Ashraf Mohamed Nawi

Mutation and Chaos in Nonlinear Models of Heredity

We shall explore a nonlinear discrete dynamical system that naturally occurs in population systems to describe a transmission of a trait from parents to their offspring. We consider a Mendelian inheritance for a single gene with three alleles and assume that to form a new generation, each gene has a possibility to mutate, that is, to change into a gene of the other kind. We investigate the derived models and observe chaotic behaviors of such models.

Strange Attractors in the Vannimenus Model on an Arbitrary Order Cayley Tree

We consider the Vannimenus model on a Cayley tree of arbitrary order k with competing nearest-neighbour interactions J1 and next-nearest-neighbour interactions J2 and J3 in the presence of an external magnetic field h. In this paper we study the phase diagram of the model using an iterative scheme for a renormalized effective nearest-neighbour coupling Kr and effective field per site Xr for spins on the rth level; it recovers, as particular cases, previous works by Vannimenus, Inawashiro et al, Mariz et al and Ganikhodjaev and Uǧuz. Each phase is characterized by a particular attractor and the phase diagram is obtained by following the evolution and detecting the qualitative changements of these attractors. These changements can be either continuous or abrupt, respectively characterizing second- or first- order phase transitions. We present a few typical attractors and at finite temperatures, several interesting features (evolution of reentrances, separation of the modulated region into few disconnected pieces, etc) are exhibited for typical values of parameters.

Attractors on Ising model with restricted interactions on Cayley tree of order 2

We consider an Ising model on a Cayley tree with competing interactions of the next-nearest-neighbours of two types: prolonged and one-level interactions only. More recently, Ganikhodjaev and Zakaria investigated the same model and proved that its phase diagram contain only four phases, namely, ferromagnetic, paramagnetic, antiferromagnetic and antiphase. In this paper we reinvestigate the phase diagram of this model using an iterative scheme, that is developed for a renormalized effective nearest-neighbour coupling Kr and effective field per site Xr for spins on the n-th level of a Cayley tree with competing one-level J0 and prolonged Jp next-nearest-neighbour interactions between Ising spins on the tree. We find an intermediate range of Jp/J0 values where Xr and Kr iterate to a finite attractor in the X - K plane.

Two Potts Models on Cayley Tree of Arbitrary Order

On a Cayley tree of arbitrary order k we consider two different Potts models with competing nearest-neighbour interactions J1 and next-nearest-neighbour interactions Jp and Jo, where coupling Jp corresponds to interaction of spins belonging to the same branch of the tree (prolonged) and coupling Jo corresponds to interaction of spins belonging to the same shell of the tree (one-level) and find for each model in addition to the expected paramagnetic, ferromagnetic and antiferromagnetic phases, an intermediate range of coupling values where the local magnetization has chaotic oscillatory glass-like behaviour. We also show that the ranges corresponding two models are different.