In order to study the convection limits of surface fires and interactions between backfires and main fires,several experiments are conducted in a large space indoor laboratory: in which the effects of ambient wind spe...In order to study the convection limits of surface fires and interactions between backfires and main fires,several experiments are conducted in a large space indoor laboratory: in which the effects of ambient wind speeds and changing temperatures can be avoided.The research shows that:(1) there is a convection field in front of coming fires in which the wind speed direction is toward the fire.In the convection area,the lower part has higher wind speed and when the height is taller than a certain value the convection wind speed is not significant;(2) the backfire and the main fire interact with each other even though they are far apart.When they come near each other to a certain distance,they begin to draw each other.This increases their rates of spread toward each other significantly.For surface fires with a fire line intensity of 160?kW\5m -1 ,their rate of spread increases by 27%.展开更多
The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated th...The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually fol- lowed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an en- hanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly （SSTA） in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the at- mospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.展开更多
Interactions involving chemical reagents,solid particles,gas bubbles,liquid droplets,and solid surfaces in complex fluids play a vital role in many engineering processes,such as froth flotation,emulsion and foam forma...Interactions involving chemical reagents,solid particles,gas bubbles,liquid droplets,and solid surfaces in complex fluids play a vital role in many engineering processes,such as froth flotation,emulsion and foam formation,adsorption,and fouling and anti-fouling phenomena.These interactions at the molecular,nano-,and micro scale significantly influence and determine the macroscopic performance and efficiency of related engineering processes.Understanding the intermolecular and surface interactions in engineering processes is of both fundamental and practical importance,which not only improves production technologies,but also provides valuable insights into the development of new materials.In this review,the typical intermolecular and surface interactions involved in various engineering processes,including Derjaguin–Landau–Verwey–Overbeek(DLVO)interactions(i.e.,van der Waals and electrical doublelayer interactions)and non-DLVO interactions,such as steric and hydrophobic interactions,are first introduced.Nanomechanical techniques such as atomic force microscopy and surface forces apparatus for quantifying the interaction forces of molecules and surfaces in complex fluids are briefly introduced.Our recent progress on characterizing the intermolecular and surface interactions in several engineering systems are reviewed,including mineral flotation,petroleum engineering,wastewater treatment,and energy storage materials.The correlation of these fundamental interaction mechanisms with practical applications in resolving engineering challenges and the perspectives of the research field have also been discussed.展开更多
T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions ...T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions however,in specific applications these joints undergo pull loading.De-lamination/de-bond nucleation and its growth is one of the most common failure mechanisms in a fiber reinforced composite structure.Crack growth takes place due to the induced interlaminar normal and shear stresses between different structural constituents when a load is applied.In this study,Finite Element Analysis has been performed using cohesive contact interactions on a composite T-joint to simulate the pull out test conditions.A simplified shell based model coupled with CZM is proposed,which can evaluate the failure initiation and progression accurately with lesser computational efforts.The final failure occurred at a displacement of 4.71 mm at the computed failure load of 472.57 kgf for basic configuration.Computed Failure load for the padded configuration is 672.8 kgf and corresponding displacement is 4.6 mm.The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted failure displacements and failure load calculated were correlating reasonably well with the experiment.展开更多
The hydration film on particle surface plays an important role in bubble-particle adhesion in mineral flotation process. The thicknesses of the hydration films on natural hydrophobic coal and hydrophilic mica surfaces...The hydration film on particle surface plays an important role in bubble-particle adhesion in mineral flotation process. The thicknesses of the hydration films on natural hydrophobic coal and hydrophilic mica surfaces were measured directly by atomic force microscopy (AFM) based on the bending mode of the nominal constant compliance regime in AFM force curve in the present study. Surface and solid-liquid interfacial energies were calculated to explain the forming mechanism of the hydration film and atomic force microscopy data. The results show that there are significant differences in the structure and thickness of hydration films on coal and mica surfaces. Hydration film formed on mica surface with the thickness of 22.5 nm. In contrast, the bend was not detected in the nominal constant compliance regime. The van der Waals and polar interactions between both mica and coal and water molecules are characterized by an attractive effect, while the polar attractive free energy between water and mica (-87.36 mN/m) is significantly larger than that between water and coal (-32.89 mN/m), which leads to a thicker and firmer hydration layer on the mica surface. The interfacial interaction free energy of the coal/water/bubble is greater than that of mica. The polar attractive force is large enough to overcome the repulsive van der Waals force and the low energy barrier of film rupture, achieving coal particle bubble adhesion with a total interfacial free energy of-56.30 mN/m.展开更多
