627 research outputs found
Families of piecewise linear maps with constant Lyapunov exponent
We consider families of piecewise linear maps in which the moduli of the two
slopes take different values. In some parameter regions, despite the variations
in the dynamics, the Lyapunov exponent and the topological entropy remain
constant. We provide numerical evidence of this fact and we prove it
analytically for some special cases. The mechanism is very different from that
of the logistic map and we conjecture that the Lyapunov plateaus reflect
arithmetic relations between the slopes.Comment: 26 pages, 13 figure
Emergence of hierarchical networks and polysynchronous behaviour in simple adaptive systems
We describe the dynamics of a simple adaptive network. The network
architecture evolves to a number of disconnected components on which the
dynamics is characterized by the possibility of differently synchronized nodes
within the same network (polysynchronous states). These systems may have
implications for the evolutionary emergence of polysynchrony and hierarchical
networks in physical or biological systems modeled by adaptive networks.Comment: 4 pages, 4 figure
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
Combinatorics of linear iterated function systems with overlaps
Let be points in , and let
be a one-parameter family of similitudes of : where
is our parameter. Then, as is well known, there exists a
unique self-similar attractor satisfying
. Each has
at least one address , i.e.,
.
We show that for sufficiently close to 1, each has different
addresses. If is not too close to 1, then we can still have an
overlap, but there exist 's which have a unique address. However, we
prove that almost every has addresses,
provided contains no holes and at least one proper overlap. We
apply these results to the case of expansions with deleted digits.
Furthermore, we give sharp sufficient conditions for the Open Set Condition
to fail and for the attractor to have no holes.
These results are generalisations of the corresponding one-dimensional
results, however most proofs are different.Comment: Accepted for publication in Nonlinearit
Unstable dimension variability, heterodimensional cycles, and blenders in the border-collision normal form
Chaotic attractors commonly contain periodic solutions with unstable
manifolds of different dimensions. This allows for a zoo of dynamical phenomena
not possible for hyperbolic attractors. The purpose of this Letter is to
demonstrate these phenomena in the border-collision normal form. This is a
continuous, piecewise-linear family of maps that is physically relevant as it
captures the dynamics created in border-collision bifurcations in diverse
applications. Since the maps are piecewise-linear they are relatively amenable
to an exact analysis and we are able to explicitly identify parameter values
for heterodimensional cycles and blenders. For a one-parameter subfamily we
identify bifurcations involved in a transition through unstable dimension
variability. This is facilitated by being able to compute periodic solutions
quickly and accurately, and the piecewise-linear form should provide a useful
test-bed for further study
Synchronization of many nano-mechanical resonators coupled via a common cavity field
Using amplitude equations, we show that groups of identical nano-mechanical
resonators, interacting with a common mode of a cavity microwave field,
synchronize to form a single mechanical mode which couples to the cavity with a
strength dependent on the square sum of the individual mechanical-microwave
couplings. Classically this system is dominated by periodic behaviour which,
when analyzed using amplitude equations, can be shown to exhibit
multi-stability. In contrast groups of sufficiently dissimilar nano-mechanical
oscillators may lose synchronization and oscillate out of phase at
significantly higher amplitudes. Further the method by which synchronization is
lost resembles that for large amplitude forcing which is not of the Kuramoto
form.Comment: 23 pages, 11 figure
Analysis of the shearing instability in nonlinear convection and magnetoconvection
Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced
Assessing the influence of one astronomy camp over 50 years
The International Astronomical Youth Camp has benefited thousands of lives
during its 50-year history. We explore the pedagogy behind this success, review
a survey taken by more than 300 previous participants, and discuss some of the
challenges the camp faces in the future.Comment: 10 pages, 4 figure
In good company: risk, security and choice in young people's drug decisions
This article draws on original empirical research with young people to question the degree to which 'individualisation of risk', as developed in the work of Beck and Giddens, adequately explains the risks young people bear and take. It draws on alternative understandings and critiques of 'risk' not to refute the notion of the reflexive individual upon which 'individualisation of risk' is based but to re-read that reflexivity in a more hermeneutic way. It explores specific risk-laden moments â young people's drug use decisions â in their natural social and cultural context of the friendship group. Studying these decisions in context, it suggests, reveals the meaning of 'risk' to be not given, but constructed through group discussion, disagreement and consensus and decisions taken to be rooted in emotional relations of trust, mutual accountability and common security. The article concludes that 'the individualisation of risk' fails to take adequate account of the significance of intersubjectivity in risk-decisions. It argues also that addressing the theoretical overemphasis on the individual bearer of risk requires not only further empirical testing of the theory but appropriate methodological reflection
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