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61.
62.
Naonobu Tanaka Rei Momose Azusa Takahashi-Nakaguchi Tohru Gonoi Jane Fromont Jun'ichi Kobayashi 《Tetrahedron》2014
Six new indole alkaloids, hyrtimomines F–K (1–6), were isolated from Okinawan marine sponges Hyrtios spp. The structures of 1–6 were elucidated on the basis of spectroscopic analysis. Hyrtimomine F (1) is a structurally unique bisindole alkaloid possessing an α-keto-?-caprolactam ring, while hyrtimomine G (2) is a symmetrical bisindole alkaloid. Hyrtimomines H–K (3–6) are indole alkaloids possessing β-carboline skeleton with an imidazolium unit. Antimicrobial activities of hyrtimomines F–K (1–6) were evaluated. 相似文献
63.
Effect of forewing and hindwing interactions on aerodynamic forces and power in hovering dragonfly flight 总被引:1,自引:0,他引:1
Dragonflies are four-winged insects that have the ability to control aerodynamic performance by modulating the phase lag (phi) between forewings and hindwings. We film the wing motion of a tethered dragonfly and compute the aerodynamic force and power as a function of the phase. We find that the out-of-phase motion as seen in steady hovering uses nearly minimal power to generate the required force to balance the weight, and the in-phase motion seen in takeoffs provides an additional force to accelerate. We explain the main hydrodynamic interaction that causes this phase dependence. 相似文献
64.
Filipa M.B. L William L. Ledger Jane W. Davidson David M. Howard Georgina L. Jones 《Journal of voice》2007,21(6):754-761
The success of professional operatic singers depends upon the quality of their vocal mechanism. This is known to be sensitive to changes in the endocrine environment. Despite a widespread belief among singers that vocal quality changes according to the stage of the menstrual cycle, this has received little attention. In particular, the possibility that use of the contraceptive pill might stabilize vocal quality by "dampening" hormonal fluctuations has not previously been studied systematically. Here, we show that drospirenone containing oral contraceptive pill (Yasmin, Schering AG, West Sussex, UK) with antiandrogenic and antimineralocorticoid properties demonstrates a significant reduction in the irregularity of the pattern of vibration of the vocal folds during the performance of highly trained classical singers. This study constitutes the first double blind, randomized placebo controlled trial to assess the effects of the contraceptive pill on the patterns of vibration of the vocal folds during the performance of Western classical singing repertoire. 相似文献
65.
Fluorescence imaging of cells and tissue can be used to evaluate β-NADH redox and location. At low temperature, β-NADH fluorescence
intensity increases and therefore sensitivity of imaging increases. In this paper, the temperature dependence of fluorescence
was evaluated for β-NADH in glycerol/water solution and in trehalose/sucrose glass. The average fluorescence lifetime for
NADH in glycerol/water is 0.66 ns, compared with 5.3 ns in trehalose/ sucrose at 20°C. Emission spectra were recorded from
290 to 12 K. The fluorescence of β-NADH in glycerol/water increases ∼16 fold and the emission shifts about 35 nm to the blue
as temperature decreases. Much smaller change is seen for fluorescence of β-NADH in sugar glass. Below 77 K, the β-NADH spectral
features did not change significantly with temperature change, and so no increase in sensitivity is obtained by going to very
low temperatures. It is suggested that the sensitivity of β-NADH fluorescence is related to water relaxation around the excited
state molecule. Differences in water in various tissues may contribute to β-NADH fluorescence changes when cells are altered. 相似文献
66.
One‐Step Multicomponent Self‐Assembly of a First‐Generation Sierpiński Triangle: From Fractal Design to Chemical Reality 下载免费PDF全文
Rajarshi Sarkar Kai Guo Dr. Charles N. Moorefield Prof. Mary Jane Saunders Prof. Chrys Wesdemiotis Prof. George R. Newkome 《Angewandte Chemie (International ed. in English)》2014,53(45):12182-12185
A novel terpyridine‐based architecture that mimics a first‐generation Sierpiński triangle has been synthesized by multicomponent assembly and features tpy? CdII? tpy connectivity (tpy=terpyridine). The key terpyridine ligands were synthesized by the Suzuki cross‐coupling reaction. Mixing two different terpyridine‐based ligands and CdII in a precise stoichiometric ratio (1:1:3) produced the desired fractal architecture in near‐quantitative yield. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and transmission electron microscopy. 相似文献
67.
Shaofei Song Jingjie Jiang Ehsan Nikbin Jane Y. Howe Ian Manners Mitchell A. Winnik 《Chemical science》2022,13(2):396
Self-assembly of crystalline-coil block copolymers (BCPs) in selective solvents is often carried out by heating the mixture until the sample appears to dissolve and then allowing the solution to cool back to room temperature. In self-seeding experiments, some crystallites persist during sample annealing and nucleate the growth of core-crystalline micelles upon cooling. There is evidence in the literature that the nature of the self-assembled structures formed is independent of the annealing time at a particular temperature. There are, however, no systematic studies of how the rate of cooling affects self-assembly. We examine three systems based upon poly(ferrocenyldimethylsilane) BCPs that generated uniform micelles under typical conditions where cooling took pace on the 1–2 h time scale. For example, several of the systems generated elongated 1D micelles of uniform length under these slow cooling conditions. When subjected to rapid cooling (on the time scale of a few minutes or faster), branched structures were obtained. Variation of the cooling rate led to a variation in the size and degree of branching of some of the structures examined. These changes can be explained in terms of the high degree of supersaturation that occurs when unimer solutions at high temperature are suddenly cooled. Enhanced nucleation, seed aggregation, and selective growth of the species of lowest solubility contribute to branching. Cooling rate becomes another tool for manipulating crystallization-driven self-assembly and controlling micelle morphologies.In the self-assembly of crystalline-coil block copolymers in solution, heating followed by different cooling rates can lead to different structures. 相似文献
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70.
As part of a larger project concerning the sorption capacities of carbonate fluoroapatites, the physical and surface properties of the synthetic carbonate fluoroapatite and mineral francolite retained for this work have been carefully examined. The average particle size of the powdered samples, determined by laser granulometry, is around 30 microm. Their specific surface areas, measured according to the N(2) BET method, are 8.8+/-0.1 and 13.9+/-0.1 m(2).g(-1), respectively, for the synthetic and the mineral compound. The solubility of both solids has been studied under undersaturation initial conditions. The synthetic compound has a solubility product of 10(-103+/-2), but the mineral francolite, which is highly substituted and poorly crystalline, is more soluble and dissolves incongruently. The amphoteric properties of the hydrous carbonate fluoroapatites surfaces have also been investigated through zeta-potential measurements and potentiometric titrations in KNO(3) medium at 25 degrees C. The experimental data have been interpreted using the computer program FITEQL 3.2, applying either the nonelectrostatic or the constant capacitance model. For both solids, the values of the surface acidity constants determined with the two models are very close, suggesting a weak contribution of the electrostatic interactions. Moreover, the more acidic surface of the synthetic compound compared to that of the mineral one is assigned to the differences in crystallinity and chemical composition between the two solids. 相似文献