1,720,990 research outputs found
Source region characterstics of coronal mass ejections and their interplanetary propagation
No full textMulti-wavelength Investigations of Solar Eruptive Phenomena
No full textSolar eruptive phenomena correspond to various kind of transient activities occurring in the solar atmosphere in the form of flares, prominence eruptions and coronal mass ejections. They mostly originate from solar active regions which consist of complex magnetic structures extending from the deeper sub-photospheric layers, crossing through the photosphere to the coronal heights. An eruptive flare typically spreads across all the atmospheric layers of the Sun and involves substantial mass motions and particle acceleration. Multi-wavelength observations are thus crucial to probe the underlying physical processes occurring at different layers and regions at and above the photosphere.
In this thesis, I have studied some key aspects of solar eruptive phenomena such as solar flare, prominence eruption, coronal implosion, failed eruption, and sigmoid-to-arcade evolution. These investigations have employed contemporary multi-wavelength solar observations with superior resolution. The imaging and spectroscopic capabilities of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) have been extensively utilized to investigate the thermal and nonthermal energy release processes associated with different stages of the eruptive phenomena. Complementary to RHESSI X-ray measurements, we have combined solar observations at Extreme Ultraviolet (EUV), Ultraviolet (UV), Microwave (MW), optical, and radio wavelengths to investigate the complex physical processes occurring at different atmospheric layers of the Sun during the eruptive events.
We study two spectacular prominence eruptions and associated flare activities which occurred in active regions NOAA 10656 on 2004 August 18 (event I) and NOAA 11548 on 2012 August 18 (event II) with the motivation to identify the prominence destabilization through the observations of pre-eruption phase and pre-flare activity. The violent eruption of the prominences is accompanied by
major flares. We also explore the signatures of magnetic reconnection in the corona and discuss the thermal and non-thermal effects driven by prominence eruption during their eruptive phase. During event I, three localized episodes of energy release were observed in the vicinity of the filament before the eruption that produced intense heating along with non-thermal emission. The prominence eruption was accompanied with an X1.8 flare during which multiple HXR bursts were observed up to 100–300 keV energies. We have noted striking HXR coronal source at 50–100 keV energy band that was formed at the time of detachment of the prominence from the source region. From the location, timing, strength, and spectrum of HXR emission, we conclude that the prominence eruption was driven by distinct events of magnetic reconnection occurring in the current sheet below the erupting prominence. During event II, we observed multitude of coronal activities in the form of a blowout jet, rapid evolution of a flux rope above the prominence, and events of episodic energy release. Out of these activities, the flux rope exhibited the most dramatic evolution, characterized by splitting and rotation along with localized brightenings during its outward expansion. The prominence underwent catastrophic loss of equilibrium with the onset of an M1.8 flare, suggesting large-scale energy release by magnetic reconnection. During the impulsive phase of the flare, a plasmoid eruption was observed below the apex f erupting prominence at multiple EUV channels. The temporal, spatial and kinematic correlations between erupting prominence and plasmoid imply that the magnetic reconnection supported the fast ejection of prominence in the lower corona.\
Flare research has been dominated by the study of eruptive flares because of their large-scale structure and long duration. On the other hand, it is rather challenging to investigate energy release processes in confined flares due to their rapid evolution in a compact region that impose severe observational constraints. Now with the availability of observations at unprecedented temporal, spatial, and spectral resolutions from RHESSI and SDO, we have made an effort to investigate the triggering mechanism and magnetic reconnection scenario in a confined M4.0
flare in AR NOAA 11302 on 2011 September 26. From this case study, we infer some important conclusions about the evolution of flare loops and thermal/nonthermal emissions within the confined environment of active region corona. This event was associated with a magnetic transient which was observed ∼1 minute prior to the flare onset at the early flare location within the inner core region. The spectral, temporal, and spatial properties of magnetic transients suggest that the sudden changes in the small-scale magnetic field have likely triggered the flare by destabilizing the highly sheared pre-flare magnetic configuration.
We have studied a confined eruption (or failed eruption) of a flux rope which occurred in AR NOAA 10646 on 2004 July 14. After striking pre-flare phase, we observed a major M6.2 flare during which a large flux rope and associated prominence material underwent confined eruption. A major highlight of the preflare phase lies in the observation of large-scale contraction in overlying coronal
loops for a span of ∼30 minutes during which the overlying loops underwent an altitude decrease of ∼20 Mm (40% of the initial height) during pre-flare phase. The impulsive phase of the flare is characterized by multiple non-thermal peaks during which very high plasma temperature (T ∼30 MK) and substantial nonthermal characteristics were observed. The time-evolution of thermal energy
exhibits a good correspondence with the variations in cumulative non-thermal energy which suggest that the energy of accelerated particles efficiently converted to hot flare plasma implying validation of the Neupert effect in terms of flare energetics.
Finally, we have presented a multi-wavelength investigation of a sigmoid-toarcade development in AR 11719 on 2013 April 11. The study aims to explore several crucial aspects involved during the process of solar eruption right from the formation stage of coronal EUV sigmoid to the post-eruption phase of the source region. The evolution of sigmoid was observed at 94 ˚A images which implies that the structure comprised of very high temperature plasma. The sigmoid eruption was accompanied with a large M6.5 two-ribbon flare which is characterized by a prolonged rise phase of ∼21 minutes. We have especially emphasized morphological and spatial evolution of flare sources during the prolonged rise phase and discussed their observational disparities with the standard flare model
Eruption of solar magnetic flux ropes and associated flaring activity: observational perspectives
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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
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