Electrical resistivity tomography mapping of beachrocks: application to the island of Thassos (N. Greece)   总被引：1，自引：0，他引：1  

Psomiadis David  Tsourlos Panagiotis  Albanakis Konstantinos 《Environmental Earth Sciences》2009,59(1):233-240

Electrical resistivity tomography (ERT) technique is widely used in mapping subsurface electrical properties. In this study, ERT was used to map a beachrock outcrop, extended both inland, under beach sediments, and seawards, on and under seafloor sediments. Mapping of beachrock is considered important because it can help evaluate the lateral and vertical extend of the formation. Fast and reliable mapping of beachrocks may contribute in several applications like engineering and construction, coastal management, recreational reformation as well as scientific approaches like coastal evolution research, and palaeo-environmental studies. The outcome of the survey was the mapping of the formation with centimeter precision, especially towards the sea. Special processing was applied to the data in order to constrain the inversion procedure to include the known sea water layer.  相似文献   

A Timoshenko finite element straight beam with internal degrees of freedom          下载免费PDF全文

Denis Caillerie  Panagiotis Kotronis  Robert Cybulski 《国际地质力学数值与分析法杂志》2015,39(16):1753-1773

We present hereafter the formulation of a Timoshenko finite element straight beam with internal degrees of freedom, suitable for nonlinear material problems in geomechanics (e.g., beam type structures and deep pile foundations). Cubic shape functions are used for the transverse displacements and quadratic for the rotations. The element is free of shear locking, and we prove that one element is able to predict the exact tip displacements for any complex distributed loadings and any suitable boundary conditions. After the presentation of the virtual power and the weak form formulations, the construction of the elementary stiffness matrix is detailed. The analytical results of the static condensation method are provided. It is also proven that the element introduced by Friedman and Kosmatka in 1 , with shape functions depending on material properties, is derived from the new beam element. Validation is provided using linear and material nonlinear applications (reinforced concrete column under cyclic loading) in the context of a multifiber beam formulation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Development of the SAR TT-OSL procedure for dating Middle Pleistocene dune and shallow marine deposits along the southern Cape coast of South Africa   总被引：1，自引：0，他引：1  

Zenobia Jacobs  Richard G. Roberts  Terry J. Lachlan  Panagiotis Karkanas  Curtis W. Marean  David L. Roberts 《Quaternary Geochronology》2011,6(5):491-513

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.  相似文献   

Mineralogy and geochemical environment of formation of the Perama Hill high-sulfidation epithermal Au-Ag-Te-Se deposit, Petrota Graben, NE Greece   总被引：1，自引：0，他引：1  

Panagiotis Christos Voudouris  Vasilios Melfos  Paul G. Spry  Robert Moritz  Constantinos Papavassiliou  George Falalakis 《Mineralogy and Petrology》2011,103(1-4):79-100

  相似文献   

Provenance analysis of Eocene–Oligocene turbidite deposits in Pindos Foreland Basin, fold and thrust belt of SW Greece: constraints from framework petrography and bulk-rock geochemistry     

Panagiotis A. Konstantopoulos  Avraam Zelilidis 《Arabian Journal of Geosciences》2013,6(12):4671-4700

The provenance of Eocene–Oligocene turbidites from the Pindos Foreland Basin, SW Greece, has been constrained using petrographical and geochemical techniques. Modal petrographic analysis of the studied sandstones shows that the source area comprises sedimentary, metamorphic, and plutonic igneous rocks deposited in a recycled orogenic environment and in magmatic arc province. The relative proportions of the detrital components indicate that the Late Eocene–Early Oligocene sandstones of West Peloponnesus are quartz-rich and were primarily derived from granitic and metamorphic basement rocks typically of a tectonically active area. Major, trace, and rare earth element (REE) concentrations in both sandstones and mudstones complement the petrographical data indicating an active continental margin/continental island arc signature. All the samples are light REE, enriched relative to heavy REE (HREE), with flat HREE pattern and positive Eu anomalies, suggesting that the processes of intra-crustal differentiation (involving plagioclase fractionation) were not of great importance. The results derived from the multi-element diagrams also suggest an active margin character and a mafic/ultramafic source rock composition.  相似文献   

Full‐scale dynamic response of an RC building under weak seismic motions using earthquake recordings,ambient vibrations and modelling     

Clotaire Michel  Philippe Guguen  Saber El Arem  Jacky Mazars  Panagiotis Kotronis 《地震工程与结构动力学》2010,39(4):419-441

