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Electrical, Computer, Communications and Mechatronics Engineering (ICECCME), International Conference on

作者： António B. Pereira Joana D. Batista Nélia M. Silva Bernardo Mascate Department of Mechanical Engineering TEMA - Centre for Mechanical Technology and Automation University of Aveiro Aveiro Portugal Department of Mathematics CIDMA- Centrefor Research & Development in Mathematics and Applications University of Aveiro Aveiro Portugal Home Comfort Operations Components (AvP/MFOl) Bosch Termotecnologia S.A. Aveiro Portugal

ISBN: (数字)9798350391183

ISBN: (纸本)9798350391190

Heat pumps are increasingly becoming a key solution in the quest for decarbonization, offering a significant advantage over traditional boilers due to their superior energy efficiency. Not only can heat pumps provide both heating and cooling, but they also achieve thermal efficiencies exceeding 500%, which can seem to defy conventional expectations. The outdoor unit of a heat pump consists of about twenty main components, one of which is a complex network of copper pipes and sheets welded to valves, connectors, and other fittings. This set involves over thirty welded joints, highlighting a significant opportunity for reducing manufacturing time through process optimization. Copper is a critical material extensively used in various applications due to its excellent thermal and electrical conductivity. However, these very properties make welding copper particularly challenging, especially when aiming to automate and streamline industrial processes. Traditionally, connecting copper pipes and fittings is done through brazing, yet alternative methods such as LASER welding, electron beam welding, resistance welding, friction welding, and ultrasonic welding also exist. This study focuses on the ultrasonic welding of copper, aiming to identify the optimal parameters that maximize the mechanical strength of overlapping joints and ensure effective tube sealing. Experimental results showed that for copper sheets, the best shear strength was 277 MPa, that is 97.7 % of the parent metal, with ductile rupture, achieved with a welding time of 3 seconds and a pressure of 6 bar. For tube sealing, the optimal conditions were a welding time of 3 seconds and a pressure of 4 bar. For both scenarios, the same variables were used, retention time of 0.62 s, initial pressure of 2 bar, retention pressure of 2 bar and sonotrode rising pressure of 3 bar. The analysis reveals that ultrasonic welding of copper can achieve both robust mechanical strength and reliable sealing, making it a promis

关键词： Heat pumps Welding Fitting Conductivity Thermal conductivity Valves Acoustics Copper Optimization Bars

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Workers benchmarking using multi-directional efficiency analysis in a manufacturing production system

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Procedia Computer Science 2022年 200卷 1451-1460页

作者： Eugénio M. Rocha Ângela F. Brochado Ana Moura Department of Mathematics University of Aveiro 3810-193 Portugal Center for Research and Development in Mathematics and Applications (CIDMA) Aveiro 3810-193 Portugal Department of Economics Management Industrial Engineering and Tourism University of Aveiro 3810-193 Portugal Systems for Decision Support Research Group (GOVCOPP) Aveiro 3810-193 Portugal

The human factor plays a relevant role in all manual or partially automatic production systems, specially, the ones showing reliable and balanced dynamics. In the literature, parametric or survey-based models are quite common for performance evaluation of production workers. In this work, multi-directional efficiency analysis is used instead, for root cause analysis of product reworks and bottlenecks occurrence, according to four worker-related parameters: experience time, wage, delay time and response time. The approach allows to identify individual inefficiencies per tuple worker/working shift and to cluster them according to similar inefficiency parameters. In addition, this work opens a path to new applications of multi-directional efficiency analysis to problems in the manufacturing industry.

关键词： multi-directional efficiency analysis bottleneck workers performance clustering manufacturing production system

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Smaller Keys for the McEliece Cryptosystem: A Convolutional Variant with GRS Codes

arXiv

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arXiv 2021年

作者： Almeida, Paulo Beltrá, M. Napp, D. Sebastião, C. CIDMA - Center for Research and Development in Mathematics and Applications Dept. of Mathematics University of Aveiro Portugal Dept. of Mathematics University of Alicante Spain

In this paper we present a variant of the McEliece cryptosystem that possesses several interesting properties, including a reduction of the public key for a given security level. In contrast to the classical McEliece cryptosystems, where block codes are used, we propose the use of a convolutional encoder to be part of the public key. The permutation matrix is substituted by a polynomial matrix whose coefficient matrices have columns with weight zero or at least weight two. This allows the use of Generalized Reed-Solomon (GRS) codes which translates into shorter keys for a given security level. Hence, the private key is constituted by a generator matrix of a GRS code and two polynomial matrices containing large parts generated completely at random. In this setting the message is a sequence of messages instead of a single block message and the errors are added throughout the sequence. We discuss possible structural and ISD attacks to this scheme. We conclude presenting the key sizes obtained for different parameters and estimating the computational cost of encryption and decryption *** Codes 94A60 (Primary), 94B10, 68P25, 68P30, 11T71 © 2021, CC BY.

