After surveying the spectra of 39 prominences observed by the Multi-channel Infrared Solar Spectrograph at Purple Mountain Observatory and the 25 cm coronagraph at the Norikura Solar Observatory, we found that about 2...After surveying the spectra of 39 prominences observed by the Multi-channel Infrared Solar Spectrograph at Purple Mountain Observatory and the 25 cm coronagraph at the Norikura Solar Observatory, we found that about 28% of them show small spatial scale (6''–8'') and short time scale (tens of seconds to a few minutes), unusual large broadening and large shift velocities in spectral lines including Hα, Hβ, H, Ca II H, Ca II K, Ca II 8542?, He I D3 and He I 10830?. We present in detail two typical events observed respectively on 2002 May 27 and 1981 August 2. The full-width at half maximum of the widest profile of the 2001 prominence is 1.8? for Hα and 2.9 ? for He I 10830?, while that of the 1981 prominence is 5.3 ? for Hβ, 3.6 ? for Ca II K, 4.0 ? for Ca II H and 2.8 ? for He I D3. Such broadenings generally occur at a level of several-thousand kilometres above the chromosphere. Further, most of these prominences manifest a rotation of (0.4–1.35)×10<SUP>-2</SUP> rads s<SUP>?1</SUP> pointing to the Sun and large line-of-sight velocities of 20–200 km s<SUP>?1</SUP>. Some of these events correspond in time to an enhancement or a small peak in the GOES X-ray flux, indicating the existence of high energy process at work. These prominences generally display discernible changes in the Hα morphology around the time of large broadening, but do not show Hα brightening or overall eruption except for a few small surge-like events, hence, they are hardly observed in daily Hα patrols. According to the characteristics of their Hα structures and spectral properties, we infer these events are small-scale eruptions similar to nano-flares, which may contribute to the mass and energy transported into the corona. Large turbulent velocities of 25–120 km s<SUP>?1</SUP> are responsible for the observed broadenings.展开更多
Many authors have studied the regularity and properties of evolution and eruption of the helical prominence observationally or theoretically. We proposed that Lundquist field may be a good configuration to describe th...Many authors have studied the regularity and properties of evolution and eruption of the helical prominence observationally or theoretically. We proposed that Lundquist field may be a good configuration to describe the inner magnetic distribution of the helical promincence by analyzing this kind of quiescent and eruptive prominences. In this note,we discuss the stable criterion of Lundquist field according to energy principle and compare theory with observational data of 28 helical prominences. This work not only has confirmed the close relation between the Lundquist field and the helical prominence, but al-展开更多
The solar flare is one of the most violent explosions,and can disturb the near-Earth space weather.Except for commonly single-peaked solar flares in soft X-ray,some special flares show intriguing a two-peak feature th...The solar flare is one of the most violent explosions,and can disturb the near-Earth space weather.Except for commonly single-peaked solar flares in soft X-ray,some special flares show intriguing a two-peak feature that is deserved much more attentions.Here,we reported a confined two-peaked solar flare and analyzed the associated eruptions using high-quality observations from Educational Adaptive-optics Solar Telescope and Solar Dynamics Observatory.Before the flare,a magnetic flux rope(MFR)formed through partially tether-cutting reconnection between two sheared arches.The flare occurred after the MFR eruption that was confined by the overlying strong field.Interestingly,a small underlying filament immediately erupted,which was possibly destabilized by the flare ribbon.The successive eruptions were confirmed by the analysis of the emission measure and the reconnection fluxes.Therefore,we suggest that the two peaks of the confined solar flare are corresponding to two episodes of magnetic reconnection during the successive eruptions of the MFR and the underlying filament.展开更多
Mg-Gd-Y-Zr alloy,as a typical magnesium rare-earth(Mg-RE)alloy,is gaining popularity in the advanced equipment manufacturing fields owing to its noticeable age-hardening properties and high specific strength.However,i...Mg-Gd-Y-Zr alloy,as a typical magnesium rare-earth(Mg-RE)alloy,is gaining popularity in the advanced equipment manufacturing fields owing to its noticeable age-hardening properties and high specific strength.However,it is extremely challenging to prepare wrought components with large dimensions and complex shapes because of the poor room-temperature processability of Mg-Gd-Y-Zr alloy.Herein,we report a wire-arc directed energy deposited(DED)Mg-10.45Gd-2.27Y-0.52Zr(wt.%,GW102K)alloy with high RE content presenting a prominent combination of strength and ductility,realized by tailored nanoprecipitates through an optimized heat treatment procedure.Specifically,the solution-treated sample exhibits excellent ductility with an elongation(EL)of(14.6±0.1)%,while the aging-treated sample at 200°C for 58 h achieves an ultra-high ultimate tensile strength(UTS)of(371±1.5)MPa.Besides,the aging-treated sample at 250°C for 16 h attains a good strength-ductility synergy with a UTS of(316±2.1)MPa and a EL of(8.5±0.1)%.Particularly,the evolution mechanisms of precipitation response induced by various aging parameters and deformation behavior caused by nanoprecipitates type were also systematically revealed.The excellent ductility resulted from coordinating localized strains facilitated by active slip activity.And the ultra-high strength should be ascribed to the dense nano-β'hampering dislocation motion.Additionally,the shearable nano-β1 contributed to the good strength-ductility synergy.This work thus offers insightful understanding into the nanoprecipitates manipulation and performance tailoring for the wire-arc DED preparation of large-sized Mg-Gd-Y-Zr components with complex geometries.展开更多
