arXiv subjects

Zlatko Vasilkoski

Publications and source records attributed to Zlatko Vasilkoski.

3 recordsLinked to original sources

arXiv2011

Desynchronization of systems of coupled Hindmarsh-Rose oscillators

It is widely assumed that neural activity related to synchronous rhythms of large portions of neurons in specific locations of the brain is responsible for the pathology manifested in patients' uncontrolled tremor and other similar diseases. To model such systems Hindmarsh-Rose (HR) oscillators are considered as appropriate as they mimic the qualitative behaviour of neuronal firing. Here we consider a large number of identical HR-oscillators interacting through the mean field created by the corresponding components of all oscillators. Introducing additional coupling by feedback of Pyragas type, proportional to the difference between the current value of the mean-field and its value some time in the past, Rosenblum and Pikovsky (Phys. Rev. E 70, 041904, 2004) demonstrated that the desirable desynchronization could be achieved with appropriate set of parameters for the system. Following our experience with stabilization of unstable steady states in dynamical systems, we show that by introducing a variable delay, desynchronization is obtainable for much wider range of parameters and that at the same time it becomes more pronounced.

nlin.CD↗

arXiv2008

The Electrostatic Component of the Disjoining Pressure and the Pore Creation Rate in Electroporation Models and Theory

Under externally applied electric fields, lipid membranes tend to permeate and change their electrical resistance by the combined processes of pore creation and pore evolution (expansion or contraction). This study is focused on the pore creation process, represented by an empirical expression currently used in the electroporation (EP) models, for which an alternative theoretically based expression was provided. The choice of this expression was motivated by the role the DLVO's (disjoining) pressures may play in the process of EP. The electrostatic energy effects on each sides of a lipid membrane were evaluated in terms of the electrostatic component of the disjoining pressure. Thus the pore creation energy considerations in the current EP models, associated with the necessity of an idealized non conducting circular pre-pore were avoided. As a result, a new expression for the onset of the electroporation was proposed. It was found that this new theoretically determined expression is in good agreement with the one estimated from an experiment that specifically targeted the pore nucleation by eliminating the pore evolution process. Furthermore, the proposed expression is dependent on the electrolyte and the lipid properties and should provide better predictability than the currently used pore creation EP model, which is only temperature dependent.

physics.bio-ph↗

arXiv2006

The effect of electric fields on lipid membranes

Contrary to existing theoretical models, experimental evidence points out that electroporation (membrane defect formation under external electric fields) starts to occur within the range of transmembrane voltages that cells may routinely experience, curiously, just above the range of transmembrane voltages involved in neural signal transmission. Understanding the underlying principles of electric fields-lipid membrane interactions seems to carry a great biological importance. An argument is presented toward understanding the theoretical aspects of electroporation by using the DLVO theory, which has not been recognized previously in the context of electroporation. Further, the dispersion interactions (with its quantum nature), of the double layer counterions and membrane lipid molecules over the Stern layer are emphasized. The sign of these forces is such that they compress the membrane. A parallel is drawn to the theory of thin films. The argument is that the external electric field breaks the symmetry of the disjoining pressures on both sides of a lipid membrane, resulting in a protrusion of only few lipid molecules. That compromises the membrane stability on a nanoscale and makes it traversable to ions. The presented estimate based on these arguments is consistent to electroporation experiments and existing numerical simulations.

physics.bio-ph↗