Plataforma Off-shore com Turbina Eólica Simulação e Controlo

O objetivo deste trabalho é o de simular e controlar a plataforma de um aerogerador flutuante. Este aerogerador flutuante consiste numa plataforma do tipo semi-submersível, nomeadamente o DeepCwind acoplado a um aerogerador de 5 MW, mais especificamente o NREL offshore 5-MW baseline wind turbine. Descreve-se o modelo físico do aerogerador flutuante, a formulação teórica a ele subjacente, bem como a caraterização dos diferentes estados do vento e do mar utilizados para simulação. O modelo não linear do aerogerador flutuante foi simulado, utilizando o FAST como emulador do aerogerador flutuante, para condições ambientais determinísticas, por forma a compreender a dinâmica associada à plataforma. Modelos lineares foram obtidos, por linearização do modelo não linear, aplicando técnicas de identificação de sistemas e utilizando o módulo de linearização do simulador FAST. Estes modelos foram posteriormente comparados, utilizando um único modelo para síntese de controladores. Controladores esses, desenvolvidos com base num modelo linear simplificado que consiste no pitch da plataforma, transformando o problema global da plataforma num problema bidimensional. Projetou-se um controlador proporcional-integral-derivativo (PID) e um controlador em espaço de estados por colocação de pólos. A simulação do modelo não linear, com o controlo do pitch da plataforma, para diferentes condições ambientais, demonstrou o bom desempenho dos controladores. Foi possível com ambos os controladores garantir os requisitos do sistema controlado, em que se exigia que se evitasse ressonâncias e em que o pitch da plataforma fosse nulo, por forma a garantir a perpendicularidade do plano das pás (plano do rotor) do aerogerador em relação à direção do vento.

A portrait of the Spanish accounting community

This study presents a portrait of the Spanish academic accountingcommunity in 1995, based upon a questionnaire circulated to Spanishaccounting academics in 1995 and upon an analysis of authorship andcitations in the main Spanish accounting journals. The approach tothese analyses is grounded in similar studies which have been carriedout in the United States, Spain and elsewhere. but the combination oftechniques used in this study is particularly broad in range.The results of the study are used to describe a range ofcharacteristics of Spanish accounting academics, for example,publications records and length of academic experience. The analysisof publications produces a ranking by institutional affiliation ofthe most significant contributors to current debates on accounting.Citation analysis is used to identify the range and extent ofinternational influences upon the Spanish academic accountingcommunity, and to provide an additional ranking by institutionalaffiliation of the most frequently cited sources A significantfinding was that the nature and extent of international influence hadchanged very little over the ten year period since Spain entered theEuropean Union and started to implement European Directives.Perceptions of journal quality were elicited by questionnaire. Fortyfive journals, Spanish and international are included in a listranked for perceived importance as outlets for publication. and assources of support for teaching and research. The results of thisexercise show that Spanish journals were ranked low relative tojournals published in the United Kingdom and United States.Finally the study examines the extent of purpose upon Spanishaccounting academies to publish, by presenting results of a questionabout criteria for promotion, and also by examining and increasingtendency to publish co-authored work.

On the throughput-WIP trade-off in queueing systems, diminishing returns and the threshold property: A linear programming approach

We present a new unifying framework for investigating throughput-WIP(Work-in-Process) optimal control problems in queueing systems,based on reformulating them as linear programming (LP) problems withspecial structure: We show that if a throughput-WIP performance pairin a stochastic system satisfies the Threshold Property we introducein this paper, then we can reformulate the problem of optimizing alinear objective of throughput-WIP performance as a (semi-infinite)LP problem over a polygon with special structure (a thresholdpolygon). The strong structural properties of such polygones explainthe optimality of threshold policies for optimizing linearperformance objectives: their vertices correspond to the performancepairs of threshold policies. We analyze in this framework theversatile input-output queueing intensity control model introduced byChen and Yao (1990), obtaining a variety of new results, including (a)an exact reformulation of the control problem as an LP problem over athreshold polygon; (b) an analytical characterization of the Min WIPfunction (giving the minimum WIP level required to attain a targetthroughput level); (c) an LP Value Decomposition Theorem that relatesthe objective value under an arbitrary policy with that of a giventhreshold policy (thus revealing the LP interpretation of Chen andYao's optimality conditions); (d) diminishing returns and invarianceproperties of throughput-WIP performance, which underlie thresholdoptimality; (e) a unified treatment of the time-discounted andtime-average cases.

The Spanish motor industry in the first third of the 20th Century: A lost opportunity

The Spanish automobile industry had a late start. Although the country proved capable of short production runs of high-quality vehicles during the first third of the century it never managed to build up its own industry, unlike Great Britain, France, or Italy. What then, were the critical shortcomings that prevented the establishment of large Spanish motor manufacturers? Put another way, why did all of the companies set up during the first half-century fail to survive? This paper attempts to shed some light on these questions, employing a wide-ranging analysis of both internal and external factors affecting the industry. A feeble internal market, lack of resources and production factors are usually adduced as reasons, as are Spain's general economic backwardness and the role played by the public authorities. However, this paper mainly focuses on the internal factors concerning company strategy and organisation. A comparison with the Italian case helps put the traditional arguments in proper perspective and highlights those covering business strategies. Finally, we argue that a broad range of factors needs to be analysed to fully understand why Spain failed to establish a motor industry.

