It’s never too early in the year to start planning a break from the stress of city life,and southwest China’s charming Guizhou Province is a destination that should be right at the top of your list.
Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challe...Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challenge in accurately shaping aluminum alloy panels.In this study,the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic(210/250 MPa)and plastic(380/420 MPa)ranges at 180℃by stress relaxation and tensile tests as well as microstructure characterization.The findings reveal that compared with those under elastic loadings,in-plane anisotropy(IPA)values of the stress relaxation amount,yield strength and fracture elongation under plastic loadings are reduced by 60%–80%,70%–90% and 72%–89%,respectively.Similarly,IPA values of precipitate size in grains and PrecipitationFree Zones(PFZ)width at grain boundaries under plastic loading decrease by 31.4%and 94.4%respectively.These results indicate plastic loading significantly weakens the anisotropic SRA behavior,owing to numerous uniformly distributed fine T1phases and small IPA values of both T1precipitates size and PFZ width in various loading directions.Compared with those of elastic loadingaged alloys,yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1precipitates,narrowed PFZ and numerous sheared and rotated T1phases at different locations during tensile process.The uniformly distributed larger Kernel Average Misorientation(KAM)and Schmidt factor values of the plastic loading-aged alloy,as well as the cross-slip generated,also help to enhance the strength and ductility of the alloy.展开更多
Metallic glasses(MGs),a metastable material far from equilibrium,exhibit intricate dynamic relaxation behaviors.The challenge lies in developing a model that accurately describes the dynamics and deforma-tion mechanis...Metallic glasses(MGs),a metastable material far from equilibrium,exhibit intricate dynamic relaxation behaviors.The challenge lies in developing a model that accurately describes the dynamics and deforma-tion mechanisms of MG.This paper introduces a model integrating dynamic relaxation with deformation behavior.Validation through dynamic mechanical analysis,stress relaxation,creep,and strain recovery tests confirm the existence of four deformation modes:elasticity,anelasticity fromβrelaxation,anelas-ticity fromαrelaxation at low temperatures,and viscoplasticity fromαrelaxation at high temperatures.The model captures all of these deformation modes.The dynamical mechanical spectrum and stress re-laxation spectrum unveil dynamic features during glass to liquid transition,and a simple and effective experimental method was developed for identifying ultra-low-frequency dynamic relaxation.This work provides new perspectives on the study of relaxation dynamics in glassy states and establishes impor-tant connections between dynamic relaxation behavior and deformation mechanisms.These findings lay a theoretical and experimental foundation for the broad application of MGs.展开更多
Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were ...Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were generat-ed with internal excitation by multiphoton photolysis of CHBr_(3)at 248 nm,and its rotational temperature was found to relax to the flow temperature in a few microseconds by colliding with bath gas.The relaxation rate coefficients for CH(X^(2)Π,v=0)radical in He,Ar,and N_(2)flow were obtained by time-resolved laser-induced fluorescence measurements,ranging from 10^(-12)cm^(3)·molecule^(-1)·s^(-1)to 10^(-11)cm^(3)·molecule^(-1)·s^(-1).The N_(2)flow exhibits the highest relax-ation rate for CH(X^(2)Π)radical due to its additional rovibrational levels,which allow for more efficient energy dissipation during collisions compared to monoatomic gases.The Ar flow shows a larger relaxation rate than He flow due to its greater polarizability and stronger long-range interaction with the CH(X^(2)Π)radical.展开更多
Two CoⅡ-based complexes,{[Co(dps)_(2)(N_(3))_(2)]·H_(2)O}_n(1)and[Co(dps)_(2)(N_(3))_(2)]_n(2),show a 1D chain and a 3D network,respectively.The central CoⅡions in the complexes have the same coordination envir...Two CoⅡ-based complexes,{[Co(dps)_(2)(N_(3))_(2)]·H_(2)O}_n(1)and[Co(dps)_(2)(N_(3))_(2)]_n(2),show a 1D chain and a 3D network,respectively.The central CoⅡions in the complexes have the same coordination environment with the[Co(dps)_(4)(N_(3))_(2)]unit.Although the differences in crystal parameters are nearly negligible,their magnetic properties are very different.AC susceptibility data show that 1 behaves as a typical field-induced single-ion magnet(SIM)with the out-of-phase(χ_(M)”)signals,while 2 shows ac signals ofχ_(M)”without peaks even under applied dc filed within our measurement window.Far-IR magneto-spectra(FIRMS)show strong spin-phonon couplings at 0 T in 2,likely making the magnetic relaxation in 2 fast,while the couplings are negligible in 1.Small spin-phonon coupling in 1 likely leads to slower magnetic relaxation,making 1 a SIM.The difference in the properties is due to the structural rigidity of 2 in its 3D network,leading to stronger spin-phonon coupling.Combined high-field EPR(HF-EPR)and FIRMS studies give spin-Hamiltonian parameters,including D=64.0(9)cm^(-1),|E|=15.7(2)cm^(-1)for 1 and D=80.0(2)cm^(-1),|E|=19.0(1)cm^(-1)for 2.展开更多
Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the de...Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.展开更多
BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the cli...BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the clinical symptoms of achalasia associated with increased LES pressure.AIM To identify the safety and efficacy of POEM for patients with normal LES integrated relaxation pressure(LES-IRP).METHODS The clinical data of patients who underwent POEM successfully in The First Medical Center of Chinese PLA General Hospital were retrospectively analyzed.A total of 481 patients who underwent preoperative high-resolution manometry(HRM)at our hospital were ultimately included in this research.According to the HRM results,the patients were divided into two groups:71 patients were included in the normal LES-IRP group(LES-IRP<15 mmHg)and 410 patients were included in the increased LES-IRP group(LES-IRP≥15 mmHg).Clinical characteristics,procedure-related parameters,adverse events,and outcomes were compared between the two groups to evaluate the safety and efficacy of POEM for patients with normal LES-IRP.RESULTS Among the 481 patients included in our study,209 were males and 272 were females,with a mean age of 44.2 years.All patients underwent POEM without severe adverse events.The median pre-treatment Eckardt scores of the normal LES-IRP and increased LES-IRP groups were 7.0 and 7.0(P=0.132),respectively,decreasing to 1.0 and 1.0 post-treatment(P=0.572).The clinical success rate of the normal LES-IRP group was 87.3%(62/71),and that of the increased LES-IRP group was 91.2%(374/410)(P=0.298).Reflux symptoms were measured by the GerdQ questionnaire,and the percentages of patients with GerdQ scores≥9 in the normal LES-IRP and increased LES-IRP groups were 8.5%and 10.7%,respectively(P=0.711).After matching,the rates of clinical success and the rates of GerdQ score≥9 were not significantly different between the two groups.CONCLUSION Our results suggest that POEM is safe and effective for achalasia and patients with normal LES-IRP.In addition,in patients with normal LES-IRP,compared with those with increased LES-IRP,POEM was not associated with a greater incidence of reflux symptoms.展开更多
