Strong Surface‐Termination Effect on Electroresistance in Ferroelectric Tunnel Junctions

Tunnel electroresistance in ferroelectric tunnel junctions (FTJs) has attracted considerable interest, because of a promising application to nonvolatile memories. Development of ferroelectric thin‐film devices requires atomic‐scale band‐structure engineering based on depolarization‐field effects at interfaces. By using FTJs consisting of ultrathin layers of the prototypical ferroelectric BaTiO₃, it is demonstrated that the surface termination of the ferroelectric in contact with a simple‐metal electrode critically affects properties of electroresistance. BaTiO₃ barrier‐layers with TiO₂ or BaO terminations show opposing relationships between the polarization direction and the resistance state. The resistance‐switching ratio in the junctions can be remarkably enhanced up to 10⁵% at room temperature, by artificially controlling the fraction of BaO termination. These results are explained in terms of the termination dependence of the depolarization field that is generated by a dead layer and imperfect charge screening. The findings on the mechanism of tunnel electroresistance should lead to performance improvements in the devices based on nanoscale ferroelectrics.     

Reusable Floating Beads with Immobilized Xylose-Fermenting Yeast Cells for Simultaneous Saccharification and Fermentation of Lime-Pretreated Rice Straw

Novel bioreactor beads for simultaneous saccharification and fermentation (SSF) of lime-pretreated rice straw (RS) into ethanol were prepared. Genetically modified Saccharomyces cerevisiae cells expressing genes encoding xylose reductase, xylitol dehydrogenase, and xylulokinase were immobilized in calcium alginate beads containing inorganic lightweight filler particles to reduce specific gravity. For SSF experiments, the beads were floated in slurry composed of lime-pretreated RS and enzymes and incubated under CO₂ atmosphere to reduce the pH for saccharification and fermentation. Following this reaction, beads were readily picked up from the upper part of the slurry and were directly transferred to the next vessel with slurry. After 240 h of incubation, ethanol production by the beads was equivalent to that by free cells, a trend that was repeated in nine additional runs, with slightly improved ethanol yields. Slurry with pre-saccharified lime-pretreated RS was subjected to SSF with floating beads for 168 h. Although higher cell concentrations in beads resulted in more rapid initial ethanol production rates, with negligible diauxic behavior for glucose and xylose utilization, no improvement in the ethanol yield was observed. A fermentor-scale SSF experiment with floating beads was successfully performed twice, with repeated use of the beads, resulting in the production of 40.0 and 39.7 g/L ethanol. There was no decomposition of the beads during agitation at 60 rpm. Thus, this bioreactor enables reuse of yeast cells for efficient ethanol production by SSF of lignocellulosic feedstock, without the need for instruments for centrifugation or filtration of whole slurry.     

Oxygen-Deficient Anatase Precipitated from High-Temperature Plasma

Feeding atomized aqueous solutions containing TiCl₄ into an argon high-temperature inductively coupled plasma (ICP) resulted in the formation of mixtures of white and blue particles. The mixtures consisted of anatase and an extra phase of rutile. Adding oxygen to the ICP led to the production of a single phase of white anatase. The blue particles could be characterized as oxygen-deficient anatase. Electrophoretic mobility measurements indicated that Na+ participated in determining the surface potential of the mixtures. The oxygen defects may provide the adsorption sites to Na+.     

Superconducting telecommunication cable studies in Japan

Large capacity and long distance telecommunications media are fields in which full use of the excellent properties of superconducting coaxial cables may be applied. By employing a new conductor structure, characteristics of a 1.6 mm miniature superconducting coaxial pair were remarkably improved in a short time. Features such as low-loss (of the order of 1 dB km^?1 at 1 GHz), broad-band and low cross-talk etc. were demonstrated for these coaxial pairs.In cryogenic envelope studies, the 20–200 m long envelopes have been manufactured for evaluating thermal insulation and investigating cable cooling performance. Cooling experiments on the envelope, including cable splice, are now in progress.     

Ultrasonic attenuation monitoring of fatigue damage in low carbon steels with electromagnetic acoustic resonance (EMAR)

We studied microstructure evolution during tension-compression fatigue in low carbon steels, containing C: 0.15 mass%. In situ monitoring of axial-shear-wave attenuation and velocity was achieved with electromagnetic acoustic resonance (EMAR), which is a combination of the resonant spectroscopy technique and a noncontacting electromagnetic acoustic transducer (EMAT). Transduction occurs with the magnetostriction effect and is the key to establish a continuous monitoring of microstructural changes in the surface region of the metals with high sensitivity. We found for the first time that the attenuation is highly sensitive to the accumulated fatigue damage, showing a minimum around 20% of the whole life. This phenomenon is interpreted in terms of drastic change of dislocation mobility and rearrangement, which is supported by TEM observation for dislocation structure. This technique has the potential to assess the damage advance and to predict the fatigue life of metals.     

固溶处理对添加Si的Cu-10Ni-8Sn合金胞状沉淀的影响

利用定量金相的方法,研究了固溶-退火条件(温度和时间)对添加0.2%Si的Cu-10Ni-8Sn合金450℃时效时晶界处胞状物的形核与长大的影响.在450℃时效过程中,基体的硬度几乎不受固溶-退火条件的影响.然而,时效过程中固溶-退火条件对胞状物的形核与长大的影响却非常显著.当固溶-退火温度或时间增加时,Si对于胞状沉淀的抑制作用下降.随固溶-退火温度或者时间的增加,淬火态样品中存在于基体晶粒和晶界上的Ni31Si12相颗粒被粗化.因此,可以认为,经较高温度或较长时间固溶-退火的样品时效时,Ni31Si12相颗粒占据胞状物在晶界上的形核位置并抑制胞状物前沿界面迁移的作用降低了.     

Effects of the additions of B,P, dSn,and Sb on oxygen assisted hydrogen embrittlement of nickel

Effects of additions of B, P, Sn, and Sb on hydrogen embrittlement of nickel were examined on specimens cathodically charged with hydrogen. Tensile specimens were annealed either in vacuum or in a dry hydrogen gas. Undoped, Sn-doped, and Sb-doped materials annealed in vacuum revealed high susceptibility to intergranular hydrogen embrittlement, while the susceptibility was greatly reduced when the materials were annealed in hydrogen. The deleterious effect of vacuum annealing was proposed to result from grain boundary penetration of oxygen from the annealing environment. Additions of a small amount of B and P almost completely suppressed the IGHE of specimens annealed in vacuum. It is suggested that the effect of these elements on grain boundary penetration of oxygen is an important factor for their beneficial effects on IGHE. Addition of Sn somewhat increased the ductility of hydrogen charged specimens annealed both in vacuum and in hydrogen, indicating that this element is not deleterious. Addition of Sb increased the embrittlement susceptibility of specimens annealed in hydrogen. However, the deleterious effect of Sb was not serious in spite of the high concentration of Sb that was examined.