Large D gravity and low D strings

We show that in the limit of a large number of dimensions a wide class of nonextremal neutral black holes has a universal near-horizon limit. The limiting geometry is the two-dimensional black hole of string theory with a two-dimensional target space. Its conformal symmetry explains the properties of massless scalars found recently in the large-D limit. For black branes with string charges, the near-horizon geometry is that of the three-dimensional black strings of Horne and Horowitz. The analogies between the α′ expansion in string theory and the large-D expansion in gravity suggest a possible effective string description of the large-D limit of black holes. We comment on applications to several subjects, in particular to the problem of critical collapse.

End point of Hawking radiation

The formation and semiclassical evaporation of two-dimensional black holes is studied in an exactly solvable model. Above a certain threshold energy flux, collapsing matter forms a singularity inside an apparent horizon. As the black hole evaporates the apparent horizon recedes and meets the singularity in a finite proper time. The singularity emerges naked, and future evolution of the geometry requires boundary conditions to be imposed there. There is a natural choice of boundary conditions which matches the evaporated black hole solution onto the linear dilaton vacuum. Below the threshold energy flux no horizon forms and boundary conditions can be imposed where infalling matter is reflected from a timelike boundary. All information is recovered at spatial infinity in this case.

Soluble models in two-dimensional dilaton gravity

A one-parameter class of simple models of two-dimensional dilaton gravity, which can be exactly solved including back-reaction effects, is investigated at both classical and quantum levels. This family contains the RST model as a special case, and it continuously interpolates between models having a flat (Rindler) geometry and a constant curvature metric with a nontrivial dilaton field. The processes of formation of black hole singularities from collapsing matter and Hawking evaporation are considered in detail. Various physical aspects of these geometries are discussed, including the cosmological interpretation.

Radio Imaging of the Very-High-Energy γ-Ray Emission Region in the Central Engine of a Radio Galaxy

The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 1012 electron volts and are bright sources of very-high-energy (VHE) γ-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE γ-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.

Evolution and Stellar Content of AGN Host Galaxies

In this dissertation, Active Galactic Nuclei (AGN) and their host galaxies are discussed. Together with transitional events, such as supernovae and gamma-ray bursts, AGN are the most energetic phenomena in the Universe. The dominant fraction of their luminosity originates from the center of a galaxy, where accreting gas falls into a supermassive black hole, converting gravitational energy to radiation. AGN have a wide range of observed properties: e.g. in their emission lines, radio emission, and variability. Most likely, these properties depend significantly on their orientation to our line-of-sight, and to unify AGN into physical classes it is crucial to observe their orientation-independent properties, such as the host galaxies. Furthermore, host galaxy studies are essential to understand the formation and co-evolution of galactic bulges and supermassive black holes. In this thesis, the main focus is on observationally characterizing AGN host galaxies using optical and near-infrared imaging and spectroscopy. BL Lac objects are a class of AGN characterized by rapidly variable and polarized continuum emission across the electromagnetic spectrum, and coredominated radio emission. The near-infrared properties of intermediate redshift BL Lac host galaxies are studied in Paper I. They are found to be large elliptical galaxies that are more luminous than their low redshift counterparts suggesting a strong luminosity evolution, and a contribution from a recent star formation episode. To analyze the stellar content of galaxies in more detail multicolor data, especially observations at blue wavelengths, are essential. In Paper III, optical - near-infrared colors and color gradients are derived for low redshift BL Lac host galaxies. They show bluer colors and steeper color gradients than inactive ellipticals which, most likely, are caused by a relatively young stellar population indicating a different evolutionary stage between AGN hosts and inactive ellipticals. In Paper II, near-infrared imaging of intermediate redshift radio-quiet quasar hosts is used to study their luminosity evolution. The hosts are large elliptical galaxies, but they are systematically fainter than the hosts of radio-loud quasars at similar redshifts, suggesting a link between the luminosity of the host galaxies and the radio properties of AGN. In Paper IV, the characteristics of near-infrared stellar absorption features of low redshift radio galaxies are compared with those of inactive early-type galaxies. The comparison suggests that early-type galaxies with AGN are in a different evolutionary stage than their inactive counterparts. Moreover, radio galaxies are found to contain stellar populations containing both old and intermediate age components.

