The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films...The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films annually in more than 20 languages,personalized recommendations are essential to highlight relevant content.To overcome the limitations of traditional recommender systems-such as static latent vectors,poor handling of cold-start scenarios,and the absence of uncertainty modeling-we propose a deep Collaborative Neural Generative Embedding(C-NGE)model.C-NGE dynamically learns user and item representations by integrating rating information and metadata features in a unified neural framework.It uses metadata as sampled noise and applies the reparameterization trick to capture latent patterns better and support predictions for new users or items without retraining.We evaluate CNGE on the Indian Regional Movies(IRM)dataset,along with MovieLens 100 K and 1 M.Results show that our model consistently outperforms several existing methods,and its extensibility allows for incorporating additional signals like user reviews and multimodal data to enhance recommendation quality.展开更多
Stop-start vehicles(SSVs)represent a potential alternative for improving internal combustion engine(ICE)efficiency.SSVs provide ICEs with the functionality of turning the engine off during traffic halts and restarting...Stop-start vehicles(SSVs)represent a potential alternative for improving internal combustion engine(ICE)efficiency.SSVs provide ICEs with the functionality of turning the engine off during traffic halts and restarting it without intervention by the driver.This strategy reduces fuel consumption,especially in dense urban traffic areas,and contributes to emissions reduction to meet green emissions targets.The most widely adopted SSV system has a mechanical interface to connect the electric starter motor to the ICE,which requires increased robustness compared with standard starting motors.This requirement allows the motor to withstand a higher number of engine start cycles compared with a standard starting motor.Nevertheless,it is a critical problem for wider adoption of SSVs.As SSV systems usually are based on the conventional starting system,its durability and noise remains a critical issue to be addressed by automakers.The typical pinion-ring gear interface uses intermittent gear meshing to form a transient coupling interface.The research reported here presents the development of an innovative mechanical interface for starting systems,called the permanent coupling(PC)-type interface,which reduces noise and increases durability compared with the existing design.The results obtained by a functional prototype of the PC-type mechanical interface confirm the feasibility of the proposed concept.The methodology is based on a product development process integrated with lumped-parameter modeling and virtual simulation aimed at reducing failures during prototype test-ing.The new mechanical interface was proven to be a good candidate for increasing the use of SSVs in the automotive market.展开更多
When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, base...When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, based on the steady state equivalent circuit of the induction motor.The corresponding expressions are derived, and the corresponding curves are also drawn, from which the initial starting frequency range can be determined properly and easily. The initial starting frequency range is the common range, in which the starting torque should be high enough and the starting current low enough.Some other useful formulas are also derived.These results are significant for electrical drive designers to make the starting schemes. The effects of the increase of the stator and the rotor resistances on the starting torque and the initial starting frequency range are also discussed, which is caused by the skin effects of the high order harmonics present in the PWM inverter output voltage.展开更多
With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic de...With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic development and are forced to close,or enterprises that move out without conforming to the environment,become a gray area within the city.Most of the existing assessments are conducting single assessment of some indicators,but than their actual benefits.Through the field investigation on the starting area of Handan Economic Development Zone,and the evaluation on the nature of land use,development intensity,investment and output,and idle land,inefficient land use in the park is identified.According to different evaluation results,different update and promotion methods are put forward.The research could provide a new evaluation method and idea for subsequent renewal and development of urban industrial parks.展开更多
The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting...The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.展开更多
Analyzed working principle and starting process of asynchronous motor direct torque control system. In order to solve the problem of serious fluctuation of starting current in traditional control scheme, the author pu...Analyzed working principle and starting process of asynchronous motor direct torque control system. In order to solve the problem of serious fluctuation of starting current in traditional control scheme, the author puts forward a new kind of starting method which can limit voltage value to achieve the goal of reducing fluctuation of the current by increasing zero voltage vectors during the stage of starting. The author has also carried on simulation study on the system, and the result of simulation study shows that this method is effectual.展开更多
