1,720,984 research outputs found
On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs
No full textWe investigate the detectability of Zeeman broadening in optical Stokes I spectra of slowly rotating sun-like stars. To this end, we apply the LTE spectral line inversion package SPINOR to very-high quality CES data and explore how fit quality depends on the average magnetic field, Bf. One-component (OC) and two-component (TC) models are adopted. In OC models, the entire surface is assumed to be magnetic. Under this assumption, we determine formal 3 sigma upper limits on the average magnetic field of 200G for the Sun, and 150 G for 61 Vir (G6V). Evidence for an average magnetic field of similar to 500 G is found for 59 Vir (G0V), and of similar to 1000G for HD68456 (F6V). A distinction between magnetic and non-magnetic regions is made in TC models, while assuming a homogeneous distribution of both components. In our TC inversions of 59 Vir, we investigate three cases: both components have equal temperatures; warm magnetic regions; cool magnetic regions. Our TC model with equal temperatures does not yield significant improvement over OC inversions for 59 Vir. The resulting Bf values are consistent for both. Fit quality is significantly improved, however, by using two components of different temperatures. The inversions for 59 Vir that assume different temperatures for the two components yield results consistent with 0-450 G at the formal 3 sigma confidence level. We thus find a model dependence of our analysis and demonstrate that the influence of an additional temperature component can dominate over the Zeeman broadening signature, at least in optical data. Previous comparable analyses that neglected effects due to multiple temperature components may be prone to the same ambiguities
Quiet Sun magnetic fields observed by Hinode: Support for a local dynamo
Get PDFContext. The Hinode mission has revealed copious amounts of horizontal flux covering the quiet Sun. Local dynamo action has been proposed to explain the presence of this flux. Aims. We sought to test whether the quiet Sun flux detected by Hinode is due to a local or the global dynamo by studying long-term variations in the polarisation signals detectable at the disc centre of the quiet Sun between November 2006 and May 2012, with particular emphasis on weak signals in the internetwork. Methods. The investigation focusses on line-integrated circular polarisation Vtot and linear polarisation LPtot profiles obtained from the Fe I 6302.5 Å absorption line in Hinode SOT/SP. Results. Both circular and linear polarisation signals show no overall variation in the fraction of selected pixels from 2006 until 2012. There is also no variation in the magnetic flux in this interval of time. The probability density functions (PDF) of the line-of-sight magnetic flux can be fitted with a power law from 1.17 × 1017 Mx to 8.53 × 1018 Mx with index α = −1.82 ± 0.02 in 2007. The variation of α’s across all years does not exceed a significance of 1σ. Linearly polarised features are also fitted with a power law, with index α = −2.60 ± 0.06 in 2007. Indices derived from linear polarisation PDFs of other years also show no significant variation. Conclusions. Our results show that the ubiquitous horizontal polarisation on the edges of bright granules seen by Hinode are invariant during the minimum of cycle 23. This supports the notion that the weak circular and linear polarisation is primarily caused by a
Observation of a bright coronal downflow by SOHO/EIT
No full textA distinct coronal downflow has been discovered in the course of a prominence
eruption associated coronal mass ejection (CME) imaged by EIT (Extreme ultraviolet
Imaging Telescope) and LASCO (Large Angle Spectrometric Coronagraph) on board SOHO (Solar
and Heliospheric Observatory) on 5-Mar.-2000. Evolution of the prominences seen by EIT
was tracked into the LASCO/C2 and C3 field-of-view where they developed as the core of a
typical three-part CME. In contrast to the inflow structures reported earlier in the
literatures, which were dark and were interpreted as plasma voids moving down, the
downflow reported here was bright. The downflow, which was only seen in EIT FOV had an onset
time that coincided with the deceleration phase of the core of the CME. The downflow
showed a rapid acceleration followed by a strong deceleration. The downflow followed a
curved path which may be explained by material following the apex of a contracting
magnetic loop sliding down along other field lines, although other explanations are
also possible. Irrespective of the detailed geometry, this observation provides support
for the pinching off of the field lines drawn-out by the erupting prominences and
the contraction of the arcade formed by the reconnection.
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
LONG RANGE RADIATIVE HEAT TRANSFER IN MULTILAYERED MEDIA
No full textThermal energy transport is vital to the performance and reliability of engineered systems. In applications like electronic cooling, energy conversion, and material processing, managing heat transfer is key to maintaining efficiency and stability. Heat transfer occurs when there is a difference in temperature. It happens mainly through two mechanisms: radiation and conduction. Radiation is a transfer of heat via electromagnetic waves. All matter above absolute zero emits thermal radiation, driven by electronic, molecular, and lattice oscillations within the material. Thermal conduction refers to the diffusion of heat within a material or across materials in contact, driven by molecular collisions that transfer kinetic energy from high to low temperature regions until equilibrium is reached. Convection is a form of thermal conduction in which heat transfer occurs through the bulk motion of a fluid. [1], [2
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