1,720,993 research outputs found
Dinamiche ed effetti pedogenetici delle specie erbacee pioniere e definitive lungo una cronosequenza glaciale delle Alpi occidentali (Parco Nazionale Gran Paradiso)
No full textA partire dalla fine della piccola età glaciale, le coltri glaciali dell’Artide e delle Alpi hanno subito generalmente forti contrazioni, esponendo superfici via via sempre più vaste alla pedogenesi e alla colonizzazione vegetale. L’approccio comunemente più utilizzato per lo studio delle successioni primarie in ambiente periglaciale prevede la definizione di una cronosequenza, intesa come serie consecutiva di superfici deglacializzate da periodi differenti e noti. Negli ultimi 50 anni, ecologi e pedologi si sono occupati di molteplici aspetti legati alle dinamiche della vegetazione, del suolo e delle interazioni tra i due comparti del sistema lungo varie cronosequenze glaciali. L’effetto delle specie arboree, arbustive ed erbacee sulle proprietà chimiche e lo sviluppo del suolo è stato altresì approfondito in numerosi contesti ambientali. Tuttavia, l’impatto di specie erbacee riconducibili a stadi differenti della successione (ossia, pioniere e definitive) sulla biogeochimica del suolo in una successione primaria risulta tuttora poco noto. L’obiettivo del lavoro è valutare l’interdipendente dinamica del sistema suolo-pianta lungo una cronosequenza glaciale, evidenziando modificazioni ecosistemiche tocastiche/deterministiche operate da specie pioniere e definitive.
Lo studio è stato condotto sul detrito morenico del ghiacciaio del Lauson nel Parco Nazionale Gran Paradiso (Cogne, AO) dove è stato possibile identificare e datare sei differenti stadi della cronosequenza, distribuiti in un arco temporale di circa 170 anni. La vegetazione è stata rilevata su 18 plot permanenti (tre per stadio) tramite metodo fitosociologico. In seguito, sono stati calcolati la copertura vegetale delle piante vascolari e delle crittogame, gli indici di diversità specifica e il numero di specie e la copertura di due differenti gruppi funzionali: il gruppo delle specie pioniere (riconducibili a Thlaspietea rotundifolii) e quello delle specie tipiche di prateria alpina (riconducibili a Caricetea curvulae). Parallelamente è stato condotto un approfondimento specifico sulla struttura dei popolamenti di due specie obiettivo: Saxifraga oppositifolia L. subsp. glandulifera Vacc., specie spiccatamente pioniera, e Silene acaulis (L.) Jacq. subsp. bryoides (Jord.) Nyman, specie marcatamente più esigente. Per ciascun individuo presente nei plot sono stati rilevati due
diametri perpendicolari e la relativa media è stata assunta come indicatore dell’età. In corrispondenza di ciascun stadio della cronosequenza è stato aperto un profilo pedologico e sono stati prelevati i campioni di ogni orizzonte individuato per la caratterizzazione chimica. Per valutare l’influenza delle specie obiettivo sul chimismo e l’evoluzione del suolo, sono stati prelevati, in ogni stadio della cronosequenza, campioni di suolo sotto gli individui delle due specie e in aree prive di vegetazione. Infine, le stesse piante eradicate per la raccolta dei suoli sono state campionate per le analisi chimiche in laboratorio dei tessuti fotosintetici.
Il numero e la copertura delle specie pioniere raggiungono i valori massimi rispettivamente dopo 10 e 40 anni dalla deglacializzazione, mentre il numero e la copertura delle specie tipiche di prateria alpina raggiungono il loro massimo a 140 e 65 anni dal ritiro del ghiacciaio. Lungo la cronosequenza, il suolo
sottostante gli individui di S. oppositifolia e S. acaulis risulta maggiormente arricchito in nutrienti rispetto ai suoli delle aree prive di copertura vegetale. S. acaulis, specie a pulvino compatto, esercita un’influenza più importante rispetto a S. oppositifolia (specie a portamento prostrato e lasso) e contribuisce ad accumulare da 1.3 a 8.9 g kg-1 di C nel suolo (da 0.2 a 3.3 g kg -1 nelle aree prive di copertura vegetale). L’azoto presenta concentrazioni sotto le soglie di rilevabilità nei suoli privi di copertura vegetale, mentre aumenta nei suoli sotto le piante e con il tempo dalla deglacializzazione, equilibrando i rapporti stechiometrici C:N:P dei suoli più sviluppati verso valori favorevoli per l’affermarsi della vegetazione.
Complessivamente lungo la cronosequenza glaciale del Lauson è stata rilevata una colonizzazione precoce e ricca in specie nei micro-siti favorevoli per l’insediamento. L’effetto dovuto dall’insediamento delle specie erbacee pioniere stimola lo sviluppo del substrato, pressoché inerte nelle primissime fasi dalla deglacializzazione, predisponendo la successiva colonizzazione delle specie più competitive di prateria. Le specie tipiche della prateria alpina attecchiscono sporadicamente già nelle prime fasi post-glaciali, tuttavia incrementano significativamente in termini di numerosità e copertura solamente dopo che il suolo ha acquisito un’iniziale funzionalità. Tali evidenze supportano un determinismo biotico della successione primaria, riscontrabile già nelle prime fasi post-glaciali. Tuttavia, dopo circa 170 anni la copertura vegetale si attesta intorno al 30%, ancora lontana (anche in termini di composizione) dalla comunità climax del curvuleto, pertanto non raggiunta. L’ecosistema permane inoltre C-N-limitato mentre il P appare il macroelemento maggiormente a disposizione per la crescita vegetale
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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