Ophiolites of the eastern Vardar Zone, N. Greece

In the present thesis, the geochemistry, petrology and geochronology of ophiolite complexes from central northern Greece were studied in detail in order to gain insights on the petrogenetic pathways and geodynamic processes that lead to their formation and evolution. The major- and trace-element content of minerals and whole rocks from all four ophiolite complexes was determined using high-precision analytical equipment. These results were then coupled with Nd and Sr isotopic measurements. In order to precisely place the evolution of these ophiolites in time, U-Pb geochronology on zircons was conducted using a SHRIMP-II. The data obtained suggest that the ophiolites studied invariably show typical characteristics of subduction-zone magmatism (e.g. negative Nb anomalies, Th enrichment). In N-MORB-normalised multielement profiles the high field-strength elements display patterns that vary from depleted to N-MORB-like. Chondrite-normalised rare-earth element (REE) profiles show flat heavy-REE patterns suggesting a shallow regime of source melting for all the ophiolites, well within the stability field of spinel lherzolite. The majority of the samples have light-REE depleted patterns. 87Sr/86Sr isotopic ratios range from 0.703184 to 0.715853 and are in cases influenced by alteration. The εNd values are positive (the majority of the mafic samples is typically 7.1-3.1) but lower than N-MORB and depleted mantle. With the exception of the Thessaloniki ophiolite that has uniform island-arc tholeiitic chemical characteristics, the rest of the ophiolites show dual chemistry consisting of rocks with minor subduction-zone characteristics that resemble chemically back-arc basin basalts (BABB) and rocks with more pronounced subduction-zone characteristics. Tectonomagmatic discrimination schemes classify the samples as island-arc tholeiites and back-arc basin basalts or N-MORB. Melting modelling carried out to evaluate source properties and degree of melting verifies the dual nature of the ophiolites. The samples that resemble back-arc basin basalts require very small degrees of melting (<10%) of fertile sources, whereas the rest of the samples require higher degrees (25-15%) of melting. As deduced from the present geochemical and petrological investigation, the ophiolites from Guevguely, Oraeokastro, Thessaloniki, and Chalkidiki represent relics of supra-subduction zone crust that formed in succeeding stages of island-arc rifting and back-arc spreading as well as in a fore arc setting. The geochronological results have provided precise determination of the timing of formation of these complexes. The age of the Guevguely ophiolite has been determined as 167±1.2 Ma, that of Thessaloniki as 169±1.4 Ma, that of Kassandra as 167±2.2 Ma and that of Sithonia as 160±1.2 Ma.In der vorliegenden Arbeit werden neue geochemische, petrologische und geochronologische Ergebnisse für verschiedene Ophiolith-Komplexe aus dem zentralen Teil Nordgriechenlands präsentiert und im Rahmen petrogenetischer and geodynamischer Modelle diskutiert. Ein neues Modell für die Genese dieser Ophiolith-Komplexe wird vorgestellt. Von allen vier oben genannten Ophiolith-Komplexen wurden Proben genommen und die Haupt- und Spurenelementgehalte von Mineralen und am Gesamtgestein mit moderner Analytik untersucht. Ergänzend wurden die Nd- und Sr-Isotopie bestimmt. Die Bestimmung des Alters der Ophiolith-Komplexe erfolgte anhand von Einzelzirkondatierungen unter Verwendung von SHRIMP II. Anhand der gewonnen Daten kann festgestellt, dass die Ophiolithe typische Merkmale für einen subduktionsbezogenen Magmatismus aufweisen, wie z.B. eine negative Nb-Anomalie und eine Anreicherung in Th. Die HFS-Elemente zeigen typische Muster zwischen verarmten Mantel und N-MORB in N-MORB-normalisierten Diagrammen. In C1-normalisierten Diagrammen zeigen die schweren Seltenen Erdelemente flache Muster, was auf eine Schmelzbildung in geringer Tiefe, innerhalb des Stabilitätsfeldes von Spinell-Lherzolith schließen lässt. Der Großteil der Proben zeigt eine Verarmung an leichten Seltenen Erdelementen. Die 87Sr/86Sr-Isotopie zeigt Werte zwischen 0,703184 und 0,715853 und ist in einzelnen Fällen durch Alteration beeinflusst. Die εNd-Werte sind positiv (für den Hauptteil der mafischen Proben liegt sie zwischen 7,1 und 3,1) aber niedriger als N-MORB und verarmter Mantel. Mit Ausnahme des Ophiolith-Komplexes von Thessaloniki, der die chemische Signatur von Inselbogen-Tholeiiten aufweist, besitzen alle anderen untersuchten Ophiolithe entweder nur untergeordnet einen subduktionsbezogenen chemischen Charakter, die denen von Back-Arc Becken Basalten (BABB) ähnelt, oder ihre chemische Signatur ist signifikant subduktionsbezogen. In Diskriminationsdiagrammen für den geotektonischen Rahmen liegen die Proben in den Feldern für Islandbogen-Tholeiite und Back-Arc Becken Basalte oder N-MORB. Der doppelfache chemische Charakter wird auch bestätigt durch petrogenetische Modellierung. Die Proben mit Back-Arc Becken Charakter benötigen nur einen geringen Grad an Schelzbildung (<10 %) einer fertilen Mantelquelle, wohingegen alle andern Proben einen höheren Grad an Aufschelzung (15–25%) aufzeigen. Basierend auf den geochemischen und petrologischen Untersuchungen kann festgehalten werden, dass die Ophiolith-Komplexe von Guevguely, Oraeokastro, Thessaloniki und Chalkidiki Relikte einer ozeanischen Kruste mit Supra-Subduktionszonen-Charakter darstellen, die Phasen von Inselbogen-Rifting und Back-Arc-Rifting beinhalten. Die geochronologischen Daten belegen mitteljurassische Alter für die Ophiolithe: 167±1,2 Ma für Guevguely, 169±1,4 Ma für Thessaloniki, 167±2,2 Ma für Kassandra und 160±1,2 für Sithonia. Das Alter der magmatischen Serie von Chortiatis, einer niedrig-K Diorite dominierten Serie östlich der Ophiolith-Komplexe, kann mit 159±4.2 Ma angeben werden

