Complex organic molecules in comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy): detection of ethylene glycol and formamide

A spectral survey in the 1 mm wavelength range was undertaken in the long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m telescope of the Institut de radioastronomie millim\'etrique (IRAM) in April and November-December 2013. We report the detection of ethylene glycol (CH$_2$OH)$_2$ (aGg' conformer) and formamide (NH$_2$CHO) in the two comets. The abundances relative to water of ethylene glycol and formamide are 0.2-0.3% and 0.02% in the two comets, similar to the values measured in comet C/1995 O1 (Hale-Bopp). We also report the detection of HCOOH and CH$_3$CHO in comet C/2013 R1 (Lovejoy), and a search for other complex species (methyl formate, glycolaldehyde).Comment: Accepted for publication as a Letter in Astronomy and Astrophysic

Análisis de los diferentes tipos de desvulcanizado en la caracterización de nuevos materiales elastoméricos formados por la mezcla de estireno butadieno-caucho natural y mezclados con neumáticos fuera de uso (GTR)

En este artículo se propone la creación de un nuevomaterial útil para la industria a partir de la mezcla con rodillos de dos elastómeros vírgenes al 50% (estireno-butadieno (SBR) y caucho natural (NR)) con neumáticos fuera de uso (GTR). Estos neumáticos han sido previamente desvulcanizados siguiendo diversas técnicas, las cuales serán analizadas en este artículo, para posteriormente realizarse su mezcla con el elastómero virgen SBR/NR y los aditivos correspondiente, volviéndose a vulcanizar este nuevo material con el fin de que alcance las propiedades mecánicas, térmicas y de estructura que permitan su utilización en la industria. Concretamente se han analizado tres tipos de muestras; una primera formada por el elastómero virgen (SBR/NR), una segunda añadiendo al SBR/NR, GTR en la proporción de 20 phr (parts perhundred rubber), y una tercera añadiendo al SBR/NR, GTR en la proporción de 40 phr (en los ensayos mecánicos se han utilizado más porcentajes, con el finde proporcionar mayor fiabilidad en los resultados). El GTR recibido ha sido desvulcanizado aplicando diferentes técnicas: sin desvulcanizar (dn); desvulcanizado mecánicamente (dm); desvulcanizado química y mecánicamente (dcm); y desvulcanizado mediante microondas (dmw). Todos estos compuestos han sido ensayados con diferentes pruebas; Mecánicas, de Densidad de entrecruzamiento, de Análisis Térmicogravimétrico y del Ensayo de Microscopía

Comportamiento dieléctrico de materiales compuestos reforzados con Ground Tire Rubber (GTR)

La masiva fabricación de neumáticos y la dificultad para su eliminación o almacenamiento constituye un grave problema medioambiental. En la actualidad, se utilizan diversos métodos para el reciclaje de neumáticos, como la trituración mecánica, en la que se separa el caucho vulcanizado del acero y las fibras, utilizándose este caucho en numerosas aplicaciones como pavimentos, aislantes, calzados, etc.Con el presente estudio se pretende dar una nueva salida a los neumáticos fuera de uso (GTR), demostrándose su utilidad como dieléctricos. Para ello, se ha combinado GTR con policloruro de vinilo (PVC), obteniendo un material compuesto de matriz polimérica reforzado con GTR. Se ha caracterizado el comportamiento dieléctrico paralas diversas mezclas del PVC con GTR (desde el 0% al 70% de GTR), en un rango de temperaturas que varía desde los 30ºC hasta los 130ºC, y con unas frecuencias desde 1·10-2 Hz, hasta 1·107 Hz. Los ensayos eléctricos han permitido el análisis de la permitividad, la resistividad, el factor de pérdidas dieléctricas y los módulos de relajación (Arrhenius). Se ha comprobado como todas estas propiedades aumentan a bajas temperaturas (30ºC). Asimismo, también se observa que la evolución de estos parámetros varía significativamente en función de la frecuencia y la temperatura

