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201.
Letícia Fleck Fadel Miguel Jorge Daniel Riera Ignacio Iturrioz 《国际地质力学数值与分析法杂志》2008,32(15):1857-1881
The numerical fracture analysis of non‐homogeneous rock or concrete dowels subjected to shear and compression is described in detail. The method of analysis allows the consideration of scale and rate effects due to material non‐homogeneity and fracture. The proposed approach is verified by comparing numerical predictions with experimental results reported in the literature for a series of small rock samples, since experimental evidence for large bodies is not yet available (2007). Results generated by Monte Carlo simulation using the so‐called discrete element method to model the dowels suggest that a simple three parameters law can be used to predict the relationship between tangential stress at the base and lateral distortion. It is observed that the larger the size of the cubes, the smaller both the peak tangential stress and the rupture distortion. Size effects are also evaluated in samples with vertical restraint. The influence of loading rate is likewise numerically assessed for two sample sizes. The effect is compatible with experimental evidence available for concrete using small samples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
202.
203.
This paper gives a brief presentation of the study on foundation of a residential business complex. The unfavourable geotechnical conditions of the site considered led to the need to improve the natural foundation soil. The most favourable and rational solution for providing safety and stability of structures was the combination of gravel and a sub-base. Computations were done as follows: analysis of the stress–strain state by using the parameters of the natural non-improved soil and analyses performed by using the parameters of the improved soil. The results from these analyses were used for analysis of the integral soil–structure system. Hence, complete information on the possibility for optimisation of the foundation structure was obtained. 相似文献
204.
L. Michaille J.B. Clifford J.C. Dainty † T. Gregory J.C. Quartel F.C. Reavell R.W. Wilson N.J. Wooder 《Monthly notices of the Royal Astronomical Society》2001,328(4):993-1000
We present the results of a mesospheric sodium monitoring programme at La Palma carried out through five campaigns of one week each, from 1999 September to 2000 August. The yearly averaged parameters of the layer (the sodium column density and the width) are given. We show that the short time-scale dynamics of the layer are governed by the sporadic layers with an average frequency of one event per night. The influence of the short time-scale dynamics of the layer on an adaptive optics system working on the William Herschel Telescope is quantified. It appears that it is a small effect in terms of defocus error. Finally, we present data obtained during the Perseid meteor shower and show that the dynamics of the sodium layer undergoes a transition with the meteoric activity. 相似文献
205.
John J. Matese Patrick G. Whitman Daniel P. Whitmire 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):77-87
We investigate the distribution of Oort cloud comet perihelia. The data considered includes comets having orbital elements
of the two highest quality classes with original energies designated as new or young. Perihelion directions are determined
in galactic, ecliptic and geocentric equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically
for evidence of adiabatic galactic tidal dynamics, an impulse-induced shower and observational bias. The only bias detected
is the well-known deficiency of observations with perihelion distances q > 2.5 AU. There is no significant evidence of a seasonal
dependence. Nor is there a substantive hemispherical bias in either ecliptic or equatorial coordinates. There is evidence
for a weak stellar shower previously detected by Biermann which accounts for ≈ 10% of the total observations. Both the q bias
and the Biermann star track serve to weaken the evidence for a galactic tidal imprint. Nevertheless, statistically significant
asymmetries in galactic latitude and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component
perpendicular to the galactic disk. The longitude signal implies that ≈ 20% of new comets need an additional dynamical mechanism.
Known disk non-uniformities and an hypothetical bound perturber are discussed as potential explanations. We conclude that
the detected dynamical signature of the galactic tide is real and is not an artifact of observational bias, impulsive showers
or poor data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
206.
M. Bruno G. Cremonese S. Marchi 《Monthly notices of the Royal Astronomical Society》2006,367(3):1067-1071
In this work, we calculate the vapour and neutral Na production rates on the Moon, as due to the impacts of meteoroids in the radius range of 10−8 –0.15 m. We limit our calculations to this size range, since meteoroids with radius larger than 0.15 m have not been found to be important for the production of the exosphere in a time interval comparable with that of the observations.
We have considered a new dynamical model of the flux of meteoroids at the heliocentric distance of the Moon, regarding objects in the radius range of 10−2 –0.15 m. Instead, the flux of smaller meteoroids (radius range 10−8 –10−2 m) has been calculated using the two distributions adopted by Cintala and Love & Brownlee.
The results of our model are that (i) the neutral Na production rate is ∼3–4.9 × 104 atoms cm−2 s−1 , slightly larger than the previous estimates (∼2–3 × 104 atoms cm−2 s−1 ) , and (ii) only about 6 per cent of neutral Na is produced by the impacts of meteoroids in the size range 10−3 –0.15 m, whereas about 94 per cent of the Na comes from the 10−5 –10−3 m size range. 相似文献
We have considered a new dynamical model of the flux of meteoroids at the heliocentric distance of the Moon, regarding objects in the radius range of 10
The results of our model are that (i) the neutral Na production rate is ∼3–4.9 × 10
207.
Walter Winter 《Earth, Moon, and Planets》2006,99(1-4):285-307
Because the propagation of neutrinos is affected by the presence of Earth matter, it opens new possibilities to probe the
Earth’s interior. Different approaches range from techniques based upon the interaction of high energy (above TeV) neutrinos
with Earth matter, to methods using the MSW effect on the oscillations of low energy (MeV to GeV) neutrinos. In principle,
neutrinos from many different sources (sun, atmosphere, supernovae, beams etc.) can be used. In this talk, we summarize and
compare different approaches with an emphasis on more recent developments. In addition, we point out other geophysical aspects
relevant for neutrino oscillations. 相似文献
208.
A. Tokovinin T. Travouillon 《Monthly notices of the Royal Astronomical Society》2006,365(4):1235-1242
New measurements of optical turbulence profile at the Cerro Pachón observatory in Chile are analysed jointly with previously published data to model the variations of the intensity and thickness of the ground layer and free atmosphere under a variety of observing conditions. This work is motivated by the need to predict statistically the performance of ground-layer adaptice optics. We find that the ground-layer profile can be represented by a decaying exponent with a scale height of 20–40 m, increasing to 100 m under bad conditions. The zone from 6 to 500 m contributes typically about 61 per cent to the total integral, the latter causing a median seeing of 0.77 arcsec. Turbulence integrals in the ground layer and in free atmosphere vary independently of each other, in 50 per cent of cases they deviate by less than 1.8 times from their respective median values. The existence of periods with low turbulence in the free atmosphere and their importance for adaptive optics is stressed. 相似文献
209.
ICE, the electric field experiment on DEMETER 总被引:9,自引:0,他引:9
210.