1,721,011 research outputs found
Shallow upper mantle rheology and secular ice sheets fluctuations
No full textOn time scales from decades to centuries, continental cryospheric forcing in response to climate change constitutes a major source of isostatic disequilibrium that may influence future regional sea level variations. Current vertical displacements and gravity field variations are often estimated neglecting rheological effects and thus assuming a fully elastic response of the Earth. In this study, we adopt a more general point of view, aiming at describing ongoing surface movements resulting from recent glacial instabilities, also taking into account the effects associated with shallow upper mantle and crustal rheologies. Our computations are based on the Post–Widder Laplace inversion formula, which permits the straightforward computation of load-deformation coefficients for steady state and transient rheologies up to very high harmonic degrees. Using a surface load with a simple geometry and time history, we compare the classical elastic solutions to those obtained considering the rheological response of the shallow upper mantle. While at the center of the ice sheet rheology only magnifies the elastic response, the pattern and time history of vertical displacement at the ice sheet margins show a greater complexity, mainly due to the development of lateral forebulges whose shape and amplitude are particularly sensitive to the rheology of the shallow upper mantle. In this region, assuming an elastic rheology is generally appropriate on a century time scale, but significant deviations from a purely elastic response (both sign and amplitude) are observed at longer time scales or when a low viscosity zone with Maxwell rheology is taken into account
Glacio-isostatic adjustment in the Po plain and in the northern Adriatic region
No full textVertical movements in the Po plain (northern Italy) are controlled by natural and anthropogenic
effects. Since Italy is located in the far–field of the former late Pleistocene ice sheets, isostatic deformations are
primarily driven by melt water loading and represent a major component of long–term natural movements across
the entire Mediterranean. In addition to far–field sources, here we consider the isostatic effects of melting of the
nearby Wu ̈rm Alpine ice–sheet, suggesting that it is possible to put bounds on its maximum thickness, extent
and chronology by Holocene relative sea level observations from the northern Adriatic. Using various plausible
ice models, and adopting a viscosity profile that matches Holocene relative sea level observations in the
Mediterranean, we find that melting of the Alpine ice sheet is always responsible for upward movements in the
Po plain, currently at rates of * 0.5 mm/yr. When both far– and near–field sources are considered, the rate of
sea level change in the Venetian Lagoon for the most reasonable mantle rheology and melting chronology is
negative, i.e., opposite to that attributed to human activity and recent climatic variations. However, its amplitude
(fractions of mm/yr) is small compared to the secular signal observed by tide gauges (*2 mm/yr), which makes
glacial isostasy a second–order mechanism of sea level variation in this region
Post glacial readjustment, sea level variations, subsidence and erosion along the Italian coasts
No full textOngoing sea level variations and vertical land movements measured by tide gauges and continuous GPS stations along the Italian coasts stem from several factors acting on different spatiotemporal scales. Conversely to tectonics and anthropogenic effects, which are characterized by a heterogeneous signal, the adjustment of solid Earth and geoid to the melting of the late– Pleistocene ice sheets results in a smooth long–wavelength pattern of sea level variation and vertical deformation across the Mediterranean, mostly driven by the melt water load added to the basin. In this work we define upper and lower bounds of the effects of glacial isostatic adjustment (GIA) on current sea level variations and vertical ground movements along the coasts of Italy. For plausible mantle viscosity profiles we explore to what extent the spatial variability of observed rates may be attributed to delayed isostatic recovery of both solid Earth and geoid. In addition, we show that long–wavelength patterns of sea level change are tuned by the effects of GIA, and that coastal retreat in Italy is broadly correlated with the expected ongoing rates of post–glacial sea level variations
Bounds on the time-history and Holocene mass budget of Antarctica from sea-level records in SE Tunisia
No full textSolving the sea–level equation for a Maxwell Earth, we analyze the sensitivity of Holocene sea–level records in SE Tunisia to the time–history of remote ice sheets. Assuming that mantle viscosity increases moderately with depth, we find that in this region the sea–level variations driven by the Northern Hemisphere ice sheets cancel, so that the late–Holocene sea–level high–stand suggested by the geological record merely reflects the melting history of Antarctica. New insight into the history of this ice sheet is obtained analyzing the information contained in a revised set of relative sea–level observations for sites across the Mediterranean covering the last 8 kyrs. From a trial–and–error misfit analysis, it holds true that in this region the match between model predictions and observations improves when the volume of water released from Antarctica is well below the value imposed by the ICE3G chronology and when a sudden meltwater pulse is allowed between 8 and 7 kyrs before present, corresponding to the epoch of the catastrophic rise event known as CRE3
La Scuola Ecologica di Chicago: un classico ancora attuale
No full textNegli studi urbani, quando si parla di classici un posto certamente di rilievo è occupato dalla Scuola Ecologica di Chicago. L’approccio ecologico è forse quello dove “studioso” e “studiati” sono più vicini (a volte quasi indistinguibili), quello che dà più importanza al rapporto tra uomo e territorio, e a come l’individuo si lega ed è condizionato dall’ambiente in cui vive. Riguardo al modo di fare ricerca sottolinea la necessità di “sporcarsi le mani e i bordi dei pantaloni”, di andare cioè sul territorio studiato e rimanerci a lungo e ininterrottamente, “mescolandosi” alla gente che si studia per capirne i problemi da vicino.
Il mio contributo si snoda proprio attorno all’attualità di questa Scuola dal punto di vista teorico e metodologico, basandosi su materiale e spunti raccolti in un periodo come Visiting Research Scholar alla New York University. Anzitutto, vengono individuati alcuni autori che sembrano proseguire l’approccio ecologico negli ultimi anni: Elijah Anderson, Mario Small e Mitchell Duneier. Inoltre, sono presentati alcuni estratti di interviste svolte con prestigiosi sociologi statunitensi: Herbert Gans, Harvey Molotch, John Logan, Neil Brenner, Richard Alba e Ruth Horowitz. Attraverso queste interviste cerco di capire meglio l’eredità della Scuola di Chicago negli studi urbani statunitensi, nonchè se e come venga “applicato” oggi l’approccio ecologico nella ricerca empirica
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
Tra mobilità e stanzialità. Le persone senza dimora nello spazio pubblico urbano
No full textIn questo contributo si propone, sulla base di una serie di ricerche condotte nel territorio bolognese, alcune riflessioni sulla mobilità urbana della persona senza dimora, una figura che in questi ultimi anni è stata assunta dalle politiche e dai servizi sociali come paradigmatica dell’esclusione sociale. Si tratterà di verificare se il riferimento all’assenza di una dimora fissa implichi necessariamente una elevata mobilità geografica e l’assenza di forme di radicamento nel territorio. Una mobilità che depriverebbe gli individui sul piano relazionale e li collocherebbe al di fuori di ogni legame significativo con il contesto in cui si trovano, facendo di essi altrettante “persone a parte” in un “mondo a parte”
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