15,161 research outputs found
Orientation of \u3ci\u3eHylobius Pales\u3c/i\u3e and \u3ci\u3ePachylobius Picivorus\u3c/i\u3e (Coleoptera: Curculionidae) to Visual Cues
Pitfall traps with above-ground silhouettes of various colors and diameters were used in field tests to evaluate the role of vision in host orientation by adult pales weevils, Hylobius pales, and pitch-eating weevils, Pachylobius picivorus. White traps (11 em outer diameter) baited with ethanol and turpentine caught significantly more weevils than similarly baited black or green traps (11 cm outer diameter). Trap diameter (range of 6-22 cm outer diameter) did not affect trap catch. Pitfall traps can be used to monitor root weevil populations in young pine plantations and Christmas tree farms, where they are major pests. These results demonstrate that visual and chemical cues can be integrated to improve trap efficiency
Taking stock of SLSN and LGRB host galaxy comparison using a complete sample of LGRBs
Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are both
explosive transients with very massive progenitor stars. Clues about the nature
of the progenitors can be found by investigating environments in which such
transients occur. While studies of LGRB host galaxies have a long history,
dedicated observational campaigns have only recently resulted in a high enough
number of photometrically and spectroscopically observed SLSN hosts to allow
statistically significant analysis of their properties. In this paper we make a
comparison of the host galaxies of hydrogen-poor (H-poor) SLSNe and the
Swift/BAT6 sample of LGRBs. In contrast to previous studies we use a complete
sample of LGRBs and we address a special attention to the comparison
methodology and the selection of SLSN sample whose data have been compiled from
the available literature. At intermediate redshifts (0.3 < z < 0.7) the two
classes of transients select galaxies whose properties (stellar mass,
luminosity, star-formation rate, specific star-formation rate and metallicity)
do not differ on average significantly. Moreover, the host galaxies of both
classes of objects follow the fundamental metallicity relation and the
fundamental plane of metallicity. In contrast to previous studies we show that
at intermediate redshifts the emission line equivalent widths of the two
populations are essentially the same and that the previous claims regarding the
higher fraction of SLSN hosts among the extreme emission line galaxies with
respect to LGRBs are mostly due to a larger fraction of strong-line emitters
among SLSN hosts at z < 0.3, where samples of LGRB hosts are small and poorly
defined.Comment: 7 pages, 4 figures, accepted to Astronomy & Astrophysic
1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope
We present near-infrared H-band (1.65 micron) surface photometry of 558
galaxies in the Coma Supercluster and in the Virgo cluster. This data set,
obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat
Infrared Telescope, is aimed at complementing, with observations of mostly
early-type objects, our NIR survey of spiral galaxies in these regions,
presented in previous papers of this series. Magnitudes at the optical radius,
total magnitudes, isophotal radii and light concentration indices are derived.
We confirm the existence of a positive correlation between the near-infrared
concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only
available in electronic form upon request to [email protected])Comment: 12 pages, 6 figures. Accepted for publication in A&A
Where does galactic dust come from?
Here we investigate the origin of the dust mass (Mdust) observed in the Milky Way (MW) and of dust scaling relations found in a sample of local galaxies from the DGS and KINGFISH surveys. To this aim, we model dust production from Asymptotic Giant Branch (AGB) stars and supernovae (SNe) in simulated galaxies forming along the assembly of aMW-like halo in a well-resolved cosmic volume of 4 cMpc using the GAMESH pipeline. We explore the impact of different sets of metallicity and mass-dependent AGB and SN dust yields on the predicted Mdust. Our results show that models accounting for grain destruction by the SN reverse shock predict a total dust mass in the MW, that is a factor of ~4 less than observed, and cannot reproduce the observed galaxy-scale relations between dust and stellar masses, and dust-togas ratios and metallicity, with a smaller discrepancy in galaxies with low metallicity (12 + log(O/H) < 7.5) and low stellar masses (Mstar < 107 M⊙). In agreement with previous studies, we suggest that competing processes in the interstellar medium must be at play to explain the observed trends. Our result reinforces this conclusion by showing that it holds independently of the adopted AGB and SN dust yields
Neural Modeling and Control of Diesel Engine with Pollution Constraints
The paper describes a neural approach for modelling and control of a
turbocharged Diesel engine. A neural model, whose structure is mainly based on
some physical equations describing the engine behaviour, is built for the
rotation speed and the exhaust gas opacity. The model is composed of three
interconnected neural submodels, each of them constituting a nonlinear
multi-input single-output error model. The structural identification and the
parameter estimation from data gathered on a real engine are described. The
neural direct model is then used to determine a neural controller of the
engine, in a specialized training scheme minimising a multivariable criterion.
