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The changes in the oxidation state of vanadium in artificial and natural seawater samples were studied by electrothermal atomic absorption spectrometry (ETAAS) with a direct injection of a resin suspension. V(IV) and V(V) were extracted as the complex with Chromazurol B and with N-cinnamoyl-N-2,3-xylylhydroxylamine, respectively, using a suspension of an anion-exchange resin and determined by ETAAS independently. The detection limits of both methods were 0.02 ng ml(-1) for 40 ml of a sample solution. The recovery tests for an artificial seawater sample spiked with V(IV) and/or V(V) were carried out carefully. The results showed that the recoveries of V(IV) or V(V) were 99.2-109% and the standard deviations were 1-6%. The total V was also determined after V(V) was reduced by ascorbic acid. In artificial seawater at pH 7.8, V(V) was stable but V(IV) was oxidized rapidly. In acidified artificial seawater (pH 2.0), V(IV) was oxidized slowly but only a small tendency of such reduction of V(V) was observed. In a natural seawater sample, V(IV) was not detected. The acidification of the natural seawater sample resulted in the reduction of V(V). 相似文献
986.
Hierarchical multi-objective decision systems for general resource allocation problems 总被引:2,自引:0,他引:2
We consider optimization methods for hierarchical power-decentralized systems composed of a coordinating central system and plural semi-autonomous local systems in the lower level, each of which possesses a decision making unit. Such a decentralized system where both central and local systems possess their own objective function and decision variables is a multi-objective system. The central system allocates resources so as to optimize its own objective, while the local systems optimize their own objectives using the given resources. The lower level composes a multi-objective programming problem, where local decision makers minimize a vector objective function in cooperation. Thus, the lower level generates a set of noninferior solutions, parametric with respect to the given resources. The central decision maker, then, parametric with respect to the given resources. The central decision maker, then, chooses an optimal resource allocation and the best corresponding noninferior solution from among a set of resource-parametric noninferior solutions. A computational method is obtained based on parametric nonlinear mathematical programming using directional derivatives. This paper is concerned with a combined theory for the multi-objective decision problem and the general resource allocation problem.The authors are indebted to Professor G. Leitmann for his valuable comments and suggestions. 相似文献
987.
The short-range part of the nucleon-nucleon interaction is treated in the one-quark and gluon-exchange approximation. The S-wave phase shifts are calculated using the resonating group method. The nucleon-nucleon, ΔΔ and hidden color channels are taken into account. The spatial symmetry [42] is slightly preferred over the fully orbital symmetric state by the larger probability (89%) with which it is contained asymptotically in the nucleon-nucleon channel and by the quark-quark interaction. The orbital [42] symmetry requires a node in the relative S-wave function between the two nucleons. This yields a hard-core phase shift for the singlet and triplet S-waves. 相似文献
988.
Mediating Order and Modulating Porosity by Controlled Hydrolysis in a Phosphonate Monoester Metal–Organic Framework 下载免费PDF全文
Benjamin S. Gelfand Racheal P. S. Huynh Roger K. Mah Prof. George K. H. Shimizu 《Angewandte Chemie (International ed. in English)》2016,55(47):14614-14617
A crystalline and permanently porous copper phosphonate monoester framework has been synthesized from a tetraaryl trigonal phosphonate monoester linker. This material has a surface area over 1000 m2 g?1, as measured by N2 sorption, the highest reported for a phosphonate‐based metal–organic framework (MOF). The monoesters result in hydrophobic pore surfaces that give a low heat of adsorption for CO2 and low calculated selectivity for CO2 over N2 and CH4 in binary mixtures. By careful manipulation of synthetic conditions, it is possible to selectively remove some of the monoesters lining the pore to form a hydrogen phosphonate while giving an isomorphous structure. This increases the affinity of the framework for CO2 giving higher ambient uptake, higher heat of adsorption, and much higher calculated selectivity for CO2 over both N2 and CH4. Formation of the acid groups is noteworthy as complexation with the parent acid gives a different structure. 相似文献
989.
Takumi Goto Satoshi Matsuyama Hiroki Nakamori Yasuhisa Sano Yoshiki Kohmura Makina Yabashi 《Synchrotron Radiation News》2016,29(4):32-36
Ultra-bright and high-coherence X-rays are now being used in synchrotron radiation facilities and X-ray free electron laser facilities. X-ray focusing techniques are essential to take full advantage of these excellent X-ray light sources. To meet the strong demand, high-quality X-ray focusing optics have been developed owing to the advancement of ultraprecision machining and measurement. State-of-the-art refractive lenses [1], zone plates [2], and Laue lenses [3] can be used to achieve X-ray focusing to a spot a few tens of nanometers. 相似文献
990.
Soo Jin Lee Moo Lyong Seo Young-A. Lee Jong Hwa Jung Masaki Kogiso Toshimi Shimizu 《Tetrahedron》2008,64(7):1301-1308
Three long chain alanine-based amphiphiles (1-3) possessing either a saturated long alkyl chain group or unsaturated groups as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated using EF-TEM, SEM, CD, XRD, and FTIR. The d-form (1) and the l-form (2) enantiomers showed the opposite CD signals. Furthermore, electron micrographs of the self-assembled 1 and 2 exhibited right- and left-handed helical structures, respectively. The helical structures of amphiphiles 1 and 2 were developed into tubular structures by slow cooling. On the other hand, in the helical ribbon growth process, the helical pitch and ribbon width were changed in fast cooling process. The findings strongly imply that the helical ribbon growth of alanine-based amphiphiles can be induced by two different pathways. This mechanism, quite different from that observed for sugar- and cholesterol-based tubes, is a rare example for a tube formation process. 相似文献