系数究竟是1／3还是1／4

本指出对一大学教材中一题线围绕法的不同理解会有两种不同的答案，并说明产生系数差别的原因。     

浅谈“物质”一词

物质的概念,是物理学中最重要的概念之一。在中学物理和化学课本中,都曾多次用到“物质”一词。在中学物理课本中,引用了列宁对一般物质概念所下的定义:“物质是作用于我们的感官而引起感觉的东西。”并已指出,电场和磁场等都是物质。而中学化学课本中,在阐述原子--分子论的观点时指出:“物质都是由分子组成的,而分子是由原子组成的。”     

Transverse Zeeman background correction method for air mercury measurement

By utilizing a natural mercury lamp, the transverse Zeeman background correction method, which is used for trace mercury measurement in air, is studied. In this paper, a natural mercury lamp is used as a light source, and is placed in a 1.78-T magnetic field. The lamp emits two linearly polarized light beams σ± and π of 253.65-nm resonance line, which are used as bias light and absorbing light, respectively. A polarization modulation system is used to allow σ± and π light beams to pass through alternately with a certain frequency. A multipath optical cell with 12-m optical path is used to increase optical distance. Based on the system described above, the influence caused by UV absorbing gases, such as NO2, SO2, acetone, benzene, and O3, is analyzed. The results show that it may reduce the detection limit when the concentrations of these gases exceed 83.4 ppm, 20.3 ppm, 142.3 ppm, 0.85 ppm, and 0.55 ppm, respectively. The detection limit of the system is calculated and can achieve up to 1.44 ng/m3 in 10 minutes. Measurements on mercury sample gas and air are carded out, and the measured data are compared with the data of RA-915 mercury analyzer （Russia）. The result shows that the correlation coefficient reaches up to 0.967. The experimental results indicate that the transverse Zeeman background correction method can be used to quantify trace mercury in air with high-precision.     

基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法研究

精确的背景校正决定着冷原子吸收法检测痕量汞的检测下限,研究了基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法.汞灯光源253.65 nm共振谱线在磁场中垂直于磁场方向产生σ-,σ+和π三个线偏振光.利用超高分辨率光谱仪获取不同磁场强度下汞样品池对σ-,σ+和π线偏振光的吸光度,分析横向塞曼效应背景校正方法所需的最小磁场强度;在1.78 T强磁场强度下,分析了窄带吸收气体苯、宽带吸收气体丙酮对横向塞曼效应背景校正大气汞检测方法可能存在的干扰;利用σ-,σ+作为背景光,π线偏振光作为吸收光,对不同长度的饱和汞蒸气样品池测量,精确背景校正后,吸光度拟合曲线R值达到0.99.实验结果表明基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法可以实现精确背景校正,能够应用于大气环境痕量汞检测.     

对“高压送电”一节教学的体会

在进行初中物理课“高压送电”一节的教学时,差不多每次都要遇到一个共同性的问题,那就是在学完这一节之后,学生容易“发叉”,自己推出一个与实际情况完全相反的结论。初中物理教材在讲述远距离送电要升高电压时是这样论述的:“从焦耳—楞次定律的公式 Q=0.24I~2Rt 来看,……要减少输电线路上的电能损耗,可以……减少线路中的电流强度,……根据电功率公式 N=IV,在保持功率不变的前提下,要减小输电线路中的电流强度,必须升高输电电压。这就是采用高压输电的道理。”(山东省初中课本((物理》1975年版)有些学生在学完这节内容后,结合以前学过的欧姆定律公式,便会进行如下的推论:因     

二极管激光腔衰荡光谱测量大气NO_3自由基

本文介绍了基于外部调制二极管激光器(波长661.85 nm,线宽为0.3 nm)为光源的腔衰荡光谱技术探测环境大气中NO3自由基.通过改变外部调制信号,优化二极管激光器的输出光谱,获得NO3自由基的有效吸收截面;探讨了大气中的其他气体成分(O3,NO2和水蒸气)对NO3自由基的测量干扰;考虑PFA管的壁碰撞损耗和过滤膜的损耗,初步量化本系统的NO3自由基进气效率约为70%.当时间分辨率为7 s时,在实验室环境下,系统的探测限为2.0 pptv.将本系统初步应用于夜间大气中NO3自由基的测量(2 h),获得了NO3自由基的浓度主要在17.9—51.7 pptv之间,平均浓度为36.3 pptv,实际的探测限为3.5 pptv;由于NO3自由基进气效率的不确定性等因素,系统的测量误差约为±8%(1σ).实验结果表明,二极管激光腔衰荡光谱技术可实现大气中NO3自由基的高灵敏度在线探测.     

Enhancement of subgap conductance in a graphene superconductor junction by valley polarization

We theoretically study the differential conductance of a graphene/graphene superconductor junction, where the valley polarization of Dirac electrons is considered in the nonsuperconducting region. It is shown that the subgap conductance will increase monotonically with the valley-polarization strength when the chemical potential μ is near the Dirac point μ≤ 3?(? is the superconducting gap), whereas it will decrease monotonically when μ is far away from the Dirac point, μ≥ 5?.The former case is induced by the specular Andreev reflection while the retro-reflection accounts for the later result. Our findings may shed light on the control of conductance of a graphene superconductor junction by valley polarization.     

α、β、γ、X射线与现代物理

本文介绍了α、β、γ、X射线的概念,并分析了其产生的机制,在此基础上又阐述了它们的应用及它们对近代物理学发展的重要作用。