The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limit...The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.展开更多
In this paper,we consider the extension of the concave integral from classical crispσ-algebra to fuzzyσ-algebra of fuzzy sets.Firstly,the concept of fuzzy concave integral on a fuzzy set is introduced.Secondly,some ...In this paper,we consider the extension of the concave integral from classical crispσ-algebra to fuzzyσ-algebra of fuzzy sets.Firstly,the concept of fuzzy concave integral on a fuzzy set is introduced.Secondly,some important properties of such integral are discussed.Finally,various kinds of convergence theorems of a sequence of fuzzy concave integrals are proved.展开更多
Mechanical analysis of cylinders being upset between spherical concave platen and concave supporting plate is conducted. Rigid-plastic mechanical models for cylinders are presented. When the ratio of height to diamete...Mechanical analysis of cylinders being upset between spherical concave platen and concave supporting plate is conducted. Rigid-plastic mechanical models for cylinders are presented. When the ratio of height to diameter, is larger than 1, there exists two-dimensional tensile stress in the deformed body, when the ratio is smaller than 1, there exists shear stress in static hydraulic zone. The former breaks through the theory that there is three-dimensional compressive stress irrespective of any ratio of height to diameter. The latter satisfactorily explains the mechanism of layer-like cracks in disk-shaped forgings and the flanges of forged gear axles. The representation of the two models makes the upsetting, theory into correct and perfect stage.展开更多
Recently, the theory of valuations on function spaces has been rapidly growing. It is more general than the classical theory of valuations on convex bodies. In this paper, all continuous, SL(n) and translation invaria...Recently, the theory of valuations on function spaces has been rapidly growing. It is more general than the classical theory of valuations on convex bodies. In this paper, all continuous, SL(n) and translation invariant valuations on concave functions and log-concave functions are completely classified, respectively.展开更多
To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface,a series of experiments are conducted in the present investigation.Four concave surfaces including one semi...To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface,a series of experiments are conducted in the present investigation.Four concave surfaces including one semi-cylindrical concave surface and three parabolic concave surfaces with different width-to-depth ratios are tested under three typical Reynolds numbers(Re=5000,10000 and 15000)and several dimensionless nozzle-to-surface distances ranging from 1 to 8.The results show that the concave curvature has a clear impact on chevron-nozzle jet impingement heat transfer,tightly dependent on jet Reynolds number and impinging distance.In general,the semicylindrical concave surface produces the highest longitudinally-averaged Nusselt number at the leading line of concave surface.Under a low jet Reynolds number,the parabolic concave surface with a highly curved curvature produces higher longitudinally-averaged Nusselt number at the leading line and more uniform longitudinally-averaged Nusselt number distribution along the curvilinear direction.However,the longitudinally-averaged Nusselt number at the leading line of concave surface is the lowest for the highly curved surface under a high jet Reynolds number and large impinging distance.In comparison with the round-nozzle,chevron nozzle plays a more significant role on improving jet impingement heat transfer at small impinging distances.展开更多
Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects.The expe...Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects.The experiments were conducted by employing a piccolo tube with one single jet hole over a wide range of parameters：jet Reynolds number from 27000 to 130000,relative nozzle to surface distance from 3.3 to 30,and relative surface curvature from 0.005 to 0.030.Experimental results indicate that the surface curvature has opposite effects on heat transfer characteristics.On one hand,an increase of relative nozzle to surface distance（increasing jet diameter in fact）enhances the average heat transfer around the surface for the same curved surface.On the other hand,the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter.Finally,experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect.This work contributes to a better understanding of the curvature effects on heat transfer of a round jet impingement on concave surfaces,which is of high importance to the design of the aircraft anti-icing system.展开更多
In this paper,we consider a singular elliptic system with both concave non-linearities and critical Sobolev-Hardy growth terms in bounded domains.By means of variational methods,the multiplicity of positive solutions ...In this paper,we consider a singular elliptic system with both concave non-linearities and critical Sobolev-Hardy growth terms in bounded domains.By means of variational methods,the multiplicity of positive solutions to this problem is obtained.展开更多