Detection of Formaldehyde Towards the Extreme Carbon Star IRC+10216

We report the detection of H2CO (formaldehyde) around the carbon-rich AGB star, IRC+10216. We find a fractional abundance with respect to molecular hydrogen of x(H2CO)= (1.3 {+1.5}{-0.8}) x 10^{-8}. This corresponds to a formaldehyde abundance with respect to water vapor of x(H2CO)/x(H2O)=(1.1 +/- 0.2) x 10^{-2}, in line with the formaldehyde abundances found in Solar System comets, and indicates that the putative extrasolar cometary system around IRC+10216 may have a similar chemical composition to Solar System comets. However, we also failed to detect CH3OH (methanol) around IRC+10216 and our upper limit of x(CH3OH)/x(H2O) < 7.7 x 10^{-4}, (3 sigma), indicates that methanol is substantially underabundant in IRC+10216, compared to Solar System comets. We also conclude, based on offset observations, that formaldehyde has an extended source in the envelope of IRC+10216 and may be produced by the photodissociation of a parent molecule, similar to the production mechanism for formaldehyde in Solar System comet comae. Preliminary mapping observations also indicate a possible asymmetry in the spatial distribution of formaldehyde around IRC+10216, but higher signal-to-noise observations are required to confirm this finding. This study is based on observations carried out with the IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). (abridged)Comment: accepted to ApJ, 45 pages, 11 figure

Millimetre continuum observations of comet C/2009 P1 (Garradd)

Little is known about the physical properties of the nuclei of Oort cloud comets. Measuring the thermal emission of a nucleus is one of the few means for deriving its size and constraining some of its thermal properties. We attempted to measure the nucleus size of the Oort cloud comet C/2009 P1 (Garradd). We used the Plateau de Bure Interferometer to measure the millimetric thermal emission of this comet at 157 GHz (1.9 mm) and 266 GHz (1.1 mm). Whereas the observations at 266 GHz were not usable due to bad atmospheric conditions, we derived a 3-sigma upper limit on the comet continuum emission of 0.41 mJy at 157 GHz. Using a thermal model for a spherical nucleus with standard thermal parameters, we found an upper limit of 5.6 km for the radius. The dust contribution to our signal is estimated to be negligible. Given the water production rates measured for this comet and our upper limit, we estimated that Garradd was very active, with an active fraction of its nucleus larger than 50%.Comment: Accepted for publication in Astronomy & Astrophysics. 5 pages, 2 figure

Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes

From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of October 24, 2007, we derive 14 N/15N = 139 +/- 26 in HCN, and 14N/15N = 165 +/- 40 in CN, establishing that HCN has the same non-terrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp) after a reanalysis of previously published measurements. These results are compatible with HCN being the prime parent of CN in cometary atmospheres. The 15N excess relative to the Earth atmospheric value indicates that N-bearing volatiles in the solar nebula underwent important N isotopic fractionation at some stage of Solar System formation. HCN molecules never isotopically equilibrated with the main nitrogen reservoir in the solar nebula before being incorporated in Oort-cloud and Kuiper-belt comets. The 12C/13C ratios in HCN and CN are measured to be consistent with the terrestrial value.Comment: Accepted for publication in the Astrophysical Journal (Letters) 4 page

Distributed neural system for general intelligence revealed by lesion mapping

General intelligence (g) captures the performance variance shared across cognitive tasks and correlates with real-world success. Yet it remains debated whether g reflects the combined performance of brain systems involved in these tasks or draws on specialized systems mediating their interactions. Here we investigated the neural substrates of g in 241 patients with focal brain damage using voxel-based lesion–symptom mapping. A hierarchical factor analysis across multiple cognitive tasks was used to derive a robust measure of g. Statistically significant associations were found between g and damage to a remarkably circumscribed albeit distributed network in frontal and parietal cortex, critically including white matter association tracts and frontopolar cortex. We suggest that general intelligence draws on connections between regions that integrate verbal, visuospatial, working memory, and executive processes