2,366 research outputs found
Spatial-temporal forecasting the sunspot diagram
We attempt to forecast the Sun's sunspot butterfly diagram in both space
(i.e. in latitude) and time, instead of the usual one-dimensional time series
forecasts prevalent in the scientific literature. We use a prediction method
based on the non-linear embedding of data series in high dimensions. We use
this method to forecast both in latitude (space) and in time, using a full
spatial-temporal series of the sunspot diagram from 1874 to 2015. The analysis
of the results shows that it is indeed possible to reconstruct the overall
shape and amplitude of the spatial-temporal pattern of sunspots, but that the
method in its current form does not have real predictive power. We also apply a
metric called structural similarity to compare the forecasted and the observed
butterfly cycles, showing that this metric can be a useful addition to the
usual root mean square error metric when analysing the efficiency of different
prediction methods
The influence of noise on scalings for in-out intermittency
We study the effects of noise on a recently discovered form of intermittency,
referred to as in-out intermittency. This type of intermittency, which reduces
to on-off in systems with a skew product structure, has been found in the
dynamics of maps, ODE and PDE simulations that have symmetries. It shows itself
in the form of trajectories that spend a long time near a symmetric state
interspersed with short bursts away from symmetry. In contrast to on-off
intermittency, there are clearly distinct mechanisms of approach towards and
away from the symmetric state, and this needs to be taken into account in order
to properly model the long time statistics. We do this by using a
diffusion-type equation with delay integral boundary condition. This model is
validated by considering the statistics of a two-dimensional map with and
without the addition of noise.Comment: Submitted to Physical Review E, also available at
http://www.eurico.web.co
The influence of density stratification and multiple nonlinearities on solar torsional oscillations
Analyses of recent helioseismic data have produced ample evidence for
substantial dynamical variation of the differential rotation within the solar
convection zone. Given the inevitable difficulties in resolving the precise
nature of variations at deeper layers, much effort has recently gone into
determining theoretically the expected modes of behaviour, using nonlinear
dynamo models. Two important limitations of these models are that they have so
far included only one form of nonlinearity, and as yet they have not taken into
account the density stratification in the solar convection zone. Here we
address both of these issues by studying the effects of including density
stratification, as well as including an alpha--quenching nonlinearity in
addition to the previously studied effects of the Lorentz force on the
differential rotation. We find that observationally important features found in
the earlier uniform density models remain qualitatively unchanged, although
there are quantitative differences. This is important as it provides more
realistic theoretical predictions to be compared with and guide observations,
especially in the deeper regions where the uncertainties in the inversions are
larger. However the presence of an effective alpha-quenching nonlinearity
significantly reduces the amplitudes of the oscillations.Comment: 8 pages, 13 figures; to appear in Astronomy and Astrophysic
Non-normal parameter blowout bifurcation: an example in a truncated mean field dynamo model
We examine global dynamics and bifurcations occurring in a truncated model of
a stellar mean field dynamo. This model has symmetry-forced invariant subspaces
for the dynamics and we find examples of transient type I intermittency and
blowout bifurcations to transient on-off intermittency, involving laminar
phases in the invariant submanifold. In particular, our model provides examples
of blowout bifurcations that occur on varying a non-normal parameter; that is,
the parameter varies the dynamics within the invariant subspace at the same
time as the dynamics normal to it. As a consequence of this we find that the
Lyapunov exponents do not vary smoothly and the blowout bifurcation occurs over
a range of parameter values rather than a point in the parameter space.Comment: Full paper with figures, also available on the web page
http://www.maths.qmw.ac.uk/~eoc. Physical Review E, accepte
Exercise-Derived Microvesicles: A Review of the Literature
Initially suggested as simple cell debris, cell-derived microvesicles (MVs) have now gained acceptance as recognized players in cellular communication and physiology. Shed by most, and perhaps all, human cells, these tiny lipid-membrane vesicles carry bioactive agents, such as proteins, lipids and microRNA from their cell source, and are produced under orchestrated events in response to a myriad of stimuli. Physical exercise introduces systemic physiological challenges capable of acutely disrupting cell homeostasis and stimulating the release of MVs into the circulation. The novel and promising field of exercise-derived MVs is expanding quickly, and the following work provides a review of the influence of exercise on circulating MVs, considering both acute and chronic aspects of exercise and training. Potential effects of the MV response to exercise are highlighted and future directions suggested as exercise and sports sciences extend the realm of extracellular vesicles
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