共查询到19条相似文献,搜索用时 480 毫秒
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由于海洋动力学和目标起伏引起发射信号包络的时变衰减,相应于频域就是频率扩展,这种信道称为频率扩展信道,又名快速衰落信道(FFD)。在FFD信道中,理想信道的最佳检测器——匹配滤波器的性能将有所下降,Baggenstoss已经证明FFD信道的最佳检测器是分段副本相关器(SRC)。近年来出现的小波变换具有和宽带相关处理相似的计算结构,所以文章拟从连续小波变换的理论和性质出发,推导FFD信道小波变换域最佳检测器的形式,并针对一个仿真算例,进一步用Monte-Carlo实验计算出该检测器的性能曲线,结果表明该检测器的性能优于小波域的副本相关器。 相似文献
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我们研究了一种新的白光联合变换相关器,即在频谱面上利用液晶光阀对联合傅氏干涉谱进行变换,然后用白光做为液晶光阀的读出光,实现相关变换。利用部份相干光传播模式,导出这种白光联合相关器保留了对复振幅的线性运算能力,结果表明,这种相关器能得到较好的相关结果,并能有效地抑制相干噪声。 相似文献
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本文提出了一种基于拉普拉斯滤波的形态相关器(LBMC),用来改进传统光学形态相关器的性能.与形态相关器不同,在执行最后的傅里叶变换之前,LBMC还须对传统形态相关器的联合功率谱做拉普拉斯能谱强度滤波处理.计算机模拟测试结果表明,与线性相关和形态相关器相比,LBMC能够产生强而尖锐的相关信号,具有更强的识别能力.当输入图像受椒盐噪声影响时,LBMC保持了高且稳定的自相关-互相关比和峰噪比,从而表现出更强的鲁棒性.尽管当乘法照明因子大于1时,LBMC丧失了传统MC的照明不变识别能力,但其保证相当高的识别度. 相似文献
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分析了自适应多用户信号检测器在多址干扰与窄带干扰共存条件下的系统性能,理论推导软件模拟结果证实它能有效地同时消除多址干扰和窄带干扰带来的影响。 相似文献
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针对正交频分复用(OFDM)系统中由于信道快时变导致的子载波间干扰(ICI),基于基扩展模型,提出了一种时变信道下OFDM系统联合迭代信道估计与符号检测算法.该算法将基于基扩展模型的最小均方误差信道估计算法与一种类似于串行干扰抵消的符号检测方式相结合,并利用插值和滤波过程进一步消除噪声影响,进而通过联合迭代获得较为精确的符号检测结果.同时,利用带状矩阵近似降低算法的计算复杂度,在复杂度与算法性能之间取得比较好的折中.理论分析和仿真结果表明,在快时变信道条件下,这种新的联合迭代信道估计与符号检测算法可有效地提高系统性能. 相似文献
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Ali Asghar Mowlavi Mohammad Hadi Hadizadeh Yazdi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,660(1):104-107
We have applied a pile-up Monte Carlo simulation code on gamma spectrum of a prompt gamma neutron activation analysis (PGNAA) system. The code has been run in nonparalyzable mode for a specific geometry of a PGNAA system with 241Am-9Be source and NaI(Tl) detector to obtain the distortion due to “pile-up” in the pulse height of gamma spectrum. The results show that the main background in the nitrogen region of interest (ROI) is due to two pile-ups. We have also evaluated the variation of count rate and total photon sampling over the Monte Carlo spectra. At high count rates, not only the nitrogen ROI but also carbon ROI, and hydrogen peak are disturbed strongly. Comparison between the results of simulations and the experimental spectra has shown a good agreement. The code could be used for other source setups and different gamma detection systems. 相似文献
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Aki Miyake Takahiro NishiokaShailendra Singh Hisashi MoriiHidenori Mimura Toru Aoki 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,654(1):390-393
A CdTe detector with a Gd converter has been developed and investigated as a neutron detector for neutron imaging. The fabricated Gd/CdTe detector with the 25 μm thick Gd was designed on the basis of simulation results of thermal neutron detection efficiency and spatial resolution. The energy resolution of the Gd/CdTe detector is less than 4 keV, which is enough to discriminate neutron capture gamma rays from background gamma emission. The Gd/CdTe detector shows the detection of neutron capture gamma ray emission in the 155Gd(n, γ)156Gd, 157Gd(n, γ)158Gd and 113Cd(n, γ)114Cd reactions and characteristic X-ray emissions due to conversion-electrons generated inside the Gd film. The observed efficient thermal neutron detection with the Gd/CdTe detector shows its promise in neutron radiography application. 相似文献
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Siu‐Kay Chow 《中国工程学刊》2013,36(1):83-88
Abstract A detection scheme is developed under the assumption that a true target‐generated acoustic signal is accompanied by a weak frequency‐shifted replica. Our analysis shows that the correlation between the signal and its corresponding frequency‐shifted replica is the decisive factor. Optimum filtering techniques and performance measures are discussed. In the cases where the signal spectrum and the spectra of its replicas are overlapping, it is found that the performance will decrease with increase of overlap. Depending on the shape of the spectra, such degradation may be drastic. 相似文献
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J.D. Burrows P.A. Butler K.A. Connell G.D. Jones A.N. James A.M.Y. El-Lawindy T.P. Morrison J. Simpson R. Wadsworth 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1984,227(2):259-265
