This paper presents an overview of dielectric patch(DP)antennas developed in recent years.The employed DP resonator composed of a DP and a bottom substrate is analyzed comprehensively here,enabling the easy realizatio...This paper presents an overview of dielectric patch(DP)antennas developed in recent years.The employed DP resonator composed of a DP and a bottom substrate is analyzed comprehensively here,enabling the easy realization of a quasi-planar DP antenna.It combines the dual advantages of the conventional microstrip patch(MP)antenna and dielectric resonator(DR)antenna in terms of profile,gain,bandwidth,radiation efficiency,and design freedom.Furthermore,the DP antenna inherits the multi-mode characteristic of the DR antenna,thus it has a large number of high-order modes,including TMmn mode and TEmn mode.The high-order modes are widely applied,for example,by combining with the dominant TM10 mode to expand the bandwidth,or selecting multiple higher-order modes to implement a high-gain antenna.Additionally,the non-radiation high-order modes are also utilized to produce natural radiation null in filtering antenna design.In this paper,the design theories and techniques of DP antenna are introduced and investigated,including calculation and control methods of the resonant mode frequencies,analysis of the radiation mechanism,and applications of the multi-mode characteristic.This overview could provide guidance for the subsequent antenna design,thus effectively avoid time-consuming optimization.展开更多
The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of ...The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can't be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.展开更多
Performance prediction for centrifugal pumps is now mainly based on numerical calculation and most of the studies merely focus on one model. Therefore, the research results are not representative. To make an improveme...Performance prediction for centrifugal pumps is now mainly based on numerical calculation and most of the studies merely focus on one model. Therefore, the research results are not representative. To make an improvement of numerical calculation method and performance prediction for centrifugal pumps, performance of six centrifugal pump models at design flow rate and off design flow rates, whose specific speed are different, were simulated by using commercial code FLUENT. The standard k-t turbulence model and SIMPLEC algorithm were chosen in FLUENT. The simulation was steady and moving reference frame was used to consider the impeller-volute interaction. Also, how to dispose the gap between impeller and volute was presented and the effect of grid number was considered. The characteristic prediction model for centrifugal pumps is established according to the simulation results. The head and efficiency of the six models at different flow rates are predicted and the prediction results are compared with the experiment results in detail. The comparison indicates that the precision of head and efficiency prediction are all less than 5%. The flow analysis indicates that flow change has an important effect on the location and area of low pressure region behind the blade inlet and the direction of velocity at impeller inlet. The study shows that using FLUENT simulation results to predict performance of centrifugal pumps is feasible and accurate. The method can be applied in engineering practice.展开更多
Distributed energy resources have been proven to be an effective and promising solution to enhance power system resilience and improve household-level reliability.In this paper,we propose a method to evaluate the reli...Distributed energy resources have been proven to be an effective and promising solution to enhance power system resilience and improve household-level reliability.In this paper,we propose a method to evaluate the reliability value of a photovoltaic(PV)energy system with a battery storage system(BSS)by considering the probability of grid outages causing household blackouts.Considering this reliability value,which is the economic profit and capital cost of PV+BSS,a simple formula is derived to calculate the optimal planning strategy.This strategy can provide household-level customers with a simple and straightforward expression for invested PV+BSS capacity.Case studies on 600 households located in eight zones of the US for the period of 2006 to 2015 demonstrate that adding the reliability value to economic profit allows households to invest in a larger PV+BSS and avoid loss of load caused by blackouts.Owing to the differences in blackout hours,households from the 8 zones express distinct willingness to install PV+BSS.The greater the probability of blackout,the greater revenue that household can get from the PV+BSS.The simulation example shows that the planning strategy obtained by proposed model has good economy in the actual operation and able to reduce the economic risk of power failure of the household users.This model can provide household with an easy and straightforward investment strategy of PV+BSS capacity.展开更多
The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decrease...The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of the band gap, and the additional absorption, are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the more important factors influencing the photovoltaic activity of Cu2O film.展开更多
