Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced in...Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced into boron particles,investigating the impact of PDA content on the energetic behavior of boron.The results indicated that the PDA coating formed a fishing net structure on the surface of boron particles.The heat release results showed that the combustion calorific value of B@PDA was higher than that of the raw boron.Specifically,the actual combustion heat of boron powder in B@10%PDA increased by 38.08%.Meanwhile,the DSC peak temperature decreased by 100.65℃under similar oxidation rate compared to raw boron.Simultaneously,the B@PDA@AP and B@AP composites were prepared,and their combustion properties were evaluated.It was demonstrated that B@10%PDA@AP exhibited superior performance in terms of peak pressure and burning time,respectively.The peak pressure is 12.43 kPa more than B@AP and burning time is 2.22 times higher than B@AP.Therefore,the coating of PDA effectively inhibits the oxidization of boron during storage and enhances the energetic behavior of boron and corresponding composites.展开更多
For a distributed drive electric vehicle（DDEV） driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. A...For a distributed drive electric vehicle（DDEV） driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. And direct yaw-moment control（DYC） has been widely studied and applied to vehicle stability control. Good vehicle handling performance： quick yaw rate transient response, small overshoot, high steady yaw rate gain, etc, is required by drivers under normal conditions, which is less concerned, however. Based on the hierarchical control methodology, a novel control system using direct yaw moment control for improving handling performance of a distributed drive electric vehicle especially under normal driving conditions has been proposed. The upper-loop control system consists of two parts： a state feedback controller, which aims to realize the ideal transient response of yaw rate, with a vehicle sideslip angle observer; and a steering wheel angle feedforward controller designed to achieve a desired yaw rate steady gain. Under the restriction of the effect of poles and zeros in the closed-loop transfer function on the system response and the capacity of in-wheel motors, the integrated time and absolute error（ITAE） function is utilized as the cost function in the optimal control to calculate the ideal eigen frequency and damper coefficient of the system and obtain optimal feedback matrix and feedforward matrix. Simulations and experiments with a DDEV under multiple maneuvers are carried out and show the effectiveness of the proposed method： yaw rate rising time is reduced, steady yaw rate gain is increased, vehicle steering characteristic is close to neutral steer and drivers burdens are also reduced. The control system improves vehicle handling performance under normal conditions in both transient and steady response. State feedback control instead of model following control is introduced in the control system so that the sense of control intervention to drivers is relieved.展开更多
Numerical simulation is used to investigate the flow field in a model centrifugal fan for steam power stations in order to improve the performance. During testing the model fan, it is found that the efficiency is only...Numerical simulation is used to investigate the flow field in a model centrifugal fan for steam power stations in order to improve the performance. During testing the model fan, it is found that the efficiency is only 62.5% with inlet box, without it the efficiency is 83%. In addition, the strong vibration of test rig is observed with inlet box. It would be highly desirable if the aerodynamics of the fan could be studied. Therefore, numerical simulation is carried out to investigate the internal flow characteristics of a model fan with inlet box. The results from CFD analysis show that the whole region of the inlet box is occupied by a spiral vortex rotating inversely as the rotor＇s direction, which significantly affect the most flow＇region inside the fan. For this reason, a dummy plate is arranged in the inlet box to impede the generation of the spiral vortex, the results from CFD after the reform demonstrate that the modification is quiet effective, the former large spiral vertex has been destroyed effectively, the large one is superseded in favor of two small vortexes. However, two small vortexes have little effect on the inner flow of the rotor and the following parts. Finally, the efficiency of the model fan is improved by the test and the strong vibration of the test rig disappears. This type of modification has been used in steam power stations, the fan efficiency raises to 84% successfully.展开更多
The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two di...The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.展开更多
Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images an...Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers＇ properties.After HCISO_3 treatment for 2 h,the fibers＇ strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G＇ band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.展开更多
In this paper, we investigated the effect of rapid thermal annealing （RTA） on solar cell performance. An opto-electric conversion efficiency of 11.75% （Voc = 0.64 V, Jsc = 25.88 mA/cm2, FF=72.08%） was obtained und...In this paper, we investigated the effect of rapid thermal annealing （RTA） on solar cell performance. An opto-electric conversion efficiency of 11.75% （Voc = 0.64 V, Jsc = 25.88 mA/cm2, FF=72.08%） was obtained under AM 1.5G when the cell was annealed at 300℃ for 30 s. The annealed solar cell showed an average absolute efficiency 1.5% higher than that of the as-deposited one. For the microstructure analysis and the physical phase confirmation, X-ray diffraction （XRD）, Raman spectra, front surface reflection （FSR）, internal quantum efficiency （IQE）, and X-ray photoelectron spectroscopy （XPS） were respectively applied to distinguish the causes inducing the efficiency variation. All experimental results implied that the RTA eliminated recombination centers at the p-n junction, reduced the surface optical losses, enhanced the blue response of the CdS buffer layer, and improved the ohmic contact between Mo and Cu（In, Ga）Se2 （CIGS） layers. This leaded to the improved performance of CIGS solar cell.展开更多
