1,720,955 research outputs found
Quantitative modelling of fine scale auroral emissions and electric fields at sub-second resolution
No full textThe structuring and dynamics of auroral emissions at fine spatial and temporal scales, down to tens of metres and fractions of a second, is an oft-observed but poorly understood phenomenon. One particular theory for such fine scale structure involves magnetic reconnection in the auroral acceleration region initiating Alfven waves which structure and energise the precipitating particles. Such theories are testable using measurements of the ionospheric electric fields associated with the observed fine scale structure. This thesis presents attempts to measure ionospheric electric fields, using a novel model that tracks emission from a long-lived ion produced at times of auroral particle precipitation, so that the theories that seek to explain the fine scale structuring of the aurora can be evaluated. However, such modelling requires knowledge of the energy spectrum of the precipitation, and the resulting emissions, at the spatial and temporal resolutions of the observed fine scale aurora.This thesis presents such new work concerning the modelling of auroral electron energy spectra and fine scale auroral emissions at sub-kilometre and sub-second resolutions using ground based observations, and the subsequent application of a novel method to estimate ionospheric electric fields using a long-lived ion produced during times of auroral precipitation. Two novel methods are presented. The first method utilises a fusion of multi-monochromatic auroral observations at optical and near-infrared (NIR) wavelengths together with simultaneous radar observations. The second uses only multimonochromatic observations, to be used when complementary radar observations are unavailable. Each technique is applied to an observed auroral event to determine the energy spectra of the precipitating electrons and resulting 3-D distribution of auroral emissions. Modelled images of the emissions verify the accuracy of the recovered spectra.The recovered spectra are used as input to a novel model which solves the continuity equation of a long-lived ion produced at times of auroral precipitation. This model uses a parameterised ion velocity, and optimises the velocity parameters by comparing observed and modelled images of emission from this ion. A simple velocity parameterisation, a uniform flow perpendicular to the magnetic field, yields plasma velocities of 0.4-2.4 km s-1, with the plasma velocities being enhanced at times when the auroral brightness is high. Comparison of the recovered velocities to radar observations of ionospheric plasma velocities shows agreement in direction, but the recovered velocities are larger, more so when the aurora is brighter. Electric fields, inferred from the modelled plasma velocities, of up to 120 mV m-1 are found at the time when the auroral brightness was intensified. A more complex flow parameterisation is presented and tested, but does not succeed for the event analysed.</p
Dataset for Horizontal electric fields from flow of auroral O+(2P) ions at sub-second temporal resolution
No full textAuroral Structure and Kinetics (ASK) data for
Tuttle, et al. (2020), Horizontal electric fields from flow of auroral O+(2P) ions at sub-second resolution Ann. Geophys., doi:10.5194/angeo-38-845-2020
ZIP file contains images in PNG format. The four sections of the images are:
Top-left: ASK1, N2 1P, 673.0 nm
Bottom-left: ASK2, O+ 2D-2P, 732.0 nm
Bottom-right: ASK3, OI, 777.4 nm
Top-right: The other 3 images reproduced in RGB format, with ASK1,2,3 in
the R,G,B channels respectively.
For more information see the readme.txt file.</span
Horizontal electric fields from flow of auroral O<sup>+</sup>(<sup>2</sup>P) ions at sub-second temporal resolution
Full text linkElectric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit orderof- magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure; knowing their true magnitude and temporal variability is important for a theoretical understanding of auroral processes. We present a unique method to estimate ionospheric electric fields in the region close to (kilometre scale) a dynamic auroral arc by solving the continuity equation for the metastable OC.2P/ ions, which emit as they move under the influence of electric fields during their 5 s lifetime. The main advantage of this optical method is the increase in temporal resolution over other methods such as ground-based radars. Simultaneous measurements of emission at 732.0 nm (from the OC.2P/ ions) and prompt emissions at 673.0 nm (N2) and 777.4 nm (O), all at high spatial (100 m) and temporal (0.05 s) resolution, are used in the solution of the continuity equation, which gives the dynamic changes of the OC ion population at all heights in a 3D volume close to the magnetic zenith. Perspective effects are taken into account by a new geometric method, which is based on an accurate estimate of the magnetic zenith position. The emissions resulting from the metastable ions are converted to brightness images by projecting them onto the plane of the ground, and the projected images are then compared with the measured images. The flow velocity of the ions is a free parameter in the solution of the continuity equation; the value that minimises the difference between the modelled and observed images is the extracted flow velocity at each time step.We demonstrate the method with an example event during the passage of a brightening arc feature, lasting about 10 s, in which the inferred electric fields vary between 20 and 120mVm1. These inferred electric fields are compared with SuperDARN measurements, which have an average value of 30mVm1. An excellent agreement is found in the magnitude and direction of the background electric field; an increase in magnitude during the brightening of the arc feature supports theories of small-scale auroral arc formation and electrodynamics.</p
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
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