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Summary Hourly measurements of solar irradiance in the wave band excluding photosynthetically active radiation (PAR) and solar irradiance (SI) were made over a 12-month period at the National Observatory of Athens, for obtaining the ratios of PAR to SI. These irradiance ratios exhibit dependence on sky conditions, with slightly larger values being observed under cloudy skies and seasonal variations, attributable to changes in local air mass climatology. The highest values have been obtained during the growing season (April–September). The mean annual value of 0.473 observed for the irradiance ratio in the PAR band compares favorably with values reported in the literature for different locations over a wide geographical area.With 2 Figures 相似文献
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Maria D. Papanikolaou Maria V. Triantaphyllou Ellen S. Platzman Philip L. Gibbard Conall Mac Niocaill Martin J. Head 《第四纪科学杂志》2011,26(5):523-540
The chronostratigraphy of a long, onshore Early–Middle Pleistocene marine sedimentary sequence on the south‐east part of Zakynthos island, Greece, is presented. Correlation of the succession with the isotope record of Ocean Drilling Program Site 963 reveals the combined influence of tectonics and eustacy in this area. The sequence is divided into three formations by two main unconformities that apparently relate to sea‐level lowstands associated with two major northern hemisphere glaciations, those of marine isotope stages (MIS) 22 and 12. The Zakynthos sequence in many ways is comparable with the Italian Valle di Manche section. Magnetostratigraphic and rock magnetic analyses, supported by biostratigraphy, document the position of the Matuyama/Brunhes Chron boundary (0.77 Ma), the top and base of the Jaramillo Subchron (0.99–1.07 Ma), the Cobb Mountain Subchron (1.173–1.185 Ma) and the top of the Olduvai Subchron (1.78 Ma). The underlying strata are constrained exclusively by detailed nannofossil biostratigraphy extending at least to the lowermost Pleistocene at around 2.54 Ma and therefore certainly incorporating the base of the Olduvai Subchron (1.95 Ma) and possibly the Gauss/Matuyama Chron boundary (2.58 Ma). In addition, a remarkable increase in sedimentation rate (from 3.2 and 28 cm ka?1 to 167 cm ka?1) and hence resolution above the Matuyama/Brunhes boundary (Middle Pleistocene) reveals one short‐lived magnetic excursion, possibly 17a (0.66 Ma), within the normal polarity Brunhes Chron. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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A discussion of the effects of soil-structure interaction on the dynamic response of linear structures which respond as single-degree-of-freedom systems in their fixed-base condition is presented. The structures are presumed to be supported at the surface of a homogeneous, elastic halfspace and to be excited at the base. The free-field ground motions investigated include a harmonic motion, a relatively simple pulse-type excitation and an actual earthquake record. Comprehensive response spectra are presented for a range of the parameters defining the problem, and the results are used to assess the accuracy of a simple, approximate method of analysis in which the system is represented by a viscously damped, simple oscillator. Special attention is given to defining the conditions under which the interaction effect is of sufficient importance to warrant consideration in design. The method of analysis used to obtain the numerical data reported herein is reviewed only briefly, the emphasis of the paper being on the interpretation of the results. 相似文献
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Factors affecting the distribution of potentially toxic elements in surface soils around an industrialized area of northwestern Greece 总被引：2，自引：0，他引：2
Alexandra Petrotou Konstantinos Skordas Georgios Papastergios Anestis Filippidis 《Environmental Earth Sciences》2012,65(3):823-833
In order to investigate the factors influencing the distribution of 32 potentially toxic elements in the Ptolemais–Kozani
basin, northwestern Greece, 38 soil samples were collected and analyzed. Concentrations of Al, Ca, Fe, K, Mg, Mn, Na, P, Ti,
Ba, Co, Cr, Cu, La, Li, Ni, Pb, Sc, Sr, V, Y, and Zn were determined by ICP-AES and concentrations of As, Bi, Cd, Cs, Mo,
Rb, Sb, Th, Tl, and U by ICP-MS. Bivariate analysis, principal component analysis, and geostatistical analysis were employed
to investigate the factors influencing the distribution of the elements determined in the study area. The results indicate
that the distribution of the majority of elements determined, especially for Cr, Ni, and associated elements, is greatly influenced
by the geology and geomorphology of the study area. Principal component analysis has yielded four factors that explain over
77% of the total variance in the data. These factors are as follows: lithophilic elements that are associated with Al silicates
minerals of K (factor I: 29.4%), ultramafic rocks (factor II: 20.5%), elements that are coprecipitated with Fe and Mn oxides
(factor III: 18.0%), and anthropogenic activities (factor IV: 9.3%). The anthropogenic activities that influence the distribution
of several potentially toxic elements (i.e., Cd, Cu, Pb, Zn) are agricultural practices and the deposition of fly ash in the
vicinity of the local power stations. 相似文献
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Abstract Detailed single-channel continuous seismic reflection profiling data from four gulfs as well as onshore neotectonic investigations have allowed the study of the neotectonic structure of the Hellenic arc along a complete transverse section from its external area in the trench to the internal back-arc area.