We use the photon Green-function method to study the quantum resonant dipole-dipole interaction（RDDI） induced by an Ag nanosphere（ANP）.As the distance between the two dipoles increases,the RDDI becomes weaker,whic...We use the photon Green-function method to study the quantum resonant dipole-dipole interaction（RDDI） induced by an Ag nanosphere（ANP）.As the distance between the two dipoles increases,the RDDI becomes weaker,which is accompanied by the influence of the higher-order mode of the ANP on RDDI declining more quickly than that of the dipole mode.Across a broad frequency range（above 0.05 eV）,the transfer rate of the RDDI is nearly constant since the two dipoles are fixed at the proper position.In addition,this phenomenon still exists for slightly different radius of the ANPs.We find that the frequency corresponding to the maximum transfer rate of RDDI exhibits a monotonic decrease by moving away one dipole as the other dipole and the ANP are kept fixed.In addition,the radius of ANP has little effect on this.When the two dipoles are far from the ANP,the maximum transfer rate of the RDDI takes place at the frequency of the dipole mode.In contrast,when the two dipoles are close to the ANP,the higher-order modes come into effect and they will play a leading role in the RDDI if they match the transition frequency of the dipole.Our results may be used in a biological detector and have a certain guiding significance for further application.展开更多
The interaction between a flotation reagent and mineral surface not only depends on the bonding atom, but also depends on the adjacent atom of mineral surface, a flotation reagent and the medium in the system of flota...The interaction between a flotation reagent and mineral surface not only depends on the bonding atom, but also depends on the adjacent atom of mineral surface, a flotation reagent and the medium in the system of flotation. Energy equation of a reagent interacting with mineral surface has been deduced from this model. Results of the studies indicate that the interaction energy between mineral surface and a reagent is about several dozen kJ/mol, and the relationship between adsorbing concentration of xanthate on mineral surface and interaction energy is the exponent form.展开更多
Fertilizer input for agricultural food production, as well as the discharge of domestic and industrial water pollutants, increases pressures on locally scarce and vulnerable water resources in the North China Plain. I...Fertilizer input for agricultural food production, as well as the discharge of domestic and industrial water pollutants, increases pressures on locally scarce and vulnerable water resources in the North China Plain. In order to：（a） understand pollutant exchange between surface water and groundwater,（b） quantify nutrient loadings, and（c） identify major nutrient removal pathways by using qualitative and quantitative methods, including the geochemical model PHREEQC） a one-year study at a wheat（Triticum aestivum L.） and maize（Zea mays L.） double cropping system in the Baiyang Lake area in Hebei Province, China, was undertaken. The study showed a high influence of low-quality surface water on the shallow aquifer. Major inflowing pollutants into the aquifer were ammonium and nitrate via inflow from the adjacent Fu River（up to 29.8 mg/L NH4-N and 6.8 mg/L NO3-N）, as well as nitrate via vertical transport from the field surface（up to 134.8 mg/L NO3-N in soil water）. Results from a conceptual model show an excess nitrogen input of about 320 kg/ha/a. Nevertheless,both nitrogen species were only detected at low concentrations in shallow groundwater,averaging at 3.6 mg/L NH4-N and 1.8 mg/L NO3-N. Measurement results supported by PHREEQC-modeling indicated cation exchange, denitrification, and anaerobic ammonium oxidation coupled with partial denitrification as major nitrogen removal pathways. Despite the current removal capacity, the excessive nitrogen fertilization may pose a future threat to groundwater quality. Surface water quality improvements are therefore recommended in conjunction with simultaneous monitoring of nitrate in the aquifer, and reduced agricultural N-inputs should be considered.展开更多
Based on the interface shear tests,the macro-and meso-mechanical behaviors of interaction between coral sand and different structure surfaces are studied,in which CCD camera is used to capture digital images to analyz...Based on the interface shear tests,the macro-and meso-mechanical behaviors of interaction between coral sand and different structure surfaces are studied,in which CCD camera is used to capture digital images to analyze the evolution of the interaction band and a particle analysis apparatus is applied to studying the distribution characteristics of particle morphology.This study proposes four-stage evolution process based on the shear stress−strain curve.During the shear process,coral sand particles slide and rotate within the interaction band,causing the changes in shear stress and vertical displacement.In addition,the effects of structure surface roughness on shear strength,volume change and particle breakage are illustrated that the greater the roughness of slabs is,the larger the shear stress is,the more obvious the contraction effect is and the more the particles break.Furthermore,the change in particle’s 3D morphology during the breakage will change not only their size but also other morphological characteristics with convergence and self-organization.展开更多
