Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioni...Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.展开更多
Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been...Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.展开更多
The electrolysis of water powered by renewable energy sources offers a promising method of"green hydrogen"production,which is considered to be at the heart of future carbon-neutral energy systems.In the past...The electrolysis of water powered by renewable energy sources offers a promising method of"green hydrogen"production,which is considered to be at the heart of future carbon-neutral energy systems.In the past decades,researchers have reported a number of hydrogen evolution reaction(HER)electrocatalysts with activity comparable to that of commercial Pt/C,but most of them are tested within a small current density range,typically no more than 500 mA cm^(-2).To realize the industrial application of hydrogen production from water electrolysis,it is essential to develop high-efficiency HER electrocatalysts at high current density(HCD≥500 mA cm^(-2)).Nevertheless,it remains challenging and significant to rational design HCD electrocatalysts for HER.In this paper,the design strategy of HCD electrocatalysts is discussed,and some HCD electrocatalysts for HER are reviewed in seven categories(alloy,metal oxide,metal hydroxide,metal sulfide/selenide,metal nitride,metal phosphide and other derived electrocatalysts).At the end of this article,we also pro-pose some viewpoints and prospects for the future development and research directions of HCD electrocatalysts for HER.展开更多
Forecasting of ocean currents is critical for both marine meteorological research and ocean engineering and construction.Timely and accurate forecasting of coastal current velocities offers a scientific foundation and...Forecasting of ocean currents is critical for both marine meteorological research and ocean engineering and construction.Timely and accurate forecasting of coastal current velocities offers a scientific foundation and decision support for multiple practices such as search and rescue,disaster avoidance and remediation,and offshore construction.This research established a framework to generate short-term surface current forecasts based on ensemble machine learning trained on high frequency radar observation.Results indicate that an ensemble algorithm that used random forests to filter forecasting features by weighting them,and then used the AdaBoost method to forecast can significantly reduce the model training time,while ensuring the model forecasting effectiveness,with great economic benefits.Model accuracy is a function of surface current variability and the forecasting horizon.In order to improve the forecasting capability and accuracy of the model,the model structure of the ensemble algorithm was optimized,and the random forest algorithm was used to dynamically select model features.The results show that the error variation of the optimized surface current forecasting model has a more regular error variation,and the importance of the features varies with the forecasting time-step.At ten-step ahead forecasting horizon the model reported root mean square error,mean absolute error,and correlation coefficient by 2.84 cm/s,2.02 cm/s,and 0.96,respectively.The model error is affected by factors such as topography,boundaries,and geometric accuracy of the observation system.This paper demonstrates the potential of ensemble-based machine learning algorithm to improve forecasting of ocean currents.展开更多
When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop thr...When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.展开更多
A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the allo...A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.展开更多
The reverse generation current under high-gate-voltage stress condition in LDD nMOSFET＇s is studied. We find that the generation current peak decreases as the stress time increases. We ascribe this finding to the dom...The reverse generation current under high-gate-voltage stress condition in LDD nMOSFET＇s is studied. We find that the generation current peak decreases as the stress time increases. We ascribe this finding to the dominating oxide trapped electrons that reduce the effective drain bias, lowering the maximal generation rate. The density of the effective trapped electrons affecting the effective drain bias is calculated with our model.展开更多
