The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdow...The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdown delay time(T_(d))and breakdown strength(E_(b))were compared,based on analysis on the two breakdown modes namely wavefront mode and post-wave mode.It was found that T_(d) is more suitable to characterize the susceptibility of ore particles to electrical breakdown in HVP breakage than E_(b).A probabilistic model based on the Weibull distribution is developed to describe the relation of breakdown probability to T_(d).Regression analyses were conducted to investigate how operating parameters and particle properties influence Td and size reduction degree of ore particles in HVP breakage.The regressed models demonstrate potential capability to predict metallic minerals content and HVP breakage degree based on operating parameters and particle properties.展开更多
Dielectric ceramic capacitors have attracted significant interest in advanced pulsed power systems owing to their ultrahigh power density and fast charge/discharge capabilities. The low breakdown strength(E_(b)) of di...Dielectric ceramic capacitors have attracted significant interest in advanced pulsed power systems owing to their ultrahigh power density and fast charge/discharge capabilities. The low breakdown strength(E_(b)) of dielectric ceramics poses a major bottleneck for achieving high recoverable energy storage density(W rec). In this study, using ingenious chemical component design, we achieved an ultrahigh Eb of 800 kV/cm and an excellent W rec value of 9.48 J/cm^(3) in the simple component 0.92NaNbO_(3)–0.08SmFeO_(3) ceramic. Finite element simulations corroborate that the optimized grain boundary network enables more uniform electric field distribution and effective suppression of breakdown propagation. The superior energy storage characteristics originate from two synergistic mechanisms:(Ι) the incorporation of SmFeO_(3) suppresses grain growth, resulting in refined microstructure with increased grain boundary density that substantially enhances E_(b);(II) the introduction of Sm^(3+) and Fe^(3+) ions causes a mismatch between the A/B site ions, inducing lattice distortion and high disorder, which enhances the local random fields and relaxor behavior. This study establishes a promising pathway for designing high-energy-density dielectric ceramic capacitors.展开更多
In this letter,we demonstrate the effect ofγirradiation on the lateral AlGaN/GaN Schottky barrier diodes(SBDs)with self-terminated recessed anode structure and low work-function metal tungsten(W)as anode.For a compre...In this letter,we demonstrate the effect ofγirradiation on the lateral AlGaN/GaN Schottky barrier diodes(SBDs)with self-terminated recessed anode structure and low work-function metal tungsten(W)as anode.For a comprehensive evaluation of the radiation-resistance performance of the device,the total dose ofγirradiation is up to 100 kGy with irradiation time of 20 h.Attributed to the barrier lowering effect of the W/GaN interface induced byγirradiation observed in the experiment,the extracted turnon voltage(VON)defined at anode forward current of 1 mA decreases from 0.47 to 0.43 V.Meanwhile,benefiting from the reinforced Schottky interface treated by post-anode-annealing,a high breakdown voltage(BV)of 1.75 kV is obtained for theγ-irradiated AlGaN/GaN SBD,which shows the promising application for the deep-space radiation environment and promotes the development of radiation-resistance research for GaN SBDs.展开更多
Hydraulic fracturing is a commonly used stimulation technique for production optimization in various geological formations such as tight sandstone,shale,coal bed methane,and heat extraction in geothermal reservoirs.Br...Hydraulic fracturing is a commonly used stimulation technique for production optimization in various geological formations such as tight sandstone,shale,coal bed methane,and heat extraction in geothermal reservoirs.Breakdown pressure is a vital component in hydraulic fracture job design,which is affected by various parameters including rock strength and depth.Various methods including modelling and experimental approaches exist to quantify the breakdown pressure.There have been many strategies to reduce this pressure for efficient and economical hydraulic fracture jobs,especially when this pressure exceeds pump capacity.This study provides a detailed review of breakdown pressure in terms of fundamentals,influencing factors,and estimation approaches.In addition,different strategies are also presented to reduce the breakdown pressure along with cost analysis.Lastly,research gaps pertinent to this area are highlighted for emphasis in future research.Specifically,it has been found that high breakdown pressure is associated with challenges,but there are no comprehensive techniques and strategies to lower this pressure in formations with very high in situ stress profiles or complicated tectonic settings.Developing such methods is important to minimize operational failures,lower costs and reduce the environmental risks during reservoir exploitation.This study reviews the fundamentals,influencing factors,and estimation methods of breakdown pressure and provides a deep understanding of the strategies for its reduction.The study also presents the cost analyses,and highlights research gaps for future investigation.展开更多
