874 research outputs found
Low frequency noise controls on-off intermittency of bifurcating systems
A bifurcating system subject to multiplicative noise can display on-off
intermittency. Using a canonical example, we investigate the extreme
sensitivity of the intermittent behavior to the nature of the noise. Through a
perturbative expansion and numerical studies of the probability density
function of the unstable mode, we show that intermittency is controlled by the
ratio between the departure from onset and the value of the noise spectrum at
zero frequency. Reducing the noise spectrum at zero frequency shrinks the
intermittency regime drastically. This effect also modifies the distribution of
the duration that the system spends in the off phase. Mechanisms and
applications to more complex bifurcating systems are discussed
Quantum impurity approach to a coupled qubit problem
We consider a system of two qubits at the ends of a finite length 1D cavity.
This problem is mapped onto the double-Kondo model which is also shown to
describe the low energy physics of a finite length quantum wire with resonant
levels at its ends. At the Toulouse point the ground state energy and the
average populations and correlations of the qubits or resonant levels at zero
temperature are computed. These results show that the effective interactions
between the qubits or resonant levels can be used to probe their associated
Kondo length scale.Comment: New version (accepted in Europhysics Letters
AMAPstudio: a 3D Interactive Software Suite for Plants Architecture Modelling
Plants architecture modelling results in building complex models. Turning them into simulators requires strong interaction between scientists and software developers. The AMAPstudio project adapts a methodology that has been successfully conducted in the forestry modelling field for 12 years. It focuses on a long-term supported software environment and a strong customized technical backing to help modellers integrate their simulators in highly 3D interactive softwar
On thermal effects in solid state lasers: the case of ytterbium-doped materials
A review of theoretical and experimental studies of thermal effects in
solid-state lasers is presented, with a special focus on diode-pumped
ytterbium-doped materials. A large part of this review provides however general
information applicable to any kind of solid-state laser. Our aim here is not to
make a list of the techniques that have been used to minimize thermal effects,
but instead to give an overview of the theoretical aspects underneath, and give
a state-of-the-art of the tools at the disposal of the laser scientist to
measure thermal effects. After a presentation of some general properties of
Yb-doped materials, we address the issue of evaluating the temperature map in
Yb-doped laser crystals, both theoretically and experimentally. This is the
first step before studying the complex problem of thermal lensing (part III).
We will focus on some newly discussed aspects, like the definition of the
thermo-optic coefficient: we will highlight some misleading interpretations of
thermal lensing experiments due to the use of the dn/dT parameter in a context
where it is not relevant. Part IV will be devoted to a state-of-the-art of
experimental techniques used to measure thermal lensing. Eventually, in part V,
we will give some concrete examples in Yb-doped materials, where their
peculiarities will be pointed out
- …