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Search Results: 1 - 10 of 462308 matches for " Evangelos A. Baltas "
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Assessment of Climate Change Impacts in Greece: A General Overview  [PDF]
Maria A. Mimikou, Evangelos A. Baltas
American Journal of Climate Change (AJCC) , 2013, DOI: 10.4236/ajcc.2013.21005

The climatic and hydrological systems are tightly related and any induced changes cause chained interactions. In an attempt to adequately manage water resources in Greece, a series of experiments were conducted with different GCMs in selected study areas to understand this interplay. This paper is an overview of the studies carried out in the Aliakmon, the Upper Acheloos, the Portaikos, and the Pinios basins, where the regional hydrological cycle was evaluated on river basin spatial scale to assess regional impacts and variability. The impacts of climate change on the water resources are presented in a synthetic quantitative way, in order to draw general conclusions concerning the trends of the hydrological indicators. A good agreement was observed between the different climatic experiments, and the trends on the selected hydrological indicators demonstrate an increase in temperature and PET, reduction in the mean annual precipitation and runoff, and a shifting of the snowmelt period towards the winter, while the snowpack storage was proved to be a controlling factor. It is accentuated that relatively small decreases in the mean annual precipitation cause dramatic increase of reservoir risk levels of annual firm water supply and energy production. As a result, radical increases of reservoir storage volume are required to maintain firm water and energy yields at tolerable risk levels. The adaptive capacity of the country is not that high, and a series of serious actions need to be taken in order to mitigate the effects of climate change and assess its impacts.

Impact on Water Resources in a Mountainous Basin under the Climate Change Transient Scenario (UKTR)  [PDF]
E. A. Baltas
American Journal of Climate Change (AJCC) , 2014, DOI: 10.4236/ajcc.2014.31010

The impact of climate change on the hydrological regime and water resources in the basin of Venetikos river, in Greece is assessed. A monthly conceptual water balance model was calibrated in this basin using historical hydro meteorological data. This calibrated model was used to estimate runoff under a transient scenario (UKTR) referring to year 2080. The results show that the mean annual runoff, mean winter and summer runoff values, annual maximum and minimum values, as well as, monthly maximum and minimum, will be reduced. Additionally, an increase of potential and actual evapotranspiration was noticed due to temperature increase.

Technical Note: Determination of the SCS initial abstraction ratio in an experimental watershed in Greece
E. A. Baltas, N. A. Dervos,M. A. Mimikou
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2007,
Abstract: The present study was conducted in an experimental watershed in Attica, Greece, using observed rainfall/runoff events. The objective of the study was the determination of the initial abstraction ratio of the watershed. The average ratio (Ia/S) of the entire watershed was equal to 0.014. The corresponding ratio at a subwatershed was 0.037. The difference was attributed to the different spatial distribution of landuses and geological formations at the extent of the watershed. Both of the determined ratios are close to the ratio value of 0.05 that has been suggested from many studies for the improvement of the SCS-CN method.
Research on the initial abstraction – storage ratio and its effect on hydrograph simulation at a watershed in Greece
E. A. Baltas,N. A. Dervos,M. A. Mimikou
Hydrology and Earth System Sciences Discussions , 2007,
Abstract: The present research was conducted at an experimental watershed in the prefecture of Attica, Greece, using the selected observed rainfall-runoff events from a four-year time period. The objectives of this study were two: The first was the determination of the initial abstraction Ia – watershed storage S ratio. The average ratio (Ia/S) was equal to 0.014. The corresponding ratio at a subwatershed was 0.037. The difference was attributed to the different spatial distribution of landuses at the extent of the watershed. The second objective of the study was to examine the effect of the SCS empirical equation on hydrograph simulation. This was investigated through the comparison between the observed and two different simulated hydrographs at each one out of eighteen selected storm events. The simulated hydrographs were calculated by applying on the watershed's unit hydrograph two time distributions of excess rainfall that derived from the SCS method using two different approaches. In the first approach, the initial abstraction was determined from the observed rainfall-runoff data, while in the second, it was calculated using the SCS empirical equation. It was found that the SCS empirical equation estimates greater amount of initial abstraction and leads to the delayed start of the excess rainfall and the simulated runoff. This resulted in the overestimation of the peak flow rate and the time to peak at the majority of the storm events.
