火焰原子吸收光谱法连续测定高纯铋锭中痕量铜、银、锌

建立了用火焰原子吸收光谱法在同一体系中连续测定铋锭中的铜、银、锌的方法。试样用硝酸溶解,在稀盐酸介质中,分别于原子吸收光谱仪波长324.7,328.1,213.8nm处,使用空气-乙炔火焰连续测定铜、银、锌的含量。在最佳实验条件下,铜的质量浓度在0.20~0.80mg/L范围内与吸光度线性关系良好,加标回收率为94.5%~101.8%。银的质量浓度在0.5~2.0mg/L范围内与吸光度成线性关系,加标回收率为97.3%~102.6%。锌的质量浓度在0.10~0.40mg/L范围内与吸光度成线性关系,加标回收率为96%~106.3%。火焰原子吸收光谱法测定铋锭中的铜、银、锌,相对标准偏差(n=11)均小于8.0%,测定结果与理论值基本一致。     

Synthesis of [1,2,3]triazolo[1,5-a]quinoxalin-4(5H)-ones through copper-catalyzed tandem reactions of N-(2-haloaryl)propiolamides with sodium azide

A simple and efficient approach for the synthesis of [1,2,3]triazolo[1,5-a]quinoxalin-4(5H)-ones is described. The methodology is based on a tandem reaction of 1-(2-haloaryl)propiolamides with sodium azide through a [3 + 2] azide-alkyne cycloaddition and intramolecular Ullmann-type C-N coupling process.     

Minority carrier lifetime control in power semiconductor devices by fast neutron irradiation

A new technology for controlling reduction of minority carrier lifetime of power semiconductor devices was given in this paper, using fast neutron irradiation in nuclear reactor. The effects of high frequency thyristor by fast neutron irradiation is mainly discussed. Furthermore, a comparison is made with electron irradiated, ⁶⁰Co-gamma irradiated and gold diffused devices. The conclusion shows, the trade-off of forward voltage drop and turn-off time of fast neutron irradiated devices is alike with gold diffused devices, while the leakage current is less than that of gold diffused devices, and not different from the electron or Gamma irradiated devices. Moreover, the deep energy levels of fast neutron irradiation in silicon was shown in this paper, and a single dominant level of Ec-0.44eV is identified for controlling minority carrier lifetime.     

体液中亚硝酸盐的顶空气相色谱分析方法

论述了在一定的条件下将体液中亚硝酸盐转变为有机的硝基化合物继而进行顶端空间气相色谱分析的方法。可直接测定血清、尿液、胃液等。它抗干扰性强,特异性好,其灵敏度高出化学比色法１００倍。ＲＳＤ为６．０％,平均回收率为９４．１％,最低检出浓度为１μｇ／Ｌ。方法简便、快速、准确。     

Improving Erythritol Production of <Emphasis Type="Italic">Aureobasidium pullulans</Emphasis> from Xylose by Mutagenesis and Medium Optimization

The biotransformation of xylose, the second most abundant sugar, has been a hot topic in recent years. In this work, Aureobasidium pullulans CGMCC3.0837 was subjected to UV mutagenesis to improve its erythritol production from xylose. The erythritol production of the obtained mutant ER35 was 50.92 % (17.28 g/L) higher than that of the parent strain. Response surface methodology was applied to optimize the medium composition. Yeast extract, KH₂PO₄, and citric acid were the key factors influencing erythritol synthesis, and the optimal concentrations were 17.82, 0.76, and 6.60 g/L, respectively. Under the optimized conditions, 31.75 and 31.42 g/L erythritol were obtained in shake flasks and in a 5-L fermentor, respectively. ER35 also showed a good consuming ability on xylose mother liquor with a final erythritol production of 26.35 g/L. This report provided insights into the potential of A. pullulans for the production of erythritol using xylose as a carbon source.     

