The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron or...The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.展开更多
A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edg...A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edge subsiding,and cracking,can easily appear,owing to poor specific sti ness in the radial direction.Some e ective fixation methods based on a filling principle have been applied by researchers,including approaches based on wax,polyethylene glycol,iron powder,and(especially)ice.However,few studies have addressed the optimization of the cutting parameters.This study focused on optimizing the cutting parameters to obtain a better surface roughness(calculated as a roughness average or Ra)and surface morphology in the machining of an aluminum alloy honeycomb by an ice fixation method.A Taguchi method and an analysis of variance were used to analyze the e ects and contributions of spindle speed,cutting depth,and feed rate.The optimal cutting parameters were determined using the signal-to-noise ratio combined with the surface morphology.An F-value and P-value were calculated for the value of the Ra,according to a"smaller is better"model.Additionally,the optimum cutting parameters for machining the aluminum honeycomb by ice fixation were found at different levels.The results of this study showed that the optimal parameters were a feed rate of 50 mm/min,cutting depth of 1.2 mm,and spindle speed of 4000 r/min.Feed rate was the most significant factor for minimizing Ra and improving the surface morphology,followed by spindle speed.The cutting depth had little e ect on Ra and surface morphology.After optimization,the value of Ra could reach 0.218μm,and no surface morphology deterioration was observed in the verified experiment.Thus,this research proposes optimal parameters based on ice fixation for improving the surface quality.展开更多
Thermochemical two-step CO_(2) splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels.However,the harsh CO_(2) splitting conditions,the limited oxygen release kinetics an...Thermochemical two-step CO_(2) splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels.However,the harsh CO_(2) splitting conditions,the limited oxygen release kinetics and capacity of metal oxides block further promoted the CO yield and solar-to-fuel energy efficiency.Here,we propose a different carbon cycle assisted by Ni/La_(2)O_(3) via coupling methane decomposition with thermochemical CO_(2) splitting,replacing conventional metal oxides cycle.Superior performance was demonstrated with methane conversion reached around 94%with almost pure H_(2) generation.Encouragingly,CO_(2) conversion of 98%and CO yield of 6.9 mmol g^(-1) derived from CO_(2) were achieved,with peak CO evolution rate(402 mL min^(-1) g^(-1))of orders of magnitude higher than that in metal oxide process and outstanding thermodynamic solar-to-fuel energy efficiency(55.5%vs.18.5%).This was relevant to the synergistic activation of La_(2)O_(3) and Ni for CO_(2) in carbon cycle,thus improving CO_(2) splitting reaction with carbon species.展开更多
We present simultaneous broad-band radio observations on the abnormal emission mode from PSR B1859+07using the Five-hundred-meter Aperture Spherical radio Telescope(FAST).This pulsar shows peculiar emission,which take...We present simultaneous broad-band radio observations on the abnormal emission mode from PSR B1859+07using the Five-hundred-meter Aperture Spherical radio Telescope(FAST).This pulsar shows peculiar emission,which takes the form of occasional shifts of emission to an early rotational phase and mode change of emission at the normal phase.We confirm all these three emission modes with our data sets,including the B(burst)and Q(quiet)modes of the non-shifted pulses and the emission shift mode with a quasi-periodicity of 155 pulses.We also identify a new type of emission shift event,which has emission at the normal phase during the event.We studied polarization properties of these emission modes in detail,and found that they all have similar polarization angle curve,indicating the emissions of all these three modes are from the same emission height.展开更多
