Multiple and variable speed electrical generator systems for large wind turbines

A cost effective method to achieve increased wind turbine generator energy conversion and other operational benefits through variable speed operation is presented. Earlier studies of multiple and variable speed generators in wind turbines were extended for evaluation in the context of a specific large sized conceptual design. System design and simulation have defined the costs and performance benefits which can be expected from both two speed and variable speed configurations

Restoration of Acipenser sturio L., 1758 in Germany: Growth characteristics of juvenile fish reared under experimental indoor conditions

The survival of the highly endangered Acipenser sturio L., 1758 depends nearly exclusively upon the establishment of captive broodstocks. Such measures were initiated in Germany in 1996, due to a transfer of 40 artificially reproduced individuals from France under a co-operation agreement. We report the results of rearing these fish for a period of 3 years under freshwater conditions. During the first year the fish being exclusively fed frozen chironomid larvae (N = 40) grew from a median of 27 cm (with range of 23-31 cm), averaging 71 g (42-112 g), to 43 cm (38-51 cm) and 280 g (168-505 g) at a mean temperature of 20 °C (13-27 °C). Following their transfer to larger tanks (approx. 5 m³) at a mean temperature of 21 °C (17-24 °C), the fish (N = 27) reached a length of 68 cm (56-76 cm), averaging 1 281 g (512-2 097 g) at the end of the second year. Decreasing growth and increasing food conversion rates (FCR) during the first four months of the third year made us change the food composition (addition of large chironomids, krill and small marine fish). An increase in growth and a decrease in FCR was observed over the next four months resulting in a median length of 76 cm (58-89 cm), with a weight of 1 827 g (855-3 462 g) at the end of the third year (N = 27). Our fish showed rather large differences in growth, with some individuals reaching the maximum weight gain observed in wild fish, thus indicating the potential to optimise results by future testing involving additional natural food items in order to develop a formulated diet to stimulate early sexual maturation.La supervivencia del altamente amenazado Acipenser sturio L., 1758 depende casi exclusivamente del establecimiento de stocks de cría en cautividad. Tales medidas fueron iniciadas en Alemania en 1996, gracias a la transferencia desde Francia bajo un convenio de cooperación de 40 individuos reproducidos artificialmente. Presentamos los resultados de la cría de estos peces por un periodo de tres años en condiciones dulceacuícolas. Durante el primer año los peces (N = 40) siendo alimentados exclusivamente con larvas congeladas de quironómidos crecieron desde una media de 27 cm (con rango de 23-31 cm), promediando 71 g (42-112 g), a 43 cm (38-51) y 280 g (168-505 g) a una temperatura media de 20 °C (13-27 °C). A continuación de su traslado a tanques más grandes (de aproximadamente 5 m³) a una temperatura media de 21 °C (17-24 °C), los peces (N = 27) alcanzaron una longitud de 68 cm (56-76 cm), promediando 1 281 g (521-2 097 g) al final del segundo año. La disminución del crecimiento y el incremento de las tasas de con versión de alimento (TCA) durante los primeros cuatro meses del tercer año nos hicieron cambiar la composición del alimento (adición de quironómidos de gran tamaño, krill y pequeños peces marinos). Un incremento en el crecimiento y una disminución de las TCA fueron observados durante los cuatro meses siguientes resultando una longitud media de 76 cm (58-89 cm), con un peso de 1 827 g (855-3 462 g) al final del tercer año (N = 27). Nuestros peces mostraron numerosas diferencias en crecimiento, con algunos individuos alcanzando la mayor ganancia en peso observada en peces silvestres, indicando así el potencial para optimizar resultados por futuras pruebas que incluyan alimentos naturales adicionales en orden a evaluar una dieta formulada para estimular la maduración sexual temprana.Instituto Español de Oceanografí

Single electron-phonon interaction in a suspended quantum dot phonon cavity

An electron-phonon cavity consisting of a quantum dot embedded in a free-standing GaAs/AlGaAs membrane is characterized in Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.Comment: 4 pages, 4 figure

Data-driven prognostics for critical electronic assemblies and electromechanical components

