Synthesis of Polysubstituted Pyridopyrimidines,Pyrimidines, and Pyrazoles Based on 1,1-Bis(1H-benzotriazol-1-yl)-and 1,1-Bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,4,4-trichloro-2-nitrobuta-1,3-dienes

Russian Journal of Organic Chemistry - The reaction of 3,4,4-trichloro-1,1-bis(3,5-dimethyl-1H-pyrazol-1-yl)-2-nitrobuta-1,3-diene with 2-aminopyridine gave a polysubstituted...     

Wannier-Stark effect and electron-phonon interaction in macroporous silicon structures with SiO2 nanocoatings

We investigated the contribution of electron-phonon interaction to the broadening parameter Γ of the Wannier-Stark ladder levels in oxidized macroporous silicon structures with different concentration of Si-O-Si states (TO and LO phonons). The obtained value of the Wannier-Stark ladder parameter Γ is much less than the djacent level energy evaluated from giant oscillations of resonance electron scattering on the surface states. We determined the influence of broadening on the oscillation amplitude in IR absorption spectra as interaction of the surface multi-phonon polaritons with scattered electrons. This interaction transforms the resonance electron scattering in samples with low concentration of Si-O-Si states into ordinary scattering on ionized impurities for samples with high concentration of Si-O-Si states. The transformation takes place at the scattering lifetime coinciding with the period of electron oscillations in the surface electric field.     

Low-temperature photoluminescence of II–VI films obtained by close-spaced vacuum sublimation

Low-temperature photoluminescence (PL) spectra of CdTe and ZnTe films obtained by a close-spaced volume sublimation technique under different technological conditions (substrate temperatures) were investigated. Analysis of the experimental results made it possible to conclude that the nature of the structure of the PL spectra observed experimentally is caused by the recombination of the excitons bound to shallow neutral acceptors, donor–acceptor pairs with the participation of the complex acceptors, and the presence of the extended defects like dislocations. The presence of neutral acceptors is related to the Li, Na, P or Cu residual impurities. As a result of the study of the PL spectra of CdTe and ZnTe films the optimal temperature conditions of their growth were determined as the substrate temperature T_s=623 K and 673 K, respectively.     

Fast dynamic holographic recording based on conductive ionic metal-alkanoate liquid crystals and smectic glasses

Recordings of dynamic holograms with microsecond relaxation times under the action of nanosecond laser pulses are obtained in composites on the base of a novel class of liquid crystals (LCs) in ionic metal-alkanoates. Holographic parameters and relaxation characteristics are measured for doped lyotropic ionic LC, for sandwichlike cells (consisting of a dye layer and a layer of the lyotropic ionic LC), and for colored ionic smectic glasses. The structure of the materials is investigated by use of the small-angle x-ray technique. The mechanism of resonance nonlinearity in photosensitive centers and mechanisms of the grating erasure connected with a charge transport in the ionic conductive LC matrix are discussed.     

Synthesis of fluorinated 2,6-heptanediones and 2-oxa-6- azabicyclo[2.2.2]octanes from 1,4-dihydropyridines

Electrophilic fluorination of Hantzsch-type 1,4-dihydropyridines with Selectfluor^® led to the formation of new fluorinated 2,6-heptanediones - dialkyl 2,4-diacetyl-2,4-difluoro-3-phenylpentanedioates. Novel 2,6-heptanedione derivatives in reaction with hydrazine hydrate easily form 6-amino-4,7-difluoro-3-hydroxy-1,3-dimethyl-5-oxo-8-phenyl-2-oxa-6-azabicyclo[2.2.2]octanes instead of the corresponding diazepine derivatives. The obtained 2-оxa-6-azabicyclo[2,2,2]octanes are thermally stable at the temperatures below 50°С. At higher temperatures rearrangement of 2-oxa-6-azabicyclo[2,2,2]octanes offers new fluorine-containing pyrazolinone derivatives - alkyl esters of 2-fluoro-2-((4-fluoro-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-yl)(phenyl)methyl)-3-oxobutanoates.     

On genera of polyhedra

We consider the stable homotopy category S of polyhedra (finite cell complexes). We say that two polyhedra X,Y are in the same genus and write X ∼ Y if X _p ≅ Y _p for all prime p, where X _p denotes the image of Xin the localized category S _p . We prove that it is equivalent to the stable isomorphism X∨B ₀ ≅Y∨B ₀, where B ₀ is the wedge of all spheres S ⁿ such that π _n ^S (X) is infinite. We also prove that a stable isomorphism X ∨ X ≅ Y ∨ X implies a stable isomorphism X ≅ Y.