爆炸载荷作用下节理岩体远区振动传播规律的三维离散元数值模拟

爆炸引起岩体结构振动是一个非常复杂的力学过程。其中包括：炸药爆炸产生的高压气体与药包周围岩体的相互作用；爆炸近区岩体的破碎与运动；波在宕体中的传播及岩体的振动等。本文提出了爆炸近区岩体的简化力学模型，以此为基础借助三维离散元法模拟了节理岩体中的爆破过程，重点讨论了波在爆炸远区岩体中的传播规律，分析了与岩体结构面有关的主要参数对岩体结构振动的影响，主要工作如下：1．提出了爆生气体与岩体结构相互作用的简化模型，通过爆生气体的状态方 程，实现了岩体运动与空腔内压力的祸合作用，由此给出了一种简单的加载方式，用于分析爆炸远区的应力波传播规律。2．采用离散元法模拟了不同加载方式下单排块体模型中波的传播问题，将计算结果与解析解比较，验证了本文计算方法的可靠性。通过对单层和三层离散元模型的计算，提高了对波在岩体中传播规律的认识。3．岩体的节理刚度是离散元模型中比较重要的参数，本文在Goodman提出的等效弹性模量的概念基础上，通过对波动方程的分析，将节理刚度、节理间距与岩体结构中的波速联系起来，给出了刚性块体模型的节理法向刚度、切向刚度与岩体中纵波、横波波速之间的简单关系式。4．采用二维离散元刚性块体模型，研究了节理岩体中集中药包爆炸的远区岩体结构振动衰减规律。分析了节理岩体的阻尼特性、节理刚度、节理方向等因素对岩体结构振动特性的影响，并给出了相应的无量纲拟合公式。5．采用离散元法数值模拟得到了岩体中爆炸地表振动波形，其基本特征与大量现场实验测定的结果比较接近，并且给出了垂直振动速度随着比距离衰减的基本规律。以上的工作对于认识节理岩体中的爆破引起岩体结构振动的机理是非常有益的。本文主要研究爆破远区振动波的衰减规律，爆源附近的块体单元偏大，对最人垂直振动速度波的频率有一定的影响，还需要在今后的工作中加以完善。

Assessment of cattle genetic introgression into domestic yak populations using mitochondrial and microsatellite DNA markers

Hybridization between yak Poephagus grunniens and taurine Bos taurus or indicine B. indicus cattle has been widely practiced throughout the yak geographical range, and gene flow is expected to have occurred between these species. To assess the impact of cattle admixture on domestic yak, we examined 1076 domestic yak from 29 populations collected in China, Bhutan, Nepal, India, Pakistan, Kyrgyzstan, Mongolia and Russia using mitochondrial DNA and 17 autosomal microsatellite loci. A cattle diagnostic marker-based analysis reveals cattle-specific mtDNA and/or autosomal microsatellite allele introgression in 127 yak individuals from 22 populations. The mean level of cattle admixture across the populations, calculated using allelic information at 17 autosomal microsatellite loci, remains relatively low (mY(cattle) = 2.66 +/- 0.53% and Q(cattle) = 0.69 +/- 2.58%), although it varies a lot across populations as well as among individuals within population. Although the level of cattle admixture shows a clear geographical structure, with higher levels of admixture in the Qinghai-Tibetan Plateau and Mongolian and Russian regions, and lower levels in the Himalayan and Pamir Plateau region, our results indicate that the level of cattle admixture is not significantly correlated with the altitude across geographical regions as well as within geographical region. Although yak-cattle hybridization is primarily driven to produce F-1 hybrids, our results show that the subsequent gene flow between yak and cattle took place and has affected contemporary genetic make-up of domestic yak. To protect yak genetic integrity, hybridization between yak and cattle should be tightly controlled.

Effects of Prenatal Exposure to a 50-Hz Magnetic Field on One-Trial Passive Avoidance Learning in 1-Day-Old Chicks

We investigated memory impairment in newly hatched chicks following in ovo exposure to a 50-Hz magnetic field (MF) of 2 mT (60 min/day) on embryonic days 12-18. Isolated and paired chicks were used to test the effect of stress during training, and memory retention was tested at 10, 30, and 120 min, following exposure to a bitter-tasting bead (100% methylanthranilate). Results showed that memory was intact at 10 min in both isolated and paired chicks with or without MF exposure. However, while isolated chicks had good memory retention levels at 30 and 120 min, those exposed to MF did not. The results suggest a potential disruption of memory formation following in ovo exposure to MF, with this effect only evident in the more stressed, isolated chicks. Bioelectromagnetics 31:150-155, 2010. (C) 2009 Wiley-Liss. Inc.