1,721,004 research outputs found
Constructing mean electron distributions from hard X-ray spectra of solar flares
Get PDFThe Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission provides information on high resolution X-ray spectra emitted by collisional bremsstrahlung of thermal and non-thermal electrons with ions in solar flares. One of the aims of the mission is to infer information about the acceleration and transport mechanisms of hard X-ray emitting electrons and 7-ray emitting ions in solar flares. I investigate events observed during distinct attenuator states of the satellite, which have unique characteristics in their photon and mean electron distributions. Such characteristics include evidence of low energy cutoff features and other such physically real bump and dip features. In the framework of a colli-sionally thin bremsstrahlung model and an adjustable thermal function I forward fit these to the background-removed count flux data, using least squares minimization via OSPEX (Object Spectroscopy Executive). Along with Chi-Square Tests, I present random and non- systematic residuals to show goodness of fit. Conversion from count rate to count flux and then to photon flux spectra is a traditional approach to modelling hard X-ray spectra, but is significantly unreliable due to its dependence on parametric electron distribution approximations. Model independent hard X-ray spectra can be non-trivially calculated using the Detector Response Matrix (DRM) and are computed using a sequence of algorithms solving a linear system of equations, which present an inversion problem characterized by numerical instability due to the non-diagonal nature of the DRM. The extent of such instability is unique for different DRM configurations, hence different under each attenuator state. We then address the solution of this inversion problem- by using a regularization algorithm with the aim of inferring accurate and useful electron distribution spectra. Adjustment of this procedure to convert directly between counts and electrons, which is a one step rather than two step process, presents more robust and detailed information about features of electron dynamics during flares. Significant features such as low and high energy cutoffs tell us much about electron acceleration properties and energy losses in the flare evolution. Comparing regularized solutions in each event through different approaches will allow for confirmation of the existence or non-existence of such features. This innovative regularization technique is capable of portraying a truer interpretation of both hard X-ray and mean electron spectra
Investigating jets in the lower-to-mid solar atmosphere : observations & numerical simulations
No full textUnderstanding the fine structures and transient phenomena associated with the origins of the fast solar wind, in the lower-to-mid solar atmosphere, remains one of the biggest unanswered questions in solar physics today. A variety of jet-like transient events appear in cool plasmas in the form of spicules, macrospicules and surges. Transient and explosive jet-like phenomena are not only dominant in the lower solar atmosphere in UV and EUV temperatures but, also, in the mid-to-upper coronal atmosphere at X-Ray (10-300 key) and soft X-ray (1-10 key) temperatures. The recent launch of highly tuned space observatories, such as Hinode (2006) and STEREO (2007) and more recently SDO (2010), provide a wealth of data concerning the complex dynamics ongoing within the thin band of atmosphere above the photospheric surface of the Sun. In the lower-to-mid solar atmosphere the hot and the cold plasma are separated at the solar transition region. Beneath this layer mass and energy are coupled from the solar interior into the hot outer solar atmosphere via a number of different physical mechanisms which are controlled by either wave-driven or magnetic reconnect ion driven processes. Spicules are one of the most common features in the lower-to-mid solar atmosphere and have recently become the subject of significant debate with regard to their principle formation mechanisms. The spicule family tree can be classified into three branches, namely, type-I, type-II and macrospicule. Both type-I spicules and macrospicules are generally believed to be formed through unique processes. Type-I spicules are wave driven and macrospicules are driven by an explosive magnetic reconnect ion process. The recently discovered type-II spicules (2007) pose an interesting problem such that they are thought to exhibit characteristics from both models. Consequently, type-II spicules are interesting for a number of reasons, i.e., they might address the long standing questions concerning the origin of the fast solar wind and the coronal heating problem. In this thesis we examine the nature of spicular structures in the lower-to-mid solar atmosphere through observational analysis with supporting numerical simulations (via SAC: Sheffield Advanced Code: Shelyag et al, 2008). The observational approach is two-fold, involving a spectroscopic study of jets observed in polar coronal holes, for both on-disk and off-limb events, as well as, a multi-instrumental imaging approach involving recently launched instruments. The numerical simulations are three-fold. We will investigate the wave-driven model behind type-I spicule formation in 3D. the process of magnetic flux emergence in the solar chromosphere in 2.5D to understand the process leading to macrospicule formation and magnetic reconnection in 2.5D in order to investigate type-II spicule formation. In supporting our numerical models with high spatial, temporal and spectral resolution observations we have discovered a number of interesting phenomena. Firstly, we have modelled the formation of transition region quakes (TRQs). We have evaluated the response of the transition region to the propagation of p-modes from the lower chromosphere and acoustic wave energy transmission in 3D. Secondly, we have simulated convection flows associated with type-I spicules in the corona, which is the first example of any convection based process in the corona. In this spectroscopic analysis, we successfully isolated an important criteria in controlling the heating potential of macrospicules, i.e., the helicity of the magnetic flux emergence.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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