1,720,957 research outputs found
Aceleración de cálculos de estructura electrónica mediante el uso de Procesadores Gráficos Programables
No full textEn este trabajo se presenta una implementación de cálculo de estructura electrónica, basado en la Teoría de los Funcionales de la Densidad (DFT)[1], especialmente diseñada para ser ejecutada sobre un procesador gráfico (GPU). Como base de los desarrollos se utiliza un software existente, Molecole[2]. Siguiendo la literatura sobre el tema se implementan los algoritmos eficientes conocidos. Sin embargo, se introducen adaptaciones novedosas que tienen en cuenta tanto las características del hardware sobre el cual se trabaja, así como los tipos particulares de sistemas moleculares en los que se enfoca. El atractivo de este tipo de hardware es su gran poder de cómputo, producto de la arquitectura altamente paralelizada que implementa. En los cálculos en los cuales se puede aprovechar este paralelismo es posible obtener mejoras importantes en los tiempos de ejecución. Además de las mejoras en performance, se tiene en cuenta otro aspecto importante: la precisión numérica con la que se opera. Únicamente los procesadores gráficos más actuales y costosos soportan operaciones de precisión doble, y su rendimiento en comparación con las operaciones de precisión simple es aproximadamente diez veces menor[3]. Por estas razones y dado que la implementación original (Molecole) utiliza operaciones de punto flotante de precisión doble, también se analiza el impacto que tiene el uso de operaciones de precisión simple en el resultado final del cálculo. Con el software desarrollado se logra una implementación que está a la par del reconocido Gaussian ’03[4] en términos de calidad numérica, pero con una reducción en los tiempos de cómputo de hasta aproximadamente diez veces (10x) al comparar con una ejecución serial, y de hasta cuatro veces (4x), al comparar con una ejecución paralelizada en cuatro cores de CPU. Se realizan también comparaciones con el software original Molecole, SIESTA[5] y finalmente con una implementación para procesador convencional (CPU), análoga a la desarrollada en GPU. Por último, se espera que la experiencia lograda a través de la resolución de los diversos problemas encontrados al trabajar sobre este tipo de hardware sea generalizable a futuros proyectos. Es más, los resultados obtenidos no solo motivan a avanzar con el trabajo presentado, sino que también demuestran la utilidad de estos procesadores para acelerar tanto cálculos como los presentados así como posiblemente otros similares.This work presents an implementation of electronic structure calculations based on the Density Functionals Theory (DFT)[1], specifically designed to be executed on a graphics processor (GPU). As the basis of the developments an existing software is used: Molecole[2]. Following the literature on this subject, the known efficient algorithms are implemented. However, novel adaptations that take into account both the characteristics of the used hardware, and the particular types of molecular systems in which this work focuses, are introduced. The appeal of such hardware is its great computational power, which is a product of the highly parallelized architecture it implements. In calculations where this parallelism can be exploited, it is possible to obtain significant improvements in execution times. In addition to execution performance improvements, another important aspect is taken into account: the numerical accuracy. Only the latest and costly graphics processors support double-precision operations, and its performance compared to single-precision operations is approximately ten times lower[3]. For these reasons and because the original implementation (Molecole) uses double-precision floating point operations, the impact over the final result of single-precision operations is analyzed. With the software developed in this work an implementation which is at par with the known Gaussian ’03 [4] in terms of numerical quality, but with a reduction in computing time to about ten times (10x) is achieved, by comparing to a serial execution, and to four times (4x) by comparing to a parallelized execution over four CPU cores. Other comparisons are also made between the original software Molecole, SIESTA[5] and an implementation that targets conventional processors (CPU), but analogous to the one developed for GPU. Finally, it is to be expected that the experience gained through solving the various problems encountered when working on this type of hardware could be generalized to future projects. Moreover, the results not only motivate to advance with the present work, but also demonstrate the usefulness of these processors to speed up these type of calculations and possibly other similar.Fil: Nitsche, Matías Alejandro. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
