高饱和黏土中爆炸波作用下直埋聚乙烯管的动力响应

为了解决爆破作业对近距离埋地管道的安全评估问题，对高饱和粘土中爆炸波作用下聚乙烯(polyethylene, PE)管道进行了一系列管道动态响应的原型实验，得到了不同药量下管道动应变、动压力的实验数据和管体及地面的振速数据。实验结果表明:PE管动应变峰值同比例距离具有良好的幂函数衰减关系，在6～11 m/kg1/3比例距离范围内，PE管的环向峰值应变衰减指数（绝对值）比轴向峰值应变衰减指数大；管道动态响应的主振频率略高于土体的主振频率，两者在同一量级，管道合成速度衰减指数大体和管道轴向应变衰减指数相当；压电陶瓷片所测得的电压信号和同测点的应变变化率信号具有较强的相关性。高饱和黏性土由于含水量较高，近距离柔性PE管因受到局部冲击会产生较大的环向应变，管道安全计算时应充分考虑这一因素；随着比例距离的增大，环向应变水平降低，轴向应变水平相对增强；压电陶瓷片因为具有良好可靠的动态性能，作为埋地管道现场监测的技术手段值得采用和推广。     

从一道题的错解说弹簧振子

本文对一道高考模拟试卷中引发热议的多项选择题做了详细的分析和深入的讨论.本期同时发表的还有陆天明老师的《对一道双平衡位置振动问题的讨论》.二文各有千秋.     

电解液中的电流刍议

金属是依靠物体内部自由电子的定向移动而导电的,这类物体叫做电子导体．若电源与电解池构成回路,在金属导线内,载流子是自由电子,但在电解池中仍然依靠自由电子的流动吗？实验表明,在电解质溶液中,是依靠正、负离子的定向运动传递电荷的,即载流子是正、负离子而不是电子．     

例说力学的瞬时规律和过程规律

【例1】(2009年高考浙江理综卷第24题)某校物理兴趣小组决定举行遥控赛车比赛;比赛路径如图1所示.赛车从起点A出发,沿水平直线轨道运动到B后,由B点进入半径为R的光滑竖直圆轨道,离开竖直圆轨道后继续在光滑平直轨道上运动到C     

尿素溶液法合成纳米AlN粉体

以尿素为固体氮源,甲醇为溶剂,AlCl3·6H2O为铝源,采用尿素溶液法制备了纳米AlN粉体.采用FT-IR对前驱盐进行了结构分析,并通过XRD和SEM分别对最终煅烧产物进行了结构和形貌的表征.重点研究了尿素/金属摩尔比R值和煅烧温度对合成产物的晶体结构和形貌的影响.结果发现: AlN的纯度随R值的增加而增大,R值大于6可以获得单一AlN相,R值小于6获得AlN和Al2O3的混合相;此外,R值也直接影响到AlN纳米粉体和团聚颗粒的形貌,所制备AlN纳米粉体的粒径和团聚的球状颗粒的粒径随R值的增加出现细化的趋势.     

小角度斜向入流条件下复式断面明渠流速重分布线性理论

自然界中复式河道的来流方向常受径流量、滩槽形态影响,往往与主槽存在小幅度夹角,使得目前基于顺直河道假定的漫滩水流大量的理论成果难以适用.为研究斜向入流影响,采用平面二维浅水方程描述沿程均匀的复式断面明渠水流运动,选取斜向角度作为小参数,运用摄动法推导了小角度(θ20°)斜向入流条件下复式河道流速分布的线性解析解,并利用数值模拟结果进行验证,流速分布吻合较好.理论分析结果表明,斜向来流时由于出现垂直于河道方向流速分量,使得顺河道方向流速沿河宽分布偏离正向来流情况下的对称形态而重新分布,入流侧流速减小而对岸流速增大;在斜向角度θ=13°且滩槽水深比为3∶8的情况下,偏离幅度可达21.8%,该幅度随滩槽水深比的减小而增大.该文针对斜向来流对流速分布的修正将为进一步研究复式河道泥沙运动和河流演变提供更为准确的水动力条件.     

Moiré superlattice modulations in single-unit-cell FeTe films grown on NbSe2 single crystals

Interface can be a fertile ground for exotic quantum states, including topological superconductivity, Majorana mode, fractal quantum Hall effect, unconventional superconductivity, Mott insulator, etc. Here we grow single-unit-cell (1UC) FeTe film on NbSe₂ single crystal by molecular beam epitaxy (MBE) and investigate the film in-situ with a home-made cryogenic scanning tunneling microscopy (STM) and non-contact atomic force microscopy (AFM) combined system. We find different stripe-like superlattice modulations on grown FeTe film with different misorientation angles with respect to NbSe₂ substrate. We show that these stripe-like superlattice modulations can be understood as moiré pattern forming between FeTe film and NbSe₂ substrate. Our results indicate that the interface between FeTe and NbSe₂ is atomically sharp. By STM-AFM combined measurement, we suggest that the moiré superlattice modulations have an electronic origin when the misorientation angle is relatively small (≤ 3°) and have structural relaxation when the misorientation angle is relatively large (≥ 10°).     

赏析历年湖北高考数学文化背景题

《普通高中数学课程标准（实验）》将“体现数学的文化价值”作为高中数学课程的十项基本理念之一,提出：数学课程应帮助学生了解数学在人类文明发展中的作用,逐步形成正确的数学观．为此,高中数学课程提倡体现数学的文化价值,并在适当的内容中提出对“数学文化”的学习要求．     

Experimental Observations Indicating the Topological Nature of the Edge States on HfTe_5

The topological edge states of two-dimensional topological insulators with large energy gaps furnish ideal conduction channels for dissipationless current transport. Transition metal tellurides X_(Te5)X=Zr, Hf) are theoretically predicted to be large-gap two-dimensional topological insulators, and the experimental observations of their bulk insulating gap and in-gap edge states have been reported, but the topological nature of these edge states still remains to be further elucidated. Here, we report our low-temperature scanning tunneling microscopy/spectroscopy study on single crystals of HfTe5. We demonstrate a full energy gap of ～80 meV near the Fermi level on the surface monolayer of HfTe5 and that such an insulating energy gap gets filled with finite energy states when measured at the monolayer step edges. Remarkably, such states are absent at the edges of a narrow monolayer strip of one-unit-cell in width but persist at both step edges of a unit-cell wide monolayer groove. These experimental observations strongly indicate that the edge states of HfTe5 monolayers are not trivially caused by translational symmetry breaking, instead they are topological in nature protected by the 2 D nontrivial bulk properties.     

建立时空图 教学相对论

时空图以直观清晰的几何图象,用来理解、解释和讨论狭义相对论所依据的原理以及运动学效应,有利于学生建立崭新的时空观,使自然界的基本物理图景得到更新和不断完善．