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651.
Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations 下载免费PDF全文
Pavel P. Povinec Jozef Masarik Ivan Sýkora Andrej Kováčik Juraj Beňo Matthias M. M. Meier Rainer Wieler Matthias Laubenstein Vladimir Porubčan 《Meteoritics & planetary science》2015,50(5):880-892
Results of nondestructive gamma‐ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Ko?ice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic‐ray particles in the space affecting radionuclides with different half‐lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre‐atmospheric radius of the meteoroid was 50 ± 5 cm. In two Ko?ice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble‐gas cosmic‐ray exposure age of the Ko?ice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Ko?ice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long‐term average flux of galactic cosmic rays of 4.8 particles cm?2 s?1, whereas the short‐lived radionuclide activities are more consistent with a flux of 7.0 protons cm?2 s?1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall. 相似文献
652.
Lidija Krstevska Ljubomir Tashkov Vladimir Gocevski Mihail Garevski 《Bulletin of Earthquake Engineering》2010,8(2):421-450
The seismic stability of the facade brick-masonry walls of the machinery building of the Beauharnois powerhouse near Montreal,
Quebec, Canada were investigated numerically by use of non-linear models and applying experimental methods on site and on
the IZIIS’ seismic shake-table. The dynamic properties of the machinery building were obtained by ambient vibration measurements.
Based on these results, a model of a representative part of the building, consisting of steel frames and brick masonry wall,
was designed and constructed to the reduced scale at the IZIIS’ Dynamic Testing Laboratory and then tested on the two-component
shake-table. The geometry of the original structure was completely scaled to 1/3, consisting of many realistically simulated
details such us: brick layers, steel columns, openings, window frames, steel connectors between brick layers, number of layers,
brick dimensions, etc. The material used for the model was: original steel for the frame structure and bricks of reduced mechanical
properties for the masonry wall, close to the similitude requirements according to the Backingham’s theorem, valuable for
adequate artificial—mass simulation model as well as true replica simulation model. More than 50 seismic tests were performed
considering the design earthquake Nahanni NWT, H1, with a time scaling factor of 31/2, and acceleration scaling factor 1, according to the model design rules. The intensity of the applied input earthquake excitation
was from 0.05 to 1.2 g. The design peak acceleration of Nahanni earthquake was 0.2 g. The cracks development was stated at
0.7 g input acceleration. These were concentrated around the openings. No collapse happened even under the strongest earthquake
input. The numerical part of this paper deals with formulation/application of the critical plane approach to seismic analysis
of masonry structures. Starting with the constituents, i.e. mortar and bricks, the macroscopic strength properties of masonry
were established based on numerical homogenization. Generally, based on all the performed experimental tests, considering
some simplifications and assumptions in the constructing details, as well as in the design of the model, the global conclusion
is that the existing wall is very well incorporated in the steel structure of the powerhouse. The complementary stiffness
of the steel frame and the brick masonry wall produces interactive deformation of the system. Only local cracking and relative
displacement between the wall and the steel frames could be expected in the case of a strong earthquake. 相似文献
653.
Vladimir Lyakhovsky Amir Sagy Yuval Boneh Ze’ev Reches 《Pure and Applied Geophysics》2014,171(11):3143-3157
Slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub-millimeter to tens of meters. The properties of these zones apparently control fault strength and slip stability. Here we present a new model of wear in a three-body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock. The derivations for steady-state conditions lead to a scaling relation for the damage front velocity considered as the wear-rate. The model predicts that the wear-rate is a function of the shear-stress and may vanish when the shear-stress drops below the microfracturing strength of the fault host rock. The simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite. The model is also valid for relatively large confining pressures, small damage-induced change of the bulk modulus and significant degradation of the shear modulus, which are assumed for seismogenic zones of earthquake faults. The presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a “propagating damage front” and the evolution of a third-body layer. 相似文献
654.
Jean-Louis Le Mouël Vladimir Kossobokov Vincent Courtillot 《Journal of Atmospheric and Solar》2010,72(1):62-76
We analyze the longest temperature series from Prague, Bologna and Uccle. We partition daily minimum and maximum temperatures and their differences in two subsets as a function of high vs low solar activity, using the superimposed epochs method. Differences display patterns with significant amplitudes and time constants ~3 months. These are recognized in all stations and are stable against a change in the analyzed period. Amplitude of variations is ~1 °C. Differences between average annual values corresponding to high vs low activity periods are also ~1 °C. Solar activity may account for these long-term temperature variations. These variations also present local characteristics, which may render identification of a global correlation delicate. We discuss possible physical mechanisms by which solar variation could force climate changes (e.g. through solar activity itself, the EUV part of the solar flux, cosmic rays, the downward ionosphere-earth current density, etc.). 相似文献