Adsorption and inhibitive properties of benzimidazole derivatives in acid mild steel corrosion

Eight diazoles were investigated as corrosion inhibitors of mild steel in 1 M hydrochloric acid using gravimetric and polarization techniques. It was found that the inhibition efficiency increased with the increase of organic substrate concentration, while the adsorption followed the Frumkin isotherm. A correlation between the electronic parameters (induction and mesomeric effects of the substituents, ionization potential values) as well as those of the chemical structure (molecular area) of diazoles molecules and their inhibiting properties was looked for. The results obtained show that a definite interdependence exists but it is not as simple and straightforward as might be expected.     

Einige fragen der tunneltheorie der wasserstoffüberspannung—II. Die temperaturabhängigkeit der stromdichte und die beträge der quanteneffekte

The dimensions of the potential barrier involved in hydrogen and deuterium evolution on mercury are computed from the experimental values of the effective activation energies on the assumption that the barrier has a parabolic shape. The ratio of the pre-exponential factors and the isotopic separation factor obtained theoretically in this manner are in good agreement with experimental data. The calculation shows that the tunnel effect plays a substantial but still moderate role in the case under study. Comparison with the results of an earlier derivation based on Eckart's potential function allows the determination of the most probable shape of the true barrier. The usually assumed dimensions are shown to be incorrect.

Résumé

On calcule les dimensions de la barrière de potentiel pour le dégagement d'hydrogène et de deutérium sur le mercure en partant des valeurs expérimentales de l'énergie d'activation et en supposant que la barrière a une forme parabolique. Le rapport des facteurs préexponentiels et le facteur de séparation isotopique ainsi obtenus théoriquement sont en accord avec les données expérimentales. Le calcul montre que l'effet tunnel ne peut être négligé mais qu'il ne joue cependant qu'un rôle moyen dans le cas étudié. La comparaison avec les résultats d'une dérivation précédente partant de la fonction de potentiel d'Eckart permet de déterminer la forme la plus probable de la barrière de potentiel. Il est montré que les valeurs habituellement admises pour les dimensions de cette barrière ne sont pas correctes.     

Diffusion of ellipsoidal granular particles in shear flow

The diffusion of nonspherical particles has not been well understood due to the complexity of their contact mechanics and self-organization of their orientations. We perform discrete element method simulations of monodisperse ellipsoids in a shear flow with Lees-Edwards boundary conditions to quantify the relation between the diffusion coefficient and the flow parameters. The results indicate that the particle aspect ratio strongly affects the diffusion coefficient by influencing the particle orientation and alignment. We develop a scaling law for the diffusion coefficient perpendicular to the flow direction, D_yy, which combines the influences of the shear rate , the solids fraction f, the effective particle diameter d_eff and the particle aspect ratio Z. We show that , where k_d is a dimensionless pre-factor, and a fit is obtained for the functional form of χ(f, Z). This scaling law will be useful in developing continuum transport models for applications.     

Collision dynamics of elliptically polarized solitons in Coupled Nonlinear Schrödinger Equations

We investigate numerically the collision dynamics of elliptically polarized solitons of the System of Coupled Nonlinear Schrödinger Equations (SCNLSE) for various different initial polarizations and phases. General initial elliptic polarizations (not sech$sech$-shape) include as particular cases the circular and linear polarizations. The elliptically polarized solitons are computed by a separate numerical algorithm. We find that, depending on the initial phases of the solitons, the polarizations of the system of solitons after the collision change, even for trivial cross-modulation. This sets the limits of practical validity of the celebrated Manakov solution. For general nontrivial cross-modulation, a jump in the polarization angles of the solitons takes place after the collision (‘polarization shock’). We study in detail the effect of the initial phases of the solitons and uncover different scenarios of the quasi-particle behavior of the solution. In majority of cases the solitons survive the interaction preserving approximately their phase speeds and the main effect is the change of polarization. However, in some intervals for the initial phase difference, the interaction is ostensibly inelastic: either one of the solitons virtually disappears, or additional solitons are born after the interaction. This outlines the role of the phase, which has not been extensively investigated in the literature until now.     

Numerical implementation of the asymptotic boundary conditions for steadily propagating 2D solitons of Boussinesq type equations

In the present paper, a difference scheme on a non-uniform grid is constructed for the stationary propagating localized waves of the 2D Boussinesq equation in an infinite region. Using an argument stemming form a perturbation expansion for small wave phase speeds, the asymptotic decay of the wave profile is identified as second-order algebraic. For algebraically decaying solution a new kind of nonlocal boundary condition is derived, which allows to rigorously project the asymptotic boundary condition at the boundary of a finite-size computational box. The difference approximation of this condition together with the bifurcation condition complete the algorithm. Numerous numerical validations are performed and it is shown that the results comply with the second-order estimate for the truncation error even at the boundary lines of the grid. Results are obtained for different values of the so-called ‘rotational inertia’ and for different subcritical phase speeds. It is found that the limits of existence of the 2D solution roughly correspond to the similar limits on the phase speed that ensure the existence of subcritical 1D stationary propagating waves of the Boussinesq equation.     

Spectrum-preserving Amplification of Ultra-broadband Optical Pulses

Abstract

An amplifier scheme which allows control of the spectrum of the amplified pulse is proposed. The spectral components of the initial pulse are sent into laterally shifted regions of the amplifying medium, which enables control of the gain of particular frequency components. By the use of a properly formed pump, spectral narrowing during amplification can be avoided. A ‘spectrum preserving’ amplification of ultra-broadband (f.w.h.m. of about 30 nm) nanosecond pulses is demonstrated.     

Shear dispersion in dense granular flows

We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Péclet number squared, as in classical Taylor–Aris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.     

Recursive model free controller: Application to friction compensation and trajectory tracking

In this paper friction compensation and trajectory tracking scheme is proposed for an X-Y robot using a Recursive Model Free Controller (RMFC). This controller is based on the theory of piecewise continuous systems which are a particular class of hybrid systems with autonomous switchings and controlled impulses. RMFC uses only the robot position measurements and does not require knowledge of electromechanical system parameters. The proposed control scheme is validated on a real time X-Y robot system.     

A computational algorithm for pole assignment of linear single-input systems

An efficient computational solution of the pole assignment problem of linear single-input systems is presented. It is based on orthogonal reduction of the closed-loop system matrix to upper (quasi-) triangular form whose 1 × 1 or 2 × 2 diagonal blocks correspond to the desired poles. The algorithm proposed is numerically stable and performs equally well with real and complex, distinct, and multiple desired poles. The number of the computational operations is less than6n^{3}, the necessary array storage being2n^{2} + 6nworking precision words, wherenis the order of the system.