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排序方式: 共有90条查询结果,搜索用时 31 毫秒
41.
Bernardi Mara S. Africa Pasquale C. de Falco Carlo Formaggia Luca Menafoglio Alessandra Vantini Simone 《Mathematical Geosciences》2021,53(8):1781-1812
Mathematical Geosciences - Recent advances in satellite technologies, statistical and mathematical models, and computational resources have paved the way for operational use of satellite data in... 相似文献
42.
Tanvir N. R. Le Floc’h E. Christensen L. Caruana J. Salvaterra R. Ghirlanda G. Ciardi B. Maio U. D’Odorico V. Piedipalumbo E. Campana S. Noterdaeme P. Graziani L. Amati L. Bagoly Z. Balázs L. G. Basa S. Behar E. De Cia A. Valle M. Della De Pasquale M. Frontera F. Gomboc A. Götz D. Horvath I. Hudec R. Mereghetti S. O’Brien P. T. Osborne J. P. Paltani S. Rosati P. Sergijenko O. Stanway E. R. Szécsi D. Tot́h L. V. Urata Y. Vergani S. Zane S. 《Experimental Astronomy》2021,52(3):219-244
Experimental Astronomy - At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer... 相似文献
43.
In performance-based seismic design, as adopted by several building codes worldwide, the structural performance is verified against ground motions that have predetermined exceedance return periods at the site of interest. Such a return period is evaluated by means of probabilistic seismic hazard analysis (PSHA), and the corresponding ground motion is often represented by the uniform hazard spectrum (UHS). The structural performance for ground motions larger than those considered in this design approach is, typically, not explicitly controlled under the assumption that they are sufficiently rare. On one hand, this does not achieve uniform safety at sites characterized by different design ground motions corresponding to the same return period; on the other hand, exceedances of the design spectra are systematically observed over large areas, for example in Italy. The latter issue is because of the nature of UHS, the exceedance of which is likely-to-almost-certain when the construction site is in the epicentral area of moderate-to-high magnitude earthquakes (ie, the design spectrum may be not conservative at these locations), especially if PSHA is based on seismic source zones. The former is partially because of the systematic difference of ground motions for return periods larger than the design one at the different sites. Quantification of the expected ground motion given the exceedance of the design ground motions (ie, the recently introduced as the expected peak-over-threshold or POT) can be of help in quantitatively assessing these issues. In the study, a procedure to compute the POT distribution is derived first; second, POT spectra are introduced and used to help understanding why and how seismic structural reliability of code-conforming structures decreases as the seismic hazard of the site increases; third, expected and 95th percentile POT maps are shown for Italy to discuss how much high hazard sites are exposed to much larger peak-over-threshold with respect to mid-hazard and low-hazard sites; finally the POT is discussed with respect to the slope of the hazard curve (in log-log scale) at the threshold, a known proxy for ground motion beyond design. All data presented in the maps are made available for the interested reader as a supplemental archive. 相似文献
44.
Here we outline some recent activities in the theory and phenomenology of Galactic cosmic rays, in the light of the great precision of direct cosmic ray measurements reached in the last decade. In the energy domain of interest, ranging from a few GeV/nucleon to tens of TeV/nucleon, data have revealed some novel features requiring an explanation. We shall emphasize the importance of a more refined modeling, of achieving a better assessment of theoretical uncertainties associated to the models, and of testing key predictions specific of different models against the rich datasets available nowadays. Despite the still shaky theoretical situation, several hints have accumulated suggesting the need to go beyond the approximation of a homogeneous and non-dynamical diffusion coefficient in the Galaxy. 相似文献
45.
Pasquale Panettiere Gianni Cortecci Enrico Dinelli Alberto Bencini Massimo Guidi 《Applied Geochemistry》2000,15(10):2127
Individual and monthly precipitation samples from the polluted atmosphere of Bologna (Emilia-Romagna province) were collected during March 1996 to May 1997 and analyzed for major ions in solution and S isotopes in dissolved SO4.Weighted mean enrichment factors relative to seawater are found to be 1.0 for Na, 15.2 for K, 105 for Ca, 3.3 for Mg, 17.3 for SO4 and 663 for HCO−3. Very good positive correlations are observed for the Ca2+–Mg2+–HCO−3–SO2−4–NO−3 system, indicating that dissolution of Ca (±Mg)-carbonate particles by H2SO4 and HNO3 from combustion of oil and gas is a major process controlling the chemical composition of rain and snow. Na+ and Cl− in monthly precipitation derive essentially from sea spray, but the contribution of Na+ from continental sources is appreciable in a number of individual rains. NH+4 appears to be on average more abundant in spring and summer precipitation, its main sources being microbial activity in soils and application of fertilizers. K+ is probably of continental origin from soil dust.The S isotopic composition of SO4 is systematically positive, with mean δ34S values of +3.2±1.6‰ (n=40) in individual precipitation and +2.8±1.4‰ (n=12) in monthly precipitation. These isotopic compositions are interpreted in terms of a dominant contribution of S from anthropogenic emissions and subordinate contributions from biogenic and marine sources. Pollutant SO4 is estimated to have a δ34S value in the range +2.5 to +4.5‰, whereas a distinctive δ34S of −4.5‰ or lower indicates SO4 from oxidation of biogenic gases.The isotopic and chemical compositions of SO4 do not depend on wind direction, thus testifying to a mostly local source for pollutant S in the Bologna atmosphere. 相似文献
46.
Water-tunnel measurements of velocity, turbulence and scalar concentration for three model urban canopies with aspect ratios A r of building height-to-width of 0.25, 1 and 3 are presented. The measurements for the canopies with A r = 1 and 3 are new, while the measurements for A r = 0.25 were previously published. A passive scalar was continuously released from a near-ground point source, and the concentration was measured at several distances from the source and at different heights above the ground. Plume spreads, concentration and distance from the source were non-dimensionalized using length, time and velocity scales reflecting the geometry of the buildings. The scaling collapses the data for all aspect ratios and is valid when the vertical extent of the plume is smaller than the canopy height. The observed plume spreads are compared with analytical relations, which predict linear growth in both transverse and vertical directions. The observed mean concentration is compared with a Gaussian dispersion model that predicts a ?2 power-law decay with distance from the source. 相似文献
47.
48.
The hierarchical clustering observed in cold dark matter simulations results in highly clumped galactic halos. If the dark matter in our halo is made of weakly interacting massive particles (WIMPs), their annihilation products should be detectable in high density and nearby clumps. We consider WIMPs to be neutralinos and calculate the synchrotron flux from their annihilation products in the presence of the Galactic magnetic field. We derive a self-consistent emission spectrum including pair annihilation, synchrotron self-absorption, and synchrotron self-Compton reactions. The resulting radiation spans microwave frequencies that can be observed over the anisotropies in the cosmic microwave background. These synchrotron sources should be identifiable as WIMP clumps by their spatial structure and their distinctive radio spectrum. 相似文献
49.
50.
Giuseppe Pasquale Raffaella De Matteis Annalisa Romeo Rosalba Maresca 《Journal of Seismology》2009,13(1):107-124
The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been
struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are
records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were
recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model
and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation
of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from
the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting
(pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse
faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with
horizontal σ
3 (plunge 0°, trend 230°) and subvertical σ
1 (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators. 相似文献