This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in...This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in place of the shift operator for the implementation of MFPR by using a low-cost fixed-point DSE The experimental results with an alternative control strategy validated the feasibility of the proposed MFPR current controller for the PWM VSC during voltage unbalance.展开更多
This paper proposes a current control scheme for a grid-connected pulse width modulator(PWM) voltage source converter(GC-VSC) under imbalanced and distorted supply voltage conditions.The control scheme is implemented ...This paper proposes a current control scheme for a grid-connected pulse width modulator(PWM) voltage source converter(GC-VSC) under imbalanced and distorted supply voltage conditions.The control scheme is implemented in the positive synchronously rotating reference frame and composed of a single proportional integral(PI) regulator and multi-frequency resonant controllers tuned at the frequencies of 2ω and 6ω,respectively.The experimental results,with the target of eliminating the active power oscillations and current harmonics on a prototype GC-VSC system,validate the feasibility of the proposed current control scheme during supply voltage imbalance and distortion.展开更多
This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven second...This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven secondary sources,taking as an example ion acceleration by target normal sheath acceleration.The Pearson linear correlation of maximum return current amplitude and proton spectrum cutoff energy is found to be in the range from~0.70 to 0.94.kA-scale return currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons.Their precise measurement is demonstrated using an inductive scheme that allows operation at high repetition rates.Thus,return currents can be used as a metrological online tool for the optimization of many laser-driven secondary sources and for diagnosing their stability.In particular,in two parametric studies of laser-driven ion acceleration,we carry out a noninvasive online measurement of return currents in a tape target system irradiated by the 1 PW VEGA-3 laser at Centro de Láseres Pulsados:first the size of the irradiated area is varied at best compression of the laser pulse;second,the pulse duration is varied by means of induced group delay dispersion at best focus.This work paves the way to the development of feedback systems that operate at the high repetition rates of PW-class lasers.展开更多
Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to charact...Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to characterize F-region currents using magnetic data from the MSS-1(Macao Science Satellite-1) and Swarm satellite missions.Our approach employs a toroidal field representation,utilizing spherical harmonics to capture spatial variations and Fourier series to represent temporal dynamics.Two models,Model-A and Model-B,derived from distinct datasets,are constructed to represent current patterns at altitudes of 450 km and 512 km,respectively.Our models successfully capture the primary spatial structures and seasonal variations of polar field-aligned currents.Additionally,they accurately reproduce the localized inter-hemispheric field-aligned currents observed in mid and low latitudes during solstices,particularly between 14:00 and 16:00 magnetic local times.These findings enhance our understanding of ionospheric F-region currents and contribute to more precise geomagnetic field modeling.展开更多
Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure throug...Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.展开更多
In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies...In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies to the Sun and Earth currents systems with solar activity from 1996 to 2019. A decrease in the correlation between sun-related energies and sunspot number was observed over solar cycles 23 and 24 (0.88 for the solar cycle 23 and 0.66 for the solar cycle 24), with a drop in the speed of magnetic disturbances in the solar wind. These results could be attributed to the decrease in Sun’s magnetic field toroidal component magnitude induced by a weak in sunspots number and solar flares during the solar cycle 24. A weak in the Earth currents systems (auroral electrojet current, ring current, and magnetopause current) is also observed. During the decrease in the Earth currents, several peaks are observed, indicating a nonlinear dependence in the Earth currents variation (ring current, auroral electrojet current, and magnetopause current) from solar cycle 23 to solar cycle 24. This could be attributed to the Corotating Interaction Regions (CIRs) observed during the declining phase of solar cycle 23 and the deep minimum preceding solar cycle 24.展开更多
