A comparative three-dimensional(3D)analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic(MHD)stratified environment is presented.Flow is estimated to be suspended in a D...A comparative three-dimensional(3D)analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic(MHD)stratified environment is presented.Flow is estimated to be suspended in a Darcy-Forchheimer medium.Soret and Dufour responses are also accommodated in the flow field.A moving(rotating)coordinate system is exercised to examine the bidirectionally stretched flow fields(flow,heat transfer,and mass transfer).Nanofluid is compounded by taking ethylene glycol/sodium alginate as base fluid and ferric-oxide(Fe3O4)as nanoparticles.Governing equations are handled by the application of optimal homotopy asymptotic method(OHAM),where convergence parameters are optimized through the classical least square procedure.The novel mechanism(hidden physics)due to appearing parameters is explored with the assistance of tabular and graphical expositions.Outcomes reveal the double behavior state for temperature field with thermal stratification/Dufour number,and for concentration field with Soret number due to the presence of turning points.展开更多
Two-dimension (2D) fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture ...Two-dimension (2D) fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of soli...The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered. The governing partial differential equations are simplified by dimensionless variables and similarity transformations, and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique. It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.展开更多
Reservoir porous rocks usually consist of more than two types of matrix materials, forming a randomly heterogeneous material. The determination of the bulk modulus of such a medium is critical to the elastic wave disp...Reservoir porous rocks usually consist of more than two types of matrix materials, forming a randomly heterogeneous material. The determination of the bulk modulus of such a medium is critical to the elastic wave dispersion and attenuation. The elastic moduli for a simple matrix-inclusion model are theoretically analyzed. Most of the efforts assume a uniform inclusion concentration throughout the whole single-material matrix. However, the assumption is too strict in real-world rocks. A model is developed to estimate the moduli of a heterogeneous bimaterial skeleton, i.e., the host matrix and the patchy matrix. The elastic moduli, density, and permeability of the patchy matrix differ from those of the surrounding host matrix material. Both the matrices contain dispersed particle inclusions with different concentrations. By setting the elastic constant and density of the particles to be zero, a double-porosity medium is obtained. The bulk moduli for the whole system are derived with a multi-level effective modulus method based on Hashin's work. The proposed model improves the elastic modulus calculation of reservoir rocks, and is used to predict the kerogen content based on the wave velocity measured in laboratory. The results show pretty good consistency between the inversed total organic carbon and the measured total organic carbon for two sets of rock samples.展开更多
Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction(ORR).The facile rational stru...Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction(ORR).The facile rational structure engineering with abundant isolated active metal atoms is highly desirable but challenging.Herein,we demonstrate that atomically dispersed Fe sites(Fe-N4 moieties)on the hierarchical porous nitrogen-doped carbon matrix(Fe-SA-PNC)for high ORR activity can be achieved by a dual-template assisted strategy.By thermal decomposition of NH_(4)Cl template,the nitrogen-doped carbon matrix is generated based on the interaction with carbon precursor of citric acid.Meanwhile,the introduction of NaCl template facilitates the formation of hierarchical porous structures,which enable more active sites exposed and improve the mass transfer.Interestingly,the dual-template strategy can inhibit the formation of iron carbide nanoparticles(NPs)by generating porous structures and avoiding of the rapid loss of nitrogen during pyrolysis.The as-made Fe-SA-PNC catalysts with well-defined Fe-N_(4)active sites exhibit highly efficient ORR activity with a half-wave potential of 0.838 V versus the reversible hydrogen electrode,as well as good stability and methanol tolerance,outperforming the commercial Pt/C.The zinc-air battery(ZAB)constructed by Fe-SA-PNC also shows a higher peak power density and specific discharging capacity than that of Pt-based ZAB.The present work provides the facile strategy for tailoring nitrogen doping and porous structures simultaneously to prevent the formation NPs for achieving the well-dispersed and accessible single-atom active sites,paving a new way to design efficient electrocatalysts for ORR in fuel cells.展开更多
