Axisymmetric modes of rotating relativistic stars in the Cowling approximation     

José A. Font  Harald Dimmelmeier  Anshu Gupta  Nikolaos Stergioulas 《Monthly notices of the Royal Astronomical Society》2001,325(4):1463-1470

Axisymmetric pulsations of rotating neutron stars can be excited in several scenarios, such as core collapse, crust- and core-quakes or binary mergers, and could become detectable in either gravitational waves or high-energy radiation. Here, we present a comprehensive study of all low-order axisymmetric modes of uniformly and rapidly rotating relativistic stars. Initial stationary configurations are appropriately perturbed and are numerically evolved using an axisymmetric, non-linear relativistic hydrodynamics code, assuming time-independence of the gravitational field (Cowling approximation). The simulations are performed using a high-resolution shock-capturing finite-difference scheme accurate enough to maintain the initial rotation law for a large number of rotational periods, even for stars at the mass-shedding limit. Through Fourier transforms of the time evolution of selected fluid variables, we compute the frequencies of quasi-radial and non-radial modes with spherical harmonic indices l =0 , 1, 2 and 3, for a sequence of rotating stars from the non-rotating limit to the mass-shedding limit. The frequencies of the axisymmetric modes are affected significantly by rotation only when the rotation rate exceeds about 50 per cent of the maximum allowed. As expected, at large rotation rates, apparent mode crossings between different modes appear. In addition to the above modes, several axisymmetric inertial modes are also excited in our numerical evolutions.  相似文献   

Changing return periods of weather-related impacts: the attribution challenge     

Peter A. Stott  Nikolaos Christidis  Richard A. Betts 《Climatic change》2011,109(3-4):263-268

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POC and particulate Th export fluxes estimated using Th/U disequilibrium in an enclosed Eastern Mediterranean region (Saronikos Gulf and Elefsis Bay, Greece) in seasonal scale     

Nikolaos Evangeliou  Heleny Florou 《Geochimica et cosmochimica acta》2011,75(19):5367-5388

Activity concentrations of the naturally occurring, short-lived and highly particle-reactive radionuclide tracer ²³⁴Th in the dissolved and particulate phase were determined at 7 shallow-water stations (maximum depths: 30 (S.1 and S.2), 65 (S.3), 97 (S.5), 105 (S.6) and 220 m (S.4 and S.7) in Saronikos Gulf and Elefsis Bay (central Aegean Sea, Greece) during 3 seasonal cruises (summer 2008, autumn 2008 and winter 2009) to assess the time scales of the dynamics and the depositional fate of particulate matter (POC, particulate ²³⁴Th). For that reason, in situ filtrating systems were deployed in several depths of the water column consisting of GF/A disc prefilters to scavenge particulate fraction of ²³⁴Th and organic carbon and impregnated cartridges to adsorb dissolved ²³⁴Th.The obtained data showed average particulate ²³⁴Th activity concentrations of 3.7 ± 0.4 Bq m⁻³ in summer, 2.1 ± 0.2 Bq m⁻³ in autumn and 2.4 ± 0.2 Bq m⁻³ in winter. The respective average dissolved ²³⁴Th activity concentrations were 30.1 ± 2.8 Bq m⁻³ in summer, 30.2 ± 2.9 Bq m⁻³ in autumn and 27.4 ± 3.0 Bq m⁻³ in winter. The activity ratios of total ²³⁴Th and its long-lived conservative parent ²³⁸U were below unity in most of the stations indicating radioactive disequilibrium throughout the water column, thus very dynamic trace-metal scavenging and particle export from the water column. These profiles (²³⁴Th and ²³⁸U) were used to estimate the export fluxes and scavenging rates of ²³⁴Th, as well as their residence times in the water column. The average cumulative export fluxes of particulate ²³⁴Th were estimated to be 33 ± 4 Bq m⁻² d⁻¹ in summer, 35 ± 5 Bq m⁻² d⁻¹ in autumn and 45 ± 6 Bq m⁻² d⁻¹ in winter, whereas the respective average cumulative scavenging rates of dissolved ²³⁴Th were 39 ± 5, 33 ± 5 and 50 ± 7 Bq m⁻² d⁻¹. Moreover, the cumulative average residence times of ²³⁴Th were 25 ± 4 d in summer, 45 ± 6 d in autumn and 64 ± 7 d in winter 2009 for the dissolved fraction and 4 ± 1, 3 ± 1 and 4 ± 1 d for the particulate one, respectively.POC/ ratio profiles decreased versus depth showing a variety of marine processes, such as loss of POC due to dissolution after biological activity, impact of minerals in particle sinking and microbial remineralization. Average cumulative export fluxes of POC were 162 ± 18 mmol m⁻² d⁻¹ in summer, 107 ± 19 mmol m⁻² d⁻¹ in autumn and 157 ± 25 mmol m⁻² d⁻¹ in winter 2009. The seasonal data of POC fluxes certified the existence of phytoplankton bloom in winter for Saronikos Gulf. In addition, after evaluating the maxima of POC fluxes in Elefsis Bay (a small embayment in northern Saronikos Gulf) during summer, potential bloom of phytoplankton also concluded; this approach is in agreement with previous data of the same area. Finally, the elevated POC concentrations and fluxes in the region certify that the Gulf is still one of the most organic polluted in the Mediterranean Sea.  相似文献   

