High-frequency pulsed(HFP)gas tungsten arc welding(GTAW)has shown excellent performance in welding of aluminum alloys in recent years,which makes itself a promisingly potential technique for part manufacturing in avia...High-frequency pulsed(HFP)gas tungsten arc welding(GTAW)has shown excellent performance in welding of aluminum alloys in recent years,which makes itself a promisingly potential technique for part manufacturing in aviation industry.However,existing researches generally focuses on the effect of a single parameter while lacks multivariable researches.Considering of the fact that gap and misalignment are inevitable in real part clamping,adaptive intelligent welding is usually used during automatic manufacturing,which means under the control of filler wire amount per length of a weld,other parameters including current,welding speed and wire feed speed during one single weld are changing according to the specific clamping situation.Therefore,the influence of specific energy input led by different welding parameters within one adaptive welding program on microstructure and mechanical property of the weld needs to be clarified.This study investigates the effect of welding heat input(ranging from 1048.3 J/mm to 825.6 J/mm within one adaptive welding program control)on the formation quality of 3.25 mm thick 6061 aluminum alloy joints fabricated by HFP-GTAW with 4043 filler wire.According to the obtained results,non-monotonic relationship between heat input and porosity,with an optimal minimum of 4.92%achieved at an intermediate heat input of 856.8 J/mm.The 21.2%decrease of energy input during welding process would reduce the average grain size in the weld center and adjacent to fusion line by 18.6%and 19.4%,respectively.The ratios between fluctuation range to minimum value in average yield and the relative ranges of yield strength and ultimate tensile strength across the tested heat inputs were 14.7%and 12.7%,respectively.The findings provide a general overview on how the microstructure and mechanical properties would fluctuate in an adaptively controlled HFP-GTAW fabricated aluminum alloy weld.展开更多
A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can i...A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.展开更多
Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturba...Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr（CO3）2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.展开更多
The high-frequency pulse tube cryocooler(HPTC)represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components.However,limited to the non-ideal ...The high-frequency pulse tube cryocooler(HPTC)represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components.However,limited to the non-ideal gas effect of4He,the HPTC is hard to obtain high cooling performance in the liquid helium temperature range.3He as the working fluid can effectively improve the cooling performance of the HPTC,but the high cost hinders its wide application.In consideration of both cooling performance and cost-effectiveness,this paper explores the feasibility of utilizing^(3)He-^(4)He mixtures as the working fluid for HPTCs.Firstly,the experimental results of a developed HPTC based4He are reported.With a total power consumption of 575 W,the lowest temperature of 3.26 K was observed.And the measured cooling power at 4.2 K was 20.8 mW.Then the theoretical utmost efficiency of the cryocooler was calculated in terms of the thermophysical properties of the working fluids,using ^(3)He-^(4)He mixtures with different compositions as the working fluids.The whole machine modeling of the HPTC was further carried out,and the influence of the working fluids with different components on the structural parameters such as double-inlet and inertance tube,and operating parameters such as pressure and frequency were analyzed.The calculated results show that the cooling power is expected to be increased to36 mW and 53 mW if the equimolar ^(3)He-^(4)He mixture and pure ^(3)He are used,respectively.展开更多
Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into...Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into the new β phase during the pulsed current-assisted aging process,and then the newly formed β phase is mainly transformed into the β_(t) phase,with occasional transition to new α_(p) phase,leading to a remarkable grain refinement,especially for the lamellarαs phases.In comparison to conventional aging treatment,the pulsed current-assisted aging approach achieves a significant enhancement in strength without degrading ductility,yielding an excellent mechanical property combination:a yield strength of 932 MPa,a tensile strength of 1042 MPa,and an elongation of 12.2%.It is primarily ascribed to the increased fraction of β_(t) phases,the obvious grain refinement effect,and the slip block effect induced by the multiple-variantαs colonies distributed within β_(t) phases.展开更多
Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively invest...Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively investigated.Macroscopic morphology,microstructure,and interfacial structure of the joints were analyzed using scanning electron microscope,energy dispersive spectrometer,and X-ray diffractometer(XRD).The results show that magnetic pulse welding of dissimilar Mg/Fe metals is achieved using an Al interlayer,which acts as a bridge for deformation and diffusion.Specifically,the AZ31B/AA1060 interface exhibits a typical wavy morphology,and a transition zone exists at the joint interface,which may result in an extremely complex microstructure.The microstructure of this transition zone differs from that of AZ31B magnesium and 1060 Al alloys,and it is identified as brittle intermetallic compounds(IMCs)Al_(3)Mg_(2) and Al_(12)Mg_(17).The transition zone is mainly distributed on the Al side,with the maximum thickness of Al-side transition layer reaching approximately 13.53μm.Incomplete melting layers with varying thicknesses are observed at the primary weld interface,while micron-sized hole defects appear in the transition zone of the secondary weld interface.The AA1060/DC56D interface is mainly straight,with only a small number of discontinuous transition zones distributed intermittently along the interface.These transition zones are characterized by the presence of the brittle IMC FeAl_(3),with a maximum thickness of about 4μm.展开更多
