利用地下水污染事件的观测资料估算弥散度

以洛阳市的一起地下水污染事件为例,利用观测资料估算了该区潜水含水层的弥散度。在分析区域水文地质条件的基础上,对地下水实际平均流速进行了估算,然后采用直线作图法分别按一维、二维模型估算了弥散度。结果表明,由于概化的地下水流向与真实的地下水流向的不一致,以及径向流的存在,二维模型概化不合理;结果还表明“尺度效应”明显存在。     

重掺Sb硅单晶中氧沉淀的研究

本文用化学腐蚀和透射电镜及其能谱分析研究了重掺Sb硅单晶中的氧沉淀。化学腐蚀结果表明,Sb的掺入有促进形核的作用,但其最大成核速率仍在750℃左右。随着退火时间的延长,沉淀密度首先增加,而后又下降。透射电镜观察到氧沉淀呈平行四边形平板状,并发现有氧沉淀群及与沉淀相连的位错缠结,但未发现层错。对氧沉淀大小的测量结果表明,它的生长满足t~(3′4)规律。能谱分析指出,Sb元素不参与氧沉淀。为解释Sb的掺入促进形核,本文提出了空位和间隙硅原子影响氧沉淀形成的模型。按此模型,单位体积晶坯的自由能变化应为ΔG_v=-ΔH_v(O)(T_e(O)-T)/T_e(O)-ΔH_v(Si)(T-T_e(Si))/T_e(Si)假设Sb的掺入增加空位浓度,减小间隙硅原子浓度。为此,间隙硅原子的饱和温度将降低。由上式,ΔG_v将随Sb浓度的增加而为更大的负值。因此,氧沉淀形核速率将随掺Sb浓度的增加而加速。     

关于建筑产品质量问题的法律思考

建筑产品是建筑业生产的物质成果,建筑产品质量的好坏与人们的日常生活和国民经济的发展有密切关系。本文试图从法律角度论述如何保证建筑产品质量的问题。     

点平庸空间与点离散空间

本文定义了两类拓扑空间─—点平庸空间与点离散空间，讨论了它们的一些拓朴性质，得到了一系列有意义的结果．     

Digital Elevation Modeling不确定性对地形参数影响的空间分布特征分析

Digital elevation modeling(DEM)是基础地理数据之一,从其中可以提取多种地形参数,DEM不确定性对提取的地形参数具有一定的影响.选择坡度、上坡集水面积和地形指数作为研究对象,在DEM不确定性模拟的基础上,研究DEM不确定性对地形参数影响的空间分布特征.研究发现:DEM不确定性对坡度的影响没有明显的空间分布特征,对上坡集水面积和地形指数具有明显的空间分布特征.DEM不确定性对上坡集水面积影响的空间分布特征为:总体上分布均匀,在河道及附近、水库区域影响大于其它地区;DEM不确定性对地形指数影响的空间分布特征为:总体上分布均匀,在河道及附近、水库、平地地区影响大于其它地区.不同DEM不确定性程度对地形参数影响的空间分布特征相似.     

嵌套式移动Agent网络管理模型的研究

为提高传统静态网络管理方式的效率,将移动Agent技术应用于网络管理,依据迁移代码与任务代码分离编码的思想,应用任务Agent和巡航Agent构造了嵌套式移动Agent网络管理模型并进行了相应的试验研究.研究结果表明,与传统静态网络管理方式相比,嵌套式移动Agent网络管理方式具有更大的灵活性、可重用性、智能性和分布性.     

Shotgun sequence assembly and recent segmental duplications within the human genome

Complex eukaryotic genomes are now being sequenced at an accelerated pace primarily using whole-genome shotgun (WGS) sequence assembly approaches. WGS assembly was initially criticized because of its perceived inability to resolve repeat structures within genomes. Here, we quantify the effect of WGS sequence assembly on large, highly similar repeats by comparison of the segmental duplication content of two different human genome assemblies. Our analysis shows that large (> 15 kilobases) and highly identical (> 97%) duplications are not adequately resolved by WGS assembly. This leads to significant reduction in genome length and the loss of genes embedded within duplications. Comparable analyses of mouse genome assemblies confirm that strict WGS sequence assembly will oversimplify our understanding of mammalian genome structure and evolution; a hybrid strategy using a targeted clone-by-clone approach to resolve duplications is proposed.     

The DNA sequence and comparative analysis of human chromosome 5

Chromosome 5 is one of the largest human chromosomes and contains numerous intrachromosomal duplications, yet it has one of the lowest gene densities. This is partially explained by numerous gene-poor regions that display a remarkable degree of noncoding conservation with non-mammalian vertebrates, suggesting that they are functionally constrained. In total, we compiled 177.7 million base pairs of highly accurate finished sequence containing 923 manually curated protein-coding genes including the protocadherin and interleukin gene families. We also completely sequenced versions of the large chromosome-5-specific internal duplications. These duplications are very recent evolutionary events and probably have a mechanistic role in human physiological variation, as deletions in these regions are the cause of debilitating disorders including spinal muscular atrophy.     

Microstructures and mechanical properties of as-extruded Mg–5Sn–1Zn–xAl(x=1, 3 and 5) alloys

As-extruded Mg–5Sn–1Zn–xAl alloys(x=1, 3, and 5) were fabricated by hot extrusion. The experimental results revealed that the yield strength of alloys initially decreased and then increased with the increase of Al content. These changes were mainly attributed to the difference in crystallographic texture and volume fractions of second phases. The ultimate tensile strength, yield strength, and elongation of the alloys were greater than 310 MPa, 227 MPa, and 11%, respectively. The strain hardening ability of the alloys was also discussed.     

关于线性代数教学方法的思路

通过对线性代数教学内容的分析,提出以线性方程组为主线索的教学方法,使学生在学习本课程时可以更加清晰地把握线性代数的整体结构和主要内容.另外,本文指出了线性代数与初等代数的最大区别,给出了解决线性代数问题的一个非常基本的思想方法--化普通等式为矩阵等式.