The composite time scale(CTS)provides a stable,accurate,and reliable time scale for modern society.The improvement of CTS’s real-time performance will improve its stability,which strengths related applications’perfo...The composite time scale(CTS)provides a stable,accurate,and reliable time scale for modern society.The improvement of CTS’s real-time performance will improve its stability,which strengths related applications’performance.Aiming at this goal,a method achieved by determining the optimal calculation interval and accelerating adjustment stage is proposed in this paper.The determinants of the CTS’s calculation interval(characteristics of the clock ensemble,the measurement noise,the time and frequency synchronization system’s noise and the auxiliary output generator noise floor)are studied and the optimal calculation interval is obtained.We also investigate the effect of ensemble algorithm’s initial parameters on the CTS’s adjustment stage.A strategy to get the reasonable initial parameters of ensemble algorithm is designed.The results show that the adjustment stage can be finished rapidly or even can be shorten to zero with reasonable initial parameters.On this basis,we experimentally generate a distributed CTS with a calculation interval of 500 s and its stability outperforms those of the member clocks when the averaging time is longer than1700 s.The experimental result proves that the CTS’s real-time performance is significantly improved.展开更多
The present work is based on the comparative study between “Blade-Element- Momentum” (BEM) analysis and “Computational-Fluid-Dynamics” (CFD) analysis of small-scale horizontal axis wind turbine blade. In this stud...The present work is based on the comparative study between “Blade-Element- Momentum” (BEM) analysis and “Computational-Fluid-Dynamics” (CFD) analysis of small-scale horizontal axis wind turbine blade. In this study, the pitch is considered as fixed and rotor speed is variable. Firstly, the aerodynamic characteristics of three different specialized airfoils were analyzed to get optimum design parameters of wind turbine blade. Then BEM was performed with the application of the open source wind turbine design and performance computation software Q-Blade v0.6. After that, CFD simulation was done by Ansys CFX software. Here, k-ω “Shear-Stress-Transport” (SST) model was conducted for three-dimensional visualization of turbine performance. However, the best coefficient of performance was observed at 6o angle of attack. At this angle of attack, in the case of BEM, the highest coefficient of performance was 0.47 whereby CFD analysis, it was 0.43. Both studies showed good performance prediction which was a positive step to accelerate the continuous revolution in wind energy sector.展开更多
An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and f...An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC （LZ） ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.展开更多
Boron doped diamond(BDD)performs well in electrochemical oxidation for organic pollutants thanks to its wide electrochemical window and superior chemical stability.We presented a method to obtain well-adherent large-s...Boron doped diamond(BDD)performs well in electrochemical oxidation for organic pollutants thanks to its wide electrochemical window and superior chemical stability.We presented a method to obtain well-adherent large-scale BDD/Nb electrode by the modified hot filament chemical vapor deposition system(HFCVD).SiC particles were sand blasted to enhance the adhesion of BDD coating.The BDD coating was then deposited on both sides of Nb which was placed vertically and closely with filament grids on both sides.The BDD/Nb electrodes had no deformation because the thermal deformations of the BDD films on both sides of the Nb substrate conteracted each other during cooling process after deposition.The surface morphology and purity of the BDD/Nb electrode were analyzed by Raman and scanning elestron microscope(SEM)techniques.Scratch test was used to investigate the adhesion of BDD films.The electrochemical performances were measured by cyclic voltammetry test.The BDD electrode at the B/C ratio of 2 000×10^(-6) held a higher oxygen evolution potential thanks to its high sp3 carbon content.Accelerated life test illustrated that the sandblasting pretreatment obviously enhanced the adhesion of BDD coating which resulted in a longer service duration than the un-sandblasted one.展开更多
To obtain the key subelements that may influence the scaling of gas-as injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based...To obtain the key subelements that may influence the scaling of gas-as injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas gas combustion fiowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas-gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner fiowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multi- element injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied.展开更多
Using the DEA analysis method,on the basis of the national panel data from 2002 to 2014,this paper made a comparative analysis on the rice production performance before and after the implementation of direct grain sub...Using the DEA analysis method,on the basis of the national panel data from 2002 to 2014,this paper made a comparative analysis on the rice production performance before and after the implementation of direct grain subsidy policy,and made an empirical analysis on the relationship between the direct grain subsidy policy and the changes in the rice production performance. The results showed that the effect of the direct grain subsidy policy on promoting the rice production performance is declining year by year,largely because drop of scale efficiency. Besides,there are problems of serious redundancy in agricultural subsidy,unreasonable resource allocation,leading to low performance and resource waste of rice production.展开更多
