Dynamics and spectra of excited states of water-micellar suspensions of single-walled carbon nanotubes

The dynamics of the photoinduced differential absorption and excited-state bleaching spectra of single-walled carbon nanotubes suspended in a micellar solution were studied in the spectral range from 40 to 1000 nm within a time interval from 70 fs to 150 ps under excitation by 50-fs pulses with photon energies 2 and 4 eV. The bleaching and absorption bands were observed in the spectra; the positions of the bleaching peaks were independent of the photon energy of the exciting femtosecond pulse in the range 2–4 eV. It was established that, for delay times shorter than 1 ps, the shape of the differential spectrum of excited nanotubes coincided with the shape of the second derivative of the absorption spectrum of unexcited nanotubes in the frequency range of exciting pulse above 18000 cm^?1 (the range of absorption bands of metallic nanotubes). In the frequency range below 16000 cm^?1 (the range of absorption peaks of semiconducting nanotubes), the bleaching peaks in the differential spectrum of excited nanotubes undergo a high-frequency shift of 200–300 cm^?1 with respect to the second-derivative spectrum of unexcited nanotubes. The excited-state relaxation rate constants were measured. They are well approximated by the exponential dependences and depend on the probe-pulse wavelength. An assumption was made about the nature of the observed spectra of excited nanotubes and about the excitation relaxation.     

Mechanisms of 5'-O-Benzoyl-2,3'-anhydrothymidine Reactions with Nucleophiles: II. Kinetics of the Reaction with Triethylammonium Tetrazolide in DMF

The reaction of 5'-O-benzoyl-2,3'-anhydrothymidine with triethylammonium tetrazolide in DMF at 100-120°C is described by a second-order kinetic equation, following the first-order kinetics in each of the reactants. On the basis of the experimental activatin parameters, H298 = 80 kJ/mol, S = -116 J× mol^{- 1} K^{- 1}, a mechanism was proposed, according to which in the rate-determining stage of S_N2 reaction triethylammonium tetrazolide attacks the C^{3 '} atom of 5'-O-benzoyl-2,3'-anhydrothymidine with simultaneous loosening of the C^{3 '}ÄO² anhydro bond.     

Ionic impurities in nematic liquid crystal doped with quantum dots CdSe/ZnS

We investigated the dielectric losses and the ionic currents in the nematic liquid crystal (NLC) doped with semiconductor quantum dots (QDs) of CdSe/ZnS core – shell type and covered with trioctylphosphine oxide (TOPO) molecules. The dielectric loss tangent of the NLC composites increased with increasing the QDs concentration from 0.1 to 0.3 wt%. The density of mobile ions in the composites increased linearly and the average values of ions mobility in the composites decreased with increasing the QDs concentration. The fast ions with the mobility of about 10^–10 m²/V·s and the slow ions with the mobility of about 10^–11 m²/V·s were detected in the NLC composites. The growth of the content of slow ions took place with increasing the QDs concentrations. Increasing the dielectric loss tangent was observed with increasing the duration of sonication time of the NLC composites to prepare homogeneous suspensions. The fragmentation of the CdS/ZnS shell as a result of the sonication may lead to the appearance of the slow ions in the NLC composites.     

The finite-element simulation of low-frequency bimorph transducers for the diagnostics and activation of oil wells

Through the developed technique, the finite-element optimization and the experimental validation of the construction and parameters of low-frequency bimorph piezoelectric transducers designed for the diagnostics and activation of oil wells are carried out.     

Ferromagnetic Resonance of FeNi/Cu/FeNi Thin Film on Coplanar Waveguide with Operating Frequency of 1 to 20 GHz

Russian Physics Journal - The paper presents the calculation results of the coplanar waveguide geometry using the method of conformal mapping and computerized simulation with COMSOL Multiphysics...     

Dynamics of a Three-Component Delocalized Nonlinear Vibrational Mode in Graphene

Physics of the Solid State - The dynamics of a three-component nonlinear delocalized vibrational mode in graphene is studied with molecular dynamics. This mode, being a superposition of a root and...