1,720,966 research outputs found
Principal Component Analysis of Quantum Correlation
No full textThe concept of the quantum correlation matrix for observables leads to the application of PCA (Principal Component Analysis) also for quantum systems in Hilbert space. The consistency of PCA for quantum systems, is illustrated in the case of a qubit system with two Pauli matrices as observables and a density matrix polarized along the third one. As the main application of this theory, it is shown that the principal components are able to generate a class of quantum channels and depolarizing operators mapping density matrices (even pure states) to maximally mixed state
Il blocco, un esteso fenomeno meteorologico non lineare che ha pesantemente influenzato l’inverno 2016-17 in Italia
Full text linkThe persistence of strong snowfalls in both Central and Southern Italy between December 2016 and January 2017 has been the most dramatic effect of a particular quasi-steady meteorological situation known as Ω block. This situation has concerned a large European area as well. It is worth to stress that this meteorological pattern is usually associated with length of time larger than that typical of meteorological weather. In the present paper we will: 1) show that, in the context of the non-linear quasi-geostrophic dynamics of the atmosphere at the synoptic scale, the Ω block is the result of an interplay between Rossby waves and zonal flows; 2) provide, in accordance with the statistics of the above blocks, the standard duration of the corresponding meteorological configuration which, in any case, is candidate to the break up via dynamical instability
Analisi del fenomeno di blocco atmosferico osservato a Trieste tra agosto 2003 ed agosto 2018
Full text linkIl blocco atmosferico è una configurazione dell'atmosfera particolarmente stabile, caratterizzata dalla persistenza di alta pressione (anticiclone di blocco) che interrompe la propagazione delle perturbazioni atlantiche provenienti da ovest.
L'analisi matematica mostra che generalmente un blocco può essere ottenuto dalla sovrapposizione di un opportuno
usso medio zonale e un'onda di Rossby e che ha un decorso di circa 15 giorni, periodo ben più alto dei tipici pochi giorni di alternanza "bel tempo-brutto tempo"
Shallow water sea-floor morphologies around Asinara Island (NW Sardinia, Italy)
No full textSide scan sonar, high-resolution seismic and multibeam data collected off the coast of Asinara Island in the northernmost part of Sardinia have revealed the occurrence of four distinct acoustical patterns that can be related to four main sea-bed types. The four facies represent fine sand (Type A), medium to
coarse sand (Type B), patchy sand cover between basement outcrops (Type C) and a predominantly sandy sea-floor colonized by the seagrass Posidonia Oceanica (Type P). The distribution of the sea-bed types indicates that the study area is characterized by a rather complex morphological setting.
A remarkable physiographic difference exists between the eastern and western sector of the island, with the latter being affected by strong, westerly winds, mainly the so-called ‘‘Mistral’’. The wave climate in this area is dominated by wind waves, which can reach a maximum height of 8m during winter storms.
Sediments are mobilized at water depths greater than 30m from the sea surface during these energetic oceanographic regimes. We infer that dune fields and sand ribbons are deposited by strong offshore flows along the sea-bed resulting as a consequence of wave- and wind-induced onshore water
transport
The role of Internal Solitary Waves on deep-water sedimentary processes. The case of up-slope migrating sediment waves off the Messina Strait
Full text linkSubaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal
environments, and continental slopes exposed to strong currents, where they are formed by current
shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily
observed in marine environments where no such current exists; the physical processes driving their
formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced
by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves.
We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that
ISWs formed at the interface between intermediate and surface waters are refracted by topography.
Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave
field is due to refraction of such ISWs. Combining field observations and numerical modelling, we
show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing
bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom
topography matches the observed deflection of the sand waves; and predicted migration rates of sand
waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure
of continental margins and it represents a promising link between the geological and oceanographic
communities
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
Model Reduction for Parametrized Optimal Control Problems in Environmental Marine Sciences and Engineering
Full text linkWe propose reduced order methods as a suitable approach to face parametrized optimal control problems governed by partial differential equations, with applications in en- vironmental marine sciences and engineering. Environmental parametrized optimal control problems are usually studied for different configurations described by several physical and/or geometrical parameters representing different phenomena and structures. The solution of parametrized problems requires a demanding computational effort. In order to save com- putational time, we rely on reduced basis techniques as a reliable and rapid tool to solve parametrized problems. We introduce general parametrized linear quadratic optimal control problems, and the saddle-point structure of their optimality system. Then, we propose a POD-Galerkin reduction of the optimality system. Finally, we test the resulting method on two environmental applications: a pollutant control in the Gulf of Trieste, Italy and a solution tracking governed by quasi-geostrophic equations, in its linear and nonlinear version, describing North Atlantic Ocean dynamic. The two experiments underline how reduced order methods are a reliable and convenient tool to manage several environmental optimal control problems, for different mathematical models, geographical scale as well as physical meaning
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
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