Stratospheric ozone variations in the northern and the southern hemisphere during the period 1957–1990     

John Xanthakis  Constantine Poulakos  Christos S. Zerefos 《Earth, Moon, and Planets》1993,60(2):109-125

The fluctuation and the periodicities of the total ozone layer for the period 1957–1990 is studied. Monthly total ozone data from 32 ground based stations have been analysed. It is shown that the maxima and the minima of the monthly values of total ozone for each year and for the whole period in question do not necessarily occur in March or in April and in September or October but range from March till July and from September till December respectively. Periodicities of 3, 4 and 6 months have been revealed. Finally the maxima and the minima of the total ozone data were examined. The variation of the whole phenomenon is analytically expressed with the help of an algebraic formula and can represent the observed monthly ozone values with an accuracy of 97%.  相似文献   

An empirical analysis of IOPCF oil spill cost data     

Christos A. Kontovas  Harilaos N. Psaraftis  Nikolaos P. Ventikos 《Marine pollution bulletin》2010,60(9):1455-18097

This paper reports on recent analysis of oil spill cost data assembled by the International Oil Pollution Compensation Fund (IOPCF). Regression analyses of clean-up costs and total costs have been carried out, after taking care to convert to current prices and remove outliers. In the first place, the results of this analysis have been useful in the context of the ongoing discussion within the International Maritime Organization (IMO) on environmental risk evaluation criteria. Furthermore, these results can be useful in estimating the benefit of regulations that deal with the protection of marine environment and oil pollution prevention.  相似文献   

Conflicts at sea between artisanal and industrial fishers: Inter-sectoral interactions and dispute resolution in Senegal     

Carolyn DuBois  Christos Zografos 《Marine Policy》2012

Conflicts between artisanal and industrial fishermen—targeting increasingly scarce resources in Senegal—are posing a serious threat to human security and are only symbolically addressed by the country's fisheries governance regime. Severely outmatched in terms of political influence and size, artisanal fishermen are more vulnerable to the fallout of conflicts at sea. The loss of fishing materials threatens the livelihoods of fishermen and their families; collisions and violence between members of the two sectors often result in injury and death. This study examines at-sea interactions between Senegal's artisanal and industrial sectors and the formal and informal mechanisms in place for managing them. Conflictive interactions are found to co-exist alongside cooperative ones and both emerge in response to changes in marine resource abundance and management. Formal systems in place to mediate at-sea conflicts are ineffective and seldom used by artisanal fishermen, who either accept their losses, attempt to informally resolve conflicts with industrial actors or resort to violence.  相似文献   

Appropriate SCF basis sets for orbital studies of galaxies and a 'quantum-mechanical' method to compute them     

Constantinos Kalapotharakos  Christos Efthymiopoulos  Nikos Voglis 《Monthly notices of the Royal Astronomical Society》2008,383(3):971-988

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Ordered and chaotic Bohmian trajectories     

George Contopoulos  Christos Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2008,102(1-3):219-239

We discuss the issue of ordered and chaotic trajectories in the Bohmian approach of Quantum Mechanics from points of view relevant to the methods of Celestial Mechanics. The Bohmian approach gives the same results as the orthodox (Copenhagen) approach, but it considers also underlying trajectories guided by the wave. The Bohmian trajectories are rather different from the corresponding classical trajectories. We give examples of a classical chaotic system that is ordered quantum-mechanically and of a classically ordered system that is mostly chaotic quantum mechanically. Then we consider quantum periodic orbits and ordered orbits, that can be represented by formal series of the “third integral” type, and we study their asymptotic properties leading to estimates of exponential stability. Such orbits do not approach the “nodal points” where the wavefunction ψ vanishes. On the other hand, when an orbit comes close to a nodal point, chaos is generated in the neighborhood of a hyperbolic point (called X-point). The generation of chaos is maximum when the X-point is close to the nodal point. Finally we remark that high order periodic orbits may behave as “effectively ordered” or “effectively chaotic” for long times before reaching the period.  相似文献   

Climate change effects on the marine characteristics of the Aegean and Ionian Seas     

