We report local nitride-stressor engineering in combination with quantum-size tunability in Ge quantum dots (QDs) for tailoring photoluminescence (PL) wavelength and exciton lifetime. Spherical-shaped Ge QDs with tunable diameters ranging from 25–90 nm embedded within layers of thermally-grown SiO2 and chemical-vapor-deposited Si3N4 were fabricated by thermal oxidation of lithographically-patterned poly-Si0.85Ge0.15 pillars on top of buffer layers of SiO2 and Si3N4, respectively, in a self-organization approach. The effects of local stressors and quantum confinement on the strain and optical properties of Ge QDs were systematically investigated using Raman and PL measurements. We observed that when Ge QD diameter gets smaller than 60 nm, quantum confinement sets in and has a predominant influence on PL wavelength and exciton lifetime. Our self-organized Ge QD/Si3N4 system provides a generic building block for the fabrication of active photonic devices on Si3N4 platform.
SUMMARYImage registration is an important topic in medical image analysis. It is usually used in 2D mosaics to construct the whole image of a biological specimen or in 3D reconstruction to build up the structure of an examined specimen from a series of microscopic images. Nevertheless, owing to a variety of factors, including microscopic optics, mechanisms, sensors, and manipulation, there may be great differences between the acquired image slices even if they are adjacent. The common differences include the chromatic aberration as well as the geometry discrepancy that is caused by cuts, tears, folds, and deformation. They usually make the registration problem a difficult challenge to achieve. In this paper, we propose an efficient registration method, which consists of a feature-based registration approach based on analytic robust point matching (ARPM) and a refinement procedure of the feature-based Levenberg-Marquardt algorithm (FLM), to automatically reconstruct 3D vessels of the rat brains from a series of microscopic images. The registration algorithm could speedily evaluate the spatial correspondence and geometric transformation between two point sets with different sizes. In addition, to achieve subpixel accuracy, an FLM method is used to refine the registered results. Due to the nonlinear characteristic of FLM method, it converges much faster than most other methods. We evaluate the performance of proposed method by comparing it with well-known thin-plate spline robust point matching (TPS-RPM) algorithm. The results indicate that the ARPM algorithm together with the FLM method is not only a robust but efficient method in image registration. key words: brain mapping, medical image registration, analytic robust point matching (ARPM), Levenberg-Marquardt algorithm, spatial correspondence, neuro-informatics
A bright blue emission material, bis {(benzimidazol-2-yl) Pyridenato} magnesium (MgBIP) used for organic light emitting devices, has been synthesized. The decomposition temperature was observed at 517 °C and no melting transition (Tm) of MgBIP was observed up to 400 °C. For three-layer LED devices with the configuration of ITO/NPB/MgBIP/ Alq3/MgAg, the white light emission covering the whole visible region from 400 to 750 nm with the maximum brightness of 2770 cd/m2and current density of 304 mA/cm2was observed.
Rapid prototyping (RP) is a new technology to fabricate a prototype part layer-by-layer. This technique has been achieved in many industrial sectors, but parts fabricated using this technique exhibit low mechanical properties, this makes it difficult to apply to fast growing applications. This technology can not only effectively save production time and cost of the prototypes, but also produce complicated product. In this study, we investigate the effect of the addition of halloysite nanotubes on mechanical properties of nanocomposites made by the RP process. Test specimens were fabricated using tetrafunctional polyester acrylate (TPA) and 1, 6 hexanediol diacrylate (HDDA) photopolymer as a matrix material and halloysite nanotubes as a reinforcing material. The adhesion between TPA/HDDA and halloysite nanotubes has been improved by using surface modification of a silane coupling agent. When compared with neat photopolymer, the tensile strength of nanocomposites decreased by about 22%, because the halloysites had poor interfacial adhesion. Silane treatment of halloysites using 3-aminopropyl triethoxysilane was succeeded to improve tensile strength of nanocomposites (2 phr halloysite nanotubes) by 31%.
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