Acquisition and loss of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Prevotella intermedia over a 5-year period: effect of a triclosan/copolymer dentifrice

Objectives: The present study describes the natural history of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Prevotella intermedia over a 5-year period and the effect of a triclosan/copolymer dentifrice on these organisms in a normal adult population. Material and Methods: Subgingival plaque samples were collected from 504 adult volunteers. Probing pocket depths (PPD) and relative attachment levels were measured using an automated probe. Participants were matched for disease status (CPI), plaque index, age and gender, and allocated to receive either a triclosan/copolymer or placebo dentifrice. Re-examination and subgingival plaque sampling was repeated after 1, 2, 3, 4 and 5 years. P. gingivalis, A. actinomycetemcomitans and P. intermedia were detected and quantitated using an enzyme linked immunosorbent assay. Logistic regression and generalised linear modelling were used to analyse the data. Results: This 5-year longitudinal study showed considerable volatility in acquisition and loss (below the level of detection) of all three organisms in this population. Relatively few subjects had these organisms on multiple occasions. While P. gingivalis was related to loss of attachment and to PPD greater than or equal to3.5 mm, there was no relationship between A. actinomycetemcomitans or P. intermedia and disease progression over the 5 years of the study. Smokers with P. gingivalis had more PPD greater than or equal to3.5 mm than smokers without this organism. There was no significant effect of the triclosan dentifrice on P. gingivalis or A. actinomycetemcomitans . Subjects using triclosan were more likely to have P. intermedia than those not using the dentifrice; however this did not translate into these subjects having higher levels of P. intermedia and its presence was uniform showing no signs of increasing over the course of the study. Conclusion: The present 5-year longitudinal study has shown the transient nature of colonisation with P. gingivalis , A. actinomycetemcomitans and P. intermedia in a normal adult population. The use of a triclosan-containing dentifrice did not lead to an overgrowth of these organisms. The clinical effect of the dentifrice would appear to be independent of its antimicrobial properties.

On the robustness of short-term interest rate models

This paper investigates the robustness of a range of short–term interest rate models. We examine the robustness of these models over different data sets, time periods, sampling frequencies, and estimation techniques. We examine a range of popular one–factor models that allow the conditional mean (drift) and conditional variance (diffusion) to be functions of the current short rate. We find that parameter estimates are highly sensitive to all of these factors in the eight countries that we examine. Since parameter estimates are not robust, these models should be used with caution in practice.

Os fundos de investimento imobiliário listados em bolsa e as variáveis que influenciam seus retornos

Os fundos de investimento imobiliário combinam características tanto do mercado imobiliário, fonte de seus rendimentos, quanto do mercado de capitais, ambiente em que são negociados. O impacto de cada um desses mercados subjacentes no comportamento, desempenho e risco dessa classe de ativos não é, no entanto, ainda claramente definida, sendo um dos grandes temas em análise, tanto na literatura acadêmica, quanto na indústria de fundos internacionais. Em face da significativa expansão dessa alternativa de investimento no mercado brasileiro, no presente estudo foram analisadas as variáveis que influenciam os retornos dos fundos imobiliários brasileiros para uma amostra de fundos listados em Bolsa de Valores de São Paulo, período de 2008-2013. Seguindo a metodologia de Clayton e Mackinnon (2003), os fatores explicativos dos retornos foram decompostos em quatro componentes principais, sendo três fatores de retorno de mercado (mercado de ações, mercado de renda fixa e mercado imobiliário) e risco idiossincrático. De acordo com a estatística descritiva, os fundos imobiliários da amostra apresentaram maior retorno em relação aos demais mercados, exceto em comparação com o mercado imobiliário, porém com menor risco. As análises de correlação, regressão e decomposição da variância indicam que o mercado de ações e o mercado imobiliário direto são, em geral, significativos no modelo, porém explicam apenas cerca de 15% da volatilidade dos retornos dos fundos da amostra. À luz da Moderna Teoria do Portfólio, esses resultados indicam que a inclusão de fundos imobiliários pode ter potencial diversificador numa carteira multi-ativo, seja aumentando o retorno total de uma carteira formada de ações e títulos de renda fixa, sem acréscimo em risco; ou mantendo o retorno dessa carteira, com diminuição da volatilidade, ampliando assim a fronteira eficiente da carteira. Esse efeito questiona o tradicional equilibrium fund de carteiras de investimentos formadas apenas de ações e renda fixa e aponta os fundos imobiliários como uma alternativa de investimento diversificadora, enquanto classe de ativo única. A análise de subamostras por tipologia indica, porém, que o papel diversificador dos fundos imobiliários está atrelado ao tipo de empreendimento que lastreia esse fundo, uma vez que os fatores explicativos e seus impactos nos retornos diferem de uma tipologia para outra. Esse resultado tem importantes implicações no critério de seleção a ser adotado tanto por investidores para seleção de ativos para uma carteira otimizada, como para gestores de fundos imobiliários na formatação e gestão desses produtos. Conclui-se também que os retornos dos fundos, de certo modo, refletem seu caráter híbrido, mas o modelo decomposto em 4 componentes não é suficiente para explicar os retornos dos fundos imobiliários, uma vez que o modelo estendido, demonstrou que outras variáveis, inclusive parâmetros desses próprios mercados, além de variáveis macroeconômicas e as características de cada fundo (eg. market-to-book, tamanho), podem ser responsáveis por explicar considerável parte da variância dos retornos dos FIIs.

