Electrical characterization of homoepitaxial diamond p–n junction

Electrical properties of homoepitaxial diamond p–n⁺ junction of boron (B)-doped p-type layer and phosphorus-doped n-type layer on Ib (111) diamond single crystal have been characterized. Current–voltage characteristics show a clear rectifying property with rectification ratio of over 10⁵ at ± 10 V. From capacitance–voltage characteristics, it is found that a spatial distribution of space-charge density N_i of the p–n⁺ junction is not uniform and N_i at a middle region of the space-charge layer formed at zero bias voltage is higher than that of other region of the space-charge layer. This peculiar characteristic can be explained by superposition of two effects; one is the deep dopant effect due to B atoms in the p-type layer, which makes to reduce N_i at around the edge of the space-charge layer formed at zero bias voltage. The other is the compensation of B acceptors by impurity atoms diffusing during the p–n⁺ interface and incorporating during the growth of p-type layer, which makes to reduce N_i at the vicinity of the p–n⁺ interface.     

Structure and properties of injection‐molded polypropylenes with different molecular weight distribution and tacticity characteristics

Two series of polypropylenes with different molecular weight distribution and tacticity characteristics were injection molded into flexural test specimens by varying cylinder temperature and the effects of the molecular weight distribution and tacticity on the structure and properties of the moldings were studied. Measured propertied were flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and structures studied were crystallinity, the thickness of skin layer, a*‐axis‐oriented component fraction and crystalline orientation functions. The relations between the structures and properties were also studied. It was found that the molecular weight distribution and tacticity characteristics affect the properties mainly through the molecular orientation and crystallinity, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2142–2156, 2002     

The oxidation properties of fourth generation single-crystal nickel-based superalloys

The fourth-generation nickel-based single-crystal superalloys, which contain large amounts of refractory metals for strengthening and platinum group metals for topologically close-packed phase prevention, show excellent high-temperature strength. However, these alloying elements seem to decrease high-temperature oxidation resistance. In this study, nickel-based superalloys with various amounts of tantalum, rhenium, and ruthenium were examined in isothermal and cyclic exposures at 1,100°C to investigate the effect on the oxide growth rate and resistance to scale spallation. Ruthenium and rhenium were found to degrade the oxidation resistance by the vaporization of their oxide. Tantalum-rich oxide in the spinel layer acts to stabilize ruthenium and rhenium oxide in the scale. The addition of hafnium and yttrium is effective in improving the oxidation resistance of ruthenium-containing nickel-based superalloys.     

Simultaneous Perturbation Stochastic Approximation with Norm‐Limited Update Vector

This paper addresses the convergence of simultaneous perturbation stochastic approximation (SPSA) with a norm‐limited update vector. We first illustrate an unstable solution of the standard SPSA algorithm which motivates the consideration of a modified version, where the norm of the update vector is limited to a certain value. Next, a result on the almost‐sure convergence is presented by reducing the modified algorithm into the standard SPSA algorithm and restricting the probability distribution for the perturbation to a Bernoulli distribution. Finally, we apply the modified algorithm to a system identification problem to demonstrate its performance.     

Ergonomics solution for crossing collisions based on field assessment of visual environment at urban intersections in Japan

This paper aims to assess quantitatively the actual visual environment of uncontrolled urban downtown intersections in Japan in relation to frequently occurring crossing collisions and to discuss the safety countermeasures for them. In Field Study 1 dealing with direct visibility, our ultra-wide-angle photograph analysis revealed that most of the right/left-ward visible range at 11 intersections were insufficient to check safety, and the quality of direct visibility was closely associated with causing crossing collisions. The countermeasures to reduce a blind area were determined to be a top priority. In Field Study 2 dealing with indirect visibility, more than half of the 25 traffic convex mirrors had marked shortcomings for preventive safety, and ergonomics guidelines ensuring indirect visibility were proposed for installing traffic convex mirrors. Low-cost/low-technology-oriented countermeasures are highly recommended to obtain clear/sufficient images of crucial information satisfying drivers' requirements on traffic convex mirrors in accordance with those ergonomics guidelines was highly recommended. Crossing collisions could be prevented by improvement of poor direct and indirect visibility.     

Evaluation of absorption of micro-droplets on paper for creation of paper-based microstructures

This study clarifies the absorption behavior of micro-droplets of water on treated paper to support the design of functional microstructures, such as electronics and micro-fluid channels, on paper. The period of time between when a micro-droplet of water ejected from an ink-jet head lands on the paper’s surface and its complete disappearance by absorption was defined as the micro-sizing degree (MSD), and an MSD measurement method was established. The MSD was evaluated using microscopic high-speed video images of the side view recorded every millisecond. Several grades of commercially available ink-jet paper media and laboratory sheets having different levels of water repellency prepared from a pulp and a sizing agent were examined. The MSD of commercial ink-jet papers, which are known to absorb water very quickly, was 3–6 ms. Weakly sized laboratory sheets exhibited a lower MSD of 2–3 ms. The absorption behavior was analyzed in terms of the capillary pressure with and without the Laplace pressure; the theoretical and experimental results agreed moderately well. The results indicated that the Laplace pressure cannot be neglected in the analysis. The MSD of a wet surface where a preceding micro-droplet had already landed was higher than that on a dry or partially wet surface, presumably because water remains inside pores for an unexpectedly long time.     

