Centrifuge model tests on sand specimen under extensional load     

H. Wolf  D. Knig  Th. Triantafyllidis 《国际地质力学数值与分析法杂志》2005,29(1):25-47

The appearance of shear banding in granular materials has been investigated intensively during the last decades and is still of ongoing importance in terms of understanding the stress–strain behaviour of the material, the localization phenomena and the interaction between soil and structure. Only less attention has been paid to the occurrence of systems of shear bands although such systems can be identified in geotechnical structures as well as in geological formations. In this paper we present results of experiments on sand specimens under extensional load in natural gravity as well as in increased gravity in the centrifuge where the influence of the stress level on the geometry of a shear band pattern, specified by the spacing of the shear bands and the angle between failure surfaces and minor stress direction, has been investigated. X‐ray technique has been used to visualize the failure zones inside the specimen, an optical measurement system called Digital Image Correlation has been applied to identify and observe the appearing deformation mechanism on the sides of the specimens in natural gravity as well as during the flight in the centrifuge. It can be shown that the geometry of the shear band pattern is sparsely influenced by the change of the stress level. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The influence of the brightness of the asteroidal dust bands on the gegenschein     

Tadashi Mukai  Masanori Fujino  Ryosuke Nakamura  Fumihiko Usui 《Icarus》2003,162(2):337-343

The position and shape of the Gegenschein’s maximum brightness provide information on the structure of the interplanetary dust cloud. We show that the asteroidal dust bands, extended near the anti-solar point, play an important role in determining both the position of the maximum brightness and the shape of the Gegenschein. After removing the asteroidal dust bands from an observation of the Gegenschein on November 2, 1997, it was found that the maximum brightness point shifted −0.4° in ecliptic latitude, i.e., to the south of the ecliptic plane, at an ecliptic longitude of 180°, in contrast to a latitude value of +0.1° when the dust bands were included. Furthermore, the part of the Gegenschein to the south of the ecliptic plane was brighter than the northern part at the time of observation. Referring to the cloud model of T. Kelsall et al. (1998, Astrophy. J. 508, 44-73), it can be estimated that the ascending node of the symmetry plane of the dust cloud is 57°^−3°_+7° when its inclination is 2.03° ? 0.50°.  相似文献   

A new exact method for line radiative transfer   总被引：1，自引：0，他引：1  

Moshe Elitzur  Andrés Asensio Ramos 《Monthly notices of the Royal Astronomical Society》2006,365(3):779-791

We present a new method, the coupled escape probability (CEP), for exact calculation of line emission from multi-level systems, solving only algebraic equations for the level populations. The CEP formulation of the classical two-level problem is a set of linear equations , and we uncover an exact analytic expression for the emission from two-level optically thick sources that holds as long as they are in the 'effectively thin' regime. In a comparative study of a number of standard problems, the CEP method outperformed the leading line transfer methods by substantial margins.
The algebraic equations employed by our new method are already incorporated in numerous codes based on the escape probability approximation. All that is required for an exact solution with these existing codes is to augment the expression for the escape probability with simple zone-coupling terms. As an application, we find that standard escape probability calculations generally produce the correct cooling emission by the C  ii 158-μm line but not by the ³P lines of O  i .  相似文献   

Correlations between diffuse interstellar bands and atomic lines     

G. A. Galazutdinov  Giulio Manicò  Valerio Pirronello  Jacek Kre&#;owski 《Monthly notices of the Royal Astronomical Society》2004,355(1):169-177

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A far-infrared molecular and atomic line survey of the Orion KL region     

M. R. Lerate  M. J. Barlow  B. M. Swinyard  J. R. Goicoechea  J. Cernicharo  T. W. Grundy  T. L. Lim  E. T. Polehampton  J.-P. Baluteau  S. Viti  J. Yates 《Monthly notices of the Royal Astronomical Society》2006,370(2):597-628

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Low-temperature single crystal reflection spectra of forsterite     

H. Suto  H. Sogawa  S. Tachibana  C. Koike  H. Karoji  A. Tsuchiyama  H. Chihara  K. Mizutani  J. Akedo  K. Ogiso  T. Fukui  S. Ohara 《Monthly notices of the Royal Astronomical Society》2006,370(4):1599-1606

The infrared reflectivities of crystalline forsterite (Mg₂SiO₄) were measured for the temperature range 295–50 K for each crystal axis, between wavenumber 5000 and 100 cm⁻¹. The reflection spectra show clear dependence of temperature; most of the bands become more intense, sharper and their peak positions shift to higher wavenumber with decreasing temperature. Reflection spectra were fitted with dispersion formula of damped oscillator model of the dielectric constants and the oscillator parameters in the model were derived. The absorption spectra of forsterite particle are calculated with the derived dielectric constants to show that the forsterite features are good thermal indicator for cold temperature range below 295 K.  相似文献   

Blueshifted diffuse interstellar bands in the spectrum of HD 34078     

G. A. Galazutdinov  G. Manicò  J. Kre&#;owski † 《Monthly notices of the Royal Astronomical Society》2006,366(3):1075-1080

In this paper, we report the very first observation of diffuse interstellar bands (DIBs) that, in the spectrum of HD 34078 (AE Aur), are blueshifted with respect to the normal position that they have in other objects, where the rest-wavelength velocity frame is determined using very sharp interstellar atomic lines or molecular features. Only reasonably narrow DIBs seemingly show this effect, which is absent in broader ones. The result is confirmed independently using three different spectrographs attached to two different telescopes.  相似文献   

On the identification of the C₆₀⁺ interstellar features     

G. A. Galazutdinov  J. Kreowski  F. A. Musaev  P. Ehrenfreund  B. H. Foing 《Monthly notices of the Royal Astronomical Society》2000,317(4):750-758

The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions.  相似文献   

An infrared proper motion study of the Orion bullets     

J.-K. Lee  M. G. Burton 《Monthly notices of the Royal Astronomical Society》2000,315(1):11-20

We report the first infrared proper motion measurements of the HerbigHaro objects in OMC-1 using a 4-yr time baseline. The [Fe  ii ]-emitting bullets are moving of the order of 0.08 arcsec per year, or at about 170 km s¹. The direction of motion is similar to that inferred from their morphology. The proper motions of H₂-emitting wakes behind the [Fe  ii ] bullets, and of newly found H₂ bullets, are also measured. H₂ bullets have smaller proper motion than [Fe  ii ] bullets, while H₂ wakes with leading [Fe  ii ] bullets appear to move at similar speeds to their associated bullets. A few instances of variability in the emission can be attributed to dense, stationary clumps in the ambient cloud being overrun, setting up a reverse-oriented bullet. Differential motion between [Fe  ii ] bullets and their trailing H₂ wakes is not observed, suggesting that these are not separating, and also that they have reached a steady-state configuration over at least 100 yr. The most distant bullets have, on average, larger proper motions, but are not consistent with free expansion. Nevertheless, an impulsive, or short-lived (<<1000 yr), duration for their origin seems likely.  相似文献   

Observations of a curving molecular outflow from V380 Ori-NE: further support for prompt entrainment in protostellar outflows     

C. J. Davis  W. R. F. Dent  H. E. Matthews  I. M. Coulson  M. J. McCaughrean 《Monthly notices of the Royal Astronomical Society》2000,318(3):952-960

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