Robust order selection of mixtures of regression models with random effects

Finite mixtures of regression models with random effects are a very flexible statistical tool to model data, as these models allow to model the heterogeneity of the population and to account for multiple correlated observations from the same individual at the same time. The selection of the number of components for these models has been a long-standing challenging problem in statistics. However, the majority of the existent methods for the estimation of the number of components are not robust and, therefore, are quite sensitive to outliers. In this article we study a robust estimation of the number of components for mixtures of regression models with random effects, investigating the performance of trimmed information and classification criteria comparatively to the performance of the traditional information and classification criteria. The simulation study and a real-world application showcase the superiority of the trimmed information and classification criteria in the presence of contaminated data.Fundação para a Ciência e Tecnologia (FCT

Sensores de fibra ótica para meios desafiantes

With the present work, the development of fiber optic sensor solutions for the application in challenging media was intended. New sensor structures based on the post-processing of optical fibers were addressed, taking into account their sensitivity to variations in the external environment. In a first stage, fiber Bragg gratings were embedded in lithium batteries, to monitor temperature in situ and operando. Due to the harsh chemical environment of the battery, fiber optic sensors revealed to be the most advantageous alternative, when comparing to the electronic sensors. Fiber sensors exhibited good sensitivities and fast responses, besides being less invasive, thus they did not compromise the battery response. Furthermore, they were chemically stable. Still in the framework of this theme, and with the objective of monitoring possible strain and pressure variations inside the batteries, new sensors based on in-line Fabry-Perot cavities have been proposed. These sensors were characterized in lateral load, strain, and temperature. In a later stage, the study focused on the development of configurations that allowed to obtain high-resolution and/or sensitivity sensors. One of such configurations was obtained by creating a hollow microsphere at the fiber tip. The sensor was used to detected concentration variations and refractive index of glycerin and water mixtures. The influence of the diaphragm size in the sensor response was also studied, as well as the temperature response. New sensors based on multimode interference have also been characterized, using a coreless silica fiber tip. First, the influence of different parameters, such as length and diameters were analyzed. The sensors were tested in different solutions of glucose and water. It was observed that the sensor diameter is a decisive factor in obtaining devices that are more sensitive to refractive index and, consequently, to concentration. The determination of the thermo-optic coefficient of water/ethanol mixtures was also addressed using a multimode fiber interferometer sensor. Finally, a multimode interferometer sensor was functionalized by depositing agarose throughout the structure, allowing to optimize the response of the sensors to the external environment.Com o presente trabalho pretendeu-se explorar soluções de sensores em fibra ótica para a aplicação em meios desafiantes. Novas estruturas sensoras baseadas em pós-processamento de fibra ótica foram abordadas, tendo em consideração a sua sensibilidade a variações do meio externo. Numa primeira etapa, foram embebidas redes de Bragg no interior de baterias de lítio, para monitorizar variações de temperatura in situ e operando. Devido ao complexo meio químico da bateria, os sensores em fibra ótica revelaram ser uma alternativa mais vantajosa em relação aos sensores elétricos, não só pela sensibilidade e rápida resposta, mas também pelo fato de não afetarem o desempenho da bateria. Além disso, os sensores usados revelaram ser pouco invasivos e quimicamente estáveis. Ainda no âmbito deste tema, e com o objetivo de monitorizar possíveis deformações e variações de pressão no interior da bateria de lítio, foram desenvolvidos novos sensores baseados em cavidades de Fabry-Perot do tipo in-line. Esses sensores foram caraterizados em pressão lateral, deformação e temperatura. Numa fase posterior, o estudo centrou-se no desenvolvimento de configurações que permitissem a obtenção de sensores com elevada resolução e/ou sensibilidade. Uma das configurações consistiu na formação de uma microesfera oca na ponta de uma fibra ótica. Esse sensor foi utilizado para detetar variações de concentração e índice de refração de misturas de glicerina e água. A influência do tamanho do diafragma na resposta do sensor também foi estudada, assim como a resposta em temperatura. Em seguida, desenvolveram-se novos sensores baseados em interferência multimodo, utilizando para tal uma ponta de fibra de sílica sem núcleo. Numa primeira abordagem analisou-se a influência de diferentes parâmetros, como o comprimento e o diâmetro dos sensores. Os sensores foram expostos a diferentes soluções de glucose e água. Verificou-se que o diâmetro do sensor é um fator decisivo para a obtenção de dispositivos mais sensíveis ao índice de refração e, consequentemente, à concentração. Foi também desenvolvido um sensor baseado em interferência multimodo que permitiu determinar o coeficiente termo-ótico de misturas de etanol e água. Por fim, procedeu-se à funcionalização de um sensor baseado em interferência multimodo através da deposição de agarose ao longo da estrutura, permitindo assim otimizar a sua resposta a variações do meio externo.Programa Doutoral em Engenharia Físic