Simulations show the effect of the pollution constraint weighting on a
trajectory tracking of the engine speed. Neural networks, which are flexible
and parsimonious nonlinear black-box models, with universal approximation
capabilities, can accurately describe or control complex nonlinear systems,
with little a priori theoretical knowledge. The presented work extends optimal
neuro-control to the multivariable case and shows the flexibility of neural
optimisers. Considering the preliminary results, it appears that neural
networks can be used as embedded models for engine control, to satisfy the more
and more restricting pollutant emission legislation. Particularly, they are
able to model nonlinear dynamics and outperform during transients the control
schemes based on static mappings.Comment: 15 page
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The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures
Tests of the new Rossby wave theories that have been developed over the past decade to account for discrepancies between theoretical wave speeds and those observed by satellite altimeters have focused primarily on the surface signature of such waves. It appears, however, that the surface signature of the waves acts only as a rather weak constraint, and that information on the vertical structure of the waves is required to better discriminate between competing theories. Due to the lack of 3-D observations, this paper uses high-resolution model data to construct realistic vertical structures of Rossby waves and compares these to structures predicted by theory. The meridional velocity of a section at 24° S in the Atlantic Ocean is pre-processed using the Radon transform to select the dominant westward signal. Normalized profiles are then constructed using three complementary methods based respectively on: (1) averaging vertical profiles of velocity, (2) diagnosing the amplitude of the Radon transform of the westward propagating signal at different depths, and (3) EOF analysis. These profiles are compared to profiles calculated using four different Rossby wave theories: standard linear theory (SLT), SLT plus mean flow, SLT plus topographic effects, and theory including mean flow and topographic effects. Our results support the classical theoretical assumption that westward propagating signals have a well-defined vertical modal structure associated with a phase speed independent of depth, in contrast with the conclusions of a recent study using the same model but for different locations in the North Atlantic. The model structures are in general surface intensified, with a sign reversal at depth in some regions, notably occurring at shallower depths in the East Atlantic. SLT provides a good fit to the model structures in the top 300 m, but grossly overestimates the sign reversal at depth. The addition of mean flow slightly improves the latter issue, but is too surface intensified. SLT plus topography rectifies the overestimation of the sign reversal, but overestimates the amplitude of the structure for much of the layer above the sign reversal. Combining the effects of mean flow and topography provided the best fit for the mean model profiles, although small errors at the surface and mid-depths are carried over from the individual effects of mean flow and topography respectively. Across the section the best fitting theory varies between SLT plus topography and topography with mean flow, with, in general, SLT plus topography performing better in the east where the sign reversal is less pronounced. None of the theories could accurately reproduce the deeper sign reversals in the west. All theories performed badly at the boundaries. The generalization of this method to other latitudes, oceans, models and baroclinic modes would provide greater insight into the variability in the ocean, while better observational data would allow verification of the model findings
Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies
Tracing molecular hydrogen content with carbon monoxide in low-metallicity
galaxies has been exceedingly difficult. Here we present a new effort, with
IRAM 30-m observations of 12CO(1-0) of a sample of 8 dwarf galaxies having
oxygen abundances ranging from 12+logO/H=7.7 to 8.4. CO emission is detected in
all galaxies, including the most metal-poor galaxy of our sample (0.1 Zsun); to
our knowledge this is the largest number of 12CO(1-0) detections ever reported
for galaxies with 12+logO/H<=8 (0.2 Zsun) outside the Local Group. We calculate
stellar masses (Mstar) and star-formation rates (SFRs), and analyze our results
by combining our observations with galaxy samples from the literature.
Extending previous results for a correlation of the molecular gas depletion
time, tau(dep), with Mstar and specific SFR (sSFR), we find a variation in
tau(dep) of a factor of 200 or more (from <50 Myr to 10 Gyr) over a spread of
1000 in sSFR and Mstar. We exploit the variation of tau(dep) to constrain the
CO-to-H2 mass conversion factor alpha(CO) at low metallicity, and assuming a
power-law variation find alpha(CO) \propto (Z/Zsun)^1.9, similar to results
based on dust continuum measurements compared with gas mass. By including HI
measurements, we show that the fraction of total gas mass relative to the
baryonic mass is higher in galaxies that are metal poor, of low mass, and of
high sSFR. Finally, comparisons of the data with star-formation models of the
molecular gas phases suggest that, at metallicities Z/Zsun<=0.2, there are some
discrepancies with model predictions.Comment: 18 pages, 15 figures, accepted for publication in A&
Feeding AGN: new results from the NUGA survey
The NUGA project is a high-resolution (0.5''-1'') CO survey of low luminosity
AGN including the full sequence of activity types (Seyferts, LINERs and
transition objects). NUGA aims to systematically study the different mechanisms
for gas fueling of AGNs in the Local Universe. In this paper we discuss the
latest results of this recently completed survey, which now includes newly
acquired subarcsec resolution observations for all targets of the sample. The
large variety of circumnuclear disk morphologies found in NUGA galaxies (m=1,
m=2 and stochastic instabilities) is a challenging result that urges the
refinement of current dynamical models. In this paper we report on new results
obtained in 4 study cases for NUGA: NGC4826, NGC7217, NGC4579 and NGC6951Comment: 4 pages, 2 figures. Contributed talk to appear in "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei," Proc. IAU 222 (Gramado,
Brazil), eds. Th. Storchi Bergmann, L.C. Ho, H.R. Schmit
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