Based on concave function, the problem of finding the sparse solution of absolute value equations is relaxed to a concave programming, and its corresponding algorithm is proposed, whose main part is solving a series o...Based on concave function, the problem of finding the sparse solution of absolute value equations is relaxed to a concave programming, and its corresponding algorithm is proposed, whose main part is solving a series of linear programming. It is proved that a sparse solution can be found under the assumption that the connected matrixes have range space property(RSP). Numerical experiments are also conducted to verify the efficiency of the proposed algorithm.展开更多
High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,tempe...High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.展开更多
Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ＇technologies＇. Understanding the basic principles in the design of the ...Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ＇technologies＇. Understanding the basic principles in the design of the unique surface structures is of great importance in the manufacture or synthesis of micro- and nano- devices in MEMS or NEMS. This study is right inspired by this effort, focusing on the mechanics of wet adhesion between fibers having concave tips and a flat substrate via capillary forces. We show that the concave surface can effectively enhance the wet adhesion by reducing the effective contact angle of the fiber, firmly pinning the liquid bridge at its circumferential edge. A critical contact angle is identified below which the adhesion strength can achieve its maximum, being insensitive to the contact angle between the fiber and liquid. The analytical expression for the critical angle is derived. Then a tentative design for the profile of concave surfaces is proposed, considering the effects of chamfering size, deformation and buckling, etc. The effect of liquid volume on the wet adhesion of multiple-fiber system is also discussed.展开更多
Inspired by shark’s skin in nature,a non-smooth surface could be an ideal model for changing the flow characteristics of fluids on the object surface.To analyze the effect of a non-smooth surface with concaves on the...Inspired by shark’s skin in nature,a non-smooth surface could be an ideal model for changing the flow characteristics of fluids on the object surface.To analyze the effect of a non-smooth surface with concaves on the maglev train aerodynamic performances and to investigate how the concave size affects the aerodynamic forces and flow structure of a maglev train,four 1/10th scaled maglev train models are simulated using an Improved Delayed Detached Eddy Simulation(IDDES)method.The numerical strategy used in this study is verified by comparison with the wind tunnel test results,and the comparison shows that the difference was in a reasonable range.The results demonstrate that the concaves could effectively reduce the tail car pressure drag,thus reducing the total drag,and that the smaller the concave size was,the better the drag reduction effect would be.The change in the lift with the concave size was more significant than that of the drag,and the tail car lift of R1(0.0012H),R2(0.0024H),and R3(0.0036H)train models was 30.1%,43.0%,and 44.5%less than that of the prototype,respectively.In addition,different flow topologies of the wake are analyzed.The width and height of the vortex core of the counter-rotating vortices tended to decrease with the concave size.Thus,from the point of view of ensuring the operating safety of a maglev train,a non-smooth surface with small-size concaves is recommended.展开更多
The average photoelectric conversion efficiency(PCE)of a bare mono crystalline silicon solar cell is 14.71%±0.03%under AM1.5.It decreases to 14.20%±0.005%when covering an un-doped flat glass on the solar cel...The average photoelectric conversion efficiency(PCE)of a bare mono crystalline silicon solar cell is 14.71%±0.03%under AM1.5.It decreases to 14.20%±0.005%when covering an un-doped flat glass on the solar cell,and it goes down to 14.10%±0.005%by using a 5 wt%Eu^3+doped glass.The absorptions of the Eu^3+doped CPM glass one-to-one match the excitation spectra at 362,381,393,400,413 and464 nm,which are related to the transitions of 7 F0→(5 D4,5 G2,5 L6,5 D3),7 F1→5 D3,and 7 F0→5 D2,respectively.In addition,a concave pyramid microstructure(CPM)is embedded in the glass surface to increase light transmittance.The average PCE increases to 14.61%±0.07%when a 5 wt%Eu^3+doped CPM glass covers on the silicon solar cell.Compared with the un-doped flat glass,a net increase of the PCE is0.41%,where the 0.16%increment of PCE is from the lighting trapping of the CPM structure,and the downshifting of near ultraviolet(NUV)light by Eu^3+ion donates the other 0.25%increment.It confirms that the as-prepared Eu^3+doped CPM glass has a good downshifting and antireflection function.展开更多