Desenvolvimento de um microdispositivo biomédico para a separação e deformação de eritrócitos

Este relatório descreve o trabalho efetuado durante o 2º ano do curso de Mestrado em Tecnologia Biomédica no Instituto Politécnico de Bragança (IPB). Este trabalho consistiu no desenvolvimento de um dispositivo biomédico à micro escala, que tivesse a capacidade de num único passo, realizar a separação e a deformação das células da camada de plasma. Inicialmente foi feita uma revisão de literatura onde foram abordados alguns temas de relevante interesse para uma melhor compreensão do presente estudo, como a biomicrofluídica, escoamento sanguíneo e técnicas e polímeros imprescindíveis para todo o processo de micro-fabricação. Numa etapa posterior, durante o percurso no CEIT, Universidade de Navarra, Espanha, foi realizada a primeira fase experimental deste projeto, ou seja, o desenho e fabricação do dispositivo. O passo limitante desta fase foi a fabricação dos moldes, através da técnica de fotolitografia, tendo sido necessário otimizar o protocolo desta técnica, na tentativa de obter os melhores resultados. Seguidamente, no Instituto Politécnico de Bragança procedeu-se ao estudo do escoamento sanguíneo nos dispositivos desenvolvidos no CEIT, com o objetivo de analisar o efeito das diferentes constrições presentes nas geometrias, o efeito da velocidade, o efeito dos diferentes hematócritos e o efeito da deformabilidade das células na camada de plasma. Assim, conclui-se que, quanto maior for a razão de expansão, maior é a espessura da camada de plasma a jusante da constrição. Relativamente aos caudais, aferiu-se que estes não têm grande influência na camada de plasma e face ao hematócrito, aferiu-se que à medida que se aumenta o hematócrito, a camada de plasma tende a diminuir. Adicionalmente e através do dispositivo que melhores resultados se obtiveram na etapa anterior, efetuou-se o estudo da rigidez celular, tentando mais uma vez compreender qual o efeito que a rigidez teria sobre a espessura camada de plasma. Para tal, foi necessário criar uma série de protocolos que possibilitassem a indução da rigidez celular. Por último, foram realizadas comparações entre a camada de plasma na presença de células saudáveis e a camada de plasma quando foi induzida rigidez nessas mesmas células, tendo-se concluído, que à medida que diminui a deformabilidade da célula, a espessura da camada de plasma tem tendência a diminuir. This report describes the work performed during the 2nd year of the Master in Biomedical Technology at Instituto Politécnico de Bragança (IPB). The work consisted in designing and developing a biomedical micro-device that had the capacity, in a single step, to perform the separation of red blood cells as well as study their deformation under different flow conditions. The initial step consisted on performing a literature survey, to review the topics relevant to a better understanding of the persent project, including biomicrofluidics, blood flow, as well as polymers and techniques involved in the full process of micro-fabrication. After drawing series of geometries, the first steps towards the conception of the devices were carried out during the course of stay in CEIT, University of Navarra, Spain, which included the design and manufacture of the molds required for micro-channel fabrication by soft-lithography. The mold fabrication step was performed using photolithography and required an extensive trial-and-error experimental study, to optimize the protocol of this technique in an attempt to obtain better results in terms of accuracy and feature definition. The devices manufactured in the previous step were used at IPB to study the flow of blood with the aim of analyzing the effect of various parameters on the size of the plasma layer and therefore on red blood cell separation. This study included the effect of constrictions present in different geometries, the effect of the velocity of the fluid and the effect of different hematocrit levels. It was found that the flow rate does not greatly influence the size of the plasma layer. On the other hand, an increase in the expansion ratio (due to a presence of the constriction) induces a larger plasma layer downstream of the expansion, while an increase in hematocrit level reduces the size of the plasma layer. For the flow rates measured, the results showed a slight influence on the plasma layer whereas for the hematocrits tested, the results revealed that as it increases the hematocrit, the plasma layer tends to decrease. The device which achieved the best results in terms of cell separation was then used to study the effect of the cell stiffness on the size of the plasma layer. For this purpose it was necessary to create a series of protocols that enabled the modification of cell rigidity or deformability. The size of the plasma layer was then analyzed in the case of cells with increased rigidity (corresponding to diseased cells) and compared to the results with the healthy cells showing that the thickness of the plasma layer decreases as the cells become more rigid.Este trabalho teve a cooperação da Universidade de Navarra, e do Centro de Investigação (CEIT)