There is a contradiction between the evolution rate of materials and the time resolution of SR-CT characterization in the in situ synchrotron radiation computed tomography(SR-CT)characterization of ultrafast evolution...There is a contradiction between the evolution rate of materials and the time resolution of SR-CT characterization in the in situ synchrotron radiation computed tomography(SR-CT)characterization of ultrafast evolution process.The sampling strategy of the ultra-sparse angle is an effective method for improving time resolution.Accurate reconstruction under sparse sampling conditions has always been a bottleneck problem.In recent years,convolutional neural networks have shown outstanding advantages in sparse-angle CT reconstruction given the development of deep learning.However,existing ideas did not consider the expression of high-frequency details in neural networks,limiting their application in accurate SR-CT characterization.A novel high-frequency information-constrained deep learning network(HFIC-Net)is proposed in response to this problem.Additional high-frequency information constraints are added to improve the accuracy of the reconstruction results.Further,a series of numerical reconstruction experiments are conducted to verify this new method,and the results indicate that the reconstruction results of HFIC-Net method effectively improve reconstruction quality.This new method uses only eight-angle projections to achieve the reconstruction effect of the filtered backprojection method(FBP)method in 360 projections.The results of the HFIC-Net method demonstrate clear boundaries and accurate detailed structures,correcting the misinformation caused by using other methods.For quantitative evaluation,the SSIM used to evaluate image structure similarity is increased from 0.1951,0.9212,and 0.9308 for FBP,FBP-Conv,and DDC-Net,respectively,to 0.9620 for HFIC-Net.Finally,the results of actual SR-CT experimental data indicate that the new method can suppress artifacts and achieve accurate reconstruction,and it is suitable for the in situ SR-CT accurate characterization of ultxafast evolution process.展开更多
In the past few years,efforts have been made to extend the sensitivity of surface nuclear magnetic resonance(SNMR)to short relaxation times,typical for strongly bound water,which,for example,occurs in partially satura...In the past few years,efforts have been made to extend the sensitivity of surface nuclear magnetic resonance(SNMR)to short relaxation times,typical for strongly bound water,which,for example,occurs in partially saturated soils.The two limiting factors for the sensitivity are the dead time after the excitation pulse and the duration of the pulse itself.To enable short pulses,while also achieving proper depths of investigation,high pulse amplitudes are needed.This makes it necessary to consider the Bloch-Siegert effect,i.e.the counter-rotating component and the parallel component of the excitation field have significant influence on the excitation.If an untuned transmitter circuit is used,the pulse shape will also be non-sinusoidal.In this paper,we demonstrate that this influences SNMR measurements with short pulses in two ways:On one hand,the pulse shape influences the phase of the fundamental frequency oscillation.On the other,at very high pulse amplitudes,other frequency components of the excitation field start to influence the excitation.The behavior of the macroscopic magnetizations in the subsurface during the pulse is simulated by solving the Bloch equations,using the pulse shape as an input.Since these calculations are computational expensive,we propose a lookup scheme that allows a time efficient modeling of the obtained SNMR data.展开更多
Pulse tube cryocoolers are widely employed in cryogenic systems,where gas contamination has become a critical factor limiting both performance and service life.To further investigate the condensation behavior of conta...Pulse tube cryocoolers are widely employed in cryogenic systems,where gas contamination has become a critical factor limiting both performance and service life.To further investigate the condensation behavior of contaminants,this study develops a two-dimensional axisymmetric model of a linear-type cryocooler to simulate the transport and deposition processes of trace CO_(2),evaluating the impact of contamination on system pressure drop under various operating conditions.Results indicate that CO_(2)diffusion is primarily driven by concentration gradients.The CO_(2)deposition rate increases markedly at low temperatures and high concentrations,with over 90%of deposition occurring in the cold-end heat exchanger.Under different concentration distributions,dry ice predominantly accumulates in the cold-end heat exchanger;however,notable differences emerge in the pulse tube.In the uniform distribution case,CO_(2)tends to deposit along the inner wall of the pulse tube,whereas in the gradual release scenario,deposition mainly occurs on the cold-end flow straightening mesh screen.Dry ice deposition significantly increases the pressure drop across the system and decreases the pressure wave amplitude,resulting in a degradation of cooling capacity.This study lays a foundation for further investigation into the thermal properties of contaminant layers and provides theoretical guidance for optimizing cold-end components to improve contamination resilience.展开更多
The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdow...The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdown delay time(T_(d))and breakdown strength(E_(b))were compared,based on analysis on the two breakdown modes namely wavefront mode and post-wave mode.It was found that T_(d) is more suitable to characterize the susceptibility of ore particles to electrical breakdown in HVP breakage than E_(b).A probabilistic model based on the Weibull distribution is developed to describe the relation of breakdown probability to T_(d).Regression analyses were conducted to investigate how operating parameters and particle properties influence Td and size reduction degree of ore particles in HVP breakage.The regressed models demonstrate potential capability to predict metallic minerals content and HVP breakage degree based on operating parameters and particle properties.展开更多