In order to recover the SiO_2 contained in the mother liquor in the course ofNaY zeolite synthesis to minimize pollution, the influence of various preparation conditions on thefiltering velocity of gel slurry was stud...In order to recover the SiO_2 contained in the mother liquor in the course ofNaY zeolite synthesis to minimize pollution, the influence of various preparation conditions on thefiltering velocity of gel slurry was studied using the SiO_2/Al_2O_3 gel recovered from the NaYmother liquor in the laboratory. The results of study had shown that at a SiO_2/Al_2O_3 ratio in thefeed equating to 9∶1 the SiO_2 recovery rate and Al_2O_3 utilization rate were high with a fasterflow velocity of the filtrate. The pH value of the system had great impact on the flow velocity offiltrate. Between the two methods for regulating the pH value, the one for formation ofsilica/alumina gel slurry by addition of sulfuric acid prior to adding aluminium sulfate in thesolution could secure a faster filtration velocity. The filtration velocity was decreased in tandemwith increasing SiO_2 concentration in mother liquor, meanwhile an increase in dry filter cakeyield.展开更多
In today＇s competitive environment the key element is the differentiation of business which will lead to success. Especially in international markets where there＇s much more intense competition, it is more important...In today＇s competitive environment the key element is the differentiation of business which will lead to success. Especially in international markets where there＇s much more intense competition, it is more important for businesses to enter with innovations that make a difference to their consumers. Innovation is also important for competitive export-oriented production in globalization. In global competition, innovation is the key factor for sustainable success. Increases in the efficiency, profitability of firms make it possible to enter new markets and extend present markets by obtaining advantage of competition. In order to determine accurate strategies, the connection between innovation and exports must be understood better. The aim of this study is to determine the innovation capability and export performance of Turkish export firms. Another aim is to examine the relationship between firm characteristics and innovation capability. Innovation capability of export firms is measured by INNOVSCALE which was developed by Vicente, Abrantes, and Teixeira （2015）. Export performance is measured by APEV scale which was developed by Lages, Lages, and Lages （2005）. The study uses data collected from 83 firms located in Kayseri. Results obtained by using SPSS indicate that there is a positive relationship between innovation capability and export performance. The results of the ANOVA analysis, innovation capability differ in terms of firm size and export earnings. Innovation capability does not differ in terms of sector, operating years, share of export earnings in the whole revenues, exporting periods, or internationalization levels.展开更多
Virtual world simulation offers tremendous potential opportunities to improve, and optimize, individual and collective echelon training for the military. The US Army Research Laboratory (ARL) Military Open Simulator E...Virtual world simulation offers tremendous potential opportunities to improve, and optimize, individual and collective echelon training for the military. The US Army Research Laboratory (ARL) Military Open Simulator Enterprise Strategy (MOSES) project’s charter is to investigate simulation-based training technology for use in military specific training domains. Of particular interest are attributes of virtual worlds such as geographically distributed large-scale trainee support. We have initiated a series of experiments to determine appropriate benchmarks for simulator performance and to determine appropriate independent variables in order to create a robust predictive model that will enable virtual world training scenario designers to calculate, a priori, the number of trainees that may synchronously operate in a virtual world. The present paper’s purposes were to determine the effect that virtual world region fidelity had on server performance and determine whether this independent variable would be appropriate for inclusion into our predictive model. We found that region fidelity had a statistically significant effect on the simulator’s processor memory usage but had no significant effect on the simulator’s vertical scalability, CPU usage nor network performance. In this paper, we discourse on the purpose of this research, our experimental methodology and results, and discuss the significance of our findings.展开更多
Whether a decision group does its function or not directly depends on the rationality of its characters. The decision science, also with other correlation disciplines, wants to know how the group characters affect the...Whether a decision group does its function or not directly depends on the rationality of its characters. The decision science, also with other correlation disciplines, wants to know how the group characters affect the group performance. Although there are great deals of means to describe the group characters theoretically and practically, in this paper, we consider that the integrity character of a group is composed of the group scale, the constitution and the structure. So the research on how group characters affect the group performance should focus on the three aspects. In order to grasp the present research situation and clear the prospective direction of the studies, we will summarize the study on how the group characters affect the group performance from these three aspects.展开更多
基金the National Key Research and Development Program of China(Grant No.2021YFA1402102)the National Natural Science Foundation of China(Grant No.62171249)the Fund by Tsinghua University Initiative Scientific Research Program.