The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency sh...The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency should be accounted for in the mechanical behaviors of nanoscale structures. In the current investigation, the influence of free surface energy on the nonlinear primary resonance of silicon nanoshells under soft harmonic external excitation is studied. In order to obtain more accurate results,the interaction between the first, third, and fifth symmetric vibration modes with the main oscillation mode is taken into consideration. Through the implementation of the Gurtin-Murdoch theory of elasticity into the classical shell theory, a size-dependent shell model is developed incorporating the effect of surface free energy. With the aid of the variational approach, the governing differential equations of motion including both of the cubic and quadratic nonlinearities are derived. Thereafter, the multi-time-scale method is used to achieve an analytical solution for the nonlinear size-dependent problem. The frequency-response and amplitude-response of the soft harmonic excited nanoshells are presented corresponding to different values of shell thickness and surface elastic constants as well as various vibration mode interactions. It is depicted that through consideration of the interaction between the higher symmetric vibration modes and the main oscillation mode, the hardening response of nanoshell changes to the softening one. This pattern is observed corresponding to both of the positive and negative values of the surface elastic constants and the surface residual stress.展开更多
An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account o...An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achieve- ment of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.展开更多
This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on...This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.展开更多
The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field ...The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE) satellite using the test particle Monte Carlo(TPMC) method. The primary goal is to obtain a comprehensive understanding of surface pressure and skin friction on the spacecraft surface and assess the sensitivity of aerodynamic drag to the gas-surface interaction(GSI) models. Results indicate that surface pressure is mainly distributed on the front of the satellite body and panels while skin friction is primarily distributed on the sides. In addition, as the GSI model changes from diffuse to specular reflection, the total drag coefficient is reduced at operation altitudes above 170 km. Therefore, the satellite surface should be processed so carefully that the GSI remains far from diffuse reflection from the view point of the drag-reduce design.展开更多
The coupling interaction between an individual optical emitter and the propagating surface plasmon polaritons in a graphene microribbon （GMR） waveguide is investigated by numerical calculations, where the emitter is...The coupling interaction between an individual optical emitter and the propagating surface plasmon polaritons in a graphene microribbon （GMR） waveguide is investigated by numerical calculations, where the emitter is situated above the GMR or in the same plane of the GMR, The results reveal a multimode coupling mechanism for the strong interaction between the emitter and the propagating plasmonic waves in graphene. When the emitter is situated in the same plane of the GMR, the decay rate from the emitter to the surface plasmon polaritons increases more than 10 times compared with that in the case with the emitter above the GMR.展开更多
The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previo...The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional （Q3D） vegetated surface flow model with a two-dimensional （2D） saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations （SWEs） with the implicit finite difference solution of Navier-Stokes equations （NSEs） for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations （SGFEs）. The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.展开更多
In this work,an improved understanding of electron sheath theory is provided using both fluid and kinetic approaches while elaborating on their implications for plasma–surface interactions.A fluid model is proposed c...In this work,an improved understanding of electron sheath theory is provided using both fluid and kinetic approaches while elaborating on their implications for plasma–surface interactions.A fluid model is proposed considering the electron presheath structure,avoiding the singularity in electron sheath Child–Langmuir law which overestimates the sheath potential.Subsequently,a kinetic model of electron sheath is established,showing considerably different sheath proflles in respect to the fluid model due to non-Maxwellian electron velocity distribution function and flnite ion temperature.The kinetic model is then further generalized and involves a more realistic truncated ion velocity distribution function.It is demonstrated that such a distribution function yields a super-thermal electron sheath whose entering velocity at the sheath edge is greater than the Bohm criterion prediction.Furthermore,an attempt is made to describe the electron presheath–sheath coupling within the kinetic framework,showing a necessary compromise between a realistic sheath entrance and the inclusion of kinetic effects.Finally,the secondary electron emissions induced by sheath-accelerated plasma electrons in an electron sheath are analysed and the influence of backscattering is discussed.展开更多
