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141.
用衍射屏平移相因子计算夫琅禾费衍射场强分布 总被引:3,自引:0,他引:3
用Fresnel-Kirchhoff衍射积分求解夫琅禾费衍射场分布时引入衍射屏平移相因子,可简化对较复杂衍射屏夫琅禾费衍射的讨论,加深对衍射、干涉现象的理解. 相似文献
142.
When the base connected cochain DG algebra is cohomologically bounded, it is proved that the difference between the amplitude
of a compact DG module and that of the DG algebra is just the projective dimension of that module. This yields the unboundedness
of the cohomology of non-trivial regular DG algebras.
When A is a regular DG algebra such that H(A) is a Koszul graded algebra, H(A) is proved to have the finite global dimension. And we give an example to illustrate that the global dimension of H(A) may be infinite, if the condition that H(A) is Koszul is weakened to the condition that A is a Koszul DG algebra. For a general regular DG algebra A, we give some equivalent conditions for the Gorensteiness.
For a finite connected DG algebra A, we prove that Dc(A) and Dc(A
op) admit Auslander-Reiten triangles if and only if A and A
op are Gorenstein DG algebras. When A is a non-trivial regular DG algebra such that H(A) is locally finite, Dc(A) does not admit Auslander-Reiten triangles. We turn to study the existence of Auslander-Reiten triangles in Dlfb(A) and Dlfb (A
op) instead, when A is a regular DG algebra.
This work was supported by the National Natural Science Foundation of China (Grant No. 10731070) and the Doctorate Foundation
of Ministry of Education of China (Grant No. 20060246003) 相似文献
143.
Zdeněk Strakoš 《Numerical Algorithms》2009,51(3):363-379
Given a nonsingular complex matrix and complex vectors v and w of length N, one may wish to estimate the quadratic form w
*
A
− 1
v, where w
* denotes the conjugate transpose of w. This problem appears in many applications, and Gene Golub was the key figure in its investigations for decades. He focused
mainly on the case A Hermitian positive definite (HPD) and emphasized the relationship of the algebraically formulated problems with classical
topics in analysis - moments, orthogonal polynomials and quadrature. The essence of his view can be found in his contribution
Matrix Computations and the Theory of Moments, given at the International Congress of Mathematicians in Zürich in 1994. As in many other areas, Gene Golub has inspired
a long list of coauthors for work on the problem, and our contribution can also be seen as a consequence of his lasting inspiration.
In this paper we will consider a general mathematical concept of matching moments model reduction, which as well as its use in many other applications, is the basis for the development of various approaches for estimation
of the quadratic form above. The idea of model reduction via matching moments is well known and widely used in approximation
of dynamical systems, but it goes back to Stieltjes, with some preceding work done by Chebyshev and Heine. The algebraic moment matching problem can for A HPD be formulated as a variant of the Stieltjes moment problem, and can be solved using Gauss-Christoffel quadrature. Using
the operator moment problem suggested by Vorobyev, we will generalize model reduction based on matching moments to the non-Hermitian
case in a straightforward way. Unlike in the model reduction literature, the presented proofs follow directly from the construction
of the Vorobyev moment problem.
The work was supported by the GAAS grant IAA100300802 and by the Institutional Research Plan AV0Z10300504. 相似文献
144.
We use a semiclassical approximation to study the transport through the weakly open chaotic Sinai quantum billiards which can be considered as the schematic of a Sinai mesoscopic device,with the diffractive scatterings at the lead openings taken into account.The conductance of the ballistic microstructure which displays universal fluctuations due to quantum interference of electrons can be calculated by Landauer formula as a function of the electron Fermi wave number,and the transmission amplitude can be expressed as the sum over all classical paths connecting the entrance and the exit leads.For the Sinai billiards,the path sum leads to an excellent numerical agreement between the peak positions of power spectrum of the transmission amplitude and the corresponding lengths of the classical trajectories,which demonstrates a good agreement between the quantum theory and the semiclassical theory. 相似文献
145.
研究了在三值噪声和热噪声扰动下的RLC电路的平均输出幅度增益. 利用随机平均法和Shapiro-Loginov公式, 得到了平均输出幅度增益的精确表达式. 通过计算机模拟, 画出了平均输出幅度增益与平坦系数、有噪声和无噪声时, 输出信号振幅与输入信号频率之间的关系曲线. 从结果来看, 系统产生了双值噪声驱动的RLC电路中(文献[11])没有的随机共振现象, 甚至还出现了双共振峰. 相似文献
146.
We study the performances of quantum channel adaptive [4,1] code transmitting in a joint amplitude damping and dephasing channel, the [6,2] code transmitting in an amplitude damping channel by combining the encoding, noise process, and decoding as one effective channel. We explicitly obtain the entanglement fidelities. The recovery operators of the [6,2] code are given. The performance is nearly optimal compared with that of the optimal method of semidefinite programming. 相似文献
147.
148.
Aiming at the poor detection rate of multi-frequency weak signals under a strong background of noise, a novel method based on adaptive stochastic resonance (SR) theory is proposed in this paper. The optimal parameters can be obtained automatically via measurement by establishing an adaptive SR system model and using the reverse location method. After passing through the adaptive SR system, the spectrum values of all eight signals greatly improve, the largest spectrum value gain increases from 12.41 to 2033 when the frequency is 0.01?Hz, which is an improvement of a factor of 162.8, and the signal-to-noise ratio (SNR) gain of the whole system is 10.3134?dB. Under the condition of different input noise intensities and signal amplitudes, the mean SNR of the system increases from –13.1136 to –2.7614?dB, which is a 78.9% increase, and the largest SNR gain is 13.4702?dB when the noise intensity D?=?1.2 and signal amplitude A?=?0.11. Compared to the single optimal spectrum value, when defining multiple optimum spectrum values as the SNR criterion, the detection sensitivity is less than 0.35 when the input noise intensity is between 0.5 and 2.5, and the sensitivity value is 6.29 times higher when D?=?2.5. The system successfully realizes the adaptive detection of twelve weak signals, and the SNR gain is 7.9743?dB, which improves the channel capacity of signal detection. The experimental results demonstrate the high efficiency and strong applicability of the system, improving the signal processing efficiency and speed of signal transmission. 相似文献
149.
为提高研磨抛光加工表面质量,利用Matlab软件编制程序对不同参数下轨迹曲线曲率进行计算分析。结果表明,转速比对磨粒运动轨迹曲线曲率影响很大;相同转速比下的曲线曲率呈现周期性变化,曲率变化幅值很小;磨粒径向距离越大,曲率变化越剧烈,工件边缘处容易产生曲率突变;考虑到对磨粒径向距离的影响,偏心距不宜太大或太小。同时,磨粒初始角度对磨粒轨迹曲线曲率形状没有影响。该研究可为研磨抛光设备的设计提供理论指导。 相似文献
150.
针对传统的Canny算法在平滑滤波时对图像边缘检测的影响,以及需要预先设定高低阈值等缺点,本文提出了一种新的Canny边缘检测算法。首先采用自适应中值滤波对图像进行处理;其次,添加45°和135°方向的梯度模板来计算梯度幅值;最后,采用Otsu算法计算经梯度幅值运算得到图像的高低阈值。实验结果表明,该改进的Canny算法具有良好的抗噪性能,并且能精确的检测出边缘信息。 相似文献