关键词： Convolutional codes

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Twisting shadows: Light rings, lensing, and shadows of black holes in swirling universes

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Physical Review D 2024年第10期109卷 104020-104020页

作者： Zeus S. Moreira Carlos A. R. Herdeiro Luís C. B. Crispino Programa de Pós-Graduação em Física Universidade Federal do Pará 66075-110 Belém Pará Brazil 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

Using the Ernst formalism, a novel solution of vacuum general relativity was recently obtained [Phys. Rev. D 106, 064014 (2022)], describing a Schwarzschild black hole (BH) immersed in a nonasymptotically flat rotating background, dubbed swirling universe, with the peculiar property that north and south hemispheres spin in opposite directions. We investigate the null geodesic flow and, in particular, the existence of light rings in this vacuum geometry. By evaluating the total topological charge w, we show that there exists one unstable light ring (w=−1) for each rotation sense of the background. We observe that the swirling background drives the Schwarzschild BH light rings outside the equatorial plane, displaying counterrotating motion with respect to each other, while (both) corotating with respect to the swirling universe. Using backward ray-tracing, we obtain the shadow and gravitational lensing effects, revealing a novel feature for observers on the equatorial plane: the BH shadow displays an odd Z2 (north-south) symmetry, inherited from the same type of symmetry of the spacetime itself: a twisted shadow.

关键词： Classical black holes Gravitation

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Exotic Compact Objects and the Fate of the Light-Ring Instability

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Physical Review Letters 2023年第6期130卷 061401-061401页

作者： Pedro V. P. Cunha Carlos Herdeiro Eugen Radu Nicolas Sanchis-Gual 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 Departamento de Astronomía y Astrofísica Universitat de València Dr. Moliner 50 46100 Burjassot (València) Spain

Ultracompact objects with light rings (LRs) but without an event horizon could mimic black holes (BHs) in their strong gravity phenomenology. But are such objects dynamically viable? Stationary and axisymmetric ultracompact objects that can form from smooth, quasi-Minkowski initial data must have at least one stable LR, which has been argued to trigger a spacetime instability; but its development and fate have been unknown. Using fully nonlinear numerical evolutions of ultracompact bosonic stars free of any other known instabilities and introducing a novel adiabatic effective potential technique, we confirm the LRs triggered instability, identifying two possible fates: migration to nonultracompact configurations or collapse to BHs. In concrete examples we show that typical migration (collapse) timescales are not larger than ∼103 light-crossing times, unless the stable LR potential well is very shallow. Our results show that the LR instability is effective in destroying horizonless ultracompact objects that could be plausible BH imitators.

关键词： General relativity Astronomical black holes

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THE DEGREES OF THE ORIENTATION-PRESERVING AUTOMORPHISM GROUPS OF TOROIDAL MAPS AND HYPERMAPS

arXiv

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arXiv 2023年

作者： Fernandes, Maria Elisa Piedade, Claudio Alexandre Center for Research and Development in Mathematics and Applications Department of Mathematics University of Aveiro Portugal Centro de Matemática da Universidade do Porto Universidade do Porto Portugal

This paper is an exploration of the faithful transitive permutation representations of the orientation-preserving automorphisms groups of highly symmetric toroidal maps and hypermaps. The main theorems of this paper give a list of all possible degrees of these specific groups. This extends prior accomplishments of the authors, wherein their focus was confined to the study of the automorphisms groups of toroidal regular maps and hypermaps. In addition the authors bring out the recently developed GAP package corefreesub that can be used to find faithful transitive permutation representations of any group. With the aid of this powerful tool, the authors show how Schreier coset graphs of the automorphism groups of toroidal maps and hypermaps can be easily *** Codes 05E18, 20B25, 52B11 © 2023, CC BY.

