262,441 research outputs found
Multi-dimensional models of the interior of stars
No full textThis is a talk entitled "Multi-dimensional models of the interior of stars" given at the 22nd ACME Conference on Computational Mechanics on 4 April, 2014. The talk describes the numerical choices made during the early development of a time-implicit code for stellar hydrodynamics, MUSIC. Authors: J. Pratt, I. Baraffe, T. Goffrey, et al.<br
Nonradial oscillations in classical Cepheids: the problem revisited
No full textContext.We analyse the presence of nonradial oscillations in Cepheids, a problem that has not been theoretically revised since the work of Dziembowski (1977, Acta Astron., 27, 95) and Osaki (1977, PASJ, 29, 235). Our analysis is motivated by a work of Moskalik et al. (2004, ASPC, 310, 498), which reports the detection of low-amplitude periodicities in
a few Cepheids of the large Magellanic cloud. These newly discovered periodicities
were interpreted as nonradial modes.
Aims.Based on linear nonadiabatic stability analysis, our goal is to reanalyse the presence and stability of nonradial modes, taking into account improvement in the main input physics required for the modelling of Cepheids.
Methods.We compare the results obtained from two different numerical methods used to solve
the set of differential equations: a matrix method and the Ricatti method.
Results.We show the limitation of the matrix method for finding low-order p-modes (), because of their dual character in evolved stars such as Cepheids. For higher order
p-modes, we find excellent agreement between the two methods.
Conclusions.No nonradial instability is found below , whereas many unstable nonradial modes
exist for higher orders. We also find that nonradial modes remain unstable,
even at hotter effective temperatures than the blue edge of the Cepheid
instability strip, where no radial pulsations are expected
The importance of non-local effects: numerical studies of compressible convection in the young sun
No full textThis is a short talk "The importance of non-local effects: numerical studies of compressible convection in the young sun" given as an Astrophysics Seminar "Tuesday Talks" at the University of Exeter on 14 June 2016. This talk presents a numerical study of stellar convection that reveals the impact of non-local convection on stellar dynamics and stellar structure. The particular focus is on the changing statistics for convective overshooting at the base of the convection zone, and preliminary results are reported. Authors: J. Pratt, I. Baraffe, T. Goffrey, et al.<br
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Understanding the Depths of Brown Dwarfs and Giant Exoplanets: Modelling Substellar Atmospheres
No full textThe absence or lack of steady hydrogen fusion in the cores of brown dwarfs means these objects cool over time by radiating away their internal thermal energy. The rate at which these objects cool is regulated by the atmosphere, which imprints its complex and changing chemical composition of molecules and condensates onto the emitted radiation. A reliable model of the atmosphere and its evolution over time therefore lies at the core of our understanding of brown dwarfs and substellar objects. Over the last decade the WISE mission has uncovered the coolest spectral type known as the Y dwarfs. These objects have effective temperatures a few times greater than Jupiter, and thus provide excellent analogs for Jovian-like worlds outside of our solar system. Accurate and reliable atmosphere and evolution models are important for placing mass and age constraints on these newly discovered objects and understanding the rich chemistry and physics taking place in their atmospheres. In this thesis, I present a new set of solar metallicity atmosphere and evolutionary models for very cool brown dwarfs and self-luminous giant exoplanets, which is termed ATMO 2020. Atmosphere models are generated with the state-of-the-art 1D radiative-convective equilibrium code ATMO, and are used as surface boundary conditions to calculate the interior structure and evolution of 0.0005-0.075 solar mass objects. These models include several key improvements to the input physics used in previous models available in the literature. First, the use of a new H-He equation of state including ab initio quantum molecular dynamics calculations has raised the mass by ~1-2% at the stellar-substellar boundary and has altered the cooling tracks around the hydrogen and deuterium burning minimum masses. A second key improvement concerns updated molecular opacities in our atmosphere model ATMO, which now contains significantly more line transitions required to accurately capture the opacity in these hot atmospheres. This leads to warmer atmospheric temperature structures, further changing the cooling curves and predicted emission spectra of substellar objects. I present significant improvement for the treatment of the collisionally broadened potassium resonance doublet, and highlight the importance of these lines in shaping the red-optical and near-infrared spectrum of brown dwarfs. This is highlighted through improved comparisons to the observed spectra of benchmark objects. I generate three different grids of model simulations, one using equilibrium chemistry and two using non-equilibrium chemistry due to vertical mixing, all three computed self-consistently with the pressure-temperature structure of the atmosphere. I show the impact of vertical mixing on emission spectra and in colour-magnitude diagrams, and highlight wavelength regions which can be used of infer the strength of vertical mixing in cool brown dwarfs.Science and Technology Facilities Counci