Communiquer la genèse de l’organisation : l’invention rhétorique de Québec solidaire

La thèse aborde le « trou noir de la genèse » dans l’étude des organisations, c’est-àdire comment une organisation en vient à exister pour la première fois. Elle montre comment la genèse s’accomplit à travers l’agencement de multiples composantes (humaines, symboliques, matérielles), articulées à travers les interactions. S’appuyant sur une analyse détaillée des interactions performées durant le congrès fondateur d’un parti politique au Québec tenu durant l’année 2006, elle identifie et discute les diverses stratégies et tactiques employés par les artisanes et artisans de cette fondation pour mettre en acte l’existence de ce nouvel agent collectif. Autrement dit, la thèse mène à une recension des manières de « communiquer la genèse ». Cela inclut l’usage de narratifs unificateurs, la gestion des identités, la mise en place de principes à travers des documents fondateurs, et la création d’une voix collective, à la fois partagée et négociée par les divers agents impliqués dans ce processus. Ces accomplissements mettent en lumière la dimension résolument rhétorique de l’organisation, conçus en tant que « stratégies pour rendre compte d’une situation », pour nommer sa structure et ses composantes primordiales à travers « l’usage du langage comme moyen symbolique d’induire la coopération ». La configuration rhétorique de discours, d’objets, de corps, de dispositifs spatiaux et physiques, et d’impératifs économiques, politiques et institutionnels à l’oeuvre dans les organisations procure un nouvel éclairage sur les modes d’existence de l’organisation. Par le fait de recenser les composantes « essentielles » ou « fondatrices » du parti politique investigué, et par l’analyse de celle-ci à l’aide des concepts de la théorie rhétorique du dramatisme, la thèse développe une perspective novatrice pour l’étude de la constitution communicative des organisations.

Structure et interactions de bulles d'espace-temps en relativité générale

Nous analysons des bulles d'espace-temps d'épaisseur finie en relativité générale. Les conditions d'énergie sont utilisées afin d'obtenir un ensemble de critères permettant de restreindre la structure du bord de la bulle. Dans le cas des bulles statiques et à symétrie sphérique, nous obtenons quatre inégalités différentielles équivalentes aux trois conditions d'énergie les plus communes. Nous montrons qu'elles sont équivalentes à un ensemble de deux inégalités différentielles simples lorsque le potentiel gravitationnel effectif a une forme particulière. Nous paramétrons alors l'espace-temps de manière à rendre la vérification de ces inégalités plus simple lorsqu'il sera question de bulles d'espace-temps. Nous traitons en particulier quatre formes de bulles, toutes caractérisées par un extérieur de type Schwarzschild de Sitter. Nous montrons que notre méthode donne les bons résultats lorsque la limite où l'épaisseur de la bulle tend vers zéro est prise. Nous terminons par un traitement succinct du problème d'une onde gravitationnelle se propageant dans un nuage de bulles d'espace-temps.

How Could Emergency Modify our Normal Ethics Standards? A Brief Review of Selected Chapters in Emergency Ethics

Compte-rendu / Review

La déqualification des immigrantes universitaires : le rôle de l’origine ethnique

