Sun, 06 Jul 2008 03:47:02 BST CiteULike: dchens Wang http://www.citeulike.org/user/dchen/author/Wang CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2880966 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 3. (2007)</i><br /><br />The homogeneous and heterogeneous nucleation of a Lennard-Jones liquid is investigated using the umbrella sampling method. The free energy cost of forming a nucleating droplet is determined as a function of the quench depth, and the saddle point nature of the droplets is verified using an intervention technique. The structure and symmetry of the nucleating droplets are found for a range of temperatures. We find that for deep quenches the nucleating droplets become more anisotropic and diffuse with no well-defined core or surface. The environment of the nucleating droplets forms randomly stacked hexagonal planes. This behavior is consistent with a spinodal nucleation interpretation. We also find that the free energy barrier for heterogeneous nucleation is a minimum when the lattice spacing of the impurity equals the lattice spacing of the equilibrium crystalline phase. If the lattice spacing of the impurity is different, the crystal grows into the bulk instead of wetting the impurity. Homogeneous and heterogeneous nucleation of Lennard-Jones liquids Hui Wang Harvey Gould W Klein doi:10.1103/PhysRevE.76.031604 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 3. (2007) 2008-06-10T21:23:56-00:00 2007 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 76 3 APS 2007 nucleation pre simulation http://www.citeulike.org/user/dchen/article/2767689 <i>Physical Review Letters, Vol. 100, No. 8. (2008)</i><br /><br />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. Solvent-Induced DNA Conformational Transition B Gu FS Zhang ZP Wang HY Zhou doi:10.1103/PhysRevLett.100.088104 Physical Review Letters, Vol. 100, No. 8. (2008) 2008-05-07T23:28:21-00:00 2008 Physical Review Letters 100 8 APS 2008 biology people http://www.citeulike.org/user/dchen/article/2761599 <i>Physical Review Letters, Vol. 100, No. 15. (2008)</i><br /><br />Two species of particles in a binary granular system typically do not have the same mean kinetic energy, in contrast to the equipartition of energy required in equilibrium. We investigate the role of the heating mechanism in determining the extent of nonequipartition of kinetic energy. In most experiments, different species are unequally heated at the boundaries. We show by event-driven simulations that differential boundary heating affects nonequipartition even in the bulk of the system. This conclusion is fortified by studying numerical and solvable stochastic models without spatial degrees of freedom. In both cases, even in the limit where heating events are rare compared to collisions, the effect of the heating mechanism persists. Heating Mechanism Affects Equipartition in a Binary Granular System Hong Wang Narayanan Menon doi:10.1103/PhysRevLett.100.158001 Physical Review Letters, Vol. 100, No. 15. (2008) 2008-05-06T14:42:31-00:00 2008 Physical Review Letters 100 15 APS 2008 grains people temperature http://www.citeulike.org/user/dchen/article/2751731 <i>Physical Review Letters, Vol. 99, No. 16. (2007)</i><br /><br />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. Time-Resolved Shadowgraphs of Material Ejection in Intense Femtosecond Laser Ablation of Aluminum Nan Zhang Xiaonong Zhu Jianjun Yang Xiaolei Wang Mingwei Wang doi:10.1103/PhysRevLett.99.167602 Physical Review Letters, Vol. 99, No. 16. (2007) 2008-05-03T23:46:49-00:00 2007 Physical Review Letters 99 16 APS 2007 focus material nano people http://www.citeulike.org/user/dchen/article/2731415 <i>Proceedings of the National Academy of Sciences, Vol. 102, No. 7. (15 February 2005), pp. 2299-2304.</i><br /><br />A densely packed granular system is an example of an out-of-equilibrium system in the jammed state. It has been a longstanding problem to determine whether this class of systems can be described by concepts arising from equilibrium statistical mechanics, such as an effective temperature and compactivity. The measurement of the effective temperature is realized in the laboratory by slowly shearing a closely packed ensemble of spherical beads confined by an external pressure in a Couette geometry. All of the probe particles considered in this study, independent of their characteristic features, equilibrate at the same temperature, given by the packing density of the system. 10.1073/pnas.0409911102 Experimental measurement of an effective temperature for jammed granular materials Chaoming Song Ping Wang Hernan Makse doi:10.1073/pnas.0409911102 Proceedings of the National Academy of Sciences, Vol. 102, No. 7. (15 February 2005), pp. 2299-2304. 2008-04-29T00:38:58-00:00 2005 Proceedings of the National Academy of Sciences 102 7 2299 2304 grains jamming makse temperature http://www.citeulike.org/user/dchen/article/2713887 <i>Physical Review Letters, Vol. 91, No. 22. (24 November 2003), 224501.</i> Flow and Fracture in Drying Nanoparticle Suspensions ER Dufresne EI Corwin NA Greenblatt J Ashmore DY Wang AD Dinsmore JX Cheng XS Xie JW Hutchinson DA Weitz doi:10.1103/PhysRevLett.91.224501 Physical Review Letters, Vol. 91, No. 22. (24 November 2003), 224501. 2008-04-24T18:38:32-00:00 2003 Physical Review Letters 91 22 224501 American Physical Society dinsmore drying weitz http://www.citeulike.org/user/dchen/article/2186364 <i>Science, Vol. 312, No. 5780. (16 June 2006), pp. 1631-1633.</i><br /><br />We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles. 10.1126/science.1125151 Measurement of Forces Inside a Three-Dimensional Pile of Frictionless Droplets J Zhou S Long Q Wang AD Dinsmore doi:10.1126/science.1125151 Science, Vol. 312, No. 5780. (16 June 2006), pp. 1631-1633. 2008-01-01T22:04:40-00:00 2006 Science 312 5780 1631 1633 dinsmore emulsion force qualifier http://www.citeulike.org/user/dchen/article/2453898 <i>J. Phys. Chem. B, Vol. 103, No. 20. (20 May 1999), pp. 4177-4184.</i><br /><br />Abstract: In supercooled o-terphenyl (OTP), subsets of probe molecules in more mobile environments can be selectively photobleached. The time required for the remaining slower-than-average probes to be redistributed into an equilibrium set of environments has been measured. At Tg + 4 K (Tg = 243 K), this exchange time is 6 times greater than the average probe rotational correlation time. These results are compared to previous optical measurements at Tg + 1 K (Cicerone, M. T.; Ediger, M. D. J. Chem. Phys. 1995, 103, 5684), which showed that the exchange time is more than 100 times the rotational correlation time, and to multidimensional NMR experiments on deuterated OTP at Tg + 10 K (Bohmer, R.; et al. Europhys. Lett. 1996, 36, 55), which showed that the exchange time is nearly equal to the correlation time. These results in aggregate suggest that a new relaxation process in equilibrium supercooled liquids emerges only at temperatures very near Tg. A model for selective photobleaching is proposed. The model reproduces the experimental data reasonably well and indicates that the photobleaching efficiency of a given probe is only weakly correlated with its rotational correlation time. How Long Do Regions of Different Dynamics Persist in Supercooled o-Terphenyl? CY Wang MD Ediger doi:10.1021/jp984149x J. Phys. Chem. B, Vol. 103, No. 20. (20 May 1999), pp. 4177-4184. 2008-03-01T22:25:47-00:00 1999 J. Phys. Chem. B 103 20 4177 4184 ediger heterogeneity systemtools