1,589 research outputs found
Equal-time correlation function for directed percolation
We suggest an equal-time n-point correlation function for systems in the
directed percolation universality class which is well defined in all phases and
independent of initial conditions. It is defined as the probability that all
points are connected with a common ancestor in the past by directed paths.Comment: LaTeX, 12 pages, 8 eps figure
Boundary-induced nonequilibrium phase transition into an absorbing state
We demonstrate that absorbing phase transitions in one dimension may be
induced by the dynamics of a single site. As an example we consider a
one-dimensional model of diffusing particles, where a single site at the
boundary evolves according to the dynamics of a contact process. As the rate
for offspring production at this site is varied, the model exhibits a phase
transition from a fluctuating active phase into an absorbing state. The
universal properties of the transition are analyzed by numerical simulations
and approximation techniques.Comment: 4 pages, 4 figures; minor change
Numerical Study of Local and Global Persistence in Directed Percolation
The local persistence probability P_l(t) that a site never becomes active up
to time t, and the global persistence probability P_g(t) that the deviation of
the global density from its mean value rho(t)- does not change its
sign up to time t are studied in a one-dimensional directed percolation process
by Monte Carlo simulations. At criticality, starting from random initial
conditions, both P_l(t) and P_g(t) decay algebraically with exponents theta_l ~
theta_g ~ 1.50(2), which is in contrast to previously known cases where theta_g
< theta_l. The exponents are found to be independent of the initial density and
the microscopic details of the dynamics, suggesting that theta_l and theta_g
are universal exponents. It is shown that in the special case of directed-bond
percolation, P_l(t) can be related to a certain return probability of a
directed percolation process with an active source (wet wall).Comment: revtex, 7 pages, including 6 eps figure
Generalized scaling relations for unidirectionally coupled nonequilibrium systems
Unidirectionally coupled systems which exhibit phase transitions into an
absorbing state are investigated at the multicritical point. We find that for
initial conditions with isolated particles, each hierarchy level exhibits an
inhomogeneous active region, coupled and uncoupled respectively. The particle
number of each level increases algebraically in time as
with different exponents in each domain. This inhomogeneity is a quite
general feature of unidirectionally coupled systems and leads to two
hyperscaling relations between dynamic and static critical exponents. Using the
contact process and the branching-annihilating random walk with two offsprings,
which belong to the DP and PC classes respectively, we numerically confirm the
scaling relations.Comment: 4 pages, 3 figures, 1 tabl
Binary spreading process with parity conservation
Recently there has been a debate concerning the universal properties of the
phase transition in the pair contact process with diffusion (PCPD) . Although some of the critical exponents seem to coincide with
those of the so-called parity-conserving universality class, it was suggested
that the PCPD might represent an independent class of phase transitions. This
point of view is motivated by the argument that the PCPD does not conserve
parity of the particle number. In the present work we pose the question what
happens if the parity conservation law is restored. To this end we consider the
the reaction-diffusion process . Surprisingly this
process displays the same type of critical behavior, leading to the conclusion
that the most important characteristics of the PCPD is the use of binary
reactions for spreading, regardless of whether parity is conserved or not.Comment: RevTex, 4pages, 4 eps figure
Effect of Vinyl and Silicon Monomers on Mechanical and Degradation Properties of Bio-Degradable Jute-Biopol® Composite
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Composites of jute fabrics (Hessian cloth) and Biopol® were prepared by compression molding process. Three types of Biopol® (3-hydroxbutyrate-co-3-hydroxyvalarate) such as D300G, D400G and D600G, depending on the concentration of 3-hydroxyvalarate (3HV) in 3-hydroxbutyrate (3HB) were taken for this purpose. Mechanical properties such as tensile strength (TS), bending strength (BS), elongation at break (Eb) and impact strength (IS) of the jute-Biopol® composites were studied. It was found that the composite with D400G produced higher mechanical properties in comparison to the other two types of Biopol®. To increase mechanical properties as well as interfacial adhesion between fiber and matrix, 2-ethyl hydroxy acrylate (EHA), vinyl tri-methoxy silane (VMS) and 3-methacryloxypropyl tri-methoxy silane (MPS) were taken as coupling agents. Enhanced mechanical properties of the composites were obtained by using these coupling agents. Biopol® D400G composites showed the highest mechanical properties. Among the coupling agents EHA depicts the highest increase of mechanical properties such as tensile strength (80%), bending strength (81%), elongation at break (33%) and impact strength (130%) compared pure Biopol. SEM investigations demonstrate that the coupling agents improve the interfacial adhesion between fiber and matrix. The surface of the silanized jute was characterized by FTIR and found the deposition of silane on jute fiber was observed. Soil degradation test proved that the composite prepared with EHA treated jute exhibits better degradation properties in comparison to pure Biopol®
Epidemic spreading with immunization and mutations
The spreading of infectious diseases with and without immunization of
individuals can be modeled by stochastic processes that exhibit a transition
between an active phase of epidemic spreading and an absorbing phase, where the
disease dies out. In nature, however, the transmitted pathogen may also mutate,
weakening the effect of immunization. In order to study the influence of
mutations, we introduce a model that mimics epidemic spreading with
immunization and mutations. The model exhibits a line of continuous phase
transitions and includes the general epidemic process (GEP) and directed
percolation (DP) as special cases. Restricting to perfect immunization in two
spatial dimensions we analyze the phase diagram and study the scaling behavior
along the phase transition line as well as in the vicinity of the GEP point. We
show that mutations lead generically to a crossover from the GEP to DP. Using
standard scaling arguments we also predict the form of the phase transition
line close to the GEP point. It turns out that the protection gained by
immunization is vitally decreased by the occurrence of mutations.Comment: 9 pages, 13 figure
Influence of diffusion on models for non-equilibrium wetting
It is shown that the critical properties of a recently studied model for
non-equilibrium wetting are robust if one extends the dynamic rules by
single-particle diffusion on terraces of the wetting layer. Examining the
behavior at the critical point and along the phase transition line, we identify
a special point in the phase diagram where detailed balance of the dynamical
processes is partially broken.Comment: 6 pages, 9 figure
Matrix Product Eigenstates for One-Dimensional Stochastic Models and Quantum Spin Chains
We show that all zero energy eigenstates of an arbitrary --state quantum
spin chain Hamiltonian with nearest neighbor interaction in the bulk and single
site boundary terms, which can also describe the dynamics of stochastic models,
can be written as matrix product states. This means that the weights in these
states can be expressed as expectation values in a Fock representation of an
algebra generated by operators fulfilling quadratic relations which
are defined by the Hamiltonian.Comment: 11 pages, Late
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