The MOSFET gate currents of high k gate dielectrics due to direct tunneling are investigated by using a new direct tunneling current model developed.The model includes both the inversion layer quantization effect with...The MOSFET gate currents of high k gate dielectrics due to direct tunneling are investigated by using a new direct tunneling current model developed.The model includes both the inversion layer quantization effect with finite barrier height and the polysilicon depletion effect.The impacts of dielectric constant and conduction band offset as well as the band gap on the gate current are discussed.The results indicate that the gate dielectric materials with higher dielectric constant,larger conduction band offset and the larger band gap are necessary to reduce the gate current.The calculated results can be used as a guide to select the appropriate high k gate dielectric materials for MOSFETs.展开更多
In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed ...In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.展开更多
Neutral beam injection is one of the main plasma heating methods in nuclear fusion devices. In order to support the scientific study of the Experimental Advanced Superconducting Tokamak （EAST）, a megawatt-level high...Neutral beam injection is one of the main plasma heating methods in nuclear fusion devices. In order to support the scientific study of the Experimental Advanced Superconducting Tokamak （EAST）, a megawatt-level high current ion source is designed and manufactured in the ASIPP, and the progress and preliminary test results will be presented in this paper.展开更多
By means of flow visualization and quantitative measurement, the diffusion pattern and concentration distribution characteristics of high concentration jets vertically discharged into shallow moving waterbody were exp...By means of flow visualization and quantitative measurement, the diffusion pattern and concentration distribution characteristics of high concentration jets vertically discharged into shallow moving waterbody were experimentally investigated in water channel. The interactions between the high concentration jets and environmental flow conditions were analysed, and the formulae of impinging point coordinate and transverse spread angle are gained from data analysis. Experimental results indicate that the jets show complicated flow patterns and diffusion characteristics in near region, which are different from common submerged jets, and spread downstream in the manner of density currents.展开更多
Electrocoagulation process using high current intensity to treat palm oil mill effluent(POME) was investigated in this study.Various operating parameters such as electrolysis time, inter-electrode distance and initial...Electrocoagulation process using high current intensity to treat palm oil mill effluent(POME) was investigated in this study.Various operating parameters such as electrolysis time, inter-electrode distance and initial pH were carried out to determine the efficient process condition on the removal of chemical oxygen demand(COD),biological oxygen demand(BOD) and suspended solids(SS).The highest treatment was achieved at 50 min with the removal efficiencies for COD, BOD and SS obtained as 85%, 83%, and 84%, respectively.More than 50 min treatment showed the fluctuated trends of removal efficiencies which can be considered insignificant.The application of higher current resulted in higher removals of organics while the gas bubbles also assisted in removing the pollutant particles by floatation.In an inter-electrode distance study, the removal efficiency decreased when inter-electrode distance was either higher or lower than 10 mm due to the increase of solution resistance and the decrease of anode active surface area.In initial pH study, it was found that high removal efficiencies were achieved in slightly acidic POME sample rather than in neutral or basic condition.An electrocoagulation process by using the optimum operating parameters was able to remove COD, BOD and SS up to 95%, 94% and 96% respectively.The experimental results confirm that application of high current intensity in electrocoagulation provided high treatment efficiency at a reduced reaction time.展开更多
Developing highly effective and stable non-noble metalbased bifunctional catalyst working at high current density is an urgent issue for water electrolysis(WE).Herein,we prepare the N-doped graphene-decorated NiCo all...Developing highly effective and stable non-noble metalbased bifunctional catalyst working at high current density is an urgent issue for water electrolysis(WE).Herein,we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam(NiCo@C-NiCoMoO/NF)for water splitting.NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction(HER:39/266 mV;OER:260/390 mV)at±10 and±1000 mA cm^(−2).More importantly,in 6.0 M KOH solution at 60℃ for WE,it only requires 1.90 V to reach 1000 mA cm−2 and shows excellent stability for 43 h,exhibiting the potential for actual application.The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet,which not only increase the intrinsic activity and expose abundant catalytic activity sites,but also enhance its chemical and mechanical stability.This work thus could provide a promising material for industrial hydrogen production.展开更多
Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process a...Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.展开更多
Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of ...Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis： the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.展开更多
In this study, compounded surface modification technology-high current pulsed electron beam （HCPEB） ＋ micro-plasma oxidation （MPO） was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of...In this study, compounded surface modification technology-high current pulsed electron beam （HCPEB） ＋ micro-plasma oxidation （MPO） was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of ZK60 Mg alloy after single MPO and HCPEB＋MPO compounded treatment were investigated by SEM. The results showed that the density of the ceramic layer of HCPEB＋MPO-treated ZK60 Mg alloy was improved and defects were reduced compared to that under MPO treatment alone. Surface modified layer of ZK60 Mg alloys treated by HCPEB＋MPO was divided into three zones, namely the top loose ceramic zone, middle compact zone and inside HCPEB-induced melted zone. Corrosion resistance of ZK60 Mg alloy before and after the compounded surface modification was measured in a solution of 3.5% NaCl by potentiodynamic polarization curves. It was found that the corrosion current density of ZK60 Mg alloys could be reduced by about three orders of magnitude, from 311μA/cm^2 of the original sample to 0.2μA/cm^2 of the HCPEB＋MPO-treated sample. This indicates the great application potential of the HCPEB＋MPO compounded surface modification technology in improving the corrosion resistance of ZK60 Mg alloys in the future.展开更多
Radiation simulation utilizing plasma radiation sources (PRS) generates a large number of undesirable debris, which may damage the expensive diagnosing detectors. An ultra fast shutter (UFS) driven by pulsed high curr...Radiation simulation utilizing plasma radiation sources (PRS) generates a large number of undesirable debris, which may damage the expensive diagnosing detectors. An ultra fast shutter (UFS) driven by pulsed high current can erect a physical barrier to the slowly moving debris after allowing the passage of X-ray photons. The UFS consists of a pair of thin metal foils twisting the parallel axes in a Nylon cassette, compressed with an outer magnetic field, generated from a fast capacitor bank, discharging into a single turn loop. A typical capacitor bank is of 7.5μF charging voltages varying from 30 kV to 45 kV, with corresponding currents of approximately 90 kA to140 kA and discharging current periods of approximately 13.1μs. A shutter closing time as fast as 38 microseconds has been obtained with an aluminium foil thickness of 100 micrometers and a cross-sectional area of 15 mm by 20 mm. The design, construction and the expressions of the valve-closing time of the UFS are presented along with the measured results of valve-closing velocities.展开更多
An efficient method for the isolation and purification of 12,13-dihydroxyeuparin from Radix Eupatorii Chinensis by high speed counter-current chromatography (HSCCC) was established in this paper. The ether extracts of...An efficient method for the isolation and purification of 12,13-dihydroxyeuparin from Radix Eupatorii Chinensis by high speed counter-current chromatography (HSCCC) was established in this paper. The ether extracts of Radix Eupatorii Chinensis were purified by HSCCC with a solvent system of hexyl hydride-ethyl acetate-methanol-water (1:2:1:2, v/v/v/v). The upper phase was used as the stationary phase and the lower phase as the mobile phase. About 8.4 mg of 12, 13-dihydroxyeuparin was obtained from 200 mg of ether extracts from Radix Eupatorii Chinensis in one-step HSCCC separation, with the purity of 96.71%, as determined by HPLC. After methanol- water recrystallization, the purity of 12,13-dihydroxyeuparin reached 99.83%. Such a simple and effective method was fairly useful to prepare pure compound as reference substances for related study on Radix Eupatorii Chinensis.展开更多
Sea surface temperature(SST)in the Yellow Sea Warm Current(YSWC)pathway is sensitive to the East Asian Winter Monsoon(EAWM)and YSWC.However,the role of the YSWC in the evolution of regional SST remains unclear.Here,we...Sea surface temperature(SST)in the Yellow Sea Warm Current(YSWC)pathway is sensitive to the East Asian Winter Monsoon(EAWM)and YSWC.However,the role of the YSWC in the evolution of regional SST remains unclear.Here,we present new U 37 k′based SST and grain size sequences spanning the last 6092 years in the sediment core Z1,which was retrieved from the central Yellow Sea muddy area.Overall,U 37 k′-SST gradually increased since 6.1 ka BP,with a series of centennial-scale fl uctuations.Its variation was mainly caused by EAWM when YSWC was weak between 6.1 and~3.9 ka BP,as shown by the end-member content of