We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature ^87 Rb atoms. The Doppler broad- en...We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature ^87 Rb atoms. The Doppler broad- ened background is effectively eliminated with the pulse shaping method and the spectrum modulation technique. The combination of the pulse shaping method and the spectra modulation technique provides a potential approachto reduce background of at least 99%.展开更多
The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 ...The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 × 10-13@1 s is employed for the light source. By using a periodically poled lithium niobate, the femtosecond pulse operating in 1556 nm is frequency-doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor. Through sweeping the carrier envelope offset frequency （fceo）, the 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve. After the frequency correction, the measured result agrees well with the previous experiment on this transition. The entire potential candidate of optical frequency standard for system configuration is compact and robust, providing a telecommunication applications.展开更多
A high-resolution two-photon spectrum of 5S1/2 → 5P3/2 → 5D5/2 transitions in a thermal SSRb vapor cell is presented by using an optical frequency comb and a cw laser. The fluorescence of 6P3/2 → 5S1/2 spontaneous ...A high-resolution two-photon spectrum of 5S1/2 → 5P3/2 → 5D5/2 transitions in a thermal SSRb vapor cell is presented by using an optical frequency comb and a cw laser. The fluorescence of 6P3/2 → 5S1/2 spontaneous emission is detected when the cw laser frequency is scanned from the 5S1/2 ground state to 5P3/2 hyperfine levels and the optical frequency comb repetition rate is fixed. The hyperfine splittings （Ff = 2-5） of the 5D5/2 excited state are well resolved. The dependences of fluorescence intensities on the cw laser intensity and temperature of SSRb vapor eel1 are studied, respectively. The experimental results are in good agreement with the theoretical analyses.展开更多
A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in mol...A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.展开更多
In this paper, we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system （Perylene dissolved in chloroform solution） by shaping the femtosecond pulses...In this paper, we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system （Perylene dissolved in chloroform solution） by shaping the femtosecond pulses with simple phase patterns （cosinusoidal and π phase step-function shape）. The control efficiency of the two-photon transition probability is correlated with both the laser field and the molecular absorption bandwidth. Our results demonstrate that, the two-photon transition probability in a molecular system can be reduced but not completely eliminated by manipulating the laser field, and the control efficiency is minimal when the molecular absorption bandwidth is larger than twice the laser spectral bandwidth.展开更多
The optical frequency comb has been widely used in precision measurement. In this study, a multi-peak fitting approach is first proposed to fit the two-photon transition spectrum which overlaps with the neighboring tr...The optical frequency comb has been widely used in precision measurement. In this study, a multi-peak fitting approach is first proposed to fit the two-photon transition spectrum which overlaps with the neighboring transition in Rb-87. The multi-peak fitting approach is used to eliminate the frequency shift affected by the neighboring transition. With locking the carrier envelope offset frequency at 1/4 repetition frequency, the transition frequency is measured to be 770569132739.9 +/- 5.8 kHz, which agrees well with the previous result recommended by Comite International des Poids et Mesures.展开更多
A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency com...A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an original way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.展开更多
Temperature-programmed desorption(TPD)is a fundamental technique in surface science and heterogeneous catalysis for characterizing adsorption behavior,and for extracting key parameters such as adsorption energy.Howeve...Temperature-programmed desorption(TPD)is a fundamental technique in surface science and heterogeneous catalysis for characterizing adsorption behavior,and for extracting key parameters such as adsorption energy.However,the majority of existing TPD data is accessible in the form of published images,which lacks structured and quantitative datasets.This constrains its utility for rigorous quantitative analysis and computational modelling.Using carbon monoxide(CO)which is a widely adopted probe molecule,a curated and standardized dataset of CO-TPD is constructed,encompassing 14 transition-metal single-crystal surfaces,including copper(Cu)and ruthenium(Ru).By systematically extracting numerical data points from published spectra and applying normalization,essential spectral features such as peak shape are fully preserved.The dataset also documents relevant experimental parameters,including heating rates,and was developed using a standardized protocol for data collection and quality control.This resource serves as both a reference library to support the deconvolution of TPD spectra from complex catalysts and an experimental benchmark for calibrating parameters in theoretical models.By providing a reliable and accessible data function,this work advances the microscopic understanding and the rational design of catalyst active centers.展开更多
