1,720,956 research outputs found
Spatio-temporal behavior of magnetohydrodynamic turbulence.
Full text linkLa turbulencia es un fenómeno ubicuo, observable en escenarios desde un flujo neutro en la Tierra, hasta en fluidos cargados en el espacio. A su vez, el plasma representa más del 99% de la materia visible. Pese a ser tan común, la turbulencia en plasma es sumamente compleja y complicada de estudiar, ya que a las dificultades propias de un flujo neutro (interacción no lineal en la ecuación de Navier-Stokes, preponderantemente), se agregan las interacciones con campos electromagnéticos, autogenerados y externos, por el acoplamiento entre las ecuaciones de Maxwell y de Navier-Stokes. Entre todas las descripciones existentes del comportamiento del plasma, el modelo magnetohidrodinámico (MHD), que trata al plasma como un único fluido, se emplea para un amplio rango de aplicaciones astrofísicas y de física espacial. Esto se debe a que, a pesar de su (relativa) simpleza, captura adecuadamente tanto el comportamiento macroscópico como la cascada energética desde las grandes escalas hasta las escalas de disipación. En esta tesis estudiamos, mediante simulaciones numéricas directas 3D, algunos de los aspectos fundamentales de la turbulencia MHD, tales como la transferencia espectral de energía o la multiplicidad de escalas temporales presentes, tanto en el caso isotrópico como en los anisótropos. Analizamos el comportamiento espacio-temporal de los campos magnético y de velocidades estudiando el espectro de energías y los tiempos de descorrelación, para los casos de campo magnético medio nulo, pequeño, mediano y grande. Esto nos permite distinguir el efecto físico dominante en una amplia variedad de situaciones. También analizamos los espectros espacio-temporales de los campos de Elsässer, variando independientemente el campo magnético medio (nulo, pequeño, intermedio y grande) y la helicidad cruzada (nula, pequeña y grande). Además de permitirnos distinguir el efecto dominante, observamos contrapropagación de fluctuaciones Alfvénicas debido a reflexiones producidas por inhomogeneidades en el campo magnético total.Turbulence is an ubiquitous phenomenon in the universe, observed in scenarios such as neutral flows on Earth, and also in situations like charged fluids in space. At the same time, plasma represents more than 99% of visible matter. Despite being so common, plasma turbulence is extremely complex and complicated to study, since to the difficulties of a neutral flow (non-linear interaction in the Navier-Stokes equation, predominantly), the interactions with electromagnetic fields self-generated and external are added, by coupling between Maxwell and Navier-Stokes equations. Among all existing descriptions of the plasma behavior, the magnetohydrodynamic (MHD) model, which treats plasma as a single fluid, is used in a wide range of astrophysical and space physics applications. The main reason to this is that, despite its (relative) simplicity, this model adequately captures both the macroscopic behavior and the energy cascade from the large scales to the dissipation scales. In this thesis we study, using direct 3D numerical simulations, some of the fundamental aspects of MHD turbulence, such as the spectral transfer of energy and the multiplicity of temporal scales present, both in isotropic and anisotropic cases. We analyze the spatio-temporal behavior of the magnetic fields and velocities by studying the energy spectrum and the decorrelation times, for cases with null, small, medium and large mean magnetic field. This allows us to distinguish the dominant physical effect in a wide variety of situations. We also analyze the spatio-temporal spectra of the Elsässer fields, independently varying the mean magnetic field (null, small, intermedite and large) and the cross helicity (null, small and high). In addition to allowing us to distinguish the dominant effect, we observe counterpropagation of Alfénic fluctuations due to reflections produced by inhomogeneities in the total magnetic field.Fil: Lugones, Rodrigo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Spatio-temporal behavior of magnetohydrodynamic turbulence.
