Aeroelastic self-oscillations of gas seal wall

The channel with a moving wall is considered to describe aeroelastic oscillations induced by gas flow. One of the channel walls has two degrees of freedom and it is supported by springs and dampers. The multi-fields investigation method is based on simulation transient gas flow in the channel to calculate aerodynamic forces acting on the wall. Corresponding rigidity and damping gas flow parameters obtained from these loads are included into the wall oscillations model for the stability analysis. The models are developed for two channel types: with smooth and finned wall. Aeroelastic stability boundary is shown for both channels. An effect of structural parameters on the realization of convergent oscillation and self-oscillation modes is shown too. A paradox of system destabilization with the increasing damping is observed for a certain parameter set

Cosmological solutions in multidimensional model with multiple exponential potential

A family of cosmological solutions with $(n+1)$ Ricci-flat spaces in the theory with several scalar fields and multiple exponential potential is obtained when coupling vectors in exponents obey certain relations. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. It is proved that power-law solutions may take place only when coupling vectors are linearly independent and exponential dependence occurs for linearly dependent set of coupling vectors. A subfamily of solutions with accelerated expansion is singled out. A generalized isotropization behaviours of certain classes of general solutions are found. In quantum case exact solutions to Wheeler-DeWitt equation are obtained and special "ground state" wave functions are considered.Comment: 22 pages, 1 figur

Manganese(II) Bromide Compound with Diprotonated 1-Hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole: Dual Emission and the Effect of Proton Transfers

An organic–inorganic cation–anion manganese(II) tetrabromide compound with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole, [H3L][MnBr4][H2O], has been synthesized and investigated. The compound has a few possible pathways for proton transfers, which play an important role in the observed luminescence, optical, and magnetic properties. The proton transfers result in the appearance of two-band luminescence. One band is caused by the Mn(II) d-d transitions. The other band is caused by the transition from the triplet state of organic cation and the d-d transition of manganese(II) coupled through {[H3L]}-{[MnBr4]}-{[H2O]} vibrations. The optical absorption spectra of [H3L][MnBr4][H2O] indicate the presence of two direct and one indirect band transitions. The reason for the two-band luminescence and complex optical absorption in [H3L][MnBr4][H2O] were additionally considered using the DFT calculations

Coherent phonons in Bi2Se3 induced by a powerful THz pulse

Using the electro-optic detection method we have detected coherent phonons of Eg1, Eu1, Eg2, and A1g1 symmetry generated in a crystalline film of Bi2Se3 by a powerful single-cycle THz pulse. Coherent excitation of Raman active modes is interpreted as a result of three-and four-phonon interactions in the anharmonic crystal lattice of Bi2Se3

Coherent phonons in Bi

Using the electro-optic detection method we have detected coherent phonons of Eg1, Eu1, Eg2, and A1g1 symmetry generated in a crystalline film of Bi2Se3 by a powerful single-cycle THz pulse. Coherent excitation of Raman active modes is interpreted as a result of three-and four-phonon interactions in the anharmonic crystal lattice of Bi2Se3

Restrictions in ATP diffusion within sarcomeres can provoke ATP-depleted zones impairing exercise capacity in chronic obstructive pulmonary disease

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New Aspects of the Synthesis of <i>closo</i>-Dodecaborate Nitrilium Derivatives [B₁₂H₁₁NCR]⁻ (R = <i>n</i>-C₃H₇, <i>i</i>-C₃H₇, 4-C₆H₄CH₃, 1-C₁₀H₇): Experimental and Theoretical Studies

The preparation of novel nitrilium derivatives of closo-dodecaborate anion [B12H11NCR]−, R = n-C3H7, i-C3H7, 4-C6H4CH3, 1-C10H7 is described. Target compounds were obtained in good yields (up to 73%). The synthesis of target borylated nitrilium derivatives was characterised by the simplicity of the chemical apparatus and the absence of the necessity for the purification of desired compounds. The crystal structures of previously obtained [B12H11NCCH3]− and novel [B12H11NCC3H7]− were established with the help of X-ray structure analysis. DFT-analysis of several nitrilium derivatives [B12H11NCR]−, R = CH3, C3H7, 4-CH3C6H4 was carried out. The main peculiarities of the C≡N bond of the exo-polyhedral substituent were revealed in terms of bond lengths, bond orders and atomic charges. The LUMO orbitals of the systems considered were examined for understanding of the electrophilic nature of the nitrilium derivatives of the closo-dodecaborate anion

Synthesis of Disubstituted Carboxonium Derivatives of <i>Closo</i>-Decaborate Anion [2,6-B₁₀H₈O₂CC₆H₅]⁻: Theoretical and Experimental Study

A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of closo-decaborate anion [2,6-B10H8O2CC6H5]− was carried out. The proposed synthesis of the target product was based on the interaction between the anion [B10H11]− and benzoic acid C6H5COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product [B10H9OC(OH)C6H5]−. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C4H9)4N)[2,6-B10H8O2CC6H5] was established with the help of X-ray structure analysis. The reaction pathway for the formation of [2,6-B10H8O2CC6H5]− was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of closo-borate anions

Nucleophilic Substitution Reactions in the [B3H8]&minus; Anion in the Presence of Lewis Acids

As a result of our study on the interaction between the octahydrotriborate anion with nucleophiles (Nu = THF, Ph3P, Ph2P-(CH2)2-PPh2 (dppe), Ph3As, Et3N, PhNH2, C5H5N, CH3CN, Ph2CHCN)) in the presence of a wide range of Lewis acids (Ti(IV), Hf(IV), Zr(IV), Al, Cu(I), Zn, Mn(II), Co(II) halides and iodine), a number of substituted derivatives of the octahydrotriborate anion [B3H7Nu] are obtained. It is found that the use of TiCl4, AlCl3, ZrCl4, HfCl4, CuCl and iodine leads to the highest product yields. In this case, it is most likely that the reaction proceeds through the formation of an intermediate [B3H7-HMXnx], which was detected by NMR spectroscopy. The structures of [Ph3P&middot;B3H7] and [PhNH2&middot;B3H7] were determined by X-ray diffraction