Comparison of hydrogen gas embrittlement of austenitic and ferritic stainless steels

Hydrogen-induced slow crack growth (SCG) was compared in austenitic and ferritic stainless steels at 0 to 125 °Cand 11 to 216 kPa of hydrogen gas. No SCG was observed for AISI 310, while AISI 301 was more susceptible to hydrogen embrittlement and had higher cracking velocity than AL 29-4-2 under the same test conditions. The kinetics of crack propagation was modeled in terms of the hydrogen transport in these alloys. This is a function of temperature, microstructure, and stress state in the embrittlement region. The relatively high cracking velocity of AISI 301 was shown to be controlled by the fast transport of hydrogen through the stress-induced α′ martensite at the crack tip and low escape rate of hydrogen through the γ phase in the surrounding region. Faster accumulation rates of hydrogen in the embrittlement region were expected for AISI 301, which led to higher cracking velocities. The mechanism of hydrogen-induced SCG was discussed based upon the concept of hydrogen-enhanced plasticity. Formerly Research Associate of the University of Illinois     

Effects of gamma irradiation on the distribution of calcium ions in grass shrimp (Phenaeus monodon F.) muscle

Effects of medium-dose (5 kGy) irradiation on the calcium ion distribution in shrimp muscle were studied using an electron microprobe (EDX) and an electron microscope. In irradiated shrimp muscle cells, the calcium ions in the sarcoplasmic reticulum and nuclei were not released to the myofibrils, and remained in situ during 8 days storage at 4°C after irradiation. However, without irradiation the concentration of calcium ions in the myofibrils of muscle cells increased after the same storage period. The distribution of calcium ions could play a role in the softening of shrimp meat, induced by proteinase.     

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.     

Sigma adaptive fuzzy sliding mode control of a class of nonlinear systems

Based on fuzzy approximators of nonlinear functions, a new adaptive fuzzy sliding mode control scheme is proposed for a class of nonlinear plants. In comparison with most existing methods, in which the parameter projection algorithm is often involved to prevent the estimated value of the input gain function from evolving into zero, the proposed control law has shown its success and simplicity in tackling the case when the value of the estimated input gain function becomes zero during online operations. A variant of adaptive law with dead-zone sigma-modification is introduced to help achieve this goal. The bounding parameters of the model approximation error and the external disturbance are all regarded as unknown constants in this paper, and adaptive laws for them are devised for tracking purposes. Based on Lyapunov's stability theory the proposed controller has been shown to render the tracking error arbitrarily close to zero. A comparably good tracking performance is obtained as illustrated by the simulation results for an inverted pendulum system.     

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene polymer waveguide

The passive optical properties of a silicon nanoparticle-embedded benzocyclobutene (BCB) waveguide were investigated. The silicon nanoparticles, of a size varying from 6 to 25?nm, were prepared by vapor condensation. The transmission modes and losses were examined by the prism coupler and cut-back methods. A He-Ne laser beam with a wavelength of 6328?? was used to measure the effective index and thickness of the waveguide. Laser light could be efficiently coupled into the BCB waveguide when the embedded Si nanoparticles were smaller than 6?nm. The film thickness and effective index of the Si-embedded BCB waveguide were measured to be 1.825?μm and 1.565, respectively. The optical transmission losses of the pure BCB and Si-embedded ridge waveguides measured by the cut-back method were 0.85 and 1.63?dB?cm(-1), respectively. Although the optical loss was increased by the embedded Si, the disturbance of the output contour was quite small. This result demonstrates that the nanoparticle-embedded polymer waveguide may be used for optoelectronic integrated circuits.     

Photoluminescence of Si nanocrystallites and amorphous oxygen-containing si nanoparticles: the reversible effect of ambient atmosphere on luminescence

Si nanocrystallites of various sizes and oxygen-containing Si nanoparticles with different oxygen contents were prepared by vapor condensation. The Si nanocrystallites showed a visible light emission from 500 nm to 900 nm with the peak at 800 nm, and the intensity of photoluminescence increased with decreasing the particle size. This photoluminescence observed in vacuum could be quenched by air and hydrogen, and reappeared after the sample chamber was evacuated. The oxygen-containing Si nanoparticles consisting mainly of Si oxide were amorphous and had an average particle size of approximately 20 nm. Increasing the oxygen content of nanoparticles caused a blueshift of the absorption edge in the transmission spectra. A blue-green photoluminescence with two peaks at 500 nm and 800 nm was observed from these oxygen-containing Si nanoparticles. The luminescence intensity increased with the oxygen content of nanoparticles, and was very sensitive to the ambient atmosphere. Much lower intensity was observed in air, but higher intensity could be recovered in vacuum. Surface states and oxygen-induced luminescent centers were proposed to be responsible for the photoluminescence from the Si nanocrystallites and oxygen-containing Si nanoparticles, respectively. The reversible ambient effect in both cases could be explained by surface charge redistribution during the gas adsorption and desorption processes.     

