Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Stacks in canonical RNA pseudoknot structures   In this paper we study the distribution of stacks in $k$-noncrossing,
$\tau$-canonical RNA pseudoknot structures ($<k,\tau> $-structures). An RNA
structure is called $k$-noncrossing if it has no more than $k-1$ mutually
crossing arcs and $\tau$-canonical if each arc is contained in a stack of
length at least $\tau$. Based on the ordinary generating function of
$<k,\tau>$-structures \cite{Reidys:08ma} we derive the bivariate generating
function ${\bf T}_{k,\tau}(x,u)=\sum_{n \geq 0} \sum_{0\leq t \leq \frac{n}{2}}
{\sf T}_{k, \tau}^{} (n,t) u^t x^n$, where ${\sf T}_{k,\tau}(n,t)$ is the
number of $<k,\tau>$-structures having exactly $t$ stacks and study its
singularities. We show that for a certain parametrization of the variable $u$,
${\bf T}_{k,\tau}(x,u)$ has a unique, dominant singularity. The particular
shift of this singularity parametrized by $u$ implies a central limit theorem
for the distribution of stack-numbers. Our results are of importance for
understanding the ``language'' of minimum-free energy RNA pseudoknot
structures, generated by computer folding algorithms.

25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th