1,721,001 research outputs found
Properties of dual multiloop amplitudes
No full textPrevious results on the dual multiloop amplitude are extended by obtaining, from the unitarization procedure, the measure and domain of integration. The singularities of the amplitude, which arise from end points in the integration domain, are discussed by exploiting the simple geometrical interpretation of the theory. In particular, we investigate the singularities which give rise to divergences in planar diagrams as well as Pomeranchuk-like singularities in nonplanar ones
On the introduction history and plant ecology of the alien Salpichroa origanifolia in Tuscany (Italy)
No full textInvasive alien species (IAS) are a major threat to biodiversity worldwide. The invasion of Salpichroa origanifolia (Lam.) Baillon (Solanaceae), an herbaceous climber native to South America, is recently rising concern in several Mediterranean countries. In North America, Australia, Japan, and New Zealand, where S. origanifolia has a longer history of introduction it already poses a threat to critical habitats and native species. We, therefore, recommend listing it as an invasive alien species of EU concern and include it in the EPPO list. In Tuscany (central Italy), S. origanifolia has successfully colonised a mesophile forest (San Rossore Regional Park), showing to be a strong competitor towards the resident understorey vegetation, which also led to the progressive depletion of the soil seed bank [1]. Although its first record in the Regional Park is from 1996, it is only in recent years that this species has massively spread. Giving insight into the spatio-temporal stages of alien invasion (transport, colonization, establishment, and spread) is important for planning targeted and effective conservation measures. Furthermore, explaining the arrival and spread of S. origanifolia within the Regional Park provides information to reduce the risk of introducing potential IAS.
First aim of this research was to trace the history of introduction of S. origanifolia in Tuscany, and the invasion routes within the Regional Park. Moreover, we studied which environmental factors, primarily illumination and soil moisture, may have favoured the establishment at the current invasion spots, and the ecology (reproductive biology, functional traits) of this species in the introduced area. The invader S. origanifolia proved to adapt well to different light conditions, due to its ability to allocate resources differently between leaves and rhizomes
Effects of the invasive alien Salpichroa origanifolia on the soil seed bank of a mixed forest (San Rossore, Migliarino, Massaciuccoli Regional Park, Pisa).
No full textSalpichroa origanifolia (Lam.) Baillon is a perennial herb of the Solanaceae family, native to the temperate regions of South America, where it grows from 0 to 2500 m asl, often behaving as a ruderal species. The species is naturalised in Europe, is not listed as an invasive alien species of EU concern and is not included in any of the EPPO lists. Although reports from European countries are scarce, S. origanifolia has been found spreading rapidly in southern Switzerland and the Canary Islands. In Italy, the species is present in most regions and its status was recently changed from naturalised to invasive in Campania and Calabria (1). Pathways of introduction can be unintentional, through trade in seeds and potted plants containing seeds or stem fragments, or intentional, as ornamental, or melliferous plant. The first report for Tuscany dates to 1923, but around 2000 the species was still considered rare (5). Salpichroa origanifolia was not present in San Rossore before 2000 (2), and it was accidentally found in cut stone pine plantations and near the buildings at the entrance to the reserve in 2008 (3). Ten years later, S. origanifolia showed a clear invasive habit, forming dense stands at forest edges, under isolated trees and inside the forest, especially in correspondence of fallen trees.
Phenological and morphological traits of this species contribute to its invasiveness. Shoots vegetate from March to December, and the flowering period is very long, from April to October. Plants spread rapidly producing scrambling and rooting aerial stems, and two types of rhizomes: fine fleshy, 3-5 mm in diameter, just below the soil surface, and around 7-mm-thick deep growing woody rhizomes.
This study assessed the competitiveness of S. origanifolia against native forest species, by analysing the weekly emergence and the biomass achieved after 11 weeks. The soil seed bank was collected in the forest of San Rossore, from two sites with different levels of S. origanifolia invasion: one with a low (LD So) and one with a high (HD So) density. Two additional treatments, arranged in a split-plot design, were imposed: light conditions (full sunlight/canopy shade) and the presence or absence of S. origanifolia rhizomes. The light treatment was set to test if the invasiveness of S. origanifolia and its effect on the soil seed bank varied between undergrowth and open areas. Results showed that, in both sites, the presence of S. origanifolia rhizomes did not inhibit either the germination rate or the biodiversity of native plants. However, in the full light treatment, the presence of S. origanifolia increased the germination rate, suggesting that shading by this invasive species had an initial positive effect on the understorey species. Results concerning biomass differed between sites. In the low-density site, we observed a difference in the biomass of native species between treatments with or without S. origanifolia. In the former case, the biomass was reduced by about a half. In the high-density site, the biomass of the native species was generally very low, independently on the presence of S. origanifolia rhizomes. This is to impute to the emergence of S. origanifolia seedlings from the soil seed bank, which were very competitive against native species. In fact, their biomass was fivefold higher than that of the native seedlings. Furthermore, the biomass achieved by a single S. origanifolia seedling was 2 g, whereas that of a seed bank seedling was just 0.05 g
Utilità degli erbari virtuali per ricostruire i percorsi di introduzione e diffusione delle specie aliene.