A capping layer for black phosphorus（BP） field-effect transistors（FETs） can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. W...A capping layer for black phosphorus（BP） field-effect transistors（FETs） can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. We perform low-temperature hydrogenation on Al2 O3 capped BP FETs. The hydrogenated BP devices exhibit a pronounced improvement of mobility from 69.6 to 107.7 cm2 v-1 s-1, and a dramatic decrease of subthreshold swing from8.4 to 2.6 V/dec. Furthermore, high/low frequency capacitance-voltage measurements suggest reduced interface defects in hydrogenated BP FETs. This could be due to the passivation of interface traps at both Al2 O3/BP and BP/SiO2 interfaces with hydrogen revealed by secondary ion mass spectroscopy.展开更多
A novel slow-down set waveform is proposed to improve the set performance and a 1 kb phase change random access memory chip fabricated with a 13nm CMOS technology is implemented to investigate the set performance by d...A novel slow-down set waveform is proposed to improve the set performance and a 1 kb phase change random access memory chip fabricated with a 13nm CMOS technology is implemented to investigate the set performance by different set programming strategies based on this new set pulse. The amplitude difference （I1 - I2） of the set pulse is proved to be a crucial parameter for set programming. We observe and analyze the cell characteristics with different I1 - I2 by means of thermal simulations and high-resolution transmission electron microscopy, which reveal that an incomplete set programming will occur when the proposed slow-down pulse is set with an improperly high I1 - I2. This will lead to an amorphous residue in the active region. We also discuss the programming method to avoid the set performance degradations.展开更多
In this paper, we conduct research on the pushover methodology and the applications on the bridge seismic performance improvement scenarios. Bridge is an important part of the traffic lifeline engineering, and after t...In this paper, we conduct research on the pushover methodology and the applications on the bridge seismic performance improvement scenarios. Bridge is an important part of the traffic lifeline engineering, and after the earthquake, if the bridge damage, that will hinder the timely disaster relief operations, increase secondary disasters, not only cause the direct or indirect losses of people＇ s life and property, also affect the post-disaster recovery and reconstruction. Therefore, seismic design of the bridges has been people＇ s attention. From the earthquake when the bridge failure mechanism and the failure process point of view, to adjust the overall layout design of bridge structure, fundamentally improve the structural seismic performance as a whole. Our research proposes the novel paradigm for the corresponding challenges that will be meaningful.展开更多
Synchronous machines are dedicated to the specific application. They are generally employed in rolling mills, pumps, fans, and compressors like reprobating and centrifugal drives, pulp and paper processing, water trea...Synchronous machines are dedicated to the specific application. They are generally employed in rolling mills, pumps, fans, and compressors like reprobating and centrifugal drives, pulp and paper processing, water treatment, mining, and in cement industries. As a synchronous motor, the performance is reduced for the given excitation while the load increases. When operated as synchronous generators, both power loads and lighting loads depend on the output from the armature winding. This paper presents an alternative choice in which by providing an additional winding in the stationary armature, when operated as a Double Winding Synchronous Motor (DWSyM), it becomes possible to operate in maximum power factor by adjusting the loads on both the stator windings. When operated as conventional motor, for the load current of 3.5 A, the efficiency is 55% and power factor is 0.55, for the same excitation when second winding is connected to a load current of 1 A, the efficiency is improved to 77.6% and power factor is improved to 0.66. The main focus of this machine is to improve the performance of the machine for the reduced excitation and minimum load. For the reduced excitation, the performance can be improved by loading both the windings. While operated as Double Winding Synchronous Generator (DWSyG), two stator outputs are available which help to separate the power and lighting circuits. Hence, interruption in the lighting circuit can be limited, this machine can be considered as Twin generator.展开更多
A reasonable parameter configuration helps improve the data transmission performance of the Licklider Transmission Protocol(LTP).Previous research has focused mainly on parameter optimization for LTP in simplified sce...A reasonable parameter configuration helps improve the data transmission performance of the Licklider Transmission Protocol(LTP).Previous research has focused mainly on parameter optimization for LTP in simplified scenarios with one to two hops or multihop scenarios with a custody mechanism of the Bundle Protocol(BP).However,the research results are not applicable to communications in Complex Deep Space Networks(CDSNs)without the custody mechanism of BP that are more suitable for deep space communications with LTP.In this paper,we propose a model of file delivery time for LTP in CDSNs.Based on the model,we propose a Parameter Optimization Design Algorithm for LTP(LTP-PODA)of configuring reasonable parameters for LTP.The results show that the accuracy of the proposed model is at least 6.47%higher than that of the previously established models based on simple scenarios,and the proposed model is more suitable for CDSNs.Moreover,the LTP parameters are optimized by the LTP-PODA algorithm to obtain an optimization plan.Configuring the optimization plan for LTP improves the protocol transmission performance by at least 18.77%compared with configuring the other parameter configuration plans.展开更多
