Quasi-hemispherical magnetized collisionless shocks have been generated at the SG-II laser facility through the interaction between a laserproduced supersonic plasma flow and a magnetized ambient plasma,exhibiting an ...Quasi-hemispherical magnetized collisionless shocks have been generated at the SG-II laser facility through the interaction between a laserproduced supersonic plasma flow and a magnetized ambient plasma,exhibiting an angular asymmetric shock profile accompanied by asymmetric ion acceleration.We have conducted test particle simulations using the electromagnetic fields derived from 2D MHD simulations to investigate the asymmetry of ion acceleration.The simulations reproduce the angular asymmetry of the shock and the ion acceleration observed in experiments.The results indicate that shock drift acceleration is the primary mechanism for ion energization in the present quasiperpendicular magnetized shock.The asymmetric shock structure caused by nonuniform ambient plasma forms an asymmetric accelerated electric field,ultimately leading to angular asymmetric ion acceleration,which is consistent with space observations and our experimental results.Our study provides a plausible explanation for the discrepancies reported in previous ion acceleration experiments,and could contribute to understanding of the collisionless shock acceleration.展开更多
Fluorinated motifs are prevalent in both pharmaceuticals and agrochemicals.The incorporation of fluorine-containing moieties to drug candidates has emerged as a potent strategy for lead optimization in pharmaceutical ...Fluorinated motifs are prevalent in both pharmaceuticals and agrochemicals.The incorporation of fluorine-containing moieties to drug candidates has emerged as a potent strategy for lead optimization in pharmaceutical research and development.While extensive research has been devoted to constructing molecules that incorporate a trifluoromethylthio(SCF_(3)−)group on a stereogenic carbon,the synthesis of trifluoromethylthiolated alkanes featuring a SCF_(3)-substituted stereogenic carbon at non-activated site remains understudied.Herein,we report a Cu-catalyzed regio-and enantioselective hydroallylation of 1-trifluoromethylthiolated alkenes.Important to the process is the regio-and enantioselective Cu-H insertion to SCF_(3)-substituted alkene to form chiralα-SCF_(3) alkyl copper intermediates,outcompeting unproductive insertion to the coupling partner,and eventually proceed to afford optically active homoallylic trifluoromethylthiolated products.展开更多
Alkaline water electrolysis(AWE)represents a promising approach for green hydrogen production,yet the development of high-performance separators with gas impermeability,high ion conductivity,and stability under alkali...Alkaline water electrolysis(AWE)represents a promising approach for green hydrogen production,yet the development of high-performance separators with gas impermeability,high ion conductivity,and stability under alkaline operating conditions has proven challenging.To address this challenge,we develop a pre-concentration regulated phase separation strategy for scalable fabrication of asymmetric hierarchical porous membranes(AHPMs)for AWE.The resulting AHPMs demonstrate a hierarchical structure composed of an ultrathin dense skin layer and highly interconnected porous support.Benefitting from the structural advantages,the AHPMs exhibit outstanding characteristics,including a high bubble point pressure up to 12.4 bar,extremely low area resistance of 0.03Ωcm^(2) in 30 wt%KOH at 80℃,and excellent hydrophilicity and long-term alkaline stability.When applied in AWE with commercial catalysts,the AHPMs achieved an impressive current density of 1.9 A cm^(-2) at 2.0 V in 30 wt%KOH and the anodic hydrogen contents(AHCs)below 0.5 vol.%at a low current density of 0.1 A cm^(-2),differential pressure of 2 bar,and temperature of 80℃.Moreover,AHPMs demonstrate exceptional stability over 2,400 h of continuous operation and maintain superior performance in a 1 Nm^(3) h^(-1) industrialscale electrolyzer stack.This work advances the development of efficient separators for highperformance AWE systems,contributing to the advancement of hydrogen technologies in sustainable energy applications.展开更多
We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as ...We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as M2,carrying two-point mutations of F97L and M242F relative to the wild-type SSCR,was constructed by site-directed mutagenesis,exhibited simultaneously improved activity toward ethyl 2′-ketopantothenate(K-PaOEt)and isopropanol,and could effectively catalyze the stereoselective reduction of K-PaOEt to(R)-PaOEt by using isopropanol as the sacrificial co-substrate to regenerate NADPH.After screening six commercially available carriers,an amino resin LXTE-700 was identified as the best solid support for the immobilization of M2 via the glutaraldehyde activation method.Upon optimization of the immobilization process and reaction conditions,the fabricated immobilized enzyme M2@amino resin demonstrated excellent recyclability and reusability,with the complete conversion of K-PaOEt to(R)-PaOEt being still realized after 12 cycles of reuse.Finally,M2@amino resin-catalyzed synthesis of(R)-PaOEt was successfully implemented in continuous-flow,accomplishing a 6.3 times higher space-time yield than that with the batch synthesis(529.2 versus 84 g L^(-1) d^(-1)).Our developed flow biocatalysis system also features an outstanding operational stability,as evidenced by the 100%conversion rate achieved after 15 consecutive days of operation.展开更多
