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51.
This article describes an analytical method for the separation, preconcentration and determination of 232Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of 232Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. 232Th adsorbed on the resin was easily eluted using 5 mL of 0.8 M HNO3. An enrichment factor of 40 was achieved for 232Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of 232Th-binding organic ligand on the retention of 232Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on 232Th recovery, indicating that at this low pH, 232Th was dissociated from the 232Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4 h and a low detection limit of 0.0038 ng/L for 232Th, and was successfully applied to the determination of 232Th in seawater samples collected from coastal areas, Japan. 相似文献
52.
53.
Thermodynamic interactions between arbitrarily branched flexible “comb” molecules (with branches of uniform length affixed to backbones of uniform length but with the number of branches on a molecule and their placement arbitrary) are treated by Zimm's perturbation method to obtain results valid to the double contact approximation. Thus, bimolecular cluster configurations with one and two intermolecular contacts, but not more, are correctly accounted for. This general result is applied to “random” combs (with the number of branches per comb uniform, but the placement random) and to “heterogeneous” combs (with both the number of branches on a molecule and their placement random). Results for the random combs are very similar to those reported earlier for “symmetrical” combs (with f uniform branches disposed at points along the backbone chain so as to subdivide it into f + 1 equal sections), but the second virial coefficient for the random model is slightly the larger when the number of branches per chain is small and the fraction of the molecule in the backbone is at least a few per cent. Since random combs are uniform in mass, the osmotic pressure and light-scattering second virial coefficients are alike; but for a system of heterogeneous combs the virial coefficients differ from one another, and from the random comb result, when the mean number of branches f? per chain is small and they are of appreciable length in comparison to the backbone. This behavior reflects the heterogeneity in both molecular mass and dimensions existing under these circumstances. As f? increases and/or the mean fraction of segments in the chain backbone becomes large, coincidence with the random comb result is approached. The double-contact second virial coefficients for both random and heterogeneous combs are obtained in closed analytical expression that are much more easily reduced to numerical results than the expression for symmetrical combs given earlier. These two models also correspond better than the symmetrical combs to materials actually obtainable. 相似文献
54.
利用基于Green函数的 Tight-binding 理论,对phenalenyl构成的单分子器件电极耦接点变化情况下的电子输运特性进行了研究.通过理论计算,得出了分子与原子线电极间接点变化对电子输运的影响.结果显示电子通过phenalenyl分子器件的概率随着分子与电极的耦合点的变化而改变.当耦接点改变时,不仅电子通过phenalenyl分子的概率变化,而且无源正负能量开关器件的特征也发生变化.所得结果还揭示出在应用phenalenyl分子器件时,只需改变电极耦接,就可以获得具有不同电子学特性的分子器件. 相似文献
55.
Jian Zheng Keiko Tagami Shigeo Uchida 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):171-175
After the nuclear accident at TEPCO’s Fukushima Dai-ichi power station in March, hydrogen explosions and reactor building
explosion resulted in releases of radionuclides in the environment. Severe radioactive cesium and iodine contaminations have
been observed in fallout deposition samples and soils in the East Japan. Radioactive cesium, iodine, uranium, and transuranic
radionuclides were set as the monitoring targets in food safety tests. However, so far, only radioactive cesium and iodine
were daily measured and reported by the Ministry of Health, Labour, and Welfare. The tedious and time consuming conventional
alpha spectrometric method hampered the emergency monitoring U contamination in foods. In this work, we propose a simple and
rapid analytical method for 238U and 235U/238U isotope ratio analysis in fresh vegetables. This method was applied to the emergency monitoring of radioactive contamination
after the nuclear accident at TEPCO’s Fukushima Dai-ichi power station. The results showed no U contamination in fresh vegetables
collected in Chiba and Ibaraki prefectures in April and May, 2011. 相似文献
56.
利用基于紧密耦合理论的格林函数方法,考虑到每一个碳原子的π轨道电子,对3苯环构成的纳米分子桥的量子传输特性进行了理论研究。得出了从分子桥的一个端点到另外两个端点的电子传输概率。 利用基于Fisher-Lee公式的流密度方法,在传输概率出现峰值的能量点E=±0.42, ±1.06 和±1.5处,计算了分子桥内部的电流分布。其数值结果用图形模拟表示出来。我们发现传输谱与入射电子能量相关,并且紧密地依赖与分子能级。其结果显示电子流分布完全符合Kirchhoff量子动量守恒定律。 相似文献
57.
Summary. General error estimates are proved for a class of finite element schemes for nonstationary thermal convection problems with temperature-dependent coefficients. These variable coefficients turn the diffusion and the buoyancy terms to be nonlinear, which increases the nonlinearity of the problems. An argument based on the energy method leads to optimal error estimates for the velocity and the temperature without any stability conditions. Error estimates are also provided for schemes modified by approximate coefficients, which are used conveniently in practical computations.Mathematics Subject Classification (2000): 65M12, 65M60, 76M10 相似文献
58.
N. Watanabe K. Kuroda K. Abe N. Koshizuka M. Tagami Y. Shiohara 《Physica C: Superconductivity and its Applications》1998,300(3-4):301-308
The polarized Raman spectra of Nd1+xBa2−xCu3O7−δ (−0.023≤x≤0.107) and Pr1+xBa2−xCu3O7−δ (0.01≤x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm−1 in Nd 1:2:3 and 4 cm−1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x(yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 相似文献
59.
60.
[reaction: see text] Treatment of sarcophytoxide with trimethylsilyl trifluoromethanesulfonate afforded an aromatic ketone as an unusual cyclization product. The modified Mosher's method and X-ray analysis performed on the aromatic ketone revealed that it is a 4:1 mixture of 8(R)- and 8(S)-enantiomers. It also suggested that the precursor ketone has 8(R)-configuration, which is contradictory to that expected from the ordinary epoxide-ketone rearrangement. 相似文献