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Evolution of a Long-lived Sunspot Group and Its Associated Solar-terrestrial Events 被引量:1
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作者 Gui-QingZhang Li-RongTian 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2005年第1期77-86,共10页
A long-lived sunspot group (AR9604) on the south hemisphere that lasted five solar rotations and produced some strong bursts is analyzed. The focus is on its evolving features. Its whole life was successfully maintain... A long-lived sunspot group (AR9604) on the south hemisphere that lasted five solar rotations and produced some strong bursts is analyzed. The focus is on its evolving features. Its whole life was successfully maintained by four Emerging Flux Regions (EFRs). Apart from the one that lasted only a short time and did not produce any bursts, the other three EFRs have the following common features: (1) A positive writhe of magnetic flux tubes and a twist of the field lines of the same sign, indicating kink instability. (2) A clockwise rotation and a high tilt because the writhe was right-handed. (3) A compact 'island δ' structure of the sunspot group indicating concentrated kink instability. Since magnetic reconnection easily occurs at the kinked point of a very kink-unstable flux tube, these features should be the inducement of the strong bursts. 展开更多
关键词 sun - active region evolution
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Multiple cycles of magnetic activity in the Sun and Sun-like stars and their evolution
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作者 Elena Aleksandrovna Bruevich Vasily Vladimirovich Bruevich Boris Pavlovich Artamonov 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2018年第7期21-36,共16页
The wavelet transform method for high-quality time-frequency analysis is applied to sets of observations of relative sunspot numbers and stellar chromosphere fluxes of 10 Sun-like stars. Wavelet analysis of solar data... The wavelet transform method for high-quality time-frequency analysis is applied to sets of observations of relative sunspot numbers and stellar chromosphere fluxes of 10 Sun-like stars. Wavelet analysis of solar data shows that in a certain interval of time there are several cycles of activity with pe- riods of duration which vary considerably from each other: from quasi-biennial cycles to lO0-yr cycles. Cyclic activity was detected in almost all Sun-like stars that we examined, even those that previously were not considered as stars with cyclic activity according to analysis using a Scargle periodogram. The durations of solar and stellar cycles significantly change during the observation period. 展开更多
关键词 sun activity - multiple cycles - sun-like stars ACTIVITY
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Phase evolution of plasma sprayed Al_2O_3-13%TiO_2 coatings derived from nanocrystalline powders 被引量:2
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作者 路学成 阎殿然 +3 位作者 杨勇 董艳春 何继宁 张建新 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2013年第10期2951-2956,共6页
Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 (mass fraction), which were reconstituted into micrometer-sized granu... Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 (mass fraction), which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then A1203-13%TiO2 nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that A1203 retains the same a phase as the raw material during sintering, while TiO2 changes from anatase to futile. During plasma spraying, some a-A1203 phases solidify to form metastable y-A1203, and the volume fraction of a-A1203 decreases as CPSP increases. However, peaks of the TiO2 phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO2 is dissolved easily in y-A1203 or z-A1203'TiO2 phase. After heat treatment, y-A1203 in the coatings transforms to a-A1203, and rutile is precipitated. 展开更多
关键词 A1203-13%TiO2 nanocrystalline powder NANOCOATINGS phase evolution
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Evolution of the Level of Sunspot Activity in Solar Cycles I. Evolution in the Descending Phase 被引量:2
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作者 Jia-Long Wang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2006年第3期354-362,共9页
