Microplastics often co-occur with a variety of organic contaminants in aquatic environment and pose combined risks to aquatic wildlife. Here, we investigated joint effects of microsized polystyrene(mPS, 5 μm) and an ...Microplastics often co-occur with a variety of organic contaminants in aquatic environment and pose combined risks to aquatic wildlife. Here, we investigated joint effects of microsized polystyrene(mPS, 5 μm) and an organophosphate pesticide chlorpyrifos on zebrafish,using multiple endpoints at both fish individual and gut microbiota levels. It was revealed that mPS ingested by zebrafish accumulated in gut and liver, and caused oxidative stress, hyperactive swimming performance and histological damages in fish, and induced disorders and diversity alterations of the gut microbial community. More importantly, mPS exhibited considerable adsorption capacity against chlorpyrifos, and those adsorbing chlorpyrifos presented greater effects on fish individuals but no different effects on gut microbiota compared to single mPS exposure. Together with body residues of chlorpyrifos in zebrafish,it was proposed that the joint effects between mPS and chlorpyrifos were attributed to the chlorpyrifos released from mPS within zebrafish. The present results provided a comprehensive understanding of joint effects of mPS and contaminants co-occurring in the environment and emphasized the importance of considering the adsorbed chemicals in toxicological studies of microplastics.展开更多
The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fibe...The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as 0.01 mN and 0.03 ~m, respectively. The NbTi fibers with diameters ranging from 22.9 to 115 ~m were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remark- able stick-slip phenomenon. Notably, the fiber＇s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber＇s frictional behavior. The simulation results were consistent with the experimental data qualitatively.展开更多
A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of t...A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of the MTHE tubes was proposed and compared with previous experimental data in the Reynolds number range of 500—1 800. The average deviation of the correlation in calculating the Nusselt number was about 6.59%. The entrance effect in the thermal entrance region was discussed. In the same range of Reynolds number, the pressure drop and friction coefficient were found to be considerably higher than those predicted by the conventional correlations. The product of friction factor and Reynolds number was also a constant, but much higher than the conventional.展开更多
As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this proce...As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this procedure,more efficient protection can be acquired via adding additives(in the form of particle,powder,sheet,etc.)into solutions and producing composite coatings.These additives result in more efficient protection against wear via getting stuck in the cracks and pores of coatings and rising the thickness,hardness,and diminishing the porosity size and content.The efficiency of each additive can be changed owing to its intrinsic properties like melting point,size,participation type(reactive,partly reactive,or inert)and potential of zeta.In this review,the effects of distinct additives in nano-and micro-scale size on wear behavior of PEO coatings on Mg and its alloys is going to be reviewed.展开更多
A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication pr...A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation（SOR） iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.展开更多
A novel wet-chemical method was presented for the preparation of the micro-sized and uniform spherical Ag powders on a mass-production scale.The well-defined particles were synthesized by mixing the iron(II) sulfate h...A novel wet-chemical method was presented for the preparation of the micro-sized and uniform spherical Ag powders on a mass-production scale.The well-defined particles were synthesized by mixing the iron(II) sulfate heptahydrate solution with silver nitrate solution directly by high-speed stirring at room temperature.It is found that a large number of micro-sized and uniform spherical particles with rough surfaces are obtained.The mass ratio of iron(II) sulfate heptahydrate to silver nitrate greatly affects the shape of particles,and when it is relatively low,spherical particles cannot be obtained.The reaction temperature has a great impact on the particle size.As the reaction temperature increases from 8 to 15°C,the mean diameter of particles decreases from 3.5 to 1.6 μm.The additive n-methyl-2-pyrrolidone improves the surface smoothness and compactness of the particles while the particle size is kept unchanged.Scanning electron microscopy,X-ray diffractometry and energy dispersive X-ray analysis were used to characterize the particle products.展开更多
