589 research outputs found
Chemical post-processing of magneto-hydrodynamical simulations of star-forming regions: robustness and pitfalls
No full textA common approach to model complex chemistry in numerical simulations is via post-processing of existing magneto-hydrodynamic simulations, relying on computing the evolution of chemistry over the dynamic history of a subset of particles from within the raw simulation. Here, we validate such a technique, assessing its ability to recover the abundances of chemical species, using the chemistry package krome. We also assess, for the first time, the importance of the main free input parameters, by means of a direct comparison with a self-consistent state-of-the-art simulation in which chemistry was directly coupled to hydrodynamics. We have found that the post-processing is highly reliable, with an accuracy at the per cent level, even when the most relaxed input parameters are employed. In particular, our results show that the number of particles used does not affect significantly the average properties, although it suppresses the appearance of possibly important spatial features. On the other hand, the choice of the integration time-step plays a crucial role. Longer integration time-steps can produce large errors, as the post-processing solution will be forced towards chemical equilibrium, a condition that does not always necessarily apply. When the interpolation-based reconstruction of chemical properties is performed, the errors further increase up to a factor of ∼2. Concluding, our results suggest that this technique is extremely useful when exploring the relative quantitative effect of different chemical parameters and/or networks, without the need of re-running simulations multiple times, but some care should be taken in the choice of particles sub-sample and integration time-step
A new proxy to estimate the cosmic ray ionization rate in dense cores
Get PDFCosmic rays are a global source of ionization, and the ionization fraction represents a fundamental parameter in the interstellar medium. Ions couple to magnetic fields, and affect the chemistry and the dynamics of star-forming regions as well as planetary atmospheres. However, the cosmic ray ionization rate represents one of the bottlenecks for astrochemical models, and its determination is one of the most puzzling problems in astrophysics. While for diffuse clouds reasonable values have been provided from observations, for dense clouds, due to the lack of rotational transitions, this is not possible, and estimates are strongly biased by the employed model. We present here an analytical expression, obtained from first principles, to estimate the cosmic ray ionization rate from observational quantities. The theoretical predictions are validated with high-resolution 3D numerical simulations and applied to the well-known core L1544; we obtained an estimate of ζ2 ∼2-3 × 10-17 s-1. Our results and the analytical formulae provided represent the first model-independent robust tool to probe the cosmic ray ionization rate in the densest part of star-forming regions (on spatial scales of R ≤ 0.05 pc). An error analysis is presented to give statistical relevance to our study
Invoking the little god of dispossession: Chilean dictatorship and political poetics in Mª José Ferrada.
Get PDFLa dictadura chilena ha sido abordada desde múltiples perspectivas e instancias, entre
las que destaca la literaria. En este artículo se pretende hablar de una de las voces más señaladas
de la llamada generación de la posdictadura o generación de los hijos de la dictadura, la de la
escritora María José Ferrada. Con el objetivo de comprender mejor sus estrategias particulares de
aproximación al citado hecho histórico, se analizan dos de sus libros, el poemario Niños, y el
álbum ilustrado La tristeza de las cosas, dedicados a las personas que fueron asesinadas o hechas
desaparecer bajo el régimen de Pinochet. Ferrada emplea el lenguaje poético y las fuentes
documentales para crear un universo propio en el que la memoria se reconstruye desde la
humanidad previa a la atrocidad. Lo cotidiano se transfigura en espacio político de
posicionamiento, donde las víctimas recuperan su relato personal. La voz comprometida de esta
autora chilena se dirige al público infantil, porque los niños y niñas también merecen saber lo que
ocurrió. Y porque, además, estos textos funcionan como caja de resonancia de la barbarie actual.The Chilean dictatorship has been approached from multiple perspectives and
instances, among which the literary one stands out. This article aims to talk about one of the most
outstanding voices of the so-called post-dictatorship generation or generation of the children of
the dictatorship, that of the writer María José Ferrada. In order to better understand her particular
strategies of approaching the aforementioned historical fact, two of her books are analyzed, the
poetry book Niños and the picturebook La tristeza de las cosas, dedicated to the people who were
murdered or made to disappear under the Pinochet regime. Ferrada uses poetic language and
documentary sources to create a universe of her own in which memory is reconstructed from
humanity prior to the atrocity. Everyday life is transfigured into a political space of positioning,
where the victims recover their personal stories. The committed voice of this Chilean author
addresses the children’s audience, because children also deserve to know what happened. And
because, in addition, these texts function as a sounding board for current barbarism
Synthetic observations of HD towards high-mass starless cores
No full textYoung massive stars are usually found embedded in dense and massive molecular clumps and are known for being highly obscured and distant. During their formation process, deuteration is regarded as a potentially good indicator of the formation stage. Therefore, proper observations of such deuterated molecules are crucial, but still, hard to perform. In this work, we test the observability of the transition o-HD-, using a synthetic source, to understand how the physical characteristics are reflected in observations through interferometers and single-dish telescopes. In order to perform such tests, we post-processed a magneto-hydrodynamic simulation of a collapsing magnetized core using the radiative transfer code POLARIS. Using the resulting intensity distributions as input, we performed single-dish (APEX) and interferometric (ALMA) synthetic observations at different evolutionary times, always mimicking realistic configurations.
