At the electrochemical deposition of alloys various phenomena are observed that lead to changes in the kinetics and thermodynamics of the processes. In particular, as a result of changing in the ...nature of the electrode surface, both the exchange current densities and the transfer coefficients of each of the components changed. Further, during the formation of solid solutions, the equilibrium potentials of the components change due to the non-zero enthalpy and entropy of mixing. At the deposition of eutectic-type alloys (that is, a mixture of grains of individual components), each of the metals does not deposit on the entire electrode surface but only on its own surface. In the latter case, there is a change in the diffusion pattern of the components as compared to the deposition of individual metals: it remains unchanged in the outer part of the diffusion layer but there is a condensation of the diffusion fields of the components near the surface, similar to the case of diffusion to the matrix of microelectrodes or to individual nuclei of a new phase. This also leads to a change in the diffusion part of the overpotential of the components’ deposition. The diffusion of ions of the discharging negative component of an alloy representing a mechanical mixture of the metals’ A and B grains to the grain surface of this component in the model of a partially blocked electrode is considered. At a constant potential, the local current density of the component is shown to increase as a result of the diffusion acceleration. The magnitude of the relative increase in the current and the corresponding magnitude of apparent depolarization are found, as compared between the deposition of an individual metal and the codeposition of the same component into an alloy.
New semiclassical quantization conditions for the energy levels of pseudoscalar, vector, and pseudovector mesons as composite systems formed by two relativistic arbitrary-mass fermions interacting ...both via nonsingular confining potentials and singular confining funnel-type potentials involving Coulomb (chromodynamical) interaction were derived. The respective analysis was performed within the relativistic quasipotential approach based on the covariant Hamiltonian formulation of quantum field theory via a transition from the momentum representation in Lobachevsky space to the three-dimensional configuration representation for the case of a composite system of two relativistic spin particles that have arbitrary masses.
The effect of an interplay between electrostatic and excluded volume interactions on the conformational behavior of a dipolar chain has been studied theoretically and by means of molecular dynamics ...simulations. Every monomer unit of the dipolar chain comprises a dipole formed by a charged group of the chain and an oppositely charged counterion. The counterion is assumed to freely move around the chain but keeping the distance between oppositely charged ions (the dipole length) fixed. The novelty of the developed mean-field theory is that variations of the dipole parameters (the dipole length and the counterion size) have been accounted for in both electrostatic and excluded volume contributions to the total free energy of the dipolar chain. It has been shown that conformational transitions between swollen and collapsed states of the chain can be induced by fine-tuning the balance between electrostatic and excluded volume interactions. In particular, in low-polar media not only globule but also extended coil conformations can be realized even under strong electrostatic attraction. The results of MD simulations of a dipolar chain with variable dipolar length support theoretical conclusions.
The locus of extrema (ridges) for heat capacity, thermal expansion coefficient, compressibility, and density fluctuations for model particle systems with Lennard-Jones (LJ) potential in the ...supercritical region have been obtained. It was found that the ridges for different thermodynamic values virtually merge into a single Widom line at T < 1.1T c and P < 1.5P c and become practically completely smeared at T < 2.5T c and P < 10P c, where T c and P c are the critical temperature and pressure. The ridge for heat capacity approaches close to critical isochore, whereas the lines of extrema for other values correspond to density decrease. The lines corresponding to the supercritical maxima for argon and neon are in good agreement with the computer simulation data for LJ fluid. The behavior of the ridges for LJ fluid, in turn, is close to that for the supercritical van der Waals fluid, which is indicative of a fairly universal behavior of the Widom line for a liquid–gas transition.
A new relativistic semiclassical expression is derived for leptonic decay widths of vector mesons as a composite system of two quarks having equal masses and interacting via a funnel-like potential. ...This new expression is compared with its nonrelativistic spinless and relativistic spin and spinless analogs. The effect of the spins of equal-mass quarks forming vector mesons on the behavior of the leptonic decay widths of these mesons is analyzed. This analysis is performed within the relativistic quasipotential approach based on the covariant Hamiltonian formulation of quantum field theory by means of a transition from the momentum representation in Lobachevsky space to the three-dimensional relativistic configuration representation for the case of a composite system of two relativistic spin equal-mass particles.