Smoothed cepstral peak prominence(CPPs)is a measurement of the distance from the prominent cepstral peak to the linear regression line directly beneath it.Variations of CPPs data acquisition and analysis lead to the c...Smoothed cepstral peak prominence(CPPs)is a measurement of the distance from the prominent cepstral peak to the linear regression line directly beneath it.Variations of CPPs data acquisition and analysis lead to the complexity of the clinical cut-off values,and there are no agreeable values for a specific voice disorder,such as hypokinetic dysarthria associated with Parkinson’s disease(PD).This study examined the CPPs in people with hypokinetic dysarthria associated with PD compared with healthy participants.Results demonstrated significant differences in speech tasks of sustained vowel and connected speech,with CPPs of connected speech more sensitive to dysphonia and gender difference in PD participants.Males in PD participants presented higher CPPs for sustained vowels and lower CPPs for connected speech than females.It is implied that a consistent clinical application protocol is necessary,and multiple acoustic measures are needed to ensure the accuracy of clinical decisions.展开更多
Determining whether sevoflurane sedation in children leads to“pseudo”prominent leptomeningeal contrast enhancement(pLMCE)on 3 Tesla magnetic resonance imaging will help reduce overdiagnosis by radiologists and clari...Determining whether sevoflurane sedation in children leads to“pseudo”prominent leptomeningeal contrast enhancement(pLMCE)on 3 Tesla magnetic resonance imaging will help reduce overdiagnosis by radiologists and clarify the pathophysiological changes of pLMCE.展开更多
In this paper,the definition,connotation,and internal relationship of mountains,rivers,forests,farmlands,lakes,and grasslands in China are elaborated,and the current situation of ecological restoration projects for mo...In this paper,the definition,connotation,and internal relationship of mountains,rivers,forests,farmlands,lakes,and grasslands in China are elaborated,and the current situation of ecological restoration projects for mountains,rivers,forests,farmlands,lakes,and grasslands was introduced.Moreover,the problems that have arisen in the specific implementation process of pilot projects were analyzed,such as unclear target positioning,inaccurate analysis of ecological problems,insufficient engineering design systematicness,weak operability of evaluation standards,and weak coordination in engineering management.The development direction and major needs for the protection and restoration of mountains,rivers,forests,farmlands,lakes,and grasslands in the future have been proposed from four aspects:theoretical research,engineering design,effect evaluation,and monitoring and supervision.展开更多
Prominent coronary artery(CA)flow observed on a fetal echocardiogram has been associated with fetal growth restriction and myocardial dysfunction.We present two cases with this finding,in the presence of congenital he...Prominent coronary artery(CA)flow observed on a fetal echocardiogram has been associated with fetal growth restriction and myocardial dysfunction.We present two cases with this finding,in the presence of congenital heart disease(CHD)and absence of growth restriction or myocardial dysfunction.Both the cases rapidly progressed to extremis,necessitating emergent delivery.Our cases highlight the importance of recognizing prominent CA flow in fetuses with CHD as a potential marker for in utero distress.展开更多
Magnetic flux ropes are characterized by coherently twisted magnetic field lines,which are ubiquitous in magnetized plasmas.As the core structure of various eruptive phenomena in the solar atmosphere,flux ropes hold t...Magnetic flux ropes are characterized by coherently twisted magnetic field lines,which are ubiquitous in magnetized plasmas.As the core structure of various eruptive phenomena in the solar atmosphere,flux ropes hold the key to understanding the physical mechanisms of solar eruptions,which impact the heliosphere and planetary atmospheres.The strongest disturbances in the Earth’s space environments are often associated with large-scale flux ropes from the Sun colliding with the Earth’s magnetosphere,leading to adverse,sometimes catastrophic,space-weather effects.However,it remains elusive as to how a flux rope forms and evolves toward eruption,and how it is structured and embedded in the ambient field.The present paper addresses these important questions by reviewing current understandings of coronal flux ropes from an observer’s perspective,with an emphasis on their structures and nascent evolution toward solar eruptions,as achieved by combining observations of both remote sensing and in-situ detection with modeling and simulation.This paper highlights an initiation mechanism for coronal mass ejections(CMEs)in which plasmoids in current sheets coalesce into a’seed’flux rope whose subsequent evolution into a CME is consistent with the standard model,thereby bridging the gap between microscale and macroscale dynamics.展开更多
During vertebrate embryonic development,neural crest-derived ectomesenchyme within the maxillary prominences undergoes precisely coordinated proliferation and differentiation to give rise to diverse craniofacial struc...During vertebrate embryonic development,neural crest-derived ectomesenchyme within the maxillary prominences undergoes precisely coordinated proliferation and differentiation to give rise to diverse craniofacial structures,such as tooth and palate.However,the transcriptional regulatory networks underpinning such an intricate process have not been fully elucidated.Here,we perform single-cell RNA-Seq to comprehensively characterize the transcriptional dynamics during mouse maxillary development from embryonic day(E)10.5eE14.5.Our single-cell transcriptome atlas of~28,000 cells uncovers mesenchymal cell populations representing distinct differentiating states and reveals their developmental trajectory,suggesting that the segregation of dental from the palatal mesenchyme occurs at E11.5.Moreover,we identify a series of key transcription factors(TFs)associated with mesenchymal fate transitions and deduce the gene regulatory networks directed by these TFs.Collectively,our study provides important resources and insights for achieving a systems-level understanding of craniofacial morphogenesis and abnormality.展开更多
Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments. Using high resolution Ha data obse...Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments. Using high resolution Ha data observed by the New Vacuum Solar Telescope, we present the structures of barbs and material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2, respectively. During the evolution of the filament barb, several paral- lel tube-shaped structures formed and the width of the structures ranged from about 2.3 Mm to 3.3 Mm. The parallel tube-shaped structures merged together accompanied by material flows from the spine to the barb. Moreover, the boundary between the barb and surrounding atmosphere was very neat. The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament. However, the large-scale patchy counter-streaming flows were detected in the filament. The flows in one patch of the filament have the same direction but flows in the adjacent patch have opposite direction. The patches of two opposite flows with a size of about 10＂ were alternately exhibited along the spine of the filament. The velocity of these material flows ranged from 5.6 km s^-1 to 15.0 km s^-1. The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament. Our results confirm that the large-scale counter- streaming flows with a certain width along the threads of solar filaments exist and are coaligned well with the threads.展开更多
High-resolution Ha observations indicate that filaments consist of an as- sembly of thin threads. In quiescent filaments, the threads are generally short, whereas in active region filaments, the threads are generally ...High-resolution Ha observations indicate that filaments consist of an as- sembly of thin threads. In quiescent filaments, the threads are generally short, whereas in active region filaments, the threads are generally long. In order to explain these observational features, we performed one-dimensional radiative hydrodynamic sim- ulations of filament formation along a dipped magnetic flux tube in the framework of the chromospheric evaporation-coronal condensation model. The geometry of a dipped magnetic flux tube is characterized by three parameters, i.e., the depth （D）, the half-width （w） and the altitude （h） of the magnetic dip. A survey of the parame- ters in numerical simulations shows that when allowing the filament thread to grow in 5 days, the maximum length （Lth） of the filament thread increases linearly with w, and decreases linearly with D and h. The dependence is fitted into a linear function Lth = 0.84w --0.88D - 2.78h ＋ 17.31 （Mm）. Such a relation can qualitatively explain why quiescent filaments have shorter threads and active region filaments have longer threads.展开更多
We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromos...We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromospheric reconnection which ejected cool and dense material with transverse velocity of about 21–28 km s-1 and initial Doppler velocity of 12 km s^-1. This surge is similar to the injection of newly formed filament materials from their footpoints, except that the surge here occurred in a relatively weak magnetic environment of 100 G. Thus, we discuss the possibility of filament material replenishment via the erupting mass in such a weak magnetic field, which is often associated with quiescent filaments. It is found that the local plasma can be heated up to about 1.3 times the original temperature, which results in an acceleration of about –0.017 km s^-2. It can lift the dense material up to 10 Mm and higher with an inclination angle smaller than 50°, namely the typical height of active region filaments, but it can hardly inject the material up to those filaments higher than 25 Mm, like some quiescent filaments. Thus, we think that the injection model does not work well in describing the formation of quiescent filaments.展开更多
Prominence plumes are evacuated upflows that emerge from bubbles below prominences,whose formation mechanism is still unclear.Here we present a detailed study of plumes in a quiescent prominence using the high-resolut...Prominence plumes are evacuated upflows that emerge from bubbles below prominences,whose formation mechanism is still unclear.Here we present a detailed study of plumes in a quiescent prominence using the high-resolution Hαfiltergrams at the line center as well as line wing at±0.4 A from the New Vacuum Solar Telescope.Enhancements of brightening,blue shifts,and turbulence at the fronts of plumes are found during their formation.Some large plumes split at their heads and finger-shaped structures are formed between them.Blue-shifted flows along the bubble-prominence interface are found before and during the plume formation.Our observations are consistent with the hypothesis that prominence plumes are related to coupled Kelvin-Helmholtz and Rayleigh-Taylor(KH/RT)instabilities.Plume splittings and fingers are evidence of RT instability,and the flows may increase the growth rate of KH/RT instabilities.However,the significant turbulence at plume fronts may suggest that the RT instability is triggered by the plumes penetrating into the prominence.In this scenario,extra mechanisms are necessary to drive the plumes.展开更多
Solar filaments are an intriguing phenomenon,like cool clouds suspended in the hot corona.Similar structures exist in the intergalactic medium as well.Despite being a long-studied topic,solar filaments have continuall...Solar filaments are an intriguing phenomenon,like cool clouds suspended in the hot corona.Similar structures exist in the intergalactic medium as well.Despite being a long-studied topic,solar filaments have continually attracted intensive attention because of their link to coronal heating,coronal seismology,solar flares and coronal mass ejections(CMEs).In this review paper,by combing through the solar filament-related work done in the past decade,we discuss several controversial topics,such as the fine structures,dynamics,magnetic configurations and helicity of filaments.With high-resolution and highsensitivity observations,combined with numerical simulations,it is expected that resolving these disputes will definitely lead to a huge leap in understanding the physics related to solar filaments,and even shed light on galactic filaments.展开更多
