Accretion disks around black holes: dynamical evolution, meridional circulations and gamma ray bursts

We study the hydrodynamical evolution of massive accretion disks around black holes, formed when a neutron star is disrupted by a black hole in a binary system. Initial conditions are taken from 3D calculations of coalescing binaries. Assuming azimuthal symmetry, we follow the time dependence of the disk structure for 0.2 seconds. We use an ideal gas e.o.s., and assume that all the dissipated energy is radiated away. The disks evolve due to viscous stresses, modeled with an alpha law. We study the disk structure, and the strong meridional circulations that are established and persist throughout our calculations. These consist of strong outflows along the equatorial plane that reverse direction close to the surface of the disk and converge on the accretor. In the context of GRBs, we estimate the energy released from the system in neutrinos and through magnetic-dominated mechanisms, and find it can be as high as 10^52 erg and 10^51 erg respectively, during an estimated timescale of 0.1-0.2 seconds. neutrino-anti neutrino annihilation is likely to produce bursts from only an impulsive energy input (the annihilation luminosity scales as t^(-5/2)) and so would be unable to account for a large fraction of bursts with complicated light curves. However a gas mass ~0.1-0.25 Msun survives in the orbiting debris, enabling strong magnetic fields (~10^16 Gauss) to be anchored in the dense matter long enough to power short GRBs. We also investigate the continuous energy injection that arises as the black hole slowly swallows the rest of the disk and discuss its consequences on the GRB afterglow emission.Comment: Accepted for publication in ApJ, 30 pages, 7 figure

Automatic categorization of abstracts through Bayesian networks

This thesis presents a method for assigning abstracts of Artificial Intelligence papers to their area of the field. The technique is implemented by the use of a Bayesian network where relevant keywords extracted from the abstract being categorized, are entered as evidence and inferencing is made to determine potential subject areas. The structure of the Bayesian network represents the causal relationship between Artificial Intelligence keywords and subject areas. Keyword components of the network are selected from precategorized abstracts. The work reported here is part of a larger project to automatically assign papers to reviewers for Artificial Intelligence conferences. The process of assigning papers to reviewers begins by using the inference system reported here to derive Artificial Intelligence subject areas for such papers. Based on those subjects, another module can select reviewers according to their specialization and limited by conflicts of interest

Observational evidence for a broken Li Spite plateau and mass-dependent Li depletion

We present NLTE Li abundances for 88 stars in the metallicity range -3.5 < [Fe/H] < -1.0. The effective temperatures are based on the infrared flux method with improved E(B-V) values obtained mostly from interstellar NaI D lines. The Li abundances were derived through MARCS models and high-quality UVES+VLT, HIRES+Keck and FIES+NOT spectra, and complemented with reliable equivalent widths from the literature. The less-depleted stars with [Fe/H] < -2.5 and [Fe/H] > -2.5 fall into two well-defined plateaus of A_{Li} = 2.18 (sigma = 0.04) and A_{Li} = 2.27 (sigma = 0.05), respectively. We show that the two plateaus are flat, unlike previous claims for a steep monotonic decrease in Li abundances with decreasing metallicities. At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance A_{Li} = 2.64, which agrees well with current predictions (A_{Li} = 2.72) from standard Big Bang nucleosynthesis. Adopting the Kurucz overshooting model atmospheres increases the Li abundance by +0.08 dex to A_{Li} = 2.72, which perfectly agrees with BBN+WMAP.Comment: A&A Letters, in pres

Los parques biblioteca en Colombia, o las bibliotecas en los parques. Antecedentes de un discurso político y arquitectónico

This paper is the result of research whose objective was to investigate the genesis of Library Parks as an expression of political and architectural discourse in Colombia. For this purpose, a methodology based on a comparative historiography of the phenomenon of libraries and educational buildings built in public parks as a government policy at the beginning of the 20th century, and later, in the interstice between the 20th and 21st centuries, is proposed. The conclusions show that, contrary to the general perception, the library park model is not an ex novo phenomenon of the contemporary world. In this sense, the results evidence not only the identification of a set of antecedent projects of this phenomenon, built between 1932 and 1940, but also a set of existing correlations between political and architectural discourses, as a predetermining reflection of a system of thought that gave rise to the library park model.Este artigo é o resultado de um projeto de pesquisa cujo objetivo era investigar a gênese dos Parques-Biblioteca como expressão de um discurso político e arquitetônico na Colômbia. Para este fim, é proposta uma metodologia baseada em uma historiografia comparativa do fenômeno das bibliotecas e edifícios educacionais construídos em parques públicos como política governamental no início do século XX e, posteriormente, no interstício entre o século XX e o século XXI. Os resultados mostram que, ao contrário da percepção geral, o modelo de parques-bibliotecas não é um fenômeno ex novo próprio do mundo contemporâneo. Neste sentido, os resultados mostram não apenas a identificação de um conjunto de projetos antecedentes deste fenômeno, construídos entre 1932 e 1940, mas também um conjunto de correlações existentes entre discursos políticos e discursos arquitetônicos como reflexão predeterminante de um sistema de pensamento que deu origem ao modelo dos parques-biblioteca.Este artículo es el resultado de una investigación cuyo objetivo fue indagar en la génesis de los Parques Biblioteca, como expresión de un discurso político y arquitectónico en Colombia. Para este efecto, se plantea una metodología sustentada en una historiografía comparada del fenómeno de las bibliotecas y los edificios educativos construidos en parques públicos como política de gobierno, a inicios del siglo XX y, posteriormente, en el intersticio entre el siglo XX y el XXI. Las conclusiones evidencian que, contrario a la percepción general, el modelo de parques bibliotecas no es un fenómeno ex novo, propio del mundo contemporáneo. En este sentido, los resultados muestran no solo la identificación de un conjunto de proyectos antecedentes de este fenómeno, construidos entre 1932 y 1940, sino además un conjunto de correlaciones existentes entre los discursos políticos y los discursos arquitectónicos, como reflexión predeterminante de un sistema de pensamiento, que dio origen al modelo de los parques bibliotecas