No full textIl legame tra specie aliene e conservazione della biodiversità è molto stretto. Le invasioni biologiche figurano tra le prime cinque cause dirette della perdita di biodiversità e la Convenzione sulla Diversità Biologica del 1992 individua le “specie aliene” come un ostacolo alla conservazione in-situ della biodiversità, rendendo necessario “prevenire l’introduzione, controllare e/o eradicare le specie aliene che minacciano gli ecosistemi, gli habitat o le singole specie” (CBD art. 8, comma h). La legislazione europea (Reg. UE 1143/2014) indica la prevenzione e l’intervento precoce come i metodi più efficaci e meno costosi per il controllo delle invasioni biologiche, dando grande importanza alla individuazione e priorizzazione dei percorsi di introduzione di queste specie verso l’Europa e tra gli Stati membri.
La ricostruzione del percorso di una specie aliena non è semplice. Negli ultimi decenni i dati sulla loro presenza sono incrementati esponenzialmente grazie alla nascita di numerosi database dedicati alla raccolta di segnalazioni naturalistiche e al crescente coinvolgimento dei cittadini. Tuttavia, rimangono scarse le informazioni per il passato, indispensabili sia per individuare i punti di arrivo e i vettori di introduzione di queste specie, che per tracciarne le prime vie di diffusione.
La digitalizzazione degli erbari e la loro diffusione on-line sta rendendo disponibile una gran mole di dati, spesso corredati da indicazioni sull’habitat colonizzato e sulla fenologia della specie, utilissimi per ricostruire il percorso delle specie aliene e per stabilire quali fattori possono favorirne o ostacolarne la stabilizzazione.
Salpichroa origanifolia (Lam.) Baillon è una Solanacea nativa dell’Argentina. Sebbene al momento non sia inserita tra le specie aliene di interesse unionale, recentemente sta assumendo carattere invasivo in diverse aree del Mediterraneo. In questa ricerca abbiamo utilizzato i database EASIN e GBIF e diversi erbari virtuali per ricostruirne i tempi di introduzione e le vie di diffusione nella regione EPPO. Ciò ha permesso di attestare la presenza di S. origanifolia già nel 1849 in Francia, nel 1855 in Germania, nel 1897 in Algeria, nel 1901 nei Paesi Bassi e nel 1906 in Italia. Le annotazioni sulle tavole degli erbari riportano, che in Italia e in Algeria la specie manifestava già allora la tendenza a spontaneizzare e rivelano che le principali vie di introduzione sono state gli Orti Botanici e i porti. I luoghi di ritrovamento indicano che gli habitat preferenziali di colonizzazione sono le coste, sia sabbiose che rocciose, le zone ruderali e il verde urbano. L’incremento temporale delle segnalazioni evidenzia una rapida diffusione di S. origanifolia lungo le coste mediterranee e atlantiche, da cui la specie è poi penetrata verso l’interno seguendo i corsi d’acqua. Nei climi più freddi e continentali non è stata, invece, riscontrata alcuna radiazione e la specie è rimasta, finora, confinata nei punti di arrivo
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
Resprouting Control of Ailanthus altissima by Means of Cut and Stump Covering: Experimental Evidence for a Promising Technique
Full text linkAilanthus altissima is an invasive tree threatening the biodiversity in natural and disturbed habitats of temperate regions, primarily because of its high resprouting vigor. To test the effect of light exclusion on stem and root sprouting, black covers were applied on the cut stumps of 3-year-old saplings grown in pots. The treatments were as follows: SL, stumps exposed to light; SH, only stumps covered; SPH, the entire pot covered; C, intact control plants. The covers were removed when the root sprouts appeared. The emergence of stem and root sprouts was checked weekly, and their number and biomass were determined at the growth peak (cut I and III) and the end (cut II and IV) of two seasons after cutting. Stem sprouts were produced only in the first growth season in SL and SH and never in SPH and the controls. The number and biomass of the root sprouts were the highest in SH at cut I and in SL in the following cuts. In SH, the sprouting ceased completely after cut I, suggesting a rapid consumption of root reserves, while in SL and SPH, repeated cutting progressively reduced the sprouting vigor. We concluded that covering the stems after cutting is a promising technique to control ailanthus resprouting without the use of herbicides
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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