1,721,014 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
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
Mapping the Circumgalactic Medium: Connecting Galaxies to their Environment
No full textThesis (Ph.D.)--University of Washington, 2022The work presented in this dissertation provides the groundwork for understanding key unresolved questions in the study of galaxy evolution: the circumgalactic medium (CGM) and the role of environment. I present a new survey that has the power to drastically improve our understanding of the CGM and use it to estimate the size of the CGM as a function of galactic mass. In addition, a novel method to reconstruct the cosmic web using \textit{Physarum polycephalum} slime mold is presented and applied to the SDSS surveys. This cosmic web reconstruction was released publicly with SDSS DR17 and will allow exciting connections between galaxies and their environments to be illuminated, to distances greater than other previous catalogs
The Physical Connection between Cosmic Gas Flows, Supermassive Black Holes Growth, and Galaxy Evolution
No full textThesis (Ph.D.)--University of Washington, 2022The circumgalactic medium (CGM) represents a key interface in the processes of galactic evolution. Here, the gas which enters galaxies through mergers and filaments and the gas expelled from a disk through stellar and black hole feedback intersect, maintaining a reservoir that will shape a galaxy throughout its lifetime. However, due to the diffuse and difficult-to- observe nature of this gaseous region, the degree to which galactic processes impact it are still uncertain, making the CGM a natural laboratory for testing the impact of different feedback models. The CGM of Milky Way-mass galaxies are the best targets for these analyses as these galaxies lie at the turnover mass during which galaxies switch from being dominated by stellar processes and become dominated by supermassive black hole (SMBH) or active galactic nucleus (AGN) processes.My focus of my thesis work is in exploring the impact of supermassive black hole (SMBH) feedback on the evolution of Milky Way-mass (MW-mass) galaxies in hydrodynamic sim- ulations. We use simulations from the N-body+Smoothed particle hydrodynamics code, ChaNGa, and include a 25 Mpc cosmological volume, Romulus25, and a suite of ”genet- ically modified” (GM) galaxies. These GM galaxies originate from nearly identical initial conditions resulting in minor modifications to their accretion histories that maintain the large scale structure and final halo mass of the original simulation. We find that (1) the SMBH propagates metals from the disk out into CGM, (2) the mass of metals retained by the galaxy depends on its deviation from the M-sigma relation, and (3) black hole accretion histories can be influenced by larger scale galaxy accretion physics, which work in tandem to quench star formation
The Carbon Cycle of Galactic Atmospheres: Connecting Star-Formation and Cosmic Gas Flows with the Physical Conditions of the Circumgalactic Medium
Get PDFThesis (Ph.D.)--University of Washington, 2025The diffuse gaseous atmosphere surrounding the star-filled inner region of a galaxy is known as its circumgalactic medium (CGM). Galaxies draw gas from the CGM to fuel star formation; internal processes within the galaxies, in turn produce feedback that ejects gas and material back out into the CGM. This constant cycling of gas allows the CGM to maintain a record of how a galaxy builds its star population and holds key information on how galaxies begin to quench. By investigating this record, we can tell a richer story of a galaxy's past and make strides in predicting its future. In this dissertation I describe the work I have done using observations and analytical models focused on the metal ion C IV to answer two main questions. First, is there a correlation between the pc-scale physics of black hole growth and the global, kpc-scale gas flows of the CGM in observations, and how does this compare to simulations? Garza et al. (2024) suggest that C iv column density does not vary with SMBH mass; however, sSFR is highly correlated with the ionization content of the CGM. This raises the question: what do C IV observations reveal about the ionization state, temperature, and processes responsible for this ionization mechanism in the CGM? Garza et al. (2025) investigates whether a dichotomy exists for C IV between star-forming and passive galaxies (9.5 ≤ log10 M*/M⊙ ≤ 11.2). Results are statistically consistent (≥ 99%) with dichotomy findings for C iv in sub-L* galaxies (Bordoloi et al., 2014) and O VI in L* galaxies (Tumlinson et al., 2011). This suggests that C IV is more O VI-like than "low-ion-like," indicating it traces gas maintained by star formation and/or feedback, unlike other low-ionization state gas (e.g., H I, Si II, C III). In a follow-up paper, we find that C IV and O VI are kinematically coincident but the relationship between these intermediate to high ions and lower ions is not straightforward. To explore the origins of C IV and O VI, we employed a simple cooling flow model under collisional ionization (PI) and find that O VI is very consistent with the predictions for an expected temperature range, while C IV is not consistent and has column densities on average 2.5 times higher than the predictions. Since C IV has a lower ionization energy than O vi, it is possible that C vi has contributions from both the warm/hot phase and from the cool photoionized (PI) phase. Any successful model of the CGM which incorporates multiphase conditions, must result in ionized gas containing C IV and O VI that is kinematically coexist, but "avoids" existing at the same temperature and density. Ultimately, these analyses help us understand the complex relationships governing galaxy star formation rates, feedback from their supermassive black holes, and the contents of their diffuse gaseous halos
Galactic Gas Flows from Halo to Disk: Kinematics and Tomography in the Milky Way’s Low-Velocity Circumgalactic Medium
No full textThesis (Ph.D.)--University of Washington, 2022The evolution of galaxies is closely linked to the exchange of gas between their disk and the circumgalactic medium (CGM) – the massive, extended, diffuse halo of gas in which galaxies are embedded. Recent advances in high-resolution spectroscopy have enabled observers to firmly establish the key role played by the CGM in the life cycle of galaxies: it is the hiding place of at least half of all galactic baryons, acting as a massive reservoir that replenishes the supply of fuel for star formation via gas accretion onto the disk. However, this nearly-invisible halo gas is challenging to observe, and we are still missing a complete picture of its distribution, kinematics, and multiphase structure. In this thesis, I use the Milky Way as a case study to shed light on the nature of cool and warm CGM gas flows, taking advantage of the abundance of quasar and stellar sightlines which probe the Galactic CGM. In particular, I focus on the behavior of low-velocity gas, which is often overlooked by CGM studies because it is difficult to measure in isolation. I show that local CGM gas is predominantly inflowing, place constraints on the inflowing cloud sizes, and determine that these clouds lie close to the disk. I use a novel spectral differencing technique to correct for foreground absorption along sightlines through the Galactic halo, and present the first unobscured measurements of the Milky Way’s extended low-velocity CGM. The results demonstrate that either the warm CGM does not have a spherical morphology, as is often assumed for star-forming galaxies, or that the Milky Way is not a typical star-forming galaxy. Finally, I find that inflow velocities are higher for warmer gas, suggesting a picture in which warm accreting gas slows down and cools as it approaches the disk. The mass accretion rates of these inflows indicate that a significant fraction of star-formation fuel may accrete onto the disk at low velocities
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
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