Magnetic field evolution in OBA stars     

A.?F.?KholtyginEmail author  S.?N.?Fabrika  N.?A.?Drake  V.?D.?Bychkov  L.?V.?Bychkova  G.?A.?Chountonov  T.?E.?Burlakova  G.?G.?Valyavin 《Kinematics and Physics of Celestial Bodies》2010,26(4):181-191

The applications of the spectral analysis methods discovered by Kirchhoff for the investigation of stellar magnetic fields are considered. The statistical properties of the mean magnetic fields for OBA stars have been investigated by analyzing data from two catalogs of magnetic fields. It is shown that the mean effective magnetic field ℬ of a star can be used as a statistically significant characteristic of its magnetic field. The magnetic field distribution functions F(ℬ) have been constructed for B-type and chemically peculiar (CP) stars, which exhibit a power-law dependence on ℬ. A sharp decrease in F(ℬ) in the range of weak magnetic fields has been found. The statistical properties of the magnetic fluxes for main-sequence stars, white dwarfs, and neutron stars are analyzed.  相似文献   

聚类分析在物源分析中的应用——以伊通盆地鹿乡断陷为例     

丁鸿儒  郭巍  刘群  那晓敏  马琳  孙守亮 《世界地质》2010,29(3):466-472

鹿乡断陷近年来虽在油气勘探方面取得了一系列成果,但该区存在多物源方向交汇、沉积体系划分不清晰;而经典的物源分析方法操作复杂,可靠性差。笔者应用统计学方法,对研究区重矿物的相对含量进行聚类分析,结合研究区砂岩等厚图,对鹿乡断陷双阳组各段的物源方向进行分析,结果表明:在双阳组一段沉积时期,研究区存在西南、南部和东部3个物源方向;在双阳组二段沉积时期,研究区存在东部、南部、西南和西北4个物源方向;在双阳组三段沉积时期,研究区存在东部和西北部2个物源方向。双阳组沉积时期,西北和南部方向物源的沉积物供给呈现"弱--强--弱"的变化特点,东部方向物源的沉积物供给不断减弱。沉积体系的规模受控于沉积速率。  相似文献   

Granite generation and rapid unroofing related to strike-slip faulting, Aysén, Chile     

Francisco Herv  Robert J. Pankhurst  Robert Drake  Myrl E. Beck Jr.  Constantino Mpodozis 《Earth and Planetary Science Letters》1993,120(3-4):375-386

A stock of biotite-muscovite-garnet leucogranite crops out in the lower course of Río Cisnes as an unusual minor lithology within the predominantly dioritic to tonalitic North Patagonian Batholith. Foliated and unfoliated varieties are present—the former are nearer to the main lineament of the Liquin˜e-Ofqui Fault Zone (LOFZ). Two-feldspar thermometry indicates equilibration temperatures above 600°C, for pressures probably not over 3 kbar, as suggested by the Mn-rich garnet composition. A Rb-Sr whole-rock isochron age of 9.6 ± 0.4 Ma (1σ error) probably indicates the time of magma crystallization. ⁴⁰Ar-³⁹Ar ages of 6.6 ± 0.3 Ma on muscovite and 5.5 ± 0.4 Ma on biotite are cooling ages from which a moderate average uplift/denudation rate ( 1 mm/yr) may be calculated. Paucity of occurrence, distribution close to the LOFZ and a near minimum-melt composition all suggest that the leucogranite magma was derived by partial melting of the lower crust, perhaps by decompression melting at a time when uplift/denudation rates were high (4 mm/yr or more are required). Regional evidence for rapid Holocene uplift in the immediate vicinity of the LOFZ substantiates the feasibility of the proposed petrogenetic model, which may be valid in other strike-slip orogenic environments.  相似文献   

Distribution and formation of rock varnish in southern Tunisia     

N. A. Drake  M. T. Heydeman  K. H. White 《地球表面变化过程与地形》1993,18(1):31-41

Field observations, chemical analysis, electron and light microscopy and radiolabelling experiments provide information on the characteristics, formation and distribution of Fe and Mn rock varnishes in southern Tunisia. Unstable rocks are not surface-coated, but when broken they commonly reveal internal microbial solution fronts. Stable rocks are coated in Fe, and more rarely Mn, rock varnishes. Radiolabelling indicates the presence of many respiring microbes on both Fe and Mn varnishes. Microscopy shows fungi and bacteria, both on the Fe varnishes and within the rock. Only rare, microcolonial fungi occur on Mn varnishes, suggesting that the microbes are within or beneath the varnish. The abundance of microorganisms supports a biogenic origin for rock varnishes. Different microbial communities appear to be involved in Fe and Mn varnish formation. Microbes appear to live beneath the surface of unstable rocks but coat stable rocks which cannot be penetrated, apparently to avoid u.v. light and desiccation. This explains the concentration of elements that form u.v. opaque minerals and clays. The origin of these elements is external to the substrate. These results suggest that rock varnish dating and paleoenvironmental techniques can be applied in southern Tunisia.  相似文献   

Partitioning of Ni between olivine and silicate melt: the “Henry's law problem” reexamined: reply to discussion by B. Mysen     

Michael J. Drake  John R. Holloway 《Geochimica et cosmochimica acta》1982,46(2):299

  相似文献   

Pyroxene-melt equilibria     

Roger L. Nielsen  Michael J. Drake 《Geochimica et cosmochimica acta》1979,43(8):1259-1272