The impact of the financial crisis exacerbated the students＇ employment situation, and the current situation of college students＇ entrepreneurial activities is worrying, which urgently need a systematic support prog...The impact of the financial crisis exacerbated the students＇ employment situation, and the current situation of college students＇ entrepreneurial activities is worrying, which urgently need a systematic support program to be support and guide to the main business college. Based on the analysis of current situation and problems, this paper tries to build a entrepreneurial support system of contemporary college students as core, of tripartite coordinating community, university and government as basis to promote the healthy and sustainable development of entrepreneurial activities for the ultimate purpose of the entrepreneurial support system, to promote the healthy and sustainable development of entrepreneurial activities.展开更多
In response to the need for robust black-start strategies in modern smart grids during blackouts,this paper proposes a two-stage black-start model that integrates wind turbines(WT),photovoltaic generators(PV),and ener...In response to the need for robust black-start strategies in modern smart grids during blackouts,this paper proposes a two-stage black-start model that integrates wind turbines(WT),photovoltaic generators(PV),and energy storage systems(ESS).The system restoration path model in the first stage utilizes the Dijkstra algorithm to create a skeleton network and formulate a post-outage generator start-up plan.The second stage involved a load pick-up model,structured as a mixed-integer linear programming problem,aimed at restoring the load with the assistance of the ESS.This stage was designed for computational efficiency,allowing solutions to be obtained using standard commercial solvers.The performance and efficacy of the proposed model were demonstrated through its application to modified IEEE 39/118-bus transmission systems,with the results affirming its high efficiency and effectiveness in power system restoration scenarios.展开更多
This paper investigates the start-up and shutdown phases of a five-bladed closed-impeller centrifugal pump through experimental analysis,capturing the temporal evolution of its hydraulic performances.The study also pr...This paper investigates the start-up and shutdown phases of a five-bladed closed-impeller centrifugal pump through experimental analysis,capturing the temporal evolution of its hydraulic performances.The study also predicts the transient characteristics of the pump under non-rated operating conditions to assess the accuracy of various machine learning methods in forecasting its instantaneous performance.Results indicate that the pump’s transient behavior in power-frequency mode markedly differs from that in frequency-conversion mode.Specifically,the power-frequency mode achieves steady-state values faster and exhibits smaller fluctuations before stabilization compared to the other mode.During the start-up phase,as the steady-state flow rate increases,inlet and outlet pressures and head also rise,while torque and shaft power decrease,with rotational speed remaining largely unchanged.Conversely,during the shutdown phase,no significant changes were observed in torque,shaft power,or rotational speed.Six machine learning models,including Gaussian Process Regression(GPR),Decision Tree Regression(DTR),and Deep Learning Networks(DLN),demonstrated high accuracy in predicting the hydraulic performance of the centrifugal pump during the start-up and shutdown phases in both power-frequency and frequency-conversion conditions.The findings provide a theoretical foundation for improved prediction of pump hydraulic performance.For instance,when predicting head and flow rate during power-frequency start-up,GPR achieved absolute and relative errors of 0.54 m(7.84%)and 0.21 m3/h(13.57%),respectively,while the Feedforward Neural Network(FNN)reported errors of 0.98 m(8.24%)and 0.10 m3/h(16.71%).By contrast,the Support Vector Machine Regression(SVMR)and Generalized Additive Model(GAM)generally yielded less satisfactory prediction accuracy compared to the other methods.展开更多
Synthesis technology and properties of cordierite from solid waste resources/Tan Qitong,Zhao Huizhong,Yu Jun,Zhang Han,Tan Liqiang//Naihuo Cailiao.-2024,58(3):185 Abstract:To effectively utilize solid waste resources ...Synthesis technology and properties of cordierite from solid waste resources/Tan Qitong,Zhao Huizhong,Yu Jun,Zhang Han,Tan Liqiang//Naihuo Cailiao.-2024,58(3):185 Abstract:To effectively utilize solid waste resources and relieve resource constraints,cordierite refractory raw materials were prepared according to the chemical composition of cordierite,using 12 mass%fused magnesia dust powder,40 mass%fused corundum dust powder and 48 mass%quartz tailings as starting materials.展开更多
High-quality services in today’s mobile networks require stable delivery of bandwidth-intensive network content.Multipath QUIC(MPQUIC),as a multipath protocol that extends QUIC,can utilize multiple paths to support s...High-quality services in today’s mobile networks require stable delivery of bandwidth-intensive network content.Multipath QUIC(MPQUIC),as a multipath protocol that extends QUIC,can utilize multiple paths to support stable and efficient transmission.The standard coupled congestion control algorithm in MPQUIC synchronizes these paths to manage congestion,meeting fairness requirements and improving transmission efficiency.However,current algorithms’Congestion Window(CWND)reduction approach significantly decreases CWND upon packet loss,which lowers effective throughput,regardless of the congestion origin.Furthermore,the uncoupled Slow-Start(SS)in MPQUIC leads to independent exponential CWND growth on each path,potentially causing buffer overflow.To address these issues,we propose the CC-OLIA,which incorporates Packet Loss Classifcation(PLC)and Coupled Slow-Start(CSS).The PLC distinguishes between congestion-induced and random packet losses,adjusting CWND reduction accordingly to maintain throughput.Concurrently,the CSS module coordinates CWND growth during the SS,preventing abrupt increases.Implementation on MININET shows that CC-OLIA not only maintains fair performance but also enhances transmission efficiency across diverse network conditions.展开更多
