触头用银合金粉末的氧化性能和氧化后的组织结构

通过热重实验和扫描电子显微等方法，研究了４种触头用银合金粉末的氧化性能及氧化后的组织结构。发现Ａｇ－Ｓｎ－ＲＥ合金粉末氧化以后，在粉末表层形成一层纯银层，其组织结构理想；它的氧化性能最好，适于制备触头材料。Ａｇ－Ｓｎ－ＲＥ合金粉末的优良氧化性能与其氧化后理想的组织结构有关。稀土元素可以降低合金粉末的氧化温度，其它影响作用有待于进一步研究。     

A novel definition of the overall hyper-wiener index for unsaturated hydrocarbons

By replacing the distances between pairs of vertices with the relative distances, we define a novel overall hyper-Wiener index (NOR); the novel overall hyper-Wiener index extends the usefulness of the hyper-Wiener index and the overall hyper-Wiener index to unsaturated hydrocarbons.     

Short syntheses of (−)-clavaminol A and deacetyl (+)-clavaminol H

Concise stereoselective syntheses of (?)-clavaminol A and deacetyl (+)-clavaminol H have been achieved from simple starting materials. Highlights of the synthesis for (?)-clavaminol A include a highly diastereoselective chelation-controlled hydride reduction of an amino ketone to give the anti amino alcohol directly, and NaBH₄-mediated dehalogenation. The main synthetic approach for deacetyl (+)-clavaminol H features a highly diastereoselective chelation-controlled hydride reduction of the amino ketone to construct the anti amino alcohol and a palladium catalyzed hydrogenation reaction at the final step.     

The sequestration of U(VI) on functional β-cyclodextrin-attapulgite nanorods

Eight elastomeric composites (NRU, GR1–GR4, NRBG08–NRBG24) containing mixtures of different proportions of heavy metal additives (Bi, W, Gd and Sb) have been synthesized and examined as protective shields. The NRU sample was a pure rubber matrix and served as a reference sample for heavy metal modified composites. Experimental procedure used for evaluation of the composite shields and their attenuation properties was based on the utilization of HPGe spectrometry and analysis of X-ray fluorescence radiation intensity of the heavy metal additives in the following energy ranges for: Sb (20–35 keV), Gd (35–55 keV), W (55–70 keV) and Bi (70–90 keV). The main contributor to the induced X-ray fluorescence radiation within the shield is Bi additive and the intensity of the X-ray radiation generated within the energy range of 70–90 keV strongly depends on its concentration. It was found that decreasing concentration of the Bi fraction from 0.35 (GR samples) to 0.15 (NRBG samples) results in significant lowering Bi X-ray fluorescence radiation within the 70–90 keV energy range. Secondary effect of decreasing Bi concentration was efficient diminishing excitation processes for lower Z heavy metal additives (W, Gd and Sb, GR vs. NRBG samples). As the final quality parameter of the shielding properties for the examined elastomers, dose reduction factor (DRF) coefficients were calculated for each shield. It was found, that the best shielding properties are observed for composites with lower Bi concentration (0.15 vs. 0.35 Bi mass fraction) with only slight further improvement of their parameters (DRF) with increasing of Gd concentration (Gd mass fraction 0.08, 0.16 and 0.24). The most efficient dose reduction composite was found to be NRBG24 elastomer with DRF value 0.47 (53 % dose reduction) for ca. 2 mm and 0.44 g/cm² layer thickness.     

On the pitch of dialogue in Chinese Putonghua

In order to improve the naturalness of TTS speech so as to represent the cadence of natural speech, it is necessary to have a study on the pitch of spontaneous speech. Based on the 973 telephone corpus, the pitch ranges and pitch registers of 1084 intonation phrases are analyzed. It is found that intonation phrases can be classified according to their ranges and registers, and this is related to their positions in dialogue exchange. Compared with read speech, the pitch patterns in dialogue are more variable.     

On the consistency of credibility premiums regarding Esscher principle

In this paper, we investigate the problems of convergence of experience-based ratemakings regarding the Esscher principle. In addition to the Bayes and the classical credibility premiums, we suggest a new credibility formula for the Esscher premium. Then we show the convergence of the Bayes and the newly defined credibility premiums towards the individual premium and point out that the classical credibility premium does not generally converge to the individual premium by presenting a sufficient and necessary condition under which the classical credibility Esscher premium converges to the individual premium. A simulation study is carried out to illustrate the theoretical conclusions.     

距离深度域最小二乘矩阵滤波器的设计与应用

本文通过最小二乘原理设计出针对拷贝向量进行处理的矩阵滤波器,给出了其详细的推导过程。它可用于距离深度域上的预滤波,在抑制阻带干扰的同时,保证通带信号尽可能不失真。设计过程中发现根据最小二乘原理设计矩阵滤波器比二阶锥规划等其他寻优方法更快捷。最小二乘矩阵滤波器除了能在保证通带尽量不失真的前提下达到很好的阻带抑制效果之外,还可以在任意距离深度设定通、阻带,尤其适用于阵列在探测过程中抑制强干扰对于弱目标源的影响。     

无定型钼硫化物/还原氧化石墨烯的辐射合成及其电催化析氢性能

钼硫化物被认为是一种高效的电催化析氢反应的催化剂,因此其合成方法受到了广泛的研究和关注。本文以四硫代钼酸铵和氧化石墨为前驱体,利用γ射线对其辐照还原,一步法制备了钼硫化物/还原氧化石墨烯(Mo S_x/RGO)复合材料。通过X射线光电子能谱、X射线衍射、透射电子显微镜、Raman光谱等表征手段确认复合材料中的Mo Sx为无定型结构,且氧化石墨烯得到了有效的还原。同时系统研究了吸收剂量、前驱体配比对复合材料作为析氢反应催化剂性能的影响。结果发现,Mo Sx/RGO复合材料具有优异的催化性能,其催化起始电压为110 m V,在电流密度为10 m A·cm~(-2)时过电势仅为160 m V,Tafel斜率为46 m V·dec~(-1),说明该催化剂催化析氢机理为Volmer-Heyrovesy机理。此外,Mo Sx/RGO复合材料还具有良好的催化稳定性。     

阳离子表面活性剂存在下水/有机两相体系中双环戊二烯氢甲酰化

研究了在阳离子表面活性剂存在下水/有机两相中水溶性铑配合物RhCI(CO)(TPPTS)2(TPPTS:P(m-C6H4SO3Na)3)催化双环戊二烯氢甲酰化反应,考察了反应温度、催化剂浓度、不同水溶性膦配体TPPTS和TPPDS(C5H5P(m-C6H4SO3Na)2),以及表面活性剂结构对催化反应的影响.结果表明,...