CBPF - Publicações Revistas
Not a member yet
262 research outputs found
Sort by
Modular localization and the holistic structure of causal quantum theory, a historical perspective
Get PDFRecent insights into the conceptual structure of localization in QFT ("modular localization") led to clarications of old unsolved problems.The oldest one is the Einstein-Jordan conundrum which led Jordan in1925 to the discovery of quantum eld theory. This comparison of fluctuations in subsystems of heat bath systems (Einstein) with those resulting from the restriction of the QFT vacuum state to an open subvolume (Jordan) leads to a perfect analogy; the globally pure vacuum state becomes upon local restriction a strongly impure KMS state. This phenomenon of localization-caused thermal behavior as well as the vacuum-polarization clouds at the causal boundary of the localization region places localization n QFT into a sharp contrast with quantum mechanics and justies the attribute "holstic". In fact it positions the E-J Gedankenexperiment into the same conceptual category as the cosmological constant problem and the Unruh Gedankenexperiment. The holistic structure of QFT resulting from "modular localization" also leads to a revision of the conceptual origin of the crucial crossing property which entered particle theory at the time of the bootstrap S-matrix approach but suered from incorrect use in the S-matrix settings of the dual model and string theory. The new holistic point of view, which strengthens the autonomous aspect of QFT, also comes with new messages for gauge theory by exposing the clash between Hilbert space structure and localization and presenting alternative solutions based on the use of stringlocal elds in Hilbert space. Among other things this leads to a radical reformulation of the Englert- Higgs symmetry breaking mechanism
The Periodic Table of the Elements: The search for transactinides and beyond
Get PDFThe Periodic Table of Mendeleev, initially proposed on the basis of 66 elements, and containing 82 elements at the time of Moseley (1887−1915), describes nowadays 118 elements. The huge challenge of this scientific adventure was, and still is, the development of technologies and methods capable of producing elements of atomic number Z > 103, known as superheavy elements (SHE), or transactinides. This paper presents a survey of experiments and theoretical approaches that led physicists and chemists of today to discover and characterize a number of SHE isotopes. A glance is also given to the feasibility studies performed by scientists aiming to going beyond Z = 118, building-up further neutron-rich nuclides and reaching the ultimate goal of creating long-living new elements at the edge of the Table
Ronald Shellard, quatro décadas de amizade verdadeira e grande admiração
Get PDFEdição Especial em homenagem a Ronald C. Shellar
From UCLA to CBPF and the University of Virginia : A scientific journey of two friends, Ronald Cintra Shellard and P. Q. Hung
No full textEdição Especial em homenagem a Ronald C. Shellar
Using Deep Learning Transformer Networks to Identify Symptoms Associated with COVID-19 on Twitter
Get PDFThis study aims to present a methodology to identify, through Twitter posts, predefined symptomsof COVID-19 aided by Deep Learning techniques, namely Transformers Networks. The proposed approachwas evaluated on a public Twitter database in Brazilian Portuguese, using user reports of COVID-19 symptoms.We mine the Twitter database, extract phrases with symptoms, compare distributions, and build a database toconstruct high accuracy Deep Learning networks, which can be used to identify symptoms. We use a crossvalidationprocedure to evaluate the result’s performance. Additionally, we interpret the results using a LocalInterpretable Model-Agnostic Explanations (LIME) algorithm. We identified 907 tweets containing one or moreof the 14 previously chosen COVID-19 symptoms. The most frequently reported symptoms were a cough (392),headache (154), runny nose (143), fever (124), nausea (106), and diarrhea (105) amongst users who reported atleast one symptom. The BERT architecture identified all 14 symptoms reported in Twitter phrases in Portuguese,resulting in identifying each symptom with over 97% accuracy and over 0.95 of AUC-ROC at the test dataset.This project is a step towards a complementary tool to identify symptoms in future automated clinical settings,e.g., medical chatbots, to support faster clinical assessment in Portuguese
A computational algorithm for determining the parameters of a spectral line
Get PDFEste trabalho apresenta o desenvolvimento e a valida\c{c}\~{a}o de um algoritmo computacional cuja finalidade \'{e} ajustar linhas isoladas de um espectro \'{o}ptico obtendo os valores para os par\^{a}metros de um perfil Voigt ou Pseudo-Voigt. A recupera\c{c}\~{a}o destes par\^{a}metros \'{e} importante para o estudo do espectro de emiss\~{a}o de plasma produzido por laser. Os espectros testados foram bem aproximados pelas fun\c{c}\~{o}es ajustadas e a rotina de ajuste mostrou-se muito promissora para linhas espectrais isoladas. O m\'{e}todo \'{e} avaliado e testado usando linhas simuladas e aplicado a dados experimentais da linha \textit{H} (656,273 nm) do hidrog\^{e}nio. Os par\^{a}metros do ajuste foram utilizados para determinar a densidade e a temperatura do plasma
Ronald Cintra Shellard, física de altas energias e colaborações internacionais
Get PDFEdição Especial em homenagem a Ronald C. Shellar