Measuring intangibles' productivity. Empirical evidence from Spanish firms

As companies and shareholders begin to note the potential repercussions of intangible assets uponbusiness results, the inability of the traditional financial statement model to reflect these new waysof creating business value has become evident. Companies have widely adopted newmanagement tools, covering in this way the inability of the traditional financial statement model toreflect these new ways of creating business value.However, there are few prior studies measuring on a quantifiable manner the level of productivityunexplained in the financial statements. In this study, we measure the effect of intangible assets onproductivity using data from Spanish firms selected randomly by size and sector over a ten-yearperiod, from 1995 to 2004. Through a sample of more than 10,000 Spanish firms we analyse towhat extent labour productivity can be explained by physical capital deepening, by quantifiedintangible capital deepening and by firm s economic efficiency (or total factor productivity PTF).Our results confirm the hypothesis that PTF weigh has increased during the period studied,especially on those firms that have experienced a significant raise in quantified intangible capital,evidencing that there are some important complementary effects between capital investment andintangible resources in the explanation of productivity growth. These results have significantdifferences considering economic sector and firm s dimension.

Management information systems: The balanced scorecard in Spanish public universities

Organisations are becoming increasingly aware of the need for management information systems, due largely to the changing environment and a continuous process of globalisation. All of this means that managers need to adapt the structures of their organisations to the changes and, therefore, to plan, control and manage better. The Spanish public university cannot avoid this changing (demographic, economic and social changes) and globalising (among them the convergence of European qualifications) environment, to which we must add the complex organisation structure, characterised by a high dispersion of authority for decision making in different collegiate and unipersonal organs. It seems obvious that these changes must have repercussions on the direction, organisation and management structures of those public higher education institutions, and it seems natural that, given this environment, the universities must adapt their present management systems to the demand by society for the quality and suitability of the services they provide.

A consistency test of the time trade-off

This paper tests the internal consistency of time trade-off utilities.We find significant violations of consistency in the direction predictedby loss aversion. The violations disappear for higher gauge durations.We show that loss aversion can also explain that for short gaugedurations time trade-off utilities exceed standard gamble utilities. Ourresults suggest that time trade-off measurements that use relativelyshort gauge durations, like the widely used EuroQol algorithm(Dolan 1997), are affected by loss aversion and lead to utilities thatare too high.

A test of the predictive validity of non-linear QALY models using time trade-off utilities

This paper presents a test of the predictive validity of various classes ofQALY models (i.e., linear, power and exponential models). We first estimatedTTO utilities for 43 EQ-5D chronic health states and next these states wereembedded in health profiles. The chronic TTO utilities were then used topredict the responses to TTO questions with health profiles. We find that thepower QALY model clearly outperforms linear and exponential QALY models.Optimal power coefficient is 0.65. Our results suggest that TTO-based QALYcalculations may be biased. This bias can be avoided using a power QALY model.

Trade-off between formal and informal care in Spain

The remarkable growth of older population has moved long term care to the front ranks of the social policy agenda. Understanding the factors that determine the type and amount of formal care is important for predicting use in the future and developing long-term policy. In this context we jointly analyze the choice of care (formal, informal, both together or none) as well as the number of hours of care received. Given that the number of hours of care is not independent of the type of care received, we estimate, for the first time in this area of research, a sample selection model with the particularity that the first step is a multinomial logit model. With regard to the debate about complementarity or substitutability between formal and informal care, our results indicate that formal care acts as a reinforcement of the family care in certain cases: for very old care receivers, in those cases in which the individual has multiple disabilities, when many care hours are provided, and in case of mental illness and/or dementia. There exist substantial differences in long term care addressed to younger and older dependent people and dependent women are in risk of becoming more vulnerable to the shortage of informal caregivers in the future. Finally, we have documented that there are great disparities in the availability of public social care across regions.

Price regulation of plastic money: A critical assessment of Spanish rules

Recent decisions by the Spanish national competition authority (TDC) mandate paymentsystems to include only two costs when setting their domestic multilateral interchange fees(MIF): a fixed processing cost and a variable cost for the risk of fraud. This artificiallowering of MIFs will not lower consumer prices, because of uncompetitive retailing; but itwill however lead to higher cardholders fees and, likely, new prices for point of saleterminals, delaying the development of the immature Spanish card market. Also, to the extent that increased cardholders fees do not offset the fall in MIFs revenue, the task of issuing new cards will be underpaid relatively to the task of acquiring new merchants, causing an imbalance between the two sides of the networks. Moreover, the pricing scheme arising from the decisions will cause unbundling and underprovision of those services whose costs are excluded. Indeed, the payment guarantee and the free funding period will tend to be removed from the package of services currently provided, to be either provided by third parties, by issuers for a separate fee, or not provided at all, especially to smaller and medium-sized merchants. Transaction services will also suffer the consequences that the TDC precludes pricing them in variable terms.