Fabrication of highly homogeneous Al‐doped TiO2 nanotubes by nanolamination of atomic layer deposition

Conformal parallel arrays of Al‐doped TiO₂ nanotubes were fabricated by atomic layer deposition. TiO₂/Al₂O₃ bilayered shells were grown on a polycarbonate template by various cyclic sequences of TiO₂ and Al₂O₃. The doping level of Al could be tuned by the fraction of cycle number of Al₂O₃. From the depth profiles measured by second ion mass spectrometry, Al is uniformly distributed across the thickness, which is also supported by the analyses of X‐ray diffraction, X‐ray photoelectron spectroscopy, and Raman spectroscopy. A uniform bulk solubility of ~7 at.% and the surface concentration of ~18 at.% were observed with the cycle ratio of Al₂O₃: TiO₂ at 0.04.     

Synthesis and properties of novel phosphorus‐containing bismaleimide/epoxy resins

A novel soluble phosphorus‐containing bismaleimide (BMI) monomer, bis(3‐maleimidophenyl)phenylphosphine oxide (BMIPO), was synthesized by the imidization of bis(3‐aminophenyl) phenylphosphine oxide, in which its structural characterization was identified with ¹H‐NMR, ¹³C‐NMR, and Fourier transform infrared spectra. The BMIPO resin, with five‐membered imide rings and high phenyl density, was an excellent flame retardant with a high glass‐transition temperature (T_g), onset decomposition temperature, and limited oxygen index. In phosphorus‐containing BMI/epoxy/4,4′‐methylene dianiline (DDM)‐cured resins, homogeneous products were obtained from all proportions without phase separation. Because of the higher reactivity of BMIPO/DDM relative to that of 4,4′‐bismaleimidodiphenylmethane (BMIM)/DDM, the increase in the BMIPO/BMIM ratio in this blending resin increased the recrosslinking hazards of the postcuring stage and so lowered the T_g value and thermal stability. The thermal stability of the BMI/epoxy‐cured system was lower than that of the epoxy‐cured system because of the introduction of a phosphide group into BMIPO, whereas for the T_g value and flame retardancy, the former was significantly higher than the latter: the higher the BMIPO content in the blend, the higher the flame retardancy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2080–2089, 2002; DOI 10.1002/app.10607     

Self-calibration of a general hexapod manipulator using cylinder constraints

This paper presents a novel self-calibration strategy for a general hexapod manipulator to overcome weaknesses and embrace merits of existing approaches. A commercial trigger probe and a cylindrical gauge block are adopted in the present approach. The algorithm is formulated to solve a nonlinear least squares problem that takes all measurement errors into account. The simulation results show that the proposed algorithm has the following advantages: (1) it is capable of calibrating the position and orientation of the gripper or spindle on the platform; (2) it completely avoids the unobservability of certain parameters due to mobility constraints on the passive joints; (3) the hardware of the calibration system is more compact and cost-effective than that adopted in the existing approaches; and (4) the algorithm is numerically robust, efficient and effective, while the calibrated parameter errors are expected to be with the same order of the measurement errors. Due to these merits, the present scheme is attractive for an autonomous hexapod manipulator when a great precision is required in a workspace of five degrees-of-freedom.     

Crystallization characteristics of the Ti53Cu47 amorphous alloy

A thin Ti₅₃Cu₄₇ amorphous ribbon was prepared by rapid quenching from the melt. The crystallization behavior was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The DSC results indicated that the activation energy for crystallization was 170 or 150 kJ/mole (1.76 or 1.55 eV/atom) based on the Kissinger or Arrhenius plot, respectively, which is close to that of chemical diffusion in the TiCu alloy: 166 kJ/mol (1.72 eV/atom). The Johnson-Mehl-Avrami (JMA) plot exhibited a linearity, with an exponent of n=2.0 ±0.2. The XRD patterns revealed the transformation to the equilibrium γ-TiCu phase. However, broad peaks due to nanocrystalline grains were not observed. From the TEM analysis, there was a metastable phase with an fcc structure based on the Cu structure pre-existing in the as-quenched ribbon. Only a few TiCu particles in the nanoscale dimension were observed to precipitate from the amorphous matrix upon both continuous and isothermal heatings. A theoretical calculation demonstrates that amorphous Ti₅₃Cu₄₇ has a very low nucleation frequency and thus, a low tendency to form nanocrystals.