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- 摘要
- 关键词
- 实验方案
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[IEEE 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Krakow, Poland (2018.10.16-2018.10.18)] 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - A Newton-Conjugate-Gradient Method in L <sup>p</sup> Banach Spaces for Three-Dimensional Microwave Imaging
摘要： Microwave imaging is a diagnostic technique for inspecting dielectric and conducting materials based on electromagnetic scattering. Although usually developed with reference to two-dimensional configurations (tomography), it allows a quite 'natural' extension to three-dimensional targets. In this paper, a full-wave three-dimensional approach is developed. The inverse scattering problem is solved, in a regularized way, by using a Newton-conjugate-gradient method. The main novelty concerns the nonconventional framework in which the approach is developed, i.e., the Lp Banach spaces. The paper describes the mathematical formulation of the method. Moreover, numerical results are reported and discussed in order to assess the capabilities and limitations of the proposed technique.
关键词： Banach spaces,inverse problems,Newton schemes,Imaging techniques,conjugate gradient method,microwaves
更新于2025-09-23 15:22:29
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Evaluation of replicas manufactured in a 3D-printed nanoimprint unit
摘要： Nanoimprint lithography has become a useful tool to prepare elements containing nanoscale features at quite reasonable cost, especially if the fabrication elements are created in the own laboratory. We have designed and fabricated a whole nanoimprint manufacturing system and analyzed the resulting surfaces using ad hoc packages developed on an open-software AFM image analysis suite. To complete the work, a number of polymers have been thoroughly studied in order to select the best material for this implementation. It turned out that the best alternative was not always the same, but depended on the application. A comparative study of the polymers, which takes into account the values and dispersion of numerous sample parameters, has been carried out. As a large number of samples was prepared, an automatized procedure for characterization of nanoimprint surfaces had to be set up. The procedure includes figures of merit for comparative purposes. Materials without the requirement of a solvent were found to be superior for most nanoimprint applications. A large dispersion of the samples was found.
关键词： oriented gradient,nanoimprint,polymer,replica,photoresist
更新于2025-09-23 15:22:29
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Energy harvesting properties of the functionally graded flexoelectric microbeam energy harvesters
摘要： Flexoelectricity may be an excellent candidate for piezoelectricity in micro and nano scaled energy harvesters due to its strong size dependency. In this paper, a size dependent analytical model of the cantilever-based functionally graded flexoelectric energy harvesters is developed. The Hamilton’s principle is used to derive the governing equations. By means of the Galerkin’s method, the approximated closed-form solutions of electrical output and energy conversion efficiency are obtained. For the functionally graded flexoelectric energy harvester, the effective flexoelectric response is controlled by not only the flexocoupling coefficient but also its first derivative. Numerical results of a 3μm-thick Polyvinylidene Fluoride/ Strontium Titanate composed functionally graded flexoelectric energy harvester demonstrate that when the volume fraction exponent varies from zero to infinity, the optimal working frequency gradually reduces from 41407Hz to 7761Hz and the optimal load resistance gradually increases from 0.99MΩ to 83.91 MΩ. Meanwhile, shrinking the thickness from 3μm to 0.3μm will highly increase the normalized power density and the energy conversion efficiency about one and two orders, respectively. Moreover, when the strain gradient elastic coefficient becomes larger, the natural frequency will increase while the corresponding maximum electrical output will decrease.
关键词： Functionally graded materials,Flexoelectric effect,Cantilever beam,Strain gradient elastic effect,Energy harvesters
更新于2025-09-23 15:22:29
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Research on Image Smoothing Diffusion Model with Gradient and Curvature Features
摘要： In this paper, two image smoothing models are proposed for the visual inspection of high-density flexible IC package substrates with strict requirements on line-width and line distance which are applied to the de-noising of high-density flexible IC package substrate images. First of all, the two models proposed in this paper combines the level set curvature feature of the image with gradient threshold, using more abundant second-order differential information as the detection factor to remove noise in image. Secondly, theoretical analysis shows that the de-noised image obtained by the two models proposed can retain more detailed texture information and edge information of the original image. What is more, the experimental analysis shows that the proposed models have the highest structural similarity and peak signal-to-noise ratio, and have a relatively high edge-preserving index and the lowest mean squared error compared with other models. In particular, the de-noised image through Model 1 has the highest structural similarity and peak signal to noise ratio, as well as the lowest mean squared error. The de-noised image through Model 2 has a relatively high edge retention index. The methods proposed in this paper can effectively remove the noise of the image of the high-density flexible IC package substrate, and can retain the original details and edges information of the image.
