3,938 research outputs found
Modelling CO emission from hydrodynamic simulations of nearby spirals, starbursting mergers, and high-redshift galaxies
We model the intensity of emission lines from the CO molecule, based on
hydrodynamic simulations of spirals, mergers, and high-redshift galaxies with
very high resolutions (3pc and 10^3 Msun) and detailed models for the
phase-space structure of the interstellar gas including shock heating, stellar
feedback processes and galactic winds. The simulations are analyzed with a
Large Velocity Gradient (LVG) model to compute the local emission in various
molecular lines in each resolution element, radiation transfer and opacity
effects, and the intensity emerging from galaxies, to generate synthetic
spectra for various transitions of the CO molecule. This model reproduces the
known properties of CO spectra and CO-to-H2 conversion factors in nearby
spirals and starbursting major mergers. The high excitation of CO lines in
mergers is dominated by an excess of high-density gas, and the high turbulent
velocities and compression that create this dense gas excess result in broad
linewidths and low CO intensity-to-H2 mass ratios. When applied to
high-redshift gas-rich disks galaxies, the same model predicts that their
CO-to-H2 conversion factor is almost as high as in nearby spirals, and much
higher than in starbursting mergers. High-redshift disk galaxies contain giant
star-forming clumps that host a high-excitation component associated to gas
warmed by the spatially-concentrated stellar feedback sources, although CO(1-0)
to CO(3-2) emission is overall dominated by low-excitation gas around the
densest clumps. These results overall highlight a strong dependence of CO
excitation and the CO-to-H2 conversion factor on galaxy type, even at similar
star formation rates or densities. The underlying processes are driven by the
interstellar medium structure and turbulence and its response to stellar
feedback, which depend on global galaxy structure and in turn impact the CO
emission properties.Comment: A&A in pres
Unanimity Rule on networks
We introduce a model for innovation-, evolution- and opinion dynamics whose
spreading is dictated by unanimity rules, i.e. a node will change its (binary)
state only if all of its neighbours have the same corresponding state. It is
shown that a transition takes place depending on the initial condition of the
problem. In particular, a critical number of initially activated nodes is
needed so that the whole system gets activated in the long-time limit. The
influence of the degree distribution of the nodes is naturally taken into
account. For simple network topologies we solve the model analytically, the
cases of random, small-world and scale-free are studied in detail.Comment: 7 pages 4 fig
Environmental regulation of cloud and star formation in galactic bars
The strong time-dependence of the dynamics of galactic bars yields a complex
and rapidly evolving distribution of dense gas and star forming regions.
Although bars mainly host regions void of any star formation activity, their
extremities can gather the physical conditions for the formation of molecular
complexes and mini-starbursts. Using a sub-parsec resolution hydrodynamical
simulation of a Milky Way-like galaxy, we probe these conditions to explore how
and where bar (hydro-)dynamics favours the formation or destruction of
molecular clouds and stars. The interplay between the kpc-scale dynamics (gas
flows, shear) and the parsec-scale (turbulence) is key to this problem. We find
a strong dichotomy between the leading and trailing sides of the bar, in term
of cloud fragmentation and in the age distribution of the young stars. After
orbiting along the bar edge, these young structures slow down at the
extremities of the bar, where orbital crowding increases the probability of
cloud-cloud collision. We find that such events increase the Mach number of the
cloud, leading to an enhanced star formation efficiency and finally the
formation of massive stellar associations, in a fashion similar to
galaxy-galaxy interactions. We highlight the role of bar dynamics in decoupling
young stars from the clouds in which they form, and discuss the implications on
the injection of feedback into the interstellar medium, in particular in the
context of galaxy formation.Comment: MNRAS accepte
Hawking radiation of massive modes and undulations
We compute the analogue Hawking radiation for modes which posses a small wave
vector perpendicular to the horizon. For low frequencies, the resulting mass
term induces a total reflection. This generates an extra mode mixing that
occurs in the supersonic region, which cancels out the infrared divergence of
the near horizon spectrum. As a result, the amplitude of the undulation
(0-frequency wave with macroscopic amplitude) emitted in white hole flows now
saturates at the linear level, unlike what was recently found in the massless
case. In addition, we point out that the mass introduces a new type of
undulation which is produced in black hole flows, and which is well described
in the hydrodynamical regime.Comment: 37 pages, 8 figures, published versio
Conformally related massless fields in dS, AdS and Minkowski spaces
In this paper we write down the equation for a scalar conformally coupled