Salinity changes in the World Ocean since 1950 in relation to changing surface freshwater fluxes   总被引：1，自引：0，他引：1  

Nikolaos Skliris  Robert Marsh  Simon A. Josey  Simon A. Good  Chunlei Liu  Richard P. Allan 《Climate Dynamics》2014,43(3-4):709-736

Global hydrographic and air–sea freshwater flux datasets are used to investigate ocean salinity changes over 1950–2010 in relation to surface freshwater flux. On multi-decadal timescales, surface salinity increases (decreases) in evaporation (precipitation) dominated regions, the Atlantic–Pacific salinity contrast increases, and the upper thermocline salinity maximum increases while the salinity minimum of intermediate waters decreases. Potential trends in E–P are examined for 1950–2010 (using two reanalyses) and 1979–2010 (using four reanalyses and two blended products). Large differences in the 1950–2010 E–P trend patterns are evident in several regions, particularly the North Atlantic. For 1979–2010 some coherency in the spatial change patterns is evident but there is still a large spread in trend magnitude and sign between the six E–P products. However, a robust pattern of increased E–P in the southern hemisphere subtropical gyres is seen in all products. There is also some evidence in the tropical Pacific for a link between the spatial change patterns of salinity and E–P associated with ENSO. The water cycle amplification rate over specific regions is subsequently inferred from the observed 3-D salinity change field using a salt conservation equation in variable isopycnal volumes, implicitly accounting for the migration of isopycnal surfaces. Inferred global changes of E–P over 1950–2010 amount to an increase of 1 ± 0.6 % in net evaporation across the subtropics and an increase of 4.2 ± 2 % in net precipitation across subpolar latitudes. Amplification rates are approximately doubled over 1979–2010, consistent with accelerated broad-scale warming but also coincident with much improved salinity sampling over the latter period.  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   

Modelling the impact of Black Sea water inflow on the North Aegean Sea hydrodynamics     

Margarita Tzali  Sarantis Sofianos  Anneta Mantziafou  Nikolaos Skliris 《Ocean Dynamics》2010,60(3):585-596

