On the theory of Chebyshev polynomials in wave-equation migration     

Panos G. Kelamis 《Geophysical Journal International》1988,94(3):421-426

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Rainfall erosivity in Italy: a national scale spatio-temporal assessment   总被引：2，自引：0，他引：2  

Pasquale Borrelli  Nazzareno Diodato  Panos Panagos 《International Journal of Digital Earth》2016,9(9):835-850

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Modelling monthly soil losses and sediment yields in Cyprus     

Christos G. Karydas  Panos Panagos 《International Journal of Digital Earth》2016,9(8):766-787

The aim of this study was to map soil erosion on the Mediterranean island of Cyprus. The G2 model, an empirical model for month-time step erosion assessments, was used. Soil losses in Cyprus were mapped at a 100?m cell size, while sediment yields at a sub-basin scale of 0.62?km² mean size. The results indicated a mean annual erosion rate of 11.75?t?ha^?1?y^?1, with October and November being the most erosive months. The 34% of the island's surface was found to exceed non-sustainable erosion rates (>10?t?ha^?1?y^?1), with sclerophyllous vegetation, coniferous forests, and non-irrigated arable land being the most extensive non-sustainable erosive land covers. The mean sediment delivery ratio (SDR) was found to be 0.26, while the mean annual specific sediment yield (SSY) value for Cyprus was found to be 3.32?t?ha^?1?y^?1. The annual sediment yield of the entire island was found to be 2.746?Mt?y^?1. This study was the first to provide complete and detailed erosion figures for Cyprus at a country scale. The geodatabase and all information records of the study are available at the European Soil Data Centre (ESDAC) of the Joint Research Centre (JRC).  相似文献   

Effects of salinity on mineralogy and chemical composition of Cerastoderma edule and Monodonta articulata shells     

R. Neri  G. Schifano  C. Papanicolaou 《Marine Geology》1979,30(3-4):233-241

Shells of the mollusks Cerastoderma (Cerastoderma) edule (Linnaeus 1758) and Monodonta (Osilinus) articulata Lamark 1822 from salt evaporate basins in western Sicily are studied and the effect of environmental conditions (particularly salinity and water chemistry) on mineralogy and chemical composition is investigated and discussed.

The elements determined both in seawater and shell carbonate are: Ca, Mg, Mn, Fe, Ni, Co, Cu, Zn, Sr and Pb.

Both species studied discriminate against all the minor and trace elements determined; the degree of such discrimination, for some elements, is inversely related to salinity.

The mineralogical composition of the shells (Monodonta has a mixed mineralogy while Cerastoderma is entirely aragonitic) appears to be controlled neither by temperature nor by salinity.

In Monodonta shells direct correlations have been found between the following parameters: calcite-Sr (in younger shells only), calcite-Fe, calcite-Pb (in older shells only), calcite-Zn, salinity-Mg and salinity-Pb, whereas inverse correlations were observed between calcite and Sr (in older shells only) and calcite and Pb (in younger shells only). In Cerastoderma shells a direct correlation was found between salinity and Fe and Mg.

The thickness of the shells appears, in both species, to be an inverse linear function of salinity.  相似文献   

What is the contribution of time-dependent deformation in tunnel convergence?     

Villy Kontogianni  Panos Psimoulis  Stathis Stiros 《Engineering Geology》2006,82(4):264-267

Tunnel excavation produces stress changes to the ground and strain to the support lining, leading to the closure (convergence) or instability of the excavated area. Convergence recorded after section excavation is assigned to: (i) strain resulting from the progressive tunnel front advance (face advance effect) and (ii) the time-dependent properties of the soil material (ground creep effect). In the present study, based on the geodetic monitoring records of two recent road tunnels in Greece, a simple methodology to estimate the contribution of each of the two effects is presented. Our analysis reveals that at least half of the total deformation of the examined tunnel sections is due to ground creep, indicating that the major portion of tunnel deformation is due to the time-dependent properties of the ground; a result supported by previous studies from other tunnels as well.  相似文献   

Earthquake response of a multiblock nuclear reactor graphite core: Experimental model vs simulations          下载免费PDF全文

Elia Voyagaki  Panos Kloukinas  Matt Dietz  Luiza Dihoru  Tony Horseman  Olafur Oddbjornsson  Adam J. Crewe  Colin A. Taylor  Alan Steer 《地震工程与结构动力学》2018,47(13):2601-2626

