Estimating the Ages of Bars: Implications for the Bar-AGN-Star Formation Connection

In an effort to elevate to higher grounds our understanding on the impact of the formation and evolution of bars in the formation and evolution of galaxies, we have developed a diagnostic tool to distinguish between recently formed and evolved bars. Our method was applied in the study of a sample of 14 galaxies and revealed that, apparently, AGN activity tends to appear in galaxies which have young bars rather than evolved bars. This suggests that the time scale for the fueling of AGN by bars is short, and may help to explain, for instance, why there is not a clear correlation between the presence of bars and AGN in galaxies.Comment: 4 pages including 2 figures and 1 table; contributed talk to appear in the proceedings of the IAU Symp. 222, The Interplay among Black Holes, Stars and ISM in Galactic Nuclei, Th. Storchi Bergmann, L.C. Ho, H.R. Schmitt, eds., held in Gramado, March 200

Presencia de Anagrus flaveolus en la Argentina parasitoide de un insecto dañino del trigo y maíz (Insecta - Hymenoptera - Mymaridae)

p.19-23Se cita por primera vez pora la fauna argentina al mimárido Anagrus flaveolus Waterhouse, 1913. Se trata de una especie de amplia distribución que tiene como hospedadores a posturas de varias especies de homópteros de las familias Detphacidae, Cercopidae y Cicadellidae. Lo hemos criado a partir de posturas de Delphacodes haywardi Muir, 1929, depositadas en plantas de trigo (Tritricum aestivum L.). En la presente contribución se evaluó el porcentaje de parasitoidismo de esta especie en campos de trigo sobre los huevos del delfácido antes mencionado y el mismo parámetro fue medido en condiciones de laboratorio. Se registró la duración de su ciclo de vida y se realizaron pruebas para observar su comportamiento frente a posturas de otros homópteros auquenorrincos, de ellas se comprobó que A. flaveolus parasitoidiza en condiciones de laboratorio a los huevos de Amplicephalus simpliciusculus Linnavouri,1995 (Homóptera - Deltocephalinae)

The establishment of Aceratoneuromyia indica (Hymenoptera: Eulophidae) in three biogeographical regions of Argentina

Specimens of the eulophid Aceratoneuromyia indica (Silvestri) were recovered from fruit fly pupae collected in three Argentinian biogeographical regions. A total of 11 A. indica specimens was obtained from pupae of the tephritid Anastrepha fraterculus (Wiedemann) in Las Yungas and Paranaense subtropical rain forest regions, and 10 A. indica specimens were recovered from pupae of the tephritid Ceratitis capitata (Wiedemann) in Chacoan subtropical dry forest region.Thus, A. indica was recovered approximately 38 years after its first release in Argentina.Fil: Ovruski Alderete, Sergio Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Schliserman, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: De Coll, Olga R.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Peñaloza, Claudia. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Oroño, Luis Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Colina, Carolina del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentin

VLA observations of candidate high-mass protostellar objects at 7 mm

We present radio continuum observations at 7 mm made using the Very Large Array towards three massive star forming regions thought to be in very early stages of evolution selected from the sample of Sridharan et al. (2002). Emission was detected towards all three sources (IRAS 18470-0044, IRAS 19217+1651 and IRAS 23151+5912). We find that in all cases the 7 mm emission corresponds to thermal emission from ionized gas. The regions of ionized gas associated with IRAS 19217+1651 and IRAS 23151+5912 are hypercompact with diameters of 0.009 and 0.0006 pc, and emission measures of 7.0 x 10^8 and 2.3 x 10^9 pc cm^(-6), respectively.Comment: 17 pages, 5 figures, accepted by The Astronomical Journa

An Infrared 2D-COS Study of Fibril Formation

Aprovat per Decret de l'Alcaldia de 06-07-200

Giant isotope effect in the incoherent tunneling specific heat of the molecular nanomagnet Fe8

Time-dependent specific heat experiments on the molecular nanomagnet Fe8 and the isotopic enriched analogue 57Fe8 are presented. The inclusion of the 57Fe nuclear spins leads to a huge enhancement of the specific heat below 1 K, ascribed to a strong increase in the spin-lattice relaxation rate Gamma arising from incoherent, nuclear-spin-mediated magnetic quantum tunneling in the ground-doublet. Since Gamma is found comparable to the expected tunneling rate, the latter process has to be inelastic. A model for the coupling of the tunneling levels to the lattice is presented. Under transverse field, a crossover from nuclear-spin-mediated to phonon-induced tunneling is observed.Comment: Replaced with version accepted for publication in Physical Review Letter

