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221.
This paper considers the scattering of a plane, time-harmonic wave by an inclusion with heterogeneous nonlinear elastic properties embedded in an otherwise homogeneous linear elastic solid. When the inclusion and the surrounding matrix are both isotropic, the scattered second harmonic fields are obtained in terms of the Green's function of the surrounding medium. It is found that the second harmonic fields depend on two independent acoustic nonlinearity parameters related to the third order elastic constants. Solutions are also obtained when these two acoustic nonlinearity parameters are given as spatially random functions. An inverse procedure is developed to obtain the statistics of these two random functions from the measured forward and backscattered second harmonic fields. 相似文献
222.
An improved visualization-based force-measurement technique for short-duration hypersonic facilities 总被引:2,自引:0,他引:2
This article is concerned with describing and exploring the limitations of an improved version of a recently proposed visualization-based
technique for the measurement of forces and moments in short-duration hypersonic wind tunnels. The technique is based on tracking
the motion of a free-flying body over a sequence of high-speed visualizations; while this idea is not new in itself, the use
of high-speed digital cinematography combined with a highly accurate least-squares tracking algorithm allows improved results
over what have been previously possible with such techniques. The technique precision is estimated through the analysis of
artificially constructed and experimental test images, and the resulting error in acceleration measurements is characterized.
For wind-tunnel scale models, position measurements to within a few microns are shown to be readily attainable. Image data
from two previous experimental studies in the T5 hypervelocity shock tunnel are then reanalyzed with the improved technique:
the uncertainty in the mean drag acceleration is shown to be reduced to the order of the flow unsteadiness, 2–3%, and time-resolved
acceleration measurements are also shown to be possible. The response time of the technique for the configurations studied
is estimated to be ∼0.5 ms. Comparisons with computations using the DLR TAU code also yield agreement to within the overall
experimental uncertainty. Measurement of the pitching moment for blunt geometries still appears challenging, however. 相似文献
223.
Laurence Leherte 《Journal of mathematical chemistry》2001,29(1):47-83
Three different methods are applied to generate low resolution molecular electron density (ED) distribution functions: a crystallography-based formalism, an analytical approach which allows the calculation of a promolecular ED distribution in terms of a weighted summation over atomic ED distributions, and a wavelet-based multiresolution analysis approach. Critical point graph representations of the molecular ED distributions are then generated by locating points where the gradient of the density is equal to zero, and further considered for pairwise molecular superpositions of thrombin inhibitors using a Monte Carlo/Simulated Annealing technique. 相似文献
224.
225.
Laurence Charles Christophe Chendo Salom Poyer 《Rapid communications in mass spectrometry : RCM》2020,34(Z2)
This review covers applications of ion mobility spectrometry (IMS) hyphenated to mass spectrometry (MS) in the field of synthetic polymers. MS has become an essential technique in polymer science, but increasingly complex samples produced to provide desirable macroscopic properties of high‐performance materials often require separation of species prior to their mass analysis. Similar to liquid chromatography, the IMS dimension introduces shape selectivity but enables separation at a much faster rate (milliseconds vs minutes). As a post‐ionization technique, IMS can be hyphenated to MS to perform a double separation dimension of gas‐phase ions, first as a function on their mobility (determined by their charge state and collision cross section, CCS), then as a function of their m/z ratio. Implemented with a variety of ionization techniques, such coupling permits the spectral complexity to be reduced, to enhance the dynamic range of detection, or to achieve separation of isobaric ions prior to their activation in MS/MS experiments. Coupling IMS to MS also provides valuable information regarding the 3D structure of polymer ions in the gas phase and regarding how to address the question of how charges are distributed within the structure. Moreover, the ability of IMS to separate multiply charged species generated by electrospray ionization yields typical IMS‐MS 2D maps that permit the conformational dynamics of synthetic polymer chains to be described as a function of their length. 相似文献
226.
227.
Michel Franck-Neumann Michel Miesch Alain Cott Laurence Gross Bernard Metz 《Tetrahedron: Asymmetry》1993,4(12):2475-2482
The resolution of the cyclobutenic ester 1 using chiral lactols is described. After a stereospecific reaction sequence (cyclopropanation followed by an acidic solvolysis), the enantiomerically pure diquinanes 10 are obtained. 相似文献
228.
Highly enantioenriched equivalents of cyclic dienes have been readily prepared by asymmetric allylation of unsaturated aldehydes using a chiral allyltitanium reagent, followed by a ring-closing metathesis. The resulting β-hydroxy allylsilanes react stereoselectively with a wide variety of electrophilic reagents. 相似文献
229.