18,906 research outputs found

    Controlling rigid formations of mobile agents under inconsistent measurements

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    Despite the great success of using gradient-based controllers to stabilize rigid formations of autonomous agents in the past years, surprising yet intriguing undesirable collective motions have been reported recently when inconsistent measurements are used in the agents' local controllers. To make the existing gradient control robust against such measurement inconsistency, we exploit local estimators following the well known internal model principle for robust output regulation control. The new estimator-based gradient control is still distributed in nature and can be constructed systematically even when the number of agents in a rigid formation grows. We prove rigorously that the proposed control is able to guarantee exponential convergence and then demonstrate through robotic experiments and computer simulations that the reported inconsistency-induced orbits of collective movements are effectively eliminated.Comment: 10 page

    Adsorption and binding dynamics of graphene-supported phospholipid membranes using the QCM-D technique

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    We report on the adsorption dynamics of phospholipid membranes on graphene-coated substrates using the quartz crystal microbalance with dissipation monitoring (QCM-D) technique. We compare the lipid vescle interaction and membranne formation on gold and silicon dioxide QCM crystal surfaces with their graphene oxide (GO) and reduced (r)GO coated counterparts, and report on the different lipid structures obtained. We establish graphene derivative coatings as support surfaces with tuneable hydrophobicity for the formation of controllable lipid structures. One structure of interest formed are lipid monolayer membrannes which were formed on rGO, which are otherwise challenging to produce. We also demonstrate and monitor biotin-avidin binding on such a membranne, which will then serve as a platform for a wide range of biosensing applications. The QCM-D technique could be extended to both fundamental studies and applications of other covalent and non-covalent interactions in 2-dimensional materials

    Part 3: Systemic risk in ecology and engineering

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    The Federal Reserve Bank of New York released a report -- New Directions for Understanding Systemic Risk -- that presents key findings from a cross-disciplinary conference that it cosponsored in May 2006 with the National Academy of Sciences' Board on Mathematical Sciences and Their Applications. ; The pace of financial innovation over the past decade has increased the complexity and interconnectedness of the financial system. This development is important to central banks, such as the Federal Reserve, because of their traditional role in addressing systemic risks to the financial system. ; To encourage innovative thinking about systemic issues, the New York Fed partnered with the National Academy of Sciences to bring together more than 100 experts on systemic risk from 22 countries to compare cross-disciplinary perspectives on monitoring, addressing and preventing this type of risk. ; This report, released as part of the Bank's Economic Policy Review series, outlines some of the key points concerning systemic risk made by the various disciplines represented - including economic research, ecology, physics and engineering - as well as presentations on market-oriented models of financial crises, and systemic risk in the payments system and the interbank funds market. The report concludes with observations gathered from the sessions and a discussion of potential applications to policy. ; The three papers presented in this conference session highlighted the positive feedback effects that produce herdlike behavior in markets, and the subsequent discussion focused in part on means of encouraging heterogeneous investment strategies to counter such behavior. Participants in the session also discussed the types of models used to study systemic risk and commented on the challenges and trade-offs researchers face in developing their models.Financial risk management ; Financial markets ; Financial stability ; Financial crises

    The role of ultrasound-driven microbubble dynamics in drug delivery : from microbubble fundamentals to clinical translation

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    In the last couple of decades, ultrasound-driven microbubbles have proven excellent candidates for local drug delivery applications. Besides being useful drug carriers, microbubbles have demonstrated the ability to enhance cell and tissue permeability and, as a consequence, drug uptake herein. Notwithstanding the large amount of evidence for their therapeutic efficacy, open issues remain. Because of the vast number of ultrasound- and microbubble-related parameters that can be altered and the variability in different models, the translation from basic research to (pre)clinical studies has been hindered. This review aims at connecting the knowledge gained from fundamental microbubble studies to the therapeutic efficacy seen in in vitro and in vivo studies, with an emphasis on a better understanding of the response of a microbubble upon exposure to ultrasound and its interaction with cells and tissues. More specifically, we address the acoustic settings and microbubble-related parameters (i.e., bubble size and physicochemistry of the bubble shell) that play a key role in microbubble cell interactions and in the associated therapeutic outcome. Additionally, new techniques that may provide additional control over the treatment, such as monodisperse microbubble formulations, tunable ultrasound scanners, and cavitation detection techniques, are discussed. An in-depth understanding of the aspects presented in this work could eventually lead the way to more efficient and tailored microbubble-assisted ultrasound therapy in the future

    Distributed formation control for autonomous robots

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