9,508 research outputs found
Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical composition analysis and metallicity-luminosity relations
(Abridged) We performed a multiwavelength analysis of a sample of starburst
galaxies that show the presence of a substantial population of very young
massive (WR) stars. Here we present the global analysis of the derived
photometric and chemical properties. We compare optical/NIR colours and the
physical properties (reddening coefficient, equivalent widths of the emission
and underlying absorption lines, ionization degree, electron density, and
electron temperature) and chemical properties with previous observations and
galaxy evolution models. Attending to their absolute B-magnitude many of them
are not dwarf galaxies, but they should be during their quiescent phase. We
found that both C(Hb) and Wabs increase with increasing metallicity. We
detected a high N/O ratio in objects showing strong WR features. The ejecta of
the WR stars may be the origin of the N enrichment in these galaxies. We
compared the abundances provided by the direct method with those obtained using
empirical calibrations, finding that (i) the Pilyugin method is the best
suitable empirical calibration, (ii) the relations between the oxygen abundance
and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give
acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results
provided by empirical calibrations based on photoionization models are
systematically 0.2-0.3 dex higher than the values derived from the direct
method. The O and N abundances and the N/O ratios are related to the
optical/NIR luminosity; the dispersion is consequence of the differences in the
star-formation histories. Galaxies with redder colours tend to have higher
oxygen and nitrogen abundances. Our detailed analysis is fundamental to
understand the nature of galaxies showing strong starbursts, as well as to know
their star formation history and the relationships with the environment.Comment: 30 pages, 22 figures, accepted to A&A. Updated with the final
version
Mu-tau neutrino refraction and collective three-flavor transformations in supernovae
We study three-flavor collective neutrino transformations in the
dense-neutrino region above the neutrino sphere of a supernova core. We find
that two-flavor conversions driven by the atmospheric mass difference and the
13-mixing angle capture the full effect if one neglects the second-order
difference between the muon and tau neutrino refractive index. Including this
"mu-tau matter term" provides a resonance at a density of approximately 3 x
10^7 g cm^-3 that typically causes significant modifications of the overall
electron neutrino and antineutrino survival probabilities. This effect is
surprisingly sensitive to deviations from maximal 23-mixing, being different
for each octant.Comment: 9 pages, 7 figures. New presentation of results, version to be
published in PR
The tidally disturbed luminous compact blue galaxy Mkn 1087 and its surroundings
We present new broad-band optical and near-infrared CCD imaging together with
deep optical intermediate-resolution spectroscopy of Mkn 1087 and its
surrounding objects. We analyze the morphology and colors of the stellar
populations of the brightest objects, some of them star-formation areas, as
well as the kinematics, physical conditions and chemical composition of the
ionized gas associated with them. Mkn 1087 does not host an Active Galactic
Nucleus, but it could be a Luminous Compact Blue Galaxy. Although it was
classified as a suspected Wolf-Rayet galaxy, we do not detect the spectral
features of these sort of massive stars. Mkn 1087 shows morphological and
kinematical features that can be explained assuming that it is in interaction
with two nearby galaxies: the bright KPG 103a and a dwarf ()
star-forming companion. We argue that this dwarf companion is not a tidal
object but an external galaxy because of its low metallicity [12+log(O/H) =
8.24] with respect to the one derived for Mkn 1087 [12+log(O/H) = 8.57] and its
kinematics. Some of the non-stellar objects surrounding Mkn 1087 are connected
by bridges of matter with the main body, host star-formation events and show
similar abundances despite their different angular distances. These facts,
together their kinematics, suggest that they are tidal dwarf galaxies formed
from material stripped from Mkn 1087. A bright star-forming region at the south
of Mkn 1087 (knot #7) does not show indications of being a tidal galaxy or the
product of a merging process as suggested in previous works. We argue that Mkn
1087 and its surroundings should be considered a group of galaxies.Comment: Accepted by A&A, 21 pages, 13 figures, 8 table
When giving some away makes sense to jump-start the diffusion process.