The capture zones of the continuous and pulsed guidance laws in the pursuit-evasion game are analytically discussed in this paper to provide deep insights into the capturability distinction between the continuous guid...The capture zones of the continuous and pulsed guidance laws in the pursuit-evasion game are analytically discussed in this paper to provide deep insights into the capturability distinction between the continuous guidance law and the pulsed guidance law.Specifically,first,in the pursuit-evasion game,various capture cases are defined regarding the Zero-Effort Miss distance(ZEM)to facilitate the capturability analysis.Then,for both the evader and the pursuer,the Linear-Quadratic Differential Game(LQDG)guidance laws concerning the continuous acceleration and the pulsed acceleration are converted into a unified form.In each capture case,the optimal solution existence conditions are derived,and the corresponding capture zones are formulated.The discussion on the capture zones shows that if the optimal solution exists,the distinction between the pulsed guidance law and the continuous guidance law can be neglected under small guidance effort weight.However,the capture zone of the continuous guidance law is larger than that of the pulsed guidance law with large pursuer guidance effort weight,but smaller with large evader guidance effort weight.Finally,various simulations are conducted to illustrate the distinction of the continuous and pulsed guidance laws,as well as the impact of the acceleration ratio and the time constant ratio on the capturability.展开更多
Pulsed dynamic electrolysis(PDE),driven by renewable energy,has emerged as an innovative electrocatalytic conversion method,demonstrating significant potential in addressing global energy challenges and promoting sust...Pulsed dynamic electrolysis(PDE),driven by renewable energy,has emerged as an innovative electrocatalytic conversion method,demonstrating significant potential in addressing global energy challenges and promoting sustainable development.Despite significant progress in various electrochemical systems,the regulatory mechanisms of PDE in energy and mass transfer and the lifespan extension of electrolysis systems,particularly in water electrolysis(WE)for hydrogen production,remain insufficiently explored.Therefore,there is an urgent need for a deeper understanding of the unique contributions of PDE in mass transfer enhancement,microenvironment regulation,and hydrogen production optimization,aiming to achieve low-energy consumption,high catalytic activity,and long-term stability in the generation of target products.Here,this review critically examines the microenvironmental effects of PDE on energy and mass transfer,the electrode degradation mechanisms in the lifespan extension of electrolysis systems,and the key factors in enhancing WE for hydrogen production,providing a comprehensive summary of current research progress.The review focuses on the complex regulatory mechanisms of frequency,duty cycle,amplitude,and other factors in hydrogen evolution reaction(HER)performance within PDE strategies,revealing the interrelationships among them.Finally,the potential future directions and challenges for transitioning from laboratory studies to industrial applications are proposed.展开更多
Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absor...Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absorb and dissipate energy and avoid melt formation.In this study,200 W nanosecond pulsed laser was used to irradiate granite.The effects of laser parameters on the thermal cracking morphology,temperature field,warming pattern,and Leeb hardness of the granite surface were analyzed.The optimal laser parameters for softening granite were determined by performing objective optimization in MATLAB using granite's melting point as the reference.Nanoindentation techniques were employed to assess the softening characteristics of the granite surface along the longitudinal direction.The results showed that three main forms of thermal damage occurred on the granite surface:oxidative decomposition,spalling,and melting.The damage state was affected by the average laser power,with the pulse width and repetition frequency affecting surface damage differently.Appropriate laser parameters effectively controlled the melt damage on the granite surface,and irradiation with nanosecond pulsed lasers effectively reduced surface hardness.However,excessive power can generate large amounts of hard melts and weaken the softening effect.展开更多
BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thick...BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thickness of nearly 60 nm forms on the substrate,and then a c-axis perpendicularly oriented Ba M thin film grows on the buffer layer.Atomic force microscopy results indicate that the Ba M thin film exhibits a spiral island growth mode on the buffer layer.Magnetic hysteresis loop results confirm that the buffer layer exhibits no significant magnetic anisotropy,while the Ba M thin film exhibits perpendicular magnetic anisotropy.The out-of-plane coercivity decreases with increasing Ba M thin-film thickness due to the combined effect of grain size growth and lattice strain relaxation.The 200 nm thick film exhibits optimum magnetic properties with M_(s)=319 emu/cm^(3) and H_(c)=1546 Oe.展开更多
Water-cooled system have significantly enhanced the power generation efficiency of offshore wind turbines.However,these innovative systems are susceptible to substantial biological fouling,maintenance challenges,and h...Water-cooled system have significantly enhanced the power generation efficiency of offshore wind turbines.However,these innovative systems are susceptible to substantial biological fouling,maintenance challenges,and high upkeep costs.Therefore,the development of a specialized front-end filter tailored for direct current water-cooled system is importance.This involves the integration of dimensionally stable anode(DSA)and nickel alloy cathode,valued for their corrosion resistance in seawater,into a novel front-end filter system for Water-cooled applications.This system has the dual capability of generating hydrogen and chlorine for self-cleaning purposes.Implementing a flushing pulse electrolysis mode,it effectively mitigates electrode failure induced by cathodic calcium and magnesium deposition,thereby significantly prolonging electrode lifespan.Laboratory tests comprising system assembly and performance evaluations were conducted,with the system programmed to operate for 5 minutes every 24 hours under continuous flushing by natural seawater to simulate real-world conditions.After more than 11 months of continuous flushing,observations reveal that the DSA mesh and nickel alloy mesh maintain intact structural integrity and normal functioning.Subsequent 1꞉1 physical prototype Sea trial further validated the soundness of the system design and electrolytic control parameters.展开更多
Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining...Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.展开更多
