917 resultados para GOLD
Resumo:
.How do you answer the question: “How well is your VLE being used?” City College Southampton rose to the challenge with the creation, development and implementation of a highly motivational ‘Gold, Silver and Bronze’ benchmarking system to evaluate and recognise quality of content and activity on its College Moodle system. The results are impressive.
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he 1,3-dipolar cycloaddition between glycine-derived azlactones with maleimides is efficiently catalyzed by the dimeric chiral complex [(S-a)-Binap.AuTFA](2). The alanine-derived oxazolone only reacts with tert-butyl acrylate giving anomalous regiochemistry, which is explained and supported by Natural Resonance Theory and Nucleus Independent Chemical Shifts calculations. The origin of the high enantiodiscrimination observed with maleimides and tert-butyl acrylate is analyzed using DFT computed at M06/Lanl2dz//ONIOM(b3lyp/Lanl2dz:UFF) level. Several applications of these cycloadducts in the synthesis of new proline derivatives with a 2,5-trans-arrangement and in the preparation of complex fused polycyclic molecules are described.
Resumo:
The synthesis of a GSK 2(nd) generation inhibitor of the hepatitis C virus, by enantioselective 1,3-dipolar cycloaddition between a leucine derived iminoester and tert-butyl acrylate, was studied. The comparison between silver(I) and gold(I) catalysts in this reaction was established by working with chiral phosphoramidites or with chiral BINAP. The best reaction conditions were used for the total synthesis of the hepatitis C virus inhibitor by a four step procedure affording this product in 99% ee and in 63% overall yield. The origin of the enantioselectivity of the chiral gold(I) catalyst was justified according to DFT calculations, the stabilizing coulombic interaction between the nitrogen atom of the thiazole moiety and one of the gold atoms being crucial.
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unavailable<br>H. Sun's e-mail address is shy780327@siom.ac.cn.
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[EN]In this report we present the tags we use when annotating the gold standard of syntactic functions and the decisions taken during its annotation. The gold standard is a necessary resource to evaluate the rulebased surface syntactic parser (the one based on the Constraint Grammar formalism), and, moreover, it can be useful to develop and evaluate statistical parsers. The tags we are presenting here follow the Constraint Grammar (CG) formalism (Karlsson et al., 1995). In fact, last experiments show that good results have been obtained when parsing with CG (Karlsson et al., 1995; Samuelsson and Voutilainen,1997; Tapanainen and Järvinen, 1997; Bick, 2000).
Resumo:
Absolute f-values for 7 transitions in the first spectra of 4 elements have been measured using the atomic beam absorption technique. The equivalent widths of the absorption lines are measured with a photoelectric scanner and the atomic beam density is determined by continuously weighing a part of it with a sensitive automatic microbalance. The complete theory is presented and corrections are calculated to cope with gas absorption by the deposit on the microbalance pan and atoms which do not stick to the pan. An additional correction for the failure of the assumption of effusive flow in the formation of the atomic beam at large densities has been measured experimentally.
The following f-values were measured:
Fe: fλ3720 = 0.0430 ± 8%
Cu: fλ3247 = 0.427 ± 4.5%, fλ3274 = 0.206 ± 4.7%, fλ2492 = 0.0037 ± 9%
Cd: fλ3261 = 0.00190 ± 7%, fλ2288 = 1.38 ± 12%
Au: fλ2428 = 0.283 ± 5.3%
Comparison with other accurately measured f-values, where they exist, shows agreement within experimental errors.
Resumo:
The presence of giant diamagnetism in Au nanorods, NRs, is shown to be a possible consequence of field induced currents in the surface electrons. The distance, Delta , between quantum surface energy levels has been calculated as a function of the NRs radius. Note that those electrons occupying states for which Delta > k(B)T are steadily orbiting with constant orbital moment. The diamagnetic response induced when a field is turned on remains constant during the time the field is acting. As the NRs radius increases, Delta decreases and accordingly the electron fraction available to generate constant currents decreases, consequently the surface diamagnetic susceptibility decreases towards its bulk value. The surface electronic motion induced by the axial applied field on electrons confined into a cylindrical surface accounts with extremely good quantitative agreement for the giant diamagnetism recently measured and reported.
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We report on space-selective co-precipitation of silver and gold nanoparticles in Ag+, Au3+ co-doped silicate glasses by irradiation of femtosecond laser pulses and subsequent annealing at high temperatures. The color of the irradiated area in the glass sample changed from yellow to red with the increase of the annealing temperature. The effects of average laser power and annealing temperature on precipitation of the nanoparticles were investigated. A reasonable mechanism was proposed to explain the observed phenomena. (c) 2006 Elsevier Ltd. All rights reserved.
Resumo:
We report on three-dimensional precipitation of Au nanoparticles in gold ions-doped silicate glasses by a femtosecond laser irradiation and further annealing. Experimental results show that PbO addition plays the double roles of inhibiting hole-trapped centers generation and promoting formation and growth of gold nanoparticles. Additionally, glass containing PbO shows an increased non-linear absorption after femtosecond laser irradiation and annealing. The observed phenomena are significant for applications such as fabrications of three-dimensional multi-colored images inside transparent materials and three-dimensional optical memory, and integrated micro-optical switches. (c) 2007 Elsevier B.V. All rights reserved.
Resumo:
This academic work is based on the study of the gold standard, its evolution over the years, their periods of boom and crisis. We will also discuss the arguments that some economists back the return to this monetary system.