Advanced intensity measures(IMs)based on an inelastic deformation spectrum improved the evaluation of the median engineering demand parameters(EDPs)and reduced dispersion.In this regard,an optimized two-degreefreedom(...Advanced intensity measures(IMs)based on an inelastic deformation spectrum improved the evaluation of the median engineering demand parameters(EDPs)and reduced dispersion.In this regard,an optimized two-degreefreedom(2DOF)modal pushover-based scaling procedure(2DMPS)has been developed for a nonlinear dynamic analysis of asymmetric in-plan buildings.The 2DMPS procedure scales ground motions to approach close enough to a target value of the inelastic displacement of the first-mode inelastic 2DOF modal stick,extended for structures with significant contributions of higher modes.Further,4-,6-and 13-story RC SMRF buildings were selected for analyses using ground motion records scaled by the 2DMPS procedure,the modal pushover-based scaling method(MPS),and ASCE/SEI 7-16 scaling procedures.The median values of EDPs on scaled records closely matched the benchmark results.The bias in the EDP values due to the scaled records in every group regarding their median value was lower than the dispersion of the 21 unscaled records.These results generally demonstrate the accuracy and efficiency of the 2DMPS method.Additionally,the 2DOF modal stick’s inelastic response spectra are better suited for calculating seismic demands for one-way asymmetric-plan structures than the SDOF inelastic response spectra.展开更多
We report for the first time the combination of directed evolution focused on enhancing and reversing the stereoselectivity of an enzyme with Cu(I)-mediated click chemistry(CuAAC),providing an asymmetric click approac...We report for the first time the combination of directed evolution focused on enhancing and reversing the stereoselectivity of an enzyme with Cu(I)-mediated click chemistry(CuAAC),providing an asymmetric click approach for versatile chiral triazoles products.In this study,the halohydrin dehalogenase HheG was used as the enzyme which was evolved to induce a stereoselective ring-opening reaction of cyclic epoxides in the presence of NaN3 with the formation of chiral azido products.Two mutants of opposite stereopreference were generated,which convert cyclohexene oxide as well as cycloheptene oxide to(1S,2S)-2-azidocyclohexanol,(1R,2R)-2-azidocyclohexanol,(1S,2S)-2-azidocycloheptanol and(1R,2R)-2-azidocycloheptanol with essentially high stereoselectivity.The chiral products were then subjected to CuAAC in reactions with structurally different alkynes.Since HheG was found to be compatible with Cu(I),the process was also performed successfully in a unique 2-step one-pot process leading to various chiral triazoles.In order to understand the enhancement and reversal of the evolved enantioselectivity,QM and MD computations were performed.This approach harnesses the modifiability and high stereoselectivity of the evolved biocatalysts in combination with click chemistry.It holds great potential for diverse fields,particularly in the area of pharmaceuticals.展开更多
All-soluble all-iron flow batteries are considered a promising technology for low-cost and large-scale energy storage.In the past few years,efforts have been taken to design various iron chelates to enhance the cyclin...All-soluble all-iron flow batteries are considered a promising technology for low-cost and large-scale energy storage.In the past few years,efforts have been taken to design various iron chelates to enhance the cycling stability of negative electrolytes,while ignoring the kinetic mismatch and the corresponding battery design strategies,which greatly limited the performance of all-soluble all-iron flow batteries.In this regard,combining experimental analysis and numerical simulation,this work analyzed the kinetic performance of iron chelates on the negative side and conducted further investigations on battery asymmetric structure design to balance mass transport and electrochemical reactions within the battery.Results show that the reaction rate constant of the Fe(Ⅱ)(BIS-TRIS)^(2-)/Fe(Ⅲ)(BIS-TRIS)^(-)redox couple is 1:48×10^(-5)cm s^(-1),significantly lower than that of the positive electrolyte(6.0×10^(-5)cm s^(−1)),which limits the performance of the battery.Utilizing an asymmetric electrode design to increase active reaction sites and enhance convection is a critical strategy in achieving balanced mass transport and reaction activity between the positive and negative electrolytes.More notably,the battery with asymmetric geometric characteristics demonstrates a remarkable energy efficiency reaching up to 80.17%at 80 mA cm^(−2),which is 7.95%higher than that of the symmetric structure.This research provides theoretical guidance for the structural design of key components of batteries and reduces the cost of trial and error.展开更多
The increasing demand for artillery firepower,coupled with the growing size of gun barrels,imposes significant challenges on servo system performance.To address these challenges while ensuring fast and stable response...The increasing demand for artillery firepower,coupled with the growing size of gun barrels,imposes significant challenges on servo system performance.To address these challenges while ensuring fast and stable response,this paper proposes an adaptive robust controller based on an asymmetric barrier Lyapunov function(ABLF).The controller design incorporates both load and driver states through a backstepping synthesis.The overshoot and lag of barrel position errors are constrained within asymmetric boundaries,accounting for complex rotational uncertainties via an adaptive law and linear extended state observers(LESO).Simulations and experiments under typical artillery operating conditions validate the effectiveness and dynamic tracking performance of the proposed control strategy in comparison with other methods.展开更多
