1,721,266 research outputs found
Succession dynamics of Pine Barrens riverside savannas: a landscape-survey approach
No full textPine Barrens riverside savannas are acidic seepage fens found on the flood terraces of streams and rivers of the New Jersey Pine Barrens. Ecologically, they are comprised of six distinct vegetation communities, each listed as globally rare or imperiled. While pollen indicates that some individual savannas may have persisted in an open state for over 8,000 years, floristic studies conducted over the past century suggest a rapid decline in their distribution over that period. Savannas have historically been subject to extensive human exploitation for their iron and turf resources. However, all extant sites have been largely protected from direct anthropogenic alteration for the past 150 years. Succession, then, appears to be the most likely driver of this recent decline in savanna distribution. The goals of this study were to quantify the rate of decline based on a single dataset, identify the dominant succession patterns within the system, and suggest directions for future research. Using a variety of GIS and data visualization techniques, a multifaceted data exploration approach was taken to characterize succession dynamics over a 62-year period across multiple spatial and temporal scales. Dramatic loss of savanna cover was confirmed, with a decrease in total savanna area study-wide of 71.3% between 1940 and 2002. This study-wide decline was generally linear for each of three general classes of savanna (wet, graminoid and shrub). At the site level, these patterns were much more variable; apparently based on the distribution of savanna at the start of the study. Two distinct patterns of succession were apparent: one of locally persistent graminoid savanna, and one consistent with a shifting mosaic driven by rapid succession and disturbance from both fire and flood. Rapid declines appear to be driven primarily by the shifting mosaic that is not in a steady state. Persistent patches do show signs of slow decline through incursion of Atlantic white cedar. One potential causal factor, the composition of vegetation adjacent to savanna patches did not appear to have any influence on succession dynamics. The focus of future research should be on the influence of changing natural disturbance regimes and the factors that maintain locally persistent savanna patches.M.S.Includes bibliographical referencesby David C Smit
Deposition in supercritical fluids: from silver to semiconductors
No full textThere is great interest in developing new routes to novel functional materials, particularly for heterogeneous nanocomposites of metals or semiconductors with polymeric hosts. Supercritical fluids have become important media for the synthesis of such nanocomposites largely because of their unique properties, but also through their perceived environmental benefits over conventional routes. In this feature article, we focus on the deposition of silver and semiconductor nanoparticles into polymer substrates by use of supercritical fluids. These processes develop nanocomposites with distinct characteristics for optical and biomedical applications. The preparation and characterisation of silver and semiconductor nanoparticles is described and a brief discussion is also extended to some other novel deposition systems in supercritical fluids
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
The use of the middle latency response as an indicator of anaesthetic depth: an investigation using a slow induction of propofol anaesthesia
No full textObservation of excitons and trions in monolayer WS<sub>2</sub> using resonance Raman spectroscopy
No full textAppropriate 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
Measurements of the population lifetime of D band and G? band phonons in single-walled carbon nanotubes
No full textWe report time-resolved incoherent anti-Stokes Raman scattering measurements of the dynamics of the D and G? bands in single-walled carbon nanotubes at excitation energies of 1.51 and 1.63 eV over the temperature range 4–330 K. The measurements indicate that the population lifetimes (1 ps) of the phonons responsible for the D band are dependent on nanotube type. The temperature dependencies are consistent with anharmonic decay of the phonons into one low (<190 cm–1) and one high energy phonon
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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