This article presented a facile fabrication process for polydimethylsiloxane(PDMS)composite gold nanotris⁃octahedra(Au NTOH)for a flexible SERS sensor with high sensitivity.Specifically,Au NTOH with excellent SERS beh...This article presented a facile fabrication process for polydimethylsiloxane(PDMS)composite gold nanotris⁃octahedra(Au NTOH)for a flexible SERS sensor with high sensitivity.Specifically,Au NTOH with excellent SERS behaviors was synthesized using a seed-mediated growth method and the dimensions of the Au NTOH was easily tuned.In addition,the influence of size on the SERS performance of their monolayers was systematically investigated,and the Au NTOH with the size of 61 nm possessed the best SERS performance.Importantly,a hydrophilic-substrateassisted interfacial self-assembled monolayer transfer technique was proposed to transfer Au NTOH onto PDMS films,resulting in forming flexible and transparent Au NTOH@PDMS substrates.Furthermore,the excellent signal homoge⁃neity of this substrate was demonstrated and the sensitivity was verified by a measurement of crystal violet(CV)as low as 1×10^(-8) mol/L.As a result,this SERS sensor is progressing for applying in the identification of trace contaminants in broad fields.展开更多
Two metal-organic frameworks(MOFs),trans-[Co(L)(μ_(2)-H_(2)O)(H_(2)O)2]·2H_(2)O(1)and cis-[Mn(L)(Bipy)](2)(H_(2)L=2,2'-dimethyl-4,4'-biphenyldicarboxylic acid,Bipy=4,4'-bipyridine),have been synthesi...Two metal-organic frameworks(MOFs),trans-[Co(L)(μ_(2)-H_(2)O)(H_(2)O)2]·2H_(2)O(1)and cis-[Mn(L)(Bipy)](2)(H_(2)L=2,2'-dimethyl-4,4'-biphenyldicarboxylic acid,Bipy=4,4'-bipyridine),have been synthesized and character-ized by FTIR,thermogravimetric analysis(TGA),powder and single crystal X-ray diffraction.MOF 1 crystallizes in the triclinic system with a P1 space group and contains two crystallographically different Coions.Each trans-[CoO_(6)]octahedron is connected byμ_(2)-H_(2)O and L^(2-)ligand with a bis(unidentate)coordination mode to produce a 2D sql topological network.MOF 2 crystallizes in the monoclinic system with a C2/c space group.The Mncation adopts a cis-[MnO_(4)N_(2)]octahedron as a 6-connected node and is linked by L^(2-)ligand as a 4-connected node to gener-ate a binodal(4,6)-connected 3D fsc framework.The intermolecular interactions in 1 and 2 have been investigated by 3D Hirshfeld surface analyses and 2D fingerprint plots to reveal that the main interactions are H…H and O…H/H…O contacts in 1,and H…H and C…H/H…C contacts in 2.The TGA indicated that 1 and 2 were stable below 390 and 370℃,respectively.展开更多
In this paper,we propose an RLC equivalent circuit model theory which can accurately predict the spectral response and resonance characteristics of metamaterial absorption structures,extend its design,and characterize...In this paper,we propose an RLC equivalent circuit model theory which can accurately predict the spectral response and resonance characteristics of metamaterial absorption structures,extend its design,and characterize the parameters of the model in detail.By employing this model,we conducted computations to characterize the response wavelength and bandwidth of variously sized metamaterial absorbers.A comparative analysis with Finite Difference Time Domain(FDTD)simulations demonstrated a remarkable level of consistency in the results.The designed absorbers were fabricated using micro-nano fabrication processes,and were experimentally tested to demonstrate absorption rates exceeding 90%at a wavelength of 9.28μm.The predicted results are then compared with test results.The comparison reveals good consistency in two aspects of the resonance responses,thereby confirming the rationality and accuracy of this model.展开更多
In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’d...In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.展开更多
Mesoporous carbon supports mitigate platinum(Pt)sulfonic poisoning through nanopore-confined Pt deposition,yet their morphological impacts on oxygen transport remain unclear.This study integrates carbon support morpho...Mesoporous carbon supports mitigate platinum(Pt)sulfonic poisoning through nanopore-confined Pt deposition,yet their morphological impacts on oxygen transport remain unclear.This study integrates carbon support morphology simulation with an enhanced agglomerate model to establish a mathematical framework elucidating pore evolution,Pt utilization,and oxygen transport in catalyst layers.Results demonstrate dominant local mass transport resistance governed by three factors:(1)active site density dictating oxygen flux;(2)ionomer film thickness defining shortest transport path;(3)ionomer-to-Pt surface area ratio modulating practical pathway length.At low ionomer-to-carbon(I/C)ratios,limited active sites elevate resistance(Factor 1 dominant).Higher I/C ratios improve the ionomer coverage but eventually thicken ionomer films,degrading transport(Factors 2–3 dominant).The results indicate that larger carbon particles result in a net increase in local transport resistance by reducing external surface area and increasing ionomer thickness.As the proportion of Pt situated in nanopores or the Pt mass fraction increases,elevated Pt density inside the nanopores exacerbates pore blockage.This leads to the increased transport resistance by reducing active sites,and increasing ionomer thickness and surface area.Lower Pt loading linearly intensifies oxygen flux resistance.The model underscores the necessity to optimize support morphology,Pt distribution,and ionomer content to prevent pore blockage while balancing catalytic activity and transport efficiency.These insights provide a systematic approach for designing high-performance mesoporous carbon catalysts.展开更多
Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleif...Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleifera saponin(COS)was purified using AB-8 macroporous adsorption resin,and its composition and structure were analyzed.The effects of different mole fractions of COS(αCOS)on surface tension(γ),oil-water interfacial tension(IFT),emulsification,and foam properties of COS-SCG binary mixed systems were investigated in mixtures of SCG with purified COS.The stability ofγand foamability under diverse environmental conditions were also discussed.The results indicated that the COS-SCG system exhibited remarkable surface-active synergism.The minimum critical micelle concentration(cmc)of the mixed system was lower than that of SCG,and adding a small mole fraction of COS(1%-2%)induced a synergistic reduction ofγ.Specifically,the cmc andγwere 2.50×10-4 mol/L and 23.1 mN/m forαCOS=1%,respectively.The system exhibited exceptional IFT reduction capacity,achieving a minimum value of 1.42 mN/m atαCOS=10%.The mixed system reached a foaming volume(atαCOS=50%)and foam stability(atαCOS=75%)were 51.0 mL and 97.37%,respectively.Microscopic analysis further confirmed these outstanding foam properties.Moreover,the COS-SCG system displayed reducedγwith enhanced foaming volume under elevated temperatures(35-75℃)and salinity(0-20 g/L).However,acidic conditions and hard water compromised bothγstability and foamability.展开更多
Based on the criteria for additional surface acidity generation in composite oxides and composite fluorides proposed by Tanabe and Kemnitz et al.A hypothesis for the origin of additional surface acidity in solid compo...Based on the criteria for additional surface acidity generation in composite oxides and composite fluorides proposed by Tanabe and Kemnitz et al.A hypothesis for the origin of additional surface acidity in solid composites with the same metal cations is proposed.The surface acidsites of We analyze three types of solid composite systems,that is,CrF_(3)/Cr_(2)O_(3),MgF_(2)/MgO,and ZnF_(2)/ZnO,is systematically analyzed,which agrees with experimental results.Accordingly,the origin of additional surface acidity in these solid composites is reasonably explained,and the types of acidic sites are also predicted.展开更多
To solve the problem of sealing between the barrel and the rubber ring of shell body during an launching process of aerodynamic extinguishing cannon, a rubber sealing model with bionic dimpled characteristics was esta...To solve the problem of sealing between the barrel and the rubber ring of shell body during an launching process of aerodynamic extinguishing cannon, a rubber sealing model with bionic dimpled characteristics was established based on the theory of bionic dimpled drag reduction and the principle of rubber sealing. In condition that the bionic dimpled characteristic diameters were 1, 2, 3, 4, and 5 mm, respectively, by numerical simulation, the influence of the installing compression of the rubber sealing ring on its surface stress and deformation was analyzed, and sealing performance of the rubber ring with different diameters of bionic dimpled was studied. The results show that the deformation of rubber ring appears prominent nonlinear characteristics when compression is increased from 1.5 mm to 2.5 ram. When the compression is 2.5 mm, the equivalent compression stress on the sealing areas of both sides of the rubber seal is greater than the working pressure of aerodynamic extinguishing cannon, which could meet the sealing requirement and would not cause leakage. So the rubber sealing ring with bionic dimpled surface possesses a good sealing characteristic and has no negative effect on the sealing of shell body; When the compression is 2.5 mm, the larger equivalent stress on the edge of sealing ring and the more even stress distribution in the high pressure area are generated due to the smaller compressive stress on the bionic dimple areas, which lays a foundation for the drag reduction characteristics of the shell body＇s rubber ring with bionic dimpled surface.展开更多
Superalloys are grouped as hard-to-cut materials with relatively poor machinability.Tool wear is considered one of the main machinability attributes in machining superalloys.Although numerous works have been reported ...Superalloys are grouped as hard-to-cut materials with relatively poor machinability.Tool wear is considered one of the main machinability attributes in machining superalloys.Although numerous works have been reported on factors governing tool life in machining superalloys,no study was found on the effect of nanoparticles stability on nanofluid performance and consequently resulted tool wear morphologies.In the present work,the nanoparticles were reinforced by means of improving the stability of the base fluid.To that accomplished,the surface active agent (surfactant) was added to the base cutting fluid as a reinforcing element.The effects of new lubricant on the tool wear morphology of A286 works parts were assessed.展开更多
Since the volume variation of silicon particles during cycling,the binding spots between Cu current collector and silicon anode raised to be one of the critical binding problems.In this work,an amino-modified Cu curre...Since the volume variation of silicon particles during cycling,the binding spots between Cu current collector and silicon anode raised to be one of the critical binding problems.In this work,an amino-modified Cu current collector(Cu^(*))is fabricated to tackle this issue.The amino groups on Cu^(*)surface increase its hydrophilicity,which is conducive to the curing process of aqueous slurry on its surface.Meanwhile,these amino groups can form abundant amide bonds with carboxyl groups from the adopted polyacrylic acid(PAA)binder.The combined action composed of the covalent bond and mechanical interlocking could reduce the contact loss inside the electrode.However,high concentration silane coupling agent treatment will weaken the surface roughness of Cu^(*)and weaken mechanical interlocking.What is more,the insulation of silane coupling agent reduces the conductivity of Cu and increases the impedance of battery.Considering the effect of silane coupling agent comprehensively,electrochemical performance of Cu^(*)-0.05%is best.展开更多
