A numerical study of macro-mesoscopic mechanical properties of gangue backfill under biaxial compression

Based on the Particle Flow Code(PFC^(2D)) program,we set up gangue backfill models with different gangue contents and bond strength,and studied the stress-strain behaviours,the pattern of shear band and force chains,motion and fragmentation of particles under biaxial compression.The results show that when the bond strength or contents of gangue are high,the peak strength is high and the phenomena of post-peak softening and fluctuation are obvious.When gangue contents are low,the shape of the shear band is symmetrical and most strong force chains transfer in soil particles.With an increase in gangue content,the shape of the shear band becomes irregular and the majority of strong force chains turn to transfer in gangue particles gradually,most of which distribute along the axial direction.When the gangue content is higher than 50%,the interconnectivity of strong force chains decreases gradually:at the same time,the strong force chains become tilted and the stability of the system tends to decrease.With an increase in external loading,the coordination numbers of the system increase at first and then decrease and the main pattern of force chains changes into columnar from annular.However,after the forming of the advantageous shear band,the force chains external to the shear band maintain their columnar shape while the inner ones bend obviously.As a result,annular force chains form.

波阻抗多约束反演

当前流行的恢复波阻抗的方法是用人工方法从叠加速度中提取低频分量，然后加入到相对阻抗中去形成绝对波阻抗。这种方法主观因素太强，又存在着频率5Hz～10Hz左右的谱的缺口．不够可靠。此外，还有一些纯数学的方法，如时域最小熵的谱外推法等。但这些方法缺乏地质上先验信息构成的约束，也存在着不可靠性。本文提出了一种多约束反演方法。它利用了声测井资料，加入了地震记录所欠缺的低频和高频的约束，也利用叠后保真剖面，加入了中频约束和层位约束。因此，能减少反演的多解性，能较好地与声测对比；又由于加入了层位约束，构造显示也较清楚。这种反演是一维的道反演，又是批量运行，具有使用方便和效率高的优点。

High Performance Compressed Sampling for OFDM-UWB Systems

In order to solve the problem of high-speed sampling in OFDM based ultra wide band(UWB) systems, this paper first gives analysis on the applicability of existing compressed sampling methods. Then, on the basis of an established segmented observation model, it presents an optimized parallel segmented compressed sampling(OPSCS) scheme based on Hadamard matrix. The orthogonal Hadamard matrix is adopted to construct the segmented measurement matrix with any dimensions, thus orthogonal or quasi-orthogonal multiplex observation sequences are obtained, and the restricted isometry property is improved. The optimized orthogonal matching pursuit algorithm is also used for the known sparsity avoiding iterative operation. Researches show that the proposed method can effectively reduce the sampling rate in OFDM-UWB systems, and also has a good ability of noise resisting that it achieves a high system performance better than the existing schemes of compressed sampling and even Nyquist rate sampling.

Plastic deformation behavior of Fe_(40)Ni_(40)P_(14)B_6 bulk metallic glass investigated by nanoindentation

Fe40Ni40P14B6 bulk metallic glass rods have been prepared by water quenching the fluxed alloy. The deformation behavior was investigated by nanoindentation tests and compressing tests. The average hardness and elastic modulus of the as-prepared Fe40Ni40P14B6 BMG (bulk metallic glass) measured by nanoindentation tests are 8.347 and 176.61 GPa respectively. The displace- ment-load curve shows “pop-in” characteristics which correspond to the loading rate bursts. Many shear bands around the indent were observed. The as-prepared Fe-based BMG exhibits a compressive plastic strain of 5.21%, which is much larger than that of other Fe-based glassy alloys and most of other BMGs.

低孔隙度低渗透率砂岩的声波特性实验研究

用实验方法探讨了气驱水过程中低孔隙度低渗透率砂岩的纵横波速度、纵横波速比、弹性模量等参数随不同含气饱和度的变化 ;同时在频率域内探讨了纵横波的主频、带宽、品质因素Q随不同含气饱和度的变化。实验表明 ,10 %～2 0 %的气体可使低孔隙度低渗透率砂岩岩心的纵波速度、纵横波速比迅速下降 ;而低孔隙度低渗透率岩心的纵波主频、带宽、品质因素Q也与含气饱和度有明显的关系 ,10 %～ 2 0 %的气体可使其纵波主频、带宽及Q值显著下降 ,这种降低的趋势比纵波速度、纵横波速比更急剧更敏感。用纵波主频、带宽、品质因素Q比用纵波速度和纵横波速比更能反映低孔隙度低渗透率岩层是否含气体。