Experimental-theoretical Method Research Articles

Reaction Diffusion Model of the Enzymatic Erosion of Insoluble Fibrillar Matrices

Predicting the time course of in vivo biodegradation is a key issue in the design of an increasing number of biomedical applications such as sutures, tissue analogs and drug-delivery devices. The design of such biodegradable devices is hampered by the absence of quantitative models for the enzymatic erosion of solid protein matrices. In this work, we derive and simulate a reaction diffusion model for the enzymatic erosion of fibrillar gels that successfully reproduces the main qualitative features of this process. A key aspect of the proposed model is the incorporation of steric hindrance into the standard Michaelis–Menten scheme for enzyme kinetics. In the limit of instantaneous diffusion, the model equations are analogous to the standard equations for enzymatic degradation in solution. Invoking this analogy, the total quasi-steady-state approximation is used to derive approximate analytical solutions that are valid for a wide range of in vitro conditions. Using these analytical approximations, an experimental–theoretical method is derived to unambiguously estimate all the kinetic model parameters. Moreover, the analytical approximations correctly describe the characteristic hyperbolic dependence of the erosion rate on enzyme concentration and the zero-order erosion of thin fibers. For definiteness, the analysis of published experimental results of enzymatic degradation of fibrillar collagen is demonstrated, and the role of diffusion in these experiments is elucidated.

Evaluating the residual life of salt pillars

Thus, the completed studies have made it possible to develop a technology and methodology, based on the compensation method, for measuring the load on the edges of inter-chamber pillars. An experimental-theoretical method has also been proposed for estimating the residual life of such pillars in excavated sections of potassium mines. The results of full-scale measurements established that the edge regions of interchamber pillars located near the boundary of a cave-in (region of chamber 103 in our investigation) are in the supercritical state. For a subsidence rate of 1.5 mm/day at the surface, the residual life of such pillars is estimated to be 7–8 months. The zone loaded by bearing pressure from the caved-in rock is shifted toward the interior of the goal (regiona of chamber 120). The load factor of the pillars exceeds the allowable value [C]=0.4 specified by standards for “rigid” interchamber pillars in the mines of the Verknekamsk Potassium Salt Deposit, which accounts for their “compliant” regime of deformation. Thus, to reduce the strains of the water-protective stratum and prevent water above the deposit from entering the mine, the region of chamber 120 must be filled.

ESTIMATION METHOD AND EXPERIMENTAL INVESTIGATION OF STRESS-STRAIN STATE FOR TENSILE RC INCLUDING ASSESSMENT OF SHRINKAGE AND NON-LINEAR STRAINS

In this paper, a stress-strain state is analysed for hardening reinforced concrete due shrinkage, increase of physical parameters and non-linear strains of concrete. A method has been developed for assessment of initial stress-strain for reinforced concrete specimens subjected to short-term loading. Stresses and strains in reinforcement and concrete are estimated by experimental-theoretical method and σ—ε diagram for tensile concrete including the descending branch is defined. Experimental investigations of tensile reinforced and non-reinforced members have been carried out for defining the descending part of σ—ε diagram. Sufficient agreement of experimental and predicted data have been achieved. The method and results of these investigations have been applied for design and building of water cleaning equipment made from cast-in-situ and pre-cast concrete. Stress-strain state of structures has been determined for different stages of construction and each of them the required technology has been chosen. Careful examination of structures of the buildings built allows to conclude that the above method can used for calculation and design of cast-in-situ and pre-cast reinforced concrete structures.

ESTIMATION METHOD AND EXPERIMENTAL INVESTIGATION OF STRESS-STRAIN STATE FOR TENSILE RC INCLUDING ASSESSMENT OF SHRINKAGE AND NON-LINEAR STRAINS

Summary In this paper, a stress-strain state is analysed for hardening reinforced concrete due shrinkage, increase of physical parameters and non-linear strains of concrete. A method has been developed for assessment of initial stress-strain for reinforced concrete specimens subjected to short-term loading. Stresses and strains in reinforcement and concrete are estimated by experimental-theoretical method and σ—e diagram for tensile concrete including the descending branch is defined. Experimental investigations of tensile reinforced and non-reinforced members have been carried out for defining the descending part of σ—e diagram. Sufficient agreement of experimental and predicted data have been achieved. The method and results of these investigations have been applied for design and building of water cleaning equipment made from cast-in-situ and pre-cast concrete. Stress-strain state of structures has been determined for different stages of construction and each of them the required technology has been ch...

Experimental-theoretical method of studying residual process stresses in products made of composites

Experimental-theoretical method of studying residual process stresses in products made of composites

Experimental-theoretical method for determining the stress intensity factor

Experimental-theoretical method for determining the stress intensity factor