Changsha,a typical city in central China,was selected as the study area to assess the variations of ecosystem service value on the basis of land-use change. The analysis not only included the whole city but also the u...Changsha,a typical city in central China,was selected as the study area to assess the variations of ecosystem service value on the basis of land-use change. The analysis not only included the whole city but also the urban district where the landscape changed more rapidly in the center of the city. Two LANDSAT TM data sets in 1986 and 2000 and land use data of five urban districts from 1995 to 2005 were used to estimate the changes in the size of six land use categories. Meanwhile,previously published value coefficients were used to detect the changes in the value of ecosystem services delivered by each land category. The result shows that the total value of ecosystem services in Changsha declines from $1 009.28 million per year in 1986 to $938.11 million per year in 2000. This decline is largely attributable to the increase of construction land,and the conversion from woodland and water body to cropland to keep the crop production. In the five districts,there is $6.19 million decline in ecosystem service value between 1995 and 2005. Yuelu District has the highest unit ecosystem service value while Yuhua District has the lowest one. This may be attributed to the greater conversion from cropland and grassland to woodland and water body with the increase of construction land in Yuelu District. It is suggested that the increase rate of construction land should be controlled rigorously and the area of woodland and water body should be increased or at least retained in the study area.展开更多
The method for calculating wall surface heat storage coefficient was introduced,and the coefficients of several common walls with light-weight external thermal insulation materials and the traditional solid clay brick...The method for calculating wall surface heat storage coefficient was introduced,and the coefficients of several common walls with light-weight external thermal insulation materials and the traditional solid clay brick wall were calculated.In order to study the impact of light-weight external thermal insulation materials,a contrasting experiment was carried out between an external insulated room and an uninsulated room in August,2010,in Chongqing,China.The result shows that outside surface heat storage coefficient of the insulated wall is much less than that of the traditional wall.However,during sunny time,the surface temperature of external walls of the insulated room is obviously higher than that of the uninsulated room.In different orientations,due to different amounts of solar radiation and being irradiated in different time,the contrasting temperature difference(CTD) appears different regularity.In a word,using light-weight external thermal insulation materials has a negative impact on building surrounding thermal environment and people's health.Finally,some suggestions on how to eliminate the impact,such as improving the surface condition of the building envelop,and plating vertical greening,are put forward.展开更多
An active pipe-embedded building envelope, which is an external wall or roof with pipes embedded inside, was presented. This structure may utilize the circulating water in the pipe to transfer heat or coolth inside di...An active pipe-embedded building envelope, which is an external wall or roof with pipes embedded inside, was presented. This structure may utilize the circulating water in the pipe to transfer heat or coolth inside directly. This kind of structure is named ＂active pipe-embedded building envelope＂ due to dealing with the thermal energy actively inside the structure mass by circulating water. This structure not only deals with thermal energy before the external disturbance becomes cooling/heating load by using the circulating water, but also may use low-grade energy sources such as evaporative cooling, solar energy, and geothermal energy. In the meantime, this structure can also improve the indoor thermal comfort by tempering the internal wall surface temperature variation due to the thermal removal in the mass. This work further presents the thermal performance of this structure under a typical hot summer weather condition by comparing it with that of the conventional external wall/roof with numerical simulation. The results show that this pipe-embedded structure may reduce the external heat transfer significantly and reduce the internal wall surface temperature for improving thermal comfort. This work also presents the effects of the water temperature and the pipe spacing on the heat transfer of this structure. The internal surface heat transfer may reduce by about 2.6 W/mE when the water temperature reduces by 1℃ as far as a brick wall with pipes embedded inside is concerned. When the pipe spacing reduces by 50 mm, the internal wall surface heat flux can also reduce by about 2.3 W/m2.展开更多
Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction effic...Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction efficiency were studied. The results show that silicon extraction efficiency increases with increasing the reaction time and Na OH-to-CBM mass ratio. There are two stages for the desilication process of the calcined boron mud. The overall desilication process follows the shrinking-core model, and the first and second stages of the process were determined to obey the shrinking-core model for surface chemical reaction and the diffusion through the product layer, respectively. The activation energies of the first and second stages were calculated to be 44.78 k J/mol and 15.94 k J/mol, respectively.展开更多