Electrochemical water splitting represents a sustainable technology for hydrogen(H_(2))production.However,its large-scale implementation is hindered by the high overpotentials required for both the cathodic hydrogen e...Electrochemical water splitting represents a sustainable technology for hydrogen(H_(2))production.However,its large-scale implementation is hindered by the high overpotentials required for both the cathodic hydrogen evolution reaction(HER)and the anodic oxygen evolution reaction(OER).Transition metal-based catalysts have garnered significant research interest as promising alternatives to noble-metal catalysts,owing to their low cost,tunable composition,and noble-metal-like catalytic activity.Nevertheless,systematic reviews on their application as bifunctional catalysts for overall water splitting(OWS)are still limited.This review comprehensively outlines the principal categories of bifunctional transition metal electrocatalysts derived from electrospun nanofibers(NFs),including metals,oxides,phosphides,sulfides,and carbides.Key strategies for enhancing their catalytic performance are systematically summarized,such as heterointerface engineering,heteroatom doping,metal-nonmetal-metal bridging architectures,and single-atom site design.Finally,current challenges and future research directions are discussed,aiming to provide insightful perspectives for the rational design of high-performance electrocatalysts for OWS.展开更多
Polyamorphous transition refers to the transformation between two distinct amorphous states with identical composition.This phenomenon is intriguing in the field of physics and offers avenues for glass material design...Polyamorphous transition refers to the transformation between two distinct amorphous states with identical composition.This phenomenon is intriguing in the field of physics and offers avenues for glass material design.Recently,polyamorphous transitions have been frequently observed in glassy materials.However,the transition pathway has yet to be established,which is essential for understanding its structural origins.Here,we present evidence from 12 different types of metallic glasses spanning 7 orders of magnitude in timescales,demonstrating that polyamorphous transitions consistently occur after the devitrification process,between two supercooled liquid phases(Ⅰ and Ⅱ).Notably,we observe a decrease in liquid fragility and heat capacity following the transition,suggesting that the polyamorphous transition is associated with the fragile-to-strong transition(FST)in liquids.These findings elucidate the detailed structural pathway of the polyamorphous transition,via glass I→devitrification→liquid I→fragile-strong transition→liquid II,and incorporate the FST into a cohesive framework for its understanding.展开更多
Based on datasets from the International Best-Track Archive for Climate Stewardship(IBTrACS)and the fifth major global reanalysis produced by ECMWF(ERA5),the authors found that 29%of tropical cyclones(TCs)in the weste...Based on datasets from the International Best-Track Archive for Climate Stewardship(IBTrACS)and the fifth major global reanalysis produced by ECMWF(ERA5),the authors found that 29%of tropical cyclones(TCs)in the western North Pacific underwent extratropical transition(ET)from 1979 to 2022,with the frequency of ET events showing a slow decreasing trend.The extratropical transition tropical cyclones(ETCs)are classified into four clusters using the k-means clustering method based on their track patterns:recurving ETCs,westward ETCs,northwestward ETCs,and abnormal track ETCs.The transition process of recurving ETCs mostly occurs after the recurvature is completed,while 63.7%of the westward ETCs complete their transition after landfall.Abnormal track ETCs undergo transition over high-latitude oceans.Northwestward ETCs have the longest duration and slowest transition speed during the ET period,resulting in a prolonged impact.The ET process occurs at the edges of the western Pacific subtropical high(WPSH),with higher frequency during westward extension and lower during eastward retreat.While westward ETCs transition through surface friction effects,others complete ET in the northwest baroclinic zone of the WPSH.展开更多
The post-embryonic development of shoot apices in higher plants progresses through three distinct phases:the juvenile phase,adult vegetative phase,and reproductive phase.The transition from vegetative to reproductive ...The post-embryonic development of shoot apices in higher plants progresses through three distinct phases:the juvenile phase,adult vegetative phase,and reproductive phase.The transition from vegetative to reproductive growth represents a critical developmental transition that affects plant adaptability(Poethig 2003;Baurle and Dean 2006).展开更多
Transition-metal dichalcogenides hosting multiple competing structural and electronic phases are thus ideal platforms for constructing polytype heterostructures with emergent quantum properties.However,controlling pha...Transition-metal dichalcogenides hosting multiple competing structural and electronic phases are thus ideal platforms for constructing polytype heterostructures with emergent quantum properties.However,controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging.In this study,we realize vertical/lateral polytype heterostructures in a hole-doped Mott insulator via thermal annealing-induced structural transitions.Raman spectroscopy,atomic force microscopy and scanning Kelvin probe force microscopy confirm the coexistence of T-H polytype heterostructures.Atomic-scale scanning tunneling microscopy/spectroscopy measurements reveal the transparent effect in 1H/1T vertical heterostructures,where positive bias voltage induces in a pronounced superposition of the√13×√13 CDW of the 1T-layer on the 1H-layer.By systematically comparing the 1T/1H and 1T/1T interfaces,we demonstrate that the metallic 1H-layer induces a Coulomb screening effect on the 1T-layer,suppressing the formation of CDW domain walls and forming more ordered electronic states.These results clarify the interfacial coupling between distinct quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype heterostructures with tunable electronic properties.展开更多
