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31.
William H. Pearson Joseph E. Celebuski Yam-Foo Poon Brian R. Dixon Jeffrey H. Glans 《Tetrahedron letters》1986,27(52):6301-6304
Cyclization of heterosubstituted ω-azidodienes 11 provides fused bicyclic 3-pyrrolines 12 in one operation. These pyrrolines are potentially useful intermediates for natural products synthesis, as illustrated by further functionalization. 相似文献
32.
The temporal course of masking and the auditory filter shape 总被引:1,自引:0,他引:1
B C Moore P W Poon S P Bacon B R Glasberg 《The Journal of the Acoustical Society of America》1987,81(6):1873-1880
Recent experiments have shown that frequency selectivity measured in tone-on-tone simultaneous masking improves with increasing delay of a brief signal relative to the onset of a longer duration gated masker. To determine whether a similar improvement occurs for a notched-noise masker, threshold was measured for a 20-ms signal presented at the beginning, the temporal center, or the end of the 400-ms masker (simultaneous masking), or immediately following the masker (forward masking). The notch width was varied systematically and the notch was placed both symmetrically and asymmetrically about the 1-kHz signal frequency. Growth-of-masking functions were determined for each temporal condition, for a noise masker without a spectral notch. These functions were used to express the thresholds from the notched-noise experiment in terms of the level of a flat-spectrum noise which would produce the same threshold. In simultaneous masking the auditory filter shapes derived from the transformed data did not change significantly with signal delay, suggesting that the selectivity of the auditory filter does not develop over time. In forward masking the auditory filter shapes were sharper than those for simultaneous masking, particularly on the high-frequency side, which was attributed to suppression. 相似文献
33.
Kevin Hing-Nin Poon Yu-Ling Cheng 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):211-222
Quartz crystal microbalance (QCM) was used to study the self-assembly of per-6-thio-β-cyclodextrin (t7-βCD) on gold surfaces, and the subsequent inclusion interactions of immobilized βCD with adamantane-poly(ethylene glycol)
(5,000 MW, AD-PEG), 1-adamantanecarboxylic acid (AD-C) and 1-adamantylamine (AD-A). From a 50 μM solution of t7-βCD in 60:40 DMSO:H2O, a t7-βCD layer was formed on gold with surface density of 71.7 ± 2.7 pmol/cm2, corresponding to 80 ± 3% of close-packed monolayer coverage. Gold sensors with immobilized t7-βCD were then exposed alternately to six different concentrations of AD-PEG, 500 μM AD-C or 500 μM AD-A aqueous solutions
for association, and water for dissociation. Association of AD-PEG conformed to a Langmuir isotherm, with a best fit equilibrium
constant K = 125,000 ± 18,000 M−1. For AD-C and AD-A, association (k
a
) and dissociation (k
d
) rate constants were extracted from kinetic profiles by fitting to the Langmuir model, and equilibrium constants were calculated.
The parameters for AD-C were found to be: k
a
= 100 ± 5 M−1 s−1, k
d
= 110 (±18) × 10−4 s−1, and K = 9,400 ± 1,700 M−1. For AD-A, k
a
= 58 ± 6 M−1 s−1, k
d
= 154 (±7) × 10−4 s−1, and K = 3,800 ± 400 M−1. The results demonstrate the utility of QCM as a tool for studying small molecule surface adsorption and guest–host interactions
on surfaces. More specifically, the kinetic and thermodynamic data of AD-C, AD-A, and AD-PEG inclusion with immobilized t7-βCD form a basis for further surface association studies of AD-X conjugates to advance surface sensory and coupling applications. 相似文献
34.
The internal space of a N = 4 supersymmetric model with Wess–Zumino term has a connection with totally skew-symmetric torsion
and holonomy in SP(n). We study the mathematical background of this type of connection. In particular, we relate it to classical Hermitian geometry,
construct homogeneous as well as inhomogeneous examples, characterize it in terms of holomorphic data, develop its potential
theory and reduction theory.
Received: 1 October 1999 / Accepted: 30 January 2000 相似文献
35.
In this paper, we formulate two classes of problems, the colored range query problems and the colored point enclosure query problems to model multi-dimensional range and point enclosure queries in the presence of categorical information. Many of these problems are difficult to solve using traditional data structural techniques. Based on a new framework of combining sketching techniques and traditional data structures, we obtain two sets of results in solving the problems approximately and efficiently. In addition, the framework can be employed to attack other related problems by finding the appropriate summary structures. 相似文献
36.
Chi-Kwong Li Yiu-Tung Poon Nung-Sing Sze 《Proceedings of the American Mathematical Society》2005,133(2):369-377
We characterize linear maps between different rectangular matrix spaces preserving Ky Fan norms.
37.
38.
The work uses the data in the TTS mode of BATSE to analyze the time lags and pulse widths of GRB960113 and GRB960722 in high
as well as low energy bands. The results show that their time lags increase monotonously. This phenomenon can reasonably be
interpreted with the model of internal shock waves of γ-ray bursts (GRB). Perhaps we obtain the direct observational evidence
for the fireball model of GRBs for the first time. 相似文献
39.
We report the demonstration of electro-optical tunable time delay and advance using a silicon feedback-microring resonator integrated with p-i-n diodes. By controlling the feedback and round-trip phase shifts through the carrier-injection-based free-carrier dispersion effect, we obtain a large dynamic time tuning range (-88 ps to 110 ps) upon dc bias voltage change in the range of few tens of millivolts at a given resonance wavelength. We also demonstrate tunable time delay and advance at different resonance wavelengths within 0.76 nm wavelength range. 相似文献
40.
Waveguides at interfaces with a linearly graded permittivity between a metal and a dielectric are studied. Analytic expressions for the dispersion relations, modes, losses, and cutoff wavelengths are derived and agree well with simulations. The gradation results in anomalous dispersion, a reduction in the energy velocity, and increased field confinement in the metal-dielectric transition region. These effects lead to increased propagation losses, which are sensitive to the spatial extent of the interface gradation. 相似文献