Chicha (2009) constate un « trou noir » dans la littérature en ce qui a trait au processus qui engendre une plus forte déqualification à l’endroit des immigrantes universitaires. Ce « trou noir » est considéré comme problématique. D’une part, le gouvernement québécois tente de mettre en place des politiques d’immigration qui recrutent des immigrants ayant un capital humain élevé dans l’espoir qu’ils s’insèrent facilement sur marché de l’emploi. D’autre part, la présence plus marquée de déqualification de ce bassin de main d’œuvre démontre un écart entre la volonté politique et la situation réelle en emploi de ces immigrants. Il semble donc exister un problème de discrimination systémique lorsqu’il est question de déqualification des travailleuses immigrantes. Par souci d’équité et dans l’espoir d’avoir une meilleure compréhension du processus menant à la déqualification des immigrantes les objectifs de cette thèse sont de 1- mieux saisir le concept de discrimination en emploi et 2- mettre en place des mesures mieux adaptées pour s’attaquer à cette discrimination. Pour expliquer ce « trou noir », nous considérons que l’approche systémique est pertinente à cause de sa une vision holistique. Nous avons rencontré 52 immigrantes universitaires qui ont partagé leur parcours professionnel pré et post-migratoire. Les thématiques abordées touchaient à de nombreux sujets telles que leur formation, leur expérience professionnelle, leur stratégie d’unité familiale immigrante, leurs démarches concernant tant le processus de reconnaissance de leurs diplômes étrangers que leur insertion sur le marché de l’emploi, le climat de travail, etc. Les résultats de cette recherche indiquent que la discrimination en emploi est toujours présente sur le marché de l’emploi au Québec. De plus, l’origine ethnique, tel que la couleur de la peau, affecte les attitudes, comportements et propos des acteurs du milieu du travail à l’endroit des xiii immigrantes universitaires. L’application des typologies de Van Laer et Janssens (2011) et de Bonilla-Silva (2006) contribue à l’identification des attitudes, des comportements et des propos pouvant être considérés comme étant du racisme subtil. L’un des avancements de cette thèse est l’amélioration du cadre d’analyse systémique afin de mieux comprendre les difficultés à l’emploi des immigrantes universitaires. Les différentes théories empruntées de la psychologie sociale telles que les théories de similarité attraction, de catégorisation sociale et de qualité d’échanges entre subordonné et supérieur (Roberson et Block, 2001) permettent de peaufiner ce cadre d’analyse systémique, puisqu’il permet de mieux saisir les relations, parfois complexes, qui peuvent s’établir entre les différents acteurs et résulter en de la discrimination flagrante ou subtile.

Caracterización de la cultura organizacional y lineamientos de intervención para la implementación de procesos de cambio en las organizaciones. Caso empresa sector financiero

El presente Trabajo de Grado busca caracterizar la cultura organizacional de una empresa del sector Financiero en Colombia y realizar orientaciones de acciones para el cambio organizacional de acuerdo con la estrategia de perdurabilidad establecida por la Alta Dirección de dicha empresa. Para este fin, se realiza una cuidadosa revisión y actualización del estado del arte de los conceptos clave ¨Cultura Organizacional¨ y ¨Cambio Organizacional¨. Es de resaltar que para el primero de ellos, se toma como punto de partida el estado del arte sobre Cultura Organizacional realizado por el profesor Carlos Eduardo Méndez Álvarez y cuyo marco temporal abarca desde los orígenes del concepto en el siglo XIX hasta el año 2006. Asimismo, luego de una cuidadosa revisión de los Modelos de Cambio Organizacional existentes y de la realidad de la empresa objeto de estudio, se adopta el Modelo ADKAR que consta de cinco fases: Conciencia del Cambio, Deseo, Conocimiento, Capacidad – Habilidad y Refuerzo. Asimismo, a partir de la construcción de un fundamento teórico sólido y a través de la aplicación de la metodología para describir la Cultura Organizacional en Colombia MEDECO se busca una aproximación a la Cultura Organizacional de la empresa objeto de estudio con el fin de describir e identificar los rasgos predominantes de su cultura organizacional y entregar una propuesta final con los rasgos necesarios que alientan la consecución exitosa de los procesos de cambio.

Further evidence for variable synchrotron emission in XTE J1118+480 in outburst

We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ~10 s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHKs photometry, as in the previous outburst, exhibits especially large-amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power law of slope α=-0.78+/-0.07, where F_ν~ν^α. There is no compelling evidence for evolution in the slope over five nights, during which time the source brightness decayed along almost the same track as seen in variations within the nights. We conclude that both short-term variability and longer timescale fading are dominated by a single component of constant spectral shape. We cannot fit the SED of the IR variability with a credible thermal component, either optically thick or thin. This IR SED is, however, approximately consistent with optically thin synchrotron emission from a jet. These observations therefore provide indirect evidence to support jet-dominated models for XTE J1118+480 and also provide a direct measurement of the slope of the optically thin emission, which is impossible, based on the average spectral energy distribution alone.

