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Over-the-Air Calibration of Active Antenna Arrays Using Multisine
Publication . Jordão, Marina; Belo, Daniel; Caldeirinha, Rafael F. S.; Oliveira, Arnaldo S. R.; Carvalho, Nuno Borges de
A novel over-the-air (OTA) beamforming calibration procedure is proposed, which can be applied to different types of multiple-input multiple-output (MIMO) transmitting antennas. The method consists of using two tones on each antenna element, the main tone, and the tickle tone. The latter one operates in a different frequency for each antenna element and is used to obtain the optimum phase that needs to be set for each element to generate a beam in the desired direction, at the main tone frequency. The novel method was applied to linear, planar, 3-D antennas, and noncollocated multiantennas to validate its applicability to different antenna types. Line-of-Sight (LOS) and non-LOS experimental results demonstrate that the method can be used to retrieve the required phase to fully control the antenna radiation pattern. An optimum radiation pattern and lowest error vector magnitude (EVM) can be achieved even under high multipath effects/non-LOS conditions. A comparison between the performance and the application of the array factor (AF) theory is presented for practical indoor scenarios, demonstrating the effectiveness of the method. It is demonstrated that the method may be an alternative to the calibration of nonstandard MIMO antennas, where the AF computation is complex or not possible.
A Insolvência de Micro, Pequenas e Médias Empresas: Entre o CIRE e a Proposta de Diretiva
Publication . Correia, Xavier Marques; Conceição, Ana Filipa Ferreira Colaço da
Face à reconhecida importância das micro, pequenas e médias empresas no tecido
empresarial nacional, europeu e mundial, o debate em torno da modernização e simplificação
do Direito da Insolvência ganha igualmente relevância, procurando-se encontrar soluções
jurídicas adequadas à realidade e aos desafios das MPME. Perante a progressiva integração
e harmonização do direito europeu, importa assegurar que as MPME dispõem de
mecanismos eficazes, céleres e acessíveis, que promovam a sua recuperação e reforcem a
confiança no regime da insolvência.
Perception of Safety Tourism in Colombia
Publication . Antošová, Gabriela; Lima Santos, Luís; Stradová, Sara
Colombia is notorious for drug cartels and internal armed conflicts that have persisted in the country for more than 50 years. With the peace agreement signed in 2016 Colombia gradually became a country with strong tourism potential in Latin America. Supported by movie tourism and dark tourism, the influx of tourists to Colombia registered considerable increases. Colombia became a popular destination for recreation and beach stays, for adventure and experience tourism; and ecotourism has a dominant role related to the cultivation of coffee. However, Colombia presents natural risks and security risks that support the low level of peace and the low quality of life indicator as a tourism destination. The existence of a greater number of flights and low-cost booking systems, allows to increase interest in new non-traditional places, avoiding mass tourism, which can be an advantage for many travel agencies in the Czech and Portuguese markets that seek authentic and relatively unknown places. Despite the threat of the pandemic COVID-19, tourist packages to Colombia were analysed. Considering the main objective of the study, to assess the perception of security in Colombia, a questionnaire was carried out to identify the risks associated with this destination. To allow a comparison of the perception of safety with the Global Safety index, the responses of 206 potential tourists, 103 from Portugal and 103 from the Czech Republic, were selected. The results show that the destination Colombia is perceived as more dangerous by potential tourists than by actual tourists who have visited it and perceive it as much safer and more attractive.
FSplines: A Software for Linear Stability Analysis of Thin-Walled Structures, Version 2.0
Publication . Chicaiza, Ángel; Prola, Luis; Gala, Pedro; Chicaiza, Cristhian; Ortiz, Marcia
FSplines is a (geometrically) linear stability analysis tool of thin-walled structures with open section (useful for cold-formed steel profiles), that enables obtaining the bifurcation stresses (critical stress, load and moment) and the respective buckling modes by the Finite Strip Method (FSM). The Finite Strip Method: (i) allows analyzing prismatic steel members (commercial structural profiles), (ii) is an alternative to the Finite Element Method (FEM), and (iii) has some important advantages over FEM. In the present article, two variants of the FSM are presented: (i) the Semi-Analytical Finite Strip Method (SAFSM), where use is made of trigonometric functions and (ii) the Splines Finite Strip Method (SFSM), employing spline functions. The SAFSM has the advantage of being less time consuming. Its main restriction is the fact that it only allows modelling simple supported members (pinned restrained). The SFSM most important advantage is the ability to model members with all kinds of boundary conditions. This method is, however, more time consuming. It is worth noting that the bifurcation analysis, performed by the computer application FSplines, is required for the design of cold formed members according to the specifications of international standards. FSplines 2.0 is the second version of the computer application here presented. In this second improved version more cross-sections are available, and more section properties are presented.
State of the art of accessible development for smart devices: From a disable and not impaired point of view
Publication . Silva, João de Sousa e; Pereira, António; Gonçalves, Ramiro; Gomes, Sílvia
The need and benefits of digital accessibility are evident and, with the current ubiquitous trends, the profits are hugely potentiated. However, the fast evolution is instigating some issues in this area's accessibility. To understand the conceivable impact of these issues' tenacity in society, general accessibility features are explained as a reasonable application for all parties. Nevertheless, the potential of ubiquitous computation in order to promote social integration of citizens with impairments is focused and elucidated. The benefits of applying so much effort on accessibility as well as on usability is asserted and related to universal design. Hence, in order to promote a more universal applications development, the mobile operating systems available in the market, which are more plausible to be chosen and used by people with impairments, are scrutinized and shown from a standpoint of a developer that has accessibility and usability concerns. The paper leads to the conclusions that ubiquitous computation may have power to nullify impairments but, to be assistive, several issues regarding the devices and the operating system that runs on them have to be taken in mind and considered.