Cuprous oxide(Cu_(2)O) is one of the most promising catalysts for electrochemical conversion of CO_(2) into value-added C_(2) products.The efficiency of CO_(2)-to-C_(2) conversion is highly dependent on the Cu_(2)O cr...Cuprous oxide(Cu_(2)O) is one of the most promising catalysts for electrochemical conversion of CO_(2) into value-added C_(2) products.The efficiency of CO_(2)-to-C_(2) conversion is highly dependent on the Cu_(2)O crystal plane orientation and the corresponding adsorbed ^(*)CO species.Herein,we constructed high-index crystal planes(311) in Cu_(2)O(CO-Cu_(2)O) via a facile self-selective CO-induced strategy under a CO atmosphere,which was verified by high-resolution transmission electron microscopy(HR-TEM) and atomic force microscopy(AFM) results.By exploiting the high surface energy of the high index crystal planes,^(*)CO species are stabilized in CO-Cu_(2)O during CO_(2)RR,resulting in exceptional catalytic performance for CO_(2)-to-C_(2)products.In situ infrared spectroscopy revealed that both atop-type(^(*)CO_(atop)) and hollow-type(^(*)CO_(hollow)) adsorption of ^(*)CO species occurred on the CO-Cu_(2)O.The asymmetric C-C coupling energy barrier between ^(*)CO_(atop) and ^(*)CO_(hollow) in(311) crystal plane decreases by 47.8 % compared to the symmetric coupling of ^(*)CO_(atop) in conventional(100) crystal planes.Consequently,the Faradaic efficiency of C_(2) products generated with CO-Cu_(2)O was increased by as high as 100 % compared to that with pristine Cu_(2)O.展开更多
The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was est...The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.展开更多
A nonfused ring electron acceptor(NFREA),designated as TT-Ph-C6,has been synthesized with the aim of enhancing the power conversion efficiency(PCE)of organic solar cells(OSCs).By integrating asymmetric phenylalkylamin...A nonfused ring electron acceptor(NFREA),designated as TT-Ph-C6,has been synthesized with the aim of enhancing the power conversion efficiency(PCE)of organic solar cells(OSCs).By integrating asymmetric phenylalkylamino side groups,TT-Ph-C6 demonstrates excellent solubility and its crystal structure exhibits compact packing structures with a three-dimensional molecular stacking network.These structural attributes markedly promote exciton diffusion and charge carrier mobility,particularly advantageous for the fabrication of thick-film devices.TT-Ph-C6-based devices have attained a PCE of 18.01%at a film thickness of 100 nm,and even at a film thickness of 300 nm,the PCE remains at 14.64%,surpassing that of devices based on 2BTh-2F.These remarkable properties position TT-Ph-C6 as a highly promising NFREA material for boosting the efficiency of OSCs.展开更多
Traffic emissions directly impact indoor air quality in near-road buildings.Adjustable wind deflectors on building roofs were previously shown to be effective in mitigating air pollution for ideal city-type environmen...Traffic emissions directly impact indoor air quality in near-road buildings.Adjustable wind deflectors on building roofs were previously shown to be effective in mitigating air pollution for ideal city-type environments.This was based on the hypothesis that wind deflectors promoted higher pollutant removal by reducing the dependence on turbulent fluctuations.However,the question of whether such a deflector system would work in a more complex city-type environment such as an asymmetric street canyon remains unanswered.In addition,the fundamental impact a deflector could impart on flow dynamics within street canyons in the context of pollution removal through differing mechanisms also requires further research.The current study seeks to answer both questions by introducing adjustable wind deflectors for step-up and step-down asymmetric canyons with two traffic flow directions.For the step-down canyon,the deflectors promoted CO reduction in building facades by 73.55%and 34.79%from leeward and windward walls under a Cross Road Pollution(CRP)source.A 16.57%reduction was achieved on side walls under a Side Road Pollution(SRP)source.However,apart from the 13.87%CO reduction across windward walls under the CRP source,the wind deflectors predominantly resulted in detrimental results for step-up canyons.The ratio of pollution exchange rate achieved by mean flow-induced fluxes and total pollution exchange rate(θ),Sherwood number is the ratio of convective and diffusive mass transfer(Sh)and average canyon concentration(C_(canyon))were used as indices to investigate pollution removal mechanisms.Although both Shv/s C_(canyon)andθv/sC C_(canyon)relationships exhibited good inverse correlations when the deflector was positioned at different locations,the Shv/s C_(canyon)showed superior performance in distinguishing the scenarios where a deflector was involved and when not.This implies that the introduction of wind deflectors impacted more in effecting convective fluxes than fluctuations for pollution removal.展开更多
The application of polymer electrolytes is expected to revitalize solidstate lithium metal batteries(SSLMBs)with high energy density and enhanced safety.However,practical deployment faces challenges from inadequate me...The application of polymer electrolytes is expected to revitalize solidstate lithium metal batteries(SSLMBs)with high energy density and enhanced safety.However,practical deployment faces challenges from inadequate mechanical properties of electrolyte and unstable interfaces in high-voltage SSLMB s.Herein,we design an asymmetric composite solid-state electrolyte(ACSE)composed of a cellulose framework in situ self-assembled with zeolitic imidazolate framework nanosheets(CP@MOF)embedded in a polymer matrix.The CP@MOF network provides the electrolyte with an elastic modulus of 1.19 GPa,effectively resisting Li dendrite penetration.Furthermore,theoretical calculations guided the compositional design of ACSE to address asynchronous interfacial requirements at cathode/electrolyte and anode/electrolyte interfaces,facilitating stable interphase formation and thus ensuring prolonged cycling of SSLMBs.Consequently,Li symmetric cells achieve extended cycling stability(>5000 h)with minimal polarization.The NCM811|Li full cell maintains 84.9%capacity retention after 350 cycles.Notably,assembled NCM811 pouch cells deliver practical energy densities of 337.9 Wh kg^(-1)and 711.7 Wh L^(-1),demonstrating exceptional application potential.This work provides novel insights into the application of ACSEs for high-energy-density SSLMBs.展开更多