Finantial risk analysis of portuguese textile and tourism companies

Textile and tourism sectors are two important industries in the Portuguese economy. However, its high exposure to both internal and international economic volatility make the companies operating in these economic sectors particularly vulnerable to economic crises, such as the ones which have been impacting Portugal and the European Union. The objective of this paper is to evaluate and understand the impact of size and age on the financial health of textile and tourism companies, measured by economic indices. An empirical based model is proposed. Its implications are derived and tested on a sample of 4061 Portuguese companies from textile and tourism sectors, during the period 2005-2009. The findings suggest that age has a major impact on the risk of failure, rather than size. Whereas the effect of age is generally positive regarding the financial health of the company, the effect of size is less clear and ultimately depends on the age of the company.

The impact of size and age of the company on assessing financial risk

Textiles and tourism sectors are two important sectors in Portuguese economy. Its high exposure to both internal and international economy volatility transform the companies operating in these economic sectors especially vulnerable to recent economic crises in Portugal and European Union. The objective of this paper is to evaluate and understand the impact of size and age on the financial health of textile and tourism companies, measured by economic indices. An empirical based model is proposed. Its implications are derived and tested on a sample of 4061 Portuguese companies from textile and tourism sector, during the period 2005-2009. The results conclude that age has a stronger impact on the risk of failure than size. Whereas the effect of age is generally positive regarding the financial health of the company, the effect of size is less clear and depends on the age of the company.

Financial Risk Analysis of Portuguese Textile and Tourism Companies

Textile and tourism sectors are two important industries in the Portuguese economy. However, its high exposure to both internal and international economic volatility make the companies operating in these economic sectors particularly vulnerable to economic crises, such as the ones which have been impacting Portugal and the European Union. The objective of this paper is to evaluate and understand the impact of size and age on the financial health of textile and tourism companies, measured by economic indices. An empirical based model is proposed. Its implications are derived and tested on a sample of 4061 Portuguese companies from textile and tourism sectors, during the period 2005-2009. The findings suggest that age has a major impact on the risk of failure, rather than size. Whereas the effect of age is generally positive regarding the financial health of the company, the effect of size is less clear and ultimately depends on the age of the company.

Financial Risk Analysis of Portuguese Textile and Tourism Companies

Textile and tourism sectors are two important industries in the Portuguese economy. However, its high exposure to both internal and international economic volatility make the companies operating in these economic sectors particularly vulnerable to economic crises, such as the ones which have been impacting Portugal and the European Union. The objective of this paper is to evaluate and understand the impact of size and age on the financial health of textile and tourism companies, measured by economic indices. An empirical based model is proposed. Its implications are derived and tested on a sample of 4061 Portuguese companies from textile and tourism sectors, during the period 2005-2009. The findings suggest that age has a major impact on the risk of failure, rather than size. Whereas the effect of age is generally positive regarding the financial health of the company, the effect of size is less clear and ultimately depends on the age of the company.

The impact of size and age of the company on assessing financial risk.

Textiles and tourism sectors are two important sectors in Portuguese economy. Its high exposure to both internal and international economy volatility transform the companies operating in these economic sectors especially vulnerable to recent economic crises in Portugal and European Union. The objective of this paper is to evaluate and understand the impact of size and age on the financial health of textile and tourism companies, measured by economic indices. An empirical based model is proposed. Its implications are derived and tested on a sample of 4061 Portuguese companies from textile and tourism sector, during the period 2005-2009. The results conclude that age has a stronger impact on the risk of failure than size. Whereas the effect of age is generally positive regarding the financial health of the company, the effect of size is less clear and depends on the age of the company.

Volatilidade implícita: Importância na valorização das opções financeiras e significado dos índices de volatilidade implícita

Mestrado em Contabilidade Internacional

A hybrid PSO-ANFIS approach for short-term wind power prediction in Portugal

The increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Wind power prediction plays a key role in tackling these challenges. The contribution of this paper is to propose a new hybrid approach, combining particle swarm optimization and adaptive-network-based fuzzy inference system, for short-term wind power prediction in Portugal. Significant improvements regarding forecasting accuracy are attainable using the proposed approach, in comparison with the results obtained with five other approaches.

Risk Aversion in a Mixed-Integer Nonlinear Approach to Support Decision-Making for a Hydro Power Producer

In this paper, a mixed-integer nonlinear approach is proposed to support decision-making for a hydro power producer, considering a head-dependent hydro chain. The aim is to maximize the profit of the hydro power producer from selling energy into the electric market. As a new contribution to earlier studies, a risk aversion criterion is taken into account, as well as head-dependency. The volatility of the expected profit is limited through the conditional value-at-risk (CVaR). The proposed approach has been applied successfully to solve a case study based on one of the main Portuguese cascaded hydro systems.

