The recrystallization nucleation processes of two cold-rolled Al-Mg-Si/SiCpcomposites with different contents of Mg are investigated mainly by dynamic mechanical analyzer (DMA) and electron microscopy including high...The recrystallization nucleation processes of two cold-rolled Al-Mg-Si/SiCpcomposites with different contents of Mg are investigated mainly by dynamic mechanical analyzer (DMA) and electron microscopy including high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) andhigh-resolution transmission electron microscopy (HRTEM). Internal friction and electron microscopy results show that solute atom clusters are present in association with dislocationsin supersaturated cold-rolled composites. During recrystallization process, the internal friction peak position of Al-Mg-Si/3SiCp/2Mg (volume fraction,%) is higher than that of Al-Mg-Si/3SiCp(volume fraction,%) due to more solute atom clusters formed in association with the dislocations in the cold-rolled composite with a much higher Mg content, indicating a strongerresistance for the recrystallization nucleation.展开更多
The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. T...The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. Two typical internal friction peaks were detected corresponding to heating and cooling processes, respectively. The heating peak corresponds to a recrystallization process of deformed Al particles, which is influenced by many extrinsic parameters, such as measuring frequency, strain amplitude, heating rate, power particle size and compacting pressure. However, the intrinsic nature of the peak is originated from the micro-sliding of the weak-bonding interfaces between Al particles and increased dislocation density induced in compressing. The cooling peak with the activation energy of (1.64±0.06) eV is associated with the grain boundary relaxation, which can be interpreted as the viscous sliding of grain boundaries. The similar phenomena are also found in the Mg green powder compact.展开更多
The effects of solution-aging treatment on the microstructures, mechanical properties and internal friction of Ti- 55.06%Ni-0.3%Cr (mole fraction) alloy were investigated by means of tensile test, dynamic mechanical...The effects of solution-aging treatment on the microstructures, mechanical properties and internal friction of Ti- 55.06%Ni-0.3%Cr (mole fraction) alloy were investigated by means of tensile test, dynamic mechanical analysis (DMA) and spherical aberration electron microscopy (SAEM). The results show that the aged alloys with Cr3Ni2 phase always exhibit higher tensile strength and hardness than those of solution-treated alloy without Cr3Ni2 phase, and the aging peak temperature presents at 375 ℃. It is also found that the internal friction peak (tan 6) value decreases with increasing the frequency. There are two internal friction peaks corresponding to the B2(austenite)→R and R→M(martensite) transformations upon cooling, but only one corresponding to the reverse M→B2 transformation upon heating in both solution-treated and 375 ℃-aged alloys, due to the superposition of Mand R phase transformation. Besides, the position of internal friction peaks in the alloy after aging at 375 ℃ shifts to higher temperature. This is attributed to the decrease of Cr and Ni content, and the decline of lattice deformation and transformation resistance, all of which are related to the precipitation of Cr3Ni2 phase in the solution-aged alloys.展开更多
A fitting process is used to measure the cavity loss and the quasi Fermi level separation for Fabry Pérot semiconductor lasers.From the amplified spontaneous emission (ASE) spectrum,the gain spectrum and sing...A fitting process is used to measure the cavity loss and the quasi Fermi level separation for Fabry Pérot semiconductor lasers.From the amplified spontaneous emission (ASE) spectrum,the gain spectrum and single pass ASE obtained by the Cassidy method are applied in the fitting process.For a 1550nm quantum well InGaAsP ridge waveguide laser,the cavity loss of about ~24cm -1 is obtained.展开更多
The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA...The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.展开更多
The present article has been fine-tuned with the investigation of mixed convection Darcy-Forchheimer flow of ZnO-SAE50 oil nanolubricant over an inclined rotating disk under the influence of uniform applied magnetic f...The present article has been fine-tuned with the investigation of mixed convection Darcy-Forchheimer flow of ZnO-SAE50 oil nanolubricant over an inclined rotating disk under the influence of uniform applied magnetic field applied to various industries.The current study has been enriched with additional consideration of slip flow,thermal radiation,viscous dissipation,Joulian dissipation and internal heating.In view of augmentation of thermal conductivity of nanolubricant,a new micro-nano-convection model namely Patel model has been invoked.The specialty of this model involves the effects of specific surface area and nano-convection due to Brownian motion of nanoparticles,kinetic theory based micro-convection,liquid layering and particle concentration.Suitably transformed governing equations have been solved numerically by using Runge-Kutta-Fehlberg scheme.An analysis of the present study has shown that applied magnetic field,porosity of the medium,velocity slip and inertia coefficient account for the slowing down of radial as well as tangential flow of ZnO-SAE50 oil nanolubricant,thereby leading to an improvement in velocity and thermal boundary layers.展开更多