It remains challenging to conduct an efficient dynamic façade design.In this article authors try to address this issue introducing the façade daylighting performance improvement(FDPI)indicator aimed to evalu...It remains challenging to conduct an efficient dynamic façade design.In this article authors try to address this issue introducing the façade daylighting performance improvement(FDPI)indicator aimed to evaluate the performance of a dynamic(adaptive)façade from its daylighting performance point of view.To illustrate the FDPI application the authors introduced the preliminary dynamic façade concept for an office building located in Tel Aviv(Hot-summer Mediterranean Climate Csa)with further shape modification based on the daylighting performance analysis compared to the three alternatives representative of different typologies of dynamic façades.Al Bahr,One Ocean and The University of Southern Denmark façade systems were simulated under the same weather and building conditions of the preliminary dynamic façade concept and were considered as a benchmark for the study.The final dynamic façade concept elaborated by the authors in the preliminary comparative workflow showed noticeable daylight performance improvement with respect to the case studies comparative scenarios.The FDPI metric allowed to estimate a daylighting performance improvement of 43%of the final dynamic façade concept over the case study dynamic façade that showed the best performance in the daylighting simulations.展开更多
The purpose of this paper is to investigate the performance improvement mechanism of a high power vertical centrifugal pump by using numerical calculations.Therefore,a comparative study of energy losses and internal f...The purpose of this paper is to investigate the performance improvement mechanism of a high power vertical centrifugal pump by using numerical calculations.Therefore,a comparative study of energy losses and internal flow characteristics in the original and optimized models was carried out with special attention to the hydraulic component matching.The optimized model(model B)was obtained by optimizing the vaned diffuser and volute based on the original model(model A),mainly the diffuser inlet diameter,diffuser inlet vane angle,volute channel inlet width and volute throat area were changed.Firstly,the comparative results on performance and energy losses of two models showed that the efficiency and head of model B was significantly increased under design and part-load conditions.It is mainly due to the dramatic reduction of energy loss PL in the diffuser and volute.Then,the comparisons of PL and flow patterns in the vaned diffuser showed that the matching optimization between the model B impeller outlet flow angle and diffuser inlet vane angle resulted in a better flow pattern in both the circumferential and axial directions of the diffuser,which leads to the PL3 reduction.The meridian velocity Vm of model B was significantly increased at diffuser inlet regions and resulted in improvements of flow patterns at diffuser middle and outlet regions as well as pressure expansion capacity.Finally,the comparisons of PL and flow characteristics in the volute showed that the turbulence loss reduction in the model B volute was due to the flow pattern improvement at diffuser outlet regions which provided better flow conditions at volute inlet regions.The matching optimization between the diffuser and volute significantly reduced the turbulence loss in volute sections 1–4 and enhanced the pressure expansion capacity in sections 8–10.展开更多
Various nanostructures of the organic semiconductor (OSC)films have been reported to enhance the organic field-effect transistors (OFETs)sensing performance. However,complicated fabrication processes hinder their ap- ...Various nanostructures of the organic semiconductor (OSC)films have been reported to enhance the organic field-effect transistors (OFETs)sensing performance. However,complicated fabrication processes hinder their ap- plications.In this work,we have effectively enhanced the sensitivity of the OFET-based sensors only by adjusting substrate temperature in OSC preparation and surface treatment of the dielectric layer.The relative sensitivity of the device can be enhanced by 5 times.The flexible sensors with polymer dielectric also exhibit high sensitivity because the less smooth surface of the polymer provides the OSCs with smaller grain size.Therefore,this work reveals the trade-off effects of the OSCs grain size on both transistor characteristic and chemic.al sensing performance,and provides a simple and extensively applicable strategy for OFETs sensitivity improvement.展开更多
The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influe...The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance.In this paper,mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights.The refrigerating capacity,volume efficiency and adiabatic efficiency of the SSC are calculated and discussed.Three prototypes,with different meshing clearance heights,were manufactured to study the internal influence mechanisms.The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results.Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%-7.98%and 5.92%-9.4%,respectively.Based on the models,analysis under varying meshing clearance heights and working conditions was performed.Taking into account working performance,actual manufacturing conditions and manufacturing cost limitations,a meshing clearance height range from 0.01 mm to 0.08 mm is suggested.This study can provide important theoretical data and experimental support for the design,manufacturing and optimization of single screw compressors.展开更多
Dielectric elastomer actuators (DEAs) are an emerging class of polymer actuation devices and have extensive application prospect in the field of robotics because of their light weight, high efficiency and large deform...Dielectric elastomer actuators (DEAs) are an emerging class of polymer actuation devices and have extensive application prospect in the field of robotics because of their light weight, high efficiency and large deformation. A cone DEA is manufactured and its working principle is analyzed. To obtain the deformation of elastomer and movement of DEA in advance, a finite element method (FEM) simulation is performed first. According to the working principle, two working equilibrium points of DEA, corresponding to the displacements of DEA with voltage off and on, are obtained and validated by experiments, thus work output in a workcycle is computed. Experiments show that the actuator can respond quickly when voltage is applied and can return to its original position rapidly when voltage is released. Simulation results agree well with experimental ones and the feasibility of DEA simulation is proved, and causes for the small difference between them in displacement output are analyzed. The performance of the actuator is improved from the aspects of both displacement and force output. A diamond four-bar linkage mechanism is used as the preload part and a displacement output of 17 mm is obtained. The force output of one actuating unit is about 1.77 N, so three actuating units are assembled in parallel and the force output is heightened to as high as 5.07 N.展开更多
