Internal friction of hydrogen-doped metallic glasses of high glass forming ability

Seven multi-component metallic glasses of high glass forming ability (four Zr-based, a Mg-based, a Pd-based and a La-based glasses) have been hydrogenized electrolytically and internal friction has been measured at temperatures between 80 and 400 K. Hydrogen damping has been observed in every alloy; the internal friction peak is quite broad, where the peak value increases and then decreases and the peak temperature decreases with increasing hydrogen content. Compared with the results of the hydrogen damping in binary metallic glasses so far reported, the peak height versus peak temperature relation is generally shifted to higher temperature side in multi-component glasses, the origin of which has been discussed.     

Development of a desktop swarm robot system based on pheromone communication

Complex and adaptive population behavior emerges in social insects. In ants, in particular, pheromone communication is the key to understanding their swarm intelligence. This article proposes a swarm robot system based on pheromone communication, and reports on the current status of the development of our robot system. We believe that the system could be used in swarm robotics and complex systems education.     

Distribution and enumeration of attractors in probabilistic boolean networks

Many mathematical models for gene regulatory networks have been proposed. In this study, the authors study attractors in probabilistic Boolean networks (PBNs). They study the expected number of singleton attractors in a PBN and show that it is (2 - (1=2)/sup L-1)/sup n/, where n is the number of nodes in a PBN and L is the number of Boolean functions assigned to each node. In the case of L = 2, this number is simplified into 1.5/sup n/. It is an interesting result because it is known that the expected number of singleton attractors in a Boolean network (BN) is 1. Then, we present algorithms for identifying singleton and small attractors and perform both theoretical and computational analyses on their average case time complexities. For example, the average case time complexities for identifying singleton attractors of a PBN with L = 2 and L = 3 are O(1.601/sup n/) and O(1.763/sup n/), respectively. The results of computational experiments suggest that these algorithms are much more efficient than the naive algorithm that examines all possible 2/sup n/ states.     

Response characteristics of all-solid-state pH sensor using Li5YSi4O12 glass

A new type of all-solid-state pH sensor was investigated for the monitoring of pH in high temperature. The all-solid-state pH sensor consists of two half-cells: indicator electrode using the Li₅YSi₄O₁₂ glass and an Ag/AgCl reference electrode coated with Nafion film. A stable Nafion film was achieved by heat treating at 100 °C for 1 h. The electromotive force (EMF) of the all-solid-state pH sensor decreased linearly with pH increase in water in accordance with the Nernst's equation. The all-solid-state pH sensor operated stably up to 80 °C. The sensitivity of the all-solid-state pH sensor against pH was high, and the EMF was also scarcely influenced by the presence of inorganic ions such as Li⁺, Na⁺ and Cl⁻. It was practically confirmed by the pH titration test that the all-solid-state pH sensor behaved similar to the commercial pH meter with the conventional glass electrode. In addition, the all-solid-state pH sensor showed same equivalence point both at high temperature and low temperature operations.     

Microstructural Characterization of High-Thermal-Conductivity Aluminum Nitride Ceramic

An aluminum nitride (AlN) ceramic with a thermal conductivity value of 272 W·(m·K)⁻¹, which is as high as the experimentally measured thermal conductivity of an AlN single crystal, was successfully fabricated by firing at 1900°C with a sintering aid of 1 mol% Y₂O₃ under a reducing N₂ atmosphere for 100 h. Oxygen concentrations were determined to be 0.02 and 0.03 mass% in the grains and in the grain-boundary phases, respectively. Neither stacking fault in the grains nor crystalline phase in the grain-boundary regions was found by transmission electron microscopy. An amorphous phase possessing yttrium and oxygen elements was detected between the grains as thin films with a thickness of <1 nm. Because the amount of grain-boundary phase was small, the high-thermal conductivity of the ceramic was attributable to the low oxygen concentration in the AlN grains.     

Sintering chemical reactions to increase thermal conductivity of aluminium nitride

Chemical reactions to increase thermal conductivity by decreasing oxygen contents during AlN sintering with an Y₂O₃ additive in a reducing nitrogen atmosphere with carbon were investigated. They were: Al₂O₃ + N₂ + 3CO ⇋ 2AlN + 3CO₂, Al₂Y₄O₉ + N₂ + 3CO ⇋ 2AlN + 2Y₂O₃ + 3CO₂ and Y₂O₃ + N₂ + 3CO ⇋ 2YN + 3CO₂. Some of the CO₂ gas reduced to CO gas in the presence of carbon by a chemical reaction: CO₂ + C ⇋ 2CO. These reactions were confirmed by examining oxygen contents, the grain boundary phases of the sintered AlN, and the trapped CO and CO₂ gases in the sintered bodies. These reducing reactions proceed with increasing sintering temperature and periods, and hence the thermal conductivity is increased.     

