Research of capture mechanisms with strong capture adaptability and stable grasp is important to solve the problem of launch and recovery of torpedo-shaped autonomous underwater vehicles(AUVs).A multi-loop coupling ca...Research of capture mechanisms with strong capture adaptability and stable grasp is important to solve the problem of launch and recovery of torpedo-shaped autonomous underwater vehicles(AUVs).A multi-loop coupling capture mechanism with strong adaptability and high retraction rate has been proposed for the launch and recovery of torpedo-shaped AUVs with different morphological features.Firstly,the principle of capturing motion retraction is described based on the appearance characteristics of torpedo-shaped AUVs,and the configuration synthesis of the capture mechanism is carried out using the method of constrained chain synthesis.Secondly,the screw theory is employed to analyze the degree of freedom(DoF)of the capture mechanism.Then,the 3D model of the capture mechanism is established,and the kinematics and dynamics simulations are carried out.Combined with the capture orientation requirements of the capture mechanism,the statics and vibration characteristics analyses are carried out.Furthermore,considering the capture process and the underwater working environment,the motion characteristics and hydraulics characteristics of the capture mechanism are analyzed.Finally,a principle prototype is developed and the torpedo-shaped AUVs capture experiment is completed.The work provides technical reserves for the research and development of AUV capture special equipment.展开更多
Purpose The aim of the study was to identify factors associated with prolonged time to return to full performance(RTFP)in athletes with recent severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection.Metho...Purpose The aim of the study was to identify factors associated with prolonged time to return to full performance(RTFP)in athletes with recent severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection.Methods Prospective cohort study with cross sectional analysis.A total of 84 athletes with confirmed SARS-CoV-2 infection assessed at a coronavirus disease 2019 recovery clinic gave a history of age,sex,type/level of sport,co-morbidities,pre-infection training hours,and 26 acute SARS-CoV-2 symptoms from 3 categories(“nose and throat”,“chest and neck”,and“whole body”/systemic).Data on days to RTFP were obtained by structured interviews.Factors associated with RTFP were demographics,sport participation,history of co-morbidities,pre-infection training history,and acute symptoms(type,number).Outcomes were:(a)days to RTFP(median,interquartile range(IQR))in asymptomatic(n=7)and symptomatic athletes(n=77),and(b)hazard ratios(HRs;95%confidence interval)for symptomatic athletes with vs.without a factor(univariate,multiple models).HR<1 was predictive of higher percentage chance of prolonged RTFP.Significance was p<0.05.Results Days to RTFP were 30 days(IQR:23–40)for asymptomatic and 64 days(IQR:42–91)for symptomatic participants(p>0.05).Factors associated with prolonged RTFP(univariate models)were:females(HR=0.57;p=0.014),endurance athletes(HR=0.41;p<0.0001),co-morbidity number(HR=0.75;p=0.001),and respiratory disease history(HR=0.54;p=0.026).In symptomatic athletes,prolonged RTFP(multiple models)was significantly associated with increased“chest and neck”(HR=0.85;p=0.017)and“nose and throat”(HR=0.84;p=0.013)symptoms,but the association was more profound between prolonged RFTP and increased total number of“all symptoms”(HR=0.91;p=0.001)and“whole body”/systemic(HR=0.82;p=0.007)symptoms.Conclusion A larger number of total symptoms and specifically“whole body”/systemic symptoms during the acute phase of SARS-CoV-2 infection in athletes is associated with prolonged RTFP.展开更多
In order to evaluate the heating performance of gas engine heat pump（GEHP） for air-conditioning and hot water supply, a test facility was developed and experiments were performed over a wide range of engine speed（1...In order to evaluate the heating performance of gas engine heat pump（GEHP） for air-conditioning and hot water supply, a test facility was developed and experiments were performed over a wide range of engine speed（1400-2600 r/min）, ambient air temperature（2.4-17.8 ℃） and condenser water inlet temperature（30-50℃）. The results show that as engine speed increases from 1400 r/min to 2600 r/min, the total heating capacity and energy consumption increase by about 30% and 89%, respectively; while the heat pump coefficient of performance（COP） and system primary energy ratio（PER） decrease by 44% and 31%, respectively. With the increase of ambient air temperature from 2.4 ℃ to 17.8 ℃, the heat pump COP and system PER increase by 32% and 19%, respectively. Moreover, the heat pump COP and system PER decrease by 27% and 15%, respectively, when the condenser water inlet temperature changes from 30 ℃ to 50 ℃. So, it is obvious that the effect of engine speed on the performance is more significant than the effects of ambient air temperature and condenser water inlet temperature.展开更多