In order to study the stability control mechanism of a concave slope with circular landslide, and remove the influence of differences in shape on slope stability, the limit analysis method of a simplified Bishop metho...In order to study the stability control mechanism of a concave slope with circular landslide, and remove the influence of differences in shape on slope stability, the limit analysis method of a simplified Bishop method was employed. The sliding body was divided into strips in a three-dimensional model, and the lateral earth pressure was put into mechanical analysis and the three-dimensional stability analysis methods applicable for circular sliding in concave slope were deduced. Based on geometric structure and the geological parameters of a concave slope, the influence rule of curvature radius and the top and bottom arch height on the concave slope stability were analyzed. The results show that the stability coefficient decreases after growth, first in the transition stage of slope shape from flat to concave, and it has been confirmed that there is a best size to make the slope stability factor reach a maximum. By contrast with average slope, the stability of a concave slope features a smaller range of ascension with slope height increase, which indicates that the enhancing effect of a concave slope is apparent only with lower slope heights.展开更多
The effect of wind environment is becoming increasingly important in analyzing and selecting sites for better naturalventilation of residential buildings, external comfort, and pollution dispersion. The mainpurpose of...The effect of wind environment is becoming increasingly important in analyzing and selecting sites for better naturalventilation of residential buildings, external comfort, and pollution dispersion. The mainpurpose of this study was to develop a setof methods for wind environment assessment in coastal concave terrains. This set of methods can be used to provide quantifiableindicators of preferable wind conditions and help site analysis. Firstly, a total of 20 types of coastal bays with concave terrains inEast Asia were characterized to find ideal locations. The selected areas were divided into five categories according to the mainterrain features. Then a sample database for the concave terrains was compiled for modelling comparisons. Secondly, a number ofkey wind variables were identified. Computational fluid dynamics （CFD） models of the typical coastal concave terrains identifiedas a result of the study were created, and the local wind environments were simulated with input from geographic informationsystem （GIS） and statistic package for social science （SPSS） analysis. A measure of wind suitability was proposed that takes windvelocity and wind direction into account using GIS. Finally, SPSS was used to find the relationship between wind suitability andkey terrain factors. The results showed that wind suitability was significantly associated with terrain factors, especially altitude.The results suggest that residential building sites should be selected such that their bay openings face the direction of the prevailingwind and that the opposite direction should be avoided.展开更多
Wedged and V-shaped cells have advantages on depressing strong absorption bands and keeping the photo windows wide open without absorption block.Alternatively,this work presents a concave cell design,which is construc...Wedged and V-shaped cells have advantages on depressing strong absorption bands and keeping the photo windows wide open without absorption block.Alternatively,this work presents a concave cell design,which is constructed by a plano-convex CaF_2 lens in combination with a flat plate.Mathematical equations have been provided for data treatment with Matlab programs.The result indicates that the concave cell has advantages similar to the V-shaped cell.Reflection-absorption measurements of ethanol have been conducted on the cell in mid-IR region for demonstration.The spectrum obtained from the concave cell can easily be interpreted to regenerate its normal spectrum,which is fitting well with the spectrum taken in a conventional thin-layer cell.The concave cell is easier to construct and more convenient to operate,willing to have popular usages.展开更多
The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bu...The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.展开更多
The development of a general discrete element method for irregularly shaped particles is the core issue of the simulation of the dynamic behavior of granular materials.The general energy-conserving contact theory is u...The development of a general discrete element method for irregularly shaped particles is the core issue of the simulation of the dynamic behavior of granular materials.The general energy-conserving contact theory is used to establish a universal discrete element method suitable for particle contact of arbitrary shape.In this study,three dimentional(3D)modeling and scanning techniques are used to obtain a triangular mesh representation of the true particles containing typical concave particles.The contact volumebased energy-conserving model is used to realize the contact detection between irregularly shaped particles,and the contact force model is refined and modified to describe the contact under real conditions.The inelastic collision processes between the particles and boundaries are simulated to verify the robustness of the modified contact force model and its applicability to the multi-point contact mode.In addition,the packing process and the flow process of a large number of irregular particles are simulated with the modified discrete element method(DEM)to illustrate the applicability of the method of complex problems.展开更多
