Nitride-based laser diodes using thick n-AlGaN layers

We obtained 1 μm crack-free AlGaN layers up to an AlN molar fraction of 0.4 by growing directly on low-temperature-deposited buffer layers. The buffer layer is effective for growing AlGaN layers without the stress caused by the lattice mismatch. We also demonstrated nitride-based laser diodes with such a 1 μm crack-free n-AlGaN cladding layer/n-AlGaN contact layer/low-temperature-deposited buffer layer/sapphire structure, which showed a clear single spot in a far field pattern. The AlGaN-based structure can suppress optical leakage from the waveguide region to the underlying layer. The threshold current of the laser diode is about 230 mA, which is comparable to or better than that of our laser diodes with the conventional GaN-based structure.     

Crystallization in blends of isotactic polypropylene with polyethylene-b-poly(ethylene-co-butylene)-b-polyethylene block copolymer

In this study, isothermal crystallization in blends of isotactic polypropylene (i-PP) with polyethylene-b-poly(ethylene-co-butylene)-b-polyethylene block copolymer (CEBC) was investigated using a polarized photometer, polarized microscope and differential scanning calorimeter. Half time of crystallizaiton (τ_1/2) is increasing with increasing CEBC content in i-PP/CEBC blends. Avrami index and rate constant of crystal growth decrease with increasing CEBC content in i-PP/CEBC blends. On the contrary, heat of fusion of i-PP crystal in the blends is almost constant against the variation of CEBC content in i-PP/CEBC blends. Hence, it is pointed out that blending i-PP with CEBC caused only retardation of rate of crystalline growth and change in mechanism of crystalline growth from three dimensional to two dimensional growth. Received: 19 May 1999/Revised version: 15 July 1999/Accepted: 19 July 1999     

Influence of small amount of glass fibers on mechanical properties of discontinuous recycled carbon fiber-reinforced thermoplastics

The effect of residual contamination, such as glass fibers (GFs), on the application of discontinuous recycled carbon fibers (rCFs) is still unclear. In this study, GFs are used to substitute rCF at volume fractions (Vfs) of 0%, 1%, 2%, and 5% in carbon fiber paper-reinforced thermoplastics fabricated through a papermaking process. After an investigation with the three-point bending tests, the flexural modulus will not decrease when the GF content increased. Unlike the flexural modulus, the flexural strength decreased with an increase in the GF volume. In order to illustrate the effect of small amount of GF on flexural modulus, a modified rule of mixture (ROM) is used to derive a coefficient, Factor c₁, depicting the effect caused by discontinuous and randomly distributed reinforcement fibers. Furthermore, modified Halpin–Tsai model with Factor c₁ illustrated that the experiment results of flexural modulus is not decreased as fast as predicted results. Therefore, small amount of GF will not affect the application of rCF.     

Effects of Particle Sizes on Sintering Behavior of 316L Stainless Steel Powder

In rapidly evolving powder injection molding technology, the wide prevalence of various microstructures demands the powders of smaller particle sizes. The effects of particle size on the sintering behavior are critical to not only shape retention of microstructure but also its mechanical properties. This study investigates the effects of three different particle sizes on the sintering behavior of the 316L stainless steel (STS316L) samples, prepared by powder injection molding, via the dilatometry experiments. For this purpose, the STS316L powders of three different mean particle sizes, i.e., 2.97, 4.16, and 8.04 μm, were produced for STS316L. The samples for the dilatometry test were prepared through powder-binder mixing, injection molding, and solvent and thermal debinding. Dilatometry experiments were carried out with the samples in a H₂ atmosphere at three different heating rates of 3, 6, and 10 K/min. The shrinkage data obtained by dilatometry experiments was collected and analyzed to help understand the densification and the sintering behaviors in terms of particles size and heating rate. The master sintering curve (MSC) model was used to quantify the effects of particle sizes. In addition, we investigated the microstructure evolutions in terms of particles sizes.     

Penetration behavior of water solution containing radioactive species into dried concrete/mortar and epoxy resin materials

Penetration behavior of radionuclides such as ¹³⁷Cs into dried concrete material, dried mortar material and epoxy paint for a few dozen days was observed using a solution containing fission products extracted from irradiated fuels to obtain fundamental information on the radionuclide penetration rate and depth. Hardly any radionuclides could penetrate into the epoxy paint. The radionuclide solution penetrated into concrete and mortar materials to a depth of a few millimeters for a few dozen days. The penetration behavior observed near the surface of concrete and mortar materials was similar to the diffusion of nuclides in media such as water-saturated concrete, bentonite and cement materials.     

