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The signals of a single-pulse echo (SE) generated on nonresonant excitation of an inhomogeneously broadened two-level system by a radio-frequency pulse (RFP), against the background of which a magnetic video pulse (MVP) of certain length has been switched on, have been described analytically. It is established that under the conditions of such excitation several SE signals are formed whose generation moments are determined by the duration and amplitudes of the RFP and MVP. The amplitudes of some of these signals depend on the Rabi frequency according to a quadratic law, and the amplitudes of others depend on this frequency according to a biquadratic law. It has been established that the mechanism underlying the appearance of these signals is associated with zero beats arising as a result of superposition of the magnetization fluctuations at variable frequencies and at a frequency of detuning from resonance. It is shown that in the limiting case, where the RFP duration considerably exceeds the duration of the MVP or is comparable with it, the number of SE signals decreases to two. Theoretical results on the formation of SE and the dependence of the amplitude of these signals on the MVP amplitude agree with the experimental data on NMR pulsed signals in ferromagnetic materials. 相似文献
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Endoscopic Observation of Tissue by Narrowband Illumination 总被引:6,自引:0,他引:6
Kazuhiro Gono Kenji Yamazaki Nobuyuki Doguchi Tetsuo Nonami Takashi Obi Masahiro Yamaguchi Nagaaki Ohyama Hirohisa Machida Yasushi Sano Shigeaki Yoshida Yasuo Hamamoto Takao Endo 《Optical Review》2003,10(4):211-215
We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer. 相似文献
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由于互联网层叠模型中多层都存在重复的保护与恢复机制,致使互联网的实现极其复杂,造成网络传输效率较低,而且拥塞。随着密集波分复用(DWDM)的广泛使用和网络底层性能的大幅度提高,已经不需要再对网络中多层进行重复保护与恢复。在此基础上,采用了未来光互联网3层 (应用层、IP层和光互联层) 协议模型,并对其中的光互联层的保护进行了深入的研究,提出了部分共享备用路径保护(P-SPP)方法。此模型能充分利用IP层电子的灵活恢复机制与光互联层的快速保护与恢复机制,提高光互联网的传输性能,以适应目前高速发展的互联网对传输带宽的要求。 相似文献
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On a nonlinear multigrid algorithm with primal relaxation for the image total variation minimisation
Digital image restoration has drawn much attention in the recent years and a lot of research has been done on effective variational partial differential equation models and their theoretical studies. However there remains an urgent need to develop fast and robust iterative solvers, as the underlying problem sizes are large. This paper proposes a fast multigrid method using primal relaxations. The basic primal relaxation is known to get stuck at a ‘local’ non-stationary minimum of the solution, which is usually believed to be ‘non-smooth’. Our idea is to utilize coarse level corrections, overcoming the deadlock of a basic primal relaxation scheme. A further refinement is to allow non-regular coarse levels to correct the solution, which helps to improve the multilevel method. Numerical experiments on both 1D and 2D images are presented. 相似文献
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食品质量与安全是政府、食品行业以及消费者十分关注的问题。为了保证食品质量与安全,需要对食品中的风险因子进行检测。传统的分析方法如生物化学方法和仪器分析方法(色谱法、色谱-质谱法)存在前处理比较复杂,耗时,对样品具有破坏性及无法获取目标物空间信息等缺点。因此,开发快速,无损,实时和可视化的检测技术十分重要,这也是食品领域研究的热点。近年来,高光谱成像技术融合了成像和光谱两种技术,可以作为一种用于食品质量和安全评估的非破坏性和实时检测的工具。拉曼光谱成像技术可以同时获得待测物的光谱和空间信息,具有快速,无损和低成本等优点,在食品安全评价和质量控制中也得到了成功应用。质谱成像技术不需要标记和染色,即可实现样品组织表面待测物的可视化和高通量分析。它作为一种分子可视化技术,可以获得食品中营养成分及内、外源性有害物质的空间分布信息,在食品领域也表现出良好的应用前景。本文检索了近几年国内外发表的成像技术在食品研究中的相关文献,介绍了高光谱成像技术、拉曼光谱成像技术和质谱成像技术的原理,并综述了它们在食品安全与质量控制中的应用。此外,本文分析和讨论了这几种成像技术的优缺点,并对成像技术在食品领域的发展前景做出了展望。 相似文献