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201.
Zizak Giorgio Cignoli Francesco Benecchi Sergio 《Applied physics. B, Lasers and optics》1990,50(1):67-70
In order to obtain OH concentration measurements in atmospheric pressure flames from saturated fluorescence signal, we have developed a stationary four-level model. A general relationship between the measured upper state population and the total number density has been derived. The effects of the imbalance between the rotational transfer rates in the upper and ground states is analyzed. We show that in the case of comparable rotational rates, the results of our treatment are similar to the ones obtained with the balanced cross rate model. A set of complementary data which should facilitate absolute OH concentration measurements is also pointed out. 相似文献
202.
Daniele Passarella Sergio Riva Gabriele Grieco Francesco Cavallo Begoña Checa Federica Arioli Elena Riva Daniela Comi Bruno Danieli 《Tetrahedron: Asymmetry》2009,20(2):192-197
The convenient synthesis of both enantiomers of the piperidine alkaloids such as dumetorine and epidihydropinidine is described. Pure enantiomers of 2-(2-hydroxy-ethyl)-piperidine-1-carboxylic acid tert-butyl ester are used as a common starting material. The syntheses are based on a RCM reaction and on methylation of the piperidine ring according to Beak–Lee methodology, respectively. 相似文献
203.
The palladium-catalyzed arylation of aryl bromides can be carried out in the presence of bidentate phosphines, such as dppm, dppe, dppf, and Xantphos under mild conditions. The experimental results and the DFT calculations fully support for this reaction a mechanism proceeding by an intermolecular proton abstraction. 相似文献
204.
205.
In this paper we will generalize the representation theory developed for finite Tarski algebras given in [7]. We will introduce
the notion of Tarski space as a generalization of the notion of dense Tarski set, and we will prove that the category of Tarski
algebras with semi-homomorphisms is dually equivalent to the category of Tarski spaces with certain closed relations, called
T-relations. By these results we will obtain that the algebraic category of Tarski algebras is dually equivalent to the category
of Tarski spaces with certain partial functions. We will apply these results to give a topological characterization of the
subalgebras.
Received August 21, 2005; accepted in final form December 5, 2006. 相似文献
206.
207.
208.
J. Betzabe Gonzlez‐campos Evgen Prokhorov Gabriel Luna‐Brcenas A. Mendoza Galvn Isaac C. Sanchez Sergio M. Nuo Donlucas B. Garcia‐Gaitan Yuriy Kovalenko 《Journal of Polymer Science.Polymer Physics》2009,47(9):932-943
Relaxations in chitin have been investigated in the temperature range 298–523 K using impedance spectroscopy in the frequency range 10−1–108 Hz. The objective was to detect a glass‐transition temperature for this naturally occurring, semicrystalline polysaccharide. The impedance study was complemented with X‐ray diffraction, thermogravimetric, and differential scanning calorimetry measurements. Preliminary impedance data treatment includes the subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content for further analysis. When all these aspects are taken into account, two relaxations are clearly revealed in the impedance data. For the first time, evidence is presented for a relaxation process, which exhibits a non‐Arrhenius temperature dependence, in dry α‐chitin (∼0.1% moisture content), and likely represents the primary α‐relaxation. This evidence suggests a glass transition temperature for chitin of 335 ± 10 K estimated on the basis of the temperature dependence of the conductivity and of the relaxation time. A second relaxation in dry α‐chitin, not previously reported in the literature, is observed from 353 K to the onset of thermal degradation (∼483 K) and is identified as the σ‐relaxation often associated with proton mobility. It exhibits a normal Arrhenius‐type temperature dependence with activation energy of 113 ± 3 kJ/mol. The latter has not been previously reported in the literature. A high frequency secondary β‐relaxation is also observed with Arrhenius activation energy of 45 ± 1 kJ/mol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 932–943, 2009 相似文献
209.
Sergio Alvarez-Andrade N. Balakrishnan Laurent Bordes 《Annals of the Institute of Statistical Mathematics》2009,61(4):887-903
This paper proposes an inferential method for the semiparametric proportional hazards model for progressively Type-II censored
data. We establish martingale properties of counting processes based on progressively Type-II censored data that allow to
derive the asymptotic behavior of estimators of the regression parameter, the conditional cumulative hazard rate functions,
and the conditional reliability functions. A Monte Carlo study and an example are provided to illustrate the behavior of our
estimators and to compare progressive Type-II censoring sampling plans with classical Type-II right censoring sampling plan. 相似文献
210.
Luis G.G.V. Dias da Silva Sergio E. Ulloa Tigran V. Shahbazyan 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):37
We study the interplay between impurity scattering and Coulomb interaction effects in the absorption spectrum of neutral bound magnetoexcitons confined in quantum-ring structures. Impurity scattering breaks the rotational symmetry of the ring system, introducing characteristic features in the optical emission. Signatures of the optical Aharonov–Bohm effect are still present for weak scattering and strong Coulomb screening. Furthermore, an impurity-induced modulation of the absorption strength is present even for a strong impurity potential and low screening. This behavior is likely responsible of recent experimental observations in quantum-ring structures. 相似文献