We present the results of a study on the north-south asymmetry of solar filaments at low（〈50°） and high（〉60°） latitudes using daily filament numbers from January 1998 to November 2008（solar cycle 23）...We present the results of a study on the north-south asymmetry of solar filaments at low（〈50°） and high（〉60°） latitudes using daily filament numbers from January 1998 to November 2008（solar cycle 23）. It is found that the northern hemisphere is dominant at low latitudes for cycle 23. However, a similar asymmetry does not occur for solar filaments at high latitudes. The present study indicates that the hemispheric asymmetry of solar filaments at high latitudes in a cycle appears to have little connection with that at low latitudes. Our results support that the observed magnetic fields at high latitudes include two components： one comes from the emergence of the magnetic fields from the solar interior and the other comes from the drift of the magnetic activity at low latitudes.展开更多
We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm...We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line （PIL） shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Ha filtergrams from the Big Bear Solar Observatory （BBSO） Ha archive and magnetograms observed with the Helioseismic and Magnetic Imager （HMI） on board the Solar Dynamics Observatory （SDO）. Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere （northern hemisphere） mainly have left-bearing （fight- bearing） barbs and positive （negative） magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.展开更多
Lyα(Lyα,1216 A)is the strongest emission line in the solar ultraviolet spectrum.In the present work,we obtained a Lyαenhancement catalog covering flares larger than B1 class from the GOES/EUVS data during 2010-2016...Lyα(Lyα,1216 A)is the strongest emission line in the solar ultraviolet spectrum.In the present work,we obtained a Lyαenhancement catalog covering flares larger than B1 class from the GOES/EUVS data during 2010-2016.We focused on the 242 B-class events which are less investigated,however,show non-negligible Lyαemission enhancement.We found that on average the Lyαpeak of B-class flares is 0.85%stronger than the background.For the flare energetics,it is found that the weaker the soft X-ray(SXR)flare,the larger the ratio of the radiated energy in Lyαto SXR.Using the RHESSI data and multi-wavelength observations taken by SDO-AIA,we diagnose the thermal and non-thermal properties of several flares.Three case studies show that the coincidence of the Lyαpeak with the SXR time-derivative peak is not a sufficient condition of the nonthermal property of a Lyαmicroflare.The Lyαenhancement in the microflares may be caused by the nonthermal electron beams or/and thermal conduction.However for typeⅢevents,we found that the delay of the Lyαpeak with respect to the SXR peak can be attributed to either the Lyαemission from a filament erupted or the cooling of the thermal plasma in flare loops.Furthermore,interestingly the Lyαemission from filaments can not only occur in the decay phase of the flare,but also in the preflare phase.In this case,the Lyαemission was originated from an erupted filament which probably initiated the flare.展开更多
Solar filaments,hypothermia and dense structures suspended in the solar corona are formed above the magnetic polarity inversion line.Polar crown filaments(PCFs)at high-latitude regions of the Sun are of profound signi...Solar filaments,hypothermia and dense structures suspended in the solar corona are formed above the magnetic polarity inversion line.Polar crown filaments(PCFs)at high-latitude regions of the Sun are of profound significance to the periodic variation of solar activities.In this paper,we statistically analyze PCFs by using full disk Ha data from 1912 to 2018,which were obtained by Kodaikanal Solar Observatory(KODA,India),National Solar Observatory(NSO,USA),Kanzelhohe Solar Observatory(KSO,Austria),Big Bear Solar Observatory(BBSO,USA),and Huairou Solar Observing Station(HSOS,China).We first manually identify PCFs from every solar image based on the centennial data,and record the latitude and other features corresponding to the PCFs.Then we plot the PCF latitude distribution as a function of time,which clearly shows that PCFs rush to the poles at the ascending phase of each solar cycle.Our results show that the filaments drift toward mid-latitude covering solar cycle 15 to 24 after the PCFs reach the highest latitudes.The poleward migration rates of PCFs are calculated in ten solar cycles,and the range is about 0.12 degree to 0.50 degree per Carrington Rotation(CR).We also investigate the north-south(N-S)asymmetry of migration rates and the normalized N-S asymmetry index.展开更多
The cyclical behaviors of sunspots, flares and coronal mass ejections （CMEs） for 54 months from 2008 November to 2013 April after the onset of Solar Cycle （SC） 24 are compared, for the first time, with those of SC...The cyclical behaviors of sunspots, flares and coronal mass ejections （CMEs） for 54 months from 2008 November to 2013 April after the onset of Solar Cycle （SC） 24 are compared, for the first time, with those of SC 23 from 1996 November to 2001 April. The results are summarized below. （i） During the maximum phase, the number of sunspots in SC 24 is significantly smaller than that for SC 23 and the number of flares in SC 24 is comparable to that of SC 23. （ii） The number of CMEs in SC 24 is larger than that in SC 23 and the speed of CMEs in SC 24 is smaller than that of SC 23 during the maximum phase. We individually survey all the CMEs （1647 CMEs） from 2010 June to 2011 June. A total of 161 CMEs associated with so- lar surface activity events can be identified. About 45% of CMEs are associated with quiescent prominence eruptions, 27% of CMEs only with solar flares, 19% of CMEs with both active-region prominence eruptions and solar flares, and 9% of CMEs only with active-region prominence eruptions. Comparing the association of the CMEs and their source regions in SC 24 with that in SC 23, we notice that the characteristics of source regions for CMEs during SC 24 may be different from those of SC 23.展开更多
基金Support by the National Natural Science Foundation of China.
