Browsing by Issue Date, starting with "2022-10-07"
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- Vector sensors for underwater : acoustic communicationsPublication . Bozzi, Fabricio de Abreu; Jesus, S. M.Acoustic vector sensors measure acoustic pressure and directional components separately. A claimed advantage of vector sensors over pressure-only arrays is the directional information in a collocated device, making it an attractive option for size-restricted applications. The employment of vector sensors as a receiver for underwater communications is relatively new, where the inherent directionality, usually related to particle velocity, is used for signal-to-noise gain and intersymbol interference mitigation. The fundamental question is how to use vector sensor directional components to bene t communications, which this work seeks to answer and to which it contributes by performing: analysis of acoustic pressure and particle velocity components; comparison of vector sensor receiver structures exploring beamforming and diversity; quanti cation of adapted receiver structures in distinct acoustic scenarios and using di erent types of vector sensors. Analytic expressions are shown for pressure and particle velocity channels, revealing extreme cases of correlation between vector sensors' components. Based on the correlation hypothesis, receiver structures are tested with simulated and experimental data. In a rst approach, called vector sensor passive time-reversal, we take advantage of the channel diversity provided by the inherent directivity of vector sensors' components. In a second approach named vector sensor beam steering, pressure and particle velocity components are combined, resulting in a steered beam for a speci c direction. At last, a joint beam steering and passive time-reversal is proposed, adapted for vector sensors. Tested with two distinct experimental datasets, where vector sensors are either positioned on the bottom or tied to a vessel, a broad performance comparison shows the potential of each receiver structure. Analysis of results suggests that the beam steering structure is preferable for shorter source-receiver ranges, whereas the passive time-reversal is preferable for longer ranges. Results show that the joint beam steering and passive time-reversal is the best option to reduce communication error with robustness along the range.
- Mutant Ataxin-2 expression in aged animals aggravates neuropathological features associated with Spinocerebellar Ataxia type 2Publication . Afonso, Inês T.; Lima, Patrícia; Conceição, André; Matos, Carlos A; Nóbrega, ClévioSpinocerebellar ataxia type 2 (SCA2) is a rare autosomal, dominantly inherited disease, in which the affected individuals have a disease onset around their third life decade. The molecular mechanisms underlying SCA2 are not yet completely understood, for which we hypothesize that aging plays a role in SCA2 molecular pathogenesis. In this study, we performed a striatal injection of mutant ataxin-2 mediated by lentiviral vectors, in young and aged animals. Twelve weeks post-injection, we analyzed the striatum for SCA2 neuropathological features and specific aging hallmarks. Our results show that aged animals had a higher number of mutant ataxin-2 aggregates and more neuronal marker loss, compared to young animals. Apoptosis markers, cleaved caspase-3, and cresyl violet staining also indicated increased neuronal death in the aged animal group. Additionally, mRNA levels of microtubule-associated protein 1 light-chain 3B (LC3) and sequestosome-1 (SQSTM1/p62) were altered in the aged animal group, suggesting autophagic pathway dysfunction. This work provides evidence that aged animals injected with expanded ataxin-2 had aggravated SCA2 disease phenotype, suggesting that aging plays an important role in SCA2 disease onset and disease progression.
- A controvérsia envolta no conceito e contabilização da goodwill e o seu impacto nas demonstrações financeiras de empresas cotadas no Portuguese Stock Índex (PSI)Publication . Casimiro, Ana Francisca Pinto; Martins, Ana Isabel RitaA presente dissertação tem quatro objetivos principais: a identificação das principais controvérsias sobre a noção de goodwill, a identificação das principais controvérsias na contabilização do goodwill, a identificação de conceitos e indicadores de gestão assentes no goodwill e a avaliação da incorporação do goodwill nas Demonstrações Financeiras de empresas cotadas no Portuguese Stock Index (PSI). De acordo com a literatura contabilística o goodwill corresponde à diferença entre o valor da empresa e o seu património líquido avaliado a valores de mercado. Perspetivas diferentes e conceitos divergentes podem, na elaboração de pesquisas teóricas ou empíricas, gerar resultados divergentes, conclusões equívocas e demonstrações financeiras com resultados distorcidos, entre outros desafios de ordem teórica e prática. A presente dissertação procura definir o conceito de goodwill e as controvérsias envoltas na sua contabilização, bem como a investigação das normas, para a mensuração do mesmo, bem como conceitos como goodwill subjetivo, core-goodwill, goodwill negativo, concentração de atividades empresariais e testes de imparidade ao goodwill. Os dados do estudo foram recolhidos a partir dos relatórios e contas de entidades pertencentes ao PSI em 2022, durante um período de sete anos, sendo o ano inicial 2015 e o ano final 2021. Foram comparados os resultados e o seu impacto nas demonstrações financeiras no total do ativo das entidades e a importância do goodwill no mesmo. A análise incorpora também a compreensão das rúbricas estudadas, nomeadamente o goodwill líquido, e o peso do goodwill no total do ativo nas entidades em estudo. Foi ainda analisado o impacto da Covid-19 no valor do goodwill e no total do ativo das entidades incluídas no estudo. Os resultados mais relevantes demonstram que, em média, o goodwill apresenta um peso de 7,7% no total do ativo das entidades, no período estudado, pelo que é uma rúbrica com um peso considerável no ativo; a situação pandémica que advém da Covid- 19 não teve impacto nas rúbricas estudadas, de acordo com os relatórios e contas das entidades em 2021 que fazem menção ao tema.