1,720,997 research outputs found
Biological Recursion and Digital Systems: Conceptual Tools for Analysing Man-Machine Interaction
No full textThe theory of numbers, the theory of computation and well-known biological and neurological studies on cognition and consciousness all indicate the concept of recursion as their common denominator. Mathematical recursion owes its meaning and properties to a dual relationship between its results, which always constitute a sequence, and the operator that generated them, which is instead invariant. This article proposes that this duality in recursion originates from the duality between the biological homeostatic equilibrium in living systems and the adaptive physico-chemical changes required to sustain such equilibria. Such duality gives order and meaning to the experiences of a living system. One of the many implications of this innovative perspective is that this duality can decouple computational results from our intuitive order relations, and that this can cause a rarefaction of the capacity of digital systems to convey communication and favour adaptation to the environment
Electronic properties and interlayer coupling of twisted MoS2/NbSe2 heterobilayers
No full textIn this paper we present first-principles calculations, based on both density functional theory and maximallylocalized Wannier functions, to study the electronic properties and interlayer coupling of twisted MoS2/NbSe2heterobilayers. We accurately investigate different stacking configurations and commensurate twist anglesby including an in-depth analysis of the interlayer van der Waals interaction. The metallic character of theinvestigated heterostructures is dominated, at the Fermi energy, by the NbSe2atomic orbitals and shows astrong dependence on the twist angle. Notably, at the smallest considered twist angle, band structure flatteningat the Fermi energy shows up, which should result in a lower conductivity of the metallic heterobilayer.The electrostatic potential analysis reveals no significant modification of the potential pattern with respect tothe potentials of the isolated layers, with the exception of the interface region. A moderate electronic chargeredistribution, compatible with electronically weakly coupled layers, is set up following the formation of theinterface. The dependence of the electronic structure on the twist angle acts as a new degree of freedom fortuning properties relevant in electronic device applications
PHONON-PLASMON COOPERATIVE EFFECTS IN THE DILUTE LARGE-BIPOLARON GAS - A POSSIBLE MECHANISM FOR HIGH-TC SUPERCONDUCTIVITY
No full textA Hamiltonian for two interacting electrons coupled with longitudinal phonons and plasmons is wt up. The phonons are treated in the Frohlich scheme and the plasmons in the single-pole approximation. We are interested in systems with low electron density (n less-than-or-equal-to 10(20)-10(21)) such as high-T(c) superconductors. It is shown that, in this density range, the electron dynamics do not simply screen the electrostatic interaction but, also, cooperates to the bipolaron formation. Furthermore we find that the binding energies and the effective mass depend on the electronic density. The features of the effective electron-electron potential are discussed, mainly for what concerns the self-energy terms and the long-range tail; the former depends on the pair state and the second shows that the plasmon field tends to screen all the electrostatic interactions, even the electron-phonon one. It is also shown that the Hamiltonian formulation is equivalent to a dielectric formulation where the total dielectric function of the system is the sum of the dielectric function appropriate for an ionic of the system is the sum of the dielectric function appropriate for an ionic material and that appropriate for the electron gas. Within this model we calculate the Bose-condensation critical temperature of a system of correlated pairs and free carriers in a two-fluid model at thermodynamical equilibrium
POLARON AND BIPOLARON COEXISTENCE IN HIGH T-C SUPERCONDUCTIVITY
No full textA model for high T-c superconductivity in which polarons and bipolarons coexist is studied. The bipolarons are assumed to be in a bound or resonant state depending on the total charge carrier density and are allowed to decay into a pair of independent polarons. The critical temperature as a function of the total charge carrier density and of the ratio of the superconducting density to the superconducting charge carrier mass is calculated and compared with the experimental data. It is shown that the dependence on the total charge carrier density of the bipolaron resonant energy and of the bipolaron-polaron decay probability is important in order to obtain a satisfactory agreement with the experimental data
On the boson-fermion model of superconductivity
No full textThe existence of pair excitations in a Fermi gas interacting via a short-range attractive potential is investigated. Within the ladder approximation to the Bethe-Salpeter equation for the effective two-particle interaction, evidence of pair excitation is found at energies slightly larger than the chemical potential. The link between those excitations and a boson-fermion model of superconductivity (Phys. Lett. A, 196 (1995) 359) is discussed. In particular it is shown that the charge carrier density dependence of the pair excitation (boson) energy, assumed phenomenologically in the boson-fermion model, is consistent with the properties of the interacting Fermi gas studied. These results give support to the microscopic origin of the phenomenological boson-fermion model of superconductivity
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
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