We synthesized octapod Cu-Au bimetallic alloy with a concave structure by employing a replacement reaction between Au PPh3Cl and Cu nanocubes. Using the Cu nanocube as sacrificial templates, we have successfully gener...We synthesized octapod Cu-Au bimetallic alloy with a concave structure by employing a replacement reaction between Au PPh3Cl and Cu nanocubes. Using the Cu nanocube as sacrificial templates, we have successfully generated high-active sites on alloy nanocrystals by carefully tuning the replacement reaction and growth. The key is to afford the proper concentration of Au PPh3Cl-TOP to the reaction solution. When the Au precursor with high concentration is injected into the galvanic replacement reaction, the growth dominated the process and hollowed octapod Cu-Au alloy was obtained. In contrast, when the concentration of the Au precursor is low, the replacement reaction can only take place at the nanocrystals, leading to generate Cu-Au nanocages. This work provides an effective strategy for the preparation of hollow bimetallic nanocrystals with high-active sites.展开更多
It is concluded from the results of testing the frequency characteristics of the sub micron precision machine tool servo control system, that the existence of several oscillating modalities is the main factor that aff...It is concluded from the results of testing the frequency characteristics of the sub micron precision machine tool servo control system, that the existence of several oscillating modalities is the main factor that affects the performance of the control system. To compensate for this effect,several concave filters are utilized in the system to improve the control accuracy. The feasibility of compensating for several oscillating modalities with a single concave filter is also studied. By applying a modified Butterworth concave filter to the practical system, the maximum stable state output error remains under ±10 nm in the closed loop positioning system.展开更多
The differential equations of movement along the concave profile of the grate, consisting of three broken lines, are integrated on Maple 9.5 under initial conditions, using separate functions, and graphs of the depend...The differential equations of movement along the concave profile of the grate, consisting of three broken lines, are integrated on Maple 9.5 under initial conditions, using separate functions, and graphs of the dependence of movement and speed over time are presented. The graphs show the patterns of change in displacement and speed at different angles, friction coefficient of seeds along grate with a broken line of a concave profile.展开更多
基金financially supported by the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.24qnpy041)the Science and Technology Innovation Key R&D Program of Chongqing(Grant No.CSTB2023TIAD-STX0030)。
文摘The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.
基金Supported in part by the National Social Science Foundation of China(19BTJ020)。
文摘In this paper,we consider the extension of the concave integral from classical crispσ-algebra to fuzzyσ-algebra of fuzzy sets.Firstly,the concept of fuzzy concave integral on a fuzzy set is introduced.Secondly,some important properties of such integral are discussed.Finally,various kinds of convergence theorems of a sequence of fuzzy concave integrals are proved.
基金National Natural Science Foundation of China(No.59235101)
文摘Mechanical analysis of cylinders being upset between spherical concave platen and concave supporting plate is conducted. Rigid-plastic mechanical models for cylinders are presented. When the ratio of height to diameter, is larger than 1, there exists two-dimensional tensile stress in the deformed body, when the ratio is smaller than 1, there exists shear stress in static hydraulic zone. The former breaks through the theory that there is three-dimensional compressive stress irrespective of any ratio of height to diameter. The latter satisfactorily explains the mechanism of layer-like cracks in disk-shaped forgings and the flanges of forged gear axles. The representation of the two models makes the upsetting, theory into correct and perfect stage.
基金Supported by Foundation of China Scholarship Council(201808430267)the Education Department of Hunan Province(16C0635)the Natural Science Foundation of Hunan Province(2017JJ3085)
文摘Recently, the theory of valuations on function spaces has been rapidly growing. It is more general than the classical theory of valuations on convex bodies. In this paper, all continuous, SL(n) and translation invariant valuations on concave functions and log-concave functions are completely classified, respectively.
