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81.
82.
The [C6H6O]+˙ ion from C6H5OC4H9 is structurally similar to the molecular ion from phenol as demonstrated by 13C labeling. 相似文献
83.
Carl Nordling 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1972,84(4):144-153
Eine Substanzprobe, auf die Röntgen-Strahlung einwirkt, emittiert Photo- und Auger-Elektronen. Die Energiespektren der emittierten Elektronen geben Informationen über die Elektronen-struktur in der Probe — und zwar von den innersten atomaren Niveaus und ihrer Abhängigkeit von der chemischen Umgebung bis hin zu den Molekülorbitalen der Valenzelektronen sowie der Bandstruktur bei Festkörpern. Solche Elektronenspektren können jetzt mit hochauflösenden Instrumenten registriert werden; ihre Analyse ergibt neue Aspekte für die Untersuchung der chemischen Bindung. Die zu diesem Zweck entwickelte und inzwischen zu einem hohen Grad von Vollkommenheit ausgebaute Methode der Elektronenspektroskopie wird im folgenden als ESCA (Electron Spectroscopy for Chemical Analysis) bezeichnet. 相似文献
84.
We show, for any operatorT from aC(K)-space into a Banach space with rank (T)≤n, the inequality
, whereC≤4.671 is a numerical constant. The factor (1+logn)1−1/p
is asymptotically correct. This inequality extends a result of Jameson top ≠ 2. Several applications are given — one is a positive solution of a conjecture of Rosenthal and Szarek: For 1≤p<q<2,
相似文献
85.
Carl Bender Fred Cooper L. M. Simmons Jr. Pinaki Roy Greg Kilcup 《Journal of statistical physics》1991,64(1-2):395-428
We discuss the randomly driven systemdx/dt= -W(x) +f(t), wheref(t) is a Gaussian random function or stirring force withf(t)f(t)=2(t–t), andW(x) is of the formgx
1+2. The parameter is a measure of the nonlinearity of the equation. We show how to obtain the correlation functionsx(t)f(t)···x(t(
n))
f
as a power series in. We obtain three terms in the expansion and show how to use Padé approximants to analytically continue the answer in the variable. By using scaling relations, we show how to get a uniform approximation to the equal-time correlation functions valid for allg and. 相似文献
86.
Congo red (CR) is an azo dye which not only preferentially binds to elastin, an extracellular matrix protein found in the media of arterial vessel walls, but also fluoresces when it binds to this protein. Protein solubilization data following laser irradiation of elastin:CR suspensions determined that the amount of elastin solubilized by laser irradiation increased with the increase in CR. The saturation point of CR to elastin was attained when 400 g CR was added to 20 mg elastin suspension. When 20 ml of a 5% CR solution in 5% dextrose was administered intravenously, the CR was absorbed in levels sufficient to produce fluorescence of the main arteries in rabbits. Layers of tissue both in the media of the vessels and at the endothelial/intimal interface were clearly differentiated. Therefore, the elastin:CR complex appears to be an ideal system in which the elastin fluorescence could aid in distinguishing between normal and diseased tissue in certain pathological conditions, such as atherosclerosis and some types of breast tumors. 相似文献
87.
The approximation order provided by a directed set {S
h
}
h>0 of spaces, each spanned by thehZ
d
-translates of one function, is analyzed. The nearoptimal approximants of [R2] from eachs
h
to the exponential functions are used to establish upper bounds on the approximation order. These approximants are also used on the Fourier transform domain to yield approximations for other smooth functions, and thereby provide lower bounds on the approximation order. As a special case, the classical Strang-Fix conditions are extended to bounded summable generating functions.The second part of the paper consists of a detailed account of various applications of these general results to spline and radial function theory. Emphasis is given to the case when the scale {s
h
} is obtained froms
1 by means other than dilation. This includes the derivation of spectral approximation orders associated with smooth positive definite generating functions. 相似文献
88.
Carl Mayer Clinton Ludlow Green Werner Trueb Peter Christian Wlchli Conrad Hans Eugster 《Helvetica chimica acta》1978,61(2):905-921
Degradation of palustrin to (?)-dihydropalustramic acid ((2R,6S,1′S)-[6-(1′-hydroxypropyl)-2-piperidyl]acetic acid), and the structure of palustrin and palustridin The structure of the macrocyclic alkaloid palustrin is shown to be 1a . Its piperidine unit can be obtained as (?)-dihydropalustramic acid ( 6a ) by the following sequence of degradation reactions (Scheme 1): catalytic hydrogenation of 1a followed by methylation and Hofmann degradation provides the allyl base 4 . the regioselectivity of the Hofmann elimination is explained by intramolecular proton abstraction at C(3) by C(18)-O?. Catalytic reduction of 4 and subsequent acidic hydrolysis yielded 6a and N, N-dimethylputrescine (?N,N-dimethyl-1,4-butanediamine; 7 ). Loss of the N-alkyl group in the formation of 6a occurs during the catalytic hydrogenation step. This interpretation is supported by the results of model experiments. The position of the double bond in 1a is deduced from the IR. spectrum of the bromo-δ-lactone 19 prepared by treatment of 1a with N-bromosuccinimide at pH 4 (Scheme 3). Some of our previously published results on the degradation of dihydropalustrin ( 2a ) are obviously at variance with the newly proposed structure for palustrin ( 1a ). They can easily be explained by assuming a partial hydrogenolysis of the C(17)-N(1) bond during the preparation of dihydropalustrin from palustrin. Periodate cleavage of dihydropalustramic acid methyl ester ( 6b ) liberates propionaldehyde, which can be trapped by working at pH 7.5 (Scheme 2); at lower pH values it condenses rapidly with the simultaneously generated 3,4,5,6-tetrahydropyridine derivative 15 . The structure of the condensation product is proposed to be 16 on the basis of the isolation of its hydrogenation product, an isomeric dihydropalustramic acid ( 17 ). 相似文献
89.
Carl Nordling 《Angewandte Chemie (International ed. in English)》1972,11(2):83-92
A substance on which X-rays fall emits photoelectrons and Auger electrons. The energy spectra of the electrons emitted provide information about the electronic structure in the specimen, ranging from the innermost atomic levels and their dependence on the chemical environment to the molecular orbitals of the valence electrons and the band structure in solids. Electron spectra of this nature can now be recorded with high-resolution instruments; their analysis offers new aspects for investigation of chemical composition. The method of electron spectroscopy developed for this purpose, which has now been developed to a high degree of perfection, will be referred to in the following discussion as ESCA (Electron Spectroscopy for Chemical Analysis). 相似文献
90.
Ab initio calculations using both pseudopotential and double and triple-ζ all-electron basis sets, with and without electron correlation (MP2, QCISD), have been performed on the λ4-sulfanyl (SH3), λ4-selanyl (SeH3), and λ4-tellanyl (TeH3) radicals. All-electron basis sets of double-ζ quality predict that SH3 and SeH3 correspond to transition states on their respective potential energy surfaces. In contrast, the pseudopotentials of Hay and Wadt predict that SH3 and SeH3 correspond to local minima at the QCISD level of theory while the pseudopotentials of Christiansen and Stevens predict transition states. By comparison, TeH3 proved to be a local minimum at all levels of theory. Interestingly, when a very large (triple-ζ) all-electron basis set was used, SH3 proved to be a transition state; however, in this instance the potential energy surface was found to be much flatter than in the case for which a double-ζ basis set was used, suggesting that further improvements in the basis set may lead to a local minimum. Further improvements in the all-electron selenium basis also led to a local minimum for SeH3 at the QCISD level of theory. © 1995 by John Wiley & Sons, Inc. 相似文献