The rapid development of micro-electronics raises the demand of their power sources to be simplified,miniaturized and highly integratable with other electronics on a chip.In-plane Micro-sized energy storage devices(ME...The rapid development of micro-electronics raises the demand of their power sources to be simplified,miniaturized and highly integratable with other electronics on a chip.In-plane Micro-sized energy storage devices(MESDs),which are composed of interdigitated electrodes on a single chip,have aroused particular attentions since they could be easily integrated with other miniaturized electronics,reducing the complexity of overall chip design via removing complex interconnections with bulky power sources.This review highlights the achievements in the device fabrication of in-plane MESDs,as well as their integration and intelligent designs.We also discussed the current challenges and future perspectives for the development of in-plane MESDs.展开更多
Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and ...Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and the formation of unstable solid electrolyte interphases during cycling,leading to rapid capacity decay and short cycle life of lithium-ion batteries.When addressing such issues,binder plays key roles in obtaining good structural integrity of silicon anodes.Herein,we report a biopolymer composite binder composed of rigid poly(acrylic acid)(PAA)and flexible silk fibroin(SF)tailored for micro-sized silicon anodes.The PAA/SF binder shows robust gradient binding energy via chemical interactions between carboxyl and amide groups,which can effectively accommodate large volume change of silicon.This PAA/SF binder also shows much stronger adhesion force and improved binding towards high-surface/defective carbon additives,resulting in better electrochemical stability and higher coulombic efficiency,than conventional PAA binder.As such,micro-sized silicon/carbon anodes fabricated with novel PAA/SF binder exhibit much better cyclability(up to 500 cycles at 0.5 C)and enhanced rate capability compared with conventional PAA-based anodes.This work provides new insights into the design of functional binders for high-capacity electrodes suffering from large volume change for the development of nextgeneration lithium batteries.展开更多
Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. I...Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. In this work, the possibility of using micro-size metakaolin(MSK) particles to improve the compressive strength of HVFA paste before and after subjecting to high temperatures was studied. To produce HVFA paste, cement was partially substituted with 70% fly ash(FA), by weight. After that, FA was partially substituted with MSK at ratios fluctuating from 5% to 20% with an interval of 5%, by weight. The effect of MSK on the workability of HVFA mixture was measured. After curing, specimens were subjected to different high temperatures fluctuating from 400 to 1000 ℃ with an interval of 200 ℃ for 2 h. The results were analyzed by different techniques named X-ray diffraction(XRD), thermogravimetry(TGA) and scanning electron microscopy(SEM). The results showed that the incorporation of MSK particles into HVFA mixture exhibited a negative effect on the workability and a positive effect on the compressive strength before and after firing.展开更多
The main results obtained from the experimental and engineering investigation on the heat evolution and cracking risk of a furnace concrete block were presented. The heat evolution of experimental mortars containing m...The main results obtained from the experimental and engineering investigation on the heat evolution and cracking risk of a furnace concrete block were presented. The heat evolution of experimental mortars containing micro-slag under different environmental temperatures was instrumented in order to investigate the self-catalyzed effect, which was discovered in engineering. More-over,the thermal stress of the furnace concrete due to heat temperature rise was calculated to evaluate the cracking risk of mass concrete containing micro-slag due to self-catalyzed effect. The experimental results illustrate that with the development of hydration and initial temperature of mixture, the hydra-tion can be also accelerated and temperature of concrete will be continued to rise, which was the self-catalyzed effect. And the thermal stress due to self-catalyzed effect could not result in the cracking of furnace concrete.展开更多
