太阳风等离子体输出流量的全日面二维结构

本文根据1983年十个 Carrington 周(1733—1742)期间的 K-日冕亮度、行星际闪烁(IPS)观测和光球磁场观测,首次探讨了太阳风等离子体质量、动量和能量输出流量 F_M,F_P 和 F_E 的全日面二维平均结构及其与光球磁场结构的关系.     

Identification and quantitation of phenylalanine, tyrosine and dihydroxyphenylalanine in the thoracic nervous system of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry

Phenylalanine, tyrosine and dihydroxyphenylalanine (DOPA) were identified unambiguously and quantitatively determined in single ventral thoracic nerve cords from the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry. Deuterium-labelled analogues of each compound were added to a single ventral thoracic nerve cord in hydrochloric acid; the tissue was homogenised and the suspension centrifuged. The remaining hydrochloric acid was eliminated azeotropically by repeated additions of acetonitrile followed by evaporation under a stream of nitrogen and the resultant residue derivatised by reaction with hexafluoroisopropanol and pentafluoropropionic anhydride. Under negative-ion chemical ionisation conditions, the hexafluoroisopropanol-pentafluoropropionyl derivatives produced characteristic ions which were sufficiently abundant to be suitable for selected-ion monitoring. This method is highly specific and gave a limit of detection below the nanogram level. The amounts of phenylalanine, tyrosine and DOPA in a single ventral thoracic nerve cord were, respectively, 194 +/- 81, 347 +/- 88 and 11 +/- 11 ng per tissue.     

Non-linearity of calibration in the determination of anions by ion-chromatography with suppressed conductivity detection

Traces of simple inorganic anions may be determined by chromatographic separation with an alkaline eluent and conductimetric detection, which involves “suppressing” the background conductivity of the eluent by neutralization to form a sparingly dissociated species. Over a wide range of determinand concentration, e.g., two decades, non-linearity of the calibration may become evident, leading to errors of up to 100% at lower concentrations if linearity is assumed (a linear fit of the data usually gives a correlation coefficient>0.99, which may lead to false confidence). The curvature arises from displacement of eluent ions by the determinand and the consequent re-equilibration of the conjugate acid in the suppressed eluate. Even if the distribution of determinand in the peak is ideally Gaussian, the observed conductivity peak may be distorted and calibration will then be non-linear. The best linearity is obtained with the most strongly basic eluent, but other characteristics must also be considered, e.g., run time, peak separation. With a carbonate eluent, the curvature is demonstrated empirically for chloride, nitrate and sulphate calibrations. A second-order fit gives errors of < 10%. With a more strongly basic borate eluent, the deviation from linearity is negligible, but elution times are longer and may be inconvenient in some circumstances.     

锂离子电池硅基负极材料的研究进展

硅基材料是新一代高容量锂离子蓄电池负极材料的典型代表,近年来已成为理论研究和应用研究的热点.本文介绍了锂离子电池硅基负极材料的制备方法、电化学性能及其研究现状,分析了硅材料作为锂离子电池负极材料存在的问题;讨论了硅材料作为锂离子电池负极材料的研究前景.并指出若能克服目前存在问题,将有望成为新一代锂离子电池负极材料.     

Quantitative electron holography of biased semiconductor devices

Electron holography is used to measure electrostatic potential profiles across reverse-biased Si p-n junctions in situ in the transmission electron microscope. A novel sample geometry based on focused ion-beam milling is developed, and results are obtained for a range of sample thicknesses and bias voltages to allow the holographic contrast to be interpreted. The physical and electrical nature of the sample surface, which is affected by sample preparation and electron beam irradiation, is discussed.     

Performance of the Orion 97-70 total residual chlorine electrode at low concentrations and its application to the analysis of cooling waters

The performance characteristics of the Orion 97-70 total residual chlorine electrode have been determined and the electrode has been found to give a near-theoretical response down to chlorine concentrations in the range 1-5 mug/1. Within-batch relative standard deviations are about 6-8% at concentrations above 50 mug/1. and 10-15% at lower levels. The method is virtually free from interferences (only strong oxidizing agents such as permanganate interfere) but large variations in salinity affect the calibration by changing the conditional standard potential. The best performance at low concentrations (<50 mug/1.) is achieved only if the manufacturer's recommended procedure is changed, namely by using a more dilute iodide reagent, stirring constantly, adding the iodide reagent before the buffer solution and using chloramine-T as a standard.     

类氖钛X射线激光实验研究

在“星光”装置上采用预脉冲技术和透-反射线聚焦系统成功地进行了类氛钛x射线激光实验.测量了TiXⅢ,3s-3p,J=0～1激光线的增益系数.首次实验研究了预脉冲能量不同时,激光线强度随泵浦激光能量的变化及其发散角和偏转角.