22 research outputs found
A general creation-annihilation model with absorbing states
A one dimensional non-equilibrium stochastic model is proposed where each
site of the lattice is occupied by a particle, which may be of type A or B. The
time evolution of the model occurs through three processes: autocatalytic
generation of A and B particles and spontaneous conversion A to B. The
two-parameter phase diagram of the model is obtained in one- and two-site mean
field approximations, as well as through numerical simulations and exact
solution of finite systems extrapolated to the thermodynamic limit. A
continuous line of transitions between an active and an absorbing phase is
found. This critical line starts at a point where the model is equivalent to
the contact process and ends at a point which corresponds to the voter model,
where two absorbing states coexist. Thus, the critical line ends at a point
where the transition is discontinuous. Estimates of critical exponents are
obtained through the simulations and finite-size-scaling extrapolations, and
the crossover between universality classes as the voter model transition is
approached is studied.Comment: 9 pages and 17 figure
Semi-flexible trimers on the square lattice in the full lattice limit
Trimers are chains formed by two lattice edges, and therefore three monomers.
We consider trimers placed on the square lattice, the edges belonging to the
same trimer are either colinear, forming a straight rod with unitary
statistical weight, or perpendicular, a statistical weight being
associated to these angular trimers. The thermodynamic properties of this model
are studied in the full lattice limit, where all lattice sites are occupied by
monomers belonging to trimers. In particular, we use transfer matrix techniques
to estimate the entropy of the system as a function of . The entropy
is a maximum at and our results are compared to earlier
studies in the literature for straight trimers (), angular trimers
() and for mixtures of equiprobable straight and angular
trimers ().Comment: 6 pages, 4 figure
Entropy of chains placed on the square lattice
We obtain the entropy of flexible linear chains composed of M monomers placed
on the square lattice using a transfer matrix approach. An excluded volume
interaction is included by considering the chains to be self-and mutually
avoiding, and a fraction rho of the sites are occupied by monomers. We solve
the problem exactly on stripes of increasing width m and then extrapolate our
results to the two-dimensional limit to infinity using finite-size scaling. The
extrapolated results for several finite values of M and in the polymer limit M
to infinity for the cases where all lattice sites are occupied (rho=1) and for
the partially filled case rho<1 are compared with earlier results. These
results are exact for dimers (M=2) and full occupation (\rho=1) and derived
from series expansions, mean-field like approximations, and transfer matrix
calculations for some other cases. For small values of M, as well as for the
polymer limit M to infinity, rather precise estimates of the entropy are
obtained.Comment: 6 pages, 7 figure
Limited dissemination of the wastewater treatment plant core resistome
Horizontal gene transfer is a major contributor to the evolution of bacterial genomes and can facilitate the dissemination of antibiotic resistance genes between environmental reservoirs and potential pathogens. Wastewater treatment plants (WWTPs) are believed to play a central role in the dissemination of antibiotic resistance genes. However, the contribution of the dominant members of the WWTP resistome to resistance in human pathogens remains poorly understood. Here we use a combination of metagenomic functional selections and comprehensive metagenomic sequencing to uncover the dominant genes of the WWTP resistome. We find that this core resistome is unique to the WWTP environment, with <10% of the resistance genes found outside the WWTP environment. Our data highlight that, despite an abundance of functional resistance genes within WWTPs, only few genes are found in other environments, suggesting that the overall dissemination of the WWTP resistome is comparable to that of the soil resistome