Vacuum gaps have rapid dynamic dielectric recovery speed while SF6 gaps have high insulation strength. The series-connected vacuum and SF6 gaps are used as the main switch(MS), which combines their advantages. The wor...Vacuum gaps have rapid dynamic dielectric recovery speed while SF6 gaps have high insulation strength. The series-connected vacuum and SF6 gaps are used as the main switch(MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF6 gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance(DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker(VCB) and SF6 gas circuit breaker(GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker(CB) based on series-connected vacuum and SF6 gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage(TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.展开更多
Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the...Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the world. The authors proposed the microplastics recovery device composed of the plates. Besides, the device consists of the tilted inlet/outlet and the horizontal part. In the water flow such as the tidal and ocean currents, the microplastics can be extracted from the main flow due to the vortex flow generated at the inner part of this device. In this research, the effects of the flow velocity and the inlet/outlet tilt angle on the capture performance were investigated experimentally and numerically. In the numerical simulations using the discrete phase model, the tilt angle was changed in a range between 30 degrees and 150 degrees in increments of 15 degrees, and the particle tracks of plastics were derived in steady condition. On the other hand, the capture performances in three cases of tilt angle 45 degrees, 120 degrees and 150 degrees were compared by circulation type water channel tests in which the plastics denser than the water were swept away 30 times every flow velocity. As the result, it seems that the tilt angle of 120 degrees is suitable for the wide range of the flow velocity in river and ocean.展开更多
As of February 28th,2019,27 textile and apparel listed companies in Shanghai, Shenzhen and Hong Kong have unveiled their annual performance reports. Overall, most brands have achieved growth. There are 13 brands, acco...As of February 28th,2019,27 textile and apparel listed companies in Shanghai, Shenzhen and Hong Kong have unveiled their annual performance reports. Overall, most brands have achieved growth. There are 13 brands, accounting for 48% of the total, whose operating income and net profit increased.展开更多
Purpose: The aim of the present study is to examine the performance of young Japanese cross-country skiers of different competitive levels with the use of Yo-Yo tests and the 12-minute run test (12MRT) that have been ...Purpose: The aim of the present study is to examine the performance of young Japanese cross-country skiers of different competitive levels with the use of Yo-Yo tests and the 12-minute run test (12MRT) that have been demonstrated to be related to each level, and to know which test is suitable for different competitive performance. Methods: Elite group (N = 9) was 16.9 ± 0.3 years and moderate trained group (N = 22) was 16.1 ± 0.9 years. The testing sessions consisted of the following: 1) Vertical jump and 50m sprint;2) the Yo-Yo tests level 1 and 2 (intermittent recovery);3) 12MRT. Results: Results showed the vertical jump heights and 50m sprint that no significant both performances differences were found among the two groups. Significant the Yo-Yo tests and 12MRT performances differences were found between the two groups (p < 0.05). Performance test (%) showed the ratio of moderate trained group towards elite group. The Yo-Yo tests performance was low enough compared with the result of 12MRT in moderate trained group. Conclusions: It is therefore valid to assume that low Yo-Yo tests performance due to immature anaerobic in cross-country skiers was a new limiting factor in the competitive level.展开更多
A new SiC superjunction power MOSFET device using high-k insulator and p-type pillar with an integrated Schottky barrier diode(Hk-SJ-SBD MOSFET)is proposed,and has been compared with the SiC high-k MOSFET(Hk MOSFET),S...A new SiC superjunction power MOSFET device using high-k insulator and p-type pillar with an integrated Schottky barrier diode(Hk-SJ-SBD MOSFET)is proposed,and has been compared with the SiC high-k MOSFET(Hk MOSFET),SiC superjuction MOSFET(SJ MOSFET)and the conventional SiC MOSFET in this article.In the proposed SiC Hk-SJ-SBD MOSFET,under the combined action of the p-type region and the Hk dielectric layer in the drift region,the concentration of the N-drift region and the current spreading layer can be increased to achieve an ultra-low specific on-resistance(Ron,sp).The integrated Schottky barrier diode(SBD)also greatly improves the