Deep infrared imaging and spectroscopy of the nearby late M‐dwarf DENIS‐P J104814 –395606     

R. Neuhuser  E.W. Guenther  J. Alves  N. Grosso  Ch. Leinert  Th. Ratzka  Th. Ott  M. Mugrauer  F. Comern  A. Eckart  W. Brandner 《Astronomische Nachrichten》2002,323(5):447-452

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The ALFA Laser: Beam Relay and Control System     

T. Ott  W. Hackenberg  S. Rabien  A. Eckart  S. Hippler 《Experimental Astronomy》2000,10(1):89-101

The ALFA laser subsystem uses a 4 watt continuous wave laser beam to produce an artificial guide star in the mesospheric sodium layer as a reference for wavefront sensing. In this article we describe the system design, focusing on the layout of the beam relay system. It consists of seven mirrors, four of which are motor-controlled in closed loop operation accounting for turbulences inside the dome and flexure of the main telescope.The control system features several computers which are located close to analysis and control units. The distribution of the tasks and their interaction is presented, as well as the graphical user interface used to operate the complete system. This is followed by a discussion of the aircraft detection system ALIENS. This system shuts off the laser beam when an object passes close to the outgoing laser.  相似文献   

Neoproterozoic tectonothermal evolution of the Central Eastern Desert, Egypt: a slow velocity tectonic process of core complex exhumation     

Harald Fritz  David R. Dallmeyer  Eckart Wallbrecher  Jürgen Loizenbauer  Georg Hoinkes  Peter Neumayr  Ali A. Khudeir 《Journal of African Earth Sciences》2002,34(3-4)

Regional cooling in the course of Neoproterozoic core complex exhumation in the Central Eastern Desert of Egypt is constraint by ⁴⁰Ar/³⁹Ar ages of hornblende and muscovite from Meatiq, Sibai and Hafafit domes. The data reveal highly diachronous cooling with hornblende ages clustering around 580 Ma in the Meatiq and the Hafafit, and 623 and 606 Ma in the Sibai. These ⁴⁰Ar/³⁹Ar ages are interpreted together with previously published structural and petrological data, radiometric ages obtained from Neoproterozoic plutons, and data on sediment dynamics from the intramontane Kareim molasse basin. Early-stage low velocity exhumation was triggered by magmatism initiated at 650 Ma in the Sibai and caused early deposition of molasses sediments within rim synforms. Rapid late stage exhumation was released by combined effect of strike-slip and normal faulting, exhumed Meatiq and Hafafit domes and continued until 580 Ma. We propose a new model that adopts core complex exhumation in oblique island arc collision-zones and includes transpression combined with lateral extrusion dynamics. In this model, continuous magma generation weakened the crust leading to facilitation of lateral extrusion tectonics. Since horizontal shortening is balanced by extension, no major crustal thickening and no increase of potential energy (gravitational collapse) is necessarily involved in the process of core complex formation. Core complexes were continuously but slowly exhumed without creating a significant mountain topography.  相似文献   

The preliminary heat flow map of Europe and some of its tectonic and geophysical implications     

Vladimír Čermák  Eckart Hurtig 《Pure and Applied Geophysics》1978,117(1-2):92-103

The heat flow map of Europe was derived from 2605 existing observations, which for this purpose were supplemented by numerous results of deep borehole temperatures, gradients and local heat flow patterns. In areas without data the heat flow field was extrapolated on the basis of the regional tectonic structure and the observed correlation of heat flow and the age of the last tectono-thermal event. The heat flow pattern as obtained in the map may be described by two components: (i) regional part and (ii) local part of the measured surface geothermal activity. The regional part of the heat flow field in Europe is dominated on the whole by a general north-east to south-west increase of the geothermal activity, which is an obvious consequence of the tectonic evolution, the major heat flow provinces corresponding thus to the principal tectonic units. The geothermal fine structure (local part) superimposing the former is mainly controlled by local tectonics, especially by the distribution of the deep reaching fracture zones and by the hydrogeological parameters. The correlation between the heat flow pattern and the crustal structure allows some preliminary geophysical implications: (a) areas of the increased seismicity may be connected with the zones of high horizontal temperature gradient, (b) increased surface heat flow may be generally observed in the zones of weakened crustal thickness, (c) there are considerable regional variations in the calculated temperature on the Moho-discontinuity, as well as in the upper mantle heat flow contribution.  相似文献   

