Improving Bayesian analysis for LISA Pathfinder using an efficient Markov Chain Monte Carlo method

We present a parameter estimation procedure based on a Bayesian framework by applying a Markov Chain Monte Carlo algorithm to the calibration of the dynamical parameters of the LISA Pathfinder satellite. The method is based on the Metropolis-Hastings algorithm and a two-stage annealing treatment in order to ensure an effective exploration of the parameter space at the beginning of the chain. We compare two versions of the algorithm with an application to a LISA Pathfinder data analysis problem. The two algorithms share the same heating strategy but with one moving in coordinate directions using proposals from a multivariate Gaussian distribution, while the other uses the natural logarithm of some parameters and proposes jumps in the eigen-space of the Fisher Information matrix. The algorithm proposing jumps in the eigen-space of the Fisher Information matrix demonstrates a higher acceptance rate and a slightly better convergence towards the equilibrium parameter distributions in the application to LISA Pathfinder data. For this experiment, we return parameter values that are all within ～1σ of the injected values. When we analyse the accuracy of our parameter estimation in terms of the effect they have on the force-per-unit of mass noise, we find that the induced errors are three orders of magnitude less than the expected experimental uncertainty in the power spectral density.     

Geochemical controls on leaching of lignite-fired combustion by-products from Greece

The mobility of inorganic pollutants is of key concern for a range of industrial and engineering applications of fly ash produced during the combustion of lignite in power generation. This paper investigates the role that the geochemical features of lignite, the ash composition and the partitioning of elements during combustion play in determining leaching properties of lignite fired by-products. The work is based on surveys on three lignite-fired power plants in Greece. Calcium-rich ashes show a high abatement potential for SO₂ and other gaseous pollutants. For most elements, the concentrations in the parent lignite and the ashes follow the same trend. Relative enrichments in Cd, Co, Cr, Cu, Mo, Ni, Pb, U, V, W, Zn fingerprint the regional and local geological settings of the lignite basins. The total and leachable concentrations of highly volatile elements are strongly influenced by the interaction with ubiquitous free lime. A broad array of elements is highly insoluble in alkaline ash, while a few oxyanionic-forming elements display substantial mobility. Their mode of occurrence in the parent lignite plays a primary role in the leaching of combustion ashes. The outcomes of this study may assist in addressing the impact of co-firing high ash or high Ca alternative fuels on the leaching properties of combustion by-products.     

Influence of frequency‐dependent soil–structure interaction on the fragility of R/C bridges

Bridge performance under earthquake loading can be significantly influenced by the interaction between the structure and the supporting soil. Even though the frequency dependence of the interaction mentioned in this study has long been documented, the simplifying assumption that the dynamic stiffness is dominated by the mean or predominant excitation frequency is still commonly made, primarily as a result of the associated numerical difficulties when the analysis has to be performed in the time domain. This study makes use of the advanced lumped parameter models recently developed 1 in order to quantify the impact of the assumption on the predicted fragility of bridges mentioned in this study. This is achieved by comparing the predicted vulnerability for the case of a reference, well studied, actual bridge using both conventional, frequency‐independent, Kelvin–Voigt models and the aforementioned lumped parameter formulation. Analysis results demonstrate that the more refined consideration of frequency dependence of soil–structure interaction at the piers and the abutments of a bridge not only leads to different probabilities of failure for given intensity measures but also leads to different hierarchy and distribution of damage within the structure for the same set of earthquake ground motions even if the overall probability of exceeding a given damage state is the same. The paper concludes with the comparative assessment of the effect for different soil conditions, foundation configurations, and ground motion characteristics mentioned in this study along with the relevant analysis and design recommendations. Copyright © 2016 John Wiley & Sons, Ltd.     

