检索结果-南通市图书馆

Magnetohydrostatic modeling of the solar atmosphere

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2022年第8期65卷 1710-1726页

作者： ZHU XiaoShuai NEUKIRCH Thomas WIEGELMANN Thomas State Key Laboratory of Space Weather National Space Science CenterChinese Academy of SciencesBeijing 100190China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Mathematics and Statistics University of St AndrewsSt Andrews KY169SSUK Max-Planck-Institut f¨ur Sonnensystemforschung G¨ottingen 37077Germany

Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the low plasma β has been widely studied and used to model the coronal magnetic structure. While the force-freeness assumption is well satisfied in the solar corona, the lower atmosphere is not force-free given the high plasma β. Therefore, a magnetohydrostatic(MHS) equilibrium which takes into account plasma forces, such as pressure gradient and gravitational force, is considered to be more appropriate to describe the lower atmosphere. This paper reviews both analytical and numerical extrapolation methods based on the MHS assumption for calculating the magnetic fields and plasma in the solar atmosphere from measured magnetograms.

关键词： magnetic field photosphere chromosphere corona

The conditional mitochondrial protein complexome in the Arabidopsis thaliana root and shoot

在线全文

学校读者我要写书评

暂无评论

Plant Communications 2023年第5期4卷 172-190页

作者： Youjun Zhang Silvia Martinez Jaime Mustafa Bulut Alexander Graf Alisdair R.fernie Center of Plant Systems Biology and Biotechnology 4000 PlovdivBulgaria max-planck-institut f€ur Molekulare Pflanzenphysiologie Am Muhlenberg 114476 Potsdam-GolmGermany

Protein complexes are important for almost all biological processes.Hence,to fully understand how cells work,it is also necessary to characterize protein complexes and their dynamics in response to various cellular cues.Moreover,the dynamics of protein interaction play crucial roles in regulating the(dis)association of protein complexes and,in turn,regulating biological processes such as metabolism.Here,mitochondrial protein complexes were investigated by blue native PAGE and size-exclusion chromatography under conditions of oxidative stress in order to monitor their dynamic(dis)associations.Rearrangements of enzyme interactions and changes in protein complex abundance were observed in response to oxidative stress induced by menadione treatment.These included changes in enzymatic protein complexes involving g-amino butyric acid transaminase(GABA-T),D-ornithine aminotransferase(D-OAT),or proline dehydrogenase 1(POX1)that are expected to affect proline metabolism.Menadione treatment also affected interactions between several enzymes of the tricarboxylic acid(TCA)cycle and the abundance of complexes of the oxidative phosphorylation pathway.In addition,we compared the mitochondrial complexes of roots and shoots.Considerable differences between the two tissues were observed in the mitochondrial import/export apparatus,the formation of super-complexes in the oxidative phosphorylation pathway,and specific interactions between enzymes of the TCA cycle that we postulate may be related to the metabolic/energetic requirements of roots and shoots.

关键词： mitochondrial complexes BN-PAGE size-exclusion chromatography TCA cycle

Models and observations of sunspot penumbrae

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2009年第11期52卷 1670-1677页

作者： BORRERO Juan Manuel max planck institut fr sonnensystemforschung Max Planck Strasse 2 D 37191 Katlenburg-Lindau Germany

The mysteries of sunspot penumbrae have been under an intense scrutiny for the past 10 years. During this time, some models have been proposed and refuted, while the surviving ones had to be modified, adapted and evolved to explain the ever-increasing array of observational constraints. In this contribution I will review two of the present models, emphasizing their contributions to this field, but also pinpointing some of their inadequacies to explain a number of recent observations at very high spatial resolution (0.32 ). To help explaining these new observations I propose some modifications to each of those models. These modifications bring those two seemingly opposite models closer together into a general picture that agrees well with recent 3D magneto-hydrodynamic simulations.

关键词： sunspots magnetic fields spectropolarimetry magnetohydrodynamics

Mock catalogues for large surveys:Lessons from Gaia and implications for CSST

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2023年第11期66卷 239-240页

作者： Tristan Cantat-Gaudin max-planck-institut für Astronomie Heidelberg69117Germany

Experience in large stellar surveys,such as Gaia,has shown that synthetic catalogues are very useful for preparing the data and evaluating scientific results(see the Gaia Universe model snapshot,ref.[1],as an example).This experience holds especially for complex datasets that provide not only positions and apparent magnitudes,but also proper motions,multi-band photometry,and spectroscopy.

