Three-dimensional simulations of turbulent convective mixing in ONe and CO classical nova explosions

Classical novae are thermonuclear explosions that take place in the envelopes of accreting white dwarfs in binary systems. The material piles up under degenerate conditions, driving a thermonuclear runaway. The energy released by the suite of nuclear processes operating at the envelope heats the material up to peak temperatures about 100 - 400 MK. During these events, about 10-3 - 10-7 Msun, enriched in CNO and, sometimes, other intermediate-mass elements (e.g., Ne, Na, Mg, Al) are ejected into the interstellar medium. To account for the gross observational properties of classical novae (in particular, the large concentrations of metals spectroscopically inferred in the ejecta), models require mixing between the (solar-like) material transferred from the secondary and the outermost layers (CO- or ONe-rich) of the underlying white dwarf. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, the feasibility of this mechanism has been explored in the framework of CO white dwarfs, while mixing with different substrates still needs to be properly addressed. Three-dimensional simulations of mixing at the core-envelope interface during nova outbursts have been performed with the multidimensional code FLASH, for two types of substrates: CO- and ONe-rich. We show that the presence of an ONe-rich substrate, as in "neon novae", yields larger metallicity enhancements in the ejecta, compared to CO,rich substrates (i.e., non-neon novae). A number of requirements and constraints for such 3-D simulations (e.g., minimum resolution, size of the computational domain) are also outlined.Comment: Accepted for publication in Astronomy & Astrophysic

Distance-Based Methods: Ripley’s K function vs. K density function

In this paper, we propose an analytical and methodological comparison between two of the most known distance-based methods in the evaluation of the geographic concentration of economic activity. These two methods are Ripley’s K function, a cumulative function popularised by Marcon and Puech (2003) that counts the average number of neighbours of each point within a circle of a given radius, and K density function, a probability density function of point-pair distances introduced by Duranton and Overman (2005), which considers the distribution of distances between pairs of points. To carry out this comparison, we first apply both methodologies to an exhaustive database containing Spanish manufacturing establishments and we evaluate the spatial location patterns obtained from both analysis. After an initial analysis, we realise that although these functions have always been treated as substitutes they should be considered as complementary, as both cumulative function and probability density function provide relevant and necessary information about the distribution of activity in space. Therefore, our next step will be to assess what are the advantages and disadvantages of each methodology from a descriptive and analytical way.

In vitro screening of the effect of three glucosinolate derived nitriles on soil-borne fungi

Glucosinolates are allelochemicals present in all plants of the order Capparales that are hydrolysed by endogenous enzymes (myrosinases) forming a variety of compounds with biological activity. ‘Biofumigation’ is the term used to describe the effect of these compounds on soil-borne pathogens and it has normally been attributed to isothiocyanates. At acidic pH and in the presence of redox co-factors such as glutathione, glucosinolate hydrolysis yields also nitriles, which are more hydrophilic and stable than isothiocyanates. Three nitriles (allyl-, benzyl- and phenethyl cyanide) were tested against soil borne fungi of economic importance: Aphanomyces euteiches var. pisi, Gaeumannomyces graminis var. tritici and Verticillium dahliae. The nitriles were initially tested at 1 mM and four additional concentrations were further tested in order to determine LD50. At 1 mM, allyl cyanide showed in all cases less than 10% inhibition and it did not inhibit fungi growth at higher concentrations. LD50 of benzyl cyanide was 2.5 mM for Verticillium and Aphanomyces, whereas it was as low as 0.5 mM for Gaeumannomyces. LD50 of phenyl ethyl cyanide was 2.5 mM for Verticillium, 1.4 mM Gaeumannomyces and 1.25 mM Aphanomyces. Although nitriles are generally less toxic than ITCs, their role in biofumigation should not be disregarded

