Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides

Using a second-order perturbative Green's functions approach we determined the normal state single-particle spectral function $A(\vec{k},\omega)$ employing a minimal effective model for iron-based superconductors. The microscopic model, used before to study magnetic fluctuations and superconducting properties, includes the two effective tight-binding bands proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and inter-orbital local electronic correlations, related to the Fe-3d orbitals. Here, we focus on the study of normal state electronic properties, in particular the temperature and doping dependence of the total density of states, $A(\omega)$, and of $A(\vec{k},\omega)$ in different Brillouin zone regions, and compare them to the existing angle resolved photoemission spectroscopy (ARPES) and previous theoretical results in ferropnictides. We obtain an asymmetric effect of electron and hole doping, quantitative agreement with the experimental chemical potential shifts as a function of doping, as well as spectral weight redistributions near the Fermi level as a function of temperature consistent with the available experimental data. In addition, we predict a non-trivial dependence of the total density of states with the temperature, exhibiting clear renormalization effects by correlations. Interestingly, investigating the origin of this predicted behaviour by analyzing the evolution with temperature of the k-dependent self-energy obtained in our approach, we could identify a number of specific Brillouin zone points, none of them probed by ARPES experiments yet, where the largest non-trivial effects of temperature on the renormalization are present.Comment: Manuscript accepted in Physics Letters A on Feb. 25, 201

The continuum description with pseudo-state wave functions

Benchmark calculations are performed aiming to test the use of two different pseudo-state bases on the the Multiple Scattering expansion of the total Transition amplitude (MST) scattering framework. Calculated differential cross sections for p-6He inelastic scattering at 717 MeV/u show a good agreement between the observables calculated in the two bases. This result gives extra confidence on the pseudo-state representation of continuum states to describe inelastic/breakup scattering.Comment: 4 pages, 2 figures. Published in Physical Review

Ejection of a Low Mass Star in a Young Stellar System in Taurus

We present the analysis of high angular resolution VLA radio observations, made at eleven epochs over the last 20 years, of the multiple system T Tauri. One of the sources (Sb) in the system has moved at moderate speed (5-10 km/s), on an apparently elliptical orbit during the first 15 years of observations, but after a close (< 2 AU) encounter with the source Sa, it appears to have accelerated westward to about 20 km/s in the last few years. Such a dramatic orbital change most probably indicates that Sb has just suffered an ejection - which would be the first such event ever detected. Whether Sb will ultimately stay on a highly elliptical bound orbit, or whether it will leave the system altogether will be known with about five more years of observations.Comment: 4 pages, accepter in ApJ Letter

The redshift and broad band spectral energy distribution of NRAO 150

Context. NRAO 150 is one of the brightest radio and mm AGN sources on the northern sky. It has been revealed as an interesting source where to study extreme relativistic jet phenomena. However, its cosmological distance has not been reported so far, because of its optical faintness produced by strong Galactic extinction. Aims. Aiming at measuring the redshift of NRAO 150, and hence to start making possible quantitative studies from the source. Methods. We have conducted spectroscopic and photometric observations of the source in the near-IR, as well as in the optical. Results. All such observations have been successful in detecting the source. The near-IR spectroscopic observations reveal strong H$\alpha$ and H$\beta$ emission lines from which the cosmological redshift of NRAO 150 ($z=1.517\pm0.002$) has been determined for the first time. We classify the source as a flat-spectrum radio-loud quasar, for which we estimate a large super-massive black-hole mass $\sim5\times 10^{9} \mathrm{M_\odot}$. After extinction correction, the new near-IR and optical data have revealed a high-luminosity continuum-emission excess in the optical (peaking at $\sim2000$\,\AA, rest frame) that we attribute to thermal emission from the accretion disk for which we estimate a high accretion rate, $\sim30$\,% of the Eddington limit. Conclusions. Comparison of these source properties, and its broad-band spectral-energy distribution, with those of Fermi blazars allow us to predict that NRAO 150 is among the most powerful blazars, and hence a high luminosity -although not detected yet- $\gamma$-ray emitter.Comment: 8 pages, 4 figure

Tailoring the frictional properties of granular media

A method of modifying the roughness of soda-lime glass spheres is presented, with the purpose of tuning inter-particle friction. The effect of chemical etching on the surface topography and the bulk frictional properties of grains is systematically investigated. The surface roughness of the grains is measured using white light interferometry and characterised by the lateral and vertical roughness length scales. The underwater angle of repose is measured to characterise the bulk frictional behaviour. We observe that the co-efficient of friction depends on the vertical roughness length scale. We also demonstrate a bulk surface roughness measurement using a carbonated soft drink.Comment: 10 pages, 17 figures, submitted to Phys. Rev.

The missing atom as a source of carbon magnetism

Atomic vacancies have a strong impact in the mechanical, electronic and magnetic properties of graphene-like materials. By artificially generating isolated vacancies on a graphite surface and measuring their local density of states on the atomic scale, we have shown how single vacancies modify the electronic properties of this graphene-like system. Our scanning tunneling microscopy experiments, complemented by tight binding calculations, reveal the presence of a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be associated with the formation of local magnetic moments and implies a dramatic reduction of the charge carriers' mobility. While vacancies in single layer graphene naturally lead to magnetic couplings of arbitrary sign, our results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene samples just by randomly removing single C atoms.Comment: Accepted for publication in Physical Review Letter

Reproductive biology of lesser spotted dogfish Scyliorhinus canicula (L., 1758) in the Cantabrian Sea

This paper examines sexual maturity of the female lesser spotted dogfish Scyliorhinus canicula (L., 1758) in the Cantabrian Sea (north of Spain). Analyses made using data collected from commercial trawlers during 1994 and 1995 showed that females reach sexual maturity at a length of 54.2 cm, and the mean egg-laying size is 56.4 ± 0.94 cm. At least one in six adult female dogfish carried egg-capsules during the study period. Sex-ratio by depth strata indicates a larger proportion of females in deeper waters. Mature and spawning females were found at depths ranging from 100 m to more than 400 m, with their proportion being larger in the deeper strata.No disponibl

A SENSITIVITY ANALYSIS OF ORGANIC VERSUS CONVENTIONAL SYSTEMS OF SHEEP-FARMING

In the Mediterranean Agriculture, the organic production constitutes a real possibility for sustainable development, it can keep a population in these areas and provide it with a decent work. This paper try to establish differences between conventional and organic systems of production, so that observation of these differences would lead to conclusions relating to the level of efficiency of one system as against the other. To achieve this objective, the research team analyzed the evolution of seventeen milk sheep farms in various places in the Castilla y León Region for a whole year. The study consisted in the modeling of the results of a Cobb-Douglas production function. The findings reveal that organic farms have higher production levels with the same combination of inputs. This result is a guarantee of future for this type of production and guarantee of feasibility for these areas