 900 and 1 200 mg/kg) on the soil organic matter content, pH, Pb uptake and nutritional quality of pak choi (Brassica rapa L. Chinensis Group) grown in the soils contaminated by four levels (800, 1 200, 1 600 and 2 000 mg/kg) of Pb. The results showed that 900 mg/kg soil amendment increased the soil organic matter content by 24.19%- 60.00%, but had no significant influence on soil pH. Comparing with control (without amendment application), the security and nutritional quality of pak choi were obviously improved by applying the soil amendment. In detail, 900 mg/kg soil amendment improved the content of Vc of pak choi growing in 800, 1 200, 1 600 and 2 000 mg/kg Pb-contaminated soils by 13.27%-69.30%, the content of soluble sugar by 54.17%- 87.50%, the dry matter weight by 28.36%-33.39%, and decreased the content of Pb by 19.11%-35.72% and the content of crude fiber by 20.83%-31.03%, respectively. These data indicated that the composite amendment can be used for the in situ repair of Pb-contaminated soils, and the recommended dosage is 900 mg/kg.
文摘The slogan of“Combination of medicine and engineering”proposed in“Made in China 2025”has aroused great attention to higher engineering education.However,it is a difficult problem and challenge for schools and educators to effectively adapt to the economic and social development,train new medical and engineering talents,and explore and cultivate new subject growth points.In order to deal with engineering change and a new round of scientific and technological revolution,facing the challenge of new engineering construction.This paper will combine the reality and characteristics of colleges and universities,analyze the problems existing in the current medical engineering cross-graduate training,and put forward countermeasures and suggestions to promote the progress and development of science and technology in colleges and universities.
基金supported by Air Force Office of Scientific Research (Grant No. FA9550-08-1-0201) supervised by Dr. John Schmisseur and then the Department of Mathematics at University of Texas at Arlington
文摘A new vortex identification criterion called W-method is proposed based on the ideas that vorticity overtakes deformation in vortex.The comparison with other vortex identification methods like Q-criterion and λ_2-method is conducted and the advantages of the new method can be summarized as follows:(1) the method is able to capture vortex well and very easy to perform;(2) the physical meaning of W is clear while the interpretations of iso-surface values of Q and λ_2 chosen to visualize vortices are obscure;(3)being different from Q and λ_2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, W is pretty universal and does not need much adjustment in different cases and the iso-surfaces of W=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated;(4) both strong and weak vortices can be captured well simultaneously while improper Q and λ_2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared;(5) W=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate W, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow,the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.
基金the National Natural Science Foundation of China(Grant No.11702159)the EU-China Joint Project Drag Reduction via Turbulent Boundary Layer Flow Control(Grant No.690623).
文摘It is commonly known that riblets with sharper tip generally have better turbulent drag reduction capacity,which,however,poses great challenges for manufacturing and makes the riblets vulnerable to tip erosion.In this study,we show that a scalloped riblet which is not as sharp in the tip as corresponding triangular riblet with same height-width ratio,nevertheless has a larger protrusion height,a quantity solely depending on the riblet shape and calculated through a boundary element algorithm in this study,and thus a higher projected drag reduction rate.In addition,it is found that,when subjected to tip rounding,this scalloped riblet performs better in terms of protrusion height than corresponding parabolic riblet,which indicates stronger resilience to riblet tip erosion.With the class of scalloped riblets,designed by smoothly connecting two third-order polynomials and thus the tip sharpness and valley curvature can be well defined,it is revealed that two mechanisms,one for the valley curvature at the viscous limit and one for the tip sharpness at infinite deep limit,determine the protrusion height,and thus the projected drag reduction capacity.Direct numerical simulations are then carried out to investigate controlled boundary layer transition with the scalloped riblet of width s+=20 and 5+=60.A 7.8%drag reduction in the turbulent region is found for the smaller riblet with a preferable transition delay,while for the larger riblet transition is promoted and drag is increased in the turbulent region.It is also found that the area fraction of high drag region around the riblet tips is basically the same for the two cases.Surprisingly,even higher drag is found around the tip region for the smaller drag-reducing riblets.On the other hand,a much smaller drag coefficient is found in the valley of the smaller riblet,which results in the reduction of turbulent drag.It is thus inferred that the issue of sharp riblet tip,that hard to manufacture and deteriorate substantially when subjected to tip erosion,could be mitigated by optimization of the riblet geometry.
