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Characteristics of Langmuir Turbulence in the Ocean Mixed Layer
This study uses large-eddy simulation (LES) to investigate the characteristics of Langmuir turbulence through the turbulent kinetic energy (TKE) budget. Based on an analysis of the TKE budget a velocity scale for Langmuir turbulence is proposed. The velocity scale depends on both the friction velocity and the surface Stokes drift associated with the wave field. The scaling leads to unique profiles of nondimensional dissipation rate and velocity component variances when the Stokes drift of the wave field is sufficiently large compared to the surface friction velocity. The existence of such a scaling shows that Langmuir turbulence can be considered as a turbulence regime in its own right, rather than a modification of shear-driven turbulence.
Comparisons are made between the LES results and observations, but the lack of information concerning the wave field means these are mainly restricted to comparing profile shapes. The shapes of the LES profiles are consistent with observed profiles. The dissipation length scale for Langmuir turbulence is found to be similar to the dissipation length scale in the shear-driven boundary layer. Beyond this it is not possible to test the proposed scaling directly using available data. Entrainment at the base of the mixed layer is shown to be significantly enhanced over that due to normal shear turbulence
Density Functional Theory of a Curved Liquid-Vapour Interface: Evaluation of the rigidity constants
It is argued that to arrive at a quantitative description of the surface
tension of a liquid drop as a function of its inverse radius, it is necessary
to include the bending rigidity k and Gaussian rigidity k_bar in its
description. New formulas for k and k_bar in the context of density functional
theory with a non-local, integral expression for the interaction between
molecules are presented. These expressions are used to investigate the
influence of the choice of Gibbs dividing surface and it is shown that for a
one-component system, the equimolar surface has a special status in the sense
that both k and k_bar are then the least sensitive to a change in the location
of the dividing surface. Furthermore, the equimolar value for k corresponds to
its maximum value and the equimolar value for k_bar corresponds to its minimum
value. An explicit evaluation using a short-ranged interaction potential
between molecules, shows that k is negative with a value around minus 0.5-1.0
kT and that k_bar is positive with a value which is a bit more than half the
magnitude of k. Finally, for dispersion forces between molecules, we show that
a term proportional to log(R)/R^2 replaces the rigidity constants and we
determine the (universal) proportionality constants.Comment: 28 pages; 5 figures; accepted for publication in J. Phys.: Condens.
Matter (2013
Gene-knockdown in the honey bee mite Varroa destructor by a non-invasive approach : studies on a glutathione S-transferase
Peer reviewedPublisher PD
Spin-dependent charge recombination along para-phenylene molecular wires
We have used an efficient new quantum mechanical method for radical pair
recombination reactions to study the spin-dependent charge recombination along
PTZ--Ph--PDI molecular wires. By comparing our
results to the experimental data of E. Weiss {\em et al.} [J. Am. Chem. Soc.
{\bf 126}, 5577 (2004)], we are able to extract the spin-dependent (singlet and
triplet) charge recombination rate constants for wires with . These
spin-dependent rate constants have not been extracted previously from the
experimental data because they require fitting its magnetic field-dependence to
the results of quantum spin dynamics simulations. We find that the triplet
recombination rate constant decreases exponentially with the length of the
wire, consistent with the superexchange mechanism of charge recombination.
However, the singlet recombination rate constant is nearly independent of the
length of the wire, suggesting that the singlet pathway is dominated by an
incoherent hopping mechanism. A simple qualitative explanation for the
different behaviours of the two spin-selective charge recombination pathways is
provided in terms of Marcus theory. We also find evidence for a magnetic
field-independent background contribution to the triplet yield of the charge
recombination reaction, and suggest several possible explanations for it. Since
none of these explanations is especially compelling given the available
experimental evidence, and since the result appears to apply more generally to
other molecular wires, we hope that this aspect of our study will stimulate
further experimental work.Comment: 12 pages, 10 figure
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