Raman spectroscopy as a versatile tool to study organic biradicals

Since -conjugated organic molecules were probed as potential semiconducting materials, suitable for replacing the widely used silicon technologies, their structural, optical and conductive properties have been under study to improve their application in organic electronics and to make possible their ad hoc synthesis. In this sense, the modification of the -electron delocalization path is one of the available tools to tune the properties of the molecules to obtain the desired characteristics for the fabrication of these devices. One of the parameters employed to tailor -conjugated organic molecules for organic electronics is the diradical character. A progressive change in the diradical contribution to the ground electronic state structure can tune some of the main system features, highlighting the HOMO-LUMO energy gap and the aggregation mode. The main drawback of this approach is the loss of chemical stability when increasing the diradical character of these molecules. On the other hand, the -electron delocalization can be interrupted introducing a perpendicularly conjugated path. The competition of these two cross-conjugated patterns leads to a new 2-dimensional delocalization scenario that changes the electronic properties of the studied materials. In this project, we present a stable quinoidal quaterthiophene diradical that possess outstanding stability and conductivity properties. [1] The combination of the diradical character together with the possibility to delocalize the electron density through two different perpendicular paths explain its exceptional behavior in comparison with the other members of the series, or with its linearly conjugated analogues. The balance between these two properties has been evaluated through UV-Vis-NIR electronic spectroscopy and Raman and IR vibrational spectroscopy in the neutral and charged forms of the target molecule and similar non-cross-conjugated samples.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Sobre puntos de la gramática particularmente resistentes al cambio: cuatro (largos) siglos en la evolución de las relativas oblicuas de lugar. Un análisis variacionista

Mediante la utilización del paradigma variacionista y el empleo de un corpus integrado por textos de inmediatez comunicativa, mayoritariamente de carácter epistolar, en esta investigación se analiza un caso de la sintaxis particularmente resistente al cambio: la alternancia entre soluciones pronominales (que y, en menor medida, cual) y adverbiales (donde) en las relativas oblicuas locativas desde el siglo XVI hasta la primera mitad del XX. De los tres análisis de regresión independientes realizados, uno por cada periodo (siglos XVI, XVIII y XX), se deriva un avance paulatino, aunque moderado, de las formas pronominales a lo largo de los siglos y la progresiva disminución del adverbio donde. Con todo, algunos factores lingüísticos se revelan especialmente persistentes en la explicación de la variabilidad (semántica, función sintáctica y categoría del antecedente, junto al priming estructural y la sintaxis de la cláusula regente), lo que dificulta la progresión del cambio. Con respecto a los factores extralingüísticos, la frecuencia de los relativos pronominales en los contextos comunicativos más distantes, así como su uso preferente por parte de las élites sociales y las generaciones adultas, muestra que estas formas se han adscrito a lo largo de la historia a los registros más formales y prestigiosos.Based on the principles and methods of variationism in a corpus composed by ego-documents, this study analyses a case of syntax variation that has proved to be particularly resistant to change in Spanish: the alternation between pronouns (que/el cual) and adverbs (donde) in oblique relatives. Of the three independent mixed-effect regression analyses performed, one for each of the periods considered (16th, 18th and 20th centuries), a moderate progression of the pronominal forms throughout the centuries has been observed. However, some linguistic factors are especially pervasive in explaining the variability (i.e. semantics, syntactic function and the category of antecedent, along with structural priming and the syntax of the regent clause), which hinders the progression of the change. As regards the extra-linguistic axis, the frequency of the pronominal relatives in the more distant communicative contexts, as well as the recurrent preferential use of them by social elites and the adult generations, shows that these forms have been mainly ascribed in almost every period to the most formal and prestigious contexts

Los límites de la variación: adverbios y pronombres en subordinadas de relativo del siglo XVI. Sociolingüística histórica a partir de un corpus de inmediatez comunicativa