grain size.However,after YSWC was fully developed,i.e.,since~3.9 ka BP,it exerted critical eff ects on SST evolution in its pathway.The 1010-and 538-year cycles of the SST sequence indicated a basic control of solar activity on the oceanic conditions in the Yellow Sea.It is suggested that the variation of total solar irradiance was amplifi ed by thermohaline circulation and then transmitted to the Yellow Sea through the EAWM.Meanwhile,the tropical Pacifi c signal of El Niño was transmitted to the YSWC through the Kuroshio Current.The dual properties of warm water transported by YSWC to compensate the EAWM and driving by Kuroshio Current closely linked the variation of SST in the YSWC pathway to the Northern Hemisphere high latitude climate and the tropical Pacifi c.These fi ndings highlight the signifi cance of YSWC on regional SST evolution and its teleconnection to high and low latitude forcing,which grains a better understanding of the long-term evolution of SST in the middle latitude Yellow Sea.展开更多
Extensive usage of highly conductive carbon materials with large specific surface area(e.g.,carbon nanotubes,CNTs)in lithium ion batteries(LIBs),especially as current collector of anodes,suffers from low initial coulo...Extensive usage of highly conductive carbon materials with large specific surface area(e.g.,carbon nanotubes,CNTs)in lithium ion batteries(LIBs),especially as current collector of anodes,suffers from low initial coulombic efficiency(ICE),large interfacial resistance,and severe embrittlement,as the large specific surface area often results in severe interfacial decomposition of the electrolyte and the formation of thick and fluffy solid electrolyte interphase(SEI)during cycling of LIBs.Herein,we demonstrate that when the CNT-based current collector and Na foil(which are being stacked intimately upon each other)are being placed in Na+-based organic electrolyte,local redox reaction between the Na foil and the electrolyte would occur spontaneously,generating a thin and homogeneous NaF-based passivating layer on the CNTs.More importantly,we found that owing to the weak solvation behaviors of Na+in the organic electrolyte,the resulting passivation layer,which is rich in NaF,is thin and dense;when used as the anode current collector in LIBs,the pre-existing passivating layer can function effectively in isolating the anode from the solvated Li+,thus suppressing the formation of bulky SEI and the destructive intercalation of solvated Li+.The relevant half-cell(graphite as anode)exhibits a high ICE of 92.1%;the relevant pouch cell with thus passivated CNT film as current collectors for both electrodes(LiCoO_(2)as cathode,graphite as anode)displays a high energy density of 255 Wh kg^(-1),spelling an increase of 50%compared with that using the conventional metal current collectors.展开更多
基金funded by the National Natural Science Foundation of China(52077004)Anhui Electric Power Company of the State Grid(52120021N00L).
文摘Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.
文摘Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.
文摘The electrolysis of water powered by renewable energy sources offers a promising method of"green hydrogen"production,which is considered to be at the heart of future carbon-neutral energy systems.In the past decades,researchers have reported a number of hydrogen evolution reaction(HER)electrocatalysts with activity comparable to that of commercial Pt/C,but most of them are tested within a small current density range,typically no more than 500 mA cm^(-2).To realize the industrial application of hydrogen production from water electrolysis,it is essential to develop high-efficiency HER electrocatalysts at high current density(HCD≥500 mA cm^(-2)).Nevertheless,it remains challenging and significant to rational design HCD electrocatalysts for HER.In this paper,the design strategy of HCD electrocatalysts is discussed,and some HCD electrocatalysts for HER are reviewed in seven categories(alloy,metal oxide,metal hydroxide,metal sulfide/selenide,metal nitride,metal phosphide and other derived electrocatalysts).At the end of this article,we also pro-pose some viewpoints and prospects for the future development and research directions of HCD electrocatalysts for HER.
基金The fund from Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)under contract No.SML2020SP009the National Basic Research and Development Program of China under contract Nos 2022YFF0802000 and 2022YFF0802004+3 种基金the“Renowned Overseas Professors”Project of Guangdong Provincial Department of Science and Technology under contract No.76170-52910004the Belt and Road Special Foundation of the National Key Laboratory of Water Disaster Prevention under contract No.2022491711the National Natural Science Foundation of China under contract No.51909290the Key Research and Development Program of Guangdong Province under contract No.2020B1111020003.