A cylindrical chamber with a rotating bottom holds significant potential for application in cell culture bioreactors due to its ability to generate more stable swirling flows.In order to control vortex breakdown withi...A cylindrical chamber with a rotating bottom holds significant potential for application in cell culture bioreactors due to its ability to generate more stable swirling flows.In order to control vortex breakdown within the chamber,this study first establishes a computational fluid dynamics simulation coupled with the level set method.Verified by experimental results in literature,this method accurately simulates the position and shape of vortex breakdown,and also predicts the critical Reynolds numbers for the appearance and detachment of vortex breakdown bubbles from the center.Additionally,it precisely captures the gas-liquid interface and depicts the vortex breakdown phenomenon in the air above the liquid for the first time.Finally,it predicts the impact of physical property of gas-liquid systems on vortex breakdown in response to significant changes in viscosity of microbial process systems.展开更多
To delay the vortex breakdown position of the slender delta wing,this study innovativelyproposes the application of control near the Leading-Edge Vortex(LEV)core sweeping path,whichis called Coupled Core Rotation Dual...To delay the vortex breakdown position of the slender delta wing,this study innovativelyproposes the application of control near the Leading-Edge Vortex(LEV)core sweeping path,whichis called Coupled Core Rotation Dual Synthetic Jets(CCR-DSJ)control.The results show that thevortex breakdown points at each angle of attack are moved backward after control,and the max-imum delayed displacement is 32.4%of the root chord at 30°.Besides,there is a linear relationshipbetween the breakdown position and the angle of attack after control,indicating that CCR-DSJcontrol has a significant effect on the pressure gradient of the vortex axis.Furthermore,the lift coef-ficient C_(L)is enhanced after control,with a maximum CLincrement of 0.078 at 27°,and an effectiveincrement interval of[25°,32°].This interval is different from most previous studies,which isdirectly related to the position of the actuators.According to the lift change mechanism,the anglesof attack are divided into three stages:Stage 1(a=15°–25°),Stage 2(a=25°–32°),and Stage 3(a=32°–40°).In conclusion,CCR-DSJ control can significantly change the pressure distribution,thereby offering promising prospects for the flight stage of the slender delta wing.展开更多
This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the format...This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the formation ofβ-crystals in isotactic polypropylene(iPP)by adding aβ-nucleator.It examines how varying concentrations ofβ-nucleator and elastomer(POE)impact the aggregation structure of PP insulation and its conductivity and breakdown characteristics in the DC field.The results indicated that at aβ-nucleator agent content of 0.1 wt%,the samples with various POE contents achieved the highest crystallinity,the maximum proportion ofβ-crystals and the most uniform elastomer distribution.The nucleating agent facilitates the formation ofβ-crystals in PP and enhances the order degree of the elastomer molecular chains,thereby improving their crystallization capabilities.Evaluations of DC performances and trap characteristics reveal that when the amount of theβ-nucleator is set at 0.1 wt%,the sample demonstrates the lowest trap density,an exceptional and lower electric field coefficient of conductivity at elevated electric fields and a superior DC field breakdown strength at 90°C.Compared to samples withoutβ-nucleator,the reduction of DC field breakdown strength for PPBx-0.1 from 25°C to 90°C is approximately 4.86%lower.This improvement is attributed to the ability of theβ-nucleator to improve the aggregation structure between PP and POE while optimising the stability of the two-phase interface.Thus,although DC electrical characteristics are maintained at normal temperatures,the DC characteristics are significantly improved at elevated temperatures.展开更多
The demand for energy-efficient and environmental-friendly power grid construction has made the exploitation of bio-based electrical epoxy resins with excellent properties increasingly important.This work developed th...The demand for energy-efficient and environmental-friendly power grid construction has made the exploitation of bio-based electrical epoxy resins with excellent properties increasingly important.This work developed the bio-based electrotechnical epoxy resins based on magnolol.High-performance epoxy resin(DGEMT)with a double crosslinked points and its composites(Al_(2)O_(3)/DGEMT)were obtained taking advantages of the two bifunctional groups(allyl and phenolic hydroxyl groups)of magnolol.Benefitting from the distinctive structure of DGEMT,the Al_(2)O_(3)/DGEMT composites exhibited the advantages of intrinsically high thermal conductivity,high insulation,and low dielectric loss.The AC breakdown strength and thermal conductivity of Al_(2)O_(3)/DGEMT composites were 35.5 kV/mm and 1.19 W·m-1·K-1,respectively,which were 15.6%and 52.6%higher than those of petroleum-based composites(Al_(2)O_(3)/DGEBA).And its dielectric loss tanδ=0.0046 was 20.7%lower than that of Al_(2)O_(3)/DGEBA.Furthermore,the mechanical,thermal and processing properties of Al_(2)O_(3)/DGEMT are fully comparable to those of Al_(2)O_(3)/DGEBA.This work confirms the feasibility of manufacturing environmentally friendly power equipment using bio-based epoxy resins,which has excellent engineering applications.展开更多
Electrolyte selection for Plasma Electrolytic Oxidation(PEO)of magnesium is important as this determines composition,morphology and properties of resultant coatings that are urgently sought after for protection of Mg ...Electrolyte selection for Plasma Electrolytic Oxidation(PEO)of magnesium is important as this determines composition,morphology and properties of resultant coatings that are urgently sought after for protection of Mg alloys from corrosion and wear in harsh environments.However,electrolyte design is often performed heuristically,which hampers the development and optimisation of new PEO processes.Here,we attempt to achieve a mechanistic understanding of electrochemical and microstructural aspects of anodic films evolution at the prebreakdown stages of PEO treatments of magnesium in aqueous alkaline solutions of NaAlO_(2),Na_(3)PO_(4),Na F and Na_(2)SiO_(3).Systematic studies have shown that magnesium self-passivation by MgO/Mg(OH)_(2)can be compromised by both chemical and mechanical instabilities developed due to side effects of anodic reactions.Stable initiation of PEO process requires maintaining surface passivity in a wide range of p H,which can be achieved only by combining self-depositing passivators with those binding dissolved magnesium into insoluble compounds.展开更多
