Shao Yuan-Zhi

Correlated Noises in a Prey–Predator Ecosystem

We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however, leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment, whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.

Nonequilibrium dynamical phase transition of 3D kinetic Ising/Heisenberg spin system

We have studied the nonequilibrium dynamic phase transitions of both three-dimensional (3D) kinetic Ising and Heisenberg spin systems in the presence of a perturbative magnetic field by Monte Carlo simulation. The feature of the phase transition is characterized by studying the distribution of the dynamical order parameter. In the case of anisotropic Ising spin system (ISS), the dynamic transition is discontinuous and continuous under low and high temperatures respectively, which indicates the existence of a tri-critical point (TCP) on the phase \linebreak boundary separating low-temperature order phase and high-temperature disorder phase. The TCP shifts towards the higher temperature region with the decrease of frequency, i.e. TTCP=1.33×exp(−ω/30.7). In the case of the isotropic Heisenberg spin system (HSS), however, the situation on dynamic phase transition of HSS is quite different from that of ISS in that no stable dynamical phase transition was observed in kinetic HSS after a threshold time. The evolution of magnetization in the HSS driven by a symmetrical external field after a certain duration always tends asymptotically to a disorder state no matter what an initial state the system starts with. The threshold time τ depends upon the amplitude H0, reduced temperature T/TC and the frequency ω as τ = C.ωα.H0−β.(T/TC)−γ.

Synchronization in a Mutualism Ecosystem Induced by Noise Correlation

Understanding the cause of the synchronization of population evolution is an important issue for ecological improvement. Here we present a Lotka–Volterra-type model driven by two correlated environmental noises and show, via theoretical analysis and direct simulation, that noise correlation can induce a synchronization of the mutualists. The time series of mutual species exhibit a chaotic-like fluctuation, which is independent of the noise correlation, however, the chaotic fluctuation of mutual species ratio decreases with the noise correlation. A quantitative parameter defined for characterizing chaotic fluctuation provides a good approach to measure when the complete synchronization happens.

Transition from Superparamagnetism to Ferromagnetic Single-Domain in a Heisenberg Model for Nano-cluster Magnetic System

By considering a magnetic system of an ensemble of nanometer clusters without any external magnetic field, the Monte Carlo simulation of the Heisenberg model is used to investigate the transition from a superparamagnetism to a ferromagnetic single-domain state, which is caused by the growth of the clusters. We studied the variation of the dynamic growth exponent P and the transition critical size of the cluster Nc against the reduced temperature t and the uniaxial anisotropy constant A. We found that the growth exponent maximized at a certain temperature, other than being taken as a universal constant as some researchers suggested previously.

Soft magnetic properties and brittleness of boron-doped Sendust alloy

In this paper, static and dynamic magnetic properties as well as brittleness improvement of the boron-microalloyed Sendust ribbons prepared by rapid quenching were investigated. A discussion associated with soft magnetic properties and brittleness improvement of the boron-doped Sendust alloys is given in detail.