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Time series clustering of air quality monitoring stations – The study case of the Beijing municipality

AIP Conference Proceedings 2024年第1期3094卷

作者： Gabriel Chicale Cossa Marco Costa A. Manuela Gonçalves Escola Superior de Negócios e Empreendedorismo de Chibuto Universidade Eduardo Mondlane Vila do Chibuto - Gaza Mozambique University of Aveiro ESTGA – Águeda School of Technology and Management & CIDMA – Centre for Research and Development in Mathematics and Applications Campus Universitário de Santiago 3810-193 Aveiro Portugal University of Minho Department of Mathematics & Centre of Mathematics Campus de Azurém 4800-058 Guimarães Portugal

Since air pollution is a major public health concern, collecting and analyzing air quality indicators data is very important for monitoring pollution. Data on these indicators are generally collected through air quality monitoring stations located in specific areas. In this study, 12 monitoring sites belonging to the Beijing Municipal Environmental Monitoring center air pollution monitoring network are clustered based on their similarity in terms of hourly or monthly concentrations of some air pollutants. The hourly data was collected from these stations between March 2013 and February 2017. The clustering procedure was performed through average linkage and partitioning around medoids algorithms. The preliminary results obtained from the hierarchical algorithm show the presence of two clusters that are well distinguished with meaningful interpretation while the two obtained from the partitional algorithm are not well distinguished.

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The effect of Skyrme-Chern-Simons dynamics on gauged Skyrmions in 2+1 dimensions

arXiv

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arXiv 2023年

作者： Navarro-Lérida, Francisco Radu, Eugen Tchrakian, D.H. Departamento de Física Teórica IPARCOS Ciencias Físicas Universidad Complutense de Madrid MadridE-28040 Spain Departamento de Matemática Universidade de Aveiro Center for Research and Development in Mathematics and Applications Campus de Santiago Aveiro3810-183 Portugal School of Theoretical Physics Dublin Institute for Advanced Studies Burlington Road Dublin 4 Ireland Department of Computer Science National University of Ireland Maynooth Maynooth Ireland

We study the Skyrmion of the SO(2) gauged O(3) sigma model in 2 + 1 dimensions in the presence of a Skyrme–Chern-Simons (SCS) term, and compare its properties with the corresponding properties of the Skyrmion in the presence of the usual Chern-Simons (CS) term. We find that these properties are qualitatively largely similar in both cases, meaning that the SCS density can be employed as an alternative to the CS term also in higher dimensions, most importantly in even dimensions where no CS term is defined, e.g., in 3 + 1 dimensions. The SCS density employed here is defined in terms of the pair of SO(2) × SO(2) gauge fields and an auxiliary O(5) Skyrme scalar, which is contracted to an effective O(3) Skyrme scalar. Technically, this study maps the methods to be applied in higher dimensional examples. Copyright © 2023, The Authors. All rights reserved.

关键词： Quantum theory

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Spontaneous vectorization of electrically charged black holes

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Physical Review D 2021年第4期103卷 044004-044004页

作者： João M. S. Oliveira Alexandre M. Pombo Centro de Astrofísica e Gravitação—CENTRA Departamento de Física Instituto Superior Técnico—IST Universidade de Lisboa—UL Avenida Rovisco Pais 1 1049-001 Lisboa Portugal Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA) Campus de Santiago 3810-183 Aveiro Portugal

In this work, we generalize the spontaneous scalarization phenomena in Einstein-Maxwell-scalar models to a higher spin field. The result is an Einstein-Maxwell-vector model wherein a vector field is nonminimally coupled to the Maxwell invariant by an exponential coupling function. We show that the latter guarantees the circumvention of an associated no-hair theorem when the vector field has the form of an electric field. Different than its scalar counterpart, the new spontaneously vectorized Reissner-Nordström (RN) black holes are, always, undercharged while being entropically preferable. The solution profile and domain of existence are presented and analyzed.

关键词： Alternative gravity theories Classical black holes General relativity

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The role of the Callan-Witten anomaly density as a Chern-Simons term in Skyrme model

arXiv

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arXiv 2023年

We consider axially symmetric solutions of the U(1) gauged Skyrme model supplemented with a Callan-Witten (CW) anomaly density term. The main properties of the solutions are studied, several specific features introduced by the presence of the CW term being identified. We find that the solitons possess a nonzero angular momentum proportional to the electric charge, which in addition to the usual Coulomb part, acquires an extra (topological) contribution from the CW term. Specifically, it is shown that the slope of mass/energy M vs. electric charge Qe and angular momentum J can be both positive and negative. Furthermore, it is shown that the gauged Skyrmion persists even when the quartic (Skyrme) kinetic term disappears. Copyright © 2023, The Authors. All rights reserved.

