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341.
The finite‐element formulation and integration algorithms developed in Part I are used to analyse a number of practical problems involving unsaturated and saturated soils. The formulation and algorithms perform well for all the cases analysed, with the robustness of the latter being largely insensitive to user‐defined parameters such as the number of coarse time steps and error control tolerances. The efficiency of the algorithms, as measured by the CPU time consumed, does not depend on the number of coarse time steps, but may be influenced by the error control tolerances. Based on the analyses presented here, typical values for the error control tolerances are suggested. It is also shown that the constitutive modelling framework presented in Part I can, by adjusting one constitutive equation and one or two material parameters, be used to simulate soils that expand or collapse upon wetting. Treating the suction as a strain variable instead of a stress variable proves to be an efficient and robust way of solving suction‐dependent plastic yielding. Moreover, the concept of the constitutive stress is a particularly convenient way of handling the transition between saturation and unsaturation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
342.
343.
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
344.
LOVISA ZILLÉN IAN SNOWBALL PER SANDGREN TANIA STANTON 《Boreas: An International Journal of Quaternary Research》2003,32(4):612-626
Varved lake sediments can be used to set multiple environmental proxies within a calendar year time scale. We undertook a systematic survey of lakes in the Province of Värmland, west central Sweden, with the aim of finding continuous varved lake sediment sequences covering the majority of the Holocene. In Fennoscandia, such sediments have previously only been recorded in northern Sweden and in southern and central Finland. By following a selective process and fieldwork we discovered three new varved sites (i.e. Furskogstjärnet, Mötterudstjärnet and Kälksjön). We found that lakes with varved sediments have several common lake morphometry properties and lake catchment characteristics such as maximum water depth, maximum water depth/lake surface area ratio, catchment soil types, altitude and number of inflows. Varve chronologies, supported by AMS-14 C dating and tephrochronology were established for two of the sediment profiles. These varve chronologies are the longest geological records with an annual resolution known to exist in Sweden. In Furskogstjärnet, the AMS- 14 C dates based on terrestrial plant macrofossils at several levels deviate significantly from the varve based time-depth curve. In Motterudstjarnet, a fully reasonable time-depth model based on the 14 C dates gives older ages in the lower part of the sequence compared to the varve chronology. These results highlight that seemingly acceptable AMS radiocarbon dates may be erroneous. They also point to the fact that varved lake sediments are reliable geological archives with respect to chronological control and accuracy. Thus, these archives should be of prime interest for studies of climate and environmental change undertaken with the aim of providing sub-decadal resolution proxy data sets. 相似文献
345.
346.
O. Tamuz T. Mazeh S. Zucker † 《Monthly notices of the Royal Astronomical Society》2005,356(4):1466-1470
We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular. 相似文献
347.
N. Ivanova K. Belczynski J. M. Fregeau F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584
We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past. 相似文献
348.
We use the observed polarization properties of a sample of 26 powerful radio galaxies and radio-loud quasars to constrain the conditions in the Faraday screens local to the sources. We adopt the cosmological redshift, low-frequency radio luminosity and physical size of the large-scale radio structures as our 'fundamental' parameters. We find no correlation of the radio spectral index with any of the fundamental parameters. The observed rotation measure is also independent of these parameters, suggesting that most of the Faraday rotation occurs in the Galactic foreground. The difference between the rotation measures of the two lobes of an individual source, as well as the dispersion of the rotation measure, shows significant correlations with the source redshift, but not with the radio luminosity or source size. This is evidence that the small-scale structure observed in the rotation measure is caused by a Faraday screen local to the sources. The observed asymmetries between the lobes of our sources show no significant trends with each other or other source properties. Finally, we show that the commonly used model for the depolarization of synchrotron radio emission by foreground Faraday screens is inconsistent with our observations. We apply alternative models to our data and show that they require a strong increase of the dispersion of the rotation measure inside the Faraday screens with cosmological redshift. Correcting our observations with these models for redshift effects, we find a strong correlation of the depolarization measure with redshift and a significantly weaker correlation with radio luminosity. We do not find any (anti-)correlation of depolarization measure with source size. All our results are consistent with a decrease in the order of the magnetic field structure of the Faraday screen local to the sources for increasing cosmological redshift. 相似文献
349.
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
350.