Printed micro-supercapacitor exhibits its flexibility in geometry design and integration,showing unprecedented potential in powering the internet of things and portable devices.However,the printing process brings unde...Printed micro-supercapacitor exhibits its flexibility in geometry design and integration,showing unprecedented potential in powering the internet of things and portable devices.However,the printing process brings undesired processing defects(e.g.,coffee ring effect),resulting in severe self-discharge of the printed micro-supercapacitors.The impact of such problems on device performance is poorly understood,limiting further development of microsupercapacitors.Herein,by analyzing the self-discharge behavior of fully printed micro-supercapacitors,the severe self-discharge problem is accelerated by the ohmic leakage caused by the coffee ring effect on an ultrathin polymer electrolyte.Based on this understanding,the coffee ring effect was successfully eradicated by introducing graphene oxide in the polymer electrolyte,achieving a decline of 99%in the self-discharge rate.Moreover,the micro-supercapacitors with uniformly printed polymer electrolyte present 7.64 F cm^(-3)volumetric capacitance(14.37 mF cm^(-2)areal capacitance),exhibiting about 50%increase compared to the one without graphene oxide addition.This work provides a new insight to understand the relationship between processing defects and device performance,which will help improve the performance and promote the application of printed micro-supercapacitors.展开更多
Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to ...Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to describe such two kinds of size effects on the yield strength is a very practical challenge.In this study,according to experimental observations,a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’yield strength.An analytical solution for the simple model is derived.It reveals that the yield strength is a function of average grain-size or precipitate-size,which is able to reasonably explain size effects on yield strength.The typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases,but also able to theoretically address the unexplained Hall-Petch relationship between theprecipitate size and the yield strength of nickel-based superalloys.展开更多
Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrins...Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrinsically sluggish electron/ion transport.Herein,in-situ encapsulation ofα-Fe_(2)O_(3) nanoparticles into micro-sized ZnFe_(2)O_(4) capsules is facilely fulfilled through a co-precipitation process and followed by heat-treatment at optimal calcination temperature.The porous ZnFe_(2)O_(4) scaffold affords a synergistic confinement effect to suppress the grain growth ofα-Fe2 O3 nanocrystals during the calcination process and to accommodate the stress generated by volume expansion during the charge/discharge process,leading to an enhanced interfacial conductivity and inhibit electrode pulverization and mechanical failure in the active material.With these merits,the preparedα-Fe_(2)O_(3)/Fe_(2)O_(4) composite delivers prolonged cycling stability and improved rate capability with a higher specific capacity than soleα-Fe_(2)O_(3) and Fe_(2)O_(4).The discharge capacity is retained at 700 mAh g-1 after 500 cycles at 200 mA g^(-1) and 940 mAh g^(-1) after 50 cycles at 100 m A g^(-1).This work provides a new perspective in designing transition metal oxides for advanced lithium-ion batteries with superior electrochemical properties.展开更多
The Debao MS4.8 earthquake occurred in western Guangxi on August 5,2021,near where the Jingxi MS5.2 earthquake occurred in 2019.To study the increasing seismicity in western Guangxi,it is necessary to determine whethe...The Debao MS4.8 earthquake occurred in western Guangxi on August 5,2021,near where the Jingxi MS5.2 earthquake occurred in 2019.To study the increasing seismicity in western Guangxi,it is necessary to determine whether there was an anomaly related to the earthquake source near the Pingxiang gravity station,which is located approximately 100 km from the epicenter of the Debao MS4.8 earthquake.In this study,the R-value scoring method was used to analyze the anomaly and evaluate the prediction efficiency of the double frequency(DF)micro-seismic signal vertical displacement(referred to as vertical displacement,VD)and the absolute value of monthly extreme rate(referred to as the monthly rate).Results show that earthquakes larger than MS4.0 in the 350 km range from the Pingxiang station tend to coincide with yearly typhoons,and the VD of micro-seismic signals correspondingly changes from low to high.The Debao MS4.8 earthquake occurred during a gradual VD increase from 0.05×10^(-6)to 0.10×10^(-6)m.When discussing the relationships among R,the rate threshold,and the effective duration of prediction,the rate threshold of the micro-seismic signal converges from 0.00039×10^(-6)to 0.00031×10^(-6)m/month,the effective duration of prediction is approximately 6-10 months,and R also converges from 0.29 to 0.31.By comparing the results of three gPhone gravity stations in Guangxi,we found that the increase of short-term VD before the Debao earthquake was related to the enhancement of the DF micro-seismic signal excited by the typhoon.When the typhoon track was perpendicular to the coastline of China,the possibility of an earthquake occurring was increased.This study provides evidence and reference for the future occurrence period of earthquakes above MS4.0 in western Guangxi.展开更多
