100 research outputs found
Improved diagnostic criteria for digital flexor tendon sheath pathology using contrast tenography
Entropy-induced smectic phases in rod-coil copolymers
We present a self-consistent field theory (SCFT) of semiflexible (wormlike)
diblock copolymers, each consisting of a rigid and a flexible part. The
segments of the polymers are otherwise identical, in particular with regard to
their interactions, which are taken to be of an Onsager excluded-volume type.
The theory is developed in a general three-dimensional form, as well as in a
simpler one-dimensional version. Using the latter, we demonstrate that the
theory predicts the formation of a partial-bilayer smectic-A phase in this
system, as shown by profiles of the local density and orientational
distribution functions. The phase diagram of the system, which includes the
isotropic and nematic phases, is obtained in terms of the mean density and
rigid-rod fraction of each molecule. The nematic-smectic transition is found to
be second order. Since the smectic phase is induced solely by the difference in
the rigidities, the onset of smectic ordering is shown to be an entropic effect
and therefore does not have to rely on additional Flory-Huggins-type repulsive
interactions between unlike chain segments. These findings are compared with
other recent SCFT studies of similar copolymer models and with computer
simulations of several molecular models.Comment: 13 pages, 8 figure
Tests of Dynamical Scaling in 3-D Spinodal Decomposition
We simulate late-stage coarsening of a 3-D symmetric binary fluid. With
reduced units l,t (with scales set by viscosity, density and surface tension)
our data extends two decades in t beyond earlier work. Across at least four
decades, our own and others' individual datasets (< 1 decade each) show viscous
hydrodynamic scaling (l ~ a + b t), but b is not constant between runs as this
scaling demands. This betrays either the unexpected intrusion of a
discretization (or molecular) lengthscale, or an exceptionally slow crossover
between viscous and inertial regimes.Comment: Submitted to Phys. Rev.
3D Spinodal Decomposition in the Inertial Regime
We simulate late-stage coarsening of a 3D symmetric binary fluid using a
lattice Boltzmann method. With reduced lengths and times l and t respectively
(scales set by viscosity, density and surface tension) our data sets cover 1 <
l
100 we find clear evidence of Furukawa's inertial scaling (l ~ t^{2/3}),
although the crossover from the viscous regime (l ~ t) is very broad. Though it
cannot be ruled out, we find no indication that Re is self-limiting (l ~
t^{1/2}) as proposed by M. Grant and K. R. Elder [Phys. Rev. Lett. 82, 14
(1999)].Comment: 4 pages, 3 eps figures, RevTex, minor changes to bring in line with
published version. Mobility values added to Table
Coincident molecular auxeticity and negative order parameter in a liquid crystal elastomer
Auxetic materials have negative Poisson's ratios and so expand rather than contract in one or several direction(s) perpendicular to applied extensions. The auxetics community has long sought synthetic molecular auxetics - non-porous, inherently auxetic materials which are simple to fabricate and avoid porosity-related weakening. Here, we report, synthetic molecular auxeticity for a non-porous liquid crystal elastomer. For strains above ~0.8 applied perpendicular to the liquid crystal director, the liquid crystal elastomer becomes auxetic with the maximum negative Poisson's ratio measured to date being -0.74 ± 0.03 - larger than most values seen in naturally occurring molecular auxetics. The emergence of auxeticity coincides with the liquid crystal elastomer backbone adopting a negative order parameter, QB = -0.41 ± 0.01 - further implying negative liquid crystal ordering. The reported behaviours consistently agree with theoretical predictions from Warner and Terentjev liquid crystal elastomer theory. Our results open the door for the design of synthetic molecular auxetics
Wildfire Altering Terrestrial Precursors of Disinfection Byproducts in Forest Detritus
Effet de quelques traits des arbres sur la répartition des eaux de pluie en forêts tem-pérées et boréales —synthèse bibliographique
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