In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-li...In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-link capacitors.The voltage pulses required by inductance-based initial position detection can cause unequal discharge of the series capacitors,shifting the neutral-point voltage away from half of DC-link voltage(U_(dc)/2).This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors,so the 360°electrical period can no longer be evenly partitioned into six sectors during initial rotor position detection.To address this issue,this paper proposes a detection-pulse injection sequence that explicitly accounts for the asymmetric voltage vectors of the FSTP inverter.With the proposed sequence,the initial rotor position can be identified within a 30°electrical sector.The method requires no additional voltage or current sensors,and experimental results confirm its feasibility.展开更多
The transient behavior of DC-link voltage(DCV)significantly affects the low-voltage ride-through for phase-locked loop(PLL)-based grid-connected doubly-fed induction generator(DFIG)systems.This study investigates the ...The transient behavior of DC-link voltage(DCV)significantly affects the low-voltage ride-through for phase-locked loop(PLL)-based grid-connected doubly-fed induction generator(DFIG)systems.This study investigates the DCV transient behavior of a PLL-based DFIG system under asymmetrical grid faults.First,by considering the coupling characteristics of positive and negative sequence(PNS)components,a nonlinear largesignal model of DCV is developed.Furthermore,the transient characteristics of DCV under varying parameters are analyzed using phase trajectory diagrams.In addition,the transient stability(TS)mechanism of DCV during asymmetrical faults is examined through an en-ergy function approach.The analysis indicates that the transient instability of DCV is primarily associated with the control characteristics of PNS PLLs,while the TS level of DCV is mainly determined by the power coordination control between the rotor side converter and grid side converter.Moreover,a coordinated control strategy is proposed to enhance the TS of DCV under asymmet-rical grid faults.Finally,both simulation and experimental results are presented to validate the theoretical analysis and the effectiveness of the proposed strategy.展开更多
Catalytic asymmetric dearomatization(CADA)has emerged as a powerful strategy for transforming planar aromatic systems into three-dimensional chiral architectures[1].Notably,the Büchner reaction and arene cyclopro...Catalytic asymmetric dearomatization(CADA)has emerged as a powerful strategy for transforming planar aromatic systems into three-dimensional chiral architectures[1].Notably,the Büchner reaction and arene cyclopropanation excel in constructing complex polycyclic frameworks[2].However,current methods predominantly rely on diazo compounds as carbene precursors(Scheme1a),which pose safety risks and limit functional group compatibility.展开更多
As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding...As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.展开更多
The textures and microstructures of hot-and cold-rolled sheets of an AA 5454 aluminium alloy were studied,with special attention paid to comparing the texture development for the symmetric and asymmetric cold rolling....The textures and microstructures of hot-and cold-rolled sheets of an AA 5454 aluminium alloy were studied,with special attention paid to comparing the texture development for the symmetric and asymmetric cold rolling.Scanning electron microscopy with electron-backscatter diffraction was used to monitor the development of the microstructure in the differently deformed and additionally annealed samples.Details of the formations and transformations of individual texture components occurring during the rolling processes were observed and discussed.The average grain sizes,textures and mechanical properties were correlated and explained for the symmetric and asymmetric cold-rolled samples.The asymmetric rolling is beneficial in terms of deep drawability because it reduces the planar anisotropy of the annealed material due to the decrease of the Cube,Goss,rotated-Cube and η-fibre texture components and at the same time strengthens X1-and X2-fibre texture components which are shear texture components and improve deep drawability.During the asymmetric cold rolling,the temperature increases due to friction,triggering recrystallisation processes and leading to larger grains.It is also confirmed that asymmetric cold rolling uses less rolling force and consequently less energy to produce a final material with better formability,particularly earing.展开更多
We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW...We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.展开更多
Isosteviol,the hydrolysate of stevioside,has attracted increasing attention from scientists because of its special molecular skeleton and extensive biological activities.In recent years,due to the continuous rise of o...Isosteviol,the hydrolysate of stevioside,has attracted increasing attention from scientists because of its special molecular skeleton and extensive biological activities.In recent years,due to the continuous rise of organocatalysis,an increasing number of organocatalysts based on isosteviol have been devised and synthesized to facilitate a range of highly enantioselective asymmetric synthesis.The isosteviol-type organocatalysts reported in the literature over the past decade and their applications in asymmetric catalysis are systematically analyzed and elaborated in order to provide assistance for the further design,synthesis,and application of organocatalysis derived from isosteviol.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12205298 and 12175230)the Natural Science Foundation of Heilongjiang Province of China(Grant No.LH2024A010)+1 种基金the Fundamental Research Funds for the Central Universities,Controversial and Disruptive Projects of the Chinese Academy of Sciences(Grant No.FGSDFX-0001)the USTC Research Funds of the Double First-Class Initiative(Grant No.YD2140002006).
