Detailed spin-wave spectra of magneto-electric LiNiPO4 have been measured by neutron scattering at low temperatures in the commensurate (C) antiferromagnetic (AF) phase with TN = 20.8 K. An anomalous low-energy mode is observed at the modulation vector of the incommensurate (IC) AF phase appearing above TN . A linear spin-wave model based on Heisenberg exchange couplings and single ion anisotropies accounts for all the observed spin-wave dispersions and intensities. Along the b axis an unusually strong next-nearest-neighbor AF coupling competes with the dominant nearest-neighbor AF exchange interaction and causes the IC structure.

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Experimental studies in Al-4.0 wt% Cu alloys were conducted in samples of different sizes in which the effect of convection increases with increasing sample diameter. Detailed measurements of dendrite tip radii and the primary arm spacing have been carried out under both diffusive and convective growth conditions. The experimental results on tip radius and primary spacing show a good agreement with the microsolvability theory and Hunt-Lu model, respectively, for diffusive growth processes. In larger samples where convection effects are present, an inhomogeneous microstructure develops. A localized growth model is proposed to explain the spatio-temporal microstructure formation under convective growth conditions. The key parameter in this model is the effective diffusion coefficient which increases with the sample diameter and plays the decisive role in selecting the length scales of the solidification microstructures under convective growth conditions.