In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order hom...In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order homogenization(ROH)approach.The ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization methods.Due to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained analytically.Introducing the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive model.This method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical nature.This approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading conditions.Three sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic model.Furthermore,the model is validated against experimental measurements,confirming its accuracy and reliability.展开更多
Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the die...Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the dielectric and relaxor properties of NBT,various dopants such as Sr,K,Li and Bi are incorporated into the NBT structure.These modifications significantly alter the dielectric constant and relaxation behavior,demonstrating a dominant influence of dopant on the material properties.Among these,the solid solution of BaTiO_(3)(BT)with NBT is widely investigated due to its ability to stabilize the perovskite structure and improve dielectric performance.However,the temperature-dependent stability of dielectric properties remains a critical challenge for high-temperature applications.In this study,(1-x)(0.75Na_(0.5)Bi_(0.5)TiO_(3)-0.25BaTiO_(3))-xBaZrO_(3)(NBT-BT-xBZ,x=0,0.08,0.14,and 0.20)ceramics were prepared by a solid-state reaction method.The effect of BaZrO_(3)(BZ)addition on the structural,dielectric,and energy storage properties was systematically investigated.In addition,the phase transition and relaxation behaviors were also analyzed based on the modified Curie-Weiss law,Vogel-Fulcher relation,and Lorentz-type empirical law.Methods The starting materials were powders of high purity Na_(2)CO_(3),Bi_(2)O_(3),TiO_(2),BaCO_(3),and ZrO_(2).The powders were weighed according to a stoichiometric ratio(with 1%excess of Na and Bi)and ground with ethanol in a ball mill at 300 r/min for more than 12 h,and the weight ratio of raw material to ethanol and zirconium balls was 1:1:2.The dried material was heat-treated at 850℃ for 2 h to promote the formation of NBT-BT-BZ.After further grinding for 12 h,the samples were mixed with a small amount of polyvinyl alcohol(PVA).The samples were sintered in air at 1150℃for 2 h and cooled to room temperature.The phase composition of the ceramic samples was determined by an model D8 ADVANDCE X-ray diffractometer(D8 ADVANDCEXRD,Bruker AXS Ltd.,Germany)with Cu target Kαrays,at X-ray wavelengthλof 1.5406Å,2θin the range of 10°to 80°,applied voltage of 40 kV,and a current of 500 mA.A silver paste was coated on the two surfaces as electrodes and heat-treated at 700℃ for 10 min.The dielectric properties of the ceramic samples were determined at different frequencies by a model DMS-1000 high-temperature dielectric temperature spectroscope(BALAB Tech.Co.,China)with at a ramp rate of 3(°)/min in a temperature range from room temperature to 450℃.The overdamped(200Ω)discharge tests for bulk ceramic samples were performed by a model CFD-005 discharge tester(Gogo(GG)Instruments Technology,China)).Results and discussion The XRD patterns indicate that all the ceramic samples have a perovskite structure without any detectable secondary phase,proving that zirconium ions can completely enter the lattice and form a solid solution.Based on the locally magnified XRD peaks,the XRD peak shape shifts towards lower angles as a whole as the BZ content increases.This indicates that the overall volume of the crystal cell shows an expansion as the Zr ions replace Ti ions due to different ionic radii of Zr and Ti ions.The SEM images show that the grain size gradually increases with increasing the BZ content.The addition of BZ promotes the grain growth.However,this gradually slows down with the increase of content up to x of 0.20.The limited grain size variation appears in the latter two samples.All the samples show a relatively dense morphology.The Curie temperature of the NBT-0.25BT ceramic samples is 256℃,which is similar to the reported results.The Curie temperature decreases gradually with the increase of BZ additive,and the dielectric temperature spectrum flattens out,indicating that the enhanced structural and temperature stability of the NBT-BT-BZ ceramics.The maximum values of all dielectric constants correspond to temperatures that increase with frequency,indicating a dielectric relaxor behavior.A frequency dispersion is accompanied at near the Curie temperature,which can be ascribed to the thermal evolution of the tetragonal polar nanoregions(PNRs)and the mixing effect of the transition from tripartite to tetragonal PNRs.Theγvalues obtained from the experimental data at 100 kHz are 1.79,1.83,1.89,and 1.92 for NBT-BT,NBT-BT-0.08BZ,NBT-BT-0.14BZ,and NBT-BT-0.20BZ,respectively.Theγvalue increases gradually with the addition of the BZ content,showing an enhanced relaxation of the NBT-BT-BZ ceramics.The comparison of discharge current curves and energy density of all the ceramics indicate that the addition of BZ significantly improves the discharge current and energy storage performance.A high discharging energy density(Wd)of 1.6 J·cm^(-3) with a fast discharging speed(τ0.9)of 75 ns is obtained for the ceramic samples with x of 0.14.This can be attributed to an increased relaxation as the BZ content increases.Conclusions NBT-BT-BZ ceramics were prepared by a solid-state reaction method.The XRD patterns revealed a phase transition from a tetragonal phase to a pseudocubic phase as the BZ content increased.The dielectric relaxation behavior of the ceramics could be described by three empirical laws(i.e.,modified Curie-Weiss law,Vogel-Fulcher relation and Lorentz-type empirical law).The dielectric relaxation followed the modified Curie-Weiss law and the Vogel-Fulcher relationship.The parametersγand Ea,which were obtained to evaluate the relaxation behavior,increased at a higher BZ content.The Lorentz-type relationship effectively described the temperature dependence of the dielectric constant on both the low-and high-temperature sides within a specific temperature range for all the ceramics.展开更多
The reconfigurable intelligent surfaces(RIS)can reconfigure the wireless channel environment by manipulating the propagation of incident electromagnetic waves.Specifically,we consider using multi-RIS to improve the sy...The reconfigurable intelligent surfaces(RIS)can reconfigure the wireless channel environment by manipulating the propagation of incident electromagnetic waves.Specifically,we consider using multi-RIS to improve the system throughput of limited feedback multiple input single output(MISO)system in an energy efficiency manner.The critical challenge lies in the joint design of channel acquisition and beamforming which are usually based on codebook with limited precision.To solve this,we propose a semi-definite relaxation(SDR)based beamforming design scheme while considering the effect of cascaded channel acquisition.First,a channel quantization scheme is proposed by exploiting the channel sparsity in double-RIS aided MISO system.Second,an optimization problem of maximizing the system throughput is established to derive the channel quantization vector which also serves as the beamforming vector,with the consideration of the constraints of transmission power,RISs phase-shift.Third,a SDR based iterative optimization algorithm is proposed to solve the problem with low complexity.Finally,simulation results show that our proposed algorithm can improve the system throughput efficiently.展开更多