文摘After surveying the spectra of 39 prominences observed by the Multi-channel Infrared Solar Spectrograph at Purple Mountain Observatory and the 25 cm coronagraph at the Norikura Solar Observatory, we found that about 28% of them show small spatial scale (6''–8'') and short time scale (tens of seconds to a few minutes), unusual large broadening and large shift velocities in spectral lines including Hα, Hβ, H, Ca II H, Ca II K, Ca II 8542?, He I D3 and He I 10830?. We present in detail two typical events observed respectively on 2002 May 27 and 1981 August 2. The full-width at half maximum of the widest profile of the 2001 prominence is 1.8? for Hα and 2.9 ? for He I 10830?, while that of the 1981 prominence is 5.3 ? for Hβ, 3.6 ? for Ca II K, 4.0 ? for Ca II H and 2.8 ? for He I D3. Such broadenings generally occur at a level of several-thousand kilometres above the chromosphere. Further, most of these prominences manifest a rotation of (0.4–1.35)×10<SUP>-2</SUP> rads s<SUP>?1</SUP> pointing to the Sun and large line-of-sight velocities of 20–200 km s<SUP>?1</SUP>. Some of these events correspond in time to an enhancement or a small peak in the GOES X-ray flux, indicating the existence of high energy process at work. These prominences generally display discernible changes in the Hα morphology around the time of large broadening, but do not show Hα brightening or overall eruption except for a few small surge-like events, hence, they are hardly observed in daily Hα patrols. According to the characteristics of their Hα structures and spectral properties, we infer these events are small-scale eruptions similar to nano-flares, which may contribute to the mass and energy transported into the corona. Large turbulent velocities of 25–120 km s<SUP>?1</SUP> are responsible for the observed broadenings.
基金Project supported by the National Natural Science Foundation of China
文摘Many authors have studied the regularity and properties of evolution and eruption of the helical prominence observationally or theoretically. We proposed that Lundquist field may be a good configuration to describe the inner magnetic distribution of the helical promincence by analyzing this kind of quiescent and eruptive prominences. In this note,we discuss the stable criterion of Lundquist field according to energy principle and compare theory with observational data of 28 helical prominences. This work not only has confirmed the close relation between the Lundquist field and the helical prominence, but al-
基金supported by grants of the National Natural Foundation of China(NSFC12073016)the open topic of the Yunnan Key Laboratory of Solar Physics and Space Science(YNSPCC202217)。
文摘The solar flare is one of the most violent explosions,and can disturb the near-Earth space weather.Except for commonly single-peaked solar flares in soft X-ray,some special flares show intriguing a two-peak feature that is deserved much more attentions.Here,we reported a confined two-peaked solar flare and analyzed the associated eruptions using high-quality observations from Educational Adaptive-optics Solar Telescope and Solar Dynamics Observatory.Before the flare,a magnetic flux rope(MFR)formed through partially tether-cutting reconnection between two sheared arches.The flare occurred after the MFR eruption that was confined by the overlying strong field.Interestingly,a small underlying filament immediately erupted,which was possibly destabilized by the flare ribbon.The successive eruptions were confirmed by the analysis of the emission measure and the reconnection fluxes.Therefore,we suggest that the two peaks of the confined solar flare are corresponding to two episodes of magnetic reconnection during the successive eruptions of the MFR and the underlying filament.
基金National Natural Science Foundation of China (52275374, 52205414)Xi’an Jiaotong University Basic Research Funds for Freedom of Exploration and Innovation-Student Programs (xzy022023066)+3 种基金Key Research and Development Projects of Shaanxi Province (2023-YBGY-361)Young Elite Scientists Sponsorship Program by CAST (2021QNRC001)State Key Laboratory for Mechanical Behavior of Materials (20212311)Xiaomi Foundation through Xiaomi Young Scholar Program
文摘Mg-Gd-Y-Zr alloy,as a typical magnesium rare-earth(Mg-RE)alloy,is gaining popularity in the advanced equipment manufacturing fields owing to its noticeable age-hardening properties and high specific strength.However,it is extremely challenging to prepare wrought components with large dimensions and complex shapes because of the poor room-temperature processability of Mg-Gd-Y-Zr alloy.Herein,we report a wire-arc directed energy deposited(DED)Mg-10.45Gd-2.27Y-0.52Zr(wt.%,GW102K)alloy with high RE content presenting a prominent combination of strength and ductility,realized by tailored nanoprecipitates through an optimized heat treatment procedure.Specifically,the solution-treated sample exhibits excellent ductility with an elongation(EL)of(14.6±0.1)%,while the aging-treated sample at 200°C for 58 h achieves an ultra-high ultimate tensile strength(UTS)of(371±1.5)MPa.Besides,the aging-treated sample at 250°C for 16 h attains a good strength-ductility synergy with a UTS of(316±2.1)MPa and a EL of(8.5±0.1)%.Particularly,the evolution mechanisms of precipitation response induced by various aging parameters and deformation behavior caused by nanoprecipitates type were also systematically revealed.The excellent ductility resulted from coordinating localized strains facilitated by active slip activity.And the ultra-high strength should be ascribed to the dense nano-β'hampering dislocation motion.Additionally,the shearable nano-β1 contributed to the good strength-ductility synergy.This work thus offers insightful understanding into the nanoprecipitates manipulation and performance tailoring for the wire-arc DED preparation of large-sized Mg-Gd-Y-Zr components with complex geometries.
文摘Smoothed cepstral peak prominence(CPPs)is a measurement of the distance from the prominent cepstral peak to the linear regression line directly beneath it.Variations of CPPs data acquisition and analysis lead to the complexity of the clinical cut-off values,and there are no agreeable values for a specific voice disorder,such as hypokinetic dysarthria associated with Parkinson’s disease(PD).This study examined the CPPs in people with hypokinetic dysarthria associated with PD compared with healthy participants.Results demonstrated significant differences in speech tasks of sustained vowel and connected speech,with CPPs of connected speech more sensitive to dysphonia and gender difference in PD participants.Males in PD participants presented higher CPPs for sustained vowels and lower CPPs for connected speech than females.It is implied that a consistent clinical application protocol is necessary,and multiple acoustic measures are needed to ensure the accuracy of clinical decisions.
