Comment on "Renormalization-group theory for the phase-field crystal equation".

Athreya, Goldenfeld, and Dantzig [Phys. Rev. E 74, 011601 (2006)] claim that the current implementation of the renormalization-group method neglects the proper ordering of renormalization and differentiation. Their analysis is, however, based on the wrong multiple-scales method results.

Hydrodynamic coarsening in striped pattern formation with a conservation law.

We observed in numerical simulations that the interaction of striped-pattern-forming instability and a neutrally stable zero mode induces patterns of domains of upflow hexagons coexisting with domains of downflow hexagons. They appear only when hydrodynamic flow is present.

Competition of spiral-defect chaos and rolls in Rayleigh-Bénard convection under shear flow.

Computer simulations of domain coarsening of Rayleigh-Bénard convective patterns under horizontal shear flow are carried out. The model calculations reported here explicitly include the hydrodynamic interaction of the order parameter field and provide a description of the spiral-defect chaos which competes with the roll pattern. We observe shear banding at moderate strain rates.

Renormalization-group theoretical reduction of the Swift-Hohenberg model.

The Swift-Hohenberg model of the cellular pattern formation is exploited with a proto renormalization-group (RG) scheme. The method dispenses with the explicit perturbation solutions which are required in the standard RG approach. The RG equations obtained are the well-known reductive perturbation results such as a rotationally covariant amplitude equation and the nonlinear phase equations.

Hydrodynamic interactions in ordering process of two-dimensional quenched block copolymers.

The hydrodynamic coarsening of microphase separation in two-dimensional diblock copolymers is studied using numerical simulations. Results for symmetric and asymmetric block copolymers are compared. In contrast to the formation of the hexagonal phase where hydrodynamic flow appears not to be effective in enhancing domain coarsening, the late-time evolution of the lamellar phase proceeds faster, thus leading to a different power-law scaling with the addition of coupling of the velocity field to the order parameter.

Reductive renormalization of the phase-field crystal equation.

It has been known for some time that singular perturbation and reductive perturbation can be unified from the renormalization-group theoretical point of view: Reductive extraction of space-time global behavior is the essence of singular perturbation methods. Reductive renormalization was proposed to make this unification practically accessible; actually, this reductive perturbation is far simpler than most reduction methods, such as the rather standard scaling expansion. However, a rather cryptic exposition of the method seems to have been the cause of some trouble. Here, an explicit demonstration of the consistency of the reductive renormalization-group procedure is given for partial differentiation equations (of a certain type, including time-evolution semigroup type equations). Then, the procedure is applied to the reduction of a phase-field crystal equation to illustrate the streamlined reduction method. We conjecture that if the original system is structurally stable, the reductive renormalization-group result and that of the original equation are diffeomorphic.

Nucleation, growth, and coarsening of crystalline domains in order-order transitions between lamellar and hexagonal phases.

Using the numerical solution of the time-dependent Ginzburg-Landau equation, we study the entire process of transformation between the lamellar and the hexagonal phases from the early-stage nucleation and growth to the late-stage coarsening regime. The metastable crystalline structure that nucleates first is identified in terms of the mean-field theory under the single-wave-number approximation. This has been borne out by the numerically efficient preparation of single-crystal structure developed via the noise-induced self-organization. We also present results for the scaling of the late-time domain growth, which is quantified by two measures: the structure factor and the orientational correlation function. In particular, the growth exponent is shown to be robust and indifferent to conservation of the order parameter.

Effect of noise on ordering of hexagonal grains in a phase-field-crystal model.

We present a quantitative analysis of grain morphology of self-organizing hexagonal patterns based on the phase-field crystal model to examine the effect of stochastic noise on grain coarsening. We show that the grain size increases with increasing noise strength, resulting in enhanced hexagonal orientation due to noise up to some critical noise level above which the system becomes disordered.

Stripe domain coarsening in geographical small-world networks on a Euclidean lattice.

We study phase ordering dynamics of spatially periodic striped patterns on the small-world network that is derived from a two-dimensional regular lattice with distance-dependent random connections. It is demonstrated numerically that addition of spatial disorder in the form of shortcuts makes the growth of domains much slower or even frozen at late times.

Anisotropic scattering profiles of charged gels in a deformed state.

The structure factor of weakly charged polymer gels under external mechanical strain is calculated considering both thermal and frozen concentration fluctuations as well as the screening of ionic interactions. The butterfly patterns are discussed based on our result.

Ordering process in quenched block copolymers at low temperatures

We have studied domain growth of symmetric diblock copolymers undergoing microphase separation at low temperatures. We introduce a phenomenological nonlinear diffusion model with order-parameter-dependent mobility. Performing two-dimensional simulations, we find that the time-dependent scattering function exhibits dynamical scaling with a logarithmic growth law in the strong segregation limit where surface diffusion is the relevant mechanism for coarsening.

Reductive use of renormalization group

It has been recognized that singular perturbation and reductive perturbation can be unified from the renormalization group (RG) theoretical point of view. However, the recognition has been only formal in the sense that it has not given us any new insight nor provided any new technical advantage over the usual RG approach. With our approach, the proto RG method proposed here, we can clearly show that system reduction is the key to singular perturbation methods. The approach also makes the calculation of singular perturbation results more transparent than the conventional RG approach. Consequently, for example, a consistent and easy RG derivation of the rotational covariant Newell-Whitehead-Segel equation is possible.