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991.
为了实现直接序列扩频(DSSS)信号快速捕获的同时降低数据量和硬件资源消耗,引入了压缩感知理论改进部分匹配滤波-快速傅里叶变换(PMF-FFT)算法,提出了基于压缩感知改进的部分匹配滤波-快速傅里叶变换(CSPMF-FFT)算法。该算法将PMF-FFT算法与压缩感知理论相结合,先对信号进行稀疏性分析和压缩观测,然后从少量压缩观测值中重构信号,并利用输出的峰值信息估算信号的多普勒频移和码相位,从而实现捕获。理论分析和仿真实验表明,相较于PMF-FFT捕获算法,CSPMF-FFT算法能在成功完成捕获的同时有效地减少相关器的数目和FFT变换的运算量,从而降低系统数据量和硬件资源压力,为基于压缩感知的扩频信号处理技术研究奠定了基础。 相似文献
992.
993.
994.
在红外成像探测系统中,对红外图像背景进行有效的抑制是准确检测出弱小目标的前提条件.基于目标在空域局部灰度稳定和时域运动连续的约束,提出了一种基于时空域滤波的红外弱小目标背景抑制新方法.首先,利用引导滤波保存图像细节和时域偏微分方程提取图像中突变区域的优势,实现对图像空域与时域中平稳和强起伏不同特征复杂背景进行抑制处理;然后,将时空域背景抑制结果利用相与操作算子处理完成对高度类似弱小目标信号的剔除;最后,为恢复前期抑制结果中丢失的目标信息,利用时空域融合结果作为引导图像进行进一步优化处理,得到最终背景抑制结果.仿真实验采用两组低信杂比运动弱小目标红外图像序列进行方法验证,并将该方法与几种背景抑制方法进行了比较,实验结果表明:该方法无论从主观视觉还是客观评价指标上均优于其他几种方法. 相似文献
995.
This paper has demonstrated the study on the adsorption kinetics of orthoxylene on silica gel with a novel experimental methodology. In the method, there was a differential adsorption bed (DAB) where the solid adsorbent always contacted with the same bulk concentration of the adsorbate vapor, and the DAB was monitored with near-infrared diffuse reflectance spectroscopy (NIRDRS) continuously as well as non-invasively. Local partial least squares (PLS) algorithm was suggested to replace normal global PLS method in multivariate calibration models for processing NIRDRS data, because the concentration of the adsorbate on the adsorbent varied greatly as the adsorption process was going on. In this way, we, conveniently as well as promptly, obtained instantaneous adsorption rates of several orthoxylene/silica gel adsorption processes under different conditions like partial pressure of orthoxylene vapor and velocity of gas, and discovered that the adsorption process was physical adsorption, and mainly controlled by external diffusion. 相似文献
996.
Ivana Antol Mario Barbatti Mirjana Eckert-Maksić Hans Lischka 《Monatshefte für Chemie / Chemical Monthly》2008,139(4):319-328
The properties of formamide, its protonated form and interaction complexes with lithium and sodium cations were studied in electronically excited singlet states by means of high-level multireference ab initio methods. The vertical excitation energies show a marked influence on protonation with particular large effects found for the O-protonated form as compared to neutral formamide. Complexation with Li+ and Na+ leads to a pronounced shift of the nO–π* state to higher energies while the π–π* state moves in opposite direction. Geometry optimizations in the lowest excited singlet show strong geometrical effects leading to pyramidalization at the N and C atoms. The photodynamical simulations performed for formamide in the first excited singlet state show that the main primary deactivation path is CN dissociation with a lifetime of about 420?fs. 相似文献
997.
Densities, ρ, of the binary systems {difurylmethane + (ethanol or propan-1-ol or butan-1-ol or pentan-1-ol or hexan-1-ol)} have been measured
with an Anton Paar DMA 4500 vibrating-tube densimeter over the entire composition range at 288.15 and 308.15 K and atmospheric
pressure. The measured and literature densities of [difurylmethane + n-alkanol] binary systems have been used to check the validity of the relationship describing the dependence of density on
composition. This relation is useful for obtaining interpolated ρ values corresponding to the experimental data. Excess molar volumes (V
mE) of each mixture, limiting (V
m,i
E,∞) and excess partial (V
m,i
E) molar volumes and the limiting partial molar expansion (E
p,i
∞) of both components of each binary system have been examined to provide insight into the temperature variations of the intermolecular
interactions and molecular packing efficiencies. The results have been discussed in terms of specific intermolecular interactions
and structural effects. 相似文献
998.
Guang-hui Cai 《Journal of mathematical chemistry》2008,43(1):375-385
Consider the partly linear regression model Y = xβ + g(t) + e where the explanatory x is erroneously measured, and both t and the response Y are measured exactly, the random error e is ρ−-mixing. Let be a surrogate variable observed instead of the true x in the primary survey data. Assume that in addition to the primary data set containing N observations of , which is ρ−-mixing data sets, an independent validation data containing n observations of is available. The exact observations on x may be obtained by some expensive or diffcult procedures for only a small subset of subjects enrolled in the study. In this
paper, inspired by Berberan-Santos et al. [J. Math. Chem. 37 (2005)101], a semiparametric method with the primary data is
employed to obtain the estimators of β and g(·) based on the least squares criterion with the help of validata. The proposed estimators are proved to be strongly consistent.
相似文献
999.
Chain configuration influences phase behavior of blends of poly(methyl methacrylate) (PMMA) of different tactic configurations (syndiotacticity, isotacticity, or atacticity) with poly(L ‐lactic acid) (PLLA). Blends system of sPMMA/PLLA is immiscible with an asymmetry‐shaped UCST at ~250 °C. The phase behavior of the sPMMA/PLLA blend is similar to the aPMMA/PLLA blend that has been already proven in the previous work to exhibit similar UCST temperatures (230–250 °C) and asymmetry shapes in the UCST diagrams. On the other hand, the iPMMA/PLLA blend remains immiscible up to thermal degradation without showing any transition to UCST upon heating. The blend system with UCST, that is, sPMMA/PLLA, can be frozen in a state of miscibility by quenching to rapidly solidify from the homogeneous liquid at UCST, where the Tg‐composition relationship for the sPMMA/PLLA blend fits well with the Gordon‐Taylor Tg model with k = 0.15 and the blend's T leads to χ12 = ?0.26 for the UCST‐quenched sPMMA/PLLA blend. Both parameters (k and χ) as characterized for the frozen miscible blend suggest a relatively weak interaction between the two constituents (sPMMA and PLLA) in the blends. The interaction strength is likely not strong enough to maintain a thermodynamic miscibility when the blend is at ambient temperature or any lower temperatures below UCST. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2355–2369, 2008 相似文献
1000.
Xi Lu Huayang Wang Zhengting Cai Dacheng Feng 《International journal of quantum chemistry》2008,108(2):334-338
In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The concerned system is HO + CH4 → H2O + CH3, of which the partial potential energy surface is constructed by the coupling between vibrational models and reactive coordinates. Then we explain the formation mechanism of the reactive resonance state by the partial potential energy surface. Finally, we estimated the lifetime of the resonance state, and it is about 45fs. The study of the reactive resonance in a polyatomic reaction is more than just an extension from a typical atom + diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of the transient collision complex in the critical transition‐state region. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献