A one-step procedure to hydrophilize monodisperse poly（chloromethyl-styrene-co-divinylbenzene） beads has been presented with 2-hydroxy-3-[4-（hydroxymethyl）-1H-1,2,3-triazol-1-yl]propy1 2-methylacrylate（HTMA） as ...A one-step procedure to hydrophilize monodisperse poly（chloromethyl-styrene-co-divinylbenzene） beads has been presented with 2-hydroxy-3-[4-（hydroxymethyl）-1H-1,2,3-triazol-1-yl]propy1 2-methylacrylate（HTMA） as monomer by surface-initiated atom transfer radical polymerization（SI-ATRP）.The length of the grafted poly（HTMA） chain was varied via controlling the ratio of HTMA to initiator on the surface of the beads.Using these grafted beads as the stationary phase in hydrophilic interaction chromatography,good separation was obtained for nucleosides in the mobile phase of acetonitrile-water.It was also found that the retention time and selectivity of solutes showed a positive relationship with the length of the grafted poly（HTMA） chain.展开更多
The mechanisms of Y on the wettability,surface tension,and interactions between the Ni-20 Co-20 Cr-10 Al-ξY alloys and MgO ceramics at 1873 K were investigated by sessile drop experiments.The results of nonlinear fit...The mechanisms of Y on the wettability,surface tension,and interactions between the Ni-20 Co-20 Cr-10 Al-ξY alloys and MgO ceramics at 1873 K were investigated by sessile drop experiments.The results of nonlinear fitting showed that the equilibrium contact angles and Y concentrations were approximately in accord with the log-normal distribution law.The equilibrium contact angles changed from 101.5°to 140.5°with Y increasing from 0 wt.%to 1.23 wt.%.Cross-sectional microstructure observations revealed that the thermal dissociation of ceramics occurred and the released[O]atoms can react with Y to produce Y_(2)O_(3) reaction layer along three-phase interphase area.Wetting kinetics analyses indicated that surface tension of the melt droplets had been positively correlated with the Y concentrations,and it increased from 737.8–1045.1 mN/m.Meanwhile,the pinning effect of the rough substrate surface on the three-phase line hindered the spreading of the liquid on ceramics.The change in total free energy of the alloys/ceramics system was considered as the key factor affecting the wettability.Moreover,the surface morphology and thermodynamic stability of ceramics also had some influence on the wettability.展开更多
This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten at...This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten atoms than hydrogen atoms, though a few of the latter can also penetrate into the tungsten material. When the incidence angle is greater than 75%, the incident CH2 particles are reflected without break-ups. Below this angle, a W-C layer of about 0.5 nm is formed with another C, H-rich layer depositing on top of it. The molecular dynamics （MD） approach has proved to be a powerful tool to solve the structural problems at atomic length scale of various materials. Some of its possible applications to the railway track materials have also been discussed.展开更多
The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer Sys...The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer System. In that framework, an innovative approach based on the application of the Bayesian Mixing Model (MixSIAR) analysis on water isotopes (oxygen-18, deuterium and tritium) was performed. Moreover, to assess the relevance of the model outputs, Pearson’s correlation and Principal Component Analysis (PCA) have been done. A complex relationship between surface water and groundwater has been found. Sixty percent (60%) of groundwater samples are made of more than 70% river water and rainwater;while 31.25% of surface water samples are made of about 84% groundwater. To safeguard sustainable water resources for the well-being of the local communities, surface water and groundwater must be managed as a unique component in the Kandi basin.展开更多
文摘In order to study the convection limits of surface fires and interactions between backfires and main fires,several experiments are conducted in a large space indoor laboratory: in which the effects of ambient wind speeds and changing temperatures can be avoided.The research shows that:(1) there is a convection field in front of coming fires in which the wind speed direction is toward the fire.In the convection area,the lower part has higher wind speed and when the height is taller than a certain value the convection wind speed is not significant;(2) the backfire and the main fire interact with each other even though they are far apart.When they come near each other to a certain distance,they begin to draw each other.This increases their rates of spread toward each other significantly.For surface fires with a fire line intensity of 160?kW\5m -1 ,their rate of spread increases by 27%.
