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171.
设 f : R2→R2 是一同胚, f (∝)=∝. 该文证明了f 是拟共形映射的充要条件是f 保持曲线的双圆性质不变. 相似文献
172.
In this paper, we obtain a version of subordination lemma for hyperbolic disk relative to hyperbolic geometry on the unit disk D. This subordination lemma yields the distortion theorem for Bloch mappings f ∈ H(B^n) satisfying ||f||0 = 1 and det f'(0) = α ∈ (0, 1], where||f||0 = sup{(1 - |z|^2 )n+1/2n det(f'(z))[1/n : z ∈ B^n}. Here we establish the distortion theorem from a unified perspective and generalize some known results. This distortion theorem enables us to obtain a lower bound for the radius of the largest univalent ball in the image of f centered at f(0). When a = 1, the lower bound reduces to that of Bloch constant found by Liu. When n = 1, our distortion theorem coincides with that of Bonk, Minda and Yanagihara. 相似文献
173.
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175.
JPEG图像是最流行的隐写载体之一,但隐写分析的最新进展表明,如何设计安全的JPEG隐写算法仍是一个困难的问题.本文提出了一种新的JPEG自适应隐写方法.自适应隐写难点在于设计失真函数合理反应修改量化DCT系数造成的嵌入失真.由于量化DCT系数绝对值的大小能够反应JPEG图像主要统计特性,本文根据DCT系数大小关系设计失真函数,结合STC(Syndrome Trellis Codes)编码,分别给出了使用nsF5修改方式的单层嵌入方法以及使用加减一修改方式的双层嵌入方法.实验表明,本文单层嵌入方法比nsF5安全性高,双层嵌入方法比nsF5以及Filler’s Method抵抗多种检测的能力更强. 相似文献
176.
Tsutomu Asano Shota Sano Toshihiko Okabe Takumi Sano Chie Sawatari 《Journal of Macromolecular Science: Physics》2018,57(5):317-332
Using a modified method developed from Vonk's method, detailed values of crystallinity and crystal disorder were obtained by wide angle X-ray diffraction (WAXD). In Vonk's method, the crystallinity (w) is determined by extrapolation of the WAXD experimental curve back to zero scattering angle, while the distortion factor (k) is determined by the inclination of the experimental curve at zero scattering angle. In our new method, both w and k are determined at the same time by using the least squares method. In order to show the efficiency of our method, the new fitting procedure was applied to the experimental values of polyethylene and polyethylene terephthalate as measured by Vonk, and the values of w and k determined by our new method were compared with those found by Vonk's method. The new fitting method has the advantage that it uses the whole experimental curve. Moreover, our modified Vonk's method enables us to discuss crystal distortions as arising from first-kind (thermal) disorder and second-kind (paracrystalline) disorder. 相似文献
177.
Xiaojun Tang Feng Zhang Wenjing Wang Chunrui Tang Yuntao Liang Fuchao Tian 《光谱学快报》2018,51(3):134-138
Addressing the problem of baseline drift or distortion in Fourier transform infrared spectra when analyzing gas continuously at scene, a novel and simple method is proposed to identify and treat spectral baseline drift. Firstly, the spectral baseline was corrected with the common approach followed by standard gas analysis. Then, absorbance of analytes was reconstructed and reduced from the corrected spectrum. Finally, a Fourier transform was performed with the difference spectrum, and the first four-line strengths were used as feature variables to determine if baseline distortion occurred. In the end of this paper, this approach has been applied in the field of wellhead gas logging with Fourier transform infrared. The application results showed that all the spikes had been removed from the raw logging curves, confirming that this approach could be used to identify spectral baseline distortion accurately. 相似文献
178.
剪切光束成像(sheared-beam imaging,SBI)技术是一种利用三束剪切相干激光照明的非传统成像技术,该技术通过探测器阵列接收目标反射回波的散斑图进行计算成像,在对远距离暗弱目标高分辨率成像方面有着独特的优势.大气湍流引起的光束波前畸变是影响SBI成像质量的一个关键因素,因此本文从湍流引起的激光波前畸变对目标频谱信息提取的影响入手,建立了光束波前畸变对成像影响的理论模型.利用多层相位屏模型模拟了近地25 km大气对SBI光束传输的影响.通过计算机仿真,得到了不同激光发射孔径和不同成像距离时SBI的成像结果.仿真结果表明,选取合适的发射孔径尺寸可以有效缓解湍流对光束波前质量的影响,从而提升成像质量.在Hutchin的研究基础上,对孔径选择范围的已有研究成果进行了扩展与深化.给出了SBI系统发射孔径尺寸选取的建议,为SBI对不同高度目标成像的像质差异分析提供了参考. 相似文献
179.
A lot of work has focused on compensating nonlinear distortions of the microspeaker under large excitation, yet it is unclear at which level the effect of nonlinear distortion is imperceptible or not annoying. In this study virtual listening tests were performed to evaluate the deterioration of sound quality in music signals with different levels of nonlinear distortion by a microspeaker. Binaural recordings of the music played by the microspeaker were made at different voltage levels, adjusted to the same RMS power, and afterwards reproduced by a low distortion reference headphone. The “double-blind triple-stimulus with hidden reference” method was used in the listening tests. Listeners were required to not only discern the distortion, but also rank the severity of the distortion. The effects of several factors including subject, program material and distortion level on the perceived distortion are discussed. 相似文献
180.
Mengkun Zhu & Xinzhong Huang 《数学研究》2016,49(1):23-32
Some sharp estimates for coefficients, distortion and the growth order are
obtained for harmonic mappings $f \in TL^{\alpha}_H,$ which are locally univalent harmonic mappings
in the unit disk $\mathbb{D}:=\{z:|z|<1\}.$ Moreover, denoting the subclass $TS^{\alpha}_H$ of the
normalized univalent harmonic mappings, we also estimate the growth of $|f|,$ $f \in TS^α_H,$ and their covering theorems. 相似文献