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81.
82.
Joseph G. Cannon Teresa Lee James A. Beres H. Duane Goldman 《Journal of heterocyclic chemistry》1980,17(7):1633-1636
A synthetic sequence leading to the title compounds began with methyl 5,6-dimethoxy-2-tetralone-3-carboxylate and involved a multi-step construction of the heterocyclic ring. The trans-fused isomer was isolated from the cyclization step. However, the possibility of formation of some cis-fused isomer cannot be precluded. 相似文献
83.
A new laser approach for the isotopically selective analysis of noble gases is presented. This approach uses noble gas atoms prepared in the 1s
5 metastable state. Hyperfine levels in the 1s
5 and 2p
9 states form two-level systems in Ne, Ar, Kr, and Xe which can be excited by a commercially available single-frequency laser system. Absorption of photons from such a laser, and the resulting momentum transfer, can be used to selectively deflect the desired isotope from a supersonic atomic beam into a detection area. Light from the same laser can then be used to selectively count atoms of the desired isotope using the photon-burst technique. Thus, enrichment and selective detection are accomplished with a single laser in a single pass through the apparatus.The problem of analyzing for85Kr in a sample of noble gases extracted from the air is examined in detail. This is a stringent test of the selectivity of this approach because85Kr has the same nuclear spin, and thus similar hyperfine splittings, as naturally occurring83Kr. Calculations indicate that isotopic selectivity of the new approach is easily adequate to resolve85Kr in a 1010 excess of83Kr. 相似文献
84.
John R. Cannon Hong-Ming Yin 《Numerical Methods for Partial Differential Equations》1990,6(2):177-191
In this article we transform a large class of parabolic inverse problems into a nonclassical parabolic equation whose coefficients consist of trace type functionals of the solution and its derivatives subject to some initial and boundary conditions. For this nonclassical problem, we introduce a variational form by defining a new function. Both continuous and discrete Galerkin procedures are illustrated in this paper. The error estimates are also derived. 相似文献
85.
K. Vajravelu J.R. Cannon J. Leto R. Semmoum S. Nathan M. Draper D. Hammock 《Journal of Mathematical Analysis and Applications》2003,277(2):609-623
Solutions for a class of coupled nonlinear differential equations, arising in free convection flow at a vertical flat plate embedded in a saturated porous medium at high Reynolds numbers in the presence of heat sources (or sinks) and with nonlinear density temperature variation, are obtained. Further, using the Schauder theory and numerical results, existence and analyticity results are established. 相似文献
86.
For a hyperbolic once-punctured-torus bundle over a circle, a choice of normalization determines a family of arcs in the Riemann sphere. We show that, in each arc in the family, the set of cusps is dense and forms a single orbit of a finitely generated semigroup of Möbius transformations. This was previously known for the case of the complement of the figure-eight knot. 相似文献
87.
B. D. Cannon T. J. Whitaker G. K. Gerke B. A. Bushaw 《Applied physics. B, Lasers and optics》1988,47(2):201-206
We have investigated several effects of optical pumping in the hyperfine spectrum of the6s6p
1
P
16s
2
1
S
0 transition in137Ba. Most of these effects are explained by absorption strength changes which occur because of redistribution of population among magnetic substates. At very low laser intensities, no redistribution effects are observed. At higher intensities, it is possible to either empty the magnetic substates that are accessible to optical excitation, or to redistribute the population among these states until a steady-state condition is achieved. The first case results in the familiar disappearance of a hyperfine line. The less familiar second case can result in peak-height ratios in the Ba1
P
11
S
0 hyperfine spectrum that differ by almost a factor of three from the low-intensity case. In this second case, the observed linewidth can either broaden or narrow, depending on whether redistribution decreases or increases absorption strength. At high intensities, saturation effects dominate and branching to intermediateD states becomes apparent. We report here the result of a numerically integrated rate equation model which shows good agreement with our experiments. 相似文献
88.
J.W. Foulk III R.M. Cannon G.C. Johnson R.O. Ritchie 《Journal of the mechanics and physics of solids》2007,55(4):719-743
A micromechanical model is developed for grain bridging in monolithic ceramics. Specifically, bridge formation of a single, non-equiaxed grain spanning adjacent grains is addressed. A cohesive zone framework enables crack initiation and propagation along grain boundaries. The evolution of the bridge is investigated through a variance in both grain angle and aspect ratio. We propose that the bridging process can be partitioned into five distinct regimes of resistance: propagate, kink, arrest, stall, and bridge. Although crack propagation and kinking are well understood, crack arrest and subsequent “stall” have been largely overlooked. Resistance during the stall regime exposes large volumes of microstructure to stresses well in excess of the grain boundary strength. Bridging can occur through continued propagation or reinitiation ahead of the stalled crack tip. The driving force required to reinitiate is substantially greater than the driving force required to kink. In addition, the critical driving force to reinitiate is sensitive to grain aspect ratio but relatively insensitive to grain angle. The marked increase in crack resistance occurs prior to bridge formation and provides an interpretation for the rapidly rising resistance curves which govern the strength of many brittle materials at realistically small flaw sizes. 相似文献
89.
Chunhui Huang Cannon B. Wille Huaibing He Vijay Bhasker Gangula Reddy Ravi P. Nargund Songnian Lin Anandan Palani 《Tetrahedron letters》2017,58(12):1219-1222
The late-stage modification of native peptides to alter and/or enhance their properties and functions is attractive but formidably challenging. Peptide lipidation is one of the effective strategies to overcome short half-life and rapid clearance. Herein, we report a late-stage installation of a fatty acid lipid onto fully elaborated peptides, using glucagon as an example, through regio- and chemoselective functionalization of tryptophan with high potency and remarkable in vivo half-life extension. 相似文献
90.
[reaction: see text] A new halo-Mannich-type reaction is reported using cyclopropyl carbonyl-derived enolates and sulfonyl-protected imines. Chiral oxazolidinones auxiliaries were found to be effective for completely controlling the stereochemistry of the products. Variations in the oxazolidinone, protecting group, and imine components show this to be a quite general reaction. The initial iodo-Mannich products were found to be readily cyclized in the presence of triethylamine to afford the resulting protected pyrrolidines, which could be readily deprotected under standard conditions. 相似文献