文摘Quasi-hemispherical magnetized collisionless shocks have been generated at the SG-II laser facility through the interaction between a laserproduced supersonic plasma flow and a magnetized ambient plasma,exhibiting an angular asymmetric shock profile accompanied by asymmetric ion acceleration.We have conducted test particle simulations using the electromagnetic fields derived from 2D MHD simulations to investigate the asymmetry of ion acceleration.The simulations reproduce the angular asymmetry of the shock and the ion acceleration observed in experiments.The results indicate that shock drift acceleration is the primary mechanism for ion energization in the present quasiperpendicular magnetized shock.The asymmetric shock structure caused by nonuniform ambient plasma forms an asymmetric accelerated electric field,ultimately leading to angular asymmetric ion acceleration,which is consistent with space observations and our experimental results.Our study provides a plausible explanation for the discrepancies reported in previous ion acceleration experiments,and could contribute to understanding of the collisionless shock acceleration.
基金the National Key R&D Program of China(No.2021YFF0701700)the National Natural Science Foundation of China(Nos.22271264 and 21971228)for financial support.
文摘Fluorinated motifs are prevalent in both pharmaceuticals and agrochemicals.The incorporation of fluorine-containing moieties to drug candidates has emerged as a potent strategy for lead optimization in pharmaceutical research and development.While extensive research has been devoted to constructing molecules that incorporate a trifluoromethylthio(SCF_(3)−)group on a stereogenic carbon,the synthesis of trifluoromethylthiolated alkanes featuring a SCF_(3)-substituted stereogenic carbon at non-activated site remains understudied.Herein,we report a Cu-catalyzed regio-and enantioselective hydroallylation of 1-trifluoromethylthiolated alkenes.Important to the process is the regio-and enantioselective Cu-H insertion to SCF_(3)-substituted alkene to form chiralα-SCF_(3) alkyl copper intermediates,outcompeting unproductive insertion to the coupling partner,and eventually proceed to afford optically active homoallylic trifluoromethylthiolated products.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52273059 and 52473219)the Natural Science Foundation of Tianjin(Grant Nos.22JCYBJC01030 and 23JCYBJC00650)provided by Yantai Tayho Advanced Materials Group Co.,Ltd.
文摘Alkaline water electrolysis(AWE)represents a promising approach for green hydrogen production,yet the development of high-performance separators with gas impermeability,high ion conductivity,and stability under alkaline operating conditions has proven challenging.To address this challenge,we develop a pre-concentration regulated phase separation strategy for scalable fabrication of asymmetric hierarchical porous membranes(AHPMs)for AWE.The resulting AHPMs demonstrate a hierarchical structure composed of an ultrathin dense skin layer and highly interconnected porous support.Benefitting from the structural advantages,the AHPMs exhibit outstanding characteristics,including a high bubble point pressure up to 12.4 bar,extremely low area resistance of 0.03Ωcm^(2) in 30 wt%KOH at 80℃,and excellent hydrophilicity and long-term alkaline stability.When applied in AWE with commercial catalysts,the AHPMs achieved an impressive current density of 1.9 A cm^(-2) at 2.0 V in 30 wt%KOH and the anodic hydrogen contents(AHCs)below 0.5 vol.%at a low current density of 0.1 A cm^(-2),differential pressure of 2 bar,and temperature of 80℃.Moreover,AHPMs demonstrate exceptional stability over 2,400 h of continuous operation and maintain superior performance in a 1 Nm^(3) h^(-1) industrialscale electrolyzer stack.This work advances the development of efficient separators for highperformance AWE systems,contributing to the advancement of hydrogen technologies in sustainable energy applications.
基金the Science and Technology R&D Major Project of Jiangxi Province(No.20244AFI92001)the National Natural Science Foundation of China(Nos.22071033 and 21801047)for the financial supports.
文摘We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as M2,carrying two-point mutations of F97L and M242F relative to the wild-type SSCR,was constructed by site-directed mutagenesis,exhibited simultaneously improved activity toward ethyl 2′-ketopantothenate(K-PaOEt)and isopropanol,and could effectively catalyze the stereoselective reduction of K-PaOEt to(R)-PaOEt by using isopropanol as the sacrificial co-substrate to regenerate NADPH.After screening six commercially available carriers,an amino resin LXTE-700 was identified as the best solid support for the immobilization of M2 via the glutaraldehyde activation method.Upon optimization of the immobilization process and reaction conditions,the fabricated immobilized enzyme M2@amino resin demonstrated excellent recyclability and reusability,with the complete conversion of K-PaOEt to(R)-PaOEt being still realized after 12 cycles of reuse.Finally,M2@amino resin-catalyzed synthesis of(R)-PaOEt was successfully implemented in continuous-flow,accomplishing a 6.3 times higher space-time yield than that with the batch synthesis(529.2 versus 84 g L^(-1) d^(-1)).Our developed flow biocatalysis system also features an outstanding operational stability,as evidenced by the 100%conversion rate achieved after 15 consecutive days of operation.
文摘Advanced intensity measures(IMs)based on an inelastic deformation spectrum improved the evaluation of the median engineering demand parameters(EDPs)and reduced dispersion.In this regard,an optimized two-degreefreedom(2DOF)modal pushover-based scaling procedure(2DMPS)has been developed for a nonlinear dynamic analysis of asymmetric in-plan buildings.The 2DMPS procedure scales ground motions to approach close enough to a target value of the inelastic displacement of the first-mode inelastic 2DOF modal stick,extended for structures with significant contributions of higher modes.Further,4-,6-and 13-story RC SMRF buildings were selected for analyses using ground motion records scaled by the 2DMPS procedure,the modal pushover-based scaling method(MPS),and ASCE/SEI 7-16 scaling procedures.The median values of EDPs on scaled records closely matched the benchmark results.The bias in the EDP values due to the scaled records in every group regarding their median value was lower than the dispersion of the 21 unscaled records.These results generally demonstrate the accuracy and efficiency of the 2DMPS method.Additionally,the 2DOF modal stick’s inelastic response spectra are better suited for calculating seismic demands for one-way asymmetric-plan structures than the SDOF inelastic response spectra.
