OFDM系统数字成形滤波器阶数有限效应

从OFDM系统子载波正交性要求出发,讨论了数字成形滤波器阶数有限效应。通过分析、仿真,定量描述了数字成形滤波器阶数有限效应对成形滤波器频谱的扩展;并据此提出了抑制数字成形滤波器阶数有限效应的措施。

谐振势阱中有限粒子玻色—爱因斯坦凝聚的数值计算

从统计力学原理出发,用数值方法研究了三维等方谐振势阱中有限粒子数玻色子系统的化学势及其导数随温度的变化.结果表明,粒子数有限的系统没有一级相变,但在有限温度发生玻色—爱因斯坦凝聚;利用化学势二阶导数的极小值定义的玻色—爱因斯坦凝聚临界温度很好地符合实验结果.

Dimensionality and Finite Number Effect on BCS Transition of Atomic Fermi Gas

The effect of finite number and dimensionality has been discussed in thispaper. The finite number effect has a negative correction to final temperature for 2D or 3D atomicFermi gases. The changing of final temperature obtained by scanning from BEC region to BCS regionare 10% or so with N ≤ 10~3 and can be negligible when N 】 10~3. However, in ID atomic Fermi gas,the effect gives a positive correction which greatly changes the final temperature in Fermi gas.This behavior is completely opposed to the 2D and 3D cases and a proper explanation is still to befound. Dimensionality also has a positive correction, in which the more tightly trapping, the higherfinal temperature one gets with the same particle number. A discussion is also presented.

Optimal design of structural parameters for shield cutterhead based on fuzzy mathematics and multi-objective genetic algorithm

In order to improve the strength and stiffness of shield cutterhead, the method of fuzzy mathematics theory in combination with the finite element analysis is adopted. An optimal design model of structural parameters for shield cutterhead is formulated,based on the complex engineering technical requirements. In the model, as the objective function of the model is a composite function of the strength and stiffness, the response surface method is applied to formulate the approximate function of objective function in order to reduce the solution scale of optimal problem. A multi-objective genetic algorithm is used to solve the cutterhead structure design problem and the change rule of the stress-strain with various structural parameters as well as their optimal values were researched under specific geological conditions. The results show that compared with original cutterhead structure scheme, the obtained optimal scheme of the cutterhead structure can greatly improve the strength and stiffness of the cutterhead, which can be seen from the reduction of its maximum equivalent stress by 21.2%, that of its maximum deformation by 0.75%, and that of its mass by 1.04%.

Analysis of strain variation in cross shear zone of plate during snake hot rolling

In order to study the distribution of equivalent and shear strain of aluminum alloy plate during snake hot rolling, several coupled thermo-mechanical finite element models(FEM) are established. Effects of speed ratio and offset distance on strain distribution of the plate are analyzed. The length of cross shear zone is defined to have a better understanding of the deformation characteristic in cross shear zone, which is the essential difference from symmetrical rolling in deformation zone. The results show that the equivalent strain and shear strain of lower part both increase with the increase of speed ratio, while the upper part decreases; the equivalent strain through the whole thickness decreases with ascending offset distance, while the shear strain of lower part increases. The length of cross shear zone quickly increases with ascending speed ratio and slightly decreases with ascending offset distance. The "positive" and "negative" cross shear zones are formed with the increase of speed ratio and offset distance, respectively. The value of the sensitivity coefficient of speed ratio is an order of magnitude bigger than the offset distance. However, the shear strain at center point increases with the ascending speed ratio and offset distance for different mechanism. As speed ratio increases, the asymmetry of the distribution of equivalent is becoming larger and the shear strain is generated in the same direction in cross shear zone. The FEM results agree well with experimental results.

Casimir Effect at Finite Temperature in the Presence of One Fractal Extra Compactified Dimension

We discuss the Casimir effect for massless scalar fields subject to the Diriehlet boundary conditions on the parallel plates at finite temperature in the presence of one fraetal extra eompactified dimension. We obtain the Casimir energy density with the help of the regularization of multiple zeta function with one arbitrary exponent and further the renormalized Casimir energy density involving the thermal corrections. It is found that when the temperature is sumciently high, the sign of the Casimir energy remains negative no matter how great the scale dimension 6 is within its allowed region. We derive and calculate the Casimir force between the parallel plates affected by the fractal additional compactified dimension and surrounding temperature. The stronger thermal influence leads the force to be stronger. The nature of the Casimir force keeps attractive.