Growth of Strontium Titanate Thin Films of Controlled Thickness by the Hydrothermal–Electrochemical Method

Strontium titanate thin films were grown on titanium electrodes up to ca. 2 μm in thickness by a hydrothermal–electrochemical method using electrolysis performed potentiostatically by the three-electrode cell technique. The film thickness increased monotonically with an increase in the quantity of electricity passed through the Ti electrode, and could be controlled accurately by this factor. Grown films were composed of a surface layer having an invariant thickness of ca. 0.2 μm and an inner layer grown by electrolysis. The lattice parameter of the cubic SrTiO₃ film was analyzed to be 3.919 A.     

DEGRADATION AND STABILISATION OF POLYMERIC MATERIALS

The adsorption of 4-methylbiphenyl, sodium dodecylbenzenesulfonate (NaDBS), and phenol on a β-cyclodextrin epichlorohydrin network polymers at 25°C has been studied. The isotherm of 4-methylbiphenyl fits well with the Freundlich equation at a concentration range from 10^?5 to 10^?4 mol/l. The isotherms of NaDBS and phenol deviate from a straight line in the investigated concentration range.     

Multi-Modal Speech Recognition Using Optical-Flow Analysis for Lip Images

This paper proposes a multi-modal speech recognition method using optical-flow analysis for lip images. Optical flow is defined as the distribution of apparent velocities in the movement of brightness patterns in an image. Since the optical flow is computed without extracting the speaker's lip contours and location, robust visual features can be obtained for lip movements. Our method calculates two kinds of visual feature sets in each frame. The first feature set consists of variances of vertical and horizontal components of optical-flow vectors. These are useful for estimating silence/pause periods in noisy conditions since they represent movement of the speaker's mouth. The second feature set consists of maximum and minimum values of integral of the optical flow. These are expected to be more effective than the first set since this feature set has not only silence/pause information but also open/close status of the speaker's mouth. Each of the feature sets is combined with an acoustic feature set in the framework of HMM-based recognition. Triphone HMMs are trained using the combined parameter sets extracted from clean speech data. Noise-corrupted speech recognition experiments have been carried out using audio-visual data from 11 male speakers uttering connected digits. The following improvements of digit accuracy over the audio-only recognition scheme have been achieved when the visual information was used only for silence HMM: 4% at SNR = 5 dB and 13% at SNR = 10 dB using the integral information of optical flow as the visual feature set.     

Analysis of tungsten film electrodeposited from a ZnCl2-NaCl-KCl melt

Microparts for micro-electro-mechanical systems (MEMS) are becoming increasingly important, and the Lithographie Galvanoformung Abformung (LIGA) process for producing such parts is attracting attention [1]. However, as this process requires the step of electroplating in aqueous solution, only copper, nickel and their alloys can be used because of the limit of the potential window of water. We have been attempting to apply the electroplating of refractory metals in molten salts to the LIGA process or to the surface coating of conventional LIGA microparts in order to give higher strength and heat resistance for the microparts. Herein we report the characteristics of a tungsten film electrodeposited from a ZnCl₂-NaCl-KCl melt at 250 °C.     

High-performance FCBGA based on multi-layer thin-substrate packaging technology

We developed a new concept flip-chip ball grid array (FCBGA) based on multi-layer thin-substrate (MLTS) packaging technology in order to meet the strong demand for high-density, high-performance, and low-cost LSI packages. The most important feature of MLTS packaging is that, only a high-density and high-performance MLTS remains by removing the metal plate after mounting an LSI chip. The MLTS packaging offers the advantages of (1) good registration accuracy, which makes higher-density and finer-pitch pattering possible; (2) an ideal multi-layer structure that is highly suitable for high-speed and high-frequency applications; (3) excellent flip-chip mounting reliability, which makes higher-pin-count and finer-pitch area array flip-chip interconnection possible; (4) excellent reliability, supported by use of high T_g (glass transition temperature) resin; and (5) a cost-effective design achieved as a result of fewer layers fabricated with fine-pitch patterning.We successfully produced a high-performance FCBGA prototype based on our MLTS packaging technology. The prototype comprises an LSI chip connected to approximately 2500 bonding pads arranged in 240 μm pitch area array, and 1296 I/O pads for BGA. The prototype FCBGA’s excellent long-term reliability was demonstrated through a series of tests conducted on it.     

Fluid flow and heat transfer of natural convection around large horizontal cylinders: Experiments with air

Natural convective flows of air around large horizontal cylinders were investigated experimentally. The main concerns were the turbulent transition mechanisms and the heat transfer characteristics of turbulent flows. The cylinders were heated with uniform heat flux and their diameters were varied from 200 to 1200 mm to enable experiments over a wide range of modified Rayleigh numbers, Ra_D^* = 1.0 × 10⁸ to 5.5 × 10¹¹. The flow fields around the cylinders were visualized with smoke to investigate the turbulent transition mechanisms. The results show that three‐dimensional flow separations occur first at the trailing edge of the cylinder when Ra_D^* exceeds 3.5 × 10⁹, and the separation points shift upstream with increasing Rayleigh numbers. These separations become a trigger to the turbulent transition and transitional and turbulent flows appear downstream of the separations at higher Rayleigh numbers. However, they occupy a relatively small portion of the cylinder surfaces even at the maximum Rayleigh numbers of the present experiments. The local heat transfer coefficients were also measured. The results show that the coefficients are increased significantly in the transitional and turbulent regions compared with the laminar coefficients. Moreover, the present results for air were compared with previous results for water and the effects of Prandtl number on the flow and heat transfer were discussed. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 293–305, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10080     

Phonon scattering and thermal conduction mechanisms of sintered aluminium nitride ceramics

From thermal diffusivity measurements of sintered AIN at temperatures ranging from 100 to 1000 K, the phonon mean free path of AIN was calculated in order to investigate phonon scattering mechanisms. The calculated mean phonon scattering distance was increased with decreasing temperature. The mean phonon-defect scattering distances were respectively limited to about 50 nm at temperatures ranging from 100 to 270 K and about 30 nm at temperatures ranging from 100 to 700 K, for AIN specimens with a room-temperature thermal conductivity of 220 and 121 Wm^–1 K^–1 containing 0.1 and 1.4 wt % oxygen, respectively. These short phonon-defect scattering distances were considered to correspond to the separation of oxygen-related internal defects in AIN grains. Calculation of the mean phonon scattering frequencies indicated that the phonon scattering is dominated by phonon-defect scattering at temperatures below 270 K for an AIN specimen with an oxygen content of 0.1 wt %, and at temperatures below 350 K for an AIN specimen with an oxygen content of 1.4 wt %.     

Low-Temperature Sintering and High Thermal Conductivity of YLiO2-Doped AlN Ceramics

The present work indicates through thermodynamic considerations that YLiO₂ additive is beneficial for low-temperature sintering of AlN ceramics. Pressureless sintering of commercially available AIN powders with simultaneous additions of YLiO₂ and CaO resulted in materials with high thermal conductivity (170 W·m^–1·K^–1 after sintering at 1600°C for 6 h). It is demonstrated that improvement of thermal conductivity is possible at low firing temperature by use of sintering aids.     

Conductivity of Tazheranite Ceramics Synthesized by Controlling Composition

Tazheranite ceramics with controlled compositions were synthesized by solid-phase reaction, and their conductivity was measured using the complex impedance method. The CaO content in tazheranite compositions showed the highest conductivity at around 15 mol%. In particular, Ca_0.81Ti_0.04O_y sintered bodies revealed the highest conductivity, and this value agreed very closely with that of 15 mol% CaO-stabilized ZrO₂.