共查询到20条相似文献,搜索用时 15 毫秒
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Wave-front reconstruction with use of the Fourier transform has been validated through theory and simulation. This method provides a dramatic reduction in computational costs for large adaptive (AO) systems. Because such a reconstructor can be expressed as a matrix, it can be used as an alternative in a matrix-based AO control system. This was done with the Palomar Observatory AO system on the 200-in. Hale telescope. Results of these tests indicate that Fourier-transform wave-front reconstruction works in a real system. For both bright and dim stars, a Hudgin-geometry Fourier-transform method produced performance comparable to that of the Palomar Adaptive Optics least squares. The Fried-geometry method had a noticeable Strehl ratio performance degradation of 0.043 in the K band (165-nm rms wave-front error added in quadrature) on a dim star. 相似文献
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K. C. Johnson 《Applied Physics A: Materials Science & Processing》1981,25(3):357-360
The phenomenon of image reconstruction from an absorptionless volume hologram is analyzed using coupled-wave diffraction theory.
Reconstruction efficiency formulas are derived, which apply when the hologram intermodulation component is negligible and
when no extraneous diffracted orders of significant amplitude are generated. Both transmission and reflection holograms are
considered, and the analysis is developed for diffraction geometries in which polarization effects are appreciable. 相似文献
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In the medical computer tomography(CT) field, total variation(TV), which is the ?1-norm of the discrete gradient transform(DGT), is widely used as regularization based on the compressive sensing(CS) theory. To overcome the TV model’s disadvantageous tendency of uniformly penalizing the image gradient and over smoothing the low-contrast structures, an iterative algorithm based on the ?0-norm optimization of the DGT is proposed. In order to rise to the challenges introduced by the ?0-norm DGT, the algorithm uses a pseudo-inverse transform of DGT and adapts an iterative hard thresholding(IHT) algorithm, whose convergence and effective efficiency have been theoretically proven. The simulation demonstrates our conclusions and indicates that the algorithm proposed in this paper can obviously improve the reconstruction quality. 相似文献
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层析成像图像重建算法综述 总被引:1,自引:0,他引:1
介绍了层析成像技术的图像重建算法,并从正向问题数学模型的简化和反向问题数学模型的映射结构的角度比较了各种算法的特点和优劣。研究表明:用本质是线性算法的各种变换方法重建图像存在严重失真,而卷积滤波的引入可以使变换方法的重建效果有所改善;基于导数搜索的迭代算法对初始值依赖性强、收敛速度慢并且容易陷入局部最优解;基于Fourier变换的方法具有本质的局限性;小波变换则可以同时刻画图像时域和频域的细节特征;有限元法通过重建对象像素的智能划分可以简化正问题的复杂性;而具有物理背景的蒙特卡罗法、模拟退火法、遗传算法、粒子滤波法及神经网络法更适合于复杂且非线性的图像重建;智能化、仿生化、并行化以及各种算法的融合是层析成像图像重建算法的发展趋势。 相似文献
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Image reconstruction from amplitude-only and phase-only data in the fractional Fourier domain applying the inverse fractional Fourier transform is analyzed on the examples of perfect edges of different contrasts and real-world image. 相似文献
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Longhi S 《Optics letters》2008,33(5):473-475
A simple design of spatially finite one-dimensional and bidimensional waveguide arrays, showing self-imaging properties, is proposed. Image reconstruction insensitive to array truncation is achieved by the introduction of short waveguide interruptions (waveguide segmentation), which act as a focusing lens for discretized light. 相似文献
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《Magnetic resonance imaging》1995,13(1):97-103
For echo-planar imaging (EPI), failure to time-reverse alternate echoes results in aliasing in the image. We encountered image artifacts in EPI acquired on a system with sequential sampling. After examining the source of these image artifacts, we concluded that the artifacts were a result of the type of sampling method used in data acquisition and the way the time-reversal of alternate echoes was carried out prior to Fourier transformation. Two methods are demonstrated to obtain artifact-free EPI with sequential data sampling. 相似文献
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V. G. Bagrov D. M. Gitman S. P. Gavrilov Sh. M. Shvartsman 《Russian Physics Journal》1975,18(3):351-354
A general theory is derived for the creation of pairs of spinless particles from vacuum in the presence of an electromagnetic field. If the exact solutions of the Klein-Gordon equation are known for the particle in the given external field, the pair-creation problem can be solved. 相似文献
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Photoinduced emission of cooper pairs from superconductors 总被引:1,自引:0,他引:1
Under certain conditions specified in this work, a Cooper pair can be emitted from a superconductor upon the absorption of one ultraviolet photon. The spectra of the excited electron pair carry direct information on the energy and angular pair correlation. These statements are concluded from a formal and numerical analysis based on the Bardeen-Cooper-Schrieffer theory for superconductivity. 相似文献
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G. Li 《Journal of Molecular Spectroscopy》2010,263(1):123-125
The Fourier-transform infrared emission spectra of BO were recorded using a Bruker IFS 125 HR spectrometer. The observed spectrum of BO in the 1200-2100 cm−1 region contains three bands: the fundamental bands of 11BO and 10BO and a hot band of 11BO with band origins measured to be 1861.9242(97), 1915.3071(09) and 1838.3773(68) cm−1, respectively. 相似文献
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为了提高图像分辨率,从软件的角度出发,对低分辨率图像序列重建高分辨率图像的原理和算法实现开展了研究,提出从多个低分辨率图像序列中获取更高分辨率图像的方法。通过采用基于光流场的金字塔分层结构实现由粗到精的图像配准,获取了亚像素的运动估计。在采用多帧低分辨率图像进行亚像素级配准后,提出采用动态自适应确定正则化参数的方法,构造了简单的正则化代价函数,建立了低分辨率图像与高分辨率图像之间关系的重建模型,仿真实验结果表明该超分辨率重建算法水平和垂直方向上分辨率各增加一倍,与其他算法相比清晰度更高,计算时间不到传统POCS算法的一半。 相似文献