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排序方式： 共有5712条查询结果，搜索用时 15 毫秒
41.
Yi-Du Yang 《计算数学(英文版)》2000,18(4):413-418
In this paper, we discuss a posteriori error estimates of the eigenvalue $lambda_h$ given by Adini nonconforming finite element. We give an asymptotically exact error estimator of the $lambda_h$. We prove that the order of convergence of the $lambda_h$ is just 2 and the $lambda_h$ converge from below for sufficiently small $h$. 相似文献
42.
CHENG Zhiyuan;JI Zhou;GAO Yansheng;SU Hua;YAN Peipei;XIA Aili 《光子学报》2022,51(12):24-35
Laser optical field imaging system transmits multiple laser beams to scan the target for imaging. When the new optical field imaging theory is applied in practical engineering, the inevitable multi beam intensity jitter effect will cause fluctuation in intensity amplitude. In the subsequent reconstruction of spectrum components based on the spectrum iteration theory, the fluctuation in light intensity amplitude will cause the reconstruction spectrum error, which will lead to degradation of imaging quality in further. Aiming at the problem of image quality degradation of optical field imaging caused by laser beam intensity disturbance, an approximate calculation method based on the demodulation ratio of light field echo signal is proposed in this study. First, the interference light field signals with different frequencies in optical field echo signal are demodulated. The demodulated optical field echo signal is affected by random fluctuations of the beam intensity amplitude. The phase closure coefficient is calculated based on the multi beam phase closure theory and an isospectral sampling array is constructed. Then, according to the principle of isospectral iterative reconstruction, the high-order spectral components can be obtained by iteratively solving the lower order spectral components in turn. In this study, the influence model of the light intensity perturbation factor on reconstructed spectrum component error is established, and the influence mechanism of light intensity perturbation on image quality is revealed. Due to the amplitude fluctuation effect of beam intensity, the disturbance factor of beam intensity fluctuates randomly, which affects the accuracy of spectral signal reconstruction and reduces the imaging quality. In order to eliminate the influence of light intensity disturbance on image quality, the influence of light intensity disturbance factor on reconstructed spectral signal should be suppressed. In the weak turbulence scene, the scale coefficient of the disturbance factor of multi-beam intensity can be approximated by the demodulation component of laser echo signal. The light intensity perturbation factor is calculated by the scale coefficient of demodulation echo signal. The value of laser beam intensity perturbation factor is substituted into the spectrum reconstruction model. Finally, the spectrum of eliminating light intensity disturbance factor is obtained. The target image is obtained by performing an inverse Fourier transform of signal spectrum component, and the image index of target is calculated to evaluate the reconstructed image quality. The demodulation ratio of optical field imaging method is analyzed and verified based on the simulation experiment. The simulation experiment results show that the demodulation ratio method suppresses the light intensity disturbance and improves the reconstruction image quality. The demodulation ratio method can effectively suppress the degradation effect of light intensity disturbance and improve the image quality. The validity of the demodulation ratio method is verified based on the desktop experimental platform. The experimental results show that the image sharpness is significantly improved, and the three image quality evaluation indexes of the reconstructed image Strehl ratio, peak signal-to-noise ratio and structural similarity are all improved, which further proves the effectiveness of the demodulation ratio method. The imaging error correction model of light intensity perturbation factor is proposed and the corresponding demulation ratio solution is proposed in optical field imaging system. This study provides an effective theoretical guidance for the suppression of light intensity perturbation factor and the improvement of image quality in actual optical field imaging. The research shows that the proposed demodulation ratio method can effectively suppress the influence of beam intensity disturbance on image quality, and effectively reduce the requirements of beam intensity stability and multi-beam intensity consistency for optical field imaging, thus reducing the difficulty of optical field imaging engineering. The research can provide technical support for experimental research and application transformation of optical field imaging technology. 相似文献
43.
Guan ZHOU;Libo LI;Di FU;Yafei ZHANG;Yutao FENG;Changhai LIU 《光子学报》2022,51(6):286-295
The wind information of the middle and upper atmosphere is very important to study the coupling of the upper and lower atmosphere and energy, to ensure the smooth development of spacecraft space activities, and to carry out medium and long-term meteorological predictions. The doppler asymmetric spatial heterodyne wind measurement technology is a technique based on the Fourier transform of the interferogram to realize the detection of the doppler frequency shift of the wind. Doppler asymmetric spatial heterodyne is a new passive wind detection technology. For the interferometer, the processing and assembly errors of optical components and structural components, and the aberration of the optical system will distort the interference image. Introducing inversion error in the process of wind speed measurement. The current research on DASH interferogram distortion has not analyzed the influence of interferogram distortion on the accuracy of Doppler phase inversion and lacks the quantitative theoretical basis for the design, processing, and adjustment of Doppler asymmetric spatial heterodyne. In this paper, we analyzed the sources of different distortion in Doppler asymmetric spatial heterodyne. Then by adding different types and sizes of interferogram distortions to the interferograms of the red and green oxygen emission line, the simulation compares the difference between the distorted interferogram’s and the ideal interferogram’s Doppler phase. By adding optical distortion, local bending, slanted fringes and frequency changed these four different forms of interferogram distortion, we got the influence of distortion on the accuracy of Doppler phase inversion. The results show that the Doppler phase error will increase with the increase of the target wind field and interferogram distortion. The Doppler phase error of optical distortion is also will increase with the increase of the target wind field but will fluctuate increase with the increase of interferogram distortion. Among these four different forms of interferogram distortion, the local bending of fringes has the greatest influence on Doppler phase inversion. The phase error increases by 0.113‰ for each additional pixel of the local bending. But the maximum phase error is only 0.03‰ under the condition of 2% distortion. To further explore the influence of local bending sizes and location, we simulate various interferograms with local bending of different sizes and locations. The result shows that the Doppler phase error fluctuation decreases and gradually converges when the size increases. And the phase error fluctuates with the change of position. The fluctuation amount in the first half is small, and the fluctuation in the second half increases gradually. The phase error generated by the same bending at the sampling center is larger than that at the sampling edge. Therefore, attention should be paid to the small distortion in the sampling center area, and if necessary, interferogram correction should be performed to reduce the phase error. The simulation of errors caused by local bending on systems with different fringe frequencies shows that the same amount of bending will have a greater impact on systems with high fringe frequencies. In addition, interferogram with a low signal-to-noise ratio usually uses multiple rows of pixels of the interferogram to reduce uncertainty of phase. Local modulation is reduced when multiple rows of pixels of the distorted interferogram are merged. In order to find out the actual impact of the distorted interferogram in multiple rows of pixels of interferogram, we simulate different interferograms with local bending of different local bending max offset, in different signal-to-noise ratio and modulation. The result shows that even local modulation is reduced when multiple rows of pixels of the distorted interferogram are merged, but the phase uncertainty of the interferogram will not increase. Therefore, even if the interferogram has defects, multiple rows of pixels can be merged to increase the signal-to-noise ratio and reduce the phase uncertainty. This article may provide a quantitative theoretical reference for the design, processing, and adjustment of the Doppler asymmetric spatial heterodyne. 相似文献
44.
