2,816 research outputs found
Erd\H{o}s-Ko-Rado for random hypergraphs: asymptotics and stability
We investigate the asymptotic version of the Erd\H{o}s-Ko-Rado theorem for
the random -uniform hypergraph . For , let and . We show that with probability
tending to 1 as , the largest intersecting subhypergraph of
has size , for any . This lower bound on is
asymptotically best possible for . For this range of and ,
we are able to show stability as well.
A different behavior occurs when . In this case, the lower bound on
is almost optimal. Further, for the small interval , the largest intersecting subhypergraph of
has size , provided that .
Together with previous work of Balogh, Bohman and Mubayi, these results
settle the asymptotic size of the largest intersecting family in
, for essentially all values of and
Continuous and discontinuous absorbing-state phase transitions on Voronoi-Delaunay random lattices
We study absorbing-state phase transitions in two-dimensional
Voronoi-Delaunay (VD) random lattices with quenched coordination disorder.
Quenched randomness usually changes the criticality and destroys discontinuous
transitions in low-dimensional nonequilibrium systems. We performed extensive
simulations of the Ziff-Gulari-Barshad (ZGB) model, and verified that the VD
disorder does not change the nature of its discontinuous transition. Our
results corroborate recent findings of Barghatti and Vojta [Phys. Rev. Lett.
{\bf 113}, 120602 (2014)] stating the irrelevance of topological disorder in a
class of random lattices that includes VD and raise the interesting possibility
that disorder in nonequilibrium APT may, under certain conditions, be
irrelevant for the phase coexistence. We also verify that the VD disorder is
irrelevant for the critical behavior of models belonging to the directed
percolation and Manna universality classes.Comment: 7 pages, 6 figure
Local vs. long-range infection in unidimensional epidemics
We study the effects of local and distance interactions in the unidimensional
contact process (CP). In the model, each site of a lattice is occupied by an
individual, which can be healthy or infected. As in the standard CP, each
infected individual spreads the disease to one of its first-neighbors with rate
, and with unitary rate, it becomes healthy. However, in our model, an
infected individual can transmit the disease to an individual at a distance
apart. This step mimics a vector-mediated transmission. We observe the
host-host interactions do not alter the critical exponents significantly in
comparison to a process with only L\'evy-type interactions. Our results
confirm, numerically, early field-theoretic predictions.Comment: 8 pages, 6 figures, to appear on Frontiers in Physic
Quantum Dissipation in a Neutrino System Propagating in Vacuum and in Matter
Considering the neutrino state like an open quantum system, we analyze its
propagation in vacuum or in matter. After defining what can be called
decoherence and relaxation effects, we show that in general the probabilities
in vacuum and in constant matter can be written in a similar way, which is not
an obvious result in this approach. From this result, we analyze the situation
where neutrinos evolution satisfies the adiabatic limit and use this formalim
to study solar neutrinos. We show that the decoherence effect may not be
bounded by the solar neutrino data and review some results in the literature.
We discuss the current results where solar neutrinos were used to put bounds on
decoherence effects through a model-dependent approach. We conclude explaining
how and why this models are not general and we reinterpret these constraints.Comment: new version: title was changend and was added a table. To appear at
Nucl. Physic.
Contact process on a Voronoi triangulation
We study the continuous absorbing-state phase transition in the contact
process on the Voronoi-Delaunay lattice. The Voronoi construction is a natural
way to introduce quenched coordination disorder in lattice models. We simulate
the disordered system using the quasistationary simulation method and determine
its critical exponents and moment ratios. Our results suggest that the critical
behavior of the disordered system is unchanged with respect to that on a
regular lattice, i.e., that of directed percolation
A feasibility study with survival in swine model
Transrectal access still has some unsolved issues such as spatial orientation,
infection, access and site closure. This study presents a simple technique to
perform transcolonic access with survival in a swine model series. A new
technique for NOTES perirectal access to perform retroperitoneoscopy,
peritoneoscopy, liver and lymphnode biopsies was performed in 6 pigs, using
Totally NOTES technique. The specimens were extracted transanally. The
flexible endoscope was inserted through a posterior transmural incision and
the retrorectal space. Cultures of bacteria were documented for the
retroperitoneal space and intra abdominal cavity after 14 days. Rectal site
was closed using non-absorbable sutures. There was no bowel cleansing, nor
preoperative fasting. The procedures were performed in 6 pigs through
transcolonic natural orifice access using available endoscopic flexible
instruments. All animals survived 14 days without complications, and cultures
were negative. Histopathologic examination of the rectal closure site showed
adequate healing of suture line and no micro abscesses. The results of
feasibility and safety of experimental Transcolonic NOTES potentially brings
new frontiers and future wider applications for minimally invasive surgery.
The treatment of colorectal, abdominal and retroperitoneal diseases through a
flexible Perirectal NOTES Access (PNA) is a promising new approach
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