InAs/AlAs superlattice structures have significant potential for application in low-noise avalanche photodetectors.With their performance in practical applications linked to the fundamental physical properties of carr...InAs/AlAs superlattice structures have significant potential for application in low-noise avalanche photodetectors.With their performance in practical applications linked to the fundamental physical properties of carrier relaxation time,this study investigated the carrier relaxation times of InAs/AlAs superlattices across various monolayers,temperatures,and carrier concentrations.Our investigation indicated that relaxation times span several tens of picoseconds,confirming that high-quality interfaces do not significantly reduce relaxation times in the way defect states might.Moreover,our study demonstrates that adjustments to the superlattice period can effectively modulate both the bandgap and carrier relaxation times,potentially impacting the performance of avalanche photodiodes by altering the electron-phonon interaction pathways and bandgap width.We established that lower temperatures contribute to an increase in the bandgap and the suppression of high-frequency optical phonon vibrations,thereby lengthening the relaxation times.Additionally,our observations indicate that in InAs/AlAs superlattices,the relaxation time increases as the excitation power increases,owing to the phonon bottleneck effect.These insights into InAs/AlAs superlattice carrier dynamics highlight their applicability in enhancing avalanche photodetectors,and may contribute to the optimized design of superlattices for specific applications.展开更多
The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-...The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-spun(Fe_(0.5)Co_(0.5))_(75)B_(21)Nb_(4) metallic glasses(MGs)is studied.On the premise of maintaining a fully amorphous phase,appropriate CT and relaxation annealing are conducive to achieving the synergistic effect of increasing saturation magnetization(M_(s))and reducing coercivity(H_(c)).Shallow CT at 213 K optim-ally enhances the soft magnetic properties of MGs.Given its low activation energy of nucleation and increased activation energy of growth,appropriate CT is beneficial for achieving uniform annealed nanocrystals in amorphous phases.The correlation between free volumes(FVs)and potential energy suggests that the variation in Hc depends on the expansion and contraction behavior of amorphous phases after different CT processes.The fitting formulas of H_(c)–d_(m) and Ms–Hv correlations demonstrate that soft magnetic parameters have a solid linear relationship with the contents of FVs and degree of dense random packing.Moreover,pitting resistance is improved by ap-propriate CT and relaxation annealing.This improvement is characterized by the promotion of the stability of the Nb-rich passive film formed during electrochemical corrosion in 3.5wt%NaCl solution.展开更多
Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum a...Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum alloy largely pre-deformed(LPD)by 80%have been systematically investigated.The stress relaxation ratio of the LPD alloy reaches approximately 94%regardless of the initial stress(50–350 MPa)after ageing for 12 h at 140°C.This relaxation ratio is about 2.9 and 1.8 times that in the T4 tempered alloy(27.6%under 50 MPa and 31.5%under 150 MPa)and T3 tempered alloy(37.6%under 50 MPa and 51.2%under 150 MPa),respectively.The microstructures,comprised of GP zones/θ'precipitates plus dislocation tangles,and tensile properties in the stress-relaxation-aged LPD alloys remain basically invariant with different initial stresses,as is vital importance for property consistency at different locations of the formed part.Under the same SRA condition,the LPD alloy has an increase of 150–230 MPa in yield strength relative to T3/T4 tempered alloy and obtains a uniform elongation of about 8%.A simple dislocation-based constitutive model accurately describing stress relaxation enhanced by the high dislocation density is established and embedded in the finite element package through a user subroutine.Simulations and experimental verifications show the LPD alloy sheet parts exhibit a nearly zero springback(<5%)after unloading in contrast to the springback larger than 65%in the T3/T4 alloy sheet parts under the same condition.Our findings demonstrate the high-dislocation-density-enhanced SRA response enables a high-performance springback-free age forming of Al alloy sheet.展开更多
The stretching-induced phase transition of biodegradable poly(butylene succinate)(PBS)was explored using a combination of mechanical testing and in situ wide angle X-ray diffraction characterization.The phase transiti...The stretching-induced phase transition of biodegradable poly(butylene succinate)(PBS)was explored using a combination of mechanical testing and in situ wide angle X-ray diffraction characterization.The phase transition fromαphase toβphase can be effectively triggered by severe stretching,in which the threshold strain is dependent on the PBS crystallites.Interestingly,thisα-βphase transition can be reversed immediately once mechanical stretching begins to be released.It should be pointed out that the finish ofβ-αphase transition reversed,corresponding to the disappearance of the generatedβphase,does not necessarily need the external stretching to completely release.For the relaxation-reversed phase transition,the evolution of the normalizedβ-phase fraction exhibited a similar correlation with the stress released.It was indicated that the decay kinetics followed a stretching-dominant mechanism,and the amount ofβphase generated just prior to relaxation had a negligible influence on the reversed phase transition.展开更多
Most material distribution-based topology optimization methods work on a relaxed form of the optimization problem and then push the solution toward the binary limits.However,when benchmarking these methods,researchers...Most material distribution-based topology optimization methods work on a relaxed form of the optimization problem and then push the solution toward the binary limits.However,when benchmarking these methods,researchers use known solutions to only a single form of benchmark problem.This paper proposes a comparison platform for systematic benchmarking of topology optimization methods using both binary and relaxed forms.A greyness measure is implemented to evaluate how far a solution is from the desired binary form.The well-known ZhouRozvany(ZR)problem is selected as the benchmarking problem here,making use of available global solutions for both its relaxed and binary forms.The recently developed non-penalization Smooth-edged Material Distribution for Optimizing Topology(SEMDOT),well-established Solid Isotropic Material with Penalization(SIMP),and continuation methods are studied on this platform.Interestingly,in most cases,the grayscale solutions obtained by SEMDOT demonstrate better performance in dealing with the ZR problem than SIMP.The reasons are investigated and attributed to the usage of two different regularization techniques,namely,the Heaviside smooth function in SEMDOT and the power-law penalty in SIMP.More importantly,a simple-to-use benchmarking graph is proposed for evaluating newly developed topology optimization methods.展开更多