Messiniakos Gulf is an asymmetric NW-SE structure with considerable tilt towards the NE. It is the direct continuation of the continental slope from the trench to the island arc (Peloponnesus, Crete, Dodekannese). Argolikos Gulf is an almost symmetric NW-SE graben occupying the northern edge of the Cretan back-arc basin. Saronikos Gulf is a multi-complex structure of a NW-SE graben in the SW (Epidaurus Basin) and alternation of E-W horsts and grabens in the North. Its neotectonic evolution is characterized by the Plio-Quaternary volcanic arc activity. Southern Evoikos Gulf is a relatively shallow neotectonic graben in the back-arc area at the northern prolongation of the Cycladic Platform.
Each of the above neotectonic basins has its own characteristics which are probably due to their geodynamic position in the Hellenic arc. In general, there is a decrease in the neotectonic deformation, the sediment thickness and the sedimentation rates from SW to NE, going from the periphery to the core of the arc. 相似文献
Messiniakos Gulf is an asymmetric NW-SE structure with considerable tilt towards the NE. It is the direct continuation of the continental slope from the trench to the island arc (Peloponnesus, Crete, Dodekannese). Argolikos Gulf is an almost symmetric NW-SE graben occupying the northern edge of the Cretan back-arc basin. Saronikos Gulf is a multi-complex structure of a NW-SE graben in the SW (Epidaurus Basin) and alternation of E-W horsts and grabens in the North. Its neotectonic evolution is characterized by the Plio-Quaternary volcanic arc activity. Southern Evoikos Gulf is a relatively shallow neotectonic graben in the back-arc area at the northern prolongation of the Cycladic Platform.
Each of the above neotectonic basins has its own characteristics which are probably due to their geodynamic position in the Hellenic arc. In general, there is a decrease in the neotectonic deformation, the sediment thickness and the sedimentation rates from SW to NE, going from the periphery to the core of the arc. 相似文献
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Anestis J. Romaides Christopher Jekeli Donald H. Eckhardt Charles L. Taylor 《Journal of Geodesy》1991,65(4):230-242
An experiment was conducted in 1987 in search for a possible non-Newtonian component to gravity. The test compared accurately measured gravity values on a 600 m tower with upward continued surface gravity. The results indicated a dominant attractive non-Newtonian force that asymptotically approached -540 µGal at the top of the tower. An exhaustive search of possible error sources led to the discovery that our surface data did not accurately represent some of the local topographic features. The surface survey was supplemented by gravity data to remove some of the biases that were caused by the misrepresentation. In addition, a rigorous terrain correction was applied to the surface data resulting in terrain-corrected Bouguer anomalies. These anomalies were then upward continued using two independent techniques. The terrain effect was added back to the predicted values at altitude. With this procedure almost the entire non-Newtonian effect was explained. Currently we find no conclusive evidence for a non-Newtonian force over the range of several hundred meters. 相似文献
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G.?MihalakakouEmail author M.?Santamouris N.?Papanikolaou C.?Cartalis A.?Tsangrassoulis 《Pure and Applied Geophysics》2004,161(2):429-451
An intelligent data-driven method is used in the present study for investigating, analyzing and quantifying the urban heat island phenomenon in the major Athens region where hourly ambient air-temperature data are recorded at twenty-three stations. The heat island phenomenon has a serious impact on the energy consumption of buildings, increases smog production, while contributing to an increasing emission of pollutants from power plants, including sulfur dioxide, carbon monoxide, nitrous oxides and suspended particulates. The intelligent method is an artificial neural network approach in which the urban heat island intensity at day and nighttime are estimated using as inputs several climatic parameters. Various neural network architectures are designed and trained for the output estimation, which is the daytime and nighttime urban heat island intensity at each station for a two-year time period. The results are tested with extensive sets of non-training measurements and it is found that they correspond well with the actual values. Furthermore, the influence of several input climatic parameters measured at each station, such as solar radiation, daytime and nighttime air temperature, and maximum daily air temperature, on the urban heat island intensity fluctuations is investigated and analyzed separately for the day and nighttime period. From this investigation it is shown that heat island intensity is mainly influenced by urbanization factors. A sensitivity investigation has been performed, based on neural network techniques, in order to adequately quantify the impact of the above input parameters on the urban heat island phenomenon. 相似文献
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A recently proposed procedure for interrelating the steady-state and transient responses of multi-degree-of-freedom, classically damped linear systems is extended to non-classically damped systems. The extension is formulated for baseexcited systems, and it is illustrated by simple examples. 相似文献