As environmental protection agencies enact new regulations for automotive fuel economy and emission, the toroidal continuously variable transmissions (CVTs) keep on contribute to the advent of system technologies for ...As environmental protection agencies enact new regulations for automotive fuel economy and emission, the toroidal continuously variable transmissions (CVTs) keep on contribute to the advent of system technologies for better fuel consumption of automobiles with internal combustion engines (ICE). Toroidal CVTs use infinitely adjustable drive ratios instead of stepped gears to achieve optimal performance. Toroidal CVTs are one of the earliest patents to the automotive world but their torque capacities and reliability have limitations in the past. New developments and implementations in the control strategies, and several key technologies have led to development of more robust toroidal CVTs, which enables more extensive automotive application of toroidal CTVs. This paper concerns with the current development, upcoming and progress set in the context of the past development and the traditional problems associated with toroidal CVTs.展开更多
With rapid economy growth,building energy consumption in China has been gradually increased.The energy consumption and indoor environmental quality of 51 office buildings in Hainan Province,a hot and humid area,were s...With rapid economy growth,building energy consumption in China has been gradually increased.The energy consumption and indoor environmental quality of 51 office buildings in Hainan Province,a hot and humid area,were studied through collection of verified data in site visits and field tests.The result revealed that,electricity accounted for 99.79% of the total energy consumption,natural gas 0.17%,and diesel 0.04%.The air conditioning dominated the energy use with a share of 43.18%,equipment in the particular areas 26.90%,equipment in the office rooms 11.95%,lighting system 8.67%,general service system 7.57%,and miscellaneous items 1.73%.Statistical method including six indicators obtained the energy consumption benchmark with upper limit of 98.31 kW-h/m2 and lower limit of 55.26 kW-h/m2.According to ASHRAE standard(comfortable standard) and GB/T 18883-2002(acceptable standard),the indoor environmental quality of 51 sampled office buildings was classified into three ranks:good,normal and bad.With benchmark of building energy consumption combined with indoor environmental quality,it was found that only 3.92% of sampled buildings can be identified as the best performance buildings with low energy consumption and advanced indoor environmental quality,and the buildings classified into normal level accounted for the maximum ratio.展开更多
Since rough surface scattering has a great impact on the accuracy of the propagation prediction algorithm,an integrated algorithm for indoor propagation prediction including rough surface scattering is proposed here.T...Since rough surface scattering has a great impact on the accuracy of the propagation prediction algorithm,an integrated algorithm for indoor propagation prediction including rough surface scattering is proposed here.This algorithm is composed of a three dimensional(3D) ray tracing algorithm based on binary space partitioning(BSP) and a diffuse scattering algorithm based on Oren-Nayar's theory.Lack of accuracy and prohibitive time consumption are the main drawbacks of the existing ray tracing based propagation prediction models.To defy these shortcomings,the balanced BSP tree is used in the proposed algorithm to accelerate the ray tracing,while the nearest object priority technique(NOP) and in contact surface(ICS) is used to eliminate the repeated rayobject intersection tests.Therefore,the final criteria of this study are the time consumption as well as accuracy by predicting the field strength and the number of received signals.Using the proposed approaches,our algorithm becomes faster and more accurate than the existing algorithms.A detailed comparative study with existing algorithms shows that the proposed algorithm has at most 37.83%higher accuracy and 34.44%lower time consumption.Moreover,effects of NOP and ICS techniques and scattering factor on time and ray prediction accuracy are also presented.展开更多
The effect of two nighttime ventilation strategies on cooling and heating energy use is investigated for a prototype office building in several northern America climates, using hourly building energy simulation softwa...The effect of two nighttime ventilation strategies on cooling and heating energy use is investigated for a prototype office building in several northern America climates, using hourly building energy simulation software (DOE2.1E). The strategies include: scheduled-driven nighttime ventilation and a predictive method for nighttime ventilation. The maximum possible energy savings and peak demand reduction in each climate is analyzed as a function of ventilation rate, indoor-outdoor temperature difference, and building thermal mass. The results show that nighttime ventilation could save up to 32% cooling energy in an office building, while the total energy and peak demand savings for the fan and cooling is about 13% and 10%, respectively. Consequently, finding the optimal control parameters for the nighttime ventilation strategies is very important. The performance of the two strategies varies in different climates. The predictive nighttime ventilation worked better in weather conditions with fairly smooth transition from heating to cooling season.展开更多
