Transferred plasma jet as a tool to improve the wettability of inner surfaces of polymer tubes

The wettability of the inner surfaces of vinyl, polyurethane, and silicone tubes was modified using an atmospheric pressure plasma jet operated in argon. A specific plasma jet configuration, transferred plasma jet, developed at Sao Paulo State University was utilized. It has been shown that it is possible to homogeneously alter the inner wall wettability of 1-m-long tubes, while providing safe plasma source usage for the operator. The water contact angle for three tube materials, i.e., vinyl, polyurethane, and silicone, changed from 98°, 86°, and 109° to 55°, 45°, and 40°, respectively.     

Transport phenomena in metal nanocomposites

Ferromagnetic nanocomposites are the special case of metal composites; they are of practical interest for spintronics. Temperature dependences of resistivity ρ(T) and thermoelectric power α(T) of ferromagnetic nanocomposites with the composition Co _x (Al₂O₃)_{100 ? x} (36.6 ≤ x ≤ 52.5 at %) are investigated near the percolation threshold (x _p ≈ 43.3 at %) in a temperature range of 77–300 K. Sizes of Co nanoparticles are no larger than 25 nm. Specific features are observed in the dependences α(T) in the form of a kink at T _b ≈ 170 K. The analysis of the structural and electrical schematics as well as energy diagrams of percolation channels of electrons shows that only the diffusion thermoelectric power appears in Co nanoparticles, at which α(T) is the linear function. No mechanisms of the thermoelectric power caused by nanosizes of Co particles or by electron tunneling between them are found. The kink of the α(T) linear dependence is explained by the existence of the oxide shell of Co nanoparticles. It is assumed that the temperature dependences of energy barriers of oxide shells of metal nanoparticles (including ferromagnetic ones) in oxygen-containing dielectric matrices determine the features of α(T) and ρ(T) dependences of such nanocomposites.     

Method of calculating the fields of residual stresses and plastic strains in cylindrical specimens with allowance for surface hardening anisotropy

A mathematical model is proposed for calculating the stress-strain state of a cylindrical specimen, which arises as a result of plastic surface hardening leading to material deformation anisotropy. The model adequacy is verified through comparisons with experimental data for cylindrical specimens made of 30KhGSA and St. 45 steels. A method of identifying model parameters on the basis of results of a fundamental experiment is developed. Good agreement of the calculated and experimental data is demonstrated.     

Formation of polymer–colloid complexes of aluminoxane particles with poly(acrylic acid) and its copolymers with acrylamide

Formation of polymer–colloid complexes formed by positively charged aluminoxane particles with a size of ~4.6 nm, which constitute the main part of the dispersed phase in aluminum polyhydroxychloride sols with poly(acrylic acid) and acrylic acid copolymers with acrylamide, is studied. Conditions of preparing water-soluble polymer–colloid complexes are determined. It is shown that water-soluble polycomplexes are obtained through the interaction of aluminoxane particles with acrylic acid–acrylamide copolymers containing no more than 0.8 mol% acrylic acid units. In the polymer–colloid complex, aluminoxane particles are uniformly distributed over polyelectrolyte macromolecules and the optimum composition is attained at the molar ratio of components Z equal to 1:1. In semidilute solutions, the addition of aluminoxane particles to the copolymer brings about formation of the gel featuring viscoelastic properties. For all copolymers, the maximally elastic properties of the gels are attained at Z ≈ 1.     

Simulation of disk extruder operation

Mathematical simulation of thermoplastic polymer processing by a disk extruder was considered. The results were compared with experimental data obtained in an extruder of a 200 mm diameter. The developed technique of calculation allows selection of design parameters of operational parts and disk speed for preset output of the disk extruder as well as energy-power parameters of extrusion.     

Comparison of SERS effectiveness of copper substrates prepared by different methods: what are the values of enhancement factors?

Surface‐enhanced Raman scattering (SERS) spectroscopy is an analytical method for the detection of low amounts of analytes adsorbed on an appropriate coinage metal (Au, Ag, Cu) surface. Generally, the values of the enhancement factor are the highest on silver, lower on gold and relatively very low on copper. In this study, we have focused on the estimation of the enhancement factors of copper surface/substrates formed by different preparation procedures. The SERS activity of large electrochemically prepared substrates and colloidal systems is compared. The surface morphology of the large substrates was studied using scanning electron microscopy and atomic force microscopy. The size distribution of colloidal nanoparticles was monitored by dynamic light scattering. The values of enhancement factor are in both cases more than 10⁵ for the FT‐SERS spectra, demonstrating the fundamental role of nanostructured copper as a substrate material at the excitation wavelength (1064 nm) used. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction of intersecting shocks with a flat-plate boundary layer in the presence of an entropy layer

Gas flow and heat transfer on the surfaces of sharp and blunt plates is experimentally investigated in the presence of two forward-looking wedges at the Mach numbers M = 5, 6, and 8 and the Reynolds numbers up to Re_∞L = 27×10⁶. It is shown that the entropy layer generated by a small bluntness of the leading edge of the plate can considerably change the heat transfer, the gas pressure, and the friction in the zone of interference of the shock with the plate boundary layer. Under certain conditions a small plate bluntness can also lead to a qualitative change in the flow structure. The effect of constriction of the channel between the wedges on the interference flow is studied.     

Collapse in coupled nonlinear Schrödinger equations: Sufficient conditions and applications

In this paper we study blow-up phenomena in general coupled nonlinear Schrödinger equations with different dispersion coefficients. We find sufficient conditions for blow-up and for the existence of global solutions. We discuss several applications of our results to heteronuclear multispecies Bose-Einstein condensates and to degenerate boson-fermion mixtures.