Doctor of Philosophy

dissertationHuman Immunodeficiency Virus Type 1 (HIV-1), the causative agent of AIDS, encodes four proteins (Nef, Vif, Vpr and Vpu) that have evolved specific roles in promoting efficient viral replication and dissemination. A key attribute of these viral factors is their ability to interfere with multiple host defense mechanisms through one of two ways: manipulation of the ubiquitin proteasome system (UPS) or altered intracellular protein trafficking. In particular, Vpu is a small integral membrane protein that is expressed late in the viral life cycle and found only within HIV-1 and some related simian immunodeficiency virus (SIV) isolates. Vpu antagonizes multiple cellular targets that are involved in innate and adaptive immunity, including the restriction factor BST-2, a family member of cellular "intrinsic" proteins that serve to restrict viral replication immediately following viral infection. In this work, we show that Vpu downregulates the chemokine receptor CCR7 on the surface of HIV-1-infected primary CD4+ T cells by sequestering the protein in a perinuclear compartment (the trans-Golgi Network: TGN). This compromises the migratory potential of T cells in a CCR7-dependent manner and may have major implications in HIV-1 pathogenesis. Additionally, we clarify the mechanisms by which Vpu relies on cullin-RING Ligases (CRLs), one of the largest classes of E3 Ubiquitin Ligases within the UPS, to downregulate host proteins from the cell surface. Through the use of a neddylation iv inhibitor, a post-translational modification necessary for CRL activity, we establish that Vpu-mediated BST-2, CCR7 and Natural T and B cell antigen (NTB-A) downregulation is CRL-independent. This provides further support that Vpu is a multifunctional accessory protein that has evolved several ways to interfere with its cellular targets

Stochastic inversion of InSAR data to assess the probability of pressure penetration into the lower caprock at In Salah

AbstractWe carried out stochastic inversions of InSAR data to assess the probability that pressure perturbations resulting from CO2 injection into well KB-502 at In Salah penetrated into the lower caprock seal above the reservoir. We employed inversions of synthetic data to evaluate the factors that affect the vertical resolution of overpressure distributions, and to assess the impact of various sources of uncertainty in prior constraints on inverse solutions. These include alternative pressure-driven deformation modes within reservoir and caprock, the geometry of a sub-vertical fracture zone in the caprock identified in previous studies, and imperfect estimates of the rock mechanical properties. Inversions of field data indicate that there is a high probability that a pressure perturbation during the first phase of injection extended upwards along the fracture zone ∼150m above the reservoir, and less than 50% probability that it reached the Hot Shale unit at 1500m depth. Within the uncertainty bounds considered, we conclude that it is very unlikely that the pressure perturbation approached within 150m of the top of the lower caprock at the Hercynian Unconformity. The results are consistent with previous deterministic inversion and forward modeling studies

Opaque or transparent? A link between neutrino optical depths and the characteristic duration of short gamma-ray bursts

Cosmological gamma ray bursts (GRBs) are thought to occur from violent hypercritical accretion onto stellar mass black holes, either following core collapse in massive stars or compact binary mergers. This dichotomy may be reflected in the two classes of bursts having different durations. Dynamical calculations of the evolution of these systems are essential if one is to establish characteristic, relevant timescales. We show here for the first time the result of dynamical simulations, lasting approximately one second, of post--merger accretion disks around black holes, using a realistic equation of state and considering neutrino emission processes. We find that the inclusion of neutrino optical depth effects produces important qualitative temporal and spatial transitions in the evolution and structure of the disk, which may directly reflect upon the duration and variability of short GRBs.Comment: Accepted for publication in ApJ Letter