基金supported jointly by the National Natural Science Foundation of China(Grant No.91337216)the Special Fund for Public Welfare Industry(Meteorology),administered by the Chinese Ministry of Finance and the Ministry of Science and Technology(Grant No.GYHY201406001)the CAS XDA(Grant No.11010402)
文摘The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually fol- lowed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an en- hanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly （SSTA） in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the at- mospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.
文摘Interactions involving chemical reagents,solid particles,gas bubbles,liquid droplets,and solid surfaces in complex fluids play a vital role in many engineering processes,such as froth flotation,emulsion and foam formation,adsorption,and fouling and anti-fouling phenomena.These interactions at the molecular,nano-,and micro scale significantly influence and determine the macroscopic performance and efficiency of related engineering processes.Understanding the intermolecular and surface interactions in engineering processes is of both fundamental and practical importance,which not only improves production technologies,but also provides valuable insights into the development of new materials.In this review,the typical intermolecular and surface interactions involved in various engineering processes,including Derjaguin–Landau–Verwey–Overbeek(DLVO)interactions(i.e.,van der Waals and electrical doublelayer interactions)and non-DLVO interactions,such as steric and hydrophobic interactions,are first introduced.Nanomechanical techniques such as atomic force microscopy and surface forces apparatus for quantifying the interaction forces of molecules and surfaces in complex fluids are briefly introduced.Our recent progress on characterizing the intermolecular and surface interactions in several engineering systems are reviewed,including mineral flotation,petroleum engineering,wastewater treatment,and energy storage materials.The correlation of these fundamental interaction mechanisms with practical applications in resolving engineering challenges and the perspectives of the research field have also been discussed.
文摘T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions however,in specific applications these joints undergo pull loading.De-lamination/de-bond nucleation and its growth is one of the most common failure mechanisms in a fiber reinforced composite structure.Crack growth takes place due to the induced interlaminar normal and shear stresses between different structural constituents when a load is applied.In this study,Finite Element Analysis has been performed using cohesive contact interactions on a composite T-joint to simulate the pull out test conditions.A simplified shell based model coupled with CZM is proposed,which can evaluate the failure initiation and progression accurately with lesser computational efforts.The final failure occurred at a displacement of 4.71 mm at the computed failure load of 472.57 kgf for basic configuration.Computed Failure load for the padded configuration is 672.8 kgf and corresponding displacement is 4.6 mm.The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted failure displacements and failure load calculated were correlating reasonably well with the experiment.
基金Project(2014BAB01B03)supported by the National Key Technology R&D Program During the 12th Five-Yean Plan of ChinaProject(51774286)supported by the National Natural Science Foundation of ChinaProject(BK20150192)supported by the Natural Science Foundation of Jiaaagsu Province,China
文摘The hydration film on particle surface plays an important role in bubble-particle adhesion in mineral flotation process. The thicknesses of the hydration films on natural hydrophobic coal and hydrophilic mica surfaces were measured directly by atomic force microscopy (AFM) based on the bending mode of the nominal constant compliance regime in AFM force curve in the present study. Surface and solid-liquid interfacial energies were calculated to explain the forming mechanism of the hydration film and atomic force microscopy data. The results show that there are significant differences in the structure and thickness of hydration films on coal and mica surfaces. Hydration film formed on mica surface with the thickness of 22.5 nm. In contrast, the bend was not detected in the nominal constant compliance regime. The van der Waals and polar interactions between both mica and coal and water molecules are characterized by an attractive effect, while the polar attractive free energy between water and mica (-87.36 mN/m) is significantly larger than that between water and coal (-32.89 mN/m), which leads to a thicker and firmer hydration layer on the mica surface. The interfacial interaction free energy of the coal/water/bubble is greater than that of mica. The polar attractive force is large enough to overcome the repulsive van der Waals force and the low energy barrier of film rupture, achieving coal particle bubble adhesion with a total interfacial free energy of-56.30 mN/m.
