Amorphization of Ti1−x Mn x

Three amorphous Ti_1−x Mn _x alloy powders, withx = 0.4, 0.5, and 0.6, were prepared by mechanical alloying (MA) of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by X-ray diffraction (XRD) and high-resolution transmission elec- tron microscopy (HRTEM). The crystallization temperatures for these alloys detected by dif- ferential scanning calorimetry (DSC) varied from 769 to 830 K. The calculated enthalpies of mixing in these amorphous phases are relatively small compared with those for other Ti-base binary alloys. The criteria for solid-state amorphization reaction are examined. It is suggested that the kinetics of nucleation and growth favors the formation of the amorphous phases and the supply of atoms for nucleation and growth is predominantly through the defective regions induced by MA. Formerly Graduate Student, National Tsing Hua University     

The improvement of short-channel effects due to oxidation-inducedboron redistribution for counter-implantation p-MOSFET's

Delayed appearance of short-channel effects in the threshold voltage falloff has been observed for counterimplantation p-MOSFETs. The phenomenon is attributed to the oxidation-induced boron redistribution along the channel. SUPREM-3 and MINIMOS-5 and the Orlowski method were used to quantitatively characterize this behavior. Quite good agreement between simulation and experimental data were obtained. It was found that the device characteristics of submicrometer counterimplanted p-MOSFETs are improved due to the effects of boron redistribution near the channel edge     

Fabrication of TiO2 nanotubes by atomic layer deposition and their photocatalytic and photoelectrochemical applications

The formation of TiO(2) nanotubes was conducted by atomic layer deposition (ALD) with tris-(8-hydroxyquinoline) gallium (GaQ(3)) nanowires as a template at different substrate temperatures, 50, 100, and 200?°C. TiO(2) nanotubes were formed only at 50 and 100?°C. Although a higher growth rate at 50?°C was observed, nanotubes with better uniformity, conformality, and less residual chloride were obtained at 100?°C because of a different formation mechanism. A photocatalysis test of TiO(2) nanotubes prepared by different cycle numbers at 100?°C was conducted. It showed that TiO(2) nanotubes prepared by 400 cycles of ALD and treated at 700?°C for 1 h to form anatase phase had the best photocatalytic performance. Compared with P-25, the nanotubes showed higher photocatalytic degradation of rhodamine B and water splitting efficiency.     

Effects of internal flow modification on the cell performance enhancement of a PEM fuel cell

This study presents a numerical investigation on the cell performance enhancement of a proton exchange membrane fuel cell (PEMFC) using the finite element method (FEM). The cell performance enhancement in this study has been accomplished by the transverse installation of a baffle plate and a rectangular block for the modification of flow pattern in the flow channel of the fuel cell. The baffle plates (various gap ratios, λ = 0.005–10) and the rectangular block (constant gap ratio, λ = 0.2) are installed along the same gas diffusion layer (GDL) in the channel at constant Reynolds number for the purpose of investigating the cell performance. The results show that the transverse installation of a baffle plate and a rectangular block in the fuel flow channel can effectively enhance the local cell performance of a PEMFC. Besides, the effect of a rectangular block on the overall cell performance is more obvious than a baffle plate.     

Fabrication of TiN inverse opal structure and Pt nanoparticles by atomic layer deposition for proton exchange membrane fuel cell

A titanium nitride (TiN) inverse opal structure was fabricated on carbon paper as a support of Pt for application in proton exchange membrane fuel cell (PEMFC). Polystyrene spheres with different diameters were coated on carbon paper by spin coating in multilayers as a template. Titanium dioxide (TiO₂) thin film was then deposited on the template by atomic layer deposition (ALD). The TiN inverse opal structure was fabricated by direct nitridation of TiO₂ in flowing ammonia atmosphere at above 800 °C. Platinum nanoparticles were then deposited uniformly on TiN by ALD. The performances of PEMFC using Pt@TiN@carbon paper composite as electrodes were examined. The homemade electrodes showed at least 13 times higher platinum specific power density than commercial E-Tek electrodes.     