基金support from the National Key Research and Development Program of China(No.2023YFA0914100/2023YFA0914102)the National Natural Science Foundation of China(Nos.22077029 and 22034002)+2 种基金the Science Fund for Distinguished Young Scholars of Hunan Province(No.2021JJ10034)support from the National Natural Science Foundation of China(No.22276049)M.M.acknowledge the support from the National Natural Science Foundation of China(No.22276050).
文摘We report for the first time the combination of directed evolution focused on enhancing and reversing the stereoselectivity of an enzyme with Cu(I)-mediated click chemistry(CuAAC),providing an asymmetric click approach for versatile chiral triazoles products.In this study,the halohydrin dehalogenase HheG was used as the enzyme which was evolved to induce a stereoselective ring-opening reaction of cyclic epoxides in the presence of NaN3 with the formation of chiral azido products.Two mutants of opposite stereopreference were generated,which convert cyclohexene oxide as well as cycloheptene oxide to(1S,2S)-2-azidocyclohexanol,(1R,2R)-2-azidocyclohexanol,(1S,2S)-2-azidocycloheptanol and(1R,2R)-2-azidocycloheptanol with essentially high stereoselectivity.The chiral products were then subjected to CuAAC in reactions with structurally different alkynes.Since HheG was found to be compatible with Cu(I),the process was also performed successfully in a unique 2-step one-pot process leading to various chiral triazoles.In order to understand the enhancement and reversal of the evolved enantioselectivity,QM and MD computations were performed.This approach harnesses the modifiability and high stereoselectivity of the evolved biocatalysts in combination with click chemistry.It holds great potential for diverse fields,particularly in the area of pharmaceuticals.
基金supported by the National Natural Science Foundation of China(No.52106265)Natural Science Foundation of Tianjin Province,China(No.23JCZDJC01090)+1 种基金Guangdong Major Project of Basic and Applied Basic Research(2023B0303000002)High level of special funds(G03034K001).
文摘All-soluble all-iron flow batteries are considered a promising technology for low-cost and large-scale energy storage.In the past few years,efforts have been taken to design various iron chelates to enhance the cycling stability of negative electrolytes,while ignoring the kinetic mismatch and the corresponding battery design strategies,which greatly limited the performance of all-soluble all-iron flow batteries.In this regard,combining experimental analysis and numerical simulation,this work analyzed the kinetic performance of iron chelates on the negative side and conducted further investigations on battery asymmetric structure design to balance mass transport and electrochemical reactions within the battery.Results show that the reaction rate constant of the Fe(Ⅱ)(BIS-TRIS)^(2-)/Fe(Ⅲ)(BIS-TRIS)^(-)redox couple is 1:48×10^(-5)cm s^(-1),significantly lower than that of the positive electrolyte(6.0×10^(-5)cm s^(−1)),which limits the performance of the battery.Utilizing an asymmetric electrode design to increase active reaction sites and enhance convection is a critical strategy in achieving balanced mass transport and reaction activity between the positive and negative electrolytes.More notably,the battery with asymmetric geometric characteristics demonstrates a remarkable energy efficiency reaching up to 80.17%at 80 mA cm^(−2),which is 7.95%higher than that of the symmetric structure.This research provides theoretical guidance for the structural design of key components of batteries and reduces the cost of trial and error.
文摘The increasing demand for artillery firepower,coupled with the growing size of gun barrels,imposes significant challenges on servo system performance.To address these challenges while ensuring fast and stable response,this paper proposes an adaptive robust controller based on an asymmetric barrier Lyapunov function(ABLF).The controller design incorporates both load and driver states through a backstepping synthesis.The overshoot and lag of barrel position errors are constrained within asymmetric boundaries,accounting for complex rotational uncertainties via an adaptive law and linear extended state observers(LESO).Simulations and experiments under typical artillery operating conditions validate the effectiveness and dynamic tracking performance of the proposed control strategy in comparison with other methods.
基金the financial support from the National Natural Science Foundation of China (Nos.U23A20677,22022610 and 52400137)"Pioneer" and "Leading Goose" R&D Program of Zhejiang (Nos.2022C03146 and 2023C03017)+2 种基金China Postdoctoral Science Foundation (No.2024T170805)Zhejiang Provincial Natural Science Foundation of China (No.LDT23E06015B06)the support of the Research Computing Center in College of Chemical and Biological Engineering at Zhejiang University for assistance with the calculations。
文摘Cuprous oxide(Cu_(2)O) is one of the most promising catalysts for electrochemical conversion of CO_(2) into value-added C_(2) products.The efficiency of CO_(2)-to-C_(2) conversion is highly dependent on the Cu_(2)O crystal plane orientation and the corresponding adsorbed ^(*)CO species.Herein,we constructed high-index crystal planes(311) in Cu_(2)O(CO-Cu_(2)O) via a facile self-selective CO-induced strategy under a CO atmosphere,which was verified by high-resolution transmission electron microscopy(HR-TEM) and atomic force microscopy(AFM) results.By exploiting the high surface energy of the high index crystal planes,^(*)CO species are stabilized in CO-Cu_(2)O during CO_(2)RR,resulting in exceptional catalytic performance for CO_(2)-to-C_(2)products.In situ infrared spectroscopy revealed that both atop-type(^(*)CO_(atop)) and hollow-type(^(*)CO_(hollow)) adsorption of ^(*)CO species occurred on the CO-Cu_(2)O.The asymmetric C-C coupling energy barrier between ^(*)CO_(atop) and ^(*)CO_(hollow) in(311) crystal plane decreases by 47.8 % compared to the symmetric coupling of ^(*)CO_(atop) in conventional(100) crystal planes.Consequently,the Faradaic efficiency of C_(2) products generated with CO-Cu_(2)O was increased by as high as 100 % compared to that with pristine Cu_(2)O.