The commonly used Poisson rectangular pulse(PRP)model,employed for simulating high-resolution residential water consumption patterns(RWCPs),relies on calibration via medium-resolution RWCPs obtained from practical mea...The commonly used Poisson rectangular pulse(PRP)model,employed for simulating high-resolution residential water consumption patterns(RWCPs),relies on calibration via medium-resolution RWCPs obtained from practical measurements.This introduces inevitable uncertainty stemming from the measured RWCPs,which consequently impacts the precision of model simulations.Here we enhance the accuracy of the PRP model by addressing the uncertainty of RWCPs.We established a critical sampling size of 2000 household water consumption patterns(HWCPs)with a data logging interval(DLI)of 15 min to attain dependable RWCPs.Through Genetic Algorithm calibration,the optimal values of the PRP model's parameters were determined:pulse frequency lλ=91 d^(-1),mean of pulse intensity E(I)=0.346 m^(3) h^(-1),standard deviation of pulse intensity STD(I)=0.292 m^(3) h^(-1),mean of pulse duration E(D)=40 s,and standard deviation of pulse duration STD(D)=55 s.Furthermore,validation was conducted at both HWCP and RWCP levels.We recommend a sampling size of2000 HWCPs and a DLI of30 min for PRP model calibration to balance simulation precision and practical implementation.This study significantly advances the theoretical foundation and real-world application of the PRP model,enhancing its role in urban water supply system management.展开更多
Annual variations of interstellar scintillation can be modelled to constrain parameters of the ionized interstellar medium.If a pulsar is in a binary system,then investigating the orbital parameters is possible throug...Annual variations of interstellar scintillation can be modelled to constrain parameters of the ionized interstellar medium.If a pulsar is in a binary system,then investigating the orbital parameters is possible through analysis of the orbital variation of scintillation.In observations carried out from 2011 to 2020 by the European Pulsar Timing Array radio telescopes,PSRs J0613-0200and J0636+5128 show strong annual variations in their scintillation velocity,while the former additionally exhibits an orbital fluctuation.Bayesian theory and Markov-chain-Monte-Carlo methods are used to interpret these periodic variations.We assume a thin and anisotropic scattering screen model,and discuss the mildly and extremely anisotropic scattering cases.PSR J0613-0200is best described by mildly anisotropic scattering,while PSR J0636+5128 exhibits extremely anisotropic scattering.We measure the distance,velocity,and degree of anisotropy of the scattering screen for our two pulsars,finding that scattering screen distances from Earth for PSRs J0613-0200 and J0636+5128 are 316_(-20)^(+28)pc and 262_(-38)^(+96)pc,respectively.The positions of these scattering screens are coincident with the shell of the Local Bubble towards both pulsars.These associations add to the growing evidence of the Local Bubble shell as a dominant region of scattering along many sightlines.展开更多
Stem cell research has become a hot topic in biology,as the understanding of stem cell biology can provide new insights for both regenerative medicine and clinical treatment of diseases.Accurately deciphering the fate...Stem cell research has become a hot topic in biology,as the understanding of stem cell biology can provide new insights for both regenerative medicine and clinical treatment of diseases.Accurately deciphering the fate of stem cells is the basis for understanding the mechanism and function of stem cells during tissue repair and regeneration.Cre-loxP-mediated recombination has been widely applied in fate mapping of stem cells for many years.However,nonspecific labeling by conventional cell lineage tracing strategies has led to discrepancies or even controversies in multiple fields.Recently,dual recombinase-mediated lineage tracing strategies have been developed to improve both the resolution and precision of stem cell fate mapping.These new genetic strategies also expand the application of lineage tracing in studying cell origin and fate.Here,we review cell lineage tracing methods,especially dual genetic approaches,and then provide examples to describe how they are used to study stem cell fate plasticity and function in vivo.展开更多
