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71.
Waldemar Velte 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1962,13(6):591-600
Summary The linear fluid motion in a horizontal pipe heated from below is considered, when the temperature field outside the pipe is linear. By the method of small perturbations it is shown that the fluid motion becomes unstable for a critical value of the Rayleigh number, i.e., there is an additional convective motion, the streamlines of which are concentric curves in the plane of a cross-section of the pipe.
Die Untersuchung wurde vom Wirtschaftsministerium des Landes Baden-Württemberg gefördert. 相似文献
Die Untersuchung wurde vom Wirtschaftsministerium des Landes Baden-Württemberg gefördert. 相似文献
72.
Ohne Zusammenfassung 相似文献
73.
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75.
The acid-catalysed (HCl or SnCl4) reaction of alkyl 2,3 dideoxy-glyc-2-enopyranosides or 3,4,6-tri-O-acetyl-D-glycals with thiols leads to mixtures of alkyl 2,3-dideoxy-1-thio-glyc-2-enopyranosides and 3-S-alkyl-3-thioglycals. Under equilibrium conditions the latter are the preponderant products of the reaction. Cross experiments have confirmed the intermediacy of the allylic carbocation in the reaction. A rationalization of the substitution reactions of 1,2- and 2,3-unsaturated sugars based on HSAB principle has been proposed. 相似文献
76.
The convergence of the full perturbation theory expansion for the Fermi contact term in the spin-spin coupling constant of hydrogen fluoride has been studied. By examining the contribution of higher virtual states as the basis set is expanded to 18 atomic orbitals, it is shown that at this level of approximation the expansion does not converge. The need to also establish convergence before accepting values calculated from configuration interaction wavefunctions is discussed.The Puerto Rico Nuclear Center is operated by the University of Puerto Rico for the United States Atomic Energy Commission under Contract No. AT(40-1)-1833. 相似文献
77.
Abstract— The kinetics and the direct, the 9,10-dibromo- (DBA) and the 9,10-diphenylanthracene- (DPA) enhanced chemiluminescence of tert-butyl α-peroxylactone 1, with and without α-deuteration, was investigated in order to probe the mechanism of direct chemiexcitation by these hyperenergetic molecules. The small secondary isotope effect on the rates and activation parameters suggests that a diradical mechanism is obtained. The partitioning of the diradical intermediate into excited vs ground state product and the yield of triplet excited product are moderately (ca. 5-fold) increased by α-deuteration, but the singlet yield is unaffected. A convenient and useful chemiluminescence method for the determination of fluorescence quantum yields has been developed. 相似文献
78.
Ruikson S.O. Nunes Waldemar D. Bastos João Manoel S. Pitot 《Mathematical Methods in the Applied Sciences》2020,43(3):1230-1242
In the present paper, we study energy decay and exact boundary controllability for a system of n one-dimensional linear wave equations coupled in parallel. The control obtained is a square integrable of the Neuman type for initial data with finite energy. The controllability time is near optimal value. We treat the case of control in the whole boundary and also in part of it. 相似文献
79.
The primary objective of this study was to explore nonlinear characteristics, if any, of the surface myoelectrical (EMG) activity of the biceps muscle during simulated maximum voluntary contraction at a reference arm posture (MVCRP), and at an elevated static arm work posture (EAWP) observed on the manufacturing assembly line. The results showed that positive Lyapunov exponents existed for each of the trials in both work postures. The statistical test of significance showed that surface EMG of the biceps brachii was more chaotic under the MVCRP condition as compared to the EWAP condition. Based on the Kaplan-Yorke dimension, it was observed that the recorded two types of time series EMG data were similar in complexity. The study also found a significant difference in fractal dimensions between the two postures. It was concluded that the nonlinear dynamical EMG properties expressed in terms of the Lyapunov exponents, Kaplan-Yorke dimension, and fractal dimensions could be used as sensitive indices for evaluation of the level of muscular efforts under static work conditions. 相似文献
80.
We show that the supremum norm of solutions with small initial data of the generalized Benjamin-Bona-Mahony equation ut-△ut=(b,▽u)+up(a,▽u)in x?Rn,n≥2, with integer p≥3 , decays to zero like t-2/3 if n=2 and like t-1+6, for any δ0, if n≥3, when t tends to infinity. The proofs of these results are based on an analysis of the linear equation ut-△=(b,▽u)) and the associated oscillatory integral which may have nonisolated stationary points of the phase function. 相似文献