EN10253
How rigid are viruses?
Viruses have traditionally been considered dangerous entities capable of infecting and mutating plant and animal genetic codes. In recent years, however, viruses have been explored for applications ranging from drug delivery and gene therapy to nano-technology. Monodispersity, surface chemistry, temperature and pH stability make viruses versatile tools for photonic and electronic templates. Although structures of many viruses are known, their properties remain largely unexplored. In this paper we employ light scattering to analyze the mechanical rigidity and inter-virion coupling of Wiseana iridovirus (WIV). The measurements indicate unexpectedly high Young's modulus ~7 GPa, a surprising value for a biological objects that we traditionally consider in the class of 'Soft Materials'. This modulus is higher than the modulus of usual hard plastics. We show that the hard DNA core is the reason for so high WIV rigidity. The results also indicate a strong mechanical coupling between individual virion particles. The obtained results and the developed technique for analysis of virus rigidity might be very helpful for various bio- and nano- technologies and for studies of other nanoscale objects.
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BR10615
Microstructure and oxygen concentration of YBCO
The microstructure and oxygen concentration profoundly affect the
electronic properties of the high-temperature superconductor
YBa2Cu3Odelta-7 (YBCO). Using quantitative high-resolution electron
microscopy, we measured the local atomic structure associated with
twinning in several YBCO samples. We observed inhomogeneities in the
lattice parameter ratios on the scale of the twin domains that are
ubiquitous in YBCO. This result was surprising because YBCO is
generally considered to have well defined lattice parameters. Our
measurements reveal that features commonly considered to be twin
boundaries often do not have a true twinning symmetry and are more
accurately described as phase boundaries. Furthermore, the
lattice-parameter ratios in a single sample tend to oscillate back and
forth between two different values from domain to domain, apparently
due to the local variation of oxygen concentration. As a result, we
expect these samples to have locally variable superconducting
properties. Furthermore, one can easily imagine a material with a
network of superconducting channels dispersed within an insulating
matrix. Such a network could have profound implications for theories of
flux pinning and superconductivity in YBCO.
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LS11726
Fluctuations of a liquid surface: from the molecular scale to
the scale of capillary waves
The fluctuations in the local density of molecules in a liquid
depend sensitively on whether the density is measured close to the
liquid's surface. Far from the surface the density fluctuations are
mild and molecular in range but close to it they are dominated by
long-wavelength "capillary" waves along the surface, with the
interfacial tension and gravity acting as the dominant restoring
forces.
In this paper we show that to describe the full spectrum of
density fluctuations from the molecular scale up to the scale
of capillary waves, one must take account of the energy associated
with *bending* the surface as described by the interface's
bending rigidity. Two of the important results are (1) that the
bending rigidity for the interface between phase-separated
colloid-polymer mixtures is *negative*, with the result that
capillary waves are "more violent", less restricted by interfacial
tension, at smaller wavelengths, and (2) that on approach to the
critical point it vanishes proportionally to the interfacial tension
rather than, as had often been supposed, varying proportionally to
the product of the tension and the square of the correlation length,
thereby approaching a finite, non-zero limit. Both features are shown
to be in accord with what is found in computer simulations.
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BM10751
Stone Wales defects are unstable in planar graphene
Defects in graphene are extremely important because they alter its
electronic and magnetic properties. We have predicted that Stone
Wales defects in planar graphene are unstable [1]. This is surprising
because the opposite was believed based on Molecular Dynamics
simulations and experiments in carbon nanotubes [2]. Despite this
previous belief, our prediction is natural. Stone Wales defects
comprise two pentagon-heptagon defects whose heptagons share one
side. Each pentagon-heptagon defect is the core of an edge
dislocation and the Stone Wales defect is a dipole formed by two edge
dislocations that have opposite Burgers vectors and share the same
gliding line. In an unstressed sample, planar linear elasticity
implies that the two dislocations glide towards each other and
annihilate. To show this, we have numerically solved the dynamics of
a novel periodized discrete elasticity model on the hexagonal lattice
and obtained the stable cores of different edge dislocations and
dipoles. Recent experimental results by Meyer et al at Lawrence
Berkeley National Laboratories confirm our prediction. They use a
novel imaging technique based on a TEM microscope to observe the
evolution of Stone Wales and other defects created by irradiation of
a graphene membrane [3]. These defects annihilate within a few
seconds thereby leaving a perfect lattice. These time scales are
several orders of magnitude longer than typical ones in Molecular
Dynamics simulations (pico to nanoseconds).
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LQ11682A
Antimatter is seen to bounce from a matter wall
If you were to ask scientists what antimatter does
when it comes into contact with ordinary matter, all of them
will reply: "annihilation".
This is actually also the layman's general idea of the
matter-antimatter interaction: they are expected to cancel out
each other immediately in a burst of energy.
However, what we report in this paper is that this is only true
half the time. Our measurements show that, when a bunch of low energy
antiprotons hits an aluminum wall, around half of them are reflected and,
in our experimental conditions, can still travel tens of centimeters
from the reflecting wall.
What's the trick? Actually, none. What we observe is connected to
an effect known since the century-old Rutherford-Geiger-Marsden
experiments: when a charged particle approaches an atom,
and steals into its electron cloud, the Coulomb force exerted by
the nucleus is able to deflect its trajectory.
Through interactions with many atoms, the incident (anti)particle
can eventually be pushed backwards.
So why was this not seen before with antimatter? It's because most studies
were done at relatively high energies, where the annihilation probability
is much higher than the reflection probability.
But this is not true at very low energies, where reflection is
greatly enhanced.
The principal difficulty was to find out a set of data taken at very, very
low energy, in the heaps of data taken by the OBELIX experiment, around
a decade ago, at CERN.
While the antiprotons with "normal" energies annihilated soon after
impacting on the wall, the ones with 1000 times less energy showed
this unexpected behaviour.
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LS11568
Does the expansion of spacetime do the same thing to physical
theories that scaling up lengths and times does in flat space?
If so, we could understand some issues in cosmology the same
way we do when the temperature and pressure of water is tuned
to eliminate the distinction between liquid and vapor. This
idea would effect such a vast simplification that it has found
many adherants. On the other hand, there has never been a clear
demonstration that the formalism --- known as the Renormaliztion
Group --- either should or should not apply to cosmology. In
this paper I analyze the model that is the paradigm for all
systems with a one dimensional order parameter and I show that
its cosmological evolution is not correctly described by the
Renormalization Group. My analysis makes use of a nonperturbative
resummation technique due to the Russian cosmologist Alexei
Starobinsky. Although the Renormalization Group does not describe
the effects of cosmological expansion, the good news is that
Starobinsky's technique does, and it is even simpler to use.