The protection effectiveness of traditional Lightning Strike Protection(LSP)for composite rotor blade of helicopter can be diminished due to the explosion risk in overlapping attachment under lightning strike,so a new...The protection effectiveness of traditional Lightning Strike Protection(LSP)for composite rotor blade of helicopter can be diminished due to the explosion risk in overlapping attachment under lightning strike,so a new protection method based on Air Breakdown and insulating adhesive layer(AB-LSP method)was designed to avoid it.In this study,a numerical method was developed to simulate the electrical breakdown,and verified by experiment results.Based on this method,a Finite Element Model(FEM)was established to investigate the effect of two factors(breakdown strength and initial ablation temperature of adhesive layer)on the LSP effectiveness.The results show that the breakdown strength impacts more to the ablation damage in composite than that of high-temperature resistance.Then,another FEM was established to predict the ablation damage by lightning strike in the AB-LSP method protected composite rotor blade.The mechanisms and potential key parameters(magnitude of lightning current,discharge channel location,adhesive layer thickness,and air gap width)that could affect the protection effectiveness were analyzed.The introduction of air breakdown changes the current conduction path and reduces explosion risk.After rational design,this method can offer effective lightning protection for composite helicopter rotor blade and other composite structures.展开更多
Scrap metals are typically covered with surface contaminants,such as paint,dust,and rust,which can significantly affect the emission spectrum during laser-induced breakdown spectroscopy(LIBS)based sorting.In this stud...Scrap metals are typically covered with surface contaminants,such as paint,dust,and rust,which can significantly affect the emission spectrum during laser-induced breakdown spectroscopy(LIBS)based sorting.In this study,the effects of paint layers on metal surfaces during LIBS classification were investigated.LIBS spectra were collected from metal surfaces painted with black and white paints by ablation with a nanosecond pulsed laser(wavelength=1064 nm,pulse width=7 ns).For the black-painted samples,the LIBS spectra showed a broad background emission,emission lines unrelated to the target metals,large shot-to-shot variation,and a relatively low signal intensity of the target metal,causing poor classification accuracy even at high shot numbers.Cleaning the black paint layer by ablating over a wide area prior to LIBS analysis resulted in high classification accuracy with fewer shot numbers.A method to determine the number of cleaning shots necessary to obtain high classification accuracy and high throughput is proposed on the basis of the change in LIBS signal intensity during cleaning shots.For the white-painted samples,the paint peeled off the metal surface after the first shot,and strong LIBS signals were measured after the following shot,which were attributed to the nanoparticles generated by the ablation of the paint,allowing an accurate classification after only two shots.The results demonstrate that different approaches must be employed depending on the paint color to achieve high classification accuracy with fewer shot numbers.展开更多
Horizontal well intensive fracturing is a critical technology used to stimulate unconventional oil and gas reservoirs.Accurate prediction of wellbore breakdown pressure is conducive to optimal fracturing design and im...Horizontal well intensive fracturing is a critical technology used to stimulate unconventional oil and gas reservoirs.Accurate prediction of wellbore breakdown pressure is conducive to optimal fracturing design and improvement of the reservoir stimulation effect.In this work,the three-dimensional displacement discontinuity method(DDM)is used to characterize fracture deformation and fracture closure after the pumping pressure relief.The influences of key parameters such as the minimum horizontal principal stress,fracture spacing,the Young's modulus,the Poisson's ratio and pumping pressure on the breakdown pressure are analyzed.The results show that,assuming that the fracture half-length is a,the breakdown pressure outside the fracture surface area increases significantly within 2a in the direction of the minimum horizontal principal stress and a in the directions of the vertical stress and maximum horizontal principal stress before pressure relief.The breakdown pressure of the modified zipper-type fracturing in the later stage is lower.When the fracture spacing is small,the fracture breakdown pressure decreases after the modified zipper-type fracturing of two horizontal wells.The fracture breakdown pressure of the first fractured well reaches a maximum when the fracture spacing is a-1.5a,and the breakdown pressure decreases with increasing well spacing.展开更多