This study investigates the nonlinear resonance responses of suspended cables subjected to multi-frequency excitations and time-delayed feedback.Two specific combinations and simultaneous resonances are selected for d...This study investigates the nonlinear resonance responses of suspended cables subjected to multi-frequency excitations and time-delayed feedback.Two specific combinations and simultaneous resonances are selected for detailed examination.Initially,utilizing Hamilton’s variational principle,a nonlinear vibration control model of suspended cables under multi-frequency excitations and longitudinal time-delayed velocity feedback is developed,and the Galerkin method is employed to obtain the discrete model.Subsequently,focusing solely on single-mode discretization,analytical solutions for the two simultaneous resonances are derived using the method of multiple scales.The frequency response equations are derived,and the stability analysis is presented for two simultaneous resonance cases.The results demonstrate that suspended cables exhibit complex nonlinearity under multi-frequency excitations.Multiple solutions under multi-frequency excitation can be distinguished through the frequency–response and the detuning-phase curves.By adjusting the control gain and time delay,the resonance range,response amplitude,and phase of suspended cables can be modified.展开更多
The advancement of imaging resolution has made the impact of multi-frequency composite jitter in satellite platforms on non-collinear time delay and integration(TDI)charge-coupled device(CCD)imaging systems increasing...The advancement of imaging resolution has made the impact of multi-frequency composite jitter in satellite platforms on non-collinear time delay and integration(TDI)charge-coupled device(CCD)imaging systems increasingly critical.Moreover,the accuracy of jitter detection is constrained by the limited inter-chip overlap region inherent to non-collinear TDI CCDs.To address these challenges,a multi-frequency jitter detection method is proposed,achieving sub-pixel level error extraction.Furthermore,a multi-frequency jitter fitting approach utilizing a scale-adjustable sliding window is introduced.For composite multi-frequency jitter,spectral analysis decomposes the relative jitter error curve,while the scale-adjustable sliding window enables frequency-division fitting and modeling.Validation experiments using Gaofen-8(GF-8)remote sensing satellite imagery detected jitter at 0.65,20,and 100 Hz in the cross-track direction and at 0.5,100,and 120 Hz in the along-track direction,demonstrating the method’s precision in detecting platform jitter at sub-pixel accuracy(<0.2 pixels)and its efficacy in fitting and modeling for non-collinear TDI CCD imaging systems subject to multi-frequency jitter.展开更多
Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential ...Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential applications in spintronics, Bose–Einstein distribution populates magnon states across all energies from opposite eigenmodes, and hence the magnon spin current is largely compensated. Contrary to this common observation,here, we show that magnets with X-type AFM stacking, where opposite magnetic sublattices form orthogonal intersecting chains, support giant magnon spin currents with minimal compensation. Our model Hamiltonian calculations predict magnetic chain locking of magnon spin currents in these X-type magnets, significantly reducing their compensation ratio. In addition, the one-dimensional nature of the chain-like magnetic sublattices enhances magnon spin conductivities surpassing those of two-dimensional ferromagnets and canonical altermagnets. Notably, uncompensated X-type magnets, such as odd-layer antiferromagnets and ferrimagnets, can exhibit magnon spin currents polarized opposite to those expected by their net magnetization. These unprecedented properties of X-type magnets, combined with their inherent advantages resulting from AFM coupling, offer a promising new path for low-power high-performance spintronics.展开更多
Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which ...Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which is utilized to produce clean hydrogen,is investigated in this work.Analysis has been done on a 20-cell stack.Steel end plates,bipolar plates,and an electrolyte concentration of 6 M potassium hydroxide are all included in the model.The Butler-Volmer kinetics equations are used to simulate the electrode surfaces.Ohmic losses are taken into consideration in both the electrode and electrolyte phases,although mass transport constraints in the gas phase are not.Using an auxiliary sweep to solve equations,the model maintains an isothermal condition at 85℃ while adjusting the average cell voltage between 1.3 and 1.8 V.The results show that lower shunt currents in the outlet channels as opposed to the intake channels are the result of the electrolyte’s lower effective conductivity in the upper channels,which is brought on by a lower volume fraction of the electrolyte.Additionally,it has been seen that the shunt currents intensify as the stack gets closer to the conclusion.Efficiency is calculated by dividing the maximum energy output(per unit of time)that a fuel cell operating under comparable conditions might produce by the electrical energy needed to generate that output inside the stack.At first,energy efficiency increases due to the rise in coulombic efficiency,peaking around 1400 mA.The subsequent decline after reaching 1400 mA is linked to an increase in stack voltage at elevated current levels.展开更多
Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Mo...Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Moreover,ultrafast lasergenerated spin currents appear to play an important role in the switching process.Here,we try to separately detect the spin current from Gd in a Co/Gd bilayer system using terahertz time-domain spectroscopy.To this aim,we use different capping,buffer and embedded layers in order to tune the spin-to-charge and spin-current propagation and identify currents from each of the layers.We attribute the observed THz emission in all layers to the transition metal demagnetization induced spin currents,and detect no contribution from the Gd demagnetization.We attribute this absence of Gd-induced THz signal to the potentially slow demagnetization of Gd,which shift the emission spectra to lower frequencies,below our detection capabilities.These results highlight the limitations in using materials suffering from the so-called critical slowdown for the optimization of spintronic THz emitters.展开更多
0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability...0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability(Harris,2020;Chubarenko et al.,2016).展开更多
The paper proposes an experimental method of material inspection,which is based on digital processing of multi-frequency eddy current measurement data.The influences of various factors(conductivity,the gap between the...The paper proposes an experimental method of material inspection,which is based on digital processing of multi-frequency eddy current measurement data.The influences of various factors(conductivity,the gap between the sample surface and the sensor,the thickness of the sample) on the obtained hodographs are examined by taking the aluminum alloys for example,and the possibility of separation of various factors is analyzed.The results obtained are indicative of how much promise the proposed method offers for the inspection and testing of products made of aluminum alloys.展开更多
Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and coppe...Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.展开更多
Based on the diurnal consecutively observed data in the offshore area of Jiaonan in 2005, the paper tries to make a preliminary analysis of the specificity of ocean currents, tidal current property and residual curren...Based on the diurnal consecutively observed data in the offshore area of Jiaonan in 2005, the paper tries to make a preliminary analysis of the specificity of ocean currents, tidal current property and residual current property in the area in observing dates. Then on the basis of observed data analysis and by employing the split-step method, the paper conducts a numerical simulation of the tidal current field, which can show the M2 tidal constituent tidal wave system, current ellipse distribution, maximum current velocity distribution and time-dependent current field. The calculated results agree well with the observed data, which can on the one hand reflect the basic specificities of temporal and spatial distribution of the M2 tidal constituent current field to some extent, and, on the other hand, offer more information about the hydrodynamic condition. So the paper would provide a scientific basis for the making of sea environment protection plans in the offshore area of Jiaonan under certain conditions.展开更多
The ocean surface currents are reconstructed from the satellite remote sensing data containing altimeter-derived sea surface height and QuikSCAT satellite-derived wind data. Based on the method proposed by Lagerloef, ...The ocean surface currents are reconstructed from the satellite remote sensing data containing altimeter-derived sea surface height and QuikSCAT satellite-derived wind data. Based on the method proposed by Lagerloef, a global weekly 0.5°×0.5°ocean surface current product was obtained over the period 2000 - 2008 by combining the geostrophic currents estimated from sea surface height with Ekman current estimated from the wind stress. Particularly, weight functions were introduced when calculating the Ekman currents to eliminate the discontinuity near 25°S and 25°N. These satellite-derived currents have been compared with TAO current meter and the SCUD product, respectively. The comparison showed that satellite-derived currents not only could capture the characteristics of ocean surface currents but also had high accuracy and reliability. The result showed that this innovatory method was effective.展开更多
The two-dimensional hydrodynamic model, MIKE21, is applied to simulate the tidal currents and sediment concentration in the radial sand ridges of the South Yellow Sea. Results are in accordance with in situ observatio...The two-dimensional hydrodynamic model, MIKE21, is applied to simulate the tidal currents and sediment concentration in the radial sand ridges of the South Yellow Sea. Results are in accordance with in situ observations. Then the variations of tidal currents and suspended sediment concentration caused by reclamation and artificial islands projects are simulated. The results show that the impacts are limited around the project areas. After the projects, the fan-shaped, Jianggang centered tidal current pattern would be replaced by a pattern which is formed by two tidal paths. One locates at the Xiyang channel in north-south direction, and the other locates at the Huangshayang channel in east-west direction. The reclamation of Tiaozini separates the waters into south portion and north portion. The changes of sediment concentrations coincide with those of currents. Both the sediment concentrations and tidal currents increase at the northwest of Dongsha and the south of Gaoni, while both decrease at the north and south of Tiaozini, and the east and southwest of Dongsha.展开更多