Neotectonic evolution of northwestern-continental Greece

The post-Miocene sedimentary and structural evolution of NW-continental Greece changes from west to east.In the west, along the Ionian coast, the tectonic activity of the Mio-Pliocene marine sedimentation is reflected in olisthostromes and intrafoliated folds. During the emergence of the area at the Pliocene/Pleistocene boundary, low angle thrusting, dissolution cleavage and open NNW to NNE trending folds, were developed. This horizontal shortening is the result of active plate convergence between the Apulian plate and the Aegean plate. Subsequent vertical movements continuing till the precent, produces mainly NNW and ENE directed faults.In the east, between the Ionian coast and Pindus thrust, nonmarine sedimentation began, in the middle Pliocene, on a folded and partially eroded substratum. Long fault bounded intramountaneous basins formed during general uplift and extension in three directions: NNW, ENE and WNW. Extension in both areas, resulting from NNW and ENE faults, is interpreted in terms of the action of upwelling convective currents induced by the Hellenic subduction. As the Aegean back arc extension migrated slowly westwards, the whole study area was gradually affected by WNW trending grabens.

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Zusammenfassung Spätmiozäne Sedimentationsprozesse sowie strukturelle Entwicklung ändern sich in NW kontinental-Griechenland in E-W Richtung.An der Ionischen Küste wurden während der spätmiozänen Absenkung des Sedimentationsraumes mächtige Olisthostrome und intrafoliale Falten gebildet. An der Grenze des Plio/Pleistozäns wurden flache überschiebungen, Lösungsschieferung und NNW bis NNE streichende, geöffnete Falten entwickelt. Diese tektonische Strukturen sind das Ergebnis aktiver Plattenkonvergenz zwischen der apulischen lithosphären-Platte und der ägäischen Platte. Während der postorogenen Aufhebung sind NNW und ENE streichende Verwerfungen entstanden.Im mittleren Pliozän wurden im Raum zwischen Ionischem Meer und der Pindos überschiebung auf dem gefalteten und teilweise erodierten Untergrund vorwiegend limnisch-terrestrische Sedimente abgelagert. Während der postorogenen Ausweitung sind Absenkungsräume in NNW- und ENE Richtung entstanden. Sie sind vermutlich das Ergebnis von Konvektionsströmungen innerhalb der Asthenosphäre, die durch die Hellenische Subduktion hervorgerufen wurden.Die Krustenausdehnung im ägäischen »back-arc basin« hat sich kontinuierlich gegen Westen verlagert, so da\ West-Griechenland zusätzlich von WNW streichenden Grabenstrukturen weitgehend deformiert ist.

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Résumé La partie nord-occidentale de la Grèce continentale montre, d'est en ouest, une modification des processus sédimentaires et structuraux.A l'ouest, le long de la cÔte ionienne, la sédimentation marine subsidente tardi-miocène s'est accompagnée de puissants olisthostromes et de plis intrafoliaux. La limite Pliocène-Pleistocène a vu se développer des charriages peu inclinés et des plis ouverts NNE à NNW accompagnés d'une schistosité de dissolution. Ce raccourcissement horizontal est le résultat de la convergence des plaques apulienne et égéenne. Il a été suivi de mouvements subséquents verticaux, encore actifs aujourd'hui, responsables de failles de directions NNW et ENE.Plus à l'est, entre la cÔte ionienne et le charriage du Pinde, une sédimentation continentale s'est installée, au Pliocène moyen, sur le substratum plissé et partiellement érodé. Au cours du soulèvement post-orogénique, des bassins intramontagneux de grabens se sont formés selon trois directions: NNW, ENE et WNW. Les deux premières sont interprétées comme le résultat de courants de convection induits dans l'asthénosphère par la subduction hellénique. Les grabens WNW seraient en relation avec le déplacement progressif vers l'ouest de la zone d'extension crustale du bassin d'arrière-arc égéen.

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Relationships of Phytoplankton with Certain Environmental Factors in the South Euboikos Gulf (Greece)

Abstract. The abundance and taxonomic diversity of phytoplankton have been studied in relation to certain environmental factors in the South Euboikos Gulf, a restricted tidal embayment on the eastern coast of Greece. The northern part of the gulf with higher tidal current, influenced by sewage and industrial effluents, showed high concentrations of nutrients, a greater total density of phytoplankton, relatively high chlorophyll a content, and a lower taxonomic diversity when compared with the southern part. The phytoplankton cycle was largely due to changes in diatom concentration. A slight variation in the occurrence of species and dominance could be observed along the salinity gradients.     

