Technical Physics Letters最新文献

Abstract

A method for deriving the Navier–Stokes equation with allowance for inhomogeneities of any order on the Laplace operator using the Boltzmann kinetic equation is proposed. The solution method is based on the theory of nonequilibrium phenomena and the entropy growth principle. The calculation has been carried out to find additional inhomogeneous terms on the Laplace operator in the right-hand side of the Navier–Stokes equation. New-type fundamental solutions to the stationary parabolic equation have been predicted, which are significant for application in solving some problems of mathematical physics.

Abstract

Using the constructed Lagrange function (L) and calculated dissipative function (dot {Q}), a general system of dynamic equations has been obtained to describe the motion of a cylindrical body completely immersed in a fluid. It is assumed that the body is hinged at its one end where the origin of coordinates is selected. The free end can make almost any motions and is elastically held by a spring at an arbitrary point. The problem is solved in a spherical coordinate system in which differential equations of motion are derived in terms of two independent angular variables (theta ) and (varphi ) taking into account the viscosity (eta ) of a continuum.

Abstract

It was experimentally found that speeds of hot submerged jets appearing in case of laser induced nucleation boiling of water near the tip of optical fiber submerged in water decrease exponentially with increasing laser power (heat flux). This result was obtained for a closed cylindrical cuvette where hot jets collided with walls and slipped the cuvette boundary transferring heat to it. The obtained result is to be taken into account in performing precise laser–induced surface cleaning inside confined volumes, in developing medical technologies for laser therapy of pathologically changed vessels or cysts, and in other applications.

Abstract—The results of numerical simulation of unsteady free convection developing near a suddenly heated plate, on which protrusions in the form of adiabatic cylinders of double height with respect to the diameter are arranged in a staggered order, are presented. The calculations were performed according to the Reynolds equations using a differential model of turbulent stresses. The range of variation of the Grashof number (plotted according to the thickness of the free convective flow), in which a significant intensification of heat transfer can be achieved, has been determined. It is shown that the best conditions for intensification are created if the longitudinal pitch in the array of protrusions is approximately twenty times the diameter of the latter.

Abstract—The behavior of a “water-in-oil” emulsion stabilized with asphaltenes under the action of an inhomogeneous alternating electric field has been studied. The experimental technique was based on the use of microfluidics, optical microscopy, and high-speed video filming. The dependences of quantitative estimates of the parameters characterizing the dynamics of the emulsion destruction on the frequency and amplitude of the applied field have been obtained. The technique will be useful in developing efficient methods for breaking emulsions and modifying the existing technologies for separating oil emulsions into phases.

Abstract

A new approach to the creation of millimeter-wave radio imaging systems is proposed. This approach is based on the use of an array receiver consisting of a densely packed (pixel size of 4 mm) array of planar mixers located in the focal plane of a quasi-optical objective, with application of the frequency-modulated continuous-wave radar technique. It has been demonstrated that the implementation of the heterodyne type of reception makes it possible to increase the distance range of the array radio imaging system up to ~100 m while maintaining the angular resolution at the previous level.

Abstract

The dynamics of the interfacial tension coefficient at the interface between water and model solutions of asphaltenes of different concentrations in toluene has been studied. It has been shown that, over time, the interfacial tension decreases due to the adsorption of asphaltene molecules at the interface. With an increase in the concentration of asphaltenes in the solution, the decrease in interfacial tension occurs more intensively. The results of a study of the elongation of a water drop in a solution under the influence of an electric field are presented. It is shown that after the formation of an adsorption film, a higher electric field must be applied to stretch the droplet, and the relative elongation depends nonlinearly on the applied voltage.

Abstract

It was found that in the region of the percolation threshold, depending on the dominance of one or another conduction mechanism, the temperature dependence of the specific volume resistivity ρ(T) of the polymer composite based on a matrix of ethylene vinyl acetate is significantly transformed. With an increase in the CB content, there is a decrease by several orders of magnitude in the maximum value of the relative resistivity ρ(T)_max/ρ₂₀ in its temperature dependence. Peroxide crosslinking of matrix macromolecules leads to a change in the nature of the temperature dependence of resistivity.

Abstract

The main results of non-linear optical, spectral and current–voltage characteristics research of pyridine organic conjugated molecule-carbon nanoparticles combined system have been presented. The perspective of these materials further study in global trends of modern search of materials for optical limiting has been demonstrated also in the present paper.

Abstract

A plasma-chemical method for the modification of silicon carbide particles is presented, which makes it possible to obtain particles with a controlled surface morphology. The variable parameter of particle processing was the ratio of the fraction of plasma-forming (Ar) and additional (H) gases. It was shown that at Ar/H = 100/0, the formation of a carbon shell is observed; at Ar/H ratios of 91/9 and 84/16, the particles are characterized by a carbon shell decorated with silicon nanoparticles or nanowires, respectively. The modified particles were analyzed using scanning electron microscopy and Raman spectroscopy.