The role of relaxation oscillator models in application fields such as modeling dynamic systems and image analysis is discussed. A short review of the Van der Pol, Wilson-Cowan and Terman-Wang relaxation oscillators is given. The key property of such nonlinear oscillators, i.e., the oscillator phase shift (called the Phase Response Curve) as a result of external pulse stimuli is indicated as a fundamental mechanism to achieve and sustain synchrony in networks of coupled oscillators. It is noted...

A hybrid model of red blood cell production, where cells are considered as discrete objects while intra-cellular proteins and extra-cellular biochemical substances are described with continuous models, is proposed. Spatial organization and regulation of red blood cell production (erythropoiesis) are investigated. Normal erythropoiesis is simulated in two dimensions, and the influence on the output of the model of some parameters involved in cell...

This work presents new application of the random field theory in medical imaging. Results from both integral geometry and random field theory can be used to detect locations with significantly increased radiotracer uptake in images from positron emission tomography (PET). The assumptions needed to use these results are verified on a set of real and simulated phantom images. The proposed method of detecting activation (locations with increased radiotracer concentration) is used to quantify the quality...

The following is an expository article meant to give a simplified introduction to applications of topology to DNA.

This work aims to extend in two distinct directions results recently obtained in [10]. In a first step we focus on the possible extension of our results to the time dependent case. Whereas in the second part some preliminary numerical simulations aim to give orders of magnitudes in terms of numerical costs of direct 3D simulations. We consider, in the first part, the time dependent rough problem for a simplified heat equation in a straight channel that mimics the axial...

We propose and analyze a mathematical model of hematopoietic stem cell dynamics. This model takes into account a finite number of stages in blood production, characterized by cell maturity levels, which enhance the difference, in the hematopoiesis process, between dividing cells that differentiate (by going to the next stage) and dividing cells that keep the same maturity level (by staying in the same stage). It is described by a system of n nonlinear differential equations with n delays. We study...

We consider the Keller-Segel-Navier-Stokes system $$\left\{\begin{array}{cc}{n}_t+𝐮·\nabla n=\Delta n-\nabla ·\left(n\nabla v\right),\hfill & x\in \Omega ,t>0,\hfill \\ v_t+𝐮·\nabla v=\Delta v-v+w,\hfill & x\in \Omega ,t>0,\hfill \\ w_t+𝐮·\nabla w=\Delta w-w+n,\hfill & x\in \Omega ,t>0,\hfill \\ {𝐮}_t+(𝐮·\nabla )𝐮=\Delta 𝐮+\nabla P+n\nabla \phi ,\nabla ·𝐮=0,\hfill & x\in \Omega ,t>0,\hfill \end{array}\right.$$ which is considered in bounded domain $\Omega \subset {ℝ}^N$$(N\in \{2,3\}...$

In this article we consider a system of equations that describes a class of mass-conserving aggregation phenomena, including gravitational collapse and bacterial chemotaxis. In spatial dimensions strictly larger than two, and under the assumptions of radial symmetry, it is known that this system has at least two stable mechanisms of singularity formation (see e.g. M. P. Brenner et al. 1999, Nonlinearity 12, 1071-1098); one type is self-similar, and may be viewed as a trade-off between diffusion...