Effective Dielectric Response of Metamaterials

We use a homogenization procedure for Maxwell's equations in order to obtain in the local limit the frequency ($\omega$) dependent macroscopic dielectric response $\epsilon^M(\omega)$ of metamaterials made of natural constituents with any geometrical shape repeated periodically with any structure. We illustrate the formalism calculating $\epsilon^M(\omega)$ for several structures. For dielectric rectangular inclusions within a conducting material we obtained a very anisotropic response which changes along one direction from conductor-like at low $\omega$ to a resonant dielectric-like at large $\omega$, attaining a very small reflectance at intermediate frequencies unrelated to surface plasmon excitation and which can be tuned through geometrycal tayloring. A similar behavior is obtained for other shapes close to the percolation threshold.Comment: 16 pages 7 figures. Accepted in Phys. Rev. B (2009-06-08

Causal analysis of the pinion teeth failure in a limestone Reclaimer

This paper presents a causal analysis of an unexpected failure of the pinion teeth of a large reducer installed in a limestone reclaimer which is part of a raw material transportation system of a cement factory. The Montano methodology is applied. It includes a collection of documentation, evidences, evaluation of failure mechanism by visual inspection and some hypothesis and their validation based on the analysis of the material resistance. It is demonstrated that although the teeth of the pinion were made of a suitable material and cemented correctly, they worked overloaded due to the presence of large rocks in the raw material. A resulting increase of contact tensions in the teeth over the allowed limits led to a fatigue failure process which is described in this work. The results of the analysis can be of great interest in order to develop preventive measures and avoid future undesired plant stoppages and economic losses

A Core AFLP Map of Aposporic Tetraploid \u3cem\u3ePaspalum Notatum\u3c/em\u3e (Bahiagrass)

Paspalum notatum (Bahiagrass) is a perennial rhizomatous species that reproduces by aposporous apomixis. Tetraploid races (2n=4x=40) are widely distributed from Central to South America and constitute one of the most valuable natural forage grasses for the subtropical areas of Paraguay, southern Brazil and north-eastern Argentina. Apospory in the species is controlled by a single locus, which exhibits a distorted segregation ratio. The objectives of this work were to develop a core genetic linkage map of the species by using AFLP markers and characterize the genomic region related to apospory

Water vapor radiative effects on short-wave radiation in Spain

This work was supported by the Spanish Ministry of Economy and Competitiveness through project CGL2014-56255-C2. Support from the Junta de Extremadura (Research Group Grant GR15137) is gratefully acknowledged. Work at the Universidad de Valladolid is supported by project CMT2015-66742-R. Work at the Universidad de Granada was supported by the Andalusia Regional Government (Project P12-RNM-2409) and the Spanish Ministry of Economy and Competitiveness and FEDER funds under the projects CGL2016-81092-R and “Juan de la Cierva-Formación” program (FJCI-2014-22052).In this work, water vapor radiative effect (WVRE) is studied by means of the Santa Barbara's Disort Radiative Transfer (SBDART) model, fed with integrated water vapor (IWV) data from 20 ground-based GPS stations in Spain. Only IWV data recorded during cloud-free days (selected using daily insolation data) were used in this study. Typically, for SZA = 60.0 ± 0.5° WVRE values are around − 82 and − 66 Wm−2 (first and third quartile), although it can reach up − 100 Wm−2 or decrease to − 39 Wm−2. A power dependence of WVRE on IWV and cosine of solar zenith angle (SZA) was found by an empirical fit. This relation is used to determine the water vapor radiative efficiency (WVEFF = ∂WVRE/∂IWV). Obtained WVEFF values range from − 9 and 0 Wm−2 mm−1 (− 2.2 and 0% mm−1 in relative terms). It is observed that WVEFF decreases as IWV increases, but also as SZA increases. On the other hand, when relative WVEFF is calculated from normalized WVRE, an increase of SZA results in an increase of relative WVEFF. Heating rates were also calculated, ranging from 0.2 Kday−1 to 1.7 Kday−1. WVRE was also calculated at top of atmosphere, where values ranged from 4 Wm−2 to 37 Wm−

Light yield determination in large sodium iodide detectors applied in the search for dark matter

Application of NaI(Tl) detectors in the search for galactic dark matter particles through their elastic scattering off the target nuclei is well motivated because of the long standing DAMA/LIBRA highly significant positive result on annual modulation, still requiring confirmation. For such a goal, it is mandatory to reach very low threshold in energy (at or below the keV level), very low radioactive background (at a few counts/keV/kg/day), and high detection mass (at or above the 100 kg scale). One of the most relevant technical issues is the optimization of the crystal intrinsic scintillation light yield and the efficiency of the light collecting system for large mass crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators) dark matter search project large NaI(Tl) crystals from different providers coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc Underground Laboratory. In this paper we present the estimates of the NaI(Tl) scintillation light collected using full-absorption peaks at very low energy from external and internal sources emitting gammas/electrons, and single-photoelectron events populations selected by using very low energy pulses tails. Outstanding scintillation light collection at the level of 15~photoelectrons/keV can be reported for the final design and provider chosen for ANAIS detectors. Taking into account the Quantum Efficiency of the PMT units used, the intrinsic scintillation light yield in these NaI(Tl) crystals is above 40~photoelectrons/keV for energy depositions in the range from 3 up to 25~keV. This very high light output of ANAIS crystals allows triggering below 1~keV, which is very important in order to increase the sensitivity in the direct detection of dark matter

Background analysis and status of the ANAIS dark matter project

ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set up at the new facilities of the Canfranc Underground Laboratory (LSC), a large scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation positive result using the same target and technique. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up. The comparison of the background model for the ANAIS-25 prototypes with the experimental results is presented. ANAIS crystal radiopurity goals have been achieved for Th-232 and U-238 chains, but a Pb-210 contamination out-of-equilibrium was identified, whose origin has been studied. The high light collection efficiency obtained with these prototypes allows to anticipate an energy threshold of the order of 1 keVee. A new detector, with improved performances, was received in March 2015 and very preliminary results are shown.Comment: 6 pages, 7 figure