1,720,996 research outputs found
STRUCTURE FUNCTIONS IN A WALL-TURBULENT SHAR FLOW
No full textWavelet and quadrant analyses were applied to turbulent velocity data in order to investigate the transition from the anisotropy of energy-containing eddies to the isotropy of the inertial subrange scales. The quadrant analysis of the wavelet coefficients of longitudinal and vertical velocity components allows the evaluation of the velocity structure functions and the momentum cospectrum as a function of the separation distance and of the quadrants. In an isotropic condition the contribution both of ejections and sweeps (even quadrants), and both of reflections and deflections (odd quadrants), has to be equal. The analysis has shown that in neutrally stratified conditions the transition to isotropy occurs in a frequency range (0.2 < r/z < 3) usually referred to as internal to the inertial subrange (r is separation distance, z is height). In the transition region, as in the isotropic region, the velocity structure functions still agree with the 1941 and 1962 Kolmogorov theories; but on the other hand the structure functions of the even and odd quadrants are fitted by power laws of different slopes in the transition region. The proposed analysis allows the investigation within the transition region of the different dynamical structure in the energy transfer from the energy-containing scales to the isotropic scales
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
Organized motion and radiative perturbations in the nocturnal canopy sublayer above an even-aged pine forest
Full text linkUsing time series measurements of velocity, carbon dioxide and water vapour concentration, and temperature collected just above a 15 m tall even-aged pine forest, we quantify the role of organized motion on scalar and momentum transport within the nocturnal canopy sublayer (CSL). We propose a framework in which the nocturnal CSL has two end-members, both dominated by organised motion. These end-members represent fully developed turbulent flows at near-neutral or slightly stable stratification and no turbulence for very stable stratification. Our analysis suggests that ramps dominate scalar transport for near-neutral and slightly stable conditions, while linear canopy waves dominate the flow dynamics for very stable conditions. For intermediate stability, the turbulence is highly damped and often dominated by fine scale motions. Co-spectral analysis suggests that ramps are the most efficient net scalar mass-transporting agent while linear canopy waves contribute little to net scalar transport between the canopy and atmosphere for averaging intervals that include complete wave cycles. However, canopy waves significantly contribute to the spectral properties of the scalar time series. Ramps are the most frequently occurring organised motion in the nocturnal CSL for this site. Numerous night-time runs, however, resided between these two end-members. Our analysis suggests that when radiative perturbations are sufficient large (>20 W m-2 in net radiation), the flow can switch from being highly damped fine-scale turbulence to being organized with ramp-like properties. We also found that when ramps are already the dominant eddy motion in the nocturnal CSL, radiative perturbations have a minor impact on scalar transport. Finally, in agreement with previous studies, we found that ramps and canopy waves have comparable length scales of about 30-60 metres. Consequences to night-time flux averaging are also discussed
The relative importance of ejections and sweeps to momentum transfer in the atmospheric boundary layer
No full textVariations 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
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
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