Development of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> Producing Higher Levels of Sulfur Dioxide and Glutathione to Improve Beer Flavor Stability

Sulfur compounds, such as sulfite (SO₂), hydrogen sulfide (H₂S), and glutathione (GSH), play different roles in beer flavor stability. SO₂ and GSH have antiaging effects which are helpful to improve the flavor stability of beer, whereas H₂S is undesirable to beer flavor because of its unpleasant aroma. Here, we report the development of Saccharomyces cerevisiae which produces higher levels of SO₂ and GSH but lower level of H₂S to improve beer flavor stability by nongenetic engineering approaches. After two rounds of UV mutagenesis coupled with specific plate screening methods, one promising mutant named MV16 was obtained. Compared with the original strain, the SO₂ and GSH production of MV16 in fermenting liquor increased by 31% and 30.2%, respectively, while H₂S content decreased by 74.9%, and the DPPH radical clearance and the resistance staling value of beer fermented by MV16 increased by 24.6% and 33.0%, respectively. The antioxidizability of the mutant was improved significantly. The strategy adopted in our study could be used to obtain S. cerevisiae of improved antiaging properties, and the mutant would be safe for public use.     

Microwave- and nitronium ion-enabled rapid and direct production of highly conductive low-oxygen graphene

Currently the preferred method for large-scale production of solution-processable graphene is via a nonconductive graphene oxide (GO) pathway, which uncontrollably cuts sheets into small pieces and/or introduces nanometer-sized holes in the basal plane. These structural changes significantly decrease some of graphene's remarkable electrical and mechanical properties. Here, we report an unprecedented fast and scalable approach to avoid these problems and directly produce large, highly conductive graphene sheets. This approach intentionally excludes KMnO(4) from Hummers' methods and exploits aromatic oxidation by nitronium ions combined with the unique properties of microwave heating. This combination promotes rapid and simultaneous oxidation of multiple non-neighboring carbon atoms across an entire graphene sheet, thereby producing only a minimum concentration of oxygen moieties sufficient to enable the separation of graphene sheets. Thus, separated graphene sheets, which are referred to as microwave-enabled low-oxygen graphene, are thermally stable and highly conductive without requiring further reduction. Even in the absence of polymeric or surfactant stabilizers, concentrated dispersions of graphene with clean and well-separated graphene sheets can be obtained in both aqueous and organic solvents. This rapid and scalable approach produces high-quality graphene sheets of low oxygen content, enabling a broad spectrum of applications via low-cost solution processing.     

Effect of Fe3+ on the reduction of Np(VI) with 1,1-dimethylhydrazine

Tissues, eggs and bile of adult Atlantic cod raised in captivity and fed natural food with no additional halogenated compounds of any kind were analyzed by neutron activation. There was a large difference in the tissue distributions of extractable organic chlorine (EOCl) and bromine (EOBr). Liver lipid had the lowest levels of EOBr and EOCl, of all the components investigated, and eggs had the highest levels of EOCl. Heart contained the most EOBr and EOCl per unit lipid, of the tissues. The presence of a larger proportion of EOBr than EOCl in bile suggests a higher rate of excretion of EOBr. The EOCl concentratios found in cod egg lipids were about 5 times higher than the highest values previously reported for EOCl in lipid.     

PPt课件对课堂演示实验的互补作用

在PPt课件中利用动画模拟演示实验是必要的,其教学效果值得关注。     

"5 12"汶川地震震后龙门山山前地表塌陷成因探讨

应用NND有限差分格式求解轴对称可压缩N-S方程,研究了不同驻室与 环境压力比条件下欠膨胀超声速射流近场的失稳特性. 计算结果表明欠膨胀超声速射流的失 稳机制根据射流激波结构的特征可分为3种失稳模式：具有规则反射激波结构和单一剪切层 特征的射流不稳定性;带有马赫反射激波结构和双剪切层特征的射流不稳定性;具有弯曲马 赫杆和高度欠膨胀射流的不稳定性. 对于欠膨胀超声速射流,沿射流方向重复出现拟周期性 的射流激波结构是射流稳定发展的特征,这种射流激波结构的消失是射流开始失稳的标志.