In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicle...In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.展开更多
Innovation in the period product category has experienced a boost in recent years as part of the growing interest in women’s health products.Disruptive brands,start-ups and the area of Fem Tech are key areas to watch...Innovation in the period product category has experienced a boost in recent years as part of the growing interest in women’s health products.Disruptive brands,start-ups and the area of Fem Tech are key areas to watch.Collectively they are destigmatizing this category,and we can finally use the word“period”in marketing,as well as talking about the issues women deal with.Simultaneously,there has been an explosion in products in the sexual health category and a move away from outdated,reserved language.展开更多
The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key ...The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key role.In this work,X70 steels with different start cooling temperatures were prepared through thermo-mechanical control process.The quasi-polygonal ferrite(QF),granular bainite(GB),bainitic ferrite(BF)and martensite-austenite constituents were formed at the start cooling temperatures of 780℃(C1),740℃(C2)and 700℃(C3).As start cooling temperature decreased,the amount of GB decreased,the microstructure of QF and BF increased.Microstructure characteristics of the three samples,such as high-angle grain boundaries(HAGBs),MA constituents and crystallographic orientation,also varied with the start cooling temperatures.C2 sample had the lowest DBTT value(−86℃)for its highest fraction of HAGBs,highest content of<110>oriented grains and lowest content of<001>oriented grains parallel to TD.The high density of{332}<113>and low density of rotated cube{001}<110>textures also contributed to the best impact toughness of C2 sample.In addition,a modified model was used in this paper to quantitatively predict the approximate DBTT value of steels.展开更多
The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–S...The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport （SST） k–x two-equation Reynolds averaged Navier– Stokes （RANS） model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.展开更多
文摘The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films annually in more than 20 languages,personalized recommendations are essential to highlight relevant content.To overcome the limitations of traditional recommender systems-such as static latent vectors,poor handling of cold-start scenarios,and the absence of uncertainty modeling-we propose a deep Collaborative Neural Generative Embedding(C-NGE)model.C-NGE dynamically learns user and item representations by integrating rating information and metadata features in a unified neural framework.It uses metadata as sampled noise and applies the reparameterization trick to capture latent patterns better and support predictions for new users or items without retraining.We evaluate CNGE on the Indian Regional Movies(IRM)dataset,along with MovieLens 100 K and 1 M.Results show that our model consistently outperforms several existing methods,and its extensibility allows for incorporating additional signals like user reviews and multimodal data to enhance recommendation quality.
基金ZEN S.A.Indus-tria Metalurgica(www.zensa.com.br)for sponsoring and funding the project.
文摘Stop-start vehicles(SSVs)represent a potential alternative for improving internal combustion engine(ICE)efficiency.SSVs provide ICEs with the functionality of turning the engine off during traffic halts and restarting it without intervention by the driver.This strategy reduces fuel consumption,especially in dense urban traffic areas,and contributes to emissions reduction to meet green emissions targets.The most widely adopted SSV system has a mechanical interface to connect the electric starter motor to the ICE,which requires increased robustness compared with standard starting motors.This requirement allows the motor to withstand a higher number of engine start cycles compared with a standard starting motor.Nevertheless,it is a critical problem for wider adoption of SSVs.As SSV systems usually are based on the conventional starting system,its durability and noise remains a critical issue to be addressed by automakers.The typical pinion-ring gear interface uses intermittent gear meshing to form a transient coupling interface.The research reported here presents the development of an innovative mechanical interface for starting systems,called the permanent coupling(PC)-type interface,which reduces noise and increases durability compared with the existing design.The results obtained by a functional prototype of the PC-type mechanical interface confirm the feasibility of the proposed concept.The methodology is based on a product development process integrated with lumped-parameter modeling and virtual simulation aimed at reducing failures during prototype test-ing.The new mechanical interface was proven to be a good candidate for increasing the use of SSVs in the automotive market.