Based on 25 hours shipboard ADCP measurements across semi-enclosed bay mouth（Kemen Channel）, time series of tidal currents over 12 sites, which distribute evenly along the transect, were constructed to improve our u...Based on 25 hours shipboard ADCP measurements across semi-enclosed bay mouth（Kemen Channel）, time series of tidal currents over 12 sites, which distribute evenly along the transect, were constructed to improve our understanding of tidal characteristics and residuals in this region. The tidal currents in Kemen Channel were identified as the regular semidiurnal and reversing tidal flows, with its behaviour more like standing waves. Moreover, the flood currents in the lower layers were found to be ahead of that in the upper layers and vice versa for ebb tides. The major of tidal ellipse for M2 constituent was found to be larger close to the southern side of the channel, with its incline also increasing toward the south. The signs of M4 constituent were also found mainly nearby the end points of this transect, indicating the importance of nonlinearity in tidal dynamics due to the shallower topography. A two-layer structure was found for the residual currents in Kemen Channel, flowing northeastwardly out of the Bay in upper 20m and southwestwardly into the bay in the lowers. Besides approximate 4.81×10^8 m^3 water exchanges were determined between the Luoyuan Bay and outer seas by the calculation of tidal flux through Kemen Channel.展开更多
A direct tunneling model through gate dielectric s in CMOS devices in the frame of WKB approximation is reported.In the model,an im proved one-band effective mass approximation is used for the hole quantization, wher...A direct tunneling model through gate dielectric s in CMOS devices in the frame of WKB approximation is reported.In the model,an im proved one-band effective mass approximation is used for the hole quantization, where valence band mixing is taken into account.By comparing to the experiments, the model is demonstrated to be applicable to both electron and hole tunneling c urrents in CMOS devices.The effect of the dispersion in oxide energy gap on the tunneling current is also studied.This model can be further extended to study th e direct tunneling current in future high-k materials.展开更多
The tidal current duration （TCD） and velocity （TCV） and suspended sediment concentration （SSC） were measured in the dry season in December, 2011 and in the flood season in June, 2012 at the upper part of the Nor...The tidal current duration （TCD） and velocity （TCV） and suspended sediment concentration （SSC） were measured in the dry season in December, 2011 and in the flood season in June, 2012 at the upper part of the North Channel of Changjiang Estuary. They were assimilated with the measured data in 2003, 2004, 2006 and 2007, using the tidal range＇s proportion conversion. Variations in TCD and TCV, preferential flow and SSC have been calculated. Influences of typical engineering projects such as Qingcaosha fresh water reservoir, Yangtze River Bridge, and land reclamation on the ebb and flood TCD, TCV and SSC in the North Channel for the last 10 years are discussed. The results show that： （1） currently, in the upper part of North Channel, the ebb tide dominates; after the construction of the typical projects, ebb TCD and TCV tends to be larger and the vertical average ebb and flood SSC decrease during the flood season while SSC increases during the dry season; （2） changes in the vertical average TCV are mainly contributed by seasonal runoff variation during the flood season, which is larger in the flood season than that in the dry season; the controlling parameters of increasing ebb TCD and TCV are those large-scale engineering projects in the North Channel; variation in SSC may result mainly from the reduction of basin annual sediment loads, large-scale nearshore projects and so on.展开更多
基金Project (No. 50577056) supported by the National Natural Science Foundation of China
文摘This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in place of the shift operator for the implementation of MFPR by using a low-cost fixed-point DSE The experimental results with an alternative control strategy validated the feasibility of the proposed MFPR current controller for the PWM VSC during voltage unbalance.
基金supported by the National Natural Science Foundation of China(No.50907057)the National High-Tech Research and Development Program (863) of China(No.2007AA05Z419)
文摘This paper proposes a current control scheme for a grid-connected pulse width modulator(PWM) voltage source converter(GC-VSC) under imbalanced and distorted supply voltage conditions.The control scheme is implemented in the positive synchronously rotating reference frame and composed of a single proportional integral(PI) regulator and multi-frequency resonant controllers tuned at the frequencies of 2ω and 6ω,respectively.The experimental results,with the target of eliminating the active power oscillations and current harmonics on a prototype GC-VSC system,validate the feasibility of the proposed current control scheme during supply voltage imbalance and distortion.
