1,721,034 research outputs found
Using JWST to Investigate the Crab Nebula’s Synchrotron Emission
No full textThis work takes advantage of the James Webb Space Telescope’s (JWST) 1.6 − 30 μm observing
range and provides one of the first looks at the variations in the Crab Nebula’s synchrotron index in
the mid infrared. We used new, synchrotron-dominated images of the Crab Nebula taken at 4.8 μm
and 11.3 μm to search for evidence of a cooling break and multiple particle populations in the Crab
Nebula’s infrared synchrotron spectrum. We created a high resolution, spectral index map between
4.8 μm and 11.3 μm to investigate the spectral and morphological distribution of ultra-relativistic
particles in the Crab Nebula. We found that the JWST 4.8 μm to 11.3 μm spectral index, α,
steepens from ∼ 0.4 ± 0.02 in the torus and ∼ 0.5 ± 0.02 in the jet structures to ∼ 0.65 ± 0.04 in the
outer parts of the nebula, indicating the synchrotron cooling persists in the infrared. The spectral
index also steepens faster towards the southwest (bottom right) edge of the nebula compared to the
other edges, potentially indicating the existence of multiple particle populations within the nebula.
We filled in the Crab Nebula’s synchrotron spectrum in the mid-infrared by finding the total flux
through the two JWST images and using the index map to derive the synchrotron flux at 5.6 μm,
18 μm, and 21 μm. We found that the Spitzer 3.6 μm and 4.5 μm, JWST 4.8 μm and 11.3 μm, and
derived 5.6 μm, 18.0 μm, and 21.0 μm fluxes follow a power law relationship of gradually changing
slope that increases with increasing frequency within the uncertainties. This change in slope along
with synchrotron cooling indicated by the JWST 4.8 μm to 11.3 μm spectral index map indicates a
cooling break between the radio and near infrared
Multi-wavelength observations of pulsar wind nebulae and composite supernova remnants.
No full textUniversity of Minnesota Ph.D. dissertation. October 2009. Major: Astrophysics. Advisors: Charles E. Woodward and Robert D. Gehrz. 1 computer file (PDF); xiii, 183 pages.Multi-wavelength studies of pulsar wind nebulae (PWNe) and supernova remnants (SNRs) lead to a better understanding of their evolutionary development, the interaction of supernovae (SNe) and pulsar winds with their surroundings, and nucleosynthesis and production and processing of dust grains by SNe. PWNe and composite supernova remnants, in particular, are unique laboratories for the study of the energetic pulsar winds, particle injection processes, and the impact of PWNe on the evolving SNR. They provide information on SNR shock properties, densities and temperatures, and the chemical composition and the ionization state of the material ejected by SNe. SNRs also serve as laboratories for the study of dust production and processing in SNe. While X-ray observations yield important information about the SN progenitor, hot gas properties, SN explosion energy, and the surrounding interstellar medium (ISM), the IR can provide crucial information about the faint non-thermal emission, continuum emission from dust, and forbidden line emission from SN ejecta. Combining observations at a wide range of wavelengths provides a more complete picture of the SNR development and helps better constrain current models describing a SNR's evolution and its impact on the surrounding medium. This thesis focuses on a multi-wavelength study of PWNe in various stages of their evolution and investigates their interaction with the expanding SN ejecta and dust and the SNR reverse shock. The study of these interactions can provide important information on the SNR properties that may otherwise be unobservable.Temim, Tea. (2009). Multi-wavelength observations of pulsar wind nebulae and composite supernova remnants.. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/57372
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
- …
