Defying the conventional wisdom regarding first-order transitions, solidsolid displacive transformations are often accompanied by pronounced pretransitional phenomena. Generally, these phenomena are indicative of some mesoscopic lattice deformation that "anticipates" the upcoming phase transition. Among these precursive effects is the observation of the so-called "tweed" pattern in transmission electron microscopy in a wide variety of materials. We have investigated the tweed deformation in a two dimensional model system, and found that it arises because the compositional disorder intrinsic to any alloy conspires with the natural geometric constraints of the lattice to produce a frustrated, glassy phase. The predicted phase diagram and glassy behavior have been verified by numerical simulations, and diffraction patterns of simulated systems are found to compare well with experimental data. Analytically comparing to alternative models of strain-disorder coupling, we show that the present model best accounts for experimental observations.

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We propose a method for suppressing the intensity of the worst ghost pulse (a single ghost pulse between two long marker blocks) resulting from intrachannel four-wave mixing (FWM) in strongly dispersion-managed on-off keying optical transmissions by inverting the optical phases of the marker blocks surrounding the ghost pulse. We show both analytically and numerically that the method provides substantial suppression of the maximum ghost pulse energy. The suppression is experimentally verified in 40-Gbit/s transmission experiment over a 100-km non-zero-dispersion-shifted fiber. The proposed method may extend the reach of high-bit-rate optical transmission systems in which intrachannel FWM is the dominating nonlinear penalty.

Motivated by recent observations of coherent Ge island formation during growth of Ge on Si (100), we have carried out a theoretical study of the elastic energies associated with the evolution of a uniform strained overlayer as it segregates into coherent islands. In the context of a two-dimensional model, we have explored the conditions under which coherent islands may be energetically favored over both uniform epitaxial films and dislocated islands. We find that if the interface energy (for dislocated islands) is more than about 15% of the surface energy, then there is a range of island sizes for which the coherent island structure is preferred.

We study electromigration in a driven diffusive lattice gas (DDLG) whose continuous Monte Carlo dynamics generate higher particle mobility in areas with lower particle density. At low vacancy concentrations and low temperatures, vacancy domains tend to be faceted: the external driving force causes large domains to move much more quickly than small ones, producing exponential domain growth. At higher vacancy concentrations and temperatures, even small domains have rough boundaries: velocity differences between domains are smaller, and modest simulation times produce an average domain length scale which roughly follows L ∼ t ζ , where ζ varies from roughly .55 at 50% filling to roughly .75 at 70% filling. This growth is faster than the t 1/3 behavior of a standard conserved order parameter Ising model. Some runs may be approaching a scaling regime. A simple scaling picture which neglects velocity fluctuations, but includes the cluster size dependence of the velocity, predicts growth with L ∼ t 1/2 . At low fields and early times, fast growth is delayed until the characteristic domain size reaches a crossover length which follows L cross ∝ E −β . Rough numerical estimates give β = .37 and simple theoretical arguments give β = 1/3. Our conclusion that small driving forces can significantly enhance coarsening may be relevant to the YB 2 Cu 3 O 7−δ electromigration experiments of Moeckly et al. [13].