1,720,973 research outputs found
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
Dynamiques de l'intrication et des corrélations dans les simulateurs quantiques
No full textQuantum simulation platforms such as cold atoms, superconducting circuits, and trapped ions enable the experimental investigation of quantum many-body systems, with important implications for quantum technologies. In this thesis, we investigate how entanglement and correlations develop in such systems and how they can be harnessed both for the theoretical study of models relevant to condensed matter physics and for practical applications in quantum metrology. We begin by focusing on the adiabatic preparation of quantum many-body ground states. In particular, we show that quantum simulators can probe the link between spectral degeneracy and Spontaneous Symmetry Breaking, as pioneered by P.W. Anderson. We prove that odd-sized spin-½ systems exhibiting time-reversal symmetry sustain a net magnetization even away from the thermodynamic limit, thanks to an exact spectral degeneracy. Moreover, the symmetry-broken state exhibits scalable spin squeezing, a key resource for quantum metrology. We then turn to a different paradigm of evolution: quench dynamics. In particular, we show that monitoring the real-time evolution of correlations allows for the experimental measurement of the dispersion relation of fundamental excitations. In the case of two-dimensional long-range ordered systems, such as the dipolar XY model, these excitations are spin waves, leading to sharp features in the evolution of two-point correlation functions. Conversely, in one-dimensional systems, fundamental excitations have a fermionic nature, and their detection requires the measurement of non-local correlation functions. The latter, while inaccessible in condensed matter, are instead well suited to quantum simulators with individually addressable degrees of freedom.Les plateformes de simulation quantique telles que les atomes froids, les circuits supraconducteurs et les ions piégés permettent l'étude expérimentale des systèmes quantiques à plusieurs corps, avec des implications majeures pour les technologies quantiques. Dans cette thèse, nous étudions comment l'intrication et les corrélations se développent dans de tels systèmes, et comment elles peuvent être exploitées à la fois pour l'étude théorique de modèles pertinents en physique de la matière condensée, et pour des applications pratiques en métrologie quantique. Nous commençons par nous concentrer sur la préparation adiabatique des états fondamentaux de systèmes quantiques à plusieurs corps. En particulier, nous montrons que les simulateurs quantiques peuvent sonder le lien entre la dégénérescence spectrale et la brisure spontanée de symétrie, tel que formulé par P.W. Anderson. Nous démontrons que des systèmes de spins 1/2 en nombre impair, présentant une symétrie de renversement temporel, possèdent une aimantation nette même en dehors de la limite thermodynamique, grâce à une dégénérescence spectrale exacte. De plus, l'état à symétrie brisée présente de la compression de spin (spin squeezing) qui croit d'autant plus que le système est grand, une ressource clé pour la métrologie quantique. Nous nous tournons ensuite vers un autre paradigme d'évolution : la dynamique de quench. En particulier, nous montrons que le suivi de l'évolution en temps réel des corrélations permet la mesure expérimentale de la relation de dispersion des excitations fondamentales. Dans le cas de systèmes bidimensionnels à ordre à longue portée, comme le modèle XY dipolaire, ces excitations sont des ondes de spin, menant à des signatures marquées dans l'évolution des fonctions de corrélation à deux points. En revanche, dans les systèmes unidimensionnels, les excitations fondamentales ont une nature fermionique, et leur détection nécessite la mesure de fonctions de corrélation non locales. Ces dernières, inaccessibles en matière condensée, sont en revanche particulièrement adaptées aux simulateurs quantiques disposant de degrés de liberté adressables individuellement
Dynamiques de l'intrication et des corrélations dans les simulateurs quantiques
No full textQuantum simulation platforms such as cold atoms, superconducting circuits, and trapped ions enable the experimental investigation of quantum many-body systems, with important implications for quantum technologies. In this thesis, we investigate how entanglement and correlations develop in such systems and how they can be harnessed both for the theoretical study of models relevant to condensed matter physics and for practical applications in quantum metrology. We begin by focusing on the adiabatic preparation of quantum many-body ground states. In particular, we show that quantum simulators can probe the link between spectral degeneracy and Spontaneous Symmetry Breaking, as pioneered by P.W. Anderson. We prove that odd-sized spin-½ systems exhibiting time-reversal symmetry sustain a net magnetization even away from the thermodynamic limit, thanks to an exact spectral degeneracy. Moreover, the symmetry-broken state exhibits scalable spin squeezing, a key resource for quantum metrology. We then turn to a different paradigm of evolution: quench dynamics. In particular, we show that monitoring