The pulse shape discrimination technique plays a pivotal role in neutron field measurements using organic scintillator detectors,and the particle-type labeling accuracy of the pulse waveform dataset has a significant ...The pulse shape discrimination technique plays a pivotal role in neutron field measurements using organic scintillator detectors,and the particle-type labeling accuracy of the pulse waveform dataset has a significant impact on its performance,especially with the growing use of machine learning methods.In this study,a high-accuracy labeling method for pulse waveform datasets based on the time-of-flight(TOF)filtering method,an improved charge comparison method(CCM),and the coincidence measurement method is proposed.The relationship between the experimental parameters and the chance coincidence proportion in the TOF measurement was derived to reduce contamination from chance coincidences at the experimental level.Based on this,an experiment was conducted to obtain raw data using the^(241)AmBe source,and a piled-up identification algorithm based on reference waveform cross-correlation and differential analysis was designed to filter out piled-up pulses.To improve the labeling accuracy,the CCM was optimized,a simple method of selecting the TOF interval for a lower chance coincidence proportion was proposed,and a low-amplitude pulse waveform dataset construction method based on coincidence measurements was developed.To verify these methods,eight pulse waveform datasets were constructed using different combinations of the proposed approaches.Three neural network structures and a corresponding evaluation parameter were designed to test the quality of these datasets.The results showed that the particle identification performance of the CCM was significantly improved after optimization,with the neutron-to-gamma-ray misidentification rate reduced by more than 35%.The proposed accuracy improvement methods reduced ambiguous identification results from these artificial neural networks by more than 50%.展开更多
Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-de...Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-density matter,understanding planetary science,and laser-driven fusion energy.However,experimental efforts in this regime have been limited by the lack of accessibility of over-critical densities and the poor spatiotemporal resolution of conventional diagnostics.Over the last decade,the advent of femtosecond brilliant hard X-ray free-electron lasers(XFELs)has opened new horizons to overcome these limitations.Here,for the first time,we present full-scale spatiotemporal measurements of solid-density plasma dynamics,including preplasma generation with tens of nanometer scale length driven by the leading edge of a relativistic laser pulse,ultrafast heating and ionization at the main pulse arrival,the laser-driven blast wave,and transient surface return current-induced compression dynamics up to hundreds of picoseconds after interaction.These observations are enabled by utilizing a novel combination of advanced X-ray diagnostics including small-angle X-ray scattering,resonant X-ray emission spectroscopy,and propagation-based X-ray phase-contrast imaging simultaneously at the European XFEL-HED beamline station.展开更多
The photoionization of a hydrogen atom from its ground state with ultra-fast chirped pulses is investigated by numerically solving the time-dependent Schrodinger equation within length,velocity,and Kramers-Henneberger...The photoionization of a hydrogen atom from its ground state with ultra-fast chirped pulses is investigated by numerically solving the time-dependent Schrodinger equation within length,velocity,and Kramers-Henneberger gauges.Converged results for all gauges for chirp-free pulses agree with the prediction of dynamic interference for ground state hydrogen atoms predicted recently by Jiang and Burgdorfer[Opt.Express 26,19921(2018)].In addition,we investigated photoelectron spectra of hydrogen atoms by chirped laser pulses,and showed that dynamic interference effect will be weaken for pulses with increasing linear chirp.Our numerical results can be understood and discussed in terms of an interplay of photoelectron wavepackets from first and second halves of laser enevelop,including the ac Stark energy level shift of the photoelectron final state and atomic stabilization effect at ultra-high intensities.展开更多
基金supported by the Commercial Aircraft Corporation of China Ltd.(Grant No.COMAC-SFGS-2024–569)Fundamental Research Funds for the Central Universities and Institute of Marine Equipment,Shanghai Rising-Star Program of Science and Technology Commission of Shanghai Municipality(Grant No.23QA1404700)+1 种基金National Natural Science Foundation of China(Grant No.52475384,52505409)China Postdoctoral Science Foundation(Grant No.2024M761963)。
文摘High-frequency pulsed(HFP)gas tungsten arc welding(GTAW)has shown excellent performance in welding of aluminum alloys in recent years,which makes itself a promisingly potential technique for part manufacturing in aviation industry.However,existing researches generally focuses on the effect of a single parameter while lacks multivariable researches.Considering of the fact that gap and misalignment are inevitable in real part clamping,adaptive intelligent welding is usually used during automatic manufacturing,which means under the control of filler wire amount per length of a weld,other parameters including current,welding speed and wire feed speed during one single weld are changing according to the specific clamping situation.Therefore,the influence of specific energy input led by different welding parameters within one adaptive welding program on microstructure and mechanical property of the weld needs to be clarified.This study investigates the effect of welding heat input(ranging from 1048.3 J/mm to 825.6 J/mm within one adaptive welding program control)on the formation quality of 3.25 mm thick 6061 aluminum alloy joints fabricated by HFP-GTAW with 4043 filler wire.According to the obtained results,non-monotonic relationship between heat input and porosity,with an optimal minimum of 4.92%achieved at an intermediate heat input of 856.8 J/mm.The 21.2%decrease of energy input during welding process would reduce the average grain size in the weld center and adjacent to fusion line by 18.6%and 19.4%,respectively.The ratios between fluctuation range to minimum value in average yield and the relative ranges of yield strength and ultimate tensile strength across the tested heat inputs were 14.7%and 12.7%,respectively.The findings provide a general overview on how the microstructure and mechanical properties would fluctuate in an adaptively controlled HFP-GTAW fabricated aluminum alloy weld.