Taking the 13-point smoothed monthly sunspot number,Ri, and the deviation of the 13 associated monthly sunspot numbers from the smoothed one, Di, as a number-pair describing the global level of sunspot activity, the e... Taking the 13-point smoothed monthly sunspot number,Ri, and the deviation of the 13 associated monthly sunspot numbers from the smoothed one, Di, as a number-pair describing the global level of sunspot activity, the evolution of the level is statistically studied for the period from the month which is just 48 months before the minimum to the minimum in the descending phase, using the observed data of Solar Cycles 10 to 22. Our results show (1) for 46 months (94%) of the studied 49 months it is found that for a given month, the distribution of the 13 pairs which come from the 13 solar cycles on a log Ri - Di plane may be fitted by a straight line with a correlation coefficient larger than the critical one at confidence level a = 5%, and for 36 months (73%) the fitting is even better, for a = 1%; (2) time variations of these two parameters and their correlations in the studied period can be described respectively by functions of time, whose main trends may be expressed by a linear or simple curvilinear function; (3) the evolutionary path of the level of sunspot activity may be represented by a logarithmic function as log/~ = 0.704 lnDi - 0.291. 展开更多
关键词 sun - sunspots - active level evolution
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Enhancement of the thermostability of β-1,3-1,4-glucanase by directed evolution 被引量:2
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作者 ZHANG Xiu-yan RUAN Hui +3 位作者 MU Lin HE Guo-qing TANG Xing-jun CHEN Qi-he 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2006年第11期1948-1955,共8页
In order to improve the thermostability of β- 1,3-1,4-glucanase, evolutionary molecular engineering was used to evolve the β-1,3-1,4-glucanase from Bacillus subtilis ZJF-1A5. The process involves random mutation by ... In order to improve the thermostability of β- 1,3-1,4-glucanase, evolutionary molecular engineering was used to evolve the β-1,3-1,4-glucanase from Bacillus subtilis ZJF-1A5. The process involves random mutation by error-prone PCR and DNA shuffling followed by screening on the filter-based assay. Two mutants, EGsl and EGs2, were found to have four and five amino acid substitutions, respectively. These substitutions resulted in an increase in melting temperature from Tm=62.5℃ for the wild-type enzyme to Tm=65.5℃ for the mutant EGsl and 67.5℃ for the mutant EGs2. However, the two mutated enzymes had opposite approaches to produce reducing sugar from lichenin with either much higher (28%) for the former or much lower (21.6%) for the latter in comparison with their parental enzymes. The results demonstrate that directed evolution is an effective approach to improve the thermostability of a mesophilic enzyme. 展开更多
关键词 Directed evolution Error-prone PCR DNA shuffling β- 1 3-1 4-glucanase Thermostability
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The Formation and Evolution of the Sun and the Source of Star Energy as Well as the Sunspots and Flares of the Sun 被引量:1
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作者 Cuixiang Zhong 《Journal of Physical Science and Application》 2019年第2期17-25,共9页
Nebula theory is the most widely accepted hypothesis about the formation and evolution of the Solar System. This theoryholds that the Sun is formed from a collapsed gas cloud 4.57 billion years ago;when the core tempe... Nebula theory is the most widely accepted hypothesis about the formation and evolution of the Solar System. This theoryholds that the Sun is formed from a collapsed gas cloud 4.57 billion years ago;when the core temperature of the gas cloud rises to 10million K, the thermonuclear reaction of hydrogen fusion into helium is ignited, then the Sun become a star;once the hydrogen in thecore is exhausted, the life of the star will end. But the limited hydrogen element obviously cannot satisfy such a long-termthermonuclear reaction, in order to sustain long-term thermonuclear reactions, a steady stream of fuel must be obtained from space.So the existing hypothesis about the formation and evolution of the Solar System has serious defects. Thus the author has studied theformation of the Moon, the Earth and the Sun, and discovered the formation of the Sun and the real source of star energy. The authorcould also explain many solar activity phenomena such as sunspots, flares, prominences, etc. 展开更多
关键词 sun FORMATION evolution star energy sunSPOTS flares.
