The lattice energy of forsterite. Charge distribution and formation enthalpy of the SiO 4 4− ion     

Michele Catti 《Physics and Chemistry of Minerals》1981,7(1):20-25

In the lattice energy expression of forsterite, based on a Born-Mayer (electrostatic+repulsive+dispersive) potential, the oxygen charge z _o, the hardness parameter ρ and the repulsive radii r _Mg and r _Si appear as unknown parameters. These were determined by calculating the first and second partial derivatives of the energy with respect to the cell edges, and equalizing them to quantities related to the crystal elastic constants; the overdetermined system of equations was solved numerically, minimizing the root-mean-square deviation. To test the results obtained, the SiO ₄ ^4? ion was assumed to move in the unit-cell, and the least-energy configuration was sought and compared with the experimental one. By combining the two methods, the optimum set of parameters was: z _o=?1.34, ρ=0.27 Å, r _Mg=0.72 Å, r _Si=0.64 Å. The values ?8565.12 and ?8927.28 kJ mol^?1 were obtained, respectively, for the lattice energy E _Land for its ionic component E _L ⁰ ,which accounts for interactions between Mg²⁺ and SiO ₄ ^4? ions only. The charge distribution calculated on the SiO ₄ ^4? ion was discussed and compared with other results. Using appropriate thermochemical cycles, the formation enthalpy and the binding energy of SiO ₄ ^4? were estimated to be: ΔH _f(SiO ₄ ^4? )=2117.6 and E(SiO ₄ ^4? )=708.6 kJ mol^?1, respectively.  相似文献   

Generalized Regularization Techniques with Constraints for the Analysis of Solar Bremsstrahlung X-ray Spectra     

Eduard?P.?KontarEmail author  Michele?Piana  Anna?Maria?Massone  A.?Gordon?Emslie  John?C.?Brown 《Solar physics》2004,225(2):293-309

Hard X-ray spectra in solar flares provide knowledge of the electron spectrum that results from acceleration and propagation in the solar atmosphere. However, the inference of the electron spectra from solar X-ray spectra is an ill-posed inverse problem. Here, we develop and apply an enhanced regularization algorithm for this process making use of physical constraints on the form of the electron spectrum. The algorithm incorporates various features not heretofore employed in the solar flare context: Generalized Singular Value Decomposition (GSVD) to deal with different orders of constraints; rectangular form of the cross-section matrix to extend the solution energy range; regularization with various forms of the smoothing operator; and preconditioning of the problem. We show by simulations that this technique yields electron spectra with considerably more information and higher quality than previous algorithms.  相似文献   

Mesozoic to Tertiary tectonic history of the Mirdita ophiolites, northern Albania   总被引：3，自引：0，他引：3  

Valerio  Bortolotti  Michele  Marroni  Luca  Pandolfi  Gianfranco  Principi 《Island Arc》2005,14(4):471-493

Abstract In this paper, a summary of the tectonic history of the Mirdita ophiolitic nappe, northern Albania, is proposed by geological and structural data. The Mirdita ophiolitic nappe includes a subophiolite mélange, the Rubik complex, overlain by two ophiolite units, referred to as the Western and Eastern units. Its history started in the Early Triassic with a rifting stage followed by a Middle to Late Triassic oceanic opening between the Adria and Eurasia continental margins. Subsequently, in Early Jurassic time, the oceanic basin was affected by convergence with the development of a subduction zone. The existence of this subduction zone is provided by the occurrence of the supra‐subduction‐zone‐related magmatic sequences found in both the Western and Eastern units of the Mirdita ophiolitic nappe. During the Middle Jurassic, continuous convergence resulted in the obduction of the oceanic lithosphere, in two different stages – the intraoceanic and marginal stages. The intraoceanic stage is characterized by the westward thrusting of a young and still hot section of oceanic lithosphere leading to the development of a metamorphic sole. In the Late Jurassic, the marginal stage developed by the emplacement of the ophiolitic nappe onto the continental margin. During this second stage, the emplacement of the ophiolites resulted in the development of the Rubik complex. In the Early Cretaceous, the final emplacement of the ophiolites was followed by the unconformable sedimentation of the Barremian–Senonian platform carbonate. From the Late Cretaceous to the Middle Miocene, the Mirdita ophiolitic nappe was translated westward during the progressive migration of the deformation front toward the Adria Plate. In the Middle to Late Miocene, a thinning of the whole nappe pile was achieved by extensional tectonics, while the compression was still active in the westernmost areas of the Adria Plate. On the whole, the Miocene deformations resulted in the uplift and exposition of the Mirdita ophiolites as observed today.  相似文献   

