Density and temperature determination of neutral hydrogen in coronal structures     

R. M. Bonnet  G. Tsiropoula 《Solar physics》1982,75(1-2):139-143

High-resolution filtergrams in L have been obtained with a rocket borne instrument and evidence several loop shaped structures which can be seen as absorption features over the solar surface. The optical thickness of these coronal structures is measured with respect to nearby unabsorbed disk features. Their shape and dimension being known from the images, the determination of the neutral hydrogen temperature and density is possible. It is found that temperatures below 10⁵ K and densities of a few 10⁴ hydrogen atoms cm^–3 are compatible with the opacities observed in the structures.  相似文献   

Mixed nonparametric–parametric probabilistic model for earthquake reliability of an inelastic reinforced concrete frame structure     

C. Desceliers  G. Bonnet  S. Hamza  P. Delmotte 《Bulletin of Earthquake Engineering》2010,8(4):921-935

The paper is devoted to the study of uncertainties when studying buildings under seismic loading. These uncertainties are related to the simplifications used when constructing the model (model uncertainties) and to the numerical data needed at the computation stage (data uncertainties). It has been shown in previous papers that nonparametric models are able, in the case of linear dynamics, to deal simultaneously with these two kinds of uncertainties. The paper presents an extension of this kind of model by taking into account a “mixed” approach for concrete frame structures, which uses a nonparametric model for the part of the structure which behaves linearly and a parametric approach for the parts of the structure (plastic hinges) which behave non-linearly. A numerical application is presented in the case of a residential building.  相似文献   

Local amplification of deep mining induced vibrations part.2: Simulation of ground motion in a coal basin     

J.F. Semblat  N. Lokmane  L. Driad-Lebeau  G. Bonnet 《Soil Dynamics and Earthquake Engineering》2010

This work investigates the impact of deep coal mining induced vibrations on surface constructions using numerical tools. An experimental study of the geological site amplification and of its influence on mining induced vibrations has already been published in the previous paper (Part 1: Experimental evidence for site effects in a coal basin). Measurements have shown the existence of an amplification area in the southern part of the basin where drilling data have shown the presence of particularly fractured and soft stratigraphic units. The present study, using the boundary element method (BEM) in the frequency domain, first investigates canonical geological structures in order to get general results for various sites. The amplification level at the surface is given as a function of the shape of the basin and of the velocity contrast with the bedrock. Next, the particular coal basin previously studied experimentally (Driad-Lebeau et al. [1]) is modeled numerically by BEM. The amplification phenomena characterized numerically for the induced vibrations are found to be compatible with the experimental findings such as: amplification level, frequency range and location. Finally, the whole work was necessary to fully assess the propagation and amplification of mine induced vibrations. The numerical results quantifying amplification can also be used to study other coal basins or various types of alluvial sites.  相似文献   

Drainage network expansion of the Salagou drainage basin (S. France): an example of relief response to recent climate change?     

Stéphane Bonnet  Mélanie Besnard  & Jean Van den Driessche 《地学学报》2001,13(3):214-219

Continental erosion is known to be strongly controlled by climate but the way by which geomorphological systems respond to climate change still remains poorly understood. Recent numerical modelling suggests that drainage networks are subjected to strong spatial fluctuations but few studies of natural systems have addressed this phenomenon because of the difficulty of documenting the evolution of erosional landscapes. A detailed field analysis has allowed reconstruction of the past topography of a drainage basin located in southern France where remnants of a past landscape are well preserved. A change from a smooth to a present-day dissected landscape is observed and related to a change in the dominant processes of erosion. This evolution is interpreted in terms of fluctuations in drainage network extent in response to a Holocene increase in precipitation.  相似文献   

Limb-darkening observations between 1800 and 2900 Å     

R. M. Bonnet  J. E. Blamont 《Solar physics》1968,3(1):64-81

We succeeded in several attempts at measuring the solar limb-darkening in the continuous spectrum between 1800 Å and 2900 Å. Good spectroheliograms were obtained during a rocket flight in November 1964 and during a balloon flight in October 1966 at 2190 Å, 2665 Å, 2885 Å, and 1980 Å, 2235 Å respectively. A rocket flown at the beginning of 1967 provided excellent spectra allowing the measurement of center-to-limb variation in the continuum and lines from 1800 Å to 2800 Å.The first series of pictures yielded absolute values of the central intensity leading to a minimum temperature close to 4700 °K. The continuous opacity of the photosphere layers has been deduced from the two first experiments. It seems that a non-metallic source of continuous absorption must be taken into account between 2500 Å and 3000 Å. Moreover, as the source functions for the shortest wavelengths show a very flat variation near the minimum temperature, it seems that the transition zone between the photosphere and the chromosphere must be very gradual.These results are discussed in the light of the latest results deduced from the new spectra obtained.  相似文献