关键词： spectroscopy survey holds

Quasi-periodic outflows observed by the X-Ray Telescope onboard Hinode in the boundary of an active region

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2010年第12期10卷 1307-1314页

作者： Li-Jia Guo Hui Tian Jian-Sen He School of Earth and Space Sciences Peking University Beijing 100871 China guolijia32 @ 163. com max-planck-institut fur sonnensystemforschung 37191 Katlenburg-Lindau Germany

Persistent outflows have recently been detected at the boundaries of some active regions. Although these outflows are suggested to be possible sources of the slow solar wind, the nature of these outflows is poorly understood. Through an analy- sis of an image sequence obtained by the X-Ray Telescope onboard the Hinode spacecraft, we found that quasi-periodic outflows are present in the boundary of an active region. The flows are observed to occur intermittently, often with a period of 5-10 min. The proj ected flow speed can reach more than 200 km s^-1, while its distribution peaks around 50 km s^-1. This sporadic high-speed outflow may play an important role in the mass loading process of the slow solar wind. Our results may imply that the outflow of the slow solar wind in the boundary of the active region is intermittent and quasiperiodic in nature.

关键词： solar wind -- Sun： UV radiation -- active region

Data-driven Simulations of Magnetic field Evolution in Active Region 11429:Magneto-frictional Method Using PENCIL CODE

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2024年第2期24卷 74-82页

作者： P.Vemareddy Jorn Warnecke Ph.A.Bourdin Indian institute of Astrophysics Sarjapur roadII BlockKoramangalaBengaluru-560034India max-planck-institut für sonnensystemforschung Justus-von-Liebig-Weg 3D-37077 GöttingenGermany institute of Physics University of GrazUniversitätsplatz 5A-8010 GrazAustria

Coronal magnetic fields evolve quasi-statically over long timescales and dynamically over short timescales.As of now there exist no regular measurements of coronal magnetic fields,and therefore generating the coronal magnetic field evolution using observations of the magnetic field at the photosphere is a fundamental requirement to understanding the origin of transient phenomena from solar active regions(ARs).Using the magneto-friction(Mf)approach,we aim to simulate the coronal field evolution in the solar AR 11429.The Mf method is implemented in the open source PENCIL CODE along with a driver module to drive the initial field with different boundary conditions prescribed from observed vector magnetic fields at the photosphere.In order to work with vector potential and the observations,we prescribe three types of bottom boundary drivers with varying free-magnetic energy.The Mf simulation reproduces the magnetic structure,which better matches the sigmoidal morphology exhibited by Atmospheric Imaging Assembly(AIA)images at the pre-eruptive time.We found that the already sheared field further driven by the sheared magnetic field will maintain and further build the highly sheared coronal magnetic configuration,as seen in AR 11429.Data-driven Mf simulation is a viable tool to generate the coronal magnetic field evolution,capturing the formation of the twisted flux rope and its eruption.

关键词： Sun corona-Sun evolution-Sun magnetic fields-Sun photosphere

J-comb: An image fusion algorithm to combine observations covering different spatial frequency ranges

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2022年第9期65卷 138-156页

作者： Sihan Jiao Yuxin Lin Xiangyu Shui Jingwen Wu Zhiyuan Ren Di Li National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Centre for Astrochemical Studies Max-Planck-Institut f¨ur Extraterrestrische PhysikGarching 85748Germany Astrophysics Department Munich UniversityMunich 81679Germany NAOC-UKZN Computational Astrophysics Centre University of KwaZulu-NatalDurban 4000South Africa

