Mechanical alloying in the Al-Bi alloy system

Mechanical alloying (MA) was carried out to investigate the MA behaviour of the immiscible Al-10, 30 at % Bi alloys. After the MA processing, the Al and Bi were finely and homogeneously alloyed. The Bi crystallite size decreased to 25 nm and 30 nm in the Al-10 at % Bi and Al-30 at % Bi alloys, respectively. By increasing the MA time, the hardness increased up to a value of 80 H _v, which is larger than that obtained from the rule of mixtures. The lattice parameter of Bi decreased by about 0.27%, which shows the formation of a non-equilibrium hcp Bi super-saturated solid solution. The extended solubility of Al in Bi was 1.9% in the Al-30 at % Bi alloy. Due to the extended solubility, depression of the melting temperature of hcp Bi was confirmed in the mechanically alloyed Al-Bi alloys. The maximum depression in the temperature was about 10 K. The measured values corresponded well with those estimated from the extrapolation of the solidus line.     

Characterization of AlGaAs microstructure fabricated by AlGaAs/GaAsmicromachining

An AlGaAs/GaAs micromachining technique that is compatible with laser diode fabrication process is described. AlGaAs structural layers and GaAs sacrificial layers are prepared by metal organic vapor phase epitaxy. Reactive dry etching with chlorine is used to fabricate high-aspect structures. Peroxide/ammonium hydroxide solution is used for selective etching of the sacrificial layer. Since the epitaxial layer has low stress, precise undeformed microstructures are obtained. Good compatibility with the LD process makes it possible to integrate microcantilever beams with LD's without degradation of LD characteristics. Microcantilever beams of AlGaAs are characterized by directly measuring stiffness and natural frequencies. A fracture test is also performed on the AlGaAs microcantilever beams. The average fracture stress of AlGaAs is found to be 1 GPa at 1% strain, which shows that the material is strong enough to support the micrometer scale structures     

Rupture nucleation on an interface with a power-law relation between stress and displacement discontinuity

We consider rupture initiation and instability on a displacement-weakening interface. It is assumed to follow a power-law relation between a component of displacement discontinuity (whether tensile opening in mode I or shear slippage in modes II or III) and the reduction from peak strength of a corresponding component of stress (normal or shear stress) on the interface. That is, the stress decrease from peak strength, as the interface discontinuity develops, is assumed to be proportional to displacement-discontinuity to some exponent n > 0. The study is done in the 2D context of plane or anti-plane strain, for an initially coherent interface which is subjected to a locally peaked “loading” stress which increases quasi-statically in time. We seek to establish the instability point, when no further quasi-static solution exists for growth of the ruptured zone along the interface, so that dynamic rupture ensues. We have previously addressed the case of linear displacement-weakening (n = 1), and proven the remarkable result that for an unbounded solid, the length of the displacement-weakening zone along the interface at instability is universal, in the sense of being independent of the detailed spatial distribution of the locally peaked loading stress. Present results show that such universality does not apply when n differs from 1. Also, if n < 2/3, there is no phase of initially quasi-static enlargement of the rupturing zone; instead instability will occur as soon as the maximum value of the loading stress reaches the peak strength. We first employ an energy approach to give a Rayleigh–Ritz approximation for the dependence of quasi-static rupture length and maximum displacement-discontinuity on the loading stress distribution of a quadratic form. Results, depending on curvature of the loading distribution, show that qualitative features of the displacement-discontinuity development are significantly controlled by n, with the transition noted at n = 2/3. Predictions of the simple energy approach are in reasonable quantitative agreement with full numerical solutions and give qualitative features correctly.     

The relation between stress and particle velocity for Rayleigh pulses

Summary In this note, the relationship between the stress and the particle velocity for Rayleigh pulses which propagate along a free surface of an elastic isotropic half-space is discussed.Dedicated to Prof. Dr. Dr. h. c. Franz Ziegler on the occasion of his 60^th birthday     

Design, fabrication, and evaluation of crystal-cored fibers for efficient second-harmonic generation based on Cerenkov-radiation-type phase matching

A formulation for calculating the optical second-harmonic power based on the Cerenkov-radiation-type phase matching is derived for a crystal-cored fiber. The prerequisite condition for high efficiency is expressed by a simple relation by use of the refractive indices of a core crystal, a core radius, and a fundamental wavelength. An organic crystal-cored fiber is designed and practically fabricated by the guiding principle derived here. A blue second-harmonic wave of 1.4 mW is obtained from a 1-mm-long fiber by use of a 60-mW semiconductor laser, and the second-harmonic intensity agrees well with the prediction. Degradation of the organic core crystal caused by the generated blue wave is observed, and the lifetime of the device is evaluated.     