文摘When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, based on the steady state equivalent circuit of the induction motor.The corresponding expressions are derived, and the corresponding curves are also drawn, from which the initial starting frequency range can be determined properly and easily. The initial starting frequency range is the common range, in which the starting torque should be high enough and the starting current low enough.Some other useful formulas are also derived.These results are significant for electrical drive designers to make the starting schemes. The effects of the increase of the stator and the rotor resistances on the starting torque and the initial starting frequency range are also discussed, which is caused by the skin effects of the high order harmonics present in the PWM inverter output voltage.
文摘With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic development and are forced to close,or enterprises that move out without conforming to the environment,become a gray area within the city.Most of the existing assessments are conducting single assessment of some indicators,but than their actual benefits.Through the field investigation on the starting area of Handan Economic Development Zone,and the evaluation on the nature of land use,development intensity,investment and output,and idle land,inefficient land use in the park is identified.According to different evaluation results,different update and promotion methods are put forward.The research could provide a new evaluation method and idea for subsequent renewal and development of urban industrial parks.
基金the continued support of Key Laboratory of Inlet and Exhaust system Technology (Nanjing University of Aeronautics and Astronautics), ChinaMinistry of Education, National Science and Technology Major Project of China (Nos. 2017-V-0004-0054, 2019-II-0007-0027, Y2022II-0005-0008)+6 种基金Defense Industrial Technology Development Program of China (No. JCKY2019605D001)Advanced Jet Propulsion Creativity Center of AEAC of China (No. HKCX2020-02-011)China Postdoctoral Science Foundation (No. 2022M721598)Jiangsu Funding Program for Excellent Postdoctoral Talent of China (No. 2022ZB214)the Youth Fund Project of Natural Science Foundation of Jiangsu Province of China (No. BK20230891)the National Natural Science Foundation of China (No. 12332018)Science Center for Gas Turbine Project, China (P2022-B-I-006-001) and some other related foundations
文摘The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.
文摘Analyzed working principle and starting process of asynchronous motor direct torque control system. In order to solve the problem of serious fluctuation of starting current in traditional control scheme, the author puts forward a new kind of starting method which can limit voltage value to achieve the goal of reducing fluctuation of the current by increasing zero voltage vectors during the stage of starting. The author has also carried on simulation study on the system, and the result of simulation study shows that this method is effectual.
文摘The impact of the financial crisis exacerbated the students＇ employment situation, and the current situation of college students＇ entrepreneurial activities is worrying, which urgently need a systematic support program to be support and guide to the main business college. Based on the analysis of current situation and problems, this paper tries to build a entrepreneurial support system of contemporary college students as core, of tripartite coordinating community, university and government as basis to promote the healthy and sustainable development of entrepreneurial activities for the ultimate purpose of the entrepreneurial support system, to promote the healthy and sustainable development of entrepreneurial activities.
基金Science and Technology Project of the State Grid,Shanxi Electric Power Research Institute.(Project name:Research on equivalent inertia and frequency response characteristics of induction motors and applications of black-start scheme in power grids,project number:52053022000 J).
文摘In response to the need for robust black-start strategies in modern smart grids during blackouts,this paper proposes a two-stage black-start model that integrates wind turbines(WT),photovoltaic generators(PV),and energy storage systems(ESS).The system restoration path model in the first stage utilizes the Dijkstra algorithm to create a skeleton network and formulate a post-outage generator start-up plan.The second stage involved a load pick-up model,structured as a mixed-integer linear programming problem,aimed at restoring the load with the assistance of the ESS.This stage was designed for computational efficiency,allowing solutions to be obtained using standard commercial solvers.The performance and efficacy of the proposed model were demonstrated through its application to modified IEEE 39/118-bus transmission systems,with the results affirming its high efficiency and effectiveness in power system restoration scenarios.
基金financially supported by Science and Technology Project of Quzhou(Grant Nos.2023K256,2023NC08)Research Grants Program of Department of Education of Zhejiang Province(No.Y202455709)+1 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LZY21E050001)University-Enterprise Cooperation Program for Visiting Engineers in Higher Education Institutions in Zhejiang Province(No.FG2020215).