Structural fine-tuning is of significant importance to enhance the magnetic anisotropy and elucidate the magneto-structural relationship for single molecule magnets(SMMs).For this purpose,two mononuclear Dy^(3+) SMMs:...Structural fine-tuning is of significant importance to enhance the magnetic anisotropy and elucidate the magneto-structural relationship for single molecule magnets(SMMs).For this purpose,two mononuclear Dy^(3+) SMMs:[Dy{HB(pz)3}2(Sal)](1) and [Dy{HB(pz)_(3)}_(2)(MeO-Sal)](2),where HB(pz)_(3)^(-)represents hydro tris(pyrazolyl)borate,Sal denotes salicyiaidehyde and MeO-Sal stands for 5-methoxysalicylaldehyde,were designed and synthesized.Single crystal X-ray diffraction tests show that the two SMMs have very similar eight-coordinated molecule structures,although the introducing of-MeO substituent on salicyiaidehyde ligand induces the changes on the molecule packing mode and the space group.Both the two SMMs have a Dy-O_(aryloxidebond) that is significantly shorter than other Dy-O/N bonds,which defines the orientation of main anisotropy axis of the ground Kramers doublets and engenders the slow relaxation of the magnetization behavior,as evidenced by the magnetic susceptibility and the ab initio calculation.Though with an electron-donating substituent on the axial Sal ligand in 2,the collective magnetic anisotropy is not enhanced and the corresponding magneto-structural relationship is discussed based on the experimental and theoretical calculation results.In addition,as neutral molecules,1 and 2 are soluble in several common organic solvents,like CH_(2)Cl_(2),CHCl_(3),THF and so on.展开更多
This paper deals with the problem of robust stabilization for uncertain Takagi-Sugeno(T-S)fuzzy neutral systems with input delays and distributed delays.The purpose is to design a state feedback fuzzy controller with ...This paper deals with the problem of robust stabilization for uncertain Takagi-Sugeno(T-S)fuzzy neutral systems with input delays and distributed delays.The purpose is to design a state feedback fuzzy controller with a H∞performance such that the resulting closed-loop system is robustly stable.Sufficient conditions for the solvability of the problem are obtained by utilizing proper Lyapunov functional together with the linear matrix inequality(LMI)approach,especially two different improved results on robust H∞controller design with relaxed conditions are obtained.Finally,we provide two examples to verify the effectiveness of our design method and give some principle for choosing the proper controller under certain circumstances.展开更多
Metal foils have emerged as one of the promising materials for anode-free batteries due to their high energy density and scalability in production.The unclear lithium plating/stripping kinetics of metal foil current c...Metal foils have emerged as one of the promising materials for anode-free batteries due to their high energy density and scalability in production.The unclear lithium plating/stripping kinetics of metal foil current collectors in anode-free batteries was addressed by using the non-destructive distribution of relaxation times(DRT)analysis to systematically investigate the lithium transport behavior of 14 metal foils and its correlation with electrochemical performance.By integrating energy-dispersive spectro scopy(EDS),cyclic voltammetry(CV),and galvanostatic testing,the exceptional properties of indium(In),tin(Sn),and silver(Ag)were revealed:the Li-In alloying reaction exhibits high reversibility,Li-Sn alloys demonstrate outstanding cycling stability,and the Li-Ag solid-solution mechanism provides an ideal lithium deposition interface on the silver substrate.The DRT separates the polarization internal resistance of lithium ions passing through the SEI layer(R_(sei),τ2)and the polarization internal resistance of lithium ions undergoing charge transfer reaction at the electrolyte/electrode interface(R_(ct),τ3)by decoupling the electrochemical impedance spectroscopy(EIS).For the first time,the correlation betweenτ2,τ3,and the cycle life/Coulombic efficiency of alloy/solid-solution metals was established,while non-alloy metals are not suitable for this method due to differences in lithium deposition mechanisms.This study not only illuminates the structure-property relationship governing the lithium kinetics of metal foil electrodes but also provides a novel non-destructive analytical strategy and theoretical guidance for the rational design of stable anodes in high-energy-density batteries,facilitating the efficient screening and optimization of anode-free battery.展开更多
This paper is devoted to the existence results for a class of neutral abstract fractional differential equations involving the composite relaxation process.Based on the Laplace transform,the semigroup theory and the W...This paper is devoted to the existence results for a class of neutral abstract fractional differential equations involving the composite relaxation process.Based on the Laplace transform,the semigroup theory and the Wright functions,we first introduce a definition of mild solutions to the considered problem.By means of the noncompactness of measure and the fixed point technique,we establish existence criteria of solutions.Finally,an example is presented to illustrate our main result.展开更多
The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented w...The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented which integrates 2D NMR T_(1)-T_(2) relaxation measurements with molecular dynamics(MD)simulations of hydrocarbons confined in the nanopores of kerogen.The integrated NMR-MD technique is demonstrated using T_(1)-T_(2) measurements of kerogen isolates and organic-rich chalks saturated with heptane,together with MD simulations of heptane completely dissolved in a realistic kerogen model.The NMR-MD results are used to extract the swelling ratio and nanopore size distribution of kerogen as a function of depth in the reservoir.The effects of organic nanoconfinement on the T_(1) relaxation dispersion and T_(2) residual dipolar coupling of heptane are investigated,as well as the effect of downhole effective stress on the kerogen nanopore size as a function of depth and compaction.Potential applications in partially depleted gas shale reservoirs are discussed,including CO_(2) utilization/geostorage,geostorage of green H_(2),and integration of the NMR-MD technique with thermodynamic models for predicting the competitive sorption of gas mixtures in kerogen.展开更多
文摘It’s never too early in the year to start planning a break from the stress of city life,and southwest China’s charming Guizhou Province is a destination that should be right at the top of your list.
基金support from the Key Program of the National Natural Science Foundation of China(No.51235010)。
文摘Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challenge in accurately shaping aluminum alloy panels.In this study,the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic(210/250 MPa)and plastic(380/420 MPa)ranges at 180℃by stress relaxation and tensile tests as well as microstructure characterization.The findings reveal that compared with those under elastic loadings,in-plane anisotropy(IPA)values of the stress relaxation amount,yield strength and fracture elongation under plastic loadings are reduced by 60%–80%,70%–90% and 72%–89%,respectively.Similarly,IPA values of precipitate size in grains and PrecipitationFree Zones(PFZ)width at grain boundaries under plastic loading decrease by 31.4%and 94.4%respectively.These results indicate plastic loading significantly weakens the anisotropic SRA behavior,owing to numerous uniformly distributed fine T1phases and small IPA values of both T1precipitates size and PFZ width in various loading directions.Compared with those of elastic loadingaged alloys,yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1precipitates,narrowed PFZ and numerous sheared and rotated T1phases at different locations during tensile process.The uniformly distributed larger Kernel Average Misorientation(KAM)and Schmidt factor values of the plastic loading-aged alloy,as well as the cross-slip generated,also help to enhance the strength and ductility of the alloy.
