Physical and mathematical modeling of a supersonic flow around a cylinder with a porous insert

Results of numerical and experimental modeling of a supersonic flow (M_∞ = 4.85) around a model of a streamwise-aligned cylinder with a cellular-porous insert permeable for the gas on the frontal face of the cylinder are described. Experimental data on the influence of the pore structure and the length of the porous cylindrical insert on the model drag, pressure on the frontal face of the cylinder, and flow pattern are obtained. Numerical modeling includes solving Favre-averaged Navier-Stokes equations, which describe the motion of a viscous compressible heat-conducting gas. The system is supplemented with a source term taking into account the drag of the porous body within the framework of the continuum model of filtration. Data on pressure and velocity fields inside the porous body are obtained in calculations, and the shape of an effective pointed body whose drag is equal to the drag of the model considered is determined. The calculated results are compared with the measured data and schlieren visualization of the flow field.     

Studying the behavior of reduced graphene oxide particles at the water-air interface

Reduced graphene oxide (RGO) particles were obtained from natural and artificial graphite using chemical reduction. The particles were placed on an aqueous subphase surface in a Langmuir trough from suspensions in carbon tetrachloride. Compression isotherms of layers of RGO particles were obtained for different amounts of the substance deposited on the subphase. Layers on the aqueous subphase surface were studied using a Brewster microscope and measurements of the surface potential. Comparison of the obtained data made it possible to determine the stage of the formation of a continuous RGO layer.     

Fabrication of highly porous bioresorbable polymer matrices using supercritical carbon dioxide

A new method for fabrication of highly porous bioresorbable polymer structures on the basis of various aliphatic polyesters for tissue engineering has been successfully designed and worked out. It has been shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide into press forms at temperatures from 20 to 40°C through a nozzle of a certain diameter under atmospheric or elevated (up to 6 MPa) CO₂ pressure allows obtaining polymer matrices with a desired structure and morphology and mean porosity of up to 96 vol % with high reproducibility and avoiding the use of toxic organic solvents. The effect of chemical composition and molecular mass of starting polymers, as well as temperature and CO₂ pressure in the reaction cell and the receiver, on the morphology and internal structure of fabricated samples was studied using the method of scanning-electron microscopy.     

Self-action dynamics of ultrashort electromagnetic pulses

The self-action dynamics of three-dimensional wave packets whose width is on the order of the carrier frequency is studied under fairly general assumptions concerning the dispersion properties of the medium. The condition for the wave field collapse is determined. Self-action regimes in a dispersion-free medium and in media with predominance of anomalous or normal group velocity dispersions are numerically investigated. It is shown that, for extremely short pulses, nonlinearity leads not only to the self-compression of the wave field but also to a “turn-over” of the longitudinal profile. In a dispersionless medium, the formation of a shock front within the pulse leads to the nonlinear dissipation of linearly polarized radiation and to self-focusing stabilization. For circularly polarized radiation, the wave collapse is accompanied by the formation of an envelope shock wave.     

Effect of electrophysical activation of components on adhesive interaction in polymer composites

The key problem in designing polymeric composites is ensuring a sufficiently strong adhesive bond between the polymer and the filler (or the reinforcement). One method for strengthening the intermolecular interaction at the phase interface is electrophysical activation of the particle surface. We have investigated the absorption activity and adhesiveness of powdered inorganic fillers and polymeric binders with triboelectric activation and activation in a corona discharge. We consider a broad class of disperse materials. We show that electrophysical activation of powdered materials causes changes in the concentration of donor and acceptor centers on the particle surface and in the adsorption activity of the materials as a whole. The presented results can be used for goal-directed selection of the most effective method of activation for disperse materials; they also are evidence for the important role of adsorption forces in the adhesion phenomenon.Report presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October 1995).Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 734–741, November–December, 1995.     

Self-focusing of laser radiation in cluster plasma

The self-focusing of laser radiation in plasma with ionized gaseous clusters is studied both analytically and numerically. An electrodynamic model is proposed for cluster plasma in a field of ultrashort laser pulse. The radiation self-action dynamics are studied using the equation for wave-field envelope with allowance for the electronic nonlinearity of the expanded plasma bunches and the group-velocity dispersion in a nanodispersive medium. It is shown that, for a laser power exceeding the self-focusing critical power, the wave-field self-compression occurs in a medium with dispersion of any type (normal, anomalous, or combined). Due to the strong dependence of the characteristic nonlinear field on the size of ionized cluster, the corresponding processes develop faster than in a homogeneous medium and give rise to the ultrashort pulses.     

Triphenylphosphonium Trifluoromethanesulfonate in Reactions with Epoxy Derivatives

Russian Journal of Organic Chemistry -