Anwendung von piezoelektrischen Motoren in einem 1,5-Tesla Hochfeld-MR-Tomographen

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Besteht die Aufgabe, präzise und automatisch gesteuerte Einrichtungen für die MR-Tomographie (MRT) zu entwickeln, so läßt sich eine störungsfreie Schnittbilddarstellung auch nur mit MR-kompatiblen Komponenten erreichen. Diesbezüglich haben Untersuchungen gezeigt, daß insbesondere Materialien mit geringen magnetischen Suszeptibilitäten und elektrischen Leitfähigkeiten hierfür geeignet sind. Sollen elektromotorische Antriebskonzepte für die Automatisierung verwendet werden, so lassen sich konventionelle Elektromotoren, aufgrund ihrer im allgemeinen hohen ferromagnetischen Materialanteile und magnetfeldabhängigen Funktionsweise, nicht anwenden. Erhebliche Kraftwirkungen, Magnetfeld-Homogenitätsstörungen und funktionelle Beeinträchtigungen des Motors können die Folge sein. Auf der Suche nach alternativen MR-kompatiblen elektrischen Antriebslösungen fanden sich neuartige Motorkonzepte, sogenannte "Piezomotoren". Diese Motoren können ohne Ferromagnetika, Spulen- und Magnetsysteme ausgeführt und betrieben werden. Da die Auswirkungen dieser Motoren auf die Schnittbildqualität nicht bekannt waren, wurden zwei Piezomotoren unterschiedlicher Bauart im MRT-Isozentrum untersucht

EXAMINING THE VALUE OF ERROR CORRECTION STRATEGIES FOR ORAL PROFICIENCY USED BY BENINESE EFL TEACHERS AT SECONDARY SCHOOL LEVEL

This study focuses on the value of error correction strategies used by Beninese EFL teachers in promoting learners’ oral proficiency in secondary school level. It aims firstly, at identifying the effectiveness of strategies that teachers can adopt in correcting errors in EFL classes. Secondly, at pointing out the difficulties teachers face when correcting their students’ oral proficiency errors and lastly, at exploring the importance of error correction in the improvement of their students’ oral communicative ability. The respondents of this study are EFL teachers and students in a secondary school located in the Littoral region of Benin. The qualitative research method was adopted. In this trend, questionnaires and interviews were used to gather reliable data. The analysis of the collected data revealed that EFL teachers adopt indirect correction technique as the most effective technique to correct learners’ oral proficiency errors. It is also revealed that most of EFL teachers lack appropriate teaching experience. Besides, teachers face difficulties such as learner’s anxiety and lack of motivation during English teaching sessions. Unlike the general observation, findings have revealed that students are afraid of speaking English language not because they are discouraged by their teacher’s error correction technique, but they fear of being laughed at by their mates. They assert that they prefer to be corrected by their teacher and not by their mates. As conclusion, teachers are encouraged to take into account learner’s affective filter during corrective feedback by adopting more indirect strategies such as recasts and delayed error correction technique. The study has finally revealed that both teachers and students testify the significance of error correction in the development of EFL beginners’ oral communicative ability.Cette étude se concentre sur la valeur des stratégies de correction d’erreurs utilisées par les enseignants béninois d’Anglais, langue étrangère dans la promotion de la compétence orale des apprenants au niveau de l’enseignement secondaire. Ce travail vise tout d’abord à identifier l’efficacité des stratégies que les enseignants peuvent adopter pour corriger les erreurs dans les classes. Ensuite, il examine les difficultés rencontrées par les enseignants dans le processus de correction des erreurs de leurs apprenants. Cet article met enfin un accent particulier sur valeur de la correction des erreurs dans l’amélioration de la communication orale des apprenants. La population cible est composée des enseignants et apprenants de la langue anglaise dans l’une des écoles secondaires dans la partie méridionale du Benin. La méthode de recherche qualitative a été adoptée pour mener cette recherche. Dans cette tendance, des questionnaires, un guide d’entretien sont les instruments utilisés pour recueillir des données fiables. L’analyse des données collectées a révélé que les enseignants estiment que la stratégie la plus efficace pour corriger les erreurs de compétence orale chez les apprenants est la méthode indirecte. Il est également révélé que la plupart des enseignants n’ont pas assez de qualification et d’expérience professionnelle. En outre, les enseignants sont confrontés à des difficultés telles que le problème de timidité et manque de motivation chez les apprenants en situation d’apprentissage d’Anglais. Contrairement au constat général, les résultats ont révélé que les apprenants ont peur de parler Anglais non pas parce qu’ils sont découragés par la technique de correction utilisés par leur professeur, mais ils ont peur de se faire ridiculiser par leurs camarades. En conclusion, les enseignants sont encouragés à prendre en compte le coté émotionnel des apprenants dans le processus de la correction des erreurs en adoptant des stratégies plus indirectes telles que la refonte et la technique de correction d’erreur retardée. L’étude a finalement révélé que les enseignants et les apprenants témoignent de l’importance de la correction des erreurs dans le développement de la capacité de communication orale des apprenants débutants d’Anglais, langue étrangère.  Article visualizations

