Zhang Su-Hua

The first order Freedericksz transition at saturation point for weak anchoring NLC cells

On the basis of the modified Rapini-Papoular expression for the anchoring energy, the properties of the transition at saturation point for weak anchoring NLC cells has been studied analytically. We find that this transition may be of second order, as is usually predicted by many authors; however, it may also be first order. Whether it is first or second order is determined by the material, anchoring energy and thickness of the cell. The conditions for first order transition are deduced by an analytical method, and the results of calculation are shown by graph for κ (= K 11 / K 33 ) values 0.8, 0.6 and 0.4. The saturation field strengths for the first order transition case are calculated and shown in the table.

The synchronization of FitzHugh-Nagumo neuron network coupled by gap junction ∗

It is well known that the strong coupling can synchronize a network of nonlinear oscillators. Synchronization provides the basis of the remarkable computational performance of the brain. In this paper the FitzHugh–Nagumo neuron network is constructed. The dependence of the synchronization on the coupling strength, the noise intensity and the size of the neuron network has been discussed. The results indicate that the coupling among neurons works to improve the synchronization, and noise increases the neuron random dynamics and the local fluctuations; the larger the size of network, the worse the synchronization. The dependence of the synchronization on the strength of the electric synapse coupling and chemical synapse coupling has also been discussed, which proves that electric synapse coupling can enhance the synchronization of the neuron network largely.

Properties of Hydrated Alkali Metals Aimed at the Ion Channel Selectivity

The hydration structure properties of different alkali metal ions with eight water molecules and potassium ions with different numbers of water molecules are studied using the mixed density functional theory, B3LYP, with 6-311G basis set. The hydration structures are obtained from structure optimization and the optimum numbers of water molecules in the innermost hydration shell for the alkali metal ions are found. Some useful information about the ion channel selectivity is presented.

The bistable state of a twisted nematic liquid crystal cell with weak anchoring boundary

On the basis of the modified general Rapini–Papoular expression for the anchoring energy, a twisted nematic liquid crystal cell has been studied analytically. In this paper, a new variable is introduced and is suitable for the calculation of the threshold point and the saturation point. The free energy being smallest in the equilibrium state, we find that bistable states can be formed from the uniform twisted state plus the disturbed state, the disturbed state plus the saturation state, and the uniform twisted state plus the saturation state.

Environmental Impacts on Spiking Properties in Hodgkin–Huxley Neuron with Direct Current Stimulus

Based on the well accepted Hodgkin–Huxley neuron model, the neuronal intrinsic excitability is studied when the neuron is subject to varying environmental temperatures, the typical impact for its regulating ways. With computer simulation, it is found that altering environmental temperature can improve or inhibit the neuronal intrinsic excitability so as to influence the neuronal spiking properties. The impacts from environmental factors can be understood that the neuronal spiking threshold is essentially influenced by the fluctuations in the environment. With the environmental temperature varying, burst spiking is realized for the neuronal membrane voltage because of the environment-dependent spiking threshold. This burst induced by changes in spiking threshold is different from that excited by input currents or other stimulus.

The influences of surface polarization on NLC cells

The influence of the surface polarization, Ps , on a nematic liquid crystal (NLC) cell is investigated analytically. Flexoelectric polarization is considered, but selective ion absorption is ignored. The differential equations are derived for tilt angle, θ, of director n and the corresponding boundary conditions based on Gibbs free energy, and their solutions discussed. Equations for the reduced threshold voltage, uth , and the reduced saturation voltage, usat , are deduced and the relationships between uth , usat and reduced strength of surface polarization, p, derived.

Dynamical Properties of Potassium Ion Channels with a Hierarchical Model

It is well known that potassium ion channels have higher permeability than K ions, and the permeable rate of a single K ion channel is about 108 ions per second. We develop a hierarchical model of potassium ion channel permeation involving ab initio quantum calculations and Brownian dynamics simulations, which can consistently explain a range of channel dynamics. The results show that the average velocity of K ions, the mean permeable time of K ions and the permeable rate of single channel are about 0.92 nm/ns, 4.35 ns and 2.30×108 ions/s, respectively.

The spike timing precision of FitzHugh-Nagumo neuron network coupled by gap junctions

It has been proved recently that the spike timing can play an important role in information transmission, so in this paper we develop a network with N-unit FitzHugh–Nagumo neurons coupled by gap junctions and discuss the dependence of the spike timing precision on synaptic coupling strength, the noise intensity and the size of the neuron ensemble. The calculated results show that the spike timing precision decreases as the noise intensity increases; and the ensemble spike timing precision increases with coupling strength increasing. The electric synapse coupling has a more important effect on the spike timing precision than the chemical synapse coupling.

Electrostatic Interactions Determining the Selectivity of KcsA Channel and Its Mutants

We perform the density functional theory and Brownian dynamics simulations based on the three-dimensional structure of the WT KcsA channel and its mutants. Our data suggest that the electrostatic interactions between the channels and cations, within the signature sequence of K+ channels, determine the selectivity of the channel.

The Use of an 'Effective Potential' to Describe the Directed Motion of a Two-State Molecular Motor

Force generation and directed motion of molecular motors using a simple two-state model are studied in the paper. Here we consider the asymmetric and periodic potential in the model. The symmetric and periodic potential is adopted to describe the interactions between motor proteins and filaments that are periodic and polar. The flux and the slope of the effective potential as functions of the temperature and transition rates are calculated in the two-state model. The ratio of the slope of the effective potential to the flux is also calculated. It is concluded that the directed motion of motor proteins is relevant to the effective potential. The slope of the effective potential corresponds to an average force. The non-vanishing force therefore implies that detailed balance is broken in the process of transition between different states. Moreover, we compare the theoretical relationship of load force and velocity with the experimental data. It is shown that they are consistent