12,900 research outputs found
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
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 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
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