Lagrangian relaxation method for price-based unit commitment problem

The unit commitment problem consists of determining the schedules for power generating units and the generating level of each unit. The decisions concern which units to commit during each time period and at what level to generate power to meet the electricity demand. The problem is a typical scheduling problem in an electric power system. The electric power industry is undergoing restructuring and deregulation. This article developes a stochastic programming model which incorporates power trading. The uncertainty of electric power demand or electricity price are incorporated into the unit commitment problem. It is assumed that demand and price uncertainty can be represented by a scenario tree. A stochastic integer programming model is proposed in which the objective is to maximize expected profits. In this model, on/off decisions for each generator are made in the first stage. The approach to solving the problem is based on Lagrangian relaxation and dynamic programming.     

Melting behavior of MgO-based inert matrix fuels containing (Pu,Am)O2−x

The melting behavior of MgO-based inert matrix fuels containing (Pu,Am)O_2−x ((Pu,Am)O_2−x-MgO fuels) was experimentally investigated. Heat-treatment tests were carried out at 2173 K, 2373 K and 2573 K each. The fuel melted at about 2573 K in the eutectic reaction of the Pu-Am-Mg-O system. The (Pu,Am)O_2−x grains, MgO grains and pores grew with increasing temperature. In addition, Am-rich oxide phases were formed in the (Pu,Am)O_2−x phase by heat-treatment at high temperatures. The melting behavior was compared with behaviors of PuO_2−x-MgO and AmO_2−x-MgO fuels.     

Effect of compound mineral powders on workability and rheological property of HPC

The compounding effect of silica fume (SF) with phosphorus slag (PS) or limestone (LS) powder is investigated in this paper. It is found that such a compounding can achieve various rheological behavior of HPC. The compound powders of PS with SF lower plastic viscosity and yield stress of fresh concrete, but increase the slump and promote continuous flowability of concrete greatly. However, the compounding of LS with SF increases the yield stress, but decreases both slump and slump flow of concrete, although the viscosity remains broadly unchanged compared with the concrete containing LS only. It is demonstrated that rheological property can be highly correlated with the surface characteristic of each component of the compound powders. Based on the experimental work, the appropriate fractions of the components in these compounds, especially the optimum content of SF, have been suggested for improving rheological property of HPC.     

Miscibility study of polymer blends composed of semirigid thermotropic liquid crystalline polycarbonate,poly(vinyl alcohol), and chitosan

Miscibility of binary and ternary polymer blends composed of thermotropic liquid crystalline polycarbonate (LCPC), poly(vinyl alcohol) (PVA), and chitosan was investigated by viscosity method, FTIR spectrum, and scanning electron microscope techniques. Effect of addition of chitosan as a compatibilizer on miscibility and morphology of binary LCPC/chitosan and PVA/chitosan and ternary LCPC/PVA/chitosan polymer blends was discussed. These measurements indicated that addition of chitosan into the blends of LCPC with PVA leads to an increase of miscibility and a formation of clear fibril structures on fractured surfaces, which are due to intermolecular hydrogen‐bonding interaction between LCPC, PVA, and chitosan chains. It was suggested that side‐chain hydroxy group of PVA and amino and hydroxy groups of chitosan play an important role in the formation of miscible phase and improvement of morphology in binary and ternary blends composed of LCPC, PVA, and chitosan. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1616–1622, 2004     

X-Ray Detected Magnetic Resonance at Sub-THz Frequencies Using a High Power Gyrotron Source

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy which makes use of X-ray Magnetic Circular Dichroism (XMCD) to probe the resonant precession of local magnetization components in a strong microwave pump field. In Sections?1 and 2, we briefly review the conceptual bases of XDMR and the potential interest of increasing the pumping frequency up to the THz frequency range. In Sections?3–5, we discuss the feasibility of such challenging experiments. Starting from a comparison of experiments carried out either in the transverse (TRD) or longitudinal (LOD) detection geometries, we show that XDMR measurements at sub-THz frequencies require a substantial increase in pumping power: this is where a gyrotron source looks most appropriate. It is the aim of this paper to discuss how to conduct such experiments, emphasis being laid on feasibility tests recently carried out at the ESRF using a refurbished version of Gyrotron FU-II built at the FIR-FU. In this context, we propose a new detection scheme of sub-THz XDMR spectra based on the concept of frequency-mixing in LOD geometry.