Electromagnetic anisotropic characteristics in micro-sized water bamboo blind shape are observed by high frequency electromagnetic computation,which is applied to the material constants estimation.In assuming that the...Electromagnetic anisotropic characteristics in micro-sized water bamboo blind shape are observed by high frequency electromagnetic computation,which is applied to the material constants estimation.In assuming that the micro-sized unit structure is repeated in 3-dimensional space and its size is much smaller than the electromagnetic wave length,the micro-sized electromagnetic field calculation is carried out.If the micro-structure shapes of the material are different even if they are the same volume rate,different dielectric constant characteristics are provided.The reasons are considered to be a generation of de-electrification within the dielectric material.展开更多
The coagulation time and position of micro-sized non-metallic inclusions in molten metal during ultrasonic separation process were investigated, and the motion course of micro-sized non-metallic inclusions in an ultra...The coagulation time and position of micro-sized non-metallic inclusions in molten metal during ultrasonic separation process were investigated, and the motion course of micro-sized non-metallic inclusions in an ultrasonic standing wave field was numerically simulated. The results of theoretical analysis and numerical simulation show that the movement of inclusions depends on the balance between the acoustic radiation force, effective buoyancy force and viscous drag force. It is presented that micro-sized inclusions, agglomerated at antinode-planes may be removed further with horizon tal ultrasound.``展开更多
The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development eff...The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.展开更多
A modified torsion pendulum apparatus is developed for measuring the shear modu- lus of single filaments with uniform micro-sized diameter. A single filament fixed at both ends and with a ring-shaped mass attached at ...A modified torsion pendulum apparatus is developed for measuring the shear modu- lus of single filaments with uniform micro-sized diameter. A single filament fixed at both ends and with a ring-shaped mass attached at the middle is used as a clamped-clamped torsion pendulum. The shear modulus of single filaments can be expressed as a function of the oscillation frequency of the torsion pendulum. The oscillation motion is measured with a CCD laser displacement sensor, and its frequency is determined by the Fast Fourier Transform （FFT） method. The shear moduli of three types of filaments： copper wires, tungsten wires and carbon fibers are accurately measured with this technique. It is found that the size effect in shear moduli of both copper wires and tungsten wires is minor. Finally, the error analysis of our measurement technique is presented in detail.展开更多
The development of small and micro-sized enterprises is of vital significance for the steady and rapid social economy. In recent years, the developing environment for the small and micro-sized enterprises in Hubei pro...The development of small and micro-sized enterprises is of vital significance for the steady and rapid social economy. In recent years, the developing environment for the small and micro-sized enterprises in Hubei province has become increasingly severe, and the problems such as high management cost, high taxes and fees, financing difficulties, and labor shortages of the small and micro-sized enterprises have been more obvious, so that the further development, transformation, and upgrading of the small and micro-sized enterprises are severely restricted. In order to promote the development of the small and micro-sized enterprises, the developing environment for the small and micro-sized enterprises should be further optimized, the tax environment for supporting the development of the small and micro-sized enterprises should be well improved, the financing system should be promoted to be sound, the industrial structure should be actively adjusted, and also the development quality should be increased.展开更多
The survival problems are always the core problems of the small and micro-sized enterprises in our country, and the financial management, as the important key factor influencing the small and micro-sized enterprises, ...The survival problems are always the core problems of the small and micro-sized enterprises in our country, and the financial management, as the important key factor influencing the small and micro-sized enterprises, has more and more impact on its survival and development. However, the important problem existing presently is that the significance of the financial management is mostly ignored in the small and micro-sized enterprises, pursuing the short-term economic benefit blindly, which decreases the risk resistance of the small and micro-sized enterprises severely, so that a mass of the small and micro-sized enterprises with poor survivability and extremely short life cycle are occurred. This text analyzes the problems existing in the financial management of the small and micro-sized enterprises around the above several prominent problems, and discusses the corresponding suggestions to promote the sound development of the small and micro-sized enterprises in our country.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 21936004, 21806055)the Joint Funds of the National Natural Science Foundation of China (No. U1901220)+2 种基金the Guangdong Provincial Department of Science and Technology (No. 2019A1515011583)Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (No. SML2021SP208)Innovative Research Team of Department of Education of Guangdong Province (No. 2020KCXTD005)。
