There does not exist an enumerable family of context-free grammars that generates the class of single-valued languages

Translated from Matematicheskie Zametki, Vol. 50, No. 1, pp. 34–40, July, 1991.     

Stereoselective electrocatalytic cyclization of 3-substituted 2,2-dicyanocyclopropane-1,1-dicarboxylic acid esters to form 6-substituted (1R,5R,6R)*-4,4-dialkoxy-5-cyano-2-oxo-3-azabicyclo[3.1.0]hexane-1-carboxylic acid esters

Electrolysis of 3-substituted 2,2-dicyanocyclopropane-1,1-dicarboxylic acid esters in alcohols in an undivided cell in the presence of NaBr or NaOAc afforded 6-substituted (1R,5R, 6R)*-4,4-dialkoxy-5-cyano-2-oxo-3-azabicyclo[3.1.0]hexane-1-carboxylic acid esters in 80–95% yields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 102–107, January, 2006.     

The synthesis and adsorption properties of polyvinylchloride nanofilms with ligand groups

Polyvinylchloride (PVC) samples with a fairly developed surface were prepared by the spontaneous removal of the solvent (benzyl alcohol) from a polymer gel. The surface of the product was modified to obtain ethanolocyclame and sodium acetocyclame nanofilms. The structure and composition of the nanofilms were studied by IR Fourier spectroscopy. The adsorption of nitrogen vapor at ?196°C and benzene and water at 20°C on the nanofilms was investigated. Surface modification was shown to increase the stability of PVC in water and benzene and the specific surface area and volume of nanopores. The conclusion was drawn that nanofilm ligand groups could stoichiometrically interact with water and benzene molecules on PVC with a modified surface.     

Coherent population transfer in molecules coupled with a dissipative environment by intense ultrashort chirped pulse. II. A simple model

We have developed a simple and physically clear picture of adiabatic rapid passage (ARP) in molecules in solution by careful examination of all the conditions needed for ARP. The relaxation effects were considered in the framework of the Landau-Zener model for random crossing of levels. The model enables us to include into consideration non-Markovian Gaussian-correlated noise. It explains all the numerical results obtained in the first paper of the series [B. D. Fainberg and V. A. Gorbunov, J. Chem. Phys. 117, 7222 (2002)], in particular, that for positive chirp pulse excitation relaxation favors more efficient population transfer with respect to the relaxation-free system with frozen nuclear motion. We also relate parameters of non-Markovian Gaussian-correlated noise with irreversible dephasing time of an optical transition by calculating the photon echo signal attenuation.     

Functional electronics with discrete integrators based on superionic conductors

The possibilities for developing devices on the basis of superionic conductors for measuring and providing advance electric energy consumption and determining the integral index of luminous energy are considered. It is experimentally shown that the consumed charge and the illumination intensity in a certain time interval can be measured without feeding power to the devices. The measuring transducers are easy to design and realize. The reliability and reproducibility of results are supported.     

Liquid adsorption chromatography of polyethers: experiments and simulation

The adsorption behavior of poly(ethylene glycol) (PEG) in reversed-phase chromatography is studied both experimentally and theoretically and a computer simulation of chromatograms is performed on the basis of these studies. The experimental conditions were: different reversed-phase adsorbents and a solvent methanol–water system as the mobile phase. At varying mobile phase compositions highly resolved chromatograms of PEG samples were obtained, in which all peaks could be identified, and the dependencies of the distribution coefficient on the degree of polymerization for PEG molecules were evaluated by processing these chromatograms. The data were interpreted by using a theory of homopolymers based on a continuum Gaussian chain model of flexible macromolecules and a slit-like model of pores of stationary phase. The theory proved to describe well the experimental data in the whole range of studied molecular masses, and the thermodynamic parameters characterizing interactions of ethylene oxide repeating units in PEG molecules with the adsorbent pore walls have been determined from the comparison of the theory with the experimental data. The dispersion of chromatographic peaks corresponding to individual oligomer molecules is also estimated. In the system studied the peak width occurred to be proportional to the distribution coefficient of corresponding macromolecule. The theory is used to develop a computer-assisted procedure for simulation of chromatograms for samples of linear homopolymers. Using the obtained data on the thermodynamic parameters and the estimates of peak dispersion, chromatograms are simulated for PEG samples at two different chromatographic conditions. These simulated chromatograms were in good quantitative agreement with the real chromatograms.     

Mössbauer spectroscopy of237Np in solid solutions of actinide dioxides

Emission Mössbauer (nuclear gamma-resonance) spectra of²³⁷Np resulting from the alpha-decay of²⁴¹Am in solid solutions AmO₂–ThO₂ and AmO₂–UO₂ prepared by precipitation from LiF–NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO₂ and NpAl₂. The possibility is stated of managing the form of the emission Mössbauer spectra of²³⁷Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of²³⁷Np in solid solution NpO₂–ThO₂ with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO₂ contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np⁴⁺ and Np⁵⁺ states observed in the NpO₂–ThO₂ solid solution at low concentrations of neptunium dioxide.     

Materials based on cellulose fabric and PVC with porous structures formed by jointed aza- and oxa-aza-crown macromolecules

A material with porous structures formed by jointed aza- and oxa-aza-crowns with peripheral OHgroups is synthesized on the basis of cellulose fabric and PVC transformed into hydroxyethylcyclam. Mesopores are mainly observed on the fiber surface. The specific surface of the material is 6 m²/g; the volume of free space is 0.112 cm³/g. Assuming the internal pores have a disk-like shape, their width is estimated at 2 nm. The material sorbs vapors of aliphatic and aromatic hydrocarbons, alcohols, aldehydes, ketones, amines, amides, nitriles, and sulfoxides. It also swells to a limited degree in organic solvents. When sulfuric acid or sodium hydroxide is sorbed in the pores, compounds of them with H⁺- and OH^–-conducting systems of hydrogen bonds are formed.     

Prototype of a Two-Wave Radiometric System of the Millimeter Wavelength Range for Remote Sensing of the Atmosphere and Features of Atmospheric Absorption at Kara-Dag According to Field Measurements

Radiophysics and Quantum Electronics - We discuss the results of the atmospheric absorption studies on the territory of the Kara-Dag radio astronomy station in Crimea in the millimeter-wavelength...