The industrial digitalisation enables the adoption of robust, data-driven maintenance strategies that increase safety and reliability of critical assets such as electronics. And yet, an implementation of data-driven methods which primarily address the industrialisation of diagnostic and prognostic strategies is opposed by various, application specific challenges. This thesis collates such restricting factors encountered within the oil and gas industry, in particular for the critical electrical systems and components in upstream deep drilling tools. A fleet-level, tuned machine learning approach is presented that classifies the operational state (no-failure/ failure) of downhole tool printed circuit board assemblies. It supports maintenance decision making under varying levels of failure costs and fleet reliability scenarios. Applied within a maintenance scheme it has the potential to minimise non-productive time while increasing operational reliability. Likewise, a tailored and efficient deep learning data pipeline is proposed for a component-level forecast of the end of life of electromagnetic relays. It is evaluated using high resolution life-cycle data which has been collected as a part of this thesis. In combination with a failure analysis, the proposed method improves the prognostics capabilities compared to traditional methods which have been proposed so far in order to assess the operational health of electromagnetic relays. Two case studies underpin the need for tailored prognostic methods in order to provide viable solutions that can de-risk deep drilling operations. In consequence, the proposed approaches alleviate the pressure on current maintenance strategies which can no longer meet the stringent reliability requirements of upstream assets

Remote participation during glycosylation reactions of galactose building blocks: Direct evidence from cryogenic vibrational spectroscopy

The stereoselective formation of 1,2‐cis‐glycosidic bonds is challenging. However, 1,2‐cis‐selectivity can be induced by remote participation of C4 or C6 ester groups. Reactions involving remote participation are believed to proceed via a key ionic intermediate, the glycosyl cation. Although mechanistic pathways were postulated many years ago, the structure of the reaction intermediates remained elusive owing to their short‐lived nature. Herein, we unravel the structure of glycosyl cations involved in remote participation reactions via cryogenic vibrational spectroscopy and first principles theory. Acetyl groups at C4 ensure α‐selective galactosylations by forming a covalent bond to the anomeric carbon in dioxolenium‐type ions. Unexpectedly, also benzyl ether protecting groups can engage in remote participation and promote the stereoselective formation of 1,2‐cis‐glycosidic bonds

Electrophysiological and molecular genetic evidence for sympatrically occuring cryptic species in African weakly electric fishes (Teleostei : Mormyridae : Campylomormyrus)

For two sympatric species of African weakly electric fish, Campylomormyrus tamandua and Campylomormyrus numenius, we monitored ontogenetic differentiation in electric organ discharge (EOD) and established a molecular phylogeny, based on 2222 bp from cytochrome b, the S7 ribosomal protein gene, and four flanking regions of unlinked microsatellite loci. In C tamandua, there is one common EOD type, regardless of age and sex, whereas in C numenius we were able to identify three different male adult EOD waveform types, which emerged from a single common EOD observed in juveniles. Two of these EOD types formed well supported clades in our phylogenetic analysis. In an independent line of evidence, we were able to affirm the classification into three groups by microsatellite data. The correct assignment and the high pairwise FST values support our hypothesis that these groups are reproductively isolated. We propose that in C numenius there are cryptic species, hidden behind similar and, at least as juveniles, identical morphs. (c) 2005 Elsevier Inc. All rights reserved

Adaptive radiation in African weakly electric fish (Teleostei : Mormyridae : Campylomormyrus): a combined molecular and morphological approach

We combined multiple molecular markers and geometric morphometrics to revise the current taxonomy and to build a phylogenetic hypothesis for the African weakly electric fish genus Campylomormyrus. Genetic data (2039 bp DNA sequence of mitochondrial cytochrome b and nuclear S7 genes) on 106 specimens support the existence of at least six species occurring in sympatry. We were able to further confirm these species by microsatellite analysis at 16 unlinked nuclear loci and landmark-based morphometrics. We assigned them to nominal taxa by comparisons to type specimens of all Campylomormyrus species recognized so far. Additionally, we showed that the shape of the elongated trunk-like snout is the major source of morphological differentiation among them. This finding suggests that the radiation of this speciose genus might have been driven by adaptation to different food sources