Browsing by Subject "Spatial resolution"
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Item Open Access Bean-Livingston surface barriers for flux penetration in Bi 2Sr 2CaCu 2O 8+δ single crystals near the transition temperature(2011) Mihalache V.; Dede, M.; Oral, A.; Miu L.The first field for magnetic flux penetration H p in Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) single crystals near the critical temperature T c was investigated from the local magnetic hysteresis loops registered for different magnetic field H sweeping rates by using a scanning Hall probe microscope (SHPM) with ∼1 μm effective spatial resolution. Evidences for a significant role of the surface barrier were obtained: the asymmetric shape of the magnetization loops and an anomalous change in the slope of H p(T) close to T c. © 2011 Elsevier B.V. All rights reserved.Item Open Access Beyond Nyquist sampling: a cost-based approach(Optical Society of America, 2013) Özçelikkale, A.; Özaktaş, Haldun M.A sampling-based framework for finding the optimal representation of a finite energy optical field using a finite number of bits is presented. For a given bit budget, we determine the optimum number and spacing of the samples in order to represent the field with as low error as possible. We present the associated performance bounds as trade-off curves between the error and the cost budget. In contrast to common practice, which often treats sampling and quantization separately, we explicitly focus on the interplay between limited spatial resolution and limited amplitude accuracy, such as whether it is better to take more samples with lower amplitude accuracy or fewer samples with higher accuracy. We illustrate that in certain cases sampling at rates different from the Nyquist rate is more efficient.Item Open Access Detection of compound structures using a gaussian mixture model with spectral and spatial constraints(Institute of Electrical and Electronics Engineers Inc., 2014) Arı, C.; Aksoy, S.Increasing spectral and spatial resolution of new-generation remotely sensed images necessitate the joint use of both types of information for detection and classification tasks. This paper describes a new approach for detecting heterogeneous compound structures such as different types of residential, agricultural, commercial, and industrial areas that are comprised of spatial arrangements of primitive objects such as buildings, roads, and trees. The proposed approach uses Gaussian mixture models (GMMs), in which the individual Gaussian components model the spectral and shape characteristics of the individual primitives and an associated layout model is used to model their spatial arrangements. We propose a novel expectation-maximization (EM) algorithm that solves the detection problem using constrained optimization. The input is an example structure of interest that is used to estimate a reference GMM and construct spectral and spatial constraints. Then, the EM algorithm fits a new GMM to the target image data so that the pixels with high likelihoods of being similar to the Gaussian object models while satisfying the spatial layout constraints are identified without any requirement for region segmentation. Experiments using WorldView-2 images show that the proposed method can detect high-level structures that cannot be modeled using traditional techniques. © 1980-2012 IEEE.Item Open Access Fourier transform magnetic resonance current density imaging (FT-MRCDI) from one component of magnetic flux density(IOP Publishing, 2010-05-17) Ider, Y. Z.; Birgul, O.; Oran, O. F.; Arıkan, Orhan; Hamamura, M. J.; Muftuler, L. T.Fourier transform (FT)-based algorithms for magnetic resonance current density imaging (MRCDI) from one component of magnetic flux density have been developed for 2D and 3D problems. For 2D problems, where current is confined to the xy-plane and z-component of the magnetic flux density is measured also on the xy-plane inside the object, an iterative FT-MRCDI algorithm is developed by which both the current distribution inside the object and the z-component of the magnetic flux density on the xy-plane outside the object are reconstructed. The method is applied to simulated as well as actual data from phantoms. The effect of measurement error on the spatial resolution of the current density reconstruction is also investigated. For 3D objects an iterative FT-based algorithm is developed whereby the projected current is reconstructed on any slice using as data the Laplacian of the z-component of magnetic flux density measured for that slice. In an injected current MRCDI scenario, the current is not divergence free on the boundary of the object. The method developed in this study also handles this situation.Item Open Access Super-resolution using multiple quantized images(IEEE, 2010) Özçelikkale, Ayça; Akar, G. B.; Özaktas, Haldun M.In this paper, we study the effect of limited amplitude resolution (pixel depth) in super-resolution problem. The problem we address differs from the standard super-resolution problem in that amplitude resolution is considered as important as spatial resolution. We study the trade-off between the pixel depth and spatial resolution of low resolution (LR) images in order to obtain the best visual quality in the reconstructed high resolution (HR) image. The proposed framework reveals great flexibility in terms of pixel depth and number of LR images in super-resolution problem, and demonstrates that it is possible to obtain target visual qualities with different measurement scenarios including images with different amplitude and spatial resolutions.