Space ion electric propulsion has been widely used in the north-south position maintenance and orbit transfer missions for high-orbit satellites.However,unexpected electric breakdown by ion electric propulsion systems...Space ion electric propulsion has been widely used in the north-south position maintenance and orbit transfer missions for high-orbit satellites.However,unexpected electric breakdown by ion electric propulsion systems is still a challenging problem that needs to be solved,as it affects reliability.Based on the analysis of in-orbit and ground test data of ion thrusters from simulation and experimental results,the main influencing factors of induced electric breakdown are clarified and the mechanisms of induced electric breakdown are analyzed.It is found that the main factors inducing breakdown are the voltage and electric field strength between the grids.In addition,by monitoring the waveform of plasma discharge,the temporal characteristics of breakdown can be defined as three stages of“breakdown-spark-loop response”.Thus,three kinds of engineering suppression methods for breakdown of static vacuum with periodic short-term heating,electrode surface polishing and sealing insulation with plasma,add energy suppression circuit are carried out,and the experimental results show that the electric breakdown frequency can be reduced by about 30%.展开更多
An analytical breakdown model under on state condition for high voltage RESURF LDMOS is proposed.The model considers the drift velocity saturation of carriers and influence of parasitic bipolar transistor.As a result...An analytical breakdown model under on state condition for high voltage RESURF LDMOS is proposed.The model considers the drift velocity saturation of carriers and influence of parasitic bipolar transistor.As a result,electric field profile of n drift in LDMOS at on state is obtained.Based on this model,the electric SOA of LDMOS can be determined.The analytical results partially fit to our numerical (by MEDICI) and experiment results.This model is an aid to understand the device physics during on state accurately and it also directs high voltage LDMOS design.展开更多
FB （floating-body） and BC （body-contact） partially depleted SOI nMOSFETs with HBC（half-back-channel） implantation are fabricated. Test results show that such devices have good performance in delaying the occurre...FB （floating-body） and BC （body-contact） partially depleted SOI nMOSFETs with HBC（half-back-channel） implantation are fabricated. Test results show that such devices have good performance in delaying the occurrence of the “kink” phenomenon and improving the breakdown voltage as compared to conventional PDSOI nMOS- FETs,while not decreasing the threshold voltage of the back gate obviously. Numerical simulation shows that a reduced electrical field in the drain contributes to the improvement of the breakdown voltage and a delay of the “kink” effect. A detailed analysis is given for the cause of such improvement of breakdown voltage and the delay of the “kink” effect.展开更多
Breakdown voltage （Vbd） and charge to breakdown （Qbd） are two parameters often used to evaluate gate oxide reliability. In this paper,we investigate the effects of measurement methods on Vbd and Qbd of the gate ox...Breakdown voltage （Vbd） and charge to breakdown （Qbd） are two parameters often used to evaluate gate oxide reliability. In this paper,we investigate the effects of measurement methods on Vbd and Qbd of the gate oxide of a 0.18μm dual gate CMOS process. Voltage ramps （V-ramp） and current ramps （J-ramp） are used to evaluate gate oxide reliability. The thin and thick gate oxides are all evaluated in the accumulation condition. Our experimental results show that the measurement methods affect Vbd only slightly but affect Qbd seriously,as do the measurement conditions.This affects the I-t curves obtained with the J-ramp and V-ramp methods. From the I-t curve,it can be seen that Qbd obtained using a J-ramp is much bigger than that with a V-ramp. At the same time, the Weibull slopes of Qbd are definitely smaller than those of Vbd. This means that Vbd is more reliable than Qbd, Thus we should be careful to use Qbd to evaluate the reliability of 0.18μm or beyond CMOS process gate oxide.展开更多
A unified breakdown model of SOI RESURF device with uniform,step,or linear drift region doping profile is firstly proposed.By the model,the electric field distribution and breakdown voltage are researched in detail fo...A unified breakdown model of SOI RESURF device with uniform,step,or linear drift region doping profile is firstly proposed.By the model,the electric field distribution and breakdown voltage are researched in detail for the step numbers from 0 to infinity.The critic electric field as the function of the geometry parameters and doping profile is derived.For the thick film device,linear doping profile can be replaced by a single or two steps doping profile in the drift region due to a considerable uniformly lateral electric field,almost ideal breakdown voltage,and simplified design and fabrication.The availability of the proposed model is verified by the good accordance among the analytical results,numerical simulations,and reported experiments.展开更多
基金The financial supports from National Natural Science Foundation of China(Nos.52574313,52204272 and 52074091)to this project。
文摘The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdown delay time(T_(d))and breakdown strength(E_(b))were compared,based on analysis on the two breakdown modes namely wavefront mode and post-wave mode.It was found that T_(d) is more suitable to characterize the susceptibility of ore particles to electrical breakdown in HVP breakage than E_(b).A probabilistic model based on the Weibull distribution is developed to describe the relation of breakdown probability to T_(d).Regression analyses were conducted to investigate how operating parameters and particle properties influence Td and size reduction degree of ore particles in HVP breakage.The regressed models demonstrate potential capability to predict metallic minerals content and HVP breakage degree based on operating parameters and particle properties.
