1,858 research outputs found
Signal-to-pump back-action and self-oscillation in Double-Pump Josephson Parametric Amplifier
We present the theory of a Josephson parametric amplifier employing two pump
sources. Our calculations are based on Input-Output Theory, and can easily be
generalized to any coupled system involving parametric interactions. We analyze
the operation of the device, taking into account the feedback introduced by the
reaction of the signal and noise on the pump power, and in this framework,
compute the response functions of interest - signal and idler gains, internal
gain of the amplifier, and self-oscillation signal amplitude. To account for
this back-action between signal and pump, we adopt a mean-field approach and
self-consistently explore the boundary between amplification and
self-oscillation. The coincidence of bifurcation and self-oscillation
thresholds reveals that the origin of coherent emission of the amplifier lies
in the multi-wave mixing of the noise components. Incorporation of the
back-action leads the system to exhibit hysteresis, dependent on parameters
like temperature and detuning from resonance. Our analysis also shows that the
resonance condition itself changes in the presence of back-action and this can
be understood in terms of the change in plasma frequency of the junction. The
potential of the double pump amplifier for quantum-limited measurements and as
a squeezer is also discussed.Comment: 25 pages, 20 figures, three appendice
Hysteresis and bi-stability by an interplay of calcium oscillations and action potential firing
Many cell types exhibit oscillatory activity, such as repetitive action
potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell
membrane or reveal intracellular inositol triphosphate (IP) mediated
calcium oscillations (CaOs) by calcium-induced calcium release channels
(IP-receptor) in the membrane of the endoplasmic reticulum (ER). The
dynamics of the excitable membrane and that of the IP-mediated CaOs have
been the subject of many studies. However, the interaction between the
excitable cell membrane and IP-mediated CaOs, which are coupled by
cytosolic calcium which affects the dynamics of both, has not been studied.
This study for the first time applied stability analysis to investigate the
dynamic behavior of a model, which includes both an excitable membrane and an
intracellular IP-mediated calcium oscillator. Taking the IP
concentration as a control parameter, the model exhibits a novel rich spectrum
of stable and unstable states with hysteresis. The four stable states of the
model correspond in detail to previously reported growth-state dependent states
of the membrane potential of normal rat kidney fibroblasts in cell culture. The
hysteresis is most pronounced for experimentally observed parameter values of
the model, suggesting a functional importance of hysteresis. This study shows
that the four growth-dependent cell states may not reflect the behavior of
cells that have differentiated into different cell types with different
properties, but simply reflect four different states of a single cell type,
that is characterized by a single model.Comment: 29 pages, 6 figure
Oscillators and relaxation phenomena in Pleistocene climate theory
Ice sheets appeared in the northern hemisphere around 3 million years ago and
glacial-interglacial cycles have paced Earth's climate since then. Superimposed
on these long glacial cycles comes an intricate pattern of millennial and
sub-millennial variability, including Dansgaard-Oeschger and Heinrich events.
There are numerous theories about theses oscillations. Here, we review a number
of them in order to draw a parallel between climatic concepts and dynamical
system concepts, including, in particular, the relaxation oscillator,
excitability, slow-fast dynamics and homoclinic orbits. Namely, almost all
theories of ice ages reviewed here feature a phenomenon of synchronisation
between internal climate dynamics and the astronomical forcing. However, these
theories differ in their bifurcation structure and this has an effect on the
way the ice age phenomenon could grow 3 million years ago. All theories on
rapid events reviewed here rely on the concept of a limit cycle in the ocean
circulation, which may be excited by changes in the surface freshwater surface
balance. The article also reviews basic effects of stochastic fluctuations on
these models, including the phenomenon of phase dispersion, shortening of the
limit cycle and stochastic resonance. It concludes with a more personal
statement about the potential for inference with simple stochastic dynamical
systems in palaeoclimate science.
Keywords: palaeoclimates, dynamical systems, limit cycle, ice ages,
Dansgaard-Oeschger eventsComment: Published in the Transactions of the Philosophical Transactions of
the Royal Society (Series A, Physical Mathematical and Engineering Sciences),
as a contribution to the Proceedings of the workshop on Stochastic Methods in
Climate Modelling, Newton Institute (23-27 August). Philosophical
Transactions of the Royal Society (Series A, Physical Mathematical and
Engineering Sciences), vol. 370, pp. xx-xx (2012); Source codes available on
request to author and on http://www.uclouvain.be/ito
Bifurcation and dynamic response analysis of rotating blade excited by upstream vortices
Acknowledgements The authors acknowledge the projects supported by the National Basic Research Program of China (973 Project)(No. 2015CB057405) and the National Natural Science Foundation of China (No. 11372082) and the State Scholarship Fund of CSC. DW thanks for the hospitality of the University of Aberdeen.Peer reviewedPostprin
Imperfect Homoclinic Bifurcations
Experimental observations of an almost symmetric electronic circuit show
complicated sequences of bifurcations. These results are discussed in the light
of a theory of imperfect global bifurcations. It is shown that much of the
dynamics observed in the circuit can be understood by reference to imperfect
homoclinic bifurcations without constructing an explicit mathematical model of
the system.Comment: 8 pages, 11 figures, submitted to PR
Bifurcations and singularities for coupled oscillators with inertia and frustration
We prove that any non zero inertia, however small, is able to change the
nature of the synchronization transition in Kuramoto-like models, either from
continuous to discontinuous, or from discontinuous to continuous. This result
is obtained through an unstable manifold expansion in the spirit of J.D.
Crawford, which features singularities in the vicinity of the bifurcation. Far
from being unwanted artifacts, these singularities actually control the
qualitative behavior of the system. Our numerical tests fully support this
picture.Comment: 10 pages, 2 figure
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