Located in the cold and very cold semiarid steppe climate zone, North Dakota boasts not only long cold winters but also hot summers, which significantly increases the energy consumption of buildings. In fact, North Da...Located in the cold and very cold semiarid steppe climate zone, North Dakota boasts not only long cold winters but also hot summers, which significantly increases the energy consumption of buildings. In fact, North Dakota has the highest energy consumption per capita in residential buildings (101 MM Btu in 2013), and its energy consumption per capita in commercial buildings ranks the second (l 18 MM Btu in 2013) in the nation. When humans spend a long time indoors to escape the inclement weather, their health will be more susceptible to the indoor environment. In addition, North Dakota has the 3rd least number of green buildings certified by LEED (Leadership in Energy and Environmental Design) in the nation. This paper aims to investigate the status quo of buildings with respect to energy, health and sustainability in North Dakota, and attempts to propose strategies regarding research and higher education to rectify the current issues. These strategies include but not limited to forming the architectural engineering program, a comprehensive and interdisciplinary program in buildings.展开更多
High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC loss...High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC losses in the superconductors.Based on the dynamic process of thermomagnetic interaction,we report the results of numerical analysis of AC losses in an infinite high-temperature superconducting slab subjected to a uniform in-plane strain in an alternating external magnetic field parallel to the sample surface.The numerical analysis shows the details of electromagnetic phenomena in the slab and the dependences of AC loss on various external parameters including the uniform strain in the slab and the amplitude and frequency of the external magnetic field.In this paper,we find that whether the magnetic field fully penetrates the superconductor is the key factor that influences the features of AC loss.When the magnetic field cannot fully penetrate the superconductor,the loss rises with increasing strain or decreasing frequency.When the magnetic field can fully penetrate the superconductor,the feature is just opposite.We also analyze the effects of periodic strain on AC loss.It is interesting to find that when the periodic strain frequency equals the external magnetic field frequency,the AC loss reaches the maximum,regardless if the magnetic field fully penetrates the superconductor or not.展开更多
A model of three-dimensional helm-shaped body composed of a helm-shaped fin and inner heat sources is built in this paper. For the specified volumes of the body, fin and heat source, the constructal optimizations of t...A model of three-dimensional helm-shaped body composed of a helm-shaped fin and inner heat sources is built in this paper. For the specified volumes of the body, fin and heat source, the constructal optimizations of the body with single and multiple inner heat sources are implemented. The entransy-dissipation-rate-based equivalent thermal resistance(ETR) is minimized in the optimizations. It shows that for the helm-shaped body with multiple inner heat sources, there exist an optimal ratio of the heat source distance to the radius of the extended fin and a twice optimal radius ratio of the centre fin to the extended fin which lead to the double minimum dimensionless ETR. Comparing the optimal result of the body with helm-shaped fin with that with annular fin, the radius of the centre fin and the distance between the heat source and the center of the body are decreased, and the ETR is decreased by 9.57%. Essentially, the temperature gradient field of the helm-shaped body is more homogenous, and its global heat transfer performance is improved.展开更多
OBJECTIVE: To investigate the quality and meth- ods of clinical research literature published in for- eign Science Citation Index (SCI) journals studying the treatment of low back pain with acupuncture. To conduct ...OBJECTIVE: To investigate the quality and meth- ods of clinical research literature published in for- eign Science Citation Index (SCI) journals studying the treatment of low back pain with acupuncture. To conduct a comparative study with clinical re- search literature published in Chinese core domes- tic journals, and to understand the prospects of cur- rent research trends of acupuncture clinical studies in Western countries and China. METHODS: Studies on clinical acupuncture treat- ment of low back pain in English SCI journals and four Chinese core domestic journals dated from 2002 to 2012 were sourced and summarized for this study. Objective analysis and evaluation on the differences in subject and scope of study on low back pain by foreign and Chinese researchers were conducted. RESULTS: Forty-seven English studies and 115 Chi- nese studies met our inclusion criteria. A keyword search revealed different kinds of low back pain re- lated conditions in English and Chinese studies. The English studies were broad in scope, while the Chinese studies were more focused. There were al-so differences in the understanding and definition of concepts and study orientation. CONCI.IJSION: More study should be undertaken to understand the contradictions that acupuncture faces in view of modern research to further ad- vance the field.展开更多
基金Project(LH201236)supported by the Pre-research Project of Equipment Development Department of China
文摘The recrystallization nucleation processes of two cold-rolled Al-Mg-Si/SiCpcomposites with different contents of Mg are investigated mainly by dynamic mechanical analyzer (DMA) and electron microscopy including high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) andhigh-resolution transmission electron microscopy (HRTEM). Internal friction and electron microscopy results show that solute atom clusters are present in association with dislocationsin supersaturated cold-rolled composites. During recrystallization process, the internal friction peak position of Al-Mg-Si/3SiCp/2Mg (volume fraction,%) is higher than that of Al-Mg-Si/3SiCp(volume fraction,%) due to more solute atom clusters formed in association with the dislocations in the cold-rolled composite with a much higher Mg content, indicating a strongerresistance for the recrystallization nucleation.
