7,259 research outputs found
Fixed-to-Variable Length Distribution Matching
Fixed-to-variable length (f2v) matchers are used to reversibly transform an
input sequence of independent and uniformly distributed bits into an output
sequence of bits that are (approximately) independent and distributed according
to a target distribution. The degree of approximation is measured by the
informational divergence between the output distribution and the target
distribution. An algorithm is developed that efficiently finds optimal f2v
codes. It is shown that by encoding the input bits blockwise, the informational
divergence per bit approaches zero as the block length approaches infinity. A
relation to data compression by Tunstall coding is established.Comment: 5 pages, essentially the ISIT 2013 versio
A new balance index for phylogenetic trees
Several indices that measure the degree of balance of a rooted phylogenetic
tree have been proposed so far in the literature. In this work we define and
study a new index of this kind, which we call the total cophenetic index: the
sum, over all pairs of different leaves, of the depth of their least common
ancestor. This index makes sense for arbitrary trees, can be computed in linear
time and it has a larger range of values and a greater resolution power than
other indices like Colless' or Sackin's. We compute its maximum and minimum
values for arbitrary and binary trees, as well as exact formulas for its
expected value for binary trees under the Yule and the uniform models of
evolution. As a byproduct of this study, we obtain an exact formula for the
expected value of the Sackin index under the uniform model, a result that seems
to be new in the literature.Comment: 24 pages, 2 figures, preliminary version presented at the JBI 201
Destruction of very simple trees
We consider the total cost of cutting down a random rooted tree chosen from a
family of so-called very simple trees (which include ordered trees, -ary
trees, and Cayley trees); these form a subfamily of simply generated trees. At
each stage of the process an edge is chose at random from the tree and cut,
separating the tree into two components. In the one-sided variant of the
process the component not containing the root is discarded, whereas in the
two-sided variant both components are kept. The process ends when no edges
remain for cutting. The cost of cutting an edge from a tree of size is
assumed to be . Using singularity analysis and the method of moments,
we derive the limiting distribution of the total cost accrued in both variants
of this process. A salient feature of the limiting distributions obtained
(after normalizing in a family-specific manner) is that they only depend on
.Comment: 20 pages; Version 2 corrects some minor error and fixes a few typo
Mycosphaerella podagrariae - a necrotrophic phytopathogen forming a special cellular interaction with its host Aegopodium podagraria
We present a new kind of cellular interaction found between Mycosphaerella podagrariae and Aegopodium podagraria, which is remarkably different to the interaction type of the obligate biotrophic fungus Cymadothea trifolii, another member of the Mycosphaerellaceae (Capnodiales, Dothideomycetes, Ascomycota) which we have described earlier. Observations are based on both conventional and cryofixed material and show that some features of this particular interaction are better discernable after chemical fixation. We were also able to generate sequences for nuclear ribosomal DNA (complete SSU, 5.8 S and flanking ITS-regions, D1–D3 region of the LSU) confirming the position of M. podagrariae within Mycosphaerellacea
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