Dependability in Aggregation by Averaging

Aggregation is an important building block of modern distributed applications, allowing the determination of meaningful properties (e.g. network size, total storage capacity, average load, majorities, etc.) that are used to direct the execution of the system. However, the majority of the existing aggregation algorithms exhibit relevant dependability issues, when prospecting their use in real application environments. In this paper, we reveal some dependability issues of aggregation algorithms based on iterative averaging techniques, giving some directions to solve them. This class of algorithms is considered robust (when compared to common tree-based approaches), being independent from the used routing topology and providing an aggregation result at all nodes. However, their robustness is strongly challenged and their correctness often compromised, when changing the assumptions of their working environment to more realistic ones. The correctness of this class of algorithms relies on the maintenance of a fundamental invariant, commonly designated as "mass conservation". We will argue that this main invariant is often broken in practical settings, and that additional mechanisms and modifications are required to maintain it, incurring in some degradation of the algorithms performance. In particular, we discuss the behavior of three representative algorithms Push-Sum Protocol, Push-Pull Gossip protocol and Distributed Random Grouping under asynchronous and faulty (with message loss and node crashes) environments. More specifically, we propose and evaluate two new versions of the Push-Pull Gossip protocol, which solve its message interleaving problem (evidenced even in a synchronous operation mode).Comment: 14 pages. Presented in Inforum 200

Job satisfaction in hotel employess: a systematic review of the literature

Hotel employees' job satisfaction is very important to their performance. In a systematic review of the previous literature on hotel employees, it was found that the most studied variable was job satisfaction; there were no other systematic reviews on the topic. In this review, performed in the Web of Knowledge, Web of Science (Social Sciences Index Expanded, Social Sciences Citation Index, Medline), and Science Direct between 2000 and 2014, 51 studies were found.These studies indicated that satisfaction is crucial to the financial performance and prosperity of hotels and acts a mediator in customer satisfaction. Contributing to greater satisfaction are factors such as greater autonomy and independence, greater power of decision making, flexible schedules, better working conditions, and training. The factors that promote dissatisfaction are wages and reduced benefits. The studies also indicated that a higher level of job satisfaction can have a direct impact on increasing the financial performance of the hotel. The implications of this study for hoteliers and directors relates to the creation of adequate working conditions to increase job satisfaction and provide hotel employees with a greater sense of subjective well-being

Spectra: Robust Estimation of Distribution Functions in Networks

Distributed aggregation allows the derivation of a given global aggregate property from many individual local values in nodes of an interconnected network system. Simple aggregates such as minima/maxima, counts, sums and averages have been thoroughly studied in the past and are important tools for distributed algorithms and network coordination. Nonetheless, this kind of aggregates may not be comprehensive enough to characterize biased data distributions or when in presence of outliers, making the case for richer estimates of the values on the network. This work presents Spectra, a distributed algorithm for the estimation of distribution functions over large scale networks. The estimate is available at all nodes and the technique depicts important properties, namely: robust when exposed to high levels of message loss, fast convergence speed and fine precision in the estimate. It can also dynamically cope with changes of the sampled local property, not requiring algorithm restarts, and is highly resilient to node churn. The proposed approach is experimentally evaluated and contrasted to a competing state of the art distribution aggregation technique.Comment: Full version of the paper published at 12th IFIP International Conference on Distributed Applications and Interoperable Systems (DAIS), Stockholm (Sweden), June 201

Análisis cuantitativo y modelización del metabolismo de la levadura Pichia pastoris

