587 research outputs found
Critical dynamics of dipolar ferromagnets
The dynamical scaling functions for ferromagnets with dipolar interactions are computed by mode coupling theory above the critical temperature Tc. On the basis of this theory we explain apparently conflicting features of neutron scattering experiments on EuO, EuS and Fe. The position of the crossover from isotropic to dipolar critical dynamics is determined and further experiments are proposed
Renormalized field theory for the static crossover in dipolar ferromagnets
A field theoretical description for the static crossover in dipolar ferromagnets is presented. New non leading critical exponents for the longitudinal static susceptibility are identified and the existence and magnitude of the dip in the effective critical exponent of the transverse susceptibility found by matching techniques is scrutinized
Critical dynamics of ferromagnets
The crossover in the dynamics from isotropic to dipolar critical behaviour has been a matter of debate over many years. We review a mode coupling theory for dipolar ferromagnets which gives a unified explanation of the seemingly contradictory experimental situation. The shape functions, the scaling functions for the damping coefficients and the precise position of the crossover are computed. Below Tc only the exchange interaction is taken into account
The Role of Architecture in the Elastic Response of Semiflexible Polymer and Fiber Networks
We study the elasticity of cross-linked networks of thermally fluctuating
stiff polymers. As compared to their purely mechanical counterparts, it is
shown that these thermal networks have a qualitatively different elastic
response. By accounting for the entropic origin of the single-polymer
elasticity, the networks acquire a strong susceptibility to polydispersity and
structural randomness that is completely absent in athermal models. In
extensive numerical studies we systematically vary the architecture of the
networks and identify a wealth of phenomena that clearly show the strong
dependence of the emergent macroscopic moduli on the underlying mesoscopic
network structure. In particular, we highlight the importance of the full
polymer length that to a large extent controls the elastic response of the
network, surprisingly, even in parameter regions where it does not enter the
macroscopic moduli explicitly. We provide theoretical scaling arguments to
relate the observed macroscopic elasticity to the physical mechanisms on the
microscopic and the mesoscopic scale.Comment: 12 pages, 8 figures, (v3) final versio
On the critical dynamics of ferromagnets
The dynamic scaling functions for ferromagnets above and below the critical temperature are determined using mode coupling theory. Below the critical temperature we study isotropic ferromagnets taking into account the exchange interaction only and give the first numerical solution of the resulting mode coupling equations. In the paramagnetic phase we examine how the critical dynamics is modified by the addition of the dipoledipole interaction. On the basis of this theory we are able to explain in a unifying fashion the results of different experimental methods; i.e.: neutron scattering, hyperfine interaction and electron-spin resonance. Predictions for new experiments are made
Long-range and many-body effects in coagulation processes
We study the problem of diffusing particles which coalesce upon contact. With the aid of a nonperturbative renormalization group, we first analyze the dynamics emerging below the critical dimension two, where strong fluctuations imply anomalously slow decay. Above two dimensions, the long-time, low-density behavior is known to conform with the law of mass action. For this case, we establish an exact mapping between the physics at the microscopic scale (lattice structure, particle shape and size) and the macroscopic decay rate in the law of mass action. In addition, we identify a term violating this classical law. It originates in long-range and many-particle fluctuations and is a simple, universal function of the macroscopic decay rate. DOI: 10.1103/PhysRevE.87.02213
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