Model evaluation of the atmospheric boundary layer and mixed-layer evolution

In the present study, an attempt is made to assess the atmospheric boundary-layer (ABL) depth over an urban area, as derived from different ABL schemes employed by the mesoscale model MM5. Furthermore, the relationship of the mixing height, as depicted by the measurements, to the calculated ABL depth or other features of the ABL structure, is also examined. In particular, the diurnal evolution of ABL depth is examined over the greater Athens area, employing four different ABL schemes plus a modified version, whereby urban features are considered. Measurements for two selected days, when convective conditions prevailed and a strong sea-breeze cell developed, were used for comparison. It was found that the calculated eddy viscosity profile seems to better indicate the mixing height in both cases, where either a deep convective boundary layer develops, or a more confined internal boundary layer is formed. For the urban scheme, the incorporation of both anthropogenic and storage heat release provides promising results for urban applications.     

Identifying key environmental variables structuring benthic fauna for establishing a biotic typology for Greek running waters

A central aspect of the Water Framework Directive 2000/60/EC addressed to Member Countries is to proceed to type-specific ecological assessment and classification by establishing typology systems. Sixty-four permanent stream sites distributed throughout mainland Greece and islands were assessed with macroinvertebrate indicators to evaluate their ecological quality. Local and catchment scale parameters were determined and recorded to obtain an integrated assessment of the main factors affecting stream integrity and macroinvertebrate communities. Twenty-three sites were classified as reference or good status in terms of biological, chemical and hydromorphological quality with the use of various metrics. Multivariate statistical techniques were performed (MDS, BIOENV, correlation analysis and PCA) to investigate the main environmental factors structuring benthic macroinvertebrate communities and to select candidate environmental variables for establishing a biotic typology for Hellenic rivers. The results revealed relatively distinct macroinvertebrate communities within defined abiotic zones of the country. Assemblages of macroinvertebrate fauna were most strongly associated to differences in geographical position, altitude, slope, catchment area, current velocity, conductivity and water temperature. In view of the lack of sufficient data at the country level on the three last variables and after considering cause-effect relationships between large scale variables and the latter, it has been demonstrated that a number of catchment scale variables could be used as robust surrogates.     

The Contribution of Landslide Susceptibility Factors Through the Use of Rock Engineering System (RES) to the Prognosis of Slope Failures: An Application in Panagopoula and Malakasa Landslide Areas in Greece

This paper presents an application of the rock engineering system (RES) in an attempt to assess the proper landslide parameters and estimate the instability index, using two disastrous landslides in Greece which took place in Panagopoula (1971) and Malakasa (1995). RES has been developed by Hudson (Rock engineering systems: theory and practice. Ellis Horwood Limited, 1992) to determine interaction of a number of parameters in rock engineering design and calculate instability index for rock slopes. In this paper, an attempt is made to prove, how RES can be implemented in large-scale instability areas where natural slopes are associated with a variety of geomaterials (soils, rocks, weathering mantle, etc.), by selecting each time the most appropriate parameters that are relevant to the ad hoc potential slope failure and which can be quantified easiest than those of time and money consuming ones. RES approach allows the utilization of those parameters which are particularly active at the site, evaluates the importance of their interactions, taking into account the particular problems at any investigated site. The instability index for both study areas were calculated and found 89.47 for Panagopoula site and 81.59 for Malakasa (out of 100). According to the classification for landslide susceptibility by Brabb et al. (Landslide susceptibility in San Mateo County, California, 1972), both the examined case studies are classified as landslides, approving their existence as two serious slope failures. Thus, RES could be a simple and efficient tool in calculating the instability index and consequently in getting the prognosis of a potential slope failure in landslide susceptible areas, for land use and development planning processes.