This study was designed to determine the effect of different sperm preparation treatments on yak sperm quality and in vitro embryo development.Frozen-thawed semen samples were treated using swim-up or percoll gradient...This study was designed to determine the effect of different sperm preparation treatments on yak sperm quality and in vitro embryo development.Frozen-thawed semen samples were treated using swim-up or percoll gradient centrifugation methods.Sperm concentration,progressive motility,recovery of motile sperm,membrane integrity,acrosome and chromatin integrity were scored and compared in recovered samples and controls.In addition,the effects of two sperm separation treatments on embryos capable of cleavage and in vitro development to the blastocyst stage were evaluated.Swim-up separated sperm showed a higher motility,while the concentration of spermatozoa recovered and percent recovery of motile sperm were higher with percoll gradient centrifugation separation.According to the optical and electron microscopies,swim-up produced higher percentage of sperm with intact plasma membrane and acrosome than percoll gradient centrifugation separation.However,there was no difference in the percentage of sperm with intact chromatin between two treatment groups.Cell numbers in the blastocysts of two groups were not different.The blastocyst rate was similar in both groups,whereas cleavage rate was higher when swim-up was used.展开更多
Accurately predicting the trajectories of surrounding vehicles and assessing the collision risks are essential to avoid side and rear-end collisions caused by cut-in.To improve the safety of autonomous vehicles in the...Accurately predicting the trajectories of surrounding vehicles and assessing the collision risks are essential to avoid side and rear-end collisions caused by cut-in.To improve the safety of autonomous vehicles in the mixed traffic,this study proposes a cut-in prediction and risk assessment method with considering the interactions of multiple traffic participants.The integration of the support vector machine and Gaussian mixture model(SVM-GMM)is developed to simultaneously predict cut-in behavior and trajectory.The dimension of the input features is reduced through Chebyshev fitting to improve the training efficiency as well as the online inference performance.Based on the predicted trajectory of the cut-in vehicle and the responsive actions of the autonomous vehicles,two risk measurements are introduced to formulate the comprehensive interaction risk through the combination of Sigmoid function and Softmax function.Finally,the comparative analysis is performed to validate the proposed method using the naturalistic driving data.The results show that the proposed method can predict the trajectory with higher precision and effectively evaluate the risk level of a cut-in maneuver compared to the methods without considering interaction.展开更多
The influences of different design factors,as well as dummy posture,on an occupants' knee slider compression,were studied in this paper.Based on the vehicle geometry data,the simulation model,including both the mu...The influences of different design factors,as well as dummy posture,on an occupants' knee slider compression,were studied in this paper.Based on the vehicle geometry data,the simulation model,including both the multi-rigid-body and finite element(FE)part,was built up and validated with China New Car Assessment Program(C-NCAP)full impact to ensure the accuracy of the model.By adjusting the design parameters and the posture of the femur and lower leg,different factors affecting the passengers' knee slider compression were evaluated,with the help of MAthematical DYnamic MOdel(MADYMO)simulations.The study indicated that the leg posture,the stiffness of the IP and angles of the carpet have significant effects on the knee slider compression in this case.By decreasing the angle between the femur and lower leg from 133° to 124°,the maximum knee slider compression was decreased by 17.3% and by scaling the IP stiffness from 1 to 0.7,it could be decreased by 18.6%.Also,decreasing the angles of the carpet from 28° to 37°can help reduce the knee slider compression by 18.3%.展开更多
Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. T...Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.展开更多
ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy.The band offsets of the ZnO/Al_(2)O_(3) heterojunction are studied by in situ x-ray photoelectron spectroscopy.The valence band of Al_(2)O_(...ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy.The band offsets of the ZnO/Al_(2)O_(3) heterojunction are studied by in situ x-ray photoelectron spectroscopy.The valence band of Al_(2)O_(3) is found to be 3.59±0.05 eV below that of ZnO.Together with the resulting conduction band offset of 2.04±0.05 eV,this indicates that a type-I staggered band line exists at the ZnO/Al_(2)O_(3) heterojunction.展开更多
