Romanian Academy

About: Romanian Academy is a archive organization based out in Bucharest, Romania. It is known for research contribution in the topics: Population & Nonlinear system. The organization has 3662 authors who have published 10491 publications receiving 146447 citations. The organization is also known as: Academia Română & Societatea Literară Română.

Geochronology of Neogene magmatism in the Carpathian arc and intra-Carpathian area

Abstract: Neogene to Quaternary volcanism in the Carpathian-Pannonian Region was related to the youngest evolutionary stage of the Carpathian arc and the intra-Carpathian area, with subduction, extension and asthenospheric upwelling as the main driving mechanisms. Volcanism occurred between 21 and 0.1 Ma, and showed a distinct migration in time from West to East. Several groups of calc-alkaline magmatic rock-types (felsic, intermediate and mafic varieties) have been distinguished, and several minor alkalic types also occur, including shoshonitic, K-trachytic, ultrapotassic and alkali basaltic. On the basis of spatial distribution, relationship to tectonic processes and their chemical composition, the volcanic formations can be divided into: (1) areally distributed felsic calc-alkaline formations related to the initial stages of back-arc extension, (2) areally distributed intermediate calc-alkaline formations related to advanced stages of back-arc extension, (3) "arc-type" andesite volcanic formations with a complex relationship to subduction processes, and (4) alkali basaltic magmatism related to post-convergence extension. Petrological data and geotectonic reconstructions, which involve these magmatic groups, place significant con- straints on geodynamic models of the Carpathian-Pannonian area. Subduction and back-arc extension were not contempora- neous across the whole Carpathian arc and intra-Carpathian area. Instead, three major geographical segments can be defined (Western, Central, Eastern segments) with a progressively younger timing of subduction roll-back and back-arc extension: 21—11 Ma, 16—9 Ma, 14—0 Ma, respectively. Short-lived subduction-related volcanic activity can be interpreted as either an indication of a limited width of subducted crust (not greater than 200 km) or an indication of detachment of the sinking slab. Interpretation of the areally distributed felsic and intermediate calc-alkaline volcanic formations are considered as being initiated by back-arc extension induced by diapiric uprise of "fertile" asthenospheric material.

Analysis of the Swirling Flow Downstream a Francis Turbine Runner

Abstract: An experimental and theoretical investigation of the flow at the outlet of a Francis turbine runner is carried out in order to elucidate the causes of a sudden drop in the draft tube pressure recovery coefficient at a discharge near the best efficiency operating point. Laser Doppler anemometry velocity measurements were performed for both axial and circumferential velocity components at the runner outlet. A suitable analytical representation of the swirling flow has been developed taking the discharge coefficient as independent variable. It is found that the investigated mean swirling flow can be accurately represented as a superposition of three distinct vortices. An eigenvalue analysis of the linearized equation for steady, axisymmetric, and inviscid swirling flow reveals that the swirl reaches a critical state precisely (within 1.3%) at the discharge where the sudden variation in draft tube pressure recovery is observed. This is very useful for turbine design and optimization, where a suitable runner geometry should avoid such critical swirl configuration within the normal operating range.