关键词： Algebra

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PROFESSOR STEFAN G. SAMKO research: A DECADE RETROSPECTIVE

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Journal of Mathematical Sciences (United States) 2022年第3期266卷 510-516页

作者： Almeida, Alexandre Kusraeva, Zalina A. Rafeiro, Humberto Department of Mathematics Center for Research and Development in Mathematics and Applications University of Aveiro Aveiro 3810-193 Portugal Regional Mathematical Center of Southern Federal University Bolshaya Sadovaya Str. 105/42 Rostov-on-Don 344006 Russian Federation United Arab Emirates University Mathematical Sciences - (COS) Abu Dhabi Al Ain United Arab Emirates

This review article is dedicated to Professor Stefan Samko on the occasion of his 80th birthday. It contains some biographic snippets of S. Samko, as well as a bird’s-eye view on his research during the last decade. ... 详细信息

关键词： Classes of operators in complex analysis Grand type spaces Herz spaces Holomorphic Bergman type spaces Holomorphic Hölder spaces Morrey spaces Variable exponent spaces

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Some generalizations of the herglotz problem involving the Mittag–Leffler tempered fractional derivative

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AIP Conference Proceedings 2023年第1期2849卷

作者： Ricardo Almeida Center for Research and Development in Mathematics and Applications (CIDMA) Department of Mathematics University of Aveiro 3810–193 Aveiro Portugal

This paper is devoted to investigate necessary conditions of optimality for the fractional Herglotz problem, involving a general form of a tempered fractional derivative. We obtain the transversality conditions in the case of free endpoints and we study the necessary condition of optimality in the presence of higher-order derivatives.

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Distributed-order fractional variational problems with arbitrary kernels and generalized Lagrangians

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AIP Conference Proceedings 2023年第1期2849卷

作者： Natália Martins Center for Research and Development in Mathematics and Applications (CIDMA) Department of Mathematics University of Aveiro 3810–193 Aveiro Portugal

This paper presents necessary and sufficient optimality conditions for variational problems involving distributed-order fractionals derivatives with arbitrary smooth kernels and generalized Lagrangians. Many important...

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Dynamical analysis of nonlinear combined drug therapy model for HIV infection: Bayesian regularization technique intelligent networks

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Biomedical Signal Processing and Control 2024年 88卷

作者： Bilal, Muhammad Raja, Muhammad Asif Zahoor Ahmad, Iftikhar Khan, Rizwan Shoaib, Muhammad Department of Physical Science The University of Chenab Gujrat Pakistan Center for Research and Development in Mathematics and Applications Department of Mathematics University of Aveiro Aveiro3810-193 Portugal Future Technology Research Center National Yunlin University of Science and Technology 123 University Road Section 3 Yunlin Douliou Yunlin64002 Taiwan Department of Mathematics University of Gujrat Gujrat Pakistan Yuan Ze University AI Center Taoyuan320 Taiwan

The study aims to provide an overview of the design and analysis of the differential system of the Nonlinear Combined Drug Therapy Mathematical (NCDTM) model for HIV Infection. This is achieved by utilizing the artificial Neural Network with Bayesian Regularisation technique intelligent network (ANNs-BRTIN), which is a stochastic method that enhances accuracy, reliability, and efficiency in the dynamics calculation process. The NCDTM model is defined along with experiments employing integer and nonlinear mathematical forms via four classes Where the number of uninfected cells in the blood and represented by A(t) the countable number of free virus particles in the blood is represented by S(t) when RTI therapy is administered denotes the number of infected cells in the Pre-RT phase with η dosage represented by I(t), D(t) represents when RTI therapy is administered using, reflects the number of infected cells in the post-RT phase η dosage. The numerical computing of the NCDTM system is performed with Adams methods, and these results are fed to the proposed ANNs-BRTINs for finding the approximated solution of four distinct instances by incorporating 15% of the data for testing and validation and 85% for training. The presented ANNs-BRTINs accuracy is illustrated by comparing the results from the acquired dataset of the Adam method for sundry scenarios. The use of regression for testing and residual, state transitions, mean square error, error histograms, and correlation in numerical replications of the ANNs-BRTINs is also explored to confirm their capacity, validity, consistency, correctness, and competence. © 2023

关键词： Stochastic systems

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