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1.
E. Pascale I. P. Waldmann C. J. MacTavish A. Papageorgiou A. Amaral-Rogers R. Varley V. Coudé du Foresto M. J. Griffin M. Ollivier S. Sarkar L. Spencer B. M. Swinyard M. Tessenyi G. Tinetti 《Experimental Astronomy》2015,40(2-3):601-619
EChOSim is the end-to-end time-domain simulator of the Exoplanet Characterisation Observatory (EChO) space mission. EChOSim has been developed to assess the capability of the EChO mission concept to detect and characterise the atmospheres of transiting exoplanets. Here we discuss the details of the EChOSim implementation and describe the models used to represent the instrument and to simulate the detection. Software simulators have assumed a central role in the design of new instrumentation and in assessing the level of systematics affecting the measurements of existing experiments. Thanks to its high modularity, EChOSim can simulate basic aspects of several existing and proposed spectrometers including instruments on the Hubble Space Telescope and Spitzer, ground-based and balloon-borne experiments. A discussion of different uses of EChOSim is given, including examples of simulations performed to assess the EChO mission. 相似文献
2.
Nafsika Papageorgiou Christos Arvanitidis Anastasios Eleftheriou 《Estuarine, Coastal and Shelf Science》2006,70(4):643
The aim of this paper is to study the macrofaunal community dynamics and the biological–environmental interactions in the mid- and sublittoral ecosystems of the microtidal Mediterranean sandy shores. Four sandy beaches, three on the island of Crete and one on the northwest coast of Italy were selected to investigate the spatial and temporal changes in the community structure and the associated environmental variables. The littoral zone, which has not been adequately studied in the Eastern Mediterranean, presents special interest not only from the scientific point of view but also for practical reasons of ecological management. The multivariate techniques revealed that the community pattern of the sandy beach macrofauna is mainly spatial rather than temporal. There are pronounced differences in species composition and abundance of the macrofaunal assemblages of the mid- and sublittoral zone. The multicausal environmental severity hypothesis appears to be valid for the sandy beach macrofaunal communities of the Mediterranean. The abundance and composition of the macrofaunal assemblages are highly variable and are affected by the synergistic effects of many environmental variables. The polychaete taxonomic assemblage structure closely follows the macrofaunal community pattern. Differences between the two patterns may arise from the different responses that polychaetes may show to the environmental stress. 相似文献
3.
Hamdan Hamdan Nikos Andronikidis George Kritikakis Nikos Economou Zacharias Agioutantis Paul Schilizzi Chrysanthos Steiakakis Christodoulos Papageorgiou Panagiotis Tsourlos George Vargemezis Antonis Vafidis 《Environmental Earth Sciences》2014,72(5):1589-1598
In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations. 相似文献
4.
Ch. Tsitouras G. Papageorgiou T. Kalvouridis 《Celestial Mechanics and Dynamical Astronomy》1992,53(4):329-346
Runge-Kutta-Nystrom (RKN) codes for the solution of the initial value problem for the general second order differential system have been developed recently, although the methodology on which they are based was known many years ago. In this paper we try to examine the efficiency of several known general Runge-Kutta-Nystrom (GRKN) methods by posing some criteria of cost and accuracy. These methods supplied with the corresponding interpolants, have been applied to some problems of Celestial Dynamics. The results obtained show that these codes have a good response in the approximation of the solution of these problems.Department of Mechanics 相似文献
5.
S. K. Nath N. N. Biswas M. Dravinski A. S. Papageorgiou 《Pure and Applied Geophysics》2002,159(11-12):2673-2698
—?Site response was estimated at 19 sites in the Anchorage basin in south-central Alaska, using 15 local earthquakes recorded with good signal-to-noise ratio by a temporary weak motion network. The receiver-function-type horizontal-to-vertical spectral ratios (HVSR) were computed at 1–9 Hz frequency band and the resulting HVSR contour maps at 1, 5 and 9 Hz are presented here. The spatial site response distribution shows considerable variation from the foothills of the Chugach Mountains in the east to the western part of Anchorage. The site response increases by a factor of 3 and 3.5 at 1 and 5 Hz, respectively, from the area of older glacial deposits in the eastern part of the city to the area occupied by the Bootlegger Cove formation, particularly in the section adjoining Knik Arm. At 9 Hz, the variation of HVSR from the east to the west is smaller, approximately by a factor of 2. Moreover, the trend of the HVSR variation at 1 and 5 Hz shows good correlation with that of the soil class obtained from surface measurements of S-wave velocity in the 0–30?m depth range and available results on ground failure susceptibility of Anchorage. 相似文献
6.