Background:Bongardia chrysogonum(L.)Spach,also known as“Uruf-el-Deek”,has been used by rural communities for the treatment of various diseases and disorders,owing to its wide array of secondary metabolite compositio...Background:Bongardia chrysogonum(L.)Spach,also known as“Uruf-el-Deek”,has been used by rural communities for the treatment of various diseases and disorders,owing to its wide array of secondary metabolite compositions.Methods:The current study was conducted to determine the total polyphenolic content of Bongardia chrysogonum(L.)Spach as well as its potential free radical scavenging and metal-chelating antioxidant capacities.Its leaves,stems,and tubers were separately extracted using ethanol,water,and chloroform;their antioxidant activities were analyzed using in vitro models,including DPPH,ABTS,FRAP,and CUPRAC assays.The total polyphenolic content of the extracts was spectrophotometrically measured.Results:The richest polyphenolic content of the extracts was yielded by tuber chloroform and leaf ethanol extraction(215.09±0.53 mg/g extract as gallic acid equivalent and 240.74±1.12 mg/g extract as quercetin equivalent,respectively).Almost all of the tested extracts exhibited remarkable antioxidant activities,with the highest antioxidant capacity observed in the leaf extracts.On the other hand,the tuber ethanol extract demonstrated the weakest DPPH radical scavenging activity(%inhibition=49.75±0.38,P<0.01),while the tuber chloroform extract showed the weakest ABTS radical scavenging activity(%inhibition=62.61±0.06,P<0.05).These were closely followed by the tuber water extract(%inhibition=63.28±0.65,P<0.01).In terms of their FRAP and CUPRAC assays,the leaf ethanol extract was determined as the best one,with absorbance values of 3.64±0.01 and 2.22±0.01(P<0.01),respectively.Conclusion:Bongardia chrysogonum(L.)Spach possesses rich polyphenolic content and strong antioxidant activities.Thus,it could be a valuable source for the pharmaceutical industry in the prevention and treatment of diseases associated with oxidative stress.展开更多
Kuwaiti oil production faces a growing challenge in the increasing quantities of produced water generated in the production of oil. The high water cut of the produced fluid from the wells and the high salinity of the ...Kuwaiti oil production faces a growing challenge in the increasing quantities of produced water generated in the production of oil. The high water cut of the produced fluid from the wells and the high salinity of the produced water lead to significant degradation of subsurface equipment, specifically the production tubing. Debris generated through the degradation of the inner part of the tubing becomes a constituent of the scaling that deposits in the tubing and blocks the flow of the production fluid, inducing higher maintenance costs. This paper looks at the characteristics of the scaling in regard to the produced water and outlines the economic impact of the produced water induced degradation of the tubing structure.展开更多
On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission...On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission characteristics, we performed comprehensive chassis dynamometer measurements of NH3 emission from two China 5 and two China 6 light-duty gasoline vehicles (LDGVs) equipped with three-way catalytic converters (TWCs). The results showed that the distance-based emission factors (EFs) were 12.72 ± 2.68 and 3.18 ± 1.37 mg/km for China 5 and China 6 LDGVs, respectively. Upgrades in emission standards were associated with a reduction in tailpipe NH3 emission. In addition, high NH3 EFs were observed during the engine warm-up period in cold-start cases owing to the intensive emissions of incomplete combustion products and suitable catalytic temperature in the TWCs. Notably, based on the instantaneous NH3 emission rate, distinct NH3–emitting events were detected under high/extra high velocity or rapid acceleration. Furthermore, NH3 emission rates correlated well with engine speed, vehicle specific power, and modified combustion efficiency, which were more easily accessible. These strong correlations were applied to reproduce NH3 emissions from China 5/6 LDGVs. The predicted NH3 EFs under different dynamometer and real-world cycles agreed well with existing measurement and prediction results, revealing that the NH3 EFs of LDGVs in urban routes were within 8.55–11.62 mg/km. The results presented here substantially contribute to improving the NH3 emission inventory for LDGVs and predicting on-road NH3 emissions in China.展开更多
The current research of the global chassis control problem for the full drive-by-wire vehicle focuses on the control allocation (CA) of the four-wheel-distributed trac- tion/braking/steering systems. However, the pa...The current research of the global chassis control problem for the full drive-by-wire vehicle focuses on the control allocation (CA) of the four-wheel-distributed trac- tion/braking/steering systems. However, the path following performance and the handling stability of the vehicle can be enhanced a step further by automatically adjusting the vehicle speed to the optimal value. The optimal solution for the combined longitudinal and lateral motion control (MC) problem is given. First, a new variable step-size spatial transformation method is proposed and utilized in the prediction model to derive the dynamics of the vehicle with respect to the road, such that the tracking errors can be explicitly obtained over the prediction horizon at varying speeds. Second, a nonlinear model predictive con- trol (NMPC) algorithm is introduced to handle the non- linear coupling between any two directions of the vehicular planar motion and computes the sequence of the optimal motion states for following the desired path. Third, a hierarchical control structure is proposed to separate the motion controller into a NMPC based path planner and a terminal sliding mode control (TSMC) based path fol- lower. As revealed through off-line simulations, the hier- archical methodology brings nearly 1700% improvement in computational efficiency without loss of control per- formance. Finally, the control algorithm is verified through a hardware in-the-loop simulation system. Double-lane- change (DLC) test results show that by using the optimalpredictive controller, the root-mean-square (RMS) values of the lateral deviations and the orientation errors can be reduced by 41% and 30%, respectively, comparing to those by the optimal preview acceleration (OPA) driver model with the non-preview speed-tracking method. Additionally, the average vehicle speed is increased by 0.26 km/h with the peak sideslip angle suppressed to 1.9~. This research proposes a novel motion controller, which provides the full drive-by-wire vehicle with better lane-keeping and colli- sion-avoidance capabilities during autonomous driving.展开更多
Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal sta...Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.展开更多
ITO (indium oxide doped with tin) thin films were deposited on glass substrates by using ITO pellet with a composition of w(In2O3)=90% and w(SnO2)=10% by electron beam evaporated with End-Hall ion source assiste...ITO (indium oxide doped with tin) thin films were deposited on glass substrates by using ITO pellet with a composition of w(In2O3)=90% and w(SnO2)=10% by electron beam evaporated with End-Hall ion source assisted without extra heating. The rate of deposition and flow rate of oxygen were measured and changed to obtain the best properties of ITO thin films. Furthermore, the post annealing process was done in vacuum at different annealing temperatures for 2 h and at 400℃ for different keeping time, respectively. The relation between optical, electrical properties and structure was discussed in detail.展开更多
A variable parameter self-adaptive control strategy based on driving condition identification is proposed to take full advantage of the fuel saving potential of the plug-in hybrid electric bus(PHEB).Firstly,the princi...A variable parameter self-adaptive control strategy based on driving condition identification is proposed to take full advantage of the fuel saving potential of the plug-in hybrid electric bus(PHEB).Firstly,the principal component analysis(PCA)and the fuzzy c-means clustering(FCM)algorithm is used to construct the comprehensive driving cycle,congestion driving cycle,urban driving cycle and suburban driving cycle of Chinese urban buses.Secondly,an improved particle swarm optimization(IPSO)algorithm is proposed,and is used to optimize the control parameters of PHEB under different driving cycles,respectively.Then,the variable parameter self-adaptive control strategy based on driving condition identification is given.Finally,for an actual running vehicle,the driving condition is identified by relevance vector machine(RVM),and the corresponding control parameters are selected to control the vehicle.The simulation results show that the fuel consumption of using the variable parameter self-adaptive control strategy is reduced by 4.2% compared with that of the fixed parameter control strategy,and the feasibility of the variable parameter self-adaptive control strategy is verified.展开更多
Chiral microstructures exist widely in natural biological materials such as wood, bone, and climbing tendrils. The helical shape of such microstructures plays an important role in stress transfer between fiber and mat...Chiral microstructures exist widely in natural biological materials such as wood, bone, and climbing tendrils. The helical shape of such microstructures plays an important role in stress transfer between fiber and matrix,and in the mechanical properties of biological materials. In this paper, helical fiber fragmentation behavior is studied numerically using the finite-element method(FEM), and then, the effects of helical shape on fiber deformation and fracture,and the corresponding mechanical mechanisms are investigated. The results demonstrate that, to a large degree, the initial microfibril angle(MFA) determines the elastic deformation and fracture behavior of fibers. For fibers with a large MFA, the interfacial area usually has large values, inducing a relatively low fragment density during fiber fragmentation. This work may be helpful in understanding the relationship between microstructure and mechanical property in biological materials, and in the design and fabrication of bio-inspired advanced functional materials.展开更多
Number concentration and size distribution from gasoline ears are investigated at transient modes on the chassis dynamometers, which are measured using electrical low pressure impactor (ELPI) for the ECE15 and EUDC ...Number concentration and size distribution from gasoline ears are investigated at transient modes on the chassis dynamometers, which are measured using electrical low pressure impactor (ELPI) for the ECE15 and EUDC cycles. Results indicate that, during cold start, particle number emission is higher than that under hot start. It is found that the number of particles increases with the vehicle speeds. Furthermore, particles with diameter smaller than 200 nm constitute the predominant part of total emission in the entire cycle. In addition, the tentative information about composition of emitted particles is also discussed.展开更多
基金supported by the Natural Science Foundation of Jiangsu Province under Grant BK20201438by the Natural Science Research Project of Jiangsu Provincial Institutions of Higher Education under Grant 20KJA510002by the Postgraduate Research and Practice Innovation Program of Jiangsu Province under Grant KYCX202825.