Ground-based, high-resolution bolometric(sub)millimeter continuum mapping observations on spatially extended target sources are often subject to significant missing fluxes. This hampers accurate quantitative analyses. Missing flux can be recovered by fusing high-resolution images with observations that preserve extended structures. However, the commonly adopted image fusion approaches do not maintain the simplicity of the beam response function and do not try to elaborate the details of the yielded beam response functions. These make the comparison of the observations at multiple wavelengths not straightforward. We present a new algorithm, J-comb, which combines the high and low-resolution images linearly. By applying a taper function to the low-pass filtered image and combining it with a high-pass filtered image using proper weights, the beam response functions of our combined images are guaranteed to have near-Gaussian shapes. This makes it easy to convolve the observations at multiple wavelengths to share the same beam response functions. Moreover, we introduce a strategy to tackle the specific problem that the imaging at 850 μm from the present-date ground-based bolometric instrument and that taken with the planck satellite do not overlap in the fourier domain. We benchmarked our method against two other widely-used image combination algorithms, CASA-feather and MIRIAD-immerge, with mock observations of star-forming molecular clouds. We demonstrate that the performance of the J-comb algorithm is superior to those of the other two algorithms. We applied the J-comb algorithm to real observational data of the Orion A star-forming region. We successfully produced dust temperature and column density maps with ~10′′angular resolution, unveiling much greater details than the previous results. A py Thon code release of J-comb and implementation of the algorithm are available at https://***/Sihan Jiao/J-comb.

关键词： star formation molecular clouds image processing

On the error analyses of polarization measurements of the white-light coronagraph aboard ASO-S

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2019年第4期19卷 109-118页

作者： Li feng Hui Li Bernd Inhester Bo Chen Bei-Li Ying Lei Lu Weiqun Gan Key Laboratory of Dark Matter and Space Astronomy Purple Mountain Observatory Chinese Academy of Sciences max-planck-institut für sonnensystemforschung Gttingen Changchun institute of Optics Fine Mechanics and Physics Chinese Academy of Sciences

The Advanced Space-based Solar Observatory(ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections(CMEs), and their magnetism.for the study of CMEs, the payload Lyman-alpha Solar Telescope(LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial for deriving fundamental physical parameters of CMEs. To make such measurements, there are two options for a Stokes polarimeter which have been applied by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizer, the other involves both a half-wave plate and a linear polarizer. We find that the former option is subject to less uncertainty in the derived Stokes vector propagating from detector noise.The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012 C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembly in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer.

关键词： Sun:corona Sun:coronal mass ejections(CMEs) techniques:polarimeter

The role of Ca,Al and Zn on room temperature ductility and grain boundary cohesion of magnesium

在线全文

学校读者我要写书评

暂无评论

Journal of Magnesium and Alloys 2021年第5期9卷 1536-1551页

作者： Supriya Nandy Shao-Pu Tsai Leigh Stephenson Dierk Raabe Stefan Zaefferer max-planck institut für Eisenforschung Düsseldorf 40237Germany

It is know from literature that small additions(<1 wt%)of Ca,Al and Zn significantly improve the intrinsic ductility of Mg.The exact role of each element,both qualitatively and quantitatively,and their combined effect... 详细信息

It is know from literature that small additions(f Ca,Al and Zn significantly improve the intrinsic ductility of Mg.The exact role of each element,both qualitatively and quantitatively,and their combined effects,however,are poorly understood.Here we achieved a much clearer view on the quantitative role of each element with respect to ductility improvement and on the collaborative effect,particularly of Ca and Zn in Mg.Some of our findings and conclusions are in disagreement with data and interpretation found in literature.four different alloys,namely,Mg-0.1 Ca,Mg-0.1 Ca-1 Al,Mg-0.05 Ca-1 Al,Mg-0.1 Ca-2 Al-1 Zn(all are in wt%)were selected for this investigation.All alloys were treated such that approx.similar grain sizes and textures were obtained.This largely excludes the effect of extrinsic factors on ductility.EBSD-guided slip trace analyses reveal that the addition of Ca eases activation of prismatic and pyramidal II slip systems.Using in-situ deformation experiments in SEM and atom probe tomography observations of grain boundaries direct evidence is given for the individual and synergetic effects of Ca and Zn on grain boundary cohesion as an important contribution to improve the ductility of these alloys.We conclude that Ca reduces the slip anisotropy and ameliorates ductility,however,the weak grain boundary cohesion in the Mg-0.1 wt%Ca alloy limits the material’s tensile ductility.The addition of Zn alters the Ca segregation at the grain boundaries and helps to retain their cohesive strength,an effect which thus enables higher ductility and strength.The further addition of Al primarily improves the strength.The results show that the balanced influence of reduced slip anisotropy on the one hand and increased grain boundary cohesion on the other hand allow to design a high strength high ductility rare-earth free Mg alloy.

关键词： Magnesium–Calcium–Zinc alloys Ductility Slip system determination grain boundary cohesion