1,122 research outputs found
The phase transition of the diffusive pair contact process revisited
The restricted diffusive pair contact process 2A->3A, 2A->0 (PCPD) and the
classification of its critical behavior continues to be a challenging open
problem of non-equilibrium statistical mechanics. Recently Kockelkoren and
Chate [Phys. Rev. Lett. 90, 125701 (2003)] suggested that the PCPD in one
spatial dimension represents a genuine universality class of non-equilibrium
phase transitions which differs from previously known classes. To this end they
introduced an efficient lattice model in which the number of particles per site
is unrestricted. In numerical simulations this model displayed clean power
laws, indicating ordinary critical behavior associated with certain non-trivial
critical exponents. In the present work, however, we arrive at a different
conclusion. Increasing the numerical effort, we find a slow drift of the
effective exponents which is of the same type as observed in previously studied
fermionic realizations. Analyzing this drift we discuss the possibility that
the asymptotic critical behavior of the PCPD may be governed by an ordinary
directed percolation fixed point.Comment: 6 pages, 1 figur
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
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®
Absorbing Phase Transitions of Branching-Annihilating Random Walks
The phase transitions to absorbing states of the branching-annihilating
reaction-diffusion processes mA --> (m+k)A, nA --> (n-l)A are studied
systematically in one space dimension within a new family of models. Four
universality classes of non-trivial critical behavior are found. This provides,
in particular, the first evidence of universal scaling laws for pair and
triplet processes.Comment: 4 pages, 4 figure
Phase transition of the one-dimensional coagulation-production process
Recently an exact solution has been found (M.Henkel and H.Hinrichsen,
cond-mat/0010062) for the 1d coagulation production process: 2A ->A, A0A->3A
with equal diffusion and coagulation rates. This model evolves into the
inactive phase independently of the production rate with density
decay law. Here I show that cluster mean-field approximations and Monte Carlo
simulations predict a continuous phase transition for higher
diffusion/coagulation rates as considered in cond-mat/0010062. Numerical
evidence is given that the phase transition universality agrees with that of
the annihilation-fission model with low diffusions.Comment: 4 pages, 4 figures include
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
Influence of Hydrolytic and Chemical Treatment on the Mechanical Properties of Aramid and Copolyaramid Fibers
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.Commercial PPTA fibers ( Kevlar 49® and Twaron 1055®) and copolyaramid fibers (Trevar®) are subjected to various hydrolytic and chemical treatments. Tensile mod ulus, tensile strength, and elongation at break are measured, and mechanical property deterioration is compared. Copolyaramid fibers show improved hydrolytic stability and chemical resistance compared to PPTA fibers. The time dependence of degradation pro cesses can be described by two decreasing exponential functions. WAXS measurements detect only slight differences in the crystalline structure and superstructure of the treated fibers. Thus, the main origin of mechanical degradation is the destruction of intercrys talline links such as tie molecules or tie crystallites
Stochastic Model and Equivalent Ferromagnetic Spin Chain with Alternation
We investigate a non-equilibrium reaction-diffusion model and equivalent
ferromagnetic spin 1/2 XY spin chain with alternating coupling constant. The
exact energy spectrum and the n-point hole correlations are considered with the
help of the Jordan-Wigner fermionization and the inter-particle distribution
function method. Although the Hamiltonian has no explicit translational
symmetry, the translational invariance is recovered after long time due to the
diffusion. We see the scaling relations for the concentration and the two-point
function in finite size analysis.Comment: 7 pages, LaTeX file, to appear in J. Phys. A: Math. and Ge
Universality in the pair contact process with diffusion
The pair contact process with diffusion is studied by means of multispin
Monte Carlo simulations and density matrix renormalization group calculations.
Effective critical exponents are found to behave nonmonotonically as functions
of time or of system length and extrapolate asymptotically towards values
consistent with the directed percolation universality class. We argue that an
intermediate regime exists where the effective critical dynamics resembles that
of a parity conserving process.Comment: 8 Pages, 9 figures, final version as publishe
Universality class of the pair contact process with diffusion
The pair contact process with diffusion (PCPD) is studied with a standard
Monte Carlo approach and with simulations at fixed densities. A standard
analysis of the simulation results, based on the particle densities or on the
pair densities, yields inconsistent estimates for the critical exponents.
However, if a well-chosen linear combination of the particle and pair densities
is used, leading corrections can be suppressed, and consistent estimates for
the independent critical exponents delta=0.16(2), beta=0.28(2) and z=1.58 are
obtained. Since these estimates are also consistent with their values in
directed percolation (DP), we conclude that PCPD falls in the same universality
class as DP.Comment: 8 pages, 8 figures, accepted by Phys. Rev. E (not yet published
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