Simulação interactiva do mercado de energia eléctrica

A área de comercialização de energia eléctrica conheceu uma profunda mudança após a liberalização do sector eléctrico, que levou à criação de algumas entidades, as quais gerem os mercados de electricidade europeus. Relativamente a Portugal e Espanha, durante esse processo de liberalização, deu-se também um acordo que os levou à criação de um mercado conjunto, um mercado Ibérico (MIBEL). Dentro deste mercado estão contemplados dois operadores, sendo que um deles representa o pólo Português (OMIP) e o outro representa o pólo Espanhol (OMEL). O OMIP contempla os mercados a prazo, ou futuros, normalmente apresenta contratos de energia comercializada com durabilidade de semanas, meses, trimestres, semestres ou mesmo anos. Diariamente estes contratos poderão vencer no OMEL, que engloba os mercados, diário e intradiário. Este, ao contrário do OMIP negoceia para o dia seguinte (mercado diário) ou para uma determinada altura do dia (mercado intra diário). O mercado diário será o exemplo usado para a criação do simulador interactivo do mercado de energia eléctrica. Este será composto por diversos utilizadores (jogadores), que através de uma plataforma HTML irão investir em centrais de energia eléctrica, negociar licitações e analisar o funcionamento e resultados deste mercado. Este jogo subdividir-se-á então em 3 fases: 1. Fase de investimento; 2. Fase de venda (licitações); 3. Fase de mercado. Na fase do investimento, o jogador terá a possibilidade de adquirir unidades de geração de energia eléctrica de seis tipos de tecnologia: 1. Central a Carvão; 2. Central de Ciclo Combinado; 3. Central Hídrica; 4. Central Eólica; 5. Central Solar; 6. Central Nuclear. Com o decorrer das jogadas o jogador poderá aumentar a sua capacidade de investimento, com a venda de energia, sendo o vencedor aquele que mais saldo tiver no fim do número de jogadas previamente definidos, ou aquele que mais depressa atingir o saldo definido como limite pelo administrador do jogo. A nível pedagógico este simulador é muito interessante pois para além de o utilizador ficar a conhecer as tecnologias em causa e as vantagens e desvantagens das centrais de energia renovável e das centrais a combustíveis fósseis, este ganha igualmente uma sensibilidade para questões de nível ambiental, tais como o aumento dos gases de estufa e o degelo resultante do aquecimento global provocado por esses gases. Para além do conhecimento adquirido na parte de energia eléctrica este jogo dará a conhecer ao utilizador o funcionamento do mercado da energia eléctrica, bem como as tácticas que este poderá usar a seu favor neste tipo de mercado.

An artificial neural network approach for short-term wind power forecasting in Portugal

This paper presents an artificial neural network approach for short-term wind power forecasting in Portugal. The increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Hence, good forecasting tools play a key role in tackling these challenges. The accuracy of the wind power forecasting attained with the proposed approach is evaluated against persistence and ARIMA approaches, reporting the numerical results from a real-world case study.

Model risk in the pricing of exotic options

The growth experimented in recent years in both the variety and volume of structured products implies that banks and other financial institutions have become increasingly exposed to model risk. In this article we focus on the model risk associated with the local volatility (LV) model and with the Variance Gamma (VG) model. The results show that the LV model performs better than the VG model in terms of its ability to match the market prices of European options. Nevertheless, both models are subject to significant pricing errors when compared with the stochastic volatility framework.

Virtual communities of practice: investigating motivations and constraints in the processes of knowledge creation and transfer

With accelerated market volatility, faster response times and increased globalization, business environments are going through a major transformation and firms have intensified their search for strategies which can give them competitive advantage. This requires that companies continuously innovate, to think of new ideas that can be transformed or implemented as products, processes or services, generating value for the firm. Innovative solutions and processes are usually developed by a group of people, working together. A grouping of people that share and create new knowledge can be considered as a Community of Practice (CoP). CoP’s are places which provide a sound basis for organizational learning and encourage knowledge creation and acquisition. Virtual Communities of Practice (VCoP's) can perform a central role in promoting communication and collaboration between members who are dispersed in both time and space. Nevertheless, it is known that not all CoP's and VCoP's share the same levels of performance or produce the same results. This means that there are factors that enable or constrain the process of knowledge creation. With this in mind, we developed a case study in order to identify both the motivations and the constraints that members of an organization experience when taking part in the knowledge creating processes of VCoP's. Results show that organizational culture and professional and personal development play an important role in these processes. No interviewee referred to direct financial rewards as a motivation factor for participation in VCoPs. Most identified the difficulty in aligning objectives established by the management with justification for the time spent in the VCoP. The interviewees also said that technology is not a constraint.