1,721,019 research outputs found
Two-dimensional attractive fermi gas : balanced and highly polarized regimes at zero temperature
Full text linkWe study a two dimensional two species Fermi gas with attractive short-range interactions at zero
temperature, both in the unpolarized regime, which shows a BCS-BEC crossover type of superfluid
ground state, and in the highly polarized regime, corresponding to an impurity immersed in a Fermi
sea, which exhibits a transition from a polaronic to a molecular ground state. We use Diffusion Monte Carlo with Fixed Node approximation in order to calculate the energy per particle and extract the effective interactions among composite particles in the strongly interacting regime, where beyond mean field effects are crucial. In the impurity regime we calculate the evolution of the quasiparticle weight in the attractive polaronic branch as a function of the coupling. We also discuss the relevance of these results to ongoing experiments
Impurity in a Bose-Einstein condensate: study of the attractive and repulsive branch using quantum Monte-Carlo methods
No full textWe investigate the properties of an impurity immersed in a dilute Bose gas at zero temperature using quantum
Monte Carlo methods. The interactions between bosons are modeled by a hard-sphere potential with scattering
length a, whereas the interactions between the impurity and the bosons are modeled by a short-range, square-well
potential where both the sign and the strength of the scattering length b can be varied by adjusting the well depth.
We characterize the attractive and the repulsive polaron branch by calculating the binding energy and the
effective mass of the impurity. Furthermore, we investigate the structural properties of the bath, such as the
impurity-boson contact parameter and the change of the density profile around the impurity. At the unitary limit
of the impurity-boson interaction, we find that the effective mass of the impurity remains smaller than twice its
bare mass, while the binding energy scales with , where n is the density of the bath and m is the common
mass of the impurity and the bosons in the bath. The implications for the phase diagram of binary Bose-Bose
mixtures at low concentrations are also discussed
I multiformi ruoli nell’occhio del fattore di crescita basico dei fibroblasti (bFGF)
No full textLa comunicazione tra cellule è cruciale per lo sviluppo e la sopravvivenza degli organismi pluricellulari. Parte di questo intenso scambio d’informazioni è a carico dei fattori di crescita, un’ampia famiglia di polipeptidi che liberati nell’ambiente extracellulare, sono in grado di stimolare la proliferazione cellulare. I fattori di crescita propriamente detti sono quelli che controllano l’ingresso e la progressione delle cellule nel ciclo replicativi, ma in realtà la loro funzione può estendersi anche al controllo di processi differenziativi e di alcune funzioni metaboliche. Uno di questi fattori è il bFGF la cui azione si estrinseca sui fotorecettori retinici, sulle cellule gangliari retiniche, sulle cellule dell’epitelio pigmentato retinico, sulle cellule melanocitiche del melanoma, sulle cellule endoteliali e sui periciti, con multiformi aspetti sulla cornea, sulle cellule epiteliali del cristallino e sulle ghiandole lacrimali e sebacee palpebrali. In conclusione vengono prospettati i possibili trattamenti terapeutici con questo fattore di crescit
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
Quantum Monte Carlo study of the dynamic structure factor in the gas and crystal phase of hard-sphere bosons
No full textWe investigate the dynamic structure factor of a system of Bose particles at zero temperature using quantum Monte Carlo methods. Interactions are modeled using a hard-sphere potential of size a and simulations are performed for values of the gas parameter na3 ranging from the dilute regime up to densities n where the thermodynamically stable phase is a solid. With increasing density, we observe a crossover of the dispersion of elementary excitations from a Bogoliubov-type spectrum to a phonon-maxon-roton curve and the emergence of a broad multiphonon contribution accompanying the single-quasiparticle peak. In particular, for na3=0.2138, which corresponds to superfluid 4He at equilibrium density, the extracted spectrum turns out to be in good agreement with the experimental energy-momentum dispersion relation in the roton region and for higher momenta. The behavior of the spectral function at the same density in the stable solid and metastable gas phase above the freezing point is also discussed
Critical temperature of Bose Einstein condensation in trapped atomic Bose-Fermi mixtures
No full textDensity profiles of polarized Fermi gases confined in harmonic traps
Full text linkOn the basis of the phase diagram of the uniform system, we calculate the density profiles of a trapped polarized Fermi gas at zero temperature using the local density approximation. By varying the overall polarization and the interaction strength, we analyze the appearance of a discontinuity in the profile, signaling a first-order phase transition from a superfluid inner core to a normal outer shell. The local population imbalance between the two components and the size of the various regions of the cloud corresponding to different phases are also discussed. The calculated profiles are quantitatively compared with the ones recently measured by Shin [Phys. Rev. Lett. 101, 070404 (2008)]
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