The paper presents some of our advances in the study and development of optical choppers. The modulation functions we have studied for classical choppers are pointed out - for top-hat (constant intensity) light beam d...
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ISBN:
(纸本)9780819493903
The paper presents some of our advances in the study and development of optical choppers. The modulation functions we have studied for classical choppers are pointed out - for top-hat (constant intensity) light beam distributions. The eclipse choppers that, to the best of our knowledge we have introduced are also presented. We thus point out the differences between the profiles of light (laser) impulses produced by the classical devices (with rotating wheels with windows with linear edges) and the novel eclipse choppers - under patent (with windows with circular edges that produce for the circular-shaped section of the laser beam in the plane of the wheel a planetary eclipse-like effect - from which the name we have proposed for this type of device). The most convenient (from the technological and from the cost point of view) solution, with wheels with circular holes is also obtained. The advantages and the drawbacks of the various devices are discussed. Both a theoretical and an experimental approach are considered. The latter is done on a chopper module we have constructed, with prototype chopper wheels we have designed and manufactured. Throughout the study, top-hat laser beams are considered, as they are most used in laser manufacturing applications. The perspective of conducting the study on other light beams distributions (e.g., Gaussian) is also pointed out.
The computation of harmonics and interharmonics produced by AC/DC/AC conversion systems with PWM inverters is considered, and a new approach is presented. Basically, a new inverter model is introduced that is based oi...
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The computation of harmonics and interharmonics produced by AC/DC/AC conversion systems with PWM inverters is considered, and a new approach is presented. Basically, a new inverter model is introduced that is based oil the modulation function theory and is able to take into account the voltage ripple at the inverter input terminals. A rectifier model that was previously proposed and the new inverter model are first used in the framework of a direct injection procedure and, then, in all iterative harmonic and interharmonic analysis. The proposed model call be applied successfully to adjustable speed drives for asychronous motors, achieving better modeling accuracy with respect to approaches based oil simplified inverter modeling. They also allow a sensible reduction of computational burden with respect to the time-domain models. For this reason, they constitute an attractive tool inside Monte Carlo simulations for probabilistic analyses of harmonic and interharmonic distortion. Numerical experiments demonstrate the good performance of the proposed models and the need to account for the presence of interharmonics for high-power PWM drives. Copyright (C) 2009 John Wiley & Sons, Ltd.
This paper investigates the scope of usage of Genetic Algorithms (GA) for data hiding in digital images. The tool has been explored in this topic of research to achieve an optimal solution in multidimensional nonlinea...
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This paper investigates the scope of usage of Genetic Algorithms (GA) for data hiding in digital images. The tool has been explored in this topic of research to achieve an optimal solution in multidimensional nonlinear problem of conflicting nature that exists among imperceptibility, robustness, security and payload capacity. Two spatial domain data hiding methods are proposed where GA is used separately for (i) improvement in detection and (ii) optimal imperceptibility of hidden data in digital images respectively. In the first method, GA is used to achieve a set of parameter values (used as Key) to represent optimally the derived watermark in the form of approximate difference signal used for embedding. In the second method, GA is used for finding out values of parameters, namely reference amplitude (A) and modulation index (mu) both with linear and non linear transformation functions, for achieving the optimal data imperceptibility. Results on robustness for both the methods against linear, non linear filtering, noise addition, and lossy compression as well as statistical invisibility of the hidden data are reported here for some benchmark images.
This paper investigates the scope of usage of Genetic Algorithms (GA) for data hiding in digital images. The tool has been explored in this topic of research to achieve an optimal solution in multidimensional nonlinea...
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This paper investigates the scope of usage of Genetic Algorithms (GA) for data hiding in digital images. The tool has been explored in this topic of research to achieve an optimal solution in multidimensional nonlinear problem of conflicting nature that exists among imperceptibility, robustness, security and payload capacity. Two spatial domain data hiding methods are proposed where GA is used separately for (i) improvement in detection and (ii) optimal imperceptibility of hidden data in digital images respectively. In the first method, GA is used to achieve a set of parameter values (used as Key) to represent optimally the derived watermark in the form of approximate difference signal used for embedding. In the second method, GA is used for finding out values of parameters, namely reference amplitude (A) and modulation index (mu) both with linear and non linear transformation functions, for achieving the optimal data imperceptibility. Results on robustness for both the methods against linear, non linear filtering, noise addition, and lossy compression as well as statistical invisibility of the hidden data are reported here for some benchmark images.
A new approach for modeling line-commutated ac/dc/ac conversion systems is presented and discussed. It is based on the modulation function theory taking advantage of a two-step procedure in which two different models ...
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A new approach for modeling line-commutated ac/dc/ac conversion systems is presented and discussed. It is based on the modulation function theory taking advantage of a two-step procedure in which two different models are used. The goal is to achieve a reduction of the computational burden,with respect to the time domain models and better modeling accuracy with respect to classical modulation function approaches. The proposed model constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its computational efficiency and result accuracy.
Modelling of AC/DC/AC power conversion systems with PWM inverters is considered and a new model is presented and discussed. The new model is based on the modulation function theory and uses the Iterative Harmonic and ...
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ISBN:
(纸本)0780375181
Modelling of AC/DC/AC power conversion systems with PWM inverters is considered and a new model is presented and discussed. The new model is based on the modulation function theory and uses the Iterative Harmonic and Interharmonic Analysis (IHIA), taking advantage of a new inverter model. The proposed model can be applied successfully to adjustable speed drives (ASD) for asynchronous motors, achieving better modelling accuracy with respect to approaches based on simplified inverter modelling. It also allows sensible reduction of computational burdens with respect to the time domain models. For this reason, it constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Numerical experiments demonstrate the good performances of the proposed method and the need of accounting for the presence of interharmonics for high power PWM drives.
A new approach for modeling AC/DC/AC power conversion systems is presented and discussed. It is based on the modulation function theory and utilizes the concept of the Iterative Harmonic Analysis (IHA), taking advanta...
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ISBN:
(纸本)0780371739
A new approach for modeling AC/DC/AC power conversion systems is presented and discussed. It is based on the modulation function theory and utilizes the concept of the Iterative Harmonic Analysis (IHA), taking advantage of a two-step procedure In which two different models are utilized. The proposed approach can be applied successfully on HVDC systems and adjustable speed drives for synchronous and asynchronous motors, achieving better modeling accuracy with respect to classical modulation function approaches and reduction of computational burdens with respect to the time domain models. It constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its accuracy performances.
Orthogonal sequences known as m-sequences can be used in place of Walsh functions in phase switching and sideband separation in cross-correlation interferometers. functions based on three-character m-sequences may be ...
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Orthogonal sequences known as m-sequences can be used in place of Walsh functions in phase switching and sideband separation in cross-correlation interferometers. functions based on three-character m-sequences may be advantageous because they may provide a larger set of mutually orthogonal modulation and demodulation functions, and hence support a larger number of antennas for a given sequence length, than allowed by other orthogonal sequences such as Walsh functions. The reason for this advantage is that if the demodulation functions are formed from the differences of the three-character m-sequence modulation functions, then because the m-sequences obey an addition rule whereby sums or differences of m-sequences are also m-sequences, the demodulation functions are also members of the original orthogonal set. In a complete set of sequences, all the differences are of course duplicates of the original sequences. However, certain subsets of sequences have differences which are not members of the subset, and these subsets can be used to form modulation and demodulation functions which have both the desired uniqueness and orthogonality properties. While it is not obvious how to select the subsets, heuristic methods seem reasonably successful.
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