基金supported by the National Natu-ral Science Foundation of China(Nos.12472069 and 52271153)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(No.2021JC-12)+5 种基金Guo-Jian Lyu is supported by the National Natural Science Foundation of China(No.52301219)the Fundamental Research Funds for the Cen-tral Universities(No.5000230147)Yun-Jiang Wang was finan-cially supported by the National Natural Science Foundation of China(No.12472112)Y.Yang acknowledges financial support from the Research Grant Council(RGC),the Hong Kong Government through the General Research Fund(GRF)(Nos.CityU11206362 and N_CityU109/21)E.Pineda acknowledges financial support from MCIN/AEI(Nos.PID2020-112975GB-I00/10.13039/501100011033 and CEX2023-001300-M/10.13039/501100011033)Generalitat de Catalunya(No.2021SGR00343).
文摘Metallic glasses(MGs),a metastable material far from equilibrium,exhibit intricate dynamic relaxation behaviors.The challenge lies in developing a model that accurately describes the dynamics and deforma-tion mechanisms of MG.This paper introduces a model integrating dynamic relaxation with deformation behavior.Validation through dynamic mechanical analysis,stress relaxation,creep,and strain recovery tests confirm the existence of four deformation modes:elasticity,anelasticity fromβrelaxation,anelas-ticity fromαrelaxation at low temperatures,and viscoplasticity fromαrelaxation at high temperatures.The model captures all of these deformation modes.The dynamical mechanical spectrum and stress re-laxation spectrum unveil dynamic features during glass to liquid transition,and a simple and effective experimental method was developed for identifying ultra-low-frequency dynamic relaxation.This work provides new perspectives on the study of relaxation dynamics in glassy states and establishes impor-tant connections between dynamic relaxation behavior and deformation mechanisms.These findings lay a theoretical and experimental foundation for the broad application of MGs.
基金supported by the National Natural Science Foundation of China(No.22273103)the National Natural Science Foundation of China(NSFC Center for Chemical Dynamics)(No.22288201)+1 种基金Dalian Institute of Chemical Physics(DICP I202230)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(grant GJJSTD20220001)。
文摘Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were generat-ed with internal excitation by multiphoton photolysis of CHBr_(3)at 248 nm,and its rotational temperature was found to relax to the flow temperature in a few microseconds by colliding with bath gas.The relaxation rate coefficients for CH(X^(2)Π,v=0)radical in He,Ar,and N_(2)flow were obtained by time-resolved laser-induced fluorescence measurements,ranging from 10^(-12)cm^(3)·molecule^(-1)·s^(-1)to 10^(-11)cm^(3)·molecule^(-1)·s^(-1).The N_(2)flow exhibits the highest relax-ation rate for CH(X^(2)Π)radical due to its additional rovibrational levels,which allow for more efficient energy dissipation during collisions compared to monoatomic gases.The Ar flow shows a larger relaxation rate than He flow due to its greater polarizability and stronger long-range interaction with the CH(X^(2)Π)radical.
基金supported by the National Key Research and Development Program of China(No.2021YFA1600304)Joint Fund for Regional Innovation and Development(No.U20A2073)+4 种基金National Natural Science Foundation of China(Nos.22373048,21973038,61904119 and 22105089)Jiangxi Provincial Key Laboratory of Functional Molecular Materials Chemistry(No.20212BCD42018)US National Science Foundation(NSF,No.CHE-2055499)the Interdisciplinary program of Wuhan National High Magnetic Field Center(No.WHMFC202133)the support of the NSF Research Traineeship Program(No.DGE-2152168)。
文摘Two CoⅡ-based complexes,{[Co(dps)_(2)(N_(3))_(2)]·H_(2)O}_n(1)and[Co(dps)_(2)(N_(3))_(2)]_n(2),show a 1D chain and a 3D network,respectively.The central CoⅡions in the complexes have the same coordination environment with the[Co(dps)_(4)(N_(3))_(2)]unit.Although the differences in crystal parameters are nearly negligible,their magnetic properties are very different.AC susceptibility data show that 1 behaves as a typical field-induced single-ion magnet(SIM)with the out-of-phase(χ_(M)”)signals,while 2 shows ac signals ofχ_(M)”without peaks even under applied dc filed within our measurement window.Far-IR magneto-spectra(FIRMS)show strong spin-phonon couplings at 0 T in 2,likely making the magnetic relaxation in 2 fast,while the couplings are negligible in 1.Small spin-phonon coupling in 1 likely leads to slower magnetic relaxation,making 1 a SIM.The difference in the properties is due to the structural rigidity of 2 in its 3D network,leading to stronger spin-phonon coupling.Combined high-field EPR(HF-EPR)and FIRMS studies give spin-Hamiltonian parameters,including D=64.0(9)cm^(-1),|E|=15.7(2)cm^(-1)for 1 and D=80.0(2)cm^(-1),|E|=19.0(1)cm^(-1)for 2.
基金supported by the National Natural Science Foundation of China(52476200,52106244)the Guangdong Basic and Applied Basic Research Foundation(2024A1515030124)+1 种基金the Science and Technology Project of China Southern Power Grid under Grant GDKJXM20230246(030100KC23020017)the Fundamental Research Funds for the Central Universities。
文摘Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.
文摘BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the clinical symptoms of achalasia associated with increased LES pressure.AIM To identify the safety and efficacy of POEM for patients with normal LES integrated relaxation pressure(LES-IRP).METHODS The clinical data of patients who underwent POEM successfully in The First Medical Center of Chinese PLA General Hospital were retrospectively analyzed.A total of 481 patients who underwent preoperative high-resolution manometry(HRM)at our hospital were ultimately included in this research.According to the HRM results,the patients were divided into two groups:71 patients were included in the normal LES-IRP group(LES-IRP<15 mmHg)and 410 patients were included in the increased LES-IRP group(LES-IRP≥15 mmHg).Clinical characteristics,procedure-related parameters,adverse events,and outcomes were compared between the two groups to evaluate the safety and efficacy of POEM for patients with normal LES-IRP.RESULTS Among the 481 patients included in our study,209 were males and 272 were females,with a mean age of 44.2 years.All patients underwent POEM without severe adverse events.The median pre-treatment Eckardt scores of the normal LES-IRP and increased LES-IRP groups were 7.0 and 7.0(P=0.132),respectively,decreasing to 1.0 and 1.0 post-treatment(P=0.572).The clinical success rate of the normal LES-IRP group was 87.3%(62/71),and that of the increased LES-IRP group was 91.2%(374/410)(P=0.298).Reflux symptoms were measured by the GerdQ questionnaire,and the percentages of patients with GerdQ scores≥9 in the normal LES-IRP and increased LES-IRP groups were 8.5%and 10.7%,respectively(P=0.711).After matching,the rates of clinical success and the rates of GerdQ score≥9 were not significantly different between the two groups.CONCLUSION Our results suggest that POEM is safe and effective for achalasia and patients with normal LES-IRP.In addition,in patients with normal LES-IRP,compared with those with increased LES-IRP,POEM was not associated with a greater incidence of reflux symptoms.