Benedikt Halldorsson Apostolos S. Papageorgiou 《Bulletin of Earthquake Engineering》2012,10(4):1321-1337
The specific barrier model (SBM) is a particular case of a composite earthquake source model where the seismic moment is distributed in a deterministic manner on a rectangular fault plane on the basis of moment and area constraints. It is assumed that the fault surface is composed of an aggregate of subevents of equal diameter, the ‘barrier interval’. Furthermore, the subevents are assumed to rupture randomly and statistically independent of one another as the rupture front sweeps the fault plane. In the formulation of the far-field source spectrum of the SBM the ‘arrival time’ of the seismic radiation emitted by each subevent is specified via a probability density function (PDF). In the SBM the subevents are assumed to be of equal sizes (an assumption relaxed in a companion paper, referred to as Part I) and the PDF of ‘arrival times’ is assumed to be uniform. In this study we investigate the effects of different PDFs of ‘arrival times’ on the far-field source spectrum of the SBM. Different PDFs of ‘arrival times’ affect the source spectra primarily at the intermediate frequency range (between the first and second corner frequencies). Such effects become more pronounced as the earthquake magnitude increases. The far-field spectrum of seismic energy observed/recorded at a site depends on the location of the site relative to the causative fault plane, the location of rupture initiation (hypocenter) and the onset times of the rupturing subevents. All the above factors are effectively taken into account by the ‘isochrons’, which vary with source-site geometry. We investigate the selection of the appropriate PDF of seismic energy arrival times at a given site by computing isochrons for a grid of stations surrounding the earthquake fault, represented by the SBM. We show that only for stations located in a direction normal to the fault plane is the assumption of uniform PDF of ‘arrival times’ valid. At other sites non-uniform PDFs of ‘arrival times’ are observed. We identify and categorize the prevalent types of PDFs by directivity (forward vs. backward vs. neutral) and source-site distance (near-fault vs. far-field), show examples in which we group the stations accordingly. We investigate the effects of the different PDF-groups on the SBM source spectrum. Selection of the appropriate PDF for a given source-site configuration when simulating strong ground motions using the SBM in the context of the stochastic method is expected to yield more self-consistent, and physically realistic simulations. 相似文献
7.
The response of a rigid block supported on a horizontally moving foundation through a dry‐friction contact is investigated to near‐fault ground motions. Such motions can be thought of as consisting of a coherent component (‘pulse’) and an incoherent component, which can be described as a band‐limited ‘random noise’. The equation of motion of this strongly nonlinear system is reduced to a normalized form that reveals important parameters of the problem such as the critical acceleration ratio. The response of the sliding block to a set of uniformly processed near‐fault motions, covering a sufficiently wide range of magnitudes, is evaluated numerically for selected discrete values of the acceleration ratio. For each value of the critical acceleration ratio, the numerically computed residual slips are fitted with a Weibull (Gumbel type III) extreme value probability distribution. This allows the establishment of regression equations that describe accurately design sliding curves corresponding to various levels of non‐exceedance probability. The analysis reveals that the coherent component of motion contributes significantly to the response of the sliding block. Furthermore, the relevant acceleration in specifying the critical acceleration ratio is the (normalized) amplitude, αH_pulse, of the pulse and not the (normalized) amplitude of the incoherent component αH. Finally, the incoherent component is described quantitatively in terms of the root‐mean‐square acceleration aRMS, and an attempt is made to understand its influence on the response of the sliding block. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
Structures consisting of two parts, a lower part made of concrete and an upper part made of steel are investigated. In code-based seismic design of such structures several practical difficulties are encountered, due to inherent differences in the nature of dynamic response of each part. The specific issue addressed here is the analysis complications due to the different damping ratios of the two parts. Such structures are irregularly damped and have complex modes of vibration, so that their analysis cannot be handled with readily available commercial software. This work aims at providing a simple yet sufficiently accurate methodology for handling the damping irregularity of such structures, by proposing an overall equivalent damping ratio that can be applied to the complete structure for obtaining its dynamic response. This is achieved by first transforming MDOF irregular structures into equivalent 2-DOF oscillators, using the first mode characteristics of each part, and then using equivalent uniform damping ratios that are derived by means of a semi-empirical error minimization procedure. Thus, available commercial software can be applied for seismic analysis and design and the provisions of existing seismic codes can be adhered to. 相似文献
9.
The multi-axial perfectly matched layer (M-PML) is a material boundary condition for wave propagation problems in unbounded domains. It is obtained by extending the formulation of the split-field perfectly matched layer to a more general absorptive medium, for which damping profiles are specified along all dimensions of the problem. Under the hypothesis of small damping, it has been demonstrated that the stability of the system of partial differential equations of the M-PML can be related to the ratio of the damping profiles, and stable M-PML terminations for isotropic and orthotropic elastic media have been constructed. In the present work, we use the Routh–Horwitz determinants to demonstrate that the conclusions regarding the stability of M-PML for isotropic media for small damping are in fact valid for the more general case of damping coefficients of any (positive) value. The effectiveness of the M-PML is demonstrated by constructing stable terminations for the abovementioned media. The stability analysis is presented for 2-D in-plane (P-SV) wave propagation in elastic isotropic continua. 相似文献
10.
Our intention in this paper is to present the results obtained from a systematic comparative study of several high-order Runge-Kutta methods as applied in a composite problem of celestial dynamics, namely the magnetic-binary problem. 相似文献