基金Supported by the Chongging Medical Scientific Research Project(Joint Project of Chongqing Health Commission and Science and Technology Bureau),No.2022QNXM013 and No.2023MSXM016.
文摘Determining whether sevoflurane sedation in children leads to“pseudo”prominent leptomeningeal contrast enhancement(pLMCE)on 3 Tesla magnetic resonance imaging will help reduce overdiagnosis by radiologists and clarify the pathophysiological changes of pLMCE.
基金Basic Research Business Funding Project for Public Welfare Research Institutes in the Autonomous Region in 2022(kyys202201).
文摘In this paper,the definition,connotation,and internal relationship of mountains,rivers,forests,farmlands,lakes,and grasslands in China are elaborated,and the current situation of ecological restoration projects for mountains,rivers,forests,farmlands,lakes,and grasslands was introduced.Moreover,the problems that have arisen in the specific implementation process of pilot projects were analyzed,such as unclear target positioning,inaccurate analysis of ecological problems,insufficient engineering design systematicness,weak operability of evaluation standards,and weak coordination in engineering management.The development direction and major needs for the protection and restoration of mountains,rivers,forests,farmlands,lakes,and grasslands in the future have been proposed from four aspects:theoretical research,engineering design,effect evaluation,and monitoring and supervision.
文摘Prominent coronary artery(CA)flow observed on a fetal echocardiogram has been associated with fetal growth restriction and myocardial dysfunction.We present two cases with this finding,in the presence of congenital heart disease(CHD)and absence of growth restriction or myocardial dysfunction.Both the cases rapidly progressed to extremis,necessitating emergent delivery.Our cases highlight the importance of recognizing prominent CA flow in fetuses with CHD as a potential marker for in utero distress.
基金supported by the National Natural Science Foundation of China(Grant Nos.41761134088,41774150,and 11925302)CAS Key Research Program(Grant No.KZZD-EW-01-4)the fundamental research funds for the central universities,and the Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)。
文摘Magnetic flux ropes are characterized by coherently twisted magnetic field lines,which are ubiquitous in magnetized plasmas.As the core structure of various eruptive phenomena in the solar atmosphere,flux ropes hold the key to understanding the physical mechanisms of solar eruptions,which impact the heliosphere and planetary atmospheres.The strongest disturbances in the Earth’s space environments are often associated with large-scale flux ropes from the Sun colliding with the Earth’s magnetosphere,leading to adverse,sometimes catastrophic,space-weather effects.However,it remains elusive as to how a flux rope forms and evolves toward eruption,and how it is structured and embedded in the ambient field.The present paper addresses these important questions by reviewing current understandings of coronal flux ropes from an observer’s perspective,with an emphasis on their structures and nascent evolution toward solar eruptions,as achieved by combining observations of both remote sensing and in-situ detection with modeling and simulation.This paper highlights an initiation mechanism for coronal mass ejections(CMEs)in which plasmoids in current sheets coalesce into a’seed’flux rope whose subsequent evolution into a CME is consistent with the standard model,thereby bridging the gap between microscale and macroscale dynamics.
基金supported by the National Natural Science Foundation of China(82071096 to X.W,31970585,32170544,and 31801056 to Q.B.)the National Key Research and Development Program of China(2017YFC1001800 to X.W.,2018YFC1004703 to Q.B),the Fundamental research program funding of Ninth People’s Hospital affiliated to Shanghai Jiao Tong University School of Medicine(JYZZ179 to J.S.)+1 种基金the Innovative research team of high-level local universities in Shanghai(SHSMU-ZLCX20211700)the SHIPM-pi fund No.JY201803 from Shanghai Institute of Precision Medicine,Ninth People’s Hospital,Shanghai Jiao Tong University School of Medicine.
文摘During vertebrate embryonic development,neural crest-derived ectomesenchyme within the maxillary prominences undergoes precisely coordinated proliferation and differentiation to give rise to diverse craniofacial structures,such as tooth and palate.However,the transcriptional regulatory networks underpinning such an intricate process have not been fully elucidated.Here,we perform single-cell RNA-Seq to comprehensively characterize the transcriptional dynamics during mouse maxillary development from embryonic day(E)10.5eE14.5.Our single-cell transcriptome atlas of~28,000 cells uncovers mesenchymal cell populations representing distinct differentiating states and reveals their developmental trajectory,suggesting that the segregation of dental from the palatal mesenchyme occurs at E11.5.Moreover,we identify a series of key transcription factors(TFs)associated with mesenchymal fate transitions and deduce the gene regulatory networks directed by these TFs.Collectively,our study provides important resources and insights for achieving a systems-level understanding of craniofacial morphogenesis and abnormality.