基金the financial supports for this project from the National Natural Science Foundation of China(No.51776097)the Open Fund of Jiangsu Province Key Laboratory of Aerospace Power System(No.APS20A7002)the Postgraduate Research and Practice Innovation Project of Jiangsu Province(No.KYCX17 0280)
文摘To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface,a series of experiments are conducted in the present investigation.Four concave surfaces including one semi-cylindrical concave surface and three parabolic concave surfaces with different width-to-depth ratios are tested under three typical Reynolds numbers(Re=5000,10000 and 15000)and several dimensionless nozzle-to-surface distances ranging from 1 to 8.The results show that the concave curvature has a clear impact on chevron-nozzle jet impingement heat transfer,tightly dependent on jet Reynolds number and impinging distance.In general,the semicylindrical concave surface produces the highest longitudinally-averaged Nusselt number at the leading line of concave surface.Under a low jet Reynolds number,the parabolic concave surface with a highly curved curvature produces higher longitudinally-averaged Nusselt number at the leading line and more uniform longitudinally-averaged Nusselt number distribution along the curvilinear direction.However,the longitudinally-averaged Nusselt number at the leading line of concave surface is the lowest for the highly curved surface under a high jet Reynolds number and large impinging distance.In comparison with the round-nozzle,chevron nozzle plays a more significant role on improving jet impingement heat transfer at small impinging distances.
基金supported by the National Natural Science Foundation of China(No.51206008)the EU Marie Curie Actions-International Incoming Fellowships(No.FP7PEOPLE-2013-IIF-626576)
文摘Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects.The experiments were conducted by employing a piccolo tube with one single jet hole over a wide range of parameters：jet Reynolds number from 27000 to 130000,relative nozzle to surface distance from 3.3 to 30,and relative surface curvature from 0.005 to 0.030.Experimental results indicate that the surface curvature has opposite effects on heat transfer characteristics.On one hand,an increase of relative nozzle to surface distance（increasing jet diameter in fact）enhances the average heat transfer around the surface for the same curved surface.On the other hand,the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter.Finally,experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect.This work contributes to a better understanding of the curvature effects on heat transfer of a round jet impingement on concave surfaces,which is of high importance to the design of the aircraft anti-icing system.
文摘In this paper,we consider a singular elliptic system with both concave non-linearities and critical Sobolev-Hardy growth terms in bounded domains.By means of variational methods,the multiplicity of positive solutions to this problem is obtained.
文摘Based on concave function, the problem of finding the sparse solution of absolute value equations is relaxed to a concave programming, and its corresponding algorithm is proposed, whose main part is solving a series of linear programming. It is proved that a sparse solution can be found under the assumption that the connected matrixes have range space property(RSP). Numerical experiments are also conducted to verify the efficiency of the proposed algorithm.
基金Project(11174077)supported by the National Natural Science Foundation of ChinaProject(11JJ3079)supported by the Hunan Provincial Natural Science Foundation of ChinaProjects(12C0237,11C0844)supported by the Science Research Program of Education Department of Hunan Province,China
文摘High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.
基金supported by the National Natural Science Foundation of China through Grant Nos 10628205,10732050 and10872115National Basic Research Program of China through Grant No 2007CB936803,and SRF-SEM for ROCS
文摘Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ＇technologies＇. Understanding the basic principles in the design of the unique surface structures is of great importance in the manufacture or synthesis of micro- and nano- devices in MEMS or NEMS. This study is right inspired by this effort, focusing on the mechanics of wet adhesion between fibers having concave tips and a flat substrate via capillary forces. We show that the concave surface can effectively enhance the wet adhesion by reducing the effective contact angle of the fiber, firmly pinning the liquid bridge at its circumferential edge. A critical contact angle is identified below which the adhesion strength can achieve its maximum, being insensitive to the contact angle between the fiber and liquid. The analytical expression for the critical angle is derived. Then a tentative design for the profile of concave surfaces is proposed, considering the effects of chamfering size, deformation and buckling, etc. The effect of liquid volume on the wet adhesion of multiple-fiber system is also discussed.
基金This work was supported by the National Numerical Wind Tunnel Project(Grant No.NNW2018-ZT1A02).