基金supported by the National Natural Science Foundation of China (Grant Nos.52462018,52162019)the Key Project of the Natural Science Foundation of Jiangxi Province (Grant No.20252BAC250038)the Science Fund for Distinguished Young Scholars of Jiangxi Province (Grant No.20224ACB214007)。
文摘Dielectric ceramic capacitors have attracted significant interest in advanced pulsed power systems owing to their ultrahigh power density and fast charge/discharge capabilities. The low breakdown strength(E_(b)) of dielectric ceramics poses a major bottleneck for achieving high recoverable energy storage density(W rec). In this study, using ingenious chemical component design, we achieved an ultrahigh Eb of 800 kV/cm and an excellent W rec value of 9.48 J/cm^(3) in the simple component 0.92NaNbO_(3)–0.08SmFeO_(3) ceramic. Finite element simulations corroborate that the optimized grain boundary network enables more uniform electric field distribution and effective suppression of breakdown propagation. The superior energy storage characteristics originate from two synergistic mechanisms:(Ι) the incorporation of SmFeO_(3) suppresses grain growth, resulting in refined microstructure with increased grain boundary density that substantially enhances E_(b);(II) the introduction of Sm^(3+) and Fe^(3+) ions causes a mismatch between the A/B site ions, inducing lattice distortion and high disorder, which enhances the local random fields and relaxor behavior. This study establishes a promising pathway for designing high-energy-density dielectric ceramic capacitors.
基金supported in part by the Key Research and Development Projects of Shaanxi Province(Grant No.2024GX-YBXM-082)in part by the Natural Science Basic Research Program of Shaanxi Province(Grant No.2023-JC-JQ-56)+2 种基金in part by the Fundamental Research Funds for the Central Universities(Grant Nos.QTZX23076,XJSJ25014)in part by the funding of the National Key Research and Development Program of China(Grant No.2022YFB3604400)in part by the China Postdoctoral Science Foundation(Grant No.2021TQ0256).
文摘In this letter,we demonstrate the effect ofγirradiation on the lateral AlGaN/GaN Schottky barrier diodes(SBDs)with self-terminated recessed anode structure and low work-function metal tungsten(W)as anode.For a comprehensive evaluation of the radiation-resistance performance of the device,the total dose ofγirradiation is up to 100 kGy with irradiation time of 20 h.Attributed to the barrier lowering effect of the W/GaN interface induced byγirradiation observed in the experiment,the extracted turnon voltage(VON)defined at anode forward current of 1 mA decreases from 0.47 to 0.43 V.Meanwhile,benefiting from the reinforced Schottky interface treated by post-anode-annealing,a high breakdown voltage(BV)of 1.75 kV is obtained for theγ-irradiated AlGaN/GaN SBD,which shows the promising application for the deep-space radiation environment and promotes the development of radiation-resistance research for GaN SBDs.
文摘Hydraulic fracturing is a commonly used stimulation technique for production optimization in various geological formations such as tight sandstone,shale,coal bed methane,and heat extraction in geothermal reservoirs.Breakdown pressure is a vital component in hydraulic fracture job design,which is affected by various parameters including rock strength and depth.Various methods including modelling and experimental approaches exist to quantify the breakdown pressure.There have been many strategies to reduce this pressure for efficient and economical hydraulic fracture jobs,especially when this pressure exceeds pump capacity.This study provides a detailed review of breakdown pressure in terms of fundamentals,influencing factors,and estimation approaches.In addition,different strategies are also presented to reduce the breakdown pressure along with cost analysis.Lastly,research gaps pertinent to this area are highlighted for emphasis in future research.Specifically,it has been found that high breakdown pressure is associated with challenges,but there are no comprehensive techniques and strategies to lower this pressure in formations with very high in situ stress profiles or complicated tectonic settings.Developing such methods is important to minimize operational failures,lower costs and reduce the environmental risks during reservoir exploitation.This study reviews the fundamentals,influencing factors,and estimation methods of breakdown pressure and provides a deep understanding of the strategies for its reduction.The study also presents the cost analyses,and highlights research gaps for future investigation.
