Early earthquakes of the Americas     

R. L. Kovach Niu Zhijun 《《幕》》2006,29(2):145-145

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Enhanced Activity in Close T Tauri Binaries     

Gösta Gahm 《Astrophysics and Space Science》2006,304(1-4):149-152

The number of confirmed and suspected close T Tauri binaries (period days) is increasing. We discuss some systems with enhanced emission line activity and periodic line profile changes. Non-axisymmetric flows of plasma in the region between the circumbinary disk and the stars can be generated through the influence of the secondary component. Such enhanced activity is found around binaries with eccentric as well as circular orbits. We discuss our observations of the T Tauri stars RW Aurigae A and RU Lupi, which may host very close brown dwarf companions. Model simulations indicate that non-axisymmetric flows are generated around close binaries with circumbinary disks, also in systems with circular orbits.  相似文献   

Simulation of adaptive optics for the Vacuum Tower Telescope     

Anita Enmark  Thomas Berkefeld  Oskar von der Lühe  Torben Andersen 《Experimental Astronomy》2006,21(2):87-99

A simulation model of the adaptive optics of the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife, is presented. The model uses modules from the integrated model of the Euro50 extremely large telescope, and includes submodels of a Shack-Hartmann wavefront sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier low-pass filters, a reconstructor and a controller. We investigate the impact on the closed loop bandwidth of changes in controller configuration and certain system parameters, such as low pass filter bandwidth and camera integration and readout time. Control strategies were tested on simple models before implementation on the full VTT model. Using the models, different control strategies are compared.  相似文献   

The Siberian Solar Radio Telescope: the current state of the instrument,observations, and data   总被引：2，自引：0，他引：2  

Grechnev  V.V.  Lesovoi  S.V.  Smolkov  G. Ya.  Krissinel  B.B.  Zandanov  V.G.  Altyntsev  A.T.  Kardapolova  N.N.  Sergeev  R.Y.  Uralov  A.M.  Maksimov  V.P.  Lubyshev  B.I. 《Solar physics》2003,216(1-2):239-272

The Siberian Solar Radio Telescope (SSRT) is one of the world's largest solar radio heliographs. It commenced operation in 1983, and since then has undergone several upgrades. The operating frequency of the SSRT is 5.7 GHz. Since 1992 the instrument has had the capability to make one-dimensional scans with a high time resolution of 56 ms and an angular resolution of 15 arc sec. Making one of these scans now takes 14 ms. In 1996 the capability was added to make full, two-dimensional images of the solar disk. The SSRT is now capable of obtaining images with an angular resolution of 21 arc sec every 2 min. In this paper we describe the main features and operation of the instrument, particularly emphasizing issues pertaining to the imaging process and factors limiting data quality. Some of the data processing and analysis techniques are discussed. We present examples of full-disk solar images of the quiet Sun, recorded near solar activity minimum, and images of specific structures: plages, coronal bright points, filaments and prominences, and coronal holes. We also present some observations of dynamic phenomena, such as eruptive prominences and solar flares, which illustrate the high-time-resolution observations that can be done with this instrument. We compare SSRT observations at 5.7 GHz, including computed `light curves', both morphologically and quantatively, with observations made in other spectral domains, such as 17 GHz radio images, Hα filtergrams and magnetograms, extreme-ultraviolet and X-ray observations, and dynamic radio spectra.  相似文献   

A comparison of chemical and chemodynamical models     

Joachim Köppen 《Astrophysics and Space Science》2003,284(2):837-840

Representative results from a comparison of the chemical evolution of spherical collapse models without and with a intercloud medium are presented. The hot metal-rich gas distributes quickly the metals produced in supernovae throughout the galaxy, thus leading to a more homogeneous chemical evolution and flatter metallicity gradients in the gas and the stars. The stellar population is somewhat less concentrated towards the centre. The strong outflow results in a substantial loss of metals from the galaxy to its surroundings, and a lower effective yield in the galaxy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A Quantitative Method to Optimise Magnetic Field Line Fitting of Observed Coronal Loops     

Carcedo  L.  Brown  D.S.  Hood  A.W.  Neukirch  T.  Wiegelmann  T. 《Solar physics》2003,218(1-2):29-40

Many authors use magnetic-field models to extrapolate the field in the solar corona from magnetic data in the photosphere. The accuracy of such extrapolations is usually judged qualitatively by eye, where a less judgemental quantitative approach would be more desirable. In this paper, a robust method for obtaining the best fit between a theoretical magnetic field and intensity observations of coronal loops on the solar disk will be presented. The method will be applied to Yohkoh data using a linear force-free field as an illustration. Any other theoretical model for the magnetic field can be used, provided there is enough freedom in the model to optimize the fit.  相似文献   

Structurally controlled gold and sulfosalt mineralization: the Altenberg example, Salzburg Province, Austria     

H. Putz  W.H. Paar  D. Topa  J. Horner  V. Lüders 《Mineralogy and Petrology》2003,78(1-2):111-138

Summary ?In the south-eastern Altenbergkar–Silbereck area in the eastern Tauern window (Lungau, Salzburg) structurally controlled precious-metal (Au–Ag) mineralization is hosted in marbles of the Permo(?)-Mesozoic Silbereck Formation and in the underlying Variscan Central gneiss. During the Alpine otogeny both lithologies were affected by ductile deformation (shearing, D1; folding, D2/D3) and subsequent brittle deformation (tension gashes, D4; normal faulting, D5) related to the uplift and exhumation of the Tauern window. Mineralization is controlled by brittle D4 structures. NE–SW trending steeply dipping tension gashes of the “Tauerngoldgang” type occur within the Central gneiss. Three different marble-hosted ore types following fracture systems as well as foliation and bedding planes can be distinguished: 1) metasomatic replacement ores, 2) ores in tension gashes and 3) ores in talc-bearing structures, often containing high-grade gold and silver mineralization (native gold in association with Ag–Pb–Bi–sulfosalts). Four stages of mineralization can be distinguished which occur in all ore types: arsenopyrite–pyrite–pyrrhotite (first stage), Au–(Ag–Pb–Bi–sulfosalts) (second stage), base-metal sulfides and tetrahedrite–tennantite (third stage) and Ag-rich galena (fourth stage). Preliminary fluid inclusion data indicate temperatures of ore formation well above 300 °C (346 °C mean) for the second stage within the Central gneiss and temperatures between 310 and 230 °C for the second and third stages in the marble. Received October 12, 2001; revised version accepted September 5, 2002 Published online March 10, 2003  相似文献   

Richtmyer-Meshkov Experiments on the Omega Laser     

R. M. Hueckstaedt  S. H. Batha  M. M. Balkey  N. D. Delamater  J. R. Fincke  R. L. Holmes  N. E. Lanier  G. R. Magelssen  J. M. Scott  J. M. Taccetti  C. J. Horsfield  K. W. Parker  S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259

Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids, multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared to theory and numerical simulations.  相似文献   

Energetics of a galactic fountain     

I. G. Kovalenko  Yu. A. Shchekinov 《Astrophysics》1985,23(2):578-584

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Effect of metamorphism and partial melting of host rocks on zircons     

L. N. GUPTA  W. JOHANNES 《Journal of Metamorphic Geology》1985,3(3):311-323

Abstract Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting.  相似文献