Finally, column densities were derived to compare our simulations with real observations previously performed. Our derivations for o-HD are in agreement with values reported in the literature, in the range of 10cm and 10cm for single-dish and interferometric measurements, respectively.Las estrellas masivas j ́ovenes residen com ́unmente en c ́umulos moleculares densos y masivos y son conocidas por estar altamente oscurecidas y distantes. Durante su proceso de formaci ́on, la deuteraci ́on es considerada como un indicador del estado de formaci ́on potencialmente bueno. Por ende, adecuadas observaciones de tales portadores de deuterio son cruciales, sin embargo, dif ́ıciles de realizar. En este trabajo, probamos la observabilidad de la transici ́on o-HD- en mol ́eculas deuteradas, utilizando una fuente sint ́etica, intentando declarar cuan diferente es la informaci ́on obtenida desde interfer ́ometros o telescopios de un solo plato. Para abordar tales pruebas de observabilidad, post-procesamos la simulaci ́on magneto-hidrodin ́amica de una nube
colapsante, haciendo uso del c ́odigo para transferencia radiativa POLARIS. Utilizando los mapas de intensidad resultantes, realizamos observaciones sint ́eticas de tipo interferom ́etricas (ALMA) y de plato-singular (APEX) en varios estados evolutivos de la nube, siempre imitando configuraciones realistas.
Finalmente, derivamos densidades de columna para comparar nuestras simulaciones con observaciones reales anteriormente realizadas. Las densidades de columna obtenidas para el o-HD concuerdan con valores reportados en la literatura, en el rango de 10cm y 10cm para mediciones de plato-singular e interferom ́etricas, respectivamente
"There is life and death, and in between, text" : The existential qualities of poetry in Caroline Ringskog Ferrada-Noli's <em data-start="73" data-end="94">Den förlorade sonen and creative writing
No full textThis thesis examines whether poetry can be considered a particularly suitable genre for addressing existential questions, through analyzing Caroline Ringskog Ferrada-Noli's debut poetry collection, Den förlorade sonen. Employing a lyrical analysis methodology, the thesis examines the three most central existential themes in the book and how the author chooses to portray them. The aim of this analysis is also to gain a deeper understanding of my own interest in addressing existential questions through poetry and what that appeal is about. The outcome reveals that three of the most prominent existential themes in Ferrada-Noli's Den förlorade sonen are death, identity and anxiety. The studys close textual analysis demonstrates how the author writes in a highly varied form, ranging from prose-like passages to fragmented verse lines through enjambments, blank spaces, line breaks and other literary pauses. Typical lyrical devices such as imagery, metaphors, repetition, alliteration, anaphora and other various types of rhyme are also applied to influence the poem's mood, create contrasts and paradoxical connections which render certain words or themes into something more powerful and memorable. The white spaces in poetry have been shown to remind us of a certain nothingness that we cannot speak about, but which poetry in this way can. In conclusion, these lyrical devices have an essential impact on the magnitude and force of the poem's existential themes and the reader's emotional resonance.C-uppsats i kreativt skrivande</p
"There is life and death, and in between, text" : The existential qualities of poetry in Caroline Ringskog Ferrada-Noli's <em data-start="73" data-end="94">Den förlorade sonen and creative writing
No full textThis thesis examines whether poetry can be considered a particularly suitable genre for addressing existential questions, through analyzing Caroline Ringskog Ferrada-Noli's debut poetry collection, Den förlorade sonen. Employing a lyrical analysis methodology, the thesis examines the three most central existential themes in the book and how the author chooses to portray them. The aim of this analysis is also to gain a deeper understanding of my own interest in addressing existential questions through poetry and what that appeal is about. The outcome reveals that three of the most prominent existential themes in Ferrada-Noli's Den förlorade sonen are death, identity and anxiety. The studys close textual analysis demonstrates how the author writes in a highly varied form, ranging from prose-like passages to fragmented verse lines through enjambments, blank spaces, line breaks and other literary pauses. Typical lyrical devices such as imagery, metaphors, repetition, alliteration, anaphora and other various types of rhyme are also applied to influence the poem's mood, create contrasts and paradoxical connections which render certain words or themes into something more powerful and memorable. The white spaces in poetry have been shown to remind us of a certain nothingness that we cannot speak about, but which poetry in this way can. In conclusion, these lyrical devices have an essential impact on the magnitude and force of the poem's existential themes and the reader's emotional resonance.C-uppsats i kreativt skrivande</p