基金funding from the European Union’s Horizon 2020 research and innovation program through the European IMPULSE project under Grant Agreement No.871161from LASERLAB-EUROPE V under Grant Agreement No.871124+6 种基金from the Grant Agency of the Czech Republic(Grant No.GM23-05027M)Grant No.PDC2021120933-I00 funded by MCIN/AEI/10.13039/501100011033by the European Union Next Generation EU/PRTRsupported by funding from the Ministerio de Ciencia,Innovación y Universidades in Spain through ICTS Equipment Grant No.EQC2018-005230-Pfrom Grant No.PID2021-125389O A-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER,UEby“ERDF A Way of Making Europe”by the European Unionfrom grants of the Junta de Castilla y León with Grant Nos.CLP263P20 and CLP087U16。
文摘This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser–plasma interaction for laser-driven secondary sources,taking as an example ion acceleration by target normal sheath acceleration.The Pearson linear correlation of maximum return current amplitude and proton spectrum cutoff energy is found to be in the range from~0.70 to 0.94.kA-scale return currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons.Their precise measurement is demonstrated using an inductive scheme that allows operation at high repetition rates.Thus,return currents can be used as a metrological online tool for the optimization of many laser-driven secondary sources and for diagnosing their stability.In particular,in two parametric studies of laser-driven ion acceleration,we carry out a noninvasive online measurement of return currents in a tape target system irradiated by the 1 PW VEGA-3 laser at Centro de Láseres Pulsados:first the size of the irradiated area is varied at best compression of the laser pulse;second,the pulse duration is varied by means of induced group delay dispersion at best focus.This work paves the way to the development of feedback systems that operate at the high repetition rates of PW-class lasers.
基金supported by the National Natural Science Foundation of China (42250101)the Macao Foundation. The computation made use of the high-performance computing resources at the center of the MSS data processing and analysis。
文摘Accurate modeling of Earth's ionospheric F-region currents is essential for refining geomagnetic field models and understanding magnetosphere-ionosphere coupling.In this study,we develop averaged models to characterize F-region currents using magnetic data from the MSS-1(Macao Science Satellite-1) and Swarm satellite missions.Our approach employs a toroidal field representation,utilizing spherical harmonics to capture spatial variations and Fourier series to represent temporal dynamics.Two models,Model-A and Model-B,derived from distinct datasets,are constructed to represent current patterns at altitudes of 450 km and 512 km,respectively.Our models successfully capture the primary spatial structures and seasonal variations of polar field-aligned currents.Additionally,they accurately reproduce the localized inter-hemispheric field-aligned currents observed in mid and low latitudes during solstices,particularly between 14:00 and 16:00 magnetic local times.These findings enhance our understanding of ionospheric F-region currents and contribute to more precise geomagnetic field modeling.
基金supported by the program for National Natural Science Foundation of China (Nos. 52174173, 52274188, and 52104190)the Joint Funds of the National Natural Science Foundation of China (No. U24A2091)+1 种基金The Natural Science Foundation of Henan Polytechnic University (No. B2021-2)Double FirstClass Initiative of Safety and Energy Engineering (Henan Polytechnic University) (Nos. AQ20240703 and AQ20230304)。
文摘Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.
文摘In this study, we examined variability of sun-related energies, auroral electrojet current, ring current, and magnetopause current during solar cycles 23 and 24. The study revealed a dependence of sun-related energies to the Sun and Earth currents systems with solar activity from 1996 to 2019. A decrease in the correlation between sun-related energies and sunspot number was observed over solar cycles 23 and 24 (0.88 for the solar cycle 23 and 0.66 for the solar cycle 24), with a drop in the speed of magnetic disturbances in the solar wind. These results could be attributed to the decrease in Sun’s magnetic field toroidal component magnitude induced by a weak in sunspots number and solar flares during the solar cycle 24. A weak in the Earth currents systems (auroral electrojet current, ring current, and magnetopause current) is also observed. During the decrease in the Earth currents, several peaks are observed, indicating a nonlinear dependence in the Earth currents variation (ring current, auroral electrojet current, and magnetopause current) from solar cycle 23 to solar cycle 24. This could be attributed to the Corotating Interaction Regions (CIRs) observed during the declining phase of solar cycle 23 and the deep minimum preceding solar cycle 24.
基金supported in part by the National Natural Science Foundation of China(Grant No.12432001)Natural Science Foundation of Hunan Province(Grant Nos.2023JJ60527,2023JJ30152,and 2023JJ30259)the Natural Science Foundation of Changsha(KQ2202133).
