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71.
Motivated by the need for a theoretical study in a planar geometry that can easily be implemented experimentally, we study the pressure driven Poiseuille flow of a shear banding fluid. After discussing the “basic states” predicted by a one-dimensional calculation that assumes a flat interface between the bands, we proceed to demonstrate such an interface to be unstable with respect to the growth of undulations along it. We give results for the growth rate and wavevector of the most unstable mode that grows initially, as well as for the ultimate flow patterns to which the instability leads. We discuss the relevance of our predictions to the present state of the experimental literature concerning interfacial instabilities of shear banded flows, in both conventional rheometers and microfluidic channels. 相似文献
72.
Yin Ning Lee A. Fielding John Nutter Alexander N. Kulak Fiona C. Meldrum Steven P. Armes 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4346-4351
In principle, incorporating nanoparticles into growing crystals offers an attractive and highly convenient route for the production of a wide range of novel nanocomposites. Herein we describe an efficient aqueous route that enables the spatially controlled occlusion of gold nanoparticles (AuNPs) within ZnO crystals at up to 20 % by mass. Depending on the precise synthesis protocol, these AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. Remarkably, such efficient occlusion is mediated by a non‐ionic water‐soluble polymer, poly(glycerol monomethacrylate)70 (G70), which is chemically grafted to the AuNPs; pendent cis‐diol side groups on this steric stabilizer bind Zn2+ cations, which promotes nanoparticle interaction with the growing ZnO crystals. Finally, uniform occlusion of G70‐AuNPs within this inorganic host leads to faster UV‐induced photodegradation of a model dye. 相似文献
73.
An intuitive scheme for controlling the rotational quantum state of a Rydberg molecule is demonstrated experimentally. We determine the accumulated phase difference between the various components of a molecular electron wave packet, and then employ a sequence of phase-locked optical pulses to selectively enhance or depopulate specific rotational states. The angular momentum composition of the resulting wave packet, and the efficiency of the control scheme, is determined by calculating the multipulse response of the time-dependent Rydberg populations. 相似文献
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75.
H.W. Fielding R.E. Anderson P.D. Kunz D.A. Lind C.D. Zafiratos W.P. Alford 《Nuclear Physics A》1978,304(2):520-532
The (3He, n) reaction has been studied on112,116,118,120,124Sn at 25.4 MeV. Angular distributions were measured over the range 0°–25° and the results compared with predictions of zero-range DWBA calculations. In addition to the around-state transitions, L = 0 transitions were also observed to low-lying states in every case. Simple two component wave functions, as well as those obtained from a more sophisticated pairing model, are compared with the data in order to explain the appearance of the anomalously low-lying excited 0+ states observed. L = 2 transitions were observed to low-lying 2+ states, but the strength of these transitions was much less than expected from the systematics of (t, p) results for N = 50 nuclei. 相似文献
76.
THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE 总被引:1,自引:0,他引:1
In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT50 (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT50, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT50, Escape from photoreversibility did not occur at 27°C in seeds in which the GT50 had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action. 相似文献
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79.
This critical review is intended to provide an overview of the state-of-the-art in femtosecond laser technology and recent applications in ultrafast gas phase chemical dynamics. Although "femtochemistry" is not a new subject, there have been some tremendous advances in experimental techniques during the last few years. Time-resolved photoelectron spectroscopy and ultrafast electron diffraction have enabled us to observe molecular dynamics through a wider window. Attosecond laser sources, which have so far only been exploited in atomic physics, have the potential to probe chemical dynamics on an even faster timescale and observe the motions of electrons. Huge progress in pulse shaping and pulse characterisation methodology is paving the way for exciting new advances in the field of coherent control. 相似文献
80.
The solution-state NMR spectra of a per-6-substituted gamma-cyclodextrin show some interesting dynamic properties. At high temperature (353 K), the (1)H NMR spectrum shows dynamic averaging of the different conformations. This averaging is no longer observed on cooling of the cyclodextrin solution to 278 K, resulting in NMR spectra with a large (1)H and (13)C chemical shift dispersion. The complete assignment of the eight unique glucosyl residues was achieved using COSY, HSQC and exchange spectroscopy. A ROESY spectrum, with a short mixing time to reduce the effects of exchange, gives correlations that lead to the determination of the connectivity of all eight glucosyl residues. On the NMR time-scale, the cyclodextrin is highly dynamic; the lower temperature minimum energy conformation has one of the aromatic rings self-complexed and a distorted cyclodextrin torus. 相似文献