CiteULike: dchens Zhang

Solvent-Induced DNA Conformational Transition

B Gu — 2008-05-07T23:28:21-00:00

Physical Review Letters, Vol. 100, No. 8. (2008)

Modified water models with scaled charges are used to investigate solvent polarity effects on DNA structure. Several intensive molecular dynamics simulations of the DNA EcoRI dodecamer d(CGCGAATTCGCG) in different model solvents are performed. When the polarity of the solvent molecule decreases, from overpolarized to less polarized, DNA experiences the conformational transitions of constrainedB form(A-B)mixA form. We demonstrate that one important cause of these structure changes is the competition between hydration and direct cation coupling to the free oxygen atoms in the phosphate groups on DNA backbones.

Time-Resolved Shadowgraphs of Material Ejection in Intense Femtosecond Laser Ablation of Aluminum

Nan Zhang — 2008-05-03T23:46:49-00:00

Physical Review Letters, Vol. 99, No. 16. (2007)

The dynamic process of intense 50 fs laser ablation of aluminum is investigated by ultrafast time-resolved microscopy. A stripe pattern preceding phase explosion is clearly seen in the shadowgraph of 1 ns time delay. Intermittent material ejections are observed within the ejected plume after 2.5 and 7 ns time delay, respectively, which may be attributed to the material response to the generation of an extremely strong thermoelastic wave. Similar processes are also recorded in the ablation of silicon and glass samples, except for the glass samples, the intermittent material ejections are not found.

Speckle Evolution of Diffusive and Localized Waves

Sheng Zhang — 2008-05-03T19:57:29-00:00

Physical Review Letters, Vol. 99, No. 6. (2007)

We show that while the statistics of static speckle patterns are generic, fluctuations in the change within speckle patterns are greatly enhanced in the localization transition. The probability distributions of the displacement of phase singularities and the standard deviations of the changes of phase and intensity with frequency shift of incident microwave radiation are given in terms of the same expression which describes the probability distribution of total transmission. This function depends only upon a single parameter, the variance of the corresponding variable. The changing statistics in the localization transition reflects the number of underlying electromagnetic modes with which the incident wave interacts.

Shake-gels: shear-induced gelation of laponite-PEO mixtures

J Zebrowski — 2008-04-24T22:24:38-00:00

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 213, No. 2-3. (12 February 2003), pp. 189-197.

Suspensions of clay particles (laponite), mixed with poly(ethylene oxide) (PEO) undergo a dramatic shear thickening when subjected to vigorous shaking, which transforms them from a low viscosity fluid into a [`]shake-gel', a solid with elasticity sufficient enough to support its own weight. The shake-gel is reversible, relaxing back to a fluid with a relaxation time that is strongly dependent on PEO concentration. Shake-gels are observed for PEO concentrations slightly below the threshold for complete saturation of the laponite particles by the polymer. Light scattering measurements confirm that the PEO is adsorbed on the surface of the laponite particles, and suggests that shear induces a bridging between the colloidal particles, resulting in a gel network which spans the system. Desorption of the polymer reduces the bridging and thus relaxes the network.

Characterization of atomic motion governing grain boundary migration

Hao Zhang — 2008-04-15T20:22:51-00:00

Physical Review B (Condensed Matter and Materials Physics), Vol. 74, No. 11. (2006)

Molecular dynamics simulations were employed to study atomic motion within stationary and migrating asymmetric tilt grain boundaries. We employ several measures of the "complexity" of the atomic trajectories, including the van Hove correlation function, the non-Gaussian parameter, and dynamic entropy. There are two key types of dynamical events within the grain boundaries (i) a stringlike cooperative motions parallel to the tilt axis and occurring on a characteristic time scale of 25 ps and (ii) atomic motion across the grain boundary plane occurring on a characteristic time scale of 150 ps. The characteristic times associated with each type of event decreases with increasing driving force for boundary migration. We present evidence as to how the driving force biases these types of events, leading to boundary migration. While the stringlike atomic motion is an intrinsic feature of grain boundary dynamics and is important for grain boundary migration, it is the second type of event that controls grain boundary migration rates.