Anionic alternating copolymerization of epoxide and 3,4‐dihydrocoumarin and its application to networked polymers

3,4‐Dihydrocoumarin (DHCM) is an aromatic six‐membered lactone, which does not undergo anionic homopolymerization. However, it does undergo copolymerization with an epoxide. The striking feature of this copolymerization is its 1:1 alternating nature, which allows for the formation of polyesters. In this mini‐review, we describe the copolymerization behavior, the polymer structure and the advantages that can be achieved by addition of DHCM to the epoxy‐imidazole curing system. Another focus is our development of DHCM analogues, which bring the advantages of DHCM to their applications as comonomers for the curing system. Copyright © 2009 Society of Chemical Industry     

Effect of sulfhydryl oxidoreduction on permeability of cardiac tetrodotoxin-insensitive sodium channel

Effects of sulfhydryl oxidizing and reducing agents on permeability of the tetrodotoxin (TTX)-insensitive Na-channel were investigated in guinea-pig ventricular myocytes using the whole-cell patch-clamp technique. Mercury chloride (HgCl2) at 1-100 microM irreversibly blocked Na+ currents with no significant changes in the gating kinetics. In contrast, the hydrophilic sulfhydryl oxidizing agent, thimerosal at 50-100 microM little affected Na+ permeation through the Na-channel. The Hg2+-induced block of Na+ current could be readily reversed by 1,4-dithiothreitol (DTT), an agent that reduces disulfide bonds. These results indicate that the formation of sulfur-Hg-sulfur bridge is essential for Hg2+ block. Pretreatment with DTT prevented the Hg2+ block of Na+ current, whereas Zn2+ and Cd2+ retained their abilities to block Na+ current after DTT treatment. An application of Zn2+ or Cd2+ resulted in the restoration of Hg2+ sensitivity of the DTT-treated channel. A conformational model for the Na-channel with multiple free sulfhydryl groups and native disulfide bonds could account for our experimental data regarding the effects of sulfhydryl modifying agents on the channel permeability. We conclude that the cardiac TTX-insensitive Na-channel contains functionally important free sulfhydryl groups and disulfide bonds which are accessible from the extracellular side by an aqueous pathway. These sulfhydryls would be capable of modulating the Na-channel permeability by affecting the conformation of channel pore region.     

An experimental and numerical study on the forward biased SOA ofIGBTs

Thermal and electrical destructions of n-ch 600 V punchthrough type IGBTs in F.B.SOA are investigated by experiments and simulations, The cause of the thermal destruction is the thermal disappearance of built-in potential of p-n junction between the n⁺ emitter and the p base of the IGBT integral DMOSFET occurring at the critical temperature of ~650 K. Experiment and simulation results for the critical temperature show a good agreement. The cause of the electrical destruction is impact ionization at the n^- drift/n⁺ buffer junction in addition to the n^- drift/p base junctions. That triggers a positive feedback mechanism of increasing IGBT integral pnp transistor current which causes the device to lose gate controllability. The experimentally obtained critical power dissipation is ~2000 kW/cm². This value is ten times greater than BJTs. It was also found that emitter ballast resistance (EBR) plays an important role in describing the F.B.SOA of IGBTs     

Gas permeability of thin dense films from polymer blend of thermoplastic elastomer and polyolefin

Stretched thin films composed of a thermoplastic elastomer, a polystyrene‐block‐poly(ethylene butylene)‐block‐polystyrene triblock copolymer (SEBS), and polyolefins, poly(ethylene‐co‐ethylacrylate) and poly(ethylene‐co‐propylene), were obtained by blow‐molding, uniaxial stretching, and cooling to room temperature and the gas permeability of the stretched films was investigated. When the as‐blown annealed film was subjected to uniaxial stretching in the machine direction, P_O2 and P_N2 increased with an increase in the stretching ratio K and approached a constant value at high stretching ratios. In addition, P_O2/P_N2 decreased gradually with K and approached a value of 2.95–3.0. The reason for this unique gas permeation behavior is that the molecular mobility of poly(ethylene butylene) chains in a direction normal to the film increases and reaches an equilibrium state at around K = 4.5. The change in gas permeability of the stretched films can be explained using a deformation model for the SEBS matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39386.     

Accuracy of land cover area estimated from coarse spatial resolution images using an unmixing method

Many techniques intended to estimate land coverage of multiple categories occupied within each pixel from such coarse resolution data have been proposed. However, in traditional unmixing studies with coarse resolution imagery such as Advanced Very High Resolution Radiometer (AVHRR) data, it is assumed that only a few endmembers exist throughout an entire image. Therefore, it is essential to evaluate how well an unmixing method would work for various categories within pixels of coarse resolution images. In this study, the land coverage of eight classes in National Oceanic and Atmospheric Administration (NOAA) AVHRR imagery by using finer resolution Landsat Thematic Mapper (TM) imagery was estimated, and the accuracy of these estimated classes was evaluated. The results suggest that this method may be generally useful for comparing multi-spectral images in space and time.