307 research outputs found
Tumbling motion of a single chain in shear flow: a crossover from Brownian to non-Brownian behavior
We present numerical results for the dynamics of a single chain in steady
shear flow. The chain is represented by a bead-spring model, and the smoothed
profile method is used to accurately account for the effects of thermal
fluctuations and hydrodynamic interactions acting on beads due to host fluids.
It is observed that the chain undergoes tumbling motions and that its
dimensionless frequency F depends only on the Peclet number Pe with a power
law. The exponent of Pe clearly changes from 2/3 to 1 around the critical
Peclet number, indicating that the crossover reflects the competition of
thermal fluctuation and shear flow. The presented numerical results agree well
with our theoretical analysis based on Jeffery's work
Why some Distressed Firms Have Low Expected Returns. ( Revised in September. 2007 )
In recent years, empirical researchers show that firms with higher credit risk have much smaller average stock returns. This finding is opposite to the risk-reward principle and is often attributed to mispricing and market anomalies. We investigate how credit risk and expected stock return are determined in a model with production, capital structure and aggregate uncertainty. We show that, contrary to the conventional wisdom, a firm with higher credit risk can have less risky stock than the one with lower credit risk.
Implementation of Lees-Edwards periodic boundary conditions for direct numerical simulations of particle dispersions under shear flow
A general methodology is presented to perform direct numerical simulations of
particle dispersions in a shear flow with Lees-Edwards periodic boundary
conditions. The Navier-Stokes equation is solved in oblique coordinates to
resolve the incompatibility of the fluid motions with the sheared geometry, and
the force coupling between colloidal particles and the host fluid is imposed by
using a smoothed profile method. The validity of the method is carefully
examined by comparing the present numerical results with experimental viscosity
data for particle dispersions in a wide range of volume fractions and shear
rates including nonlinear shear-thinning regimes
Reentrant transition in the shear viscosity of dilute rigid rod dispersions
The intrinsic viscosity of a dilute dispersion of rigid rods is studied using
a recently developed direct numerical simulation (DNS) method for particle
dispersions. A reentrant transition from shear-thinning to the 2nd Newtonian
regime is successfully reproduced in the present DNS results around a Peclet
number , which is in good agreement with our theoretical
prediction of , at which the dynamical crossover from Brownian to
non-Brownian behavior takes place in the rotational motion of the rotating rod.
The viscosity undershoot is observed in our simulations before reaching the 2nd
Newtonian regime. The physical mechanisms behind these behaviors are analyzed
in detail
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