Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics.

Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025-1 microm(3) volumes, approximately 10(6) times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms.

The effects of patellar resurfacing in total knee arthroplasty on position sense: a prospective randomized study.

To find out the improvement of joint position sense after total knee arthroplasty with patellar resurfacing compared to total knee arthoplasty without patellar resurfacing, the study was carried out as a randomised parallel trial in patients who had stage III and IV primary osteoarthrosis of only 1 side of the knee with a 2 year follow-up. Twenty-one patients underwent patellar resurfacing and 26 patients had no patellar resurfacing. Joint position sense was evaluated by the average absolute different angle of the operated knees from the non operated knees which was the asymptomatic knee and acted as the reference knee. Position sense was improved significantly in both groups. However, the patients without patellar resurfacing had better improvement. The patients with patellar resurfacing had better results in terms of anterior knee pain and tenderness. Patellar resurfacing should be used in severe articular cartilage damage, not as a routine operation.

Spatially resolved spectroscopic mapping of polarization reversal in polycrystalline ferroelectric films: crossing the resolution barrier.

The mesoscopic reversible and irreversible polarization dynamics in polycrystalline PZT thin film capacitors are studied using local spectroscopic mapping and macroscopic first-order reversal curve measurements. The transition from a regime of short range domain wall motion to the formation of mesoscopic clusters to complete switching is observed. The fractal dimension of the clusters is consistent with the random-bond disorder model. The combination of macroscopic and local measurements allows the characteristics length scales corresponding to the transition from Rayleigh to Preisach behaviors and onset of macroscopic averaging to be determined.