1,720,976 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Cálculos de primeros principios de los parámetros del Modelo Estándar a escala del charm y más allá
No full textTesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de Lectura: 28-09-2023Esta tesis tiene embargado el acceso al texto completo hasta el 28-03-2025The search for new physics beyond the Standard Model (SM) is a
major endeavour in particle physics, and high precision comparisons
between experimental results and theoretical predictions can impose
stringent constraints on the proposed extensions. Fundamental processes
involving heavy quarks in the flavour sector play a crucial role
by giving access to many of the underlying parameters of the SM, a
successful theory with impressive levels of precision. For instance, in
recent years, the evidence of B-anomalies involving deviations from
the theory prediction in B-mesons decays has triggered both theoretical
and experimental investigations, aiming to uncover the possible
explanations, including the potential contributions from new physics
phenomena. In this context, Lattice QCD provides a first-principles
numerical approach for studying non-perturbative low-energy aspects
of the theory of the strong interaction with high accuracy. Whereas
in the light quark sector numerous calculations of fundamental parameters
have been tested using various setups, in the heavy sector
there are insufficient results and tested methodologies. Hence, it becomes
crucial to explore new strategies and approaches to ensure that
systematic uncertainties are effectively addressed and controlled.
In this thesis we present high precision results in the heavy quark
sector from Lattice QCD simulations with non-perturbative O(a)-
improved Wilson fermions and Nf = 2 + 1 dynamical flavours.
In the charm quark sector we exploit a mixed-action setup with maximally
twisted valence fermions. This approach ensures the absence
of O(a) effects proportional to heavy valence masses, thus achieving
the automatic improvement regime based on symmetry properties of
the regularization. We present precise determinations of the charm
quark mass and D(s) meson decay constants, which should improve
our current knowledge on the values of some SM parameters and
serve as sensitive probes for new physics effects.
In the bottom sector we present the first dynamical quarks calculation
of the b-quark mass with a novel approach, obtained by
combining Heavy Quark Effective Theory (HQET) and relativistic
computations together with step scaling in volume techniques to reach
by interpolation the b-quark scale and beyond. This lays the foundations
for ongoing works on transition amplitudes involving B-physics
observables, aiming at an upcoming precise determination of the |Vub| CKM matrix element.
The results described in this thesis aim to contribute to the ongoing
efforts to understand the fundamental nature of particles and their interactions, by helping to further constrain the world average results
of fundamental quantities in the heavy quark sectorLa búsqueda de nueva física más allá del Modelo Estándar (SM) es una
de las principales tareas de la física de partículas, y las comparaciones
de alta precisión entre los resultados experimentales y las predicciones
teóricas pueden imponer restricciones estrictas a las extensiones
propuestas. Los procesos fundamentales en los que intervienen quarks
pesados en el sector del sabor desempeñan un papel crucial al dar
acceso a muchos de los parámetros subyacentes del SM, una teoría
exitosa con impresionantes niveles de precisión. Por ejemplo, en los
últimos años, la evidencia de anomalías B que implican desviaciones
de la predicción de la teoría en desintegraciones de mesones B ha
desencadenado investigaciones tanto teóricas como experimentales,
con el objetivo de descubrir las posibles explicaciones, incluyendo las
contribuciones potenciales de nuevos fenómenos de la física. En este
contexto, la QCD en retículo ofrece una aproximación numérica de
primeros principios para estudiar con gran precisión aspectos no perturbativos
de baja energía de la teoría de la interacción fuerte. Mientras
que en el sector de los quarks ligeros se han probado numerosos cálculos
de parámetros fundamentales utilizando diversas metodologías,
en el sector pesado no hay suficientes resultados ni métodos probados.
De ahí que resulte crucial explorar nuevas estrategias y enfoques para
garantizar que las incertidumbres sistemáticas se abordan y controlan
eficazmente.
En esta tesis presentamos resultados de alta precisión en el sector
de los quarks pesados a partir de simulaciones de Lattice QCD
con fermiones de Wilson no-perturbativos O(a)-mejorados y sabores
dinámicos Nf = 2 + 1.
En el sector del quark charm explotamos una configuración de acción
mixta con fermiones de valencia máximamente “twisted”. Este
enfoque asegura la ausencia de efectos O(a) proporcionales a masas
de valencia pesadas, alcanzando así el régimen de improvement
automática basado en propiedades de simetría de la regularización.
Presentamos determinaciones precisas de la masa del quark charm y
de las constantes de decaimiento del mesón D(s), que deberían mejorar
nuestro conocimiento actual sobre los valores de algunos parámetros
del SM y servir como sondas sensibles para efectos de nueva física.
