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The assumption of reference station conditions is investigated for the first time across 60 rock stations belonging to the broadband and accelerometric networks of the National Observatory of Athens. We select the stations based on the established belief that they lie on rock, and provided that their data have been publicly available for long enough to yield a substantial number of recordings. No site effects studies have been conducted before for the ensemble of the stations under study. Furthermore, no ad hoc field campaigns have been performed to characterise them, save in few cases. The first step is to compile all existing information for these stations from all publicly available sources and past studies, including geology, topography, station installation, Vs30 estimates and any other known metadata. The second step is to compile ad-hoc information from maps combined with the operator's first-hand experience of the sites, to better describe the geological unit and age, along with other characteristics such as station installation and morphology. The third and largest step is to compile the first Greek ground-motion dataset on rock and to perform a detailed analysis of the recordings to estimate site-specific transfer functions and hence assess local site response characteristics for each station. A strong-motion dataset of 6840 recordings is developed and curated for this purpose, visually inspected and processed in the time and frequency domains. Single-station amplification functions (horizontal-to-vertical spectral ratios, HVSR) are estimated from the seismic data, and the site resonance characteristics are assessed, not only in the conventional way of combining horizontal components, but also assessing the transfer function's directional sensitivity. Considering that 'true' reference site behaviour implies low, flat amplification with no directional dependence, these transfer function characteristics are combined with the compiled station metadata -existing and new- to evaluate the stations' overall capacity as reference sites. The stations are grouped interms of behaviour and the preferred ones are recommended, hoping to facilitate the better use of seismic data in future hazard applications. [ABSTRACT FROM AUTHOR]

Maritime transportation constitutes a dynamic Greek economic sector. Greece accounted for 25% of the Maritime Passenger Traffic (MPT) in the European Union in 2007. However, due to the economic recession since 2009, maritime passenger transportation has been facing increasing fuel prices along with declining demand. In this paper, we develop transfer function models, including macroeconomic indicators, for forecasting the coastal and the Adriatic MPT in Greek ports. The majority of the MPT models include the Gross Domestic Product (GDP) as an explanatory variable, reflecting the financial impact on maritime flows. Although the employment and the economic crisis dummy are also used as explanatory variables, the unemployment and the oil price do not affect MPT. The coastal traffic models are generally more consistent when the seasonality trend is eliminated, while the international traffic models perform better when the inherent seasonality is considered. This first effort contributes toward filling the gap of MPT forecasting models for supporting policy-making on maritime transportation. [ABSTRACT FROM AUTHOR]

• Impedance based analysis considering grid-forming and grid-following inverter operation modes was conducted. • Proportional gain margins for the controllers have been calculated. • The transition of a microgrid from grid-connected to islanded with regard to fast interaction converter driven stability has been investigated. • Theoritical analysis matches well with the real time SIMULINK results. • A test case with a real microgrid (Gaidouromantra) has been investigated. Massive integration of power electronic devices with multiple control schemes in a wide frequency range pose new challenges regarding systems stability and reliability. Interactions between the fast control loops or between the fast control loops and passive elements of the grid, have been reported in literature and have led to introducing a new type of stability: the Fast-Interaction Converter-driven Stability (FICDS). In this paper, factors affecting the FICDS, such as tuning controller parameters, line parameters, number of interconnected inverters, are explored in four microgrid topologies, operating in grid connected and islanded mode. With the use of an impedance based model which tracks the poles of the CDS transfer functions of each system, their stability has been assessed. The obtained results have been verified via time-domain simulations. Simulations from the islanded microgrid of Gaidouromantra in Greece showcase the impact of the control parameters on the operation of the system and indicate the need for further investigation. [ABSTRACT FROM AUTHOR]

This study compares two econometric methodologies, namely a near-VAR model (the currently established methodology) and a multiple input transfer function model, in a case-study where the informational efficiency on the Athens Stock Exchange (ASE) is examined. An ad-hoc model building methodology for the multiple input transfer function model is proposed. As is argued such an approach has some comparative advantages over VAR models. Results showed that although the hypothesis of informational efficiency can be accepted for ASE with some reservations using transfer functions, the results of the VAR model are suggestive of a rejection of this hypothesis. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the paper is the definition of the material parameters of sediments in the western part of Thessaloniki useful in the prediction of strong ground motion. The region of interest is elongated in the E–W direction and is confined between the Kalochori suburb and the harbor of Thessaloniki, while in the N–S direction it is extended between the coastline and the region of sediments and outcrop rock boundary. Many geological and seismotectonic studies, as well as geophysical surveys with electrical soundings and geotechnical boreholes, contribute to our understanding of the general sedimentary structure. Nonetheless, these studies could not provide any information regarding the material stiffness in terms of shear wave velocity; the most useful parameter in site response studies. In the present paper, alternative SPAC method is used to analyze array microtremor data to determine the shear wave Vs velocity distribution in two areas at the northwestern part of the urban area of Thessaloniki. At the beginning, the differences between alternative and standard SPAC are stressed and the reliability of the first one is shown. The Rayleigh wave phase velocity dispersion curve is determined using vertical component and their inversion lead to the determination of deep Vs profiles. The existence of conventional seismic measurements (Cross Hole, Down Hole) in combination with deep Vs profiles from microtremor data are used to verify Vs values for the characteristic deposits of the area. Moreover, the correlation between theoretical transfer functions based on the determined Vs profiles with the empirical ones from ambient noise and earthquakes recordings are used to validate the Vs profiles and to have a first idea of their site response. Finally, the thickness of the Quaternary sediments in the area of interest is found to increase from the east (city) to the west and from north to south where they attain their maximum thickness (almost 500m) in consistency with other independent estimations. These sediments are distinguished in 4 horizons according to their Vs velocity, which from top to bottom are as follows: a) a layer of 80–150m/s present only at the offshore zone, b) a layer of 200–250m/s, very thin at the northern zone and until 20–55m depth at the coastal sites c) a layer of 350–450m/s down to 10–30m and 70–140m depth at the northern and offshore zones, respectively, and d) a layer of 550–650m/s until 60–200m at the north and 150–485m depth at offshore zone. [Copyright &y& Elsevier]

Normal lung function values are conventionally calculated according to prediction equations. The primary objective of this study is the development of a different method for the prediction of FVC and FEV 1 parameters, in order to achieve better correlation of the predicted values to the real ones. Using a sample from the Greek elderly population that was separated into two groups (a training and a testing one), a number of artificial neural networks were trained. Considering that men and women were studied separately and that two parameters (FVC, FEV 1 ) were the target of the study, four cases came up. In each case two neural networks were trained using different transfer functions, number of neurons and number of layers. When passing the inputs of the testing data set to the trained networks it was found that the outputs were well correlated with the corresponding measures of the sample. Furthermore, the match with the sample, for a number of neural networks developed, was better compared to the matches of Baltopoulos et al . study that used the same sample for developing prediction equations. This high match allows the potential use of neural networks for predicting not only FVC and FEV 1 but also other spirometric parameters. [ABSTRACT FROM AUTHOR]