Branching structure(BS)is a very important phenomenon in the evolution of equatorial plasma bubbles(EPBs),the mechanism of which is widely studied from observation and from simulation.However,occurrence characteristic...Branching structure(BS)is a very important phenomenon in the evolution of equatorial plasma bubbles(EPBs),the mechanism of which is widely studied from observation and from simulation.However,occurrence characteristics of branching structure of equatorial plasma bubbles(BSEPBs)have not been well addressed.In this work,we used seven-years(2012-2018)of observations from two all-sky imagers to study occurrence of BSEPBs in detail.These data reveal a high incidence of BS in EPB cases;in particular,most EPBs occurring on days with geomagnetic disturbances exhibited BS.Periods when all EPBs exhibited BS increased significantly in the 2014 solar maximum.Occurrence times of BSEPBs varied with local time;most of the BSEPBs began to appear between 21:00 and 22:00 LT.During the solar maximum,some BSEPBs were observed after midnight.The data also reveal that BSEPBs are characterized primarily by two branches or three branches.Multi-branching appeared only in the solar maximum.EPB events with different coexisting branching structures increased from 2012 to 2014 and decreased from 2014 to 2018.These results strongly suggest that BSEPB occurrence is related to solar activity and geomagnetic activity,and thus provide a new perspective for future studies of EPBs as well as enriching our understanding of ionospheric irregularity.展开更多
The helium bubble structure and growth modes near dislocations in titanium are studied using the molecular dynamics method. A helium crystal with an HCP structure in titanium is found to have a lattice constant of 1.9...The helium bubble structure and growth modes near dislocations in titanium are studied using the molecular dynamics method. A helium crystal with an HCP structure in titanium is found to have a lattice constant of 1.977 A？ at 0 K. On either side of the slip plane, helium bubbles form in the（001） plane, but they are in different growth modes. On the side of the slip plane with full atomic layers, helium bubbles grow toward the slip plane and easily cross the slip plane. In the growth process, the position of the top surface of the helium bubble remains almost unchanged. On the other side of the slip plane,the helium bubble grows initially toward the dislocation core, but it is difficult to cross the slip plane, which results in growth in the opposite direction upon reaching the slip plane.展开更多
The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equi...The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equipped with digital telemetry.An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment,which indicates the elasticity nature of shaft material against bending deformation,follows the Weibull distribution.The trends of amplitude mean,standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow.The "S" trend of the relative mean bending moment over gas flow rate,depending on the flow regime in gas-liquid stirred vessels,resulted from the competition among the nonuniformity of bubbly flow around the impeller,the formation of gas cavities behind the blades,and the gas direct impact on the impeller when gas is introduced.A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident.The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.展开更多
Developing highly efficient,environmentally friendly and cost-effective electrocatalysts for oxygen reduction reactions is crucial for electrochemical energy conversion devices such as metal/air batteries and fuel cel...Developing highly efficient,environmentally friendly and cost-effective electrocatalysts for oxygen reduction reactions is crucial for electrochemical energy conversion devices such as metal/air batteries and fuel cells.In this regard,metal-free porous carbons with their high activity,good stability and low cost show promising properties as a candidate for replacing expensive Pt-based electrocatalysts.However,it remains a major challenge to establish a template-free and green method for the synthesis of highly active metal-free carbon materials with outstanding performance over a wide pH range.In this paper,a controllable and scalable method to synthesize porous N-doped carbon nano-foams with interconnected bubble-like structures is presented.These as-prepared N-doped carbon catalysts,which were obtained by spray pyrolization and the subsequent heat treatment in the presence of NH_(3),possess activities which are well comparable to the commercial Pt/C.In addition,systematic electrochemical analyses were performed with a detailed explanation of the pore formation induced by the activation of Zn and NH_(3).In brief,this work is of great importance for the development of relevant electrochemical energy devices,particularly fuel cells and metal-air batteries.展开更多
In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on ...In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on finite volume method was adopted to solve the time-dependent multiphase flow including a compressible phase, and the PISO algorithm was included. The computed results show that this problem was calculated successfully. The gas bubble behind the nozzle, and the wave structure existing in highly compressed gas in water were captured accurately.展开更多
N-Doped 3D bubble-like porous graphene was synthesized via a simple template directed method using polystyrene nanospheres as a template and low-cost industrial melamine as the nitrogen source.The assynthesized N-3DPG...N-Doped 3D bubble-like porous graphene was synthesized via a simple template directed method using polystyrene nanospheres as a template and low-cost industrial melamine as the nitrogen source.The assynthesized N-3DPGX possessed a high specific surface area,uniform and controllable porous structure and high nitrogen doping content.Benefiting from these features,the as-obtained N-3DPG4 as an anode for sodium ion batteries delivered a high specific capacity of 310 mA h g^(-1) after 500 cycles at a current density of 0.2 A g^(-1),and also excellent rate capability as high as 169 mA h g^(-1) at 10 A g^(-1).This simple synthetic method,unique porous structure and outstanding electrochemical performance demonstrated that N-3DPG is a promising candidate for application in sodium ion batteries for large-scale electrochemical energy storage.展开更多
基金supported by the Youth Science and Technology Innovation Foundation of NSSCthe International Partnership Program of Chinese Academy of Sciences(183311KYSB20200003)+1 种基金the National Natural Science Foundation of China(41831073 and 42004138)the Open Research Project of Large Research Infrastructures of CAS–“Study on the interaction between low/mid-latitude atmosphere and ionosphere based on the Chinese Meridian Project”。
文摘Branching structure(BS)is a very important phenomenon in the evolution of equatorial plasma bubbles(EPBs),the mechanism of which is widely studied from observation and from simulation.However,occurrence characteristics of branching structure of equatorial plasma bubbles(BSEPBs)have not been well addressed.In this work,we used seven-years(2012-2018)of observations from two all-sky imagers to study occurrence of BSEPBs in detail.These data reveal a high incidence of BS in EPB cases;in particular,most EPBs occurring on days with geomagnetic disturbances exhibited BS.Periods when all EPBs exhibited BS increased significantly in the 2014 solar maximum.Occurrence times of BSEPBs varied with local time;most of the BSEPBs began to appear between 21:00 and 22:00 LT.During the solar maximum,some BSEPBs were observed after midnight.The data also reveal that BSEPBs are characterized primarily by two branches or three branches.Multi-branching appeared only in the solar maximum.EPB events with different coexisting branching structures increased from 2012 to 2014 and decreased from 2014 to 2018.These results strongly suggest that BSEPB occurrence is related to solar activity and geomagnetic activity,and thus provide a new perspective for future studies of EPBs as well as enriching our understanding of ionospheric irregularity.