文摘The composite time scale(CTS)provides a stable,accurate,and reliable time scale for modern society.The improvement of CTS’s real-time performance will improve its stability,which strengths related applications’performance.Aiming at this goal,a method achieved by determining the optimal calculation interval and accelerating adjustment stage is proposed in this paper.The determinants of the CTS’s calculation interval(characteristics of the clock ensemble,the measurement noise,the time and frequency synchronization system’s noise and the auxiliary output generator noise floor)are studied and the optimal calculation interval is obtained.We also investigate the effect of ensemble algorithm’s initial parameters on the CTS’s adjustment stage.A strategy to get the reasonable initial parameters of ensemble algorithm is designed.The results show that the adjustment stage can be finished rapidly or even can be shorten to zero with reasonable initial parameters.On this basis,we experimentally generate a distributed CTS with a calculation interval of 500 s and its stability outperforms those of the member clocks when the averaging time is longer than1700 s.The experimental result proves that the CTS’s real-time performance is significantly improved.
文摘The present work is based on the comparative study between “Blade-Element- Momentum” (BEM) analysis and “Computational-Fluid-Dynamics” (CFD) analysis of small-scale horizontal axis wind turbine blade. In this study, the pitch is considered as fixed and rotor speed is variable. Firstly, the aerodynamic characteristics of three different specialized airfoils were analyzed to get optimum design parameters of wind turbine blade. Then BEM was performed with the application of the open source wind turbine design and performance computation software Q-Blade v0.6. After that, CFD simulation was done by Ansys CFX software. Here, k-ω “Shear-Stress-Transport” (SST) model was conducted for three-dimensional visualization of turbine performance. However, the best coefficient of performance was observed at 6o angle of attack. At this angle of attack, in the case of BEM, the highest coefficient of performance was 0.47 whereby CFD analysis, it was 0.43. Both studies showed good performance prediction which was a positive step to accelerate the continuous revolution in wind energy sector.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50275086)the University of New South Wales Visiting Professorship Scheme,Australia.
文摘An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC （LZ） ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.
基金supported by the National Natural Science Foundation of China(Nos.51575269,51275232)the Six Talent Peaks Project in Jiangsu Province(No.ZBZZ005)the Zhejiang Provincial Key Laboratory for Cutting Tools(No.ZD201305)
文摘Boron doped diamond(BDD)performs well in electrochemical oxidation for organic pollutants thanks to its wide electrochemical window and superior chemical stability.We presented a method to obtain well-adherent large-scale BDD/Nb electrode by the modified hot filament chemical vapor deposition system(HFCVD).SiC particles were sand blasted to enhance the adhesion of BDD coating.The BDD coating was then deposited on both sides of Nb which was placed vertically and closely with filament grids on both sides.The BDD/Nb electrodes had no deformation because the thermal deformations of the BDD films on both sides of the Nb substrate conteracted each other during cooling process after deposition.The surface morphology and purity of the BDD/Nb electrode were analyzed by Raman and scanning elestron microscope(SEM)techniques.Scratch test was used to investigate the adhesion of BDD films.The electrochemical performances were measured by cyclic voltammetry test.The BDD electrode at the B/C ratio of 2 000×10^(-6) held a higher oxygen evolution potential thanks to its high sp3 carbon content.Accelerated life test illustrated that the sandblasting pretreatment obviously enhanced the adhesion of BDD coating which resulted in a longer service duration than the un-sandblasted one.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2009AA702)the Innovation Foundation of Beijing University of Aeronautics and Astronautics for PhD Graduates (Grant No. 430569)
文摘To obtain the key subelements that may influence the scaling of gas-as injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas gas combustion fiowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas-gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner fiowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multi- element injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied.