基金support by the National Key R&D Program of China(Grant No.2023YFA1008901)the National Natural Science Foundation of China(Grant Nos.11988102,12172009)is gratefully acknowledged.
文摘In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order homogenization(ROH)approach.The ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization methods.Due to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained analytically.Introducing the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive model.This method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical nature.This approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading conditions.Three sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic model.Furthermore,the model is validated against experimental measurements,confirming its accuracy and reliability.
基金国家自然科学基金(12104188,12474095 and 52402323)开放基金(2023KF03,KYCX24-4102)。
文摘Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the dielectric and relaxor properties of NBT,various dopants such as Sr,K,Li and Bi are incorporated into the NBT structure.These modifications significantly alter the dielectric constant and relaxation behavior,demonstrating a dominant influence of dopant on the material properties.Among these,the solid solution of BaTiO_(3)(BT)with NBT is widely investigated due to its ability to stabilize the perovskite structure and improve dielectric performance.However,the temperature-dependent stability of dielectric properties remains a critical challenge for high-temperature applications.In this study,(1-x)(0.75Na_(0.5)Bi_(0.5)TiO_(3)-0.25BaTiO_(3))-xBaZrO_(3)(NBT-BT-xBZ,x=0,0.08,0.14,and 0.20)ceramics were prepared by a solid-state reaction method.The effect of BaZrO_(3)(BZ)addition on the structural,dielectric,and energy storage properties was systematically investigated.In addition,the phase transition and relaxation behaviors were also analyzed based on the modified Curie-Weiss law,Vogel-Fulcher relation,and Lorentz-type empirical law.Methods The starting materials were powders of high purity Na_(2)CO_(3),Bi_(2)O_(3),TiO_(2),BaCO_(3),and ZrO_(2).The powders were weighed according to a stoichiometric ratio(with 1%excess of Na and Bi)and ground with ethanol in a ball mill at 300 r/min for more than 12 h,and the weight ratio of raw material to ethanol and zirconium balls was 1:1:2.The dried material was heat-treated at 850℃ for 2 h to promote the formation of NBT-BT-BZ.After further grinding for 12 h,the samples were mixed with a small amount of polyvinyl alcohol(PVA).The samples were sintered in air at 1150℃for 2 h and cooled to room temperature.The phase composition of the ceramic samples was determined by an model D8 ADVANDCE X-ray diffractometer(D8 ADVANDCEXRD,Bruker AXS Ltd.,Germany)with Cu target Kαrays,at X-ray wavelengthλof 1.5406Å,2θin the range of 10°to 80°,applied voltage of 40 kV,and a current of 500 mA.A silver paste was coated on the two surfaces as electrodes and heat-treated at 700℃ for 10 min.The dielectric properties of the ceramic samples were determined at different frequencies by a model DMS-1000 high-temperature dielectric temperature spectroscope(BALAB Tech.Co.,China)with at a ramp rate of 3(°)/min in a temperature range from room temperature to 450℃.The overdamped(200Ω)discharge tests for bulk ceramic samples were performed by a model CFD-005 discharge tester(Gogo(GG)Instruments Technology,China)).Results and discussion The XRD patterns indicate that all the ceramic samples have a perovskite structure without any detectable secondary phase,proving that zirconium ions can completely enter the lattice and form a solid solution.Based on the locally magnified XRD peaks,the XRD peak shape shifts towards lower angles as a whole as the BZ content increases.This indicates that the overall volume of the crystal cell shows an expansion as the Zr ions replace Ti ions due to different ionic radii of Zr and Ti ions.The SEM images show that the grain size gradually increases with increasing the BZ content.The addition of BZ promotes the grain growth.However,this gradually slows down with the increase of content up to x of 0.20.The limited grain size variation appears in the latter two samples.All the samples show a relatively dense morphology.The Curie temperature of the NBT-0.25BT ceramic samples is 256℃,which is similar to the reported results.The Curie temperature decreases gradually with the increase of BZ additive,and the dielectric temperature spectrum flattens out,indicating that the enhanced structural and temperature stability of the NBT-BT-BZ ceramics.The maximum values of all dielectric constants correspond to temperatures that increase with frequency,indicating a dielectric relaxor behavior.A frequency dispersion is accompanied at near the Curie temperature,which can be ascribed to the thermal evolution of the tetragonal polar nanoregions(PNRs)and the mixing effect of the transition from tripartite to tetragonal PNRs.Theγvalues obtained from the experimental data at 100 kHz are 1.79,1.83,1.89,and 1.92 for NBT-BT,NBT-BT-0.08BZ,NBT-BT-0.14BZ,and NBT-BT-0.20BZ,respectively.Theγvalue increases gradually with the addition of the BZ content,showing an enhanced relaxation of the NBT-BT-BZ ceramics.The comparison of discharge current curves and energy density of all the ceramics indicate that the addition of BZ significantly improves the discharge current and energy storage performance.A high discharging energy density(Wd)of 1.6 J·cm^(-3) with a fast discharging speed(τ0.9)of 75 ns is obtained for the ceramic samples with x of 0.14.This can be attributed to an increased relaxation as the BZ content increases.Conclusions NBT-BT-BZ ceramics were prepared by a solid-state reaction method.The XRD patterns revealed a phase transition from a tetragonal phase to a pseudocubic phase as the BZ content increased.The dielectric relaxation behavior of the ceramics could be described by three empirical laws(i.e.,modified Curie-Weiss law,Vogel-Fulcher relation and Lorentz-type empirical law).The dielectric relaxation followed the modified Curie-Weiss law and the Vogel-Fulcher relationship.The parametersγand Ea,which were obtained to evaluate the relaxation behavior,increased at a higher BZ content.The Lorentz-type relationship effectively described the temperature dependence of the dielectric constant on both the low-and high-temperature sides within a specific temperature range for all the ceramics.
