适用于任意频隙数的跳频序列族产生方法研究

在现有跳频序列产生理论的基础上,从工程实现的角度研究了一种跳频序列族的构造方法。该方法利用GF(p)上的反馈移位寄存器和若干非线性逻辑运算,产生出性能较好、可用频隙数为p^k-p^m的跳频序列,并通过有限域的多项式长除法实现了系统时间TOD与跳频状态的对应,使其具有实用性。通过对各项性能进行分析仿真,证明生成的跳频序列具有分布均匀、独立性好及线性复杂度大的特点,并易于工程实现。

Frequency in Middle of Magnon Band Gap in a Layered Ferromagnetic Superlattice

The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.

Parameter estimation of sediment in the Yellow River based on the porous medium acoustic theory

Presently,the use of sub-bottom profiler sonar signals is limited to inversing the physical parameters of the sediment in the surface layer(first layer).In this study,based on the acoustic theory of porous medium,the acoustic inversion of the physical parameters of the lower layer(second layer)sediment is studied.When acoustic waves propagate in water and sediment media,interlayer reflection and transmission,intralayer attenuation,and other processes change the energy.The reflection and transmission coefficients of acoustic waves incident perpendicularly to the water–sediment and sediment–sediment interfaces are derived,and the effects of the reflection and transmission process of acoustic waves on the amplitude are quantified.The relationship between the frequency shift and relaxation time of the transmitted signal in different particle size sediments is established to estimate the corresponding attenuation coefficient using the frequency shift of each layer signal.On this basis,combined with the diffusion process of acoustic waves,the equation for extracting the acoustic wave reflection and transmission coefficients of each layer at the interface is derived from the measured sonar signal.Further calculations show that the sediment parameters have a greater influence on the reflection coefficient,and the feasibility of calculating the physical parameters of the lower sediment using the reflection coefficient has been proved.Under the premise of obtaining the physical parameters of surface sediment,this study provides specific methods and steps for inverting the physical parameters of the lower sediment.The on-site detection in the Xiaolangdi reservoir area of the Yellow River,combined with the sediment sampling test results,proved that the proposed method of inversion of the lower sediment parameters based on the porous medium acoustic theory is feasible.