文摘Microplastics often co-occur with a variety of organic contaminants in aquatic environment and pose combined risks to aquatic wildlife. Here, we investigated joint effects of microsized polystyrene(mPS, 5 μm) and an organophosphate pesticide chlorpyrifos on zebrafish,using multiple endpoints at both fish individual and gut microbiota levels. It was revealed that mPS ingested by zebrafish accumulated in gut and liver, and caused oxidative stress, hyperactive swimming performance and histological damages in fish, and induced disorders and diversity alterations of the gut microbial community. More importantly, mPS exhibited considerable adsorption capacity against chlorpyrifos, and those adsorbing chlorpyrifos presented greater effects on fish individuals but no different effects on gut microbiota compared to single mPS exposure. Together with body residues of chlorpyrifos in zebrafish,it was proposed that the joint effects between mPS and chlorpyrifos were attributed to the chlorpyrifos released from mPS within zebrafish. The present results provided a comprehensive understanding of joint effects of mPS and contaminants co-occurring in the environment and emphasized the importance of considering the adsorbed chemicals in toxicological studies of microplastics.
基金This work is supported by the National Natural Science Foundation of China （No. 11622217）
文摘The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as 0.01 mN and 0.03 ~m, respectively. The NbTi fibers with diameters ranging from 22.9 to 115 ~m were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remark- able stick-slip phenomenon. Notably, the fiber＇s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber＇s frictional behavior. The simulation results were consistent with the experimental data qualitatively.
基金Supported by National Basic Research Program of China("973"Program,No.2011CB707203)
文摘A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of the MTHE tubes was proposed and compared with previous experimental data in the Reynolds number range of 500—1 800. The average deviation of the correlation in calculating the Nusselt number was about 6.59%. The entrance effect in the thermal entrance region was discussed. In the same range of Reynolds number, the pressure drop and friction coefficient were found to be considerably higher than those predicted by the conventional correlations. The product of friction factor and Reynolds number was also a constant, but much higher than the conventional.
文摘As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this procedure,more efficient protection can be acquired via adding additives(in the form of particle,powder,sheet,etc.)into solutions and producing composite coatings.These additives result in more efficient protection against wear via getting stuck in the cracks and pores of coatings and rising the thickness,hardness,and diminishing the porosity size and content.The efficiency of each additive can be changed owing to its intrinsic properties like melting point,size,participation type(reactive,partly reactive,or inert)and potential of zeta.In this review,the effects of distinct additives in nano-and micro-scale size on wear behavior of PEO coatings on Mg and its alloys is going to be reviewed.
基金supported by Scientific Research Foundation for Returned Scholars of Ministry of Education of China
文摘A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation（SOR） iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.
基金Project(2006AA04A110) supported by the National High-tech Research and Development Program of ChinaProject(60976076) supported by the National Natural Science Foundation of China。
文摘A novel wet-chemical method was presented for the preparation of the micro-sized and uniform spherical Ag powders on a mass-production scale.The well-defined particles were synthesized by mixing the iron(II) sulfate heptahydrate solution with silver nitrate solution directly by high-speed stirring at room temperature.It is found that a large number of micro-sized and uniform spherical particles with rough surfaces are obtained.The mass ratio of iron(II) sulfate heptahydrate to silver nitrate greatly affects the shape of particles,and when it is relatively low,spherical particles cannot be obtained.The reaction temperature has a great impact on the particle size.As the reaction temperature increases from 8 to 15°C,the mean diameter of particles decreases from 3.5 to 1.6 μm.The additive n-methyl-2-pyrrolidone improves the surface smoothness and compactness of the particles while the particle size is kept unchanged.Scanning electron microscopy,X-ray diffractometry and energy dispersive X-ray analysis were used to characterize the particle products.