文摘Forecasting of ocean currents is critical for both marine meteorological research and ocean engineering and construction.Timely and accurate forecasting of coastal current velocities offers a scientific foundation and decision support for multiple practices such as search and rescue,disaster avoidance and remediation,and offshore construction.This research established a framework to generate short-term surface current forecasts based on ensemble machine learning trained on high frequency radar observation.Results indicate that an ensemble algorithm that used random forests to filter forecasting features by weighting them,and then used the AdaBoost method to forecast can significantly reduce the model training time,while ensuring the model forecasting effectiveness,with great economic benefits.Model accuracy is a function of surface current variability and the forecasting horizon.In order to improve the forecasting capability and accuracy of the model,the model structure of the ensemble algorithm was optimized,and the random forest algorithm was used to dynamically select model features.The results show that the error variation of the optimized surface current forecasting model has a more regular error variation,and the importance of the features varies with the forecasting time-step.At ten-step ahead forecasting horizon the model reported root mean square error,mean absolute error,and correlation coefficient by 2.84 cm/s,2.02 cm/s,and 0.96,respectively.The model error is affected by factors such as topography,boundaries,and geometric accuracy of the observation system.This paper demonstrates the potential of ensemble-based machine learning algorithm to improve forecasting of ocean currents.
基金Project supported by the National Natural Science Foundation of China (Grant No.51977132)Key Special Science and Technology Project of Liaoning Province (Grant No.2020JH1/10100012)General Program of the Education Department of Liaoning Province (Grant No.LJKZ0126)。
文摘When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.
基金Projects(51101177,51401040,51171146,51171216) supported by the National Natural Science Foundation of ChinaProject(CSTC2012JJA245) supported by the Natural Science Foundation of Chongqing,China
文摘A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.
文摘The reverse generation current under high-gate-voltage stress condition in LDD nMOSFET＇s is studied. We find that the generation current peak decreases as the stress time increases. We ascribe this finding to the dominating oxide trapped electrons that reduce the effective drain bias, lowering the maximal generation rate. The density of the effective trapped electrons affecting the effective drain bias is calculated with our model.
文摘The MOSFET gate currents of high k gate dielectrics due to direct tunneling are investigated by using a new direct tunneling current model developed.The model includes both the inversion layer quantization effect with finite barrier height and the polysilicon depletion effect.The impacts of dielectric constant and conduction band offset as well as the band gap on the gate current are discussed.The results indicate that the gate dielectric materials with higher dielectric constant,larger conduction band offset and the larger band gap are necessary to reduce the gate current.The calculated results can be used as a guide to select the appropriate high k gate dielectric materials for MOSFETs.
基金supported by the National Natural Science Foundation of China (Grant 11572249)the Aerospace Technology Foundation (Grant N2014KC0068)the Aeronautical Science Foundation of China (Grant N2014KC0073)
文摘In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.
基金supported by National Natural Science Foundation of China (Nos.10875146,11075183)the Knowledge Innovation Program of the Chinese Academy of Sciences (study of the physical characteristic of arc power feedback control for the high current ion source)
文摘Neutral beam injection is one of the main plasma heating methods in nuclear fusion devices. In order to support the scientific study of the Experimental Advanced Superconducting Tokamak （EAST）, a megawatt-level high current ion source is designed and manufactured in the ASIPP, and the progress and preliminary test results will be presented in this paper.
文摘By means of flow visualization and quantitative measurement, the diffusion pattern and concentration distribution characteristics of high concentration jets vertically discharged into shallow moving waterbody were experimentally investigated in water channel. The interactions between the high concentration jets and environmental flow conditions were analysed, and the formulae of impinging point coordinate and transverse spread angle are gained from data analysis. Experimental results indicate that the jets show complicated flow patterns and diffusion characteristics in near region, which are different from common submerged jets, and spread downstream in the manner of density currents.
基金Supported by Universiti Malaysia Pahang Research Grant(RDU1803143)
文摘Electrocoagulation process using high current intensity to treat palm oil mill effluent(POME) was investigated in this study.Various operating parameters such as electrolysis time, inter-electrode distance and initial pH were carried out to determine the efficient process condition on the removal of chemical oxygen demand(COD),biological oxygen demand(BOD) and suspended solids(SS).The highest treatment was achieved at 50 min with the removal efficiencies for COD, BOD and SS obtained as 85%, 83%, and 84%, respectively.More than 50 min treatment showed the fluctuated trends of removal efficiencies which can be considered insignificant.The application of higher current resulted in higher removals of organics while the gas bubbles also assisted in removing the pollutant particles by floatation.In an inter-electrode distance study, the removal efficiency decreased when inter-electrode distance was either higher or lower than 10 mm due to the increase of solution resistance and the decrease of anode active surface area.In initial pH study, it was found that high removal efficiencies were achieved in slightly acidic POME sample rather than in neutral or basic condition.An electrocoagulation process by using the optimum operating parameters was able to remove COD, BOD and SS up to 95%, 94% and 96% respectively.The experimental results confirm that application of high current intensity in electrocoagulation provided high treatment efficiency at a reduced reaction time.
