1,720,968 research outputs found
Gas quantistici a bassa dimensionalità in geometrie curve e piatte
Full text linkI gas quantistici a bassa dimensionalità, prodotti mediante il confinamento ed il raffreddamento di atomi in configurazioni bi- o monodimensionali, mostrano una ricca varietà di proprietà di equilibrio e di non equilibrio. Le recenti tecniche sperimentali per controllare sia la loro geometria che la loro topologia, mediante l'intrappolamento di queste sistemi, ad esempio, in anelli o in gusci cavi, offrono una via promettente per lo studio della fisica quantistica a molti corpi su varietà spaziali curve. In questa tesi, discutiamo le proprietà statistico-quantistiche di gusci bosonici a simmetria sferica, analizzando i fenomeni della condensazione di Bose-Einstein e della superfluidità nel regime bidimensionale e a taglia finita. Utilizzando la formulazione della teoria quantistica dei campi mediante l'integrazione funzionale, otteniamo la equazione di stato a temperatura finita di questi sistemi a forma di guscio e, con tecniche analoghe, anche di altri superfluidi bidimensionali piatti, sia bosonici che fermionici. Inoltre, analizziamo quantitativamente le eccitazioni idrodinamiche a temperatura finita, consistenti nel primo e secondo suono in superfluidi piatti, e che sono la principale sonda della transizione di Berezinskii-Kosterlitz-Thouless. Concludiamo la nostra analisi mediante lo studio di solitoni chiari in miscele bosoniche unidimensionali, e discutendo la dinamica di tubi quasicondensati con effetto tunnel.Low-dimensional quantum gases, produced by confining and cooling atoms in two- or in one-dimensional configurations, display a rich variety of equilibrium and nonequilibrium properties. The emerging experimental techniques for controlling both their geometry and their topology, by trapping these systems, for instance, in rings or in hollow shells, offer a promising route for the investigation of quantum many-body physics in curved spatial domains. In this thesis, we discuss the quantum statistical properties of spherically-symmetric bosonic shells, analyzing the phenomena of Bose-Einstein condensation and of superfluidity in the finite-size two-dimensional regime. Adopting the functional integral formulation of quantum field theory, we obtain the finite-temperature equation of state of these shell-shaped systems, and, with similar techniques, also of two-dimensional flat superfluids, both bosonic and fermionic. Moreover, we quantitatively analyze the hydrodynamic excitations at finite temperature, which consist of the first and second sound in flat superfluids, and which are the main probe of the Berezinskii-Kosterlitz-Thouless superfluid transition. We conclude our analysis by studying bright solitons in one-dimensional Bose-Bose mixtures, and discussing the quench dynamics of tunneling quasicondensate tubes
Zero-Temperature Equation of State of a Two-Dimensional Bosonic Quantum Fluid with Finite-Range Interaction
Full text linkWe derive the two-dimensional equation of state for a bosonic system of ultracold atoms interacting with a finite-range effective interaction. Within a functional integration approach, we employ a hydrodynamic parameterization of the bosonic field to calculate the superfluid equations of motion and the zero-temperature pressure. The ultraviolet divergences, naturally arising from the finite-range interaction, are regularized with an improved dimensional regularization technique
Condensation and superfluidity of dilute Bose gases with finite-range interaction
Full text linkWe investigate an ultracold and dilute Bose gas by taking into account a finite-range two-body interaction. The coupling constants of the resulting Lagrangian density are related to measurable scattering parameters by following the effective-field-theory approach. A perturbative scheme is then developed up to the Gaussian level, where both quantum and thermal fluctuations are crucially affected by finite-range corrections. In particular, the relation between spontaneous symmetry breaking and the onset of superfluidity is emphasized by recovering the renowned Landau's equation for the superfluid density in terms of the condensate one
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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