Slow light with integrated gain and large pulse delay

We demonstrate slow and stored light in Rb vapor with a combination of desirable features: minimal loss and distortion of the pulse shape, and large fractional delay (>10). This behavior is enabled by (i) a group index that can be controllably varied during light pulse propagation, and (ii) controllable gain integrated into the medium to compensate for pulse loss. Any medium with the above two characteristics should be able to realize similarly high-performance slow light.     

Preparation and Properties of Organo-Silicon-Phosphorus Hybrid Compounds Based on 3-Aminopropyltriethoxysilane,Tetraethoxysilane, and (1-Hydroxyethylidene)diphosphonic Acid

Russian Journal of General Chemistry - The reaction of 3-aminopropyltriethoxysilane with (1-hydroxyethylidene)diphosphonic acid in 96% ethanol results in the 3-hydroxy(ethoxy)silylpropylaminium...     

Electron affinity and substituent effects in radical anions

The first vertical electron affinities EA of 13 series of molecules and free radicals D(X _i ) _n are related to the inductive (σ _I ), resonance (σ _R ^? ), and polarization (σ_α) parameters of substituents X _i by the dependences EA = EA _H + aΣσ _I + bΣσ _R/? + cΣσ_α: In radical anions D^+·(X _i ) _n , compared to radical cations D^+·(X _i ) _n , the polarization interaction is weaker or similar in magnitude but has an opposite sign. The previously unknown resonance parameters σ _R ^? of substituents SiMe₃ and CH₂SiMe₃ bound to the radical anion center H₂C=CH^?· were calculated.     

Adducts of zinc and copper(II) dialkyldithiocarbamate complexes with dibutyl-and diisobutylamines: Synthesis,structures, EPR and solid-state natural abundance <Superscript>13</Superscript>C and <Superscript>15</Superscript>N CP/MAS NMR spectra

Crystalline adducts of zinc and copper(II) dithiocarbamate complexes with dibutyl-and diisobutylamines of the general formula [M(NHR′₂)(S₂CNR₂)₂] (M = Zn, ⁶³Cu, and ⁶⁵Cu; R = CH₃ and C₂H₅; R₂ = (CH₂)₄O; R′ = C₄H₉ and i-C₄H₉) were synthesized. Their structures and spectroscopic properties were studied by EPR and solid-state natural abundance ¹³C and ¹⁵N CP/MAS NMR spectroscopy. Experimental EPR data and computer-assisted modeling confirmed the individual character of copper(II) adducts. The geometries of the copper coordination polyhedra were found to be intermediate between a tetragonal pyramid and a trigonal bipyramid (TBP). The contributions from TBP to the geometries of the adducts obtained were calculated from the EPR data. According to the X-ray diffraction data, the adduct of zinc diethyldithiocarbamate with diisobutylamine exists in two isomeric forms. The ¹³C and ¹⁵N CP/MAS NMR signals were assigned to the atomic positions in two crystallographically independent conformer molecules.     

Complexing effect of N-hydroxyphthalimides in the stereospecific polymerization of methyl methacrylate

A study was carried out on the effect of both the temperature of the reaction medium and structure of the initiator (N-hydroxyphthalimides) on the tacticity of the polymethyl methacrylate obtained under radical polymerization conditions. An increase in the amount of hydroxyl groups in the N-hydroxyphthalimide (NHPI) molecule leads to an increase in syndiotactic sequences in the macromolecule. The Fordham equation was used to calculate the differences in the activation enthalpies and entropies for addition in the iso and syndio positions in the presence of various N-hydroxyphthalimides. In all cases, formation of a syndiotactic polymer is favored.     

The role of carbon support morphology in the formation of catalytic layer of solid-polymer fuel cell

The Pt/C catalysts with similar morphology of active catalytic phase (platinum nanoparticles), which were deposited on the supports with different types of carbon structures (Vulkan XC-72 carbon black, Taunit carbon tubes, and Timrex HSAG-300 carbon support with graphite structure), were fabricated by the method of electrochemical dispersion. The effect of the carbon structure type on the electrocatalytic properties of Pt/C catalysts was studied in their operation in the three-electrode cell and in-service in the membrane-electrode assembly of air-hydrogen solid-polymer fuel cell. The Pt/C catalyst based on the Vulkan XC-72 carbon support showed the best performance. The anisotropic shape of Taunit carbon nanotubes and the microstructure of Timrex HSAG-300 carbon support do not allow us to form a catalytic layer with a large active platinum surface area and a structure, which provides an effective ionic transport and mass exchange near the platinum surface.     

Synthesis of N-glycyl-β-glycopyranosylamines, human milk fucooligosaccharide derivatives

The action of ammonium carbamate in aqueous methanol in the presence of NH₃ on three-, penta-, hexa-, octa-, and nonasaccharides of human milk and on decasaccharide (N-glycan from human immunoglobulin (IgG)) containing one or two a-l-fucose residues led to the corresponding β-glycopyranosylamines. After their N-acylation upon treatment with N-hydroxysuccinimide ester of N-Boc-glycine or N-Boc-glycine anhydride (Boc is the tert-butyloxycarbonyl) with subsequent removal of the Boc group, N-glycyl-β-glycopyranosylamines were obtained in up to 75% yield.     

Comparison of 87Rb N-resonances for D1 and D2 transitions

We report an experimental comparison of three-photon-absorption resonances (N-resonances) for the D1 and D2 optical transitions of thermal (87)Rb vapor. We find that the D2 N-resonance has better contrast, a broader linewidth, and a more symmetric line shape than the D1 N-resonance. Taken together, these factors imply superior performance for frequency standards operating on alkali D2 N-resonances, in contrast with coherent population trapping resonances, for which the D2 transition provides poorer frequency standard performance than the D1 transition.     

Conjugates of polyhedral boron compounds with carbohydrates 6. Synthesis of glycoconjugates of closo-ortho-carborane with β-lactosylamine and β-d-galactopyranosylamine derivatives as galectin bi- and trivalent ligands

Five glycoconjugates were obtained from ortho-carboranylacetic acid and β-actosylamine or β-d-galactopyranosylamine derivatives with the terminal amino group in the spacer. The glycoconjugates have different lengths of the spacer (9 to 15 atoms) and contain two or three βlactosylamine residues or one, two, or three β-d-galactopyranosylamine residues.     

Kinetics and mechanism of nickel reaction with benzyl bromide in dimethylformamide

Abstarct  The reaction of nickel with benzyl bromide in DMF has been studied. The reaction intermediates were investigated by different methods and the kinetic and thermodynamic parameters were determined. The reaction of benzyl bromide with nickel was shown to occur on the metal surface by the Langmuir-Hinshelwood scheme, with the formation of benzyl radicals which are recombined and isomerized in solution to form 1,2-diphenylethane and trace amounts of 4.4′-dimethylbiphenyl. Original Russian Text ? A.M. Egorov, S.A. Matyukhova, I.S. Kocherova, A.A. Novikova, A.V. Anisimov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 3, pp. 455–463.