Biomedical subjects

Jianlan Wu

Publications and source records attributed to Jianlan Wu.

5 recordsLinked to original sources

PubMed2005

Stability analysis of three-dimensional colloidal domains: quadratic fluctuations.

Three-dimensional domain patterns can self-assemble in a charged colloidal suspension with competing short-range attraction and long-range Yukawa repulsion. Following the investigation of the ground-state domain shapes in our previous paper, we study the stability of isolated spherical, cylindrical, and lamellar domains with respect to shape fluctuations on boundaries. In the framework of the continuum model, we expand the free energy variation to quadratic terms under the constraint of constant volume. For the three shapes (sphere, cylinder, and lamella) discussed, domains with equilibrium sizes are stable with respect to shape fluctuations, and the stability of domains decreases as the spatial symmetry decreases.

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PubMed2005

High-order mode-coupling theory for the colloidal glass transition.

A theoretical approach is developed to derive a hierarchy of mode-coupling equations for the dynamics of concentrated colloidal suspensions, which improves the prediction of the colloidal glass transition. Our derivation is based on a matrix formalism for stochastic dynamics and the resulting recursive expressions for irreducible memory functions. The 1st order truncation of the generalized mode-coupling closure recovers mode-coupling theory, whereas its 2nd and 3rd order truncations provide corrections. The predictions of the transition volume fraction and Debye-Waller parameter for the hard-sphere colloidal system improve with the increasing mode-coupling order and compare favorably with experimental measurements.

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PubMed2004

Structural arrest transitions in fluids described by two Yukawa potentials.

We study a model colloidal system where particles interact via short-range attractive and long-range repulsive Yukawa potentials. Using the structure factor calculated from the mean-spherical approximation as the input, the kinetic phase diagrams as functions of the attraction depth and the volume fraction are obtained by calculating the Debye-Waller factors in the framework of the mode-coupling theory for three different heights of the repulsive barrier. The glass-glass reentrance phenomenon in the attractive colloidal case is also observed in the presence of the long-range repulsive barrier, which results in the lower and upper glass regimes. Competition between the short-range attraction and the long-range repulsion gives rise to new regimes associated with clusters such as "static cluster glass" and "dynamic cluster glass," which appear in the lower glass regime. Along the liquid-glass transition line between the liquid regime and the lower glass regime, crossover points separating different glass states are identified.

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PubMed2004

Basis set study of classical rotor lattice dynamics.

The reorientational relaxation of molecular systems is important in many phenomenon and applications. In this paper, we explore the reorientational relaxation of a model Brownian rotor lattice system with short range interactions in both the high and low temperature regimes. In this study, we use a basis set expansion to capture collective motions of the system. The single particle basis set is used in the high temperature regime, while the spin wave basis is used in the low temperature regime. The equations of motion derived in this approach are analogous to the generalized Langevin equation, but the equations render flexibility by allowing nonequilibrium initial conditions. This calculation shows that the choice of projection operators in the generalized Langevin equation (GLE) approach corresponds to defining a specific inner-product space, and this inner-product space should be chosen to reveal the important physics of the problem. The basis set approach corresponds to an inner-product and projection operator that maintain the orthogonality of the spherical harmonics and provide a convenient platform for analyzing GLE expansions. The results compare favorably with numerical simulations, and the formalism is easily extended to more complex systems.

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PubMed2003

Gaussian factorization of hydrodynamic correlation functions and mode-coupling memory kernels.

A simple method to determine mode-coupling memory functions in generalized Langevin equations is obtained by explicitly expressing the random force of the slow hydrodynamic modes in terms of pair interactions in liquids and by Gaussian factoring the resulting multiple-point time correlation functions into products of linear correlation functions. The approach is used to derive the mode-coupling memory kernels for the velocity autocorrelation function, four-point bilinear density correlation function, and density correlation function of linear molecular liquids. These generalized Langevin equations and their associated memory kernels are useful for calculating relaxation processes and spectroscopic measurements in liquids and solvents. As a central result of our analysis, the non-Gaussian behavior of the bilinear density correlation function is quantitatively related to the nonexponential nature of linear hydrodynamic modes. This relation aids in the understanding of recent simulation results of non-Gaussian indicators in supercooled liquids.

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