618,058 research outputs found
Temporal variability of the telluric sodium layer
The temporal variability of the telluric sodium layer is investigated by
analyzing 28 nights of data obtained with the Colorado State University LIDAR
experiment. The mean height power spectrum of the sodium layer was found to be
well fit by a power law over the observed range of frequencies, 10 microhertz
to 4 millhertz. The best fitting power law was found to be 10^\beta \nu^\alpha,
with \alpha = -1.79 +/- 0.02 and \beta = 1.12 +/- 0.40. Applications to
wavefront sensing require knowledge of the behavior of the sodium layer at kHz
frequencies. Direct measurements at these frequencies do not exist.
Extrapolation from low-frequency behavior to high frequencies suggests that
this variability may be a significant source of error for laser-guide-star
adaptive optics on large-aperture telescopes.Comment: 3 pages, 3 figures, accepted for publication in Optics Letter
Constrained information flows in temporal networks reveal intermittent communities
Many real-world networks represent dynamic systems with interactions that
change over time, often in uncoordinated ways and at irregular intervals. For
example, university students connect in intermittent groups that repeatedly
form and dissolve based on multiple factors, including their lectures,
interests, and friends. Such dynamic systems can be represented as multilayer
networks where each layer represents a snapshot of the temporal network. In
this representation, it is crucial that the links between layers accurately
capture real dependencies between those layers. Often, however, these
dependencies are unknown. Therefore, current methods connect layers based on
simplistic assumptions that do not capture node-level layer dependencies. For
example, connecting every node to itself in other layers with the same weight
can wipe out dependencies between intermittent groups, making it difficult or
even impossible to identify them. In this paper, we present a principled
approach to estimating node-level layer dependencies based on the network
structure within each layer. We implement our node-level coupling method in the
community detection framework Infomap and demonstrate its performance compared
to current methods on synthetic and real temporal networks. We show that our
approach more effectively constrains information inside multilayer communities
so that Infomap can better recover planted groups in multilayer benchmark
networks that represent multiple modes with different groups and better
identify intermittent communities in real temporal contact networks. These
results suggest that node-level layer coupling can improve the modeling of
information spreading in temporal networks and better capture intermittent
community structure.Comment: 10 pages, 10 figures, published in PR
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