1,226 research outputs found

    Pseudo-intelectualismo y melancolía. La poética de la bilis negra en el Lexífanes de Luciano

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    En el mundo altamente competitivo y exhibicionista de Luciano, el hiper-aticismo, el (ab)uso de palabras rec√≥nditas y arcaicas a fin de impactar deviene en una especie de plaga. En este art√≠culo discuto c√≥mo el Lex√≠fanes se centra precisamente en las asociaciones literales y metaf√≥ricas del hiperaticismo como una enfermedad, prestando especial atenci√≥n al dictamen m√©dico -articulado en el texto por el doble del autor, Licinio-, seg√ļn el cual el personaje ep√≥nimo del di√°logo sufre de melancol√≠a. En lugar de constituir una referencia de pasada al vocabulario coloquial de la locura, la melancol√≠a -sostengo- ayuda a Luciano a asimilar a la fuerza la acumulaci√≥n de palabras pretenciosas para el desvar√≠o de un loco, un parloteo no sensitivo carente de significado. Al mismo tiempo, Luciano tambi√©n pretende exponer la presencia de la melancol√≠a en el lenguaje cultural y m√©dico de su √©poca como una enfermedad que de manera especial afecta a los ‚Äúgrandes esp√≠ritus‚ÄĚ, a las personas de inteligencia excepcional. Al llamar a Lex√≠fanes ‚Äėmelanc√≥lico‚Äô, Luciano reprende la pretensi√≥n de Lexiphanes a la vez como hiper-aticista y, no menos importante, como pseudointelectual que est√° configurando su imagen p√ļblica, temperamental y fisiol√≥gicamente, como un genio cuya atrabiliaria conformaci√≥n le permite actuar y hablar en modos extra√Īos.In Lucian‚Äôs highly competitive and exhibitionist world, hyper-Atticism, the (ab)use of recondite, archaic words for the sake of impression, has become a sort of plague. In this article, I discuss how Lexiphanes focuses precisely on the literal and metaphorical associations of hyper-Atticism as a disease, by paying particular attention on the medical verdict - articulated in the text by Lucian‚Äôs authorial double, Lycinus - that the dialogue‚Äôs eponymous character suffers from melancholia. Rather than constitute a passing reference to the colloquial vocabulary of insanity, melancholia, I argue, helps Lucian forcefully assimilate the accumulation of pretentious words to the raving of the insane, a non-sensical blabbering that is void of meaning. At the same time, Lucian aims also to expose the presence of melancholy in the cultural and medical idiom of his time as a disease that typically affects ‚Äėgreat spirits‚Äô, people of exceptional intelligence. By calling Lexiphanes ‚Äėmelancholic‚Äô, Lucian scolds Lexiphanes‚Äô pretentiousness both as a hyper-Atticist and, no less importantly, as a pseudo-intellectual who is shaping his public image, temperamentally and physiognomically, as a genius whose atrabilious constitution entitles him to act and speak in strange ways

    N-body realizations of cuspy dark matter haloes

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    We describe an algorithm for generating equilibrium initial conditions for numerical experiments with dark matter haloes. Our haloes are modelled using a general form for the mass density p{r), making it possible to represent most of the popular density profiles in the literature. The finite mass 7-models and the cuspy density profiles found in recent high-resolution cosmological TV-body simulations having a density power-law fall-off at large distances proportional to are included as special cases. The algorithm calculates the phase-space distribution function of each model assuming spherical symmetry and either an isotropic velocity dispersion tensor or an anisotropic velocity dispersion tensor of the type proposed by Osipkov and Merritt. The particle velocities are assigned according to the exact velocity distribution, making this method ideal for experiments requiring a high degree of stability. Numerical tests confirm that the resulting models are highly stable. This approach is motivated by the instabilities that arise when a local Maxwellian velocity distribution is adopted. For example, after approximating the velocity distribution by a Gaussian we show that a Hernquist halo with an initial r(^-1) density cusp immediately develops a constant density core. Moreover, after a single crossing time the orbital anisotropy has evolved over the entire system. Previous studies that use this approximation to construct halo or galaxy models could be compromised by this behaviour. Using the derived distribution functions we show the exact 1-d velocity distributions and we compare them with the Gaussian velocity distributions with the same second moment for different distances from the halo centre. We show that instabilities arise because a Gaussian velocity distribution is a very poor approximation to the true velocity distribution of particles. We also perform a series of numerical simulations evolving several dark matter halo models in isolation, with the intention of checking the stability of the initialization procedure in both configuration and velocity space. A subset of the models are evolved under the assumption that the velocity distribution at any given point is a Gaussian and the time evolution of the density profiles and velocity structure is monitored. Finally, a number of applications are discussed, including issues of relaxation in dark matter haloes as well as mergers of haloes in scattering experiments

