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991.
992.
The importance of technological processes like corrosion, ablation or deposition causes interest in the quantitative monitoring of changes at rough surfaces. Thus, there is a need for effective methods to measure the statistical parameters characterizing changes in the profile or the material composition of such objects. The speckle field scattered from the surface is used as information carrier and its change is measured by correlation. This is realized by sophisticated data acquisition and digital processing techniques. An important issue is the interpretation of the correlation output in terms of statistical parameters describing the surface change. For many random surfaces a geometrical relation between surface profile and optical phase proves satisfactory. This allows to determine the standard deviation of the profile change. For a verification, speckle decorrelation in model surfaces of known deviation is measured. The paper introduces the speckle correlation concept, outlines some history and current setups and describes methods for data evaluation. The reliability of the quantitative interpretation of the speckle decorrelation is demonstrated. The method is illustrated by studies of metal corrosion and material removal in the cleaning of historical objects by laser ablation. 相似文献
993.
994.
Wilson William L. Curtis K. Tackitt M. Hill A. Hale A. Schilling M. Boyd C. Campbell S. Dhar L. Harris A. 《Optical and Quantum Electronics》2000,32(3):393-404
The long held promise of using volume holography to deliver high performance optical storage is reviewed. The problems, which limited the development for many years, are accessed. Finally, we describe a series of innovations, which may make the technology viable at last. 相似文献
995.
996.
997.
R. S. Chen D. G. Fang K. F. Tsang Edward K. N. Yung 《International Journal of Infrared and Millimeter Waves》2000,21(9):1541-1560
An effective wavelet based multigrid preconditioned conjugate gradient method is developed to solve electromagnetic large matrix problem for millimeter wave scattering application. By using wavelet transformation we restrict the large matrix equation to a relative smaller matrix and which can be solved rapidly. The solution is prolonged as the new improvement for the conjugate gradient (CG) method. Numerical results show that our developed wavelet based multigrid preconditioned CG method can reach large improvement of computational complexity. Due to the automaticity of wavelet transformation, this method is potential to be a block box solver without physical background. 相似文献
998.
The dependence of the formation of the nanocrystalline bcc-Fe phase on the alloy composition is studied for Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) alloys. The rf-Mössbauer technique is used to determine the optimal soft magnetic properties. This technique allowed us to compare anisotropy fields in each phase present in the composite alloys. The smallest anisotropy field was found in the bcc-Fe nanograins formed in Nb- and Mo-containing alloys. 相似文献
999.
In CRYPTO 2019, Chen et al. showed how to construct pseudorandom functions (PRFs) from random permutations (RPs), and they gave one beyond-birthday secure construction from sum of Even-Mansour, namely in the single-key setting. In this paper, we improve their work by proving the multi-key security of , and further tweaking but still preserving beyond birthday bound (BBB) security. Furthermore, we use only one random permutation to construct parallelizable and succinct beyond-birthday secure PRFs in the multi-key setting, and then tweak this new construction. Moreover, with a slight modification of our constructions of tweakable PRFs, two parallelizable nonce based MACs for variable length messages are obtained. 相似文献
1000.
We report the construction, operation and performance of a transmission spectrometer for the visible to the IR (up to 3.5 μm wavelength) to measure crystals up to a temperature of 1400 °C. The spectral resolution is almost comparable to that of a commercial spectrometer. The performance of the spectrometer and some problems are demonstrated by spectra of YAG : Nd at different temperatures. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献