7,170 research outputs found
The on-off network traffic model under intermediate scaling
The result provided in this paper helps complete a unified picture of the
scaling behavior in heavy-tailed stochastic models for transmission of packet
traffic on high-speed communication links. Popular models include infinite
source Poisson models, models based on aggregated renewal sequences, and models
built from aggregated on-off sources. The versions of these models with finite
variance transmission rate share the following pattern: if the sources connect
at a fast rate over time the cumulative statistical fluctuations are fractional
Brownian motion, if the connection rate is slow the traffic fluctuations are
described by a stable L\'evy process, while the limiting fluctuations for the
intermediate scaling regime are given by fractional Poisson motion.Comment: 14
Joint assembly and genetic mapping of the Atlantic horseshoe crab genome reveals ancient whole genome duplication
Horseshoe crabs are marine arthropods with a fossil record extending back
approximately 450 million years. They exhibit remarkable morphological
stability over their long evolutionary history, retaining a number of ancestral
arthropod traits, and are often cited as examples of "living fossils." As
arthropods, they belong to the Ecdysozoa}, an ancient super-phylum whose
sequenced genomes (including insects and nematodes) have thus far shown more
divergence from the ancestral pattern of eumetazoan genome organization than
cnidarians, deuterostomes, and lophotrochozoans. However, much of ecdysozoan
diversity remains unrepresented in comparative genomic analyses. Here we use a
new strategy of combined de novo assembly and genetic mapping to examine the
chromosome-scale genome organization of the Atlantic horseshoe crab Limulus
polyphemus. We constructed a genetic linkage map of this 2.7 Gbp genome by
sequencing the nuclear DNA of 34 wild-collected, full-sibling embryos and their
parents at a mean redundancy of 1.1x per sample. The map includes 84,307
sequence markers and 5,775 candidate conserved protein coding genes. Comparison
to other metazoan genomes shows that the L. polyphemus genome preserves
ancestral bilaterian linkage groups, and that a common ancestor of modern
horseshoe crabs underwent one or more ancient whole genome duplications (WGDs)
~ 300 MYA, followed by extensive chromosome fusion
Inferring ancestral sequences in taxon-rich phylogenies
Statistical consistency in phylogenetics has traditionally referred to the
accuracy of estimating phylogenetic parameters for a fixed number of species as
we increase the number of characters. However, as sequences are often of fixed
length (e.g. for a gene) although we are often able to sample more taxa, it is
useful to consider a dual type of statistical consistency where we increase the
number of species, rather than characters. This raises some basic questions:
what can we learn about the evolutionary process as we increase the number of
species? In particular, does having more species allow us to infer the
ancestral state of characters accurately? This question is particularly
relevant when sequence site evolution varies in a complex way from character to
character, as well as for reconstructing ancestral sequences. In this paper, we
assemble a collection of results to analyse various approaches for inferring
ancestral information with increasing accuracy as the number of taxa increases.Comment: 32 pages, 5 figures, 1 table
The Genomic HyperBrowser: inferential genomics at the sequence level
The immense increase in the generation of genomic scale data poses an unmet
analytical challenge, due to a lack of established methodology with the
required flexibility and power. We propose a first principled approach to
statistical analysis of sequence-level genomic information. We provide a
growing collection of generic biological investigations that query pairwise
relations between tracks, represented as mathematical objects, along the
genome. The Genomic HyperBrowser implements the approach and is available at
http://hyperbrowser.uio.no
The role of bot squads in the political propaganda on Twitter
Social Media are nowadays the privileged channel for information spreading
and news checking. Unexpectedly for most of the users, automated accounts, also
known as social bots, contribute more and more to this process of news
spreading. Using Twitter as a benchmark, we consider the traffic exchanged,
over one month of observation, on a specific topic, namely the migration flux
from Northern Africa to Italy. We measure the significant traffic of tweets
only, by implementing an entropy-based null model that discounts the activity
of users and the virality of tweets. Results show that social bots play a
central role in the exchange of significant content. Indeed, not only the
strongest hubs have a number of bots among their followers higher than
expected, but furthermore a group of them, that can be assigned to the same
political tendency, share a common set of bots as followers. The retwitting
activity of such automated accounts amplifies the presence on the platform of
the hubs' messages.Comment: Under Submissio
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