基金supported by the National Natural Science Foundation of China(21872040)the Hundred Talents Program of Guangxi Universitiesthe Excellent Scholars and Innovation Team of Guangxi Universities。
文摘Developing highly effective and stable non-noble metalbased bifunctional catalyst working at high current density is an urgent issue for water electrolysis(WE).Herein,we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam(NiCo@C-NiCoMoO/NF)for water splitting.NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction(HER:39/266 mV;OER:260/390 mV)at±10 and±1000 mA cm^(−2).More importantly,in 6.0 M KOH solution at 60℃ for WE,it only requires 1.90 V to reach 1000 mA cm−2 and shows excellent stability for 43 h,exhibiting the potential for actual application.The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet,which not only increase the intrinsic activity and expose abundant catalytic activity sites,but also enhance its chemical and mechanical stability.This work thus could provide a promising material for industrial hydrogen production.
文摘Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.
基金The National High Technology Research and Development Program of China(863 Program)under contract No.2012AA091701the Fundamental Research Fund for the Central Universities of China under contract No.2012212020211
文摘Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis： the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.
基金supported by Liaoning BaiQianWan Talents Program of China (No. 2008921028)Doctoral Fund of Ministry of Education of China (No. 200801451082)
文摘In this study, compounded surface modification technology-high current pulsed electron beam （HCPEB） ＋ micro-plasma oxidation （MPO） was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of ZK60 Mg alloy after single MPO and HCPEB＋MPO compounded treatment were investigated by SEM. The results showed that the density of the ceramic layer of HCPEB＋MPO-treated ZK60 Mg alloy was improved and defects were reduced compared to that under MPO treatment alone. Surface modified layer of ZK60 Mg alloys treated by HCPEB＋MPO was divided into three zones, namely the top loose ceramic zone, middle compact zone and inside HCPEB-induced melted zone. Corrosion resistance of ZK60 Mg alloy before and after the compounded surface modification was measured in a solution of 3.5% NaCl by potentiodynamic polarization curves. It was found that the corrosion current density of ZK60 Mg alloys could be reduced by about three orders of magnitude, from 311μA/cm^2 of the original sample to 0.2μA/cm^2 of the HCPEB＋MPO-treated sample. This indicates the great application potential of the HCPEB＋MPO compounded surface modification technology in improving the corrosion resistance of ZK60 Mg alloys in the future.
基金This project supported by the National Nature Science Foundation of China (No. 10035020 )
文摘Radiation simulation utilizing plasma radiation sources (PRS) generates a large number of undesirable debris, which may damage the expensive diagnosing detectors. An ultra fast shutter (UFS) driven by pulsed high current can erect a physical barrier to the slowly moving debris after allowing the passage of X-ray photons. The UFS consists of a pair of thin metal foils twisting the parallel axes in a Nylon cassette, compressed with an outer magnetic field, generated from a fast capacitor bank, discharging into a single turn loop. A typical capacitor bank is of 7.5μF charging voltages varying from 30 kV to 45 kV, with corresponding currents of approximately 90 kA to140 kA and discharging current periods of approximately 13.1μs. A shutter closing time as fast as 38 microseconds has been obtained with an aluminium foil thickness of 100 micrometers and a cross-sectional area of 15 mm by 20 mm. The design, construction and the expressions of the valve-closing time of the UFS are presented along with the measured results of valve-closing velocities.