This paper uses an analytical model to examine when it makes sense to provide incentives to innovators to adopt a new product. The model allows for separate segments of innovators and imitators, each of which follows a Bass-type diffusion process. Interestingly âseedingâ the market is optimal for a limited range of situations and these do not appear to include those where there is a downturn in sales (chasm) as sales move from the first to the second segment. Research has frequently identified different segments of adopters of new products. Categorizations include innovators vs imitators (Bass, 1969; Rogers, 1995; Mahahan et al., 1990; Im et al., 2003), technophiles vs ânormalâ people, and business vs consumer users. Further, considerable effort has gone into studying the influence of members of the first group on the second. This paper focuses on when, if ever, it makes sense for a manufacture of a new product to âseedâ the market by subsidizing a few early adopters to speed the adoption process. The paper builds on earlier work by Kalish and Lilien (1983) which focused on the impact of widely available government subsidies on the adoption of socially desirable innovations (i.e. alternative energy sources) as well as the work of Jain et al. (1995). Unlike that work, we concentrate on providing subsidies (here free goods) to selective individuals in the context of a model which allows for separate segments of innovators and imitators and nests the standard Bass (1969) model.
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Regional index of sustainable economic well-being development project: final report
This report presents results from a development project carried out by nef (the new economics foundation) on behalf of emda (the East Midlands Development Agency) and Natural England, to improve the methodologies used in the calculation of the R-ISEW (Regional Index of Sustainable Economic Well-Being)
Bragg spectroscopy for measuring Casimir-Polder interactions with Bose-Einstein condensates above corrugated surfaces
We propose a method to probe dispersive atom-surface interactions by measuring via two-photon Bragg spectroscopy the dynamic structure factor of a Bose-Einstein condensate above corrugated surfaces. This method takes advantage of the condensate coherence to reveal the spatial Fourier components of the lateral Casimir-Polder interaction energy.Fil: Moreno, Gustavo Ariel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Dalvit, Diego A. R.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Calzetta, Esteban Adolfo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; Argentin
Discretized Miller approach to assess effects on boundary layer ingestion induced distortion
The performance of propulsion configurations with boundary layer ingestion (BLI) is affected to a large extent by the level of distortion in the inlet flow field. Through flow methods and parallel compressor have been used in the past to calculate the effects of this aerodynamic integration issue on the fan performance; however high-fidelity through flow methods are computationally expensive, which limits their use at preliminary design stage. On the other hand, parallel compressor has been developed to assess only circumferential distortion. This paper introduces a discretized semi-empirical performance method, which uses empirical correlations for blade and performance calculations. This tool discretizes the inlet region in radial and circumferential directions enabling the assessment of deterioration in fan performance caused by the combined effect of both distortion patterns. This paper initially studies the accuracy and suitability of the semi-empirical discretized method by comparing its predictions with CFD and experimental data for a baseline case working under distorted and undistorted conditions. Then a test case is examined, which corresponds to the propulsor fan of a distributed propulsion system with BLI. The results obtained from the validation study show a good agreement with the experimental and CFD results under design point conditions
Quantum optimal control of photoelectron spectra and angular distributions
Photoelectron spectra and photoelectron angular distributions obtained in
photoionization reveal important information on e.g. charge transfer or hole
coherence in the parent ion. Here we show that optimal control of the
underlying quantum dynamics can be used to enhance desired features in the
photoelectron spectra and angular distributions. To this end, we combine
Krotov's method for optimal control theory with the time-dependent
configuration interaction singles formalism and a splitting approach to
calculate photoelectron spectra and angular distributions. The optimization
target can account for specific desired properties in the photoelectron angular
distribution alone, in the photoelectron spectrum, or in both. We demonstrate
the method for hydrogen and then apply it to argon under strong XUV radiation,
maximizing the difference of emission into the upper and lower hemispheres, in
order to realize directed electron emission in the XUV regime
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
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