关键词： Image de-noising,Flexible integrated circuit substrate image,Gradient,Curvature
更新于2025-09-23 15:22:29
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Increased luminescent efficiency of perovskite light emitting diodes based on modified two-step deposition method providing gradient concentration
摘要： We increased the luminescent efficiency of perovskite light-emitting diodes (PeLEDs) by using a modified two-step deposition method combined with an interdiffusion process without additional solvent engineering or additive molecules. Methylammonium lead bromide (MAPbBr3) polycrystalline films with nanosized grains and low electronic disorder were fabricated by a modified two-step deposition process. The as-fabricated MAPbBr3 films showed gradient concentration characteristics as a result of a gradient distribution of the MABr. Also, the MABr-gradient concentration structure was intensified by the interdiffusion process, showing improved performance of MAPbBr3 PeLEDs with maximum current efficiency CEmax = 0.861 cd A?1 and maximum luminance = 604 cd m?2 with very narrow electroluminescence spectral width. This is the highest CEmax among MAPbBr3-based PeLEDs deposited by the two-step deposition method.
关键词： two-step deposition method,perovskite light-emitting diodes,luminescent efficiency,gradient concentration,interdiffusion process
更新于2025-09-23 15:21:21
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Flexoelectricity in Monolayer Transition Metal Dichalcogenides
摘要： Flexoelectricity, the coupling effect of the strain gradient and charge polarization, is an important route to tune electronic properties of low-dimensional materials. Here our extensive first-principles calculations reveal that structural wrinkling and corrugation will cause significant flexoelectricity in transition metal dichalcogenide (TMD) monolayers. The flexoelectricity is induced by the strain gradients created along the finite thickness of the wrinkled TMD monolayers and becomes more dominant in determining out-of-plane polarizations with decreasing wavelengths of the TMD wrinkles. According to the first-principles calculations and whole structural symmetry, a theoretical model is developed to describe the total out-of-plane polarizations and flexoelectric effect of the wrinkled TMD monolayers. The unveiled flexoelectricity in monolayer TMDs highlights a potential for their application in energy conversion devices.
关键词： energy conversion,monolayer,strain gradient,flexoelectricity,polarization,transition metal dichalcogenides
更新于2025-09-23 15:21:21
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Gradient Projection-Based Alternating Minimization Algorithm for Designing Hybrid Beamforming in Millimeter-Wave MIMO Systems
摘要： This study considers the use of alternating minimization (AltMin) framework as the main design principle in determining the optimal weights of hybrid digital and analog beamforming in millimeter-wave massive multiple-input multiple-output systems. However, such framework experiences analog beamformer design problem because analog beamformers are normally constructed using phase shifters (PSs), which result in non-convex constraints, and known solutions suffer from high computational complexity. We address this issue by proposing a simple yet efficient gradient projection (GP)-based AltMin (GP-AltMin) algorithm for hybrid beamforming design problems. In addition, when quantized PSs are adopted, we propose non-uniform PSs on the basis of the Lloyd-Max algorithm for minimizing the performance loss caused by quantization. Simulation results demonstrate that the proposed GP-AltMin algorithm not only has lower complexity but can also achieve spectral efficiency, which is comparable with or higher than those of state-of-the-art algorithms that use unquantized and low-resolution PSs.