文摘This paper investigates the start-up and shutdown phases of a five-bladed closed-impeller centrifugal pump through experimental analysis,capturing the temporal evolution of its hydraulic performances.The study also predicts the transient characteristics of the pump under non-rated operating conditions to assess the accuracy of various machine learning methods in forecasting its instantaneous performance.Results indicate that the pump’s transient behavior in power-frequency mode markedly differs from that in frequency-conversion mode.Specifically,the power-frequency mode achieves steady-state values faster and exhibits smaller fluctuations before stabilization compared to the other mode.During the start-up phase,as the steady-state flow rate increases,inlet and outlet pressures and head also rise,while torque and shaft power decrease,with rotational speed remaining largely unchanged.Conversely,during the shutdown phase,no significant changes were observed in torque,shaft power,or rotational speed.Six machine learning models,including Gaussian Process Regression(GPR),Decision Tree Regression(DTR),and Deep Learning Networks(DLN),demonstrated high accuracy in predicting the hydraulic performance of the centrifugal pump during the start-up and shutdown phases in both power-frequency and frequency-conversion conditions.The findings provide a theoretical foundation for improved prediction of pump hydraulic performance.For instance,when predicting head and flow rate during power-frequency start-up,GPR achieved absolute and relative errors of 0.54 m(7.84%)and 0.21 m3/h(13.57%),respectively,while the Feedforward Neural Network(FNN)reported errors of 0.98 m(8.24%)and 0.10 m3/h(16.71%).By contrast,the Support Vector Machine Regression(SVMR)and Generalized Additive Model(GAM)generally yielded less satisfactory prediction accuracy compared to the other methods.
文摘Synthesis technology and properties of cordierite from solid waste resources/Tan Qitong,Zhao Huizhong,Yu Jun,Zhang Han,Tan Liqiang//Naihuo Cailiao.-2024,58(3):185 Abstract:To effectively utilize solid waste resources and relieve resource constraints,cordierite refractory raw materials were prepared according to the chemical composition of cordierite,using 12 mass%fused magnesia dust powder,40 mass%fused corundum dust powder and 48 mass%quartz tailings as starting materials.
文摘High-quality services in today’s mobile networks require stable delivery of bandwidth-intensive network content.Multipath QUIC(MPQUIC),as a multipath protocol that extends QUIC,can utilize multiple paths to support stable and efficient transmission.The standard coupled congestion control algorithm in MPQUIC synchronizes these paths to manage congestion,meeting fairness requirements and improving transmission efficiency.However,current algorithms’Congestion Window(CWND)reduction approach significantly decreases CWND upon packet loss,which lowers effective throughput,regardless of the congestion origin.Furthermore,the uncoupled Slow-Start(SS)in MPQUIC leads to independent exponential CWND growth on each path,potentially causing buffer overflow.To address these issues,we propose the CC-OLIA,which incorporates Packet Loss Classifcation(PLC)and Coupled Slow-Start(CSS).The PLC distinguishes between congestion-induced and random packet losses,adjusting CWND reduction accordingly to maintain throughput.Concurrently,the CSS module coordinates CWND growth during the SS,preventing abrupt increases.Implementation on MININET shows that CC-OLIA not only maintains fair performance but also enhances transmission efficiency across diverse network conditions.
基金funded by Zhejiang Province Spearhead and Leading Goose Research and Development Key Program,grant number 2023C01239.
文摘In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.
文摘Innovation in the period product category has experienced a boost in recent years as part of the growing interest in women’s health products.Disruptive brands,start-ups and the area of Fem Tech are key areas to watch.Collectively they are destigmatizing this category,and we can finally use the word“period”in marketing,as well as talking about the issues women deal with.Simultaneously,there has been an explosion in products in the sexual health category and a move away from outdated,reserved language.
基金Project(2018XK2301) supported by the Change-Zhu-Tan National Independent Innavation Demonstration Zone Special Program,China。
文摘The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key role.In this work,X70 steels with different start cooling temperatures were prepared through thermo-mechanical control process.The quasi-polygonal ferrite(QF),granular bainite(GB),bainitic ferrite(BF)and martensite-austenite constituents were formed at the start cooling temperatures of 780℃(C1),740℃(C2)and 700℃(C3).As start cooling temperature decreased,the amount of GB decreased,the microstructure of QF and BF increased.Microstructure characteristics of the three samples,such as high-angle grain boundaries(HAGBs),MA constituents and crystallographic orientation,also varied with the start cooling temperatures.C2 sample had the lowest DBTT value(−86℃)for its highest fraction of HAGBs,highest content of<110>oriented grains and lowest content of<001>oriented grains parallel to TD.The high density of{332}<113>and low density of rotated cube{001}<110>textures also contributed to the best impact toughness of C2 sample.In addition,a modified model was used in this paper to quantitatively predict the approximate DBTT value of steels.
文摘The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport （SST） k–x two-equation Reynolds averaged Navier– Stokes （RANS） model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.