Rock blocks sliding along discontinuities can cause serious disasters,such as landslides,earthquakes,or rock bursts.The shear rate-dependent behavior is a typical time-dependent behavior of a rock discontinuity,and it...Rock blocks sliding along discontinuities can cause serious disasters,such as landslides,earthquakes,or rock bursts.The shear rate-dependent behavior is a typical time-dependent behavior of a rock discontinuity,and it is closely related to the stability of a rock block.To further study the shear rate-dependent behavior of rock discontinuities,shear tests with alternating shear rates(SASRs)were conducted on rock discontinuities with various surface morphologies.The dynamic evolution of the shear rate dependency was studied in detail based on the shear test results,and three stages were identified with respect to the shear stress and shear deformation states.The test results revealed that dynamic changes in shear stiffness and the energy storage abilities of the rock discontinuities occurred in relation to the shear rate-dependent behavior of crack growth,which increased with an increase in normal stress and/or the joint roughness coefficient.The stage of decreasing shear stiffness corresponded to a stage of noticeable shear rate-dependency,and the shear rate was found to have no influence on the initial crack stress.展开更多
Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coati...Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.展开更多
Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical micro...Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.展开更多
A magnet is an important component of a speaker,as it makes the coil move back forth,and it is commonly used in mobile information terminals.Defects may appear on the surface of the magnet while cutting it into smalle...A magnet is an important component of a speaker,as it makes the coil move back forth,and it is commonly used in mobile information terminals.Defects may appear on the surface of the magnet while cutting it into smaller slices,and hence,automatic detection of surface cutting defect detection becomes an important task for magnet production.In this work,an image-based detection system for magnet surface defect was constructed,a Fourier image reconstruction based on the magnet surface image processing method was proposed.The Fourier transform was used to get the spectrum image of the magnet image,and the defect was shown as a bright line in it.The Hough transform was used to detect the angle of the bright line,and this line was removed to eliminate the defect from the original gray image;then the inverse Fourier transform was applied to get the background gray image.The defect region was obtained by evaluating the gray-level differences between the original image and the background gray image.Further,the effects of several parameters in this method were studied and the optimized values were obtained.Experiment results show that the proposed method can detect surface cutting defects in a magnet automatically and efficiently.展开更多
Based on structural surface normal vector spherical distance and the pole stereographic projection Euclidean distance,two distance functions were established.The cluster analysis of structure surface was conducted by ...Based on structural surface normal vector spherical distance and the pole stereographic projection Euclidean distance,two distance functions were established.The cluster analysis of structure surface was conducted by the use of ATTA clustering methods based on ant colony piles,and Silhouette index was introduced to evaluate the clustering effect.The clustering analysis of the measured data of Sanshandao Gold Mine shows that ant colony ATTA-based clustering method does better than K-mean clustering analysis.Meanwhile,clustering results of ATTA method based on pole Euclidean distance and ATTA method based on normal vector spherical distance have a great consistence.The clustering results are most close to the pole isopycnic graph.It can efficiently realize grouping of structural plane and determination of the dominant structural surface direction.It is made up for the defects of subjectivity and inaccuracy in icon measurement approach and has great engineering value.展开更多
基金The National Natural Science Foundation of China(12274055)the Fundamental Research Funds for the Central Universities(04442024072)the Training Program of Innovation and Entrepreneurship for Undergraduates in Dalian Minzu University(202312026063)。
文摘This article presented a facile fabrication process for polydimethylsiloxane(PDMS)composite gold nanotris⁃octahedra(Au NTOH)for a flexible SERS sensor with high sensitivity.Specifically,Au NTOH with excellent SERS behaviors was synthesized using a seed-mediated growth method and the dimensions of the Au NTOH was easily tuned.In addition,the influence of size on the SERS performance of their monolayers was systematically investigated,and the Au NTOH with the size of 61 nm possessed the best SERS performance.Importantly,a hydrophilic-substrateassisted interfacial self-assembled monolayer transfer technique was proposed to transfer Au NTOH onto PDMS films,resulting in forming flexible and transparent Au NTOH@PDMS substrates.Furthermore,the excellent signal homoge⁃neity of this substrate was demonstrated and the sensitivity was verified by a measurement of crystal violet(CV)as low as 1×10^(-8) mol/L.As a result,this SERS sensor is progressing for applying in the identification of trace contaminants in broad fields.