During the overall processing of thin-walled parts(TWPs),the guaranteed capability of the machining process and quality is determined by fixtures.Therefore,reliable fixtures suitable for the structure and machining pr...During the overall processing of thin-walled parts(TWPs),the guaranteed capability of the machining process and quality is determined by fixtures.Therefore,reliable fixtures suitable for the structure and machining process of TWP are essential.In this review,the key role of fixtures in the manufacturing system is initially discussed.The main problems in machining and workholding due to the characteristics of TWP are then analyzed in detail.Afterward,the definition of TWP fixtures is reinterpreted from narrow and broad perspectives.Fixture functions corresponding to the issues of machining and workholding are then clearly stated.Fixture categories are classified systematically according to previous research achievements,and the operation mode,functional characteristics,and structure of each fixture are comprehensively described.The function and execution mode of TWP fixtures are then systematically summarized and analyzed,and the functions of various TWP fixtures are evaluated.Some directions for future research on TWP fixtures technology are also proposed.The main purpose of this review is to provide some reference and guidance for scholars to examine TWP fixtures.展开更多
Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, car...Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.展开更多
An in-depth understanding of the catalytic reaction mechanism is the key to designing efficient and stable catalysts. In situ transmission electron microscope(TEM) is the most powerful tool to visualize and analyze th...An in-depth understanding of the catalytic reaction mechanism is the key to designing efficient and stable catalysts. In situ transmission electron microscope(TEM) is the most powerful tool to visualize and analyze the microstructures of catalysts during catalysis. In situ TEM combined with three-dimensional(3D) electron tomography(ET) reconstruction technique enables interrogations of catalysts’ structural dynamics and chemical changes in high temporal and spatial dimensions. In this review, we discuss and summarize the recent advances in in situ TEM together with 3D ET for catalyst studies. Topics include the latest research progress of in situ TEM imaging as well as 3D visualization and quantitative analysis of catalysts. We also pay particular attention to artificial intelligence(AI)-enhanced smart 3D ET. These include deep learning(DL)-based data compression and storage for the analysis of large TEM data, recovery of wedge-shaped information lost in 3D ET reconstructions, and DL models for reducing residual artifacts in 3D reconstructed images. Finally, the challenges and development prospects of current in situ TEM and 3D ET research are discussed.展开更多
PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still...PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still under investigation. In this paper, we present our ultra-wideband observation of this pulsar using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), with simultaneous measurements in the frequency ranges 280-780 and 1250-1550 MHz. We have identified three abnormal events, each of which becomes less apparent as the frequency decreases. At 1400 MHz, the averaged profile slightly shifted after the first and third abnormal events, implying a relationship between abnormal event and profile variation. We also found a linear trend in the left-edge position of the averaged profiles between the first and third events as well as after the third event, suggesting the existence of a slow-drifting mode between the two major events. The second event has a comparatively small shift in phase and is thus categorized as a "small flare state". During the third event, a sequence of approximately nine pulses was seen to significantly weaken in all frequency bands, likely associated with the pseudo-nulling observed at 150 MHz.A three-component de-composition analysis of the normal averaged profiles shows that the trailing component is dominant at our observing frequencies, while the centre component has a comparatively steeper spectrum. We found the overall flux density in an abnormal event to slightly differ from that in an ordinary state, and the difference shows a frequency dependence. A comparison of the normal, abnormal and dimmed averaged profile indicates that the leading component is likely to be stable in all states.展开更多
基金support of Shanxi Province Major Science and Technology Projects,China (No.20191101002).
文摘The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.
基金Supported by National Key Research and Development Program of China(Grant No.2019YFB2005400)National Natural Science Foundation of China(Grant No.U1608251)+1 种基金Open project of State Key Laboratory of high performance complex manufacturing(Grant No.Kfkt2016-05)Changjiang Scholar Program of Chinese Ministry of Education(Grant No.T2017030).
