The morphology of galactic rings exterior to evolving bars: test-particle simulations     

Micaela Bagley  Ivan Minchev  Alice C. Quillen 《Monthly notices of the Royal Astronomical Society》2009,395(1):537-553

The morphology of the outer rings of early-type spiral galaxies is compared to integrations of massless collisionless particles initially in nearly circular orbits. Particles are perturbed by a quadrupolar gravitational potential corresponding to a growing and secularly evolving bar. We find that outer rings with R1R2 morphology and pseudo-rings are exhibited by the simulations even though they lack gaseous dissipation. Simulations with stronger bars form pseudo-rings earlier and more quickly than those with weaker bars. We find that the R1 ring, perpendicular to the bar, is fragile and dissolves after a few bar rotation periods if the bar pattern speed increases by more than ∼8 per cent, bar strength increases (by ≳140 per cent) after bar growth or the bar is too strong  ( Q_T > 0.3)  . If the bar slows down after formation, pseudo-ring morphology persists and the R2 ring perpendicular to the bar is populated due to resonance capture. The R2 ring remains misaligned with the bar and increases in ellipticity as the bar slows down. The R2 ring becomes scalloped and does not resemble any ringed galaxies if the bar slows down more than 3.5 per cent suggesting that bars decrease in strength before they slow down this much. We compare the morphology of our simulations to B -band images of nine ringed galaxies from the Ohio State University Bright Spiral Galaxy Survey, and we find a reasonable match in morphologies to R1R2' pseudo-rings seen within a few bar rotation periods of bar formation. Some of the features previously interpreted in terms of dissipative models may be due to transient structure associated with recent bar growth and evolution.  相似文献   

The mass–metallicity relation in galaxy clusters: the relative importance of cluster membership versus local environment     

Sara L. Ellison  Luc Simard  Nicolas B. Cowan  Ivan K. Baldry  David R. Patton  Alan W. McConnachie 《Monthly notices of the Royal Astronomical Society》2009,396(3):1257-1272

Using a large (14 857), homogenously selected sample of cluster galaxies identified in the Sloan Digital Sky Survey Data Release 4, we investigate the impact of cluster membership and local density on the stellar mass–gas phase metallicity relation (MZR). We show that stellar metallicities are not suitable for this work, being relatively insensitive to subtle changes in the MZR. Accurate nebular abundances can be obtained for 1318 cluster galaxies in our sample and we show that these galaxies are drawn from clusters that are fully representative of the parent sample in terms of mass, size, velocity dispersion and richness. By comparing the MZR of the cluster galaxies with a sample of control galaxies matched in mass, redshift, fibre covering fraction and rest-frame   g − r   colour cluster galaxies are found to have, on average, higher metallicities by up to 0.04 dex. The magnitude of this offset does not depend strongly on galactic half-light radius or cluster properties such as velocity dispersion or cluster mass. The effect of local density on the MZR is investigated, using the presence of a near neighbour and both two- and three-dimensional density estimators. For all three metrics, it is found that the cluster galaxies in locally rich environments have higher median metallicities by up to ∼0.05 dex than those in locally poor environments (or without a near neighbour). Control (non-cluster) galaxies at locally high densities exhibit similar metal enhancements. Taken together, these results show that galaxies in clusters are, on average, slightly more metal rich than the field, but that this effect is driven by local overdensity and not simply cluster membership.  相似文献   

Dynamical state of superclusters of galaxies: do superclusters expand or have they started to collapse?     

Mirt Gramann  Ivan Suhhonenko 《Monthly notices of the Royal Astronomical Society》2002,337(4):1417-1425

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Late Wuchiapingian (Late Dzhulfian,early Late Permian) limestone olistolites within the Tertiary flysch of Glypia Unit (Mount Parnon,central–eastern Peloponnesus,Greece)     

Emmanuel Skourtsos  Daniel Vachard  Alexandra Zambetakis-Lekkas  Rossana Martini  Louisette Zaninetti 《Comptes Rendus Geoscience》2002,334(12):925-931

Some olistolites reworked in a Tertiary flysch of Mount Parnon (Peloponnesus, Greece) exhibit a Late Permian assemblage, dominated by Paradunbarula (Shindella) shindensis, Hemigordiopsis cf. luquensis and Colaniella aff. minima. This association corresponds to the Late Wuchiapingian (=Late Dzhulfian), a substage whose algae and foraminifera are generally little known. Contemporaneous limestones crop out in the middle part of the Episkopi Formation in Hydra, but they are rather commonly reworked in Mesozoic and Cainozoic sequences. The palaeobiogeographical affinities shared by the foraminiferal markers of Greece, southeastern Pamir, and southern China, are very strong (up to the specific level), and are congruent with the Pangea B reconstructions. To cite this article: E. Skourtsos et al., C. R. Geoscience 334 (2002) 925–931.  相似文献   

Mortar Upscaling for Multiphase Flow in Porous Media   总被引：1，自引：0，他引：1  

Małgorzata Peszyńska  Mary F. Wheeler  Ivan Yotov 《Computational Geosciences》2002,6(1):73-100

