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61.
Sporolides A and B: structurally unprecedented halogenated macrolides from the marine actinomycete Salinispora tropica 总被引:4,自引:0,他引:4
Buchanan GO Williams PG Feling RH Kauffman CA Jensen PR Fenical W 《Organic letters》2005,7(13):2731-2734
[structure: see text] Analysis of the fermentation broth of a strain of the marine actinomycete Salinispora tropica has led to the isolation of two unprecedented macrolides, sporolides A (1) and B (2). The structures and absolute stereochemistries of both metabolites were elucidated using a combination of NMR spectroscopy and X-ray crystallography. 相似文献
62.
[reaction: see text] The expedient synthesis of a library of kanamycin B analogues is reported. The revealed SAR will guide future designs in developing kanamycin-type aminoglycoside antibiotics against drug-resistant bacteria. 相似文献
63.
1,10-Phenanthroline is derivatized and ultimately immobilized on two different polystyrene/divinylbenzene solid supports using convenient methodology. All syntheses are amenable to semiautomatic processing and are scalable for high-throughput screening. A domino copper-catalyzed coupling-cyclization reaction is used to illustrate applicability in catalytic studies. 相似文献
64.
Greg Friedman 《Proceedings of the American Mathematical Society》2004,132(10):3103-3109
Frame-spun knots are constructed by spinning a knot of lower dimension about a framed submanifold of . We show that all frame-spun knots are slice (null-cobordant).
65.
We report the realization of a nuclear magnetic resonance computer with three quantum bits that simulates an adiabatic quantum optimization algorithm. Adiabatic quantum algorithms offer new insight into how quantum resources can be used to solve hard problems. This experiment uses a particularly well-suited three quantum bit molecule and was made possible by introducing a technique that encodes general instances of the given optimization problem into an easily applicable Hamiltonian. Our results indicate an optimal run time of the adiabatic algorithm that agrees well with the prediction of a simple decoherence model. 相似文献
66.
We introduce a new class of foldable oligomers consisting of alternating rigid and flexible regions. The rigid segments overlap to give pi-stacked folded conformers whose formation is driven mostly by pi-pi molecular orbital overlaps. As the oligomer concentration increases, the folded molecular structures further self-assemble into larger nanostructures. The dynamic processes of folding and self-organization are monitored with absorption, fluorescence, and NMR spectroscopies. Our results show that folding dominates at low concentrations (< approximately 1 mM) and precedes self-assembly, which occurs over the initial concentration range of approximately 1-100 mM. 相似文献
67.
Greg W. Anderson 《Israel Journal of Mathematics》2003,138(1):139-156
Forx ∈ ℝ
n
andp≥1 put ‖x‖
p
:=(n
−1Σ|x
i|
p
)1/p
. An orthogonal direct sum decomposition ℝ2k
=E⊕E
⊥ where dimE=k and
‖x‖2/‖x‖1≤C is called here a (k, C)-splitting. By a theorem of Kašin there existsC>0 such that (k, C)-splittings exist for allk, and by the volume ratio method of Szarek one can takeC=32eπ. All proofs of existence of (k, C)-splittings heretofore given are nonconstructive.
Here we investigate the representation of (k, C)-splittings by matrices with integral entries. For everyC>8e
1/2
π
−1/2 and positive integerk we specify a positive integerN(k, C) such that in the set ofk by 2k matrices with integral entries of absolute value not exceedingN(k, C) there exists a matrix with row span a summand in a (k, C)-splitting. We haveN(k, C)≤218k
fork large enough depending onC. We explain in detail how to test a matrix for the property of representing a (k, C)-splitting. Taken together our results yield an explicit (if impractical) construction of (k, C)-splittings. 相似文献
68.
Greg Kuperberg 《Proceedings of the American Mathematical Society》2003,131(12):3893-3899
Filliman duality expresses (the characteristic measure of) a convex polytope containing the origin as an alternating sum of simplices that share supporting hyperplanes with . The terms in the alternating sum are given by a triangulation of the polar body . The duality can lead to useful formulas for the volume of . A limiting case called Lawrence's algorithm can be used to compute the Fourier transform of .
In this note we extend Filliman duality to an involution on the space of polytopal measures on a finite-dimensional vector space, excluding polytopes that have a supporting hyperplane coplanar with the origin. As a special case, if is a convex polytope containing the origin, any realization of as a linear combination of simplices leads to a dual realization of .
69.
A. Verçin 《International Journal of Theoretical Physics》2000,39(8):2063-2077
By making use of the Weyl–Wigner–Groenewold–Moyalassociation rules, acommutative product and a new quantum bracket are constructed in the spaceof operators F(H). In this way, an isomorphism between the Lie algebra ofclassical observables (with Poisson bracket) and the Lie algebra of quantumobservables with this new bracket is established. By these observations, aformulation of classical mechanics in F(H) is obtained and is shown to be the 0 limit of the Heisenberg-picture formulation of quantum mechanics. 相似文献
70.