基金supported by the National Natural Science Foundation of China(NSFC)under grant numbers 11373066,11373065 and 11203077the Yunnan Science Foundation of China under number 2013FB086+3 种基金the Talent Project of Western Light of Chinese Academy of Sciencesthe National Basic Research Program of China(973 program)under grant number G2011CB811400the Key Laboratory of Solar Activity of CAS under number KLSA 201303,KLSA 201412 and KLSA201407Youth Innovation Promotion Association of CAS(No.2011056)
文摘Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments. Using high resolution Ha data observed by the New Vacuum Solar Telescope, we present the structures of barbs and material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2, respectively. During the evolution of the filament barb, several paral- lel tube-shaped structures formed and the width of the structures ranged from about 2.3 Mm to 3.3 Mm. The parallel tube-shaped structures merged together accompanied by material flows from the spine to the barb. Moreover, the boundary between the barb and surrounding atmosphere was very neat. The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament. However, the large-scale patchy counter-streaming flows were detected in the filament. The flows in one patch of the filament have the same direction but flows in the adjacent patch have opposite direction. The patches of two opposite flows with a size of about 10＂ were alternately exhibited along the spine of the filament. The velocity of these material flows ranged from 5.6 km s^-1 to 15.0 km s^-1. The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament. Our results confirm that the large-scale counter- streaming flows with a certain width along the threads of solar filaments exist and are coaligned well with the threads.
基金Supported by the National Natural Science Foundation of China
文摘High-resolution Ha observations indicate that filaments consist of an as- sembly of thin threads. In quiescent filaments, the threads are generally short, whereas in active region filaments, the threads are generally long. In order to explain these observational features, we performed one-dimensional radiative hydrodynamic sim- ulations of filament formation along a dipped magnetic flux tube in the framework of the chromospheric evaporation-coronal condensation model. The geometry of a dipped magnetic flux tube is characterized by three parameters, i.e., the depth （D）, the half-width （w） and the altitude （h） of the magnetic dip. A survey of the parame- ters in numerical simulations shows that when allowing the filament thread to grow in 5 days, the maximum length （Lth） of the filament thread increases linearly with w, and decreases linearly with D and h. The dependence is fitted into a linear function Lth = 0.84w --0.88D - 2.78h ＋ 17.31 （Mm）. Such a relation can qualitatively explain why quiescent filaments have shorter threads and active region filaments have longer threads.
基金supported by the National Natural Science Foundation of China (41731067 and 41822404)Shenzhen Technology Project (JCYJ20170307150645407)+6 种基金the Fundamental Research Funds for the Central Universities (Grant No. HIT.BRETV.201901)the support by China Postdoctoral Science Foundation (2018M641812)support of the US NSF (AGS-1821294)the National Natural Science Foundation of China (11729301)supported by NJIT and US NSF AGS 1821294 grantpartly supported by the Korea Astronomy and Space Science Institute and Seoul National Universitythe strategic priority research program of Chinese Academy of Science (CAS) (Grant No. XDB09000000)
文摘We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromospheric reconnection which ejected cool and dense material with transverse velocity of about 21–28 km s-1 and initial Doppler velocity of 12 km s^-1. This surge is similar to the injection of newly formed filament materials from their footpoints, except that the surge here occurred in a relatively weak magnetic environment of 100 G. Thus, we discuss the possibility of filament material replenishment via the erupting mass in such a weak magnetic field, which is often associated with quiescent filaments. It is found that the local plasma can be heated up to about 1.3 times the original temperature, which results in an acceleration of about –0.017 km s^-2. It can lift the dense material up to 10 Mm and higher with an inclination angle smaller than 50°, namely the typical height of active region filaments, but it can hardly inject the material up to those filaments higher than 25 Mm, like some quiescent filaments. Thus, we think that the injection model does not work well in describing the formation of quiescent filaments.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11427803,U1731241,U1631242 and 11820101002)by CAS Strategic Pioneer Program on Space Science(Grant Nos.XDA15052200,XDA15320103,XDA15320300 and XDA15320301)+2 种基金the Jiangsu Double Innovation PlanNSFC(Grant No.11873091)Yunnan Province Basic Research Plan(No.2019FA001)。
文摘Prominence plumes are evacuated upflows that emerge from bubbles below prominences,whose formation mechanism is still unclear.Here we present a detailed study of plumes in a quiescent prominence using the high-resolution Hαfiltergrams at the line center as well as line wing at±0.4 A from the New Vacuum Solar Telescope.Enhancements of brightening,blue shifts,and turbulence at the fronts of plumes are found during their formation.Some large plumes split at their heads and finger-shaped structures are formed between them.Blue-shifted flows along the bubble-prominence interface are found before and during the plume formation.Our observations are consistent with the hypothesis that prominence plumes are related to coupled Kelvin-Helmholtz and Rayleigh-Taylor(KH/RT)instabilities.Plume splittings and fingers are evidence of RT instability,and the flows may increase the growth rate of KH/RT instabilities.However,the significant turbulence at plume fronts may suggest that the RT instability is triggered by the plumes penetrating into the prominence.In this scenario,extra mechanisms are necessary to drive the plumes.
基金supported by the National Natural Science Foundation of China(NSFC 11533005,11961131002,11733003 and U1731241)supported by the Science and Technology Development Fund of Macao(275/2017/A)。
文摘Solar filaments are an intriguing phenomenon,like cool clouds suspended in the hot corona.Similar structures exist in the intergalactic medium as well.Despite being a long-studied topic,solar filaments have continually attracted intensive attention because of their link to coronal heating,coronal seismology,solar flares and coronal mass ejections(CMEs).In this review paper,by combing through the solar filament-related work done in the past decade,we discuss several controversial topics,such as the fine structures,dynamics,magnetic configurations and helicity of filaments.With high-resolution and highsensitivity observations,combined with numerical simulations,it is expected that resolving these disputes will definitely lead to a huge leap in understanding the physics related to solar filaments,and even shed light on galactic filaments.
