Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright ba...Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.展开更多
Two factors that affect satellite retrieval of Aerosol Optical Depth(AOD) are aerosol model assumptions and the separation of surface reflectance.NASA/MODIS Dense Dark Vegetation(DDV) algorithm has been proven valuabl...Two factors that affect satellite retrieval of Aerosol Optical Depth(AOD) are aerosol model assumptions and the separation of surface reflectance.NASA/MODIS Dense Dark Vegetation(DDV) algorithm has been proven valuable in deriving aerosol distribution and properties over land;however,it cannot be applied to bright targets.As a supplement to the DDV algorithm,an algorithm to retrieve AOD over urban areas in North China in winter is developed using MODIS data,including(1) the generation and analysis of adjacent clear-days surface reflectance using MOD09 product from 2007 to 2008,and(2) seasonal aerosol models derived from AERONET data in Beijing and Xianghe sites.Ground-based measurements using sun photometers were used to validate the retrieved AOD,and the correlation coefficient(r) is up to 0.931.Especially for high AOD values(AOD>0.4),more retrievals meet the inversion accuracy.The temporal variations of retrieval errors over urban,rural and mountain regions were examined,and the results indicated that the variation of blue-band surface reflectance is less than 0.02 in a short period except for unusual weather conditions,the retrieval bias is under 0.08,and the relative error decreases as the AOD increases.展开更多
Dear Editor,CRISPR-Cas9 （clustered regularly interspaced short palin- dromic repeats-CRISPR associated） systems have been harnessed for kinds of genome manipulation, including gene editing, transcription regulation,...Dear Editor,CRISPR-Cas9 （clustered regularly interspaced short palin- dromic repeats-CRISPR associated） systems have been harnessed for kinds of genome manipulation, including gene editing, transcription regulation, and chromosome loci imaging （Dominguez et al., 2016; Komor et al., 2017）. A typical engineered CRISPR-Cas9 system is composed of a Cas9 protein and a single guide RNA （sgRNA）, which could form a protein/RNA complex to recognize and cleave DNA sequence （Hsu et al., 2014; Wright et al., 2016）.展开更多
Data from a long term measurement of Micro Rain Radar （MRR） at a mountain site （Daegwallyeong, DG, one year period of 2005） and a coastal site （Haenam, HN, three years 2004-2006） in South Korea were analyzed to ...Data from a long term measurement of Micro Rain Radar （MRR） at a mountain site （Daegwallyeong, DG, one year period of 2005） and a coastal site （Haenam, HN, three years 2004-2006） in South Korea were analyzed to compare the MRR measured bright band characteristics of stratiform precipitation at the two sites. On average, the bright band was somewhat thicker and the sharpness （average gradient of reflectivity above and below the reflectivity peak） was slightly weaker at DG, compared to those values at HN. The peak reflectivity itself was twice as strong and the relative location of the peak reflectivity within the bright band was higher at HN than at DG. Importantly, the variability of these values was much larger at HN than at DG. The key parameter to cause these differences is suggested to be the difference of the snow particle densities at the two sites, which is related to the degree of riming. Therefore, it is speculated that the cloud microphysical processes at HN may have varied significantly from un-rimed snow growth, producing low density snow particles, to the riming of higher density particles, while snow particle growth at DG was more consistently affected by the riming process, and therefore high density snow particles. Forced uplifting of cloudy air over the mountain area around DG might have resulted in an orographic supercooling effect that led to the enhanced riming of supercooled cloud drops.展开更多
Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is muc...Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is much weaker in strength than the intramolecular electron-vibration coupling for a majority of newly termed AIEgens,which leads to the emission peak position insensitive to excitonic coupling,hence the conventional excitonic model for J-aggregation cannot effectively explain their AIE phenomena.Then,using multiscale computational approach coupled with our self-developed thermal vibration correlation function rate formalism and transition-state theory,we quantitatively investigate the aggregation effect on both the radiative and the nonradiative decays of molecular excited states.For radiative decay processes,we propose that the lowest excited state could convert from a transition dipole-forbidden“dark”state to a dipole-allowed“bright”state upon aggregation.For the radiationless processes,we demonstrate the blockage of nonradiative decay via vibration relaxation(BNR-VR)in harmonic region or the removal of nonradiative decay via isomerization(RNR-ISO)or minimum energy crossing point(RNR-MECP)beyond harmonic region in a variety of AIE aggregates.Our theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally verified.Looking forward,we believe this review will benefit the deep understanding about the universality of AIE phenomenon and further extending the scope of AIE systems with novel applications.展开更多
he brightest object in the universe-at least,the brightest we've seen yetshines 500 trillion timesbrighter than the sun,and it eats a sun a day.Objects like these are rare,and despite their objective brightness,re...he brightest object in the universe-at least,the brightest we've seen yetshines 500 trillion timesbrighter than the sun,and it eats a sun a day.Objects like these are rare,and despite their objective brightness,remain elusive and hard to spot.This record-breaker was first spotted in 198o and mischaracterized as a regular old star.展开更多