Consultable des del TDXTítol obtingut de la portada digitalitzadaEl presente trabajo está centrado en el análisis y modelización del metabolismo central de la levadura Pichia pastoris. Concretamente, el objetivo de este trabajo consistió en analizar la distribución de flujos en las principales vías metabólicas del metabolismo central de esta levadura mediante distintas aproximaciones experimentales y matemáticas basadas en un modelo metabólico estequiométrico y compartimentalizado. Los datos experimentales fueron obtenidos en su mayor parte del trabajo de tesis de A. Solà (Solà, 2004, tesis doctoral, Universitat Autònoma de Barcelona), centrado en experimentos de marcaje isotópico con 13C de cultivos de P. pastoris operados en quimiostato a =0,05 y 0,16 h-1 con diferentes fuentes de carbono (glucosa, glicerol, metanol y mezclas de glicerol/metanol). Los datos fisiológicos experimentalmente obtenidos en dicho estudio se han reconciliado a través de ecuaciones de balances elementales y por grado de reductancia; además, se ha propuesto una ecuación estequiométrica para la formación de biomasa para cada condición de cultivo estudiada. Los datos reconciliados a través de ecuaciones de balances elementales se han usado para el análisis de flujos metabólicos; en primer lugar, se ha utilizado la metodología clásica; los resultados obtenidos en esta primera aproximación se compararon con datos experimentales previamente obtenidos mediante técnicas de marcaje isotópico de 13C por A. Solà. El segundo estudio ha consistido en el cálculo de flujos metabólicos introduciendo restricciones derivadas de cocientes de flujos metabólicos estimados experimentalmente mediante técnicas de 13C-RMN. Dado el reducido número de restricciones derivadas de experimentos de 13C-RMN que se pueden aplicar en este modelo metabólico (3 o 4), en un tercer estudio se ha realizado una primera aproximación a metodologías de simulación y optimización del diseño de experimentos de marcaje isotópico con el objetivo de implementar un procedimiento experimental que permitiera obtener datos suficientes para determinar con más precisión los flujos a través de determinadas rutas de la red, particularmente los relacionados a la vía de las pentosas fosfato (PP). Concretamente, para explorar esta estrategia se han realizado estudios para la optimización de un experimento de marcaje para un cultivo operado en quimiostato utilizando glicerol como fuente de carbono a =0,05h-1; la estrategia de marcaje optimizada se llevó posteriormente a cabo en el laboratorio y se analizó los patrones de marcaje de los principales metabolitos (incluyendo algunos aminoácidos) y aminoácidos proteinogénicos mediante LC-MS/MS y 2D-RMN, respectivamente. Ello ha permitido comparar y combinar datos experimentales obtenidos mediante dos estrategias de análisis para la estimación de flujos metabólicos. Así, globalmente, este trabajo permite concluir que el análisis clásico de flujos metabólicos (MFA) es una herramienta de cálculo que está limitada a redes poco complejas; sin embargo cuando se aplican restricciones derivadas del análisis por 13C-RMN al MFA, se observa que esta metodología de análisis presenta alta sensibilidad para la determinación de distribución de flujos metabólicos en el ciclo de los ácidos tricarboxílicos (TCA) y reacciones de transporte entre el citoplasma y la mitocondria. Por el contrario, utilizando una metodología de 13C-MFA basada en datos derivados de 13C-LC-MS, se observa que este método presenta poca sensibilidad en redes metabólicas compartimentalizadas, pues no permite distinguir los pools de metabolitos de un compartimiento dado (mitocondria/citoplasma). Sin embargo, este método presenta alta sensibilidad para la determinación de flujos a través de la vía de las PP. Así pues, la combinación de distintas metodologías basadas en datos de experimentos de marcaje isotópico ha permitido mejorar la información sobre el comportamiento del sistema. Finalmente, se ha llevado a cabo un análisis estructural de la red metabólica a través de la metodología del análisis de módulos elementales, así como una primera aproximación para su combinación con el análisis de flujos metabólicos basados en datos de marcaje isotópico con el objetivo de facilitar la interpretación fisiológica de los resultados, es decir, determinar cuales son las principales vías metabólicas activas bajo un estado fisiológico dado y cual es el flujo a través de dichas rutas.This study is focused on the analysis and modelling of the central carbon metabolism of the yeast Pichia pastoris. In particular, the major aim of this study was to analyze de flux distribution through the main metabolic pathways of the central metabolism of this yeast by jeans of different experimental and mathematical approaches, based on a stoichiometric and compartmentalized metabolic model. Experimental data was mostly obtained from previous studies from A. Solà (Solà, 2004, PhD thesis, Universitat Autònoma de Barcelona), describing isotopic labelling experiments with 13C of P. pastoris cells growing on chemostat cultures at a growth rate of =0.05 and 0.16 h-1, on different carbon sources (glucose, glycerol, methanol and mixtures of glycerol/methanol). The experimental physiological data obtained in A. Solà's study have been reconciliated by means of elementary and grade of reductance balance equations; moreover, a stoichiometric equation for the formation of biomass has been proposed for each of the studied growth condition. The data reconciliated by elementary balance equations have been used for metabolic flux analysis. First, the classic metabolic flux analysis methodology has been applied; the obtained results in this first approximation were compared with the experimental data previously generated from 13C-labeling experiments by A. Solà. Second, metabolic fluxes have been calculated introducing a number of restrictions derived from metabolic flux ratios experimentally estimated by 13C-NMR. Third, given the reduced number of restrictions derived from these experiments that are actually aplicable to the defined metabolic model (3 or 4), we performed a first approximation to methodologies for simulation and optimisation of isotopic labeling experiments; the aim of such approach was to implement an experimental procedure to allow for the generation of labelling data needed for the precise determination of fluxes through some pathways of the network, particularly those related to the pentose phosphate pathway (PPP). In order to explore this strategy, studies for the optimisation of a labelling experiment of cells growing on glycerol in chemostat cultures at a growth rate of 0.05 h-1 were performed. The optimised labelling strategy was subsequently implemented in the laboratory; the labelling patterns of the major metabolites (including some amino acids) of the central carbon metabolism and, of the proteinogenic amino acids, were analysed by LC-MS/MS and 2D-NMR, respectively. This allowed us comparing and combining experimental labelling data derived from two analytical strategies for the calculation of metabolic fluxes. Overall, this study illustrates that classic metabolic flux análisis (MFA) is a mathematical tool limited to networks of low complexity. Nevertheless, when restrictions derived from 13C-NMR analyses are introduced MFA, this methodology shows a high sensitivity for the calculation of the metabolic flux distribution in the tricarboxylic acid cycle (TCA) and transport reactions of TCA intermediates between cytoplasm and mitochondria. In contrast, by using a 13C-MFA methodology using data derived from 13C-LC-MS, we observe that this method shows low sensitivity for compartimentalized metabolic networks, as it did not allow distinguishing pools of a given metabolite found in different compartments (e.g. mitochondria/cytoplasm). Nevertheless, this method shows high sensitivity for determining fluxes through the PPP

