Divided-difference operators from the geometric point of view

It is presented a study of general divided-difference operators having the fundamental property of leaving a polynomial of degree n−1 when applied to a polynomial of degree n.info:eu-repo/semantics/updatedVersio

Laguerre-Hahn orthogonal polynomials on the real line

A survey is given on sequences of orthogonal polynomials related to Stieltjes functions satisfying a Riccati type differential equation with polynomial coeffcients - the so-called Laguerre-Hahn class. The main goal is to describe analytical aspects, focusing on differential equations for those orthogonal polynomials, difference and differential equations for the recurrence coeffcients, and distributional equations for the corresponding linear functionals.info:eu-repo/semantics/publishedVersio

Matrix Sylvester equations in the theory of orthogonal polynomials on the unit circle

In this paperwe characterize sequences of orthogonal polynomials on the unit circle whose Carathéodory function satisfies a Riccati differential equation with polynomial coefficients, in terms of matrix Sylvester differential equations. For the particular case of semi-classical orthogonal polynomials on the unit circle, it is derived a characterization in terms of first order linear differential systems.info:eu-repo/semantics/publishedVersio

On the second order holonomic equation for Sobolev-type orthogonal polynomials

It is presented a general approach to the study of orthogonal polynomials related to Sobolev inner products which are defined in terms of divided-difference operators having the fundamental property of leaving a polynomial of degree $n-1$ when applied to a polynomial of degree $n$. This paper gives analytic properties for the orthogonal polynomials, including the second order holonomic difference equation satisfied by them.info:eu-repo/semantics/updatedVersio

E-mail as a predictor of silence behaviors

As e-mail became the number one communication channel within organizations, problems related to this fact started to arise. Employees no longer felt in control over their inbox and the term e-mail overload started to gain more relevance. Thus, the present study sought to investigate the impacts that e-mail overload and the quality of its content can have on employees, as well as what are its consequences to the individuals. As the outcomes can vary given different situations and individuals, the study was focused particularly on silence behaviors, that until to the moment have scarce empirical research. The results of the study were obtained through an online questionnaire answered by 97 individuals. With the support of the Job Demands-Resources Model, it was possible to test mediations, moderations and moderated mediations, to verify the impact of e-mail on silence behaviors. While the results found that both work engagement and exhaustion mediate the previous relationship, it was also found that the quality of the e-mail content moderates the relation between e-mail overload and work engagement, contrary to what happens in the relationship between e-mail overload and exhaustion. Further, the moderated mediation was partially confirmed since it was verified that, e-mail quality moderates the mediation between e-mail overload and work engagement, but it does not moderate the mediation between e-mail overload and exhaustion. The present study is particularly important to close one of the existent gaps regarding silence behaviors, as the subject does not have a large body of research nor it has been connected with e-mail. Further, it can be useful for managers to understand why some employees remain silent and what can be done to overcame such behaviors.Com o e-mail a tornar-se o canal de comunicação mais utilizado dentro das organizações, alguns problemas relacionados com este fato começaram a surgir. Os funcionários deixaram de sentir qualquer controle sobre a sua caixa de correio e o terma sobrecarga de e-mail passou a ter mais relevância. O presente estudo tem como objetivo investigar quais os impactos que esta sobrecarga de e-mail bem como a qualidade do seu conteúdo podem ter nos funcionários, e quais são as consequências que poderão advir dos mesmos, afetando assim os individuos. Como as consequências podem variar consoante diferentes situações e diferentes indivíduos, o estudo foca-se particularmente em comportamentos de silêncio como possível consequência. Os resultados foram obtidos através de um questionário online, contando com a participação de 97 indivíduos. Com o apoio do modelo Job Demand-Resources, foi possível testar mediações, moderações e moderações mediadas, para verificar o impacto de e-mail nos comportamentos de silêncio. Os resultados mostraram que tanto o envolvimento no trabalho como a exaustão medeiam a relação anterior. Já a qualidade do conteúdo do e-mail modera a relação entre a sobrecarga de e-mail e o envolvimento no trabalho, ao contrário do que acontece na relação entre sobrecarga de e-mail e exaustão. Além disso, a mediação moderada foi parcialmente confirmada, uma vez que se verificou que a qualidade do e-mail modera a mediação entre a sobrecarga de e-mail e o envolvimento no trabalho, mas não modera a mediação entre a sobrecarga e a exaustão. Este estudo é particularmente importante para tentar fechar uma das lacunas existentes em relação aos comportamentos de silêncio, uma vez que a pesquisa sobre o mesmo é escassa e, a existente ainda não estudou a sua relação com o e-mail. Assim, os resultados deste estudo podem ser bastante úteis para os gestores entenderem o porquê de alguns funcionários permanecerem em silêncio e o que pode ser feito para superar estes comportamentos