La alternancia entre las formas adverbiales (donde) y pronominales (en que-cual) del relativo en subordinadas locativas del siglo XVI se analiza en estas páginas como un ejemplo de la necesidad de precisar con detalle el contexto variable (envelope of variation) en que tiene lugar cualquier fenómeno de variación. Excluidos así del estudio diversos contextos en los que esta última apenas tiene lugar (o no la tiene en absoluto), nuestros resultados presentan un panorama distinto al ofrecido por algunos trabajos previos. De este modo, hemos podido comprobar cómo, al menos en el primer español clásico, el uso del adverbio en las locativas de relativo con antecedente es claramente mayoritario sobre el pronombre que, y, además, con una clara tendencia ascendente conforme avanza la centuria. Al igual que en otros estudios donde las tradiciones textuales se han visto como potencialmente determinantes en los desenlaces de la variación, a estos resultados ha podido contribuir el tipo de corpus analizado, compuesto por textos cercanos al polo de la inmediatez comunicativa, en su mayoría, de carácter epistolar y escritos por 867 españoles de diferente condición social y dialectal. Del análisis de regresión logística emprendido (Rbrul), se deriva una preeminencia de los factores lingüísticos para explicar la variación, en especial los relacionados con la sintaxis y la semántica del antecedente, bien aisladamente, bien en interacción. Los factores extralingüísticos resultan menos explicativos, de tal manera que ni el sexo, ni el contexto migratorio ofrecen apenas diferencias entre los correspondientes grupos, si bien diversas irregularidades muestrales (v. gr. escasa presencia femenina) pueden haber introducido algún sesgo en los datos. Distinto es el caso del estatus social y el tenor de las interacciones epistolares, cuya combinación arroja resultados significativos. Con todo, estos se limitan a la primera mitad de la centuria, no así a la segunda, cuando las diferencias entre unos grupos y otros prácticamente se neutralizan. Estos resultados sugieren que las clases privilegiadas podrían haber acabado asumiendo un antiguo cambio desde abajo, característico de los estilos más informales y probablemente iniciado en los sectores populares.The variation between adverbial (donde ‘where’) and pronominal forms (en (el) que-cual ‘in which’) in prepositional relative clauses in the Spanish of the sixteenth century is analyzed under the variationism paradigm, as an example of the need to specify in detail the exact envelope of variation in which this variation really takes place. Thus, excluding from the study several contexts in which one of the variants hardly occurs, our results provide a different picture compared to some previous studies. Therefore, we have seen how, at least in the first period of Golden Age Spanish, the use of donde in locative prepositional relatives is prevalent and with a clear upward trend as the century progresses. To these results may have contributed the type of corpus analyzed, consisting of ego-documents (mainly private letters), close to the pole of communicative immediacy, written by 867 Spaniards from different social and dialectal backgrounds. The logistic regression analysis undertaken (Rbrul) shows a predominance of linguistic factors in explaining variation, especially those related to the syntax and semantics of the antecedent, either independently or in interaction. The extra-linguistic factors are less explanatory, so neither gender nor the immigration context offer significant differences between the respective groups, although some sampling irregularities in the case of gender may have introduced some bias in the data. Nevertheless, this is not the case of social status and tenor, whose interaction yields significant results. However, these are limited to the first half of the century, not the second one, when the differences between groups practically disappear. These results suggest that social elites could have ended up assimilating an old change from below, originally characteristic of more informal styles and probably started in popular sectors.La publicación se ha podido iniciar gracias a la subvención recibida por el Ministerio de Ciencia e Innovación (FFI2010-10361-E)

Two-dimensional simulations of mixing in classical novae: the effect of the white dwarf composition and mass

Context. Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass main sequence star onto a white dwarf (either CO or ONe). The material accumulates for 10+4 - 10+5 yr until ignition under degenerate conditions, resulting in a thermonuclear runaway. The nuclear energy released produces peak temperatures of about 0.1 - 0.4 GK. During these events, 10-7 - 10-3 Msun enriched in intermediate-mass elements (with respect to solar abundances) are ejected into the interstellar medium. However, the origin of the large metallicity enhancements and the inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells is not fully understood. Aims. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities that operate at the core-envelope interface can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, such multidimensional simulations have been performed for a small number of cases, and much of the parameter space remains unexplored. Methods. Here we investigate the dredge-up, driven by Kelvin-Helmholtz instabilities, for white dwarf masses in the range 0.8-1.25 Msun and different core compositions (CO-rich and ONe-rich substrates). We present a set of five numerical simulations performed in two dimensions aimed at analyzing the possible impact of the white dwarf mass (and composition) on the metallicity enhancement and on the explosion characteristics. Results. We observe greater mixing (about 30 per cent higher when measured in the same conditions), at the time we stop the simulations, and more energetic outbursts for ONe-rich substrates than for CO-rich substrates and for more massive white dwarfs.Comment: Accepted for Publication in Astronomy and Astrophysic

Distance-Based Methods: Ripley's K function vs. K density function

In this paper, we propose an analytical and methodological comparison between two of the most known distance-based methods in the evaluation of the geographic concentration of economic activity. These two methods are Ripley's K function, a cumulative function popularised by Marcon and Puech (2003) that counts the average number of neighbours of each point within a circle of a given radius, and K density function, a probability density function of point-pair distances introduced by Duranton and Overman (2005), which considers the distribution of distances between pairs of points. To carry out this comparison, we first apply both methodologies to an exhaustive database containing Spanish manufacturing establishments and we evaluate the spatial location patterns obtained from both analysis. After an initial analysis, we realise that although these functions have always been treated as substitutes they should be considered as complementary, as both cumulative function and probability density function provide relevant and necessary information about the distribution of activity in space. Therefore, our next step will be to assess what are the advantages and disadvantages of each methodology from a descriptive and analytical way