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In this paper, the study focus on the FDTD(2,2) and (2,4) methods based on the face-centered cubic (FCC). We analyze the influence of time step on the numerical dispersion of both methods has been analyzed, respectively. For the FCC-FDTD(2,2) method, numerical calculation result shows that the maximum time step defined by the Courant-Friedrichs-Levy (CFL) condition is the optimal time step to minimize the numerical dispersion in the constant spatial steps. On the contrary, with the time step approaches the CFL condition, the numerical dispersion in FCC-FDTD(2,4) method gradually decreases and then improves. The conclusion can be used to select the appropriate time step to improve the calculation accuracy of the FCC-FDTD method.

An iterative formulation of arbitrary-order FDTD method is proposed based on a face-centered cubic (FCC) in this paper. Through the distribution of electromagnetic field nodes in FCC grid, the coefficients of arbitrary-order iterative formulations are theoretically derived. We validate the proposed method by two numerical examples. The results of this studies can provide guidance for the practical application of high-order FCC-FDTD method.

The wake generated by the underwater structure can evolve into a wake vortex with a special flow structure, resulting in a change in the speed of sound distribution, which has an important impact on the propagation of parametric array in the ocean and causes fluctuations in the sound field. The difference-frequency sound wave generated by the parametric array is the core of the parametric array technology. The study of the difference-frequency sound field distribution characteristics is the basis for the development of the parametric array technology and the theory of the interaction of sound waves. The frequency domain algorithm is used to calculate and analyze the nonlinear acoustic scattering characteristics of the underwater vortex field and explore the nonlinear acoustic scattering characteristics of the wake field of a cylindrical structure under the conditions of different moments and Mach number. The results show that the spatial directivity of the nonlinear acoustic scattering field of the wake vortex will cause the directivity of the parametric acoustic field to shift. The difference-frequency wave becomes concave and convex on the opposite sides of the parabolic axis and the wave energy is focused and scattered. The focus will cause the amplitude of the wave to increase and decrease accordingly. The main lobe offset will increase as the flow velocity increases.

The echo of maneuvering targets are analyzed in this paper, which combined with Polynomial phase signals (PPSs), and compared the parameter estimation performance of PPSs based on the fractional Fourier transform(FRFT), the cubic phase function and the product cubic phase function(PCPF) for the echo characteristics. In the third section of the paper, sparse aperture imaging is performed on the aircraft, which flies smoothly and the echo is randomly missing, and the RD algorithm of the maneuvering target is compared with FRFT and PCPF algorithm.

The numerical dispersion is one of the main factors to affect the accuracy of the finite-difference time-domain (FDTD) method. It can be easy to be taken for granted that a smaller time step leads to smaller simulation errors. This paper reveals that smaller time steps do not always make more accurate results in FDTD simulations. We analytically investigated how time steps affect the numerical dispersion of two FDTD methods: the leapfrog FDTD(2,2) method and the FDTD(2,4) method. The investigations in this paper show that in the FDTD(2,2) method, a larger time step limited by the Courant-Friedrichs-Lewy (CFL) condition is more helpful to reduce the numerical dispersion error. However, in the FDTD(2,4) method, as the time step grows, the numerical dispersion error decreases at the beginning and then increases. Several numerical examples are carried out to verify our analysis.

In this paper, we present a new approach to reduce the numerical dispersion error of the arbitrary order finite-difference time-domain (FDTD) method in the desired high frequency region. By interpolation of numerical dispersion relation in one-dimensional (1D) and two-dimensional (2D) cases, the numerical disperion error can be significantly reduced for a specific bandwidth especially in the case of high frequency. Two numerical experiments are presented to validate the accuracy of the proposed method.

In order to solve the problem of electromagnetic interference in aircraft fuel measurement systems, the disturbed coupling channel is found first, and then an integrated design method for fuel measurement system is put forward. Comparison between the original system and the integrated system is given, according to which the latter design method is proved to be more anti-interference effective.

This research focuses on the issue of pricing in C2C commerce, and the relationship between pricing and customer's perception. Basing on the theories in marketing and psychology, using observation data from Taobao, this paper divides most popular goods into 5 series, takes peak value and sales volume of them, in order to find the most logical pricing level for them. Moreover, the environment of China and the characteristics of C2C platform are considered.