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71.
Suitably substituted aminoesters can be transformed to the corresponding α-aminonitriles and in the case of piperidino-acetic ester derivatives, into the biochemically important quinuclidine ring system. 相似文献
72.
The asymmetric conjugate addition of thiophenol to (E)-3-crotonoyloxazolidin-2-one catalysed by the scandium(III) triflate complex of Ph-PYBOX gave the corresponding adduct in 66% ee. Lanthanoid triflates gave lower enantioselectivities (?28% ee). 相似文献
73.
Mikko PassiniemiAri M.P. Koskinen 《Tetrahedron letters》2011,52(50):6736-6738
Garner’s aldehyde is a suitable precursor for the synthesis of both isomers of Boc-protected epi-norfuranomycin. We demonstrate the utility of trisyl chloride as an effective leaving group in the dihydrofuran formation step. We also show that TEMPO/BAIB is an effective oxidant for α-amino alcohols avoiding epimerization of the labile α-proton of the product aldehyde. 相似文献
74.
75.
We consider words together with a compatibility relation induced by a relation on letters. Unique factorization with respect
to two arbitrary word relations R and S defines the (R,S)-freeness of the semigroup considered. We generalize the stability theorem of Schützenberger and Tilson’s closure result
for (R,S)-free semigroups. The inner and the outer (R,S)-unique factorization hull and the (R,S)-free hull of a set of words are introduced and we show how they can be computed. We prove that the (R,S)-unique factorization hulls possess a defect effect, which implies a variant of a cumulative defect theorem of word semigroups.
In addition, a defect theorem of partial words is proved as a corollary. 相似文献
76.
Digital subtractive synthesis is a popular music synthesis method, which requires oscillators that are aliasing-free in a perceptual sense. It is a research challenge to find computationally efficient waveform generation algorithms that produce similar-sounding signals to analog music synthesizers but which are free from audible aliasing. A technique for approximately bandlimited waveform generation is considered that is based on a polynomial correction function, which is defined as the difference of a non-bandlimited step function and a polynomial approximation of the ideal bandlimited step function. It is shown that the ideal bandlimited step function is equivalent to the sine integral, and that integrated polynomial interpolation methods can successfully approximate it. Integrated Lagrange interpolation and B-spline basis functions are considered for polynomial approximation. The polynomial correction function can be added onto samples around each discontinuity in a non-bandlimited waveform to suppress aliasing. Comparison against previously known methods shows that the proposed technique yields the best tradeoff between computational cost and sound quality. The superior method amongst those considered in this study is the integrated third-order B-spline correction function, which offers perceptually aliasing-free sawtooth emulation up to the fundamental frequency of 7.8 kHz at the sample rate of 44.1 kHz. 相似文献
77.
Repo S Paldanius TA Hytönen VP Nyholm TK Halling KK Huuskonen J Pentikäinen OT Rissanen K Slotte JP Airenne TT Salminen TA Kulomaa MS Johnson MS 《Chemistry & biology》2006,13(10):1029-1039
The chicken genome encodes several biotin-binding proteins, including avidin and avidin-related protein 4 (AVR4). In addition to D-biotin, avidin binds an azo dye compound, 4-hydroxyazobenzene-2-carboxylic acid (HABA), but the HABA-binding properties of AVR4 are not yet known. Differential scanning calorimetry, UV/visible spectroscopy, and molecular modeling were used to analyze the binding of 15 azo molecules to avidin and AVR4. Significant differences are seen in azo compound preferences for the two proteins, emphasizing the importance of the loop between strands beta3 and beta4 for azo ligand recognition; information on these loops is provided by the high-resolution (1.5 A) X-ray structure for avidin reported here. These results may be valuable in designing improved tools for avidin-based life science and nanobiotechnology applications. 相似文献
78.
Härkönen A Paajaste J Suomalainen S Alanko JP Grebing C Koskinen R Steinmeyer G Guina M 《Optics letters》2010,35(24):4090-4092
We report on a passively mode-locked optically pumped GaSb-based semiconductor disk laser producing stable picosecond optical pulses at a 1.95 μm wavelength. The gain mirror was comprised of a 15 quantum well InGaSb/GaSb structure. A fast semiconductor saturable absorber mirror with three InGaSb/GaSb quantum wells was used to attain self-starting mode-locked operation at a fundamental repetition rate of 881.2 MHz. The laser produced pulses with 30 pJ energy and a duration of 1.1 ps within a factor of 2 of the Fourier limit. 相似文献
79.
W. C. Koskinen H. H. Cheng L. J. Jarvis B. A. Sorenson 《International journal of environmental analytical chemistry》2013,93(1-4):379-385
Abstract This research determined the relative effectiveness of supercritical fluid extraction (SFE) in extracting atrazine and its metabolites from soils which had been treated with atrazine for varying periods of time in order to characterize binding mechanisms. Aqueous methanol extraction was more effective than SFE in removing 14C atrazine residues from “aged” soils. The more polar the solvent system, the more 14C-atrazine residues were extracted. The order of polarity and extractability was aqueous methanol > SF-CO2/5% methanol > SF-CO2. Atrazine extraction efficiency using SF-CO2, and SF-CO2/.5% methanol decreased as samples “aged” in the field. The less than complete recovery of atrazine residues using the SFE technique could be seen as an indication that different binding mechanisms were involved in the retention of atrazine as well as its metabolites and that the binding mechanisms changed with time. 相似文献
80.