基金supported by the National Natural Science Foundation of China(Grant Nos.11347215,11464014,and 11104113)the Natural Science Foundation of Hunan Province,China(Grant Nos.13JJ6059 and 13JJB015)the Natural Science Foundation of Education Department of Hunan Province,China(Grant Nos.13C750 and 13B091)
文摘We use the photon Green-function method to study the quantum resonant dipole-dipole interaction（RDDI） induced by an Ag nanosphere（ANP）.As the distance between the two dipoles increases,the RDDI becomes weaker,which is accompanied by the influence of the higher-order mode of the ANP on RDDI declining more quickly than that of the dipole mode.Across a broad frequency range（above 0.05 eV）,the transfer rate of the RDDI is nearly constant since the two dipoles are fixed at the proper position.In addition,this phenomenon still exists for slightly different radius of the ANPs.We find that the frequency corresponding to the maximum transfer rate of RDDI exhibits a monotonic decrease by moving away one dipole as the other dipole and the ANP are kept fixed.In addition,the radius of ANP has little effect on this.When the two dipoles are far from the ANP,the maximum transfer rate of the RDDI takes place at the frequency of the dipole mode.In contrast,when the two dipoles are close to the ANP,the higher-order modes come into effect and they will play a leading role in the RDDI if they match the transition frequency of the dipole.Our results may be used in a biological detector and have a certain guiding significance for further application.
文摘The interaction between a flotation reagent and mineral surface not only depends on the bonding atom, but also depends on the adjacent atom of mineral surface, a flotation reagent and the medium in the system of flotation. Energy equation of a reagent interacting with mineral surface has been deduced from this model. Results of the studies indicate that the interaction energy between mineral surface and a reagent is about several dozen kJ/mol, and the relationship between adsorbing concentration of xanthate on mineral surface and interaction energy is the exponent form.
基金the Sino-Danish Centre for Education and Research, and the Technical University of Denmark for funding this project
文摘Fertilizer input for agricultural food production, as well as the discharge of domestic and industrial water pollutants, increases pressures on locally scarce and vulnerable water resources in the North China Plain. In order to：（a） understand pollutant exchange between surface water and groundwater,（b） quantify nutrient loadings, and（c） identify major nutrient removal pathways by using qualitative and quantitative methods, including the geochemical model PHREEQC） a one-year study at a wheat（Triticum aestivum L.） and maize（Zea mays L.） double cropping system in the Baiyang Lake area in Hebei Province, China, was undertaken. The study showed a high influence of low-quality surface water on the shallow aquifer. Major inflowing pollutants into the aquifer were ammonium and nitrate via inflow from the adjacent Fu River（up to 29.8 mg/L NH4-N and 6.8 mg/L NO3-N）, as well as nitrate via vertical transport from the field surface（up to 134.8 mg/L NO3-N in soil water）. Results from a conceptual model show an excess nitrogen input of about 320 kg/ha/a. Nevertheless,both nitrogen species were only detected at low concentrations in shallow groundwater,averaging at 3.6 mg/L NH4-N and 1.8 mg/L NO3-N. Measurement results supported by PHREEQC-modeling indicated cation exchange, denitrification, and anaerobic ammonium oxidation coupled with partial denitrification as major nitrogen removal pathways. Despite the current removal capacity, the excessive nitrogen fertilization may pose a future threat to groundwater quality. Surface water quality improvements are therefore recommended in conjunction with simultaneous monitoring of nitrate in the aquifer, and reduced agricultural N-inputs should be considered.