文摘Two metal-organic frameworks(MOFs),trans-[Co(L)(μ_(2)-H_(2)O)(H_(2)O)2]·2H_(2)O(1)and cis-[Mn(L)(Bipy)](2)(H_(2)L=2,2'-dimethyl-4,4'-biphenyldicarboxylic acid,Bipy=4,4'-bipyridine),have been synthesized and character-ized by FTIR,thermogravimetric analysis(TGA),powder and single crystal X-ray diffraction.MOF 1 crystallizes in the triclinic system with a P1 space group and contains two crystallographically different Coions.Each trans-[CoO_(6)]octahedron is connected byμ_(2)-H_(2)O and L^(2-)ligand with a bis(unidentate)coordination mode to produce a 2D sql topological network.MOF 2 crystallizes in the monoclinic system with a C2/c space group.The Mncation adopts a cis-[MnO_(4)N_(2)]octahedron as a 6-connected node and is linked by L^(2-)ligand as a 4-connected node to gener-ate a binodal(4,6)-connected 3D fsc framework.The intermolecular interactions in 1 and 2 have been investigated by 3D Hirshfeld surface analyses and 2D fingerprint plots to reveal that the main interactions are H…H and O…H/H…O contacts in 1,and H…H and C…H/H…C contacts in 2.The TGA indicated that 1 and 2 were stable below 390 and 370℃,respectively.
基金Supported by the National Natural Science Foundation of China(62174092)the Open Fund of State Key Laboratory of Infrared Physics(SITP-NLIST-ZD-2023-04)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB0580000)。
文摘In this paper,we propose an RLC equivalent circuit model theory which can accurately predict the spectral response and resonance characteristics of metamaterial absorption structures,extend its design,and characterize the parameters of the model in detail.By employing this model,we conducted computations to characterize the response wavelength and bandwidth of variously sized metamaterial absorbers.A comparative analysis with Finite Difference Time Domain(FDTD)simulations demonstrated a remarkable level of consistency in the results.The designed absorbers were fabricated using micro-nano fabrication processes,and were experimentally tested to demonstrate absorption rates exceeding 90%at a wavelength of 9.28μm.The predicted results are then compared with test results.The comparison reveals good consistency in two aspects of the resonance responses,thereby confirming the rationality and accuracy of this model.
文摘In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.
基金supported by the Program of Ministry of Science and Technology of China(No.2023YFB2504200)support of Shanghai Rising-Star Program(Grant No.24QB2703200)the Major Science and Technology Projects of Yunnan Province(No.202302AH360001).
文摘Mesoporous carbon supports mitigate platinum(Pt)sulfonic poisoning through nanopore-confined Pt deposition,yet their morphological impacts on oxygen transport remain unclear.This study integrates carbon support morphology simulation with an enhanced agglomerate model to establish a mathematical framework elucidating pore evolution,Pt utilization,and oxygen transport in catalyst layers.Results demonstrate dominant local mass transport resistance governed by three factors:(1)active site density dictating oxygen flux;(2)ionomer film thickness defining shortest transport path;(3)ionomer-to-Pt surface area ratio modulating practical pathway length.At low ionomer-to-carbon(I/C)ratios,limited active sites elevate resistance(Factor 1 dominant).Higher I/C ratios improve the ionomer coverage but eventually thicken ionomer films,degrading transport(Factors 2–3 dominant).The results indicate that larger carbon particles result in a net increase in local transport resistance by reducing external surface area and increasing ionomer thickness.As the proportion of Pt situated in nanopores or the Pt mass fraction increases,elevated Pt density inside the nanopores exacerbates pore blockage.This leads to the increased transport resistance by reducing active sites,and increasing ionomer thickness and surface area.Lower Pt loading linearly intensifies oxygen flux resistance.The model underscores the necessity to optimize support morphology,Pt distribution,and ionomer content to prevent pore blockage while balancing catalytic activity and transport efficiency.These insights provide a systematic approach for designing high-performance mesoporous carbon catalysts.