基金Project(51301150)supported by the National Natural Science Foundation of ChinaProject(2013KJXX-11)supported by the Special Program of Youth New-star of Science and Technology of Shaanxi Province,ChinaProject(Physics-2012SXTS05)supported by the High-level University Construction Special Program of Shaanxi Province,China
文摘The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. Two typical internal friction peaks were detected corresponding to heating and cooling processes, respectively. The heating peak corresponds to a recrystallization process of deformed Al particles, which is influenced by many extrinsic parameters, such as measuring frequency, strain amplitude, heating rate, power particle size and compacting pressure. However, the intrinsic nature of the peak is originated from the micro-sliding of the weak-bonding interfaces between Al particles and increased dislocation density induced in compressing. The cooling peak with the activation energy of (1.64±0.06) eV is associated with the grain boundary relaxation, which can be interpreted as the viscous sliding of grain boundaries. The similar phenomena are also found in the Mg green powder compact.
文摘The effects of solution-aging treatment on the microstructures, mechanical properties and internal friction of Ti- 55.06%Ni-0.3%Cr (mole fraction) alloy were investigated by means of tensile test, dynamic mechanical analysis (DMA) and spherical aberration electron microscopy (SAEM). The results show that the aged alloys with Cr3Ni2 phase always exhibit higher tensile strength and hardness than those of solution-treated alloy without Cr3Ni2 phase, and the aging peak temperature presents at 375 ℃. It is also found that the internal friction peak (tan 6) value decreases with increasing the frequency. There are two internal friction peaks corresponding to the B2(austenite)→R and R→M(martensite) transformations upon cooling, but only one corresponding to the reverse M→B2 transformation upon heating in both solution-treated and 375 ℃-aged alloys, due to the superposition of Mand R phase transformation. Besides, the position of internal friction peaks in the alloy after aging at 375 ℃ shifts to higher temperature. This is attributed to the decrease of Cr and Ni content, and the decline of lattice deformation and transformation resistance, all of which are related to the precipitation of Cr3Ni2 phase in the solution-aged alloys.
文摘A fitting process is used to measure the cavity loss and the quasi Fermi level separation for Fabry Pérot semiconductor lasers.From the amplified spontaneous emission (ASE) spectrum,the gain spectrum and single pass ASE obtained by the Cassidy method are applied in the fitting process.For a 1550nm quantum well InGaAsP ridge waveguide laser,the cavity loss of about ~24cm -1 is obtained.
文摘The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.
文摘The present article has been fine-tuned with the investigation of mixed convection Darcy-Forchheimer flow of ZnO-SAE50 oil nanolubricant over an inclined rotating disk under the influence of uniform applied magnetic field applied to various industries.The current study has been enriched with additional consideration of slip flow,thermal radiation,viscous dissipation,Joulian dissipation and internal heating.In view of augmentation of thermal conductivity of nanolubricant,a new micro-nano-convection model namely Patel model has been invoked.The specialty of this model involves the effects of specific surface area and nano-convection due to Brownian motion of nanoparticles,kinetic theory based micro-convection,liquid layering and particle concentration.Suitably transformed governing equations have been solved numerically by using Runge-Kutta-Fehlberg scheme.An analysis of the present study has shown that applied magnetic field,porosity of the medium,velocity slip and inertia coefficient account for the slowing down of radial as well as tangential flow of ZnO-SAE50 oil nanolubricant,thereby leading to an improvement in velocity and thermal boundary layers.