文摘A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edge subsiding,and cracking,can easily appear,owing to poor specific sti ness in the radial direction.Some e ective fixation methods based on a filling principle have been applied by researchers,including approaches based on wax,polyethylene glycol,iron powder,and(especially)ice.However,few studies have addressed the optimization of the cutting parameters.This study focused on optimizing the cutting parameters to obtain a better surface roughness(calculated as a roughness average or Ra)and surface morphology in the machining of an aluminum alloy honeycomb by an ice fixation method.A Taguchi method and an analysis of variance were used to analyze the e ects and contributions of spindle speed,cutting depth,and feed rate.The optimal cutting parameters were determined using the signal-to-noise ratio combined with the surface morphology.An F-value and P-value were calculated for the value of the Ra,according to a"smaller is better"model.Additionally,the optimum cutting parameters for machining the aluminum honeycomb by ice fixation were found at different levels.The results of this study showed that the optimal parameters were a feed rate of 50 mm/min,cutting depth of 1.2 mm,and spindle speed of 4000 r/min.Feed rate was the most significant factor for minimizing Ra and improving the surface morphology,followed by spindle speed.The cutting depth had little e ect on Ra and surface morphology.After optimization,the value of Ra could reach 0.218μm,and no surface morphology deterioration was observed in the verified experiment.Thus,this research proposes optimal parameters based on ice fixation for improving the surface quality.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020100)the National Key R&D Program of China(2016YFA0202-801)+1 种基金the National Natural Science Foundation of China(NSFC)grants(21676269,21706254,21878283,22022814)the Dalian Institute of Chemical Physics,CAS(DICP I201916)。
文摘Thermochemical two-step CO_(2) splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels.However,the harsh CO_(2) splitting conditions,the limited oxygen release kinetics and capacity of metal oxides block further promoted the CO yield and solar-to-fuel energy efficiency.Here,we propose a different carbon cycle assisted by Ni/La_(2)O_(3) via coupling methane decomposition with thermochemical CO_(2) splitting,replacing conventional metal oxides cycle.Superior performance was demonstrated with methane conversion reached around 94%with almost pure H_(2) generation.Encouragingly,CO_(2) conversion of 98%and CO yield of 6.9 mmol g^(-1) derived from CO_(2) were achieved,with peak CO evolution rate(402 mL min^(-1) g^(-1))of orders of magnitude higher than that in metal oxide process and outstanding thermodynamic solar-to-fuel energy efficiency(55.5%vs.18.5%).This was relevant to the synergistic activation of La_(2)O_(3) and Ni for CO_(2) in carbon cycle,thus improving CO_(2) splitting reaction with carbon species.
基金supported by the National Key R&D Program of China under grant number 2018YFA0404703the Open Project Program of the CAS Key Laboratory of FAST,NAOC,Chinese Academy of Sciences,and the Guizhou Education Department under Grant No.Qian Education Contract KY[2019]214+1 种基金supported by the West Light Foundation of the Chinese Academy of Sciences(No.2018XBQNXZ-B-023)the“Tianchi Doctoral Program 2021”。
文摘We present simultaneous broad-band radio observations on the abnormal emission mode from PSR B1859+07using the Five-hundred-meter Aperture Spherical radio Telescope(FAST).This pulsar shows peculiar emission,which takes the form of occasional shifts of emission to an early rotational phase and mode change of emission at the normal phase.We confirm all these three emission modes with our data sets,including the B(burst)and Q(quiet)modes of the non-shifted pulses and the emission shift mode with a quasi-periodicity of 155 pulses.We also identify a new type of emission shift event,which has emission at the normal phase during the event.We studied polarization properties of these emission modes in detail,and found that they all have similar polarization angle curve,indicating the emissions of all these three modes are from the same emission height.
基金supported by the National Natural Science Foundation of China(52170105)the Ministry of Science and Technology of China(2019YFD1100105)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2019043).
文摘The commonly used Poisson rectangular pulse(PRP)model,employed for simulating high-resolution residential water consumption patterns(RWCPs),relies on calibration via medium-resolution RWCPs obtained from practical measurements.This introduces inevitable uncertainty stemming from the measured RWCPs,which consequently impacts the precision of model simulations.Here we enhance the accuracy of the PRP model by addressing the uncertainty of RWCPs.We established a critical sampling size of 2000 household water consumption patterns(HWCPs)with a data logging interval(DLI)of 15 min to attain dependable RWCPs.Through Genetic Algorithm calibration,the optimal values of the PRP model's parameters were determined:pulse frequency lλ=91 d^(-1),mean of pulse intensity E(I)=0.346 m^(3) h^(-1),standard deviation of pulse intensity STD(I)=0.292 m^(3) h^(-1),mean of pulse duration E(D)=40 s,and standard deviation of pulse duration STD(D)=55 s.Furthermore,validation was conducted at both HWCP and RWCP levels.We recommend a sampling size of2000 HWCPs and a DLI of30 min for PRP model calibration to balance simulation precision and practical implementation.This study significantly advances the theoretical foundation and real-world application of the PRP model,enhancing its role in urban water supply system management.