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The Coupling Coordination Evolution Research of Economy - Ecology - Society System in Xinjiang:Based on the Interaction Perspective of Water Resources 被引量:1
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作者 Chen Junke Li Hong +1 位作者 Wang Xibo Ma Yongren 《Meteorological and Environmental Research》 CAS 2017年第5期73-77,共5页
Under the water resources perspective,coupling coordination of economy-ecology-society system in Xinjiang was taken as the research object. By building the coupling evaluation index system of the water resources-econo... Under the water resources perspective,coupling coordination of economy-ecology-society system in Xinjiang was taken as the research object. By building the coupling evaluation index system of the water resources-economy-ecology-society system,quantitative evaluation and analysis of the coupling coordination of the water resources-economy-ecology-society system from 2001 to 2014 were conducted. The results showed that benefit indexes of economic system and social system grew rapidly,while benefit indexes of water resources system and ecosystem fluctuated smoothly from 2001 to 2014; coupling state of the whole system was at rival stage,and coupling coordination was reluctant coordination type,and the coupling index was slightly higher than the coupling coordination index. Moreover,it showed that the more the coupling systems,the lower indices of coupling and the coupling coordination. 展开更多
关键词 Water resources - ECONOMY - ECOLOGY - SOCIETY SYSTEM COUPLING coordination evolution XINJIANG
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Highly enhanced visible-light photocatalytic hydrogen evolution on g-C_3N_4 decorated with vopc through π-π interaction 被引量:2
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作者 Yanan Liu Liubo Ma +4 位作者 Congcong Shen Xin Wang Xiao Zhou Zhiwei Zhao Anwu Xu 《Chinese Journal of Catalysis》 SCIE EI CAS CSCD 北大核心 2019年第2期168-176,共9页
Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides(g-C3N4),as a promising approach for converting solar energy to fuel,are attractive for tackling global energy concerns but still suffer from ... Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides(g-C3N4),as a promising approach for converting solar energy to fuel,are attractive for tackling global energy concerns but still suffer from low efficiencies.In this article,we report a tractable approach to modifying g-C3N4 with vanadyl phthalocyanine(VOPc/CN)for efficient visible-light-driven hydrogen production.A non-covalent VOPc/CN hybrid photocatalyst formed viaπ-πstacking interactions between the two components,as confirmed by analysis of UV-vis absorption spectra.The VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good stability.Under optimal conditions,the corresponding H2 evolution rate is nearly 6 times higher than that of pure g-C3N4.The role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs effectively.It is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C3N4-based hybrid systems with strong light absorption and high-efficiency carrier separation. 展开更多
关键词 VOPc/g-C3N4 π-πInteraction Visible light photocatalysis Hydrogen evolution Charge separation efficiency
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An Observational Study of the 30-50 Day Atmospheric Oscillations Part II: Temporal Evolution and Hemispheric Interaction across the Equator 被引量:3
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作者 李崇银 周亚萍 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1991年第4期399-406,共8页
In this part, the temporal evolution and interaction across the equator of 30-50 day oscillation in the atmosphere are investigated further. The annual variation of 30-50 day oscillation is quite obvious in the mid-hi... In this part, the temporal evolution and interaction across the equator of 30-50 day oscillation in the atmosphere are investigated further. The annual variation of 30-50 day oscillation is quite obvious in the mid-high latitudes. In the tropical atmosphere, the obvious interannual variation is an important property for temporal evolution of 30-50 day oscillation. The low-frequency wavetrain across the equator over the central Pacific and central Atlantic area, the movement of the long-lived low-frequency system across the equator and the meridional wind component across the equator will obviously show the interaction of 30-50 day oscillation in the atmosphere across the equator. 展开更多
关键词 EI over An Observational Study of the 30-50 Day Atmospheric Oscillations Part II Temporal evolution and Hemispheric Interaction across the Equator Nino
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2D/2D S-scheme heterojunction with a covalent organic framework and g-C_(3)N_(4) nanosheets for highly efficient photocatalytic H2 evolution 被引量:2
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作者 Pengyu Dong Aicaijun Zhang +6 位作者 Ting Cheng Jinkang Pan Jun Song Lei Zhang Rongfeng Guan Xinguo Xi Jinlong Zhang 《Chinese Journal of Catalysis》 SCIE EI CAS CSCD 2022年第10期2592-2605,共14页
