原子吸收法测定地下水硬度

测定水的硬度,一般采用经典的乙二胺四乙酸钠(EDTA)滴定法。其缺点是受操作条件(如滴定速度、反应液的温度等)的影响较大,在水质复杂、干扰因素较多时,干扰难以去除,滴定终点不易判别,测定误差较大。特别是测定大批水样时,取样量多,工作量大,花费时间长。考虑到北京地区地下水为Ca、MgHCO_3型,即构成地下水硬度的主要成分为钙盐和镁盐。因此本文用原子吸收(AAS)法测定钙、镁含量总和作为水的总硬度。测定了北京地区114个采样点的     

银河系中心的伦琴射线

两个美国研究小组同时独立地宣布,利用安置在火箭上的盖革计数器,他们发现,由银河系中心附近区域发射出来的高能伦琴射线,按其光谱组分,这些射线属于软伦琴射线,波段为3—8埃。同一类型的辐射线不能透过地球的大     

一类二阶Emden-Fowler型微分方程的若干振动条件

利用Riccati变换技术,借助Bernoulli不等式和Yang不等式以及数学分析技巧,研究了具有非线性中立项的二阶广义Emden-Fowler型微分方程的振动性,考虑非正则情形∫t0+∞a-1/β(t)dt<+∞,建立了该方程的若干振动准则。最后用2个例子说明,这些准则推广并改进了一些已有的结果,且具有较好的实用性和可操作性。     

为什麼能夠看見本身不發光的物体?為什麼看不見鏡子的面?

初中物理教本下册光学部分在§75漫反射一節中提到:“我們所以能够看見本身不發光的物体,而且从任何方向都能看見它,就是因为物体表面發生漫反射的緣故。”接着又提到:“如果反射面非常平滑,例如好的鏡子,那么光線在这面上任何部分的反射都不是漫反射,因此我們就看不見鏡子的面。”这一段確实比較难讲。在今年春季我校的教育实習中,不少实習生只能說出因為光照在物体的表面上向四面八方反射,所以在任何方向都能看見物体,而不能解釋為什么因為漫反射就能看見物体的表面。同時对於看不見鏡子的面这一點表示怀疑。本文想就这兩個問题來討論一下。     

快速分离柱高效液相色谱法测定卷烟主流烟气中的主要羰基化合物

选择2,4-二硝基苯肼(DNPH)为羰基化合物的衍生化试剂,建立了快速分离柱高效液相色谱测定卷烟主流烟气中8种羰基化合物的方法。采用经2,4-二硝基苯肼酸性溶液处理过的剑桥滤片捕集烟气,再用含2%（体积分数）吡啶的乙腈溶液进行萃取,以ZORBAX Stable Bound色谱柱(50 mm×4.6 mm,1.8 μm)进行快速分离,最后由二极管阵列检测器于365 nm下进行检测。该方法的回收率为89.1%～99.2%,相对标准偏差（RSD)在6.0%以下。该方法分析时间短,流动相消耗少,且操作简便、重复性好、回收率高。     

家庭常用12种白色固体的鉴别

化学与我们每个人息息相关,如在家庭厨房中常遇见下列药品,调味品的精盐、味精、发酵粉、淀粉、蔗糖等白色固体,那么怎样用厨房的一些简单的化学药品将其一一区别开来,这样既增加了学生学习化学的兴趣,也减少了实验室操作中的废物处理过程。厨房常见12种白色固体见表1。     

Supplementary Material: A Dynamic Model of Heavy Ion ~7Li Irradiation Mutagenesis Based on Maize Inbred Line Nutrition Difference

正Text A:Irradiation mutagenesis Heavy ion ~7Li radiation mutagenesis was performed by the HI-13 tandem accelerator at the China Institute of Atomic Energy.The radiation procedure was configured as previously described,with a     

Degradation of current–voltage and low frequency noise characteristics under negative bias illumination stress in InZnO thin film transistors

The instabilities of indium–zinc oxide thin film transistors under bias and/or illumination stress are studied in this paper. Firstly, illumination experiments are performed, which indicates the variations of current–voltage characteristics and electrical parameters(such as threshold voltage and sub-threshold swing) are dominated by the stress-induced ionized oxygen vacancies and acceptor-like states. The dependence of degradation on light wavelength is also investigated. More negative shift of threshold voltage and greater sub-threshold swing are observed with the decrease of light wavelength.Subsequently, a negative bias illumination stress experiment is carried out. The degradation of the device is aggravated due to the decrease of recombination effects between ionized oxygen vacancies and free carriers. Moreover, the contributions of ionized oxygen vacancies and acceptor-like states are separated by using the mid-gap method. In addition, ionized oxygen vacancies are partially recombined at room temperature and fully recombined at high temperature. Finally, low-frequency noise is measured before and after negative bias illumination stress. Experimental results show few variations of the oxide trapped charges are generated during stress, which is consistent with the proposed mechanism.     

环氧大豆油多元醇改性磺酸型水性聚氨酯合成与性能研究

用2-乙基己醇(异辛醇)对环氧大豆油进行开环,生成环氧大豆油多元醇,并利用其对由异佛尔酮二异氰酸酯(IPDI)、聚己内酯二元醇(PCL)和乙二胺基乙磺酸钠(AAS)为主要合成原料的磺酸型水性聚氨酯(SWPU)进行改性,考察了不同多元醇含量对磺酸型水性聚氨酯乳液以及胶膜性能的影响.首先,通过FTIR和1H-NMR证实了环氧大豆油多元醇的合成;然后经过粒径测试、耐水性测试、接触角测试、机械性能测试、TG测试等检测表明:磺酸型水性聚氨酯成功合成,随着多元醇含量的增加,水性聚氨酯乳液粒径逐渐增大;胶膜的吸水率逐渐减小,并趋于平缓;力学性能拉伸强度逐渐增强,而断裂伸长率下降.但当环氧大豆油多元醇添加量过大时,导致最后乳液无法分散,乳化失败.当多元醇含量与PCL质量比为0.2时,胶膜吸水率由50.14%减小至12.27%,接触角为103.3°,拉伸强度由8.16 MPa增至21.77 MPa.通过TG表明,分子结构中多元醇的引入,胶膜的耐热性有明显提高.     

Design of an efficient monochromatic electron source for inverse photoemission spectroscopy

A design for an efficient monochromatic electron source for Inverse Photoemission Spectroscopy(IPES)apparatus is described. The electron source consists of a Ba O cathode, a focus electrostatic lens, a hemispherical deflection monochromator(HDM), and a transfer electrostatic lens. The HDM adopts a "slit-in and slit-out" structure and the degradation of first-order focusing is corrected by two electrodes between the two hemispheres, which has been investigated by both analytical methods and electron-ray tracing simulations using the SIMION program. Through the focus lens, the HDM, and the standard five-element transfer lens, an optimal energy resolution is estimated to be about 53 MeV with a beam flux of 27 μA. Pass energy(P.E.) of 10 eV and 5 eV are discussed, respectively.