reverse recovery performance of the device.TCAD simulation results indicate that the Ron,sp of the proposed SiC Hk-SJ-SBD MOSFET is 0.67 mΩ·cm^(2)with a 2240 V breakdown voltage(BV),which is more than 72.4%,23%,5.6%lower than that of the conventional SiC MOSFET,Hk SiC MOSFET and SJ SiC MOSFET with the 1950,2220,and 2220V BV,respectively.The reverse recovery time and reverse recovery charge of the proposed MOSFET is 16 ns and18 nC,which are greatly reduced by more than 74%and 94%in comparison with those of all the conventional SiC MOSFET,Hk SiC MOSFET and SJ SiC MOSFET,due to the integrated SBD in the proposed MOSFET.And the trade-off relationship between the Ron,sp and the BV is also significantly improved compared with that of the conventional MOSFET,Hk MOSFET and SJ MOSFET as well as the MOSFETs in other previous literature,respectively.In addition,compared with conventional SJ SiC MOSFET,the proposed SiC MOSFET has better immunity to charge imbalance,which may bring great application prospects.展开更多
Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed t...Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.展开更多
The recovery of heat and water from low-grade flue gas is of considerable importance for energy conservation and environmental preservation.While the full-open absorption heat pump shows promise as a means of achievin...The recovery of heat and water from low-grade flue gas is of considerable importance for energy conservation and environmental preservation.While the full-open absorption heat pump shows promise as a means of achieving heat and water recovery,the lack of research on heat and mass transfer performance of open-type solution evaporation regeneration represents a significant impediment to its design and operation.This paper experimentally investigates the regeneration performance of an open-type spaying tower equipped with ceramic structured packings.Two different regeneration modes are proposed,namely ambient air receiver mode and flue gas receiver mode,to utilize air or low-grade flue gas as a driving source.The impact of different input parameters on the regeneration characteristics,including heat transfer capacity,water removal rate,thermal efficiency,and humidity effectiveness,are demonstrated.The findings indicate that the enhancement of regeneration can be achieved through the increase of solution flow rate,solution temperature,and flue gas flow rate in both regeneration modes.However,high solution concentration and flue gas humidity ratio can weaken water removal rates and reduce thermal efficiency.For the regeneration of CaCl_(2)-H_(2)O with a concentration of55%,flue gas around 200℃with a humidity ratio below 44 g/kg can successfully drive the solution regeneration process.When the solution concentration or flue gas humidity ratio continues to rise,additional energy is necessary for regeneration.Furthermore,the coupled heat and mass transfer coefficients are fitted,which can contribute to the design and optimization of the open-type regenerator.展开更多
Stroke remains the leading cause of long-term disability.Hemiparesis is one of the most common post-stroke motor deficits and is largely attributed to loss or disruption of the motor signals from the affected motor co...Stroke remains the leading cause of long-term disability.Hemiparesis is one of the most common post-stroke motor deficits and is largely attributed to loss or disruption of the motor signals from the affected motor cortex.As the only direct descending motor pathway,the corticospinal tract(CST)is the primary pathway to innervate spinal motor neurons,and thus,forms the neuroanatomical basis to control the peripheral muscles for voluntary movements.Here,we review evidence from both experimental animals and stroke patients,regarding CST axonal damage,functional contribution of CST axonal integrity and remodeling to neurological recovery,and therapeutic approaches aimed to enhance CST axonal remodeling after stroke.The new insights gleaned from preclinical and clinical studies may encourage the development of more rational therapeutics with a strategy targeted to promote axonal rewiring for corticospinal innervation,which will significantly impact the current clinical needs of subacute and chronic stroke treatment.展开更多
Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performance...Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performances of ordinary polymer,glycerol,polymer in"sheet-net"structure and heterogeneous weak gel at the same viscosity and concentration,the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated,and the method of improving polymer flooding effect was worked out.The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media.The viscosity of polymer agents has no positive correlation with polymer flooding effect.Although polymer of"sheet-net"structure has strong capacity in increasing viscosity,it has poor compatibility with pore throat structure of reservoir rock,low injectivity and low shear resistance.Heterogeneous weak gel system has higher adsorption and capture capacity in porous media,which is easy to retain in porous media,and can effectively establish seepage resistance in high permeability layers(zones).Compared with polymer solutions with the same viscosity or concentration,it has stronger ability to expand swept volume.Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal,and thus worsening of polymer flooding effect.Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.展开更多