En el sector del bottom presentamos el primer cálculo de quarks
dinámicos de la masa del quark b, obtenido combinando la Heavy
Quark Effective Theory (HQET) y cálculos relativistas junto con técnicas
de step scaling en volumen para alcanzar por interpolación la
escala del quark b y más allá. Esto sienta las bases para los trabajos en curso sobre las amplitudes de transición que implican observables de
la física B, con el objetivo de una próxima determinación precisa del
elemento |Vub| de matriz CKM.
Los resultados descritos en esta tesis pretenden contribuir a los
esfuerzos en curso para comprender la naturaleza fundamental de
las partículas y sus interacciones, ayudando a restringir aún más los
resultados medios mundiales de las cantidades fundamentales en el
sector de los quarks pesado
Informazione quantistica e decoerenza: il caso dei qubit in centri NV
Get PDFLo scopo di questa tesi triennale è quello di fornire un'introduzione ad alcuni concetti della computazione quantistica e comprenderne i fenomeni fisici che ne stanno alla base, dall'idea astratta di qubit fino ai più recenti studi sui centri NV, passando attraverso appropriati strumenti matematici.
Recentemente si è realizzato che l'uso delle proprietà della meccanica quantistica può migliorare drasticamente le velocità di calcolo.
È quindi cresciuto l'interesse nel campo dell'informazione quantistica.
Tra le principali difficoltà vi è il fenomeno della decoerenza, responsabile della distruzione degli stati di sovrapposizione quanto-meccanici.
Studiamo la dinamica dei sistemi quantistici aperti, soffermandoci sugli aspetti della loro evoluzione rilevanti nel passaggio dal mondo quantico al classico. A tal fine, e per una migliore comprensione della decoerenza, ricaviamo l'equazione master cui deve obbedire la matrice di densità nel noto modello di Jaynes-Cummings per l'interazione ambiente-sistema.
In particolare, descriviamo come un ristretto set di manipolazioni sul sistema ci permetta di proteggerlo dalla decoerenza e come tale tecnica, detta disaccoppiamento dinamico, si rivela un utile strumento per la realizzazione di gates quantistici nel caso dei qubit implementati sfruttando i cosiddetti centri NV del diamante
Variations on the Author
Get PDF“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
Get PDFWe 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
Precision physics and the hadronic running of : a lattice perspective
No full textPrecision measurements are a powerful tool in the search for physics beyond the Standard Model, and their impact is often limited by our control of hadronic effects. After a brief mention of the muon anomaly as an example of this challenge, I will focus on the closely related quantity , the hadronic contribution to the running of the electromagnetic coupling. I will present a recent high-precision lattice QCD determination of the hadronic vacuum polarization in the Euclidean region, achieving sub-percent accuracy and confirming tensions at space-like virtualities with data-driven estimates based on cross sections. Using the Euclidean split technique, we obtain a precise determination of the running of up to the -pole and compare it with global electroweak fits. I will conclude with an outlook on future improvements and the precision targets set by the FCC-ee program. This talk complements Tuesday’s Lattice Coffee Talk, where methodological details will be presented.
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Primordial tensor modes from inflation and their detectability with GW experiments
Get PDFL'obbiettivo di questa tesi è lo studio delle fluttuazioni quantistiche dei modi tensoriali primordiali prodotti durante l'inflazione, con particolare attenzione alla possibilità di rilevare tali modi come onde gravitazionali di background.
Una eventuale rilevazione confermerebbe ulteriormente la validità dei modelli inflazionari. Tuttavia, la densità di energia predetta per le onde gravitazionali di background è di gran lunga inferiore alla sensibilità degli attuali rivelatori. In questo lavoro noi andiamo oltre l'inflazione slow-roll standard e analizziamo nuovi modelli che ci permettono di amplificare le perturbazioni tensoriali su scale al di fuori dell'orizzonte.
Introduciamo un meccanismo che sfrutta una fase transitoria di evoluzione non-attractor per amplificare i modi tensoriali. Procediamo poi con lo studio della fenomenologia del modello, dimostrando la possibilità di amplificare la densità di energia delle onde gravitazionali fino alle scale accessibili dai rivelatori LISA, aLIGO e PTA. Calcoliamo poi il numero di e-folds di fase non-attractor necessari per assicurare la rivelazione di tali onde.
Successivamente, presentiamo un nuovo modello di bigravità, caratterizzato da un termine di accoppiamento tra un tensore privo di massa ed uno massivo.
Presentiamo un'analisi dettagliata della dinamica dei due campi tensoriali, derivando vincoli che la massa del campo deve soddisfare per poter amplificare le fluttuazioni prive di massa.
Infine, assumiamo che l'accoppiamento sia dominante per un certo numero di e-folds durante l'inflazione e diamo una stima di tale valore per i tre rivelatori sopracitati
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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