The Case of the Autonomous Region of Madeira

Tourism has been highlighted as one of the sectors with the greatest potential for expansion on a global scale, so it is important to try to understand the factors of innovation and regional competitiveness in this sector. Competitiveness, particularly in the tourism sector, has experienced in recent decades an unprecedented development of experiences and now plays a very important role in markets and industries. However, the success of the tourist destinations in the world and regional markets is in a way influenced by their relative competitiveness. In this sense, innovation is a very important catalyst for the survival and growth of tourism and it is recognized the positive impacts, revealing that the innovative behaviors and products improve financial and economic performance positively. In this PhD thesis, several topics are analyzed, although some still need future investigation, related to the importance of the regional competitiveness and innovation for the tourism sector. This investigation is made up of four empirical studies with geographic focus in the Autonomous Region of Madeira. The first study of this PhD thesis (chapter 2), entitled “Regional Competitiveness and Innovation in the Tourism Sector: A Systematic Review and Bibliometric Analysis", aims to carry out a mapping of scientific publications, intellectual knowledge, trends research and potential future lines of investigation in the areas of the regional competitiveness and tourism innovation. It is used a systematic literature review using a bibliometric approach, based on the VOSviewer Software, focusing on the creation of the intellectual structure visualization maps. The analysis type is based on the number of published articles and number of annual citations, for the period from 1900 to 2016, through the Web of Science database. The results show that the intellectual structure of the regions' competitiveness is divided into three main categories: regional competitiveness, tourism innovation and tourism cluster. The main contribution of this study is the identification of the main research trends in this area and its gaps and specific needs of future scientific research within this field of research. The second empirical study (chapter 3), entitled "Impact of Satisfaction of Tourist Events as a Regional Tourist Competitiveness Product", aims to analyze the impact and contribution of satisfaction with tourist events as a product of regional tourist competitiveness, as well as evaluate factors of competitiveness. For that, a questionnaire was carried out on the four major tourist events in the Autonomous Region of Madeira (Carnival, Flower Festival, Atlantic Festival, and Wine Festival). The sample is composed of 2262 tourists surveyed during the year 2017 and structural equation models were used as statistical method. The results show that satisfaction is reflected in the client's loyalty to the choice of a tourist destination and it also contributes, directly and indirectly to the regional tourist competitiveness. This study contributes to the valorization of local and regional events, perceived by the level of satisfaction and loyalty of tourists, as products of regional competitiveness of a tourist destination. The third empirical study (chapter 4) entitled "Entrepreneurial Craft Products as Regional Tourist Competitiveness", aims to explore and analyze the role of handcrafted products in entrepreneurship and regional tourist competitiveness. This study is based on secondary data from different sources (Regional Statistics Office of Madeira, Institute of Wine, Embroidery and Handicraft of Madeira) and it covers the last 15 years (2001 - 2015). It was made a quantitative analysis of the data through an econometric approach using Pearson's regression and correlation models. The study contributes with empirical evidence which helps us to identify the role of handcrafted products for the entrepreneurial capacity and tourist competitiveness of a region. In addition, it also contributes to the knowledge of the scientific community with particular interest in artisan entrepreneurship, cultural and regional competitiveness in the tourism sector. Finally, the fourth and final empirical study of this PhD thesis (chapter 5) entitled "Innovation as a driver of the competitiveness of business tourism", aims to analyze factors and barriers to innovation and their impact (direct and indirect) on the competitiveness of the destination and business competitiveness. Based on primary data collected by a questionnaire from a sample of 119 companies operating in the tourism sector in the Autonomous Region of Madeira (Portugal), a quantitative methodology was applied using econometric and multiple linear regression models. The study empirically identifies and tests existing relationships underlying innovation (factors and barriers) as a level for the competitiveness of destination and business. The results show important theoretical and practical implications in the contribution of innovation to destination and business competitiveness, thus contributing to filling the gaps identified in the literature.O turismo tem sido destacado como um dos setores com maior potencial de expansão à escala mundial, deste modo torna-se importante tentar compreender os fatores