Dynamic performance is important to the controlling and monitoring of the organic Rankine cycle(ORC) system so to avoid the occurrence of unwanted conditions. A small scale waste heat recovery system with organic Rank...Dynamic performance is important to the controlling and monitoring of the organic Rankine cycle(ORC) system so to avoid the occurrence of unwanted conditions. A small scale waste heat recovery system with organic Rankine cycle was constructed and the dynamic behavior was presented. In the dynamic test, the pump was stopped and then started. In addition, there was a step change of the flue gas volume flow rate and the converter frequency of multistage pump, respectively. The results indicate that the working fluid flow rate has the shortest response time, followed by the expander inlet pressure and the expander inlet temperature.The operation frequency of pump is a key parameter for the ORC system. Due to a step change of pump frequency(39.49-35.24 Hz),the expander efficiency and thermal efficiency drop by 16% and 21% within 2 min, respectively. Besides, the saturated mixture can lead to an increase of the expander rotation speed.展开更多
Concentrating Solar Power(CSP)plants offer a promising way to generate low-emission energy.However,these plants face challenges such as reduced sunlight during winter and cloudy days,despite being located in high sola...Concentrating Solar Power(CSP)plants offer a promising way to generate low-emission energy.However,these plants face challenges such as reduced sunlight during winter and cloudy days,despite being located in high solar radiation areas.Furthermore,their dispatch capacities and yields can be affected by high electricity consumption,particularly at night.The present work aims to develop an off-design model that evaluates the hourly and annual performances of a parabolic trough power plant(PTPP)equipped with a waste heat recovery system.The study aims to compare the performances of this new layout with those of the conventional Andasol 1 plant,with the aim of assessing the improvements achieved in the new design.Based on the results,it can be concluded that the new layout has increased the annual generated power to almost 183 GWh(an increase of about 7.60% is achieved compared to the Andasol 1 layout that generates 169 GWh annually).Additionally,the proposed installation has achieved an efficiency of 20.55%,which represents a 7.87% increase compared to the previous design(19.05%).The Levelized Cost of Electricity(LCOE)of the new layout has been reduced by more than 5.8% compared to the Andasol 1 plant.Specifically,it has decreased from 13.11 to 12.35 c/kWh.This reduction in LCOE highlights the improved cost-effectiveness of the newlayout,making it amore economically viable option for generating electricity compared to the conventional Andasol 1 plant.展开更多
Probabilistic seismic performance assessment method for buildings offers a valuable approach to simulate the broader regional impacts:economic losses,downtime,and casualties.A crucial aspect of this process entails ac...Probabilistic seismic performance assessment method for buildings offers a valuable approach to simulate the broader regional impacts:economic losses,downtime,and casualties.A crucial aspect of this process entails ac-counting for the spatial correlation of building performances,aiming for an accurate estimation of the probability of extreme regional losses,such as the simultaneous collapse of buildings with similar structural characteristics.In this study,a correlation model based on a Gaussian random field is employed,and several key challenges associated with its application are addressed.In addition,efficiency of five different methods of selecting station records from the same earthquake scenario is compared.The minimum number of earthquake records necessary to achieve a stable correlation result is determined.Additionally,spatial correlations derived from different his-tory earthquake events are compared.By addressing these critical issues,this research contributes to refining the reliability of probabilistic methods for regional resilience assessment.展开更多
基金supported by the Natural Science Foundation of Jiangsu Province of China(Grant No.BK20220649)the Natural Science Foundation of the Jiangsu Higher Education Institutions(Grant No.23KJB460010)+1 种基金the Key R&D Program of Jiangsu Province(Grant No.BE2022062)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.SJCX23_2143).
