2,038 research outputs found
Metallicity dependence of HMXB populations
High-mass X-ray binaries (HMXBs) might have contributed a non-negligible
fraction of the energy feedback to the interstellar and intergalactic media at
high redshift, becoming important sources for the heating and ionization
history of the Universe. However, the importance of this contribution depends
on the hypothesized increase in the number of HMXBs formed in low-metallicity
galaxies and in their luminosities. In this work we test the aforementioned
hypothesis, and quantify the metallicity dependence of HMXB population
properties. We compile from the literature a large set of data on the sizes and
X-ray luminosities of HMXB populations in nearby galaxies with known
metallicities and star formation rates. We use Bayesian inference to fit simple
Monte Carlo models that describe the metallicity dependence of the size and
luminosity of the HMXB populations. We find that HMXBs are typically ten times
more numerous per unit star formation rate in low-metallicity galaxies (12 +
log(O/H) < 8, namely < 20% solar) than in solar-metallicity galaxies. The
metallicity dependence of the luminosity of HMXBs is small compared to that of
the population size. Our results support the hypothesis that HMXBs are more
numerous in low-metallicity galaxies, implying the need to investigate the
feedback in the form of X-rays and energetic mass outflows of these high-energy
sources during cosmic dawn.Comment: 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Pseudoexfoliation: the diagnosis at first sight
info:eu-repo/semantics/publishedVersio
Determinants adoption of computer assisted auditing tools (CAATs)
During the last fifteen years, several studies on technology acceptance have been pursued, and several new models have been proposed. This paper presents a theoretical background on individual acceptance of Computer-assisted Audit Tools (CAATs) in the context of statutory auditors of a European country. The adoption of technologies in auditing is considered an important factor for efficiency increasing and effectiveness of auditing work. This study identifies the adoption determinants of CAATs; and develops a CAATs, adoption model. Quantitative research was carried out and operationalized by a survey to statutory auditors. Findings indicate that the perceived usefulness of CAATs, the effort expectancy, the facilitating conditions, and the number of auditors are the main drivers of the adoption and use of CAATs. This research presents significant contributions impacting the various stakeholders: Statutory Auditors, Statutory Auditors Firms, Institutes of Statutory Auditors, and Academy.info:eu-repo/semantics/acceptedVersio
Runoff at the micro-plot and slope scale following wildfire, central Portugal
Through their effects on soil properties and vegetation/litter cover, wildfires can strongly enhance overland flow generation and accelerate soil erosion [1] and, thereby, negatively affect land-use sustainability as well as downstream aquatic and flood zones. Wildfires are a common phenomenon in present-day Portugal, devastating in an average year some 100.000 ha of forest and woodlands and in an exceptional year like 2003 over 400.000 ha. There therefore exists a clear need in Portugal for a tool that can provide guidance to post-fire land management by predicting soil erosion risk, on the one hand, and, on the other, the mitigation effectiveness of soil conservation measures. Such a tool has recently been developed for the Western U.S.A. [3: ERMiT] but its suitability for Portuguese forests will need to be corroborated by field observations.
Testing the suitability of existing erosion models in recently burned forest areas in Portugal is, in a nutshell, the aim of the EROSFIRE projects. In the first EROSFIRE project the emphasis was on the prediction of erosion at the scale of individual hill slopes. In the ongoing EROSFIRE-II project the spatial scope is extended to include the catchment scale, so that also the connectivity between hill slopes as well as channel and road processes are being addressed. Besides ERMiT, the principal models under evaluation for slope-scale erosion prediction are: (i) the variant of USLE [4] applied by the Portuguese Water Institute after the wildfires of 2003; (ii) the Morgan–Morgan–Finney model (MMF) [5]; (iii) MEFIDIS [6]. From these models, MEFIDIS and perhaps MMF will, after successful calibration at the slope scale, also be applied for predicting catchment-scale sediment yields of extreme events
La Farmà cia Sala del mercat de Cardona
De la mateixa manera que a la resta de nuclis urbans del Principat, el segle XIII, significa per a la vila del castell de Cardona un temps de canvi, experimentant un important creixement demografic, urbanÃstic i econbmic que alhora es va traduir en el desenvolupament social dels seus habitants i de les institucions de govern comunals. A partir de la nova realitat urbana, hom distingira dins el terme del castell de Cardona als habitants de la vila (ville castri Cardone o ville Cardone) dels habitants del seu terme o ve'inat prbpiament dit (termini castri Cardone o vicinatus Cardone). Mentre que els primers eren cavallers al servei dels vescomtes o homes d'ofici; els del velnat eren els habitants dels masos que es trobaven repartits al llarg i ample del territori que conformava el terme
The CWKB particle production and classical condensate in de Sitter spacetime
The complex time WKB approximation is an effective tool in studying particle
production in curved spacetime. We use it in this work to understand the
formation of classical condensate in expanding de Sitter spacetime. The CWKB
leads to the emergence of thermal spectrum that depends crucially on horizons
(as in de Sitter spacetime) or observer dependent horizons (as in Rindler
spacetime). A connection is sought between the horizon and the formation of
classical condensate. We concentrate on de Sitter spacetime and study the
cosmological perturbation of mode with various values of . We find
that for a minimally coupled free scalar field for , the one-mode
occupation number grows more than unity soon after the physical wavelength of
the mode crosses the Hubble radius and soon after diverges as , where . The results substantiates the previous works in this
direction. We also find the correct oscillation and behaviour of at
small from a single expression using CWKB approximation for various values
of . We also discuss decoherence in relation to the formation of
classical condensate. We also find that the squeezed state formalism and CWKB
method give identical results.Comment: 19 pages, revtex, 5 figure
Runoff and erosion at the micro-plot and slope scale in a small burnt catchment, central Portugal
Wildfires can have important impacts on hydrological processes and soil erosion in forest catchments, due to the destruction of vegetation cover and changes to soil properties. However, the processes involved are non-linear and not fully understood. This has severely limited the understanding on the impacts of wildfires, especially in the up-scaling from hillslopes to catchments; in consequence, current models are poorly adapted for burnt forest conditions.
The objective of this presentation is to give an overview of the hydrological response and sediment yield from the micro-plot to slope scale, in the first year following a wildfire (2008/2009) that burnt an entire catchment nearby the Colmeal village, central Portugal. The overview will focus on three slopes inside the catchment, with samples including:
• Runoff at micro-plot scale (12 bounded plots) and slope scale (12 open plots); • Sediments and Organic Matter loss at micro-plot scale (12 bounded plots) and slope scale (12 open plots plus 3 Sediment fences); • Rainfall and Soil moisture data; • Soil Water Repellency and Ground Cover data.
The analysis of the first year following the wildfire clearly shows the complexity of runoff generation and the associated sediment transport in recently burnt areas, with pronounced differences between hillslopes and across spatial scales as well as with marked variations through time.
This work was performed in the framework of the EROSFIRE-II project (PTDC/AGR-CFL/70968/2006) which has as overall aim to predict soil erosion risk in recently burnt forest areas, including common post-fire forest management practices; the project focuses on the simultaneous measurement of runoff and soil erosion at multiple spatial scales.The results to be presented in this session are expected to show how sediment is generated, transported and exported in the Colmeal watershed; and contribute to understand and simulate erosion processes in burnt catchments, including for model development and evaluation
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