21,836 research outputs found
Fabrication of large addition energy quantum dots in graphene
We present a simple technique to fabricate graphene quantum dots in a
cryostat. It relies upon the controlled rupture of a suspended graphene sheet
subjected to the application of a large electron current. This results in the
in-situ formation of a clean and ultra-narrow constriction, which hosts one
quantum dot, and occasionally a few quantum dots in series. Conductance
spectroscopy indicates that individual quantum dots can possess an addition
energy as large as 180 meV and a level spacing as large as 25 meV. Our
technique has several assets: (i) the dot is suspended, thus the electrostatic
influence of the substrate is reduced, and (ii) contamination is minimized,
since the edges of the dot have only been exposed to the vacuum in the
cryostat.Comment: Improved version. To appear in Applied Physics Letter
Oscillations of neutral B mesons systems
The oscillation phenomenon in the neutral B mesons systems is now well
established.
The motivations and principles of the measurements are given; then the most
recent results from the LEP experiments, the CDF collaboration at Fermilab and
the SLD collaboration at SLAC are reviewed.
The present world average of the \bd meson oscillation frequency is \dmd =
0.471 \pm 0.016 \ps and the lower limit on the \bs oscillation frequency is
\dms > 12.4 \ps at 95% CL.Comment: 9 page
Chaotic scattering in solitary wave interactions: A singular iterated-map description
We derive a family of singular iterated maps--closely related to Poincare
maps--that describe chaotic interactions between colliding solitary waves. The
chaotic behavior of such solitary wave collisions depends on the transfer of
energy to a secondary mode of oscillation, often an internal mode of the pulse.
Unlike previous analyses, this map allows one to understand the interactions in
the case when this mode is excited prior to the first collision. The map is
derived using Melnikov integrals and matched asymptotic expansions and
generalizes a ``multi-pulse'' Melnikov integral and allows one to find not only
multipulse heteroclinic orbits, but exotic periodic orbits. The family of maps
derived exhibits singular behavior, including regions of infinite winding. This
problem is shown to be a singular version of the conservative Ikeda map from
laser physics and connections are made with problems from celestial mechanics
and fluid mechanics.Comment: 29 pages, 17 figures, submitted to Chaos, higher-resolution figures
available at author's website: http://m.njit.edu/goodman/publication
Sintering characteristics and properties of PuS and PuP are determined
Report on the preparation of plutonium monosulphide and plutonium monophosphide includes a description of the sintering characteristics and properties of these high-temperature compounds. data on weight loss, microstructure, density, melting point, thermal expansion, microhardness, Seebeck coefficient, and thermal diffusion are included
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
High-frequency nanotube mechanical resonators
We report on a simple method to fabricate high-frequency nanotube mechanical
resonators reproducibly. We measure resonance frequencies as high as 4.2 GHz
for the fundamental eigenmode and 11 GHz for higher order eigenmodes. The
high-frequency resonances are achieved using short suspended nanotubes and by
introducing tensile stress in the nanotube. These devices allow us to determine
the coefficient of the thermal expansion of an individual nanotube, which is
negative and is about -0.7E-5 1/K at room temperature. High-frequency
resonators made of nanotubes hold promise for mass sensing and experiments in
the quantum limit
Test evaluation of fuel cell catalysts Final report
Carbides, bromides,nitrides,and alloys tested for catalytic characteristics for ammonia and carbon nonoxide in fuel cell electrolyte
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
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