Zur Darstellung von Korngrössenverteilungen     

Dr. E. Walger 《International Journal of Earth Sciences》1965,54(2):976-1002

Zusammenfassung In Abschnitt 1–4 werden die allgemeinen Beziehungen zwischen Summenkurve als Stammkurve und Häufigkeitskurve als Ableitungskurve behandelt.In Abschnitt 5–7 werden die Zusammenhänge besprochen, die daraus weiter folgen, wenn die Abszissenteilung logarithmisch verstreckt wird oder wenn das Korngrößenmaß logarithmisch transformiert wird (Übersicht in Abb. 8). Es ergibt sich dabei, daß die Abszissenachse der Häufigkeitskurve in der fast allgemein üblichen Form (fälschlich: über logarithmisch geteilter Abszisse) linear nach einem relativierenden Korngrößenmaß von der Art der Phi-Grade oder Zeta-Grade geteilt werden muß!In Abschnitt 8 wird an Korngrößenverteilungen von Gesteinen gezeigt, daß durch Mißachtung der formalen Zusammenhänge Scheinprobleme entstehen, die die Lösung sachlicher Probleme zumindest erschweren.

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Sections 1 to 4 treat the general relations between the cumulative curve as primary curve and the frequency curve as derivative curve.Sections 5 to 7 deal with the interrelations following from that fact, if the abscissa scale is logarithmically deformed, or if the grain size measure is logarithmically transformed. These are two different cases to be clearly discerned (summary scheme see flg. 8). It shows up that the abscissa axis of the frequency curve, if plotted as generally usual (falsely: with logarithmical abscissa scale), consistently must be graduated according to a relativizing grain size measure of the kind of the phi-measure or the zeta-measure.Section 8 exemplifies by some grain size distributions of different rocks that neglection of these formal relationships may generate imaginary problems capable at least to render more difficult the solution of real problems.

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Résumé Les sections 1 à 4 traitent les relations généralement valables entre la courbe cumulative comme de la courbe primaire et la courbe de fréquence comme de la courbe derivée.Dans les sections 5 à 7 sont discutés les rapports resultants de ce fait si la division de l'abscisse est deformée logarithmiquement, ou si la mesure de la largeur des grains est transformée logarithmiquement. Ce sont là deux cas à differencier précisement (voir l'esquisse sommaire, flg. 8). Il se montre que l'abscisse de la courbe de fréquence, tracée conforme à l'usage généralement propagé (apellation erronée: «au-dessus de l'abscisse à l'échelle logarithmique»), est à diviser nécessairement selon d'une «mesure relativant» de la classe de l'échelle phi ou zeta.Dans la section 8 sont presentés des exemples des courbes granulométriques des roches différentes qui démontrent qu'en négligant les rapports mathématiques on crée des faux problèmes qui rendent plus difficile la solution des problèmes d'un caractère plutôt matériel.

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Der äolische Sandstrom aus der W-Sahara zur Atlantikküste     

Prof. Dr. Michael Sarnthein  Prof. Dr. Eckart Walger 《International Journal of Earth Sciences》1974,63(3):1065-1087

Fairly constant winds from N to NNE (Fig. 2) prevail at present at the Western Sahara coast. Accordingly, a relatively narrow field of barchan dunes of only 80 km width reaches the coast SE of Cape Blanc (Fig. 1). Very uniform pebble plains form their ground of advance in the study area 60 km wide and 18 km long. Height H, volume V, and distance D from the southern border of the study area were determined for 963 dunes from aerial photographs (Figs. 5 and 6). Data on the dune advance rate were estimated for the particular region byCoursin (1964). Consequently it was possible to calculate a dune sand discharge amounting to 93 000 m³/yr/80 km crossing the southern border of the study area at the time the aerial photographs were taken. Based on the areal distribution pattern of the dunes this sand flow probably might increase threefold within the next 800 years (Fig. 7). Corresponding to the dune sand-discharge Q_T a saltation sand-discharge (Q and q), 50–100 times larger, of 5,0 and 7–13 Mio m³/yr/80 km, respectively, reaches the Atlantic from the Sahara. The estimates were derived from two independant calculations: the dune advance rate and the wind data. If one compares the wind transported load from the Sahara with that of the mouths of large rivers (e. g. Niger River: 40 Mio. m³/yr) it seems only of minor importance. Because of the relatively coarse grain sizes (Md≈220μm) the wind sand supply is deposited mainly along the strand line. Consequently, remarkably wide sebkha plains are built forward and the shelf becomes unusually narrow. Several independent criteria (e. g. Fig. 7) suggest a fairly young age, close to 500 years of the recent barchan field. A different wind direction, from the NE, and a lowered sea-level might have resulted during the ice-ages in as much as 5 times larger wind load (? 25 Mio m³/yr) arriving at the shelf edge and from there flowing down to the deep sea as turbidity currents. The present wind load has a content of iron oxides of roughly 1.2 per thousand. This value increased to 3.2 per thousand in Pleistocene dune sands.  相似文献   