文摘This study investigates the nonlinear resonance responses of suspended cables subjected to multi-frequency excitations and time-delayed feedback.Two specific combinations and simultaneous resonances are selected for detailed examination.Initially,utilizing Hamilton’s variational principle,a nonlinear vibration control model of suspended cables under multi-frequency excitations and longitudinal time-delayed velocity feedback is developed,and the Galerkin method is employed to obtain the discrete model.Subsequently,focusing solely on single-mode discretization,analytical solutions for the two simultaneous resonances are derived using the method of multiple scales.The frequency response equations are derived,and the stability analysis is presented for two simultaneous resonance cases.The results demonstrate that suspended cables exhibit complex nonlinearity under multi-frequency excitations.Multiple solutions under multi-frequency excitation can be distinguished through the frequency–response and the detuning-phase curves.By adjusting the control gain and time delay,the resonance range,response amplitude,and phase of suspended cables can be modified.
文摘The advancement of imaging resolution has made the impact of multi-frequency composite jitter in satellite platforms on non-collinear time delay and integration(TDI)charge-coupled device(CCD)imaging systems increasingly critical.Moreover,the accuracy of jitter detection is constrained by the limited inter-chip overlap region inherent to non-collinear TDI CCDs.To address these challenges,a multi-frequency jitter detection method is proposed,achieving sub-pixel level error extraction.Furthermore,a multi-frequency jitter fitting approach utilizing a scale-adjustable sliding window is introduced.For composite multi-frequency jitter,spectral analysis decomposes the relative jitter error curve,while the scale-adjustable sliding window enables frequency-division fitting and modeling.Validation experiments using Gaofen-8(GF-8)remote sensing satellite imagery detected jitter at 0.65,20,and 100 Hz in the cross-track direction and at 0.5,100,and 120 Hz in the along-track direction,demonstrating the method’s precision in detecting platform jitter at sub-pixel accuracy(<0.2 pixels)and its efficacy in fitting and modeling for non-collinear TDI CCD imaging systems subject to multi-frequency jitter.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1403203)the National Natural Science Funds for Distinguished Young Scholar (Grant No.52325105)+2 种基金the National Natural Science Foundation of China (Grant Nos.12274411,12241405,52250418,and12404185)the Basic Research Program of the Chinese Academy of Sciences (CAS) Based on Major Scientific Infrastructures (Grant No.JZHKYPT-2021-08)the CAS Project for Young Scientists in Basic Research (Grant No.YSBR-084)。
文摘Magnon spin currents in insulating magnets are useful for low-power spintronics. However, in magnets stacked by antiferromagnetic(AFM) exchange coupling, which have recently aroused significant interest for potential applications in spintronics, Bose–Einstein distribution populates magnon states across all energies from opposite eigenmodes, and hence the magnon spin current is largely compensated. Contrary to this common observation,here, we show that magnets with X-type AFM stacking, where opposite magnetic sublattices form orthogonal intersecting chains, support giant magnon spin currents with minimal compensation. Our model Hamiltonian calculations predict magnetic chain locking of magnon spin currents in these X-type magnets, significantly reducing their compensation ratio. In addition, the one-dimensional nature of the chain-like magnetic sublattices enhances magnon spin conductivities surpassing those of two-dimensional ferromagnets and canonical altermagnets. Notably, uncompensated X-type magnets, such as odd-layer antiferromagnets and ferrimagnets, can exhibit magnon spin currents polarized opposite to those expected by their net magnetization. These unprecedented properties of X-type magnets, combined with their inherent advantages resulting from AFM coupling, offer a promising new path for low-power high-performance spintronics.