基金National Natural Science Foundation of China(22178228,22178326)
文摘A cylindrical chamber with a rotating bottom holds significant potential for application in cell culture bioreactors due to its ability to generate more stable swirling flows.In order to control vortex breakdown within the chamber,this study first establishes a computational fluid dynamics simulation coupled with the level set method.Verified by experimental results in literature,this method accurately simulates the position and shape of vortex breakdown,and also predicts the critical Reynolds numbers for the appearance and detachment of vortex breakdown bubbles from the center.Additionally,it precisely captures the gas-liquid interface and depicts the vortex breakdown phenomenon in the air above the liquid for the first time.Finally,it predicts the impact of physical property of gas-liquid systems on vortex breakdown in response to significant changes in viscosity of microbial process systems.
基金supported by the National Natural Science Foundation of China(Nos.92271110,12072352)the Major National Science and Technology Project,China(No.J2019-Ⅲ-0010-0054)。
文摘To delay the vortex breakdown position of the slender delta wing,this study innovativelyproposes the application of control near the Leading-Edge Vortex(LEV)core sweeping path,whichis called Coupled Core Rotation Dual Synthetic Jets(CCR-DSJ)control.The results show that thevortex breakdown points at each angle of attack are moved backward after control,and the max-imum delayed displacement is 32.4%of the root chord at 30°.Besides,there is a linear relationshipbetween the breakdown position and the angle of attack after control,indicating that CCR-DSJcontrol has a significant effect on the pressure gradient of the vortex axis.Furthermore,the lift coef-ficient C_(L)is enhanced after control,with a maximum CLincrement of 0.078 at 27°,and an effectiveincrement interval of[25°,32°].This interval is different from most previous studies,which isdirectly related to the position of the actuators.According to the lift change mechanism,the anglesof attack are divided into three stages:Stage 1(a=15°–25°),Stage 2(a=25°–32°),and Stage 3(a=32°–40°).In conclusion,CCR-DSJ control can significantly change the pressure distribution,thereby offering promising prospects for the flight stage of the slender delta wing.
基金supported by China Southern Power Grid Company Limited(Grant GDKJXM20222136).
文摘This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the formation ofβ-crystals in isotactic polypropylene(iPP)by adding aβ-nucleator.It examines how varying concentrations ofβ-nucleator and elastomer(POE)impact the aggregation structure of PP insulation and its conductivity and breakdown characteristics in the DC field.The results indicated that at aβ-nucleator agent content of 0.1 wt%,the samples with various POE contents achieved the highest crystallinity,the maximum proportion ofβ-crystals and the most uniform elastomer distribution.The nucleating agent facilitates the formation ofβ-crystals in PP and enhances the order degree of the elastomer molecular chains,thereby improving their crystallization capabilities.Evaluations of DC performances and trap characteristics reveal that when the amount of theβ-nucleator is set at 0.1 wt%,the sample demonstrates the lowest trap density,an exceptional and lower electric field coefficient of conductivity at elevated electric fields and a superior DC field breakdown strength at 90°C.Compared to samples withoutβ-nucleator,the reduction of DC field breakdown strength for PPBx-0.1 from 25°C to 90°C is approximately 4.86%lower.This improvement is attributed to the ability of theβ-nucleator to improve the aggregation structure between PP and POE while optimising the stability of the two-phase interface.Thus,although DC electrical characteristics are maintained at normal temperatures,the DC characteristics are significantly improved at elevated temperatures.
基金supported by the China Postdoctoral Science Foundation(No.2023M743622)Natural Science Foundation of Ningbo City(No.2024J109)+2 种基金National Natural Science Foundation of China(Nos.E52307038 and U23A20589)Ningbo 2025 Key Scientific Research Programs(Nos.2022Z111,2022Z160 and 2022Z198)the Leading Innovativeand Entrepreneur Team Introduction Program of Zhejiang(No.2021R01005).