The fabrication of S-scheme heterojunctions with fast charge transfer and good interface contacts,such as intermolecularπ–πinteractions,is a promising approach to improve photocatalytic performance.A unique two-dim... The fabrication of S-scheme heterojunctions with fast charge transfer and good interface contacts,such as intermolecularπ–πinteractions,is a promising approach to improve photocatalytic performance.A unique two-dimensional/two-dimensional(2D/2D)S-scheme heterojunction containing TpPa-1-COF/g-C_(3)N_(4) nanosheets(denoted as TPCNNS)was developed.The established maximum interfacial interaction between TpPa-1-COF NS and g-C_(3)N_(4) NS may result in aπ–πconjugated heterointerface.Furthermore,the difference in the work functions of TpPa-1-COF and g-C_(3)N_(4) results in a large Fermi level gap,leading to upward/downward band edge bending.The spontaneous interfacial charge transfer from g-C_(3)N_(4) to TpPa-1-COF at theπ–πconjugated interface area results in the presence of a built-in electric field,according to the charge density difference analysis based on density functional theory calculations.Such an enhanced built-in electric field can efficiently drive directional charge migration via the S-scheme mechanism,which enhances charge separation and utilization.Thus,an approximately 2.8 and 5.6 times increase in the photocatalytic hydrogen evolution rate was recorded in TPCNNS-2(1153μmol g^(-1) h^(-1))compared to pristine TpPa-1-COF and g-C_(3)N_(4) NS,respectively,under visible light irradiation.Overall,this work opens new avenues in the fabrication of 2D/2Dπ–πconjugated S-scheme heterojunction photocatalysts with highly efficient hydrogen evolution performance. 展开更多
关键词 Covalent organic framework g-C_(3)N_(4) π-πConjugated 2D/2D material S-Scheme heterojunction Photocatalytic hydrogen evolution
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Promoting surface reconstruction of NiFe layered double hydroxides via intercalating[Cr(C_(2)O_(4))_(3)]^(3-)for enhanced oxygen evolution 被引量:2
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作者 Yujie Wu Minglei Song +8 位作者 Yu-Cheng Huang Chung-Li Dong Yingying Li Yuxuan Lu Bo Zhou Dongdong Wang Jianfeng Jia Shuangyin Wang Yanyong Wang 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2022年第11期140-148,I0005,共10页
Rationally manipulating surface reconstruction of catalysts for water oxidation,inducing formation and dynamic accumulation of catalytically active centers still face numerous challenges.Herein,the introduction of[Cr(... Rationally manipulating surface reconstruction of catalysts for water oxidation,inducing formation and dynamic accumulation of catalytically active centers still face numerous challenges.Herein,the introduction of[Cr(C_(2)O_(4))_(3)]^(3-)into NiFe LDHs by intercalation engineering to promote surface reconstruction achieves an advanced oxygen evolution reaction(OER)activity.In view of the weak electronegativity of Cr^(3+) in[Cr(C_(2)O_(4))_(3)]^(3-),the intercalation of[Cr(C_(2)O_(4))_(3)]^(3-)is expected to result in an electron-rich structure of Fe sites in NiFe LDHs,and higher valence state of Ni can be formed with the charge transfer between Fe and Ni.The optimized electronic structure of NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs with more active Ni^(3+) species and the expedited dynamic generation of Ni^(3+) (Fe)OOH phase during the OER process contributed to its excellent catalytic property,revealed by in situ X-ray absorption spectroscopy,Raman spectroscopy,and quasi-in situ X-ray photoelectron spectroscopy.With the modulated electronic structure of metal sites,NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs exhibited promoted OER property with a lower overpotential of 236 mV at the current density of 10 mA cm^(-2).This work illustrates the intercalation of conjugated anion to dynamically construct desired Ni^(3+) sites with the optimal electronic environment for improved OER electrocatalysis. 展开更多
关键词 NiFe layered double hydroxides [Cr(C_(2)O_(4))_(3)]^(3-)intercalation Dynamic restructuring Operando spectroscopies Oxygen evolution reaction
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IRAS F21013-0739:a possible evolutionary successor of an ultraluminous infrared galaxy
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作者 Xian-Min Meng Hong Wu Chen Cao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2011年第4期419-433,共15页
We present a stellar population synthesis study of a type II luminous infrared galaxy, IRAS F21013-0739. Optical images show clear characteristics of a merger remnant. The H-band absolute magnitude is MH = -25.1, whic... We present a stellar population synthesis study of a type II luminous infrared galaxy, IRAS F21013-0739. Optical images show clear characteristics of a merger remnant. The H-band absolute magnitude is MH = -25.1, which is -2 times as luminous as L* galaxies. Stellar populations are obtained through the stellar synthesis code STARLIGHT. We find that it experienced a recent starburst (SB) phase - 100 Myr ago. By reconstructing the ultraviolet-to-optical spectrum, and adopting Calzetti et al. and Leitherer et al.'s extinction curves, we estimate the past infrared (IR) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy phase which lasted for about 100 Myr. Its i-band absolute magnitude is Mi = -22.463, and its spectral type shows type 2 active galactic nucleus (AGN) characteristics. The mass of the supermassive black-hole is estimated to be MBH = 1.6 × 107 M⊙ (lower- limit). The Eddington ratio Lbol/LEdd is 0.15, which is typical of Palomar-Green (PG) quasars. Both the nuclear SB and AGN contribute to the present IR luminosity budget, and the SB contributes -67%. On the diagram of IR color versus IR/opfical excess, it is located between IR quasars and PG quasars. These results indicate that IRAS F21013-0739 has probably evolved from a ULIRG, and it can possibly evolve into an AGN. 展开更多
关键词 INFRARED galaxies -- galaxies evolution -- galaxies starburst --galaxies: individual (IRAS F21013-0739) -- galaxies stellar content
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Tectonic Evolution of the Palaeo——Tethys in Changning——Menglian Belt and Adjacent Regions,Western Yunnan 被引量:27
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作者 Liu Benpei Feng Qinglai Fang NianqiaoChina University of Geosciences , Beijing 100083 《Journal of Earth Science》 SCIE CAS CSCD 1991年第1期21-31,共11页
The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep wate... The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean . 展开更多
关键词 Palaeo - Tethys tectonic evolution Changning - Menglian belt Lancangjiang belt Western Yunnan.
