1,721,001 research outputs found
Analisi variografica del diametro di un impianto di quercia da sughero. Un esempio di studio della corregionalizzazione in ambito forestale
No full textLa geostatistica permette di produrre modelli, stime, mappe e predizioni circa la
struttura spaziale delle dimensioni e crescita delle piante. I variogrammi hanno consentito
lo studio della dipendenza spaziale del diametro al colletto di un recente impianto di
quercia da sughero. Il nostro obiettivo è quello di quantificare la dipendenza spaziale del
diametro al colletto attraverso lo studio del suo modello spaziale stocastico. Il modello di
variogramma relativo all’intera parcella presenta un’elevata componente casuale. La suddivisione
dei dati tra il substrato granitico e quello quarzitico che compongono l’area totale
ha permesso di riconoscere modelli di variogramma maggiormente strutturati, soprattutto
per l’area granitica. Le funzioni variografiche adottate sono quella sferica per l’area
quarzitica ed esponenziale per quella granitica; in entrambi i casi l’autocorrelazione non
supera gli otto metri. La ricerca evidenzia come la componente geologica giochi un ruolo
primario nella variazione spaziale del diametro. Al contrario, a livello dell’ intera parcella
esistono una serie di fattori incidenti quali: elevazione, profondità del suolo, linee di flusso
idriche, pendenza, esposizione e orientazione, che determinano un generale effetto random.
Lo studio, inoltre, vuole dimostrare come l’analisi variografica, oltre che per la stessa
geostatistica, sia un utile strumento nelle ricerche sul comportamento delle specie forestali
in relazione allo spazio circostante.
Parole chiave: variogramma; teoria delle variabili regionalizzate; geostatistica; diametro al
colletto; quercia da sugher
Environmental mineralogy in the mining area of Montevecchio Ponente (SW Sardinia)
No full textThe Montevecchio mining area (Arbus – Guspini, Sardinia SW) has been exploited for centuries, for the
extraction of lead and zinc minerals.
The following work focuses on the study and characterization of the sources and contaminants present in
the “Cantieri Sanna” from the area of Montevecchio Ponente.
There is a large amount of mining residues in the area downstream of the washing plants, affected by
important erosion phenomena, which involve a solid transport of contaminants in solution.
These mineral residues were characterized by diffractometric (XRD) and chemical analysis (ICP-MS), after
their solubilization. The whitish biomineral patinas present along the Rio Roia Cani were also analyzed by
means of diffractometric analysis and a scanning electron microscope (SEM).
From the analysis carried out, the presence of secondary phases emerged, such as: epsomite, glaucocerinite,
goethite, hydroxyapatite, minium, nantokite, plumbojarosite and zincite, indicating a remarkable reactivity
of the tailings with atmospheric agents; these results made it possible to identify tailings as a source of
contamination. Furthermore, the presence of sub-economic contents of rare earths elements (REE), more
particularly of light rare earths elements (LREE), and of Al, Fe, Pb and Zn emerged.
Biomineralization occurs in the area was found in the streambed of rio Roja Cani; it appears like that which
forms in the bed of the rio Naracauli, described in detail in Medas et al. (2014).
SEM-EDS analysis confirm that biomineralization is mediated by bacterial activity, due to the filamentous
and tubular structures present in biofilms; furthermore, the presence of zinc and oxygen emerges from the
compositional maps, confirming that the biomineralization is composed of hydrozincite, as revealed by the
XRD analysis.