The high-frequency pulse tube cryocooler(HPTC)has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure,low vibration,and reliable operation.The gas-...The high-frequency pulse tube cryocooler(HPTC)has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure,low vibration,and reliable operation.The gas-coupled HPTC,driven by a single compressor,is currently the simplest and most compact structure.For HPTCs operating below 20 K,in order to obtain the mW cooling capacity,hundreds or even thousands of watts of electrical power are consumed,where radiation heat leakage accounts for a large proportion of their cooling capacity.In this paper,based on SAGE10,a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters(such as temperature and cooling capacity),and internal parameters(such as enthalpy flow and gas distribution)of the gas-coupled HPTC.An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC.Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power,but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section,which further enhances the refrigeration performance.The numerical calculation results were verified by experiments,and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K,and the relative Carnot efficiency at 15.5 K increased from 0.029%to 0.996%when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials.展开更多
A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by...A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.展开更多
We improve the performance of organic light-emitting diodes （OLEDs） with both a MoO3 hole injection layer （HIL） and a MoO3 doped hole transport layer （HTL）, and present a systematical and comparative investigati...We improve the performance of organic light-emitting diodes （OLEDs） with both a MoO3 hole injection layer （HIL） and a MoO3 doped hole transport layer （HTL）, and present a systematical and comparative investigation on these devices. Compared with OLEDs with only MoO3 HIL or MoO3 doped HTL, OLEDs with both MoO3 HIL and MoO3 doped HTL show superior performance in driving voltage, power efficiency, and stability. Based on the typical NPB/Alq3 heterojunction structure, OLEDs with both MoO3 HIL and MoO3 doped HTL show a driving voltage of 5.4 V and a power efficiency of 1.41 lm/W for 1000 cd/m2, and a lifetime of around 0. 88 h with an initial luminance of 5268 cd/m2 under a constant current of 190 mA/cm2 operation in air without encapsulation. While OLEDs with only MoO3 HIL or MoO3 doped HTL show higher driving voltages of 6.4 V or 5.8 V and lower power efficiencies of 1.201m/W or 1.341m/W for 1000cd/m2, and a shorter lifetime of 0.33 or 0.60h with an initial luminance of around 5122 or 5300cd/m2 under a constant current of 200 or 216mA/cm2 operation. Our results demonstrate clearly that using both MoO3 HIL and MoO3 doped HTL is a simple and effective approach to simultaneoasly improve both the hole injection and transport efficiency, resulting from the lowered energy barrier at the anode interface and the increased hole carrier density in MoO3 doped HTL.展开更多
The pollutant control performance of exhaust hoods plays a crucial role in the indoor air quality and energy consumption of ventilation systems in industrial buildings.To better understand the impact of local ventilat...The pollutant control performance of exhaust hoods plays a crucial role in the indoor air quality and energy consumption of ventilation systems in industrial buildings.To better understand the impact of local ventilation on the industrial indoor environment,this paper presents a literature review of exhaust hood performance and its improvement technologies.To create an index for evaluating the performance of exhaust hoods,the capture velocity,capture efficiency,flow ratio of pollutant emissions and exhaust airflow and energy consumption are first introduced.A number of factors affecting exhaust hood performance are assessed such as hood type,hood opening size,exhaust rate,installation distance,pollution source emission and environmental disturbance.Compared to structural improvement methods,the use of active airflow is a more effective way to improve the exhaust hood performance.The most commonly used methods for determining the exhaust rate are the controlled speed method and the flow ratio method.The use of an exhaust hood with an appropriate exhaust rate and jet parameters(for an active air-assisted hood)can effectively improve the pollutant control performance and reduce the energy consumption that would be wasted on the redundant exhaust rate.With more information focused on exhaust hood performance,this work suggests more effective strategies for improving indoor air quality and reducing energy consumption in industrial buildings.展开更多
文摘Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced into boron particles,investigating the impact of PDA content on the energetic behavior of boron.The results indicated that the PDA coating formed a fishing net structure on the surface of boron particles.The heat release results showed that the combustion calorific value of B@PDA was higher than that of the raw boron.Specifically,the actual combustion heat of boron powder in B@10%PDA increased by 38.08%.Meanwhile,the DSC peak temperature decreased by 100.65℃under similar oxidation rate compared to raw boron.Simultaneously,the B@PDA@AP and B@AP composites were prepared,and their combustion properties were evaluated.It was demonstrated that B@10%PDA@AP exhibited superior performance in terms of peak pressure and burning time,respectively.The peak pressure is 12.43 kPa more than B@AP and burning time is 2.22 times higher than B@AP.Therefore,the coating of PDA effectively inhibits the oxidization of boron during storage and enhances the energetic behavior of boron and corresponding composites.