文摘The demand for energy-efficient and environmental-friendly power grid construction has made the exploitation of bio-based electrical epoxy resins with excellent properties increasingly important.This work developed the bio-based electrotechnical epoxy resins based on magnolol.High-performance epoxy resin(DGEMT)with a double crosslinked points and its composites(Al_(2)O_(3)/DGEMT)were obtained taking advantages of the two bifunctional groups(allyl and phenolic hydroxyl groups)of magnolol.Benefitting from the distinctive structure of DGEMT,the Al_(2)O_(3)/DGEMT composites exhibited the advantages of intrinsically high thermal conductivity,high insulation,and low dielectric loss.The AC breakdown strength and thermal conductivity of Al_(2)O_(3)/DGEMT composites were 35.5 kV/mm and 1.19 W·m-1·K-1,respectively,which were 15.6%and 52.6%higher than those of petroleum-based composites(Al_(2)O_(3)/DGEBA).And its dielectric loss tanδ=0.0046 was 20.7%lower than that of Al_(2)O_(3)/DGEBA.Furthermore,the mechanical,thermal and processing properties of Al_(2)O_(3)/DGEMT are fully comparable to those of Al_(2)O_(3)/DGEBA.This work confirms the feasibility of manufacturing environmentally friendly power equipment using bio-based epoxy resins,which has excellent engineering applications.
基金supported by the UK EPSRC(grant EP/T024607/1,‘Coat IN’)provided by the Henry Royce Institute for Advanced Materials,funded through the UK EPSRC grants EP/R00661X/1,EP/S019367/1,EP/P025021/1 and EP/P025498/1support from the University of Manchester and Chinese Scholarship Council for his Ph D studies。
文摘Electrolyte selection for Plasma Electrolytic Oxidation(PEO)of magnesium is important as this determines composition,morphology and properties of resultant coatings that are urgently sought after for protection of Mg alloys from corrosion and wear in harsh environments.However,electrolyte design is often performed heuristically,which hampers the development and optimisation of new PEO processes.Here,we attempt to achieve a mechanistic understanding of electrochemical and microstructural aspects of anodic films evolution at the prebreakdown stages of PEO treatments of magnesium in aqueous alkaline solutions of NaAlO_(2),Na_(3)PO_(4),Na F and Na_(2)SiO_(3).Systematic studies have shown that magnesium self-passivation by MgO/Mg(OH)_(2)can be compromised by both chemical and mechanical instabilities developed due to side effects of anodic reactions.Stable initiation of PEO process requires maintaining surface passivity in a wide range of p H,which can be achieved only by combining self-depositing passivators with those binding dissolved magnesium into insoluble compounds.
文摘The protection effectiveness of traditional Lightning Strike Protection(LSP)for composite rotor blade of helicopter can be diminished due to the explosion risk in overlapping attachment under lightning strike,so a new protection method based on Air Breakdown and insulating adhesive layer(AB-LSP method)was designed to avoid it.In this study,a numerical method was developed to simulate the electrical breakdown,and verified by experiment results.Based on this method,a Finite Element Model(FEM)was established to investigate the effect of two factors(breakdown strength and initial ablation temperature of adhesive layer)on the LSP effectiveness.The results show that the breakdown strength impacts more to the ablation damage in composite than that of high-temperature resistance.Then,another FEM was established to predict the ablation damage by lightning strike in the AB-LSP method protected composite rotor blade.The mechanisms and potential key parameters(magnitude of lightning current,discharge channel location,adhesive layer thickness,and air gap width)that could affect the protection effectiveness were analyzed.The introduction of air breakdown changes the current conduction path and reduces explosion risk.After rational design,this method can offer effective lightning protection for composite helicopter rotor blade and other composite structures.
基金supported by the R&D Center for Valuable Recycling (Global-Top R&D Program)of the Ministry of Environment (No.2016002250003)。
文摘Scrap metals are typically covered with surface contaminants,such as paint,dust,and rust,which can significantly affect the emission spectrum during laser-induced breakdown spectroscopy(LIBS)based sorting.In this study,the effects of paint layers on metal surfaces during LIBS classification were investigated.LIBS spectra were collected from metal surfaces painted with black and white paints by ablation with a nanosecond pulsed laser(wavelength=1064 nm,pulse width=7 ns).For the black-painted samples,the LIBS spectra showed a broad background emission,emission lines unrelated to the target metals,large shot-to-shot variation,and a relatively low signal intensity of the target metal,causing poor classification accuracy even at high shot numbers.Cleaning the black paint layer by ablating over a wide area prior to LIBS analysis resulted in high classification accuracy with fewer shot numbers.A method to determine the number of cleaning shots necessary to obtain high classification accuracy and high throughput is proposed on the basis of the change in LIBS signal intensity during cleaning shots.For the white-painted samples,the paint peeled off the metal surface after the first shot,and strong LIBS signals were measured after the following shot,which were attributed to the nanoparticles generated by the ablation of the paint,allowing an accurate classification after only two shots.The results demonstrate that different approaches must be employed depending on the paint color to achieve high classification accuracy with fewer shot numbers.
