Fig.3.(a)α-particle energy spectra,and(b)decay-time distributions on a logarithmic scale for the observed 288Mc and its descendant nuclei.In the panel(a),the red histograms show the observed full-energy events,while ...Fig.3.(a)α-particle energy spectra,and(b)decay-time distributions on a logarithmic scale for the observed 288Mc and its descendant nuclei.In the panel(a),the red histograms show the observed full-energy events,while the corresponding blue histograms show the reconstructed events.The red smooth curves in panel(b)are the expected time distributions according to the corresponding half-lives extracted from this work.展开更多
Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,...Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,empowering us to study quantum behaviors of electrons in atoms,molecules,and solids with unprecedented time resolution.Following the cutoff energy law of HHG,the shortest IAP reported so far is driven with short-wavelength infrared(SWIR)pulses,which require additional broadband frequency conversion techniques and raise the bar for attosecond researches.Here,we show that with fewcycle near-infrared(NIR)laser pulses,IAP with pulse duration of 51±4 as is generated during 1-fs linear polarization gate formed by generalized double optical gating(GDOG)technique.The characterization is done with attosecond streak camera,and phase reconstruction is performed with quick phase retrieval by omega oscillation filtering(qPROOF).Furthermore,we show that the IAP generation favors certain carrier envelope phases(CEPs)in the narrow gate,i.e.,IAP is only efficiently produced for certain CEPs,which eliminates the requirement of CEP stabilization.The demonstrated scheme for IAP generation in principle has much higher conversion efficiency than the long-wave driver scheme according to the wavelength scaling law of HHG.Our work suggests an alternative way to generate ultrashort IAPs by applying GDOG on few-cycle free-CEP NIR driving pulses,and is thereby of great importance to facilitate the development of attosecond science and technology.展开更多
Most Chinese metropolitan regions have experienced rapid urbanization.Cities lying in coastal areas are prone to severe weather events.The meteorological hazards expose greater numbers of developed areas a variety of ...Most Chinese metropolitan regions have experienced rapid urbanization.Cities lying in coastal areas are prone to severe weather events.The meteorological hazards expose greater numbers of developed areas a variety of inhabitants to increased risk.This paper attempts to characterize how urbanization process,as well as monsoon climatic oscillations,affects Shanghai’s vulnerability to severe weather conditions.To assess how regional urbanization may impact vulnerability to droughts and floods,an analysis examining potential rhythmic variations was implemented.Our results indicated that the centennial scale metrological droughts and floods were a function of monsoon climate,while the decadal metrological oscillations in recent one and half centuries were primarily modified by the anthropogenic behaviors and resulting hydrologic characteristics.In view of the wide distribution,the meteorological droughts and floods are key issues for long-term social-economic harmonization in Shanghai.This study can assist in prioritizing disaster mitigation measures and ensuring regional sustainable development in the study area.展开更多
文摘Fig.3.(a)α-particle energy spectra,and(b)decay-time distributions on a logarithmic scale for the observed 288Mc and its descendant nuclei.In the panel(a),the red histograms show the observed full-energy events,while the corresponding blue histograms show the reconstructed events.The red smooth curves in panel(b)are the expected time distributions according to the corresponding half-lives extracted from this work.
基金supported by the National Key Research and Development Program of China(grant no.2019YFA0307703)the Major Research Plan of the National Natural Science Foundation of China(grant no.91850201)the National Natural Science Foundation of China(grant nos.12234020 and 11974426).
文摘Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,empowering us to study quantum behaviors of electrons in atoms,molecules,and solids with unprecedented time resolution.Following the cutoff energy law of HHG,the shortest IAP reported so far is driven with short-wavelength infrared(SWIR)pulses,which require additional broadband frequency conversion techniques and raise the bar for attosecond researches.Here,we show that with fewcycle near-infrared(NIR)laser pulses,IAP with pulse duration of 51±4 as is generated during 1-fs linear polarization gate formed by generalized double optical gating(GDOG)technique.The characterization is done with attosecond streak camera,and phase reconstruction is performed with quick phase retrieval by omega oscillation filtering(qPROOF).Furthermore,we show that the IAP generation favors certain carrier envelope phases(CEPs)in the narrow gate,i.e.,IAP is only efficiently produced for certain CEPs,which eliminates the requirement of CEP stabilization.The demonstrated scheme for IAP generation in principle has much higher conversion efficiency than the long-wave driver scheme according to the wavelength scaling law of HHG.Our work suggests an alternative way to generate ultrashort IAPs by applying GDOG on few-cycle free-CEP NIR driving pulses,and is thereby of great importance to facilitate the development of attosecond science and technology.
基金supported by National Natural Science Foundation of China(No.41220001,Z.H.ChenNo.41172167 and 41320003,G.F.Yang)+2 种基金Project funded by China Postdoctoral Science Foundation(General Program No.2012M520220 and Special Program No.2014T70059,Z.H.Chen)Opening Fund from Institute of Urban Meteorology,China Meteorological Administration,Beijing(No.UMRF201203,Z.H.Chen)the Fundamental Research Funds for the Central Universities(No.2652014058,G.F.Yang).
文摘Most Chinese metropolitan regions have experienced rapid urbanization.Cities lying in coastal areas are prone to severe weather events.The meteorological hazards expose greater numbers of developed areas a variety of inhabitants to increased risk.This paper attempts to characterize how urbanization process,as well as monsoon climatic oscillations,affects Shanghai’s vulnerability to severe weather conditions.To assess how regional urbanization may impact vulnerability to droughts and floods,an analysis examining potential rhythmic variations was implemented.Our results indicated that the centennial scale metrological droughts and floods were a function of monsoon climate,while the decadal metrological oscillations in recent one and half centuries were primarily modified by the anthropogenic behaviors and resulting hydrologic characteristics.In view of the wide distribution,the meteorological droughts and floods are key issues for long-term social-economic harmonization in Shanghai.This study can assist in prioritizing disaster mitigation measures and ensuring regional sustainable development in the study area.
