Recently,the global background concentration of ozone(O_(3))has demonstrated a rising trend.Among various methods,groun-basedmonitoring of O_(3)concentrations is highly reliable for research analysis.To obtain informa...Recently,the global background concentration of ozone(O_(3))has demonstrated a rising trend.Among various methods,groun-basedmonitoring of O_(3)concentrations is highly reliable for research analysis.To obtain information on the spatial characteristics of O_(3)concentrations,it is necessary that the groundmonitoring sites be constructed in sufficient density.In recent years,many researchers have used machine learning models to estimate surface O_(3)concentrations,which cannot fully provide the spatial and temporal information contained in a sample dataset.To solve this problem,the current study utilized a deep learning model called the Residual connection Convolutional Long Short-Term Memory network(RConvLSTM)to estimate daily maximum8-hr average(MDA8)O_(3)over Jiangsu province,China during 2020.In this research,the R-ConvLSTM model not only provides the spatiotemporal information ofMDA8 O_(3),but also involves residual connection to avoid the problem of gradient explosion and gradient disappearance with the deepening of network layers.We utilized the TROPOMI total O_(3)column retrieved fromSentinel-5 Precursor,ERA5 reanalysismeteorological data,and other supplementary data to build a pre-trained dataset.The R-ConvLSTM model achieved an overall sample-base cross-validation(CV)R^(2)of 0.955 with root mean square error(RMSE)of 9.372μg/m^(3).Model estimation also showed a city-based CV R^(2)of 0.896 with RMSE of 14.029μg/m^(3),the highest MDA8 O_(3)in spring being 122.60±31.60μg/m^(3)and the lowest in winter being 69.93±18.48μg/m^(3).展开更多
We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being ...We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium.HINSA was found in 58%PGCCs that we observed.The column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds.For clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive clouds.Nonthermal line width of 13CO is about 0-0.5 kms-1 larger than that of HINSA.One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO.Based on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.展开更多
The presence of a van Hove singularity(vHS)at the Fermi level can trigger magnetic instability by mediating a spontaneous transition from paramagnetic to magnetically ordered states.While electrostatic doping(typicall...The presence of a van Hove singularity(vHS)at the Fermi level can trigger magnetic instability by mediating a spontaneous transition from paramagnetic to magnetically ordered states.While electrostatic doping(typically achieved via ionic gating)to shift the vHS to the Fermi level provides a general mechanism for engineering such magnetism,its volatile nature often leads to the collapse of induced states upon gate field removal.Here,a novel scheme is presented for non-volatile magnetic control by utilizing ferroelectric heterostructures to achieve reversible magnetism switching.Using two-dimensional VSiN_(3),a nonmagnetic material with Mexican-hat electronic band dispersions hosting vHSs,as a prototype,it is preliminarily demonstrated that both electron and hole doping can robustly induce magnetism.Further,by interfacing VSiN_(3)with ferroelectric Sc_(2)CO_(2),reversible switching of its magnetic state via polarization-driven heterointerfacial charge transfer is achieved.This mechanism enables a dynamic transition between insulating and half-metallic phases in VSiN_(3),establishing a pathway to design multiferroic tunnel junctions with giant tunneling electroresistance or magnetoresistance.This work bridges non-volatile ferroelectric control with vHS-enhanced magnetism,opening opportunities for energy-efficient and high-performance spintronic devices and non-volatile memory devices.展开更多
With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astro...With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astronomy and space situational monitoring.As a crucial observatory site for international deep space,deep Earth,deep sea,and polar exploration,it is very important to evaluate the suitability of Dome A as an observatory site.However,owing to extreme environmental constraints,the evaluation of site conditions is mainly based on single-point measurements,making it challenging to comprehensively evaluate the effective site range and uniformity.This study integrated satellite remote sensing data to develop a cross-comparison framework for diverse indicators across Dome A,to evaluate its spatial uniformity.We find that the area surrounding the Dome A site,defined within a roughly 1°×1°latitude and longitude range,possesses excellent astronomical observation conditions.展开更多
Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fa...Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.展开更多
The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(F...The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes.Over a ten-second period,the phases shift by 18°while the amplitudes fluctuate by 6 mK.Thus,we developed the fast Fourier transform(FFT)filter method to eliminate these standing waves for every individual spectrum.The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate.Compared to other methods such as sine fitting and running median,the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%.Additionally,the FFT filter method avoids the flux loss issue encountered with some other methods.The FFT is also efficient in detecting harmonic radio frequency interference(RFI).In the FAST data,we identified three distinct types of harmonic RFI,each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1,0.5,and 0.37 MHz,respectively.The FFT filter,proven as the most effective method,is integrated into the H I data calibration and imaging pipeline for FAST(HiFAST,https://hifast.readthedocs.io).展开更多
基金supported by the National Natural Science Foundation of China(No.41604028)the Anhui Provincial Naturel Science Foundation(No.1708085QD83)+1 种基金the Anhui Science and Technology Department Major Project(No.18030801111)the Projects of Innovation and Development of Anhui Meteorological Bureau(No.CXM202102).
