Carbon and oxygen in HII regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

We present C and O abundances in the Magellanic Clouds derived from deep spectra of HII regions. The data have been taken with the Ultraviolet-Visual Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We measure pure recombination lines (RLs) of CII and OII in all the objects, permitting to derive the abundance discrepancy factors (ADFs) for O^2+, as well as their O/H, C/H and C/O ratios. We compare the ADFs with those of other HII regions in different galaxies. The results suggest a possible metallicity dependence of the ADF for the low-metallicity objects, but more uncertain for high-metallicity objects. We compare nebular and B-type stellar abundances and we find that the stellar abundances agree better with the nebular ones derived from collisionally excited lines (CELs). Comparing these results with other galaxies we observe that stellar abundances seem to agree better with the nebular ones derived from CELs in low-metallicity environments and from RLs in high-metallicity environments. The C/H, O/H and C/O ratios show almost flat radial gradients, in contrast with the spiral galaxies where such gradients are negative. We explore the chemical evolution analysing C/O vs. O/H and comparing with the results of HII regions in other galaxies. The LMC seems to show a similar chemical evolution to the external zones of small spiral galaxies and the SMC behaves as a typical star-forming dwarf galaxy.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 8 table

Influence of oxidation on the high-temperature mechanical properties of zirconia/nickel cermets

The influence of an oxidizing atmosphere on the high-temperature plasticity of zirconia/nickel cermets has been studied by conducting creep tests in air. The resulting microstructure has been characterized by scanning, conventional and high-resolution electron microscopy. Despite the large microstructural changes, the composites do not exhibit mechanical degradation.Ministerio de Ciencia y Tecnología MAT2000-1117, MAT2003-04199-C02-02Max-Planck-Gesellschaft (Germany) PMT-CT-2000-0005

Microstructural characteristics of TZP/Ni cermets plastically deformed at high temperature

The microstructure of 3 mol% Y2O3-stabilized tetragonal ZrO2/Ni (TZP/Ni) composites has been investigated for nickel concentrations of 20, 30 and 40 vol.% before and after creep tests conducted in argon atmosphere at 1250 °C under stresses between 9 and 14 MPa. The microstructures have been characterized using scanning, conventional and high-resolution transmission and analytical electron microscopy. Two types of microstructure were found depending on the presence/absence of percolation in the metal phase. The deformation process strongly affects the percolation threshold due to the elongation of metallic grains and subsequently formation of aggregates. TEM and HRTEM studies in as-received and deformed cermets show the lack of dislocation activity and the absence of secondary phases in both zirconia/zirconia and zirconia/nickel interfaces and triple junctions.Ministerio de Educación y Ciencia MAT2000-1117, MAT2003-04199-CO2-0

Offset-compensated comparator with full-input range in 150nm FDSOI CMOS-3d technology

Trabajo presentado al LASCAS celebrado en Iguazu (Brasil) del 24 al 26 de febrero de 2010.This paper addresses an offset-compensated comparator with full-input range in the 150nm FDSOI CMOS-3D technology from MIT- Lincoln Laboratory. The comparator discussed here makes part of a vision system. Its architecture is that of a self-biased inverter with dynamic offset correction. At simulation level, the comparator can reach a resolution of 0.1mV in an area of approximately 220μm2 with a time response of less than 40ns and a static power dissipation of 1.125μW.Peer Reviewe

Genetic differentiation in the southern population of the Fathead Minnow Pimephales promelas Rafinesque (Actinopterygii: Cyprinidae)

The North American cyprinid Pimephales promelas is a species with a wide distribution range, occurring in distinct hydrographic basins in Mexico, Canada, and the United States. Previous morphological and meristic analyses of P. promelas concluded that at least three subspecies exist in the midwestern and northeast region of the United States. No studies have been carried out on the Mexican population of P. promelas, but the findings of cryptic diversity in United States populations of this species, as well as in other codistributed fish species in Mexico could be an indication that Mexican populations of P. promelas consist of cryptic species. Using the mitochondrial gene cyt b and the first intron of the S7 ribosomal protein-coding nuclear gene we carried out phylogenetic and phylogeographic analyses of populations of P. promelas across its distribution range in northwestern Mexico. Using this information were analyzed the structure and differentiation level between populations of P. promelas from distinct river basins in the region in identifying cryptic diversity. Twenty-four sequences were obtained for cyt b, and 30 for S7, which included the two heterozygous alleles. The results revealed the existence of four well-differentiated lineages: (1) Yaqui in the Pacific slope; (2) Santa Maria, and (3) Casas Grandes in the Guzman Basin; and (4) Nazas+Conchos in Chihuahua state. This challenges the current taxonomy of P. promelas. Differences in the relationships between markers and the small sample size for the Santa Maria population (n = 1), indicate that our results must be corroborated with more data and morphological analyses. Biogeographic analysis of these findings suggest that the evolutionary history of P. promelas is associated with the fragmentation of the ancestral Rio Grande river system since Miocene in northwestern Mexico consistent with findings for codistributed fish species

Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations

We analyze the effects of intersite energy correlations on the linear optical properties of one-dimensional disordered Frenkel exciton systems. The absorption line width and the factor of radiative rate enhancement are studied as a function of the correlation length of the disorder. The absorption line width monotonously approaches the seeding degree of disorder on increasing the correlation length. On the contrary, the factor of radiative rate enhancement shows a non-monotonous trend, indicating a complicated scenario of the exciton localization in correlated systems. The concept of coherently bound molecules is exploited to explain the numerical results, showing good agreement with theory. Some recent experiments are discussed in the light of the present theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review