1,721,032 research outputs found
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
Primordial Nucleosynthesis In The New Age Of Cosmology: Determining Uncertainties, Examining Concordance, And Probing New Physics
No full textBig bang nucleosynthesis (BBN) has long played a key role in the standard cosmology. BBN accurately predicts the primordial light element abundances of deuterium, helium and lithium. The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density. Recent cosmic microwave background (CMB) anisotropy measurements, particularly the observations performed by the WMAP satellite, examine this concordance by independently measuring the cosmic baryon density. Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions. These uncertainties are dominated by systematic errors in nuclear cross sections. We critically analyze the cross section data, producing representations that describe this data and its uncertainties. We take into account the correlations among data, and explicitly treat the systematic errors between data sets. These cross section representations are transformed into thermal rates, and we show that the inclusion of energy correlations helps reduce the uncertainties in these thermal rates. Using these updated nuclear inputs, we compute the new BBN abundance predictions, and quantitatively examine their concordance, first with light element abundance observations and second with CMB anisotropy observations. Overall, there is satisfactory agreement between the CMB and light elements; being excellent for deuterium and marginal for helium-4. However, there exists discordance with lithium-7, suggesting unknown systematics or new physics. If we accept these observations, we can probe nuclear and particle astrophysics. We examine the constraints placed on the number of relativistic degrees of freedom during BBN. New measurements of nuclear cross sections will help reduce the theoretical uncertainties in the light element abundance predictions. New observations of light element abundances will further sharpen BBN's probe of the baryon density. With future observations of the CMB anisotropy, all of these improvements will allow even tighter constraints to be placed on nuclear and particle astrophysics.Submitted by Megan O'Donnell ([email protected]) on 2012-07-06T22:07:29Z
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An Analytic Model of Environmental Effects on Cosmic Structure Formation and an Application to Cosmic Accretion Shock
No full text"We apply this new tool to the case of cosmic accretion shocks. We investigate and quantify the effect of environmental factors on the statistical properties of these shocks. For this purpose, we explore two different models. The first ""control"" model uses a Press-Schechter mass function to describe the population of collapsed structures, and assumes that all objects accrete gas of the same density and temperature. The second model treats the accreted material as a multi-temperature, multi-density medium with densities and temperatures derived from the double distribution. We find that the shock environment significantly alters the physical impact of cosmic accretion shocks on the intergalactic medium, as well as the cosmic history of their properties."Made available in DSpace on 2015-09-25T22:35:37Z (GMT). No. of bitstreams: 2
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only104 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005
Penetration of supernova radioactivities in the solar system
No full text"We investigate the mechanism by which supernova ejecta can penetrate the solar system, and in particular, directly deposit live radioactivities on Earth. This study is motivated by the discovery of live undersea 60Fe from an event 2.8 Myr ago. The 60Fe signal is consistent with a nearby supernova explosion - occuring within a few tens of parsecs from the solar system. We present the first numerical hydrodynamic simulation of the interaction between a supernova blast and the solar wind, using the FLASH code. We find that the supernova ejecta can penetrate the solar system within the orbit of the Earth if the supernova explosion is within 10pe of the Sun. Since 10 pc marks the nominal ""kill radius"" within which biosphere damage is severe and could lead to species extinction events, the absence of paleontological evidence of such an extinction coeval with the 6°Fe deposition leads us to consider a more subtle mechanism of ejecta delivery. There exists evidence that the vast majority of heavy elements in a supernova remnant may be depleted onto grains, hence they can be considered as charged particles which do not participate in the plasma dynamics of the interaction of the supernova plasma and the solar wind. We examine the motion of these charged particles as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation and gravitational field. We find that given the large incoming velocities of the charged grains, they suffer little or no deflection within the solar system. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability, and the dust capture onto the Earth should have a geometric cross section."Submitted by Megan O'Donnell ([email protected]) on 2011-11-06T18:43:19Z
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Reason: thesis/dissertationItem marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Megan O'Donnell ([email protected]) on 2011-11-06T18:43:20Z
Item is restricted indefinitely.thesis/dissertationU of I Onl
Probing and Raising the Lithium Problems With Hadronic Gamma Rays and Cosmic -Ray Nucleosynthesis
No full text"Besides lithium, CRs also produce ""pionic"" gamma-rays through pp → pi0 → gammagamma. Thus there is an intimate link between Li and gamma-rays produced in CR interactions. In this thesis we explore this link and use it as a new, model-independent way of testing the CR nucleosynthesis of Li. We apply this tool to test a, still hypothetical, cosmological CR population. Moreover, our approach reveals yet another Li problem. The isotope 6Li is made only in CR interactions where the standard assumption is that the measured solar 6Li abundance originated from interactions of galactic cosmic-rays (GCRs) with the interstellar medium. However, by applying our tool on this fiducial case, we found that gamma-ray observations allow for only ≈ 60% of the solar 6Li abundance to be produced by standard GCRs. This result bears important consequences for the non-standard sources of 6Li nucleosynthesis such as decaying dark matter and low-energy cosmic-ray component."Made available in DSpace on 2015-09-25T22:35:37Z (GMT). No. of bitstreams: 2
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only107 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006
An Analytic Model of Environmental Effects on Cosmic Structure Formation and an Application to Cosmic Accretion Shock
No full text104 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005.We apply this new tool to the case of cosmic accretion shocks. We investigate and quantify the effect of environmental factors on the statistical properties of these shocks. For this purpose, we explore two different models. The first "control" model uses a Press-Schechter mass function to describe the population of collapsed structures, and assumes that all objects accrete gas of the same density and temperature. The second model treats the accreted material as a multi-temperature, multi-density medium with densities and temperatures derived from the double distribution. We find that the shock environment significantly alters the physical impact of cosmic accretion shocks on the intergalactic medium, as well as the cosmic history of their properties.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
Probing and Raising the Lithium Problems With Hadronic Gamma Rays and Cosmic -Ray Nucleosynthesis
No full text107 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Besides lithium, CRs also produce "pionic" gamma-rays through pp → pi0 → gammagamma. Thus there is an intimate link between Li and gamma-rays produced in CR interactions. In this thesis we explore this link and use it as a new, model-independent way of testing the CR nucleosynthesis of Li. We apply this tool to test a, still hypothetical, cosmological CR population. Moreover, our approach reveals yet another Li problem. The isotope 6Li is made only in CR interactions where the standard assumption is that the measured solar 6Li abundance originated from interactions of galactic cosmic-rays (GCRs) with the interstellar medium. However, by applying our tool on this fiducial case, we found that gamma-ray observations allow for only ≈ 60% of the solar 6Li abundance to be produced by standard GCRs. This result bears important consequences for the non-standard sources of 6Li nucleosynthesis such as decaying dark matter and low-energy cosmic-ray component.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
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
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