Statistical and neural classifiers in estimating rain rate from weather radar measurements
E. Baltas
Advances in Geosciences (ADGEO) , 2007,
Abstract: A distributed rainfall-runoff model capable for real time flood forecasting utilizing highly spatial and time resolution data was developed. The study region is located under the WSR-74 S-band 100 km radar umbrella and is equipped with a number of rain gauge recording stations, a permanent installation for flow measurement and a stage recorder. The entire basin was digitized to 2×2 km2 grid squares by implying GIS techniques. A series of rainfall events recorded producing floods were analyzed and processed. The linear channel parameter assigned to each grid-square is based on its location measured by the centroid of the grid square along the channel network. The estimation of the hill-slope and the stream velocity are calculated based on the Geographic Information System (GIS) procedures.
Integrating RFIDs and Smart Objects into a UnifiedInternet of Things Architecture  [PDF]
Evangelos A. Kosmatos, Nikolaos D. Tselikas, Anthony C. Boucouvalas
Advances in Internet of Things (AIT) , 2011, DOI: 10.4236/ait.2011.11002
Abstract: The term Internet of Things refers to the networked interconnection of objects of diverse nature, such as electronic devices, sensors, but also physical objects and beings as well as virtual data and environments. Although the basic concept of the Internet of Things sounds simple, its application is difficult and, so far, the respective existing architectural models are rather monolithic and are dominated by several limitations. The paper introduces a generic Internet of Things architecture trying to resolve the existing restrictions of current architectural models by integrating both RFID and smart object-based infrastructures, while also exploring a third parameter, i.e. the social potentialities of the Internet of Things building blocks towards shaping the “Social Internet of Things”. The proposed architecture is based on a layered lightweight and open middle-ware solution following the paradigm of Service Oriented Architecture and the Semantic Model Driven Ap-proach, which is realized at both design-time and deployment–time covering the whole service lifecycle for the corresponding services and applications provided.
Hydroxyl-platelet-activating factor exists in blood of healthy volunteers and periodontal patients
Smaragdi Antonopoulou,Alexandros Tsoupras,George Baltas,Helen Kotsifaki,Zacharias Mantzavinos,Constantinos A. Demopoulos
Mediators of Inflammation , 2003, DOI: 10.1080/09629350310001599666
Abstract: Periodontal diseases are localized chronic inflammatory conditions of the gingival and underlying bone and connective tissue. Platelet-activating factor (PAF), a potent inflammatory phospholipid mediator that has been previously detected in elevated levels in inflamed gingival tissues, in gingival crevicular fluid and in saliva, is implicated in periodontal disease. Our results from previous studies showed that the biologically active phospholipid detected in gingival crevicular fluid is a hydroxyl-PAF analogue. In this study, hydroxyl-PAF analogue was detected for the first time in human blood derived from patients with chronic periodontitis as well as from periodontally healthy volunteers. The hydroxyl-PAF analogue was purified by high-performance liquid chromatography, detected by biological assays and identified by electrospray analysis. In addition, the quantitative determination of PAF and hydroxyl-PAF analogue (expressed as PAF-like activity) showed a statistically significant increase in the ratio of hydroxyl-PAF analogue levels to PAF levels in periodontal patients, suggesting that this bioactive lipid may play a role in oral inflammation.