In countries with a moderate seismic hazard, the classical methods developed for strong motion prone countries to estimate the seismic behaviour and subsequent vulnerability of existing buildings are often inadequate and not financially realistic. The main goals of this paper are to show how the modal analysis can contribute to the understanding of the seismic building response and the good relevancy of a modal model based on ambient vibrations for estimating the structural deformation under weak earthquakes. We describe the application of an enhanced modal analysis technique (frequency domain decomposition) to process ambient vibration recordings taken at the Grenoble City Hall building (France). The frequencies of ambient vibrations are compared with those of weak earthquakes recorded by the French permanent accelerometric network (RAP) that was installed to monitor the building. The frequency variations of the building under weak earthquakes are shown to be less (∼2%) and therefore ambient vibration frequencies are relevant over the elastic domain of the building. The modal parameters extracted from ambient vibrations are then used to determine the 1D lumped‐mass model in order to reproduce the inter‐storey drift under weak earthquakes and to fix a 3D numerical model that could be used for strong earthquakes. The correlation coefficients between data and synthetic motion are close to 80 and 90% in horizontal directions, for the 1D and 3D modelling, respectively. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Dating Palaeolithic sites in southwestern Crete,Greece     

Thomas F. Strasser  Curtis Runnels  Karl Wegmann  Eleni Panagopoulou  Floyd Mccoy  Chad Digregorio  Panagiotis Karkanas  Nick Thompson 《第四纪科学杂志》2011,26(5):553-560

Discussions of dispersals of early hominins from Africa assume that Southwest Asia and the Arabian Peninsula were the primary passageways for migrations to Eurasia. The Mediterranean is usually viewed as a barrier to early hominin movements because pre‐sapiens hominins were thought to lack the technical means or the cognitive skills to construct boats. The discovery of early Palaeolithic artefacts in an archaeological survey on the Greek island of Crete challenges this view. Here we show that Palaeolithic artefacts in the Plakias region in southwestern Crete are associated with geological contexts that can be dated to the late Middle or early Late Pleistocene. Because Crete has been separated from the mainland throughout the Pleistocene, the presence of Pleistocene age artefacts there suggests that early hominins were able to cross open water. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Close Binaries in the 21 st Century: New Opportunities and Challenges     

Àlvaro Giménez  Edward Guinan  Panagiotis Niarchos  Slavek Rucinski 《Astrophysics and Space Science》2006,304(1-4):3-4

  相似文献   

Centrifuge modeling of batter pile foundations under sinusoidal dynamic excitation     

Zheng Li  Sandra Escoffier  Panagiotis Kotronis 《Bulletin of Earthquake Engineering》2016,14(3):673-697

Batter pile (or inclined pile) foundations are widely used in civil engineering structures. However, their behavior under dynamic loadings is not yet thoroughly understood. This paper presents an experimental work on the behavior of batter and vertical piles considering dynamic soil-pile-superstructure interactions. A series of dynamic centrifuge tests were performed using sinusoidal excitations. The influence of the base shaking (frequency content and amplitude) and of the height of the center of gravity of the superstructure is investigated. Seismic responses are analyzed considering the pile cap displacements and forces (total base shear, overturning and residual moments, axial forces). It is found that in certain cases batter piles play a beneficial role on the dynamic behavior of the pile foundation system. This novel experimental work provides an important database on the behavior of batter pile foundations under dynamic loadings.  相似文献   

Adaptive DTM generalization methods for tangible GIS applications     

Maria Papadogiorgaki  Panagiotis Partsinevelos 《Earth Science Informatics》2017,10(4):483-494

Several international studies attempt to construct tangible GIS systems, forming real 3D surfaces using a large number of mechanical parts along a matrix formation. Most of these attempts suffer in cost, accuracy, resolution and/or speed. In order to facilitate data handling in GIS tangible systems, the generalization process becomes crucial, accommodating compression, visualization and comprehension of spatial data under various scales. Under this perspective, the main objective of the proposed adaptive generalization approach is to provide optimized representation of 3D digital terrain models with minimum loss of information, serving specific applications. That is, to minimize the number of pixels in a raster dataset used to define a DTM, while reserving surface information and enhancing the important semantic features. To this aim, this paper presents specific computationally efficient surface generalization approaches, which can be incorporated in applications of tangible GIS systems, due to their low processing time, facilitating real-time results. The research methods developed and tested include adaptive variations of a) the Douglas-Peucker line simplification algorithm in 3D data and b) the spatial Laplace filter that estimates the significance of each node, based on its nearest neighbors. The proposed strategy also dynamically incorporates topology and semantic restraints, in order to preserve important information and depict it with variable detail level, according to the application at hand. The algorithms are evaluated on their accuracy for a specific wildfire application and for different reduction levels in two different types of terrain data. They are also compared to their original-basic implementations in terms of performance.  相似文献