We investigated ultra-efficient nano-photonic modulators based on silicon photonic crystal slot waveguides infiltrated with electro-optic polymers. The integration of Si 3 N 4 guided mode resonance grating with plasm...
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We investigated ultra-efficient nano-photonic modulators based on silicon photonic crystal slot waveguides infiltrated with electro-optic polymers. The integration of Si 3 N 4 guided mode resonance grating with plasmonic-active nanotubes are also demonstrated for surface enhanced Raman scattering.
We have investigated the effect of varying the film thickness on the surface orientation texturing in polycrystalline Si films obtained via mixed-phase solidification (MPS) of initially a-Si precursor films on SiO 2. ...
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The importance of the extracellular mechanical environment in stem cell differentiation has been extensively studied over the last decade. In neuronal cell differentiation, matrix stiffness and neurite outgrowth have ...
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ISBN:
(纸本)9781627482295
The importance of the extracellular mechanical environment in stem cell differentiation has been extensively studied over the last decade. In neuronal cell differentiation, matrix stiffness and neurite outgrowth have been correlated, highlighting the impact of matrix effects on neuronal cell morphology. In addition, on materials that approach the physiological mechanical properties of brain tissue, neurons from mixed phenotype primary cultures will prevail. However, if the same mixed culture is grown on polystyrene, glial populations are more prevalent. Enhancing the understanding of these differentiation processes will further expand the ability to design materials for neuronal implants that are conducive to neuronal survival, resist glial scarring and promote neurite outgrowth and cell connectivity. Specifically, elastomers such as poly(glycerol sebacate) (PGS) hold promise in neuronal tissue engineering, due to their mechanical tunability. PGS is biocompatible, biodegradable and possesses mechanical properties similar to that of living tissue. Neuronal cell differentiation was studied on PGS, using P19 embryonic carcinoma cells, which can be differentiated into a neuronal phenotype using retinoic acid. Varying cure temperatures of PGS including 120°, 140° and 165°C were selected, which equate to an elastic modulus of 0.07, 0.43 and 2.30 MPa respectively. Cells were characterized via immunocytochemistry. A primarily astrocytic population, with limited neuronal differentiation and neurite outgrowth were observed on the PGS 120°C. Cells grown on PGS 140°C demonstrated marked neurite outgrowth, with an increase in neuronal cells. Cells grown on the PGS 165°C exhibited the largest population of neurons, with significant neurite outgrowth. These results indicate that substrate mechanical properties do impact neuronal differentiation, but that a material with a Young's modulus similar to that of neuronal tissue (PGS 120°C) may not necessarily be the most conducive to in
Recent experimental observations indicate that bulk Sc2O3 (∼200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the ob...
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Recent experimental observations indicate that bulk Sc2O3 (∼200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain Sc2O3. Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of Sc2O3 in an effort to explain the good conduction of Sc2O3 observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of Sc2O3 solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that the presence of impurities is necessary to raise the conductivity of Sc2O3 to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately 7.5 × 10−3 ppm) and is probably present in all experiments.
We characterize “blisters”, defects observed in multilayer dielectric (MLD) coatings after exposure to acid cleaning procedures. Nanoindentation is used to make site-specific indentations across blisters to measure ...
We characterize “blisters”, defects observed in multilayer dielectric (MLD) coatings after exposure to acid cleaning procedures. Nanoindentation is used to make site-specific indentations across blisters to measure the mechanical response, especially their compliance under different conditions of loading. Two regions of statistically different mechanical response are identified within a blister defect and compared to the undisturbed regions of the MLD coating. The indentation response of blisters can vary across samples, and we suggest reasons for this variation.
We measure the mechanical response of optical multilayer dielectric (MLD) diffraction gratings, geometries which are constrained in only one transverse direction but free in the other, using nanoindentation. The resul...
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We measure the mechanical response of optical multilayer dielectric (MLD) diffraction gratings, geometries which are constrained in only one transverse direction but free in the other, using nanoindentation. The results are explained using a stress-strain model, which reveals a uniaxial yield stress of 4.1- 4.6 GPa and predicts a similar dependence of yield stress on loads for both fully-elastic and fully-plastic solutions. Following R. Hill’s model of an expanding cavity under internal pressure, we show that the indentation response of the high-aspect ratio “pillar” geometry can be expressed in terms of uniaxial yield stress rather than material hardness.
We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well-defined struc...
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We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well-defined structures. We use Brownian dynamics to model the assembly of N-clusters varying in size from two to twelve outer spheres and free energy calculations to predict the expected cluster sizes and shapes as a function of temperature and inner particle diameter. We show that the arrangements of outer spheres at finite temperatures are related to spherical codes, an ideal mathematical sequence of points corresponding to the densest possible sphere packings. We demonstrate that temperature and the ratio of the diameters of the inner and outer spheres dictate cluster morphology. We present a surprising result for the equilibrium structure of a 5-cluster, for which the square pyramid arrangement is preferred over a more symmetric structure. We show this result using Brownian dynamics, a Monte Carlo simulation, and a free energy approximation. Our results suggest a promising way to assemble anisotropic building blocks from constituent colloidal spheres.
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