How to improve open rotor aerodynamics at cruise and take-off

AbstractA key challenge in open rotor design is getting the optimum aerodynamics at both the cruise and take-off conditions. This is particularly difficult because the operation and the requirements of an open rotor are very different at cruise compared to takeoff. This paper uses CFD results to explore the impact of various design changes on the cruise and take-off flow-fields. The paper then considers how a given open rotor design is best operated at take-off to minimise noise whilst maintaining high thrust. The main findings are that various design modifications can be applied to control the flow features that lead to lost efficiency at cruise and increased noise emission at take-off. A breakdown of the lost power terms from CFD solutions demonstrates how developments in open rotor design have led to reduced aerodynamic losses. At take-off, the operating point of the open rotor should be set such that the non-dimensional lift is as high as possible, without causing significant flow separation. This can be achieved through suitable amounts of re-pitch and speed up applied to a design. Comparisons with fully three-dimensional CFD show that the amount of re-pitch required can be determined using simplified methods such as two-dimensional CFD and a Blade Element Method.This is the accepted manuscript. The final published version is available at http://aerosociety.com/News/Publications/Aero-Journal/Online/2522/How-to-improve-open-rotor-aerodynamics-at-cruise-and-takeoff

Wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions for superconducting quantum processors

We investigate die-level and wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan Josephson junctions, using multiple substrates with and without through-silicon vias (TSVs). Dolan junctions fabricated on planar substrates have the highest yield and lowest room-temperature conductance spread, equivalent to ~100 MHz in transmon frequency. In TSV-integrated substrates, Dolan junctions suffer most in both yield and disorder, making Manhattan junctions preferable. Manhattan junctions show pronounced conductance decrease from wafer centre to edge, which we qualitatively capture using a geometric model of spatially-dependent resist shadowing during junction electrode evaporation. Analysis of actual junction overlap areas using scanning electron micrographs supports the model, and further points to a remnant spatial dependence possibly due to contact resistance.Comment: 25 pages, 13 figures, 1 tabl

Financial fragmentation and SMEs’ access to finance

This paper focuses on the impact of financial fragmentation on small and medium enterprises (SMEs)’ access to finance. We combine country-level data on financial fragmentation and the ECB’s SAFE (Survey on the Access to Finance of Enterprises) data for 12 European Union (EU) countries over 2009-2016. Our findings indicate that an increase in financial fragmentation not only raises the probability of all firms to be rationed but also to be charged higher loan rates; in addition, it increases the likelihood of borrower discouragement and it impairs firms’ perceptions of the future availability of bank funds. Less creditworthy firms are even more likely to become credit rationed, suggesting a flight to quality effect in lending. However, our study also documents a potential adverse effect of increasing bank market power resulting from greater integration. This suggests that financial integration could impair firms’ financing, if not accompanied by policy initiatives aimed at maintaining an optimal level of competition in the banking sector

Research on information systems failures and successes: Status update and future directions

The final publication is available at Springer via http://dx.doi.org/10.1007/s10796-014-9500-yInformation systems success and failure are among the most prominent streams in IS research. Explanations of why some IS fulfill their expectations, whereas others fail, are complex and multi-factorial. Despite the efforts to understand the underlying factors, the IS failure rate remains stubbornly high. A Panel session was held at the IFIP Working Group 8.6 conference in Bangalore in 2013 which forms the subject of this Special Issue. Its aim was to reflect on the need for new perspectives and research directions, to provide insights and further guidance for managers on factors enabling IS success and avoiding IS failure. Several key issues emerged, such as the need to study problems from multiple perspectives, to move beyond narrow considerations of the IT artifact, and to venture into underexplored organizational contexts, such as the public sector. © 2014 Springer Science+Business Media New York

Institutional investors and corporate governance

We provide a comprehensive overview of the role of institutional investors in corporate governance with three main components. First, we establish new stylized facts documenting the evolution and importance of institutional ownership. Second, we provide a detailed characterization of key aspects of the legal and regulatory setting within which institutional investors govern portfolio firms. Third, we synthesize the evolving response of the recent theoretical and empirical academic literature in finance to the emergence of institutional investors in corporate governance. We highlight how the defining aspect of institutional investors – the fact that they are financial intermediaries – differentiates them in their governance role from standard principal blockholders. Further, not all institutional investors are identical, and we pay close attention to heterogeneity amongst institutional investors as blockholders