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This work performs the dynamic optimization of semibatch vinyl acetate (VAc)/acrylic acid (AA) suspension copolymerizations. The proposed dynamic optimization strategy is based on a direct search Complex algorithm and is used to control the copolymer composition along the batch. First, a sequential optimization procedure is used to determine the optimum AA concentration and feed rate profiles, required to provide the specified copolymer composition. In the second step, a sequential optimization procedure is coupled with a predictive controller to guarantee that the manipulation of feed flow rates can allow for attainment of the desired copolymer compositions. The optimization strategy is validated through simulation, by assuming that reactions are subject to perturbations of the reaction temperature, initiator, and VAc concentrations. It is shown that the proposed optimization strategy can be used successfully both for design of monomer feed rate profiles and removal of process disturbances during semibatch suspension copolymerizations, to keep the copolymer composition constant throughout the batch.

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Dynamic optimization of semibatch vinyl acetate/acrylic acid suspension copolymerizations

Machado

Lima

Pinto

2009

Polym Eng Sci

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A robust and flexible optimization technique for efficient shrinking of MEMS accelerometers

et al. 2009

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We report on the automated determination of the minimal required area of a MEMS accelerometer conforming to given specifications. For a realistic nonlinear sensor model this process is only possible by the use of numerical optimization, which typically has the difficulty of finding the global minimum or is time consuming. A miniaturized sensor's chip size reduces manufacturing cost and leads to more competitive package sizes and new, unforeseen applications. Size reduction is especially important for consumer applications like mobile phones and navigation devices, where an increasing demand for accelerometers is expected in the near future. With further miniaturization of a sensor it is increasingly important to find the optimal design in order to use chip area as efficiently as possible. To achieve a robust and flexible automated area reduction without loss of functionality we uniquely combine available genetic and gradient-based optimization algorithms. Furthermore, we reduce the model complexity, apply different scaling techniques and adapt optimization algorithm settings. The application to a capacitive and a piezoresistive MEMS accelerometer shows significant improvement of efficiency when compared with the use of currently available optimization algorithms.

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An adaptive feedback circuit for MEMS resonators

Fan

Siwak

Ghodssi

2011

J. Micromech. Microeng.

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The first adaptive feedback circuit capable of detecting resonant frequencies for a wide range of MEMS resonators is presented. The feedback system presented implements a hill-climbing algorithm that sweeps actuation frequencies, locking onto the resonance condition at maximum cantilever amplitude response without limitations on the frequency range. To demonstrate its adaptability, a circuit implementation of this feedback algorithm was used to detect the resonant frequency of eight different cantilever-based sensors (width (W) = 1.4 μm, length (L) = 40-75 μm, and thickness (T) = 1.8 μm), resonating at 201.0 to 592.1 kHz. Additionally, the same circuit was used to track resonant frequency shifts due to isopropanol adsorption on three different chemical sensors with no modifications. The feedback electronics integrated with these resonator sensors provide a mass resolution limit of 123 femptograms. The realization of this system will enable real-time chip-scale sensor systems, providing an alternative to external instrumentation modules that perform sensor control and monitoring.

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Cited by 5 publications

References 11 publications

Dynamic optimization of semibatch vinyl acetate/acrylic acid suspension copolymerizations

Dynamic optimization of semibatch vinyl acetate/acrylic acid suspension copolymerizations

A robust and flexible optimization technique for efficient shrinking of MEMS accelerometers

An adaptive feedback circuit for MEMS resonators

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