Über Einen Hinweis auf Asturischen Plutonismus im Rheinischen Schiefergebirge     

Dr. Eckart Schröder 《International Journal of Earth Sciences》1960,50(1):438-441

Zusammenfassung Im Devon bei Wuppertal wurden unregelmäßige Intrusivkörper eines AlbitQuarzporphyrs festgestellt, die als abgequetschte Apophysen eines granitischen Magmas von jungasturischern Alter gedeutet werden. Dieser spätorogene Plutonismus ist an den aufgefalteten subvariscischen Trog des Bergischen Landes gebunden und wird zu dem benachbarten Erzrevier des Ruhrgebietes in Beziehung gesetzt.  相似文献   

Activities of IGU Commissions and Study Groups (IGU C/SG) in connection with RC 1998     

Eckart Ehlers 《GeoJournal》1997,43(3):301-301

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The Golden meteorite fall: Fireball trajectory,orbit, and meteorite characterization     

P. G. Brown  P. J. A. McCausland  A. R. Hildebrand  L. T. J. Hanton  L. M. Eckart  H. Busemann  D. Krietsch  C. Maden  K. Welten  M. W. Caffee  M. Laubenstein  D. Vida  F. Ciceri  E. Silber  C. D. K. Herd  P. Hill  H. Devillepoix  Eleanor K. Sansom  Martin Cupák  Seamus Anderson  R. L. Flemming  A. J. Nelson  M. Mazur  D. E. Moser  W. J. Cooke  D. Hladiuk  Barbara Malečić  Maja Telišman Prtenjak  R. Nowell  The Golden Meteorite Consortium 《Meteoritics & planetary science》2023,58(12):1773-1807

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An infrared imaging search for low‐mass companions to members of the young nearby β Pic and Tucana/Horologium associations     

R. Neuhuser  E.W. Guenther  J. Alves  N. Hulamo  Th. Ott  A. Eckart 《Astronomische Nachrichten》2003,324(6):535-542

We present deep high dynamic range infrared images of young nearby stars in the Tucana/Horologium and β Pic associations, all ∼10 to 35 Myrs young and at ∼10 to 60 pc distance. Such young nearby stars are well‐suited for direct imaging searches for brown dwarf and even planetary companions, because young sub‐stellar objects are still self‐luminous due to contraction and accretion. We performed our observations at the ESO 3.5m NTT with the normal infrared imaging detector SofI and the MPE speckle camera Sharp‐I. Three arc sec north of GSC 8047‐0232 in Horologium a promising brown dwarf companion candidate is detected, which needs to be confirmed by proper motion and/or spectroscopy. Several other faint companion candidates are already rejected by second epoch imaging. Among 21 stars observed in Tucana/Horologium, there are not more than one to five brown dwarf companions outside of 75 AU (1.5″ at 50 pc); most certainly only ≤5% of the Tuc/HorA stars have brown dwarf companions (13 to 78 Jupiter masses) outside of 75 AU. For the first time, we can report an upper limit for the frequency of massive planets (∼10 M_jup) at wide separations (∼100 AU) using a meaningfull and homogeneous sample: Of 11 stars observed sufficiently deep in β Pic (12 Myrs), not more than one has a massive planet outside of ∼100 AU, i.e. massive planets at large separations are rare (≤9%). (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献