No full textLa turbulencia es un fenómeno ubicuo, observable en escenarios desde un flujo neutro en la Tierra, hasta en fluidos cargados en el espacio. A su vez, el plasma representa más del 99% de la materia visible. Pese a ser tan común, la turbulencia en plasma es sumamente compleja y complicada de estudiar, ya que a las dificultades propias de un flujo neutro (interacción no lineal en la ecuación de Navier-Stokes, preponderantemente), se agregan las interacciones con campos electromagnéticos, autogenerados y externos, por el acoplamiento entre las ecuaciones de Maxwell y de Navier-Stokes. Entre todas las descripciones existentes del comportamiento del plasma, el modelo magnetohidrodinámico (MHD), que trata al plasma como un único fluido, se emplea para un amplio rango de aplicaciones astrofísicas y de física espacial. Esto se debe a que, a pesar de su (relativa) simpleza, captura adecuadamente tanto el comportamiento macroscópico como la cascada energética desde las grandes escalas hasta las escalas de disipación. En esta tesis estudiamos, mediante simulaciones numéricas directas 3D, algunos de los aspectos fundamentales de la turbulencia MHD, tales como la transferencia espectral de energía o la multiplicidad de escalas temporales presentes, tanto en el caso isotrópico como en los anisótropos. Analizamos el comportamiento espacio-temporal de los campos magnético y de velocidades estudiando el espectro de energías y los tiempos de descorrelación, para los casos de campo magnético medio nulo, pequeño, mediano y grande. Esto nos permite distinguir el efecto físico dominante en una amplia variedad de situaciones. También analizamos los espectros espacio-temporales de los campos de Elsässer, variando independientemente el campo magnético medio (nulo, pequeño, intermedio y grande) y la helicidad cruzada (nula, pequeña y grande). Además de permitirnos distinguir el efecto dominante, observamos contrapropagación de fluctuaciones Alfvénicas debido a reflexiones producidas por inhomogeneidades en el campo magnético total.Turbulence is an ubiquitous phenomenon in the universe, observed in scenarios such as neutral flows on Earth, and also in situations like charged fluids in space. At the same time, plasma represents more than 99% of visible matter. Despite being so common, plasma turbulence is extremely complex and complicated to study, since to the difficulties of a neutral flow (non-linear interaction in the Navier-Stokes equation, predominantly), the interactions with electromagnetic fields self-generated and external are added, by coupling between Maxwell and Navier-Stokes equations. Among all existing descriptions of the plasma behavior, the magnetohydrodynamic (MHD) model, which treats plasma as a single fluid, is used in a wide range of astrophysical and space physics applications. The main reason to this is that, despite its (relative) simplicity, this model adequately captures both the macroscopic behavior and the energy cascade from the large scales to the dissipation scales. In this thesis we study, using direct 3D numerical simulations, some of the fundamental aspects of MHD turbulence, such as the spectral transfer of energy and the multiplicity of temporal scales present, both in isotropic and anisotropic cases. We analyze the spatio-temporal behavior of the magnetic fields and velocities by studying the energy spectrum and the decorrelation times, for cases with null, small, medium and large mean magnetic field. This allows us to distinguish the dominant physical effect in a wide variety of situations. We also analyze the spatio-temporal spectra of the Elsässer fields, independently varying the mean magnetic field (null, small, intermedite and large) and the cross helicity (null, small and high). In addition to allowing us to distinguish the dominant effect, we observe counterpropagation of Alfénic fluctuations due to reflections produced by inhomogeneities in the total magnetic field.Fil: Lugones, Rodrigo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
On the spatio-temporal behavior of magnetohydrodynamic turbulence in a magnetized plasma
Full text linkUsing direct numerical simulations of three-dimensional magnetohydrodynamic turbulence, the spatio-temporal behavior of magnetic field fluctuations is analyzed. Cases with relatively small, medium, and large values of a mean background magnetic field are considered. The (wavenumber) scale dependent time correlation function is directly computed for different simulations, varying the mean magnetic field value. From this correlation function, the time decorrelation is computed and compared with different theoretical times, namely, the local non-linear time, the random sweeping time, and the Alfvénic time, the latter being a wave effect. It is observed that time decorrelations are dominated by sweeping effects, and only at large values of the mean magnetic field and for wave vectors mainly aligned with this field time decorrelations are controlled by Alfvénic effects.Fil: Lugones, Rodrigo. Universidad de Buenos Aires; ArgentinaFil: Dmitruk, Pablo Ariel. Universidad de Buenos Aires; ArgentinaFil: Mininni, Pablo Daniel. Universidad de Buenos Aires; ArgentinaFil: Wang, Minmin. Bartol Research Institute; Reino UnidoFil: Matthaeus, W.H.. Bartol Research Institute; Reino Unid
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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