The evolution of Giant Molecular Filaments

In recent years there has been a growing interest in studying giant molecular filaments (GMFs), which are extremely elongated (> 100pc in length) giant molecular clouds (GMCs). They are often seen as inter-arm features in external spiral galaxies, but have been tentatively associated with spiral arms when viewed in the Milky Way. In this paper, we study the time evolution of GMFs in a high-resolution section of a spiral galaxy simulation, and their link with spiral arm GMCs and star formation, over a period of 11Myrs. The GMFs generally survive the inter-arm passage, although they are subject to a number of processes (e.g. star formation, stellar feedback and differential rotation) which can break the giant filamentary structure into smaller sections. The GMFs are not gravitationally bound clouds as a whole, but are, to some extent, confined by external pressure. Once they reach the spiral arms, the GMFs tend to evolve into more substructured spiral arm GMCs, suggesting that GMFs may be precursors to arm GMCs. Here, they become incorporated into the more complex and almost continuum molecular medium that makes up the gaseous spiral arm. Instead of retaining a clear filamentary shape, their shapes are distorted both by their climb up the spiral potential and their interaction with the gas within the spiral arm. The GMFs do tend to become aligned with the spiral arms just before they enter them (when they reach the minimum of the spiral potential), which could account for the observations of GMFs in the Milky Way.Comment: 15 pages, 11 figures, MNRAS accepte

Stress approach by media art

With a background in conceptual art and media art, and the relations between science and art, we tried to approach the concept of stress through art. Stress is a recent problem of people in several countries, and could be caused by external factors, such as social pressure, or be derived from internal factors, such as the requirement that the subject puts himself. Stress had a negative impact at several organs of the human body, but heart is the main one. Taking into account all of these aspects, and from photos of two drawings of the heart ...setup program EDIUS, that integrate all the images and sounds planned to perform the stress.info:eu-repo/semantics/publishedVersio

Filamentary fragmentation in a turbulent medium

We present the results of smoothed particle hydrodynamic simulations investigating the evolution and fragmentation of filaments that are accreting from a turbulent medium. We show that the presence of turbulence, and the resulting inhomogeneities in the accretion flow, play a significant role in the fragmentation process. Filaments which experience a weakly turbulent accretion flow fragment in a two-tier hierarchical fashion, similar to the fragmentation pattern seen in the Orion Integral Shaped Filament. Increasing the energy in the turbulent velocity field results in more sub-structure within the filaments, and one sees a shift from gravity-dominated fragmentation to turbulence-dominated fragmentation. The sub-structure formed in the filaments is elongated and roughly parallel to the longitudinal axis of the filament, similar to the fibres seen in observations of Taurus, and suggests that the fray and fragment scenario is a possible mechanism for the production of fibres. We show that the formation of these fibre-like structures is linked to the vorticity of the velocity field inside the filament and the filament's accretion from an inhomogeneous medium. Moreover, we find that accretion is able to drive and sustain roughly sonic levels of turbulence inside the filaments, but is not able to prevent radial collapse once the filaments become supercritical. However, the supercritical filaments which contain fibre-like structures do not collapse radially, suggesting that fibrous filaments may not necessarily become radially unstable once they reach the critical line-density.Comment: (Accepted for publication in MNRAS

Nominal and real wage rigidity: Does nationality matter?

We assess the differences in downward nominal and real wage rigidity between natives and immigrants in Portugal, using a matched employer-employee database and the International Wage Flexibility Project (IWFP) methodology. This methodology estimates a notional or counterfactual distribution that would prevail under wage flexibility and compares it to the empirical wage distribution. The estimated measures of wage rigidity capture the share of workers that received a wage freeze but would receive a wage cut in the absence of rigidity. We found that the differences between natives and immigrants are not substantial, but immigrants are more prone to institutional-related rigidities

The frequency and nature of 'cloud-cloud collisions' in galaxies

PublishedThis is the final version of the article. Available from Oxford Journals via the DOI in this record.We investigate cloud-cloud collisions, and GMC evolution, in hydrodynamic simulations of isolated galaxies. The simulations include heating and cooling of the ISM, self--gravity and stellar feedback. Over timescales <5 Myr most clouds undergo no change, and mergers and splits are found to be typically two body processes, but evolution over longer timescales is more complex and involves a greater fraction of intercloud material. We find that mergers, or collisions, occur every 8-10 Myr (1/15th of an orbit) in a simulation with spiral arms, and once every 28 Myr (1/5th of an orbit) with no imposed spiral arms. Both figures are higher than expected from analytic estimates, as clouds are not uniformly distributed in the galaxy. Thus clouds can be expected to undergo between zero and a few collisions over their lifetime. We present specific examples of cloud--cloud interactions in our results, including synthetic CO maps. We would expect cloud--cloud interactions to be observable, but find they appear to have little or no impact on the ISM. Due to a combination of the clouds' typical geometries, and moderate velocity dispersions, cloud--cloud interactions often better resemble a smaller cloud nudging a larger cloud. Our findings are consistent with the view that spiral arms make little difference to overall star formation rates in galaxies, and we see no evidence that collisions likely produce massive clusters. However, to confirm the outcome of such massive cloud collisions we ideally need higher resolution simulations

Catálogo das plantas vasculares citadas para a ilha de Santa Maria

XIV Expedição Científica do Departamento de Biologia - Santa Maria 2009.Foi construído um catálogo das plantas vasculares citadas para a ilha de Santa Maria com base nas obras de síntese de Trelease (1897), Palhinha (1966), Franco (1971, 1984), Franco & Afonso (1994, 1998, 2003), Hansen & Sunding (1993), Silva et al. (2005),Schäfer (2003,2005)e no Portal da Biodiversidade dos Açores (http://www.azoresbioportal.angra.uac.pt/). Nesta compilação a grafia dos nomes científicos segue a base de dados International Plant Names Index (IPNI, 2005). O presente catálogo assinala para a ilha de Santa Maria 686 taxa vasculares, correspondendo a 676 espécies, distribuídas por 123 famílias. O número de taxa nativos representa apenas 20,8 % do total de taxa presentes na ilha.ABSTRACT: A vascular plant checklist of Santa Maria Island is presented based on the published accounts of Trelease (1897), Palhinha (1966), Franco (1971, 1984), Franco & Afonso (1994, 1998, 2003), Hansen & Sunding (1993), Silva et al. (2005), Schäfer (2003, 2005) and on the The Azorean Biodiversity Portal (http://www.azoresbioportal.angra.uac.pt/). In this checklist we present the names according the International Plant Names Index (IPNI, 2005). The present checklist updates the vascular plants to 686 taxa distributed by 123 families. The number of native taxa represents only 20.8 % of Santa Maria flora

First detection of CF+ towards a high-mass protostar

We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. This detection occurred as part of an unbiased spectral survey of this object in the 0.8-3 mm range, performed with the IRAM 30m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not efficient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core.Comment: 6 page