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101.
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Nb-Au alloys near the composition Nb3Au can be quenched from the high temperature α solid solution phase field, retaining the b.c.c. structure. We report results on their superconducting, mechanical and physical properties as a function of composition. Short low temperature anneals transform these materials to the equilibrium A-15 structure with Tc up to 11K. We report results on the superconducting and physical properties of the transformed A-15 structure materials and describe how the properties of the transformed materials are affected by annealing temperature and time. 相似文献
105.
In urea and its structural analogues differences in excess of 100 ppm are found in the nitrogen screening constants for the amide- and isoamide-type structures. The nitrogen chemical shifts are interpreted within the framework of Pople's gauge dependent atomic orbital approximation using INDO molecular orbitals. It is demonstrated that this method provides reasonable values for nitrogen absolute screening constants. The experimental data reported should be useful in examinations of tautomeric equilibria in amides and related structures. 相似文献
106.
A. R. Webb B. G. Gardiner M. Blumthaler P. Forster M. Huber P. J. Krrsch 《Photochemistry and photobiology》1994,60(1):84-90
Abstract— Spectral measurements of the solar UV irradiance at the earth's surface depend critically on the characteristics of the spectroradiometers and the procedures used in their calibration. Two UV spectroradiometers were subjected to a series of laboratory tests to investigate which factors were most significant in limiting the reliability of the absolute irradiance measurements. Three independent standards of spectral irradiance were scanned by both instruments under a range of bench conditions. The results were consistent to within about 3%, most of the uncertainty being due to scattered light in the laboratory. An UV laser was used to determine the slit function of each spectrometer and the influence of internal stray light. Significant departures from the ideal cosine and azimuth responses were measured by a xenon lamp. Both spectroradiometers were kept indoors throughout the experiments. The relevance of these laboratory results is discussed with respect to the task of measuring solar UV radiation in the field. 相似文献
107.
The paper deals with the convergence of finite-difference approximations for a harmonic mixed boundary value problem. In particular the case when the boundary contains a slit is considered.Work on this paper was supported in part by NSF Grant GP-8442 and U.S. Army Grant DA-ARO(D)-31-124-G1050 at The University of Texas at Austin. 相似文献
108.
109.
S. G. Webb Major USAF J. C. Smith J. S. Turcotte Captain USAF E. Garcia 《Experimental Mechanics》1992,32(1):54-61
Local-velocity feedback (LVF) and linear-quadratic Gaussain (LQG) control schemes are implemented on passively tuned reaction
mass actuators to control the vibrations of a flexible structure. The structure is lightly damped and possesses closely coupled
low-frequency resonant modes. Both LVF and LQG controllers successfully eliminate the structure's vibrations. However, if
the passive tuning parameters of the actuators are slightly mistuned, implementing LVF control actually results in an unstable
system. On the other hand, LQG control proves to be insensitive to large changes in the passive tuning parameters of the actuators.
In fact, the system with LQG control is never unstable, no matter what the actuator's passive tuning parameters are. 相似文献
110.
L. Stefaniak I. Ando H. Yoshimizu J. Lipkowski G. A. Webb 《Journal of chemical crystallography》1991,21(1):51-55
A13C and15N CP MAS NMR study is reported for seven molecules and the results are compared with those previously obtained from solution NMR. The close agreement between the two sets of results show that the tautomeric equilibria found in solution and the solid state are the same for the compounds investigated. In all cases formA is found to be essentially the only one present. An X-ray diffraction study is presented for a molecule which is a model for formA. 相似文献