基金Project(2017YFC0805406)supported by the National Key Research and Development Program of ChinaProjects(51879142,51679123)supported by the National Natural Science Foundation of ChinaProject(2020-KY-04)supported by the Research Fund Program of the State Key Laboratory of Hydroscience and Engineering,China。
文摘Based on the interface shear tests,the macro-and meso-mechanical behaviors of interaction between coral sand and different structure surfaces are studied,in which CCD camera is used to capture digital images to analyze the evolution of the interaction band and a particle analysis apparatus is applied to studying the distribution characteristics of particle morphology.This study proposes four-stage evolution process based on the shear stress−strain curve.During the shear process,coral sand particles slide and rotate within the interaction band,causing the changes in shear stress and vertical displacement.In addition,the effects of structure surface roughness on shear strength,volume change and particle breakage are illustrated that the greater the roughness of slabs is,the larger the shear stress is,the more obvious the contraction effect is and the more the particles break.Furthermore,the change in particle’s 3D morphology during the breakage will change not only their size but also other morphological characteristics with convergence and self-organization.
文摘The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency should be accounted for in the mechanical behaviors of nanoscale structures. In the current investigation, the influence of free surface energy on the nonlinear primary resonance of silicon nanoshells under soft harmonic external excitation is studied. In order to obtain more accurate results,the interaction between the first, third, and fifth symmetric vibration modes with the main oscillation mode is taken into consideration. Through the implementation of the Gurtin-Murdoch theory of elasticity into the classical shell theory, a size-dependent shell model is developed incorporating the effect of surface free energy. With the aid of the variational approach, the governing differential equations of motion including both of the cubic and quadratic nonlinearities are derived. Thereafter, the multi-time-scale method is used to achieve an analytical solution for the nonlinear size-dependent problem. The frequency-response and amplitude-response of the soft harmonic excited nanoshells are presented corresponding to different values of shell thickness and surface elastic constants as well as various vibration mode interactions. It is depicted that through consideration of the interaction between the higher symmetric vibration modes and the main oscillation mode, the hardening response of nanoshell changes to the softening one. This pattern is observed corresponding to both of the positive and negative values of the surface elastic constants and the surface residual stress.
基金Supported by the National Natural Science Foundation of China under Grant No 51305033the Ministry of National Defense of China under Grant No 9140C340506
文摘An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achieve- ment of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51579122,51609109,and 51622902)the Natural Science Found of Jiangsu Province(Grant No.BK20160556)+1 种基金the University Natural Science Research Project of Jiangsu Province(Grant No.16kjb70003)the Key Lab Foundation for Advanced Manufacturing Technology of Jiangsu Province(Grant No.CJ1506)
文摘This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.
文摘The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE) satellite using the test particle Monte Carlo(TPMC) method. The primary goal is to obtain a comprehensive understanding of surface pressure and skin friction on the spacecraft surface and assess the sensitivity of aerodynamic drag to the gas-surface interaction(GSI) models. Results indicate that surface pressure is mainly distributed on the front of the satellite body and panels while skin friction is primarily distributed on the sides. In addition, as the GSI model changes from diffuse to specular reflection, the total drag coefficient is reduced at operation altitudes above 170 km. Therefore, the satellite surface should be processed so carefully that the GSI remains far from diffuse reflection from the view point of the drag-reduce design.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51172030,11274052,51102019,51172208,and 61274015)the National Basic Research Program of China(Grant No.2010CB923200)
文摘The coupling interaction between an individual optical emitter and the propagating surface plasmon polaritons in a graphene microribbon （GMR） waveguide is investigated by numerical calculations, where the emitter is situated above the GMR or in the same plane of the GMR, The results reveal a multimode coupling mechanism for the strong interaction between the emitter and the propagating plasmonic waves in graphene. When the emitter is situated in the same plane of the GMR, the decay rate from the emitter to the surface plasmon polaritons increases more than 10 times compared with that in the case with the emitter above the GMR.
文摘The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional （Q3D） vegetated surface flow model with a two-dimensional （2D） saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations （SWEs） with the implicit finite difference solution of Navier-Stokes equations （NSEs） for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations （SGFEs）. The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.