The complex aerodynamic interaction between tandem tilt-wing and multi-rotor directly affects the wing surface flow and rotor thrust,making it a critical factor during the tilt transition process of this configuration...The complex aerodynamic interaction between tandem tilt-wing and multi-rotor directly affects the wing surface flow and rotor thrust,making it a critical factor during the tilt transition process of this configuration of rotorcraft.The aerodynamic interaction of tandem tilt-wing and multi-rotor is investigated based on the CFD method.The aerodynamic effect of multi tilt-rotor is simulated as virtual disk modeling by adding source terms to the Navier-Stokes equations,effectively reducing the calculation time while maintaining the accuracy of aerodynamic interaction calculations.Aerodynamic forces and flow field characteristics of the tandem tilt-wing and multi-rotor under different tilt angles are compared between cases with and without aerodynamic interaction.Furthermore,the differences in aerodynamic forces between dynamic tilt transition and fixed-angle conditions were compared.The results show that the aerodynamic interaction of multi-rotor obviously increases the lift of front tilt-wing at different tilt angles,the wing lift under interaction is increased by more than 40%compared with isolated wing at tilt angle of 15°for the computation in this paper,which is related to the increase of wing flow velocity and the suppression of flow separation caused by multi-rotor;the wing blocking effect will increase rotor thrust,especially near the tilt angles of 30°and 45°;the increases of rear wing lift and rear rotor thrust under aerodynamic interaction are not significant because of suppression by the front wing’s downwash;the unsteady effects during dynamic tilting have a relatively minor impact on aerodynamic interaction,with the aerodynamic forces on the rotors and wings during the dynamic tilting process showing little difference from those under corresponding fixed tilt angles.展开更多
Peptides play important roles in chemistry,medicinal chemistry and life science,due to their high efficiency and specificity,unusual biological and therapeutic properties.As naturally occurring peptides often face wit...Peptides play important roles in chemistry,medicinal chemistry and life science,due to their high efficiency and specificity,unusual biological and therapeutic properties.As naturally occurring peptides often face with their intrinsic limitations including metabolic instability and low membrane permeability,the strategies for synthesizing unnatural amino acids and peptides are explored.Among the methods for modifying amino acids and peptides,chemo-and site-selective approaches are preferred because of the ability to fine-tuning structural features.Recently,transition metal-catalyzed C–H activation has been employed for the functionalization of amino acids and peptides.Through domino C–H activation/annulation,a series of structurally complex and diverse amino acids and peptides is constructed.This review highlights recent advances in the synthesis of unnatural amino acids and peptides via transition metal-catalyzed C–H activation/annulation.展开更多
Discussions about the future of energy sources and environmental sustainability are becoming critical on a global scale.The energy sector plays a central role in the economy,as the availability and cost of energy infl...Discussions about the future of energy sources and environmental sustainability are becoming critical on a global scale.The energy sector plays a central role in the economy,as the availability and cost of energy influence the competitiveness of economies,while the level of energy consumption impacts the standard of living for individuals.This paper aims to examine environmental challenges and steps for a sustainable transition towards a hydrogen economy,focusing on its potential as an alternative to fossil fuels and the importance of developing the hydrogen paradigm.The research methodology is based on a combination of qualitative and quantitative methods,including an analysis of global and regional trends in the energy transition,the impact of various forms of hydrogen production(green,blue,gray hydrogen)on greenhouse gas emissions,and a comparison of existing policies and strategies in different countries transitioning to a sustainable hydrogen economy.Research results show that green hydrogen,produced via electrolysis using renewable energy sources,holds the greatest potential for reducing greenhouse gas emissions,while gray and blue hydrogen can serve as transitional options.The development of the hydrogen paradigm,rooted in innovative technologies,renewable energy sources,and international cooperation,is crucial for decarbonization and the creation of a sustainable global economy,despite challenges such as high costs and the need for global coordination.The hydrogen paradigm is becoming a cornerstone of these efforts,laying the foundation for a long-term,sustainable global economy.Currently,over 180 hydrogen transport projects,60 distribution projects,80 storage projects,30 terminal and port projects,and more than 220 hydrogen production projects are under development worldwide.The global momentum of the hydrogen transition helps mitigate climate change and build a sustainable future.展开更多
A novel method for the synthesis of 2,4-disubstituted thiophenes via the reactions of N,N-disubstituted enaminones and elemental sulfur is developed.By simply heating the substrates in pure water in the presence of Na...A novel method for the synthesis of 2,4-disubstituted thiophenes via the reactions of N,N-disubstituted enaminones and elemental sulfur is developed.By simply heating the substrates in pure water in the presence of NaOH,the thiophene annulation practically takes place via the generation of one C-C and two C-S bonds via cascade dual C-H functionalization and C-N bond thiolation without using any transition metal reagent.展开更多
