Phase metastability of nanosized α-Al2O3 crystallites

The reversal of the α- to θ-Al₂O₃ phase transformation and the induced microstructure evolution of boehmite-derived discrete nanosized α-crystallites are examined. Three categories of α-crystallites smaller than 100 nm were examined and found to have similar behavior: (1) pre-existing α-crystallites, (2) α-crystallites formed in situ during the calcination of θ-crystallites of sizes near the critical size, 25 nm, and (3) α-crystallites formed in situ by the thermal treatment of as-received θ-crystallites. The α-crystallite may transform back to the θ-phase above 800 °C. The backwards θ-crystallite may also re-transform to the α-phase again. Because of the density difference between α- and θ-Al₂O₃, the strain involved in the volume expansion and shrinkage during the phase transition eventually results in the formation of a twinned and/or mosaic structure for the θ- and α-crystallites. A strain release model representing the microstructure evolution of the α- to θ-phase and the θ- to α-Al₂O₃ phase transformation is proposed.     

Low cost fabrication of diamond nano-tips on porous anodic alumina by hot filament chemical vapor deposition and the field emission effects

A novel growth method for diamond nano-tips on porous anodic alumina (PAA) by hot filament chemical vapor deposition has been investigated for the first time. Before diamond film deposition could be carried out, nano-diamond particles were deposited onto the pore surface of PAA by electrophoretic deposition at the nucleation sites. Diamond nano-tips were then successfully formed by the shape of porous alumina. The results show that a diamond nano-tip with a smaller radius has superior effects of field emission. Its threshold field and current density are 1.2 V μm(-1) and 4.0 mA cm(-2), respectively, for the case of a tip radius of about 20-30 nm.     

Complete polarization mode control of long-wavelength tunable vertical-cavity surface-emitting lasers over 65-nm tuning, up to 14-mW output power

We experimentally demonstrate a stable polarization mode operation in long-wavelength tunable vertical-cavity surface-emitting lasers over a 65-nm tuning range and the entire output power range (< 14.6 mW) at room temperature. The polarization mode control was achieved by utilizing anisotropic gain properties of quantum wells due to the difference in bond lengths between the constituent atoms at the interfaces combined with uni-axial external strain induced by a stressor. The experiments were conducted to verify this newly proposed polarization control scheme based on the spin flip model (SFM) developed to incorporate the detailed gain properties, cavity standing wave effect, self-heating effect, and strain effect. The experimental results on the tuning characteristics of polarization switching behavior and output powers were reproduced in highly agreeable manner by simulations. The relative importance of the external strain, interfacial strain at quantum wells, and the wavelength dependence of gain anisotropy are also discussed. It is also shown that the fast spin relaxation times for InP-based vertical-cavity surface-emitting lasers (VCSELs) was responsible for the inhibition of elliptic polarization states often observed for GaAs-based VCSELs. The effectiveness of the polarization control scheme was highlighted by the observed high polarization suppression ratio of 34 dB maintained for the entire wavelength and pump power ranges during the reliability testing over 2000 h. The influence of the elliptic polarization state for the optical pump laser was detected which could be explained as a memory effect of the spin-polarized electrons, supporting the validity of the SFM.     

Planar Liquid Confinement for Optical Centering of Dielectric Liquid Lenses

In this letter, planar liquid confinement structures along with concentric electrodes are proposed for the optical centering of dielectric liquid lenses at the rest state and during actuation. Both the liquid confinement structures and electrodes that are photolithographically fabricated on glass substrates share the same geometric center, thereby minimizing the deviation of the optical axis at all operation modes. Tilt angles of mesa liquid confinement structure are experimentally found to be 0.11deg in maximum and below 0.03deg during actuation for a liquid lens with a droplet of initially 7 mm in diameter.     

Automatic brain tissue segmentation in MR images using hybrid atlas forest based on confidence-weighted probability matrix

The segmentation of specific tissues in an MR brain image for quantitative analysis can assist the disease diagnosis and medical research. Therefore, a robust and accurate method for automatic segmentation is necessary. Atlas-based-method is a common and effective method of automatic segmentation where an atlas refers to a pair of image consist of an intensity image and its corresponding label image. Apart from the general multi-atlas-based methods, which propagate labels through the single atlas then fuse them, we proposed a hybrid atlas forest based on confidence-weighted probability matrix to consider the atlases set as a whole and treat each voxel differently. In the framework, we first register the atlas to the image space of target and calculate the confidence of voxels in the registered atlas. Then, a confidence-weighted probability matrix is generated and it augments to the intensity image of the atlas or target for providing spatial information of the target tissue. Third, a hybrid atlas forest is trained to gather the features and correlation information among the atlases in the dataset. Finally, the segmentation of the target tissues is predicted by the trained hybrid atlas forest. The segment performance and the components efficiency of the proposed method are evaluated on the two public datasets. Based on the experiment results and quantitative comparisons, our method can gather spatial information and correlation among the atlases to obtain an accurate segmentation.     

Magnetic properties of FeSiCr alloy powder coils made by gel casting process

Journal of Materials Science: Materials in Electronics - A molding coil is molded directly onto enameled wire using soft magnetic materials. When the molding coil size becomes smaller and thinner,...     

Resource Reuse for D2D Communication in LTE Networks by Efficient Grouping

Wireless Personal Communications - Device to device (D2D) communication is a key technology of 5G mobile communications. It allows devices to communicate by using direct links, rather than...     

Oxidative steam reforming of ethanol for hydrogen production on M/Al2O3

In this work, we investigate oxidative steam reforming (OSR) of ethanol on a series of metals under various catalytic conditions (H₂O/ethanol and O₂/ethanol ratios) to understand the reaction mechanism and to optimize the catalytic conditions for optimal hydrogen production. There are three reaction pathways for OSR using these metals. Ethanol can be oxidized to acetaldehyde on Cu, Ag and Au, and it can be dehydrated to form ethylene on Co, Ni, Pd and Pt. Ethylene can form coke and degrade catalysts after the long-term OSR. In the third pathway, ethanol preferentially breaks its C–C bond and is further oxidized to CO or CO₂ on Ru, Rh and Ir, providing optimal hydrogen production. In addition, increasing H₂O/ethanol and O₂/ethanol ratios can improve catalytic activity, attributable to atomic oxygen from H₂O and O₂ efficiently rupturing the C–C bond of ethanol. This concept explains the improved performance of OSR on the CeO₂-modified catalyst, which shows better oxygen storage capability.     

Improvement of the CFRP Mechanical Properties Using Taguchi Method to Optimize the Formation Conditions

Carbon fiber composites have high strength, high stiffness and light weight characteristics to apply to many fields, such as leisure, energy and transportation industries. The CFRP （carbon fiber reinforced polymers/plastics） composites made of carbon fibers as reinforcement and epoxy resins as matrix were prepared by drum winding process. Various parameters such as molding temperature, molding pressure and pressing time were selected as the pre-pregs were laminated to be the CFRP. The effects of fabricating parameters which affected the mechanical properties of CFRPs were analyzed by Taguchi method in this study. The results showed that molding temperature was the main factor to influence the mechanical properties of composites.