文摘Inspired by shark’s skin in nature,a non-smooth surface could be an ideal model for changing the flow characteristics of fluids on the object surface.To analyze the effect of a non-smooth surface with concaves on the maglev train aerodynamic performances and to investigate how the concave size affects the aerodynamic forces and flow structure of a maglev train,four 1/10th scaled maglev train models are simulated using an Improved Delayed Detached Eddy Simulation(IDDES)method.The numerical strategy used in this study is verified by comparison with the wind tunnel test results,and the comparison shows that the difference was in a reasonable range.The results demonstrate that the concaves could effectively reduce the tail car pressure drag,thus reducing the total drag,and that the smaller the concave size was,the better the drag reduction effect would be.The change in the lift with the concave size was more significant than that of the drag,and the tail car lift of R1(0.0012H),R2(0.0024H),and R3(0.0036H)train models was 30.1%,43.0%,and 44.5%less than that of the prototype,respectively.In addition,different flow topologies of the wake are analyzed.The width and height of the vortex core of the counter-rotating vortices tended to decrease with the concave size.Thus,from the point of view of ensuring the operating safety of a maglev train,a non-smooth surface with small-size concaves is recommended.
基金Project supported by National"Double First-class"Construction Special Funding Project(0290-X2100502)。
文摘The average photoelectric conversion efficiency(PCE)of a bare mono crystalline silicon solar cell is 14.71%±0.03%under AM1.5.It decreases to 14.20%±0.005%when covering an un-doped flat glass on the solar cell,and it goes down to 14.10%±0.005%by using a 5 wt%Eu^3+doped glass.The absorptions of the Eu^3+doped CPM glass one-to-one match the excitation spectra at 362,381,393,400,413 and464 nm,which are related to the transitions of 7 F0→(5 D4,5 G2,5 L6,5 D3),7 F1→5 D3,and 7 F0→5 D2,respectively.In addition,a concave pyramid microstructure(CPM)is embedded in the glass surface to increase light transmittance.The average PCE increases to 14.61%±0.07%when a 5 wt%Eu^3+doped CPM glass covers on the silicon solar cell.Compared with the un-doped flat glass,a net increase of the PCE is0.41%,where the 0.16%increment of PCE is from the lighting trapping of the CPM structure,and the downshifting of near ultraviolet(NUV)light by Eu^3+ion donates the other 0.25%increment.It confirms that the as-prepared Eu^3+doped CPM glass has a good downshifting and antireflection function.
基金financially supported by the China Postdoctoral Science Foundation(No.2015M580491)the National Natural Science Foundation of China(No.51404262)+1 种基金the Natural Science Foundation of Jiangsu Province(No.BK20140213)the National High Technology Research and Development Program of China(No.2012AA062004)
文摘In order to study the stability control mechanism of a concave slope with circular landslide, and remove the influence of differences in shape on slope stability, the limit analysis method of a simplified Bishop method was employed. The sliding body was divided into strips in a three-dimensional model, and the lateral earth pressure was put into mechanical analysis and the three-dimensional stability analysis methods applicable for circular sliding in concave slope were deduced. Based on geometric structure and the geological parameters of a concave slope, the influence rule of curvature radius and the top and bottom arch height on the concave slope stability were analyzed. The results show that the stability coefficient decreases after growth, first in the transition stage of slope shape from flat to concave, and it has been confirmed that there is a best size to make the slope stability factor reach a maximum. By contrast with average slope, the stability of a concave slope features a smaller range of ascension with slope height increase, which indicates that the enhancing effect of a concave slope is apparent only with lower slope heights.
基金supported by the National Natural Science Foundation of China(Nos.51208466 and 51238011)the Science and Technology Research Program of Chinese Ministry of Housing and Urban-Rural Development(No.2014R2-036)+2 种基金the Humanities and Social Sciences Research Foundation of the Ministry of Education(No.17YJAZH136)the Natural Science Foundation of Zhejiang Province(No.LY16E0 80011)the Social Sciences Planning Project of Zhejiang Province(No.12JCSH02YB),China
文摘The effect of wind environment is becoming increasingly important in analyzing and selecting sites for better naturalventilation of residential buildings, external comfort, and pollution dispersion. The mainpurpose of this study was to develop a setof methods for wind environment assessment in coastal concave terrains. This set of methods can be used to provide quantifiableindicators of preferable wind conditions and help site analysis. Firstly, a total of 20 types of coastal bays with concave terrains inEast Asia were characterized to find ideal locations. The selected areas were divided into five categories according to the mainterrain features. Then a sample database for the concave terrains was compiled for modelling comparisons. Secondly, a number ofkey wind variables were identified. Computational fluid dynamics （CFD） models of the typical coastal concave terrains identifiedas a result of the study were created, and the local wind environments were simulated with input from geographic informationsystem （GIS） and statistic package for social science （SPSS） analysis. A measure of wind suitability was proposed that takes windvelocity and wind direction into account using GIS. Finally, SPSS was used to find the relationship between wind suitability andkey terrain factors. The results showed that wind suitability was significantly associated with terrain factors, especially altitude.The results suggest that residential building sites should be selected such that their bay openings face the direction of the prevailingwind and that the opposite direction should be avoided.
