Decreasing Function Of Concentration Research Articles

Modeling the Creep Rupture of Tensile Rods in an Aggressive Medium with Account of a Variable Diffusion Coefficient

The creep rupture of a long rod subjected to tension in an aggressive medium is considered. Using a diffusion equation where the diffusion coefficient D is a monotonically decreasing function of concentration c of the medium, the diffusion penetration of elements of the aggressive medium into the material of the rod is modeled. On the border between the rod and external medium, a condition of mass transfer is assumed. The approximate method put forward for solving the diffusion equation is based on the introduction of a diffusion front. Two stages of the diffusion process are considered: penetration of the front and saturation. A comparison between solutions of the diffusion equation for proposed D(c) functions is performed. The influence of D(c) on the creep rupture of a tensile rod is evaluated using the Rabotnov kinetic theory of creep and creep rupture.

A theoretical study on the frequency-dependent electric conductivity of electrolyte solutions. II. Effect of hydrodynamic interaction

The theory on the frequency-dependent electric conductivity of electrolyte solutions proposed previously by Yamaguchi et al. [J. Chem. Phys. 127, 234501 (2007)] is extended to include the hydrodynamic interaction between ions. The theory is applied to the aqueous solution of NaCl and the concentration dependence of the conductivity agrees well with that determined by experiments. The effects of the hydrodynamic and relaxation effects are highly nonadditive in the concentrated solution, because the hydrodynamic interaction between ions affects the time-dependent response of the ionic atmosphere. The decrease in the electric conductivity is divided into the contributions of ion pair distribution at various distances. The long-range ionic atmosphere plays a major role at the concentration as low as 0.01 mol/kg, whereas the contribution of the contact ion pair region is important at 1 mol/kg. The magnitude of the contribution of the contact ion pair region is scarcely dependent on the presence of the hydrodynamic interaction. The transport number of cation is calculated to be a decreasing function of concentration as is observed in experiments.

The evolution of travelling waves in reaction-diffusion equations with monotone decreasing diffusivity. I. Continuous diffusivity

We examine the effects of a concentration dependent diffusivity on a reaction-diffusion process which has applications in chemical kinetics. The diffusivity is taken as a continuous monotone, a decreasing function of concentration that has compact support, of the form that arises in polymerization processes. We consider piecewise-classical solutions to an initial-boundary value problem. The existence of a family of permanent form travelling wave solutions is established, and the development of the solution of the initial-boundary value problem to the travelling wave of minimum propagation speed is considered. It is shown that an interface will always form in finite time, with its initial propagation speed being unbounded. The interface represents the surface of the expanding polymer matrix.

A study of the interacting FENE dumbbell model for semi-dilute polymer solutions in extensional flows

The effect of polymer concentration on the conformation of semidilute polymer solutions in extensional flows is studied via the interacting elastic dumbbell model proposed by Hess (1984), here modified to include a nonlinear Warner spring (FENE dumbbell) instead of the linear Hookean spring of the original model. The length of flow-induced conformation changes for the polymer is predicted to be a decreasing function of concentration. In particular, increasing concentration tends to inhibit large extension of the polymer due to polymer-polymer interaction. The specific birefringence is thus proportional to c−1 for semi-dilute solutions, in contrast to dilute solutions where it is known to be independent of concentration. However, the correlation between birefringence and the principle eigenvalue of the velocity gradient tensor, also found originally for dilute solutions, is predicted to occur in the semi-dilute regime. All of these predictions agree qualitatively with experimental observations.

Diffusion kinetics of a dialkyne in silicone rubber by density profiling

The technique of density profiling was used to monitor the diffusion of bishydroxycyclopentylbutadiyne (HCPB) through a silicone rubber. Reaction of HCPB with excess hydrosilane sites, unreacted during the polymer cure process, immobilized part of the diffusant and led to the development of a concentration front, or plateau, in the diffusion profiles. Kinetic modelling was used to reproduce the salient features of the profiles and to provide a means of obtaining a diffusion coefficient. The diffusion coefficient was found to be a decreasing function of concentration, in contrast to the behaviour observed in most systems.

Concentration-dependent magnetic birefringence measurements in the isotropic phase of a lyotropic liquid crystal

The concentration and temperature dependences of the Cotton-Mouton coefficient C for the binary mixture cesium perfluoro-octanoate and water close to a nearly-second-order nematic-isotropic transition are reported. It was found that (T-${T}^{\mathrm{*}}$)C is a weakly decreasing function of concentration, indicating a significant concentration dependence of the micelle structure.

Short-term intake functions for sucrose in developmentally retarded children.

Short-term (5 min.) intake functions for sucrose were determined for 11 brain-damaged, developmentally retarded children using the single-stimulus-presentation method. Sucrose intake was a decreasing function of concentration. Water intake was equal to or greater than the greatest intake of any concentration of sucrose. These intake functions lacked the ascending limb of intake functions for water and weak concentrations of sucrose which are found in other animal species and in human adults. Evidence supports the notion that severely developmencally retarded children are not ageusic but can discriminate between various concentrations of sucrose and water.