文摘This paper presents an overview of dielectric patch(DP)antennas developed in recent years.The employed DP resonator composed of a DP and a bottom substrate is analyzed comprehensively here,enabling the easy realization of a quasi-planar DP antenna.It combines the dual advantages of the conventional microstrip patch(MP)antenna and dielectric resonator(DR)antenna in terms of profile,gain,bandwidth,radiation efficiency,and design freedom.Furthermore,the DP antenna inherits the multi-mode characteristic of the DR antenna,thus it has a large number of high-order modes,including TMmn mode and TEmn mode.The high-order modes are widely applied,for example,by combining with the dominant TM10 mode to expand the bandwidth,or selecting multiple higher-order modes to implement a high-gain antenna.Additionally,the non-radiation high-order modes are also utilized to produce natural radiation null in filtering antenna design.In this paper,the design theories and techniques of DP antenna are introduced and investigated,including calculation and control methods of the resonant mode frequencies,analysis of the radiation mechanism,and applications of the multi-mode characteristic.This overview could provide guidance for the subsequent antenna design,thus effectively avoid time-consuming optimization.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2007AA05Z207)National Science and Technology Support Scheme of China (Grant No. 2008BAF34B10)Jiangsu Provincial Graduate Student Innovation Foundation of China (Grant No. CX08B_064Z)
文摘The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can't be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.
基金supported by National Outstanding Young Scientists Founds of China (Grant No. 50825902)National Natural Science Foundation of China (Grant No. 50509009)
文摘Performance prediction for centrifugal pumps is now mainly based on numerical calculation and most of the studies merely focus on one model. Therefore, the research results are not representative. To make an improvement of numerical calculation method and performance prediction for centrifugal pumps, performance of six centrifugal pump models at design flow rate and off design flow rates, whose specific speed are different, were simulated by using commercial code FLUENT. The standard k-t turbulence model and SIMPLEC algorithm were chosen in FLUENT. The simulation was steady and moving reference frame was used to consider the impeller-volute interaction. Also, how to dispose the gap between impeller and volute was presented and the effect of grid number was considered. The characteristic prediction model for centrifugal pumps is established according to the simulation results. The head and efficiency of the six models at different flow rates are predicted and the prediction results are compared with the experiment results in detail. The comparison indicates that the precision of head and efficiency prediction are all less than 5%. The flow analysis indicates that flow change has an important effect on the location and area of low pressure region behind the blade inlet and the direction of velocity at impeller inlet. The study shows that using FLUENT simulation results to predict performance of centrifugal pumps is feasible and accurate. The method can be applied in engineering practice.
基金supported by National Natural Science Foundation of China(Project 51907064)in part by China State Key Lab.of Power System(SKLD19KM09)in part by State Grid Corporation of China(1400202024222A-0-0-00)
文摘Distributed energy resources have been proven to be an effective and promising solution to enhance power system resilience and improve household-level reliability.In this paper,we propose a method to evaluate the reliability value of a photovoltaic(PV)energy system with a battery storage system(BSS)by considering the probability of grid outages causing household blackouts.Considering this reliability value,which is the economic profit and capital cost of PV+BSS,a simple formula is derived to calculate the optimal planning strategy.This strategy can provide household-level customers with a simple and straightforward expression for invested PV+BSS capacity.Case studies on 600 households located in eight zones of the US for the period of 2006 to 2015 demonstrate that adding the reliability value to economic profit allows households to invest in a larger PV+BSS and avoid loss of load caused by blackouts.Owing to the differences in blackout hours,households from the 8 zones express distinct willingness to install PV+BSS.The greater the probability of blackout,the greater revenue that household can get from the PV+BSS.The simulation example shows that the planning strategy obtained by proposed model has good economy in the actual operation and able to reduce the economic risk of power failure of the household users.This model can provide household with an easy and straightforward investment strategy of PV+BSS capacity.
文摘The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of the band gap, and the additional absorption, are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the more important factors influencing the photovoltaic activity of Cu2O film.