文摘A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.
基金This work was financially supported by the Foundation for Key Program of the Ministry of Education of China (No.207038)the Technological Achievement Conversion Program of Jiangsu Province in China (No.BA2005054)+1 种基金the High Technology Research Program of Jiangsu Province (No.BG2005026)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, China (No. 05KJD450043).
文摘Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr（CO3）2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.
基金supported by the National Natural Science Foundation of China(No.12073058)the China National Space Administration(No.D050104,D040305)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2019030)。
文摘The high-frequency pulse tube cryocooler(HPTC)represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components.However,limited to the non-ideal gas effect of4He,the HPTC is hard to obtain high cooling performance in the liquid helium temperature range.3He as the working fluid can effectively improve the cooling performance of the HPTC,but the high cost hinders its wide application.In consideration of both cooling performance and cost-effectiveness,this paper explores the feasibility of utilizing^(3)He-^(4)He mixtures as the working fluid for HPTCs.Firstly,the experimental results of a developed HPTC based4He are reported.With a total power consumption of 575 W,the lowest temperature of 3.26 K was observed.And the measured cooling power at 4.2 K was 20.8 mW.Then the theoretical utmost efficiency of the cryocooler was calculated in terms of the thermophysical properties of the working fluids,using ^(3)He-^(4)He mixtures with different compositions as the working fluids.The whole machine modeling of the HPTC was further carried out,and the influence of the working fluids with different components on the structural parameters such as double-inlet and inertance tube,and operating parameters such as pressure and frequency were analyzed.The calculated results show that the cooling power is expected to be increased to36 mW and 53 mW if the equimolar ^(3)He-^(4)He mixture and pure ^(3)He are used,respectively.
基金National Key Research and Development Program of China(2021YFB3700801)。
文摘Low-density short-duration pulsed current-assisted aging treatment was applied to the Ti-6Al-4V-0.5Mo-0.5Zr alloy subjected to different solution treatments.The results show that numerous α_(p) phases redissolve into the new β phase during the pulsed current-assisted aging process,and then the newly formed β phase is mainly transformed into the β_(t) phase,with occasional transition to new α_(p) phase,leading to a remarkable grain refinement,especially for the lamellarαs phases.In comparison to conventional aging treatment,the pulsed current-assisted aging approach achieves a significant enhancement in strength without degrading ductility,yielding an excellent mechanical property combination:a yield strength of 932 MPa,a tensile strength of 1042 MPa,and an elongation of 12.2%.It is primarily ascribed to the increased fraction of β_(t) phases,the obvious grain refinement effect,and the slip block effect induced by the multiple-variantαs colonies distributed within β_(t) phases.
文摘Dissimilar AZ31B magnesium alloy and DC56D steel were welded via AA1060 aluminum alloy by magnetic pulse welding.The effects of primary and secondary welding processes on the welded interface were comparatively investigated.Macroscopic morphology,microstructure,and interfacial structure of the joints were analyzed using scanning electron microscope,energy dispersive spectrometer,and X-ray diffractometer(XRD).The results show that magnetic pulse welding of dissimilar Mg/Fe metals is achieved using an Al interlayer,which acts as a bridge for deformation and diffusion.Specifically,the AZ31B/AA1060 interface exhibits a typical wavy morphology,and a transition zone exists at the joint interface,which may result in an extremely complex microstructure.The microstructure of this transition zone differs from that of AZ31B magnesium and 1060 Al alloys,and it is identified as brittle intermetallic compounds(IMCs)Al_(3)Mg_(2) and Al_(12)Mg_(17).The transition zone is mainly distributed on the Al side,with the maximum thickness of Al-side transition layer reaching approximately 13.53μm.Incomplete melting layers with varying thicknesses are observed at the primary weld interface,while micron-sized hole defects appear in the transition zone of the secondary weld interface.The AA1060/DC56D interface is mainly straight,with only a small number of discontinuous transition zones distributed intermittently along the interface.These transition zones are characterized by the presence of the brittle IMC FeAl_(3),with a maximum thickness of about 4μm.