基金supported by the International Scientific and Technological Cooperation Program of China (no.2009DFA31230)the Industry-University-Research Cooperation Program from Science and Technology Department of Guangdong Province (no. 2010B090400533)
文摘An efficient method for the isolation and purification of 12,13-dihydroxyeuparin from Radix Eupatorii Chinensis by high speed counter-current chromatography (HSCCC) was established in this paper. The ether extracts of Radix Eupatorii Chinensis were purified by HSCCC with a solvent system of hexyl hydride-ethyl acetate-methanol-water (1:2:1:2, v/v/v/v). The upper phase was used as the stationary phase and the lower phase as the mobile phase. About 8.4 mg of 12, 13-dihydroxyeuparin was obtained from 200 mg of ether extracts from Radix Eupatorii Chinensis in one-step HSCCC separation, with the purity of 96.71%, as determined by HPLC. After methanol- water recrystallization, the purity of 12,13-dihydroxyeuparin reached 99.83%. Such a simple and effective method was fairly useful to prepare pure compound as reference substances for related study on Radix Eupatorii Chinensis.
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42000000)the National Natural Science Foundation of China(Nos.41830539,42076051)the Open Fund Project of the Key Laboratory of Marine Sedimentology and Environmental Geology,Ministry of Natural Resources(No.MASEG201901),and the Taishan Scholar Project。
文摘Sea surface temperature(SST)in the Yellow Sea Warm Current(YSWC)pathway is sensitive to the East Asian Winter Monsoon(EAWM)and YSWC.However,the role of the YSWC in the evolution of regional SST remains unclear.Here,we present new U 37 k′based SST and grain size sequences spanning the last 6092 years in the sediment core Z1,which was retrieved from the central Yellow Sea muddy area.Overall,U 37 k′-SST gradually increased since 6.1 ka BP,with a series of centennial-scale fl uctuations.Its variation was mainly caused by EAWM when YSWC was weak between 6.1 and~3.9 ka BP,as shown by the end-member content of grain size.However,after YSWC was fully developed,i.e.,since~3.9 ka BP,it exerted critical eff ects on SST evolution in its pathway.The 1010-and 538-year cycles of the SST sequence indicated a basic control of solar activity on the oceanic conditions in the Yellow Sea.It is suggested that the variation of total solar irradiance was amplifi ed by thermohaline circulation and then transmitted to the Yellow Sea through the EAWM.Meanwhile,the tropical Pacifi c signal of El Niño was transmitted to the YSWC through the Kuroshio Current.The dual properties of warm water transported by YSWC to compensate the EAWM and driving by Kuroshio Current closely linked the variation of SST in the YSWC pathway to the Northern Hemisphere high latitude climate and the tropical Pacifi c.These fi ndings highlight the signifi cance of YSWC on regional SST evolution and its teleconnection to high and low latitude forcing,which grains a better understanding of the long-term evolution of SST in the middle latitude Yellow Sea.
基金financially supported by the National Key Research and Development Program of China(2022YFB4002103)the National Natural Science Foundation of China(22279107)。
文摘Extensive usage of highly conductive carbon materials with large specific surface area(e.g.,carbon nanotubes,CNTs)in lithium ion batteries(LIBs),especially as current collector of anodes,suffers from low initial coulombic efficiency(ICE),large interfacial resistance,and severe embrittlement,as the large specific surface area often results in severe interfacial decomposition of the electrolyte and the formation of thick and fluffy solid electrolyte interphase(SEI)during cycling of LIBs.Herein,we demonstrate that when the CNT-based current collector and Na foil(which are being stacked intimately upon each other)are being placed in Na+-based organic electrolyte,local redox reaction between the Na foil and the electrolyte would occur spontaneously,generating a thin and homogeneous NaF-based passivating layer on the CNTs.More importantly,we found that owing to the weak solvation behaviors of Na+in the organic electrolyte,the resulting passivation layer,which is rich in NaF,is thin and dense;when used as the anode current collector in LIBs,the pre-existing passivating layer can function effectively in isolating the anode from the solvated Li+,thus suppressing the formation of bulky SEI and the destructive intercalation of solvated Li+.The relevant half-cell(graphite as anode)exhibits a high ICE of 92.1%;the relevant pouch cell with thus passivated CNT film as current collectors for both electrodes(LiCoO_(2)as cathode,graphite as anode)displays a high energy density of 255 Wh kg^(-1),spelling an increase of 50%compared with that using the conventional metal current collectors.