English as a world language: its role as a lingua francaa sociolinguistic profile of students of secondary schools in Santiago Island, in the Archipelago of Cape Verde

Esta tese centra-se em aspectos relevantes do inglês como uma língua universal, no actual contexto globalizado e examina possíveis mudanças relacionadas com o seu uso, em especial no continente africano, particularmente no caso de Cabo Verde, no sentido de ponderar eventuais alternativas nas pedagogias linguísticas no ensino desta língua que impliquem uma adaptação à realidade contemporânea. Uma vez que, nos nossos tempos, o inglês é a língua de eleição para a comunicação intercultural entre povos com várias experiências culturais e linguísticas, o conhecimento deste idioma torna-se, a cada dia que passa, impreterível e indispensável, na interacção intercultural. Em África, as funções desempenhadas pelo inglês são complexas; além da língua inglesa ser usada para comunicação entre etnias, com o estatuto de língua franca, também tem o papel de preservar a identidade nacional e de estabelecer a unidade entre os povos da mesma nação. Por conseguinte, é de considerar talvez ainda com mais pertinência, a adopção de uma nova filosofia de pedagogia de ensino que permita dotar os seus cidadãos de capacidades que lhes possibilitem comunicar de forma inteligível com povos de outras culturas e línguas. O primeiro capítulo aborda aspectos teóricos relacionados com a expansão, comunicação e mudança associadas à língua inglesa e suas implicações no ensino em países onde esta não é língua nativa (L1). O segundo capítulo reflecte, em primeiro lugar, sobre a situação linguística em África e as línguas francas predominantes no continente, incluindo a língua inglesa. Considera também questões relacionadas com o multilinguismo e a identidade, bem como assuntos relacionados com as implicações da diversidade linguística para a educação dos povos africanos.

Children's work in Spanish textiles during the 19th and 20th Centuries

This essay deals with the reasons explaining children s work in 19th century textile factories and their removal during the first part of the 20th century. The inadequacy of the structure of incomes and expenditures of the household and the very low economic incentives to educate children can explain why children were in the factories and not in the school. Moreover, the marginal economic contribution to the economy of the household of a child was the same as that of his mother. This normally implied that women and children were perfect substitutes. When the family had a child at working age this allowed to replace the paid work input of the mother. With the beginnings of the 20th century a set of changes leading to the increase of women s productivity and hourly real wages, switched the situation and involved the new incorporation of women into paid work and the investment in children s human capital.

Job creation under liquidity constraints: The Spanish case

This paper shows that liquidity constraints restrict jobcreation even when labor markets are flexible. In a dynamicmodel of labor demand, I show that in an environment of imperfect capital and imperfect labor markets, firms usetemporary contracts to relax financial constraints. Evidence for the predictions of the model is presented using Spanish data from the CBBE (Central de Balances del Banco de España - Balance Sheet data from the Bank of Spain). It is shown that firms substitute temporary laborfor permanent one and use less debt as their financial position improves. In particular, it is rejected that Spanish firms operate in an environment of free capital markets and of no labor adjustment costs. The labor reform of 1984, which created temporary contracts, implied to some extent a relaxation of liquidity constraints.Accordingly, firms used these contracts more extensivelyand used less debt; however, as capital markets continueto be imperfect, permanent job creation continues to beslow. Consequently, relaxation of liquidity constraints should also be part of a job creation strategy.

Interlocking directorates in Spanish banking in the twentieth century

Spanish banking historiography asserts that the largest banks performed in the twentieth century as though they constituted a monopoly. One of their main coordination schemes would have been a network of interlocking bank directors that would include most of the financial firms. Evidence available for the 1920s and 1960s seems to confirm the veracity of this hypothesis. In this paper, more systematic evidence is presented to cover the whole twentieth century with the aim of checking whether these networks persisted over the entire period or they were by-products of temporary situations. Our results show that no general network remained for more than a decade. Therefore, it should be ruled out that interlocking directorates worked as a coordination device of an alleged banking cartel.

Earnings management in Spain. Some evidence from companies quoted in the Spanish stock exchange

After the accounting scandals that have taken place mainly in the UnitedStates during the last years, some Spanish leading authorities havedefended the idea that this kind of accounting problems cannot happen inSpain. They argue that accounting regulation in Europe, and specificallyin Spain, make more difficult the use of creative accounting practices.The objective of this paper is to identify some evidence about thesituacion in Spain. The study tries to demonstrate that some accountingpractices of several of the companies quoted in the Spanish Stock Exchangecould be qualified as earnings management.To carry out this study, the authors have analysed the accounts of the 35companies included in the stock market index IBEX 35. This index iscalculated with the share prices variations of the most importantcompanies quoted in the Spanish Stock Exchange.