基金supported by the National Nature Science Foundation of China(Nos.12027901 and 12041202)Synchrotron Radiation Joint Fund of University of Science and Technology of China(Nos.KY2090000059 and KY2090000054)。
文摘There is a contradiction between the evolution rate of materials and the time resolution of SR-CT characterization in the in situ synchrotron radiation computed tomography(SR-CT)characterization of ultrafast evolution process.The sampling strategy of the ultra-sparse angle is an effective method for improving time resolution.Accurate reconstruction under sparse sampling conditions has always been a bottleneck problem.In recent years,convolutional neural networks have shown outstanding advantages in sparse-angle CT reconstruction given the development of deep learning.However,existing ideas did not consider the expression of high-frequency details in neural networks,limiting their application in accurate SR-CT characterization.A novel high-frequency information-constrained deep learning network(HFIC-Net)is proposed in response to this problem.Additional high-frequency information constraints are added to improve the accuracy of the reconstruction results.Further,a series of numerical reconstruction experiments are conducted to verify this new method,and the results indicate that the reconstruction results of HFIC-Net method effectively improve reconstruction quality.This new method uses only eight-angle projections to achieve the reconstruction effect of the filtered backprojection method(FBP)method in 360 projections.The results of the HFIC-Net method demonstrate clear boundaries and accurate detailed structures,correcting the misinformation caused by using other methods.For quantitative evaluation,the SSIM used to evaluate image structure similarity is increased from 0.1951,0.9212,and 0.9308 for FBP,FBP-Conv,and DDC-Net,respectively,to 0.9620 for HFIC-Net.Finally,the results of actual SR-CT experimental data indicate that the new method can suppress artifacts and achieve accurate reconstruction,and it is suitable for the in situ SR-CT accurate characterization of ultxafast evolution process.
基金funded by the German Research Foundation(Deutsche Forschungsgemeinschaft-DFG)under grant MU 3318/8-1.
文摘In the past few years,efforts have been made to extend the sensitivity of surface nuclear magnetic resonance(SNMR)to short relaxation times,typical for strongly bound water,which,for example,occurs in partially saturated soils.The two limiting factors for the sensitivity are the dead time after the excitation pulse and the duration of the pulse itself.To enable short pulses,while also achieving proper depths of investigation,high pulse amplitudes are needed.This makes it necessary to consider the Bloch-Siegert effect,i.e.the counter-rotating component and the parallel component of the excitation field have significant influence on the excitation.If an untuned transmitter circuit is used,the pulse shape will also be non-sinusoidal.In this paper,we demonstrate that this influences SNMR measurements with short pulses in two ways:On one hand,the pulse shape influences the phase of the fundamental frequency oscillation.On the other,at very high pulse amplitudes,other frequency components of the excitation field start to influence the excitation.The behavior of the macroscopic magnetizations in the subsurface during the pulse is simulated by solving the Bloch equations,using the pulse shape as an input.Since these calculations are computational expensive,we propose a lookup scheme that allows a time efficient modeling of the obtained SNMR data.
基金supported by the National Natural Science Foundation of China(No.52376012)the Aeronautical Science Foundation of China(20230024047001).
文摘Pulse tube cryocoolers are widely employed in cryogenic systems,where gas contamination has become a critical factor limiting both performance and service life.To further investigate the condensation behavior of contaminants,this study develops a two-dimensional axisymmetric model of a linear-type cryocooler to simulate the transport and deposition processes of trace CO_(2),evaluating the impact of contamination on system pressure drop under various operating conditions.Results indicate that CO_(2)diffusion is primarily driven by concentration gradients.The CO_(2)deposition rate increases markedly at low temperatures and high concentrations,with over 90%of deposition occurring in the cold-end heat exchanger.Under different concentration distributions,dry ice predominantly accumulates in the cold-end heat exchanger;however,notable differences emerge in the pulse tube.In the uniform distribution case,CO_(2)tends to deposit along the inner wall of the pulse tube,whereas in the gradual release scenario,deposition mainly occurs on the cold-end flow straightening mesh screen.Dry ice deposition significantly increases the pressure drop across the system and decreases the pressure wave amplitude,resulting in a degradation of cooling capacity.This study lays a foundation for further investigation into the thermal properties of contaminant layers and provides theoretical guidance for optimizing cold-end components to improve contamination resilience.
基金The financial supports from National Natural Science Foundation of China(Nos.52574313,52204272 and 52074091)to this project。
文摘The susceptibility of ore particles to electrical breakdown plays a critical role for high voltage pulse(HVP)breakage,yet its quantitative characterization still lacks deep understanding.Two indicators,namely breakdown delay time(T_(d))and breakdown strength(E_(b))were compared,based on analysis on the two breakdown modes namely wavefront mode and post-wave mode.It was found that T_(d) is more suitable to characterize the susceptibility of ore particles to electrical breakdown in HVP breakage than E_(b).A probabilistic model based on the Weibull distribution is developed to describe the relation of breakdown probability to T_(d).Regression analyses were conducted to investigate how operating parameters and particle properties influence Td and size reduction degree of ore particles in HVP breakage.The regressed models demonstrate potential capability to predict metallic minerals content and HVP breakage degree based on operating parameters and particle properties.