Transition metal sulfides have been regarded as promising anode materials for sodium-ion batteries(SIB).However,they face the challenges of poor electronic conductivity and large volume change,which result in capacity...Transition metal sulfides have been regarded as promising anode materials for sodium-ion batteries(SIB).However,they face the challenges of poor electronic conductivity and large volume change,which result in capacity fade and low rate capability.In this work,a composite containing ultrasmall CoS(~7 nm)nanoparticles embedded in heteroatom(N,S,and O)-doped carbon was synthesized by an efficient one-step sulfidation process using a Co(Salen)precursor.The ultrasmall CoS nanoparticles are beneficial for mechanical stability and shortening Na-ions diffusion pathways.Furthermore,the N,S,and O-doped defect-rich carbon provides a robust and highly conductive framework enriched with active sites for sodium storage as well as mitigates volume expansion and polysulfide shuttle.As anode for SIB,CoS@HDC exhibits a high initial capacity of 906 mA h g^(-1)at 100 mA g^(-1)and a stable long-term cycling life with over 1000 cycles at 500 mA g^(-1),showing a reversible capacity of 330 mA h g^(-1).Meanwhile,the CoS@HDC anode is proven to maintain its structural integrity and compositional reversibility during cycling.Furthermore,Na-ion full batteries based on the CoS@HDC anode and Na_(3)V_(2)(PO_(4))_(3)cathode demonstrate a stable cycling behavior with a reversible specific capacity of~200 m A h g^(-1)at least for 100 cycles.Moreover,advanced synchrotron operando X-ray diffraction,ex-situ X-ray absorption spectroscopy,and comprehensive electrochemical tests reveal the structural transformation and the Co coordination chemistry evolution of the CoS@HDC during cycling,providing fundamental insights into the sodium storage mechanism.展开更多
Silica biomaterials including Bioglass offer great biocompatibility and bioactivity but fail to provide pore and degradation features needed for tissue engineering.Herein we report on the synthesis and characterizatio...Silica biomaterials including Bioglass offer great biocompatibility and bioactivity but fail to provide pore and degradation features needed for tissue engineering.Herein we report on the synthesis and characterization of novel amorphous silica fiber matrices to overcome these limitations.Amorphous silica fibers were fused by sintering to produce porous matrices.The effects of sacrificial polymer additives such as polyvinyl alcohol(PVA)and cellulose fibers(CF)on the sintering process were also studied.The resulting matrices formed between sintering temperatures of 1,350-1,550◦C retained their fiber structures.The matrices presented pores in the range of 50-200μm while higher sintering temperatures resulted in increased pore diameter.PVA addition to silica significantly reduced the pore diameter and porosity compared with silica matrices with or without the addition of CF.The PVA additive morphologically appeared to fuse the silica fibers to a greater extent and resulted in significantly higher compressive modulus and strength than the rest of the matrices synthesized.These matrices lost roughly 30%of their original mass in an in vitro degradation study over 40 weeks.All matrices absorbed 500 wt%of water and did not change in their overall morphology,size,or shape with hydration.These fiber matrices supported human mesenchymal stem cell adhesion,proliferation,and mineralized matrix production.Amorphous silica fiber biomaterials/matrices reported here are biodegradable and porous and closely resemble the native extracellular matrix structure and water absorption capacity.Extending the methodology reported here to alter matrix properties may lead to a variety of tissue engineering,implant,and drug delivery applications.展开更多
The present article is concerned with the heat transfer of nanofluid saturated with porous medium sandwiched between clear viscous fluid filled in a vertical channel.The model is developed to analyze the behavior of n...The present article is concerned with the heat transfer of nanofluid saturated with porous medium sandwiched between clear viscous fluid filled in a vertical channel.The model is developed to analyze the behavior of nanofluids taking into account the solid volume fraction.The governing equations are obtained based on the Darcy's law for the porous medium and Tiwari and Das model to define the nanofluid.The viscous and Darcy dissipation terms are included in the energy equation.The transformed dimensionless governing equations are solved analytically using regular perturbation.Investigations are carried out on the flow characteristics for different values of Grashof number,Brinkman number,solid volume fraction and porous parameter using water as base fluid and copper as nanoparticle.Flow and heat transfer are also observed using five different types of nanoparticles.It is found that the maximum value of Nusselt number is obtained for silver nanoparticle.展开更多
Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high(several times higher than that of traditional Li-ion batter...Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high(several times higher than that of traditional Li-ion batteries).Besides, Li–S and Li–Se batteries are low cost and environmental benign. However, the commercial applications of Li–S and Li–Se batteries are hindered by the dissolution and shuttle phenomena of polysulfide(polyselenium), the low conductivity of S(Se), etc. To overcome these drawbacks, scientists have come up with various methods, such as optimizing the electrolyte, synthesizing composite electrode of S/polymer, S/carbon, S/metal organic framework(MOF) and constructing novelty structure of battery.In this review, we present a systematic introduction about the recent progress of Li–S and Li–Se batteries, especially in the area of electrode materials, both of cathode material and anode material for Li–S and Li–Se batteries. In addition, other methods to lead a high-performance Li–S and Li–Se batteries are also briefly summarized, such as constructing novelty battery structure, adopting proper charge–discharge conditions, heteroatom doping into sulfur molecules, using different kinds of electrolytes and binders. In the end of the review, the developed directions of Li–S and Li–Se batteries are also pointed out. We believe that combining proper porous carbon matrix and heteroatom doping may further improve the electrochemical performance of Li–S and Li–Se batteries. We also believe that Li–S and Li–Se batteries will get more exciting results and have promising future by the effort of battery community.展开更多
文摘A comparative three-dimensional(3D)analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic(MHD)stratified environment is presented.Flow is estimated to be suspended in a Darcy-Forchheimer medium.Soret and Dufour responses are also accommodated in the flow field.A moving(rotating)coordinate system is exercised to examine the bidirectionally stretched flow fields(flow,heat transfer,and mass transfer).Nanofluid is compounded by taking ethylene glycol/sodium alginate as base fluid and ferric-oxide(Fe3O4)as nanoparticles.Governing equations are handled by the application of optimal homotopy asymptotic method(OHAM),where convergence parameters are optimized through the classical least square procedure.The novel mechanism(hidden physics)due to appearing parameters is explored with the assistance of tabular and graphical expositions.Outcomes reveal the double behavior state for temperature field with thermal stratification/Dufour number,and for concentration field with Soret number due to the presence of turning points.
基金the National Natural Science Foundation of China(No.90405015)the National Young Elitist Foundation(No.50425208).
文摘Two-dimension (2D) fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.
基金Supported by the National Natural Science Foundation of China under Grant No 51305080
文摘The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered. The governing partial differential equations are simplified by dimensionless variables and similarity transformations, and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique. It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.
基金Project supported by the Open Project Program of Sinopec Key Laboratory of Multi-Component Seismic Technology(No.GSYKY-B09-33)the National Key Basic Research Program of China(973Program)(No.2014CB239006)the Basic Research Program of Community Networks Program Centers(CNPC)(No.2014A-3611)
文摘Reservoir porous rocks usually consist of more than two types of matrix materials, forming a randomly heterogeneous material. The determination of the bulk modulus of such a medium is critical to the elastic wave dispersion and attenuation. The elastic moduli for a simple matrix-inclusion model are theoretically analyzed. Most of the efforts assume a uniform inclusion concentration throughout the whole single-material matrix. However, the assumption is too strict in real-world rocks. A model is developed to estimate the moduli of a heterogeneous bimaterial skeleton, i.e., the host matrix and the patchy matrix. The elastic moduli, density, and permeability of the patchy matrix differ from those of the surrounding host matrix material. Both the matrices contain dispersed particle inclusions with different concentrations. By setting the elastic constant and density of the particles to be zero, a double-porosity medium is obtained. The bulk moduli for the whole system are derived with a multi-level effective modulus method based on Hashin's work. The proposed model improves the elastic modulus calculation of reservoir rocks, and is used to predict the kerogen content based on the wave velocity measured in laboratory. The results show pretty good consistency between the inversed total organic carbon and the measured total organic carbon for two sets of rock samples.