Cardiovascular Biomarkers in ACS: State of the Art 2012
Evangelos Giannitsis,Hugo A. Katus
Conference Papers in Science , 2013, DOI: 10.1155/2013/349796
Abstract: In the setting of an acute coronary syndrome cardiac troponins are well established for the diagnosis of myocardial infarction. In particular, diagnostic protocols using high-sensitivity troponin assays are being recommended for earlier diagnosis of MI by the European Society of Cardiology (ESC) guidelines on the management of ACS without ST segment elevation. In addition to accurate detection of myocardial necrosis, cardiac troponins give complementary information on short- and long-term prognosis and facilitate the identification of patients who derive benefits from a more aggressive anticoagulation and/or early invasive therapy versus conservative therapy. Other cardiac biomarkers may help to improve earlier diagnosis or improve risk stratification. Their role is currently under investigation. The present state-of-the-art paper gives an overview on the role of cardiac troponins including recent recommendations on the use of high-sensitivity assays from the third version of the Joint ESC/ACCF/AHA/WHF infarct definition “Universal MI definition” and the ESC guidelines. In addition, an overview on the role of novel cardiac biomarkers in earlier diagnosis or risk stratification is provided. 1. Introduction Coronary artery disease is one of the leading causes of death worldwide [1]. Better understanding of the pathomechanism of disease, use of more potent dugs, and improved diagnosis have helped to reduce CV mortality although total numbers of MI increase. Nowadays cardiac troponins are the preferred biomarkers for detection of myocardial cell necrosis and are essential for the diagnosis of myocardial infarction [2, 3]. The revised ESC/ACC definition of MI that had replaced the WHO definition of MI in the year 2000 [4] is now available in its third updated version [5]. This definition is supported by all major cardiology societies and by the WHO referred to as the third Universal MI definition. More recently, novel highly sensitive cTn assays are being increasingly used in clinical practice due to their superior analytical sensitivity allowing the detection of minute myocardial damage [6, 7]. Current ESC guidelines endorse earlier diagnostic algorithms using such hsTn assays [8]. However, increasing rates of patients with detectable cTn levels, not due to an ACS, also started to confuse clinicians [9]. This paper gives an overview on the present role of cTn and hsTn assays in diagnosis, risk stratification, and guidance of therapy and provide a state-of-the-art overview on new promising biomarkers for earlier or rapid rule-out of MI and for prognostic
Learning Optimal Control via Forward and Backward Stochastic Differential Equations
Ioannis Exarchos,Evangelos A. Theodorou
Mathematics , 2015,
Abstract: In this paper we present a novel sampling-based numerical scheme designed to solve a certain class of stochastic optimal control problems, utilizing forward and backward stochastic differential equations (FBSDEs). By means of a nonlinear version of the famous Feynman-Kac lemma, we obtain a probabilistic representation of the solution to the Hamilton-Jacobi-Bellman equation, expressed in form of a system of decoupled FBSDEs. This system of FBSDEs can then be simulated employing linear regression techniques. To enhance the efficiency of the proposed scheme when treating more complex nonlinear systems, we then derive an iterative modification based on Girsanov's theorem on the change of measure, which features importance sampling. The modified scheme is capable of learning the optimal control without requiring an initial guess. We present simulations that validate the algorithm by means of a direct comparison to a closed form LQR solution, and demonstrate its efficiency in treating nonlinear dynamics as well.
Value at Risk (VaR) Historical Approach: Could It Be More Historical and Representative of the Real Financial Risk Environment?  [PDF]
Evangelos Vasileiou
Theoretical Economics Letters (TEL) , 2017, DOI: 10.4236/tel.2017.74065
Abstract: The purpose of this paper is to suggest a new approach that improves the conventional Historical Value-at-Risk (HVaR) estimations’ accuracy and can be easily applied by anyone. The main assumption for the newly suggested method is “the more representative to the financial conditions the data inputs are, the better the VaR estimations”. Volatility is assumed to be the criterion for the “representative to the financial conditions” definition. In practice, the newly suggested approach does not use the previous x days observations as data inputs in the estimation process (as the HVaR does), but the last x filtered volatility (fv) observations of a “representative to the current financial conditions dataset”. Depending on the volatility value, each observation is classified in several regimes, from which the VaR is estimated depending on the examined day’s volatility. This way the HVaR approach is more historical. The empirical findings using data from the US and the Eurozone stock market show that the newly suggested filtered volatility approach not only significantly improves the VaR estimations, but also makes these estimations much more representative of the real financial conditions. The results using the filtered volatility approach are comparable to some previously documented VaR estimations that adopt advanced econometric models. In this point, we should note advanced econometric models have the drawbacks that are not usually applied in financial markets industry because of their complexity. The newly suggested approach: (i) popularizes some of the most advanced econometric techniques, (ii) improves the VaR estimations accuracy, and (iii) enables financial risk analysts and portfolio managers to estimate the risk-return under several volatility regimes in order to help them to apply their desired investment strategy. Finally, this paper not only examines accuracy using the traditional/conventional tests [1], but also suggests some new measures for the comparison amongst different VaR models and their ability to accurately estimate the real financial risk.
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