Christos Makris  Panagiota Galiatsatou  Konstantia Tolika  Christina Anagnostopoulou  Katerina Kombiadou  Panayotis Prinos  Kondylia Velikou  Zacharias Kapelonis  Elina Tragou  Yannis Androulidakis  Gerasimos Athanassoulis  Christos Vagenas  Ioannis Tegoulias  Vassilis Baltikas  Yannis Krestenitis  Theodoros Gerostathis  Kostantinos Belibassakis  Eugen Rusu 《Ocean Dynamics》2016,66(12):1603-1635

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Winter convective precipitation variability in southeastern Europe and its connection to middle tropospheric circulation for the 60-year period, 1950–2009     

Christos J. Lolis 《Theoretical and Applied Climatology》2012,107(1-2):189-200

The inter-annual variability of winter convective precipitation rate (CPR) in southeastern Europe and its connection to 500?hPa geopotential height (GH) is examined for the period 1950–2009 by using factor analysis and canonical correlation analysis. Two GH centers of action for CPR are found. The first one is located over Italy and it is associated with the typical winter depression activity regime over the Mediterranean Sea, controlling CPR in southern Italy, the southern Balkans, west Asia Minor, and the adjacent seas. The second one is located over the British Isles and it is associated with blocking activity over western Europe being responsible for a CPR seesaw teleconnection between (1) northern Italy, the Alps and the northwestern Balkans and (2) the south central Mediterranean Sea, south of Sicily. A CPR decrease in most of the areas under study and a CPR increase in the south central Mediterranean Sea are found.  相似文献   

Scattering of waves by subterranean structures via the boundary element method     

António J.B. Tadeu  Eduardo Kausel  Christos Vrettos 《Soil Dynamics and Earthquake Engineering》1996,15(6):387-397

The boundary element method (BEM) is used to study the two-dimensional wave field generated when buried structures of arbitrary shape (i.e. inclusions) in an elastic medium are illuminated (or insonified) by dynamic line sources. Both steady-state responses and time-domain transients are presented. The problem is formulated in the frequency domain by means of appropriate Green's functions. The evaluation of the singular integrals is achieved (and to the best of the writers' knowledge, for the first time in the technical literature) in analytical form, which results in improvements in computational efficiency and accuracy. Closed-form solutions for regular geometries are then used to validate the method. The interaction of two cavities, the formation of shadow zones by inclusions and the complexity of the scattered field from bodies with irregular shapes are used as examples to demonstrate the versatility of the method. The responses computed in the time domain were invariably found to be causal, even for non-convex domains, which belies a recent assertion by some researchers that the application of boundary element methods to concave domains is associated with non-causal effects.  相似文献   

Introduction: European Land–Ocean Interaction Studies: the ELOISE thematic network     

Nicholas Murray  Klaus-Günther Barthel  Hartmut Barth  Christos Fragakis   《Continental Shelf Research》2001,21(18-19)

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Two-feldspar geothermometry: a review and revision for slowly cooled rocks   总被引：13，自引：0，他引：13  

Herbert Kroll  Christos Evangelakakis  Gerhard Voll 《Contributions to Mineralogy and Petrology》1993,114(4):510-518

Recent improvements in the experimental and thermodynamic basis of two-feldspar geothermometry allow one to recover temperatures of coexistence more reliably. Some problems, however, persist: (1) the experimental solvi by Seck (1971a) and Elkins and Grove (1990) differ from each other; (2) it is not known to what extent Na–K–Ca exchange equilibrium is approached; (3) both solvi are probably metastable with regard to Al, Si order; (4) it is difficult to judge how closely high-temperature natural feldspars compare to this situation; (5) the thermodynamic treatment neglects phase transformations; (6) the temperature dependence of the Margules parameters used to model non-ideal mixing behaviour may not be linear; (7) it is not clear which expressions should be used to describe ideal activities. With these caveats in mind we treat the problem of retrograde resetting in high-grade metamorphic rocks that were slowly cooled under essentially dry conditions. Coexisting feldspars from such rocks commonly do not plot on a common isotherm. Thus temperatures derived from such pairs using any of the proposed two-feldspar geothermometers will necessarily be in error. We suggest that the non-equilibrium compositions result from retrograde intercrystalline K–Na exchange. This exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to Al–Si exchange, which is a prerequisite for (Na,K)–Ca exchange. We use a modified version of the Fuhrman and Lindsley (1988) programme to reverse the K–Na exchange and derive concordant temperatures.  相似文献