10,932 research outputs found
Symmetry breaking in a mechanical resonator made from a carbon nanotube
Nanotubes behave as semi-flexible polymers in that they can bend by a
sizeable amount. When integrating a nanotube in a mechanical resonator, the
bending is expected to break the symmetry of the restoring potential. Here we
report on a new detection method that allows us to demonstrate such symmetry
breaking. The method probes the motion of the nanotube resonator at nearly
zero-frequency; this motion is the low-frequency counterpart of the second
overtone of resonantly excited vibrations. We find that symmetry breaking leads
to the spectral broadening of mechanical resonances, and to an apparent quality
factor that drops below 100 at room temperature. The low quality factor at room
temperature is a striking feature of nanotube resonators whose origin has
remained elusive for many years. Our results shed light on the role played by
symmetry breaking in the mechanics of nanotube resonators.Comment: manuscript and supplementary material, 7 figure
A few things I learnt from Jurgen Moser
A few remarks on integrable dynamical systems inspired by discussions with
Jurgen Moser and by his work.Comment: An article for the special issue of "Regular and Chaotic Dynamics"
dedicated to 80-th anniversary of Jurgen Mose
Field theory of bi- and tetracritical points: Relaxational dynamics
We calculate the relaxational dynamical critical behavior of systems of
symmetry by renormalization group method within the
minimal subtraction scheme in two loop order. The three different bicritical
static universality classes previously found for such systems correspond to
three different dynamical universality classes within the static borderlines.
The Heisenberg and the biconical fixed point lead to strong dynamic scaling
whereas in the region of stability of the decoupled fixed point weak dynamic
scaling holds. Due to the neighborhood of the stability border between the
strong and the weak scaling dynamic fixed point corresponding to the static
biconical and the decoupled fixed point a very small dynamic transient
exponent, of , is present in the dynamics for the
physically important case and in .Comment: 8 figure
Ionization signals from electrons and alpha-particles in mixtures of liquid Argon and Nitrogen - perspectives on protons for Gamma Resonant Nuclear Absorption applications
In this paper we report on a detailed study of ionization signals produced by
Compton electrons and alpha-particles in a Time Projection Chamber (TPC) flled
with different mixtures of liquid Argon and Nitrogen. The measurements were
carried out with Nitrogen concentrations up to 15% and a drift electric feld in
the range 0-50 kV/cm. A prediction for proton ionization signals is made by
means of interpolation. This study has been conducted in view of the possible
use of liquid Ar-N2 TPCs for the detection of gamma-rays in the resonant band
of the Nitrogen absorption spectrum, a promising technology for security and
medical applications
30 kV coaxial vacuum-tight feedthrough for operation at cryogenic temperatures
In this paper we describe the technology of building a vacuum-tight high
voltage feedthrough which is able to operate at voltages up to 30 kV. The
feedthrough has a coaxial structure with a grounded sheath which makes it
capable to lead high voltage potentials into cryogenic liquids, without risk of
surface discharges in the gas phase above the liquid level. The feedthrough is
designed to be used in ionization detectors, based on liquefied noble gases,
such as Argon or Xenon
Recommended from our members
The 2001 Omani-Swiss meteorite search campaign and recovery of Shergottite Sayh Al Uhaymir 094
Leech Parasitism of the Gulf Coast Box Turtle, Terrapene carolina major (Testudines:Emydidae) in Mississippi, USA
Ten leeches were collected from a Gulf Coast box turtle, Terrapene carolina major, found crossing a road in Gulfport, Harrison County, Mississippi, USA. Eight of the leeches were identified as Placobdella multilineata and 2 were identified as Helobdella europaea. This represents the second vouchered report of leeches from a box turtle. Helobdella europaea is reported for the first time associated with a turtle and for the second time from the New World
Preheating after N-flation
We study preheating in N-flation, assuming the Mar\v{c}enko-Pastur mass
distribution, equal energy initial conditions at the beginning of inflation and
equal axion-matter couplings, where matter is taken to be a single, massless
bosonic field. By numerical analysis we find that preheating via parametric
resonance is suppressed, indicating that the old theory of perturbative
preheating is applicable. While the tensor-to-scalar ratio, the non-Gaussianity
parameters and the scalar spectral index computed for N-flation are similar to
those in single field inflation (at least within an observationally viable
parameter region), our results suggest that the physics of preheating can
differ significantly from the single field case.Comment: 14 pages, 14 figures, references added, fixed typo
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