Learning an Approximate Model Predictive Controller with Guarantees

A supervised learning framework is proposed to approximate a model predictive controller (MPC) with reduced computational complexity and guarantees on stability and constraint satisfaction. The framework can be used for a wide class of nonlinear systems. Any standard supervised learning technique (e.g. neural networks) can be employed to approximate the MPC from samples. In order to obtain closed-loop guarantees for the learned MPC, a robust MPC design is combined with statistical learning bounds. The MPC design ensures robustness to inaccurate inputs within given bounds, and Hoeffding's Inequality is used to validate that the learned MPC satisfies these bounds with high confidence. The result is a closed-loop statistical guarantee on stability and constraint satisfaction for the learned MPC. The proposed learning-based MPC framework is illustrated on a nonlinear benchmark problem, for which we learn a neural network controller with guarantees.Comment: 6 pages, 3 figures, to appear in IEEE Control Systems Letter

Field notes on findings of threatened amphibian species in the central mountain range of western Panama

During field work along a transect in the Cordillera Central of western Panama between 2008 and 2010, we detected several populations of amphibian species which are considered as “Endangered” or “Critically Endangered” by the IUCN. Some of these species had suffered from serious population declines, probably due to chytridiomycosis, but all are generally threatened by habitat loss. We detected 53% of the Endangered and 56% of the Critically Endangered amphibian species that have previously been reported from within the investigated area. We report on findings of species that have not been found in Panama for many years, and provide locality data of newly discovered populations. There is a need to create a new protected area in the Cerro Colorado area of the Serranía de Tabasará, where we found 15% of the Endangered and Critically Endangered amphibian species known to Panama.Durante trabajo de campo en un transecto a lo largo de la Cordillera Central en el oeste de Panamá entre 2008 y 2010, encontramos varias poblaciones de anfibios que son considerados “En Peligro” o “En Peligro Crítico” por la UICN. Algunas de estas especies habían sufrido serias disminuciones de sus poblaciones, probablemente causadas por la quitridiomicosis, pero todas se encuentran amenazadas por pérdida de hábitat. Detectamos el 53% de las especies En Peligro y el 56% de las especies En Peligro Crítico que se habían reportado previamente en el área de estudio. Reportamos hallazgos de especies que no se habían avistado en Panamá por muchos años, así como localidades de poblaciones descubiertas por primera vez. Se requiere crear una nueva área de protección en los alrededores del Cerro Colorado en la Serranía de Tabasará, donde se han encontrado 15% de los anfibios En Peligro y En Peligro Crítico de todo Panamá

Managed Wikis - A New Approach for Web 2.0

Wiki projects can be edited by everyday web users directly within the web browser. Consequently, undesirable contributions like vandalism and spam cannot be ruled out. In this paper, Managed Wikis are introduced as a new approach to avoid such undesirable contributions. Editing rights are assigned according to author reputation, the quality of articles and the occurrence of patterns of suspicious edits. In the paper, the concept of Managed Wikis is evaluated by means of a simulation on the basis of Wikipedia data. The analysis proves that undesirable contributions are blocked effectively. In contrast, desirable contributions are rarely affected by the editing rights restriction. The concept of Managed Wikis addresses open as well as corporate wiki projects where undesirable edits cause significant harm. Furthermore, it can be applied to make traditional websites accessible for the web community

Stalk formation as a function of lipid composition studied by X-ray reflectivity

AbstractWe have investigated the structure and interaction of solid-supported multilamellar phospholipid bilayers in view of stalk formation as model systems for membrane fusion. The multi-component bilayers were composed of ternary and quaternary mixtures, containing phosphatidylcholines, phosphatidylethanolamines, sphingomyelin, cholesterol, diacylglycerol, and phosphatidylinositol. Analysis of the obtained electron density profiles and the pressure–distance curves reveals systematic changes in structure and hydration repulsion. The osmotic pressure needed to induce stalk formation at the transition from the fluid lamellar to the rhombohedral phase indicates how membrane fusion properties are modified by bilayer composition

Beyond Frege-Geach: neglected problems for Expressivism

This thesis is about the viability of meta-normative expressivism. On what I take to be the dominant conception of the view, it subscribes to two theses. First, that the meaning of sentences is to be explained in terms of the mental states these sentences conventionally express. Second, that there is a fundamental difference in the roles of the states expressed by normative sentences and the states expressed by descriptive sentences: descriptive sentences, according to expressivists, express mental states which are representational and non-motivational, while normative sentences express non-representational and motivational states. Expressivism has attracted many naturalistically inclined philosophers for its ability to explain many of the distinctive features of normative discourse and thought, without adding entities to our ontology that are metaphysically and epistemologically problematic. In this way, expressivism promises to preserve the legitimacy of our ordinary normative practice within a naturalistic world-view, without giving up on any of its distinctive features. Despite it’s benefits, expressivism also faces significant problems. While one of these problems, the Frege-Geach Problem, has attracted a lot of attention, there are several other problems that have not been sufficiently addressed by . But, given that the reasonable assumption that the plausibility of philosophical theories needs to be assessed holistically, it seems that one should pay attention to these problems to be able to assess expressivism’s overall plausibility. In this thesis I explain how expressivists can solve two of these problems. The first problem the dissertation is concerned with is the normative attitude problem. This is a dilemma based on the challenge that expressivists need to give an account of the nature of the attitude that normative thinking consists in. The dilemma is then that expressivists could either do this by holding that normative thinking consists in sui generis attitudes, which is uninformative and potentially in conflict with naturalism, or by holding that normative thinking reduces to attitudes fully describable in non-normative terms, which is in conflict with our intuitions about normative thinking. I argue that this dilemma is structurally identical to a dilemma which meta-normative representationalism faces (expressivism’s dialectical rival) and that expressivists can use the same theoretical resources to address the normative attitude problem meta-normative representationalists have used to address their version of the dilemma. I also argue that these resources will not only help more traditional versions of expressivism, according to which normative thinking reduces to familiar kinds of attitudes fully describable in non-normative terms, but opens up the possibility of an expressivist view according to which normative thinking consists in sui generis attitudes. The second problem I consider is a challenge to a particular expressivist project: quasi-realism. Part of this project is to show that expressivism is compatible with a web of closely connected assumptions, namely, that normative thought and discourse are truth-apt and normative judgements are beliefs. While quasi-realists have made some progress in this direction, there is one relevant phenomenon that has so far been neglected, namely, those uses of that-clauses that are associated with propositional content. This is a problematic neglect, because that-clauses figure prominently in platitudes characterizing our ordinary notions of “truth-aptitude” and “belief ”, and so expressivists need to provide a plausible account of these uses of that-clauses which fits with their allowing that normative thought and discourse are truth-apt and normative judgements are beliefs. I address this challenge as follows: I first remove any worries that one might have that a plausible account of that-clauses that helps the quasi-realist could be given, by introducing the distinction between semantics and meta-semantics and locating expressivism at the level of metasemantics. I then develop a deflationist view of that-clauses which suits the quasi-realist’s purposes. I start by giving such a view for the use of that-clauses in meaning-attributions by expanding on the work of Wilfried Sellars. I then go on to explain how the account can be generalized to the use of that-clauses in belief-attributions and propositional attitude ascriptions more generally, in a way that allows expressivists to say that normative judgements are beliefs