基金supported by the National Natural Science Foundation of China(30871903)the Fundamental Research Funds for the Gansu Universities,China(2011)
文摘This study was designed to determine the effect of different sperm preparation treatments on yak sperm quality and in vitro embryo development.Frozen-thawed semen samples were treated using swim-up or percoll gradient centrifugation methods.Sperm concentration,progressive motility,recovery of motile sperm,membrane integrity,acrosome and chromatin integrity were scored and compared in recovered samples and controls.In addition,the effects of two sperm separation treatments on embryos capable of cleavage and in vitro development to the blastocyst stage were evaluated.Swim-up separated sperm showed a higher motility,while the concentration of spermatozoa recovered and percent recovery of motile sperm were higher with percoll gradient centrifugation separation.According to the optical and electron microscopies,swim-up produced higher percentage of sperm with intact plasma membrane and acrosome than percoll gradient centrifugation separation.However,there was no difference in the percentage of sperm with intact chromatin between two treatment groups.Cell numbers in the blastocysts of two groups were not different.The blastocyst rate was similar in both groups,whereas cleavage rate was higher when swim-up was used.
基金supported in part by the Key-Area Researchand Development Program of Guangdong Province(2020B0909050003)the Program of Jiangxi(20204ABC03A13)。
文摘Accurately predicting the trajectories of surrounding vehicles and assessing the collision risks are essential to avoid side and rear-end collisions caused by cut-in.To improve the safety of autonomous vehicles in the mixed traffic,this study proposes a cut-in prediction and risk assessment method with considering the interactions of multiple traffic participants.The integration of the support vector machine and Gaussian mixture model(SVM-GMM)is developed to simultaneously predict cut-in behavior and trajectory.The dimension of the input features is reduced through Chebyshev fitting to improve the training efficiency as well as the online inference performance.Based on the predicted trajectory of the cut-in vehicle and the responsive actions of the autonomous vehicles,two risk measurements are introduced to formulate the comprehensive interaction risk through the combination of Sigmoid function and Softmax function.Finally,the comparative analysis is performed to validate the proposed method using the naturalistic driving data.The results show that the proposed method can predict the trajectory with higher precision and effectively evaluate the risk level of a cut-in maneuver compared to the methods without considering interaction.
基金Supported by the National Natural Science Foundation of China(51405050)Key Laboratory of Advanced Manufacturing Technology for Automobile Parts,Ministry of Education(2016KLMT03)Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJ1500912)
文摘The influences of different design factors,as well as dummy posture,on an occupants' knee slider compression,were studied in this paper.Based on the vehicle geometry data,the simulation model,including both the multi-rigid-body and finite element(FE)part,was built up and validated with China New Car Assessment Program(C-NCAP)full impact to ensure the accuracy of the model.By adjusting the design parameters and the posture of the femur and lower leg,different factors affecting the passengers' knee slider compression were evaluated,with the help of MAthematical DYnamic MOdel(MADYMO)simulations.The study indicated that the leg posture,the stiffness of the IP and angles of the carpet have significant effects on the knee slider compression in this case.By decreasing the angle between the femur and lower leg from 133° to 124°,the maximum knee slider compression was decreased by 17.3% and by scaling the IP stiffness from 1 to 0.7,it could be decreased by 18.6%.Also,decreasing the angles of the carpet from 28° to 37°can help reduce the knee slider compression by 18.3%.
基金Project supported by the Special Funds from the Ministry of National Science and Technology Major Instrumentation,China(Grant No.2011YQ130018)the Open Foundation of Joint Laboratory for Extreme Conditions Matter Properties,Southwest University of Science and Technology and Research Center of Laser Fusion,China Academy of Engineering Physics(Grant No.12zxjk06)the National High Technology Research and Development Program of China(863 Program)
文摘Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.
基金Supported by the Major Instrumentation Special of the Ministry of Science and Technology of China under Grant No 2011YQ130018Open Foundation of Joint Laboratory for Extreme Conditions Matter Properties,Southwest University of Sci-ence and Technology and Research Center of Laser Fusion,CAEP(No 12zxjk06)the National High-Technology Research and Development Program of China.
文摘ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy.The band offsets of the ZnO/Al_(2)O_(3) heterojunction are studied by in situ x-ray photoelectron spectroscopy.The valence band of Al_(2)O_(3) is found to be 3.59±0.05 eV below that of ZnO.Together with the resulting conduction band offset of 2.04±0.05 eV,this indicates that a type-I staggered band line exists at the ZnO/Al_(2)O_(3) heterojunction.
基金supported financially as a project(No.11911/1828MAP1).
