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41.
42.
Grzegorz Stepniak Lukasz Maksymiuk Jerzy Siuzdak 《Optical and Quantum Electronics》2007,39(15):1281-1288
Frequency response of passive optical network (PON) based on multimode fibers is investigated. The network comprises fibers,
connectors and splitters/couplers. It is shown that due to mode filtering at splitters, the frequency response is different
for different network nodes in otherwise symmetrical network. 相似文献
43.
Detrended fluctuation analysis (DFA) is a scaling method commonly used for detecting long-range correlations in non-stationary time series. The DFA method uses a trend based on polynomial fitting to extract and quantify fluctuations at different time scales. Basically, such procedure acts as a (non-dynamical) high-pass filter that removes time series components below a given time scale. As an alternative to the polynomial fitting approach, this paper proposes a DFA method based on well-known high-pass filters (e.g., Butterworth, elliptic, etc.). Numerical results show that the proposed DFA approach yields results similar to traditional DFA method. Maybe, the main advantage of the proposed DFA method is that efficient implementations of high-pass filters are available commercially. 相似文献
44.
The nonlinear filtering problem for a diffusion process whose drift and diffusion coefficients depend parametrically on a finite-state jump process involves the solution of a vector system of linear, stochastic partial differential equations. A Lie-Trotter product formula is proven to hold for this system and a recursive implementation is discussed. 相似文献
45.
Quantised phase filters with binary low and high pass amplitude response: the effect of quantisation for scale and rotation input distortions 总被引:1,自引:0,他引:1
Triantafillos Koukoulas Rupert C.D. Young Chris R. Chatwin 《Optics and Lasers in Engineering》2005,43(9):963
In the field of optical pattern recognition, there are a large number of filters that possess identification capabilities for certain kinds of input distortions. The resolution of the spectral components plays an important role in the overall processing time of a correlator that may employ such filters. In this paper, two different techniques are discussed: low pass phase filtering and high pass phase filtering. This is achieved by binarizing the amplitude information which then allows certain frequencies to pass and others to be blocked. Their response to different kinds of input distortions is presented and the effect of phase quantisation is considered in detail. 相似文献
46.
Direct or large eddy simulation of a turbulent flow field is strongly influenced by its initial or inflow boundary condition. This paper presents a new stochastic approach to generate an artificial turbulent velocity field for initial or inflow boundary condition based on digital filtering. Each velocity component of the artificial turbulent velocity field is generated by linear combination of individual uncorrelated random fields. These uncorrelated random fields are obtained by filtering random white‐noise fields. Using common elements in these linear combinations results in multi‐correlation among different velocity components. The generated velocity field reproduces locally desired Reynolds stress components and integral length scales including cross‐integral length scales. The method appears to be simple, flexible and more accurate in comparison with previously developed methods. The accuracy and performance of the method are demonstrated by numerical simulation of a homogeneous turbulent shear flow with high and low shear rates. To assess the accuracy and performance of the method, simulation results are compared with a reference simulation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
47.
Jinxia Xu Yueyan Zang Fanyong Yan Jingru Sun Yuyang Zhang Chunhui Yi 《Particle & Particle Systems Characterization》2021,38(11):2100201
Carbon dots (CDs) are emerging photoluminescent materials with excellent optical properties. However, the lack of active sites in primitive CDs has limited their development applications. Herein, functionalized carbon dots (Z-CDs) are successfully prepared by surface modification of CDs with mono (6-amino-6-deoxy) cyclodextrin (β-CD). The introduction of β-CD increases the spatial potential resistance between CDs, which effectively reduces the self-quenching effect. Moreover, the conjugated domains of Z-CDs are expanded, which improves the optical properties with a quantum yield of 48.74%. Z-CDs are able to be used in the sequential detection of morin and Al3+, and the fluorescence mechanisms are confirmed to be internal filtration effect and fluorescence resonance energy transfer, respectively. The limits of detection are 0.817 and 0.231 × 10−6 m . This study not only provides an idea to solve the problem of self-quenching of CDs but also enriches the detection means of flavonoids and ions, which is expected to be applied to biosensing and environmental monitoring. 相似文献
48.
Spectral filtering of dual lasers with a high-finesse length-tunable cavity for rubidium atom Rydberg excitation
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《中国物理 B》2021,30(7):74203-074203
We propose and demonstrate an alternative method for spectral filtering and frequency stabilization of both 780-nm and 960-nm lasers using a high-finesse length-tunable cavity(HFLTC). Firstly, the length of HFLTC is stabilized to a commercial frequency reference. Then, the two lasers are locked to this HFLTC using the Pound–Drever–Hall(PDH) method which can narrow the linewidths and stabilize the frequencies of both lasers simultaneously. Finally, the transmitted lasers of HFLTC with each power up to about 100 μW, which act as seed lasers, are amplified using the injection locking method for single-atom Rydberg excitation. The linewidths of obtained lasers are narrowed to be less than 1 k Hz, meanwhile the obtained lasers' phase noise around 750 k Hz are suppressed about 30 d B. With the spectrally filtered lasers, we demonstrate a Rabi oscillation between the ground state and Rydberg state of single-atoms in an optical trap tweezer with a decay time of(67 ± 37) μs, which is almost not affected by laser phase noise. We found that the maximum short-term laser frequency fluctuation of a single excitation lasers is at ~ 3.3 k Hz and the maximum long-term laser frequency drift of a single laser is ~ 46 k Hz during one month. Our work develops a stable and repeatable method to provide multiple laser sources of ultra-low phase noise, narrow linewidth, and excellent frequency stability, which is essential for high precision atomic experiments, such as neutral atom quantum computing, quantum simulation, quantum metrology, and so on. 相似文献
49.
介绍了阿贝-波特空间滤波的实验原理,在Matlab环境下建立了带有图形用户界面(GUI)的计算机仿真平台.不仅可以准确地完成针对不同输入图像、不同滤波要求的滤波过程,还可以通过调整滤波器参数观察滤波效果的差异,形象地展现光学空间滤波过程的物理本质,提高教学效果. 相似文献
50.