We argued that this biomineralization rules natural attenuation of zinc as already found in rio Naracauli
(Wanty et al., 2013; De Giudici et al., 2014)
The influence of the wind in the Schmallenberg virus outbreak in Europe
No full textA model previously developed for the wind-borne spread by midges of bluetongue virus in NW Europe in 2006 is here modified and applied to the spread of Schmallenberg virus in 2011. The model estimates that pregnant animals were infected 113 days before producing malformed young, the commonest symptom of reported infection, and explains the spatial and temporal pattern of infection in 70% of the 3,487 affected farms, most of which were infected by midges arriving through downwind movement (62% of explained infections), or a mixture of downwind and random movements (38% of explained infections), during the period of day (1600-2100 h, i.e. dusk) when these insects are known to be most active. The main difference with Bluetongue is the higher rate of spread of SBV, which has important implications for disease control
Statistical models for spatially explicit biological data
No full textExisting algorithms for predicting species' distributions sit on a continuum between purely statistical and purely biological approaches. Most of the existing algorithms are aspatial because they do not consider the spatial context, the occurrence of the species or conditions conducive to the species' existence, in neighbouring areas. The geostatistical techniques of kriging and cokriging are presented in an attempt to encourage biologists more frequently to consider them. Unlike deterministic spatial techniques they provide estimates of prediction errors. The assumptions and applications of common geostatistical techniques are presented with worked examples drawn from a dataset of the bluetongue outbreak in northwest Europe in 2006. Emphasis is placed on the importance and interpretation of weights in geostatistical calculations. Covarying environmental data may be used to improve predictions of species' distributions, but only if their sampling frequency is greater than that of the species' or disease data. Cokriging techniques are unable to determine the biological significance or importance of such environmental data, because they are not designed to do so
Performance di recenti imboschimenti con quercia da sughero in ex-coltivi
No full textGrowth performance of cork oak plantations recently established on farmlands in Sardinia, Italy. Recently, significant forestry activities have taken place in Sardinia thanks to EU Regulation 2080/92 funds. Some 80% of the afforestated surface has been planted with holm oak and cork oak. The latter also characterizes 89% of the reforestation area. Given the funding source, plantations have been established on farmlands. Growth performances of these recent cork oak stands have been quantitatively evaluated and compared with the performances of two experimental plots. In Gallura (north-east of Sardinia), that is the traditional cork production area and still is economically the most important cork district of the island, these new cork oak plantations have an average size of 28 ha. They have been established on lands that, before plantation, were either pastures (30%) or arable lands (70%). Plantation failures are limited to 8.8% of the total (in term of mass) and seem independent of environmental factors or plantations species composition (conifers have been frequently used as secondary species). Average growth of the stem, measured above cork at collar height, is in the range 4 to 8mm/year with a mean value of 5.5mm/year. No correlation appears with either environmental conditions or species composition of the plantations. In the first experimental plot, soil management practices (natural vegetation removal vs its cutting and mulching) does not differentiate young plants growth trends. In the control subplots (no removal) stem collar diameter is 20% smaller. Localized manual hoeing around trunk base increased the diameters by 13% but reduced cork thickness by 21%. The second experimental plot allows comparisons among 27 Mediterranean proveniences of cork oak. The trial exhibits reduced genetic influence: diameters and heights growth are significantly different only among extreme groups. In conclusion, reduced growth performances of the plantations established in farmlands is due, to some extent, to the limitations inherent with private land management (constrained to costs minimization) and, on the other hand, to the generally very limited thickness of Gallura soils. Demand for good quality commercial cork is steadily raising. To sustain the request, in the short term, it would be necessary to extend financial support for plantations care, from 5 to 10 years, or even up to the first stripping (virgin co
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
Dinamica temporale di formazioni a macchia con prevalenza di mirto
No full textL’uso di foto aeree pancromatiche ad alta risoluzione ha consentito l’analisi delle dinamiche spaziali e dell’intensità nei cambiamenti accorsi tra il 1977 e il 1998 alle strutture arbustive con alta presenza di mirto in sei aree campione della Sardegna. La coesistenza in tutti i siti dei quattro usi del suolo denominati come urbano, agricolo, boscato e macchia con mirto ha permesso lo studio dell’impatto della gestione del territorio sulla macchia mediterranea. La metodologia applicata combina l’utilizzo dei sistemi informativi geografici (GIS) con il telerilevamento per la produzione di mappe finali di cambiamento di uso e copertura del suolo che descrivono le trasformazioni del tematismo “macchia mediterranea con mirto”. I risultati mostrano che: 1) in tre località si ha una riduzione della vegetazione arbustiva superiore al 20%, spesso accompagnata da una riduzione in densità; 2) le attività di rimboschimento e l’agricoltura sono responsabili, in larga misura, della riduzione della macchia; 3) le modifiche si verificano prevalentemente ai confini tra le differenti tipologie di uso del suolo.Using high-resolution panchromatic aerial photos data we explored the magnitude and spatial arrangement of changes in Mediterranean shrubland and in its density from six study areas in Sardinia from 1977 to 1998. The areas investigated comprise four land use types: urban, farmland, forest and shrubland with presence of myrtle. The occurrence of these land use types provides the opportunity to explore the impacts of land management on vegetation structure and cover of Mediterranean shrubland. This paper combines a geographic information system (GIS) and remote sensing to produce final maps of land use and cover change focused on the transformations involved in shrubland with myrtle. Results indicate that 1) in three areas shrubland reduce its cover more than 20% and often with low canopy density; 2) forest and agriculture increasing appear the important factors in the reducing shrubland cover; 3) most land development occurs in the boundaries between different land uses
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