Who preserves contemporary art collections in Portuguese institutions? Contributions to the study of professional roles in the conservation of contemporary art

There is an apparent consensus as to when and how the discipline of conservation emerged, and yet there is still a knowledge gap on how different professional roles in collection care operate in institutional contexts. The few studies that touch upon this issue lack empirical foundations that speak to the impact of education and the professional contexts. Understanding who takes part in daily conservation and care activities, and to what extent, will give us insight into the conservator’s role and presence in the context of the conservation and care of contemporary art collections in Portugal. This investigation as three main goals: 1) Understanding who takes part in the conservation and preservation of the main contemporary art collections in Portugal, and what is the conservator’s role within that context; 2) Analysing how the role of conservators in the preservation of Portuguese contemporary art collections, relates to the international panorama; 3) Examining how conservation practices performed by “collection-caretakers” in the given context, especially by conservators, can inform about the professional identity of conservators. To meet these goals, empirical data was collected through semi structured interviews, conducted to conservation professionals working in the five main Portuguese contemporary art collections. The collected empirical data suggested the presence of conservators in Portuguese contemporary art collections seems to be mainly restricted to direct conservation interventions. Furthermore, the data suggests the role of conservators in contemporary art institutions conservation management, resonates with the German context described by Joanna Phillips and international contexts described by Jonathan Ashley-Smith and Manon D’haenens. Finally, the studied professional identity factors in this specific context, appear to be negative influencers for the professional identity development of the conservator working with contemporary art

Uncovering the role of blood vessels during spinal cord regeneration in zebrafish

The spinal cord is the region of the central nervous system responsible for the bidirectional relay of information between the brain and the rest of the body. For this reason, damages to the spinal cord can result in devastating consequences. Spinal cord injury (SCI) occurs due to a physical trauma and causes loss of motor and sensitive function. Additionally, the initial trauma provokes the disruption of the blood-spinal cord barrier (BSCB). This results in the leakage of blood to the tissue, further damaging the spinal cord. In mammals, like humans and mice (Mus musculus), endogenous attempts to repair the resulting damage occur, however, these attempts are mostly unsuccessful due to the present of growthinhibitory molecules and structures. As such, no significant recovery is accomplished. By contrast, zebrafish (Danio rerio) are able to regenerate their spinal cord and previous work from our lab showed that, during regeneration, the injured tissue revascularizes and that blood flow is observed in these vessels. In this work, we followed the recovery of the BSCB during spinal cord regeneration in zebrafish at different timepoints after injury. Our results showed that the reestablishment of the BSCB occurred between 3 dpi and 7 dpi, indicating that the new blood vessels rapidly become functional in zebrafish. In addition, in order to study the importance of revascularization after SCI, we attempted to inhibit the angiogenic process that occurs during spinal cord regeneration. Our preliminary results suggest that the inhibition of angiogenesis results in impaired motor function. However, the cellular and molecular mechanisms involved are not yet understood. These results allow a better understanding of the regenerative process in zebrafish and may provide clues regarding the fundamental differences that exist between this animal model and mammals