Thirteen years on, that case at the Aocheng Chemical Plant still bothers me, poking and prodding somewhere deep down inside of me, like a riddle that I’ll never figure out. It was during a bright midday at the plant....Thirteen years on, that case at the Aocheng Chemical Plant still bothers me, poking and prodding somewhere deep down inside of me, like a riddle that I’ll never figure out. It was during a bright midday at the plant. The workers carried their lunch boxes out to the edge of the fissured concrete lot.展开更多
HIGH LIGHT!The High Energy Photon Source(HEPS)under construction in Beijing on August 18.The project is expected to be ready for operation by the end of 2025.Once completed,the HEPS will be able to emit light that is ...HIGH LIGHT!The High Energy Photon Source(HEPS)under construction in Beijing on August 18.The project is expected to be ready for operation by the end of 2025.Once completed,the HEPS will be able to emit light that is 1 trillion times brighter than the sun,and will be open to users in fields such as aerospace,energy,environment,life science and pharmaceuticals.展开更多
For the past 45 years of reform and opening-up that began in late 1978, the Communist Party of China(CPC) has led 1.4 billion Chinese in engaging with the outside world and creating global miracles. This grand practic...For the past 45 years of reform and opening-up that began in late 1978, the Communist Party of China(CPC) has led 1.4 billion Chinese in engaging with the outside world and creating global miracles. This grand practice has nurtured a significant spirit, which in turn inspires and guides further great practices.展开更多
We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening ...We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.展开更多
At 2 a.m.on March 29,2023(Beijing Time),the Institute of High Energy Physics(IHEP)of the Chinese Academy of Sciences(CAS),together with some 40 research institutions worldwide,released their latest discoveries on the ...At 2 a.m.on March 29,2023(Beijing Time),the Institute of High Energy Physics(IHEP)of the Chinese Academy of Sciences(CAS),together with some 40 research institutions worldwide,released their latest discoveries on the brightest Gamma-Ray Burst(dubbed as GRB 221009A)ever detected by humanity.With the unique observations made by two Chinese space telescopes,namely Insight-HXMT and GECAM-C,scientists were able to accurately measure how bright and how much energy was released by this burst,which is the key to understanding this historical event.展开更多
Solitons and bifurcations for the generalized Tzitzéica type equation are studied by using the theory of dynamical systems and Hamilton function. With the help of Maple and bifurcation theory of differential equa...Solitons and bifurcations for the generalized Tzitzéica type equation are studied by using the theory of dynamical systems and Hamilton function. With the help of Maple and bifurcation theory of differential equations, the bifurcation parameter conditions and all the bifurcation phase portraits are obtained. Because the same energy value of the Hamiltonian function is corresponding to the same orbit, thus the periodic wave solutions, bright soliton and dark soliton solutions are defined.展开更多
基金sponsored by the National Natural Science Foundation of China (Grant Nos. 41475028 and 41530427)
文摘Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.
基金supported by National Natural Science Foundation of Chinafor Young Scholar (Grant No. 41101400)National Natural Science Foundation of China for Key Program (Grant No. 41130528)Opening Foundation of State Key Laboratory of Remote Sensing Science ofChina (Grant No. OFSLRSS201103)
文摘Two factors that affect satellite retrieval of Aerosol Optical Depth(AOD) are aerosol model assumptions and the separation of surface reflectance.NASA/MODIS Dense Dark Vegetation(DDV) algorithm has been proven valuable in deriving aerosol distribution and properties over land;however,it cannot be applied to bright targets.As a supplement to the DDV algorithm,an algorithm to retrieve AOD over urban areas in North China in winter is developed using MODIS data,including(1) the generation and analysis of adjacent clear-days surface reflectance using MOD09 product from 2007 to 2008,and(2) seasonal aerosol models derived from AERONET data in Beijing and Xianghe sites.Ground-based measurements using sun photometers were used to validate the retrieved AOD,and the correlation coefficient(r) is up to 0.931.Especially for high AOD values(AOD>0.4),more retrievals meet the inversion accuracy.The temporal variations of retrieval errors over urban,rural and mountain regions were examined,and the results indicated that the variation of blue-band surface reflectance is less than 0.02 in a short period except for unusual weather conditions,the retrieval bias is under 0.08,and the relative error decreases as the AOD increases.
文摘Dear Editor,CRISPR-Cas9 （clustered regularly interspaced short palin- dromic repeats-CRISPR associated） systems have been harnessed for kinds of genome manipulation, including gene editing, transcription regulation, and chromosome loci imaging （Dominguez et al., 2016; Komor et al., 2017）. A typical engineered CRISPR-Cas9 system is composed of a Cas9 protein and a single guide RNA （sgRNA）, which could form a protein/RNA complex to recognize and cleave DNA sequence （Hsu et al., 2014; Wright et al., 2016）.
