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221.
We extend a recently formulated coherence spectroscopy of dissipative media [J. Chem. Phys. 122, 084502 (2005)] from the stationary excitation limit to the time domain. Our results are based on analytical and numerical solutions of the quantum Liouville equation within the Bloch framework. It is shown that the short pulse introduces a new, controllable time scale that allows better insight into the relation between the coherence signal and the phase properties of the material system. We point to the relation between the time-domain coherence spectroscopy and the method of interferometric two-photon photoemission spectroscopy, and propose a variant of the latter method, where the two time-delayed excitation pathways are distinguishable, rather than identical. In particular, we show that distinguishability of the two excitation pathways introduces the new possibility of disentangling decoherence from population relaxation. 相似文献
222.
Tamar Ziegler 《Journal d'Analyse Mathématique》2006,99(1):249-266
We use ergodic theoretic tools to solve a classical problem in geometric Ramsey theory. LetE be a measurable subset of ℝ
m
, with
. LetV = {0,v
1,...,v
k} ⊂ ℝm. We show that fort large enough, we can find an isometric copy oftV arbitrarily close toE. This is a generalization of a theorem of Furstenberg, Katznelson and Weiss [FuKaW] showing a similar property form=k=2. 相似文献
223.
We establish the inverse conjecture for the Gowers norm over finite fields, which asserts (roughly speaking) that if a bounded function
f : V ? \mathbbC{f : V \rightarrow \mathbb{C}} on a finite-dimensional vector space V over a finite field
\mathbbF{\mathbb{F}} has large Gowers uniformity norm ||f||Us+1(V){{\parallel{f}\parallel_{U^{s+1}(V)}}} , then there exists a (non-classical) polynomial
P: V ? \mathbbT{P: V \rightarrow \mathbb{T}} of degree at most s such that f correlates with the phase e(P) = e
2πiP
. This conjecture had already been established in the “high characteristic case”, when the characteristic of
\mathbbF{\mathbb{F}} is at least as large as s. Our proof relies on the weak form of the inverse conjecture established earlier by the authors and Bergelson [3], together with new results on the structure and equidistribution of non-classical polynomials, in the spirit of the work
of Green and the first author [22] and of Kaufman and Lovett [28]. 相似文献
224.
Gideon Fleminger Beka Solomon Tamar Wolf Eran Hadas 《Applied biochemistry and biotechnology》1990,26(3):231-238
A single step periodate oxidative binding of glycoproteins to synthetic polymeric matrices is proposed. By this procedure,
the glycoprotein to be immobilized is simultaneously mixed with sodium periodate and a hydrazide-containing matrix. The carbohydrate
moieties of the protein are oxidized and react with matrix. The single step reaction is faster than the commonly-used multistep
procedure and it allows conjugation of minute amounts of glycoproteins to the matrix. 相似文献
225.
The 13C-NMR spectra of the alkaloid ajmaline () and its stereoisomers isoajmaline (), sandwichine () and isosandwichine () are reported. The different stereochemistry at C (17), C(20) and C(21) of the four isomers can be directly ascertained by chemical shifts data. 相似文献
226.
We develop an efficient technique for computing free energies corresponding to conformational transitions in complex systems by combining a Monte Carlo ensemble of trajectories generated by the shooting algorithm with umbrella sampling. Motivated by the transition path sampling method, our scheme "BOLAS" (named after a cowboy's lasso) preserves microscopic reversibility and leads to the correct equilibrium distribution. This makes possible computation of free energy profiles along complex reaction coordinates for biomolecular systems with a lower systematic error compared to traditional, force-biased umbrella sampling protocols. We demonstrate the validity of BOLAS for a bistable potential, and illustrate the method's scope with an application to the sugar repuckering transition in a solvated deoxyadenosine molecule. 相似文献
227.
A new chiral derivatizing agent for ee determination of 1,2-diols via (1)H NMR is described. (S)-(+)-N-acetylphenylglycineboronic acid (1) is synthesized in enantiomerically pure form; its reaction with chiral diols quantitatively yields cyclic boronic esters 5a-g. The latter show a remarkably high diastereodifferentiation of proton NMR signals useful for de determination. [reaction: see text] 相似文献
228.
The remote control of lipase PS site- and regioselectivity by substrate modification has been observed in the acetylation of stevioside (1) and steviolbioside (2): deglucosylation at position C-19 changed the acylation site of the sophorose moiety linked at C-13. In fact, while esterification of 1 gave mainly the corresponding 6″-O-acetylated derivative, acylation of 2 gave exclusively the 6′-O-monoester. A possible rationale has been suggested, based on the conformational behavior of the substrates in different simulated solvents. 相似文献
229.
Salvatore Sorriso Alfredo Ricci Roberto Danieli 《Journal of organometallic chemistry》1975,87(1):61-65
The electric dipole moments of the two series of molecules (CH3)3MX with M C, Si, Ge, Sn and Pb, and X Cl and Br have been determined. The two carbon compounds show behaviour different from that of the others, and this is interpreted as indicating that pX → dM back-bonding is present for the other elements of the series, and it is suggested that the extent of this back-bonding decreases with an increase in the atomic number of M. 相似文献
230.
Luigi Canonica Bruno Danieli Giordano Lesma Giovanni Palmisano Angelo Mugnoli 《Helvetica chimica acta》1987,70(3):701-716
Some steroidal analogues embodying the hitherto unknown 13(14→8)-abeo skeleton have been synthesized by Fe(II)-induced rearrangement (tandem β-fission/reductive alkylation) of 14α-hydroperoxy-7-en-6-ones. The configurational assignment was made by thorough analysis of NMR spectra; the structure of one of the products was unambiguously assessed by X-ray single-crystal analysis. 相似文献