关键词： Angular momentum

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Virial identities in relativistic gravity: 1D effective actions and the role of boundary terms

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Physical Review D 2021年第10期104卷 104051-104051页

作者： Carlos A. R. Herdeiro João M. S. Oliveira Alexandre M. Pombo Eugen Radu Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA) Campus de Santiago 3810-183 Aveiro Portugal Centro de Astrofísica e Gravitação—CENTRA Departamento de Física Instituto Superior Técnico—IST Universidade de Lisboa—UL Avenida Rovisco Pais 1 1049-001 Lisboa Portugal

Virial (aka scaling) identities are integral identities that are useful for a variety of purposes in nonlinear field theories, including establishing no-go theorems for solitonic and black hole solutions, as well as for checking the accuracy of numerical solutions. In this paper, we provide a pedagogical rationale for the derivation of such integral identities, starting from the standard variational treatment of particle mechanics. In the framework of one-dimensional (1D) effective actions, the treatment presented here yields a set of useful formulas for computing virial identities in any field theory. Then, we propose that a complete treatment of virial identities in relativistic gravity must take into account the appropriate boundary term. For General Relativity this is the Gibbons-Hawking-York boundary term. We test and confirm this proposal with concrete examples. Our analysis here is restricted to spherically symmetric configurations, which yield 1D effective actions (leaving higher-D effective actions and in particular the axially symmetric case to a companion paper). In this case, we show that there is a particular “gauge” choice, i.e. a choice of coordinates and parametrizing metric functions, that simplifies the computation of virial identities in General Relativity, making both the Einstein-Hilbert action and the Gibbons-Hawking-York boundary term noncontributing. Under this choice, the virial identity results exclusively from the matter action. For generic “gauge” choices, however, this is not the case.

关键词： General relativity Gravitation

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Publisher Correction to: Injective Hulls of Quantale-Enriched Multicategories

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Applied Categorical Structures 2021年第1期30卷 79-79页

作者： Martinelli, Eros Department of Mathematics Center for Research and Development in Mathematics and Applications University of Aveiro Aveiro Portugal

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Block belief propagation algorithm for two-dimensional tensor networks

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Physical Review B 2023年第12期108卷 125111-125111页

作者： Chu Guo Dario Poletti Itai Arad Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal University Changsha 410081 China Science Mathematics and Technology Cluster Singapore University of Technology and Design 8 Somapah Road 487372 Singapore Engineering Product Development Pillar Singapore University of Technology and Design 8 Somapah Road 487372 Singapore Centre for Quantum Technologies National University of Singapore 117543 Singapore MajuLab CNRS-UNS-NUS-NTU International Joint Research Unit UMI 3654 Singapore Faculty of Physics Technion Haifa 3200003 Israel

Belief propagation is a well-studied algorithm for approximating local marginals of multivariate probability distribution over complex networks, while tensor network states are powerful tools for quantum and classical many-body problems. Building on a recent connection between the belief propagation algorithm and the problem of tensor network contraction, we propose a block belief propagation algorithm for contracting two-dimensional (2D) tensor networks and approximating the ground state of 2D systems. The advantages of our method are threefold: (1) the same algorithm works for both finite and infinite systems; (2) it allows natural and efficient parallelization; and (3) given its flexibility, it would allow us to deal with different unit cells. As applications, we use our algorithm to study the 2D Heisenberg and transverse Ising models, and show that the accuracy of the method is on par with state-of-the-art results.

关键词： Quantum spin models Tensor network methods

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Searching for vector boson-star mergers within LIGO-Virgo intermediate-mass black-hole merger candidates

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Physical Review D 2023年第12期108卷 123020-123020页

作者： Juan Calderón Bustillo Nicolas Sanchis-Gual Samson H. W. Leong Koustav Chandra Alejandro Torres-Forné José A. Font Carlos Herdeiro Eugen Radu Isaac C. F. Wong Tjonnie G. F. Li Instituto Galego de Física de Altas Enerxías Universidade de Santiago de Compostela 15782 Santiago de Compostela Galicia Spain Department of Physics The Chinese University of Hong Kong Shatin N.T. Hong Kong Departamento de Astronomía y Astrofísica Universitat de València Dr. Moliner 50 46100 Burjassot (València) Spain Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA) Campus de Santiago 3810-183 Aveiro Portugal Department of Physics Indian Institute of Technology Bombay Powai Mumbai Maharashtra 400076 India Observatori Astronòmic Universitat de València C/ Catedrático José Beltrán 2 46980 Paterna (València) Spain

