1,720,968 research outputs found
Interaction of Submeso Motions in the Antarctic Stable Boundary Layer
No full textSubmesomotions add complexities to the structure of the stable boundary layer. Such motions
include horizontal meandering and gravity waves, in particular when the large-scale flow is
weak. The coexistence and interaction of such submeso motions is investigated through the
analysis of data collected in Antarctica, in persistent conditions of strong atmospheric stratification.
Detected horizontal meandering is frequently associated with temperature oscillations
characterized by similar time scales (30 min) at all levels (2, 4.5 and 10 m). In contrast, dirty
gravity waves superimposed on horizontal meandering are detected only at the highest level,
characterized by time scales of a few minutes. The meandering produces an energy peak in
the low-frequency spectral range, well fitted by a spectral model previously proposed for
low wind speeds. The coexistence of horizontal and vertical oscillations is observed in the
presence of large wind-direction shifts superimposed on the gradual flow meandering. Such
shifts are often related to the variation of the mean flow dynamics, but also to intermittent
events, localized in time, which do not produce a variation in the mean wind direction and
that are associated with sharp decreases in wind speed and temperature. The noisy gravity
waves coexisting with horizontal meandering persist only for a few cycles and produce bursts
of turbulentmixing close to the ground, affecting the exchange processes between the surface
and the stable boundary layer. The results confirm the importance of sharp wind-direction
changes at lowwind speed in the stable atmosphere and suggest a possible correlation between
observed gravity waves and dynamical instabilities modulated by horizontal meandering
Submeso Motions and Intermittent Turbulence Across a Nocturnal Low-Level Jet: A Self-Organized Criticality Analogy
No full textOne of the hallmarks of the stable boundary layer is the switching between turbulent (active) and non-turbulent (passive) states. In very stable conditions, the boundary layer becomes layered with fully-developed turbulence confined to a shallow region near the surface. In the quiescent region above this near-surface layer, the turbulence is weak, intermittent and detached from the ground. These conditions promote the development of a low-level jet that re-energizes the turbulence through an elevated shear layer. The Monin–Obukhov similarity theory fails in the layered stable boundary layer thereby making the quantification of mixing and transport properties challenging for numerical models. In the present study, multi-level time series from a tall (140 m) meteorological tower are analyzed using the telegraphic approximation to investigate analogies with a general class of intermittency models that include self-organized criticality. The analogy between turbulence and self-organized criticality is restricted to clustering properties of sign changes of flow variables for describing switching between turbulent and non-turbulent states. The telegraphic approximation provides a new perspective on clustering and on external and internal intermittency for periods dominated by turbulent motions, a low-level jet and submeso motions. Some of these periods are characterized by the absence of turbulence but occasionally punctuated by bursts of intermittent turbulent events. The switching probability of active–inactive states and the lifetimes of inactive states (related to intermittent turbulent bursts) show evidence of self-organized-criticality like behaviour in terms of scaling laws. The coexistence of self-organized criticality and intermittent turbulence may offer new perspectives on the genesis of scaling laws and similarity arguments, thereby improving the performance of numerical models in the stable boundary layer
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
Characteristics of Gravity Waves over an Antarctic Ice Sheet during an Austral Summer
Full text linkWhile occurrences of wavelike motion in the stable boundary layer due to the presence of a significant restoring buoyancy force are rarely disputed, their modalities and interaction with turbulence remain a subject of active research. In this work, the characteristics of gravity waves and their impact on flow statistics, including turbulent fluxes, are presented using data collected above an Antarctic Ice sheet during an Austral Summer. Antarctica is an ideal location for exploring the characteristics of gravity waves because of persistent conditions of strong atmospheric stability in the lower troposphere. Periods dominated by wavelike motion have been identified by analysing time series measured by fast response instrumentation. The nature and characteristic of the dominant wavy motions are investigated using Fourier cross-spectral indicators. Moreover, a multi-resolution decomposition has been applied to separate gravity waves from turbulent fluctuations in case of a sufficiently defined spectral gap. Statistics computed after removing wavy disturbances highlight the large impact of gravity waves on second order turbulent quantities including turbulent flux calculations
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
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
- …