Three-dimensional numerical simulation of 1GeV/Nucleon U92+ impact against atomic hydrogen

The impact of 1GeV/Nucleon U92+ projectiles against atomic hydrogen is studied by direct numerical resolution of the time-dependent wave equation for the atomic electron on a three-dimensional Cartesian lattice. We employ the fully relativistic expressions to describe the electromagnetic fields created by the incident ion. The wave equation for the atom interacting with the projectile is carefully derived from the time-dependent Dirac equation in order to retain all the relevant terms.Comment: 12 pages and 7 figures included in the tex

Nuclear Bar, Star Formation and Gas Fueling in the Active Galaxy NGC 4303

A combination of Hubble Space Telescope (HST) WFPC2 and NICMOS images are used to investigate the gas/dust and stellar structure inside the central 300 pc of the nearby active galaxy NGC 4303. The NICMOS H-band (F160W) image reveals a bright core and a nuclear elongated bar-like structure of 250 pc in diameter. The bar is centered on the bright core, and its major axis is oriented in proyection along the spin axis of the nuclear gaseous rotating disk recently detected (Colina & Arribas 1999). The V-H (F606W - F160W) image reveals a complex gas/dust distribution with a two-arm spiral structure of about 225 pc in radius. The southwestern arm is traced by young star-forming knots while the northeastern arm is detected by the presence of dust lanes. These spirals do not have a smooth structure but rather they are made of smaller flocculent spirals or filament-like structures. The magnitudes and colors of the star-forming knots are typical of clusters of young stars with masses of 0.5 to 1 x $10^5 M_{solar}, and ages of 5 to 25 million years. The overall structure of the nuclear spirals as well as the size, number and masses of the star-forming knots are explained in the context of a massive gaseous nuclear disk subject to self-gravitational instabilities and to the gravitational field created by the nuclear bar. According to the model, the gaseous disk has a mass of about 5 x 10^7 M_{solar} inside a radius of 400 pc, the bar has a radius of 150 pc and a pattern speed of about 0.5 Myr^{-1}, and the average mass accretion rate into the core (R < 8 pc) is about 0.01 M_{solar}$ yr^{-1} for about 80 Myr.Comment: ApJ, in press (February 1, 2000

String Resonances at Hadron Colliders

[Abridged] We consider extensions of the standard model based on open strings ending on D-branes. Assuming that the fundamental string mass scale M_s is in the TeV range and that the theory is weakly coupled, we discuss possible signals of string physics at the upcoming HL-LHC run (3000 fb^{-1}) with \sqrt{s} = 14 TeV, and at potential future pp colliders, HE-LHC and VLHC, operating at \sqrt{s} = 33 and 100 TeV, respectively. In such D-brane constructions, the dominant contributions to full-fledged string amplitudes for all the common QCD parton subprocesses leading to dijets and \gamma + jet are completely independent of the details of compactification, and can be evaluated in a parameter-free manner. We make use of these amplitudes evaluated near the first (n=1) and second (n=2) resonant poles to determine the discovery potential for Regge excitations of the quark, the gluon, and the color singlet living on the QCD stack. We show that for string scales as large as 7.1 TeV (6.1 TeV), lowest massive Regge excitations are open to discovery at 5\sigma in dijet (\gamma + jet) HL-LHC data. We also show that for n=1, the dijet discovery potential at HE-LHC and VLHC exceedingly improves: up to 15 TeV and 41 TeV, respectively. To compute the signal-to-noise ratio for n=2 resonances, we first carry out a complete calculation of all relevant decay widths of the second massive level string states. We demonstrate that for string scales M_s <~ 10.5 TeV (M_s <~ 28 TeV), detection of n=2 Regge recurrences at HE-LHC (VLHC) would become the smoking gun for D-brane string compactifications. Our calculations have been performed using a semi-analytic parton model approach which is cross checked against an original software package. The string event generator interfaces with HERWIG and Pythia through BlackMax. The source code is publically available in the hepforge repository.Comment: References adde