Determining the time-frequency parameters of low-power bright picosecond optical pulses by using the interferometric technique

We present an approach to the characterization of low-power bright picosecond optical pulses with an internal frequency modulation simultaneously in both time and frequency domains in practically much used case of the Gaussian shape. This approach exploits the Wigner time-frequency distribution, which can be found for these bright pulses by using a novel interferometric technique under our proposal. Then, the simplest two-beam scanning Michelson interferometer is selected for shaping the field-strength auto-correlation function of low-power picosecond pulse trains. We are proposing and considering in principle the key features of a new experimental technique for accurate and reliable measurements of the train-average width as well as the value and sign of the frequency chirp of pulses in high-repetition-rate trains. This technique is founded on an ingenious algorithm for the advanced metrology, assumes using a specially designed supplementary semiconductor cell, and suggests carrying out a pair of additional measures with exploiting this semiconductor cell. Such a procedure makes possible constructing the Wigner distribution and describing the above-listed time-frequency parameters of low-power bright picosecond optical pulses. In the appendix, we follow one of possible avenues for deriving the joint Wigner time-frequency distribution via choosing the Weil's correspondence between classical functions and operators.     

Microwave-assisted synthesis of fused pyrazolo[3,4-b]pyrazines by the reaction of ortho-aminonitrosopyrazoles and cyclic β-diketones

Novel fused pyrazolo[3,4-b]pyrazines 3 were prepared by assisted microwave cyclocondensation reaction of ortho-aminonitrosopyrazoles 1 and cyclic β-diketones 2 in dimethylformamide. This protocol provides a simple procedure for the synthesis of the title compounds with the advantages of easy work-up, mild reaction conditions and good yields.     

Finite difference on grids with nearly uniform cell area and line spacing for the wave equation on complex domains

A finite difference time-dependent numerical method for the wave equation, supported by recently derived novel elliptic grids, is analyzed. The method is successfully applied to single and multiple two-dimensional acoustic scattering problems including soft and hard obstacles with complexly shaped boundaries. The new grids have nearly uniform cell area (J-grids) and nearly uniform grid line spacing (αγ-grids). Numerical experiments reveal the positive impact of these two grid properties on the scattered field convergence to its harmonic steady state. The restriction imposed by stability conditions on the time step size is relaxed due to the near uniformity cell areas and grid line spacing. As a consequence, moderately large time steps can be used for relatively fine spatial grids resulting in greater accuracy at a lower computational cost. Also, numerical solutions for wave problems inside annular regions of complex shapes are obtained. The use of the new grids results in late time stability in contrast with other classical finite difference time-dependent methods.     

The superconductor system of 2H-Tantalum disulfide intercalated with polyglycine

It was hypothesized that the formation of polypeptide bonds inside a lamellar superconducting compound such as 2H-TaS₂ could enhance the superconducting transition temperature. The preparation of tantalum disulfide intercalated with polyglycine is described. The intercalated systems were characterized by powder X-ray diffraction and thermogravimetric analysis. Superconducting transition temperatures were also measured. The results show that the system 2H-TaS₂/polyglycine does not have a more favourableT _cvalue than 2H-TaS₂/glycine.     

Preparation of poly(vinyl chloride) at low temperature by a photochemical method

A convenient method has been developed for the polymerization of vinyl chloride at low temperatures (to at least ?75°C) by using a tungsten–iodine rather than an ultraviolet lamp, and uranyl nitrate as sensitizer. The use of predominantly visible light minimizes degradation reactions sometimes encountered with ultraviolet light. Measurements of the fraction of racemic (or syndiotactic) diads and per cent crystallinity confirm that the products resemble polymers prepared by other techniques, such as polymerization initiated by a boron alkyl. It is concluded, therefore, that the method can provide a useful alternate to the more common, organometallic system. Measurements of torsional modulus as a function of temperature were also made. As the temperature of polymerization is lowered, the fraction of racemic diads and the per cent crystallinity are increased. The higher the per cent crystallinity, the higher the glass temperature, the broader the glass transition, and the higher the modulus in the rubbery state. Thus, the increased stereoregularity permits the development of a higher level of crystallinity which, in turn, restricts the mobility of the polymer chains.     

Self-assembly in linker-modified microemulsions

Linker molecules are added to microemulsion systems to enhance the interaction between the surfactant and oil (lipophilic linkers) or water (hydrophilic linkers) phases. Previous results suggest that when lipophilic and hydrophilic linkers are combined they behave as a self-assembled surfactant at the oil/water interface. In this work we investigate this self-assembly phenomenon as a function of surfactant, linker and electrolyte concentration. We find that middle phase microemulsion appears at a specific concentration higher than the critical micelle concentration (CMC), which we denote as the critical middle phase microemulsion concentration (CmicroC). When the lipophilic linker dodecanol is added in equimolar ratio to the hydrophilic linker sodium mono- and dimethyl naphthalene sulfonate (SMDNS), the middle phase microemulsion did not appear until the surfactant sodium dihexyl sulfosuccinate (SDHS) concentration was larger than the CmicroC of the SDHS-alone system. Dodecanol is shown to segregate near the surfactant tails following a Langmuir-type adsorption process. This segregation is not affected by the electrolyte concentration but is significantly reduced when the surfactant (SDHS) concentration approaches the CmicroC. The data suggest that the self-assembly between hydrophilic and lipophilic linkers to form middle phase microemulsions is only possible if a minimum amount of surfactant is present.