Effect of Overstrength on the Seismic Behaviour of Multi-Storey Regularly Asymmetric Buildings     

Mario de Stefano  Edoardo Michele Marino  Pier Paolo Rossi 《Bulletin of Earthquake Engineering》2006,4(1):23-42

In past years, seismic response of asymmetric structures has been frequently analysed by means of single-storey models, because of their simplicity and low computational cost. However, it is widely believed that use of more realistic multi-storey models is needed in order to investigate effects of some system characteristics (such as overstrength, higher modes of vibration, etc.) that make behaviour of multi-storey schemes different from that of single-storey systems. This paper examines effects of the overstrength in element cross-sections on the seismic behaviour of multi-storey asymmetric buildings. It is shown that in actual buildings this characteristic, which is sometimes very variable both in plan and along the height of the building, may lead to distributions of ductility demands different from those expected according to the results from single-storey models. Consequently, torsional provisions, which aim at reducing ductility demands of single-storey asymmetric systems to those of the corresponding torsionally balanced systems, should be re-checked in light of the behaviour of realistic multi-storey buildings.  相似文献   

Numerical simulation of mud-flows impacting structures     

GRECO Massimo  DI CRISTO Cristiana  IERVOLINO Michele  VACCA Andrea 《山地科学学报》2019,(2)

The study of the interaction of mud-flows with obstacles is important to define inundation zones in urban areas and to design the possible structural countermeasures. The paper numerically investigates the impact of a mud-flow on rigid obstacles to evaluate the force acting on them using two different depth-integrated theoretical models, Single-Phase Model(SPM) and Two-Phase Model(TPM), to compare their performance and limits. In the first one the water-sediment mixture is represented as a homogeneous continuum described by a shearthinning power-law rheology. Alternatively, the twophase model proposed by Di Cristo et al in 2016 is used, which separately accounts for the liquid and solid phases. The considered test cases are represented by a 1D landslide flowing on a steep slope impacting on a rigid wall and a 2D mud dam-break flowing on a horizontal bottom in presence of single and multiple rigid obstacles. In the 1D test case, characterized by a very steep slope, the Two-Phase Model predicts the separation between the two phases with a significant longitudinal variation of the solid concentration. In this case the results indicate appreciable differences between the two models in the estimation of both the wave celerity and the magnitude of the impact, with an overestimation of the peak force when using the Single-Phase Model. In the 2D test-cases, where the liquid and solid phases remain mixed, even if the flow fields predicted by the two models present some differences, the essential features of the interaction with the obstacles, along with the maximum impact force, are comparable.  相似文献   

Revisiting design earthquake spectra          下载免费PDF全文

Gian Michele Calvi 《地震工程与结构动力学》2018,47(13):2627-2643

For several decades, seismologists and engineers have been struggling to perfect the shape of design spectra, analyzing recorded signals, and speculating on probabilities. This research effort produced several improvements, for example, suggesting to adopt more than one period to define a spectral shape or proposing different spectral shapes as a function of the return period of the design ground motion. The spectral shapes recommended in most modern codes are driven by considerations on uniform hazard; however, the basic assumption of adopting essentially three fundamental criteria, ie, constant acceleration at low periods, constant displacement at long periods, and constant velocity in an intermediate period range, has never been really questioned. In this opinion paper, the grounds of a constant velocity assumption is discussed and shown to be disputable and not physically based. Spectral shape based on different logics are shown to be potentially consistent with the experimental evidence and to lead to possible differences of 100% in terms of displacement and acceleration demand in the wide intermediate period range that characterizes the vast majority of structures. In this framework, the historical development of linear and nonlinear spectra is critically revisited, proposing a novel original way of defining seismic demand.  相似文献   

A lumped parameter model for time‐domain inertial soil‐structure interaction analysis of structures on pile foundations          下载免费PDF全文

Sandro Carbonari  Michele Morici  Francesca Dezi  Graziano Leoni 《地震工程与结构动力学》2018,47(11):2147-2171