基金supported by the National Natural Science Foundation of China(Grant No.12003047)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region(Grant No.2022A03013-2)+2 种基金the Natural Science Foundation of Xinjiang Uygur Autonomous Region(Grant No.2022D01D85)support by the Deutsche Forschungsgemeinschaft(DFG)through the Heisenberg programme(Project No.433075039)financial support from“Programme National de Cosmologie et Galaxies”(PNCG)of CNRS/INSU,France。
文摘Annual variations of interstellar scintillation can be modelled to constrain parameters of the ionized interstellar medium.If a pulsar is in a binary system,then investigating the orbital parameters is possible through analysis of the orbital variation of scintillation.In observations carried out from 2011 to 2020 by the European Pulsar Timing Array radio telescopes,PSRs J0613-0200and J0636+5128 show strong annual variations in their scintillation velocity,while the former additionally exhibits an orbital fluctuation.Bayesian theory and Markov-chain-Monte-Carlo methods are used to interpret these periodic variations.We assume a thin and anisotropic scattering screen model,and discuss the mildly and extremely anisotropic scattering cases.PSR J0613-0200is best described by mildly anisotropic scattering,while PSR J0636+5128 exhibits extremely anisotropic scattering.We measure the distance,velocity,and degree of anisotropy of the scattering screen for our two pulsars,finding that scattering screen distances from Earth for PSRs J0613-0200 and J0636+5128 are 316_(-20)^(+28)pc and 262_(-38)^(+96)pc,respectively.The positions of these scattering screens are coincident with the shell of the Local Bubble towards both pulsars.These associations add to the growing evidence of the Local Bubble shell as a dominant region of scattering along many sightlines.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB19000000 and XDA16010507)the National Key Research and Development Program of China(2019YFA0110403 and 2019YFA0802000)National Natural Science Foundation of China(31730112,31625019,91849202,and 82008810001)。
文摘Stem cell research has become a hot topic in biology,as the understanding of stem cell biology can provide new insights for both regenerative medicine and clinical treatment of diseases.Accurately deciphering the fate of stem cells is the basis for understanding the mechanism and function of stem cells during tissue repair and regeneration.Cre-loxP-mediated recombination has been widely applied in fate mapping of stem cells for many years.However,nonspecific labeling by conventional cell lineage tracing strategies has led to discrepancies or even controversies in multiple fields.Recently,dual recombinase-mediated lineage tracing strategies have been developed to improve both the resolution and precision of stem cell fate mapping.These new genetic strategies also expand the application of lineage tracing in studying cell origin and fate.Here,we review cell lineage tracing methods,especially dual genetic approaches,and then provide examples to describe how they are used to study stem cell fate plasticity and function in vivo.
基金support from the National Natural Science Foundation of China(Grant Nos.U20B2033,51975093)the Natural Science Foundation of Liaoning,China(Grant No.2020-YQ-09)。
文摘During the overall processing of thin-walled parts(TWPs),the guaranteed capability of the machining process and quality is determined by fixtures.Therefore,reliable fixtures suitable for the structure and machining process of TWP are essential.In this review,the key role of fixtures in the manufacturing system is initially discussed.The main problems in machining and workholding due to the characteristics of TWP are then analyzed in detail.Afterward,the definition of TWP fixtures is reinterpreted from narrow and broad perspectives.Fixture functions corresponding to the issues of machining and workholding are then clearly stated.Fixture categories are classified systematically according to previous research achievements,and the operation mode,functional characteristics,and structure of each fixture are comprehensively described.The function and execution mode of TWP fixtures are then systematically summarized and analyzed,and the functions of various TWP fixtures are evaluated.Some directions for future research on TWP fixtures technology are also proposed.The main purpose of this review is to provide some reference and guidance for scholars to examine TWP fixtures.