文摘Research of capture mechanisms with strong capture adaptability and stable grasp is important to solve the problem of launch and recovery of torpedo-shaped autonomous underwater vehicles(AUVs).A multi-loop coupling capture mechanism with strong adaptability and high retraction rate has been proposed for the launch and recovery of torpedo-shaped AUVs with different morphological features.Firstly,the principle of capturing motion retraction is described based on the appearance characteristics of torpedo-shaped AUVs,and the configuration synthesis of the capture mechanism is carried out using the method of constrained chain synthesis.Secondly,the screw theory is employed to analyze the degree of freedom(DoF)of the capture mechanism.Then,the 3D model of the capture mechanism is established,and the kinematics and dynamics simulations are carried out.Combined with the capture orientation requirements of the capture mechanism,the statics and vibration characteristics analyses are carried out.Furthermore,considering the capture process and the underwater working environment,the motion characteristics and hydraulics characteristics of the capture mechanism are analyzed.Finally,a principle prototype is developed and the torpedo-shaped AUVs capture experiment is completed.The work provides technical reserves for the research and development of AUV capture special equipment.
基金supported by funding from the International Olympic Committee(IOC)CS received a scholarship made possible through funding by the South African Medical Research Council(SAMRC)through its Division of Research Capacity Development under the SAMRC Clinician Researcher ProgrammeResearch reported in this publication was also supported by the SAMRC under a Self-Initiated Research Grant to MS.
文摘Purpose The aim of the study was to identify factors associated with prolonged time to return to full performance(RTFP)in athletes with recent severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection.Methods Prospective cohort study with cross sectional analysis.A total of 84 athletes with confirmed SARS-CoV-2 infection assessed at a coronavirus disease 2019 recovery clinic gave a history of age,sex,type/level of sport,co-morbidities,pre-infection training hours,and 26 acute SARS-CoV-2 symptoms from 3 categories(“nose and throat”,“chest and neck”,and“whole body”/systemic).Data on days to RTFP were obtained by structured interviews.Factors associated with RTFP were demographics,sport participation,history of co-morbidities,pre-infection training history,and acute symptoms(type,number).Outcomes were:(a)days to RTFP(median,interquartile range(IQR))in asymptomatic(n=7)and symptomatic athletes(n=77),and(b)hazard ratios(HRs;95%confidence interval)for symptomatic athletes with vs.without a factor(univariate,multiple models).HR<1 was predictive of higher percentage chance of prolonged RTFP.Significance was p<0.05.Results Days to RTFP were 30 days(IQR:23–40)for asymptomatic and 64 days(IQR:42–91)for symptomatic participants(p>0.05).Factors associated with prolonged RTFP(univariate models)were:females(HR=0.57;p=0.014),endurance athletes(HR=0.41;p<0.0001),co-morbidity number(HR=0.75;p=0.001),and respiratory disease history(HR=0.54;p=0.026).In symptomatic athletes,prolonged RTFP(multiple models)was significantly associated with increased“chest and neck”(HR=0.85;p=0.017)and“nose and throat”(HR=0.84;p=0.013)symptoms,but the association was more profound between prolonged RFTP and increased total number of“all symptoms”(HR=0.91;p=0.001)and“whole body”/systemic(HR=0.82;p=0.007)symptoms.Conclusion A larger number of total symptoms and specifically“whole body”/systemic symptoms during the acute phase of SARS-CoV-2 infection in athletes is associated with prolonged RTFP.
