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51.
We present N -body simulations of dissolving star clusters close to Galactic Centres. For this purpose, we developed a new N -body program called nbody6gc based on Aarseth's series of N -body codes. We describe the algorithm in detail. We report about the density wave phenomenon in the tidal arms which has been recently explained by Küpper, Macleod & Heggie. Standing waves develop in the tidal arms. The wave knots or clumps develop at the position, where the emerging tidal arm hits the potential wall of the effective potential and is reflected. The escaping stars move through the wave knots further into the tidal arms. We show the consistency of the positions of the wave knots with the theory in Just et al. We also demonstrate a simple method to study the properties of tidal arms. By solving many eigenvalue problems along the tidal arms, we numerically construct a one-dimensional coordinate system whose direction is always along a principal axis of the local tensor of inertia. Along this coordinate system, physical quantities can be evaluated. The half-mass or dissolution times of our models are almost independent of the particle number which indicates that two-body relaxation is not the dominant mechanism leading to the dissolution. This may be a typical situation for many young star clusters. We propose a classification scheme which sheds light on the dissolution mechanism. 相似文献
52.
Ernst Cloos 《International Journal of Earth Sciences》1953,41(1):145-160
Zusammenfassung Die Appalachen sind etwa 300 km breit, wovon etwa die Hälfte bedeckt und nur geophysikaisch oder aus Tiefbohrungen bekannt ist. Von den erreichbaren 150 km zwischen Baltimore und der Allegheny-Front gehört etwa die Hälfte in das Gebiet der Tektonite. Die andere Hälfte ist fast symmetrisch, etwa nach Art des Jura gefaltet, jedoch viel weniger stark zusammengeschoben.An der Südostgrenze des noch sichtbaren Kristallins herrscht Tektonik mit vertikaler oder südöstlicher Komponente vor. Nach Westen folgt ein Gebiet mit ausgesprochen nordwestlichem Vorwärtsfließen sämtlicher Elemente, und westlich der Tektonitfront ist die Faltung mehr oder weniger symmetrisch und seicht.Metamorphose nimmt bis zur Tektonitfront allmählich ab, dann aber bleiben sich Faltungsintensität, Metamorphose und die tektonischen Richtungen im wesentlichen gleich.Am Ostende des oben beschriebenen Profils liegt die Johns Hopkins University, und auf dem gleichen Profil kann man 12 Stunden mit der Eisenbahn reisen bis zur nächsten Universität. In Deutschland liegen auf der vergleichbaren Strecke quer zum Streichen zwischen Konstanz und der Rheinmündung 10 Hochschulen 1. Klasse. Der Vergleich könnte weitergeführt werden und würde erklären, warum hierzulande noch so viele und große Lücken in unserer geologischen Kenntnis bestehen. 相似文献
53.
Ernst Nowack 《International Journal of Earth Sciences》1940,31(3-4):294-296
Ohne Zusammenfassung 相似文献
54.
55.
Ohne Zusammenfassung 相似文献
56.
Ernst Nowak 《International Journal of Earth Sciences》1921,12(1-2):35-51
Ohne Zusammenfassung 相似文献
57.
Mark E. Perry Daniel S. Kahan Olivier S. Barnouin Carolyn M. Ernst Sean C. Solomon Maria T. Zuber David E. Smith Roger J. Phillips Dipak K. Srinivasan Jürgen Oberst Sami W. Asmar 《Planetary and Space Science》2011,59(15):1925-1931
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft completed three flybys of Mercury in 2008–2009. During the first and third of those flybys, MESSENGER passed behind the planet from the perspective of Earth, occulting the radio-frequency (RF) transmissions. The occultation start and end times, recovered with 0.1 s accuracy or better by fitting edge-diffraction patterns to the RF power history, are used to estimate Mercury's radius at the tangent point of the RF path. To relate the measured radius to the planet shape, we evaluate local topography using images to identify the high-elevation feature that defines the RF path or using altimeter data to quantify surface roughness. Radius measurements are accurate to 150 m, and uncertainty in the average radius of the surrounding terrain, after adjustments are made from the local high at the tangent point of the RF path, is 350 m. The results are consistent with Mercury's equatorial shape as inferred from observations by the Mercury Laser Altimeter and ground-based radar. The three independent estimates of radius from occultation events collectively yield a mean radius for Mercury of 2439.2±0.5 km. 相似文献
58.
This study focuses on the compound pahoehoe lava flow fields of the 2000 eruption on Mount Cameroon volcano, West Africa and it comprehensively documents their morphology. The 2000 eruption of Mount Cameroon took place at three different sites (sites 1, 2 and 3), on the southwest flank and near the summit that built three different lava flow fields. These lava flow fields were formed during a long‐duration (28th May–mid September) summit and flank eruption involving predominantly pahoehoe flows (sites 2 and 3) and aa flows (site 1). Field observations of flows from a total of four cross‐sections made at the proximal end, midway and at the flow front, have been supplemented with data from satellite imagery (SRTM DEM, Landsat TM and ETM+) and are used to offer some clues into their emplacement. Detailed mapping of these lava flows revealed that site 1 flows were typically channel‐fed simple aa flows that evolved as a single flow unit, while sites 2 and 3 lava flow fields were fed by master tubes within fissures producing principally tube‐fed compound pahoehoe flows. Sites 2 and 3 flows issued from ∼ 33 ephemeral vents along four NE–SW‐trending faults/fissures. Pahoehoe morphologies at sites 2 and 3 include smooth, folded and channelled lobes emplaced via a continuum of different mechanisms with the principal mechanism being inflation. The dominant structural features observed on these flow fields included: fissures/faults, vents, levees, channels, tubes and pressure ridges. Other structural features present were pahoehoe toes/lobes, breakouts and squeeze‐ups. Slabby pahoehoe resulting from slab‐crusted lava was the transitionary lava type from pahoehoe to aa observed at all the sites. Transition zones correspond to slopes of > 10°. Variations in flow morphology and textures across profiles and downstream were repetitive, suggesting a cyclical nature for the responsible processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
59.
