DYNAMIC MONTE CARLO STUDY ON THE CORRELATION BETWEEN SHAPE AND SIZE OF LINEAR POLYMER CHAINS

The correlation between shape and size of linear chains on the simple cubic lattice is investigated using a dynamicMonte Carlo technique. A positive correlation between the asphericity parameter A and the square of the end-to-end distanceR^2, as well as that between A and the square of the radius of gyration S^2, is found for both RW and SAW chains, indicatingthat a chain conformation of small size is usually more spherical than one of large size. The result can explain why the shapeof the SAW chain deviate much more from a sphere than that of the RW chain, and can also explain the similar dependenceof size and shape on chain stiffness and on the distance of the first bead of a chain from an infinitely large flat surface.

Hierarchical Bayesian Calibration and On-line Updating Method for Influence Coefficient of Automatic Dynamic Balancing Machine

Measurement error of unbalance＇s vibration response plays a crucial role in calibration and on-line updating of influence coefficient（IC）. Focusing on the two problems that the moment estimator of data used in calibration process cannot fulfill the accuracy requirement under small sample and the disturbance of measurement error cannot be effectively suppressed in updating process, an IC calibration and on-line updating method based on hierarchical Bayesian method for automatic dynamic balancing machine was proposed. During calibration process, for the repeatedly-measured data obtained from experiments with different trial weights, according to the fact that measurement error of each sensor had the same statistical characteristics, the joint posterior distribution model for the true values of the vibration response under all trial weights and measurement error was established. During the updating process, information obtained from calibration was regarded as prior information, which was utilized to update the posterior distribution of IC combined with the real-time reference information to implement online updating. Moreover, Gibbs sampling method of Markov Chain Monte Carlo（MCMC） was adopted to obtain the maximum posterior estimation of parameters to be estimated. On the independent developed dynamic balancing testbed, prediction was carried out for multiple groups of data through the proposed method and the traditional method respectively, the result indicated that estimator of influence coefficient obtained through the proposed method had higher accuracy; the proposed updating method more effectively guaranteed the measurement accuracy during the whole producing process, and meantime more reasonably compromised between the sensitivity of IC change and suppression of randomness of vibration response.

Phase transition in a two-dimensional Ising ferromagnet based on the generalized zero-temperature Glauber dynamics

At zero temperature, based on the Ising model, the phase transition in a two-dimensional square lattice is studied using the generalized zero-temperature Glauber dynamics. Using Monte Carlo （MC） renormalization group methods, the static critical exponents and the dynamic exponent are studied; the type of phase transition is found to be of the first order.

TRANSLOCATION OF A PROTEIN-LIKE CHAIN THROUGH AN INTERACTING CHANNEL

The effect of channel-protein interaction on the translocation of a protein-like chain through a finite channel under certain electric field was studied by using dynamical Monte Carlo simulations. The interior behavior of chain conformation under different interactions was investigated, such as the number of monomers outside of channel nout, monomers inside of channel nm, mean-square radius of gyration 〈 S2 〉 and the average energy 〈U〉. It shows that with strong attractive interaction, the translocation is more difficult than moderate interaction. At the same time, the dependence of translocation time with different interactions shows that moderate repulsive interaction （εcp = 0.5） accelerates the translocation. Although the waiting time for successful translocation of εep = 1.0 is the longest, the average translocation time is not very large. It is far smaller than that of εep = -1.0. The probability distributions of translocation time p（t＇） and the probability distributions of three duration times p（t1＇）, p（t2＇） and p（t3＇） were all discussed. Log-normal distributions are found. All these findings will strengthen the understanding of protein translocation.

Structure of polyelectrolyte brushes studied by coarse grain simulations

As an example of a very low friction system,Monte Carlo Brownian dynamics simulations have been used to calculate equilibrium structures of a polyelectrolyte brush grafted onto planes.The polymers were calculated in a semi-flexible coarse-grain model that is appropriate to treat the charge density of the polyion.The effect of linear charge density on the polyionx,the surface negative charge,and added salts were studied.In salt-free solution,scaling theories predicted the structure well in the lowxregion.In the highxregion,additional shrinkage was found from the theories due to counterion condensation.The effect of surface charge showed not only the repulsion of the polyion from the surface but also the shrinkage in the highxregion due to the additional counterions required for electrical neutrality.The addition of salts led to the shrinkage of the brush heights,and in the highxregion,additional extension was found.The computational strategy for calculating the friction dynamics of the system is also discussed.