de inovação e competitividade regional nesse setor. A competitividade, em particular no setor do turismo, tem enfrentado nas últimas décadas um desenvolvimento de experiências sem precedentes e desempenha agora um papel muito importante nos mercados e indústrias, no entanto o sucesso dos destinos turísticos, nos mercados mundiais e regionais é de certo modo influenciado pela sua competitividade relativa. Neste sentido, a inovação é um catalisador muito importante para a sobrevivência e crescimento de turismo e são-lhe reconhecidos os impactos positivos, revelando que os comportamentos e produtos inovadores melhoram positivamente desempenhos financeiros e económicos. Nesta tese de doutoramento são analisados vários tópicos, embora alguns ainda carecem de futura investigação, relacionados com a importância da competitividade regional e da inovação para o setor do turismo. Esta investigação é constituída por quatro estudos empíricos com foco geográfico na Região Autónoma da Madeira (RAM). O primeiro estudo desta tese de doutoramento (capítulo 2), intitulado “Competitividade Regional e Inovação no Setor do Turismo: Uma Revisão Sistemática e Análise Bibliométrica”, tem como objetivo a realização de um mapeamento, das publicações científicas, do conhecimento intelectual, das tendências de investigação realizadas e potenciais linhas futuras de investigação nas áreas da competitividade regional, cluster do turismo e inovação turística. Utiliza-se uma revisão sistemática da literatura mediante uma abordagem bibliometrica, com base no Software VOSviewer, com foco na criação dos mapas de visualização de estrutura intelectual. O tipo de análise é baseado no número de artigos publicados e número de citações anuais, para o período de 1900 a 2016, através da base de dados Web of Science. Os resultados evidenciam que a estrutura intelectual sobre a competitividade das regiões divide-se essencialmente em três grandes categorias: competitividade regional, inovação turística e cluster do turismo. O principal contributo deste estudo prende-se com a identificação das principais tendências de investigação nesta área e respetivas lacunas e necessidades específicas de investigação científica futura dentro deste campo de investigação. O segundo estudo empírico (capítulo 3), intitulado “Impacto da Satisfação dos Eventos Turísticos como Produto de Competitividade Turística Regional”, tem como objetivo analisar o impacto e contributo da satisfação com eventos turísticos enquanto produto de competitividade turística regional, bem como avaliar fatores de competitividade. Para tal foi realizado, um estudo por questionário aos quatro maiores eventos turísticos da Ilha da Madeira (carnaval, festa da flor, festival do atlântico, e festa do vinho), região insular localizada em Portugal. A amostra é composta por 2262 turistas inquiridos durante o ano de 2017 e foram utilizados modelos de equações estruturais, como método estatístico. Os resultados evidenciam que a satisfação se reflete na fidelidade do cliente quanto à escolha de um destino turístico e contribui ainda, direta e indiretamente para a competitividade turística regional. Este estudo contribui para a valorização dos eventos locais e regionais, percecionada pelo nível de satisfação e fidelização dos turistas, como produtos de competitividade regional de um destino turístico. O terceiro estudo empírico (capítulo 4) intitulado “Produtos Artesanais Empreendedores como Competitividade Turística Regional”, tem como objetivo, explorar e analisar o papel dos produtos artesanais no empreendedorismo e competitividade turística regional. Este estudo tem por base dados secundários de diferentes fontes (Direção Regional de Estatística da Madeira, Instituto do Vinho do Bordado e do Artesanato da Madeira) cobrido o período temporal dos últimos 15 anos (2001 – 2015). Foi feita uma análise quantitativa dos dados através de uma abordagem econométrica com recurso a modelos de regressão e correlação de Pearson. O estudo contribui com evidências empíricas que nos ajudam a identificar o papel dos produtos artesanais para a capacidade empreendedora e competitividade turística de uma região. Para além disso, contribui ainda para o conhecimento da comunidade científica com particular interesse no empreendedorismo artesanal, cultural e competitividade regional no setor do turismo. Finalmente, o quarto e último estudo empírico desta tese de doutoramento (capítulo 5) intitulado “Inovação como motor da competitividade do turismo empresarial”, tem como objetivo analisar fatores e barreiras de inovação e o seu impacto (direto e indireto) na competitividade do destino e competitividade empresarial. A partir de dados primários recolhidos por questionário a uma amostra de 119 empresas a operar no setor do turismo, na região autónoma da Madeira (Portugal), foi aplicado uma metodologia quantitativa com recurso a modelos econométricos e de regressão linear múltipla. O estudo identifica e testa empiricamente relações existentes e subjacentes à inovação (fatores e barreiras) enquanto alavanca para a competitividade do destino e empresarial. Os resultados evidenciam importantes implicações teóricas e práticas na contribuição da inovação para a competitividade de destino e empresarial, contribuindo assim para ao preenchimento das lacunas identificadas na literatura