基金Project(hx2013-87)supported by the Qingdao Economic and Technology Development Zone Haier Water-Heater Co.Ltd.,China
文摘In order to evaluate the heating performance of gas engine heat pump（GEHP） for air-conditioning and hot water supply, a test facility was developed and experiments were performed over a wide range of engine speed（1400-2600 r/min）, ambient air temperature（2.4-17.8 ℃） and condenser water inlet temperature（30-50℃）. The results show that as engine speed increases from 1400 r/min to 2600 r/min, the total heating capacity and energy consumption increase by about 30% and 89%, respectively; while the heat pump coefficient of performance（COP） and system primary energy ratio（PER） decrease by 44% and 31%, respectively. With the increase of ambient air temperature from 2.4 ℃ to 17.8 ℃, the heat pump COP and system PER increase by 32% and 19%, respectively. Moreover, the heat pump COP and system PER decrease by 27% and 15%, respectively, when the condenser water inlet temperature changes from 30 ℃ to 50 ℃. So, it is obvious that the effect of engine speed on the performance is more significant than the effects of ambient air temperature and condenser water inlet temperature.
基金supported by National Natural Science Foundation of China (Nos. 51407163, 51777025)National Rail Transportation Electrification and Automation Engineering Technology Research Center (No. NEEC-2017B07)+1 种基金China Postdoctoral Science Foundation (No. 2017M622370)Key scientific research projects of colleges and universities in Henan(16A470014, 19A470008)
文摘Vacuum gaps have rapid dynamic dielectric recovery speed while SF6 gaps have high insulation strength. The series-connected vacuum and SF6 gaps are used as the main switch(MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF6 gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance(DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker(VCB) and SF6 gas circuit breaker(GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker(CB) based on series-connected vacuum and SF6 gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage(TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.
文摘Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the world. The authors proposed the microplastics recovery device composed of the plates. Besides, the device consists of the tilted inlet/outlet and the horizontal part. In the water flow such as the tidal and ocean currents, the microplastics can be extracted from the main flow due to the vortex flow generated at the inner part of this device. In this research, the effects of the flow velocity and the inlet/outlet tilt angle on the capture performance were investigated experimentally and numerically. In the numerical simulations using the discrete phase model, the tilt angle was changed in a range between 30 degrees and 150 degrees in increments of 15 degrees, and the particle tracks of plastics were derived in steady condition. On the other hand, the capture performances in three cases of tilt angle 45 degrees, 120 degrees and 150 degrees were compared by circulation type water channel tests in which the plastics denser than the water were swept away 30 times every flow velocity. As the result, it seems that the tilt angle of 120 degrees is suitable for the wide range of the flow velocity in river and ocean.
文摘As of February 28th,2019,27 textile and apparel listed companies in Shanghai, Shenzhen and Hong Kong have unveiled their annual performance reports. Overall, most brands have achieved growth. There are 13 brands, accounting for 48% of the total, whose operating income and net profit increased.
文摘Purpose: The aim of the present study is to examine the performance of young Japanese cross-country skiers of different competitive levels with the use of Yo-Yo tests and the 12-minute run test (12MRT) that have been demonstrated to be related to each level, and to know which test is suitable for different competitive performance. Methods: Elite group (N = 9) was 16.9 ± 0.3 years and moderate trained group (N = 22) was 16.1 ± 0.9 years. The testing sessions consisted of the following: 1) Vertical jump and 50m sprint;2) the Yo-Yo tests level 1 and 2 (intermittent recovery);3) 12MRT. Results: Results showed the vertical jump heights and 50m sprint that no significant both performances differences were found among the two groups. Significant the Yo-Yo tests and 12MRT performances differences were found between the two groups (p < 0.05). Performance test (%) showed the ratio of moderate trained group towards elite group. The Yo-Yo tests performance was low enough compared with the result of 12MRT in moderate trained group. Conclusions: It is therefore valid to assume that low Yo-Yo tests performance due to immature anaerobic in cross-country skiers was a new limiting factor in the competitive level.