Ernst W. Schwiderski 《Marine Geodesy》2013,36(3-4):219-265
Abstract In this paper the author presents the NSWC ocean tide model of the semidiurnal principal lunar (M2) tide in an atlas of ocean tidal charts and maps. The model is the computer result of a unique combination of mathematical and empirical techniques, which was introduced, extensively tested, and evaluated by Schwiderski (1978a, 1980a, b, 1983e). The computed M2 amplitudes and phases are tabulated along with all specially labeled empirical input data on a 1° × 1 ° grid system in 42° × 71° overlapping charts covering the whole oceanic globe. Corresponding global and arctic corange and cotidal maps are included to provide a quick overview of the major tidal phenomena. Significant qualitative and quantitative features are explained and discussed for proper application. In particular, the charted harmonic constants may be used to compute instantaneous M2 ocean tides with an accuracy of better than 5 cm any time and anywhere in the open oceans. Limitations of this accuracy in coastal waters and border seas are mentioned. The following four sections of this paper deal with brief reviews, detailed evaluations, and simple improvements of general and special applications of the NSWC ocean tide model. In spite of the numerous and diverse applications with potential possibilities of erroneous interpretations, the results are gratifying without exceptions. For instance, it is concluded that the computed low‐degree spherical harmonic coefficients of the M2 ocean tide model agree with recent empirical satellite solutions as closely as one could wish for within the elaborated nonmodel error bounds. Detailed computations of all significant tidal energy terms produced the following noteworthy results: The rate of supplied tidal energy of 3.50Z1012 Watt matches Cartwright's (1977) estimate of 3.5Z1012 Watt. The rate of energy loss by bottom friction and displacement over the shelves is 1.50Z1012 Watt, which fits into Miller's (1966) estimated range of (1.4–1.7)Z1012 Watt, with a clear bias toward his preferred lower bound. Perhaps most remarkably, the computed range (0.41–0.60)Z1012 Watt for the rate of deep bottom friction work done by the unresolved fluctuating (internal or baroclinic) currents contains in its center Munk's (1966) estimate of 0.5Z1012 Watt and lies safely below Wunsch's (1975) extreme upper bound of 0.7Z1012 Watt, which both authors derived for the rate of energy needed to sustain the internal tidal circulations. As is commonly believed, the results substantiate the fact that the total rate of ocean eddy dissipation (into heat) by the averaged (surface or barotropic) currents and their fluctuating comotions is negligible within three significant figures. Finally, the total tidal energy budget of the oceans is perfectly balanced in realistic terms. Budget deficits in earlier tide models were traced to the following tacit assumptions: The ocean bottom tide is doing positive work on the oceans against the ocean tide. In fact, the bottom displacement work by the ocean tide against the bottom tide is an energy loss at the rate of 1.64Z1012 Watt. The transfer of G. I. Taylor's quadratic bottom friction term from the Irish Sea to the global oceans without accounting for major differences in area resolution scales is directly responsible for significant budget deficits in semiempirical estimates. In contrast, the hydrodynamically more consistent and realistic linear law of bottom friction encountered no serious transplantation difficulties. 相似文献
60.
Aleksandre Kandilarov Rolf Mjelde Rolf-Birger Pedersen Bjarte Hellevang Cord Papenberg Carl-Joerg Petersen Lars Planert Ernst Flueh 《Marine Geophysical Researches》2012,33(1):55-76
The Jan Mayen microcontinent was as a result of two major North Atlantic evolutionary cornerstones—the separation of Greenland
from Norway (~54 Ma), accompanied by voluminous volcanic activity, and the jump of spreading from the Aegir to the Kolbeinsey
ridge (~33 Ma), which resulted in the separation of the microcontinent itself from Eastern Greenland (~24 Ma). The resulting
eastern and western sides of the Jan Mayen microcontinent are respectively volcanic and non-volcanic rifted margins. Until
now the northern boundary of the microcontinent was not precisely known. In order to locate this boundary, two combined refraction
and reflection seismic profiles were acquired in 2006: one trending S–N and consisting of two separate segments south and
north of the island of Jan Mayen respectively, and the second one trending SW–NE east of the island. Crustal P-wave velocity
models were derived and constrained using gravity data collected during the same expedition. North of the West Jan Mayen Fracture
Zone (WJMFZ) the models show oceanic crust that thickens from west to east. This thickening is explained by an increase in
volcanic activity expressed as a bathymetric high and most likely related to the proximity of the Mohn ridge. East of the
island and south of the WJMFZ, oceanic Layers 2 and 3 have normal seismic velocities but above normal average crustal thickness
(~11 km). The similarity of the crustal thickness and seismic velocities to those observed on the conjugate M?re margin confirm
the volcanic origin of the eastern side of the microcontinent. Thick continental crust is observed in the southern parts of
both profiles. The northern boundary of the microcontinent is a continuation of the northern lineament of the East Jan Mayen
Fracture Zone. It is thus located farther north than previously assumed. The crust in the middle parts of both models, around
Jan Mayen island, is more enigmatic as the data suggest two possible interpretations—Icelandic type of oceanic crust or thinned
and heavily intruded continental crust. We prefer the first interpretation but the latter cannot be completely ruled out.
We infer that the volcanism on Jan Mayen is related to the Icelandic plume. 相似文献