22,485 research outputs found
Experiments and modelling of rate-dependent transition delay in a stochastic subcritical bifurcation
Complex systems exhibiting critical transitions when one of their governing
parameters varies are ubiquitous in nature and in engineering applications.
Despite a vast literature focusing on this topic, there are few studies dealing
with the effect of the rate of change of the bifurcation parameter on the
tipping points. In this work, we consider a subcritical stochastic Hopf
bifurcation under two scenarios: the bifurcation parameter is first changed in
a quasi-steady manner and then, with a finite ramping rate. In the latter case,
a rate-dependent bifurcation delay is observed and exemplified experimentally
using a thermoacoustic instability in a combustion chamber. This delay
increases with the rate of change. This leads to a state transition of larger
amplitude compared to the one that would be experienced by the system with a
quasi-steady change of the parameter. We also bring experimental evidence of a
dynamic hysteresis caused by the bifurcation delay when the parameter is ramped
back. A surrogate model is derived in order to predict the statistic of these
delays and to scrutinise the underlying stochastic dynamics. Our study
highlights the dramatic influence of a finite rate of change of bifurcation
parameters upon tipping points and it pinpoints the crucial need of considering
this effect when investigating critical transitions
Learning and comparing functional connectomes across subjects
Functional connectomes capture brain interactions via synchronized
fluctuations in the functional magnetic resonance imaging signal. If measured
during rest, they map the intrinsic functional architecture of the brain. With
task-driven experiments they represent integration mechanisms between
specialized brain areas. Analyzing their variability across subjects and
conditions can reveal markers of brain pathologies and mechanisms underlying
cognition. Methods of estimating functional connectomes from the imaging signal
have undergone rapid developments and the literature is full of diverse
strategies for comparing them. This review aims to clarify links across
functional-connectivity methods as well as to expose different steps to perform
a group study of functional connectomes
Chaperones as integrators of cellular networks: Changes of cellular integrity in stress and diseases
Cellular networks undergo rearrangements during stress and diseases. In
un-stressed state the yeast protein-protein interaction network (interactome)
is highly compact, and the centrally organized modules have a large overlap.
During stress several original modules became more separated, and a number of
novel modules also appear. A few basic functions, such as the proteasome
preserve their central position. However, several functions with high energy
demand, such the cell-cycle regulation loose their original centrality during
stress. A number of key stress-dependent protein complexes, such as the
disaggregation-specific chaperone, Hsp104, gain centrality in the stressed
yeast interactome. Molecular chaperones, heat shock, or stress proteins form
complex interaction networks (the chaperome) with each other and their
partners. Here we show that the human chaperome recovers the segregation of
protein synthesis-coupled and stress-related chaperones observed in yeast
recently. Examination of yeast and human interactomes shows that (1) chaperones
are inter-modular integrators of protein-protein interaction networks, which
(2) often bridge hubs and (3) are favorite candidates for extensive
phosphorylation. Moreover, chaperones (4) become more central in the
organization of the isolated modules of the stressed yeast protein-protein
interaction network, which highlights their importance in the de-coupling and
re-coupling of network modules during and after stress. Chaperone-mediated
evolvability of cellular networks may play a key role in cellular adaptation
during stress and various polygenic and chronic diseases, such as cancer,
diabetes or neurodegeneration.Comment: 13 pages, 3 figures, 1 glossar
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