123I-MIBG myocardial scintigraphy in diabetic patients: relationship with 201Tl uptake and cardiac autonomic function

The purpose of this study is to investigate the effects of aging on the human stretch reflexes. The EMG and torque responses of the stretch reflex of the wrist flexors were evoked by ramp-and-hold mechanical perturbations. The stretch reflexes were recorded at seven test conditions with different stretch velocity and muscle preload. The test results from young and older healthy adult subjects were compared. In average, the absolute amplitude of the short-latency (20-40 ms) EMG (recorded from flexor carpi radialis) reflex response was significantly lower in the older group. If the data were normalized and expressed in percentage of the maximal voluntary EMG activity, however, this group difference was not significant. There was no change in the reflex gain of the short-latency reflex with aging. For the long-latency (50-90 ms) EMG reflex response, both the normalized amplitude and the reflex gain were significantly enhanced with aging, probably through supraspinal mechanisms. There was no significant difference in the threshold velocity for the evoked EMG reflexive activities between age groups. There were also no changes in the reflexive wrist flexion torque with aging. These results suggested that the number of motor units recruited during the stretch reflex activity declined with aging although the percentage of motor units recruited was not affected by aging. It is concluded that the central regulating mechanisms of the spinal motoneuron excitability are not compromised by aging. The automatic gain compensation phenomenon is also preserved with aging.     

Zn2+对MnZn铁氧体结构、磁性能和磁热效应的影响

采用溶胶-凝胶自燃烧法制备了不同Zn2 含量的纳米MnZn铁氧体微粒,并通过XRD、VSM、TEM等方法研究了Zn2 含量对MnZn铁氧体结构、磁性能及在外磁场作用下磁热效应的影响.结果表明,Zn2 含量对MnZn铁氧体的结构与性能有重要的影响,其中成分为Mn0.8Zn0.2Fe2O4的铁氧体微粒,具有最高的饱和磁化强度和磁热效应,10mg的该样品在频率为60kHz的外磁场诱导下,20min内使得1ml去离子水升温了32℃,显示出优良的磁热性能.同时,通过调节Zn2 含量实现了MnZn铁氧体发热量的可调性.随着Zn2 含量的增加,Mn1-xZnxFe2O4的矫顽力Hc和剩余磁化强度Br不断减小,而饱和磁化强度Ms先增大后减小,在x=0.2处达到最大值,约为44.6(A·m2)/kg.     

Gigacycle fatigue data sheets for advanced engineering materials

Gigacycle fatigue data sheets have been published since 1997 by the National Institute for Materials Science. They cover several areas such as high-cycle-number fatigue for high-strength steels and titanium alloys, the fatigue of welded joints, and high-temperature fatigue for advanced ferritic heat-resistant steels. Some unique testing machines are used to run the tests up to an extremely high number of cycles such as 10¹⁰ cycles. A characteristic of gigacycle fatigue failure is that it is initiated inside smooth specimens; the fatigue strength decreases with increasing cycle number and the fatigue limit disappears, although ordinary fatigue failure initiates from the surface of a smooth specimen and a fatigue limit appears. For welded joints, fatigue failure initiates from the notch root of the weld, because a large amount of stress is concentrated at the weld toe. The fatigue strength of welded joints has been obtained for up to 10⁸ cycles, which is an extremely high number of cycles for large welded joints. The project of producing gigacycle fatigue data sheets is still continuing and will take a few more years to complete.     

Influence of substrate orientation on low-temperature epitaxial growth of ferromagnetic silicide Fe3Si on Si

Influence of substrate orientation on epitaxial growth of the ferromagnetic silicide Fe₃Si on Si was investigated using low temperature (60-300 °C) molecular beam epitaxy. Transmission electron microscopy (TEM) measurements revealed that Fe₃Si layers were epitaxially grown on Si(110) and Si(111), while random poly-crystal Fe₃Si layers were formed on Si(100). From the Rutherford backscattering spectroscopy measurements, the values of the χ_min of the Fe₃Si layers grown at 60 °C on Si(100), Si(110), and Si(111) were evaluated to be 100%, 97%, and 41%, respectively. This dependence on the substrate orientation was explained on the basis of the atomic alignments at the Fe₃Si/Si interfaces.