    Dark satellites and the morphology of dwarf galaxies

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    One of the strongest predictions of the LambdaCDM cosmological model is the presence of dark satellites orbiting all types of galaxies. We focus here on the dynamical effects of such satellites on disky dwarf galaxies, and demonstrate that these encounters can be dramatic. Although mergers with M_sat > M_d are not very common, because of the lower baryonic content they occur much more frequently on the dwarf scale than for L_*-galaxies. As an example, we present a numerical simulation of a 20% (virial) mass ratio merger between a dark satellite and a disky dwarf (akin to the Fornax dwarf galaxy in luminosity) that shows that the merger remnant has a spheroidal morphology. We conclude that perturbations by dark satellites provide a plausible path for the formation of dSph systems and also could trigger starbursts in gas rich dwarf galaxies. Therefore the transition from disky to the often amorphous, irregular, or spheroidal morphologies of dwarfs could be a natural consequence of the dynamical heating of hitherto unobservable dark satellites.Comment: Submitted to ApJ Letters. 5 pages, 4 figures. A movie showing an encounter between a disky dwarf galaxy and a dark satellite can be found at http://www.astro.rug.nl/~ahelmi/dwarfs-morphologies.htm

    The Effect of Baryons on Halo Shapes

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    Observational evidence indicates a mismatch between the shapes of collisionless dark matter (DM) halos and those of observed systems. Using hydrodynamical cosmological simulations we investigate the effect of baryonic dissipation on halo shapes. We show that dissipational simulations produce significantly rounder halos than those formed in equivalent dissipationless simulations. Gas cooling causes an average increase in halo principal axis ratios of ~ 0.2-0.4 in the inner regions and a systematic shift that persists out to the virial radius, alleviating any tension between theory and observations. Although the magnitude of the effect may be overestimated due to overcooling, cluster formation simulations designed to reproduce the observed fraction of cold baryons still produce substantially rounder halos. Subhalos also exhibit a trend of increased axis ratios in dissipational simulations. Moreover, we demonstrate that subhalos are generally rounder than corresponding field halos even in dissipationless simulations. Lastly, we analyze a series of binary, equal-mass merger simulations of disk galaxies. Collisionless mergers reveal a strong correlation between DM halo shape and stellar remnant morphology. In dissipational mergers, the combination of strong gas inflows and star formation leads to an increase of the DM axis ratios in the remnant. All of these results highlight the vital role of baryonic processes in comparing theory with observations and warn against over-interpreting discrepancies with collisionless simulations on small scales.Comment: 8 pages, 3 figures. To appear in the proceedings of the XXIst IAP Colloquium "Mass Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005, France, (Eds.) G. Mamon, F. Combes, C. Deffayet, B. Fort, EAS Publications Serie

    Thick-disk evolution induced by the growth of an embedded thin disk

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    We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically-common 5:1 encounters between initially-thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale-length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale-height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale-lengths and scale-heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation.Comment: 19 pages, 17 figures, 1 table, LaTeX (uses emulateapj.cls). Replaced to match the version accepted for publication in ApJ. Fig. 3 adde

    Cold Dark Matter Substructure and Galactic Disks

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    We perform a set of high-resolution, dissipationless N-body simulations to investigate the influence of cold dark matter (CDM) substructure on the dynamical evolution of thin galactic disks. Our method combines cosmological simulations of galaxy-sized CDM halos to derive the properties of substructure populations and controlled numerical experiments of consecutive subhalo impacts onto initially-thin, fully-formed disk galaxies. We demonstrate that close encounters between massive subhalos and galactic disks since z~1 should be common occurrences in LCDM models. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. One typical host halo merger history is used to seed controlled N-body experiments of subhalo-disk encounters. As a result of these accretion events, the disk thickens considerably at all radii with the disk scale height increasing in excess of a factor of 2 in the solar neighborhood. We show that interactions with the subhalo population produce a wealth of distinctive morphological signatures in the disk stars including: conspicuous flares; bars; low-lived, ring-like features in the outskirts; and low-density, filamentary structures above the disk plane. We compare a resulting dynamically-cold, ring-like feature in our simulations to the Monoceros ring stellar structure in the MW. The comparison shows quantitative agreement in both spatial distribution and kinematics, suggesting that such observed complex stellar components may arise naturally as disk stars are excited by encounters with subhalos. These findings highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution.Comment: 10 pages, 4 figures. To appear in the proceedings of the IAU Symposium No. 254 "The Galaxy Disk in Cosmological Context", Copenhagen 9-13 June 2008, Denmark, (Eds.) J. Andersen, J. Bland-Hawthorn & B. Nordstrom, Cambridge University Pres
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