45.
在线弹性理论的范围内,简要介绍了新近发展起来的均匀化理论（ｈｏｍｏｇｅｎｉｚａｔｉｏｎｔｈｅｏｒｙ）,并引入了误差分析方面的一些研究成果．由于均匀化理论可以详尽地考虑材料的微观结构,在生命器官组织的细观力学研究中会起到推动作用．作为应用实例,本文介绍了均匀化理论在密质骨力学性能的数值模拟中的应用． 相似文献
46.
《Arabian Journal of Chemistry》2020,13(9):7115-7131
The impregnation of magnetite (Mt) nanoparticle (NPs) onto Musa acuminata peel (MApe), to form a novel magnetic combo (MApe-Mt) for the adsorption of anionic bromophenol blue (BPB) was studied. The SEM, EDX, BET, XRD, FTIR and TGA were used to characterize the adsorbents. The FTIR showed that the OH and CO groups were the major sites for BPB uptake onto the adsorbent materials. The average Mt crystalline size on MApe-Mt was 21.13 nm. SEM analysis revealed that Mt NPs were agglomerated on the surface of the MApe biosorbent, with an average Mt diameter of 25.97 nm. After Mt impregnation, a decrease in BET surface area (14.89 to 3.80 m2/g) and an increase in pore diameter (2.25–3.11 nm), pore volume (0.0052–0.01418 cm3/g) and pH point of zero charge (6.4–7.2) was obtained. The presence of Pb(II) ions in solution significantly decreased the uptake of BPB onto both MApe (66.1–43.8%) and MApe-Mt (80.3–59.1%), compared to other competing ions (Zn(II), Cd(II), Ni(II)) in the solution. Isotherm modeling showed that the Freundlich model best fitted the adsorption data (R2 > 0.994 and SSE < 0.0013). In addition, maximum monolayer uptake was enhanced from 6.04 to 8.12 mg/g after Mt impregnation. Kinetics were well described by the pseudo-first order and liquid film diffusion models. Thermodynamics revealed a physical, endothermic adsorption of BPB onto the adsorbents, with ΔHo values of 15.87–16.49 kJ/mol, corroborated by high desorption (over 90%) of BPB from the loaded materials. The viability of the prepared adsorbents was also revealed in its reusability for BPB uptake. 相似文献
47.
Masao Masamura 《Structural chemistry》2000,11(1):41-45
The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO– (H2O)
n
for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH3NH+
3 (CH3)2NH+
2 (CH3)3NH+ (CH3)4N+. 相似文献
48.
Summary The complete error potential is used for the study of the correlation of molecules. The correlation can be seen as a relaxation of the electrons and a relaxation of the nuclei. From the Fermi sea, the electronic relaxation gives rise to a partial excitation of each orbital which collectively generates a linear, a surface or a volume pressure; the resulting forces acting on the nuclei are defined in a general theory of the intramolecular forces. H3, H
3
+
, the diatoms and the hydrid of the first nine elements are taken as examples. 相似文献
49.
正十二烷醇与环氧乙烷的加成反应动力学研究──最佳反应时间的确定张仁权,张维冰,李葵英,王万兴（齐齐哈尔轻工学院化工系,齐齐哈尔,１６１００６）关键词正十二烷醇聚氧乙烯醚,碱催化,聚合度在工业生产中脂肪醇与环氧乙烷的加成反应多采用ＫＯＨ和ＮａＯＨ等强碱... 相似文献
50.
It follows from an analysis of the error levels of TG evaluation methods that it is a conceptual error to disregard the analogies
of mass, energy and momentum streams of subordinate partial processes. This error is bypassed by means of the introduced method
of dimensionless analysis and by determining the characteristic, constants-like data of thermal processes by using the measured
data directly. These methods are very suitable for increasing the consistency of the calculated results by seeking for similarity,
even in comparisons of measurements made under very different conditions and for emphasizing the differences too, quantitatively.
With this new interpretation of TG processes, the idea of the kinetic compensation effect becomes only a consequence of the
discussed conceptual error.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献