993,679 research outputs found

    Replicated INAR(1) processes

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    Replicated time series are a particular type of repeated measures, which consist of time-sequences of measurements taken from several subjects (experimental units). We consider independent replications of count time series that are modelled by first-order integer-valued autoregressive processes, INAR(1). In this work, we propose several estimation methods using the classical and the Bayesian approaches and both in time and frequency domains. Furthermore, we study the asymptotic properties of the estimators. The methods are illustrated and their performance is compared in a simulation study. Finally, the methods are applied to a set of observations concerning sunspot data.PRODEP II

    On the Graded Identities for Elementary Gradings in Matrix Algebras over Infinite Fields

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    We find a basis for the GG-graded identities of the n×nn\times n matrix algebra Mn(K)M_n(K) over an infinite field KK of characteristic p>0p>0 with an elementary grading such that the neutral component corresponds to the diagonal of Mn(K)M_n(K)

    Estimating stellar rotation from starspot detection during planetary transits

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    A new method for determining the stellar rotation period is proposed here, based on the detection of starspots during transits of an extra-solar planet orbiting its host star. As the planet eclipses the star, it may pass in front of a starspot which will then make itself known through small flux variations in the transit light curve. If we are lucky enough to catch the same spot on two consecutive transits, it is possible to estimate the stellar rotational period. This method is successfully tested on transit simulations on the Sun yielding the correct value for the solar period. By detecting two starspots on more than one transit of HD 209458 observed by the Hubble Space Telescope, it was possible to estimate a period of either 9.9 or 11.4 days for the star, depending on which spot is responsible for the signature in the light curve a few transits later. Comparison with period estimates of HD209458 reported in the literature indicates that 11.4 days is the most likely stellar rotation period.Comment: 13 pages, 5 figure

    Estimation and forecasting in SUINAR(1) model

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    This work considers a generalization of the INAR(1) model to the panel data first order Seemingly Unrelated INteger AutoRegressive Poisson model, SUINAR(1). It presents Bayesian and classical methodologies to estimate the parameters of Poisson SUINAR(1) model and to forecast future observations of the process. In particular, prediction intervals for forecasts - classical approach - and HPD prediction intervals - Bayesian approach - are derived. A simulation study is provided to give additional insight into the finite sample behaviour of the parameter estimates and forecasts

    Power and politics in the adoption of information systems by organisations: the case of a research centre in Latin America

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    This thesis applies contributions from the social sciences to the study of power to examine how and why organisations adopt information systems. Its main concern is the set of events, actions and factors that induce an information system to become routinised in the organisational life; that is how information systems become institutionalised. I argue that the actions and events that lead to the adoption and subsequent institutionalisation of an information system are politically motivated and facilitated by power relations because information systems are chiefly instruments used by organisational actors to achieve their goals. To develop the argument I have adapted and interpreted a model rooted in social and organisational sciences. This model is used as a theoretical framework for the collection and analysis of data of two case studies. the first case centres on the collapse of the London Ambulance Service in 1992. The second and major case study focuses on a research centre in Latin America. This case study accounts for the adoption and institutionalisation of three information systems in that organisation. The application of the theoretical framework constitute a contribution in researching power and politics of information systems because it illustrates how to link data to the theory. This thesis also contributes to the theory of power and information systems because the findings of the two case studies allowed us to make inferences that complement the original theoretical model. Furthermore, those findings are propositions that information systems practitioners might convert into useful principles in assessing the political base and power relationships of the organisation for which they work. The thesis concludes by asserting that the adoption and institutionalisation of an information system necessarily imply the exercise of power of those organisation actors that own or propose the system
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