1,283 research outputs found
Different mechanics of snap-trapping in the two closely related carnivorous plants Dionaea muscipula and Aldrovanda vesiculosa
The carnivorous aquatic Waterwheel Plant (Aldrovanda vesiculosa L.) and the
closely related terrestrial Venus Flytrap (Dionaea muscipula SOL. EX J. ELLIS)
both feature elaborate snap-traps, which shut after reception of an external
mechanical stimulus by prey animals. Traditionally, Aldrovanda is considered as
a miniature, aquatic Dionaea, an assumption which was already established by
Charles Darwin. However, videos of snapping traps from both species suggest
completely different closure mechanisms. Indeed, the well-described snapping
mechanism in Dionaea comprises abrupt curvature inversion of the two trap
lobes, while the closing movement in Aldrovanda involves deformation of the
trap midrib but not of the lobes, which do not change curvature. In this paper,
we present the first detailed mechanical models for these plants, which are
based on the theory of thin solid membranes and explain this difference by
showing that the fast snapping of Aldrovanda is due to kinematic amplification
of the bending deformation of the midrib, while that of Dionaea unambiguously
relies on the buckling instability that affects the two lobes.Comment: accepted in Physical Review
Two tricritical lines from a Ginzburg-Landau expansion: application to the LOFF phase
We study the behavior of the two plane waves configuration in the LOFF phase
close to T=0. The study is performed by using a Landau-Ginzburg expansion up to
the eighth order in the gap. The general study of the corresponding grand
potential shows, under the assumption that the eighth term in the expansion is
strictly positive, the existence of two tricritical lines. This allows to
understand the existence of a second tricritical point for two antipodal plane
waves in the LOFF phase and justifies why the transition becomes second order
at zero temperature. The general analysis done in this paper can be applied to
other cases.Comment: LaTex file, 15 pages, 6 figure
The fluctuation energy balance in non-suspended fluid-mediated particle transport
Here we compare two extreme regimes of non-suspended fluid-mediated particle
transport, transport in light and heavy fluids ("saltation" and "bedload",
respectively), regarding their particle fluctuation energy balance. From direct
numerical simulations, we surprisingly find that the ratio between collisional
and fluid drag dissipation of fluctuation energy is significantly larger in
saltation than in bedload, even though the contribution of interparticle
collisions to transport of momentum and energy is much smaller in saltation due
to the low concentration of particles in the transport layer. We conclude that
the much higher frequency of high-energy particle-bed impacts ("splash") in
saltation is the cause for this counter-intuitive behavior. Moreover, from a
comparison of these simulations to Particle Tracking Velocimetry measurements
which we performed in a wind tunnel under steady transport of fine and coarse
sand, we find that turbulent fluctuations of the flow produce particle
fluctuation energy at an unexpectedly high rate in saltation even under
conditions for which the effects of turbulence are usually believed to be
small
Energy and pressure densities of a hot quark-gluon plasma
We calculate the energy and hydrostatic pressure densities of a hot
quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the
statistical average, , of the
energy-momentum-tensor operator . To leading order at high
temperature, the energy density of the long wave length modes is consistently
extracted by applying the hard-thermal-loop resummation scheme to the
operator-inserted no-leg thermal amplitudes .
We find that, for the long wave length gluons, the energy density, being
positive, is tremendously enhanced as compared to the noninteracting case,
while, for the quarks, no noticeable deviation from the noninteracting case is
found.Comment: 33 pages. Figures are not include
- …