4 research outputs found
DMRG studies of the effect of constraint release on the viscosity of polymer melts
The scaling of the viscosity of polymer melts is investigated with regard to
the molecular weight. We present a generalization of the Rubinstein-Duke model,
which takes constraint releases into account and calculate the effects on the
viscosity by the use of the Density Matrix Renormalization Group (DMRG)
algorithm. Using input from Rouse theory the rates for the constraint release
are determined in a self consistent way. We conclude that shape fluctuations of
the tube caused by constraint release are not a likely candidate for improving
Doi's crossover theory for the scaling of the polymer viscosity.Comment: 6 pages, 8 figure
Scaling of the magnetic linear response in phase-ordering kinetics
The scaling of the thermoremanent magnetization and of the dissipative part
of the non-equilibrium magnetic susceptibility is analysed as a function of the
waiting-time for a simple ferromagnet undergoing phase-ordering kinetics
after a quench into the ferromagnetically ordered phase. Their scaling forms
describe the cross-over between two power-law regimes governed by the
non-equilibrium exponents and , respectively. A relation
between , the dynamical exponent and the equilibrium exponent is
derived from scaling arguments. Explicit tests in the Glauber-Ising model and
the kinetic spherical model are presented.Comment: 7 pages, 2 figures included, needs epl.cls, version to appear in
Europhys. Let
Ageing in the critical contact process: a Monte Carlo study
The long-time dynamics of the critical contact process which is brought
suddenly out of an uncorrelated initial state undergoes ageing in close analogy
with quenched magnetic systems. In particular, we show through Monte Carlo
simulations in one and two dimensions and through mean-field theory that
time-translation invariance is broken and that dynamical scaling holds. We find
that the autocorrelation and autoresponse exponents lambda_{Gamma} and lambda_R
are equal but, in contrast to systems relaxing to equilibrium, the ageing
exponents a and b are distinct. A recent proposal to define a non-equilibrium
temperature through the short-time limit of the fluctuation-dissipation ratio
is therefore not applicable.Comment: 18 pages, 7 figures, Latex2e with IOP macros; final for
The density-matrix renormalization group
The density-matrix renormalization group (DMRG) is a numerical algorithm for
the efficient truncation of the Hilbert space of low-dimensional strongly
correlated quantum systems based on a rather general decimation prescription.
This algorithm has achieved unprecedented precision in the description of
one-dimensional quantum systems. It has therefore quickly acquired the status
of method of choice for numerical studies of one-dimensional quantum systems.
Its applications to the calculation of static, dynamic and thermodynamic
quantities in such systems are reviewed. The potential of DMRG applications in
the fields of two-dimensional quantum systems, quantum chemistry,
three-dimensional small grains, nuclear physics, equilibrium and
non-equilibrium statistical physics, and time-dependent phenomena is discussed.
This review also considers the theoretical foundations of the method, examining
its relationship to matrix-product states and the quantum information content
of the density matrices generated by DMRG.Comment: accepted by Rev. Mod. Phys. in July 2004; scheduled to appear in the
January 2005 issu