Groundwater table fluctuations recorded in zonation of microbial siderites from end-Triassic strata

In a terrestrial Triassic–Jurassic boundary succession of southern Sweden, perfectly zoned sphaerosiderites are restricted to a specific sandy interval deposited during the end-Triassic event. Underlying and overlying this sand interval there are several other types of siderite micromorphologies, i.e. poorly zoned sphaerosiderite, spheroidal (ellipsoid) siderite, spherical siderite and rhombohedral siderite. Siderite overgrowths occur mainly as rhombohedral crystals on perfectly zoned sphaerosiderite and as radiating fibrous crystals on spheroidal siderite. Concretionary sparry, microspar and/or micritic siderite cement postdate all of these micromorphologies. The carbon isotope composition of the siderite measured by conventional mass spectrometry shows the characteristic broad span of data, probably as a result of multiple stages of microbial activity. SIMS (secondary ion mass spectrometry) revealed generally higher δ13C values for the concretionary cement than the perfectly zoned sphaerosiderite, spheroidal siderite and their overgrowths, which marks a change in the carbon source during burial. All the various siderite morphologies have almost identical oxygen isotope values reflecting the palaeo-groundwater composition. A pedogenic/freshwater origin is supported by the trace element compositions of varying Fe:Mn ratios and low Mg contents. Fluctuating groundwater is the most likely explanation for uniform repeated siderite zones of varying Fe:Mn ratios reflecting alternating physiochemical conditions and hostility to microbial life/activity. Bacterially mediated siderite precipitation likely incorporated Mn and other metal ions during conditions that are not favourable for the bacteria and continued with Fe-rich siderite precipitation as the physico-chemical conditions changed into optimal conditions again, reflecting the response to groundwater fluctuations

It takes two planets in resonance to tango around K2-146

Stars and planetary system

Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms

The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings

Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms

The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings

Executive summary of European task force document on diagnostic tools in rhinology

textabstractThis Executive Summary of the EAACI Task Force document on Diagnostic Tools in Rhinology provides the readers with an overview of the currently available tools for diagnosis of nasal and sino-nasal disease, published in full version in the first issue of Clinical and Translational Allergy. A panel of European experts in the field of Rhinology have contributed to this consensus document on Diagnostic Tools in Rhinology. Important issues related to history taking, clinical examination and additional investigative tools for evaluation of the severity of nasal and sinonasal disease are briey highlighted in this executive summary