Tong-Jun Zhao

Rocking ratchets with stochastic potentials

An analysis has been made for the motion of an overdamped Brownian particle in a periodic potential subjected to a position-dependent stochastic perturbation and a sinusoidal external force. In the presence of the stochastic potentials, it is noticed that with the increasing intensity of the stochastic potentials, the maximum of the current in general decreases, while it is shifted to the higher temperature, and moreover, the correlation length also strongly influences the magnitude of the current.

THE MONTE–CARLO SIMULATION OF THE PERMEABILITY OF K ION CHANNELS

In this paper, by introducing the collision model of the K ion channel, the maximum value of ions inward the channel per second, the average velocity of ions in the channels and the average time of every ion passing through the channel are obtained. Moreover they are reconciled with the experimental data. Base on the experimental data, the empiristic potential function is deduced. With the Monte–Carlo simulation, the curve of average velocity versus time and average displacement versus time are calculated by resolving the over-damping Langevin equation with Gaussian-white noise. They are according with the experimental dada well.

Current Reversal in a Flashing Correlation Ratchet

A flashing correlation ratchet model is proposed, in which the transport of Brownian particles driven by additive colored noise of Ornstein-Uhlenbeck type in a flashing ratchet is studied by Monte Carlo simulation. The stationary current vs the noise strength and the correlation time is obtained and analyzed. For a fixed rate of potential flashing, the novel phenomena of current reversal and reentry occur. The conditions for the occurrence of these phenomena are found. The influence of the flipping rate is also discussed. This finding might be relevant to the fact that the protein motors with similar structure can move in opposite directions on the same kind of microtubule.

Two-dimensional ratchets with non-conservative impulsive force

We discuss the directed motion of overdamped Brownian particles based on a two-dimensional ratchet model with a non-conservative impulsive force field. We consider the combined effects on the stationary current due to local spatial asymmetry in the longitudinal direction as well as the constrained harmonic force in the transverse direction. We notice that the current reversal is induced by the change of colored noise strength and the dynamics in the transverse direction influences the directed motion in the longitudinal direction significantly. The non-conservative impulsive force that represents the chemical energy consumed in the conformation changing process is a crucial factor to the directed motion of the Brownian motors.

Brownian ratchets driven by flashing noise strength

The stochastic transport driven by flashing multi-noise sources in a ratchet is studied. The stationary current versus the noise strength and the colored noise correlated time r is obtained. At a fixed flip rate and strength of the colored noises, the novel phenomenon of the current reversal occurs as τ reaches a certain value. More than one reversal point exists when a flashing colored noise source and a flashing bdIite noise source are simultaneously taken into account.

A Dynamical Model on the Network of p53-Mdm2 Feedback Loop Regulated by p14/19ARF

Base on new experimental results, we give a dynamical model to study the dynamical mechanism of the negative feedback loop composed of p53 and Mdm2 proteins regulated by p14/19ARR The oscillatory behaviors for the activities of p53 and Mdm2 proteins regulated by p14/19ARF in individual of cells are described in our dynamical model. The results help us build a basal network about oscillatory behaviors among p53, Mdm2 and P14/19ARR The dynamical model and its numerical results will help us understand the oscillatory behavior among other network of different proteins.

Modeling of ATM Accumulation and ATM-Mediated Oscillation of p53

A dynamical model to study the accumulation of ATM is proposed in this work. The ATM can accumulate either with low level of DSBs and presence of NBS1 proteins in cells, or with high level of DSBs and absence of NBS1. Both the two ways trigger the cell damage repair system. The interaction in p53 networks responding to DNA damage is discovered in many researches, but the mechanism of initiating oscillation remains unclear. We examine a model shows that the ATM-NBS1 feedback loop exhibits bistability. The bistability has essential roles in the mechanism of initiate oscillation.

A Death-Survival Switch in Cell: Cross Talk between Akt and p53

A dynamical model for the p53-Mdm2 feedback loop regulated by Akt is reported in this work. By computational simulation, it reproduces the stable oscillatory pulses in p53- Mdm2 negative feedback loop which is functionally responsible for cell repair or apoptosis in individual cell. With the survival stress, in the tumor suppressor-oncoproteins networks, the model indicates the potential to exhibit the oscillation-stationary state bifurcation for the kinetics of p53, and the death-survival switch in the p53-Akt cross talk which somehow leads cell to either programmed apoptosis or survival. Its found that low Akt activation is speculated to p53 normally holding the response to cellular repair or apoptosis, but large Akt amount keeping a high Akt activation restricts p53 at a low expression level and engenders malfunctions in cellular repair or apoptosis so that the cell survives with potential probability to cancer or mutation.

Dynamical model of P53-Mdm2-P14/19ARF network to radiation in population of cells

From the recent experiments of γ radiation and models given before, we study the dynamical model of p53 and Mdm2 regulated by p14/19ARF in population of cells. In order to study how they infect the mechanism of the negative feedback loop, we give numerical results to study the oscillatory features of p53, Mdm2 and p14/19ARF in population of cells. The dynamical model and results will help us understand the oscillatory features of p53, Mdm2 and p14/19ARF to radiation in population of cells.

Synchronization Numerical Simulation of two FitzHugh-Nagumo Neurons

It is well known that a strong coupling can synchronize a population of nonlinear oscillators. It provides the basis of the remarkable computational performance of the brain. In this paper we take the FitzHugh-Nagumo model in two-dimension nonlinear differential equations to study the role of noise on the synchronization. The numerical computation shows that the neurons can achieve both the same firing frequency only in a small region when the coupling strength is very small; and two neurons synchronize for almost noise strength when the coupling strength is very large. Some illustrations are given to show the region where both neurons achieve synchronization. Our results reveal that noise plays a role in the emergence of synchronous activity in populations of FitzHugh-Nagumo neurons.