971 research outputs found
Experimental Investigation of Turbulence Diffusion — A Factor in Transportation of Sediment in Open-Channel Flow
Turbulence diffusion in open-channel flow was investigated
experimentally by photographing the spread of globules formed by the injection of an immiscible fluid
into water. The mean-square transverse deviations of the
globules at various distances downstream from the source
were computed and analyzed in an effort to determine the
shape of the velocity-correlation curve. Comparison was
made between two types of curve which fitted the deviation
data, one corresponding to a power-correlation law
and the other to an exponential-correlation law
A simple eddy viscosity formulation for turbulent boundary layers near smooth walls
The aim of this study is to improve the prediction of near-wall mean
streamwise velocity profile by using a simple method. The profile
is obtained by solving the momentum equation which is written as an ordinary
differential equation. An eddy viscosity formulation based on a near-wall
turbulent kinetic energy function (R. Absi, Analytical solutions for the
modeled -equation, ASME J. Appl. Mech. \textbf{75}, 044501, 2008) and the
van Driest mixing length equation (E.R. van Driest, On turbulent flow near a
wall, J. Aero. Sci. \textbf{23}, 1007, 1956) is used. The parameters obtained
from the profiles are used for the computation of (variables with
the superscript of + are those nondimensionalized by the wall friction velocity
and the kinematic viscosity ). Comparisons with DNS data of
fully-developed turbulent channel flows for show good
agreement (where denotes the friction Reynolds number defined by
, and the channel half-width )
Anomalous relaxation kinetics of biological lattice-ligand binding models
We discuss theoretical models for the cooperative binding dynamics of ligands
to substrates, such as dimeric motor proteins to microtubules or more extended
macromolecules like tropomyosin to actin filaments. We study the effects of
steric constraints, size of ligands, binding rates and interaction between
neighboring proteins on the binding dynamics and binding stoichiometry.
Starting from an empty lattice the binding dynamics goes, quite generally,
through several stages. The first stage represents fast initial binding closely
resembling the physics of random sequential adsorption processes. Typically
this initial process leaves the system in a metastable locked state with many
small gaps between blocks of bound molecules. In a second stage the gaps
annihilate slowly as the ligands detach and reattach. This results in an
algebraic decay of the gap concentration and interesting scaling behavior. Upon
identifying the gaps with particles we show that the dynamics in this regime
can be explained by mapping it onto various reaction-diffusion models. The
final approach to equilibrium shows some interesting dynamic scaling
properties. We also discuss the effect of cooperativity on the equilibrium
stoichiometry, and their consequences for the interpretation of biochemical and
image reconstruction results.Comment: REVTeX, 20 pages, 17 figures; review, to appear in Chemical Physics;
v2: minor correction
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