1,220 research outputs found

    Efficiency tests in the Iberian stock markets

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    This paper investigates the efficiency of the two major stock indexes of the Iberian Peninsula, the Portuguese Stock Index (PSI-20) and the Spanish Stock Index (IBEX-35). We used daily data from January 1993 to September 2001 for the Portuguese stock index and daily data from October 1990 to September 2001 for the Spanish stock index. Serial correlations, unit root tests and variance ratio tests are used to test the efficiency of these two stock indexes. Although the complementary of these tests, we used all of them to get a higher robustness of the conclusions. We examined serial correlation coefficients for successive stock index changes to test whether they are statistically equal to zero to establish the random walk nature of stock indexes. The augmented Dickey-Fuller (ADF) test are used to test the null hypothesis that the series has a unit root and the variance ratio tests are used to examine the random walk hypothesis for the series of these two stock indexes. The results of the serial correlations, unit root tests and variance ratio tests provide ambiguous evidence for the random walk hypothesis. The empirical evidence from the unit root tests do not reject the efficient market hypothesis for the two stock indexes, while the results from the variance ratio tests and serial correlations do.stock indexes, market efficiency, unit roots

    Ergodicity of polygonal slap maps

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    Polygonal slap maps are piecewise affine expanding maps of the interval obtained by projecting the sides of a polygon along their normals onto the perimeter of the polygon. These maps arise in the study of polygonal billiards with non-specular reflections laws. We study the absolutely continuous invariant probabilities of the slap maps for several polygons, including regular polygons and triangles. We also present a general method for constructing polygons with slap maps having more than one ergodic absolutely continuous invariant probability.Comment: 17 pages, 6 figure

    Hyperbolic polygonal billiards with finitely many ergodic SRB measures

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    We study polygonal billiards with reflection laws contracting the reflected angle towards the normal. It is shown that if a polygon does not have parallel sides facing each other, then the corresponding billiard map has finitely many ergodic SRB measures whose basins cover a set of full Lebesgue measure.Comment: 26 pages, 2 figure

    Innovation Modes and Firm's Performance: Evidence from Portugal

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    It has been shown that firms tend to developdifferentmodesof innovation triggeredby the relationship betweendifferenttypes ofknowledge andlearning processesunderpinning it. Thispaper aims at identifying differentmodes ofbusiness innovation; second, relating them to firms' innovative and economicperformance; and, analyzing the relationship between the different innovation modes and the economic impact of the crisis on the firms' performance. These hypotheses are tested by regression and latent class models for the Portuguese population of firms using a sample of 397 firms, stratifiedby level oftechnological intensity, firm's size andregion. Results show three firms' heterogeneous modes of innovation in termsofits relationship tothe economic and innovative performance and with significant differences in terms of resilience to the economic crisis. These findings lead toa reflection oninnovation, competitiveness and regional policy

    Renormalization of Gevrey vector fields with a Brjuno type arithmetical condition

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    We show that in the Gevrey topology,a d-torus flow close enough to linear with a unique rotation vector w is linearizable as long as w satisfies a novel Brjuno type Diophantine condition. The proof is based on the fast convergence under renormalization of the associated Gevrey vector field. It requires a multidimensional continued fractions expansion of w, and the corresponding characterization of the Brjuno type vectors.This demonstrates that renormalization methods deal very naturally with Gevrey regularity expressed in the decay of Fourier coefficients. In particular, they provide new linearization results including frequencies beyond Diophantine in non-analytic topologies.info:eu-repo/semantics/publishedVersio

    Decision-making in the penalty kick: the role of constraints in the perceptual guidance of action

