1,721,061 research outputs found
Ultra-schnelle Zweiphotonenmikroskopie für in vivo Gehirnuntersuchungen
No full textTwo-photon microscopy is an imaging technique for optical investigations in deep layers of the biological tissue (~0.5-1 mm), but the acquisition of full-frame images is relatively slow (~30 images/sec), because most microscopes use revolving mirrors for the scanning process. This work describes the development of a high-speed two-photon microscope (~1000 images/sec), using acousto-optical deflectors (AOD) as scanning devices. AODs induce several beam distortions, and this work investigates their compensation. A special focus is on beam distortions from the ‘cylindrical lens effect’, an artifact when AODs are used for highest line-scan frequencies. The newly designed microscope has a highly increased sensitivity, allowing for the detection of calcium-transients in individual spines in vivo and in vitro. This is demonstrated in measurements of an acute slice preparation of a Purkinje-cell, and in vivo in the auditory cortex.Zweiphotonenmikroskopie ist eine optische Technik um tiefe Schichten biologischen Gewebes abzubilden (~0.5-1mm Tiefe), aber die Aufnahme ganzer Bilder ist relativ langsam, hauptsächlich weil zum Scannen rotierende Spiegel benützt werden. Diese Arbeit beschreibt die Entwicklung eines zweiphotonen-Hochgeschwindigkeitsmikroskops (~1000 Bilder/sec), welches akusto-optische Deflektoren (AOD) als Scanner benützt. AODs erzeugen einige Strahlverformungen, und diese Arbeit untersucht deren Kompensation. Spezieller Fokus liegt dabei auf dem ‘Zylinderlinsen-Effekt’, der bei AODs bei hohen Linienscannfrequenzen auftritt. Das neu entwickelte Mikroskop hat eine deutlich erhöhte Empfindlichkeit, und das ermöglicht die Detektion von Kalziumsignalen in einzelnen dendritischen Spines in vitro und in vivo. Dies wird mit Messungen an Purkinje-Zellen in einem Hirnschnitt, und an einem in vivo Präparat des auditorischen Cortex gezeigt
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Kartierung der funktionellen Mikroarchitektur des primären auditorischen Kortex mit Einzelzell-Auflösung in vivo
No full textAim of the project was to create a functional map of tone-evoked neuronal activity in all cortical layers of the primary auditory cortex. For this purpose, we developed an improved two-photon imaging approach to record neuronal activity with single-cell resolution in all depths of the intact cortex. Based on this method, the functional organization of neurons in the primary auditory cortex is described, which is distinct from patterns observed in other cortical regions.Ziel der Arbeit war die Kartierung von sensorisch induzierter Nervenzellaktivität mit Einzelzellauflösung in allen Schichten des primären auditorischen Kortex. Dazu wurde ein Ansatz für Zwei-Photonen Mikroskopie entwickelt, der Messungen in vorher nicht erreichbaren Tiefen der Großhirnrinde ermöglicht. Basierend auf der Technik wird das funktionelle Organisationsmuster von Nervenzellen im primären auditorischen Kortex beschrieben, das sich von Mustern in anderen Hirnarealen unterscheidet
Development of a high resolution quantitative real time single cell RT PCR approach in living brain slices of the rat
No full textEs wurde eine schnelle und sensitive quantitative Echtzeit-RT-PCR-Methode entwickelt, mit deren Hilfe es möglich ist, die absolute Menge an mRNA-Kopien aus einzelnen Nervenzellen vitaler Gehirnschnitte der Ratte zu bestimmen. In den Anwendungsexperimenten wurde in zerebellären Purkinje-Zellen die zellspezifische Glutamatrezeptoruntereinheit GluRδ2 auf Einzelzellebene nachgewiesen und quantifiziert. In Körnerzellen wurde die entwicklungsabhängige Expressionsregulation der NMDA-Rezeptoruntereinheiten NR2B und NR2C dargestellt. Zudem wurden Entwicklungsprofile der Kationen-Chlorid-Kotransporter KCC2, KCC4 und NKCC1 sowohl auf Gewebe- als auch auf Einzelzellebene erstellt.A rapid and highly sensitive quantitative real time RT-PCR approach was established for the analysis of RNA transcript levels in individual cells of living brain slices. The approach was tested by detecting and quantifying the cell specific glutamate receptor subunit GluRδ2 in single cerebellar Purkinje cells. In cerebellar granule cells the developmental switch in the expression of the ionotropic glutamate receptor subunits NR2B and NR2C was demonstrated. Further, developmental expression profiles of different cation-chloride cotransporter types (KCC2, KCC4, NKCC1) were established on tissue as well as on single-cell level
A novel method for <i>in vivo</i> analysis of neuronal networks using two-photon laser scanning microscopy
No full textIm Rahmen dieser Studie wurde ein neuartiges Verfahren zur Beladung neuronaler Zellverbände mit Fluoreszenzfarbstoffen für die Untersuchung in vivo mittels Zwei-Photonen-Fluoreszenzlasermikroskopie entwickelt. Mit diesem Ansatz konnten über mehrer Stunden stabile Fluoreszenzsignale in Neuronen registriert werden. Nach Beladung von Neuronen der kortikalen Schicht II/III des primären somatosensorischen Kortex ("barrel cortex") narkotisierter Mäuse mit geeigneten Indikatorfarbstoffen, konnte die spontane neuronale Aktivität anhand der Kalziumtransienten mühelos registriert werden. Reizinduzierte Kalziumtransienten wurden durch Applikation von Glutamat, extrazelluläre elektrische Stimulation und durch mechanische Stimulation der kontralateralen Tasthaare ausgelöst. Diese neuartige Methode ist das erste bildgebende in vivo Verfahren zur Echtzeitmessung von neuronaler Aktivität in neuronalen Netzen mit Einzel-Zell Auflösung.This work introduces a novel approach of loading networks of neurons with fluorescent dyes for the subsequent in vivo analysis using two-photon laser scanning microscopy. After loading, the fluorescence signals remained stable for many hours. In cortical layer II/III neurons within primary somatosensory cortex (= barrel cortex) of anaesthetized mice, spontaneous neuronal activity was readily recorded. Furthermore, neuronal calcium transient were successfully evoked by the application of glutamate, by extracellular electrical stimulation and by mechanically stimulating the contralateral vibrissae. This new method is the first in vivo imaging approach for real-time monitoring of the activity of neuronal networks with single cell resolution
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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