field simultaneously for de Sitter (dS), anti-de Sitter (AdS) and Minkowski
spacetime in d-dimensions. The curvature dependence appears in a very simple
way through a conformal factor. As a consequence the process of curvature free
limit, including wave functions limit and two-points functions, turns to be a
straightforward issue. We determine a set of modes, that we call de Sitter
plane waves, which become ordinary plane waves when the curvature vanishes.Comment: 7 pages, 1 figur
Imaging extended sources with coded mask telescopes: Application to the INTEGRAL IBIS/ISGRI instrument
Context. In coded mask techniques, reconstructed sky images are
pseudo-images: they are maps of the correlation between the image recorded on a
detector and an array derived from the coded mask pattern. Aims. The
INTEGRAL/IBIS telescope provides images where the flux of each detected source
is given by the height of the local peak in the correlation map. As such, it
cannot provide an estimate of the flux of an extended source. What is needed is
intensity sky images giving the flux per solide angle as typically done at
other wavelengths. Methods. In this paper, we present the response of the
INTEGRAL IBIS/ISGRI coded mask instrument to extended sources. We develop a
general method based on analytical calculations in order to measure the
intensity and the associated error of any celestial source and validated with
Monte-Carlo simulations. Results. We find that the sensitivity degrades almost
linearly with the source extent. Analytical formulae are given as well as an
easy-to-use recipe for the INTEGRAL user. We check this method on IBIS/ISGRI
data but these results are general and applicable to any coded mask telescope.Comment: 9 pages, 6 figures, Accepted for publication in A&
Electrodialytic processes in solid matrices. New insights into batteries recycling. A review.
Electrodialytic Remediation has been widely applied to the recovery of different contaminants from numerous solid matrices solving emerging issues of environmental concern. Results and conclusions reported in studies about real contaminated matrices are summarizes in this work. The influence of the pH value on the treatment effectiveness has been widely proved highlighting the phenomenon “water splitting” in the membrane surface. This dissociation of water molecules is related to the “limiting current” which is desirable to be exceed at the Anion Exchange Membrane in order to produce the entering of protons toward solid matrix. Other important parameters for the optimization of the technique, such as the current density and the liquid to solid ratio, are also discussed through the revision of studies using real solid matrices.
This work also focusses on the pioneer proposal of electrokinetic technologies for the recycling of lithium ion batteries considering the relevance of waste properties in the design and optimization of the technique. From a thorough literature revision, it could be concluded that further experimental results are needed to allow an optimal application of the technique to the rising problem of residues from batteries. The main aim of this work is to take the first steps in the recovery of valuable metals from spent batteries, such as Li and Co, incorporating principles of green chemistry.The authors acknowledge the financial support from the “Plan Propio de Investigación de la Universidad de Málaga with Project numbers: PPIT.UMA.B1.2017/20 and PPIT.UMA.B5.2018/17 and the European project THROUGH H2020-MSCA-RISE- 2017-778045. The first author also acknowledge the postdoctoral contract obtained from University of Malaga
Breeding Birds of Arctic Bay, Baffin Island, N.W.T., with Notes on the Biogeographic Significance of the Avifauna
The known avifauna of the Arctic Bay area consists of 38 species, of which 22 are probable or proven breeders and 3 are permanent residents. Arctic Bay appears to be in a transition area between characteristic high arctic and low arctic forms. Eurasian or Greenlandic forms include breeding Ringed Plover and 'Greenland' Hoary Redpoll; and transient Wheatear, Red Knot and Ruddy Turnstone. The absence of several sea-associated species as breeders or even transients may be attributed to the normal late ice break-up in Admiralty Inlet
The Dovekie, Alle alle, as a Spring Migrant in Eastern Lancaster Sound and Western Baffin Bay
The distribution and numbers of dovekies during spring migration were studied by aerial surveys of eastern Lancaster Sound (1976, 1978, 1979) and western Baffin Bay (1978, 1979). Dovekies that nest in northwest Greenland migrated north through the study area during May. Extrapolations of recorded densities indicate that a peak of ~14 million dovekies may have been present in eastern Lancaster Sound and northwest Baffin Bay in mid-May 1978: fewer were present in May 1979, although the migration was more protracted and total numbers migrating through these areas may have been similar. Dovekies preferred offshore pack ice habitats with moderate to heavy ice cover. Possible reasons for the highly variable distributions in the three years are discussed.Key words: dovekie, Alle alle, spring migration, Lancaster Sound, Baffin Bay, aerial survey
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