Preparation and photoluminescence properties of γ-KCaPO4: Eu phosphors for near UV-based white LEDs

Novel whitish-blue phosphors based on a phosphate host matrix, γ-KCaPO₄: Eu²⁺, were prepared by a conventional solid-state reaction method using slightly phosphorus deficient conditions and their photoluminescence properties were investigated. The concentration quenching process, temperature dependence of the luminescence and decay curve were also investigated. The γ-KCaPO₄: Eu²⁺ phosphor was efficiently excited by UV-Visible light at wavelengths of 200-450 nm and exhibited a bright whitish-blue emission with a maximum peak wavelength of 473 nm. All of these characteristics suggest that the γ-KCaPO₄: Eu²⁺ phosphors combined with red phosphors could be applicable to near UV-based white LEDs, i.e., only two kinds of phosphor powders are needed for the formation of white light.     

A conservative method of wavelet neural network based meta-modeling in constrained approximate optimization

The paper aims at the development of the wavelet neural network (WNN) based conservative meta-model that satisfies the constraint feasibility of approximate optimal solution. The WNN based constraint-feasible meta-model is formulated via exterior penalty method to optimally determine interconnection weights and dilation and translation coefficients in the network. Using Ackley’s path function, the approximation performance of WNN is first tested in comparison with BPN. The proposed approach of constraint feasibility is then verified through a ten-bar planar truss problem. For constrained approximate optimization, the structural design of a composite rotor blade is explored to support the proposed strategies.     

Fabrication of Al matrix composite reinforced with submicrometer-sized Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles formed by combustion reaction between HEMM Al and V<Subscript>2</Subscript>O<Subscript>5</Subscript> composite particles during sintering

To fabricate an Al-V matrix composite reinforced with submicron-sized Al₂O₃ and Al_xV_y (Al₃V, Al₁₀V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for V₂O₅ decreased with the formation of a new product, Al-Al₂O₃-Al_xV_y, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and V₂O₅ composite powders. The in-situ reaction between Al and V₂O₅ during the HEMM and sintering transformed the Al₂O₃ and Al_xV_y (Al₃V, Al₁₀V) phases. Most of the reduced V reacted with excess the Al to form Al_xV_y (Al₃V, Al₁₀V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V₂O₅, the hardness of the Al-Al₂O₃-Al_xV_y composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V₂O₅ composite powder and sintering at 1173 K for 2 h had the highest hardness.     

Numerical study on the evaluation of tunnel shotcrete using the Impact-Echo method coupled with Fourier transform and short-time Fourier transform

This study presents a simple but robust evaluation technique of the bonding state of shotcrete applied to tunnels using Impact-Echo (IE) method and thus explores the effect of the ground types, thickness of the shotcrete, undulating surfaces and impact sources on system vibration through numerical simulations based on the finite element method. All the signals obtained from numerical simulation for various conditions are analyzed at the frequency domain using Fourier transform (FT) and at the time–frequency domain using short-time Fourier transform (STFT). As the bonding condition worsens, the resonant frequency (f_n) and the resonance duration (T_R) increase and the geometric damping ratio (D_G) decreases. The results of a comprehensive numerical analysis suggest that the shape of the contour in the time–frequency domain, the level of f_n, and the T_R and D_G values can be used as effective indicators for the evaluation of the shotcrete thickness, ground type, and bonding state. Finally, this paper presents a procedure for evaluating the tunnel shotcrete state, the shotcrete thickness, and the ground type with the IE method coupled with Fourier transform and short-time Fourier transform. Limited field tests were also performed to verify the proposed evaluation chart for tunnel shotcrete states.     

High speed SOI CMOS image sensor with pinned photodiode on handle wafer

We have fabricated SOI CMOS active pixel image sensor with pinned photodiode on handle wafer. The structure of one pixel is a four-transistor type active pixel image sensor, which consists of a reset and a source follower transistor on seed wafer, and is comprised of a photodiode, a transfer gate, and a floating diffusion on handle wafer. The photodiode could be optimized for better quantum efficiency and low dark currents because the process of a photodiode on handle wafer is independent of that of transistors on seed wafer. Most of the wavelengths are absorbed within the visible range, because the optimized photodiode is located on the handle wafer. The response time of SOI CMOS active pixel sensor was about 2 times faster than that of bulk CMOS active pixel image sensor.     

Customer-focused Internet commerce at Cisco Systems

The rapid growth in electronic commerce places strong demands on business practices to meet customer needs in a timely and cost-effective manner. This article outlines some of the tools developed by Cisco to facilitate this growth while achieving excellent customer care and employee satisfaction. Attention is given to the steps Cisco has taken to organize to meet these dual objectives     

Perovskite‐Induced Ultrasensitive and Highly Stable Humidity Sensor Systems Prepared by Aerosol Deposition at Room Temperature

A new capacitive‐type humidity sensor is proposed using novel materials and fabrication process for practical applications in sensitive environments and cost‐effective functional devices that require ultrasensing performances. Metal halide perovskites (CsPbBr₃ and CsPb₂Br₅) combined with diverse ceramics (Al₂O₃, TiO₂, and BaTiO₃) are selected as sensing materials for the first time, and nanocomposite powders are deposited by aerosol deposition (AD) process. A state‐of‐the‐art CsPb₂Br₅/BaTiO₃ nanocomposite humidity sensor prepared by AD process exhibits a significant increase in humidity sensing compared with CsPbBr₃/Al₂O₃ and CsPbBr₃/TiO₂ sensors. An outstanding humidity sensitivity (21426 pF RH%^?1) with superior linearity (0.991), fast response/recovery time (5 s), low hysteresis of 1.7%, and excellent stability in a wide range of relative humidity is obtained owing to a highly porous structure, effective charge separation, and water‐resistant characteristics of CsPb₂Br₅. Notably, this unprecedented result is obtained via a simple one‐step AD process within a few minutes at room temperature without any auxiliary treatment. The synergetic combination of AD technique and perovskite‐based nanocomposite can be potentially applied toward the development of multifunctional sensing devices.     

Enhanced thermal stability of a sputtered titanium-nitride film as a diffusion barrier for capacitor-bottom electrodes

The effect of a thin RuO_x layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuO_x/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuO_x/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no formation of a thin RuO_x layer at the RuO_x surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film by pre-annealing leads to the formation of a thin RuO_x layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity of diffusion paths. In particular, the RuO_x layer in a nonstoichiometric state is changed to the RuO₂-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer. Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the RuO_x/TiN/poly-Si/Si contact system.     

Multi-phased VSG CDMA with level clipping for high-rate transmission systems

In this letter, a multi-phased CDMA system employing a variable spreading gain (VSG) approach is proposed for high-rate applications, based on four algorithms for selecting a multi-code set. From simulation results, in addition to simple receiver structure thanks to level clipping, the multi-phased VSG CDMA system provides an high bit rate transmission, while maintaining an acceptable performance degradation.