Nikola Petrov

Electromechanical potentials in cortical bone—I. A continuum approach

An electrokinetic model to characterize the electromechanical effect in cortical bone has been developed using the basic principles of the biphasic theory of porous materials and a simple model for permeability and charge distribution for cortical bone. The model is developed analytically in Part I of this paper and is shown to account qualitatively for the principal experimental results reported to date. Part II of this paper concerns experimental analysis of this model, reporting results of low frequency testing of the dynamic characteristics of stress-generated potentials. Quantitative analysis of these results indicates that the microporosity of bone, made up of the channels around the hydroxyapatite encrusting the collagen matrix, is the compartment responsible for the electromechanical effects in fluid-saturated cortical bone. This microporous compartment would seem to be the obvious source of the electrokinetic effect, because it has the greatest surface area in bone and constitutes the rate limiting fluid flow compartment in deformation-induced fluid flow at low frequency.

AN ANATOMICAL MODEL FOR STREAMING POTENTIALS IN OSTEONS

An anatomical model for streaming potentials in osteons is developed to characterize the electromechanical effect in bone. The model accounts for the microstructure of the osteon and is based upon first principles of electrochemistry, electrokinetics, continuum mechanics and fluid dynamics. Intra-osteonal potentials and their relaxation times are numerically evaluated. Many of the previously reported observations of potentials in osteons and across macroscopic specimens are explained for the first time in terms of an electrokinetic model. The cusp-like behavior of intra-osteonal potentials is explained, the dependence of the potentials on solution viscosity and conductivity is demonstrated, and insight is gained relative to the time dependence of stress generated potentials.

A discrete model for streaming potentials in a single osteon

A mathematical model for streaming potentials in an osteon is proposed, taking into account the microstresses in the vicinity of the Haversian Canal. With the help of the finite element method, a boundary problem for the fluid pressure amplitude in the osteon is investigated when the bone sample is subjected to harmonic loading. A numerical analysis of the intra-osteonal potential is performed. It is found that there exists an azimuthal asymmetry which increases with the enlargement of the Haversian Canal. The results of the numerical modeling of the intra-osteonal potential are in accordance with the available experimental data.

Observations and light curve solutions of the eclipsing binaries KR Lyn, CSS J110212+244412, NSVS 4917488 and NSVS 7336024

We present photometric observations in Sloan filters g′, i′ of the short-period eclipsing stars KR Lyn, CSS J110212+244412, NSVS 4917488 and NSVS 7336024. The light curve solutions revealed that all targets are overcontact binaries whose components are G and K stars. Their temperature differences do not exceed 300 K but they differ considerably in size and mass. NSVS 4917488 and NSVS 7336024 reveal total eclipses and their parameters can be considered as well-determined. We found that KR Lyn, NSVS 4917488 and NSVS 7336024 are of W-subtype while CSS J110212+244412 is A-subtype W UMa-type star.