基金funded by the Korean Meteorological Administration Research and Development Program under Grant CATER 2006-2307.
文摘Data from a long term measurement of Micro Rain Radar （MRR） at a mountain site （Daegwallyeong, DG, one year period of 2005） and a coastal site （Haenam, HN, three years 2004-2006） in South Korea were analyzed to compare the MRR measured bright band characteristics of stratiform precipitation at the two sites. On average, the bright band was somewhat thicker and the sharpness （average gradient of reflectivity above and below the reflectivity peak） was slightly weaker at DG, compared to those values at HN. The peak reflectivity itself was twice as strong and the relative location of the peak reflectivity within the bright band was higher at HN than at DG. Importantly, the variability of these values was much larger at HN than at DG. The key parameter to cause these differences is suggested to be the difference of the snow particle densities at the two sites, which is related to the degree of riming. Therefore, it is speculated that the cloud microphysical processes at HN may have varied significantly from un-rimed snow growth, producing low density snow particles, to the riming of higher density particles, while snow particle growth at DG was more consistently affected by the riming process, and therefore high density snow particles. Forced uplifting of cloudy air over the mountain area around DG might have resulted in an orographic supercooling effect that led to the enhanced riming of supercooled cloud drops.
基金National Natural Science Foundation of China,Grant/Award Numbers:21788102,21973099,21973043Ministry of Science andTechnology of ChinaNationalKeyR&DPlan,Grant/Award Number:2017YFA0204501。
文摘Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and applications.We first note that the intermolecular excitonic coupling is much weaker in strength than the intramolecular electron-vibration coupling for a majority of newly termed AIEgens,which leads to the emission peak position insensitive to excitonic coupling,hence the conventional excitonic model for J-aggregation cannot effectively explain their AIE phenomena.Then,using multiscale computational approach coupled with our self-developed thermal vibration correlation function rate formalism and transition-state theory,we quantitatively investigate the aggregation effect on both the radiative and the nonradiative decays of molecular excited states.For radiative decay processes,we propose that the lowest excited state could convert from a transition dipole-forbidden“dark”state to a dipole-allowed“bright”state upon aggregation.For the radiationless processes,we demonstrate the blockage of nonradiative decay via vibration relaxation(BNR-VR)in harmonic region or the removal of nonradiative decay via isomerization(RNR-ISO)or minimum energy crossing point(RNR-MECP)beyond harmonic region in a variety of AIE aggregates.Our theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally verified.Looking forward,we believe this review will benefit the deep understanding about the universality of AIE phenomenon and further extending the scope of AIE systems with novel applications.
文摘he brightest object in the universe-at least,the brightest we've seen yetshines 500 trillion timesbrighter than the sun,and it eats a sun a day.Objects like these are rare,and despite their objective brightness,remain elusive and hard to spot.This record-breaker was first spotted in 198o and mischaracterized as a regular old star.
文摘Thirteen years on, that case at the Aocheng Chemical Plant still bothers me, poking and prodding somewhere deep down inside of me, like a riddle that I’ll never figure out. It was during a bright midday at the plant. The workers carried their lunch boxes out to the edge of the fissured concrete lot.
文摘HIGH LIGHT!The High Energy Photon Source(HEPS)under construction in Beijing on August 18.The project is expected to be ready for operation by the end of 2025.Once completed,the HEPS will be able to emit light that is 1 trillion times brighter than the sun,and will be open to users in fields such as aerospace,energy,environment,life science and pharmaceuticals.
文摘For the past 45 years of reform and opening-up that began in late 1978, the Communist Party of China(CPC) has led 1.4 billion Chinese in engaging with the outside world and creating global miracles. This grand practice has nurtured a significant spirit, which in turn inspires and guides further great practices.
基金Supported by the National Natural Science Foundation of China under Grant No 10474136.
文摘We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.
文摘At 2 a.m.on March 29,2023(Beijing Time),the Institute of High Energy Physics(IHEP)of the Chinese Academy of Sciences(CAS),together with some 40 research institutions worldwide,released their latest discoveries on the brightest Gamma-Ray Burst(dubbed as GRB 221009A)ever detected by humanity.With the unique observations made by two Chinese space telescopes,namely Insight-HXMT and GECAM-C,scientists were able to accurately measure how bright and how much energy was released by this burst,which is the key to understanding this historical event.
文摘Solitons and bifurcations for the generalized Tzitzéica type equation are studied by using the theory of dynamical systems and Hamilton function. With the help of Maple and bifurcation theory of differential equations, the bifurcation parameter conditions and all the bifurcation phase portraits are obtained. Because the same energy value of the Hamiltonian function is corresponding to the same orbit, thus the periodic wave solutions, bright soliton and dark soliton solutions are defined.