Infrared Observations of XTE J1118+480

Infrared observations of the outbursting black hole XTE J1118+480 (ATEL #383) were performed using SQIID on the Kitt Peak National Observatory 2.1m telescope. Observations spanning 2005 January 15.42-15.58 found it somewhat fainter than the previous outburst (IAUC # 7394 , # 7407 ), at average brightness J=12.91+/-0.03, H=12.50+/-0.03, K=11.95+/-0.03. The colors again correspond to an approximately flat spectrum in F_nu. No orbital variation is apparent, but there is substantial unresolved rapid variability with rms amplitude 22% in K (between 2s exposures). Further observations are planned nightly until Jan 21.

Gas streaming motions towards the nucleus of M81

We present two-dimensional stellar and gaseous kinematics of the inner 120 x 250 pc2 of the LINER/Seyfert 1 galaxy M81, from optical spectra obtained with the Gemini Multi-Object Spectrograph (GMOS) integral field spectrograph on the Gemini-North telescope at a spatial resolution of approximate to 10 pc. The stellar velocity field shows circular rotation and, overall, is very similar to the published large-scale velocity field, but deviations are observed close to the minor axis which can be attributed to stellar motions possibly associated with a nuclear bar. The stellar velocity dispersion of the bulge is 162 +/- 15 km s-1, in good agreement with previous measurements and leading to a black hole mass of M(BH) = 5.5+3.6(-2.0) x 107 M(circle dot) based on the M(BH)-Sigma relationship. The gas kinematics is dominated by non-circular motions and the subtraction of the stellar velocity field reveals blueshifts of approximate to-100 km s-1 on the far side of the galaxy and a few redshifts on the near side. These characteristics can be interpreted in terms of streaming towards the centre if the gas is in the plane. On the basis of the observed velocities and geometry of the flow, we estimate a mass inflow rate in ionized gas of approximate to 4.0 x 10-3 M(circle dot) yr-1, which is of the order of the accretion rate necessary to power the LINER nucleus of M81. We have also applied the technique of principal component analysis (PCA) to our data, which reveals the presence of a rotating nuclear gas disc within approximate to 50 pc from the nucleus and a compact outflow, approximately perpendicular to the disc. The PCA combined with the observed gas velocity field shows that the nuclear disc is being fed by gas circulating in the galaxy plane. The presence of the outflow is supported by a compact jet seen in radio observations at a similar orientation, as well as by an enhancement of the [O i]/H alpha line ratio, probably resulting from shock excitation of the circumnuclear gas by the radio jet. With these observations we are thus resolving both the feeding - via the nuclear disc and observed gas inflow, and the feedback - via the outflow, around the low-luminosity active nucleus of M81.

MAGNETIC FIELD EFFECTS NEAR THE LAUNCHING REGION OF ASTROPHYSICAL JETS

One of the fundamental properties of astrophysical magnetic fields is their ability to change topology through reconnection and in doing so, to release magnetic energy, sometimes violently. In this work, we review recent results on the role of magnetic reconnection and associated heating and particle acceleration in jet/accretion disk systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs).

Origin of 10(15)-10(16) G magnetic fields in the central engine of gamma ray bursts

Various authors have suggested that the gamma-ray burst (GRB) central engine is a rapidly rotating, strongly magnetized, (similar to 10(15)-10(16) G) compact object. The strong magnetic field can accelerate and collimate the relativistic flow and the rotation of the compact object can be the energy source of the GRB. The major problem in this scenario is the difficulty of finding an astrophysical mechanism for obtaining such intense fields. Whereas, in principle, a neutron star could maintain such strong fields, it is difficult to justify a scenario for their creation. If the compact object is a black hole, the problem is more difficult since, according to general relativity it has ""no hair"" (i.e., no magnetic field). Schuster, Blackett, Pauli, and others have suggested that a rotating neutral body can create a magnetic field by non-minimal gravitational-electromagnetic coupling (NMGEC). The Schuster-Blackett form of NMGEC was obtained from the Mikhail and Wanas`s tetrad theory of gravitation (MW). We call the general theory NMGEC-MW. We investigate here the possible origin of the intense magnetic fields similar to 10(15)-10(16) G in GRBs by NMGEC-MW. Whereas these fields are difficult to explain astrophysically, we find that they are easily explained by NMGEC-MW. It not only explains the origin of the similar to 10(15)-10(16) G fields when the compact object is a neutron star, but also when it is a black hole.