1,720,967 research outputs found
In-situ real time monitoring of epoxy/amine kinetics by remote near-infrared spectroscopy
No full textCalcium dynamics and compartmentalization in leech neurons
Full text linkThe aim of this project was to study how and where action potentials arise and propagate in the arborizations of identified neurons in the central nervous system of the leech. A major aim was to assess whether the entry of calcium is localized to distinct regions of the cells and to determine whether there are significant differences in calcium channel distribution between different types of neurons. A combination of electrophysiological techniques, optical recording and image analysis was used to approach these problems. I developed an experimental set-up for optical recordings of calcium transients by a fast CCD-camera. By use of calcium sensitive dyes I analysed in detail optical responses to electrical stimulation of neurons and the density of calcium channels, spatially and temporarily, in different neural cell types, including mechanosensory neurons and motoneurons. Fluorescence changes (∆F/F) of the membrane impermeable calcium indicator Oregon Green were measured. The dye was pressure injected into the soma of neurons under investigation. ∆F/F caused by a single action potential (AP) in mechanosensory neurons had approximately the same amplitude and time course in the soma and in distal processes. By contrast, in other neurons such as the Anterior Pagoda neuron, the Annulus Erector motoneuron, the L motoneuron and other motoneurons, APs evoked by passing depolarizing current in the soma produced much larger fluorescence changes in distal processes than in the soma. When APs were evoked by stimulating one distal axon through the root, ∆F/F was large in all distal processes, but very small in the soma. These results confirm and extend previous electrophysiological data which demonstrate that the soma of a motoneuron in the leech, as in many other invertebrates, does not generate action potentials (Stuart, 1970; Muller and Nicholls, 2 1974; Goodman and Heitler, 1979). Impulses recorded in the soma are normally only a few millivolts in amplitude. The AP of a motoneuron propagates to muscles of the body wall along segmental nerves that emerge from ganglia. The site of impulse initiation has been found to be at a distance from the soma but within the ganglion (Melinek and Muller, 1996; Gu et al. 1991). Our experiments with fluorescent transients are in accord with the concept that they result from calcium entry through voltage sensitive channels. Thus at sites where APs are found to be large, the calcium signals are large (as in peripheral axons), while at sites where spikes are small, (as in motoneuronal cell bodies) signals were weak, or non existent
Anomalous trends in conductivity during epoxy-amine reactions
No full textMeasurements were carried out of conductivity due to migrating charges as a function of extent of reaction for a series of epoxy-amine formulations. All systems were characterised by the reaction mechanism common to this generic group of materials and ~y an increase in the steady shear viscosity during reaction. The measured conductivity, however, followed one of three distinct patterns as a function of extent of reaction. Intuitively unexpected, and hence particularly interesting, was the observed increase in conductivity during reaction in sew~ral formulations. This communication marks the first time that such response has been reported in the literature. An explanation of the observed trends was offered in terms of an interplay between the contributions of extrinsic and intrinsic migrating charges to the overall (measured) conductivity. Without such information, all con'elations between the measured conductivity and the major processing parameters (viscosity, extent of reaction) remain strictly batch-specific and empirical
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
