1,721,015 research outputs found
Shallow landslides triggered by rainfall: numerical analyses on Richards’ equation based models
No full textThe clearly evident relationship of cause and effect between rainfall events and shallow landslides supports the idea that coupled approaches, unifying hydrologic and geotechnical aspects, are to be strongly encouraged and analysed. Recent contributions on this topic (e.g. Iverson, 2000) show that the role played by the partially saturated soil condition can not be ignored. The analysis of flow motion is current1y carried out by using Richards' equation (1931). In this framework a research program, on shallow landslide triggering mechanisms, taking place in partially saturated soils having different initial conditions, has been planned; this paper represents a contribution on the topic, dealing with an extensive sensitivity analysis performed on the occurring hydrologic and geotechnical parameters that have to be considered. Their evaluation is often a criticaI task, owing to the inherent difficulties in having reliable values, characterising soil conditions in a representative period of time.
A numerical approach has been chosen, using a code that solves l-D Richards' equation (Simunek et al., 1998). More that 200 analyses supply useful remarks on the application limits of the coupled approach and, owing to the basic relationships which govern the physical mechanisms, allow to ascertain the roles played by the different phenomenological factors. In particular, the adopted model has shown a rather significant dependence as far as the soil initial moisture conditions and the permeability variations are concerned. Among the different scenarios, with regard to rainfall intensity and soil hydraulic conductivity, conditions leading to positive pore pressures
rise-up in limited and well defined soil strata have been pointed out. The results of the performed analyses allow useful observations and comments on the mutuaI interaction phenomena occurring among pre-existing and triggering factors. The evidences sorted out from comparisons with case histories and literature review, help in validating the obtained results
Frane superficiali innescate da piogge intense: analisi numerica con modelli basati sull’equazione di Richards
No full text
Processi di infiltrazione e meccanismi di innesco di frane superficiali in terreni parzialmente saturi
No full textI movimenti franosi che coinvolgono le coltri di copertura dei versanti naturali rappresentano, da sempre, una delle tipologie di fenomeni cui sono attribuibili conseguenze di rilevante impatto sulle attività socio – economiche e sul patrimonio strutturale ed infrastrutturale dei territori colpiti. La mitigazione del rischio connesso a tali fenomeni rappresenta, pertanto, una delle esigenze primarie dell’odierna società civile.
In tale ambito si colloca la ricerca svolta, che affronta il problema della modellazione della fase di innesco di movimenti franosi superficiali a seguito di piogge intense. Il presente testo ne compendia, in forma necessariamente sintetica ed enunciativa, gli aspetti più significativi.
Nello studio, insieme ad un’ampia disamina degli approcci disponibili in letteratura per lo studio di tali fenomeni, l’attenzione è stata rivolta ai cosiddetti “modelli completi di versante” per l’analisi del regime delle pressioni neutre, sia positive che negative, conseguente alle precipitazioni meteoriche, secondo lo schema classico di Richards (1931). Le potenzialità ed i limiti della metodologia di analisi presa a riferimento sono stati valutati attraverso un’approfondita analisi di sensitività che si è avvalsa dell’integrazione numerica delle equazioni reggenti e dalla quale è stato possibile mettere in luce l’influenza dei fattori in gioco sui risultati conseguibili.
Sulla base di risultati acquisiti, la metodologia di analisi prescelta è stata applicata per l’analisi a ritroso di un movimento franoso occorso nel Novembre 2002 in Val Fontanabuona (Comune di San Colombano Certenoli - GE) a seguito di piogge intense, che ha coinvolto una coltre detritica Tale movimento è stato scelto come rappresentativo poiché nell’area in esame (circa 10 kmq) si sono verificati, nell’arco di meno di due ore, oltre 100 dissesti superficiali di caratteristiche simili. Sui materiali coinvolti nel dissesto è stata condotta una approfondita campagna di indagine consistente in prove in sito e di laboratorio. Una volta calibrate le grandezze significative per la costruzione del modello geotecnico dell’area in esame, lo stesso modello è stato utilizzato per l’analisi a ritroso dell’evento franoso del Novembre 2002.
I risultati ottenuti hanno consentito di riprodurre soddisfacentemente la dinamica dell’evento, sia in riferimento alla localizzazione topografica dei fenomeni di primo distacco sia in relazione alla loro evoluzione temporale
Free volume fraction and nanoholes shapes in polyvinyl acetate
No full textPositron annihilation lifetime and specific volume measurements were carried out in polyvinyl acetate, with the aim to evaluate the free volume fraction in a range of temperatures above the glass transition. Comparison with the analogous quantity calculated on the basis of the Simha-Somcynsky theory shows that the usual assumption of spherical intermolecular spaces (nanoholes) forming the free volume does not give the correct quantitative result. Although irregularly shaped, nevertheless nanoholes can be better framed in terms of flattened discs
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
- …