文摘Sodium cocoyl glycinate(SCG),an environmentally friendly anionic amino acid surfactant,is widely used in daily chemical products as an upgraded alternative to traditional surfactants.In this study,crude Camellia oleifera saponin(COS)was purified using AB-8 macroporous adsorption resin,and its composition and structure were analyzed.The effects of different mole fractions of COS(αCOS)on surface tension(γ),oil-water interfacial tension(IFT),emulsification,and foam properties of COS-SCG binary mixed systems were investigated in mixtures of SCG with purified COS.The stability ofγand foamability under diverse environmental conditions were also discussed.The results indicated that the COS-SCG system exhibited remarkable surface-active synergism.The minimum critical micelle concentration(cmc)of the mixed system was lower than that of SCG,and adding a small mole fraction of COS(1%-2%)induced a synergistic reduction ofγ.Specifically,the cmc andγwere 2.50×10-4 mol/L and 23.1 mN/m forαCOS=1%,respectively.The system exhibited exceptional IFT reduction capacity,achieving a minimum value of 1.42 mN/m atαCOS=10%.The mixed system reached a foaming volume(atαCOS=50%)and foam stability(atαCOS=75%)were 51.0 mL and 97.37%,respectively.Microscopic analysis further confirmed these outstanding foam properties.Moreover,the COS-SCG system displayed reducedγwith enhanced foaming volume under elevated temperatures(35-75℃)and salinity(0-20 g/L).However,acidic conditions and hard water compromised bothγstability and foamability.
基金The Key Research and Development Program of Zhejiang Province(2021C01003)National Natural Science Foundation of China(52025011,51971202,51872260 and 52171019)The Zhejiang Provincial Natural Science Foundation of China(LD19B030001,Z4080070 and LR23B030004)。
文摘Based on the criteria for additional surface acidity generation in composite oxides and composite fluorides proposed by Tanabe and Kemnitz et al.A hypothesis for the origin of additional surface acidity in solid composites with the same metal cations is proposed.The surface acidsites of We analyze three types of solid composite systems,that is,CrF_(3)/Cr_(2)O_(3),MgF_(2)/MgO,and ZnF_(2)/ZnO,is systematically analyzed,which agrees with experimental results.Accordingly,the origin of additional surface acidity in these solid composites is reasonably explained,and the types of acidic sites are also predicted.
基金Project(51275102)supported by the National Natural Science Foundation of ChinaProject(159070220011)supported by the Science and Technology Innovative Research Programs Foundation of Harbin city,ChinaProject(HEUCF110702)supported by the Fundamental Research Funds for the Central Universities of China
文摘To solve the problem of sealing between the barrel and the rubber ring of shell body during an launching process of aerodynamic extinguishing cannon, a rubber sealing model with bionic dimpled characteristics was established based on the theory of bionic dimpled drag reduction and the principle of rubber sealing. In condition that the bionic dimpled characteristic diameters were 1, 2, 3, 4, and 5 mm, respectively, by numerical simulation, the influence of the installing compression of the rubber sealing ring on its surface stress and deformation was analyzed, and sealing performance of the rubber ring with different diameters of bionic dimpled was studied. The results show that the deformation of rubber ring appears prominent nonlinear characteristics when compression is increased from 1.5 mm to 2.5 ram. When the compression is 2.5 mm, the equivalent compression stress on the sealing areas of both sides of the rubber seal is greater than the working pressure of aerodynamic extinguishing cannon, which could meet the sealing requirement and would not cause leakage. So the rubber sealing ring with bionic dimpled surface possesses a good sealing characteristic and has no negative effect on the sealing of shell body; When the compression is 2.5 mm, the larger equivalent stress on the edge of sealing ring and the more even stress distribution in the high pressure area are generated due to the smaller compressive stress on the bionic dimple areas, which lays a foundation for the drag reduction characteristics of the shell body＇s rubber ring with bionic dimpled surface.