基金supported by the Ministry of Science and Technology of China(Grant No.2019YFA0705600)the National Natural Science Foundation of China(Grant Nos.51822205,21875121)+2 种基金the Natural Science Foundation of Tianjin(Grant Nos.18JCJQJC46300,19JCZDJC31900)the Ministry of Education of China(Grant No.B12015)the “Frontiers Science Center for New Organic Matter”,Nankai University(Grant No.63181206)。
文摘The rapid development of micro-electronics raises the demand of their power sources to be simplified,miniaturized and highly integratable with other electronics on a chip.In-plane Micro-sized energy storage devices(MESDs),which are composed of interdigitated electrodes on a single chip,have aroused particular attentions since they could be easily integrated with other miniaturized electronics,reducing the complexity of overall chip design via removing complex interconnections with bulky power sources.This review highlights the achievements in the device fabrication of in-plane MESDs,as well as their integration and intelligent designs.We also discussed the current challenges and future perspectives for the development of in-plane MESDs.
文摘Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and the formation of unstable solid electrolyte interphases during cycling,leading to rapid capacity decay and short cycle life of lithium-ion batteries.When addressing such issues,binder plays key roles in obtaining good structural integrity of silicon anodes.Herein,we report a biopolymer composite binder composed of rigid poly(acrylic acid)(PAA)and flexible silk fibroin(SF)tailored for micro-sized silicon anodes.The PAA/SF binder shows robust gradient binding energy via chemical interactions between carboxyl and amide groups,which can effectively accommodate large volume change of silicon.This PAA/SF binder also shows much stronger adhesion force and improved binding towards high-surface/defective carbon additives,resulting in better electrochemical stability and higher coulombic efficiency,than conventional PAA binder.As such,micro-sized silicon/carbon anodes fabricated with novel PAA/SF binder exhibit much better cyclability(up to 500 cycles at 0.5 C)and enhanced rate capability compared with conventional PAA-based anodes.This work provides new insights into the design of functional binders for high-capacity electrodes suffering from large volume change for the development of nextgeneration lithium batteries.
文摘Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. In this work, the possibility of using micro-size metakaolin(MSK) particles to improve the compressive strength of HVFA paste before and after subjecting to high temperatures was studied. To produce HVFA paste, cement was partially substituted with 70% fly ash(FA), by weight. After that, FA was partially substituted with MSK at ratios fluctuating from 5% to 20% with an interval of 5%, by weight. The effect of MSK on the workability of HVFA mixture was measured. After curing, specimens were subjected to different high temperatures fluctuating from 400 to 1000 ℃ with an interval of 200 ℃ for 2 h. The results were analyzed by different techniques named X-ray diffraction(XRD), thermogravimetry(TGA) and scanning electron microscopy(SEM). The results showed that the incorporation of MSK particles into HVFA mixture exhibited a negative effect on the workability and a positive effect on the compressive strength before and after firing.
基金Funded by the Key Technologies R&D Program from Department of Science and Technology Hubei Province(200410G0121) "973" Pro-gram(001CB610704-3) from Ministry of Science and Technology of China
文摘The main results obtained from the experimental and engineering investigation on the heat evolution and cracking risk of a furnace concrete block were presented. The heat evolution of experimental mortars containing micro-slag under different environmental temperatures was instrumented in order to investigate the self-catalyzed effect, which was discovered in engineering. More-over,the thermal stress of the furnace concrete due to heat temperature rise was calculated to evaluate the cracking risk of mass concrete containing micro-slag due to self-catalyzed effect. The experimental results illustrate that with the development of hydration and initial temperature of mixture, the hydra-tion can be also accelerated and temperature of concrete will be continued to rise, which was the self-catalyzed effect. And the thermal stress due to self-catalyzed effect could not result in the cracking of furnace concrete.