Research and Development of the Coprecipitation Process for Lanthanum Germanate Oxyapatite

Although lanthanum germanate oxyapatite (La–Ge–O) has shown good potential for use as a solid electrolyte in energy storage applications, its synthesis has been challenging by either solid‐ or solution‐state methods. In this study, a new synthesis of La–Ge–O was developed through a coprecipitation technique, in which a highly concentrated homogeneous aqueous solution of La and Ge was prepared from aqueous ammonium germanate and lanthanum nitrate solutions with the addition of dilute nitric acid. Several precipitates were formed by pH manipulation, including an amorphous material obtained at pH > 3. Compared to the individual precipitation behaviors of the parent compounds, the amorphous precipitate was formed only from the aqueous two‐component mixture, and appeared to contain both metals. This material was transformed into crystalline mixtures upon heating at 1273 K. The crystalline phases were La₂Ge₃O₉ and hexagonal‐type GeO₂ when the precipitate was formed below pH 8, and the La–Ge–O and La₂Ge₂O₇ phases when the precipitate was formed around pH 8. Product formation from the coprecipitate was discussed based on X‐ray diffraction and thermal analyses. The improved availability of La–Ge–O will allow more extensive investigations of its useful properties.     

Enzymatic Analysis of Positional Distribution of Fatty Acids in Solid Fat by 1,3-Selective Transesterification with Candida antarctica Lipase B

A protocol for the analysis of the positional distribution of fatty acids (FA) in solid triacylglycerols (TAG) was developed using sn-1(3) selective alcoholysis catalyzed by immobilized Candida antarctica lipase B (CALB). One part by weight of solid fat and ten parts by weight of ethanol (99.5 %) were warmed to liquefy the fat. After adding 0.44 parts by weight of CALB, the mixture was shaken at 50 °C for 10 min then at 30 °C for 2.8 h. The recovery of 2-MAG after the 3-h transesterification reaction was ca. 85 % of the maximum theoretical yield (33 mol%), with the loss of 15 % attributable to the acyl migration from sn-2 to sn-1(3). The recovery was similar to that of the solvent-free alcoholysis of structured lipids, 1,3-dipalmitoyl, 2-oleoyl glycerol and 1,3-dioleoyl, 2-palmitoyl glycerol, conducted at 30 °C for 3 h. In contrast, the acyl migration from sn-1(3) to sn-2 was hardly observed. Because the detected acyl migration was only in the direction of sn-2 to sn-1(3), and not vice versa, it is proposed to determine the FA composition of the sn-2 position of TAG by the gas chromatographic analysis of 2-MAG fraction recovered from the enzymatic reaction mixture, and the FA composition of sn-1(3) position by a mass balance using the FA composition of TAG and of the sn-2 position as inputs. The procedure was successfully applied to palm oil and shea butter, and docosahexaenoic acid (DHA)-rich single cell oil from Aurantiochytrium sp. KH105 for the first time.     

Neuromelanin in Parkinson’s Disease: Tyrosine Hydroxylase and Tyrosinase

Parkinson’s disease (PD) is an aging-related disease and the second most common neurodegenerative disease after Alzheimer’s disease. The main symptoms of PD are movement disorders accompanied with deficiency of neurotransmitter dopamine (DA) in the striatum due to cell death of the nigrostriatal DA neurons. Two main histopathological hallmarks exist in PD: cytosolic inclusion bodies termed Lewy bodies that mainly consist of α-synuclein protein, the oligomers of which produced by misfolding are regarded to be neurotoxic, causing DA cell death; and black pigments termed neuromelanin (NM) that are contained in DA neurons and markedly decrease in PD. The synthesis of human NM is regarded to be similar to that of melanin in melanocytes; melanin synthesis in skin is via DOPAquinone (DQ) by tyrosinase, whereas NM synthesis in DA neurons is via DAquinone (DAQ) by tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). DA in cytoplasm is highly reactive and is assumed to be oxidized spontaneously or by an unidentified tyrosinase to DAQ and then, synthesized to NM. Intracellular NM accumulation above a specific threshold has been reported to be associated with DA neuron death and PD phenotypes. This review reports recent progress in the biosynthesis and pathophysiology of NM in PD.     

Simultaneous determination of five antioxidants in food by HPLC with fluorescence detection

An HPLC method with fluorescence detection was developed for the determination of propyl gallate, nordihydroguaiaretic acid, butylated hydroxyanisole (2- and 3-tert-butyl-4-hydroxyanisole), tert-butylhydroquinone and octyl gallate in edible oils and foods. The antioxidants in edible oil were isolated directly with acetonitrile saturated with n-hexane. The antioxidants in food were extracted with ethyl acetate and the extract was concentrated under vacuum. They were isolated from the residue with acetonitrile saturated with n-hexane. The acetonitrile layer was centrifuged at 5,000 rpm for 10 min. The HPLC separation was performed on a Symmetry C18 column (3.5 microns, 4.6 mm i.d. x 150 mm) using a mixture of 5% acetic acid-acetonitrile-methanol (4:3:3, v/v/v) as the mobile phase and monitored by using a fluorescence detector with time programming. Sample peaks were identified by comparison of the fluorescence spectra with those of antioxidant standards. Average recoveries of fortified antioxidants at 100 micrograms/g were 72.1-99.6%. Coefficients of variation were 0.7-7.2%.