Funcionários de hotelaria: uma revisão sistemática da literatura

With the increase of studies on hospitality professionals over the years, it is essential to perform a review on those works. This review was conducted through the databases Web of Knowledge, Web of Science (Social Sciences Index Expanded, Social Sciences Citation Index, Medline), and Science Direct. We searched for articles published between 2000 and 2014, crossing the keywords ?hospitality?, ?tourism?, and ?hotel? with the keywords ?professionals?, ?employees?, and ?workers?. Our aim was to identify the most studied variables on hospitality employees. The search process resulted on 3700 initial references, being selected 242. We verified that work satisfaction was studied in 51 articles and stress, burnout, and mental exhaustion in 31. For that reason, this review aggregates and analyses these results. This study has implications for the understanding of the roll of these variables in hospitality and tourism economic profitability, as well as in human resources management policies and individual well-being

Physical limitations of travel time based shallow water tomography

Travel-time-based tomography is a classical method for inverting sound-speed perturbations in an arbitrary environment. A linearization procedure enables relating travel-time perturbations to sound-speed perturbations through a kernel matrix. Thus travel-time-based tomography essentially relies on the inversion of the kernel matrix and is commonly called ‘linear inversion. In practice, its spatial resolution is limited by the number of resolved and independent arrivals, which is a basic linear algebra requirement for linear inversion performance. Physically, arrival independency is much more difficult to determine since it is closely related to the sound propagating channel characteristics. This paper presents a brief review of linear inversion and shows that, in deep water, the number of resolved arrivals is equal to the number of independent arrivals, while in shallow water the number of independent arrivals can be much smaller than the number of resolved arrivals. This implies that in shallow water there are physical limitations to the number of independent travel times. Furthermore, those limitations are explained through the analysis of an equivalent environment with a constant sound speed. The results of this paper are of central importance for the understanding of travel-time-based shallow water tomography