文摘Since the beginning of the 20th century,alkaline electrolysis has been used as a proven method for producing hydrogen on a megawatt scale.The existence of parasitic shunt currents in alkaline water electrolysis,which is utilized to produce clean hydrogen,is investigated in this work.Analysis has been done on a 20-cell stack.Steel end plates,bipolar plates,and an electrolyte concentration of 6 M potassium hydroxide are all included in the model.The Butler-Volmer kinetics equations are used to simulate the electrode surfaces.Ohmic losses are taken into consideration in both the electrode and electrolyte phases,although mass transport constraints in the gas phase are not.Using an auxiliary sweep to solve equations,the model maintains an isothermal condition at 85℃ while adjusting the average cell voltage between 1.3 and 1.8 V.The results show that lower shunt currents in the outlet channels as opposed to the intake channels are the result of the electrolyte’s lower effective conductivity in the upper channels,which is brought on by a lower volume fraction of the electrolyte.Additionally,it has been seen that the shunt currents intensify as the stack gets closer to the conclusion.Efficiency is calculated by dividing the maximum energy output(per unit of time)that a fuel cell operating under comparable conditions might produce by the electrical energy needed to generate that output inside the stack.At first,energy efficiency increases due to the rise in coulombic efficiency,peaking around 1400 mA.The subsequent decline after reaching 1400 mA is linked to an increase in stack voltage at elevated current levels.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFF0719200)the National Natural Science Foundation of China(Grant No.62105011)+3 种基金the French National Research Agency ANR through the UFO project(Grant No.ANR-20-CE090013)the SLAM project(Grant No.ANR-23-CE30-0047)the MAT-PULSE-Lorraine Universitéd’Excellence project(Grant No.ANR-15-IDEX-04-LUE)the France 2030 Government Grants PEPR Electronic EMCOM(Grant No.ANR-22-PEEL-0009)。
文摘Single shot all-optical switching of the magnetization by femtosecond laser pulses in rare-earth transition-metal ferrimagnetic materials is particularly promising for future ultrafast magnetic storage applications.Moreover,ultrafast lasergenerated spin currents appear to play an important role in the switching process.Here,we try to separately detect the spin current from Gd in a Co/Gd bilayer system using terahertz time-domain spectroscopy.To this aim,we use different capping,buffer and embedded layers in order to tune the spin-to-charge and spin-current propagation and identify currents from each of the layers.We attribute the observed THz emission in all layers to the transition metal demagnetization induced spin currents,and detect no contribution from the Gd demagnetization.We attribute this absence of Gd-induced THz signal to the potentially slow demagnetization of Gd,which shift the emission spectra to lower frequencies,below our detection capabilities.These results highlight the limitations in using materials suffering from the so-called critical slowdown for the optimization of spintronic THz emitters.
基金the National Natural Science Foundation of China(No.42277138)the National Key Research and Development Program of China(Nos.2024YFF0506803 and 2024YFC2815400)+2 种基金the Fundamental Research Funds for the Central Universities(Nos.202441003 and 202513032)the Shandong Province National-Level Leading Talent Supporting Project(No.2022GJJLJRC-15)the European Commission(Nos.HORIZON MSCA-2024-PF-01,101200637)。
文摘0 INTRODUCTION Microplastics are defined as small plastic debris(1μm-5 mm),which have complex properties of widerange densities(0.05-2.3 g/cm^3),diverse shapes(e.g.,beads,fibers,foam and pellets)and low degradability(Harris,2020;Chubarenko et al.,2016).
基金supported by Program for Basic Scientific Research of the State Academies of Sciences for 2013e2020the RF Ministry of Education and Science (Contract No. 02.G25.31.0063)
文摘The paper proposes an experimental method of material inspection,which is based on digital processing of multi-frequency eddy current measurement data.The influences of various factors(conductivity,the gap between the sample surface and the sensor,the thickness of the sample) on the obtained hodographs are examined by taking the aluminum alloys for example,and the possibility of separation of various factors is analyzed.The results obtained are indicative of how much promise the proposed method offers for the inspection and testing of products made of aluminum alloys.
基金National Natural Science Foundation of China (50432020)Henan Innovation Project for University Prominent Re- search Talents (2007KYCX008)+3 种基金Henan Education Department Science and Technology Project (2007430004)Henan Plan Project for College Youth Backbone TeacherHenan University of Science and Technology Major Pre-research Foundation (2005ZD003)Henan University of Science and Technology Personnel Scientific Research Foundation (of023)
文摘Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.
文摘Based on the diurnal consecutively observed data in the offshore area of Jiaonan in 2005, the paper tries to make a preliminary analysis of the specificity of ocean currents, tidal current property and residual current property in the area in observing dates. Then on the basis of observed data analysis and by employing the split-step method, the paper conducts a numerical simulation of the tidal current field, which can show the M2 tidal constituent tidal wave system, current ellipse distribution, maximum current velocity distribution and time-dependent current field. The calculated results agree well with the observed data, which can on the one hand reflect the basic specificities of temporal and spatial distribution of the M2 tidal constituent current field to some extent, and, on the other hand, offer more information about the hydrodynamic condition. So the paper would provide a scientific basis for the making of sea environment protection plans in the offshore area of Jiaonan under certain conditions.