基金supported by the National Natural Science Foundation of China(Grant No.11505120)the Project of Innovative Talents of North China University of Water Resources and Electric Power,China(Grant No.70483)
文摘The helium bubble structure and growth modes near dislocations in titanium are studied using the molecular dynamics method. A helium crystal with an HCP structure in titanium is found to have a lattice constant of 1.977 A？ at 0 K. On either side of the slip plane, helium bubbles form in the（001） plane, but they are in different growth modes. On the side of the slip plane with full atomic layers, helium bubbles grow toward the slip plane and easily cross the slip plane. In the growth process, the position of the top surface of the helium bubble remains almost unchanged. On the other side of the slip plane,the helium bubble grows initially toward the dislocation core, but it is difficult to cross the slip plane, which results in growth in the opposite direction upon reaching the slip plane.
文摘The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equipped with digital telemetry.An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment,which indicates the elasticity nature of shaft material against bending deformation,follows the Weibull distribution.The trends of amplitude mean,standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow.The "S" trend of the relative mean bending moment over gas flow rate,depending on the flow regime in gas-liquid stirred vessels,resulted from the competition among the nonuniformity of bubbly flow around the impeller,the formation of gas cavities behind the blades,and the gas direct impact on the impeller when gas is introduced.A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident.The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.
基金the National Natural Science Foundation of China(Grant No.51674299)Hunan Natural Science Foundation of China(Grant No.2018JJ3660)for their financial support.
文摘Developing highly efficient,environmentally friendly and cost-effective electrocatalysts for oxygen reduction reactions is crucial for electrochemical energy conversion devices such as metal/air batteries and fuel cells.In this regard,metal-free porous carbons with their high activity,good stability and low cost show promising properties as a candidate for replacing expensive Pt-based electrocatalysts.However,it remains a major challenge to establish a template-free and green method for the synthesis of highly active metal-free carbon materials with outstanding performance over a wide pH range.In this paper,a controllable and scalable method to synthesize porous N-doped carbon nano-foams with interconnected bubble-like structures is presented.These as-prepared N-doped carbon catalysts,which were obtained by spray pyrolization and the subsequent heat treatment in the presence of NH_(3),possess activities which are well comparable to the commercial Pt/C.In addition,systematic electrochemical analyses were performed with a detailed explanation of the pore formation induced by the activation of Zn and NH_(3).In brief,this work is of great importance for the development of relevant electrochemical energy devices,particularly fuel cells and metal-air batteries.
文摘In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on finite volume method was adopted to solve the time-dependent multiphase flow including a compressible phase, and the PISO algorithm was included. The computed results show that this problem was calculated successfully. The gas bubble behind the nozzle, and the wave structure existing in highly compressed gas in water were captured accurately.
基金supported by the National Natural Science Foundation of China(Grant No.21501049 and 21503071)the Fund of Key Scientific and Technological Project of Henan Province(No.172102210353 and 162102210070).
文摘N-Doped 3D bubble-like porous graphene was synthesized via a simple template directed method using polystyrene nanospheres as a template and low-cost industrial melamine as the nitrogen source.The assynthesized N-3DPGX possessed a high specific surface area,uniform and controllable porous structure and high nitrogen doping content.Benefiting from these features,the as-obtained N-3DPG4 as an anode for sodium ion batteries delivered a high specific capacity of 310 mA h g^(-1) after 500 cycles at a current density of 0.2 A g^(-1),and also excellent rate capability as high as 169 mA h g^(-1) at 10 A g^(-1).This simple synthetic method,unique porous structure and outstanding electrochemical performance demonstrated that N-3DPG is a promising candidate for application in sodium ion batteries for large-scale electrochemical energy storage.
