1,721,037 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Radiation Hydrodynamic Models and Simulated Observations of Radiative Feedback in Star Forming Regions
No full textThis thesis details the development of the radiation transport code torus for radiation hydrodynamic applications and its subsequent use in investigating problems regarding radiative feedback. The code couples Monte Carlo photoionization with grid-based hydrodynamics and has the advantage that all of the features available to a dedicated radiation transport code are at its disposal in RHD applications. I discuss the development of the code, including the hydrodynamics scheme, the adaptive mesh refinement (AMR) framework and the coupling of radiation transport with hydrodynamics. Extensive testing of the resulting code is also presented.
The main application involves the study of radiatively driven implosion (RDI), a mechanism where the expanding ionized region about a massive star impacts nearby clumps, potentially triggering star formation. Firstly I investigate the way in which the radiation field is treated, isolating the relative impacts of polychromatic and diffuse field radiation on the evolution of radiation hydrodynamic RDI models. I also produce synthetic SEDs, radio, Hα and forbidden line images of the bright rimmed clouds (BRCs) resulting from the RDI models, on which I perform standard diagnostics that are used by observers to obtain the cloud conditions. I test the accuracy of the diagnostics and show that considering the pressure difference between the neutral cloud and surrounding ionized layer can be used to infer whether or not RDI is occurring. Finally I use more synthetic observations to investigate the accuracy of molecular line diagnostics and the nature of line profiles of BRCs. I show that the previously unexplained lack of dominant blue-asymmetry (a blue-asymmetry is the expected signature of a collapsing cloud) in the line profiles of BRCs can be explained by the shell of material, swept up by the expanding ionized region, that drives into the cloud. The work in this thesis combines to help resolve the difficulties in understanding radiative feedback, which is a non–linear process that happens on small astrophysical timescales, by improving numerical models and the way in which they are compared with observations
Radiative-transfer modelling of the circumstellar environments of pre-main-sequence stars
Full text linkCircumstellar discs of pre-main sequence stars undergo different processes depending on the nature of the circumstellar environment, which is governed by stellar mass. I have performed numerical simulations of the circumstellar regions of classical T~Tauri stars (CTTs) and Herbig~Ae (HAe) stars using the radiative transfer code TORUS in order to test the paradigm of magnetospheric accretion in CTTs, and to ascertain the nature of the material in the inner regions of HAe discs.
The process of magnetospheric accretion (MA) involves disc material attaching to stellar magnetic field lines and impacting the photosphere, producing accretion shocks. When the magnetic field is inclined to the star, disc warps form which periodically occult the photosphere. With specific reference to the CTTs AA Tau I perform three-dimensional MA models to study this variability. By comparing synthetic photometry with observational data I show that the geometry of the system can be constrained. I go on to study Balmer line profiles in the context of MA and disc wind outflows. I present three-dimensional models of a system comprising the star, magnetosphere, disc, and disc wind, producing synthetic line profiles and images. Using these profiles I perform time-series fitting to observational data and demonstrate that the mass accretion rate, mass loss rate, and magnetosphere temperature can be constrained. I show that there is a degeneracy between wind temperature and wind acceleration which require alternative methods to constrain further. While an outflow model alternative to a sole disc wind may produce better fits to observations, MA models reproduce various observational features well.
Finally I test the hypothesis that refractory grains produce the innermost emission in HAe discs. Focussing on the HAe stars MWC 275 and AB Aur, I perform radiative equilibrium modelling to create synthetic images of these objects from which interferometric visibility profiles are produced. I show that the temperatures at which these refractory grains are required to survive are too high to be physically plausible. I also find that silicate dust is shielded when sufficiently high mass fractions of refractory grains are used, enabling the silicates to survive interior to the classical sublimation radius. While refractory dust may provide a significant contribution to the emission observed in these inner regions, this alone is not sufficient
Formation and feedback processes of massive stars in clusters
Full text linkMany uncertainties remain as to how the most massive stars are formed and how they interact with their environment via radiative and mechanical processes. This feedback may affect future generations of star formation -- triggering it by compressing gas, or hindering it by dispersing reservoirs. These scenarios can be simulated by solving the equations of hydrodynamics and radiative transfer. However, the latter is usually simplified due to its computational expense, despite its importance in determining the dynamics.
In this thesis, I describe how I increased the efficiency of the radiation hydrodynamics code, TORUS, which uses a Monte Carlo approach to solving the radiative transfer. Tens of millions of energy packets are propagated through a domain split over hundreds of processors running in parallel with Message Passing Interface (MPI). By re-examining and improving communication algorithms, I lowered the radiation run time by about a factor of ten, making it tractable to run three-dimensional simulations of massive star feedback in clusters. This includes both the stellar and diffuse radiation fields, with multiple atomic species and silicate dust grains. The full ionization states and temperatures can then be fed in to produce self-consistent synthetic observations.
I applied this to clouds of 1000 and 10,000 solar masses with surface density 0.01 g/cm^2, containing a 34 solar mass star, with photoionization and radiation pressure feedback. Photoionization is efficient at shaping and dispersing clouds. The expanding ionization front forms dense, spherical knots with pillars pointing away from the emitting star. These resemble the Pillars of Creation in the Eagle Nebula, and the proplyds observed in the Orion Nebula. In the lower-mass model, almost all material is removed from the (15.5 pc)^3 grid within 1.6 Myr; the higher mass cloud is somewhat more resistant, with 25 per cent remaining inside (32.3 pc)^3 after 4.3 Myr. Radiation pressure has a negligible effect, but will be more important for denser clouds or higher luminosities.Science and Technology Facilities Council (STFC
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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