Tensor-multi-scalar theories: relativistic stars and 3+1 decomposition

Gravitational theories with multiple scalar fields coupled to the metric and each other --- a natural extension of the well studied single-scalar-tensor theories --- are interesting phenomenological frameworks to describe deviations from general relativity in the strong-field regime. In these theories, the $N$-tuple of scalar fields takes values in a coordinate patch of an $N$-dimensional Riemannian target-space manifold whose properties are poorly constrained by weak-field observations. Here we introduce for simplicity a non-trivial model with two scalar fields and a maximally symmetric target-space manifold. Within this model we present a preliminary investigation of spontaneous scalarization for relativistic, perfect fluid stellar models in spherical symmetry. We find that the scalarization threshold is determined by the eigenvalues of a symmetric scalar-matter coupling matrix, and that the properties of strongly scalarized stellar configurations additionally depend on the target-space curvature radius. In preparation for numerical relativity simulations, we also write down the $3+1$ decomposition of the field equations for generic tensor-multi-scalar theories.Comment: 32 pages, 8 figures, 1 table, invited contribution to the Classical and Quantum Gravity Focus Issue "Black holes and fundamental fields". v3: version in press in CQG, with various improvements in response to the referees' comments. In particular, the 3+1 decomposition now allows for matte

Imaging ellipsometry of graphene

Imaging ellipsometry studies of graphene on SiO2/Si and crystalline GaAs are presented. We demonstrate that imaging ellipsometry is a powerful tool to detect and characterize graphene on any flat substrate. Variable angle spectroscopic ellipsometry is used to explore the dispersion of the optical constants of graphene in the visible range with high lateral resolution. In this way the influence of the substrate on graphene's optical properties can be investigatedComment: 3 pages, 3 figure

Real-time dynamics in spin-1/2 chains with adaptive time-dependent DMRG

We investigate the influence of different interaction strengths and dimerizations on the magnetization transport in antiferromagnetic spin-1/2 XXZ-chains. We focus on the real-time evolution of the inhomogeneous initial state with all spins pointing up along the z axis in the left half and down in the right half of the chain, using the adaptive time-dependent density-matrix renormalization group (adaptive t-DMRG). We find on time-scales accessible to us ballistic magnetization transport for small Sz-Sz-interaction and arbitrary dimerization, but almost no transport for stronger Sz-Sz-interaction, with a sharp crossover at Jz=1. At Jz=1 results indicate superdiffusive transport. Additionally, we perform a detailed analysis of the error made by the adaptive time-dependent DMRG using the fact that the evolution in the XX-model is known exactly. We find that the error at small times is dominated by the error made by the Trotter decomposition, whereas for longer times the DMRG truncation error becomes the most important, with a very sharp crossover at some "runaway" time.Comment: 13 pages, 20 figure

Terpenoid-Induced Feeding Deterrence and Antennal Response of Honey Bees

Multiple interacting stressors negatively affect the survival and productivity of managed honey bee colonies. Pesticides remain a primary concern for beekeepers, as even sublethal exposures can reduce bee immunocompetence, impair navigation, and reduce social communication. Pollinator protection focuses on pesticide application guidelines; however, a more active protection strategy is needed. One possible approach is the use of feeding deterrents that can be delivered as an additive during pesticide application. The goal of this study was to validate a laboratory assay designed to rapidly screen compounds for behavioral changes related to feeding or feeding deterrence. The results of this investigation demonstrated that the synthetic Nasonov pheromone and its terpenoid constituents citral, nerol, and geraniol could alter feeding behavior in a laboratory assay. Additionally, electroantennogram assays revealed that these terpenoids elicited some response in the antennae; however, only a synthetic Nasonov pheromone, citral, and geraniol elicited responses that differed significantly from control and vehicle detections

Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response. with close to zero ingestion rates at concentrations below 5 mu g Cl-1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 mu g Cl-1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C hamaths can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available. (C) 2009 Elsevier B.V. All rights reserved

Ein neuartiges Antriebs- und Verstellsystem zur sicheren Plazierung von Biopsienadeln im Mammagewebe

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In der Diagnostik des Mammakarzinoms werden die Mammographie und Sonographie vor allem durch die hochauflösende Magnetresonanztomographic unterstützt [2|. Ist für die weitere Diagnostik oder Therapieplanung eine Mammabiopsie indiziert, sollte sie durch das bildgebende Verfahren gestützt werden, das die Läsion am besten darstellt [1]. Durch die technische Weiterentwicklung der o.g. bildgebenden Verfahren gelingt es jetzt immer besser auch Tumoren von wenigen Millimetern im Durchmesser darzustellen [3]. Leider hat sich die Treffsicherheit der Biopsiesysteme nicht parallel dazu entwickelt, so dass eine geschlossene MRgeführte Biopsie erst ab einer Tumorgröße von 10mm durchgeführt werden sollte [4]. Gefördert durch die Deutsche Krebshilfe wurde am Institut für Mikrotechnik und Medizintechnik der Technischen Universität Berlin in enger Zusammenarbeit mit Kliniken der Charite Berlin ein neuartiges Biopsiesystem für histologische Untersuchungen von Mammatumoren im Frühstadium (< 5 mm) entwickelt, das eine vollautomatische Mammabiopsie direkt im Isozentrum eines Kernspintomographen ermöglicht, Die Steuerung und Überwachung der automatisierten Biopsie erfolgt durch einen Steuercomputer, der über Lichtwellenleiter mit dem Biopsiesystem verbunden ist. Für dieses Biopsiesystem wird ein Antriebs- und Verstellsystem vorgestellt, das eine stufenlose Einstellung der Eindringtiefe der Biopsienadcl in das Marnmagewebe und den Vorschub des Schussapparates auf einen halben Millimeter genau ermöglicht

Effect of Alternative Wheat and Feed Grain Prices on Optimum Farm Plans and Income, Faulk and Potter Counties, South Dakota

The general objectives of the research undertaken in South Dakota were: (1) To provide economic data needed by farmers to make profitable adjustments in their farming systems and production practices, and (2) To develop a research background for evaluating government farm programs under varying assumptions