基金supported in part by the National Natural Science Foundation of China(Grant No.61974015)Key R&D Project of Science and Technology Plan of the Sichuan province(Grant No.2021YFG0139)the Open Foundation of State Key Laboratory of Electronic Thin Films and Integrated Devices of China(Grant No.KFJJ201806)。
文摘A new SiC superjunction power MOSFET device using high-k insulator and p-type pillar with an integrated Schottky barrier diode(Hk-SJ-SBD MOSFET)is proposed,and has been compared with the SiC high-k MOSFET(Hk MOSFET),SiC superjuction MOSFET(SJ MOSFET)and the conventional SiC MOSFET in this article.In the proposed SiC Hk-SJ-SBD MOSFET,under the combined action of the p-type region and the Hk dielectric layer in the drift region,the concentration of the N-drift region and the current spreading layer can be increased to achieve an ultra-low specific on-resistance(Ron,sp).The integrated Schottky barrier diode(SBD)also greatly improves the reverse recovery performance of the device.TCAD simulation results indicate that the Ron,sp of the proposed SiC Hk-SJ-SBD MOSFET is 0.67 mΩ·cm^(2)with a 2240 V breakdown voltage(BV),which is more than 72.4%,23%,5.6%lower than that of the conventional SiC MOSFET,Hk SiC MOSFET and SJ SiC MOSFET with the 1950,2220,and 2220V BV,respectively.The reverse recovery time and reverse recovery charge of the proposed MOSFET is 16 ns and18 nC,which are greatly reduced by more than 74%and 94%in comparison with those of all the conventional SiC MOSFET,Hk SiC MOSFET and SJ SiC MOSFET,due to the integrated SBD in the proposed MOSFET.And the trade-off relationship between the Ron,sp and the BV is also significantly improved compared with that of the conventional MOSFET,Hk MOSFET and SJ MOSFET as well as the MOSFETs in other previous literature,respectively.In addition,compared with conventional SJ SiC MOSFET,the proposed SiC MOSFET has better immunity to charge imbalance,which may bring great application prospects.
文摘Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.
基金supported by the National Key Research and Development Program of China(No.2022YFB4100500)National Natural Science Foundation of China(No.52276003 and 52206005)China Postdoctoral Science Foundation(No.2020M681452)。
文摘The recovery of heat and water from low-grade flue gas is of considerable importance for energy conservation and environmental preservation.While the full-open absorption heat pump shows promise as a means of achieving heat and water recovery,the lack of research on heat and mass transfer performance of open-type solution evaporation regeneration represents a significant impediment to its design and operation.This paper experimentally investigates the regeneration performance of an open-type spaying tower equipped with ceramic structured packings.Two different regeneration modes are proposed,namely ambient air receiver mode and flue gas receiver mode,to utilize air or low-grade flue gas as a driving source.The impact of different input parameters on the regeneration characteristics,including heat transfer capacity,water removal rate,thermal efficiency,and humidity effectiveness,are demonstrated.The findings indicate that the enhancement of regeneration can be achieved through the increase of solution flow rate,solution temperature,and flue gas flow rate in both regeneration modes.However,high solution concentration and flue gas humidity ratio can weaken water removal rates and reduce thermal efficiency.For the regeneration of CaCl_(2)-H_(2)O with a concentration of55%,flue gas around 200℃with a humidity ratio below 44 g/kg can successfully drive the solution regeneration process.When the solution concentration or flue gas humidity ratio continues to rise,additional energy is necessary for regeneration.Furthermore,the coupled heat and mass transfer coefficients are fitted,which can contribute to the design and optimization of the open-type regenerator.
文摘Stroke remains the leading cause of long-term disability.Hemiparesis is one of the most common post-stroke motor deficits and is largely attributed to loss or disruption of the motor signals from the affected motor cortex.As the only direct descending motor pathway,the corticospinal tract(CST)is the primary pathway to innervate spinal motor neurons,and thus,forms the neuroanatomical basis to control the peripheral muscles for voluntary movements.Here,we review evidence from both experimental animals and stroke patients,regarding CST axonal damage,functional contribution of CST axonal integrity and remodeling to neurological recovery,and therapeutic approaches aimed to enhance CST axonal remodeling after stroke.The new insights gleaned from preclinical and clinical studies may encourage the development of more rational therapeutics with a strategy targeted to promote axonal rewiring for corticospinal innervation,which will significantly impact the current clinical needs of subacute and chronic stroke treatment.
