Generation of ultrabroadband terahertz radiation under optical breakdown of air by two femtosecond pulses of different frequencies

Experimental results on the generation of terahertz (THz) electromagnetic radiation under ionization of air by femtosecond pulses at fundamental and second-harmonic frequencies of a Ti-sapphire laser are presented. The mean power of the generated THz radiation as a function of the time delay between two pulses of different frequencies is found to be quasi-periodical. Theoretically, we show that efficient generation of THz radiation is governed by the inertial part of the nonlinear response of the medium, which is determined by the dynamics of population of highly excited states with subsequent emission of electrons.     

Quantum-chemical study of the mechanism of dissolution of scleroproteins in N-methylmorpholine N-oxide

Complex formation of scleroprotein models with an N-methylmorpholine N-oxide solvent was studied by the semiempirical PM3 method.     

Large Eddy Simulation of a turbulent lifted flame using multi-modal manifold-based models: Feasibility and interpretability

A general model for multi-modal turbulent combustion is achievable with two-dimensional manifold equations that use the mixture fraction and a generalized progress variable as coordinates. Information about the underlying mode of combustion is encoded in three scalar dissipation rates that appear as parameters in the two-dimensional equations. In this work, Large Eddy Simulation (LES) of a multi-modal turbulent lifted hydrogen jet flame in a vitiated coflow is performed using this new turbulent combustion model, leveraging both convolution-on-the-fly and In-Situ Adaptive Tabulation for computational tractability. The simulation predicts a lifted flame consistent with observations from past experiments. The feasibility of such a model implemented in LES is examined, and the cost per timestep is found to be comparable to conventional one-dimensional manifold-based models describing one asymptotic mode of combustion. Additionally, the model provides clear interpretability, allowing for combustion mode analysis to be performed with ease by evaluating the scalar dissipation rates and generalized progress variable source term. This analysis is used to show that the flame is stabilized by autoignition and has a trailing nonpremixed flame. Furthermore, transport of progress variable from the most reactive mixture fraction towards richer mixtures at the centerline is found to be important.     

Composition separation in the surface layers of a Ni-Cu foil during ion implantation

The effect of ion implantation on the composition and mechanical properties of rolled Ni-Cu foils is studied. The formation of a non-monotonic oscillating dependence of the chemical composition on depth associated with a presumable change in the defect structure of the material has been observed. Possible mechanisms of the observed phenomena are proposed.     

Cellulose matrix as a nanoreactor for preparing nanoparticles of nickel and its oxides using hydrazine dihydrochloride as reductant

A matrix of microcrystalline cellulose was used as a nanoreactor for the reduction of Ni(II) ions with hydrazine dihydrochloride.     

Rheological properties of mixtures of cellulose with chitin in 1-butyl-3methylimidazolium acetate of the obtained composite films obtained

Rheological properties of solutions of cellulose mixed with chitin in 1-butyl-3-methylimidazolium acetate were studied. Positive and negative deviations of values of the viscosity and activation energy E _a of viscous flow from additive values were observed. X-ray diffraction and thermogravimetric analyses were used to examine the structural organization and the thermal stability of the composite films obtained.     

Thermochemical study on the dissolution and regeneration of fibroin from solutions in imidazole-based ionic liquids

The enthalpies of dissolution of fibroin in imidazole-based ionic liquids were determined, and the contribution of polymer crystal structure decomposition to the enthalpy of dissolution was estimated. The heat of mixing of imidazole ionic liquid with water was described.     

Energies of formation and structures of point defects at tilt grain boundaries in molybdenum

The structure and formation energy of vacancies and interstitials at symmetrical tilt grain boundaries in molybdenum have been investigated by means of classical molecular dynamics. The dependence of the formation energy of these boundaries on the grain misorientation angle has been calculated. The structures of defects, energies of their formation, and diffusion mechanisms have been determined for the most stable grain boundaries.