基金the Ford-NSFC Foundation of China (No. 50122151).
文摘As environmental protection agencies enact new regulations for automotive fuel economy and emission, the toroidal continuously variable transmissions (CVTs) keep on contribute to the advent of system technologies for better fuel consumption of automobiles with internal combustion engines (ICE). Toroidal CVTs use infinitely adjustable drive ratios instead of stepped gears to achieve optimal performance. Toroidal CVTs are one of the earliest patents to the automotive world but their torque capacities and reliability have limitations in the past. New developments and implementations in the control strategies, and several key technologies have led to development of more robust toroidal CVTs, which enables more extensive automotive application of toroidal CTVs. This paper concerns with the current development, upcoming and progress set in the context of the past development and the traditional problems associated with toroidal CVTs.
基金Project(2011BAJ01B05) supported by the National Science and Technology Pillar Program during the Twelfth Five-year Plan Period of China
文摘With rapid economy growth,building energy consumption in China has been gradually increased.The energy consumption and indoor environmental quality of 51 office buildings in Hainan Province,a hot and humid area,were studied through collection of verified data in site visits and field tests.The result revealed that,electricity accounted for 99.79% of the total energy consumption,natural gas 0.17%,and diesel 0.04%.The air conditioning dominated the energy use with a share of 43.18%,equipment in the particular areas 26.90%,equipment in the office rooms 11.95%,lighting system 8.67%,general service system 7.57%,and miscellaneous items 1.73%.Statistical method including six indicators obtained the energy consumption benchmark with upper limit of 98.31 kW-h/m2 and lower limit of 55.26 kW-h/m2.According to ASHRAE standard(comfortable standard) and GB/T 18883-2002(acceptable standard),the indoor environmental quality of 51 sampled office buildings was classified into three ranks:good,normal and bad.With benchmark of building energy consumption combined with indoor environmental quality,it was found that only 3.92% of sampled buildings can be identified as the best performance buildings with low energy consumption and advanced indoor environmental quality,and the buildings classified into normal level accounted for the maximum ratio.
基金financial support under the University of Malaya Research Grant(UMRG) scheme(RG098/12ICT)
文摘Since rough surface scattering has a great impact on the accuracy of the propagation prediction algorithm,an integrated algorithm for indoor propagation prediction including rough surface scattering is proposed here.This algorithm is composed of a three dimensional(3D) ray tracing algorithm based on binary space partitioning(BSP) and a diffuse scattering algorithm based on Oren-Nayar's theory.Lack of accuracy and prohibitive time consumption are the main drawbacks of the existing ray tracing based propagation prediction models.To defy these shortcomings,the balanced BSP tree is used in the proposed algorithm to accelerate the ray tracing,while the nearest object priority technique(NOP) and in contact surface(ICS) is used to eliminate the repeated rayobject intersection tests.Therefore,the final criteria of this study are the time consumption as well as accuracy by predicting the field strength and the number of received signals.Using the proposed approaches,our algorithm becomes faster and more accurate than the existing algorithms.A detailed comparative study with existing algorithms shows that the proposed algorithm has at most 37.83%higher accuracy and 34.44%lower time consumption.Moreover,effects of NOP and ICS techniques and scattering factor on time and ray prediction accuracy are also presented.
文摘The effect of two nighttime ventilation strategies on cooling and heating energy use is investigated for a prototype office building in several northern America climates, using hourly building energy simulation software (DOE2.1E). The strategies include: scheduled-driven nighttime ventilation and a predictive method for nighttime ventilation. The maximum possible energy savings and peak demand reduction in each climate is analyzed as a function of ventilation rate, indoor-outdoor temperature difference, and building thermal mass. The results show that nighttime ventilation could save up to 32% cooling energy in an office building, while the total energy and peak demand savings for the fan and cooling is about 13% and 10%, respectively. Consequently, finding the optimal control parameters for the nighttime ventilation strategies is very important. The performance of the two strategies varies in different climates. The predictive nighttime ventilation worked better in weather conditions with fairly smooth transition from heating to cooling season.