基金supported by the National Natural Science Foundation of China,China(No.52074250).
文摘Horizontal well intensive fracturing is a critical technology used to stimulate unconventional oil and gas reservoirs.Accurate prediction of wellbore breakdown pressure is conducive to optimal fracturing design and improvement of the reservoir stimulation effect.In this work,the three-dimensional displacement discontinuity method(DDM)is used to characterize fracture deformation and fracture closure after the pumping pressure relief.The influences of key parameters such as the minimum horizontal principal stress,fracture spacing,the Young's modulus,the Poisson's ratio and pumping pressure on the breakdown pressure are analyzed.The results show that,assuming that the fracture half-length is a,the breakdown pressure outside the fracture surface area increases significantly within 2a in the direction of the minimum horizontal principal stress and a in the directions of the vertical stress and maximum horizontal principal stress before pressure relief.The breakdown pressure of the modified zipper-type fracturing in the later stage is lower.When the fracture spacing is small,the fracture breakdown pressure decreases after the modified zipper-type fracturing of two horizontal wells.The fracture breakdown pressure of the first fractured well reaches a maximum when the fracture spacing is a-1.5a,and the breakdown pressure decreases with increasing well spacing.
文摘Space ion electric propulsion has been widely used in the north-south position maintenance and orbit transfer missions for high-orbit satellites.However,unexpected electric breakdown by ion electric propulsion systems is still a challenging problem that needs to be solved,as it affects reliability.Based on the analysis of in-orbit and ground test data of ion thrusters from simulation and experimental results,the main influencing factors of induced electric breakdown are clarified and the mechanisms of induced electric breakdown are analyzed.It is found that the main factors inducing breakdown are the voltage and electric field strength between the grids.In addition,by monitoring the waveform of plasma discharge,the temporal characteristics of breakdown can be defined as three stages of“breakdown-spark-loop response”.Thus,three kinds of engineering suppression methods for breakdown of static vacuum with periodic short-term heating,electrode surface polishing and sealing insulation with plasma,add energy suppression circuit are carried out,and the experimental results show that the electric breakdown frequency can be reduced by about 30%.
文摘An analytical breakdown model under on state condition for high voltage RESURF LDMOS is proposed.The model considers the drift velocity saturation of carriers and influence of parasitic bipolar transistor.As a result,electric field profile of n drift in LDMOS at on state is obtained.Based on this model,the electric SOA of LDMOS can be determined.The analytical results partially fit to our numerical (by MEDICI) and experiment results.This model is an aid to understand the device physics during on state accurately and it also directs high voltage LDMOS design.
文摘FB （floating-body） and BC （body-contact） partially depleted SOI nMOSFETs with HBC（half-back-channel） implantation are fabricated. Test results show that such devices have good performance in delaying the occurrence of the “kink” phenomenon and improving the breakdown voltage as compared to conventional PDSOI nMOS- FETs,while not decreasing the threshold voltage of the back gate obviously. Numerical simulation shows that a reduced electrical field in the drain contributes to the improvement of the breakdown voltage and a delay of the “kink” effect. A detailed analysis is given for the cause of such improvement of breakdown voltage and the delay of the “kink” effect.
文摘Breakdown voltage （Vbd） and charge to breakdown （Qbd） are two parameters often used to evaluate gate oxide reliability. In this paper,we investigate the effects of measurement methods on Vbd and Qbd of the gate oxide of a 0.18μm dual gate CMOS process. Voltage ramps （V-ramp） and current ramps （J-ramp） are used to evaluate gate oxide reliability. The thin and thick gate oxides are all evaluated in the accumulation condition. Our experimental results show that the measurement methods affect Vbd only slightly but affect Qbd seriously,as do the measurement conditions.This affects the I-t curves obtained with the J-ramp and V-ramp methods. From the I-t curve,it can be seen that Qbd obtained using a J-ramp is much bigger than that with a V-ramp. At the same time, the Weibull slopes of Qbd are definitely smaller than those of Vbd. This means that Vbd is more reliable than Qbd, Thus we should be careful to use Qbd to evaluate the reliability of 0.18μm or beyond CMOS process gate oxide.
文摘A unified breakdown model of SOI RESURF device with uniform,step,or linear drift region doping profile is firstly proposed.By the model,the electric field distribution and breakdown voltage are researched in detail for the step numbers from 0 to infinity.The critic electric field as the function of the geometry parameters and doping profile is derived.For the thick film device,linear doping profile can be replaced by a single or two steps doping profile in the drift region due to a considerable uniformly lateral electric field,almost ideal breakdown voltage,and simplified design and fabrication.The availability of the proposed model is verified by the good accordance among the analytical results,numerical simulations,and reported experiments.
