93,274 research outputs found
A new proxy to estimate the cosmic ray ionization rate in dense cores
No full textCosmic 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
The 3D Structure of CO Depletion in High-mass Prestellar Regions
No full textDisentangling 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
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
La poesía infantil en la didáctica de la traducción: Escondido y El idioma secreto de María José Ferrada en italiano
No full textUna modalidad didáctica especialmente satisfactoria para hacer frente al desafío de traducir la poesía para niños con su conjunto interactivo de palabras, sonidos e imágenes es la traducción colectiva que permite compartir e intercambiar conocimientos y sensibilidades, desarrollando la competencia traductora de los participantes. Se presentan aquí dos proyectos didácticos de traducción colectiva, llevados a cabo y finalizados en ámbito académico: la traducción al italiano de los poemarios El idioma secreto (2013) y Escondido (2014) de la chilena María José Ferrada que destacan por sus dimensiones metafórica y simbólica, apuntaladas por ilustraciones muy sugerentes, lo que implica aprender a traducir un mundo polifacético. Si es verdad que la poesía sufre un destino de exilio, representando una marginalidad en la marginalidad de la LIJ, traducirla a otros idiomas puede contribuir a sacarla de ese exilio, confiriéndole nuevas oportunidades de vida
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
Author inscription in The Chinese slave-girl: a story of woman's life in China
No full textThis edition includes a gift inscription by author Rev. J.A. Davis, "To Rev. A. G. Russell with the warmest regards of the author J.A. Davis."Davis, John Agnell, 1839-1897
G-Rank: Unsupervised Continuous Learn-to-Rank for Edge Devices in a P2P Network
No full textRanking algorithms in traditional search engines are powered by enormous training data sets that are meticulously engineered and curated by a centralized entity. Decentralized peer-to-peer (p2p) networks such as torrenting applications and Web3 protocols deliberately eschew centralized databases and computational architectures when designing services and features. As such, robust search-and-rank algorithms designed for such domains must be engineered specifically for decentralized networks, and must be lightweight enough to operate on consumer-grade personal devices such as a smartphone or laptop computer. We introduce G-Rank, an unsupervised ranking algorithm designed exclusively for decentralized networks. We demonstrate that accurate, relevant ranking results can be achieved in fully decentralized networks without any centralized data aggregation, feature engineering, or model training. Furthermore, we show that such results are obtainable with minimal data preprocessing and computational overhead, and can still return highly relevant results even when a user’s device is disconnected from the network. G-Rank is highly modular in design, is not limited to categorical data, and can be implemented in a variety of domains with minimal modification. The results herein show that unsupervised ranking models designed for decentralized p2p networks are not only viable, but worthy of further research.https://github.com/awrgold/G-RankComputer Scienc
A Relational Unsupervised Approach to Author Identification
No full textIn the last decades speaking and writing habits have changed.
Many works faced the author identification task by exploiting frequencybased
approaches, numeric techniques or writing style analysis. Following
the last approach we propose a technique for author identification
based on First-Order Logic. Specifically, we translate the complex data
represented by natural language text to complex (relational) patterns
that represent the writing style of an author. Then, we model an author
as the result of clustering the relational descriptions associated to the
sentences. The underlying idea is that such a model can express the typical
way in which an author composes the sentences in his writings. So,
if we can map such writing habits from the unknown-author model to
the known-author model, we can conclude that the author is the same.
Preliminary results are promising and the approach seems viable in real
contexts since it does not need a training phase and performs well also
with short texts
Nd-doped polarization maintaining all-fiber laser with dissipative soliton resonance mode-locking at 905 nm
No full textFunding Information: Manuscript received February 15, 2021; revised May 14, 2021; accepted May 27, 2021. Date of publication June 1, 2021; date of current version September 13, 2021. This work was supported by RFBR under Grant 20-32-90233. (Corresponding author: Aram A. Mkrtchyan.) Aram A. Mkrtchyan, Yuriy G. Gladush, and Kirill A. Sitnik are with the Skolkovo Institute of Science and Technology, Moscow 121205, Russia (e-mail: [email protected]; [email protected]; [email protected]). Publisher Copyright: © 1983-2012 IEEE.Moving the fiber laser emission to the region below one micron may provide a cheaper, more compact and robust alternatives to the existing solid state lasers. Here, for the first time we report a neodymium mode-locked fiber laser emitting at 905 nm in the all-fiber polarization maintaining configuration. We obtain a self-starting pulse generation in nonlinear amplifying loop mirror (NALM) cavity configuration. To suppress a dominant emission at 1064 nm corresponding to a 4-level laser scheme, we use an active fiber - 920/1064 division multiplexer - active fiber sandwich-like sequence in the NALM loop. A rectangular shape dissipative soliton had nJ energy, 30 pm spectral width and 80 ÷ 430 ps width linearly depending on the pump power. Excellent agreement with numerical simulation allowed us to recover pulse shape and width for the pulses out of autocorrelation window.Peer reviewe
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