LS12752
Wire through Ice
In this work, the motion of a weighted wire encased in ice ‑ Thomson's
famous regulation experiment from the 19th century ‑ is simulated at the
molecular level. It is found that as the wire is set in motion by an
external force, the transition from a static to moving state changes
depending on the hydrophilicity of the wire, i.e., how easily water
covers the wire surface.
Ice has the peculiar property that it melts under high pressure even at
freezing temperatures. Therefore, a wire can be pushed through ice as
pressure in front of the wire locally melts the ice. The liquid water
produced by this pressure melting spontaneously surrounds a hydrophilic
('water‑loving') wire in a bubble but not a hydrophobic
('water‑fearing') one. Therefore, in order to move a hydrophobic wire,
one needs to push it harder than a similar hydrophilic one. This is an
unexpected feature of ice friction as typically hydrophobic surfaces are
the ones to slide easily on water.
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LR12112B
Select desired mechanical and electical properties for carbon nanotubes
‑ It's all about geometry !
In this paper we found ‑ with the help of easily understandable
geometric arguments ‑ how the arrangement of carbon atoms at the edge of
the tubes influences the distribution of chiralities during the growth
of carbon nanotubes. Carbon nanotubes can be described as a sheet of
carbon atoms which are arranged in hexagons like in the board game
"Settlers of Catan" and then rolled up into a tube. They have
fascinating mechanical and electrical properties depending on the way
the carbon atoms of the nanotubes are arranged after rolling the sheet,
which we call chirality. Producing nanotubes nowadays always yields a
large number of different chiralities leading to a mixture of tubes with
different properties in a nanotube sample. The superior properties of
nanotubes can be strongly enhanced if only a specific chirality with
desired properties could be chosen. Many applications are even
impossible without using only a specific chirality. The paper will help
to understand how growth conditions need to be modified to grow a
specific chirality and might also be interesting as it opens up a whole
new view on hexagons and structures constructed from them.
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ES10675
Peculiar properties of an evaporation process of globular clusters
We show that, in an escape of stars from globular clusters (the so‑called
evaporation process), the standard thermodynamic properties such as stellar
polytropes are not valid. In this paper, to examine the evaporation process,
we consider self‑gravitating open systems enclosed in a spherical container
with semipermeable reflecting walls, by means of N‑body simulations. Here we
clearly show that, in a lower‑energy region or for a rapid evaporation
process, the thermodynamic properties deviate from those for the stellar
polytrope. Nevertheless, we found that a negative specific heat occurs even
in such conditions.
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BR11446
Suppressing the magnetism of Chromium
Chromium has fascinated physicists since it was discovered in 1953 to be antiferromagnetic, a magnetism where the magnetic field of each atom is opposite to its neighbors. Although an understanding of the electrons that conduct and cause the magnetism was worked out over 30 years ago, its’ behavior when a different element, such as vanadium, replaced some of the chromium and the temperature at which the transition from nonmagnetic to magnetic is suppressed from just above room temperature to absolute zero (-459.67o Fahrenheit) is much less understood. This scenario is known as quantum criticality and recent investigations of more complex quantum critical antiferromagnets discovered highly unusual properties, such as unconventional superconductivity. These discoveries make the understanding of this quite simple metal more urgent. In our paper we demonstrate that the relatively modest changes that Chromium undergoes near criticality are due mainly to the presence of a small group of electrically conducting electrons which are relatively unchanged by the quantum critical transition. These mobile electrons are scattered much less frequently than those electrons most closely associated with the magnetism and dominate many of the physical properties. Furthermore, we demonstrated that even for vanadium concentrations well beyond that required to quench the magnetism in chromium, quantum fluctuations, finite time and spatial extent where the magnetic state appears, tend to effectively scatter the electrons responsible for the magnetism in pure Cr demonstrating the importance of quantum criticality over wide regions of composition and temperature.
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LR12115
Refrigeration using quantum statistics
It was known since the 1970’s that quantum statistics differing from the usual +/- 1 of Bose and Fermi Statistics is possible in 2D. Such “fractional” or “anyon” statistics is realized by quasiparticle excitations of fractional quantum Hall states formed by a two dimensional electron gas subject to a strong magnetic field. Among various quantum Hall states, the one with Landau level filling factor 5/2 is predicted to be particularly unusual, namely its quasiparticle statistics is “non-abelian”. For such non-abelian quantum states, there is a ground state degeneracy (and associated entropy) that grows with quasiparticle number, making this state ideal for fault-tolerant topological quantum computation. In spite of extensive research, non-abelian quantum states have not yet been confirmed in the laboratory, in part due to the limited experiments that can probe the 5/2 fractional quantum Hall effect in the bulk. In their recent Letter, Gervais and Yang have shown that if a quantum state is non-abelian, it should be possible to use its non-abelian entropy to achieve quantum refrigeration. What they have found for such state is that adiabatically increasing the number of particles in the system gives rise to a counter-intuitive cooling effect, as opposed to heating in a normal classical gas. While the authors hope it can be used to identify fractional quantum Hall states that are non-abelian, they note that the underlying principle of this refrigeration is general, and should exist in any systems that support excitations that gives rise to ground state degeneracy, including those that Majorana fermion or Ising anyon modes that have drawn significant attention in other contexts, including topological insulators and p+ip superconductors/superfluids.
