Biomechanical Study of Posterior Pelvic Fixations in Vertically Unstable Sacral Fractures: An Alternative to Triangular Osteosynthesis

Study Design Biomechanical study. Purpose To investigate the relative stiffness of a new posterior pelvic fixation for unstable vertical fractures of the sacrum. Overview of Literature The reported operative fixation techniques for vertical sacral fractures include iliosacral screw, sacral bar fixations, transiliac plating, and local plate osteosynthesis. Clinical as well as biomechanical studies have demonstrated that these conventional techniques are insufficient to stabilize the vertically unstable sacral fractures. Methods To simulate a vertically unstable fractured sacrum, 12 synthetic pelvic models were prepared. In each model, a 5-mm gap was created through the left transforaminal zone (Denis zone II). The pubic symphysis was completely separated and then stabilized using a 3.5-mm reconstruction plate. Four each of the unstable pelvic models were then fixed with two iliosacral screws, a tension band plate, or a transiliac fixation plus one iliosacral screw. The left hemipelvis of these specimens was docked to a rigid base plate and loaded on an S1 endplate by using the Zwick Roell z010 material testing machine. Then, the vertical displacement and coronal tilt of the right hemipelves and the applied force were measured. Results The transiliac fixation plus one iliosacral screw constructions could withstand a force at 5 mm of vertical displacement greater than the two iliosacral screw constructions (p=0.012) and the tension band plate constructions (p=0.003). The tension band plate constructions could withstand a force at 5° of coronal tilt less than the two iliosacral screw constructions (p=0.027) and the transiliac fixation plus one iliosacral screw constructions (p=0.049). Conclusions This study proposes the use of transiliac fixation in addition to an iliosacral screw to stabilize vertically unstable sacral fractures. Our biomechanical data demonstrated the superiority of adding transiliac fixation to withstand vertical displacement forces

Direct Observation of Capacitor Switching Using Planar Electrodes

Ferroelectric polarization switching in epitaxial (110) BiFeO3 films is studied using piezoresponse force microscopy of a model in-plane capacitor structure. The electrode orientation is chosen such that only two active domain variants exist. Studies of the kinetics of domain evolution allows clear visualization of nucleation sites, as well as forward and lateral growth stages of domain formation. It is found that the location of the reverse-domain nucleation is correlated with the direction of switching in a way that the polarization in the domains nucleated at an electrode is always directed away from it. The role of interface charge injection and surface screening charge on switching mechanisms is explored, and the nucleation is shown to be controllable by the bias history of the sample. Finally, the manipulation of domain nucleation through domain structure engineering is illustrated. These studies pave the way for the engineering and design of the ferroelectric device structures through control of individual steps of the switching process

Influence of Various Precursor Compositions and Substrate Angles on ZnO Nanorod Morphology Growth by Aqueous Solution Method

ZnO nanorods were synthesized on silicon wafer substrate with a seed zinc layer using the aqueous solution method. The influence of various precursor compositions on the morphology of the ZnO nanorods, with substrate angles at 0° and 90°, was investigated. The various ratios of hexamethylenetetramine in zinc nitrate hexahydrate were used as precursors in the synthesis of ZnO. Scanning electron micrography indicated that the growth of the ZnO nanorods with a 0° substrate angle was smaller than with a 90° substrate angle. The substrate angle is defined as the angle between the plane of the substrate and the horizontal layer of an aqueous solution. When the precursor concentration of hexamethylenetetramine is not equal to the ratio corresponding to the chemical reaction, the effect of the substrate angle on the diameter size and morphology of the ZnO nanorods is evident. Grazing incident X-ray diffraction (GIXRD) was used to characterize the structure of all samples. The diffraction patterns showed that the orientation matched the hexagonal wurtzite structure

Influence of Various Precursor Compositions and Substrate Angles on ZnO Nanorod Morphology Growth by Aqueous Solution Method

ZnO nanorods were synthesized on silicon wafer substrate with a seed zinc layer using the aqueous solution method. The influence of various precursor compositions on the morphology of the ZnO nanorods, with substrate angles at 0° and 90°, was investigated. The various ratios of hexamethylenetetramine in zinc nitrate hexahydrate were used as precursors in the synthesis of ZnO. Scanning electron micrography indicated that the growth of the ZnO nanorods with a 0° substrate angle was smaller than with a 90° substrate angle. The substrate angle is defined as the angle between the plane of the substrate and the horizontal layer of an aqueous solution. When the precursor concentration of hexamethylenetetramine is not equal to the ratio corresponding to the chemical reaction, the effect of the substrate angle on the diameter size and morphology of the ZnO nanorods is evident. Grazing incident X-ray diffraction (GIXRD) was used to characterize the structure of all samples. The diffraction patterns showed that the orientation matched the hexagonal wurtzite structure

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 μm3 volumes, approximately 106 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