Fe_(3)Sn_(2),a ferromagnetic metal with a kagome lattice,serves as an ideal platform for exploring topological electronic states and Berry curvature due to its unique band structure.However,systematic reports on the t...Fe_(3)Sn_(2),a ferromagnetic metal with a kagome lattice,serves as an ideal platform for exploring topological electronic states and Berry curvature due to its unique band structure.However,systematic reports on the transport properties of Fe_(3)Sn_(2)nanosheets remain scarce.We present temperature-dependent transport property measurements of Fe_(3)Sn_(2)nanosheets synthesized via chemical vapor deposition on Si/SiO_(2)substrates.The samples exhibit a robust anomalous Hall effect from 40 K to 300 K,along with a magnetoresistance sign reversal at 40 K at high magnetic fields,indicating a spin reorientation from in-plane to out-of-plane.Notably,a sharp crossover in the dominant transport contribution from electrons to holes near 200 K is observed,accompanied by distinct anomalous Hall behaviors in the two regimes,indicating a temperature-induced Lifshitz transition within the multi-band system.This divergence is potentially linked to a topological reconstruction of the Fermi surface across the transition.Our findings highlight the tunability of topological transport in two-dimensional kagome magnets and provide new insights into the interplay between band topology,dimensionality and magnetic order.展开更多
The glass transition temperature(T_(g))of styrene-butadiene rubber(SBR)is a key parameter determining its low-temperature flexibility and processing performance.Accurate prediction of T_(g)is crucial formaterial desig...The glass transition temperature(T_(g))of styrene-butadiene rubber(SBR)is a key parameter determining its low-temperature flexibility and processing performance.Accurate prediction of T_(g)is crucial formaterial design and application optimisation.Addressing the limitations of traditional experimental measurements and theoretical models in terms of efficiency,cost,and accuracy,this study proposes a machine learning prediction framework that integrates multi-model ensemble and Bayesian optimization by constructing a multi-component feature dataset and algorithm optimization strategy.Based on the constructed high-quality dataset containing 96 SBR samples,ninemachine learning models were employed to predict the T_(g)of SBR and compare their prediction performance.Ultimately,aGPR-XGBoost mixed model was constructed through model ensemble,achieving high-precision prediction with R^(2)values greater than 0.9 on both the training and test sets.Further feature attribution and local effect analysis were conducted using feature analysis methods such as SHAP and ALE,revealing the nonlinear influence patterns of various components on T_(g),providing a theoretical basis for SBR formulation design and T_(g)regulation.The machine learning prediction framework established in this study combines high-precision prediction with interpretability,significantly enhancing the prediction performance of the T_(g)of SBR.It offers an efficient tool for SBR molecular design and holds great potential for promotion and application.展开更多
The volume change behavior of natural gas hydrate-bearing sediment is essential as it influences settlement,strength,and stiffness,which directly affect the stability of hydrate reservoirs during hydrate extraction or...The volume change behavior of natural gas hydrate-bearing sediment is essential as it influences settlement,strength,and stiffness,which directly affect the stability of hydrate reservoirs during hydrate extraction or in response to environmental changes.The volume change is influenced not only by stress but also by the formation and dissociation of hydrates.This study adopted a customized apparatus for one-dimensional compression tests,allowing independent control of gas pressure and effective stress.Tests were conducted on samples with different hydrate saturations along various temperature-gas pressure-effective stress paths,yielding some conclusions related to compressibility and creep.An unusual phenomenon was observed under low-stress conditions:hydrate formation led to shrinkage rather than expansion.Three potential mechanisms behind this occurrence were discussed.As hydrate saturation increases,the yield stress rises while the compression and swelling indexes remain minimally affected.After hydrate dissociation,the compression curve of hydrate-bearing sediment drops to that of hydrate-free sediment.Once hydrate is formed,the compression curve of hydrate-free sediment gradually approaches that of hydrate-bearing sediment during the subsequent loading.Under low-stress conditions,the creep of both hydrate-free and hydrate-bearing sediments is very weak.However,when stress increases,significantly beyond the yield stress,the creep of both sediments increases significantly,with hydrate-bearing sediment exhibiting much greater creep than hydrate-free sediment.展开更多
基金Supported by the National Basic Research Program of China under Grant No 2012CB921603the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China under Grant No IRT13076the National Natural Science Foundation of China under Grant Nos 61378049,10934004,11404198,61575116 and 61505100
文摘We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature ^87 Rb atoms. The Doppler broad- ened background is effectively eliminated with the pulse shaping method and the spectrum modulation technique. The combination of the pulse shaping method and the spectra modulation technique provides a potential approachto reduce background of at least 99%.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61405002,91336103,10934010,61535001 and 61078026
文摘The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 × 10-13@1 s is employed for the light source. By using a periodically poled lithium niobate, the femtosecond pulse operating in 1556 nm is frequency-doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor. Through sweeping the carrier envelope offset frequency （fceo）, the 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve. After the frequency correction, the measured result agrees well with the previous experiment on this transition. The entire potential candidate of optical frequency standard for system configuration is compact and robust, providing a telecommunication applications.