The complex dynamics of a quarter‐scale model of a graphite nuclear reactor core, representative of the second generation of British advanced gas‐cooled nuclear reactors, is investigated numerically and experimentally. Advanced gas‐cooled nuclear reactor cores are polygonal, multilayer, arrays of graphite bricks, with each brick allowed to rock by design relative to each other in accordance with the boundary conditions. A 35 000 DOF, nonlinear finite element model of the core created by Atkins Nuclear, was analysed on a high performance computing facility at the University of Bristol, and a corresponding 8 t physical model, equipped with 3200 data acquisition channels, was built and tested on the University of Bristol 6‐DOF shaking table. In this paper, the two models are subjected to a series of (1) synthetic earthquake and (2) idealised harmonic input motions. The experimental data are used to compare and verify the two models and explore the dynamics of the core. A kinematic model of the response is also developed based solely on geometric constraints. The results are presented in the form of response maps and graphs. Important conclusions are drawn as to the dynamics and earthquake response of such systems, which inform numerical model validation. It is found that contrary to the case of a small number of rocking blocks that exhibit highly complex response patterns, the behaviour of the model at hand is both smooth and repeatable. An analogy between the response of the core and that of dense granular matter exhibiting particle interlocking and dilatancy is highlighted.  相似文献   

A probabilistic model for sediment entrainment:The role of bed irregularity     

Mohamed Elhakeem  A.N. Thanos Papanicolaou  Achilleas G. Tsakiris 《国际泥沙研究》2017,32(2)

A generalized probabilistic model is developed in this study to predict sediment entrainment under the incipient motion, rolling, and pickup modes. A novelty of the proposed model is that it incorporates in its formulation the probability density function of the bed shear stress, instead of the near-bed velocity fluctuations, to account for the effects of both flow turbulence and bed surface irregularity on sediment entrainment. The proposed model incorporates in its formulation the collective effects of three para-meters describing bed surface irregularity, namely the relative roughness, the volumetric fraction and relative position of sediment particles within the active layer. Another key feature of the model is that it provides a criterion for estimating the lift and drag coefficients jointly based on the recognition that lift and drag forces acting on sediment particles are interdependent and vary with particle protrusion and packing density. The model was validated using laboratory data of both fine and coarse sediment and was compared with previously published models. The study results show that all the examined models perform adequately for the fine sediment data, where the sediment particles have more uniform gra-dation and relative roughness is not a factor. The proposed model was particularly suited for the coarse sediment data, where the increased bed irregularity was captured by the new parameters introduced in the model formulation. As a result, the proposed model yielded smaller prediction errors and physically acceptable values for the lift coefficient compared to the other models in case of the coarse sediment data.  相似文献   

Α mass-reduction design concept for seismic hazard mitigation     

Aristotelis E. Charalampakis  George C. Tsiatas  Panos Tsopelas 《地震工程与结构动力学》2020,49(3):301-314

A mass reduction concept for seismic hazard mitigation is investigated herein. The proposed method is implemented through floating slabs, ie, slabs that have been seismically isolated from the skeleton of the structure. The investigation is based on time history analyses of MDOF models under scaled strong-motion seismic records complying with an EC8 spectrum. The purpose of these slabs is twofold; for selected short isolation periods, they act as a mass-damping system for the overall response of the structure, employing significantly more mass than traditional TMDs, while for longer isolation periods they provide seismic protection on their contents while effectively reducing the seismic mass of the structure. In the latter case, it is found that the response of the skeleton can be evaluated accurately from a corresponding reduced-mass model. The proposed design method does not necessarily aim at replacing existing seismic design approaches; it rather provides design versatility in the hands of the practicing engineers.  相似文献   

Methodological considerations for studying self-weight fluidization in a sedimentation column     

A.N. Papanicolaou  A.R. Maxwell 《International Journal of Mineral Processing》2006

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Norm-dependent covariance permissibility of weakly homogeneous spatial random fields and its consequences in spatial statistics     

G. Christakos  V. Papanicolaou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(6):471-478

 Permissibility of a covariance function (in the sense of Bochner) depends on the norm (or metric) that determines spatial distance in several dimensions. A covariance function that is permissible for one norm may not be so for another. We prove that for a certain class of covariances of weakly homogeneous random fields, the spatial distance can be defined only in terms of the Euclidean norm. This class includes commonly used covariance functions. Functions that do not belong to this class may be permissible covariances for some non-Euclidean metric. Thus, a different class of covariances, for which non-Euclidean norms are valid spatial distances, is also discussed. The choice of a coordinate system and associated norm to describe a physical phenomenon depends on the nature of the properties being described. Norm-dependent permissibility analysis has important consequences in spatial statistics applications (e.g., spatial estimation or mapping), in which one is concerned about the validity of covariance functions associated with a physically meaningful norm (Euclidean or non-Euclidean).  相似文献