基金financially supported by National Key R&D Plan programs(No.2017YFC0212703)the National Natural Science Foundation of China(Nos.41773117,42005088)+2 种基金the China Postdoctoral Science Foundation(No.2019M661427)Fundamental Research Funds for the Central Universities,Director’s Fund of Key Laboratory of Geographic Information Science(Ministry of Education),East China Normal University(No.KLGIS2021C02)ECNU Happiness Flower Program
文摘The secondary organic aerosol(SOA)formation mechanism and physicochemical properties can highly be influenced by relative humidity(RH)and NOx concentration.In this study,we performed a laboratory investigation of the SOA formation from toluene/OH photooxidation system in the presence or absence of NOx in dry and wet conditions.The chemical composition of toluene-derived SOA was measured using Aerodyne high-resolution timeof-flight aerosol mass spectrometer(HR-ToF-AMS).It was found that the mass concentration of toluene decreased with increasing RH and NOx concentration.However,the change of SOA chemistry composition(f_(44),O/C)with increased RH was not consistent in the condition with or without NOx.The light absorption and mass absorption coefficient(MAC)of the toluene-derived SOA only increased with RH in the presence of NOx.In contrast,MAC is invariant with RH in the absence of NOx.HR-ToF-AMS results showed that,in the presence of NOx,the increased nitro-aromatic compounds and N/C ratio concurrently caused the increase of SOA light absorption and O/C in wet conditions,respectively.The relative intensity of CHON and CHOxN family to the total nitrogen-containing organic compounds(NOCs)increased with the increasing RH,and be the major components of NOCs in wet condition.This work revealed a synergy effect of NOx and RH on SOA formation from toluene photooxidation.
基金This work is supported by NSFC of China(Grants Nos.11031003,11271183,11971105 and 11771205)and Simons Foundation.
文摘In this paper,we propose a new method to study intermittent behaviors of coupled piecewise-expanding map lattices.We show that the successive transition between ordered and disordered phases occurs for almost every orbit when the coupling is small.That is,lim inf n→∞∑1≤i,j≤m|x_(i)(n)−x_(j)(n)|=0,lim sup n→∞∑1≤i,j≤m|x_(i)(n)−x_(j)(n)|≥c_(0)>0,where xi(n)correspond to the coordinates of m nodes at the iterative step n.Moreover,when the uncoupled system is generated by the tent map and the lattice consists of two nodes,we prove a phase transition occurs between synchronization and intermittent behaviors.That is,limn→∞|x_(1)(n)−x_(2)(n)|=0 for c−1/2<1/4 and intermittent behaviors occur for|c−1/2|>1/4,where 0≤c≤1 is the coupling.
基金supported by the Department of Mathematics at University of Texas at Arlington
文摘Experimental and numerical investigations have suggested the existence of a strong correlation between the passage of coherent structures and events of bursting and intermittency. However, a detailed cause-and-effect study on the subject is rarely found in the literature due to the complexity and the nonlinear multiscale nature of turbulent flows. The primary goal of this research is to explore the motion and evolution of coherent structures during late transition, whose structure is much more ordered than that of fully developed turbulence, and their relationship with events of bursting and intermittency based on a verified high-order direct numerical simulation(DNS). The computation was carried out on a flat plate at Reynolds number 1000(based on the inflow displacement thickness) with an inflow Mach number 0.5. It is concluded that bursting and intermittency detected by stationary sensors in a transitional boundary layer actually result from the passage and development of vortical structures, and it would be more rational to design transitional turbulence models based on modelling the moving vortical structures rather than the statistical features and experimental experiences.