文摘Superalloys are grouped as hard-to-cut materials with relatively poor machinability.Tool wear is considered one of the main machinability attributes in machining superalloys.Although numerous works have been reported on factors governing tool life in machining superalloys,no study was found on the effect of nanoparticles stability on nanofluid performance and consequently resulted tool wear morphologies.In the present work,the nanoparticles were reinforced by means of improving the stability of the base fluid.To that accomplished,the surface active agent (surfactant) was added to the base cutting fluid as a reinforcing element.The effects of new lubricant on the tool wear morphology of A286 works parts were assessed.
基金Project(2019R01006)supported by the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang Province,ChinaProject(2018YFB0104300)supported by the National Key R&D Program of China。
文摘Since the volume variation of silicon particles during cycling,the binding spots between Cu current collector and silicon anode raised to be one of the critical binding problems.In this work,an amino-modified Cu current collector(Cu^(*))is fabricated to tackle this issue.The amino groups on Cu^(*)surface increase its hydrophilicity,which is conducive to the curing process of aqueous slurry on its surface.Meanwhile,these amino groups can form abundant amide bonds with carboxyl groups from the adopted polyacrylic acid(PAA)binder.The combined action composed of the covalent bond and mechanical interlocking could reduce the contact loss inside the electrode.However,high concentration silane coupling agent treatment will weaken the surface roughness of Cu^(*)and weaken mechanical interlocking.What is more,the insulation of silane coupling agent reduces the conductivity of Cu and increases the impedance of battery.Considering the effect of silane coupling agent comprehensively,electrochemical performance of Cu^(*)-0.05%is best.
基金Project(hdzy0903) supported by Hunan University Ability Training Program by the Basic Operation Costs of Central Colleges and Universities for Scientific Research
文摘Changsha,a typical city in central China,was selected as the study area to assess the variations of ecosystem service value on the basis of land-use change. The analysis not only included the whole city but also the urban district where the landscape changed more rapidly in the center of the city. Two LANDSAT TM data sets in 1986 and 2000 and land use data of five urban districts from 1995 to 2005 were used to estimate the changes in the size of six land use categories. Meanwhile,previously published value coefficients were used to detect the changes in the value of ecosystem services delivered by each land category. The result shows that the total value of ecosystem services in Changsha declines from $1 009.28 million per year in 1986 to $938.11 million per year in 2000. This decline is largely attributable to the increase of construction land,and the conversion from woodland and water body to cropland to keep the crop production. In the five districts,there is $6.19 million decline in ecosystem service value between 1995 and 2005. Yuelu District has the highest unit ecosystem service value while Yuhua District has the lowest one. This may be attributed to the greater conversion from cropland and grassland to woodland and water body with the increase of construction land in Yuelu District. It is suggested that the increase rate of construction land should be controlled rigorously and the area of woodland and water body should be increased or at least retained in the study area.
基金Project(2011BAJ03B13) supported by the National Key Technologies R&D Program of China
文摘The method for calculating wall surface heat storage coefficient was introduced,and the coefficients of several common walls with light-weight external thermal insulation materials and the traditional solid clay brick wall were calculated.In order to study the impact of light-weight external thermal insulation materials,a contrasting experiment was carried out between an external insulated room and an uninsulated room in August,2010,in Chongqing,China.The result shows that outside surface heat storage coefficient of the insulated wall is much less than that of the traditional wall.However,during sunny time,the surface temperature of external walls of the insulated room is obviously higher than that of the uninsulated room.In different orientations,due to different amounts of solar radiation and being irradiated in different time,the contrasting temperature difference(CTD) appears different regularity.In a word,using light-weight external thermal insulation materials has a negative impact on building surrounding thermal environment and people's health.Finally,some suggestions on how to eliminate the impact,such as improving the surface condition of the building envelop,and plating vertical greening,are put forward.
基金Project(51178201) supported by the National Natural Science Foundation of China Project(2011CDB292) supported by the Natural Science Foundation of Hubei Province,China
文摘An active pipe-embedded building envelope, which is an external wall or roof with pipes embedded inside, was presented. This structure may utilize the circulating water in the pipe to transfer heat or coolth inside directly. This kind of structure is named ＂active pipe-embedded building envelope＂ due to dealing with the thermal energy actively inside the structure mass by circulating water. This structure not only deals with thermal energy before the external disturbance becomes cooling/heating load by using the circulating water, but also may use low-grade energy sources such as evaporative cooling, solar energy, and geothermal energy. In the meantime, this structure can also improve the indoor thermal comfort by tempering the internal wall surface temperature variation due to the thermal removal in the mass. This work further presents the thermal performance of this structure under a typical hot summer weather condition by comparing it with that of the conventional external wall/roof with numerical simulation. The results show that this pipe-embedded structure may reduce the external heat transfer significantly and reduce the internal wall surface temperature for improving thermal comfort. This work also presents the effects of the water temperature and the pipe spacing on the heat transfer of this structure. The internal surface heat transfer may reduce by about 2.6 W/mE when the water temperature reduces by 1℃ as far as a brick wall with pipes embedded inside is concerned. When the pipe spacing reduces by 50 mm, the internal wall surface heat flux can also reduce by about 2.3 W/m2.