文摘Background:Bongardia chrysogonum(L.)Spach,also known as“Uruf-el-Deek”,has been used by rural communities for the treatment of various diseases and disorders,owing to its wide array of secondary metabolite compositions.Methods:The current study was conducted to determine the total polyphenolic content of Bongardia chrysogonum(L.)Spach as well as its potential free radical scavenging and metal-chelating antioxidant capacities.Its leaves,stems,and tubers were separately extracted using ethanol,water,and chloroform;their antioxidant activities were analyzed using in vitro models,including DPPH,ABTS,FRAP,and CUPRAC assays.The total polyphenolic content of the extracts was spectrophotometrically measured.Results:The richest polyphenolic content of the extracts was yielded by tuber chloroform and leaf ethanol extraction(215.09±0.53 mg/g extract as gallic acid equivalent and 240.74±1.12 mg/g extract as quercetin equivalent,respectively).Almost all of the tested extracts exhibited remarkable antioxidant activities,with the highest antioxidant capacity observed in the leaf extracts.On the other hand,the tuber ethanol extract demonstrated the weakest DPPH radical scavenging activity(%inhibition=49.75±0.38,P<0.01),while the tuber chloroform extract showed the weakest ABTS radical scavenging activity(%inhibition=62.61±0.06,P<0.05).These were closely followed by the tuber water extract(%inhibition=63.28±0.65,P<0.01).In terms of their FRAP and CUPRAC assays,the leaf ethanol extract was determined as the best one,with absorbance values of 3.64±0.01 and 2.22±0.01(P<0.01),respectively.Conclusion:Bongardia chrysogonum(L.)Spach possesses rich polyphenolic content and strong antioxidant activities.Thus,it could be a valuable source for the pharmaceutical industry in the prevention and treatment of diseases associated with oxidative stress.
文摘Kuwaiti oil production faces a growing challenge in the increasing quantities of produced water generated in the production of oil. The high water cut of the produced fluid from the wells and the high salinity of the produced water lead to significant degradation of subsurface equipment, specifically the production tubing. Debris generated through the degradation of the inner part of the tubing becomes a constituent of the scaling that deposits in the tubing and blocks the flow of the production fluid, inducing higher maintenance costs. This paper looks at the characteristics of the scaling in regard to the produced water and outlines the economic impact of the produced water induced degradation of the tubing structure.
基金support of the National Natural Science Foundation of China(Nos.51978404,42105100,and 41977180)the Guangdong Basic and Applied Basic Research Foundation(China)(Nos.2021A1515110297 and 2022A1515010866)the Basic Research of Shenzhen Science and Technology Innovation Commission(China)(No.JCYJ20190808145218827).
文摘On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission characteristics, we performed comprehensive chassis dynamometer measurements of NH3 emission from two China 5 and two China 6 light-duty gasoline vehicles (LDGVs) equipped with three-way catalytic converters (TWCs). The results showed that the distance-based emission factors (EFs) were 12.72 ± 2.68 and 3.18 ± 1.37 mg/km for China 5 and China 6 LDGVs, respectively. Upgrades in emission standards were associated with a reduction in tailpipe NH3 emission. In addition, high NH3 EFs were observed during the engine warm-up period in cold-start cases owing to the intensive emissions of incomplete combustion products and suitable catalytic temperature in the TWCs. Notably, based on the instantaneous NH3 emission rate, distinct NH3–emitting events were detected under high/extra high velocity or rapid acceleration. Furthermore, NH3 emission rates correlated well with engine speed, vehicle specific power, and modified combustion efficiency, which were more easily accessible. These strong correlations were applied to reproduce NH3 emissions from China 5/6 LDGVs. The predicted NH3 EFs under different dynamometer and real-world cycles agreed well with existing measurement and prediction results, revealing that the NH3 EFs of LDGVs in urban routes were within 8.55–11.62 mg/km. The results presented here substantially contribute to improving the NH3 emission inventory for LDGVs and predicting on-road NH3 emissions in China.
