9,939 research outputs found

    Biodegradable polymers based on trimethylene carbonate for tissue engineering applications

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    In the field of tissue engineering, the search for suitable materials for use in the preparation of scaffolds to host the developing tissue represents a major subject of study. Biodegradable materials show great potential in this area as, by resorbing upon performing their function, they obviate long-term biocompatibility concerns

    Civic Education in Basic School: Problems and Challenges in the Digital Age

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    This paper focus on the analysis of preliminary data of an ongoing study involving Portuguese teachers and students, in the non-disciplinary curricular area of Civic Education. The project aims at encouraging collaborative behaviour in educational communities, involving teachers and students in the development of digital contents, and at exploring different issues on citizenship education, under a case-based methodology. We believe this action research study is of relevance because it can unveil examples of good practices and innovative teaching strategies that need to be disseminated in this compulsory subject taking into account the results of recent studies, which exposed some of the inefficiency of the strategies adopted so far

    Extreme values for Benedicks-Carleson quadratic maps

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    We consider the quadratic family of maps given by fa(x)=1ax2f_{a}(x)=1-a x^2 with x[1,1]x\in [-1,1], where aa is a Benedicks-Carleson parameter. For each of these chaotic dynamical systems we study the extreme value distribution of the stationary stochastic processes X0,X1,...X_0,X_1,..., given by Xn=fanX_{n}=f_a^n, for every integer n0n\geq0, where each random variable XnX_n is distributed according to the unique absolutely continuous, invariant probability of faf_a. Using techniques developed by Benedicks and Carleson, we show that the limiting distribution of Mn=max{X0,...,Xn1}M_n=\max\{X_0,...,X_{n-1}\} is the same as that which would apply if the sequence X0,X1,...X_0,X_1,... was independent and identically distributed. This result allows us to conclude that the asymptotic distribution of MnM_n is of Type III (Weibull).Comment: 18 page

    Caracterização molecular e estrutural do sintase do óxido nítrico de Leishmania

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    Relatório de projeto no âmbito do Programa de Bolsas Universidade de Lisboa/Fundação Amadeu Dias (2011/2012). Universidade de Lisboa. Faculdade de Ciência

    Early aspects: aspect-oriented requirements engineering and architecture design

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    This paper reports on the third Early Aspects: Aspect-Oriented Requirements Engineering and Architecture Design Workshop, which has been held in Lancaster, UK, on March 21, 2004. The workshop included a presentation session and working sessions in which the particular topics on early aspects were discussed. The primary goal of the workshop was to focus on challenges to defining methodical software development processes for aspects from early on in the software life cycle and explore the potential of proposed methods and techniques to scale up to industrial applications

    Extreme Value Laws for non stationary processes generated by sequential and random dynamical systems

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    We develop and generalize the theory of extreme value for non-stationary stochastic processes, mostly by weakening the uniform mixing condition that was previously used in this setting. We apply our results to non-autonomous dynamical systems, in particular to {\em sequential dynamical systems}, given by uniformly expanding maps, and to a few classes of random dynamical systems. Some examples are presented and worked out in detail

    Extreme Value Laws for sequences of intermittent maps

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    We study non-stationary stochastic processes arising from sequential dynamical systems built on maps with a neutral fixed points and prove the existence of Extreme Value Laws for such processes. We use an approach developed in \cite{FFV16}, where we generalised the theory of extreme values for non-stationary stochastic processes, mostly by weakening the uniform mixing condition that was previously used in this setting. The present work is an extension of our previous results for concatenations of uniformly expanding maps obtained in \cite{FFV16}.Comment: To appear in Proceedings of the American Mathematical Society. arXiv admin note: substantial text overlap with arXiv:1510.0435

    Extreme Value Laws in Dynamical Systems for Non-smooth Observations

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    We prove the equivalence between the existence of a non-trivial hitting time statistics law and Extreme Value Laws in the case of dynamical systems with measures which are not absolutely continuous with respect to Lebesgue. This is a counterpart to the result of the authors in the absolutely continuous case. Moreover, we prove an equivalent result for returns to dynamically defined cylinders. This allows us to show that we have Extreme Value Laws for various dynamical systems with equilibrium states with good mixing properties. In order to achieve these goals we tailor our observables to the form of the measure at hand

    Complete convergence and records for dynamically generated stochastic processes

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    We consider empirical multi-dimensional Rare Events Point Processes that keep track both of the time occurrence of extremal observations and of their severity, for stochastic processes arising from a dynamical system, by evaluating a given potential along its orbits. This is done both in the absence and presence of clustering. A new formula for the piling of points on the vertical direction of bi-dimensional limiting point processes, in the presence of clustering, is given, which is then generalised for higher dimensions. The limiting multi-dimensional processes are computed for systems with sufficiently fast decay of correlations. The complete convergence results are used to study the effect of clustering on the convergence of extremal processes, record time and record values point processes. An example where the clustering prevents the convergence of the record times point process is given

    Speed of convergence for laws of rare events and escape rates

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    We obtain error terms on the rate of convergence to Extreme Value Laws for a general class of weakly dependent stochastic processes. The dependence of the error terms on the `time' and `length' scales is very explicit. Specialising to data derived from a class of dynamical systems we find even more detailed error terms, one application of which is to consider escape rates through small holes in these systems
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