Evolutionary models for low-mass stars and brown dwarfs: uncertainties and limits at very young ages
No full text12 pages, Latex file, uses aa.clsInternational audienceWe analyse pre-Main Sequence evolutionary tracks for low mass stars with masses based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages 1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravity and K, whereas it vanishes as gravity increases. This effect adds another source of uncertainty on evolutionary tracks at very early phases. We show that at low surface gravity (,) the common picture of vertical Hayashi lines with constant is oversimplified. The effect of a variation of initial deuterium abundance is studied. We compare our models with evolutionary tracks available in the literature and discuss the main differences. We finally analyse to which extent current observations of young systems provide a good test for pre-Main Sequence tracks
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
Author in Essay by I. A. Goncharov “Pepiniere”
No full textFeatures of the embodiment of the author’s position in the essay by I. A. Goncharov “Pepiniere” are considered. The relevance of the study is due to the poorly studied poetics of this work. A review of the scientific literature on relevant topics is performed. Methodological and theoretical definitions are given. The scientific novelty of the article is in the fact that for the first time attention is paid to artistic techniques that allow to identify the author's position in the specified literary text. The author of the article grounds her opinion from the fact that, despite the dominance of the subjective point of view, other characters’ views stand out in the work. It is concluded in the study that the text of the work represents a biographical author and author-creator. It was established that the position of the author-creator is expressed through the title, epigraphs, which are quotes, as well as through different points of view, including the author-character, the author-narrator, the characters of the work. The author of the article dwells in detail on different ways of expressing the points of view of the author-character and the author-narrator. It is proved that the point of view of the author-character and the author-narrator can intersect, they are interchanged. The author's development of the term comic “point of view” is presented in the article
Espai i identitat en l'obra de Jordi Pere Cerdà. Una geografia literària cerdaniana
No full textL'obra de l'autor nord-català Jordi Pere Cerdà (1920-2011) teixeix una cartografia literària que abasta tota dimensió espacial -real, imaginada i ficcional. Les prospeccions que assagen els seus texts es fonen en el medi natural i rural, canten a l'amor, als veïns i als éssers fantàstics del folklore català, es comprometen amb els refugiats encarant-se a tota frontera i, també, a tot abisme interior i exterior que oprimesca l'ésser. El mapatge cognitiu i literari que crea Cerdà sobrepassa qualsevol obstacle per construir espais oberts i possibles, en comunió amb l'altre. Partint d'una aproximació teòrica geocrítica, aquest treball d'investigació aprofundeix en diverses nocions sobre l'espacialitat lligades a un context convuls, ple de transformacions a nivell socioeconòmic, polític, cultural i lingüístic, el qual determinarà la vida d'un autor i d'un territori transfronterer com el de la Cerdanya i la Catalunya del Nord. En definitiva, la rica experiència vital de Jordi Pere Cerdà ens permet reflexionar sobre les relacions que vulguem establir entre els individus i amb el nostre hàbitat natural i cultural, a fi d'esdevenir membres actius que participen de la transformació dels espais que configuren les nostres identitats.The work of the North Catalan author Jordi Pere Cerdà (1920-2011) weaves a literary cartography which reaches all spatial dimensions -real, imagined and fictional. The prospections proved by their texts merge with the natural and rural environment, sing to love, neighbours and the fantastic beings of the Catalan folklore. Such prospections also commit themselves with the refugees facing every frontier and, also, facing all interior and exterior abyss that oppresses the being. The cognitive and literary mapping created by Cerdà overcomes any obstacle to construct opened and possible spaces, in communion with the other. Based on the theoretical approach called geocriticism, this research study delves into various notions about spatiality linked to a convulsive context, full of transformations at a socioeconomic, political, cultural and linguistic level; these transformations will determine the life of an author and a cross-border territory such as Cerdagne and Northern Catalonia. In short, the rich experience of Jordi Pere Cerdà allows us to reflect on the relationships we want to establish between individuals, as well as between human groups and our natural and cultural habitat, in order to become active members that participate in the transformation of the spaces that make up our identities.Programa de Doctorat en Llengües Aplicades, Literatura i Traducci
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