CCS and NH_3 Emission Associated with Low-Mass Young Stellar Objects

In this work we present a sensitive and systematic single-dish survey of CCS emission (complemented with ammonia observations) at 1 cm, toward a sample of low- and intermediate-mass young star-forming regions known to harbor water maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain. Out of the 40 star-forming regions surveyed in the CCS (2_(1)-1_(0)) line, only six low-mass sources show CCS emission: one transitional object between the prestellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars (L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T Tauri star (NGC 2071 North). Since CCS is considered an "early-time" (≲10^5 yr) molecule, we explain these results by either proposing a revision of the classification of the age of NGC 2071 North and L1251A, or suggesting the possibility that the particular physical conditions and processes of each source affect the destruction/production of the CCS. No statistically significant relationship was found between the presence of CCS and parameters of the molecular outflows and their driving sources. Nevertheless, we found a significant relationship between the detectability of CCS and the ammonia peak intensity (higher in regions with CCS), but not with its integrated intensity. This tendency may suggest that the narrower ammonia line widths in the less turbulent medium associated with younger cores may compensate for the differences in ammonia peak intensity, rendering differences in integrated intensity negligible. From the CCS detection rate we derive a lifetime of this molecule of ≃(0.7-3) × 10^4 yr in low-mass star-forming regions

La Pedagogía Hospitalaria.

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Asymptotic rejection of sinusoidal disturbances based voltage balance control in back-to-back power converters

This paper addresses the imbalance problem of the dc-link capacitor voltages in the three-level diode-clamped back-to-back power converter. In order to cope with it, a mathematical analysis of the capacitor voltage difference dynamics, based on a continuous model of the converter, is first carried out. It leads to an approximated model which contains explicitly several sinusoidal functions of time. In view of this result, the voltage imbalance phenomenon can be addressed as an output regulation problem, considering the sinusoidal functions as exogenous disturbances. Thus, a novel approach to deal with the mentioned problem in the back- to-back converter is presented. Then, the particular features of the disturbances are used to design several controllers. They all follow an asymptotic disturbance rejection approach. In this way, the estimations of the disturbances are used to apply a control law that cancels them while regulating the capacitor voltage balance as well. Finally, the performance of the proposed control laws is evaluated, presenting the simulation results obtained when the different controllers are implemented.MICINN-FEDER DPI2009-0966

An approach to the natural and engineered nanoparticles analysis in the environment by inductively coupled plasma mass spectrometry

Different approaches to the most relevant and recent studies and applications of inductively coupled plasma mass spectrometry (ICP-MS) applied to the analysis of natural and engineered nanoparticles in the environment are described. Usually several separation methods like polyacrylamide gel electrophoresis (PAGE), field-flow fractionation (FFF) and size exclusion chromatography (SEC) are used prior to the mass spectrometric measurements. In many cases the use of these hyphenated techniques provides important methodologies to know the bioavailability, mobility and toxicity of elements in life and environmental sciences. Alternatively, the capabilities of the single particle detection by ICP-MS (SD-ICP-MS) for the selective identification, characterization and determination of engineered nanoparticles will be also discussed

Experimental study of solid mixing mechanism in a 2D fluidized bed

The main mechanism of solids mixing in bubbling fluidized beds is well understood. When a bubble rises through the bed, it carries a wake of particles to the bed surface. A downflow of solids exists in the region surrounding the rising bubbles, resulting on an overall convective circulation of particles in the axial direction (1). In this work, a new method to characterize solids mixing in a 2D fluidized bed is developed. This mixing index is able to macroscopically characterize the rate of mixing in a fluidized bed by means of DIA. The mixing index is analogous to the Lacey’s mixing index of particle mixing (2). The experiments are carried out in a pseudo-2D fluidized bed using glass beads as bed material. These glass beads have the same density and diameter but half of them are painted in black (Figure-1). At the beginning of each experiment, the particles are placed in a perfectly lateral segregated state and then the fluidizing air is suddenly injected while images are recorded. Two different regions are detected in the time evolution of the mixing index. The first one is a region with a fast convective mixing, where the initial boundary between the black and white particles is broken. The second one is a region where diffusive mixing is dominant and the particles clusters are mixed with the bulk following an exponential trend (Figure-1). These two mechanisms, as well as the overall mixing time are characterized for different superficial gas velocities and particle sizes. REFERENCES M.J. Rhodes, X.S. Wang, M. Nguyen, P. Stewart, K. Liffman. Study of mixing in gas-fluidized beds using DEM model. Chem. Eng. Sci., 56(8):2859-2866, 2001. P.M.C. Lacey. Developments in the theory of particle mixing. J. Appl. Chem., 4:257-268, 1954. Please click Additional Files below to see the full abstract

Euphorbia paniculata Desf. subsp. paniculata en el sureste ibérico

Euphorbia paniculata Desf. subsp. paniculata in SE SpainPalabras clave. Euphorbia, Corología, Murcia, Almeria, España.Keywords. Euphorbia, Chorology, Murcia, Almeria, Spain

Rol de los sistemas de producción de aves y cerdos de traspatio en la emergencia y mantención de patógenos zoonóticos en Chile

En Chile la producción de aves y cerdos se concentra en unidades de producción industrial con altosestándares de productividad, calidad y bioseguridad. Este sector industrial concentra más del 85% de laspoblaciones de aves y cerdos en el país.Sin embargo, existen otras formas de producción animal. Una de ellas está en manos de pequeñosproductores, y se denomina como "producción animal de traspatio", que en Chile estaría representada pormás de 150 mil productores, 3,7 millones de aves y 400 mil cerdos.Los sistemas de producción animal de traspatio (SPT) son considerados como la forma de producción animalmás común a nivel mundial. Además, se reconoce que la mantención de estas unidades productivas juega unrol relevante para subsistencia de pequeños agricultores y su grupo familiar, siendo principalmente uncomplemento a las fuentes de alimentación que generan recursos económicos esporádicos. Sin embargo, segeneraliza a estas unidades productivas como poseedoras de severas deficiencias en bioseguridad