文摘Located in the cold and very cold semiarid steppe climate zone, North Dakota boasts not only long cold winters but also hot summers, which significantly increases the energy consumption of buildings. In fact, North Dakota has the highest energy consumption per capita in residential buildings (101 MM Btu in 2013), and its energy consumption per capita in commercial buildings ranks the second (l 18 MM Btu in 2013) in the nation. When humans spend a long time indoors to escape the inclement weather, their health will be more susceptible to the indoor environment. In addition, North Dakota has the 3rd least number of green buildings certified by LEED (Leadership in Energy and Environmental Design) in the nation. This paper aims to investigate the status quo of buildings with respect to energy, health and sustainability in North Dakota, and attempts to propose strategies regarding research and higher education to rectify the current issues. These strategies include but not limited to forming the architectural engineering program, a comprehensive and interdisciplinary program in buildings.
基金supported by the National Natural Science Foundation of China(Grant Nos.11032006,11121202 and 11202087)National Key Project of Magneto-Constrained Fusion Energy Development Program(Grant No.2013GB110002)
文摘High-temperature superconductors in superconductor apparatuses are subjected to mechanical strains under operating conditions.These strains cause the degradation of the critical current densities and influence AC losses in the superconductors.Based on the dynamic process of thermomagnetic interaction,we report the results of numerical analysis of AC losses in an infinite high-temperature superconducting slab subjected to a uniform in-plane strain in an alternating external magnetic field parallel to the sample surface.The numerical analysis shows the details of electromagnetic phenomena in the slab and the dependences of AC loss on various external parameters including the uniform strain in the slab and the amplitude and frequency of the external magnetic field.In this paper,we find that whether the magnetic field fully penetrates the superconductor is the key factor that influences the features of AC loss.When the magnetic field cannot fully penetrate the superconductor,the loss rises with increasing strain or decreasing frequency.When the magnetic field can fully penetrate the superconductor,the feature is just opposite.We also analyze the effects of periodic strain on AC loss.It is interesting to find that when the periodic strain frequency equals the external magnetic field frequency,the AC loss reaches the maximum,regardless if the magnetic field fully penetrates the superconductor or not.
基金supported by the National Natural Science Foundation of China(Grant Nos.51176203 and 51356001)the Natural Science Foundation for Youngsters of Naval University of Engineering(Grant No.HGDQNJJ15007)
文摘A model of three-dimensional helm-shaped body composed of a helm-shaped fin and inner heat sources is built in this paper. For the specified volumes of the body, fin and heat source, the constructal optimizations of the body with single and multiple inner heat sources are implemented. The entransy-dissipation-rate-based equivalent thermal resistance(ETR) is minimized in the optimizations. It shows that for the helm-shaped body with multiple inner heat sources, there exist an optimal ratio of the heat source distance to the radius of the extended fin and a twice optimal radius ratio of the centre fin to the extended fin which lead to the double minimum dimensionless ETR. Comparing the optimal result of the body with helm-shaped fin with that with annular fin, the radius of the centre fin and the distance between the heat source and the center of the body are decreased, and the ETR is decreased by 9.57%. Essentially, the temperature gradient field of the helm-shaped body is more homogenous, and its global heat transfer performance is improved.
文摘OBJECTIVE: To investigate the quality and meth- ods of clinical research literature published in for- eign Science Citation Index (SCI) journals studying the treatment of low back pain with acupuncture. To conduct a comparative study with clinical re- search literature published in Chinese core domes- tic journals, and to understand the prospects of cur- rent research trends of acupuncture clinical studies in Western countries and China. METHODS: Studies on clinical acupuncture treat- ment of low back pain in English SCI journals and four Chinese core domestic journals dated from 2002 to 2012 were sourced and summarized for this study. Objective analysis and evaluation on the differences in subject and scope of study on low back pain by foreign and Chinese researchers were conducted. RESULTS: Forty-seven English studies and 115 Chi- nese studies met our inclusion criteria. A keyword search revealed different kinds of low back pain re- lated conditions in English and Chinese studies. The English studies were broad in scope, while the Chinese studies were more focused. There were al-so differences in the understanding and definition of concepts and study orientation. CONCI.IJSION: More study should be undertaken to understand the contradictions that acupuncture faces in view of modern research to further ad- vance the field.