基金supported by the National Natural Science Foundation of China(No.41306010,41276088 and 41206002)
文摘The ocean surface currents are reconstructed from the satellite remote sensing data containing altimeter-derived sea surface height and QuikSCAT satellite-derived wind data. Based on the method proposed by Lagerloef, a global weekly 0.5°×0.5°ocean surface current product was obtained over the period 2000 - 2008 by combining the geostrophic currents estimated from sea surface height with Ekman current estimated from the wind stress. Particularly, weight functions were introduced when calculating the Ekman currents to eliminate the discontinuity near 25°S and 25°N. These satellite-derived currents have been compared with TAO current meter and the SCUD product, respectively. The comparison showed that satellite-derived currents not only could capture the characteristics of ocean surface currents but also had high accuracy and reliability. The result showed that this innovatory method was effective.
文摘The two-dimensional hydrodynamic model, MIKE21, is applied to simulate the tidal currents and sediment concentration in the radial sand ridges of the South Yellow Sea. Results are in accordance with in situ observations. Then the variations of tidal currents and suspended sediment concentration caused by reclamation and artificial islands projects are simulated. The results show that the impacts are limited around the project areas. After the projects, the fan-shaped, Jianggang centered tidal current pattern would be replaced by a pattern which is formed by two tidal paths. One locates at the Xiyang channel in north-south direction, and the other locates at the Huangshayang channel in east-west direction. The reclamation of Tiaozini separates the waters into south portion and north portion. The changes of sediment concentrations coincide with those of currents. Both the sediment concentrations and tidal currents increase at the northwest of Dongsha and the south of Gaoni, while both decrease at the north and south of Tiaozini, and the east and southwest of Dongsha.
文摘Based on 25 hours shipboard ADCP measurements across semi-enclosed bay mouth（Kemen Channel）, time series of tidal currents over 12 sites, which distribute evenly along the transect, were constructed to improve our understanding of tidal characteristics and residuals in this region. The tidal currents in Kemen Channel were identified as the regular semidiurnal and reversing tidal flows, with its behaviour more like standing waves. Moreover, the flood currents in the lower layers were found to be ahead of that in the upper layers and vice versa for ebb tides. The major of tidal ellipse for M2 constituent was found to be larger close to the southern side of the channel, with its incline also increasing toward the south. The signs of M4 constituent were also found mainly nearby the end points of this transect, indicating the importance of nonlinearity in tidal dynamics due to the shallower topography. A two-layer structure was found for the residual currents in Kemen Channel, flowing northeastwardly out of the Bay in upper 20m and southwestwardly into the bay in the lowers. Besides approximate 4.81×10^8 m^3 water exchanges were determined between the Luoyuan Bay and outer seas by the calculation of tidal flux through Kemen Channel.
文摘A direct tunneling model through gate dielectric s in CMOS devices in the frame of WKB approximation is reported.In the model,an im proved one-band effective mass approximation is used for the hole quantization, where valence band mixing is taken into account.By comparing to the experiments, the model is demonstrated to be applicable to both electron and hole tunneling c urrents in CMOS devices.The effect of the dispersion in oxide energy gap on the tunneling current is also studied.This model can be further extended to study th e direct tunneling current in future high-k materials.
文摘The tidal current duration （TCD） and velocity （TCV） and suspended sediment concentration （SSC） were measured in the dry season in December, 2011 and in the flood season in June, 2012 at the upper part of the North Channel of Changjiang Estuary. They were assimilated with the measured data in 2003, 2004, 2006 and 2007, using the tidal range＇s proportion conversion. Variations in TCD and TCV, preferential flow and SSC have been calculated. Influences of typical engineering projects such as Qingcaosha fresh water reservoir, Yangtze River Bridge, and land reclamation on the ebb and flood TCD, TCV and SSC in the North Channel for the last 10 years are discussed. The results show that： （1） currently, in the upper part of North Channel, the ebb tide dominates; after the construction of the typical projects, ebb TCD and TCV tends to be larger and the vertical average ebb and flood SSC decrease during the flood season while SSC increases during the dry season; （2） changes in the vertical average TCV are mainly contributed by seasonal runoff variation during the flood season, which is larger in the flood season than that in the dry season; the controlling parameters of increasing ebb TCD and TCV are those large-scale engineering projects in the North Channel; variation in SSC may result mainly from the reduction of basin annual sediment loads, large-scale nearshore projects and so on.
