Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution

We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2-10, Mkn 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253-0312, Tol 1457-262, Tol 1924-416 and the HII region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10420 {\AA} range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C$^{2+}$ and/or O$^{2+}$ from faint pure recombination lines (RLs) in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O vs. O/H, C/O vs. N/O and C/N vs. O/H relations for Galactic and extragalactic HII regions and comparing with results for halo stars and DLAs. We find that HII regions in star-forming dwarf galaxies occupy a different locus in the C/O vs. O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic HII regions should have the same origin than in halo stars. The comparison between the C/O ratios in HII regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for HII regions and that this coupling breaks in very low-metallicity objects.Comment: 27 pages, 12 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Societ

On the transmission of light through a single rectangular hole

In this Letter we show that a single rectangular hole exhibits transmission resonances that appear near the cutoff wavelength of the hole waveguide. For light polarized with the electric field pointing along the short axis, it is shown that the normalized-to-area transmittance at resonance is proportional to the ratio between the long and short sides, and to the dielectric constant inside the hole. Importantly, this resonant transmission process is accompanied by a huge enhancement of the electric field at both entrance and exit interfaces of the hole. These findings open the possibility of using rectangular holes for spectroscopic purposes or for exploring non-linear effects.Comment: Submitted to PRL on Feb. 9th, 200

Properties of the ionized gas in HH202. I: Results from integral field spectroscopy with PMAS

We present results from integral field spectroscopy with the Potsdam multi-Aperture Spectrograph of the head of the Herbig-Haro object HH 202 with a spatial sampling of 1"x1". We have obtained maps of different emission lines, physical conditions --such as electron temperature and density-- and ionic abundances from recombination and collisionally excited lines. We present the first map of the Balmer temperature and of the temperature fluctuation parameter, t^2. We have calculated the t^2 in the plane of the sky, which is substantially smaller than that determined along the line of sight. We have mapped the abundance discrepancy factor of O^{2+}, ADF(O^{2+}), finding its maximum value at the HH 202-S position. We have explored the relations between the ADF(O^{2+}) and the electron density, the Balmer and [O III] temperatures, the ionization degree as well as the t^2 parameter. We do not find clear correlations between these properties and the results seem to support that the ADF and t^2 are independent phenomena. We have found a weak negative correlation between the O^{2+} abundance determined from recombination lines and the temperature, which is the expected behaviour in an ionized nebula, hence it seems that there is not evidence for the presence of super-metal rich droplets in H II regions.Comment: 12 pages, 11 figures. Accepted for publication in MNRA

Caracterización del xilema de 352 coníferas

Following the traditional methods of preparation and description of wood at microscopy level, 352 descriptions of the woods of conifers were made. For the characterisation of each wood a multiple entry key was prepared, with a total of 81 features divided into four groups: tracheids with 29 features, axial parenchyma with 8, wood rays with 37 and resin canals with 7.Siguiendo los métodos tradicionales de preparación y descripción de la madera a nivel microscópico, se han realizado 352 descripciones de maderas de coníferas. Para la caracterización de cada madera se ha elaborado una clave de múltiple entrada con un total de 81 caracteres dividida en cuatro grupos: traqueidas con 29 caracteres, parénquima axial 8, radios leñosos 37 y canales resiníferos 7

Redes neuronales artificiales en el control de procesos por variables: aplicación en la fabricación de tableros de partículas

Artificial neural networks are an efficient tool for modelling production control processes using data from the actual production as well as simulated or design of experiments data. In this study two artificial neural networks were combined with the control process charts and it was checked whether the data obtained by the networks were valid for variable process control in particleboard manufacture. The networks made it possible to obtain the mean and standard deviation of the internal bond strength of the particleboard within acceptable margins using known data of thickness, density, moisture content, swelling and absorption. The networks obtained met the acceptance criteria for test values from non-standard test methods, as well as the criteria for using these values in statistical process control.Las redes neuronales artificiales son una herramienta eficaz para el modelado de los procesos de control de producción, tanto partiendo de datos de la propia producción como de datos simulados o procedentes de diseños de experimentos. En este estudio se han combinado dos redes neuronales artificiales con los gráficos de control de procesos y se ha comprobado si los datos obtenidos con ellas eran válidos para el control de producción por variables en la fabricación de tableros de partículas. Las redes han permitido obtener valores de la media y la desviación típica de la cohesión interna del tablero de partículas dentro de unos márgenes aceptables a partir de datos conocidos de espesor, densidad, contenido de humedad, hinchazón y absorción. Las redes obtenidas han cumplido con los requisitos de aceptación de valores de ensayo por métodos alternativos al normalizado y con los requisitos impuestos para su utilización en el control estadístico de procesos

Clostridioides difficile infection in a long-term convalescence hospital: A real tale of pitfalls and outdated therapy

Objective. The aim of the study was to know the char-acteristics and risk factors of Clostridioides difficile infection (CDI) in a long-term hospital is key to improve its manage-ment. Material and methods. Retrospective study with 37 pa-tients, along 43 months. We describe demographic variables, clinical data, time to diagnosis, treatment, and evolution. Results. Analysis of 46 episodes (37 patients, mean age=82.2 years). 77.8% were absolutely dependent, 41.7% had chronic kidney disease, 64.9% had received antibiotics in the previous three months, 40.5% received antibiotics at diagnosis. It was the first episode in 78.4%, and first recurrence in 21.6%. Therapy was started in the first 24 hours after diagnosis in 89.2%, mostly metronidazole. 83.3% recovered, 3 patients died from CDI, diagnosis was registered in the discharge report in 91.1%. Conclusions. Previous antibiotic therapy, high grade of dependency and renal failure were the main risk factors. There is room for improvement in CDI management at our hospital. Objective. The aim of the study was to know the characteristics and risk factors of Clostridioides difficile infection (CDI) in a long-term hospital is key to improve its management. Material and methods. Retrospective study with 37 patients, along 43 months. We describe demographic variables, clinical data, time to diagnosis, treatment, and evolution. Results. Analysis of 46 episodes (37 patients, mean age=82.2 years). 77.8% were absolutely dependent, 41.7% had chronic kidney disease, 64.9% had received antibiotics in the previous three months, 40.5% received antibiotics at diagnosis. It was the first episode in 78.4%, and first recurrence in 21.6%. Therapy was started in the first 24 hours after diagnosis in 89.2%, mostly metronidazole. 83.3% recovered, 3 patients died from CDI, diagnosis was registered in the discharge report in 91.1%. Conclusions. Previous antibiotic therapy, high grade of dependency and renal failure were the main risk factors. There is room for improvement in CDI management at our hospital

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