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SUN-domain蛋白家族在植物中的研究进展 被引量:1
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作者 吴贺 包颖 《曲阜师范大学学报(自然科学版)》 CAS 2020年第1期92-99,共8页
SUN-domain蛋白家族是植物细胞膜上核骨架与细胞骨架连接复合体(LINC)的重要组成成分,在细胞核的形态、定位和迁移以及染色体移动和配对的过程中均发挥着重要作用.由于功能域在编码基因中所在位置不同,SUN-domain蛋白家族可以分为羧基端... SUN-domain蛋白家族是植物细胞膜上核骨架与细胞骨架连接复合体(LINC)的重要组成成分,在细胞核的形态、定位和迁移以及染色体移动和配对的过程中均发挥着重要作用.由于功能域在编码基因中所在位置不同,SUN-domain蛋白家族可以分为羧基端SUN-domain蛋白(Cter-SUN)亚家族和中间SUN-domain蛋白(Mid-SUN)亚家族.Cter-SUN蛋白定位于内核膜上,而Mid-SUN蛋白在核周质、内质网上均有出现.受基因复制事件和选择性剪切事件的影响,SUN-domain蛋白家族在不同植物中的成员数目和功能作用也存在一定的差异.从系统进化上来看,SUN-domain蛋白家族的起源古老,可能出现在单细胞生物进化为多细胞生物之前.根据目前对植物SUN-domain蛋白的理解,文章阶段性总结了该蛋白家族在植物各主要类群中的成员组成、编码基因的特点和表达模式以及各蛋白的功能特性等方面的研究进展,为深入理解该蛋白家族在植物进化中的作用奠定了基础. 展开更多
关键词 sun-domain LINC 结构模型 分子进化 功能表达
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Petrographic characterization and evolution of the Karharbari coals, Talcher Coalfield, Orissa, India 被引量:2
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作者 Alok K. Singh 《International Journal of Coal Science & Technology》 EI 2016年第2期133-147,共15页
In the present study an attempt has been made to carry out the detailed petrographic characterization of the Karharbari coals of Talcher coalfield and to reconstruct the paleoenvironment conditions of coal formation u... In the present study an attempt has been made to carry out the detailed petrographic characterization of the Karharbari coals of Talcher coalfield and to reconstruct the paleoenvironment conditions of coal formation using macerals and microlithtotypes as a tool. For these purposes a large number of samples were collected following the pillar sampling method and were subjected to detailed petrographic study. The petrographic observation shows that these coals are vitrinite rich followed by the liptinite and inertinite group of macerals. On microlithotype scale, these coals shows the dominance of the vitrite followed by clarite, vitrinertite and inertite. The concentration of liptite, clarodurite, duroclarite and vitriner- toliptite are insignificant. The vitrinite reflectance ranks the Karharbari coal as high volatile bituminous 'C' to high volatile 'B' bituminous. Coal petrography based depositional models suggest peat accumulation in forested telmatic swamp. Moreover, during the time of their evolution, there were alternate phases of oxic and anoxic moor conditions with good tissue preservation. 展开更多
关键词 PETROGRAPHY RANK evolution - Karharbari Talcher coalfield
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A Monte Carlo Study of the Evolution of the Scale Height of Normal Pulsars in the Galaxy 被引量:1
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作者 Ying-Chun Wei Xin-Ji Wu +2 位作者 Qiu-He Peng Na Wang Jin Zhang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2005年第6期610-618,共9页
Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity di... Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions (δv): it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1. 展开更多
关键词 pulsar general - stars evolution - Galaxy structure - Galaxy DISK
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Abundance Gradient from Open Clusters and Implications for the Galactic Disk Evolution 被引量:3
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作者 Jin-LiangHou Rui-XiangChang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2002年第1期17-32,共16页
We compile a new sample of 89 open clusters with ages, distances and metallicities available. We derive a radial iron gradient of about -0.099±0.008 dex kpc^(-1) (unweighted) for the whole sample, which is somewh... We compile a new sample of 89 open clusters with ages, distances and metallicities available. We derive a radial iron gradient of about -0.099±0.008 dex kpc^(-1) (unweighted) for the whole sample, which is somewhat greater than the most recent determination of oxygen gradient from nebulae and young stars. By dividing the clusters into age groups, we show that the iron gradient was steeper in the past and has evolved slowly in time. Current data show a substantial scatter of the cluster metallicities indicating that the Galactic disk has undergone a very rapid, inhomogeneous enrichment. Also, based on a simple, but quite successful model of chemical evolution of the Milky Way disk, we make a detailed calculation of the iron abundance gradient and its time evolution. The predicted current iron gradient is about -0.072 dex kpc^(-1). The model also predicts a steady flattening of the iron gradient with time, which agrees with the result from our open cluster sample. 展开更多