基金supported the Innovation Talents Promotion Program of Shaanxi Province under Grant No.2021TD-08。
文摘The reconfigurable intelligent surfaces(RIS)can reconfigure the wireless channel environment by manipulating the propagation of incident electromagnetic waves.Specifically,we consider using multi-RIS to improve the system throughput of limited feedback multiple input single output(MISO)system in an energy efficiency manner.The critical challenge lies in the joint design of channel acquisition and beamforming which are usually based on codebook with limited precision.To solve this,we propose a semi-definite relaxation(SDR)based beamforming design scheme while considering the effect of cascaded channel acquisition.First,a channel quantization scheme is proposed by exploiting the channel sparsity in double-RIS aided MISO system.Second,an optimization problem of maximizing the system throughput is established to derive the channel quantization vector which also serves as the beamforming vector,with the consideration of the constraints of transmission power,RISs phase-shift.Third,a SDR based iterative optimization algorithm is proposed to solve the problem with low complexity.Finally,simulation results show that our proposed algorithm can improve the system throughput efficiently.
基金supported by the Science and Technology Innovation Program of Hunan Province(Grant No.2021RC4026)。
文摘InAs/AlAs superlattice structures have significant potential for application in low-noise avalanche photodetectors.With their performance in practical applications linked to the fundamental physical properties of carrier relaxation time,this study investigated the carrier relaxation times of InAs/AlAs superlattices across various monolayers,temperatures,and carrier concentrations.Our investigation indicated that relaxation times span several tens of picoseconds,confirming that high-quality interfaces do not significantly reduce relaxation times in the way defect states might.Moreover,our study demonstrates that adjustments to the superlattice period can effectively modulate both the bandgap and carrier relaxation times,potentially impacting the performance of avalanche photodiodes by altering the electron-phonon interaction pathways and bandgap width.We established that lower temperatures contribute to an increase in the bandgap and the suppression of high-frequency optical phonon vibrations,thereby lengthening the relaxation times.Additionally,our observations indicate that in InAs/AlAs superlattices,the relaxation time increases as the excitation power increases,owing to the phonon bottleneck effect.These insights into InAs/AlAs superlattice carrier dynamics highlight their applicability in enhancing avalanche photodetectors,and may contribute to the optimized design of superlattices for specific applications.
基金support from the National Natural Science Foundation of China(No.52271146)New 20 Items of Colleges and Universities in Jinan,China(No.202228111)University of Jinan Disciplinary Cross-Convergence Construction Project 2023,China(No.XKJC-202311).
文摘The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-spun(Fe_(0.5)Co_(0.5))_(75)B_(21)Nb_(4) metallic glasses(MGs)is studied.On the premise of maintaining a fully amorphous phase,appropriate CT and relaxation annealing are conducive to achieving the synergistic effect of increasing saturation magnetization(M_(s))and reducing coercivity(H_(c)).Shallow CT at 213 K optim-ally enhances the soft magnetic properties of MGs.Given its low activation energy of nucleation and increased activation energy of growth,appropriate CT is beneficial for achieving uniform annealed nanocrystals in amorphous phases.The correlation between free volumes(FVs)and potential energy suggests that the variation in Hc depends on the expansion and contraction behavior of amorphous phases after different CT processes.The fitting formulas of H_(c)–d_(m) and Ms–Hv correlations demonstrate that soft magnetic parameters have a solid linear relationship with the contents of FVs and degree of dense random packing.Moreover,pitting resistance is improved by ap-propriate CT and relaxation annealing.This improvement is characterized by the promotion of the stability of the Nb-rich passive film formed during electrochemical corrosion in 3.5wt%NaCl solution.
基金financially supported by the National Natural Science Foundation of China(Nos.52274404,52305441,and U22A20190)the Natural Science Foundation of Hunan province(Nos.2022JJ20065 and 2023JJ40739)+1 种基金the Science and Technology Innovation Program of Hunan Province(No.2022RC1001)the National Key R&D Program of China(No.2021YFB3400903).
文摘Obtaining zero springback and good post-form performance simultaneously is an ultimate pursuit in metal sheet forming.The stress-relaxation ageing(SRA)behavior and mechanical properties of a commercial 2219 aluminum alloy largely pre-deformed(LPD)by 80%have been systematically investigated.The stress relaxation ratio of the LPD alloy reaches approximately 94%regardless of the initial stress(50–350 MPa)after ageing for 12 h at 140°C.This relaxation ratio is about 2.9 and 1.8 times that in the T4 tempered alloy(27.6%under 50 MPa and 31.5%under 150 MPa)and T3 tempered alloy(37.6%under 50 MPa and 51.2%under 150 MPa),respectively.The microstructures,comprised of GP zones/θ'precipitates plus dislocation tangles,and tensile properties in the stress-relaxation-aged LPD alloys remain basically invariant with different initial stresses,as is vital importance for property consistency at different locations of the formed part.Under the same SRA condition,the LPD alloy has an increase of 150–230 MPa in yield strength relative to T3/T4 tempered alloy and obtains a uniform elongation of about 8%.A simple dislocation-based constitutive model accurately describing stress relaxation enhanced by the high dislocation density is established and embedded in the finite element package through a user subroutine.Simulations and experimental verifications show the LPD alloy sheet parts exhibit a nearly zero springback(<5%)after unloading in contrast to the springback larger than 65%in the T3/T4 alloy sheet parts under the same condition.Our findings demonstrate the high-dislocation-density-enhanced SRA response enables a high-performance springback-free age forming of Al alloy sheet.
基金supported by the National Natural Science Foundation of China(No.52273025).
文摘The stretching-induced phase transition of biodegradable poly(butylene succinate)(PBS)was explored using a combination of mechanical testing and in situ wide angle X-ray diffraction characterization.The phase transition fromαphase toβphase can be effectively triggered by severe stretching,in which the threshold strain is dependent on the PBS crystallites.Interestingly,thisα-βphase transition can be reversed immediately once mechanical stretching begins to be released.It should be pointed out that the finish ofβ-αphase transition reversed,corresponding to the disappearance of the generatedβphase,does not necessarily need the external stretching to completely release.For the relaxation-reversed phase transition,the evolution of the normalizedβ-phase fraction exhibited a similar correlation with the stress released.It was indicated that the decay kinetics followed a stretching-dominant mechanism,and the amount ofβphase generated just prior to relaxation had a negligible influence on the reversed phase transition.
