127 research outputs found
The Page-R{\'e}nyi parking process
In the Page parking (or packing) model on a discrete interval (also known as
the discrete R{\'e}nyi packing problem or the unfriendly seating problem), cars
of length two successively park uniformly at random on pairs of adjacent
places, until only isolated places remain. We give a probabilistic proof of the
(known) fact that the proportion of the interval covered by cars goes to
1-exp(-2) , when the length of the interval goes to infinity. We obtain some
new consequences, and also study a version of this process defined on the
infinite line
On the algebraic numbers computable by some generalized Ehrenfest urns
This article deals with some stochastic population protocols, motivated by
theoretical aspects of distributed computing. We modelize the problem by a
large urn of black and white balls from which at every time unit a fixed number
of balls are drawn and their colors are changed according to the number of
black balls among them. When the time and the number of balls both tend to
infinity the proportion of black balls converges to an algebraic number. We
prove that, surprisingly enough, not every algebraic number can be "computed"
this way
Construction of a short path in high dimensional First Passage Percolation
For First Passage Percolation in Z^d with large d, we construct a path
connecting the origin to {x_1 =1}, whose passage time has optimal order \log
d/d. Besides, an improved lower bound for the "diagonal" speed of the cluster
combined with a result by Dhar (1988) shows that the limiting shape in FPP with
exponential passage times (and thus that of Eden model) is not the euclidian
ball in dimension larger than 35
Distances in the highly supercritical percolation cluster
On the supercritical percolation cluster with parameter p, the distances
between two distant points of the axis are asymptotically increased by a factor
1+(1-p)/2+o(1-p) with respect to the usual distance. The proof is based on an
apparently new connection with the TASEP (totally asymmetric simple exclusion
process).Comment: 15 page
HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
%methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to
construct absorption spectra toward bright extra-galactic background sources at
195 kHz spectral resolution ( 0.6 \kms). We used the IRAM Plateau de
Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward
the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected
toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was
observed in absorption from ``spiral-arm'' clouds in the galactic plane
occulting W49. The complement of detectable molecular species in the 85 - 110
GHz absorption spectrum of diffuse/translucent gas is now fully determined at
rms noise level at \EBV\ = 0.32 mag (\AV\ = 1 mag)
and /\EBV\ mag overall.} %conclusions {As
with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little
between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2)
0.1. We find N(CF\p)/N(HCO\p) , N(CF\p)/N(\cch)
0.005-0.01 and because N(CF\p) increases with \EBV\ and with the
column densities of other molecules we infer that fluorine remains in the gas
phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(HCO\p) = 16
toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO)
, about 10 times higher than in dark clouds. The behaviour of
HCO is consistent with previous suggestions that it forms from C\p\ and \HH,
even when \AV\ is well above 1 mag. The survey can be used to place useful
upper limits on some species, for instance N(\hhco)/N(\HH CS) 32 toward
3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase
formation route to \hhco.}Comment: A\%A in pres
A Branching-selection process related to censored Galton-Walton processes
We obtain the asymptotics for the speed of a particular case of a particle
system with branching and selection introduced by B\'erard and Gou\'er\'e
(2010). The proof is based on a connection with a supercritical Galton-Watson
process censored at a certain level.Comment: 16 pages, 2 figure
From Hammersley's lines to Hammersley's trees
We construct a stationary random tree, embedded in the upper half plane, with
prescribed offspring distribution and whose vertices are the atoms of a unit
Poisson point process. This process which we call Hammersley's tree process
extends the usual Hammersley's line process. Just as Hammersley's process is
related to the problem of the longest increasing subsequence, this model also
has a combinatorial interpretation: it counts the number of heaps (i.e.
increasing trees) required to store a random permutation. This problem was
initially considered by Byers et. al (2011) and Istrate and Bonchis (2015) in
the case of regular trees. We show, in particular, that the number of heaps
grows logarithmically with the size of the permutation
The Brownian limit of separable permutations
We study random uniform permutations in an important class of
pattern-avoiding permutations: the separable permutations. We describe the
asymptotics of the number of occurrences of any fixed given pattern in such a
random permutation in terms of the Brownian excursion. In the recent
terminology of permutons, our work can be interpreted as the convergence of
uniform random separable permutations towards a "Brownian separable permuton".Comment: 45 pages, 14 figures, incorporating referee's suggestion
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