文摘Recently,the global background concentration of ozone(O_(3))has demonstrated a rising trend.Among various methods,groun-basedmonitoring of O_(3)concentrations is highly reliable for research analysis.To obtain information on the spatial characteristics of O_(3)concentrations,it is necessary that the groundmonitoring sites be constructed in sufficient density.In recent years,many researchers have used machine learning models to estimate surface O_(3)concentrations,which cannot fully provide the spatial and temporal information contained in a sample dataset.To solve this problem,the current study utilized a deep learning model called the Residual connection Convolutional Long Short-Term Memory network(RConvLSTM)to estimate daily maximum8-hr average(MDA8)O_(3)over Jiangsu province,China during 2020.In this research,the R-ConvLSTM model not only provides the spatiotemporal information ofMDA8 O_(3),but also involves residual connection to avoid the problem of gradient explosion and gradient disappearance with the deepening of network layers.We utilized the TROPOMI total O_(3)column retrieved fromSentinel-5 Precursor,ERA5 reanalysismeteorological data,and other supplementary data to build a pre-trained dataset.The R-ConvLSTM model achieved an overall sample-base cross-validation(CV)R^(2)of 0.955 with root mean square error(RMSE)of 9.372μg/m^(3).Model estimation also showed a city-based CV R^(2)of 0.896 with RMSE of 14.029μg/m^(3),the highest MDA8 O_(3)in spring being 122.60±31.60μg/m^(3)and the lowest in winter being 69.93±18.48μg/m^(3).
基金supported by the National Key R&D Program of China(2017YFA0402600 and 2016YFA0400702)the National Natural Science Foundation of China(Grant Nos.11988101,11803051,11725313 and 11721303)+3 种基金CAS International Partnership Program(114A11KYSB20160008)CAS“Light of West China”ProgramCAS Interdisciplinary Innovation Team and Young Researcher Grant of National Astronomical Observatoriessupported in part by the Youth Innovation Promotion Association of CAS(No.2018075)
文摘We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium.HINSA was found in 58%PGCCs that we observed.The column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds.For clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive clouds.Nonthermal line width of 13CO is about 0-0.5 kms-1 larger than that of HINSA.One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO.Based on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.
基金supported by the National Natural Science Foundation of China(Grant Nos.62174016,12474047,12204202,and 11974355)the Basic Research Program of Jiangsu(Grant No.BK20220679)+1 种基金the Fund for Shanxi“1331Project”the Research Project Supported by Shanxi Scholarship Council of China.
文摘The presence of a van Hove singularity(vHS)at the Fermi level can trigger magnetic instability by mediating a spontaneous transition from paramagnetic to magnetically ordered states.While electrostatic doping(typically achieved via ionic gating)to shift the vHS to the Fermi level provides a general mechanism for engineering such magnetism,its volatile nature often leads to the collapse of induced states upon gate field removal.Here,a novel scheme is presented for non-volatile magnetic control by utilizing ferroelectric heterostructures to achieve reversible magnetism switching.Using two-dimensional VSiN_(3),a nonmagnetic material with Mexican-hat electronic band dispersions hosting vHSs,as a prototype,it is preliminarily demonstrated that both electron and hole doping can robustly induce magnetism.Further,by interfacing VSiN_(3)with ferroelectric Sc_(2)CO_(2),reversible switching of its magnetic state via polarization-driven heterointerfacial charge transfer is achieved.This mechanism enables a dynamic transition between insulating and half-metallic phases in VSiN_(3),establishing a pathway to design multiferroic tunnel junctions with giant tunneling electroresistance or magnetoresistance.This work bridges non-volatile ferroelectric control with vHS-enhanced magnetism,opening opportunities for energy-efficient and high-performance spintronic devices and non-volatile memory devices.
基金supported by the Space Debris Research Project,China(KJSP2020010102)the National Key R&D Program of China(2022YFC2807300).
文摘With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astronomy and space situational monitoring.As a crucial observatory site for international deep space,deep Earth,deep sea,and polar exploration,it is very important to evaluate the suitability of Dome A as an observatory site.However,owing to extreme environmental constraints,the evaluation of site conditions is mainly based on single-point measurements,making it challenging to comprehensively evaluate the effective site range and uniformity.This study integrated satellite remote sensing data to develop a cross-comparison framework for diverse indicators across Dome A,to evaluate its spatial uniformity.We find that the area surrounding the Dome A site,defined within a roughly 1°×1°latitude and longitude range,possesses excellent astronomical observation conditions.
基金supported by the National Natural Science Foundation of China(Nos.52074231,52274396 and 52001258)the Chongqing Natural Science Foundation(No.cstc2020jcyj-msxmX1056).
文摘Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.
基金supported by the China National Key Program for Science and Technology Research and Development of China (2022YFA1602901,2023YFA1608204)the National SKA Program of China (No.2022SKA0110201)+5 种基金the National Natural Science Foundation of China (NSFC,grant Nos.11873051,11988101,12033008,12041305,12125302,12173016,and 12203065)the CAS Project for Young Scientists in Basic Research grant (No.YSBR-062)the K.C.Wong Education Foundationthe science research grants from the China Manned Space Projectsupport from the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the China Postdoctoral Science Foundation grant No.2024M763213
文摘The standing waves existing in radio telescope data are primarily due to reflections among the instruments,which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes.Over a ten-second period,the phases shift by 18°while the amplitudes fluctuate by 6 mK.Thus,we developed the fast Fourier transform(FFT)filter method to eliminate these standing waves for every individual spectrum.The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate.Compared to other methods such as sine fitting and running median,the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%.Additionally,the FFT filter method avoids the flux loss issue encountered with some other methods.The FFT is also efficient in detecting harmonic radio frequency interference(RFI).In the FAST data,we identified three distinct types of harmonic RFI,each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1,0.5,and 0.37 MHz,respectively.The FFT filter,proven as the most effective method,is integrated into the H I data calibration and imaging pipeline for FAST(HiFAST,https://hifast.readthedocs.io).