基金co-supported by the National Natural Science Foundation of China(Nos.U24B20157,62203031)the Natural Science Foundation of Beijing Municipality,China(No.4242041)+2 种基金the Natural Science Foundation of Zhejiang Province,China(No.LY24F030002)the Aeronautical ScienceFoundation of China(No.2024Z066051001)the Fundamental Research Funds for the Central Universities of China。
文摘The capture zones of the continuous and pulsed guidance laws in the pursuit-evasion game are analytically discussed in this paper to provide deep insights into the capturability distinction between the continuous guidance law and the pulsed guidance law.Specifically,first,in the pursuit-evasion game,various capture cases are defined regarding the Zero-Effort Miss distance(ZEM)to facilitate the capturability analysis.Then,for both the evader and the pursuer,the Linear-Quadratic Differential Game(LQDG)guidance laws concerning the continuous acceleration and the pulsed acceleration are converted into a unified form.In each capture case,the optimal solution existence conditions are derived,and the corresponding capture zones are formulated.The discussion on the capture zones shows that if the optimal solution exists,the distinction between the pulsed guidance law and the continuous guidance law can be neglected under small guidance effort weight.However,the capture zone of the continuous guidance law is larger than that of the pulsed guidance law with large pursuer guidance effort weight,but smaller with large evader guidance effort weight.Finally,various simulations are conducted to illustrate the distinction of the continuous and pulsed guidance laws,as well as the impact of the acceleration ratio and the time constant ratio on the capturability.
基金financially supported by the Key Research and Development Program of Heilongjiang Province(No.2024ZXJ03C06)National Natural Science Foundation of China(No.52476192,No.52106237)+1 种基金Natural Science Foundation of Heilongjiang Province(No.YQ2022E027)Technology Project of China Datang Technology Innovation Co.,Ltd(No.DTKC-2024-20610).
文摘Pulsed dynamic electrolysis(PDE),driven by renewable energy,has emerged as an innovative electrocatalytic conversion method,demonstrating significant potential in addressing global energy challenges and promoting sustainable development.Despite significant progress in various electrochemical systems,the regulatory mechanisms of PDE in energy and mass transfer and the lifespan extension of electrolysis systems,particularly in water electrolysis(WE)for hydrogen production,remain insufficiently explored.Therefore,there is an urgent need for a deeper understanding of the unique contributions of PDE in mass transfer enhancement,microenvironment regulation,and hydrogen production optimization,aiming to achieve low-energy consumption,high catalytic activity,and long-term stability in the generation of target products.Here,this review critically examines the microenvironmental effects of PDE on energy and mass transfer,the electrode degradation mechanisms in the lifespan extension of electrolysis systems,and the key factors in enhancing WE for hydrogen production,providing a comprehensive summary of current research progress.The review focuses on the complex regulatory mechanisms of frequency,duty cycle,amplitude,and other factors in hydrogen evolution reaction(HER)performance within PDE strategies,revealing the interrelationships among them.Finally,the potential future directions and challenges for transitioning from laboratory studies to industrial applications are proposed.
基金Project(52378425)supported by the National Natural Science Foundation of ChinaProject(1053320221044)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absorb and dissipate energy and avoid melt formation.In this study,200 W nanosecond pulsed laser was used to irradiate granite.The effects of laser parameters on the thermal cracking morphology,temperature field,warming pattern,and Leeb hardness of the granite surface were analyzed.The optimal laser parameters for softening granite were determined by performing objective optimization in MATLAB using granite's melting point as the reference.Nanoindentation techniques were employed to assess the softening characteristics of the granite surface along the longitudinal direction.The results showed that three main forms of thermal damage occurred on the granite surface:oxidative decomposition,spalling,and melting.The damage state was affected by the average laser power,with the pulse width and repetition frequency affecting surface damage differently.Appropriate laser parameters effectively controlled the melt damage on the granite surface,and irradiation with nanosecond pulsed lasers effectively reduced surface hardness.However,excessive power can generate large amounts of hard melts and weaken the softening effect.
文摘BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thickness of nearly 60 nm forms on the substrate,and then a c-axis perpendicularly oriented Ba M thin film grows on the buffer layer.Atomic force microscopy results indicate that the Ba M thin film exhibits a spiral island growth mode on the buffer layer.Magnetic hysteresis loop results confirm that the buffer layer exhibits no significant magnetic anisotropy,while the Ba M thin film exhibits perpendicular magnetic anisotropy.The out-of-plane coercivity decreases with increasing Ba M thin-film thickness due to the combined effect of grain size growth and lattice strain relaxation.The 200 nm thick film exhibits optimum magnetic properties with M_(s)=319 emu/cm^(3) and H_(c)=1546 Oe.