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    Doutoramento em Motricidade Humana, na especialidade de Ciências do DesportoThe aim of this thesis was to examine how players’ strategies influence available information on movement when performing penalty kicks. An ecological dynamics perspective of the penalty kick is initially presented as a supporting framework for recent research, as well as a plausible path to overcome the shortage of ecological validity of experimental designs that aim to capture the information-based core of players’ performance. The effect of different instructional constraints on movement patterns and outcome was analysed and results showed a significant influence on both players’ performance speed and on goalkeepers’ diving angle, although players’ efficacy remained constant. Penalty takers’ kinematics was then studied in order to understand its relation with ball’s horizontal and vertical directions, as well as the influence of ball direction on penalty kicks’ success. Kinematic variables highly correlated to ball horizontal direction were less affected by deceptive actions, demonstrating that genuine movements cannot be biased if an intended goal needs to be accomplished. Ball height influenced outcome, although physical constraints imposed on penalty takers’ movement variability (compared with other kick types) decreased the correlations between ball’s vertical direction and penalty takers’ kinematics. Developed investigation contributed to 1) clarify the influence of different strategies on players’ movements, 2) identify genuine sources of information for the anticipation of ball direction, and 3) determine the influence of ball height on penalty kick success.Esta tese tem como objectivo analisar a influência das estratégias empregues pelos jogadores sobre a informação disponível para a acção na grande penalidade. A dinâmica ecológica é apresentada como base para o enquadramento da pesquisa recente, e como opção plausível para potenciar a validade ecológica dos designs experimentais que pretendam capturar a informação sobre a qual os jogadores agem. Foi analisado o efeito da instrução sobre o comportamento dos jogadores e eficácia na grande penalidade. Os resultados demonstraram uma influência da instrução na velocidade dos jogadores e no ângulo de estiramento lateral do guardaredes, sem alterações da eficácia. De seguida, a cinemática do rematador foi analisada, procurando entender a sua relação com a direcção da bola. As variáveis cinemáticas correlacionadas com a direcção horizontal da bola foram pouco afectadas pela acção simulatória, demonstrando a impossibilidade de encobrir a acção genuína que cumpre determinado objectivo. A altura da bola influenciou a eficácia, apesar dos constrangimentos físicos impostos sobre a variabilidade de movimento dos rematadores na grande penalidade (comparada com outros tipos de remate) terem forçado uma diminuição das correlações entre a direcção vertical da bola e a cinemática dos rematadores. A investigação desenvolvida contribuiu para 1) clarificar a influência de diferentes estratégias no movimento dos rematadores, 2) identificar fontes genuínas de informação para a antecipação da direcção da bola, e 3) determinar a influência da altura da bola na eficácia da grande penalidade.FCT - Fundação para a Ciência e a Tecnologi

    Climate change impact in the Ria de Aveiro lagoon ecosystem: a case study

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    Climate change and global sea-level rise are major issues of the 21st century. The main goal of this study is to assess the physical and biogeochemical status of the Ria de Aveiro lagoon (Portugal) under future climate scenarios, using a coupled physical/ eutrophication model. The impact on the lagoon ecosystem status of the mean sea level rise (MSLR), the amplitude rise of the M2 tidal constituent (M2R), the changes in the river discharge, and the rising of the air temperature was investigated. Under MSLR and M2R, the results point to an overall salinity increase and water temperature decrease, revealing ocean water dominance. The main lagoon areas presented salinity values close to those of the ocean waters (~34 PSU), while a high range of salinity was presented for the river and the far end areas (20–34 PSU). The water temperature showed a decrease of approximately 0.5–1.5 C. The responses of the biogeochemical variables reflect the increase of the oceanic inflow (transparent and nutrient-poor water) or the reduction of the river flows (nutrient-rich waters). The results evidenced, under the scenarios, an overall decreasing of the inorganic nitrogen concentration and the carbon phytoplankton concentrations. A warm climate, although increasing the water temperature, does not seem to a ect the lagoon’s main status, at least in the frame of the model used in the study.publishe

    Micro-EDXRF, SEM-EDS and OM characterisation of tin soldering found in handle attachments of Roman situlae from Conimbriga (Portugal)

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    Tin (Sn) or a Sn-rich solder applied to copper-based artefacts has been frequently used at least, since the Ancient Greece, although scarce studies have been published concerning the technology of this metallurgical joining technique. Several filler remnants were reported to be found in a Roman collection of handle attachments of situlae or cauldrons (2nd century BCE–5th century CE) from the archaeological site of Conimbriga, a Roman city from the Lusitania Province (Portugal). All these artefacts were cast in high leaded coppers and bronzes. The present study aims to contribute to the knowledge of Sn-rich soldering, an ancientmetallurgical joining technique, by the characterisation of the fusible metallic alloy present in 10 Roman artefacts by means of micro-energy dispersive X-ray fluorescence spectrometry (micro-EDXRF), scanning electron microscopy with energy dispersive X-ray (SEM-EDS) microanalysis and optical microscope (OM) observations. Results of studied solders show the presence of Cu-Sn alloys, with Sn contents ranging from δ to η phase composition (30–60wt% Sn). As the attachments were made in leaded copper alloys, it was also observed, in some cases, the melting of the interdendritic Pb-rich chains with long-range diffusion of the solder alloy into the substrate. The fillers compositions suggest that the handle attachments have been joined to a situla body by the soldering metallurgical process with Sn or a Sn-rich alloy. The studied leaded Cu-Sn attachments, probably formulated by local craftsman, were joined into the body of a situla or cauldron with a soft solder (soldering), a common metallurgical joint from Antiquity, although no relation was found between composition or typology and the Sn or Sn-rich solder
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