731 research outputs found
(Non)Invariance of dynamical quantities for orbit equivalent flows
We study how dynamical quantities such as Lyapunov exponents, metric entropy,
topological pressure, recurrence rates, and dimension-like characteristics
change under a time reparameterization of a dynamical system. These quantities
are shown to either remain invariant, transform according to a multiplicative
factor or transform through a convoluted dependence that may take the form of
an integral over the initial local values. We discuss the significance of these
results for the apparent non-invariance of chaos in general relativity and
explore applications to the synchronization of equilibrium states and the
elimination of expansions
Optimization in Networks
The recent surge in the network modeling of complex systems has set the stage
for a new era in the study of fundamental and applied aspects of optimization
in collective behavior. This Focus Issue presents an extended view of the state
of the art in this field and includes articles from a large variety of domains
where optimization manifests itself, including physical, biological, social,
and technological networked systems.Comment: Opening article of the CHAOS Focus Issue "Optimization in Networks",
available at http://link.aip.org/link/?CHA/17/2/htmlto
Cascade control and defense in complex networks
Complex networks with heterogeneous distribution of loads may undergo a
global cascade of overload failures when highly loaded nodes or edges are
removed due to attacks or failures. Since a small attack or failure has the
potential to trigger a global cascade, a fundamental question regards the
possible strategies of defense to prevent the cascade from propagating through
the entire network. Here we introduce and investigate a costless strategy of
defense based on a selective further removal of nodes and edges, right after
the initial attack or failure. This intentional removal of network elements is
shown to drastically reduce the size of the cascade.Comment: 4 pages, 2 figures, Revte
The effects of oral contraceptives on mood and affect: a meta-analysis
Combined oral contraceptive (COC) pills are widely used by women of reproductive age, but there is still little conclusive evidence that exists about the mood-related side effects associated with their use. This meta-analysis examined the relationship between oral contraceptive use and mood effects such as depression and anxiety to determine what role, if any, that COCs may have in the worsening or improvement of women’s mood when taking them. Effect sizes compared the differences in women’s mood scores before taking COCs and after one or more cycles of use. Seventeen studies made up of 25 individual samples contributed 71 effect sizes for this analysis. The results suggest that COCs tend to contribute to a small but significant improvement in women’s overall moods. However, methodological challenges and inconsistencies make it difficult for researchers to establish any firm conclusions about the role COCs play in mood changes
CO2 Based Parachute Deployment
This paper describes the design process of a CO2 based parachute deployment system for the Akronauts Rocket Design team, with particular emphasis on the selection of methodologies of deployment as well as design iteration. The objective was to create a fully mechanical system in order to replace the black powder based systems that were used previously by the team.
Emphasis was put in creating a system that would function well at higher altitudes while also preventing damage to the parachute during deployment. This system emphasizes robustness under launch conditions
Cusp-scaling behavior in fractal dimension of chaotic scattering
A topological bifurcation in chaotic scattering is characterized by a sudden
change in the topology of the infinite set of unstable periodic orbits embedded
in the underlying chaotic invariant set. We uncover a scaling law for the
fractal dimension of the chaotic set for such a bifurcation. Our analysis and
numerical computations in both two- and three-degrees-of-freedom systems
suggest a striking feature associated with these subtle bifurcations: the
dimension typically exhibits a sharp, cusplike local minimum at the
bifurcation.Comment: 4 pages, 4 figures, Revte
Ensemble averageability in network spectra
The extreme eigenvalues of connectivity matrices govern the influence of the
network structure on a number of network dynamical processes. A fundamental
open question is whether the eigenvalues of large networks are well represented
by ensemble averages. Here we investigate this question explicitly and validate
the concept of ensemble averageability in random scale-free networks by showing
that the ensemble distributions of extreme eigenvalues converge to peaked
distributions as the system size increases. We discuss the significance of this
result using synchronization and epidemic spreading as example processes.Comment: 4 pages, 4 figure
Network synchronization: Spectral versus statistical properties
We consider synchronization of weighted networks, possibly with asymmetrical
connections. We show that the synchronizability of the networks cannot be
directly inferred from their statistical properties. Small local changes in the
network structure can sensitively affect the eigenvalues relevant for
synchronization, while the gross statistical network properties remain
essentially unchanged. Consequently, commonly used statistical properties,
including the degree distribution, degree homogeneity, average degree, average
distance, degree correlation, and clustering coefficient, can fail to
characterize the synchronizability of networks
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