基金Supported by the National Basic Research Program of China under Grant No 2012CB921603the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China under Grant No IRT13076the National Natural Science Foundation of China under Grant Nos 61378049,10934004,61575116 and 61505100
文摘A high-resolution two-photon spectrum of 5S1/2 → 5P3/2 → 5D5/2 transitions in a thermal SSRb vapor cell is presented by using an optical frequency comb and a cw laser. The fluorescence of 6P3/2 → 5S1/2 spontaneous emission is detected when the cw laser frequency is scanned from the 5S1/2 ground state to 5P3/2 hyperfine levels and the optical frequency comb repetition rate is fixed. The hyperfine splittings （Ff = 2-5） of the 5D5/2 excited state are well resolved. The dependences of fluorescence intensities on the cw laser intensity and temperature of SSRb vapor eel1 are studied, respectively. The experimental results are in good agreement with the theoretical analyses.
基金supported by the National Natural Science Foundation of China (Grant No 10574046)National Key Project for Basic Research of China (Grant Nos 2006CB806006 and 2006CB921105)+2 种基金Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT), Program for New Century Excellent Talents in University (NCET-04-0420)the Doctoral Program of High Education (Grant No 20050269011)Phosphor Program sponsored by Shanghai Science and Technology Committee (Grant No 06QH14003)
文摘A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.
基金Project supported by Shanghai Leading Academic Discipline Project (Grant No. B408)National Key Program for Basic Research of China (Grant Nos. 2006CB806006 and 2006CB921105)+1 种基金Ministry of Education of China (Grant No. 30800)Shanghai Municipal Science and Technology Commission (Grant Nos. 07DZ22025,09142200501 and 09ZR1409300)
文摘In this paper, we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system （Perylene dissolved in chloroform solution） by shaping the femtosecond pulses with simple phase patterns （cosinusoidal and π phase step-function shape）. The control efficiency of the two-photon transition probability is correlated with both the laser field and the molecular absorption bandwidth. Our results demonstrate that, the two-photon transition probability in a molecular system can be reduced but not completely eliminated by manipulating the laser field, and the control efficiency is minimal when the molecular absorption bandwidth is larger than twice the laser spectral bandwidth.
基金Supported by the National Natural Science Foundation of China under Grant Nos 91336103,10934010 and 61078026
文摘The optical frequency comb has been widely used in precision measurement. In this study, a multi-peak fitting approach is first proposed to fit the two-photon transition spectrum which overlaps with the neighboring transition in Rb-87. The multi-peak fitting approach is used to eliminate the frequency shift affected by the neighboring transition. With locking the carrier envelope offset frequency at 1/4 repetition frequency, the transition frequency is measured to be 770569132739.9 +/- 5.8 kHz, which agrees well with the previous result recommended by Comite International des Poids et Mesures.
基金Project supported by the National Basic Research Program of China (Grant No. 2012CB921603)the International Science & Technology Cooperation Program of China (Grant No. 2011DFA12490)+3 种基金the International Science & Technology Cooperation Program of Shanxi Province,China (Grant No. 2011081030)the National Natural Science Foundation of China (Grant Nos.61008012,10934004,60978001,11174187,and 11074154)the NSFC Project for Excellent Research Team of China (Grant No.61121064)the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20101401120004)
文摘A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an original way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.
基金Supported by the Robotic AI-Scientist Platform of Chinese Academy of SciencesNational Natural Science Foundation of China(22372185)+2 种基金Youth Talent Development Program of SKLCC(2025BWZ009)Natural Science Foundation of Shanxi Province(202203021221219)Research on the Construction of Scientific and Technological Innovation Think Tank of Shanxi Association for Science and Technology(KXKT202542)。
文摘Temperature-programmed desorption(TPD)is a fundamental technique in surface science and heterogeneous catalysis for characterizing adsorption behavior,and for extracting key parameters such as adsorption energy.However,the majority of existing TPD data is accessible in the form of published images,which lacks structured and quantitative datasets.This constrains its utility for rigorous quantitative analysis and computational modelling.Using carbon monoxide(CO)which is a widely adopted probe molecule,a curated and standardized dataset of CO-TPD is constructed,encompassing 14 transition-metal single-crystal surfaces,including copper(Cu)and ruthenium(Ru).By systematically extracting numerical data points from published spectra and applying normalization,essential spectral features such as peak shape are fully preserved.The dataset also documents relevant experimental parameters,including heating rates,and was developed using a standardized protocol for data collection and quality control.This resource serves as both a reference library to support the deconvolution of TPD spectra from complex catalysts and an experimental benchmark for calibrating parameters in theoretical models.By providing a reliable and accessible data function,this work advances the microscopic understanding and the rational design of catalyst active centers.
