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71.
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74.
The Speckle camera of the 3.5 m Telescopio Nazionale Galileo (TNG) has been used to measure apparent sizes and shapes of a number of main belt asteroids. The average size measurements are in a generally good agreement with the results of indirect IRAS-based radiometric techniques. The measured shapes are compared with predictions based on previously derived spin axis directions and lightcurve photometry of some of the observed objects. Also in this case the agreement is reasonable and the speckle observations allow us to discriminate in some cases between the two pole solutions usually found for each object. No clear evidence of binaries was found. The results show that the TNG speckle camera can be a powerful tool to resolve relatively large main belt asteroids and to calibrate the results of the IRAS survey. 相似文献
75.
C.S. Botzler J. Snigula R. Bender N. Drory G. Feulner G.J. Hill U. Hopp C. Maraston C. Mendes de Oliveira 《Astrophysics and Space Science》2003,284(2):393-396
The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's
main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample
of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized
for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of
the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and
Voronoi-approach.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
76.
Variable surface albedo features on Mars are likely caused by the entrainment and deposition of dust by the wind. Most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface. Some of the largest variable features, here termed mesoscale linear streaks, are up to 400 km in length and repeatedly occur in one of the smoothest regions of Mars: Amazonis Planitia. Their orientations and apparent season of variability as observed by Viking and Mars Orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms. They provide an example of the ability of large-scale winds, without significant local enhancement, to initiate dust motion on Mars. The sizes and spacing of the linear streaks may be controlled by boundary layer rolls. The repetitive formation of these streaks, over a span of more than 11 Mars years, gives one measure of the stability of Mars’ eolian processes. 相似文献
77.
The frequent use of soils and earth materials for hydraulic capping and for geo‐environmental waste containment motivated our interest in detailed modelling of changes in size and shape of macro‐pores to establish links between soil mechanical behaviour and concurrent changes in hydraulic and transport properties. The objective of this study was to use finite element analysis (FEA) to test and extend previous analytical solutions proposed by the authors describing deformation of a single macro‐pore embedded in linear viscoplastic soil material subjected to anisotropic remote stress. The FEA enables to consider more complex pore geometries and provides a detailed picture of matrix yield behaviour to explain shortcomings of approximate analytical solutions. Finite element and analytical calculations agreed very well for linear viscous as well as for viscoplastic materials, only limited for the case of isotropic remote stress due to the simplifications of the analytical model related to patterns and onset of matrix‐yielding behaviour. FEA calculations were compared with experimental data obtained from a compaction experiment in which pore deformation within a uniform modelling clay sample was monitored using CAT scanning. FEA predictions based on independently measured material properties and initial pore geometry provided an excellent match with experimentally determined evolution of pore size and shape hence lending credence to the potential use of FEA for more complex pore geometries and eventually connect macro‐pore deformation with hydraulic properties. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
78.
Harold C. CONNOLLY D. S. BURNETT Kevin D. McKEEGAN 《Meteoritics & planetary science》2003,38(2):197-224
Abstract— Minor element variations in MgAl2O4 spinel from the type B1 calcium‐aluminum‐rich inclusion (CAI) Allende TS‐34 confirm earlier studies in showing correlations between the minor element chemistry of spinels with their location within the inclusion and with the chemistry of host silicate phases. These correlations result from a combination of crystallization of a liquid produced by re‐melting event(s) and local re‐equilibration during subsolidus reheating. The correlation of the Ti and V in spinel inclusions with the Ti and V in the adjacent host clinopyroxene can be qualitatively explained by spinel and clinopyroxene crystallization prior to melilite, following a partial melting event. There are, however, difficulties in quantitative modeling of the observed trends, and it is easier to explain the Ti correlation in terms of complete re‐equilibration. The correlation of V in spinel inclusions with that in the adjacent host clinopyroxene also cannot be quantitatively modeled by fractional crystallization of the liquid produced by re‐melting, but it can be explained by partial re‐equilibration. The distinct V and Ti concentrations in spinel inclusions in melilite from the edge regions of the CAI are best explained as being affected by only a minor degree of re‐equilibration. The center melilites and included spinels formed during crystallization of the liquid produced by re‐melting, while the edge melilites and included spinels are primary. The oxygen isotope compositions of TS‐34 spinels are uniformly 16O‐rich, regardless of the host silicate phase or its location within the inclusion. Similar to other type B1 CAIs, clinopyroxene is 16O‐rich, but melilite is relatively 16O‐poor. These data require that the oxygen isotope exchange in TS‐34 melilite occurred subsequent to the last re‐melting event. 相似文献
79.
Andrew Mennim Richard A. Battye Carsten van de Bruck 《Astrophysics and Space Science》2003,283(4):633-638
We discuss the problems faced in trying to deduce the evolution of cosmological perturbations in brane-world models. There
are two natural ways to formulate the problem: one which makes the equations of motion simple and the other which makes the
boundary condition simple. Unfortunately the problem is difficult to solve, even numerically, in either formalism. We present
a more phenomenological approach which, while it does not solve the problem for any given model, illustrates some generic
features one might expect to see in the tensor part of the cosmic microwave background power spectrum. We find that the observed
scale invariance of the cosmic microwave background provides bounds on brane world models.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
D. H. Lumb A. Finoguenov R. Saxton B. Aschenbach P. Gondoin M. Kirsch I. M. Stewart 《Experimental Astronomy》2003,15(2):89-111
We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09
and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described.
We show the spatial and energy dependences of measured vignetting, outlining assumptions made in deriving the eventual agreement
between simulation and measurement. Alternate methods to confirm these are described, including an assessment of source elongation
with off-axis angle, the surface brightness distribution of the diffuse X-ray background, and the consistency of Coma cluster
emission at different position angles. A synthesis of these measurements leads to a change in the XMM calibration data base,
for the optical axis of two of the three telescopes, by in excess of 1 arcmin. This has a small but measureable effect on
the assumed spectral responses of the cameras for on-axis targets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献