In mortar space upscaling methods, a reservoir is decomposed into a series of subdomains (blocks) in which independently constructed numerical grids and possibly different physical models and discretization techniques can be employed in each block. Physically meaningful matching conditions are imposed on block interfaces in a numerically stable and accurate way using mortar finite element spaces. Coarse mortar grids and fine subdomain grids provide two-scale approximations. In the resulting effective solution flow is computed in subdomains on the fine scale while fluxes are matched on the coarse scale. In addition the flexibility to vary adaptively the number of interface degrees of freedom leads to more accurate multiscale approximations. This methodology has been implemented in the Center for Subsurface Modeling's multiphysics multiblock simulator IPARS (Integrated Parallel Accurate reservoir Simulator). Computational experiments demonstrate that this approach is scalable in parallel and it can be applied to non-matching grids across the interface, multinumerics and multiphysics models, and mortar adaptivity. Moreover unlike most upscaling approaches the underlying systems can be treated fully implicitly.  相似文献   

Water quality model of the Danube in its Bulgarian part     

Ivan Diadovski  Veska Kazantzeva 《Aquatic Sciences - Research Across Boundaries》1996,58(3):269-279

Models for predicting river water quality could assist protection and utilization of water resources under alternative management strategies. The model of the water quality characteristics of the Danube is based on an ecosystem approach. Considered are all waste water discharges and inflow of tributaries among the catchment area. The identification of model parameters is realized according to the method of integral transformation. For the performance of the model a computer program was elaborated. It is applied in predicting the water quality of the Danube considering almost 20 indicators for the abiotic and biotic parameters of river ecosystem.  相似文献   

Upper Triassic shallow water limestones in the Sinta Ridge (Banda Sea,Indonesia)     

M. Villeneuve  J. -J. Cornee  R. Martini  L. Zaninetti  J. -P. Rehault  S. Burhanudin  J. Malod 《Geo-Marine Letters》1994,14(1):29-35

Ten rock samples were dredged during the Banda Sea I cruise in the northern slope of the Sinta Ridge, which separates the North and South Banda basins. Some of the samples are limestones from a very shallow marine environment, with Upper Norian (to Rhaetian?) benthic Foraminifera. Similarities with eastern Sulawesi, Buru and Seram are consistent with an independant Upper Triassic block and the origin of the Banda Sea microcontinents is questionable.  相似文献   

Hyperboloidal precession of a dynamically symmetric satellite. Construction of normal forms of the Hamiltonian     

Ivan I. Shevchenko  Andrej G. Sokolsky 《Celestial Mechanics and Dynamical Astronomy》1995,62(4):289-304

The Norma specialized program package, intended for normalization of autonomous Hamiltonian systems by means of computer algebra, is used in studies of small-amplitude periodic motions in the neighbourhood of regular precessions of a dynamically symmetric satellite on a circular orbit. The case of hyperboloidal precession is considered. Analytical expressions for normal forms and generating functions depending on frequencies of the system as on parameters are derived. Possible resonances are considered in particular. The 6th order of normalization is achieved. Though the intermediate analytical expressions occupy megabytes of computer's main memory, final ones are quite compact. Obtained analytical expressions are applied to the analysis of stability of small-amplitude periodic motions in the neighbourhood of hyperboloidal precession.  相似文献   

On verification of the asymptotic model of the first kind     

Ivan I. Shevchenko 《Astrophysics and Space Science》1993,202(1):45-56

For the case of closed Friedmann models with the cosmological constant, an N - dependence is plotted, whereN is the conformal time of existence of the Universe, and is the ratio of the cosmological constant to its Einstein's value. The observational properties of the asymptotic model of the first kind (the so-called Al model) corresponding to the maximum of this dependence are analyzed. For the matter-dominated models, the maximum is achieved at the point = 1. Formulae for the calculation of the age of the Universe and for that of the photometric distance in the Al model are deduced. The observational properties of the A1 model are compared to the corresponding properties of the standard cosmological model ( = 0) which does not occupy any special distinguished position on the N - diagram. It is shown that from the standpoint of the modern observational cosmology these two models cannot be told one from another. However, the A1 model has better standing from the viewpoint of the strong wordings of the anthropic cosmological principle.  相似文献   

Computation of additional components of the first-order ray approximation in isotropic media     

Leo Eisner  Ivan Pšenčík 《Pure and Applied Geophysics》1996,148(1-2):227-253

This study shows that the use of the first-order additional components of the ray method in the seismic wave field modeling is easy and that it can bring a substantial improvement of the standard ray results obtained with the zero-order ray approximation only. For the calculation of a first-order additional component, spatial derivatives of the parameters of the medium and spatial derivatives of the zero-order ray amplitude term are necessary. The evaluation of the former derivatives is straightforward; the latter derivatives can be calculated approximately from neighboring rays by substituting the derivatives by finite differences. This allows an effective calculation of the first-order additional terms in arbitrary laterally varying layered media.The importance of the first-order additional terms is demonstrated by the study of individual higher-order terms of the ray series representing elementaryP andS elastodynamic Green functions for a homogeneous isotropic medium. The study shows clearly that the consideration of the first-order additional terms leads to a more substantial decrease of the difference between approximate and exact elementary Green functions than any other higher-order term. With this in mind, effects of the first-order additional terms on the ray synthetic seismograms for aVSP configuration are studied. It is shown that the use of the additional terms leads to such phenomena, unknown in the zero-order approximation of the ray method, like quasi-elliptical and transverse polarization of a singleP wave or longitudinal polarization of a singleS wave.  相似文献