26 research outputs found
Dynamical instabilities of a resonator driven by a superconducting single-electron transistor
We investigate the dynamical instabilities of a resonator coupled to a
superconducting single-electron transistor (SSET) tuned to the Josephson
quasiparticle (JQP) resonance. Starting from the quantum master equation of the
system, we use a standard semiclassical approximation to derive a closed set of
mean field equations which describe the average dynamics of the resonator and
SSET charge. Using amplitude and phase coordinates for the resonator and
assuming that the amplitude changes much more slowly than the phase, we explore
the instabilities which arise in the resonator dynamics as a function of
coupling to the SSET, detuning from the JQP resonance and the resonator
frequency. We find that the locations (in parameter space) and sizes of the
limit cycle states predicted by the mean field equations agree well with
numerical solutions of the full master equation for sufficiently weak
SSET-resonator coupling. The mean field equations also give a good qualitative
description of the set of dynamical transitions in the resonator state that
occur as the coupling is progressively increased.Comment: 23 pages, 6 Figures, Accepted for NJ
Vibrational spectra of C60C8H8 and C70C8H8 in the rotor-stator and polymer phases
C60-C8H8 and C70-C8H8 are prototypes of rotor-stator cocrystals. We present
infrared and Raman spectra of these materials and show how the rotor-stator
nature is reflected in their vibrational properties. We measured the
vibrational spectra of the polymer phases poly(C60C8H8) and poly(C70C8H8)
resulting from a solid state reaction occurring on heating. Based on the
spectra we propose a connection pattern for the fullerene in poly(C60C8H8),
where the symmetry of the C60 is D2h. On illuminating the C60-C8H8 cocrystal
with green or blue light a photochemical reaction was observed leading to a
similar product to that of the thermal polymerization.Comment: 26 pages, 8 figures, to appear in Journal of Physical Chemistry B 2nd
version: minor changes in wording, accepted version by journa
Statistics of charge transfer in a tunnel junction coupled to an oscillator
The charge transfer statistics of a tunnel junction coupled to a quantum
object is studied using the charge projection technique. The joint dynamics of
the quantum object and the number of charges transferred through the junction
is described by the charge specific density matrix. The method allows
evaluating the joint probability distribution of the state of the quantum
object and the charge state of the junction.The statistical properties of the
junction current are derived from the charge transfer statistics using the
master equation for the charge specific density matrix. The theory is applied
to a nanoelectromechanical system, and the influence on the average current and
the current noise of the junction is obtained for coupling to a harmonic
oscillator.Comment: 18 pages, 3 figure
Nanoscale spin rectifiers controlled by the Stark effect
The control of orbital and spin state of single electrons is a key ingredient
for quantum information processing, novel detection schemes, and, more
generally, is of much relevance for spintronics. Coulomb and spin blockade (SB)
in double quantum dots (DQDs) enable advanced single-spin operations that would
be available even for room-temperature applications for sufficiently small
devices. To date, however, spin operations in DQDs were observed at sub-Kelvin
temperatures, a key reason being that scaling a DQD system while retaining an
independent field-effect control on the individual dots is very challenging.
Here we show that quantum-confined Stark effect allows an independent
addressing of two dots only 5 nm apart with no need for aligned nanometer-size
local gating. We thus demonstrate a scalable method to fully control a DQD
device, regardless of its physical size. In the present implementation we show
InAs/InP nanowire (NW) DQDs that display an experimentally detectable SB up to
10 K. We also report and discuss an unexpected re-entrant SB lifting as a
function magnetic-field intensity
A GABAergic and peptidergic sleep neuron as a locomotion stop neuron with compartmentalized Ca2+dynamics.
Animals must slow or halt locomotion to integrate sensory inputs or to change direction. In Caenorhabditis elegans, the GABAergic and peptidergic neuron RIS mediates developmentally timed quiescence. Here, we show RIS functions additionally as a locomotion stop neuron. RIS optogenetic stimulation caused acute and persistent inhibition of locomotion and pharyngeal pumping, phenotypes requiring FLP-11 neuropeptides and GABA. RIS photoactivation allows the animal to maintain its body posture by sustaining muscle tone, yet inactivating motor neuron oscillatory activity. During locomotion, RIS axonal Ca2+ signals revealed functional compartmentalization: Activity in the nerve ring process correlated with locomotion stop, while activity in a branch correlated with induced reversals. GABA was required to induce, and FLP-11 neuropeptides were required to sustain locomotion stop. RIS attenuates neuronal activity and inhibits movement, possibly enabling sensory integration and decision making, and exemplifies dual use of one cell across development in a compact nervous system
Discriminated structural behaviour of C60 and C70 peapods under extreme conditions
cited By 15International audienceWe studied structural changes in C60 and C70 peapods - i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes - when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70
Fault-tolerant dynamic job scheduling policy
In this paper, we propose a scalable and fault-tolerant job scheduling framework for grid computing. The proposed framework loosely couples a dynamic job scheduling approach with the hybrid replications approach to schedule jobs efficiently while at the same time providing fault-tolerance. The novelty of the proposed framework is that it uses passive replication approach under high system load and active replication approach under low system loads. The switch between these two replication methods is also done dynamically and transparently