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991.
Polymorphism of Phosphine‐Protected Gold Nanoclusters: Synthesis and Characterization of a New 22‐Gold‐Atom Cluster 下载免费PDF全文
Qian‐Fan Zhang Paul G. Williard Lai‐Sheng Wang 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(18):2518-2525
A new Au22 nanocluster, protected by bis(2‐diphenyl‐phosphino)ethyl ether (dppee or C28H28OP2) ligand, has been synthsized and purified with high yield. Electrospray mass spectrometry shows that the new cluster has a formula of Au22(dppee)7, containing 22 gold atoms and seven dppee ligands. The cluster is found to be stable as a solid, but metastable in solution. The new cluster has been characterized by UV‐Vis‐NIR absorption spectroscopy, collision‐induced dissociation, and 31P‐NMR. The properties of the new cluster have been compared with the previous Au22(dppo)6 nanocluster (dppo = 1,8‐bis(diphenyl‐phosphino)octane or C32H36P2), which contains two fused Au11 units. All the experimental data indicate that the new Au22(dppee)7 cluster is different from the previously known Au22(dppo)6 cluster and represents a new Au22 core, which contains most likely one Au11 motif with several Au2(dppee) or Au(dppee) units. The Au22(dppee)7 cluster provides a new example of the ligand effects on the nuclearity and structural polymorphism of phosphine‐protected atom‐precise gold nanoclusters. 相似文献
992.
以全国主要电网1998年的月平均发电出力曲线、月最大负荷曲线为基础,对三峡电量的消纳、联网的错峰效益、水火电补偿等进行了分析。 相似文献
993.
In this study, the lead concentrations of chewing gum samples having different compositions were determined by solid sampling electrothermal atomic absorption spectrometry. In order to optimise the experimental conditions, the effects of pyrolysis temperature, atomization temperature, sample amount and sample thermal pre-treatment, on the analyte sensitivity were investigated. The samples were ashed at 400 °C for 2 h prior to directly determined by SS-ETAAS applying 600 °C of pyrolysis and 1600 °C of atomization temperatures without to add a modifier, acid and/or surfactant. The relationship between sample mass and integrated absorbance was linear up to 1.2 mg of sample; for higher sample mass the relationship was no longer linear, irrespective of the lead content. In addition, the thermally treated chewing gum samples were digested using concentrated HNO3. The lead concentrations found by the two methods in 27 different kinds of samples were not significantly different at 95% confidence level. The proposed solid sampling technique was fast, simple, the risks of contamination and analyte loss were low. Detection limit (3σ) for lead was 0.017 ng/g. 相似文献
994.
995.
将马氏环境中的生灭链 (GBDME)灭绝概率及平均吸收时间的计算 ,推广到马氏环境中一般生灭链 (GB DME) ,得到了关于灭绝概率及平均吸收时间的向量差分方程 . 相似文献
996.
The transport of fluid and ions in concrete mixtures is central to many aspects of concrete deterioration. As a result, transport properties are frequently measured as an indication of the durability that a concrete mixture may be expected to have. This paper is the second in a series investigating the performance of high volume fly ash (HVFA) mixtures with low water-to-cementitious ratios (w/cm) that are internally cured. While the first paper focused on strength and shrinkage, this paper presents the evaluation of the transport properties of these mixtures. Specifically, the paper presents results from: rapid chloride migration (RCM), rapid chloride penetration test (RCPT), apparent chloride diffusion coefficient, surface electrical resistivity, and water absorption. The test matrix consisted of mortar samples with two levels of class C fly ash replacement (40% and 60% by volume) with and without internal curing provided with pre-wetted lightweight fine aggregates (LWA). These mixtures are compared to plain ordinary portland cement (OPC) mortars. The results indicate that HVFA mixtures with and without internal curing provide benefits in terms of reduced transport coefficients compared to the OPC mixtures. 相似文献
997.
998.
通过运用原位吸附技术构建水/树脂反应系统,利用树脂的原位吸附来提高酒明串珠菌Oenococcus oeni CECT 4730不对称合成(R)-2-辛醇的催化效率。通过比较6种不同型号的吸附树脂对反应的影响,选出了最适的树脂AB-8。通过考察树脂的用量及水/树脂相中底物浓度对反应的影响,发现反应体系中加入一定量合适的吸附树脂,能够显著减小底物和产物的抑制,大幅度的提高初始底物浓度和反应产率。AB-8树脂加量为15g/L的水/树脂系统中,底物浓度为30g/L时,反应产率达到58%,较之水相系统提高了1.7倍。 相似文献
999.
利用γ全吸收型4π BaF2探测装置,对中子俘获反应截面进行了在线测量。基于HI-13串列加速器提供的脉冲化质子束,通过7Li(p,n) 7Be反应产生中子,构建了keV能区中子源实验条件,经屏蔽准直后的中子轰击样品,应用4π BaF2装置在线测量(n,γ)反应复合核退激时释放的瞬发γ射线级联,测量了Au、C、Nb、空白等样品。通过计算93Nb(n,γ)94Nb和197Au(n,γ)198Au两个反应的截面数据比值并与文献数据比对,检验了4π BaF2探测装置和(n,γ)反应截面在线测量技术,为在中国散裂中子源(CSNS)上顺利开展(n,γ)反应截面数据测量工作提供了技术支持。 相似文献
1000.
Qualitative identification of THz spectra of illicit drugs using self-organization feature map (SOM) artificial neural network has been demonstrated. In this paper, investigation results show that SOM has quantitatively identified drug mixtures successfully. Based on Beer’s law THz spectra data of various drug proportions were made for training dates. After analyzing the clustering algorithm of SOM, we introduced a parameter named shortest distance as a quantitative criterion for identification result. By this parameter, an automatic recognition algorithm has been developed and successfully applied to the content identification of experimental samples. Combined with our previous work, the SOM neural network can be an integrated and effective method in the identification the THz spectra of illicit drugs. 相似文献