基金supported by the National Key R&D Program of China(Grant No.2018YFA0404703)the National Natural Science Foundation of China(Grant No.11225314)+6 种基金the Open Project Program of the Key Laboratory of FAST,NAOC,Chinese Academy of Sciencesthe Project of Chinese Academy of Sciences(CAS)supported by the Special Funding for Advanced Users,budgeted and administrated by Center for Astronomical Mega-Science,Chinese Academy of Sciences(CAMS)the Max-Planck-Society(MPS)Collaborationthe financial support by the European Research Council for the ERC Synergy Grant BlackHoleCam(Grant No.610058)supported by the National Key R&D Program of China(Grant No.2017YFA0402600)the Chinese Academy of Sciences "Light of West China" Program
文摘Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.
基金supported by National Key Research and Development Program of China (2019YFA0210403)。
文摘An in-depth understanding of the catalytic reaction mechanism is the key to designing efficient and stable catalysts. In situ transmission electron microscope(TEM) is the most powerful tool to visualize and analyze the microstructures of catalysts during catalysis. In situ TEM combined with three-dimensional(3D) electron tomography(ET) reconstruction technique enables interrogations of catalysts’ structural dynamics and chemical changes in high temporal and spatial dimensions. In this review, we discuss and summarize the recent advances in in situ TEM together with 3D ET for catalyst studies. Topics include the latest research progress of in situ TEM imaging as well as 3D visualization and quantitative analysis of catalysts. We also pay particular attention to artificial intelligence(AI)-enhanced smart 3D ET. These include deep learning(DL)-based data compression and storage for the analysis of large TEM data, recovery of wedge-shaped information lost in 3D ET reconstructions, and DL models for reducing residual artifacts in 3D reconstructed images. Finally, the challenges and development prospects of current in situ TEM and 3D ET research are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.11673031,11703048,and U1731238)the Open Project Program of the Key Laboratory of FAST,NAOC+2 种基金the financial support by the European Research Council for the ERC Synergy Grant BlackHoleCam(Grant No.610058)the FAST FELLOWSHIP from Special Funding for Advanced Users,budgeted and administrated by Center for Astronomical Mega-Science,Chinese Academy of Sciences(CAMS)the MPG-CAS Joint Project "Low-Frequency Gravitational Wave Astronomy and Gravitational Physics in Space"
文摘PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still under investigation. In this paper, we present our ultra-wideband observation of this pulsar using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), with simultaneous measurements in the frequency ranges 280-780 and 1250-1550 MHz. We have identified three abnormal events, each of which becomes less apparent as the frequency decreases. At 1400 MHz, the averaged profile slightly shifted after the first and third abnormal events, implying a relationship between abnormal event and profile variation. We also found a linear trend in the left-edge position of the averaged profiles between the first and third events as well as after the third event, suggesting the existence of a slow-drifting mode between the two major events. The second event has a comparatively small shift in phase and is thus categorized as a "small flare state". During the third event, a sequence of approximately nine pulses was seen to significantly weaken in all frequency bands, likely associated with the pseudo-nulling observed at 150 MHz.A three-component de-composition analysis of the normal averaged profiles shows that the trailing component is dominant at our observing frequencies, while the centre component has a comparatively steeper spectrum. We found the overall flux density in an abnormal event to slightly differ from that in an ordinary state, and the difference shows a frequency dependence. A comparison of the normal, abnormal and dimmed averaged profile indicates that the leading component is likely to be stable in all states.
