LW11101
Environment Variation and Extinction Risk
A small isolated population of living organisms ultimately goes
extinct because of a random chain of rare events of predominance
of deaths over births. Average time to extinction, however, can be quite
large for not too small populations. Irregular variations of environmental
conditions affect the birth and death rates, once in a while decreasing
the population size and accelerating its
extinction. Earlier theoretical work assumed that the variations
of the environmental parameters, for example of the daily
temperature, look as ``white noise": they are uncorrelated, that
is completely independent from each other. The real environmental
variations, however, are correlated. One can say that they are
colored rather than white. For example, the daily temperature
varies much more gradually than what the white noise model would
predict. The complicated interplay between the color and magnitude of the
environmental variations on the one side, and the
population birth and death rates on the other side has eluded
understanding for
many years. Our work shows that the color of environmental
variations dramatically enhances the extinction risk. Our results will
help ecologists to correctly assess the viability of isolated populations.
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LS11243
The signature of QCD in baryon magnetic moments
Baryon magnetic moments are approximately described by the
celebrated Coleman-Glashow relations that assume an
exact flavor symmetry between u, d and s quarks.
The present study improves these relations by including
the SU(3)-breaking corrections given by the low-energy realization of
Quantum Chromodynamics (QCD) known as Chiral Perturbation Theory (ChPT).
Baryons are composite objects made of interacting quarks and gluons.
For this reason, their magnetic moments are different from those of
elementary fermions with the same charges and masses. Unfortunately,
a full calculation of such a simple and fundamental quantity using QCD,
the theory of the strong interaction, is not yet feasible due to its
non-perturbative nature. Nonetheless, the magnetic moments of the lightest
spin 1/2 baryons are related among themselves providing a clear manifestation
of the underlying approximate SU(3) flavor symmetry. Previous attempts to
describe the breaking of this symmetry using ChPT have encountered problems
pointing at a poor convergence of the perturbative results.
It is found that in order to obtain a good description of these
magnetic moments it is essential that the low energy
realization of the fundamental strong interaction theory fulfills the
fundamental principles of analyticity and relativistic covariance. The results
of this work provide a solution for a long standing puzzle and neatly reveal
the manifestation of QCD on a basic observable such as baryon magnetic moments.
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LR11242E
Shear induced mesostructures in biaxial liquid crystals
In 2004 a new "biaxial phase" of thermotropic (or temperature
sensitive) biaxial liquid crystalline polymers (LCPs), was discovered
experimentally by two seperate groups.
Biaxial LCPs are the brick-shaped or the ellipsoidal molecules that
have 2 length scales: a longer one along the long molecular axis and
the shorter one along the shorter axis.
It is widely hypothesized that the properties of the liquid crystal
polymers, which is seen along the long molecular axis; can also be
duplicated along the shorter axis; with a smaller time-scale. Hence
the presence of these 2 length-scales phenomena in these "smart"
materials can significantly improve the efficiency of certain
industries using semiconductor devices.
This biaxial phase, however, is very elusive at the molecular level
and extremely difficult to visualize and predict experimentally; in
the sense that they require an extreme conditions of temperature,
pressure and high magnetic field to be predicted experimentally.
To our knowledge, for the first time, we predict and present the
various phases of biaxial LCPs in the presence of an external
homogeneous shear flow, using mathematical modeling and large-scale
computation.
We discuss about the sequence of the orientational phases observed in
the selected regions of material parameter space. The underlying
hydrodynamic theory is also briefly discussed.