关键词： gradient projection,massive MIMO,Beamforming,finite resolution phase shifters,millimeter-wave
更新于2025-09-23 15:21:21
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No-reference image quality assessment using gradient magnitude and wiener filtered wavelet features
摘要： No-reference image quality assessment (NR-IQA) aims to evaluate the perceived quality of distorted images without prior knowledge of pristine version of the images. The quality score is predicted based on the features extracted from the distorted image, which needs to correlate with the mean opinion score. The prediction of an image quality score becomes a trivial task, if the noise affecting the quality of an image can be modeled. In this paper, gradient magnitude and Wiener filtered discrete wavelet coefficients are utilized for image quality assessment. In order to reconstruct an estimated noise image, Wiener filter is applied to discrete wavelet coefficients. The estimated noise image and the gradient magnitude are modeled as conditional Gaussian random variables. Joint adaptive normalization is applied to the conditional random distribution of the estimated noise image and the gradient magnitude to form a feature vector. The feature vector is used as an input to a pre-trained support vector regression model to predict the image quality score. The proposed NR-IQA is tested on five commonly used image quality assessment databases and shows better performance as compared to the existing NR-IQA techniques. The experimental results show that the proposed technique is robust and has good generalization ability. Moreover, it also shows good performance when training is performed on images from one database and testing is performed on images from another database.
关键词： Wiener filtering,Gradient magnitude,Discrete wavelet transform,No-reference image quality assessment
更新于2025-09-23 15:21:21
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Adaptability analysis of radiative transport diffusion approximation in planar-graded-index media
摘要： To study the applicability of diffusion approximation method, the influence of the optical thickness, scattering albedo, and wall emissivity of the examined medium on the accuracy of the diffusion approximation is analyzed. The accuracy is determined by comparison with results obtained by using the Monte Carlo method. By calculating the dimensionless radiation heat flux distributions at the bottom of the medium for various parameter combinations, the influence of each optical parameter is analyzed. In addition, the adaptability of the diffusion approximation method to the case of a gradient-index medium is examined. The results show that in the homogeneous-refractive-index medium and the gradient-index medium, the accuracy of diffusion approximation method is improved by an increase in the optical thickness or the scattering albedo and by a decrease in the wall emissivity. Moreover, the maximum relative errors are primarily distributed at the medium boundary and center. In the case of increased optical thickness or decreased wall emissivity, the error of the diffusion approximation method becomes stable and remains at a small value.
关键词： numerical analysis,relative error,diffusion approximation,gradient index,Radiative transfer
更新于2025-09-23 15:21:21
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[IEEE 2019 International Conference on Communication and Electronics Systems (ICCES) - Coimbatore, India (2019.7.17-2019.7.19)] 2019 International Conference on Communication and Electronics Systems (ICCES) - Synchronization of Distributed Photovoltaic Generation with an Active network using Phase Locked Loop technique
摘要： Optical tomographic imaging requires an accurate forward model as well as regularization to mitigate missing-data artifacts and to suppress noise. Nonlinear forward models can provide more accurate interpretation of the measured data than their linear counterparts, but they generally result in computationally prohibitive reconstruction algorithms. Although sparsity-driven regularizers significantly improve the quality of reconstructed image, they further increase the computational burden of imaging. In this paper, we present a novel iterative imaging method for optical tomography that combines a nonlinear forward model based on the beam propagation method (BPM) with an edge-preserving three-dimensional (3-D) total variation (TV) regularizer. The central element of our approach is a time-reversal scheme, which allows for an efficient computation of the derivative of the transmitted wave-field with respect to the distribution of the refractive index. This time-reversal scheme together with our stochastic proximal-gradient algorithm makes it possible to optimize under a nonlinear forward model in a computationally tractable way, thus enabling a high-quality imaging of the refractive index throughout the object. We demonstrate the effectiveness of our method through several experiments on simulated and experimentally measured data.
关键词： Optical phase tomography,sparse reconstruction,beam propagation method,total variation regularization,compressive sensing,stochastic proximal-gradient
更新于2025-09-23 15:21:01