We present the first systematic search for exotic compact mergers in Advanced LIGO and Virgo events. We compare the short gravitational-wave signals GW190521, GW190426_190642, GW200220_061928, and the trigger 200114_020818 (or S200114f) to a new catalog of 759 numerical simulations of head-on mergers of horizonless exotic compact objects known as Proca stars, interpreted as self-gravitating lumps of (fuzzy) dark matter sourced by an ultralight (vector) bosonic particle. The Proca star merger hypothesis is strongly rejected with respect to the black hole merger one by GW190426, weakly rejected by GW200220 and weakly favored by GW190521 and S200114f. GW190521 and GW200220 yield highly consistent boson masses of μB=8.69−0.75+0.61×10−13 eV and μB=9.13−1.30+1.18×10−13 eV at the 90% credible level. We conduct a preliminary population study of the compact binaries behind these events. Excluding (including) S200114f as a real event, and ignoring boson-mass consistencies across events, we estimate a fraction of Proca star mergers of ζ=0.27−0.25+0.43(0.39−0.33+0.38). We discuss the impact of boson-mass consistency across events in such estimates. Our results maintain GW190521 as a Proca star merger candidate and pave the way toward population studies considering exotic compact objects.

关键词： Dark matter General relativity Gravitational waves Particle dark matter Gravitational wave detectors Numerical relativity

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Quality of multiple choice questions in a numerical and statistical methods course 46

Quality of multiple choice questions in a numerical and stat...

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46th SEFI Annual Conference 2018: Creativity, Innovation and Entrepreneurship for Engineering Education Excellence

作者： Cruz, J.P. Freitas, A. Macedo, P. Seabra, D. Mathematics Department University of Aveiro Aveiro Portugal Center for Research and Development in Mathematics and Applications University of Aveiro Aveiro Portugal Polytechnical School ESTGA University of Aveiro Aveiro Portugal

ISBN: (纸本)9782873520168

The use of Multiple Choice Questions (MCQ) in written tests, supported by the digital scan and automatic correction, has been evaluated using the application of Item Response Theory methodology. A simple detection of outliers using boxplots of difficulty and discrimination values shows few cases from the 48 questions that required investigation. In overall, the six partial exams contained appropriate questions for the teaching/learning binomial in our Numerical and Statistical Methods course. The following summary could be useful to future evaluations and teaching/learning formats: • questions with lower difficult value have been practiced in several moments. This suggests a web tool to help students practicing the basic concepts when time in classes is not enough for all students;• questions designed to evaluate theoretical concepts could demand a higher ability to be answered but they are not necessarily strong discriminators between different levels of ability. This may represent a problem to define an optimal format of the test: how to design a discriminative question? A possible solution came from one question, where a simple combination of known concepts strongly increased the difficulty value. An electronic database of this type of more demanding problems could be created for students with more ability in this course;• knowing the properties of difficulty and discrimination can help the team to prepare exams that avoid the oscillatory effect in overall difficulty and avoid the dropout rate. Given the good results achieved in the last three years, with a careful balance between MCQ and open questions, we plan to keep applying and improving these evaluation procedures in our Numerical and Statistical Methods course. © Proceedings of the 46th SEFI Annual Conference 2018: Creativity, Innovation and Entrepreneurship for Engineering Education Excellence. All rights reserved.

关键词： Numerical methods

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Electromagnetic emission from axionic boson star collisions

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Physical Review D 2022年第6期106卷 064034-064034页

作者： Nicolas Sanchis-Gual Miguel Zilhão Vitor Cardoso Departamento de Astronomía y Astrofísica Universitat de València Dr. Moliner 50 46100 Burjassot (València) Spain Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA) Campus de Santiago 3810-183 Aveiro Portugal Centro de Astrofísica e Gravitação—CENTRA Departamento de Física Instituto Superior Técnico—IST Universidade de Lisboa—UL Avenida Rovisco Pais 1 1049-001 Lisboa Portugal Niels Bohr International Academy Niels Bohr Institute Blegdamsvej 17 2100 Copenhagen Denmark

We explore the dynamics of boson stars in the presence of axionic couplings through nonlinear evolutions of Einstein’s field equations. We show that, for large axionic couplings, isolated boson stars become unstable, and decay via a large burst of electromagnetic radiation, becoming less massive and more dilute. Our full nonlinear results are in good agreement with flat-space estimates for the critical couplings. We then consider head-on collisions of subcritical boson stars and study the electromagnetic and gravitational signal. Boson stars cluster around the critical point via interactions, and we argue that mergers will generically be also sources of electromagnetic radiation, in addition to gravitational waves, which can be used to place constraints on the axionic coupling if such multimessenger signals are detected.

关键词： Alternative gravity theories Dark matter Gravitational waves Numerical relativity

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