where k is a constant equal to 6.5 × 10−16 mol/cm2/s and Ω is the saturation index with respect to magnesite. This equation is consistent with spiral growth step generation controlling magnesite precipitation rates. Corresponding magnesite precipitation rates measured using mixed-flow reactors are shown to be consistent with both the rates measured by HAFM and the spiral growth theory, confirming the rate limiting mechanism. Step advancement, however, is observed to slow far faster than step generation with decreasing temperature; the activation energy for step advancement is 159 kJ/mol whereas step generation rates have an estimated activation energy of 60 kJ/mol. As such, it seems likely that at ambient temperatures magnesite growth is limited by very slow step advancement rates.  相似文献   
69.
Normal forms for the epicyclic approximations of the perturbed Kepler problem     
Giuseppe Pucacco 《New Astronomy》2012,17(5):475-482
We compute the normal forms for the Hamiltonian leading to the epicyclic approximations of the (perturbed) Kepler problem in the plane. The Hamiltonian setting corresponds to the dynamics in the Hill synodic system where, by means of the tidal expansion of the potential, the equations of motion take the form of perturbed harmonic oscillators in a rotating frame. In the unperturbed, purely Keplerian case, the post-epicyclic solutions produced with the normal form coincide with those obtained from the expansion of the solution of the Kepler equation. In all cases where the perturbed problem can be cast in autonomous form, the solution is easily obtained as a perturbation series. The generalization to the spatial problem and/or the non-autonomous case is straightforward.  相似文献   
70.
A simplified vulnerability model for the extensive liquefaction risk assessment of buildings     
Paolella  Luca  Spacagna  Rose Line  Chiaro  Gabriele  Modoni  Giuseppe 《Bulletin of Earthquake Engineering》2021,19(10):3933-3961
Bulletin of Earthquake Engineering - The quantitative assessment of natural risks offers a rational strategy to protect communities, undertake cost effective mitigation and plan the organic and...  相似文献   
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Bridge seismic isolation strategy is based on the reduction of shear forces transmitted from the superstructure to the piers by two means: shifting natural period and earthquake input energy reduction by dissipation concentrated in protection devices. In this paper, a stochastic analysis of a simple isolated bridge model for different bridge and device parameters is conducted to assess the efficiency of this seismic protection strategy. To achieve this aim, a simple nonlinear softening constitutive law is adopted to model a wide range of isolation devices, characterized by only three essential mechanical parameters. As a consequence of the random nature of seismic motion, a probabilistic analysis is carried out and the time modulated Kanai-Tajimi stochastic process is adopted to represent the seismic action. The response covariance in the state space is obtained by solving the Lyapunov equation for a stochastic linearized system. After a sensitivity analysis, the failure probability referred to extreme displacement and the mean value of dissipated energy are assessed by using the introduced stochastic indices of seismic bridge protection efficiency. A parametric analysis for protective devices with different mechanical parameters is developed for a proper selection of parameters of isolation devices under different situations.  相似文献   
64.
Landslides of the flow type involving granular geo-materials frequently result in casualties and damage to property because of the long travel distance and the high velocities that these may attain. This was true for the events that took place in Campania Region (Southern Italy) in May 1998, involving pyroclastic soils originating from explosive activities of the Somma-Vesuvius volcano. Although these phenomena have frequently affected various areas of the Campania region over the last few centuries, there were no useful geological and geotechnical references available in the aftermath of the May 1998 events. For this reason Salerno University, which was involved in the scientific management of the emergency, addressed the issue of acquiring data on the geological, geomorphological and hydrogeological features of the slopes where the landslides had taken place. The information acquired made it possible to set up a slope evolution model that is able to interpret, from a geological point of view, past and more recent landslides that had occurred in the same area. As preliminary geotechnical analyses had already validated the above model, more detailed investigations were performed both on the pore pressure regimen of the covers still in place as well as on the physical and mechanical properties of pyroclastic soils, in saturated and unsaturated conditions. The present paper begins by discussing the data acquired during the .rst phase of the studies and then goes on to illustrate the laboratory results so far obtained with the aid of approximate procedures. These help advance our knowledge of pyroclastic soils within a reasonable time frame, thus improving landslide triggering analysis.  相似文献   
65.
A new estimate of global methane emission into the atmosphere from mud volcanoes (MVs) on land and shallow seafloor is presented. The estimate, considered a lower limit, is based on 1) new direct measurements of flux, including both venting of methane and diffuse microseepage around craters and vents, and 2) a classification of MV sizes in terms of area (km2) based on a compilation of data from 120 MVs. The methane flux to the atmosphere is conservatively estimated between 6 and 9 Mt y–1. This emission from MVs is 3–6% of the natural methane sources and is comparable with ocean and hydrate sources, officially considered in the atmospheric methane budget. The total geologic source, including MVs, seepage from seafloor, microseepage in hydrocarbon-prone areas and geothermal sources, would amount to 35–45 Mt y–1. The authors believe it is time to add this parameter in the Intergovernmental Panel on Climate Change official tables of atmospheric methane sources.GEM  相似文献   
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Magnesite growth rates as a function of temperature and saturation state   总被引:1,自引:1,他引:0  
Magnesite growth rates and step velocities have been measured systematically as a function of temperature from 80 to 105 °C and saturation state in 0.1 M NaCl solutions using hydrothermal atomic force microscopy (HAFM). The observations indicate that at these conditions magnesite precipitation is dominated by the coupling of step generation via spiral growth at screw dislocations and step advancement away from these dislocations. As these two processes occur in series the slowest of these dominates precipitation rates. At 100 °C magnesite growth rates (r) determined by HAFM are consistent with
r=k(Ω-1)2,
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