基金Supported by the National Natural Science Foundation of China(No.52273056)the Science and Technology Development Program of Jilin Province,China(No.YDZJ202501ZYTS305)。
文摘Electrochemical water splitting represents a sustainable technology for hydrogen(H_(2))production.However,its large-scale implementation is hindered by the high overpotentials required for both the cathodic hydrogen evolution reaction(HER)and the anodic oxygen evolution reaction(OER).Transition metal-based catalysts have garnered significant research interest as promising alternatives to noble-metal catalysts,owing to their low cost,tunable composition,and noble-metal-like catalytic activity.Nevertheless,systematic reviews on their application as bifunctional catalysts for overall water splitting(OWS)are still limited.This review comprehensively outlines the principal categories of bifunctional transition metal electrocatalysts derived from electrospun nanofibers(NFs),including metals,oxides,phosphides,sulfides,and carbides.Key strategies for enhancing their catalytic performance are systematically summarized,such as heterointerface engineering,heteroatom doping,metal-nonmetal-metal bridging architectures,and single-atom site design.Finally,current challenges and future research directions are discussed,aiming to provide insightful perspectives for the rational design of high-performance electrocatalysts for OWS.
基金supported by the National Science Foundation of China(NSFC 52571185,52201180 and 52371148)the China Postdoctoral Science Foundation(2023T160241 and 2023M731176)+2 种基金the Natural Science Foundation of Chongqing(CSTB2025NSCQ-GPX1026)the Science and Technology Research Program of Chongqing Municipal Education Commission of China(KJQN202500526)the Foundation of Chongqing Normal University(No.24XLB019).
文摘Polyamorphous transition refers to the transformation between two distinct amorphous states with identical composition.This phenomenon is intriguing in the field of physics and offers avenues for glass material design.Recently,polyamorphous transitions have been frequently observed in glassy materials.However,the transition pathway has yet to be established,which is essential for understanding its structural origins.Here,we present evidence from 12 different types of metallic glasses spanning 7 orders of magnitude in timescales,demonstrating that polyamorphous transitions consistently occur after the devitrification process,between two supercooled liquid phases(Ⅰ and Ⅱ).Notably,we observe a decrease in liquid fragility and heat capacity following the transition,suggesting that the polyamorphous transition is associated with the fragile-to-strong transition(FST)in liquids.These findings elucidate the detailed structural pathway of the polyamorphous transition,via glass I→devitrification→liquid I→fragile-strong transition→liquid II,and incorporate the FST into a cohesive framework for its understanding.
基金supported by the National Key Research and Development Program of China [grant number 2023YFF0807000]。
文摘Based on datasets from the International Best-Track Archive for Climate Stewardship(IBTrACS)and the fifth major global reanalysis produced by ECMWF(ERA5),the authors found that 29%of tropical cyclones(TCs)in the western North Pacific underwent extratropical transition(ET)from 1979 to 2022,with the frequency of ET events showing a slow decreasing trend.The extratropical transition tropical cyclones(ETCs)are classified into four clusters using the k-means clustering method based on their track patterns:recurving ETCs,westward ETCs,northwestward ETCs,and abnormal track ETCs.The transition process of recurving ETCs mostly occurs after the recurvature is completed,while 63.7%of the westward ETCs complete their transition after landfall.Abnormal track ETCs undergo transition over high-latitude oceans.Northwestward ETCs have the longest duration and slowest transition speed during the ET period,resulting in a prolonged impact.The ET process occurs at the edges of the western Pacific subtropical high(WPSH),with higher frequency during westward extension and lower during eastward retreat.While westward ETCs transition through surface friction effects,others complete ET in the northwest baroclinic zone of the WPSH.
基金supported by grants from Biological Breeding-National Science and Technology Major Project(2023ZD04076)the National Key Research and Development Program of Hubei Province(2022BBA154)the Foundation of Hubei Hongshan Laboratory(2021hszd010).
文摘The post-embryonic development of shoot apices in higher plants progresses through three distinct phases:the juvenile phase,adult vegetative phase,and reproductive phase.The transition from vegetative to reproductive growth represents a critical developmental transition that affects plant adaptability(Poethig 2003;Baurle and Dean 2006).
基金supported by the National Natural Science Foundation of China (Grant Nos.92477128,92580137,92477205,12374200,11604063,11974422,and 12104504)the National Key R&D Program of China (MOST) (Grant No.2023YFA1406500)+3 种基金the Strategic Priority Research Program (Chinese Academy of Sciences,CAS) (Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China (Grant No.21XNLG27)supported by the Outstanding Innovative Talents Cultivation Funded Programs 2023 of the Renmin University of Chinaan outcome of “Two-dimensional anisotropic series of materials FePd2+xTe2:a structural modulation study from the atomic scale to the mesoscopic scale” (RUC25QSDL128),funded by the “Qiushi Academic-Dongliang” Talent Cultivation Project at Renmin University of China in 2025。
文摘Transition-metal dichalcogenides hosting multiple competing structural and electronic phases are thus ideal platforms for constructing polytype heterostructures with emergent quantum properties.However,controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging.In this study,we realize vertical/lateral polytype heterostructures in a hole-doped Mott insulator via thermal annealing-induced structural transitions.Raman spectroscopy,atomic force microscopy and scanning Kelvin probe force microscopy confirm the coexistence of T-H polytype heterostructures.Atomic-scale scanning tunneling microscopy/spectroscopy measurements reveal the transparent effect in 1H/1T vertical heterostructures,where positive bias voltage induces in a pronounced superposition of the√13×√13 CDW of the 1T-layer on the 1H-layer.By systematically comparing the 1T/1H and 1T/1T interfaces,we demonstrate that the metallic 1H-layer induces a Coulomb screening effect on the 1T-layer,suppressing the formation of CDW domain walls and forming more ordered electronic states.These results clarify the interfacial coupling between distinct quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype heterostructures with tunable electronic properties.