文摘Wedged and V-shaped cells have advantages on depressing strong absorption bands and keeping the photo windows wide open without absorption block.Alternatively,this work presents a concave cell design,which is constructed by a plano-convex CaF_2 lens in combination with a flat plate.Mathematical equations have been provided for data treatment with Matlab programs.The result indicates that the concave cell has advantages similar to the V-shaped cell.Reflection-absorption measurements of ethanol have been conducted on the cell in mid-IR region for demonstration.The spectrum obtained from the concave cell can easily be interpreted to regenerate its normal spectrum,which is fitting well with the spectrum taken in a conventional thin-layer cell.The concave cell is easier to construct and more convenient to operate,willing to have popular usages.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874140 and 11574072)the Fund from the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA201913)+1 种基金the National Key Research and Development Program of China(Grant No.2016YFC0401600)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant Nos.2018B741X14 and KYCX180552)。
文摘The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.
基金supported by the National Key Research and Development Program of China(2018YFA0605902)the National Natural Science Foundation of China(42176241 and 11872136).
文摘The development of a general discrete element method for irregularly shaped particles is the core issue of the simulation of the dynamic behavior of granular materials.The general energy-conserving contact theory is used to establish a universal discrete element method suitable for particle contact of arbitrary shape.In this study,three dimentional(3D)modeling and scanning techniques are used to obtain a triangular mesh representation of the true particles containing typical concave particles.The contact volumebased energy-conserving model is used to realize the contact detection between irregularly shaped particles,and the contact force model is refined and modified to describe the contact under real conditions.The inelastic collision processes between the particles and boundaries are simulated to verify the robustness of the modified contact force model and its applicability to the multi-point contact mode.In addition,the packing process and the flow process of a large number of irregular particles are simulated with the modified discrete element method(DEM)to illustrate the applicability of the method of complex problems.
基金supported by the Fundamental Research Funds for the Central Universities under Grant No.JB181404。
文摘We synthesized octapod Cu-Au bimetallic alloy with a concave structure by employing a replacement reaction between Au PPh3Cl and Cu nanocubes. Using the Cu nanocube as sacrificial templates, we have successfully generated high-active sites on alloy nanocrystals by carefully tuning the replacement reaction and growth. The key is to afford the proper concentration of Au PPh3Cl-TOP to the reaction solution. When the Au precursor with high concentration is injected into the galvanic replacement reaction, the growth dominated the process and hollowed octapod Cu-Au alloy was obtained. In contrast, when the concentration of the Au precursor is low, the replacement reaction can only take place at the nanocrystals, leading to generate Cu-Au nanocages. This work provides an effective strategy for the preparation of hollow bimetallic nanocrystals with high-active sites.
文摘It is concluded from the results of testing the frequency characteristics of the sub micron precision machine tool servo control system, that the existence of several oscillating modalities is the main factor that affects the performance of the control system. To compensate for this effect,several concave filters are utilized in the system to improve the control accuracy. The feasibility of compensating for several oscillating modalities with a single concave filter is also studied. By applying a modified Butterworth concave filter to the practical system, the maximum stable state output error remains under ±10 nm in the closed loop positioning system.
文摘The differential equations of movement along the concave profile of the grate, consisting of three broken lines, are integrated on Maple 9.5 under initial conditions, using separate functions, and graphs of the dependence of movement and speed over time are presented. The graphs show the patterns of change in displacement and speed at different angles, friction coefficient of seeds along grate with a broken line of a concave profile.
