Papers by Keyword: Periodicity

Abstract: We applied ab initio theoretical studies on the complex of C2H4 and 2HX,the results demonstrated that C2H42HX(X=F,Cl,Br,I),with increasing halogen atomic number,from HF to HI,the bond length have all increasing,however,the binding energy of complex present in the overall decreasing trend.The π bond C2H4 molecule at least interacting with 2HX(X=F,Cl,Br,I) to formation of the X-Hπ bond complex.

Abstract: Airflow temperature in mine changes with periodical change of surface air temperature, but its change pattern couldn’t be expressed by quantitative calculation currently. by differential equation of round roadway and zero dimension of boundary condition, wall rock thermal field is expressed by superposition of two thermal fields; the two thermal fields is respectively effected by annual average wind temperature and air temperature fluctuation. The paper mainly analyses wind temperature fluctuation differential equation and its definite condition; and deduces the expression of temperature fluctuation amplitude and phasing degree at different point of roadway, while surface air temperature periodically fluctuating; by calculating and analyzing, we have the conclusion that amplitude of temperature fluctuation presents downtrend of negative exponent curve with roadway length increasing; phasing degree linearly lag with roadway length increasing. The research result is greatly significant for controlling thermal damage and forecasting wind temperature for seasonal hot mine.

Abstract: A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.

Abstract: The periodicity and the trend which are the important properties of water resources become more and more variable and complex because of the influence of topography, vegetation and the human activities. Wavelet Analysis which has Multi-resolution Analysis function can provide more detail information of the nonlinear and complex system. The periodicity and the trend of precipitation in different plain regions of Handan are illuminated with Morlet Wavelet Transform in Multi-time scales in this study. It is illustrated that the same periods (5years and 9years) exist in the precipitation in different plain regions of Handan and there are the similar variety and the similar trend in the scale of 5years or 9years in different areas. This study would provide technical support for the integrated management and utilization of water resources of the local region.

Abstract: Periodic and non-periodic 1-3 type cement based piezoelectric composites were fabricated by cut and filling technique, using P(MN)ZT ceramic as functional material and cement as matrix. The influences of periodicity of piezoelectric ceramic rods in the composites on electrical properties of all the composites were discussed. The results show that the non-periodic composites have larger dielectric factor and piezoelectric strain constant than those of the periodic composite. The impedance-frequency spectra analysis indicates that the non-periodic arrangement of ceramic rods can effectively restrict the lateral structural mode of the composite, accordingly reduces the coupling resonant between the thickness resonant mode and lateral resonant mode. The thickness electromechanical coupling coefficient of non-periodic composites is larger than that of the periodic composite. With increasing the non-periodic level of P(MN)ZT ceramic in the composites, the mechanical quality factor of the composites increases gradually. Therefore, 1-3 type cement based piezoelectric composites with different special abilities can be obtained by varying the periodic arrangement of P(MN)ZT ceramic rods in the composites.

Abstract: Rescaled range (R/S) analysis has regained in popularity as a robust tool for the examination of long-term dependence. This paper modified the R/S method to determine the periodicity. We firstly apply the modified method to artificial time series for investigating the validity of the new method. Then the proposed technique is employed to research periodicity of the sunspot time series and the results indicate the robustness of the modified method.

Abstract: A periodicity result of information signal is given by Liapunov’s second method.