基金the auspices of National Natural Science Foundation of China(Nos.51827809,52077169)the National Key R&D Program of China(No.2020YFC2201100)。
文摘In this work,an improved understanding of electron sheath theory is provided using both fluid and kinetic approaches while elaborating on their implications for plasma–surface interactions.A fluid model is proposed considering the electron presheath structure,avoiding the singularity in electron sheath Child–Langmuir law which overestimates the sheath potential.Subsequently,a kinetic model of electron sheath is established,showing considerably different sheath proflles in respect to the fluid model due to non-Maxwellian electron velocity distribution function and flnite ion temperature.The kinetic model is then further generalized and involves a more realistic truncated ion velocity distribution function.It is demonstrated that such a distribution function yields a super-thermal electron sheath whose entering velocity at the sheath edge is greater than the Bohm criterion prediction.Furthermore,an attempt is made to describe the electron presheath–sheath coupling within the kinetic framework,showing a necessary compromise between a realistic sheath entrance and the inclusion of kinetic effects.Finally,the secondary electron emissions induced by sheath-accelerated plasma electrons in an electron sheath are analysed and the influence of backscattering is discussed.
基金supported by National Natural Science Foundation of China(No.20975080)Program for New Century Excellent Talents in University(No.NCET-08-0892)+1 种基金Major State Basic Research Development Program of China(No.2009CB26608)Natural Science Foundation of Ningxia Province(No.NZ0914)
文摘A one-step procedure to hydrophilize monodisperse poly（chloromethyl-styrene-co-divinylbenzene） beads has been presented with 2-hydroxy-3-[4-（hydroxymethyl）-1H-1,2,3-triazol-1-yl]propy1 2-methylacrylate（HTMA） as monomer by surface-initiated atom transfer radical polymerization（SI-ATRP）.The length of the grafted poly（HTMA） chain was varied via controlling the ratio of HTMA to initiator on the surface of the beads.Using these grafted beads as the stationary phase in hydrophilic interaction chromatography,good separation was obtained for nucleosides in the mobile phase of acetonitrile-water.It was also found that the retention time and selectivity of solutes showed a positive relationship with the length of the grafted poly（HTMA） chain.
基金supported by the National Natural Science Foundation of China(Nos.51604014 and 51404017)the National Science&Technology Pillar Program of China(No.2013BAB11B04)。
文摘The mechanisms of Y on the wettability,surface tension,and interactions between the Ni-20 Co-20 Cr-10 Al-ξY alloys and MgO ceramics at 1873 K were investigated by sessile drop experiments.The results of nonlinear fitting showed that the equilibrium contact angles and Y concentrations were approximately in accord with the log-normal distribution law.The equilibrium contact angles changed from 101.5°to 140.5°with Y increasing from 0 wt.%to 1.23 wt.%.Cross-sectional microstructure observations revealed that the thermal dissociation of ceramics occurred and the released[O]atoms can react with Y to produce Y_(2)O_(3) reaction layer along three-phase interphase area.Wetting kinetics analyses indicated that surface tension of the melt droplets had been positively correlated with the Y concentrations,and it increased from 737.8–1045.1 mN/m.Meanwhile,the pinning effect of the rough substrate surface on the three-phase line hindered the spreading of the liquid on ceramics.The change in total free energy of the alloys/ceramics system was considered as the key factor affecting the wettability.Moreover,the surface morphology and thermodynamic stability of ceramics also had some influence on the wettability.
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten atoms than hydrogen atoms, though a few of the latter can also penetrate into the tungsten material. When the incidence angle is greater than 75%, the incident CH2 particles are reflected without break-ups. Below this angle, a W-C layer of about 0.5 nm is formed with another C, H-rich layer depositing on top of it. The molecular dynamics （MD） approach has proved to be a powerful tool to solve the structural problems at atomic length scale of various materials. Some of its possible applications to the railway track materials have also been discussed.
文摘The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer System. In that framework, an innovative approach based on the application of the Bayesian Mixing Model (MixSIAR) analysis on water isotopes (oxygen-18, deuterium and tritium) was performed. Moreover, to assess the relevance of the model outputs, Pearson’s correlation and Principal Component Analysis (PCA) have been done. A complex relationship between surface water and groundwater has been found. Sixty percent (60%) of groundwater samples are made of more than 70% river water and rainwater;while 31.25% of surface water samples are made of about 84% groundwater. To safeguard sustainable water resources for the well-being of the local communities, surface water and groundwater must be managed as a unique component in the Kandi basin.