基金support from the National Natural Science Foundation of China(Grant Nos.52174313 and 52304350)thank all members of the Hebei High Quality Steel Continuous Casting Engineering Technology Research Center at North China University of Science and Technology,Tangshan,China.
文摘The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.
基金Financial support from the National Natural Science Foundation of China(22375024,21975031,21734009,51933001,22109080,and 52173174)the Natural Science Foundation of Shandong Province(No.ZR2022YQ45)+2 种基金the Taishan Scholars Program(Nos.tstp20221121 and tsqnz20221134)The Beijing Natural Science Foundation(No.2244073)supported by State Key Laboratory of Bio-Fibers and Eco-Textiles(Qingdao University)(RZ2200002821)is acknowledged.
文摘A nonfused ring electron acceptor(NFREA),designated as TT-Ph-C6,has been synthesized with the aim of enhancing the power conversion efficiency(PCE)of organic solar cells(OSCs).By integrating asymmetric phenylalkylamino side groups,TT-Ph-C6 demonstrates excellent solubility and its crystal structure exhibits compact packing structures with a three-dimensional molecular stacking network.These structural attributes markedly promote exciton diffusion and charge carrier mobility,particularly advantageous for the fabrication of thick-film devices.TT-Ph-C6-based devices have attained a PCE of 18.01%at a film thickness of 100 nm,and even at a film thickness of 300 nm,the PCE remains at 14.64%,surpassing that of devices based on 2BTh-2F.These remarkable properties position TT-Ph-C6 as a highly promising NFREA material for boosting the efficiency of OSCs.
基金funded by the Irish Environmental Protection Agencies EPA Research Programme via grant number 2019-CCRP-PhD.6.
文摘Traffic emissions directly impact indoor air quality in near-road buildings.Adjustable wind deflectors on building roofs were previously shown to be effective in mitigating air pollution for ideal city-type environments.This was based on the hypothesis that wind deflectors promoted higher pollutant removal by reducing the dependence on turbulent fluctuations.However,the question of whether such a deflector system would work in a more complex city-type environment such as an asymmetric street canyon remains unanswered.In addition,the fundamental impact a deflector could impart on flow dynamics within street canyons in the context of pollution removal through differing mechanisms also requires further research.The current study seeks to answer both questions by introducing adjustable wind deflectors for step-up and step-down asymmetric canyons with two traffic flow directions.For the step-down canyon,the deflectors promoted CO reduction in building facades by 73.55%and 34.79%from leeward and windward walls under a Cross Road Pollution(CRP)source.A 16.57%reduction was achieved on side walls under a Side Road Pollution(SRP)source.However,apart from the 13.87%CO reduction across windward walls under the CRP source,the wind deflectors predominantly resulted in detrimental results for step-up canyons.The ratio of pollution exchange rate achieved by mean flow-induced fluxes and total pollution exchange rate(θ),Sherwood number is the ratio of convective and diffusive mass transfer(Sh)and average canyon concentration(C_(canyon))were used as indices to investigate pollution removal mechanisms.Although both Shv/s C_(canyon)andθv/sC C_(canyon)relationships exhibited good inverse correlations when the deflector was positioned at different locations,the Shv/s C_(canyon)showed superior performance in distinguishing the scenarios where a deflector was involved and when not.This implies that the introduction of wind deflectors impacted more in effecting convective fluxes than fluctuations for pollution removal.
基金the financial support from the National Natural Science Foundation of China(52072307,22408198)the Fundamental Research Funds for the Central Universities(XJJSKYQD202533)。
文摘The application of polymer electrolytes is expected to revitalize solidstate lithium metal batteries(SSLMBs)with high energy density and enhanced safety.However,practical deployment faces challenges from inadequate mechanical properties of electrolyte and unstable interfaces in high-voltage SSLMB s.Herein,we design an asymmetric composite solid-state electrolyte(ACSE)composed of a cellulose framework in situ self-assembled with zeolitic imidazolate framework nanosheets(CP@MOF)embedded in a polymer matrix.The CP@MOF network provides the electrolyte with an elastic modulus of 1.19 GPa,effectively resisting Li dendrite penetration.Furthermore,theoretical calculations guided the compositional design of ACSE to address asynchronous interfacial requirements at cathode/electrolyte and anode/electrolyte interfaces,facilitating stable interphase formation and thus ensuring prolonged cycling of SSLMBs.Consequently,Li symmetric cells achieve extended cycling stability(>5000 h)with minimal polarization.The NCM811|Li full cell maintains 84.9%capacity retention after 350 cycles.Notably,assembled NCM811 pouch cells deliver practical energy densities of 337.9 Wh kg^(-1)and 711.7 Wh L^(-1),demonstrating exceptional application potential.This work provides novel insights into the application of ACSEs for high-energy-density SSLMBs.
