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91.
Wen-Shyan Hong Chen-Shiang Lee Michael Y Chiang 《Journal of organometallic chemistry》2004,689(2):277-285
The reaction of thiophene-2-carboxaldehyde thiosemicarbazone (2-C4H3SCHNNHC(S)NH2) (1) with diiron nonacarbonyl under mild conditions in anhydrous benzene yields three iron carbonyl organometallic clusters: (i) Fe2S2 square-base pyramidal cluster 2 ([Fe(CO)3]3(μ3-S)2), (ii) Fe2S2 square-base pyramidal metal carbene cluster 3 ([Fe(CO)3]2Fe(CO)2(μ3-S)2(C(NH2)NHNCH (2-C4H3S)), and (iii) double butterfly cluster 4 ([Fe(CO)3]3Fe(CO)2(μ4-S)(C,N; C(NH2)NHNCH(2-C4H3S) (μ2-S, N; SC(NH2)NNCH(2-C4H3S)), and an octahedral complex 5 (Fe(CO)2(S, N; SC(NH2)NNCH (2-C4H3S))2. These products were fully characterized spectrally. The molecular structures of 1, 3, 4, and 5 have been determined by single-crystal X-ray diffraction. 相似文献
92.
Chiang CM Lu D Huang JT Hwang CC Cho CC Fan LJ Yang YW 《Journal of the American Chemical Society》2004,126(39):12242-12243
Fluorine-substituted ethyl groups on Cu(111) were generated by thermal scission of the C-I bond in the adsorbed C2F5I. Temperature-programmed reaction spectrometry observed a novel pathway resulting in the evolution of C4F6 above 400 K. Among the various isomers, this product was identified as hexafluro-2-butyne. Although abstraction of two fluorine atoms from the starting Cu-CF2CF3 was required, Cu-CCF3 (trifluoroethylidyne) was favored over Cu-CF=CF2 (trifluorovinyl) as the intermediate because this ethyl-ethylidyne-butyne pathway was suppressed on a Cu(100) surface devoid of the key threefold hollow binding sites for ethylidyne. Once formed, perfluoroethylidyne readily coupled to afford a tightly surface-bound hexafluoro-2-butyne up to 400 K. Therefore, the C-F bonds adjacent to the metal were found to be more susceptible to the bond activation, leading the chemisorbed perfluoroethyl to eliminate two F atoms successively from the alpha-carbon. This preference for alpha-elimination rather than beta-elimination (the most favorable route in hydrocarbons) may be quite general for metal surface-mediated reactions involving fluorinated alkyl groups. 相似文献
93.
Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation 总被引:2,自引:0,他引:2
Hong H Wei CM Chou MY Wu Z Basile L Chen H Holt M Chiang TC 《Physical review letters》2003,90(7):076104
Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy. 相似文献
94.
95.
Propagation characteristics of a segmented cladding fiber 总被引:3,自引:0,他引:3
We propose a novel optical fiber design that consists of a uniform core and a segmented cladding formed by alternate regions of high and low refractive indices in the azimuthal direction. The structure is analyzed by use of the radial effective-index method, and the propagation characteristics of the structure are studied. The fiber has a highly dispersive cladding and shows characteristics similar to those of photonic-crystal fibers and holey fibers. The novel fiber offers the possibility of single-mode operation over a wide range of wavelengths with a large core diameter. 相似文献
96.
A high concentration (0.8 M) zirconium solution turned into a stable aqueous colloid of about 60 nm in size upon low temperature (96°C) incubation. Changing the acid concentration did not affect the colloidal growth rate nor the final colloid size much. However, the induction time before the rapid growth of colloidal particle could be altered. By limiting the incubation to just before the rapid growth of colloidal zirconia, and the addition of organic acids as surface modifiers, non-agglomerated primary crystallites (10 nm) of m-ZrO2 could be recovered. These modified primary crystallites could then be repeatedly flocculated and redispersed in water by adjusting the pH. 相似文献
97.
A device of multiple nano-TiO2 layers was proposed and fabricated to prevent a dye/nano-TiO2 region from serious photo-degradation. In this device, the top of the dye/TiO2 region was designed to be coated using sol-gel nano-TiO2 thin films to shield UV irradiation from the photo-degradation effect. The sol-gel TiO2 was prepared in a low temperature (75 °C) and verified as nano-sized particles and an anatase crystalline structure. Different devices of the multi-layer samples fabricated using different compositions of nano-TiO2 were produced and exposed for UV irradiation tests. Results show that the presence of the sol-gel TiO2 films coated on top of the dye/TiO2 region can significantly alleviate the dye photo-degradation under UV irradiation. This multi-layer device can effectively improve the photo-stability of the dye/TiO2 region in a UV-exposure environment. 相似文献
98.
Ching-Yuan Chiang Madan L. Puri 《Annals of the Institute of Statistical Mathematics》1984,36(1):35-50
Summary In the linear regression modelX
i=α+βci+Zi, we consider the problem of testing the subhypothesis that some (but not all) components of β are equal to 0. A class of
asymptotically distribution-free tests based on a quadratic form in aligned rank statistic is studied and the asymptotic relative
efficiencies of the proposed tests with respect to the general likelihood ratio test and the test based on least-squares estimates
of regression parameters are derived. Asymptotic optimality (à la Wald) is also discussed.
Work done under the National Science Foundation Grant MCS 8301409 and NATO Grant 1465. 相似文献
99.
We describe identification of seven components from Antrodia cinnamomea. Their structures were determined on the basis of spectral analysis and comparison with authentic samples. These compounds include two steroids (1, 2) (β-sitosterol and eburicol), two new steroids (3, 4) [methyl-4α-methylergost-8,24(28)-dien-3,7,11-trion-26-oate and methyl-4α-methylergost-8,24(28)-dien-3,11-dion-26-oate], two lignans (5, 6) [(+)-sesamin and 4-hydroxysesamin], and one long chain methyl ester (7) (methyl oleate). Among them, compounds 3 and 4 are first isolated from nature. 相似文献
100.
A study of the adsorptive stripping voltammetry of nickel, aluminium, selenium and arsenic is reported in which 2,5-dimercapto-1,3,4-thiadiazole (DMTD) has been used as a chelating agent. By a suitable choice of deposition potential, deposition time, reagent reaction time and other operating conditions, the determination of the four elements could be achieved.By the use of benzyltrimethyl ammonium methoxide as a digesting solvent, it was possible to apply the procedure to the direct determination of the four elements in biological samples. 相似文献