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991.
In measuring acoustic field vector properties either complete or partial cancellation between ambient noise energy flux and the oppositely directed one, radiated, for instance, by tone or noise-shaped point source can be found. In that case there is no matter coherent or incoherent fields interact. The phenomenon of interest is named compensation of opposing energy fluxes. The paper is focused on interaction between vertical component of the surface noise energy flux and that of bottom-reflected noise-shaped interfering signal from on-water source in the deep open ocean. Bottom-reflected weak broadband interfering signal measures the extent of resultant compensation. As the vertical projection of the signal energy flux makes the interference maximum, its power appears to be comparable to that of the surface noise and complete compensation takes place at a given frequency. Once it is the interference minimum, just partial compensation can be found. No compensation was observed for co-directional energy fluxes. 相似文献
992.
A. V. Kucherov A. V. Ivanov T. N. Kucherova A. N. Shigapov 《Kinetics and Catalysis》2006,47(6):881-890
The surface of pure mesoporous SiO2 with an MCM-41 structure has been modified by introducing Al, Zr, or W ions (1 mmol/g). The original and modified materials have been loaded with Cu2+ ions. The distribution, properties, and thermal stability of different Cu2+ sites have been studied by EPR and IR spectroscopy. The resulting catalysts have been tested for activity in ethane oxidation. The modification of original MCM-41 exerts a very strong effect on the stability of isolated Cu2+ ions on the support surface. Among the modified supports, Al-MCM-41 affords the highest thermal stability and degree of dispersion (70–80%) of the copper-containing phase. There is no correlation between the total number of surface Cu2+ sites and the catalytic activity. The specific catalytic activity (per Cu2+ ion accessible to the reactants) depends strongly on the local structure of the sites. The isolated pentacoordinated Cu2+ sites stabilized by the Al-MCM-41 surface show a comparatively high activity in the sample calcined at 520°C. The heat treatment of Cu/Al-MCM-41 at 650–750°C reduces the specific activity of the catalytic sites by a factor of ~20 without sintering the copper phase, as in the case of CuHZSM-5 zeolite. The least dispersed copper phase, which is observed in the original MCM-41 and likely consists of aggregates of weakly interacting Cu2+ ions, exhibits the highest specific activity and thermal stability. In the case of Cu/W-MCM-41, heat treatment causes both the sintering of copper particles and a decrease in the specific activity of the surface Cu2+ ions. 相似文献
993.
É. I. Ivanov G. D. Kalayanov I. M. Yaroshchenko 《Chemistry of Heterocyclic Compounds》1992,28(7):795-797
Possible routes for synthesis of 2-haloimidazo[4,5-e][1,4]diazepines are discussed. Conditions for chlorination differ for homologs of caffeine, theophylline, and theobromine. For the caffeine homolog, both the 2-chloroand 2,6,6-trichloro products are obtained depending on the synthetic conditionsTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 955–958, July, 1992. 相似文献
994.
A. V. Rybina V. V. Efimov P. A. Alekseev I. O. Troyanchuk A. S. Ivanov V. V. Sikolenko E. S. Clementyev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(6):1140-1143
The lattice dynamics of lanthanum cobaltite is investigated using the coherent inelastic neutron scattering technique in a
temperature range from 10 to 536 K, in which two phase transitions are observed: a change in the Co spin state and a metal-insulator
phase transition. The measurements were performed using an IN8 high flux thermal neutron triple-axis spectrometer (ILL, Grenoble).
Temperature changes in the phonon dispersion curves caused by the rearrangement of the electron and spin subsystems are found. 相似文献
995.
The ground state phase diagram of a general isotropic spin-3/2 system with nearest-neighbor exchange is shown to contain unconventionally ordered spin nematic and antinematic states, as well as usual ferro- and antiferromagnetic phases. The two nematic phases have spontaneously broken rotational symmetry characterized by the long-range order of the nematic director u, as well as the broken time-reversal symmetry described by the pseudospin vector σ. Nematic phase differs from antinematic one by the type of ordering in σ vectors (uniform versus staggered). The ferromagnet-nematic and antiferromagnet-antinematic phase boundaries exhibit enhanced Sp(4) symmetry and correspond to the recently studied effective theory for spin-3/2 cold gases. We discuss optical properties and topological defects in the nematic phases. 相似文献
996.
We propose a simple approach for suppressing decoherence of a wave packet excited in an anharmonic oscillator. We show that when a resonant external field forces the oscillator to follow the driving force, motion around the resonant trajectory inside a stable resonant island can be made almost completely immune to the environment. As an example, we study suppression of decoherence due to coupling to thermally populated rotations in vibrational wave packets in a Na2 molecule. 相似文献
997.
998.
Yu. M. Volovenko V. V. Ivanov A. O. Pushechnikov 《Chemistry of Heterocyclic Compounds》2002,38(2):213-218
Bromination of 1-oxo(imino, amino)benzo[4,5]imidazo[1,2-a]pyridines gave the corresponding 2-bromo derivatives. Acylation using the Vilsmeier complex in acetic anhydride gave the N-formyl and N-acetyl derivatives. The reaction of the amine with the Vilsmeier complex, acetyl acetone, ethyl acetoacetate, and 2,5-dimethoxytetrahydrofuran occurs at the amino group. 相似文献
999.
Konstantin L. Ivanov Anna A. Kravtsova Elena A. Kirillova Mikhail Ya. Melnikov Ekaterina M. Budynina 《Tetrahedron letters》2019,60(30):1952-1955
A convenient synthetic strategy for the diastereoselective assembly of spiro[azepane-4,3′-oxindoles] was developed via a Staudinger/Michael/aza-Wittig/reduction/N-deprotection reaction sequence starting from PMB-protected oxindole-substituted ethylazides. The key step of the method is a domino self-catalytic Michael/aza-Wittig reaction wherein the phosphazene moiety acts first as the catalyst and then as the reactant, resulting in the formation of a seven-membered N-heterocycle. 相似文献
1000.
A new macroscopic quantum tunneling effect is predicted for a particle of an uncompensated ferritin-type antiferromagnet in
a noncollinear phase induced by a strong magnetic field.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 5, 369–374 (10 March 1999) 相似文献