基金the financial support of this work by the Science,Technology,and Innovation Commission of Shenzhen Municipality(Program No.JCYJ20180508151856806,No.JCYJ20180306171355233)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Program No.CX201944)。
文摘Printed micro-supercapacitor exhibits its flexibility in geometry design and integration,showing unprecedented potential in powering the internet of things and portable devices.However,the printing process brings undesired processing defects(e.g.,coffee ring effect),resulting in severe self-discharge of the printed micro-supercapacitors.The impact of such problems on device performance is poorly understood,limiting further development of microsupercapacitors.Herein,by analyzing the self-discharge behavior of fully printed micro-supercapacitors,the severe self-discharge problem is accelerated by the ohmic leakage caused by the coffee ring effect on an ultrathin polymer electrolyte.Based on this understanding,the coffee ring effect was successfully eradicated by introducing graphene oxide in the polymer electrolyte,achieving a decline of 99%in the self-discharge rate.Moreover,the micro-supercapacitors with uniformly printed polymer electrolyte present 7.64 F cm^(-3)volumetric capacitance(14.37 mF cm^(-2)areal capacitance),exhibiting about 50%increase compared to the one without graphene oxide addition.This work provides a new insight to understand the relationship between processing defects and device performance,which will help improve the performance and promote the application of printed micro-supercapacitors.
基金supported by the National Natural Science Foundation of China (41630634)the China Postdoctoral Science Foundation (2017M623213)
文摘Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals.Similarly,innickel-based superalloys,the precipitate size also influences their yield strength.Then,how to describe such two kinds of size effects on the yield strength is a very practical challenge.In this study,according to experimental observations,a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’yield strength.An analytical solution for the simple model is derived.It reveals that the yield strength is a function of average grain-size or precipitate-size,which is able to reasonably explain size effects on yield strength.The typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases,but also able to theoretically address the unexplained Hall-Petch relationship between theprecipitate size and the yield strength of nickel-based superalloys.
基金financially supported by the National Natural Science Foundation of China(No.51702217)the Shenzhen Government’s Plan of Science and Technology(No.JCYJ20190808121407676)+1 种基金the Natural Science Foundation of Guangdong(No.2020A1515011127)the Shenzhen University Initiative Research Program(No.2019005)。
文摘Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrinsically sluggish electron/ion transport.Herein,in-situ encapsulation ofα-Fe_(2)O_(3) nanoparticles into micro-sized ZnFe_(2)O_(4) capsules is facilely fulfilled through a co-precipitation process and followed by heat-treatment at optimal calcination temperature.The porous ZnFe_(2)O_(4) scaffold affords a synergistic confinement effect to suppress the grain growth ofα-Fe2 O3 nanocrystals during the calcination process and to accommodate the stress generated by volume expansion during the charge/discharge process,leading to an enhanced interfacial conductivity and inhibit electrode pulverization and mechanical failure in the active material.With these merits,the preparedα-Fe_(2)O_(3)/Fe_(2)O_(4) composite delivers prolonged cycling stability and improved rate capability with a higher specific capacity than soleα-Fe_(2)O_(3) and Fe_(2)O_(4).The discharge capacity is retained at 700 mAh g-1 after 500 cycles at 200 mA g^(-1) and 940 mAh g^(-1) after 50 cycles at 100 m A g^(-1).This work provides a new perspective in designing transition metal oxides for advanced lithium-ion batteries with superior electrochemical properties.
基金supported by grants from the Seismological Science and Technology Spark Program of China Seismological Bureau(grant number XH23026C)the National Natural Science Foundation of China(grant number41204058)。
文摘The Debao MS4.8 earthquake occurred in western Guangxi on August 5,2021,near where the Jingxi MS5.2 earthquake occurred in 2019.To study the increasing seismicity in western Guangxi,it is necessary to determine whether there was an anomaly related to the earthquake source near the Pingxiang gravity station,which is located approximately 100 km from the epicenter of the Debao MS4.8 earthquake.In this study,the R-value scoring method was used to analyze the anomaly and evaluate the prediction efficiency of the double frequency(DF)micro-seismic signal vertical displacement(referred to as vertical displacement,VD)and the absolute value of monthly extreme rate(referred to as the monthly rate).Results show that earthquakes larger than MS4.0 in the 350 km range from the Pingxiang station tend to coincide with yearly typhoons,and the VD of micro-seismic signals correspondingly changes from low to high.The Debao MS4.8 earthquake occurred during a gradual VD increase from 0.05×10^(-6)to 0.10×10^(-6)m.When discussing the relationships among R,the rate threshold,and the effective duration of prediction,the rate threshold of the micro-seismic signal converges from 0.00039×10^(-6)to 0.00031×10^(-6)m/month,the effective duration of prediction is approximately 6-10 months,and R also converges from 0.29 to 0.31.By comparing the results of three gPhone gravity stations in Guangxi,we found that the increase of short-term VD before the Debao earthquake was related to the enhancement of the DF micro-seismic signal excited by the typhoon.When the typhoon track was perpendicular to the coastline of China,the possibility of an earthquake occurring was increased.This study provides evidence and reference for the future occurrence period of earthquakes above MS4.0 in western Guangxi.
