7,304 research outputs found
An Internet Heartbeat
Obtaining sound inferences over remote networks via active or passive
measurements is difficult. Active measurement campaigns face challenges of
load, coverage, and visibility. Passive measurements require a privileged
vantage point. Even networks under our own control too often remain poorly
understood and hard to diagnose. As a step toward the democratization of
Internet measurement, we consider the inferential power possible were the
network to include a constant and predictable stream of dedicated lightweight
measurement traffic. We posit an Internet "heartbeat," which nodes periodically
send to random destinations, and show how aggregating heartbeats facilitates
introspection into parts of the network that are today generally obtuse. We
explore the design space of an Internet heartbeat, potential use cases,
incentives, and paths to deployment
Breaking the chain
We consider the motion of a Brownian particle in , moving between
a particle fixed at the origin and another moving deterministically away at
slow speed . The middle particle interacts with its neighbours via
a potential of finite range , with a unique minimum at , where
. We say that the chain of particles breaks on the left- or right-hand
side when the middle particle is greater than a distance from its left or
right neighbour, respectively. We study the asymptotic location of the first
break of the chain in the limit of small noise, in the case where and is the noise intensity.Comment: 13 pages, 2 figures. v2: Corrected a mistake in proof of second part
of main theore
The identifiability of tree topology for phylogenetic models, including covarion and mixture models
For a model of molecular evolution to be useful for phylogenetic inference,
the topology of evolutionary trees must be identifiable. That is, from a joint
distribution the model predicts, it must be possible to recover the tree
parameter. We establish tree identifiability for a number of phylogenetic
models, including a covarion model and a variety of mixture models with a
limited number of classes. The proof is based on the introduction of a more
general model, allowing more states at internal nodes of the tree than at
leaves, and the study of the algebraic variety formed by the joint
distributions to which it gives rise. Tree identifiability is first established
for this general model through the use of certain phylogenetic invariants.Comment: 20 pages, 1 figur
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