Theory of internal thermal equilibrium in inhomogeneous structures

Characteristic features of the establishment of thermal balance between the phases are identified for an arbitrary P-component composite and the time constant for temperature equalization is calculated. An analysis is made to ascertain how the size distribution of the impurity phase influences the time behavior of the composite temperature. A Laplace transformation is used to find a general expression for δT ₀(t) and the specific form of this functional dependence is calculated when the particles of the finely dispersed phase have a Poisson distribution. Pis’ma Zh. Tekh. Fiz. 24, 29–36 (May 26, 1998)     

Influence of thermomechanical aging on fatigue behaviour of 2014 Al-alloy

The fatigue behaviour of 2014 Al-alloy has been studied in various thermomechanically aged conditions. It is observed that fatigue properties can be improved by a thermomechanical treatment, which would reduce the concentrations of dispersoids, provide a relatively uniform deformation structure and produce fine distribution of θ’ precipitates. Fine θ’ particles inhibit dynamic recovery and produce uniform deformation structure, which improves fatigue behaviour. Presence of dispersoids and coarse precipitate particles leads to the formation of persistent slip bands (PSBs) and a highly heterogeneous deformation structure, which cause damage to fatigue properties.     

Multiple strengthening mechanisms in nanoparticle-reinforced copper matrix composites

The multiple hardening mechanisms of a copper matrix have been presented and discussed. The pre-alloyed ball milled Cu–3 wt.%Al and the atomized Cu–0·6 wt.%Ti–2·5 wt.%TiB ₂ powders have been used as starting materials. Dispersoid particles Al ₂ O ₃ and TiB _2\thinspace _{{\bf 2}\thinspace }were formed in situ. The powders have been hot consolidated. Optical microscopy, SEM, TEM, and X-ray diffraction analysis were performed for microstructural characterization. Increase in microhardness of Cu–3 wt.%Al compacts is a consequence of the crystallite size refinement and the presence of Al ₂ O ₃ particles. High hardening of Cu–0·6 wt.%Ti–2·5 wt.%TiB ₂ is a consequence of the presence of modular structure, Cu ₄ Ti_(m), and TiB ₂ particles.     

Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al ₃ Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al ₃ Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al ₃ Zr particles and found to be rod shaped and identified to be cubic ordered L 1 ₂ phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al ₃ Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al ₃ Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.     

Interaction of charged dust particles. Debye quasimolecule

An analysis is made of an electrically neutral system of two small positive charges surrounded by a common cloud of Boltzmann-distributed electrons. This system, which simulates macroparticle interaction in a dusty plasma, is called a Debye quasimolecule. Calculations are made of the force and potential interaction energy of shielded dust particles as a function of the distance between them. It is shown that the electron shells are polarized so that the forces of attraction of the dust particles in a Debye quasimolecule predominate over the forces of repulsion of their like charges. This may occur up to distances equal to the size of the dust particles. It is concluded that metastable dusty liquids and crystals cannot exist when the electron clouds of the charged particles obey a Boltzmann distribution. Pis’ma Zh. Tekh. Fiz. 25, 83–89 (August 26, 1999)     

Kinetics of predetonation conductivity of silver azide

The kinetics of the predetonation conductivity of silver azide have been measured with nanosecond time resolution. The experimental results are accurately approximated by an equation which includes multiplication of active particles by a first-order reaction and loss of these particles by a second-order reaction. Pis’ma Zh. Tekh. Fiz. 25, 44–48 (November 26, 1999)     

Effects of nonlocality on the dynamics of streamers in positive corona discharges

Computer simulation is used to study the effect on the parameters of the streamer plasma due to the nonlocality of the electron energy distribution near the head of a streamer in air. Taking into account the nonlocality increases the electron field strength in the head and the electron density in the channel. The streamer radius decreases, while the streamer velocity and current as well as the efficiency of generating chemically active particles remain essentially the same as in the local approach. Pis’ma Zh. Tekh. Fiz. 23, 89–94 (June 26, 1997)     

Self-similarity and branching of wavelet transforms of microwave signals generated by a vircator

The turbulence regimes of an electron flow with a virtual cathode are studied. The microwave signals generated by a vircator are calculated by the method of large particles. The wavelet transforms of these signals are constructed, and it is shown that they have a complicated self-similar and branching structure. It is concluded that the turbulence of an electron flow is caused by macroscopic instabilities. Pis’ma Zh. Tekh. Fiz. 22, 92–96 (December 26, 1996)     

Superdeep penetration efficiency

The efficiency of an explosive accelerator is analyzed. The efficiency of the stream of particles in penetrating into a target to ultralarge depths is determined. Pis’ma Zh. Tekh. Fiz. 24, 81–84 (September 12, 1998)     

Some physical properties of an Al2O3-SiC-TiC composite

Ceramic samples obtained by hot pressing from a mixture of Al₂O₃ with admixtures of 23 vol.% TiC powder and 30.9 vol.% SiC whisker crystals are investigated experimentally. The resistivity of the material is measured at temperatures of 4.2–300 K, the infrared reflection spectra are recorded in the region 400–4200 cm^–1, and the temperature dependence of the Young’s modulus is investigated at temperatures up to 1300 K. As a result it is it is shown that the conductivity and optical reflection of the high-strength composite have a semimetallic character, which is due to the titanium carbide particles contained in it. Pis’ma Zh. Tekh. Fiz. 23, 52–58 (December 12, 1997)     

