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621.
具有初始织构的AZ31镁合金等通道挤压的显微组织和织构研究 总被引:1,自引:1,他引:0
利用X射线衍射技术,分析了具有初始{0002}织构的AZ31镁合金在等通道挤压(ECAP)过程中显微组织和织构的变化。结果表明:在等通道挤压过程中晶粒发生了动态再结晶,使晶粒细化,显微组织观察表明,等通道挤压能有效细化晶粒。随挤压道次增加,晶粒尺寸变小,同时晶粒均匀性得到改善。当挤压达到12道次时,平均晶粒尺寸由初始状态的30μm降低到8μm左右,晶粒尺寸降低。由于镁合金的基面滑移很容易发生,同时镁合金在初始状态有很强的{0002}基面织构,所以试样的在变形中的滑移倾向于基面滑移。材料在挤压过程中晶粒向平行于基面的方向转动,以利于晶粒的基面滑移。因此,随挤压次数的增加,基面织构强度增加,当挤压道次为12时,材料形成很强的{0002}〈1120〉织构。 相似文献
622.
给出一种新型紧凑的带陷超宽带印刷单极子天线,天线由圆形辐射贴片和有限接地平面组成。天线输入端驻波比小于2的带宽覆盖3.38-20GHz频率范围,具有16.62GHz的绝对带宽和142.7%的相对带宽。在整个频带范围内,方向图日面近似全向且对称。仿真与测量结果验证了该天线的优越性,该天线可以方便用于超宽带无线通信领域。 相似文献
623.
时间终止时,HPP故障数的Frequentist、Bayesian与Fiducial双样和多样预测 总被引:1,自引:0,他引:1
研究了时间终止时,齐次Poisson过程故障数的预测问题,根据已出现的终止时间和故障数,给出了未来故障数的经典(Frequentist)点估计、经典精确预测区间、正态近似预测区间、Bayesian精确预测区间、极大后验点估计、Fiducial精确预测区间。 相似文献
624.
625.
The motion of a lure in water is investigated experimentally and numerically. The lure motion in water of a passing water tank is observed, and the periodic motion is/ound. From the Fourier analysis, it is found that the frequency with the largest amplitude in the lateral direction depends on the lip width of the lure. To understand the lure dynamics, a numerical simulation of the flow field around the lure is performed. The shape is measured using an X-ray computer tomography and converted into a voxel model. From visualization, it is found that vortex sheds from its lip correspond to the vibration frequency of the lure. 相似文献
626.
627.
An improved three-dimensional incompressible smooth particle hydrodynamics (ISPH) model is developed to simulate the impact of regular wave on a horizontal plate. The improvement is the employment of a corrective function to enhance angular momentum conservation in a particle-based calculation. And a new estimation method is proposed to predict the pressure on the horizontal plate. Then, the model simulates the variation characteristics of impact pressures generated by regular wave slamming. The main features of velocity field and pressure field near the plate are presented. The present numerical model can be used to study wave impact load on the horizontal plate. 相似文献
628.
A cross-layer design(CLD)scheme with combination of power allocation,adaptive modulation(AM)and automatic repeat request(ARQ)is presented for space-time coded MIMO system under imperfect feedback,and the corresponding system performance is investigated in a Rayleigh fading channel.Based on imperfect feedback information,a suboptimal power allocation(PA)scheme is derived to maximize the average spectral efficiency(SE)of the system.The scheme is based on a so-called compressed SNR criterion,and has a closed-form expression for positive power allocation,thus being computationally efficient.Moreover,it can improve SE of the presented CLD.Besides,due to better approximation,it obtains the performance close to the existing optimal approach which requires numerical search.Simulation results show that the proposed CLD with PA can achieve higher SE than the conventional CLD with equal power allocation scheme,and has almost the same performance as CLD with optimal PA.However,it has lower calculation complexity. 相似文献
629.
An efficient wavelet-based finite-difference time-domain (FDTD) method is implemented for analyzing nanoscale optical devices, especially optical resonator. Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells, i.e. used memory, while analy- zing a high-index dielectric ring resonator working as an add/drop multiplexer. The main novelty is that the wave- let-based FDTD model is extended in a parallel computation environment to solve physical problems with large di- mensions. To demonstrate the efficiency of the parallelized FDTD model, a mirrored cavity is analyzed. The analysis shows that the proposed model reduces computation time and memory cost, and the parallel computation result matches the theoretical model. 相似文献
630.
在1090ES广播式自动相关监视(ADS—B)系统中,为了对飞机的位置消息进行有效编码,经度和纬度采用简洁位置报告(CPR)的形式。介绍了CPR编解码算法的基本原理,详细描述了1090ESADS—B系统中经度和纬度消息的CPR编解码方法,给出了全球位置和本地位置的编解码算法和实现步骤。 相似文献