The electronic and electromechanical properties of complex oxide superlattices are closely linked to the evolution of the structure and electrical polarization of the component layers in applied electric fields. Effor...
The electronic and electromechanical properties of complex oxide superlattices are closely linked to the evolution of the structure and electrical polarization of the component layers in applied electric fields. Efforts to deduce the responses of the individual components of the superlattice to applied fields have focused on theoretical approaches because of the limitations of available experimental techniques. Time-resolved x-ray microdiffraction provides a precise crystallographic probe of each component using the shift in wave vector and change in intensity of superlattice satellite reflections. We report in detail the methods to measure and analyze the x-ray diffraction patterns in applied electric field and their application to a 2-unit-cell BaTiO3/4-unit-cell CaTiO3 superlattice. We find that the overall piezoelectric distortion is shared between the two components. Theoretical predictions of the electromechanical properties of a superlattice with the same composition constrained to tetragonal symmetry are in excellent agreement with the experiments. Lattice instability analysis, however, suggests that the low-temperature ground state could exhibit antiferrodistortive rotations of TiO6 octahedra within and/or at the interfaces of the CaTiO3 component.
Fe2Al5 contains a Fe-Al matrix through which are threaded disordered one-dimensional chains of overlapping Al sites. We report magnetic, nuclear-magnetic-resonance (NMR), and specific-heat measurements addressing its ...
Fe2Al5 contains a Fe-Al matrix through which are threaded disordered one-dimensional chains of overlapping Al sites. We report magnetic, nuclear-magnetic-resonance (NMR), and specific-heat measurements addressing its magnetic and vibrational properties. The Curie-type susceptibility is found to be due to dilute moments, likely due to wrong-site Fe atoms. A27l NMR shift and spin-lattice relaxation measurements confirm these to be indirectly coupled through a Ruderman-Kittel-Kasuya-Yoshida-type interaction. Specific-heat results indicate a large density of low-energy vibrational modes. These excitations generate a linear-T contribution to the specific heat, which however freezes out below about 10 K. These results are attributed to the presence of anharmonic vibrational modes associated with the disordered structural chains.
Enzymatic glucose sensors based on luminescent microparticles rely on the reaction of glucose and oxygen with glucose oxidase, where the internal oxygen level is transduced via oxygen-sensitive phosphors. These sensor...
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Enzymatic glucose sensors based on luminescent microparticles rely on the reaction of glucose and oxygen with glucose oxidase, where the internal oxygen level is transduced via oxygen-sensitive phosphors. These sensors utilize nanofilm coatings comprising polyelectrolyte multilayers deposited using self-assembly to control transport of glucose, enabling tuning of the range and sensitivity by changing the coating thickness. In this work, it was also found that salt concentrations, which influence thickness and density of nanofilm coatings during multilayer deposition, also influence range, sensitivity, and degradation rate of these sensors.
Strongly nonlinear periodic waves are investigated in an initially compressed chain of spheres under Hertz contact. A harmonic excitation force disturbs the first grain with an amplitude comparable to the initial comp...
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Strongly nonlinear periodic waves are investigated in an initially compressed chain of spheres under Hertz contact. A harmonic excitation force disturbs the first grain with an amplitude comparable to the initial compression and the steady strain-wave profiles at large distances from this disturbance are compared with predictions from the long wave approximation. Two qualitatively different types of quasi-stationary periodic waves are apparent in the system: one with minimum and maximum strain values above the static value and one whose minimum strain is below and maximum value is above the initial strain. From the frequency spectrums of the calculated force between particles, new forcing functions are constructed that allow rapid formation of quasi-stationary strongly nonlinear periodic waves.
The role of dissipation on wave shape and attenuation in dry and saturated granular chains is considered experimentally and numerically. The wave dynamics in these chains includes a dissipative term based on Stoke’s ...
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The role of dissipation on wave shape and attenuation in dry and saturated granular chains is considered experimentally and numerically. The wave dynamics in these chains includes a dissipative term based on Stoke’s drag and on a new mechanism of liquid expulsion from the developing elastic contact. The latter mechanism will be shown to be necessary for comparisons of experimental and numerical results. The dissipation of energy in the region of particle contact may serve as a model for hot-spot formation in granular materials undergoing high strain-rate deformation. The shock wave profiles in granular chains, including viscous dissipation, were analytically obtained with the long wave approximation. The critical viscosity, which describes the transition from and oscillatory to a monotonous wave profile is validated using a comparison of the analytical and discrete numerical models, which agree well with one another.
We developed a miniaturized laparoscopic zoom camera that is 17 mm long, has >4X optical zoom, and works under 300 lux. This camera is suitable for advancing minimally invasive surgery. Demonstration surgery (chole...
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In 2007, the University of Windsor established formal learning outcomes for their cooperative education program and implemented new educational strategies to support the achievement of those outcomes. To gauge the eff...
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In 2007, the University of Windsor established formal learning outcomes for their cooperative education program and implemented new educational strategies to support the achievement of those outcomes. To gauge the effect of the newly implemented activities on the achievement of the learning outcomes, a survey was developed and administered to students and alumni of the unrevised program (control group) and, more recently in 2009, to students participating in the revised program (experimental group). The survey questions were designed to assess respondents' perceptions of the effect that co-op had on: their academic and career-related goals and motivation;identification of personal strengths, weaknesses and preferences;understanding of academic theory and technical knowledge;development of attributes;and the ability to effectively contribute in the workplace through identified soft and transferable industry-related skills. Students participating in co-op at the University of Windsor may complete regular or extended length work terms. Regular work terms are generally four-months in length, while extended work terms are at least eight months long, although many companies request co-op students for twelve to sixteen month periods. The survey demographics included a question about work term duration, so that the effects of work term length on learning outcomes achievement might also be examined. Although the survey revealed some positive trends related to learning outcomes achievement for control versus experimental groups, they were not at statistically significant levels. However, if the analysis was limited to students who had completed extended work terms, three areas showed changes at statistically significant levels. Decreases in positive response levels were seen for the experimental group with respect to students' abilities to identify personal weaknesses related to their academic options and personal preferences related to workplace options. An increase in posit
This study examined the structural evolution of ultrathin Hf1−xZrxO2 composite films with various mixing ratios (x=0,0.1,0.3,0.5,0.7,0.9,1) prepared by atomic layer deposition using x-ray photoelectron spectroscopy (X...
This study examined the structural evolution of ultrathin Hf1−xZrxO2 composite films with various mixing ratios (x=0,0.1,0.3,0.5,0.7,0.9,1) prepared by atomic layer deposition using x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and x-ray absorption fine structure (XAFS) analysis. As the relative Zr concentration (x) was increased, the composite films underwent a martensitic transition from monoclinic to tetragonal crystal structures near x=0.5–0.7. Zr K- and Hf L3-edge XAFS revealed a change in the local structures near the Zr and Hf atoms with changes in the crystal structure. At a low Zr content (x≤0.5), the next-nearest-neighbor coordination in the monoclinic (m) local structure showed significant structural disorder due to diverse structural reconstruction from the tetragonal (t) local structure. Combined XPS and O K-edge XAS studies revealed a decrease in the conduction-band (CB) edge energy with increasing x, whereas the valence-band edge energies were invariant. The evolution in the CB structures was analyzed using the concept of metal-ion crystal fields in the t and m cluster models.
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