Papers by Keyword: Autocorrelation Function

Abstract: This article is concerned with the analysis of ordering the arrays of TiO₂ and Al₂O₃ nanotubes using the correlation-spectral methods. As the tools, the spatial Fourier spectrum and one-dimensional autocorrelation function of SEM-image have served. It was shown that the arrays of the aluminum oxide nanotubes can have a nearly ideal ordering on a small scale at the expense of two-stage anodizing. It this case, the degree of order depends also on the purity of initial aluminum and sample preparation method. The introduced characteristics can serve as the measures of the structure order-disorder sensitive to both type and degree of order as a whole and to configuration of structural elements themselves.

Abstract: In this paper is considered the autocorrelator of ultrashort pulses based a Michelson interferometer, his schemes and operating principles. The method of measuring ultrashort pulses is given. The schemes and principles of operation of the main nodes of the autocorrelation receiver are presented: the optical-mechanical part (the construction of the Michelson interferometer) and the electronic part, which includes a photodetector module, a control and data processing unit with a speaker amplifier, and a personal computer.

Abstract: In this paper, the ordering of the arrays of TiO₂ nanotubes obtained by the method of anodic oxidation in the fluoro-containing aqueous-nonaqueous electrolytes containing glycerine and surface-active materials is investigated. For analysis of ordering, the two-dimensional Fourier spectrum, do-it-yourself configurational geometrical entropy and section of the two-dimensional autocorrelation function were used. These characteristics allow us to identify a nature of ordering in sufficient detail and to obtain the preliminary quantitative assessments of this order. It is found that, in the systems of titanium-oxide nanotubes, the stable, almost correct short-range order is established within the first coordination sphere. Such order is similar to the amorphous ordering. At the same time, the ordering of nanotubes arrays differs in detail from the amorphous one in the greater expressiveness of the typical scale the sizes of which can be estimated using the Fourier spectra as well as autocorrelation function.

Abstract: In the paper, the array ordering of the TiO₂ nanotubes obtained by method of the anodic oxidation in different modes in the fluorine-containing aqueous-non-aqueous electrolytes containing glycerin as well as the surface-active reagents is considered. It was shown that such characteristics as the two-dimensional Fourier-spectrum, autocorrelation function and its spectrum allow us to identify the ordering nature and to obtain the preliminary quantitative estimates of SEM order.

Abstract: In this scientific article the recommendations for a three-dimensional surface roughness parameters determination of mechatronics elements are developed. First of all, the measurements for surface with irregular roughness were made, what led to the determination of a 3D roughness correlation function. On that basis correlation interval in two perpendicular treatment directions was calculated and associated with number of surface roughness uncorrelated points. Secondly, the surface roughness step parameters evaluation precision in two mutually perpendicular directions was analysed. Particular attention was paid to the roughness average step RSm in the treatment longitudinal direction. As a result, the recommendations for a 3D roughness parameters determination were prepared.

Abstract: This paper investigates the construction methods of sequences with optimal autocorrelation functions. The approaches proposed by us are to convert the known optimal sequences into the required sequences. In order to arrive at our goal, we establish two conversion formulas, and summarize their performance. The proposed methods can provide lots of candidates of spread sequences for the applications of code-division multiple-access (CDMA) spread spectrum communication systems.

Abstract: Aiming at satellite-based Automatic Identification System (AIS) signals, a blind carrier frequency-offset estimation method was investigated on AWGN channels. Estimation algorithm that is based on the autocorrelation function and a suitable smoothing function was deduced to estimate the frequency-offset. Simulation results show that its accuracy is better than the earlier methods and reduced the computational complexity.

Abstract: Sea state conditions such as wind, wave and current vary in different ocean waters. Two similar offshore structures installed in two different ocean regions will yield different responses. Determining the transfer function of the structure is a system identification exercise that yields the structural response and behaviour given any sea state condition. The transfer function can be determined using available measured sea state data and structural response data. In this paper, a six-legged semisubmersible physical model is developed to a scale of 1:100 and is tested in a wave tank to measure its responses due to simulated random wave loads. The transfer functions of the semisubmersible model are then determined using the measured responses and the measured wave heights.

Abstract: According to Wiener-Khintchine theorem, autocorrelation function of an image was proved that can be used as sharpness evaluation function. An image sharpness index k is proposed and the relationship between content of high frequency components of an image and the width d of its autocorrelation function main lobe was constructed through Fourier transformation. The direct ration relationship between the sharpness index k of an image and the width d of its autocorrelation function main lobe was also validated by experiments. Theoretical analysis and experiment results indicate that d increases when an image is blurry and d decreases when the image is clear.

Abstract: To meet the demands for rough surfaces data in the research of surface engineering, contacts characteristic and so on, a new numerical simulation of rough surface is proposed. Based on FFT method, rough surface with single direction texture is simulated with circular cosine-exponent autocorrelation function (ACF), and the generated surface is rotated of different given angles respectively by rotation of reference system, then the rough surface with multi-direction texture is created by synthesizing the rotated surfaces. The simulation results show that, the ACF curves of generated surface is periodic fluctuation decay, and has a good fitting result with the predetermined ACF. The contrast result between simulated surface and measured surface shows the available of the proposed method.