文摘Using the DEA analysis method,on the basis of the national panel data from 2002 to 2014,this paper made a comparative analysis on the rice production performance before and after the implementation of direct grain subsidy policy,and made an empirical analysis on the relationship between the direct grain subsidy policy and the changes in the rice production performance. The results showed that the effect of the direct grain subsidy policy on promoting the rice production performance is declining year by year,largely because drop of scale efficiency. Besides,there are problems of serious redundancy in agricultural subsidy,unreasonable resource allocation,leading to low performance and resource waste of rice production.
文摘In order to recover the SiO_2 contained in the mother liquor in the course ofNaY zeolite synthesis to minimize pollution, the influence of various preparation conditions on thefiltering velocity of gel slurry was studied using the SiO_2/Al_2O_3 gel recovered from the NaYmother liquor in the laboratory. The results of study had shown that at a SiO_2/Al_2O_3 ratio in thefeed equating to 9∶1 the SiO_2 recovery rate and Al_2O_3 utilization rate were high with a fasterflow velocity of the filtrate. The pH value of the system had great impact on the flow velocity offiltrate. Between the two methods for regulating the pH value, the one for formation ofsilica/alumina gel slurry by addition of sulfuric acid prior to adding aluminium sulfate in thesolution could secure a faster filtration velocity. The filtration velocity was decreased in tandemwith increasing SiO_2 concentration in mother liquor, meanwhile an increase in dry filter cakeyield.
文摘In today＇s competitive environment the key element is the differentiation of business which will lead to success. Especially in international markets where there＇s much more intense competition, it is more important for businesses to enter with innovations that make a difference to their consumers. Innovation is also important for competitive export-oriented production in globalization. In global competition, innovation is the key factor for sustainable success. Increases in the efficiency, profitability of firms make it possible to enter new markets and extend present markets by obtaining advantage of competition. In order to determine accurate strategies, the connection between innovation and exports must be understood better. The aim of this study is to determine the innovation capability and export performance of Turkish export firms. Another aim is to examine the relationship between firm characteristics and innovation capability. Innovation capability of export firms is measured by INNOVSCALE which was developed by Vicente, Abrantes, and Teixeira （2015）. Export performance is measured by APEV scale which was developed by Lages, Lages, and Lages （2005）. The study uses data collected from 83 firms located in Kayseri. Results obtained by using SPSS indicate that there is a positive relationship between innovation capability and export performance. The results of the ANOVA analysis, innovation capability differ in terms of firm size and export earnings. Innovation capability does not differ in terms of sector, operating years, share of export earnings in the whole revenues, exporting periods, or internationalization levels.
文摘Virtual world simulation offers tremendous potential opportunities to improve, and optimize, individual and collective echelon training for the military. The US Army Research Laboratory (ARL) Military Open Simulator Enterprise Strategy (MOSES) project’s charter is to investigate simulation-based training technology for use in military specific training domains. Of particular interest are attributes of virtual worlds such as geographically distributed large-scale trainee support. We have initiated a series of experiments to determine appropriate benchmarks for simulator performance and to determine appropriate independent variables in order to create a robust predictive model that will enable virtual world training scenario designers to calculate, a priori, the number of trainees that may synchronously operate in a virtual world. The present paper’s purposes were to determine the effect that virtual world region fidelity had on server performance and determine whether this independent variable would be appropriate for inclusion into our predictive model. We found that region fidelity had a statistically significant effect on the simulator’s processor memory usage but had no significant effect on the simulator’s vertical scalability, CPU usage nor network performance. In this paper, we discourse on the purpose of this research, our experimental methodology and results, and discuss the significance of our findings.
基金This paper is supported by the National Nature Science Foundation （NSF） （No.70371038）, and Excellent Innovative Research Group Funds Project from the NSF of China （No. 70121001）.
文摘Whether a decision group does its function or not directly depends on the rationality of its characters. The decision science, also with other correlation disciplines, wants to know how the group characters affect the group performance. Although there are great deals of means to describe the group characters theoretically and practically, in this paper, we consider that the integrity character of a group is composed of the group scale, the constitution and the structure. So the research on how group characters affect the group performance should focus on the three aspects. In order to grasp the present research situation and clear the prospective direction of the studies, we will summarize the study on how the group characters affect the group performance from these three aspects.
