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Dotsika E.,Greek National Center For Scientific Research | Zisi N.,Greek National Center For Scientific Research | Zisi N.,Aristotle University of Thessaloniki | Tsoukala E.,Aristotle University of Thessaloniki | And 3 more authors.
Quaternary International | Year: 2011

Bones and teeth samples of Ursus ingressus from Loutra Arideas Cave (Greece) were used to determine the diet of this extinct species and to reconstruct the palaeoclimatic conditions. The age range of the fossil layers is from 32. ka BP to a maximum of 38. ka BP (radiocarbon dating). The method used was the isotopic analysis of carbonate bioapatite of fossil cave bear (U. ingressus) and brown bear (Ursus arctos) bone and tooth fragments, as well as water samples from springs of the Pindos area, the modern bear habitat. Several possible effects that may affect the isotopic composition of apatite were investigated, including age, sex, tooth type and diagenesis. The comparison of isotopic values of Greek U. ingressus to other Pleistocene Ursidae species in Europe, exhibit more positive and more variable δ13C values. These positive values are attributed mainly to diet, to bear physiology (differences among species) and to climate conditions. The diet of U. ingressus apparently was based mainly on vegetable matter, however with a variable component of animal protein. The variation observed in the δ18O values of U. arctos tooth enamel samples were attributed to environmental conditions, and through the spring waters isotopic gradient for the region of Northeastern Pindos, to differences in the bear's habitat elevation. Assuming similarity of the metabolism of modern and fossil bear species and incorporating only the effect of drinking water on the isotopic composition of body water, an equation has been derived that could be used to provide palaeoclimatic information. © 2011 Elsevier Ltd and INQUA. Source


Dritsas L.,Hellenic Air Force Academy | Tsoulkas V.N.,General Secretariat for Research and Technology | Tsoulkas V.N.,European Space Agency | Pantelous A.A.,University of Liverpool | Tzes A.,University of Patras
ISMS 2010 - UKSim/AMSS 1st International Conference on Intelligent Systems, Modelling and Simulation | Year: 2010

This paper is concerned with the investigation of robust performance of linear tracking controllers affected by unmodelled delays acting in the loop. The incentive comes from the area of Networked Control System (NCS) where the inevitable network-induced (transmission) delays are either timevarying or constant. The main contribution (based on extensive simulation work rather than strict mathematical proof) is that the tracking performance of (typical or more sophisticated) linear tracking control laws is drastically reduced when applied to NCS. The provided simulation results (i) demonstrate the impact of the network-induced delays on the tracking performance of single-input single-output NCS, (ii) provide initial guidelines for the tuning of the controllers and (iii) pave the road for further work to be done. © 2010 Crown Copyright. Source


Dotsika E.,Institute of Materials Science | Poutoukis D.,General Secretariat for Research and Technology | Kloppmann W.,Bureau de Recherches Geologiques et Minieres | Guerrot C.,Bureau de Recherches Geologiques et Minieres | And 2 more authors.
Applied Geochemistry | Year: 2010

The groundwater B concentration in Mesozoic karst, Neogene and alluvial aquifers in the West part of Chalkidiki province in Central Macedonia, Greece reaches 6.45mgL-1, which exceeds the limit of 1mgL-1, set by the European Union for drinking water. The high B contents have been detected in this area, not only near the shoreline, where seawater intrusion occurs, but also in the inland part of the basin. Multi isotope (2H, 18O, 34S, 18O(SO4), 11B, 87Sr/86Sr) data from borehole and thermal water springs allow identification of the possible B sources. The B dissolved in groundwater in the Chalkidiki area is mainly geogenic. The low δ11B values, 0-1‰, similar to those of thermal fluids from continental geothermal fields, and the low Cl/B ratio compared to seawater both indicate a geothermal origin for B and reflect deep circulation and interaction with igneous rocks. The 87Sr/86Sr ratio also indicates that the deep-aquifer granodiorite is the predominant rock source of Sr, while the shallow limestone unit has negligible effects on the dissolved Sr budget in these thermal karst waters which O and H isotopes show to be of meteoric origin. The main source of high B in borehole water is mainly mixing with B-rich geothermal water. The mixing between geothermal water and water from the Neogene aquifer is also reflected by isotopic contents of SO4. © 2010 Elsevier Ltd. Source


Dotsika E.,Greek National Center For Scientific Research | Lykoudis S.,Institute of Environmental Research and Sustainable Development | Lykoudis S.,University of Patras | Poutoukis D.,General Secretariat for Research and Technology
Global and Planetary Change | Year: 2010

This paper reviews all available stable isotopic data concerning precipitation and spring water in Greece, from the 1960s until today. Spatial variability is investigated in order to provide basic information and identify the locally significant parameters that affect isotopic distributions. The area of interest was partitioned into eight sections according to geographical location and climatic characteristics. The distance of the station from the sea and the altitude are the main factors imprinted in the isotopic signature of precipitation. Local meteoric water meteoric line (LMWL) for precipitation and spring water were calculated for each section and for Greece as a whole. Precipitation LMWLs differ from the Global Meteoric Water Line (GMWL) in various ways across Greece. Elevated deuterium excess values are observed, probably due to water vapour originating from the Aegean or the Mid-eastern Mediterranean. Spring LMWLs are more or less consistent throughout the country. Furthermore, a high resolution map of precipitation and freshwater spring (Cl- < 200 ppm and T < 25 °C) δ18O reveals several interesting features such as an orographic shadow effect induced by the Pindos Mountains, a strong climatic signal in southern Greece and a local city-microclimate effect around Athens. © 2009 Elsevier B.V. All rights reserved. Source


Pantelous A.A.,University of Liverpool | Karageorgos A.D.,National and Kapodistrian University of Athens | Tsoulkas V.N.,General Secretariat for Research and Technology | Tsoulkas V.N.,European Space Agency | Kalogeropoulos G.I.,National and Kapodistrian University of Athens
Neural, Parallel and Scientific Computations | Year: 2011

The aim of this paper is two fold. First, we want to discuss the solution properties of higher order linear descriptor matrix differential systems. Secondly, we want to extend the classical matrix rank criterion for the controllability of first order to higher order linear descriptor matrix differential systems. This criterion has been chosen and studied, since it is a typical property and requirement for many modern control systems while at the same time it emerges in a plethora of different control science applications. © Dynamic Publishers, Inc. Source

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