基金supported in part by the National Natural Science Foundation of China under Grant 52477060in part by the Tianjin Natural Science Foundation Project under Grant 24JCZDJC00250in part by the Zhejiang Leading Innovation and Entrepreneurship Team Project under Grant 2024R01012.
文摘In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-link capacitors.The voltage pulses required by inductance-based initial position detection can cause unequal discharge of the series capacitors,shifting the neutral-point voltage away from half of DC-link voltage(U_(dc)/2).This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors,so the 360°electrical period can no longer be evenly partitioned into six sectors during initial rotor position detection.To address this issue,this paper proposes a detection-pulse injection sequence that explicitly accounts for the asymmetric voltage vectors of the FSTP inverter.With the proposed sequence,the initial rotor position can be identified within a 30°electrical sector.The method requires no additional voltage or current sensors,and experimental results confirm its feasibility.
基金supported in part by Smart Grid-National Science and Technology Major Project(No.2024ZD0801400)Science and technology projects of State Grid Corporation of China(No.52272224000V).
文摘The transient behavior of DC-link voltage(DCV)significantly affects the low-voltage ride-through for phase-locked loop(PLL)-based grid-connected doubly-fed induction generator(DFIG)systems.This study investigates the DCV transient behavior of a PLL-based DFIG system under asymmetrical grid faults.First,by considering the coupling characteristics of positive and negative sequence(PNS)components,a nonlinear largesignal model of DCV is developed.Furthermore,the transient characteristics of DCV under varying parameters are analyzed using phase trajectory diagrams.In addition,the transient stability(TS)mechanism of DCV during asymmetrical faults is examined through an en-ergy function approach.The analysis indicates that the transient instability of DCV is primarily associated with the control characteristics of PNS PLLs,while the TS level of DCV is mainly determined by the power coordination control between the rotor side converter and grid side converter.Moreover,a coordinated control strategy is proposed to enhance the TS of DCV under asymmet-rical grid faults.Finally,both simulation and experimental results are presented to validate the theoretical analysis and the effectiveness of the proposed strategy.
文摘Catalytic asymmetric dearomatization(CADA)has emerged as a powerful strategy for transforming planar aromatic systems into three-dimensional chiral architectures[1].Notably,the Büchner reaction and arene cyclopropanation excel in constructing complex polycyclic frameworks[2].However,current methods predominantly rely on diazo compounds as carbene precursors(Scheme1a),which pose safety risks and limit functional group compatibility.
文摘As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.
文摘The textures and microstructures of hot-and cold-rolled sheets of an AA 5454 aluminium alloy were studied,with special attention paid to comparing the texture development for the symmetric and asymmetric cold rolling.Scanning electron microscopy with electron-backscatter diffraction was used to monitor the development of the microstructure in the differently deformed and additionally annealed samples.Details of the formations and transformations of individual texture components occurring during the rolling processes were observed and discussed.The average grain sizes,textures and mechanical properties were correlated and explained for the symmetric and asymmetric cold-rolled samples.The asymmetric rolling is beneficial in terms of deep drawability because it reduces the planar anisotropy of the annealed material due to the decrease of the Cube,Goss,rotated-Cube and η-fibre texture components and at the same time strengthens X1-and X2-fibre texture components which are shear texture components and improve deep drawability.During the asymmetric cold rolling,the temperature increases due to friction,triggering recrystallisation processes and leading to larger grains.It is also confirmed that asymmetric cold rolling uses less rolling force and consequently less energy to produce a final material with better formability,particularly earing.
基金supported by the National Natural Science Foundation of China(Grant No.12105210)the Knowledge Innovation Program of Wuhan-Basi Research(Grant No.2023010201010149)。
文摘We present a theoretical scheme to realize two-dimensional(2D)asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells(SQWs)structure with resonant tunneling.The SQW structure interacts with a weak probe laser field,a spatially independent 2D standing-wave(SW)field,and a Laguerre–Gaussian(LG)vortex field,respectively.The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation.Because of the existence of vortex light,it is possible to realize asymmetric high-order diffraction in the SQW structure,and then a 2D asymmetric grating is established.By adjusting the detunings of the probe field,vortex field,and SW field,as well as the interaction length,diffraction intensity,and direction of the 2D asymmetric electromagnetically induced grating(EIG)can be controlled effectively.In addition,the number of orbital angular momenta(OAM)and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions.High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme.Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.
基金Project supported by the National Natural Science Foundation of China(No.51403053)the University Scientific Innovation Team of Henan Province(No.24IRTSTHN017)。
文摘Isosteviol,the hydrolysate of stevioside,has attracted increasing attention from scientists because of its special molecular skeleton and extensive biological activities.In recent years,due to the continuous rise of organocatalysis,an increasing number of organocatalysts based on isosteviol have been devised and synthesized to facilitate a range of highly enantioselective asymmetric synthesis.The isosteviol-type organocatalysts reported in the literature over the past decade and their applications in asymmetric catalysis are systematically analyzed and elaborated in order to provide assistance for the further design,synthesis,and application of organocatalysis derived from isosteviol.