Two-particle interference devices and compatibility of bohmian and standard quantum mechanics

Abstract

A number of assertions have recently been made that in two-particle interference devices, Bohmian trajectories may not reproduce exactly all statistical predictions of quantum mechanics. Specifically, let two identical bosons go through identical slits arranged symmetrically with respect to a plane, with wave functions transforming into each other under the symmetry operation. Then it is claimed that pairs of particles following Bohmian trajectories and registered on a screen opposite the slits may have observable spatial distribution properties not predicted by quantum mechanics. We point out that alleged discrepancies in fact originate from a specific sampling assumption on Bohmian particles that violates their general probability distribution.     

Electrophoretic motion of two solid particles embedded in an unbounded and viscous electrolyte

 This work determines the electrophoretic motion of two colloidal particles embedded in a viscous and unbounded electrolyte. Contrary to other works in the field, the advocated method does not calculate the perturbation electric potential and the electrolyte Stokes flow in the whole fluid domain and its range of applications is not restricted to the case of uniformly charged particles embedded in a uniform electric field E _∞. The idea consists in establishing and solving thirteen Fredholm boundary integral equations (one of the second kind plus twelve of the first kind). The numerical implementation is briefly reported. Numerical benchmarks and new results are both presented and discussed with a special attention to the interactions between the particles. Received 26 February 2001     

Investigation of inhomogeneous kinetic processes in a gaseous medium excited by multiply charged ions

The space-time characteristics of track structures in a gaseous medium excited by multiply charged ions have been studied theoretically for the first time and the influence of these structures on the quality of the radiation beam from lasers has been assessed. A model has been developed to describe the diffusion and drift of heavy particles at all stages of the track evolution process. Pis’ma Zh. Tekh. Fiz. 23, 89–94 (April 26, 1997)     

Theory of the Lesage-Jeans instability in a linear chain of dust particles in plasma

The dynamics of the Lesage-Jeans instability in a linear infinite periodic chain of dust particles in plasma is studied theoretically by deriving and numerically solving the nonlinear wave equation. Pis’ma Zh. Tekh. Fiz. 25, 84–89 (September 12, 1999)     

Motion of a “drift island” in a toroidal magnetic confinement device with Coulomb scattering of the particles

A resonant drift trajectory of a charged-particle in a magnetic field (a “drift island”) can be used to remove high-energy impurities from a thermonuclear plasma and to introduce (inject) high-energy particles into the plasma. As a rule, these effects are studied neglecting the Coulomb scattering, i.e., in the collisionless approximation. In the present letter, the effect of Coulomb scattering of a particle with a resonant trajectory by plasma particles is studied. The conditions under which the drift resonance is maintained are found, i.e., the plasma densities and plasma density profiles for which the “drift island” can still move over the transverse section of the plasma are determined. Pis’ma Zh. Tekh. Fiz. 25, 19–27 (September 26, 1999)     

Interaction between relativistic charged particles and an extended strong rf field

An investigation is made of the interaction between relativistic charged particles and a high-intensity microwave electric field over long interaction lengths. The microwave field has no magnetic component over the entire interaction length. It is shown that the interaction of the relativistic particles has features which depend on the relation between the incoming particle energy and the field strength. In particular, part of a monoenergetic particle beam may be accelerated by the beam’s own energy with some of the energy being transferred from the beam to the field. Pis’ma Zh. Tekh. Fiz. 24, 80–86 (May 26, 1998)     

Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys

Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al–Zr–Ti alloys, the primary Al₃Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al–Ti, Al–Ti–Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al–3Ti–B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants.     

Acceleration of Brownian particle diffusion parallel to a fast random field with a short spatial period

It is shown that a spatially periodic random field fluctuating rapidly near zero with a fairly small spatial period may substantially accelerate the diffusion of Brownian particles parallel to this field. Pis’ma Zh. Tekh. Fiz. 24, 9–15 (November 12, 1998)     

Laser control of the state of a plasma in a selective optical trap

Laser cooling of resonant ions is shown to be applicable to the effective control of the temperature of charged particles in a low-temperature electron-ion plasma confined in a magnetic trap. Pis’ma Zh. Tekh. Fiz. 23, 28–32 (January 26, 1997)     

Role of Surfactant on Drug Release from Tablets

Abstract

The addition of a surfactanat into a tablet formulation appears to be attractive method of improve the drug release rate. The improved release rate is often associated with the effect of surfactant increasing the hydrophilicity of the dosage form thereby promoting drug dissolution. The findings of this investigation showed tha the presence of surfactant infulenced the tablet disintegration rate, producing a finer dispersion of disintergrated particles. It follows that the action of surfactant improving drug dissolution from tablets may be attributed ot the aciton of surfactnat producing fine disintegrated particles with correspondingly larger surface area for drug dissolution. It was also demonstrated that upon tablet disintergration the disinstegrated particles have a tri-moal frequency distribution.