基金supported in part by Hitech Research Center Project for Private University from the Ministry of Education, Culture, Sports, Science and Technology
文摘Electromagnetic anisotropic characteristics in micro-sized water bamboo blind shape are observed by high frequency electromagnetic computation,which is applied to the material constants estimation.In assuming that the micro-sized unit structure is repeated in 3-dimensional space and its size is much smaller than the electromagnetic wave length,the micro-sized electromagnetic field calculation is carried out.If the micro-structure shapes of the material are different even if they are the same volume rate,different dielectric constant characteristics are provided.The reasons are considered to be a generation of de-electrification within the dielectric material.
文摘The coagulation time and position of micro-sized non-metallic inclusions in molten metal during ultrasonic separation process were investigated, and the motion course of micro-sized non-metallic inclusions in an ultrasonic standing wave field was numerically simulated. The results of theoretical analysis and numerical simulation show that the movement of inclusions depends on the balance between the acoustic radiation force, effective buoyancy force and viscous drag force. It is presented that micro-sized inclusions, agglomerated at antinode-planes may be removed further with horizon tal ultrasound.``
文摘The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.
基金supported by the National Natural Science Foundation of China(No.11072084 and 11272131)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110142110039)
文摘A modified torsion pendulum apparatus is developed for measuring the shear modu- lus of single filaments with uniform micro-sized diameter. A single filament fixed at both ends and with a ring-shaped mass attached at the middle is used as a clamped-clamped torsion pendulum. The shear modulus of single filaments can be expressed as a function of the oscillation frequency of the torsion pendulum. The oscillation motion is measured with a CCD laser displacement sensor, and its frequency is determined by the Fast Fourier Transform （FFT） method. The shear moduli of three types of filaments： copper wires, tungsten wires and carbon fibers are accurately measured with this technique. It is found that the size effect in shear moduli of both copper wires and tungsten wires is minor. Finally, the error analysis of our measurement technique is presented in detail.
文摘The development of small and micro-sized enterprises is of vital significance for the steady and rapid social economy. In recent years, the developing environment for the small and micro-sized enterprises in Hubei province has become increasingly severe, and the problems such as high management cost, high taxes and fees, financing difficulties, and labor shortages of the small and micro-sized enterprises have been more obvious, so that the further development, transformation, and upgrading of the small and micro-sized enterprises are severely restricted. In order to promote the development of the small and micro-sized enterprises, the developing environment for the small and micro-sized enterprises should be further optimized, the tax environment for supporting the development of the small and micro-sized enterprises should be well improved, the financing system should be promoted to be sound, the industrial structure should be actively adjusted, and also the development quality should be increased.
文摘The survival problems are always the core problems of the small and micro-sized enterprises in our country, and the financial management, as the important key factor influencing the small and micro-sized enterprises, has more and more impact on its survival and development. However, the important problem existing presently is that the significance of the financial management is mostly ignored in the small and micro-sized enterprises, pursuing the short-term economic benefit blindly, which decreases the risk resistance of the small and micro-sized enterprises severely, so that a mass of the small and micro-sized enterprises with poor survivability and extremely short life cycle are occurred. This text analyzes the problems existing in the financial management of the small and micro-sized enterprises around the above several prominent problems, and discusses the corresponding suggestions to promote the sound development of the small and micro-sized enterprises in our country.
