1,720,988 research outputs found
Mass imbalance effect in resonant Bose-Fermi mixtures
Full text linkWe consider a homogeneous Bose-Fermi mixture, with the boson-fermion interaction tuned by a Fano-Feshbach
resonance, in the presence of mass and density imbalance between the two species. By using many-body
diagrammatic methods, we first study the finite-temperature phase diagram for the specific case of the mass-imbalanced
mixture 87Rb-40K for different values of the density imbalance. We then analyze the quantum
phase transition associated with the disappearance at zero temperature of the boson condensate above a critical
boson-fermion coupling. We find a pronounced dependence of the critical coupling on the mass ratio and a weak
dependence on the density imbalance. For a vanishingly small boson density, we derive, within our approximation,
the asymptotic expressions for the critical coupling in the limits of small and large mass ratios. These expressions
are relevant also for the polaron-molecule transition in a Fermi mixture at small and large mass ratios. The analysis
of the momentum distribution functions at sufficiently large density imbalances shows an interesting effect in the
bosonic momentum distribution due to the simultaneous presence of composite fermions and unpaired fermions
Pairing and condensation in a resonant Bose-Fermi mixture
Full text linkWe study by diagrammatic means a Bose-Fermi mixture, with boson-fermion coupling tuned by a Fano- Feshbach resonance. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling. Such quantum critical point depends very weakly on the population imbalance and, for vanishing boson densities, coincides with that found for the polaron-molecule transition in a strongly imbalanced Fermi gas, thus bridging two quite distinct physical systems
Single-particle spectral functions in the normal phase of a strongly attractive Bose-Fermi mixture
Full text linkWe calculate the single-particle spectral functions and quasiparticle dispersions for a Bose-Fermi mixture
when the boson-fermion attraction is sufficiently strong to suppress completely the condensation of bosons at
zero temperature. Within a T-matrix diagrammatic approach, we vary the boson-fermion attraction from the
critical value where the boson condensate first disappears to the strongly attractive (molecular) regime and study
the effect of both mass and density imbalance on the spectral weights and dispersions. An interesting spectrum
of particle-hole excitations mixing two different Fermi surfaces is found. These unconventional excitations could
be produced and explored experimentally with radio-frequency spectroscopy
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 a resonant Bose-Fermi mixture
Full text linkWe study resonant Bose-Fermi mixtures at zero temperature, with different relative concentrations
of the bosons. We use for the first time a Quantum Monte Carlo method with Fixed-Node approxima-
tion, to explore the system from the weak to the strong coupling limit. A repulsive interaction among
bosons is introduced to provide stability to the bosonic component. Beyond the unitarity limit, the res-
onant attractive interaction supports a bound fermionic dimer. At the many-body level, increasing the
boson-fermion coupling the system undergoes a quantum phase transition from a state with condensed bosons immersed in a Fermi sea, to a normal Fermi-Fermi mixture of the composite fermions and the bare fermions in excess. We obtain the equation of state and we characterize the momentum distributions both in the weakly and in the strongly interacting limits. We compare Quantum Monte Carlo results to T-matrix calculations, finding interesting signatures of the different many-body ground states
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
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