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391.
R. -L. Vaara M. Kuzmin P. Laukkanen R. E. Perl I. J. Vyrynen 《Applied Surface Science》2003,220(1-4):327-334
The growth and properties of Eu-induced one-dimensional reconstructions on vicinal Si(1 1 1) surface miscut in the [
] direction have been studied by low energy electron diffraction and scanning tunneling microscope in the submonolayer range. The focus has been attended to the formation of single-domain structures and the influence of preparation parameters on the domain orientation. We have found the critical conditions for the preparation of a variety of Eu-induced single-domain (n×2) and (n×1) structures. In addition, a new intermediate phase showing the 9×1 periodicity between 3×2 and 2×1 phases is detected. 相似文献
392.
N. Mironova-Ulmane V. Skvortsova A. Kuzmin I. Sildos 《Physics of the Solid State》2002,44(8):1463-1467
The effect of chemical composition and temperature on exciton-magnon interactions in NicMg1?c O single crystals was studied using optical absorption spectra in the region of the magnetic-dipole 3 A 2g (G)→3 T 2g (F) and electric-dipole 3 A 2g (F)→1 E g (D) transitions. The two zero-phonon lines at ~7800 and ~7840 cm?1 on the low-energy side of the magnetic-dipole transition band were assigned to a pure exciton transition and an exciton-one-magnon transition at the center of the Brillouin zone. The intensity of the exciton-one-magnon peak decreases rapidly with increasing magnesium ion concentration and/or temperature, to vanish altogether at T=6 K for c<0.95 and at T=130 K for c≥0.99. Thus, the contribution of long-wavelength magnons in optical absorption spectra of NicMg1?c O becomes negligible at temperatures substantially lower than the Néel point T N (the antiferromagnetic ordering temperature). This observation can be explained as being due to a substantial decrease in the characteristic spin-spin interaction length with increasing concentration of the diamagnetic magnesium impurity ions (static disorder) and/or with increasing amplitude of thermal atomic vibrations (dynamic disorder). At the same time, the peak at ~14500 cm?1, which lies in the electric-dipole transition region and corresponds to excitation of an exciton and two magnons at the Brillouin zone edge, remains visible up to the Néel temperature. This is accounted for by the short-wavelength magnons being sensitive to short-range magnetic order, which persists up to T N . 相似文献
393.
Mechanism of Photoinduced Addition of Water and Methanol to the Double Bond of 1,2-Dihydroquinolines
The kinetics and mechanism of photoinduced addition of water and methanol to the double bond of 2,2,4-trimethyl-1,2-dihydroquinoline (DHQ) bearing different substituents in the 6- and 8-positions and N-methylated DHQ were studied by flash photolysis. The reaction affords corresponding Markovnikov adducts, 4-hydroxy- and 4-methoxy-1,2,3,4-tetrahydroquinolines. On the basis of time-resolved experiments and the measurement of quantum yields of the reaction in media of different acidities or basicities, a general scheme of the reaction is suggested, which involves the formation of two intermediate species. The principal rate constants, activation parameters, and their dependence on substituents were determined. 相似文献
394.
New a posteriori error indicators based on edgewise slope‐limiting are presented. The L2‐norm is employed to measure the error of the solution gradient in both global and element sense. A second‐order Newton–Cotes formula is utilized in order to decompose the local gradient error from a ??1 finite element solution into a sum of edge contributions. The slope values at edge midpoints are interpolated from the two adjacent vertices. Traditional techniques to recover (superconvergent) nodal gradient values from consistent finite element slopes are reviewed. The deficiencies of standard smoothing procedures—L2‐projection and the Zienkiewicz–Zhu patch recovery—as applied to nonsmooth solutions are illustrated for simple academic configurations. The recovered gradient values are corrected by applying a slope limiter edge‐by‐edge so as to satisfy geometric constraints. The direct computation of slopes at edge midpoints by means of limited averaging of adjacent gradient values is proposed as an inexpensive alternative. Numerical tests for various solution profiles in one and two space dimensions are presented to demonstrate the potential of this postprocessing procedure as an error indicator. Finally, it is used to perform adaptive mesh refinement for compressible inviscid flow simulations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
395.
Procedure for Studying the Steady-State Kinetics of Oxidation of Gaseous Substrates by Hydrogen Peroxide in a Liquid Phase 总被引:1,自引:0,他引:1
A procedure was developed for studying the steady-state kinetics of oxidation of various gaseous substrates by hydrogen peroxide under conditions of the continuous release of gaseous products. The steady state of a system was provided by continuously injecting hydrogen peroxide at low conversions of the oxidized substrate. The process was monitored by measuring substrate losses in a gas phase rather than the buildup of products. This allowed us to avoid difficulties associated with further oxidation of the products. 相似文献
396.
A. Kuzmin 《Shock Waves》2016,26(6):741-747
This work addresses two- and three-dimensional turbulent flow in simple channels, modeling the air intakes of rectangular cross section. Flow regimes with a supersonic free stream and supersonic velocities at the throat or immediately downstream of the throat are considered. Bifurcations of the shock wave arising ahead of the cowl are studied numerically. Solutions of the Reynolds-averaged Navier–Stokes equations are obtained with a finite-volume solver of second-order accuracy on fine computational meshes. The solutions reveal jumps of the shock leg position with variations of the free-stream Mach number. The dependence of the shock position on the cowl slope and streamwise location of the throat is examined. 相似文献
397.
R. G. Khlebopros V. E. Zakhvataev V. P. Slepkov M. I. Kuzmin 《Journal of Structural Chemistry》2016,57(2):417-421
Based on the hypothesis advanced by S. P. Gabuda that the SiO2 molecule could undergo a transition from the linear form to the isomeric form with a ring-shaped (bent) structure, an idea is proposed that when the mantle substance melts, a phase transition of the bent SiO2 form into the linear SiO2 form can occur in the lower mantle. This phase transition might be of great importance for the lower-mantle convection processes and also for the rise of mantle plumes carrying both heat energy, and broad range of platinum group and rare elements to the Earth surface. 相似文献
398.
K. M. Zinatullina O. T. Kasaikina V. A. Kuzmin N. P. Khrameeva B. I. Shapiro 《Russian Chemical Bulletin》2016,65(12):2825-2831
The interaction kinetics of the cationic and anionic polymethine dyes with radicals has been studied. Azoinitiator AAPH, as well as tert-butyl hydroperoxide, and hydrogen peroxide were used as radical initiators in water and buffer solutions at 37 °C. It is shown that the dyes are active scavengers of peroxyl radicals. It is found that reactivity and behavior of dyes in relation to the peroxides are strongly dependent on the structure of lateral substituents in polymethine chains. 相似文献
399.
Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF3SO2)2NR (R = CH2CH=CH2, Z/E-CH=CHMe, CH2C≡CH, CH=CH=CH2, C≡CCH2) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR1 (R1 = H, CF3SO2). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide. 相似文献
400.