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121.
Giuseppe Gambolati Massimiliano Ferronato Pietro Teatini Roberto Deidda Giuditta Lecca 《国际地质力学数值与分析法杂志》2001,25(4):307-327
The solution of the poroelastic equations for predicting land subsidence above productive gas/oil fields may be addressed by the principle of virtual works using either the effective intergranular stress, with the pore pressure gradient regarded as a distributed body force, or the total stress incorporating the pore pressure. In the finite element (FE) method both approaches prove equivalent at the global assembled level. However, at the element level apparently the equivalence does not hold, and the strength source related to the pore pressure seems to generate different local forces on the element nodes. The two formulations are briefly reviewed and discussed for triangular and tetrahedral finite elements. They are shown to yield different results at the global level as well in a three‐dimensional axisymmetric porous medium if the FE integration is performed using the average element‐wise radius. A modification to both formulations is suggested which allows to correctly solve the problem of a finite reservoir with an infinite pressure gradient, i.e. with a pore pressure discontinuity on its boundary. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
122.
Michael B. Pracy Warrick J. Couch Chris Blake Kenji Bekki Craig Harrison Matthew Colless Harald Kuntschner Roberto de Propris 《Monthly notices of the Royal Astronomical Society》2005,359(4):1421-1432
We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the z = 0.32 rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O ii ]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive . By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment. 相似文献
123.
124.
William S. Burgett Michael M. Vick David S. Davis Matthew Colless Roberto De Propris Ivan Baldry Carlton Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Nicholas Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654
125.
Roberto Gilmozzi 《Experimental Astronomy》2005,19(1-3):5-13
The second decade of the third millennium will hopefully see a new generation of extremely large telescopes. These will have diameters from 30 to 100 meters and use advanced adaptive optics to operate at the diffraction limit in order to detect astronomical objects that are impossible to observe today, such as earth-like planets around nearby stars and the earliest objects in the Universe. Even for small fields of view, the requirements for detectors are daunting, with sizes of several gigapixels, very fast readout times and extremely low readout noise. In this paper I briefly review the science case for ELTs and the requirements they set on telescopes and instruments, and report on the status of the OWL 100 m telescope project and the challenges it poses. 相似文献
126.
Daniel Rosa-González Denis Burgarella Kirpal Nandra Daniel Kunth Elena Terlevich † Roberto Terlevich † 《Monthly notices of the Royal Astronomical Society》2007,379(1):357-369
We have combined multiwavelength observations of a selected sample of star-forming galaxies with galaxy evolution models in order to compare the results obtained for different star formation rate (SFR) tracers and to study the effect that the evolution of the star-forming regions has on them. We also aimed at obtaining a better understanding of the corrections due to extinction and nuclear activity on the derivation of the SFR. We selected the sample from Chandra data for the well studied region Chandra Deep Field -South (CDFS) and chose the objects that also have ultraviolet (UV) and infrared (IR) data from Galaxy Evolution Explorer ( GALEX ) and Great Observatories Origins Deep Survey (GOODS) Spitzer , respectively.
Our main finding is that there is good agreement between the extinction corrected SFR(UV) and the SFR(X), and we confirm the use of X-ray luminosities as a trustful tracer of recent star formation activity. Nevertheless, at SFR(UV) larger than about 5 M⊙ yr−1 there are several galaxies with an excess of SFR(X) suggesting the presence of an obscured active galactic nucleus (AGN) not detected in the optical spectra. We conclude that the IR luminosity is driven by recent star formation even in those galaxies where the SFR(X) is an order of magnitude higher than the SFR(UV) and therefore may harbour an AGN. One object shows SFR(X) much lower than expected based on the SFR(UV); this SFR(X) 'deficit' may be due to an early transient phase before most of the massive X-ray binaries were formed. An X-ray deficit could be used to select extremely young bursts in an early phase just after the explosion of the first supernovae associated with massive stars and before the onset of massive X-ray binaries. 相似文献
Our main finding is that there is good agreement between the extinction corrected SFR(UV) and the SFR(X), and we confirm the use of X-ray luminosities as a trustful tracer of recent star formation activity. Nevertheless, at SFR(UV) larger than about 5 M
127.
Niranjan Thatte Reinhard Genzel Harald Kroker Alfred Krabbe Lowell E. Tacconi-Garman Roberto Maiolino Matthias Tecza 《Astrophysics and Space Science》1997,248(1-2):225-234
We present new near-infrared integral field spectroscopy and adaptive optics imaging of the nucleus of NGC 1068. Using the
stellar CO absorption features in the H and K bands, we have identified a moderately extincted stellar core centered on the
nuclear position and of intrinsic size ~50 pc. We show that this nuclear stellar core is probably 5-16 × 108 years in age
and contributes at least 7% of the total nuclear luminosity of ~1 × 1011 L⊙.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
128.
129.
Alessandro Marconi Roberto Maiolino Romain G. Petrov 《Astrophysics and Space Science》2003,286(1-2):245-254
Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic
Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with
speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic
objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific
cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
130.