the real-time evolution of correlations allows for the experimental measurement of the dispersion relation of fundamental excitations. In the case of two-dimensional long-range ordered systems, such as the dipolar XY model, these excitations are spin waves, leading to sharp features in the evolution of two-point correlation functions. Conversely, in one-dimensional systems, fundamental excitations have a fermionic nature, and their detection requires the measurement of non-local correlation functions. The latter, while inaccessible in condensed matter, are instead well suited to quantum simulators with individually addressable degrees of freedom.Les plateformes de simulation quantique telles que les atomes froids, les circuits supraconducteurs et les ions piégés permettent l'étude expérimentale des systèmes quantiques à plusieurs corps, avec des implications majeures pour les technologies quantiques. Dans cette thèse, nous étudions comment l'intrication et les corrélations se développent dans de tels systèmes, et comment elles peuvent être exploitées à la fois pour l'étude théorique de modèles pertinents en physique de la matière condensée, et pour des applications pratiques en métrologie quantique. Nous commençons par nous concentrer sur la préparation adiabatique des états fondamentaux de systèmes quantiques à plusieurs corps. En particulier, nous montrons que les simulateurs quantiques peuvent sonder le lien entre la dégénérescence spectrale et la brisure spontanée de symétrie, tel que formulé par P.W. Anderson. Nous démontrons que des systèmes de spins 1/2 en nombre impair, présentant une symétrie de renversement temporel, possèdent une aimantation nette même en dehors de la limite thermodynamique, grâce à une dégénérescence spectrale exacte. De plus, l'état à symétrie brisée présente de la compression de spin (spin squeezing) qui croit d'autant plus que le système est grand, une ressource clé pour la métrologie quantique. Nous nous tournons ensuite vers un autre paradigme d'évolution : la dynamique de quench. En particulier, nous montrons que le suivi de l'évolution en temps réel des corrélations permet la mesure expérimentale de la relation de dispersion des excitations fondamentales. Dans le cas de systèmes bidimensionnels à ordre à longue portée, comme le modèle XY dipolaire, ces excitations sont des ondes de spin, menant à des signatures marquées dans l'évolution des fonctions de corrélation à deux points. En revanche, dans les systèmes unidimensionnels, les excitations fondamentales ont une nature fermionique, et leur détection nécessite la mesure de fonctions de corrélation non locales. Ces dernières, inaccessibles en matière condensée, sont en revanche particulièrement adaptées aux simulateurs quantiques disposant de degrés de liberté adressables individuellement
Equazione differenziale omogenea di secondo ordine per il grafico sunrise a 2-loop con masse arbitrarie
Full text linkÈ noto da [1] che è possibile, attraverso le Integration by Part identities (IbP identities) esprimere un qualsiasi diagramma di Feynman di topologia definita (ovvero definito da un certo set di propagatori) in termini di un numero finito di integrali comunemente noti come master integrals. In [4] è stato dimostrato che, dato un diagramma esprimibile in termini di n master integrals, le IbP identities possono essere ulteriormente sfruttate per ottenere un sistema lineare di equazioni differenziali al prim'ordine per i master integral stessi. Questo equivale a formulare un'equazione differenziale di ordine n-esimo, le cui n soluzioni sono, appunto, i master integrals relativi al diagramma di Feynman oggetto di studio. Poiché il sunrise a 2-loop a masse diverse è esprimibile in termini di 4 master integrals è lecito attendersi che l'equazione differenziale ad esso associata sia di quarto ordine. Tuttavia già in [5] è stato mostrato che in realtà è possibile ottenere un'equazione al secondo ordine per tale diagramma di Feynman. L'obiettivo principale di questa trattazione è quello di calcolare il max cut del sunrise a 2-loop a masse diverse, che rappresenta la soluzione della parte omogenea dell'equazione differenziale associata al diagramma, e quindi, attraverso una sorta di operazione di "reverse engineering", ricostruire la parte omogenea dell'equazione differenziale associata al sunrise a 2-loop a masse diverse
Machine learning approach to the extended Hubbard model
Full text linkThe 1d extended Hubbard model with soft-shoulder potential has proved itself
to be very difficult to study due its non solvability and to competition between terms of the Hamiltonian. Given this, we tried to investigate its phase diagram for filling n=2/5 and range of soft-shoulder potential r=2 by using Machine Learning techniques. That led to a rich phase diagram; calling U, V the parameters associated to the Hubbard potential and the soft-shoulder potential respectively, we found that for V3 the system is always in Tomonaga Luttinger Liquid phase, then becomes a Cluster Luttinger Liquid for 57, with a quasi-perfect crystal in the U5 region. Finally we found that for U2-3 the system shall maintain the Cluster Luttinger Liquid structure, with a residual in-block single particle mobility
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