基金Supported by the National Major Special Project of Oil and Gas During the 13th Five-Year Plan Period(NO.2016ZX05058-003-010)General Program of National Natural Science Foundation of China(NO.51574086)Postdoctoral Innovative Talent Support Program of China(NO.BX20190065)。
文摘Taking reservoir rocks and fluids of the Daqing,Dagang and Changqing oilfields as research objects,the EOR mechanisms and technical approach of polymer flooding were discussed.By comparing the displacement performances of ordinary polymer,glycerol,polymer in"sheet-net"structure and heterogeneous weak gel at the same viscosity and concentration,the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated,and the method of improving polymer flooding effect was worked out.The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media.The viscosity of polymer agents has no positive correlation with polymer flooding effect.Although polymer of"sheet-net"structure has strong capacity in increasing viscosity,it has poor compatibility with pore throat structure of reservoir rock,low injectivity and low shear resistance.Heterogeneous weak gel system has higher adsorption and capture capacity in porous media,which is easy to retain in porous media,and can effectively establish seepage resistance in high permeability layers(zones).Compared with polymer solutions with the same viscosity or concentration,it has stronger ability to expand swept volume.Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal,and thus worsening of polymer flooding effect.Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.
基金Project(2009Gk2009)supported by the Science and Technology Department Funds of Hunan Province,ChinaProject(12C0379)supported by the Scientific Research Fund of Hunan Province,ChinaProject(13QDZ04)supported by the Scientific Research Foundation for Doctors of Xiang Tan University,China
文摘Dynamic performance is important to the controlling and monitoring of the organic Rankine cycle(ORC) system so to avoid the occurrence of unwanted conditions. A small scale waste heat recovery system with organic Rankine cycle was constructed and the dynamic behavior was presented. In the dynamic test, the pump was stopped and then started. In addition, there was a step change of the flue gas volume flow rate and the converter frequency of multistage pump, respectively. The results indicate that the working fluid flow rate has the shortest response time, followed by the expander inlet pressure and the expander inlet temperature.The operation frequency of pump is a key parameter for the ORC system. Due to a step change of pump frequency(39.49-35.24 Hz),the expander efficiency and thermal efficiency drop by 16% and 21% within 2 min, respectively. Besides, the saturated mixture can lead to an increase of the expander rotation speed.
文摘Concentrating Solar Power(CSP)plants offer a promising way to generate low-emission energy.However,these plants face challenges such as reduced sunlight during winter and cloudy days,despite being located in high solar radiation areas.Furthermore,their dispatch capacities and yields can be affected by high electricity consumption,particularly at night.The present work aims to develop an off-design model that evaluates the hourly and annual performances of a parabolic trough power plant(PTPP)equipped with a waste heat recovery system.The study aims to compare the performances of this new layout with those of the conventional Andasol 1 plant,with the aim of assessing the improvements achieved in the new design.Based on the results,it can be concluded that the new layout has increased the annual generated power to almost 183 GWh(an increase of about 7.60% is achieved compared to the Andasol 1 layout that generates 169 GWh annually).Additionally,the proposed installation has achieved an efficiency of 20.55%,which represents a 7.87% increase compared to the previous design(19.05%).The Levelized Cost of Electricity(LCOE)of the new layout has been reduced by more than 5.8% compared to the Andasol 1 plant.Specifically,it has decreased from 13.11 to 12.35 c/kWh.This reduction in LCOE highlights the improved cost-effectiveness of the newlayout,making it amore economically viable option for generating electricity compared to the conventional Andasol 1 plant.
文摘Probabilistic seismic performance assessment method for buildings offers a valuable approach to simulate the broader regional impacts:economic losses,downtime,and casualties.A crucial aspect of this process entails ac-counting for the spatial correlation of building performances,aiming for an accurate estimation of the probability of extreme regional losses,such as the simultaneous collapse of buildings with similar structural characteristics.In this study,a correlation model based on a Gaussian random field is employed,and several key challenges associated with its application are addressed.In addition,efficiency of five different methods of selecting station records from the same earthquake scenario is compared.The minimum number of earthquake records necessary to achieve a stable correlation result is determined.Additionally,spatial correlations derived from different his-tory earthquake events are compared.By addressing these critical issues,this research contributes to refining the reliability of probabilistic methods for regional resilience assessment.
