Determinantal Point Processes (DPPs) are probabilistic models over all subsets a ground set of N items. They have recently gained prominence in several applications that rely on "diverse" subsets. However, t...
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ISBN:
(纸本)9781510838819
Determinantal Point Processes (DPPs) are probabilistic models over all subsets a ground set of N items. They have recently gained prominence in several applications that rely on "diverse" subsets. However, their applicability to large problems is still limited due to O(N~3) complexity of core tasks such as sampling and learning. We enable efficient sampling and learning for DPPs by introducing KronDpp, a DPP model whose kernel matrix decomposes as a tensor product of multiple smaller kernel matrices. This decomposition immediately enables fast exact sampling. But contrary to what one may expect, leveraging the Kronecker product structure for speeding up DPP learning turns out to be more difficult. We overcome this challenge, and derive batch and stochastic optimization algorithms for efficiently learning the parameters of a KronDpp.
As the refrigeration technology consumes more than 15% of worldwide consumption of electricity, the development of technologies with improved efficiency remains an important challenge. In this context, magnetic refrig...
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ISBN:
(纸本)9781479903375
As the refrigeration technology consumes more than 15% of worldwide consumption of electricity, the development of technologies with improved efficiency remains an important challenge. In this context, magnetic refrigeration is an interesting solution and this paper proposes an original magnetic refrigerator. The aim - and also the originality - of this new device is to integrate the magnetocaloric regenerator in the air gap of a Permanent Magnet Synchronous Machine (PMSM). The conventional design of PMSM stator and rotor is presented and the results lead to the construction of a prototype that enables the validation of the proposed concept. Finally, thanks to the coupling of an optimization algorithm and a 2D FEM simulation, the rotor is optimized and the air-gap flux density is greatly improved (from 0.9 T to 1.35 T).
As a result of the uncertainties and significant fluctuations of both power generation and consumption in a microgrid, the battery energy storage system (BESS) endures large oscillations in absorbing and releasing act...
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ISBN:
(纸本)9781629936017
As a result of the uncertainties and significant fluctuations of both power generation and consumption in a microgrid, the battery energy storage system (BESS) endures large oscillations in absorbing and releasing active power. This paper proposes a hybrid energy storage system (HESS) composed of supercapacitors and batteries. An optimal design method of HESS capacity is introduced so that HESS can meet the technical requirements, such as smoothing out the wind power fluctuations and the economic requirement in a microgrid. Based on the level of smoothing (LOS) of power curves, a neural network model was established to reflect the interrelationship between characteristic parameters of HESS and LOS of output power transmitted to the independent microgrid. Besides, taking the economic demand into consideration, a long-term mathematical model was built. Optimal algorithm was used to determine optimal size of HESS by optimizing the objective function, which was derived from the built model. Finally, an example indicates the effectiveness of the proposed method.
Ultrasound imaging is a popular imaging modality due to a number of favorable properties of this modality. However, the poor quality of ultrasound images makes them a bad choice for segmentation algorithms. In this pa...
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ISBN:
(纸本)9781424427604
Ultrasound imaging is a popular imaging modality due to a number of favorable properties of this modality. However, the poor quality of ultrasound images makes them a bad choice for segmentation algorithms. In this paper, we present a semi-automatic algorithm for organ segmentation in ultrasound images, by posing it as an energy minimization problem via appropriate definition of energy terms. We use graph-cuts as our optimization algorithm and employ a fuzzy inference system (FIS) to further refine the optimization process. This refinement is achieved by using the FIS to incorporate domain knowledge in order to provide additional constraints. We show that by integrating domain knowledge via FIS, the accuracy is improved significantly so that further manual refinement of object boundary is often unnecessary. Our algorithm was applied to detect prostate and carotid artery boundaries in clinical ultrasound images and shows the success of the proposed approach.
Due to the escalating costs associated with testing of precision RF components, there is a pressing need for identifying novel test methods that allow RF circuits to be tested with low cost test instrumentation. Speci...
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ISBN:
(纸本)9781424477920;9781424477937
Due to the escalating costs associated with testing of precision RF components, there is a pressing need for identifying novel test methods that allow RF circuits to be tested with low cost test instrumentation. Specifically, test costs can be lowered significantly if stimulus from a digital pattern generator can be adapted to serve as test stimulus for analog/RF circuits. In this paper, we propose a novel digital pulse based test signal generation technique for testing RF circuits. An optimized pulse stream containing a combination of spectral components within a specified RF frequency band is used as the test stimulus. The optimization is performed using a genetic optimization algorithm and allows gain and nonlinearity specifications to be computed accurately from the observed (down-converted) test response. Simulation data for an RF power amplifier shows excellent correlation of the test results with the test specification values of the device under test (DUT) while allowing all the specifications to be measured from a single data acquisition.