基金funded by the Youth Innovation Promotion Association CAS(No.202055)the National Key R&D Program of China(Nos.2019YFA0709202 and 2020YFB2009004).
文摘Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction(ORR).The facile rational structure engineering with abundant isolated active metal atoms is highly desirable but challenging.Herein,we demonstrate that atomically dispersed Fe sites(Fe-N4 moieties)on the hierarchical porous nitrogen-doped carbon matrix(Fe-SA-PNC)for high ORR activity can be achieved by a dual-template assisted strategy.By thermal decomposition of NH_(4)Cl template,the nitrogen-doped carbon matrix is generated based on the interaction with carbon precursor of citric acid.Meanwhile,the introduction of NaCl template facilitates the formation of hierarchical porous structures,which enable more active sites exposed and improve the mass transfer.Interestingly,the dual-template strategy can inhibit the formation of iron carbide nanoparticles(NPs)by generating porous structures and avoiding of the rapid loss of nitrogen during pyrolysis.The as-made Fe-SA-PNC catalysts with well-defined Fe-N_(4)active sites exhibit highly efficient ORR activity with a half-wave potential of 0.838 V versus the reversible hydrogen electrode,as well as good stability and methanol tolerance,outperforming the commercial Pt/C.The zinc-air battery(ZAB)constructed by Fe-SA-PNC also shows a higher peak power density and specific discharging capacity than that of Pt-based ZAB.The present work provides the facile strategy for tailoring nitrogen doping and porous structures simultaneously to prevent the formation NPs for achieving the well-dispersed and accessible single-atom active sites,paving a new way to design efficient electrocatalysts for ORR in fuel cells.
基金the financial support from China Scholarship Council(202108080263)Financial support by the Federal Ministry of Education and Research(BMBF)under the project“He Na”(03XP0390C)+1 种基金the German Research Foundation(DFG)under the joint German-Russian DFG project“KIBSS”(448719339)are acknowledgedthe financial support from the Federal Ministry of Education and Research(BMBF)under the project“Ka Si Li”(03XP0254D)in the competence cluster“Excell Batt Mat”。
文摘Transition metal sulfides have been regarded as promising anode materials for sodium-ion batteries(SIB).However,they face the challenges of poor electronic conductivity and large volume change,which result in capacity fade and low rate capability.In this work,a composite containing ultrasmall CoS(~7 nm)nanoparticles embedded in heteroatom(N,S,and O)-doped carbon was synthesized by an efficient one-step sulfidation process using a Co(Salen)precursor.The ultrasmall CoS nanoparticles are beneficial for mechanical stability and shortening Na-ions diffusion pathways.Furthermore,the N,S,and O-doped defect-rich carbon provides a robust and highly conductive framework enriched with active sites for sodium storage as well as mitigates volume expansion and polysulfide shuttle.As anode for SIB,CoS@HDC exhibits a high initial capacity of 906 mA h g^(-1)at 100 mA g^(-1)and a stable long-term cycling life with over 1000 cycles at 500 mA g^(-1),showing a reversible capacity of 330 mA h g^(-1).Meanwhile,the CoS@HDC anode is proven to maintain its structural integrity and compositional reversibility during cycling.Furthermore,Na-ion full batteries based on the CoS@HDC anode and Na_(3)V_(2)(PO_(4))_(3)cathode demonstrate a stable cycling behavior with a reversible specific capacity of~200 m A h g^(-1)at least for 100 cycles.Moreover,advanced synchrotron operando X-ray diffraction,ex-situ X-ray absorption spectroscopy,and comprehensive electrochemical tests reveal the structural transformation and the Co coordination chemistry evolution of the CoS@HDC during cycling,providing fundamental insights into the sodium storage mechanism.