基金supported by the National Key Laboratory of Helicopter Aeromechanics Fund(No.2024-CXPT-GF-JJ-093-05).
文摘The complex aerodynamic interaction between tandem tilt-wing and multi-rotor directly affects the wing surface flow and rotor thrust,making it a critical factor during the tilt transition process of this configuration of rotorcraft.The aerodynamic interaction of tandem tilt-wing and multi-rotor is investigated based on the CFD method.The aerodynamic effect of multi tilt-rotor is simulated as virtual disk modeling by adding source terms to the Navier-Stokes equations,effectively reducing the calculation time while maintaining the accuracy of aerodynamic interaction calculations.Aerodynamic forces and flow field characteristics of the tandem tilt-wing and multi-rotor under different tilt angles are compared between cases with and without aerodynamic interaction.Furthermore,the differences in aerodynamic forces between dynamic tilt transition and fixed-angle conditions were compared.The results show that the aerodynamic interaction of multi-rotor obviously increases the lift of front tilt-wing at different tilt angles,the wing lift under interaction is increased by more than 40%compared with isolated wing at tilt angle of 15°for the computation in this paper,which is related to the increase of wing flow velocity and the suppression of flow separation caused by multi-rotor;the wing blocking effect will increase rotor thrust,especially near the tilt angles of 30°and 45°;the increases of rear wing lift and rear rotor thrust under aerodynamic interaction are not significant because of suppression by the front wing’s downwash;the unsteady effects during dynamic tilting have a relatively minor impact on aerodynamic interaction,with the aerodynamic forces on the rotors and wings during the dynamic tilting process showing little difference from those under corresponding fixed tilt angles.
基金supported by the Natural Science Foundation of Jiangsu Province(No.BK20220409)the National Natural Science Foundation of China(No.22401153)+2 种基金the FWO[Fund for Scientific Research-Flanders(Belgium)]for financial support(recipient Erik V.Van der Eycken)the Research Council of the KU Leuven(recipient Erik V.Van der Eycken)the support of the"RUDN University Strategic Academic Leadership Program"(recipient Erik V.Van der Eycken).
文摘Peptides play important roles in chemistry,medicinal chemistry and life science,due to their high efficiency and specificity,unusual biological and therapeutic properties.As naturally occurring peptides often face with their intrinsic limitations including metabolic instability and low membrane permeability,the strategies for synthesizing unnatural amino acids and peptides are explored.Among the methods for modifying amino acids and peptides,chemo-and site-selective approaches are preferred because of the ability to fine-tuning structural features.Recently,transition metal-catalyzed C–H activation has been employed for the functionalization of amino acids and peptides.Through domino C–H activation/annulation,a series of structurally complex and diverse amino acids and peptides is constructed.This review highlights recent advances in the synthesis of unnatural amino acids and peptides via transition metal-catalyzed C–H activation/annulation.
文摘Discussions about the future of energy sources and environmental sustainability are becoming critical on a global scale.The energy sector plays a central role in the economy,as the availability and cost of energy influence the competitiveness of economies,while the level of energy consumption impacts the standard of living for individuals.This paper aims to examine environmental challenges and steps for a sustainable transition towards a hydrogen economy,focusing on its potential as an alternative to fossil fuels and the importance of developing the hydrogen paradigm.The research methodology is based on a combination of qualitative and quantitative methods,including an analysis of global and regional trends in the energy transition,the impact of various forms of hydrogen production(green,blue,gray hydrogen)on greenhouse gas emissions,and a comparison of existing policies and strategies in different countries transitioning to a sustainable hydrogen economy.Research results show that green hydrogen,produced via electrolysis using renewable energy sources,holds the greatest potential for reducing greenhouse gas emissions,while gray and blue hydrogen can serve as transitional options.The development of the hydrogen paradigm,rooted in innovative technologies,renewable energy sources,and international cooperation,is crucial for decarbonization and the creation of a sustainable global economy,despite challenges such as high costs and the need for global coordination.The hydrogen paradigm is becoming a cornerstone of these efforts,laying the foundation for a long-term,sustainable global economy.Currently,over 180 hydrogen transport projects,60 distribution projects,80 storage projects,30 terminal and port projects,and more than 220 hydrogen production projects are under development worldwide.The global momentum of the hydrogen transition helps mitigate climate change and build a sustainable future.
