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71.
Li C Thomson RK Gillon B Patrick BO Schafer LL 《Chemical communications (Cambridge, England)》2003,(19):2462-2463
A series of bis(amidate)group 4-bis(amido) complexes have been prepared, characterized and have been shown to be highly tunable precatalysts for both the intra- and intermolecular hydroamination of alkynes. 相似文献
72.
The current efficiency for the electrogeneration of cerie ion at a platinum anode falls considerably below 100% at both very small and at large current densities in both sulfuric and perchloric acid media. The maximal current efficiency is about 99.8%.Iodide ion can be titrated to iodine with an error of only about +0.3%, even under conditions where the cerie ion generation efficiency is only 98%. High titration efficiency, in spite of poor efficiency for ceric ion generation, is obtained because iodine is oxidized to iodate ion at a potential slightly in advance of the potential at which cerous ion is oxidized. Since the electrogenerated iodate ion oxidizes iodide ion only a minor fraction of the total quantity of electricity results from ceric ion generation, so the effect of its inefficient generation is greatly minimized. Satisfactory titrations of iodide ion to iodine can be performed without any cerous salt present, provided the generating current density is smaller than the limiting current density for oxidation of iodine to iodate ion. 相似文献
73.
Morton LA Zhang XH Wang R Lin Z Wu YD Xue ZL 《Journal of the American Chemical Society》2004,126(33):10208-10209
d0 Tungsten alkylidyne alkyl complex (Me3SiCH2)3W(CSiMe3)(PMe3) (4a) was found to undergo a rare, PMe3-promoted exchange with its bis(alkylidene) tautomer (Me3SiCH2)2W(=CHSiMe3)2(PMe3) (4b). Thermodynamic studies of the exchange showed that 4b is favored and gave Keq and the enthalpy and entropy of the equilibrium: DeltaH degrees = -1.8(0.5) kcal/mol and DeltaS degrees = -1.5(1.7) eu. Kinetic studies of the alpha-H migration between 4a and 4b by variable-temperature NMR gave rate constants k1 and k-1 for the reversible reactions and activation enthalpies and entropies: DeltaH1 = 16.2(1.2) kcal/mol and DeltaS1 = -22.3(4.0) eu for the forward reaction (4a --> 4b); DeltaH2 = 18.0(1.3) kcal/mol and DeltaS2 = -20.9(4.3) eu for the reverse reaction (4b --> 4a). Ab initio calculations at the B3LYP level revealed that PMe3 binds with the bis(alkylidene) tautomer relatively more strongly than with the alkylidyne tautomer and thus stabilizes the bis(alkylidene) tautomer. 相似文献
74.
The syntheses of 11β-methyl and 11β-ethylestradiol, via Grignard adducts to 11-oxoestra-1,3,5(10)-trienes, attempted modification of the Torgov total synthesis of steroids, and 11β-methylticogenin, are described. 相似文献
75.
76.
C. Bandis S.C. Langford J.T. Dickinson D.R. Ermer 《Applied Physics A: Materials Science & Processing》1999,69(7):S129-S132
We report electron and Na+ ion emission from single-crystal sodium nitrate (~10 eV band gap) upon exposure to IR (1064 nm, 1.16 eV) laser radiation. The fluence dependence of both the ion and the electron yield is highly nonlinear, and the kinetic energies of the emitted ions can reach values up to 5 eV. The fluence dependence and the ion energy distributions can be understood by a previously presented model involving multiple photon charge transfer plus electrostatic ejection of adions siting atop electron traps. Further evidence for the role of defects in the observed ion emission are provided by two-beam experiments; one beam (UV laser) is used to generate defects and the second beam (IR laser) is used to photodesorb the ions. Such experiments demonstrate that exposure of the sodium nitrate surfaces to UV laser radiation significantly increases the ion emission due to IR laser radiation. 相似文献
77.
Laurel Puchner Ann Taylor Barbara O'Donnell Kathleen Fick 《School science and mathematics》2008,108(7):313-325
This collective case study analyzes the use of manipulatives in math lessons developed and taught by 4 groups of elementary teachers (K‐8) involved in lesson study as part of a professional development program. The study found that in three of four lessons studied manipulative use was turned into an end in and of itself, rather than a tool, and that in the fourth lesson manipulative use hindered rather than helped student learning. These problems with manipulative use by teachers in the lessons provide helpful guidance for planning of future professional development for math teaching. Our conclusion contains recommendations for successful implementation of manipulatives for both teachers and professional developers. Most importantly, we stress the need to emphasize the link between pedagogy and content, not the specific use of manipulatives. 相似文献
78.
Toby D. M. Bell Dr. Sheryll Yap Chintan H. Jani Sheshanath V. Bhosale Dr. Johan Hofkens Prof. Frans C. De Schryver Prof. Steven J. Langford Prof. Kenneth P. Ghiggino Prof. 《化学:亚洲杂志》2009,4(10):1542-1550
The synthesis and photophysics of two new aminopropenyl naphthalene diimide (SANDI) dyes are reported. A general and convenient method for the synthesis of the precursor mono‐, di‐, and tetrabrominated 1,4,5,8‐naphthalene tetracarboxylic dianhydrides is described. The two core‐substituted SANDIs exhibit many of the photophysical properties required for fluorescence labeling applications including high photostability and high fluorescence quantum yields (>0.5) in the visible region of the spectrum. The emission wavelength is sensitive to the number of substituents on the NDI core, and the fluorescence decay times are in the range of ~8–12 ns for both compounds in the solvents investigated. Preliminary fluorescence emission data from single molecules of the compounds embedded in poly(methyl methacrylate) films are also reported and show that single molecules have very low yields of photobleaching, particularly the di‐substituted system. Furthermore, only a small proportion (<10 %) of the single molecules studied display fluorescence intermittencies or “blinks” in their photon trajectory. The compounds appear to be excellent candidates for applications at the single molecule level, for example, as FRET labels. 相似文献
79.
We report on the systematic open-aperture Z-scan characterization of the two-photon absorption properties in one of the most efficient solid-state Raman frequency shifters, the crystal potassium gadolinium tungstate [KGd(WO4)2]. The two-photon absorption coefficient was determined in the 370-600-nm wavelength range, with the highest value found to be approximately 1.9 cm/GW at 370 nm. Nonlinear losses are crucial in determining the conversion efficiency of the stimulated Raman scattering process when it is excited with ultrashort laser pulses with photon energy exceeding half of the bandgap. In addition, the results were analyzed within the context of a simple two-parabolic-band theoretical model to yield an effective bandgap energy value for the crystal. 相似文献
80.
Langford NK Weinhold TJ Prevedel R Resch KJ Gilchrist A O'Brien JL Pryde GJ White AG 《Physical review letters》2005,95(21):210504
We demonstrate a new architecture for an optical entangling gate that is significantly simpler than previous realizations, using partially polarizing beam splitters so that only a single optical mode-matching condition is required. We demonstrate operation of a controlled-z gate in both continuous-wave and pulsed regimes of operation, fully characterizing it in each case using quantum process tomography. We also demonstrate a fully resolving, nondeterministic optical Bell-state analyzer based on this controlled-z gate. This new architecture is ideally suited to guided optics implementations of optical gates. 相似文献