基金Supported by National Basic Research Program of China(973 Program,Grant No.2011CB711200)National Science and Technology Support Program of China(Grant No.2015BAG17B00)National Natural Science Foundation of China(Grant No.51475333)
文摘For a distributed drive electric vehicle（DDEV） driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. And direct yaw-moment control（DYC） has been widely studied and applied to vehicle stability control. Good vehicle handling performance： quick yaw rate transient response, small overshoot, high steady yaw rate gain, etc, is required by drivers under normal conditions, which is less concerned, however. Based on the hierarchical control methodology, a novel control system using direct yaw moment control for improving handling performance of a distributed drive electric vehicle especially under normal driving conditions has been proposed. The upper-loop control system consists of two parts： a state feedback controller, which aims to realize the ideal transient response of yaw rate, with a vehicle sideslip angle observer; and a steering wheel angle feedforward controller designed to achieve a desired yaw rate steady gain. Under the restriction of the effect of poles and zeros in the closed-loop transfer function on the system response and the capacity of in-wheel motors, the integrated time and absolute error（ITAE） function is utilized as the cost function in the optimal control to calculate the ideal eigen frequency and damper coefficient of the system and obtain optimal feedback matrix and feedforward matrix. Simulations and experiments with a DDEV under multiple maneuvers are carried out and show the effectiveness of the proposed method： yaw rate rising time is reduced, steady yaw rate gain is increased, vehicle steering characteristic is close to neutral steer and drivers burdens are also reduced. The control system improves vehicle handling performance under normal conditions in both transient and steady response. State feedback control instead of model following control is introduced in the control system so that the sense of control intervention to drivers is relieved.
文摘Numerical simulation is used to investigate the flow field in a model centrifugal fan for steam power stations in order to improve the performance. During testing the model fan, it is found that the efficiency is only 62.5% with inlet box, without it the efficiency is 83%. In addition, the strong vibration of test rig is observed with inlet box. It would be highly desirable if the aerodynamics of the fan could be studied. Therefore, numerical simulation is carried out to investigate the internal flow characteristics of a model fan with inlet box. The results from CFD analysis show that the whole region of the inlet box is occupied by a spiral vortex rotating inversely as the rotor＇s direction, which significantly affect the most flow＇region inside the fan. For this reason, a dummy plate is arranged in the inlet box to impede the generation of the spiral vortex, the results from CFD after the reform demonstrate that the modification is quiet effective, the former large spiral vertex has been destroyed effectively, the large one is superseded in favor of two small vortexes. However, two small vortexes have little effect on the inner flow of the rotor and the following parts. Finally, the efficiency of the model fan is improved by the test and the strong vibration of the test rig disappears. This type of modification has been used in steam power stations, the fan efficiency raises to 84% successfully.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFB0401801the National Natural Science Foundation of China under Grant Nos 61574135,61574134,61474142,61474110,61377020,61376089,and 61223005the One Hundred Person Project of the Chinese Academy of Sciences
文摘The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB932302)the National Natural Science Foundation of China(Grant Nos.11634014,51172271,51372269,and 51472264)the“Strategic Priority Research Program”of the Chinese Academy of Sciences(Grant No.XDA09040202)
文摘Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers＇ properties.After HCISO_3 treatment for 2 h,the fibers＇ strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G＇ band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60876045)the Shanghai Leading Basic Research Project, China (Grant No. 09JC1405900)+1 种基金the Shanghai Leading Academic Discipline Project, China (Grant No. S30105)the R & D Foundation of SHU-SOENs PV Joint Laboratory, China (Grant No. SS-E0700601)
文摘In this paper, we investigated the effect of rapid thermal annealing （RTA） on solar cell performance. An opto-electric conversion efficiency of 11.75% （Voc = 0.64 V, Jsc = 25.88 mA/cm2, FF=72.08%） was obtained under AM 1.5G when the cell was annealed at 300℃ for 30 s. The annealed solar cell showed an average absolute efficiency 1.5% higher than that of the as-deposited one. For the microstructure analysis and the physical phase confirmation, X-ray diffraction （XRD）, Raman spectra, front surface reflection （FSR）, internal quantum efficiency （IQE）, and X-ray photoelectron spectroscopy （XPS） were respectively applied to distinguish the causes inducing the efficiency variation. All experimental results implied that the RTA eliminated recombination centers at the p-n junction, reduced the surface optical losses, enhanced the blue response of the CdS buffer layer, and improved the ohmic contact between Mo and Cu（In, Ga）Se2 （CIGS） layers. This leaded to the improved performance of CIGS solar cell.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61474027 and 61774041
文摘A capping layer for black phosphorus（BP） field-effect transistors（FETs） can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. We perform low-temperature hydrogenation on Al2 O3 capped BP FETs. The hydrogenated BP devices exhibit a pronounced improvement of mobility from 69.6 to 107.7 cm2 v-1 s-1, and a dramatic decrease of subthreshold swing from8.4 to 2.6 V/dec. Furthermore, high/low frequency capacitance-voltage measurements suggest reduced interface defects in hydrogenated BP FETs. This could be due to the passivation of interface traps at both Al2 O3/BP and BP/SiO2 interfaces with hydrogen revealed by secondary ion mass spectroscopy.