The impact of the Black Sea Water (BSW) inflow on the circulation and the water mass characteristics of the North Aegean Sea is investigated using a high-resolution 3D numerical model. Four climatological numerical experiments are performed exploring the effects of the exchange amplitude at the Dardanelles Straits in terms of the mean annual volume exchanged and the amplitude of its seasonal cycle. Larger inflow of low salinity BSW influences the water characteristics of the whole basin. The largest salinity reduction is encountered in the upper layers of the water column, and the most affected region is the northeastern part of the basin. The winter insulation character of the BSW layer (low-salinity layer) is reduced by the seasonal cycle of the inflow (minimum during winter). The maximum atmospheric cooling coincides with the minimum BSW inflow rate, weakening the vertical density gradients close to the surface and thus facilitating the vertical mixing. The inflow rate of BSW into the North Aegean Sea constitutes an essential factor for the circulation in the basin. Increased inflow rate results into considerably higher kinetic energy, stronger circulation and reinforcement of the mesoscale circulation features. Although the position of the front between BSW and waters of Levantine origin does not vary significantly with the intensity of the BSW inflow rate, the flow along the front becomes stronger and more unstable as the inflow rate increases, forming meanders and rings. The changes in the intensity of BSW inflow rate overpower the wind and thermohaline forcing and largely determine the general circulation of the North Aegean Sea.  相似文献   

A focusing approach to ground water detection by means of electrical and EM methods: the case of Paliouri, Northern Greece     

George Vargemezis  Panayiotis Tsourlos  Alexandros Stampolidis  Ilias Fikos  Dimitrios Ballas  Nikolaos Papadopoulos 《Studia Geophysica et Geodaetica》2012,56(4):1063-1078

In this paper the main results from the implementation and interpretation of a geophysical survey carried out in Chalkidiki (Northern Greece) are presented. The objective of the geophysical survey was to study the general geological conditions of the area (stratigraphy and tectonism) and to focus on the hydrogeological behaviour of the geological formations in the area. The ultimate target was to point out the most promising locations for the successful construction of hydro wells. Since direct hydrogeological information was not available, three different geophysical techniques were applied in order to follow a step by step approach to the exploration of the study area. Firstly, the Very Low Frequency (VLF) electromagnetic method was applied since the majority of the area was dominated by the formation of ophiolites and water flow was possibly expected only in fractured zones at a relatively small depth. Secondly, at the locations of the conductive zones detected by the VLF survey additional Electrical Resistivity Tomography (ERT) sections at different scales were measured to provide more detailed information about the geometrical characteristics of them. Finally, Self-Potential (SP) measurements along the same profiles were conducted in order to provide supplementary information concerning the nature of the conductive zones such as the possible relation with electrokinetic sources. The combined interpretation of the geophysical data proved very efficient for deciding the most promising locations for the construction of hydro wells.  相似文献   

Alfvén QPOs in magnetars in the anelastic approximation     

Pablo Cerdá-Durán  Nikolaos Stergioulas  José A. Font 《Monthly notices of the Royal Astronomical Society》2009,397(3):1607-1620

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Sequential Extraction of Chromium from Contaminated Aquifer Sediments     

Jay M. Asikainen  Nikolaos P. Nikolaidis 《Ground Water Monitoring & Remediation》1994,14(2):185-191

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Vertical Distribution and Partitioning of Chromium in a Glaciof luvial Aquifer     

Nikolaos P. Nikolaidis  Gary A. Robbins  Michelle Scherer  Brian McAninch  Gordon Binkhorst  Jay Asikainen  Steven L. Suib 《Ground Water Monitoring & Remediation》1994,14(3):150-159

The vertical distribution and partitioning (between the solid and aqueous phase) of chromium in a glaciofluvial aquifer in northeastern Connecticut were assessed. Most of the chromium (99 percent of its mass) is bound to the soil. Retardation is primarily the result of binding to organic matter and adsorption to iron oxide coatings. However, other attenuation mechanisms also appear to be significant. If the degree of chromium binding observed here is representative of other chromium contaminated sites, pump-and-treat remediation will not remove the vast amount of chromium from the subsurface. However, most of the chromium may be immobile, and removal may not be required following the initial pumping to remove the mobile fraction. Further knowledge of the mechanisms that bind chromium to the soil, their reversibility, and their kinetics is essential to developing effective remediation strategies.  相似文献