基金support from the National Institute of Biomedical Imaging and Bioengineering(NIBIB)of the National Institutes of Health(#R01EB030060R01EB020640)Dr.Nukavarapu also acknowledges funding from NSF EFMA(#1908454).
文摘Silica biomaterials including Bioglass offer great biocompatibility and bioactivity but fail to provide pore and degradation features needed for tissue engineering.Herein we report on the synthesis and characterization of novel amorphous silica fiber matrices to overcome these limitations.Amorphous silica fibers were fused by sintering to produce porous matrices.The effects of sacrificial polymer additives such as polyvinyl alcohol(PVA)and cellulose fibers(CF)on the sintering process were also studied.The resulting matrices formed between sintering temperatures of 1,350-1,550◦C retained their fiber structures.The matrices presented pores in the range of 50-200μm while higher sintering temperatures resulted in increased pore diameter.PVA addition to silica significantly reduced the pore diameter and porosity compared with silica matrices with or without the addition of CF.The PVA additive morphologically appeared to fuse the silica fibers to a greater extent and resulted in significantly higher compressive modulus and strength than the rest of the matrices synthesized.These matrices lost roughly 30%of their original mass in an in vitro degradation study over 40 weeks.All matrices absorbed 500 wt%of water and did not change in their overall morphology,size,or shape with hydration.These fiber matrices supported human mesenchymal stem cell adhesion,proliferation,and mineralized matrix production.Amorphous silica fiber biomaterials/matrices reported here are biodegradable and porous and closely resemble the native extracellular matrix structure and water absorption capacity.Extending the methodology reported here to alter matrix properties may lead to a variety of tissue engineering,implant,and drug delivery applications.
文摘The present article is concerned with the heat transfer of nanofluid saturated with porous medium sandwiched between clear viscous fluid filled in a vertical channel.The model is developed to analyze the behavior of nanofluids taking into account the solid volume fraction.The governing equations are obtained based on the Darcy's law for the porous medium and Tiwari and Das model to define the nanofluid.The viscous and Darcy dissipation terms are included in the energy equation.The transformed dimensionless governing equations are solved analytically using regular perturbation.Investigations are carried out on the flow characteristics for different values of Grashof number,Brinkman number,solid volume fraction and porous parameter using water as base fluid and copper as nanoparticle.Flow and heat transfer are also observed using five different types of nanoparticles.It is found that the maximum value of Nusselt number is obtained for silver nanoparticle.
基金financially supported by the National Natural Science Foundation of China(Nos.21373195 and 51622210)the Fundamental Research Funds for the Central Universities(No.WK3430000004)
文摘Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high(several times higher than that of traditional Li-ion batteries).Besides, Li–S and Li–Se batteries are low cost and environmental benign. However, the commercial applications of Li–S and Li–Se batteries are hindered by the dissolution and shuttle phenomena of polysulfide(polyselenium), the low conductivity of S(Se), etc. To overcome these drawbacks, scientists have come up with various methods, such as optimizing the electrolyte, synthesizing composite electrode of S/polymer, S/carbon, S/metal organic framework(MOF) and constructing novelty structure of battery.In this review, we present a systematic introduction about the recent progress of Li–S and Li–Se batteries, especially in the area of electrode materials, both of cathode material and anode material for Li–S and Li–Se batteries. In addition, other methods to lead a high-performance Li–S and Li–Se batteries are also briefly summarized, such as constructing novelty battery structure, adopting proper charge–discharge conditions, heteroatom doping into sulfur molecules, using different kinds of electrolytes and binders. In the end of the review, the developed directions of Li–S and Li–Se batteries are also pointed out. We believe that combining proper porous carbon matrix and heteroatom doping may further improve the electrochemical performance of Li–S and Li–Se batteries. We also believe that Li–S and Li–Se batteries will get more exciting results and have promising future by the effort of battery community.