Absolute frequency measurement of an acetylene-stabilized laser at 1542 nm

The absolute frequency of an acetylene-stabilized laser at 1542 nm is measured at its second harmonic (771 nm) by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. Frequency stability and reproducibility of the acetylene-stabilized laser are evaluated by the femtosecond comb with a H maser as a frequency reference. The absolute frequency of a laser diode stabilized on the P(16) transition of 13C2H2 is determined to be 194 369 569 383.6(1.3) kHz. The acetylene-stabilized laser serves as an important optical frequency standard for telecommunication applications.     

Ferroelectric switching characteristics of 73/27 copolymer of vinylidene fluoride and trifluoroethylene

Ferroelectric polarization-reversal switching of vinylidene fluoride—trifluoroethylene copolymer with 73 mol % of vinylidene fluoride is investigated under a variety of conditions in an attempt to derive detailed information on the polarization reversal of the polymer. The electric-field dependence of switching time t_s obeys an exponential law. The temporal change of switching current density J is presented in the form J/(P_s ? P) versus time (P is the polarization, and P_s is its saturation value), which is free of the depolarization-field effect and discriminates in a straightforward manner between acceleration and deceleration of switching. Effects of the annealing of samples upon t_s are observed together with changes in the degree of crystallinity. Effects of space charge distribution upon t_s are investigated by applying two successive pulses, positive and negative, with varied intervals t_w between the two. The dynamics of space charge redistribution is elucidated from the t_w dependence of the t_s of the second pulse. The temperature dependence of t_s indicates that the switching becomes critically fast as the phase-transition temperature is approached.     

Molecular orbital quantities of conjugated ketenes and influence of structural variations on their electronic features

MO quantities by CNDO/2 method on several valence isomeric ketenes and structurally corresponding allene molecules were calculated to evaluate the influence of structural feature on magnitude of back-donation of oxygen n-electrons in ketene, and to rationalize an unusual cycloaddition involved in diphenyl ketene.     

Selective Homonuclear Polarization Transfer in the Tilted Rotating Frame under Magic Angle Spinning in Solids

An application of the R2TR method (1995,Chem. Phys. Lett.232,424) to selective homonuclear polarization transfer under magic angle spinning is proposed. It is shown that, for a spinning speed fast enough to remove the maximum homonuclear dipolar coupling constant ω_Dinvolved, the flip-flop and flop-flop mechanisms are suitable for recoupling the spins with a chemical shift difference larger than ω_Dand a difference comparable to or smaller than ω_D, respectively. It is also shown that, for fast polarization transfer, the off-resonance frequencies should be much higher than the RF intensity in the flip-flop condition, while for the flop-flop condition, the off-resonance frequencies should be much lower than the RF intensity. Some one- and two-dimensional experiments are proposed by utilizing the capability of the R2TR method to abruptly switch on and off the recoupling condition, and are demonstrated for triply¹³C-enriched -alanine. The mixing time required for population transfer was found to be ca. 0.5 ms for the methine and methyl¹³C spins separated by 1.5 Å and ca. 5 ms for the methyl and the carboxyl carbons separated by 2.5 Å. The experimental results and theoretical simulations show that selective polarization transfer is achieved when the difference in the isotropic chemical shifts between the relevant pair of spins and a neighboring spin is more than 1000 Hz.     

Preparation of ketones by direct reaction of grignard reagents with acid chlorides in tetrahydrofuran

Grignard reagents react with acid chlorides in tetrahydrofuran at low temperature to produce ketones in excellent yields. The results reported here strongly indicate the importance of the solvent in Grignard reagent chemistry.     

Hydroxylation of aromatic rings in an aqueous solution induced by argon arc plasma

Plasma-induced reaction in an aqueous solution of phenyl-containing amino acids resulted in the formation of several hydroxyphenyl amino acids, which was explained by the action of hydroxyl radicals generated by decomposition of water molecules by the high energy plasma.     

Fuzzy modelling environment for designing fuzzy controllers

Fuzzy control algorithms are developed based on fuzzy models of systems. The control issues are posed as multiobjective optimization problems involving goals and constraints imposed on system's variables. Two basic design modes embrace on- and off-line modes of control development. The first type of design deals with the time and state-dependent objectives and pertains to control determination based upon the current state of the fuzzy model. The second design mode gives rise to an explicit form of a fuzzy controller that is learned based on a given list of state-control associations. Both the fuzzy models as well as fuzzy controllers are realized as logic processors.     

A new convenient synthesis of γ-keto-sulfoxide

γ-Keto-sulfoxides have been very conveniently synthesized through a series of reactions from commercially available acrolein. They were obtained as crystals and shown to be effective as the vinyl ketone equivalents.     

Pyrolysis of amines: Infrared spectrum of allylimine

Infrared absorption spectrum of allylimine in the gas phase was measured for the first time. The spectrum consisted of two rotational isomers, cis and trans, around the CC bond. The relative population of the trans form was 70–80%, and the rest was for the cis form at room temperature. This intermediate molecule was produced by the thermal decomposition of diallylamine and by the isomerization of propargylamine. The vibrational assignments were made with the help of an ab initio MO calculation. The half-life in the absorption cell was about 20 min.     

Reaction of pyrazine-2,3-dicarbonitrile and 1,3-dimethyllumazine with alkyl radicals

Pyrazine-2,3-dicarbonitrile ( 1 ) reacts with alkyl radicals to give mono- 3 and di-alkylated pyrazine-2,3-dicarbonitriles 4 . Similarly 1,3-dimethyllumazine ( 2 ) reacts with alkyl radicals to give 7-alkyl-1,3-dimethyllumazines 8 as the major product. The reactivity of alkyl radicals decreases in the order tertiary, secondary, and primary, and 1 is more reactive than 2 in those radical substitution reactions.