The paper presents a lumped parameter model for the approximation of the frequency‐dependent dynamic stiffness of pile group foundations. The model can be implemented in commercial software to perform linear or nonlinear dynamic analyses of structures founded on piles taking into account the frequency‐dependent coupled roto‐translational, vertical, and torsional behaviour of the soil‐foundation system. Closed‐form formulas for estimating parameters of the model are proposed with reference to pile groups embedded in homogeneous soil deposits. These are calibrated with a nonlinear least square procedure, based on data provided by an extensive non‐dimensional parametric analysis performed with a model previously developed by the authors. Pile groups with square layout and different number of piles embedded in soft and stiff soils are considered. Formulas are overall well capable to reproduce parameters of the proposed lumped system that can be straightforwardly incorporated into inertial structural analyses to account for the dynamic behaviour of the soil‐foundation system. Some applications on typical bridge piers are finally presented to show examples of practical use of the proposed model. Results demonstrate the capability of the proposed lumped system as well as the formulas efficiency in approximating impedances of pile groups and the relevant effect on the response of the superstructure.  相似文献   

Sustainable Yield of a Hydrothermal Area: From Theoretical Concepts to the Practical Approach     

Vincenzo Piscopo  Stefano Di Luca  Michele Dimasi  Francesca Lotti 《Ground water》2019,57(2):337-348

Sustainable use of groundwater in the hydrothermal area of Viterbo (Central Italy) was analyzed. In this area, multipurposes utilization of groundwater coexists: several thermal springs and wells supply spas and public pools, cold and fresh water is used for irrigation and drinking-water. Starting from theoretical concepts, a management plan has been developed to ensure groundwater sustainability in response to the increased demand of withdrawal from thermal wells, by integrating previous hydrogeological studies, new investigations and a new finite-difference model. The most stringent constraints considered are: to maintain the quality of thermal and fresh waters, to limit the effects on the hydraulic equilibrium existing between overlapping aquifers, to ensure a significant flow to the natural thermal springs and the quality and flow rate of the spring used for drinking purposes. The practical approach included identification of the maximum pumping rate from the wells of the spas, analysis of the response time of the system under development and drafting of a safeguard and monitoring plan. The case examined takes into account the complexity of the task in defining practical measures for groundwater management on the basis of theoretical concepts of its sustainable use. A participative approach among the different water decision-makers and adaptive management in the use of groundwater resources with different quality represent the key points to overcome conflicts between different users, with the awareness of the ineludible uncertainties of the hydrogeological model.  相似文献   

The Intra-Pontide ophiolites in Northern Turkey revisited:From birth to death of a Neotethyan oceanic domain     

Michele Marroni  M.Cemal Goncüoglu  Chiara Frassi  Kaan Sayit  Luca Pandolfi  Alessandro Ellero  Giuseppe Ottria 《地学前缘(英文版)》2020,11(1):129-149

The Anatolian peninsula is a key location to study the central portion of the Neotethys Ocean(s)and to understand how its western and eastern branches were connected.One of the lesser known branches of the Mesozoic ocean(s)is preserved in the northern ophiolite suture zone exposed in Turkey,namely,the Intra-Pontide suture zone.It is located between the Sakarya terrane and the Eurasian margin(i.e.,Istanbul-Zonguldak terrane)and consists of several metamorphic and non-metamorphic units containing ophiolites produced in supra-subduction settings from the Late Triassic to the Early Cretaceous.Ophiolites preserved in the metamorphic units recorded pervasive deformations and peak metamorphic conditions ranging from blueschist to eclogite facies.In the nonmetamorphic units,the complete oceanic crust sequence is preserved in tectonic units or as olistoliths in sedimentary melanges.Geochemical,structural,metamorphic and geochronological investigations performed on ophiolite-bearing units allowed the formulation of a new geodynamic model of the entire"life"of the IntraPontide oceanic basin(s).The reconstruction starts with the opening of the Intra-Pontide oceanic basins during the Late Triassic between the Sakarya and Istanbul-Zonguldak continental microplates and ends with its closure caused by two different subductions events that occurred during the upper Early Jurassic and Middle Jurassic.The continental collision between the Sakarya continental microplate and the Eurasian margin developed from the upper Early Cretaceous to the Palaeocene.The presented reconstruction is an alternative model to explain the complex and articulate geodynamic evolution that characterizes the southern margin of Eurasia during the Mesozoic era.  相似文献   

The implementation of the Water Framework Directive in Italy: state of the art on benthic indicators and European experiences     

Michele Mistri  Alberto Basset  Gianna Casazza  & Angel Borja 《Marine Ecology》2009,30(2):212-213

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