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21.
22.
The studied Carboniferous flysch and molasse sediments from the Intra-Sudetic Basin correspond to the period from Middle Visean to Early Autunian. Main magnetic minerals carrying the natural remanent magnetization (NRM) are goethite, magnetite, maghemite and hematite, all usually secondarily formed and/or remagnetized due to several tectonometamorphic events. In most samples several NRM components were isolated. One of them is usually a Jurassic-Triassic overprint. Some others define the Westphalian-Early Permian segment of the declination and inclination trajectory for the Sudetes calculated according to the reference apparent polar wander path for the Baltica plate. The Sudetic path is slightly shifted to the east compared to the reference path, suggesting the possibility of independent movements of the Sudetes during this time. The majority of isolated NRM components are secondary and related to the Sudetic orogenic phase and later tectonometamorphic activity. 相似文献
23.
24.
In order to extend our knowledge of the performance of long-span bridges under earthquake loading the effects of spatial variability of ground motion on the structural response of cable-stayed bridges are studied; the result can be useful to practising bridge engineers. The multiple-support excitation analysis is described, and two three-dimensional models representing the modern and future trends in cable-stayed bridge design are utilized to shed some light on salient features of the seismic response characteristics of these modern bridges. In addition, models of steel- and concrete-design alternates of an existing bridge are considered. Differential ground motion records (obtained from dense instrument arrays) are used as synchronous and non-synchronous support motions; in addition, non-dispersive seismic waves travelling along the bridge are considered. The bridge response to non-uniform ground motion is compared to its response to uniform input. An overview of the unique dynamic characteristics of these cable-supported bridges is also presented. Finally, the study, which was used in the seismic design of several existing cable-stayed bridges in U.S. and Canada, indicates that the response quantities may increase substantially from the non-uniform input ground motion, especially for more rigid bridges and for bridges having different dynamic properties of the local soils at the supporting points, but the degree of increase depends upon the specific problem, in particular upon the aspects of span length, rigidity and structural redundancy. Thus, the response to non-uniform input ground motion should be examined for these bridges. 相似文献
25.
J. J. Aly 《Solar physics》1992,138(1):133-162
Some useful properties of a finite energy, constant-α, force-free magnetic field B α occupying a half-space D are presented. In particular:
- Fourier and Green representations of B α are obtained and used to derive conditions for the existence and uniqueness of a B α having a given normal component B z on the boundary ?D.
- The asymptotic behaviour of B α at infinity as well as stability results against changes in the boundary condition on ?D and in the value of α are established.
- The energy of B α is shown to be smaller than the energy of the open field having the same B z on ?D, thus confirming an earlier conjecture (Aly, 1984).
- B α is proved to not be a Taylor-Heyvaerts-Priest state, in spite of the fact that its relative helicity H is finite and that it is the only solution of the Lagrange-Euler equation associated with the problem of minimizing the energy among all the fields having the same value of H and the same B z on ?D.
26.
Philippe Paillou Ahmed El Barkooky Aly Barakat Jean-Marie Malezieux Bruno Reynard Jean Dejax Essam Heggy 《Comptes Rendus Geoscience》2004,336(16):1491-1500
Using orbital imaging radar, we have detected a large number of circular structures in the southwestern Egyptian desert, covering more than 4500 km2 close to the Gilf Kebir plateau in sandstones of Upper Cretaceous. Fieldwork confirmed that it is a new impact crater field: 13 craters from 20 m to 1 km in diameter were studied. The impact origin is confirmed by the observation of shock-related structures, such as shatter cones and planar fractures in quartz grains of breccia. Considering the extension of the crater field, it was possibly created by several meteorites that broke up when entering the atmosphere. To cite this article: P. Paillou et al., C. R. Geoscience 336 (2004).
Résumé
À partir d'images satellites issues de systèmes radar, nous avons détecté un grand nombre de structures circulaires dans le Sud-Ouest du désert égyptien, s'étendant sur plus de 4500 km2 à l'est du plateau du Gilf Kebir, dans des grès du Crétacé supérieur. Une étude sur le terrain a permis de vérifier qu'il s'agit d'un champ d'impacts météoritiques jusque là inconnu : 13 structures, d'un diamètre compris entre 20 m et 1 km, ont été reconnues comme cratères d'impact. La présence d'un grand nombre de cônes de percussion et de brèches dans lesquelles des quartz choqués à structures planaires ont été observés confirment l'hypothèse de l'impact. Considérant l'extension du champ d'impact, il a probablement été créé par plusieurs météorites qui se sont fragmentées dans l'atmosphère terrestre. Pour citer cet article : P. Paillou et al., C. R. Geoscience 336 (2004). 相似文献27.
Models of the magnetic field in the solar chromosphere and corona are still mainly based on theoretical extrapolations of photospheric measurements. For the practical calculation of the global field, the so-called source-surface model has been introduced, in which the influence of the solar wind is described by the requirement that the field be radial at some exterior (source) surface. Then the assumption that the field is current-free in the volume between the photosphere and this surface allows for its determination from the photospheric measurement. In the present paper a generalization of the source-surface model to force-free fields is proposed. In the generalized model the parameter( = ×B·B/B
2)must be non-constant (or vanish identically) and currents are restricted to regions with closed field lines. A mathematical algorithm for computing the field from boundary data is devised. 相似文献
28.
We propose a simple 2D current sheet model of a normal prominence, in which the lines of the background magnetic field have the dip structure which seems to be required for such an object to form and to be stably supported. 相似文献
29.
Ahmed Aly Kamel 《Celestial Mechanics and Dynamical Astronomy》1970,3(1):90-106
Asymptotic recurrence formulas for treating nonlinear oscillation problems are presented. These formulas are based on a Lie transform similar to that described by Deprit for Hamiltonian systems. It is shown that the basic formulas have essentially the same forms as those obtained by Deprit and by the present author in the Hamiltonian case. 相似文献
30.
Aly I. El-Kadi 《Hydrogeology Journal》2007,15(2):339-350
The effects of permeability variability on uncertainty of the results of a hydrocarbon biodegradation model are addressed.
The model includes saturated and unsaturated flow, multi-species transport, heat transport, and bacterial-growth processes.
A stochastic approach was used in the uncertainty analysis. Sensitivity analyses were conducted, taking into consideration
the effects of heterogeneity. The Monte Carlo method was used, with permeability as the input stochastic variable. Results
showed that uncertainty increases with time. This can lead to difficulties regarding cleanup decision making such as predicting
the timeframe to reach an aquifer cleanup goal. It was not possible to replace the heterogeneous system with a homogeneous
one through the use of effective parameters that preserve an equivalent behavior of the two systems. Effective permeability
is space and time dependent and also depends on values of bioactivity parameters. The study also emphasized the importance
of accurately measuring certain bacterial parameters, namely, maximum substrate uptake rate for degradation and cell yield
coefficient. Uncertainties regarding nutrient and oxygen uptake and saturation parameters were less important for the current
application.
相似文献
Aly I. El-KadiEmail: |