基金Supported by National High Technology Research and Development Program 863(Grant No.2011AA11A286)
文摘The current research of the global chassis control problem for the full drive-by-wire vehicle focuses on the control allocation (CA) of the four-wheel-distributed trac- tion/braking/steering systems. However, the path following performance and the handling stability of the vehicle can be enhanced a step further by automatically adjusting the vehicle speed to the optimal value. The optimal solution for the combined longitudinal and lateral motion control (MC) problem is given. First, a new variable step-size spatial transformation method is proposed and utilized in the prediction model to derive the dynamics of the vehicle with respect to the road, such that the tracking errors can be explicitly obtained over the prediction horizon at varying speeds. Second, a nonlinear model predictive con- trol (NMPC) algorithm is introduced to handle the non- linear coupling between any two directions of the vehicular planar motion and computes the sequence of the optimal motion states for following the desired path. Third, a hierarchical control structure is proposed to separate the motion controller into a NMPC based path planner and a terminal sliding mode control (TSMC) based path fol- lower. As revealed through off-line simulations, the hier- archical methodology brings nearly 1700% improvement in computational efficiency without loss of control per- formance. Finally, the control algorithm is verified through a hardware in-the-loop simulation system. Double-lane- change (DLC) test results show that by using the optimalpredictive controller, the root-mean-square (RMS) values of the lateral deviations and the orientation errors can be reduced by 41% and 30%, respectively, comparing to those by the optimal preview acceleration (OPA) driver model with the non-preview speed-tracking method. Additionally, the average vehicle speed is increased by 0.26 km/h with the peak sideslip angle suppressed to 1.9~. This research proposes a novel motion controller, which provides the full drive-by-wire vehicle with better lane-keeping and colli- sion-avoidance capabilities during autonomous driving.
基金financial supports from National Key R&D Program of China (2018YFC1902200)the key technologies R&D program of Tianjin (18YFZCGX00240)key R&D Program of China Automotive Technology and Research Center Co., Ltd. (18200116)。
文摘Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.
文摘ITO (indium oxide doped with tin) thin films were deposited on glass substrates by using ITO pellet with a composition of w(In2O3)=90% and w(SnO2)=10% by electron beam evaporated with End-Hall ion source assisted without extra heating. The rate of deposition and flow rate of oxygen were measured and changed to obtain the best properties of ITO thin films. Furthermore, the post annealing process was done in vacuum at different annealing temperatures for 2 h and at 400℃ for different keeping time, respectively. The relation between optical, electrical properties and structure was discussed in detail.
基金Supported by China Automobile Test Cycle Development Project(CATC2015)
文摘A variable parameter self-adaptive control strategy based on driving condition identification is proposed to take full advantage of the fuel saving potential of the plug-in hybrid electric bus(PHEB).Firstly,the principal component analysis(PCA)and the fuzzy c-means clustering(FCM)algorithm is used to construct the comprehensive driving cycle,congestion driving cycle,urban driving cycle and suburban driving cycle of Chinese urban buses.Secondly,an improved particle swarm optimization(IPSO)algorithm is proposed,and is used to optimize the control parameters of PHEB under different driving cycles,respectively.Then,the variable parameter self-adaptive control strategy based on driving condition identification is given.Finally,for an actual running vehicle,the driving condition is identified by relevance vector machine(RVM),and the corresponding control parameters are selected to control the vehicle.The simulation results show that the fuel consumption of using the variable parameter self-adaptive control strategy is reduced by 4.2% compared with that of the fixed parameter control strategy,and the feasibility of the variable parameter self-adaptive control strategy is verified.
基金supported by the National Natural Science Foundation of China(Nos.11472191,11172207,and 11272230)
文摘Chiral microstructures exist widely in natural biological materials such as wood, bone, and climbing tendrils. The helical shape of such microstructures plays an important role in stress transfer between fiber and matrix,and in the mechanical properties of biological materials. In this paper, helical fiber fragmentation behavior is studied numerically using the finite-element method(FEM), and then, the effects of helical shape on fiber deformation and fracture,and the corresponding mechanical mechanisms are investigated. The results demonstrate that, to a large degree, the initial microfibril angle(MFA) determines the elastic deformation and fracture behavior of fibers. For fibers with a large MFA, the interfacial area usually has large values, inducing a relatively low fragment density during fiber fragmentation. This work may be helpful in understanding the relationship between microstructure and mechanical property in biological materials, and in the design and fabrication of bio-inspired advanced functional materials.
文摘Number concentration and size distribution from gasoline ears are investigated at transient modes on the chassis dynamometers, which are measured using electrical low pressure impactor (ELPI) for the ECE15 and EUDC cycles. Results indicate that, during cold start, particle number emission is higher than that under hot start. It is found that the number of particles increases with the vehicle speeds. Furthermore, particles with diameter smaller than 200 nm constitute the predominant part of total emission in the entire cycle. In addition, the tentative information about composition of emitted particles is also discussed.