The 3D Structure of CO Depletion in High-mass Prestellar Regions
Get PDFDisentangling the different stages of the star formation process, in particular in the high-mass regime, is a challenge in astrophysics. Chemical clocks could help alleviate this problem, but their evolution strongly depends on many parameters, leading to degeneracy in the interpretation of the observational data. One of these uncertainties is the degree of CO depletion. We present here the first self-consistent magneto-hydrodynamic simulations of high-mass, star-forming regions at different scales, fully coupled with a nonequilibrium chemical network, which includes C-N-O bearing molecules. Depletion and desorption processes are treated time dependently. The results show that full CO depletion (i.e., all gas-phase CO frozen-out on the surface of dust grains) can be reached very quickly, in one-third or even smaller fractions of the freefall time, whether the collapse proceeds on slow or fast timescales. This leads to a high level of deuteration in a short time, both for typical tracers like N2H+, as well as for the main ion H3+, the latter being in general larger and more extended. N2 depletion is slightly less efficient, and no direct effects on N-bearing molecules and deuterium fractionation are observed. We show that CO depletion is not the only driver of deuteration, and that there is a strong impact on D frac when changing the grain size. We finally apply a two-dimensional Gaussian point-spread function to our results to mimic observations with single-dish and interferometers. Our findings suggest that the low-values observed in high-mass star-forming clumps are in reality masking a full-depletion stage in the inner 0.1 pc region
Does Lean & Agile Project Management Help Coping with Project Complexity?
No full textStill, projects in the construction sector are delivered with time delays and cost overruns. One of the reasons for poor performance was assigned to project complexity. A combination of lean construction and agile project management are hypothesized as a possible solution to cope with project complexity. In this paper we aim to understand if the implicit usage of lean and agile help coping with complexity. The research was done by means of correlation analysis on data gathered from a structured questionnaire (67 responses). In total, 51 significant correlations among 255 possible relations were found. To reduce the number of variables, factor analysis was performed. Correlation analysis on the defined factors showed 8 significant correlations among 25 relations. Several lean and agile elements were shown to significantly correlate to either reducing complexity or managing complexity. It was therefore concluded that these are promising to cope with complexity and improve project performance, which is to be confirmed in subsequent research.Integral Design & Managemen
Probability of Survival of New Manufacturing Plants: the case of Chile
Get PDFThis paper studies the probability of survival of the manufacturing plants that start producing in Chile in the period 1979-1999 using a proportional hazards model. Opposing previous empirical international evidence, the survival diminishes with age, initial size, and with the rate of growth of the plant. It also diminishes with the regional unemployment rate. Comparing companies by size, the rate of risk of death of small and medium businesses is 20.3% greater than large companies, but more interesting, this rate is unaffected by the public subsidies received by the smaller ones, after controlling simultaneously with other explanatory variables. Using four different samples from the same data, the consequences of applying different criteria that validate and/or eliminate inconsistent data are studied, obtaining significant differences in the resulting coefficientsChilean manufacturing; Entry; Survival; Duration
RLZAP: Relative Lempel-Ziv with Adaptive Pointers
No full textRelative Lempel-Ziv (RLZ) is a popular algorithm for compressing databases of genomes from individuals of the same species when fast random access is desired. With Kuruppu et al.’s (SPIRE 2010) original implementation, a reference genome is selected and then the other genomes are greedily parsed into phrases exactly matching substrings of the reference. Deorowicz and Grabowski (Bioinformatics, 2011) pointed out that letting each phrase end with a mismatch character usually gives better compression because many of the differences between individuals’ genomes are single-nucleotide substitutions. Ferrada et al. (SPIRE 2014) then pointed out that also using relative pointers and run-length compressing them usually gives even better compression. In this paper we generalize Ferrada et al.’s idea to handle well also short insertions, deletions and multi-character substitutions. We show experimentally that our generalization achieves better compression than Ferrada et al.’s implementation with comparable random-access times
- …
