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71.
Margarita A. Deneva Pepa I. Uzunova Marin N. Nenchev 《Optical and Quantum Electronics》2007,39(3):193-212
We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns),
based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR).
A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective
channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation
at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely
controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility
of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an
operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical
delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations
of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor
lasers). 相似文献
72.
73.
We present a new method for construction of high-order parametrizations of surfaces: starting from point clouds, the method we propose can be used to produce full surface parametrizations (by sets of local charts, each one representing a large surface patch – which, typically, contains thousands of the points in the original point-cloud) for complex surfaces of scientific and engineering relevance. The proposed approach accurately renders both smooth and non-smooth portions of a surface: it yields super-algebraically convergent Fourier series approximations to a given surface up to and including all points of geometric singularity, such as corners, edges, conical points, etc. In view of their C∞ smoothness (except at true geometric singularities) and their properties of high-order approximation, the surfaces produced by this method are suitable for use in conjunction with high-order numerical methods for boundary value problems in domains with complex boundaries, including PDE solvers, integral equation solvers, etc. Our approach is based on a very simple concept: use of Fourier analysis to continue smooth portions of a piecewise smooth function into new functions which, defined on larger domains, are both smooth and periodic. The “continuation functions” arising from a function f converge super-algebraically to f in its domain of definition as discretizations are refined. We demonstrate the capabilities of the proposed approach for a number of surfaces of engineering relevance. 相似文献
74.
基于CCD的物体测量平台,首先对物体图像进行预处理,继而利用Canny算子提取物体边缘,再通过本文改进的Hough变换实现对被测物体边界直线检测和重构,最后通过多项式插值算法实现物体像素尺寸到物体实际尺寸的转换.实验证明,此方法能够实现无接触式物体尺寸较高精度的测量. 相似文献
75.
H. Totsuji 《等离子体物理论文集》2012,52(1):74-77
The conduction of electrons through narrow channels formed on the surface of liquid helium is analyzed by numerical simulations. It is shown that, when electrons are strongly coupled, we have nonlinear and even negative dependence of conductance on the width of the constriction which is controlled by the gate voltage (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
76.
曲文孝 《核聚变与等离子体物理》2000,20(3):129-135
在TFTR及TEXF等装置上观测到的边界电子冷脉冲的输运现象是通常基于局部热导的瞬态输运理论所无法解释的。利用一个与电子温度剖面不变性相「容的且与在ρ=ρL(ρL≈0.7~0.8)处的局部电子热导相关的非局部电子热导模型来描述边界冷脉冲引起的电子温度变化的瞬态过程,发现此模型可定性地解释边界冷脉冲实验现象的几乎所有主要特征。 相似文献
77.
78.
Chi-Kwong Li 《Journal of Mathematical Analysis and Applications》2008,348(2):843-855
For a positive integer k, the rank-k numerical range Λk(A) of an operator A acting on a Hilbert space H of dimension at least k is the set of scalars λ such that PAP=λP for some rank k orthogonal projection P. In this paper, a close connection between low rank perturbation of an operator A and Λk(A) is established. In particular, for 1?r<k it is shown that Λk(A)⊆Λk−r(A+F) for any operator F with rank(F)?r. In quantum computing, this result implies that a quantum channel with a k-dimensional error correcting code under a perturbation of rank at most r will still have a (k−r)-dimensional error correcting code. Moreover, it is shown that if A is normal or if the dimension of A is finite, then Λk(A) can be obtained as the intersection of Λk−r(A+F) for a collection of rank r operators F. Examples are given to show that the result fails if A is a general operator. The closure and the interior of the convex set Λk(A) are completely determined. Analogous results are obtained for Λ∞(A) defined as the set of scalars λ such that PAP=λP for an infinite rank orthogonal projection P. It is shown that Λ∞(A) is the intersection of all Λk(A) for k=1,2,…. If A−μI is not compact for all μ∈C, then the closure and the interior of Λ∞(A) coincide with those of the essential numerical range of A. The situation for the special case when A−μI is compact for some μ∈C is also studied. 相似文献
79.
一种基于梯度算子和拉普拉斯算子检测医学基因芯片荧光数字图像边缘的方法.数字图像经过图像增强等预处理以后,突出了我们感兴趣的数字图像特征,根据数字图像灰度变化的趋势,用灰度变化的一阶导数(梯度算子)检测图象中的边缘区域;用灰度变化的二阶导数确定图像边缘的中心位置.最后根据某些预定的准则把满足这些准则的象素组成一条边缘. 相似文献
80.
The mixing and wave formation processes in gravity currents induced by the rupture of a vertical dam initially separating a heavy and a light liquid are studied for different channel inclination angles. The calculations are performed using the LES and RANS models. It is shown that when the heavy liquid moves down the channel slope, the longitudinal and transverse internal waves break and form turbulent mixing zones. When the heavy liquid ascends the slope, the wavy motion mode predominates. 相似文献