基金Supported by the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDA09020402the National Key Basic Research Program of China under Grant Nos 2013CBA01900,2010CB934300,2011CBA00607,and 2011CB932804+2 种基金the National Integrate Circuit Research Program of China under Grant No 2009ZX02023-003the National Natural Science Foundation of China under Grant Nos 61176122,61106001,61261160500,and 61376006the Science and Technology Council of Shanghai under Grant Nos 12nm0503701,13DZ2295700,12QA1403900,and 13ZR1447200
文摘A novel slow-down set waveform is proposed to improve the set performance and a 1 kb phase change random access memory chip fabricated with a 13nm CMOS technology is implemented to investigate the set performance by different set programming strategies based on this new set pulse. The amplitude difference （I1 - I2） of the set pulse is proved to be a crucial parameter for set programming. We observe and analyze the cell characteristics with different I1 - I2 by means of thermal simulations and high-resolution transmission electron microscopy, which reveal that an incomplete set programming will occur when the proposed slow-down pulse is set with an improperly high I1 - I2. This will lead to an amorphous residue in the active region. We also discuss the programming method to avoid the set performance degradations.
文摘In this paper, we conduct research on the pushover methodology and the applications on the bridge seismic performance improvement scenarios. Bridge is an important part of the traffic lifeline engineering, and after the earthquake, if the bridge damage, that will hinder the timely disaster relief operations, increase secondary disasters, not only cause the direct or indirect losses of people＇ s life and property, also affect the post-disaster recovery and reconstruction. Therefore, seismic design of the bridges has been people＇ s attention. From the earthquake when the bridge failure mechanism and the failure process point of view, to adjust the overall layout design of bridge structure, fundamentally improve the structural seismic performance as a whole. Our research proposes the novel paradigm for the corresponding challenges that will be meaningful.
文摘Synchronous machines are dedicated to the specific application. They are generally employed in rolling mills, pumps, fans, and compressors like reprobating and centrifugal drives, pulp and paper processing, water treatment, mining, and in cement industries. As a synchronous motor, the performance is reduced for the given excitation while the load increases. When operated as synchronous generators, both power loads and lighting loads depend on the output from the armature winding. This paper presents an alternative choice in which by providing an additional winding in the stationary armature, when operated as a Double Winding Synchronous Motor (DWSyM), it becomes possible to operate in maximum power factor by adjusting the loads on both the stator windings. When operated as conventional motor, for the load current of 3.5 A, the efficiency is 55% and power factor is 0.55, for the same excitation when second winding is connected to a load current of 1 A, the efficiency is improved to 77.6% and power factor is improved to 0.66. The main focus of this machine is to improve the performance of the machine for the reduced excitation and minimum load. For the reduced excitation, the performance can be improved by loading both the windings. While operated as Double Winding Synchronous Generator (DWSyG), two stator outputs are available which help to separate the power and lighting circuits. Hence, interruption in the lighting circuit can be limited, this machine can be considered as Twin generator.
基金supported by the Strategic Leading Project of the Chinese Academy of Sciences(No.XDA15014603).
文摘A reasonable parameter configuration helps improve the data transmission performance of the Licklider Transmission Protocol(LTP).Previous research has focused mainly on parameter optimization for LTP in simplified scenarios with one to two hops or multihop scenarios with a custody mechanism of the Bundle Protocol(BP).However,the research results are not applicable to communications in Complex Deep Space Networks(CDSNs)without the custody mechanism of BP that are more suitable for deep space communications with LTP.In this paper,we propose a model of file delivery time for LTP in CDSNs.Based on the model,we propose a Parameter Optimization Design Algorithm for LTP(LTP-PODA)of configuring reasonable parameters for LTP.The results show that the accuracy of the proposed model is at least 6.47%higher than that of the previously established models based on simple scenarios,and the proposed model is more suitable for CDSNs.Moreover,the LTP parameters are optimized by the LTP-PODA algorithm to obtain an optimization plan.Configuring the optimization plan for LTP improves the protocol transmission performance by at least 18.77%compared with configuring the other parameter configuration plans.
基金the Ministry of Science and Higher Education of the Russian Federation as part of the World-class Research Center program:Advanced Digital Technologies(contract No.075-15-2022-311 dated 20 April 2022).