基金supported by the National Natural Science Foundation of China(No.22261026).
文摘A novel method for the synthesis of 2,4-disubstituted thiophenes via the reactions of N,N-disubstituted enaminones and elemental sulfur is developed.By simply heating the substrates in pure water in the presence of NaOH,the thiophene annulation practically takes place via the generation of one C-C and two C-S bonds via cascade dual C-H functionalization and C-N bond thiolation without using any transition metal reagent.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403503,2022YFA1602802,2023YFA1607400,and 2024YFA1613200)Beijing Natural Science Foundation(Grant No.JQ23022)supported by the Synergetic Extreme Condition User Facility and the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302600)。
文摘Fe_(3)Sn_(2),a ferromagnetic metal with a kagome lattice,serves as an ideal platform for exploring topological electronic states and Berry curvature due to its unique band structure.However,systematic reports on the transport properties of Fe_(3)Sn_(2)nanosheets remain scarce.We present temperature-dependent transport property measurements of Fe_(3)Sn_(2)nanosheets synthesized via chemical vapor deposition on Si/SiO_(2)substrates.The samples exhibit a robust anomalous Hall effect from 40 K to 300 K,along with a magnetoresistance sign reversal at 40 K at high magnetic fields,indicating a spin reorientation from in-plane to out-of-plane.Notably,a sharp crossover in the dominant transport contribution from electrons to holes near 200 K is observed,accompanied by distinct anomalous Hall behaviors in the two regimes,indicating a temperature-induced Lifshitz transition within the multi-band system.This divergence is potentially linked to a topological reconstruction of the Fermi surface across the transition.Our findings highlight the tunability of topological transport in two-dimensional kagome magnets and provide new insights into the interplay between band topology,dimensionality and magnetic order.
基金supported by the National Natural Science Foundation of China(grant numbers 52250357 and 52203003).
文摘The glass transition temperature(T_(g))of styrene-butadiene rubber(SBR)is a key parameter determining its low-temperature flexibility and processing performance.Accurate prediction of T_(g)is crucial formaterial design and application optimisation.Addressing the limitations of traditional experimental measurements and theoretical models in terms of efficiency,cost,and accuracy,this study proposes a machine learning prediction framework that integrates multi-model ensemble and Bayesian optimization by constructing a multi-component feature dataset and algorithm optimization strategy.Based on the constructed high-quality dataset containing 96 SBR samples,ninemachine learning models were employed to predict the T_(g)of SBR and compare their prediction performance.Ultimately,aGPR-XGBoost mixed model was constructed through model ensemble,achieving high-precision prediction with R^(2)values greater than 0.9 on both the training and test sets.Further feature attribution and local effect analysis were conducted using feature analysis methods such as SHAP and ALE,revealing the nonlinear influence patterns of various components on T_(g),providing a theoretical basis for SBR formulation design and T_(g)regulation.The machine learning prediction framework established in this study combines high-precision prediction with interpretability,significantly enhancing the prediction performance of the T_(g)of SBR.It offers an efficient tool for SBR molecular design and holds great potential for promotion and application.
基金supported by the National Natural Science Foundation of China(Grant No.42171135)the Science and Technology Program of CNOOC Research Institute(Grant No.2023OTKK03)the“CUG Scholar”Scientific Research Funds at China University of Geosciences(Project No.2022098).
文摘The volume change behavior of natural gas hydrate-bearing sediment is essential as it influences settlement,strength,and stiffness,which directly affect the stability of hydrate reservoirs during hydrate extraction or in response to environmental changes.The volume change is influenced not only by stress but also by the formation and dissociation of hydrates.This study adopted a customized apparatus for one-dimensional compression tests,allowing independent control of gas pressure and effective stress.Tests were conducted on samples with different hydrate saturations along various temperature-gas pressure-effective stress paths,yielding some conclusions related to compressibility and creep.An unusual phenomenon was observed under low-stress conditions:hydrate formation led to shrinkage rather than expansion.Three potential mechanisms behind this occurrence were discussed.As hydrate saturation increases,the yield stress rises while the compression and swelling indexes remain minimally affected.After hydrate dissociation,the compression curve of hydrate-bearing sediment drops to that of hydrate-free sediment.Once hydrate is formed,the compression curve of hydrate-free sediment gradually approaches that of hydrate-bearing sediment during the subsequent loading.Under low-stress conditions,the creep of both hydrate-free and hydrate-bearing sediments is very weak.However,when stress increases,significantly beyond the yield stress,the creep of both sediments increases significantly,with hydrate-bearing sediment exhibiting much greater creep than hydrate-free sediment.
