1,721,096 research outputs found
A microscopic approach to thermophoresis in colloidal suspensions
No full textWe present a general description of thermophoretic phenomena in dilute suspensions of spherical colloids which lie at the basis of the Ludwig/Soret effect. We first consider how a thermal gradient affects a homogeneous fluid showing that, to linear order, no momentum flux is generated in the bulk. The presence of a colloidal particle, however, modifies the pressure tensor of the fluid, thereby creating a velocity field in the neighbourhood of the surface of the colloid, which can be calculated by use of the Navier–Stokes equation. As a consequence, momentum transfer to the colloid takes place. When this effective force is substituted into a Smoluchowski equation for the particle motion, we arrive at a simple and general expression of the Soret coefficient in terms of the colloid–liquid surface tension
First-order phase transitions, the Maxwell construction, and the momentum-space renormalization group
No full textThe behavior of a nonperturbative momentum-space renormalization group (RG) is analyzed both above and below the critical temperature. The case of a scalar order parameter and of the Ising model is studied in detail by analytical and numerical means. It is shown that this RG transformation is always well defined even inside the coexistence curve. van der Waals loops are suppressed by long-wavelength fluctuations which enforce the convexity of the free energy. The RG description emerging from this study is then compared with exact results and other approximate theories
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
Self-induced density modulations in the free expansion of Bose-Einstein condensates
No full textWe simulate numerically the free expansion of a repulsive Bose-Einstein condensate with an initially Gaussian density profile. We find a self-similar expansion only for weak interatomic repulsion. In contrast, for strong repulsion we observe the spontaneous formation of a shock wave at the surface followed by a significant depletion inside the cloud. In the expansion, contrary to the case of a classical viscous gas, the quantum fluid can generate radial rarefaction density waves with several minima and maxima. These intriguing nonlinear effects, never observed in free-expansion experiments with ultracold alkali-metal atoms, can be detected with the available setups
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
Partecipazione e didattiche per l’apprendimento nella scuola aperta
No full textAldo Visalberghi ci ha offerto un’interessante interpretazione di una “scuola aperta”
(1960), che delinea un’architettura, pedagogica, e ne traccia un preliminare manifesto,
di una certa attualità.
Un’idea di “scuola aperta”, innanzitutto, ad accogliere una vitale molteplicità
di posizioni e di apporti diversi, disegno di quanto possiamo attribuire a una composizione
plurale, multiculturale, che sa farsi sguardo interculturale, poiché «volta
a promuovere la discussione impegnativa e pur mai definitiva, a suscitare il dialogo
genuino, a realizzarsi insomma come ricerca in comune, ricerca sempre aperta,
alla critica e alla rettifica e all’ulteriore sviluppo» (Visalberghi, 1960, p. IX). Differenti
culture in relazione, approcci, traiettorie, metodologie, innervate nella storicità
degli eventi che sono in grado di trovare sintesi nella ricerca “in” comune,
attraversata da una tensione di cultura del miglioramento, che opera continuamente
(on-going) in “rettifica” e “ulteriore sviluppo
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
An unconstrained DFT approach to microphase formation and application to binary Gaussian mixtures
Full text linkThe formation of microphases in systems of particles interacting by repulsive, bounded potentials is studied by means of density-functional theory (DFT) using a simple, mean-field-like form for the free energy which has already been proven accurate for this class of soft interactions. In an effort not to constrain the configurations available to the system, we do not make any assumption on the functional form of the density profile rho(r), save for its being periodic. We sample rho(r) at a large number of points in the unit cell and minimize the free energy with respect to both the values assumed by rho(r) at these points and the lattice vectors which identify the Bravais lattice. After checking the accuracy of the method by applying it to a one-component generalized exponential model (GEM) fluid with pair potential. exp[-(r/R)(4)], for which extensive DFT and simulation results are already available, we turn to a binary mixture of Gaussian particles which some time ago was shown to support microphase formation [A. J. Archer, C. N. Likos, and R. Evans, J. Phys.: Condens. Matter 16, L297 (2004)], but has not yet been investigated in detail. The phase diagram which we obtain, that supersedes the tentative one proposed by us in a former study [M. Carta, D. Pini, A. Parola, and L. Reatto, J. Phys.: Condens. Matter 24, 284106 (2012)], displays cluster, tubular, and bicontinuous phases similar to those observed in block copolymers or oil/water/surfactant mixtures. Remarkably, bicontinuous phases occupy a rather large portion of the phase diagram. We also find two non-cubic phases, in both of which one species is preferentially located inside the channels left available by the other, forming helices of alternating chirality. The features of cluster formation in this mixture and in GEM potentials are also compared
Particle thermophoresis in liquids
No full textWe present a microscopic description of thermophoretic phenomena in dilute suspensions of spherical colloids. The specific particle/solvent interfacial interactions generate a force density field on the surrounding fluid which in turn gives rise to an effective force on the colloid. In our approach, such a force turns out to be solely related to the non-conservative anisotropic contribution to brought forth by the thermal gradient. By adopting a Smoluchowski picture of colloid motion, we find a general expression for the Soret coefficient ST, which we apply to the specific cases of neutral colloids in pure solvent and of Debye-Hückel systems. For the latter, our result for ST agrees with those obtained by previous hydrodynamic approaches
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