A siphon mechanism for supplying prominence mass

We examine a siphon-like mechanism for moving mass from the chromosphere to a gravitational well at the top of a magnetic loop to form a prominence. The calculations assume no apriori flow velocity at the loop base. Instead heating in the loop legs drives the flow. The prominence formation process requires two steps. First, the background heating rate must be reduced to on the order of 1 % of the initial heating rate required to maintain the coronal loop. This forms an initial condensation at the top of the loop. Second, the heating must take place only in the loop legs in order to produce a pressure differential which drives mass up into the well at the top of the loop. The heating rate in the loop must be increased once the prominence has begun to form or full prominence densities can not be achieved in a reasonable time. We conclude that this heating driven siphon-like mechanism is feasible for producing and maintaining prominences.     

Earth rotation in the hipparcos reference frame

New determination of the Earth orientation parameters (EOP), based on optical astrometry observations since the beginning of the century, is now under preparation by the Working group established by Commission 19 of the IAU. The Hipparcos catalog is to define the celestial reference frame in which the new series of EOP are to be described, The novelties of the prepared solution are the higher resolution (5 days) and more parameters estimated from the solution (celestial pole offsets, rheological parameters of the Earth, certain instrumental constants). The mathematical model of the solution is described, and the results based on the observations made with 46 instruments at 29 observatories and a preliminary Hipparcos catalog are presented.     

Wavelet Spectrum Analysis Of Eit/Soho Images

The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum. We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis.     

观驾山—黑岛一带信息量法找金研究

本文以成矿地质模型为依据，对观驾山—黑山岛一带的化探、物探、遥感及地质等信息变量进行了详细的分析，选取了１０个信息变量２４个标志状态；在此基础上，运用信息量法对研究区内４５８个单元的信息量值进行计算，并由此确定了研究范围内的成矿远景区。事实表明，研究区信息量成矿预测是非常有效的     

Cygnus A

Cygnus A was the first hyper-active galaxy discovered, and it remains by far the closest of the ultra-luminous radio galaxies. As such, Cygnus A has played a fundamental role in the study of virtually all aspects of extreme activity in galaxies. We present a review of jet theory for powering the double-lobed radio emitting structures in powerful radio galaxies, followed by a review of observations of Cygnus A in the radio, optical, and X-ray relevant to testing various aspects of jet theory. Issues addressed include: jet structure from pc- to kpc-scales, jet stability, confinement, composition, and velocity, the double shock structure for the jet terminus and the origin of multiple radio hotspots, the nature of the filamentary structure in the radio lobes, and the hydrodynamic evolution of the radio lobes within a dense cluster atmosphere, including an analysis of pressure balance between the various gaseous components. Also discussed are relativistic particle acceleration and loss mechanisms in Cygnus A, as well as magnetic field strengths and geometries both within the radio source, and in the intracluster medium. We subsequently review the classification, cluster membership, and the emission components of the Cygnus A galaxy. The origin of the activity is discussed. Concentrating on the nuclear regions of the galaxy, we review the evidence for an obscured QSO, also given the constraints on the orientation of the radio source axis with respect to the sky plane. We present an overview of models of central engines in AGN and observations of Cygnus A which may be relevant to testing such models. We conclude with a brief section concerning the question of whether Cygnus A is representative of powerful high redshift radio galaxies. Received October 10, 1995     

Revisiting Sustainable Development of Dry Valleys in Hengduan Mountains Region

Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities.     

The search for exsolved ferromagnesian olivines: A meteoritic survey

Abstract— Olivine grains from selected meteorites (the Springwater pallasite, the Lowicz mesosiderite, the ALH 84025 brachinite, the Krymka LL3 chondrite, and the Calcalong Creek lunar meteorite) and terrestrial rocks (San Carlos forsterite and Rockport fayalite) were studied by optical microscopy and high-precision electron microprobe analysis. Detailed microprobe traverses revealed regular igneous zoning in the Krymka and Calcalong Creek olivines. Traverses across the San Carlos forsterite grain are flat and display no chemical variations larger than the 2σ range of counting error (±0.2 mol% Fa). Traverses across olivine grains in the ALH 84025, Lowicz, and Springwater meteorites show regular patterns of periodic or wavy chemical variations well exceeding the 2σ uncertainty range. However, no lamellar structure was seen in backscattered electron images. It is suggested that the periodic chemical variations may be due to spinodal decomposition of primary, more or less homogeneous grains. I conclude that the absence of earlier reports of such variations simply means that olivine grains in equilibrated meteorites have not been examined closely enough to detect them.     

Long-Term Changes of Polar Activity of the Sun

We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during 1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles. The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed.     

Geochemistry of metabauxites in the Bergsträsser Odenwald (Mid German Crystalline Rise) and palaeoenvironmental implications

Summary Pre- to early Variscan metamorphosed volcano-sedimentary series of the western (Bergstr?sser) Odenwald have been intruded by Variscan calc-alkaline magmatites with plate margin affinities. Within the NE-SW trending metabasic and metapelitic series, intercalations of anomalously aluminous- and iron-rich compositions representing former bauxites are distinguishable. Geochemical data indicate that the Al-, Fe-rich rocks are the metamorphic equivalents of a former bauxitic-ferralitic weathering profile, now comprising spinel fels (top) with relics of pisolitic structures, corundum-chlorite fels, corundum-cordierite-plagioclase gneiss, sillimanite-cordierite-plagioclase gneiss, cordierite-plagioclase gneiss and kinzigite (base) displaying a decrease of weathering in the order as listed. The evolution of such terrestrial sediments is related to specific climatic, environmental, and physico-chemical conditions similar to those of the present-day tropical to subtropical humid regions with high seasonal rains and intensive drainage. Comparison with palaeomagnetic and palaeoclimatic data indicate that the Odenwald metabauxites originally formed during the Lower to Mid-Devonian. Our results imply that, during this geological time span, parts of the precursors of the Mid-German Crystalline Rise not only transversed low latitudes but also were exposed to terrestrial weathering.

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Zusammenfassung Die Geochemie der Metabauxite im Bergstr?sser Odenwald (Mitteldeutsche Kristallinschwelle) und ihre Bedeutung für das Pal?omilieu Im westlichen (Bergstr?sser) Odenwald intrudierten variszische Plattenrand-Kalkalkali-Magmatite in pr?- bis früh-variszische, ehemalige vulkano-sediment?re Serien. Innerhalb der heute NE-SW streichenden Metabasit- und Metapelitzüge treten lokal Al-Fe-reiche Einschaltungen auf, die strukturell und geochemisch als metamorphe ?quivalente eines ehemaligen bauxitisch-ferralitischen Verwitterungsprofils klassifiziert werden k?nnen. Sie umfassen Spinellfelse mit erhaltenen, ehemaligen zonierten Pisolithen, Korund-Chloritfelse, Korund-Cordierit-Plagioklasgneise, Sillimanit-Cordierit-Plagioklasgneise, Cordierit-Plagioklasgneise und Kinzigite. Bauxite k?nnen als terrestrische Bildungen nur unter speziellen klimatischen und physiko-chemischen Bedingungen entstehen. Pal?omagnetische und pal?oklimatische Daten legen die Bildung der ehemaligen Bauxite im unteren bis mittleren Devon nahe. Daraus folgt, da? w?hrend dieser geologischen Zeitspanne die Vorl?ufer der mitteldeutschen Kristallinschwelle bei der Norddrift nicht nur ?quatorn?he passierten, sondern auch partiell ungest?rte, terrestrische, tropisch-subtropische Verwitterungsprozesse abliefen.

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Received June 10, 1999; revised version accepted October 30, 2000