文摘It remains challenging to conduct an efficient dynamic façade design.In this article authors try to address this issue introducing the façade daylighting performance improvement(FDPI)indicator aimed to evaluate the performance of a dynamic(adaptive)façade from its daylighting performance point of view.To illustrate the FDPI application the authors introduced the preliminary dynamic façade concept for an office building located in Tel Aviv(Hot-summer Mediterranean Climate Csa)with further shape modification based on the daylighting performance analysis compared to the three alternatives representative of different typologies of dynamic façades.Al Bahr,One Ocean and The University of Southern Denmark façade systems were simulated under the same weather and building conditions of the preliminary dynamic façade concept and were considered as a benchmark for the study.The final dynamic façade concept elaborated by the authors in the preliminary comparative workflow showed noticeable daylight performance improvement with respect to the case studies comparative scenarios.The FDPI metric allowed to estimate a daylighting performance improvement of 43%of the final dynamic façade concept over the case study dynamic façade that showed the best performance in the daylighting simulations.
基金Project supported by the National Natural Science Foundation of China(Grant No.51979125)supported by the Jiangsu Provincial Science Fund for Distinguished Young Scholars(Grant No.BK20211547)+2 种基金the Technological Innovation Team Project in Colleges and Universities of Jiangsu Province(Grant No.SKJ(2021)-1)the Open Research Subject of Key Laboratory of Fluid Machinery and Engineering(Xihua University)of Sichuan Province(Grant No.LTDL-2022007)the Graduate Research and Innovation Projects of Jiangsu Province(Grant No.KYCX23_3701).
文摘The purpose of this paper is to investigate the performance improvement mechanism of a high power vertical centrifugal pump by using numerical calculations.Therefore,a comparative study of energy losses and internal flow characteristics in the original and optimized models was carried out with special attention to the hydraulic component matching.The optimized model(model B)was obtained by optimizing the vaned diffuser and volute based on the original model(model A),mainly the diffuser inlet diameter,diffuser inlet vane angle,volute channel inlet width and volute throat area were changed.Firstly,the comparative results on performance and energy losses of two models showed that the efficiency and head of model B was significantly increased under design and part-load conditions.It is mainly due to the dramatic reduction of energy loss PL in the diffuser and volute.Then,the comparisons of PL and flow patterns in the vaned diffuser showed that the matching optimization between the model B impeller outlet flow angle and diffuser inlet vane angle resulted in a better flow pattern in both the circumferential and axial directions of the diffuser,which leads to the PL3 reduction.The meridian velocity Vm of model B was significantly increased at diffuser inlet regions and resulted in improvements of flow patterns at diffuser middle and outlet regions as well as pressure expansion capacity.Finally,the comparisons of PL and flow characteristics in the volute showed that the turbulence loss reduction in the model B volute was due to the flow pattern improvement at diffuser outlet regions which provided better flow conditions at volute inlet regions.The matching optimization between the diffuser and volute significantly reduced the turbulence loss in volute sections 1–4 and enhanced the pressure expansion capacity in sections 8–10.
基金supported by the National Natural Science Foundation of China (51603151 and 51741302)the National Key Research and Development Program of China (2017YFA0103900 & 2017YFA0103904)+1 种基金 Science & Technology Foundation of Shanghai (17JC1404600) the Fundamental Research Funds for the Central Universities.
文摘Various nanostructures of the organic semiconductor (OSC)films have been reported to enhance the organic field-effect transistors (OFETs)sensing performance. However,complicated fabrication processes hinder their ap- plications.In this work,we have effectively enhanced the sensitivity of the OFET-based sensors only by adjusting substrate temperature in OSC preparation and surface treatment of the dielectric layer.The relative sensitivity of the device can be enhanced by 5 times.The flexible sensors with polymer dielectric also exhibit high sensitivity because the less smooth surface of the polymer provides the OSCs with smaller grain size.Therefore,this work reveals the trade-off effects of the OSCs grain size on both transistor characteristic and chemic.al sensing performance,and provides a simple and extensively applicable strategy for OFETs sensitivity improvement.
基金the financial support provided by the National Key R&D Program of China(NO.2016YFC0700403)Beijing Municipal Natural Science Foundation(NO.3181001)Project supported by Beijing Chaoyang District Postdoctoral Research Foundation(NO.2018ZZ-01-28)。
文摘The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance.In this paper,mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights.The refrigerating capacity,volume efficiency and adiabatic efficiency of the SSC are calculated and discussed.Three prototypes,with different meshing clearance heights,were manufactured to study the internal influence mechanisms.The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results.Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%-7.98%and 5.92%-9.4%,respectively.Based on the models,analysis under varying meshing clearance heights and working conditions was performed.Taking into account working performance,actual manufacturing conditions and manufacturing cost limitations,a meshing clearance height range from 0.01 mm to 0.08 mm is suggested.This study can provide important theoretical data and experimental support for the design,manufacturing and optimization of single screw compressors.
