排序方式: 共有28条查询结果,搜索用时 15 毫秒
1.
2.
3.
N. Lyotard W. L. Shew L. Bocquet J.-F. Pinton 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):469-476
We make time resolved velocity measurements of steel
spheres in free fall through liquid using a continuous ultrasound
technique. We explore two different ways to induce large changes in
drag on the spheres: 1) a small quantity of viscoelastic polymer
added to water and 2) altering the surface of the sphere. Low
concentration polymer solutions and/or a pattern of grooves in the
sphere surface induce an early drag crisis, which may reduce drag by
more than 50% compared to smooth spheres in pure water. On
the other hand, random surface roughness and/or high concentration
polymer solutions reduce drag progressively and suppress the drag
crisis. We also present a qualititative argument which ties the
drag reduction observed in low concentration polymer solutions to
the Weissenberg number and normal stress difference. 相似文献
4.
Li X Shew CY Liu Y Pynn R Liu E Herwig KW Smith GS Robertson JL Chen WR 《The Journal of chemical physics》2011,134(9):094504
Spin-echo small angle neutron scattering (SESANS) provides a new experimental tool for structural investigation. Due to the action of spin-echo encoding, SESANS measures a spatial correlation function in real space, as opposed to the structure factor S(Q), I(Q), in momentum (Q) space measured by conventional small angle neutron scattering. To establish the usefulness of SESANS in structural characterization, particularly for interacting colloidal suspensions, we have previously conducted a theoretical study of the SESANS correlation functions for model systems consisting of particles with uniform density profiles [X. Li, C.-Y. Shew, Y. Liu, R. Pynn, E. Liu, K. W. Herwig, G. S. Smith, J. L. Robertson, and W.-R. Chen J. Chem. Phys. 132, 174509 (2010)]. Within the same framework, we explore in the present paper the prospect of using SESANS to investigate the structural characteristics of colloidal systems consisting of particles with nonuniform intraparticle mass distribution. As an example, a Gaussian model of interacting soft colloids is used to investigate the manifestation of structural softness in a SESANS measurement. The exploration shows a characteristically different SESANS correlation function for interacting soft colloids, in comparison to that of a uniform hard sphere system. The difference arises from the Abel transform imbedded in the mathematical formalism bridging the SESANS spectra and the spatial autocorrelation function. 相似文献
5.
CY Shew C Do K Hong Y Liu L Porcar GS Smith WR Chen 《The Journal of chemical physics》2012,137(2):024907
We present small angle neutron scattering (SANS) measurements of deuterium oxide (D(2)O) solutions of linear and star sodium poly(styrene sulfonate) (NaPSS) as a function of polyelectrolyte concentration. Emphasis is on understanding the dependence of their SANS coherent scattering cross section I(Q) on the molecular architecture of single polyelectrolyte. The key finding is that for a given concentration, star polyelectrolytes exhibit more pronounced characteristic peaks in I(Q), and the position of the first peak occurs at a smaller Q compared to their linear counterparts. Based on a model of integral equation theory, we first compare the SANS experimental I(Q) of salt-free polyelectrolyte solutions with that predicted theoretically. Having seen their satisfactory qualitative agreement, the dependence of counterion association behavior on polyelectrolyte geometry and concentration is further explored. Our predictions reveal that the ionic environment of polyelectrolyte exhibits a strong dependence on polyelectrolyte geometry at lower polyelectrolyte concentration. However, when both linear and star polyelectrolytes exceed their overlap concentrations, the spatial distribution of counterion is found to be essentially insensitive to polyelectrolyte geometry due to the steric effect. 相似文献
6.
7.
8.
9.
The conformational behavior of a giant DNA mediated by condensing agents in the bulk solution has been investigated through experimental and theoretical approaches. Experimentally, a pronounced conformational hysteresis is observed for folding and unfolding processes, by increasing and decreasing the concentration of condensing agent (polyethylene glycol) (PEG), respectively. To elucidate the observed hysteresis, a semiflexible chain model is studied by using Monte Carlo simulations for the coil-globule transition. In the simulations, the hysteresis loop emerges for stiff enough chains, indicating distinct pathways for folding and unfolding processes. Also, our results show that globular state is thermodynamically more stable than coiled state in the hysteresis loop. Our findings suggest that increasing chain stiffness may reduce the chain conformations relevant to the folding pathway, which impedes the folding process. 相似文献
10.
Gasteuil Y Shew WL Gibert M Chillá F Castaing B Pinton JF 《Physical review letters》2007,99(23):234302
We have developed a small, neutrally buoyant, wireless temperature sensor. Using a camera for optical tracking, we obtain simultaneous measurements of position and temperature of the sensor as it is carried along by the flow in Rayleigh-Bénard convection, at Ra approximately 10;{10}. We report on statistics of temperature, velocity, and heat transport in turbulent thermal convection. The motion of the sensor particle exhibits dynamics close to that of Lagrangian tracers in hydrodynamic turbulence. We also quantify heat transport in plumes, revealing self-similarity and extreme variations from plume to plume. 相似文献