261 research outputs found
Invasion fronts with variable motility: phenotype selection, spatial sorting and wave acceleration
Invasion fronts in ecology are well studied but very few mathematical results
concern the case with variable motility (possibly due to mutations). Based on
an apparently simple reaction-diffusion equation, we explain the observed
phenomena of front acceleration (when the motility is unbounded) as well as
other quantitative results, such as the selection of the most motile
individuals (when the motility is bounded). The key argument for the
construction and analysis of traveling fronts is the derivation of the
dispersion relation linking the speed of the wave and the spatial decay. When
the motility is unbounded we show that the position of the front scales as
. When the mutation rate is low we show that the canonical equation
for the dynamics of the fittest trait should be stated as a PDE in our context.
It turns out to be a type of Burgers equation with source term.Comment: 7 page
Magnetic Resonance Imaging findings in a Positron Emission Tomography-Positive thoracic aortic aneurysm
peer reviewe
A linear triple quantum dot system in isolated configuration
The scaling up of electron spin qubit based nanocircuits has remained
challenging up to date and involves the development of efficient charge control
strategies. Here we report on the experimental realization of a linear triple
quantum dot in a regime isolated from the reservoir. We show how this regime
can be reached with a fixed number of electrons. Charge stability diagrams of
the one, two and three electron configurations where only electron exchange
between the dots is allowed are observed. They are modelled with established
theory based on a capacitive model of the dot systems. The advantages of the
isolated regime with respect to experimental realizations of quantum simulators
and qubits are discussed. We envision that the results presented here will make
more manipulation schemes for existing qubit implementations possible and will
ultimately allow to increase the number of tunnel coupled quantum dots which
can be simultaneously controlled
Quantum manipulation of two-electron spin states in metastable double quantum dots
We studied experimentally the dynamics of the exchange interaction between
two antiparallel electron spins in a so-called metastable double quantum dot
where coupling to the electron reservoirs can be ignored. We demonstrate that
the level of control of such a double dot is higher than in conventional double
dots. In particular, it allows to couple coherently two electron spins in an
efficient manner following a scheme initially proposed by Loss and DiVincenzo.
The present study demonstrates that metastable quantum dots are a possible
route to increase the number of coherently coupled quantum dots.Comment: 5 pages, 4 figure
High density InAlAs/GaAlAs quantum dots for non-linear optics in microcavities
Structural and optical properties of InAlAs/GaAlAs quantum dots grown by molecular beam epitaxy are studied using transmission electron microscopy, temperature- and time resolvedphotoluminescence. The control of the recombination lifetime (50 ps – 1.25 ns), and of the dot density (5.10−8 – 2.1011 cm−3) strongly suggest that these material systems can find wide applications in opto-electronic devices as focusing non linear dispersive materials as well as fast saturable absorbers
Injection of a single electron from static to moving quantum dots
We study the injection mechanism of a single electron from a static quantum
dot into a moving quantum dot created in a long depleted channel with surface
acoustic waves (SAWs). We demonstrate that such a process is characterized by
an activation law with a threshold that depends on the SAW amplitude and the
dot-channel potential gradient. By increasing sufficiently the SAW modulation
amplitude, we can reach a regime where the transfer is unitary and potentially
adiabatic. This study points at the relevant regime to use moving dots in
quantum information protocols.Comment: 5 pages, 4 figure
WIMP direct detection overview
This review on weakly interacting massive particle (WIMP) dark matter direct
detection focuses on experimental approaches and the corresponding physics
basics. The presentation is intended to provide a quick and concise
introduction for non-specialists to this fast evolving topic of astroparticle
physics.Comment: 13 pages, 6 figures, invited review for the Proc. XXth Int. Conf.
Neutrino Physics and Astrophysics, May 25-30, 2002, Munich, Germany; version
includes correction of typo in eqn.2; to appear in Nucl. Phys. B Proc. Supp
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