基金Project(51204037)supported by the National Natural Science Foundation of ChinaProject(N140204016)supported by the Fundamental Research Funds for the Central Universities,China
文摘Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction efficiency were studied. The results show that silicon extraction efficiency increases with increasing the reaction time and Na OH-to-CBM mass ratio. There are two stages for the desilication process of the calcined boron mud. The overall desilication process follows the shrinking-core model, and the first and second stages of the process were determined to obey the shrinking-core model for surface chemical reaction and the diffusion through the product layer, respectively. The activation energies of the first and second stages were calculated to be 44.78 k J/mol and 15.94 k J/mol, respectively.
基金Projects(42002266,51908288)supported by the National Natural Science Foundation of ChinaProject(2020M673654)supported by the Chinese Postdoctoral Science FoundationProject(2019K284)supported by Jiangsu Post-doctoral Research Funding Program,China。
文摘Rock blocks sliding along discontinuities can cause serious disasters,such as landslides,earthquakes,or rock bursts.The shear rate-dependent behavior is a typical time-dependent behavior of a rock discontinuity,and it is closely related to the stability of a rock block.To further study the shear rate-dependent behavior of rock discontinuities,shear tests with alternating shear rates(SASRs)were conducted on rock discontinuities with various surface morphologies.The dynamic evolution of the shear rate dependency was studied in detail based on the shear test results,and three stages were identified with respect to the shear stress and shear deformation states.The test results revealed that dynamic changes in shear stiffness and the energy storage abilities of the rock discontinuities occurred in relation to the shear rate-dependent behavior of crack growth,which increased with an increase in normal stress and/or the joint roughness coefficient.The stage of decreasing shear stiffness corresponded to a stage of noticeable shear rate-dependency,and the shear rate was found to have no influence on the initial crack stress.
基金Project(NCET-07-0228)support by the New Century Excellent Talents in University
文摘Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.
基金Project(61391) supported by the National Security Basic Research Program of ChinaProject (91016029) supported by the National Natural Science Foundation of China
文摘Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.
基金Project (51575542) supported by the National Natural Science Foundation of ChinaProject (2016CX010) supported by the Innovation-Driven Project of CSU,ChinaProject (2015CB057202) supported by the National Basic Research Program of China
文摘A magnet is an important component of a speaker,as it makes the coil move back forth,and it is commonly used in mobile information terminals.Defects may appear on the surface of the magnet while cutting it into smaller slices,and hence,automatic detection of surface cutting defect detection becomes an important task for magnet production.In this work,an image-based detection system for magnet surface defect was constructed,a Fourier image reconstruction based on the magnet surface image processing method was proposed.The Fourier transform was used to get the spectrum image of the magnet image,and the defect was shown as a bright line in it.The Hough transform was used to detect the angle of the bright line,and this line was removed to eliminate the defect from the original gray image;then the inverse Fourier transform was applied to get the background gray image.The defect region was obtained by evaluating the gray-level differences between the original image and the background gray image.Further,the effects of several parameters in this method were studied and the optimized values were obtained.Experiment results show that the proposed method can detect surface cutting defects in a magnet automatically and efficiently.
基金Project(41272304)supported by the National Natural Science Foundation of ChinaProject(51074177)jointly supported by the National Natural Science Foundation and Shanghai Baosteel Group Corporation,ChinaProject(CX2012B070)supported by Hunan Provincial Innovation Fund for Postgraduated Students,China
文摘Based on structural surface normal vector spherical distance and the pole stereographic projection Euclidean distance,two distance functions were established.The cluster analysis of structure surface was conducted by the use of ATTA clustering methods based on ant colony piles,and Silhouette index was introduced to evaluate the clustering effect.The clustering analysis of the measured data of Sanshandao Gold Mine shows that ant colony ATTA-based clustering method does better than K-mean clustering analysis.Meanwhile,clustering results of ATTA method based on pole Euclidean distance and ATTA method based on normal vector spherical distance have a great consistence.The clustering results are most close to the pole isopycnic graph.It can efficiently realize grouping of structural plane and determination of the dominant structural surface direction.It is made up for the defects of subjectivity and inaccuracy in icon measurement approach and has great engineering value.