Detection of the crystallization process of paracetamol with a multi-mode optical fiber in a reflective configuration

A configuration of a refractometer sensor is described with the aim of optically detecting the crystallization process of paracetamol. The developed sensing head is based on a conventional cleaved multi-mode fiber. The fiber tip sensor structure was submitted to contact with the liquid of interest (paracetamol fully dissolved in 40% v/v of ethanol/water) and the crystallization process of paracetamol, induced with continued exposure to air, was monitored in real time.info:eu-repo/semantics/publishedVersio

Understanding the implementation of retail self-service check-out technologies using necessary condition analysis

Purpose Self-service check-out technologies (SSTs) are becoming a trend across different retail settings, allowing companies to gain efficiency and reduce costs. Nevertheless, the success of SSTs implementation is still subject to challenges and uncertainties. This study aims to provide insights for theory and managers on the necessary conditions for the successful implementation of retail SSTs. Design/methodology/approach Based on an online survey, data from 251 participants were collected to understand the factors predicting SSTs adoption and realise what conditions are mandatory for the adoption. partial Least Squares Structural Equation Modelling (PLS-SEM) and necessary condition analysis (NCA) were used to analyse the data. Findings According to the NCA analysis results, 12 latent variables were relevant for predicting SSTs adoption, but only seven were necessary conditions for user adoption. Originality/value The complementarity of perspectives for understanding the adoption of SSTs based on the two data analysis techniques provides novel insights into theory and support for retailers' decision-making on self-service technologies (STTs) implementation.info:eu-repo/semantics/publishedVersio

Efeito da drenagem ácida da mina do Lousal nas comunidades de diatomáceas

Mestrado em GeoquímicaNa mina do Lousal foi explorada, durante 88 anos, a pirite para extracção de enxofre, tendo cessado a sua actividade em 1988. A drenagem ácida proveniente da mina e das escombreiras abandonadas provoca alterações das características físico-químicas da água e consequentemente biológicas na ribeira de Corona, devido, essencialmente, ao seu pH baixo e às elevadas concentrações de metais. Com o intuito de compreender estas alterações efectuaram-se 4 campanhas de amostragem, uma por estação do ano, em 7 locais de amostragem previamente seleccionados. As amostras de água superficial foram caracterizadas do ponto de vista físicoquímico mediante a determinação de pH, condutividade e oxigénio dissolvido, carência química de oxigénio (CQO) e da análise de elementos maiores e vestigiais por ICP-MS. As amostras de sedimento de corrente (fracção <170 μm) foram analisadas por ICP-OES. Quando presentes foram caracterizadas as comunidades epilíticas, epipsâmicas e epífitas de diatomáceas em cada local amostrado. A caracterização geoquímica das águas de superfície e dos sedimentos de corrente revelou valores muito acima do fundo geoquímico local, valores esses que de acordo com o critério estabelecido pela “Contaminated Sediment Standing Team” conferem uma elevada toxicidade ao meio aquático. Este trabalho mostra que a mina também está a provocar um impacto negativo nas comunidades de diatomáceas na área em estudo. Devido às drenagens ácidas as comunidades de diatomáceas apresentam não só modificações na sua estrutura como também anomalias na sua morfologia. ABSTRACT: Pyrite was explored for 88 years in Lousal mine for sulphur extraction. The mining activities finished in 1988. The acid mine drainage from the mine spring and the abandoned tailing deposits induce physical, chemical and biological changes in Corona stream. Those changes are due to the acidic environment and high trace metal concentration. In order to understand these changes seasonal sampling took place at 7 sites previously selected. Superficial water samples were characterized by the determination of some physical and chemical parameters (pH, conductivity, dissolved oxygen, chemical oxygen demand (COD) and trace elements by ICP-MS). Stream sediment samples (fraction <170 μm) were analysed by ICP-OES. When present the epilithic, epipsamic and epiphytic diatom communities where characterized at each sampling site. The geochemical characterization of the superficial water and stream sediments revealed much higher concentrations than the local geochemical background values, which according to the “Contaminated Sediment Standing Team” make the aquatic environment very toxic. Negative impacts on the diatom communities where also observed in the surroundings of the mine. Structural changes were detected in the diatom communities as well as morphological anomalies probably due to the acid mine drainage