基金Supported by the Project of Design of Anti-corrosion and Anti-fouling Solutions for Offshore Wind Power Water-Cooled Systems(No.E428161)the National Natural Science Foundation of China(No.42176047)。
文摘Water-cooled system have significantly enhanced the power generation efficiency of offshore wind turbines.However,these innovative systems are susceptible to substantial biological fouling,maintenance challenges,and high upkeep costs.Therefore,the development of a specialized front-end filter tailored for direct current water-cooled system is importance.This involves the integration of dimensionally stable anode(DSA)and nickel alloy cathode,valued for their corrosion resistance in seawater,into a novel front-end filter system for Water-cooled applications.This system has the dual capability of generating hydrogen and chlorine for self-cleaning purposes.Implementing a flushing pulse electrolysis mode,it effectively mitigates electrode failure induced by cathodic calcium and magnesium deposition,thereby significantly prolonging electrode lifespan.Laboratory tests comprising system assembly and performance evaluations were conducted,with the system programmed to operate for 5 minutes every 24 hours under continuous flushing by natural seawater to simulate real-world conditions.After more than 11 months of continuous flushing,observations reveal that the DSA mesh and nickel alloy mesh maintain intact structural integrity and normal functioning.Subsequent 1꞉1 physical prototype Sea trial further validated the soundness of the system design and electrolytic control parameters.
基金funded on the one hand by Agence de l'Innovation de Défense(AID)grant reference number 2021650044on the other hand by Ecole Centrale de Nantes。
文摘Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.
基金supported by the National Natural Science Foundation of China(Nos.12375297 and 12105144).
文摘The pulse shape discrimination technique plays a pivotal role in neutron field measurements using organic scintillator detectors,and the particle-type labeling accuracy of the pulse waveform dataset has a significant impact on its performance,especially with the growing use of machine learning methods.In this study,a high-accuracy labeling method for pulse waveform datasets based on the time-of-flight(TOF)filtering method,an improved charge comparison method(CCM),and the coincidence measurement method is proposed.The relationship between the experimental parameters and the chance coincidence proportion in the TOF measurement was derived to reduce contamination from chance coincidences at the experimental level.Based on this,an experiment was conducted to obtain raw data using the^(241)AmBe source,and a piled-up identification algorithm based on reference waveform cross-correlation and differential analysis was designed to filter out piled-up pulses.To improve the labeling accuracy,the CCM was optimized,a simple method of selecting the TOF interval for a lower chance coincidence proportion was proposed,and a low-amplitude pulse waveform dataset construction method based on coincidence measurements was developed.To verify these methods,eight pulse waveform datasets were constructed using different combinations of the proposed approaches.Three neural network structures and a corresponding evaluation parameter were designed to test the quality of these datasets.The results showed that the particle identification performance of the CCM was significantly improved after optimization,with the neutron-to-gamma-ray misidentification rate reduced by more than 35%.The proposed accuracy improvement methods reduced ambiguous identification results from these artificial neural networks by more than 50%.
基金funding from Grant No. HIDSS-0002 DASHH (Data Science in Hamburg-Helmholtz Graduate School for the Structure of Matter)partially supported by the Helmholtz Imaging platform through the project “Smart Phase.”
文摘Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-density matter,understanding planetary science,and laser-driven fusion energy.However,experimental efforts in this regime have been limited by the lack of accessibility of over-critical densities and the poor spatiotemporal resolution of conventional diagnostics.Over the last decade,the advent of femtosecond brilliant hard X-ray free-electron lasers(XFELs)has opened new horizons to overcome these limitations.Here,for the first time,we present full-scale spatiotemporal measurements of solid-density plasma dynamics,including preplasma generation with tens of nanometer scale length driven by the leading edge of a relativistic laser pulse,ultrafast heating and ionization at the main pulse arrival,the laser-driven blast wave,and transient surface return current-induced compression dynamics up to hundreds of picoseconds after interaction.These observations are enabled by utilizing a novel combination of advanced X-ray diagnostics including small-angle X-ray scattering,resonant X-ray emission spectroscopy,and propagation-based X-ray phase-contrast imaging simultaneously at the European XFEL-HED beamline station.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774131 and 91850114)
文摘The photoionization of a hydrogen atom from its ground state with ultra-fast chirped pulses is investigated by numerically solving the time-dependent Schrodinger equation within length,velocity,and Kramers-Henneberger gauges.Converged results for all gauges for chirp-free pulses agree with the prediction of dynamic interference for ground state hydrogen atoms predicted recently by Jiang and Burgdorfer[Opt.Express 26,19921(2018)].In addition,we investigated photoelectron spectra of hydrogen atoms by chirped laser pulses,and showed that dynamic interference effect will be weaken for pulses with increasing linear chirp.Our numerical results can be understood and discussed in terms of an interplay of photoelectron wavepackets from first and second halves of laser enevelop,including the ac Stark energy level shift of the photoelectron final state and atomic stabilization effect at ultra-high intensities.