Using a literature survey of analyses of high-Ca pyroxene and co-existing silicate melt pairs and analyses of low-Ca pyroxene-silicate melt pairs, we have performed a thermodynamic analysis of pyroxene-melt equilibria. Three sets of mixing model pairs have been considered, based on two mixing models for liquid silicate solutions and two for pyroxene solid solutions. A modified version of a model developed by Bottinga and Weill (1972) for the mixing properties of silicate melts, in which the melt is considered to be composed of independent network-forming and network-modifying quasi-lattices, more successfully accounts for variations in melt composition than does a model which considers the melt to be composed of simple oxides which mix ideally. An empirical model for the mixing properties of pyroxenes, in which the M1 and M2 sites are considered to be equivalent and are combined as a hypothetical ‘M’ site, is as successful in accounting for variations in pyroxene composition at high temperatures as an ideal multisite mixing model.Using a variety of pyroxene-melt relations, and combinations of the mixing models outlined above, we have developed several pyroxene-melt and low-Ca pyroxene-high-Ca pyroxene geothermometers which have internally-consistent precisions of approximately ±20°C (1σ). One of the two-pyroxene geothermometers has been used to calculate ‘quench’ temperatures for a number of eucrites. Computed temperatures are subsolidus, and are consistent with independent geothermometers and with petrographic observations. The equations may also be used to calculate the composition of pyroxene crystallizing from a silicate melt of known composition, with or without independent knowledge of temperature. Internally consistent precisions vary, but are approximately ± 3 mol% Fs, ± 5 mol% En, and ±4 mol% Wo (all 1σ). These equations may have application in modeling the evolution of mineral compositions during differentiation of basaltic magmas, particularly terrestrial layered intrusions and the lunar magma ocean.  相似文献   

Multiplex PCR allows simultaneous detection of pathogens in ships' ballast water     

Aridgides LJ  Doblin MA  Berke T  Dobbs FC  Matson DO  Drake LA 《Marine pollution bulletin》2004,48(11-12):1096-1101

There is enormous potential for global transfer of microorganisms, including pathogens, in ships' ballast water. We contend that a major advancement in the study of ballast-water microorganisms in particular, and of aquatic pathogens in general, will be expedited sample analysis, such as provided by the elegant technology of DNA microarrays. In order to use DNA microarrays, however, one must establish the appropriate conditions to bind target sequences in samples to multiple probes on the microarrays. We conducted proof-of-concept experiments to optimize simultaneous detection of multiple microorganisms using polymerase chain reaction (PCR) and Southern hybridization. We chose three target organisms, all potentially found in ballast water: a calicivirus, the bacterium Vibrio cholerae, and the photosynthetic protist Aureococcus anophagefferens. Here, we show simultaneous detection of multiple pathogens is possible, a result supporting the promising future use of microarrays for simultaneous detection of pathogens in ballast water.  相似文献   

原地生成宇宙成因核素^10Be和^26Al样品采集及处理   总被引：4，自引：3，他引：4  

那春光孔屏  黄费新肖伟 《岩矿测试》2006,25(2):101-106

着重介绍原地生成宇宙成因核素^10Be和^26Al理想样品的特点、野外采集注意事项、实验室分离与纯化以及加速器质谱测量用靶样制备等。  相似文献   

矢量景观指数在遥感信息提取中的应用——以乾安湖群为例   总被引：1，自引：0，他引：1  

李晓峰  张树清  庞振平  潘欣  陈铭  那晓东 《遥感学报》2008,12(2):291-296

景观方向性是景观空间格局的重要特征,能够反映和影响景观的生态流.实现快速、准确地从遥感影像上自动提取景观的方向性信息,对于景观的驱动力分析和景观异质性分析等都具有十分重要的意义.本文基于面向对象的方法对乾安县TM影像进行多尺度分割提取湖群,并利用正方像元指数SqP提高分类精度,应用矢量景观指数于分割处理后的湖群对象,提取景观的方向性信息.实验结果表明:该方法对象分割精度高(制图精度:97.8%,用户精度:97.5%),方向性信息提取准确、快速,为湖群的成因分析提供了数量化和可视化依据.本文同时结合了两方面的研究方法,提供了两方面的研究思路:一方面是景观格局指数在影像分类中的应用,另一方面是矢量景观格局理论进一步的应用扩展.  相似文献   

Recent Aeolian Origin of Surficial Gypsum Crusts in Southern Tunisia: Geomorphological,Archaeological and Remote Sensing Evidence     

N. A. Drake 《地球表面变化过程与地形》1997,22(7):641-656

Recent quarring of the surficial gypsum crusts adjacent to Djebel Sidi Bou Hellas has revealed sections typically showing a discontinuous surface gravel cover underlain by more than 7 m of microcrystalline gypsum. The location, elongate shape, form in cross-section and chemistry of this deposit suggests an aeolian origin, whereby aeolian sands have been trapped against a glacis d'erosion terrace, and subsequently consolidated by meteoric waters. One gypsum quarry revealed a midden and the remains of a Roman dwelling now buried within the crust. A radiocarbon date of organic matter in the midden and a Roman coin found within it suggest an age of AD324–345 for the deposit. This is the first firm date for a surficial gypsum crust in southern Tunisia and the age is surprisingly young. Previous studies have speculated on phases of crust development between the Villefranchian and early Holocene but none since. Remote sensing and field evidence show that gypsiferous sands are currently deflated from the dry parts of the mudflats of Chott Fedjaj. They are subsequently transported in a southwesterly trajectory and trapped against glacis on the southern margins of Chott Fedjaj, forming contemporary analogues of the Roman deposit. Sands that are not trapped form dune fields and sandflats where gypsum crusts appear to be forming today. If the source area of gypsum sands has remained constant since Roman times, then the predominant wind direction has moved 45° to the southwest since then. The other possible source of aeolian gypsum for the Roman deposit, the vast mudflats of Chott Djerid, involves an even greater change in predominant wind direction. © 1997 John Wiley & Sons, Ltd.  相似文献