Muscle synergy analysis of lower-limb movements

Dissertação de mestrado integrado em Biomedical Engineering (área de especialização em Medical Electronics)Neurological disorders and trauma often lead to impaired lower-limb motor coordination. Understanding how muscles combine to produce movement can directly benefit assistive solutions to those afflicted with these impairments. A theory in neuromusculoskeletal research, known as muscle synergies, has shown promising results in applications for this field. This hypothesis postulates that the Central Nervous System controls motor tasks through the time-variant combinations of modules (or synergies), each representing the co-activation of a group of muscles. There is, however, no unifying, evidence-based framework to ascertain muscle synergies, as synergy extraction methods vary greatly in the literature. Publications also focus on gait analysis, leaving a knowledge gap when concerning motor tasks important to daily life such as sitting and standing. The purpose of this dissertation is the development of a robust, evidence-based, task-generic synergy extraction framework unifying the divergent methodologies of this field of study, and to use this framework to study healthy muscle synergies on several activities of daily living: walking, sit-to-stand, stand-to-sit and knee flexion and extension. This was achieved by designing and implementing a cross-validated Non-Negative Matrix Factorization process and applying it to muscle electrical activity data. A preliminary study was undertaken to tune this configuration regarding cross-validating proportions, data structuring prior to factorization and evaluating criteria quantifying accuracy in modularity findings. Muscle synergies results were then investigated for different performing speeds to determine if their structure differed, and for consistency across subjects, to ascertain if a common set of muscle synergies underlay control on all subjects equally. Results revealed that the implemented framework was consistent in its ability to capture modularity (p < 0:05). The movements’ synergies also did not differ across the studied range of speeds (except one module in Knee Flexion) (p < 0:05). Additionally, a common set of muscle synergies was present across several subjects (p < 0:05), but shared commonality across every participant was only observed for the walking trials, for which much larger amounts of data were collected. Overall, the established framework is versatile and applicable for different lower-limb movements; muscle synergies findings for the examined movements may also be used as control references in assistive devices.As perturbações e traumas neurológicos afetam frequentemente a coordenação motora dos membros inferiores. Uma teoria recente em investigação neuromusculo-esquelética, denominada de sinergias musculares, tem demonstrado resultados promissores em soluções de assistência à população afetada por estes distúrbios. Esta teoria propõe que o Sistema Nervoso Central controla as tarefas motoras através de combinações variantes no tempo de módulos (ou sinergias), sendo que cada um representa a co-ativação de um grupo de músculos. No entanto, não existe nenhum processo uniformizante, empiricamente justificado para determinar sinergias musculares, porque os métodos de extração de sinergias variam muito na literatura. Para além disso, as publicações normalmente focam-se em análise da marcha, deixando uma lacuna de conhecimento em tarefas motoras do dia-a-dia, tais como sentar e levantar. O objetivo desta dissertação é o desenvolvimento de um processo robusto, genérico e empiricamente justificado de extração de sinergias em várias tarefas motoras, unindo as metodologias divergentes neste campo de estudo, e subsequentemente utilizar este processo para estudar sinergias musculares de sujeitos saudáveis em várias atividades do dia-a-dia: marcha, erguer-se de pé partir de uma posição sentada, sentar-se a partir de uma posição de pé e extensão e flexão do joelho. Isto foi alcançado através da implementação de um processo de cross-validated Non-Negative Matrix Factorization e subsequente aplicação em dados de atividade elétrica muscular. Um estudo preliminar foi realizado para configurar este processo relativamente às proporções de cross-validation, estruturação de dados antes da fatorização e seleção de critério que quantifique o sucesso da representação modular dos dados. Os resultados da extração de sinergias de diferentes velocidades de execução foram depois examinados no sentido de descobrir se este fator influenciava a estrutura dos módulos motores, assim como se semelhanças entre as sinergias de diferentes sujeitos apontavam para um conjunto comum de sinergias musculares subjacente ao controlo do movimento. Os resultados revelaram que o processo implementado foi consistente na sua capacidade de capturar a modularidade nos dados recolhidos (p < 0:05). As sinergias de todos os movimentos também não diferiram para toda a gama de velocidades estudada (exceto um módulo na flexão do joelho) (p < 0:05). Por fim, um conjunto comum de sinergias musculares esteve presente em vários sujeitos (p < 0:05), mas só esteve presente em todos os sujeitos de igual forma para a marcha, para a qual a quantidade de dados recolhida foi muito maior. Globalmente, o processo implementado é versátil e aplicável a diferentes movimentos dos membros inferiores; os resultados das sinergias musculares para os movimentos examinados podem também ser utilizado como referências de controlo para dispositivos de assistência

Structure relations for orthogonal polynomials on the unit circle

Structure relations for orthogonal polynomials on the unit circle are studied. We begin by proving that semi-classical orthogonal polynomials on the unit circle satisfy structure relations of the following type: [...]info:eu-repo/semantics/publishedVersio