基金Supported by the National Natural Science Foundation of China
文摘We present the results of a study on the north-south asymmetry of solar filaments at low（〈50°） and high（〉60°） latitudes using daily filament numbers from January 1998 to November 2008（solar cycle 23）. It is found that the northern hemisphere is dominant at low latitudes for cycle 23. However, a similar asymmetry does not occur for solar filaments at high latitudes. The present study indicates that the hemispheric asymmetry of solar filaments at high latitudes in a cycle appears to have little connection with that at low latitudes. Our results support that the observed magnetic fields at high latitudes include two components： one comes from the emergence of the magnetic fields from the solar interior and the other comes from the drift of the magnetic activity at low latitudes.
基金supported by NKBRSF (Grant Nos.2011CB811402 and 2014CB744203)the National Natural Science Foundation of China (Grant Nos.11203014,11533005 and 11025314)the grants from CSC201306190046 and CXZZ130041
文摘We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line （PIL） shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Ha filtergrams from the Big Bear Solar Observatory （BBSO） Ha archive and magnetograms observed with the Helioseismic and Magnetic Imager （HMI） on board the Solar Dynamics Observatory （SDO）. Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere （northern hemisphere） mainly have left-bearing （fight- bearing） barbs and positive （negative） magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.
基金supported by the National Key R&D Program of China under grants 2022YFF0503003(2022YFF0503000)and 2018YFA0404200the National Natural Science Foundation of China(NSFC,Grant Nos.11921003,11973012,and 11820101002)+1 种基金CAS Strategic Pioneer Program on Space Science(Grant Nos.XDA15018300,XDA15052200,XDA15320103,and XDA15320301)the mobility program(M-0068)of the Sino-German Science Center。
文摘Lyα(Lyα,1216 A)is the strongest emission line in the solar ultraviolet spectrum.In the present work,we obtained a Lyαenhancement catalog covering flares larger than B1 class from the GOES/EUVS data during 2010-2016.We focused on the 242 B-class events which are less investigated,however,show non-negligible Lyαemission enhancement.We found that on average the Lyαpeak of B-class flares is 0.85%stronger than the background.For the flare energetics,it is found that the weaker the soft X-ray(SXR)flare,the larger the ratio of the radiated energy in Lyαto SXR.Using the RHESSI data and multi-wavelength observations taken by SDO-AIA,we diagnose the thermal and non-thermal properties of several flares.Three case studies show that the coincidence of the Lyαpeak with the SXR time-derivative peak is not a sufficient condition of the nonthermal property of a Lyαmicroflare.The Lyαenhancement in the microflares may be caused by the nonthermal electron beams or/and thermal conduction.However for typeⅢevents,we found that the delay of the Lyαpeak with respect to the SXR peak can be attributed to either the Lyαemission from a filament erupted or the cooling of the thermal plasma in flare loops.Furthermore,interestingly the Lyαemission from filaments can not only occur in the decay phase of the flare,but also in the preflare phase.In this case,the Lyαemission was originated from an erupted filament which probably initiated the flare.
基金The National Natural Science Foundation of China supports this work under Grant numbers U2031202,U1531247 and U1731124the 13th Five-year Informatization Plan of Chinese Academy of Sciences under Grant number XXH13505-04the special foundation work of the Ministry of Science and Technology of China under Grant number 2014FY120300。
文摘Solar filaments,hypothermia and dense structures suspended in the solar corona are formed above the magnetic polarity inversion line.Polar crown filaments(PCFs)at high-latitude regions of the Sun are of profound significance to the periodic variation of solar activities.In this paper,we statistically analyze PCFs by using full disk Ha data from 1912 to 2018,which were obtained by Kodaikanal Solar Observatory(KODA,India),National Solar Observatory(NSO,USA),Kanzelhohe Solar Observatory(KSO,Austria),Big Bear Solar Observatory(BBSO,USA),and Huairou Solar Observing Station(HSOS,China).We first manually identify PCFs from every solar image based on the centennial data,and record the latitude and other features corresponding to the PCFs.Then we plot the PCF latitude distribution as a function of time,which clearly shows that PCFs rush to the poles at the ascending phase of each solar cycle.Our results show that the filaments drift toward mid-latitude covering solar cycle 15 to 24 after the PCFs reach the highest latitudes.The poleward migration rates of PCFs are calculated in ten solar cycles,and the range is about 0.12 degree to 0.50 degree per Carrington Rotation(CR).We also investigate the north-south(N-S)asymmetry of migration rates and the normalized N-S asymmetry index.
基金Supported by the National Natural Science Foundation of China
文摘The cyclical behaviors of sunspots, flares and coronal mass ejections （CMEs） for 54 months from 2008 November to 2013 April after the onset of Solar Cycle （SC） 24 are compared, for the first time, with those of SC 23 from 1996 November to 2001 April. The results are summarized below. （i） During the maximum phase, the number of sunspots in SC 24 is significantly smaller than that for SC 23 and the number of flares in SC 24 is comparable to that of SC 23. （ii） The number of CMEs in SC 24 is larger than that in SC 23 and the speed of CMEs in SC 24 is smaller than that of SC 23 during the maximum phase. We individually survey all the CMEs （1647 CMEs） from 2010 June to 2011 June. A total of 161 CMEs associated with so- lar surface activity events can be identified. About 45% of CMEs are associated with quiescent prominence eruptions, 27% of CMEs only with solar flares, 19% of CMEs with both active-region prominence eruptions and solar flares, and 9% of CMEs only with active-region prominence eruptions. Comparing the association of the CMEs and their source regions in SC 24 with that in SC 23, we notice that the characteristics of source regions for CMEs during SC 24 may be different from those of SC 23.