关键词 open clusters: abundances - Galaxy: formation - Galaxy: evolution
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Implementation of New OPAL Tables in Eggleton's Stellar Evolution Code 被引量:2
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作者 Xue-Fei Chen Christopher A. Tout 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2007年第2期245-250,共6页
Based on previous works of OPAL, we construct a series of opacity tables for various metaUicities Z = 0, 0.00001, 0,00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables c... Based on previous works of OPAL, we construct a series of opacity tables for various metaUicities Z = 0, 0.00001, 0,00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 (T/K) 〉 3.95 and Alexander's for log10 (T/K) 〈 3.95. At log10 (T/K) = 3.95, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars. 展开更多
关键词 radiative transfer- stars evolution - stars general
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A Note on the Mixing Length Theory and Massive Star Evolution 被引量:1
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作者 Li-Cai Deng and Da-Run Xiong ( Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing210008 National Astronomical Observatories, Chinese Academy of Sciences, Beij 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2001年第1期50-56,共7页
In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the u... In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the usual MLT, a zone of supersonic convection exists when the stellar model goes into yellow-red supergiant phase. When the modification is applied, the models of late type supergiants possess shallower convective envelopes for a given temperature compared with the normal formalism of the MLT. Therefore the stellar models made with our new formalism move to lower effective temperature by 100-400 K depending on the luminosity of the star. Such a modification does not affect the convective envelope structure of lower luminosity late type stars, as both expressions of the MLT give the same result. In these stars. 展开更多
关键词 convection - stars: supergiants - stars: massive stars - stars: evolution
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Stellar Abundance and Galactic Chemical Evolution through LAMOST Spectroscopic Survey 被引量:1
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作者 Gang Zhao Yu-Qin Chen +5 位作者 Jian-Rong Shi Yan-Chun Liang Jin-Liang Hou Li Chen Hua-Wei Zhang Ai-Gen Li 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2006年第3期265-280,共16页
A project of a spectroscopic survey of Galactic structure and evolution with a Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) is presented. The spectroscopic survey consists of two observational ... A project of a spectroscopic survey of Galactic structure and evolution with a Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) is presented. The spectroscopic survey consists of two observational modes for various targets in our Galaxy. One is a major survey of the Milky Way aimed at a systematic study of the stellar abundance and Galactic chemical evolution through low resolution (R = 1000 2000) spectroscopy. Another is a follow-up observation with medium resolution (R = 10000) spectrographs aimed at detailed studies of the selected stars with different chemical composition, kinematics and dynamics. 展开更多
关键词 techniques: spectroscopic - stars: abundances - Galaxy: structure - Galaxy:abundances - Galaxy: kinematics and dynamics - Galaxy: evolution
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