文摘Most material distribution-based topology optimization methods work on a relaxed form of the optimization problem and then push the solution toward the binary limits.However,when benchmarking these methods,researchers use known solutions to only a single form of benchmark problem.This paper proposes a comparison platform for systematic benchmarking of topology optimization methods using both binary and relaxed forms.A greyness measure is implemented to evaluate how far a solution is from the desired binary form.The well-known ZhouRozvany(ZR)problem is selected as the benchmarking problem here,making use of available global solutions for both its relaxed and binary forms.The recently developed non-penalization Smooth-edged Material Distribution for Optimizing Topology(SEMDOT),well-established Solid Isotropic Material with Penalization(SIMP),and continuation methods are studied on this platform.Interestingly,in most cases,the grayscale solutions obtained by SEMDOT demonstrate better performance in dealing with the ZR problem than SIMP.The reasons are investigated and attributed to the usage of two different regularization techniques,namely,the Heaviside smooth function in SEMDOT and the power-law penalty in SIMP.More importantly,a simple-to-use benchmarking graph is proposed for evaluating newly developed topology optimization methods.
基金Project supported by the Nature Science Foundation of Shaanxi Province (2023-JC-YB-137)National Natural Science Foundation of China (21901200)。
文摘Structural fine-tuning is of significant importance to enhance the magnetic anisotropy and elucidate the magneto-structural relationship for single molecule magnets(SMMs).For this purpose,two mononuclear Dy^(3+) SMMs:[Dy{HB(pz)3}2(Sal)](1) and [Dy{HB(pz)_(3)}_(2)(MeO-Sal)](2),where HB(pz)_(3)^(-)represents hydro tris(pyrazolyl)borate,Sal denotes salicyiaidehyde and MeO-Sal stands for 5-methoxysalicylaldehyde,were designed and synthesized.Single crystal X-ray diffraction tests show that the two SMMs have very similar eight-coordinated molecule structures,although the introducing of-MeO substituent on salicyiaidehyde ligand induces the changes on the molecule packing mode and the space group.Both the two SMMs have a Dy-O_(aryloxidebond) that is significantly shorter than other Dy-O/N bonds,which defines the orientation of main anisotropy axis of the ground Kramers doublets and engenders the slow relaxation of the magnetization behavior,as evidenced by the magnetic susceptibility and the ab initio calculation.Though with an electron-donating substituent on the axial Sal ligand in 2,the collective magnetic anisotropy is not enhanced and the corresponding magneto-structural relationship is discussed based on the experimental and theoretical calculation results.In addition,as neutral molecules,1 and 2 are soluble in several common organic solvents,like CH_(2)Cl_(2),CHCl_(3),THF and so on.
基金Research Project of Huzhou University under Grunt KYL21223。
文摘This paper deals with the problem of robust stabilization for uncertain Takagi-Sugeno(T-S)fuzzy neutral systems with input delays and distributed delays.The purpose is to design a state feedback fuzzy controller with a H∞performance such that the resulting closed-loop system is robustly stable.Sufficient conditions for the solvability of the problem are obtained by utilizing proper Lyapunov functional together with the linear matrix inequality(LMI)approach,especially two different improved results on robust H∞controller design with relaxed conditions are obtained.Finally,we provide two examples to verify the effectiveness of our design method and give some principle for choosing the proper controller under certain circumstances.
基金supported by the Quzhou Science and Technology Bureau Project(2023D023,2023D030,2023D002,and2024D028)the Joint Funds of the Zhejiang Provincial Natural Science Foundation of China(LZY23B030002)+3 种基金the Shijiazhuang Shangtai Technology Co.,Ltd.Hebei Provincial Department of Science and Technology(24291101Z)the International Cooperation Projects of Sichuan Provincial Department of Science and Technology(2021YFH0126)the Sichuan Provincial Science and Technology Department's key research project(2023YFG0203)。
文摘Metal foils have emerged as one of the promising materials for anode-free batteries due to their high energy density and scalability in production.The unclear lithium plating/stripping kinetics of metal foil current collectors in anode-free batteries was addressed by using the non-destructive distribution of relaxation times(DRT)analysis to systematically investigate the lithium transport behavior of 14 metal foils and its correlation with electrochemical performance.By integrating energy-dispersive spectro scopy(EDS),cyclic voltammetry(CV),and galvanostatic testing,the exceptional properties of indium(In),tin(Sn),and silver(Ag)were revealed:the Li-In alloying reaction exhibits high reversibility,Li-Sn alloys demonstrate outstanding cycling stability,and the Li-Ag solid-solution mechanism provides an ideal lithium deposition interface on the silver substrate.The DRT separates the polarization internal resistance of lithium ions passing through the SEI layer(R_(sei),τ2)and the polarization internal resistance of lithium ions undergoing charge transfer reaction at the electrolyte/electrode interface(R_(ct),τ3)by decoupling the electrochemical impedance spectroscopy(EIS).For the first time,the correlation betweenτ2,τ3,and the cycle life/Coulombic efficiency of alloy/solid-solution metals was established,while non-alloy metals are not suitable for this method due to differences in lithium deposition mechanisms.This study not only illuminates the structure-property relationship governing the lithium kinetics of metal foil electrodes but also provides a novel non-destructive analytical strategy and theoretical guidance for the rational design of stable anodes in high-energy-density batteries,facilitating the efficient screening and optimization of anode-free battery.
基金Supported by the Guangxi Science and Technology base and Talent Project(AD23026249,AD22080047).
文摘This paper is devoted to the existence results for a class of neutral abstract fractional differential equations involving the composite relaxation process.Based on the Laplace transform,the semigroup theory and the Wright functions,we first introduce a definition of mild solutions to the considered problem.By means of the noncompactness of measure and the fixed point technique,we establish existence criteria of solutions.Finally,an example is presented to illustrate our main result.
基金Vinegar Technologies LLC,Chevron Energy Technology Company,Rice University Consortium for Processes in Porous Media,and the American Chemical Society Petroleum Research Fund(No.ACS PRF 58859-ND6)for their financial support。
文摘The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented which integrates 2D NMR T_(1)-T_(2) relaxation measurements with molecular dynamics(MD)simulations of hydrocarbons confined in the nanopores of kerogen.The integrated NMR-MD technique is demonstrated using T_(1)-T_(2) measurements of kerogen isolates and organic-rich chalks saturated with heptane,together with MD simulations of heptane completely dissolved in a realistic kerogen model.The NMR-MD results are used to extract the swelling ratio and nanopore size distribution of kerogen as a function of depth in the reservoir.The effects of organic nanoconfinement on the T_(1) relaxation dispersion and T_(2) residual dipolar coupling of heptane are investigated,as well as the effect of downhole effective stress on the kerogen nanopore size as a function of depth and compaction.Potential applications in partially depleted gas shale reservoirs are discussed,including CO_(2) utilization/geostorage,geostorage of green H_(2),and integration of the NMR-MD technique with thermodynamic models for predicting the competitive sorption of gas mixtures in kerogen.