A gas filled avalanche detector, capable of operating at high count rates, has been developed in order to detect recoiling ions. The detector has been used to identify the signal of evaporation residue channels in the presence of strong fission competition. The performance of the detector has been investigated for the reaction of 83 and 95 MeV 18O ions on a 208Pb target. 相似文献
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N.J. Shenhav H. Stelzer 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,228(2-3):359-364
The Bragg-curve detector of the parallel plate ionization chamber type generates a signal that is a distorted replica of the original Bragg-curve. In result of this distortion, the signal peak height is not only a function of the atomic number of the heavy ion, as it is often stated, but also of the particle mass. This mass effect was studied with the aid of computer simulation, and it was found to be dependent on the Frisch grid to anode gap width and on the detector gas. The charge resolution of the detector is affected very significantly by this mass dependence of the signal peak height. Therefore, a careful selection of the detector gas and the grid to anode gap width is necessary, if good charge resolution over a wide range of heavy ions is required. 相似文献
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Hongyan Liu Yiping GuoFen Wu Yun LiuDi Zhang 《Materials Science and Engineering: B》2013,178(16):1057-1061
ZnFe2O4 replica with biological hierarchical structure was synthesized from Papilio paris by a sol–gel method followed by calcination. The crystallographic structure and morphology of the obtained samples were characterized by X-ray diffraction, field-emission scanning electron microscope, and transmittance electron microscope. The results showed that the hierarchical structures were retained in the ZFO replica of spinel structure. The magnetic behavior of such novel products was measured by a vibrating sample magnetometer. A superparamagnetism-like behavior was observed due to nanostructuration size effects. In addition, the ZFO replica with “quasi-honeycomb-like structure” showed a much higher specific capacitance of 279.4 F g−1 at 10 mV s−1 in comparison with ZFO powder of 137.3 F g−1, attributing to the significantly increased surface area. These results demonstrated that ZFO replica is a promising candidate for novel magnetic devices and supercapacitors. 相似文献
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B. A. Young T. Shutt D. Akerib É. Aubourg P. D. Barnes Jr. A. Cummings A. Da Silva J. Emes E. E. Haller S. Margulies R. R. Ross B. Sadoulet G. Smith W. Stockwell S. White 《Journal of Low Temperature Physics》1993,93(3-4):393-398
We have tested a new 60 gram germanium phonon and ionization detector to study incomplete charge collection effects in cryogenic detectors. An understanding of such effects is necessary to further improve the nuclear vs. electronic recoil discrimination capability of cryogenic detectors. The detector is operated at 20 mK. It has three concentric ionization channels, and four electric field shaping structures on its sides. Phonons are sensed using NTD Ge thermistors. First results obtained using this device and moveable radioactive sources of241Am and57Co will be presented. 相似文献
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Diane M. Markoff Vince Cianciolo Chuck L. Britton Ronald G. Cooper Geoff L. Greene 《Journal of research of the National Institute of Standards and Technology》2005,110(4):449-452
We are developing a high-efficiency neutron detector with 1 cm position resolution and coarse energy resolution for use at high-flux neutron source facilities currently proposed or under construction. The detector concept integrates a segmented 3He ionization chamber with the position sensitive, charged particle collection methods of a MicroMegas detector. Neutron absorption on the helium produces protons and tritons that ionize the fill gas. The charge is amplified in the field region around a wire mesh and subsequently detected in current mode by wire strips mounted on a substrate. One module consisting of a high-voltage plate, a field-shaping high-voltage plate, a grid and wire strips defines a detection region. For 100 % efficiency, detector modules are consecutively placed along the beam axis. Analysis over several regions with alternating wire strip orientation provides a two-dimensional beam profile. By using 3He, a 1/v absorption gas, each axial region captures neutrons of a different energy range, providing an energy-sensitive detection scheme especially useful at continuous beam sources. 相似文献