This brief presents a symbolic approach for the optimal design of low noise amplifiers through the scattering parameters. An optimization algorithm, which is also proposed in this paper, generates the optimal values o...
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ISBN:
(纸本)9781424457939
This brief presents a symbolic approach for the optimal design of low noise amplifiers through the scattering parameters. An optimization algorithm, which is also proposed in this paper, generates the optimal values of all the design parameters that meet imposed specifications on the scattering parameters. ADS simulations, using 0.35u.m CMOS technology, are presented to show the good agreement between theoretical and simulation results.
This paper discusses a model-based approach to sediment characterization using multibeam backscatter data collected offshore from Qingdao, China in 2018. In this experiment, the NORBIT wideband multibeam sonar was uti...
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ISBN:
(纸本)9781728114521
This paper discusses a model-based approach to sediment characterization using multibeam backscatter data collected offshore from Qingdao, China in 2018. In this experiment, the NORBIT wideband multibeam sonar was utilized to collect backscatter data, the angular response curves of which reflect sediment-type differences. For the synthetic analysis of experimental data, a high-frequency backscatter model based on small-slope approximation and volume-scattering theory was adapted to simulate the variation of the backscatter strength with the incident angle. Afterward, these generated model replicas were matched with experimental backscatter data using a simulated annealing optimization algorithm to estimate sediment parameters, such as sediment-water sound-speed ratio, density ratio, roughness spectral parameters, volume-scattering strength, and acoustics attenuation. The preliminary inversion results are basically consistent with the experimental data on sediment distribution and texture.
Distributed parameter control problems involving manipulation within the spatial domain arise in a variety of applications including vibration control, active noise reduction, epidemiology, tissue engineering, and can...
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ISBN:
(纸本)9781424474264
Distributed parameter control problems involving manipulation within the spatial domain arise in a variety of applications including vibration control, active noise reduction, epidemiology, tissue engineering, and cancer treatment. A state-constrained spatial field control problem motivated by a biomedical application is solved in which the manipulation occurs over a spatial field and the state field is constrained both in spatial frequency and by a partial differential equation (PDE) that effects the manipulation. An optimization algorithm combines three-dimensional Fourier series, which are truncated to satisfy the spatial frequency constraints, with exploitation of structural characteristics of the PDEs. The computational efficiency and performance of the optimization algorithm are demonstrated in a numerical example, for which the spatial tracking error is almost entirely due to the limitation on the spatial frequency of the manipulated field. The numerical results suggest that optimal control approaches have promise for controlling the release of macromolecules in tissue engineering applications.
A method is presented that approximates the solution to a nonlinear optimal control problem with quadratic cost function. We assume that the nonlinear system is accurately represented by a high-fidelity (hf) model whi...
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ISBN:
(纸本)9781479917730
A method is presented that approximates the solution to a nonlinear optimal control problem with quadratic cost function. We assume that the nonlinear system is accurately represented by a high-fidelity (hf) model which can be of high complexity or even of "black-box" type. The hf-model is oftentimes unsuitable for solving the optimal control problem. The proposed solution method is based on an Iterative Model and Trajectory Refinement (IMTR) strategy that uses a low-fidelity (lf) model to solve the optimal control problem. The lf-model is obtained through linearization of the hf-model, where the linearization point is variable by the optimization algorithm. The method is demonstrated for two problems of orbital transfer and of underactuated spacecraft attitude control with two reaction wheels. In both examples the solutions are shown to be in good agreement with the optimal solutions obtained by solving the respective nonlinear two-point-boundary value problem.
An overview of different versions of the Eleven feed and recent development is presented in the paper. Eleven feeds have a nearly constant beamwidth and a fix phase center, with a performance of an aperture efficiency...
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ISBN:
(纸本)9781467321877
An overview of different versions of the Eleven feed and recent development is presented in the paper. Eleven feeds have a nearly constant beamwidth and a fix phase center, with a performance of an aperture efficiency higher than 60%, -10 dB reflection coefficient, -0.2dB radiation efficiency, and -15dB cross-polar level, over a decade bandwidth. The Eleven feed can be very compact after applying newly developed optimization algorithms, and some new results of the feed in dual-reflector antennas are reported here.
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