基金Project supported by the National Natural Science Foundation of China (No. 50605031)the Natural Science Foundation of Jiangsu Province (No. BK2008395), China
文摘Dielectric elastomer actuators (DEAs) are an emerging class of polymer actuation devices and have extensive application prospect in the field of robotics because of their light weight, high efficiency and large deformation. A cone DEA is manufactured and its working principle is analyzed. To obtain the deformation of elastomer and movement of DEA in advance, a finite element method (FEM) simulation is performed first. According to the working principle, two working equilibrium points of DEA, corresponding to the displacements of DEA with voltage off and on, are obtained and validated by experiments, thus work output in a workcycle is computed. Experiments show that the actuator can respond quickly when voltage is applied and can return to its original position rapidly when voltage is released. Simulation results agree well with experimental ones and the feasibility of DEA simulation is proved, and causes for the small difference between them in displacement output are analyzed. The performance of the actuator is improved from the aspects of both displacement and force output. A diamond four-bar linkage mechanism is used as the preload part and a displacement output of 17 mm is obtained. The force output of one actuating unit is about 1.77 N, so three actuating units are assembled in parallel and the force output is heightened to as high as 5.07 N.
基金This work was supported by the National Key R&D Program of China(Grant No.2018Y FB0504603)the National Natural Science Foundation of China(Grant No.U1831203)+2 种基金the Strategic Pilot Projects in Space Science of China(Grant No.XDA15010400)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDY-SSW-JSC028)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2019030).
文摘The high-frequency pulse tube cryocooler(HPTC)has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure,low vibration,and reliable operation.The gas-coupled HPTC,driven by a single compressor,is currently the simplest and most compact structure.For HPTCs operating below 20 K,in order to obtain the mW cooling capacity,hundreds or even thousands of watts of electrical power are consumed,where radiation heat leakage accounts for a large proportion of their cooling capacity.In this paper,based on SAGE10,a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters(such as temperature and cooling capacity),and internal parameters(such as enthalpy flow and gas distribution)of the gas-coupled HPTC.An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC.Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power,but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section,which further enhances the refrigeration performance.The numerical calculation results were verified by experiments,and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K,and the relative Carnot efficiency at 15.5 K increased from 0.029%to 0.996%when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials.
文摘A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.
基金Supported by the National Natural Science Foundation of China under Grant No 11274402the National Basic Research Program of China under Grant No 2012CB933704+1 种基金the Natural Science Foundation of Guangdong Province under Grant No S2012020011003the Program for Changjiang Scholars and Innovative Research Team in University under Grant No IRT13042
文摘We improve the performance of organic light-emitting diodes （OLEDs） with both a MoO3 hole injection layer （HIL） and a MoO3 doped hole transport layer （HTL）, and present a systematical and comparative investigation on these devices. Compared with OLEDs with only MoO3 HIL or MoO3 doped HTL, OLEDs with both MoO3 HIL and MoO3 doped HTL show superior performance in driving voltage, power efficiency, and stability. Based on the typical NPB/Alq3 heterojunction structure, OLEDs with both MoO3 HIL and MoO3 doped HTL show a driving voltage of 5.4 V and a power efficiency of 1.41 lm/W for 1000 cd/m2, and a lifetime of around 0. 88 h with an initial luminance of 5268 cd/m2 under a constant current of 190 mA/cm2 operation in air without encapsulation. While OLEDs with only MoO3 HIL or MoO3 doped HTL show higher driving voltages of 6.4 V or 5.8 V and lower power efficiencies of 1.201m/W or 1.341m/W for 1000cd/m2, and a shorter lifetime of 0.33 or 0.60h with an initial luminance of around 5122 or 5300cd/m2 under a constant current of 200 or 216mA/cm2 operation. Our results demonstrate clearly that using both MoO3 HIL and MoO3 doped HTL is a simple and effective approach to simultaneoasly improve both the hole injection and transport efficiency, resulting from the lowered energy barrier at the anode interface and the increased hole carrier density in MoO3 doped HTL.
文摘The pollutant control performance of exhaust hoods plays a crucial role in the indoor air quality and energy consumption of ventilation systems in industrial buildings.To better understand the impact of local ventilation on the industrial indoor environment,this paper presents a literature review of exhaust hood performance and its improvement technologies.To create an index for evaluating the performance of exhaust hoods,the capture velocity,capture efficiency,flow ratio of pollutant emissions and exhaust airflow and energy consumption are first introduced.A number of factors affecting exhaust hood performance are assessed such as hood type,hood opening size,exhaust rate,installation distance,pollution source emission and environmental disturbance.Compared to structural improvement methods,the use of active airflow is a more effective way to improve the exhaust hood performance.The most commonly used methods for determining the exhaust rate are the controlled speed method and the flow ratio method.The use of an exhaust hood with an appropriate exhaust rate and jet parameters(for an active air-assisted hood)can effectively improve the pollutant control performance and reduce the energy consumption that would be wasted on the redundant exhaust rate.With more information focused on exhaust hood performance,this work suggests more effective strategies for improving indoor air quality and reducing energy consumption in industrial buildings.