Vertical dynamics of a large reservoir (Alqueva, Southern Portugal)

An integrated field campaign took place in Alqueva reservoir (Southern Portugal) from June to September 2014 with the objective of the determination of the trophic status and the analysis of the physico-chemical and biological vertical dynamics. Vertical profiles of environmental parameters, water samples for physical-chemical analyses and biological elements were monthly collected from three fixed platforms in the lacustrine zone and selected sites in the margins. Diatoms were collected from artificial substrates at discrete depths and from the margins and phytoplankton was analysed at discrete depths and from integrated samples. Preliminary results reveal that the trophic status of the lacustrine area and corresponding margins can be classified as mesotrophic, based in the vertical profiles (showing also the stratification) and in the TN:TP ratio. Diatom communities and indices did not differ between platforms, revealing the uniformity of the reservoir, in spite of its size. However, diatom taxa richness (S) and Shannon index of diversity (H’) differed with depth, with higher values at 20m depth, which is near the bottom in two sites, and clearly below the euphotic zone. A total of 62 taxa were identified in the integrated phytoplankton samples, with chlorophytes being the taxa richest group whilst cyanobacteria dominated in abundance. The observation of the phytoplankton samples collected at discrete depths revealed the presence of cyanobacteria in the bottom samples (20m and 50m). The presence of diatoms and cyanobacteria at depths far below the euphotic zone, raises the question of which environmental parameters were influencing algal development in the reservoir.This work was co-funded by the European Union through the European Regional Development Fund, framed in COMPETE 2020 (Operational Programme Competitiveness and Internationalization), through the ICT project (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and the ALOP project (ALT20-03-0145-FEDER-000004

Humidity sensor based on optical fiber coated with agarose gel

A reflective fiber optic sensor based on multimode interference for the measurement of relative humidity (RH) is proposed and experimentally demonstrated. The proposed probe is fabricated by fusion-splicing, approximately 30 mm long coreless fiber section to a single mode fiber. A hydrophilic agarose gel is coated on the coreless fiber, using the dip coating technique. When the incident light comes from the SMF to the CSF, the high-order modes are excited and propagate within the CSF. These excited modes interfere with one another as they propagate along whole CSF length, giving rise to a multimode interference (MMI). Since the effective refractive index of the agarose gel changes with the ambient relative humidity, as the environmental refractive index changes, the propagation constants for each guided mode within the CSF will change too, which leads to shifts in the output spectra. The proposed sensor has a great potential in real time RH monitoring, exhibiting a large range of operation with good stability. For RH variations in the range between 60 %RH and 98.5 %RH, the sensor presents a maximum sensitivity of 44.2 pm/%RH, and taking in consideration the interrogation system, a resolution of 1.1% RH is acquired. This sensor can be of interest for applications where a control of high levels of relative humidity is required.publishe