Numerical investigation of heat transfer enhancement on a porous vortex-generator applied to a block-heated channel

The numerical simulation is used to obtain the unsteady laminar flow and convective heat transfer in the block-heated channel with the porous vortex-generator. The general Darcy–Brinkman–Forchheimer model is adopted for the porous vortex-generator. The parameters studies including porosity, Darcy number, width-to-height ratio of porous vortex-generator and Reynolds number have been explored on heat transfer enhancement and vortex-induced vibration in detail. The results indicate that heat transfer enhancement and vortex-induced vibration increase with increasing Reynolds number and width-to-height ratio. However, the porosity has slight influence on heat transfer enhancement and vortex-induced vibration. When Darcy number is 10^?3 or 10^?4, installing a porous vortex-generator with B/h = 1.0 improves overall heat transfer the best along heated blocks, and has a strong reduction of vortex-induced vibration.     

Effect of the prominent catalyst layer surface on reactant gas transport and cell performance at the cathodic side of a PEMFC

The cell performance enhancement of a proton exchange membrane fuel cell (PEMFC) has been numerically investigated with the prominence-like form catalyst layer surface of the same composition at the cathodic half-cell of a PEMFC. The geometries of the prominence-like form catalyst layer surface are assigned as one prominence, three prominences, and five prominences catalyst layer surfaces with constant distance between two prominences in the same gas diffusion layer (GDL) for the purpose of investigating the cell performance. To confine the current investigation to two-dimensional incompressible flows, we assume that the fluid flow is laminar with a low Reynolds number 15. The results indicate that the prominence-like form catalyst layer surface can effectively enhance the local cell performance of a PEMFC.     

An Integrated Data-Driven Framework for Computing System Management

With advancement in science and technology, computing systems are becoming increasingly more complex with a growing number of heterogeneous software and hardware components. They are thus becoming more difficult to monitor, manage, and maintain. Traditional approaches to system management have been largely based on domain experts through a knowledge acquisition solution that translates domain knowledge into operating rules and policies. This process has been well known as cumbersome, labor intensive, and error prone. In addition, traditional approaches for system management are difficult to keep up with the rapidly changing environments. There is a pressing need for automatic and efficient approaches to monitor and manage complex computing systems. In this paper, we propose an integrated data-driven framework for computing system management by acquiring the needed knowledge automatically from a large amount of historical log data. Specifically, we apply text mining techniques to automatically categorize the log messages into a set of canonical categories, incorporate temporal information to improve categorization performance, develop temporal mining techniques to discover the relationships between different events, and take a novel approach called event summarization to provide a concise interpretation of the temporal patterns.     

Temporal Coupling Verification in Time Series Databases

Time series are often generated by continuous sampling or measurement of natural or social phenomena. In many cases, events cannot be represented by individual records, but instead must be represented by time series segments (temporal intervals). A consequence of this segment-based approach is that the analysis of events is reduced to analysis of occurrences of time series patterns that match segments representing the events.A major obstacle on the path toward event analysis is the lack of query languages for expressing interesting time series patterns. We have introduced SQL/LPP (Perng and Parker, 1999). Which provides fairly strong expressive power for time series pattern queries, and are now able to attack the problem of specifying queries that analyze temporal coupling, i.e., temporal relationships obeyed by occurrences of two or more patterns.In this paper, we propose SQL/LPP+, a temporal coupling verification language for time series databases. Based on the pattern definition language of SQL/LPP (Perng and Parker, 1999), SQL/LPP+ enables users to specify a query that looks for occurrences of a cascade of multiple patterns using one or more of Allen's temporal relationships (Allen, 1983) and obtain desired aggregates or meta-aggregates of the composition. Issues of pattern composition control are also discussed.     

Cracking kinetics of two-phase stainless steel alloys in hydrogen gas

The kinetics of hydrogen-induced slow crack growth (SCG) under constant load was studied in two stainless steel alloys containing mixtures of bcc and fcc phases. FERRALIUM 255, a duplex stainless steel, consisting of ∼50 pct austenite in a ferrite matrix, was tested in hydrogen gas at 0 to 100 °C with the loading axis both perpendicular and parallel to the rolling direction. In addition, specimens of AISI 301 were deformed in air in different ways to produce various amounts of bcc phase in an austenite matrix prior to testing in H₂ gas at room temperature. The kinetics of subcritical slow crack growth (SCG) in these alloys was compared with that for austenitic and for ferritic stainless steels. The SCG rates were rationalized in terms of differences in hydrogen permeation in the two phases. The results confirm that a higher rate of supply and accumulation of hydrogen in the region ahead of the crack tip allows a higher cracking velocity.