Neutrino transport with isoenergetic and neutrino-electron scattering

Solution to steady-state, bigroup neutrino transport with isoenergetic and neutrino-electron scattering have been obtained for idealized conditions representative of the outer core or envelope of a star whose inner core is undergoing gravitational collapse. The solutions are presented in a form suitable for comparison with other numerical schemes. The incident neutrino distribution was chosen to be nonequilibrium, and the solutions clearly show the tendency of the neutrinos to equilibrate via neutrino-electron scattering as they propagate through the material. Care is taken to compare solutions obtained by two completely different techniques to ensure that the solutions presented here are accurate and error free. The solutions are compared with those obtained by a simple diffusion scheme, and by a flux limited diffusion scheme. The solutions given by the latter agree well with the solutions derived here, except when the neutrino angular distribution becomes oblate.     

Active region flare rates and 8.6 mm brightness temperatures

The relationship between the flaring rates and 8.6 mm brightness temperatures of active regions has been analyzed. We find that as the 8.6 mm brightness temperature of an active region increases, a larger proportion of the energy released by the region in the form of flares is contained in progressively larger flares. At all temperatures subflares are the most frequent event. At intermediate and high temperatures about 10% of the events are flares of importance 1 or larger with flares of importance 2 or larger contributing an increasing fraction of these events as the brightness temperature increases.     

The current tectonic motion of the Northern Andes along the Algeciras Fault System in SW Colombia

Riedel, synthetic and antithetic type faults, principal displacement zones (PDZ), pull-apart basins (such as lazy-S shaped releasing bend, extensive and rhomboidal shaped and releasing sidestep basins) and minor folds located oblique to the main trace of the Algeciras Fault System (AFS) are interpreted from Landsat TM 5 images and geological mapping. These tectonic features are affecting Quaternary deposits and are related to major historical earthquakes and recent registered seismic events, indicating neotectonic activity of the structure.The AFS is classified as a right lateral wrench complex structure, with an important vertical component in which sedimentary cover and basement rocks are involved. In addition, the system represents a simple shear caused by the oblique convergence between the Nazca Plate and the northern Andes. The transpressive boundary in SW Colombia was previously located along the Eastern Frontal Fault System. However, this paper shows that the AFS constitutes the actual boundary of the current transpressive regime along the Northern Andes, which begins at the Gulf of Guayaquil in Ecuador and continues into Colombia and Venezuela.     

Variable accretion and emission from the stellar winds in the Galactic Centre

We present numerical simulations of stellar wind dynamics in the central parsec of the Galactic Centre, studying in particular the accretion of gas on to Sgr A*, the supermassive black hole. Unlike our previous work, here we use state-of-the-art observational data on orbits and wind properties of individual wind-producing stars. Since wind velocities were revised upwards and non-zero eccentricities were considered, our new simulations show fewer clumps of cold gas and no conspicuous disc-like structure. The accretion rate is dominated by a few close 'slow-wind stars' ( v _w≤ 750 km s⁻¹), and is consistent with the Bondi estimate, but variable on time-scales of tens to hundreds of years. This variability is due to the stochastic infall of cold clumps of gas, as in earlier simulations, and to the eccentric orbits of stars. The present models fail to explain the high luminosity of Sgr A* a few hundred years ago implied by Integral observations, but we argue that the accretion of a cold clump with a small impact parameter could have caused it. Finally, we show the possibility of constraining the total mass-loss rate of the 'slow-wind stars' using near infrared observations of gas in the central few arcseconds.     

Experimental assessment of Posidonia oceanica‐associated gastropods grazing on an early‐successional biofilm community: nutrient availability and species‐specific effects

Although grazing is considered an essential process controlling epiphyte biomass on seagrass leaves, there is still a lack of fundamental knowledge about the species‐specific consumption rates of the most common grazers in Mediterranean meadows. This study experimentally assessed the effect of Posidonia oceanica‐associated gastropod grazing on early successional biofilm and the species‐specific relationship between biofilm consumption rates and biofilm biomass. Two biofilms on artificial substrata, both developed in situ (in a P. oceanica meadow), one under ambient conditions and the other under nutrient‐enriched conditions, were offered in aquaria assays to nine species of grazers found in P. oceanica meadows. Biofilm consumption rates and their association with biofilm biomass were assessed. It was found that: (i) there was a positive association between biofilm consumption and biofilm biomass up to 20 mg Chl a·m^?2 for Bittium reticulatum, Gibbula ardens, Jujubinus exasperatus and Tricolia pullus; (ii) Alvania montagui, B. reticulatum and Jujubinus striatus showed the highest consumption rates and are thus expected to be amongst the leading consumers in early‐successional epiphytic communities; (iii) there was not an increase of consumption rate when a substratum colonized under nutrient‐enriched conditions was offered to any of the nine studied species. This study provides species‐specific consumption rates knowledge that is useful for the assessment of the strength of grazer–epiphyte interactions and trophic fluxes in P. oceanica meadows.     

Assessment of Holothuria arguinensis feeding rate,growth and absorption efficiency under aquaculture conditions

Holothuria arguinensis is a potential species for sea cucumber aquaculture in Europe. In a first experiment, feeding rate (FR), growth, absorption efficiency (AE) and survival of adults (135.01?±?10.87?g eviscerated weight) were assessed under sediment tank conditions. In a second experiment, the feasibility to use sea bream (Sparus aurata) biodeposits as a food source was studied for adults (168.69?±?14.59?g eviscerated weight). Individuals in the first experiment showed an increase of weight (specific growth rate (SGR)?=?0.2% d^?1), positive FRs and mean value of AE close to 80% with a mean organic matter content of 90.07?±?11.5?mg/g in the offered sediment. Sea cucumbers fed with fish biodeposits showed a reduction of weight (SGR??1), low FRs and negative values of AE. The influence of low salinity and temperature during experiments should be considered to explain these results. Indeed, sea cucumbers can be affected by a decrease of these parameters during winter months resulting in a period of inactivity.