As found from the results of studying the mechanism of polishing precision surfaces of nonmetallic parts by dispersion systems based on micro- and nanoparticles of polishing powders, the formation of ...sludge particles, a polishing powder, and grinding particles is a consequence of the Förster resonant energy transfer (FRET). This occurs in the resonator formed by two parallel surfaces of the work piece and the polishing paste. It is shown that the productivity of polishing of nonmetallic materials increases nonlinearly with an increase in the quality factor of the resonator, while the roughness of the treated surfaces deteriorates. The relationship between the quality factor and the optical length of the resonator is established, and it is shown that the maximum values of the removal rate of the treated material, the intensity of wear of the polishing powder, and the wear of the grinding surface are achieved at a certain optical length of the resonator. It is equal to the number of half waves, which is characteristic of nanoparticles of the sludge, polishing powder, and grinding material. It is shown that the productivity of polishing the parts made of nonmetallic materials and the roughness of their polished surfaces are extremely dependent on the dielectric constant diffrenece between the processed material, the polishing powder, and the dispersion system.
We theoretically study flux-flow instability in a highly disordered thin superconducting strip placed in a perpendicular magnetic field H. We find that the jump from the resistive (flux-flow) state ...to the normal one at quenching current Iq(H) above the critical current Ic(H) starts from the appearance of localized regions with suppressed superconductivity and fast-moving vortices near the edge of the strip, where vortices enter the superconductor and local current density is maximal. These regions propagate to the opposite edge and form highly resistive self-made Josephson-like links, which are unstable and evolve to the normal domains, which then expand along the superconducting strip.
On the assumption of the mixed kinetics of the process, new formulas are derived for the calculating of the diffusion coefficient, the nucleation rate, and the number of growing clusters, basing on ...the experimental curves of the time dependence of the current during the potentiostatic nucleation and growth in the electrocrystallization process. In this context, some literature experimental data are analyzed. It is shown that during crystallization on an active metal substrate, the number of nuclei can sharply increase with potential, unlike structureless substrates (such as glassy carbon) at which the nuclei number depends but weakly on the potential.
Dynamic characteristics of strongly coupled classical one-component Coulomb and Yukawa plasmas are obtained within the nonperturbative model-free moment approach without any data input from ...simulations so that the dynamic structure factor (DSF) satisfies the first three nonvanishing sum rules automatically. The DSF, dispersion, decay, sound speed, and other characteristics of the collective modes are determined using exclusively the static structure factor calculated from various theoretical approaches including the hypernetted chain approximation. A good quantitative agreement with molecular dynamics simulation data is achieved.
The evolution of the distribution pattern of an ink droplet freely falling on the wavy surface of a liquid is traced by video-recording methods. A system of travelling plane gravity–capillary waves ...with a frequency of
Hz (a wavelength of
cm) was created by a vertically oscillating pointed strip. Drops of alizarin ink with diameter
cm fell freely from the dispenser and reached contact velocity
cm/s in the mode of splash formation. In the phase of primary contact and coalescence, the colored drop spreads in agitated liquid like in a quiet medium with the formation of a cavity with its bottom covered by colored fibers, a crown, and a splash. The growing crown is surrounded by a group of thin radial trickles with vortex heads and separate spots (wakes of earlier returned ejected droplets). Subsequently, the colored liquid on the surface is divided into three independently moving formations: a finely structured area of primary contact of an irregular shape, a submerging vortex ring, and a near-surface vortex dipole. In all components of the flow, the dye is distributed in the form of thin fibers for a long time until the final phase of erosion by residual flows and molecular diffusion processes. The geometry of movement and the general structure of the separated colored areas are traced.
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