连铸新技术

非金属夹杂物、偏析和裂纹是连铸坯的三大主要质量问题.这些问题会影响金属收得率和产量.在结晶器采用电磁搅拌和电磁闸可以控制结晶器流场,从而有利于夹杂物上浮.此外,采用电磁结晶器可以防止振痕的产生,从而改善铸坯的表面质量.通过控制非金属夹杂物的化学成分,可以减少夹杂物对钢帘线、不锈钢丝等材料的负面影响,可以采用低温浇注、轻压下和电磁搅拌降低中心偏析.     

Characteristics of Strontium Aluminate Crystals Used for Long-Duration Phosphors

Sr₃Al₂O₆, SrAl₂O₄, SrAl₄O₇, and SrAl₁₂O₁₉ that have been doped with Eu²⁺ and Dy³⁺ ions have been grown by a floating-zone technique for application as long-duration phosphors. Long-duration phosphorescence with a variety of colors has been observed in SrA_l2O₄, SrAl₄O₇, and SrAl₁₂O₁₉ crystals that have been doped with Eu²⁺ and Dy³⁺ ions. The peak wavelength of the phosphorescence is 520 nm for SrAl₂O₄, 480 nm for SrAl₄O₇, and 400 nm for SrAl₁₂O₁₉. The phosphorescence is characterized by decay times that have been analyzed by a curve-fitting technique.     

LiNbO3 optical intensity modulator packaged with monitorphotodiode

The assembly technique to simply install a monitor photodiode (PD) with a LiNbO₃ (LN) Mach-Zehnder modulator in the same package is proposed. A light radiated from the Mach-Zehnder Y-branch toward the LN output facet is lead into a glass bead, which is bonded to the LN facet as a fixture of the optical fiber. The end of the glass bead is cut to have an angled face, and the radiated light is reflected normal to the LN waveguide axis and toward the PD fixed on the side of package. The curved surface of the glass bead is effective to roughly focus the light onto the PD. We demonstrate that such monitor PD outputs an intensity modulation exactly reverse to the LN output modulation with a sensitivity higher than 0.03 A/W per optical output power of LN, indicating a usability of the PD output to monitor the drift of LN modulator     

Evaluation of D(d,n)3 He reaction neutron source models for BNCT irradiation system design

A mathematical method was developed to calculate the yield,energy spectrum and angular distribution of neutrons from D(d,n)~3He(D-D)reaction in a thick deuterium-titanium target for incident deuterons in energies lower than 1.0MeV.The data of energy spectrum and angular distribution were applied to set up the neutron source model for the beam-shaping-assembly(BSA)design of Boron-Neutron-Capture-Therapy(BNCT)using MCNP-4C code. Three cases of D-D neutron source corresponding to incident deuteron energy of 1000,400 and 150 key were inves- tigated.The neutron beam characteristics were compared with the model of a 2.45 MeV mono-energetic and isotropic neutron source using an example BSA designed for BNCT irradiation.The results show significant differences in the neutron beam characteristics,particularly the fast neutron component and fast neutron dose in air,between the non-isotropic neutron source model and the 2.5 MeV mono-euergetic and isotropic neutron source model.     

Transitional processes of flow and heat transfer in a circular pipe with short static mixer

The transitional processes of flow and heat transfer in a circular pipe fitted with a short static mixer were studied with Newtonian and pseudoplastic fluids. An experimental formula, which was derived from the same concept as a well-known transition model of boundary layer flow on a flat plate, coincided well with the experimental results of friction and heat transfer. The transitional Reynolds number for heat transfer was larger than that for flow for both fluids. In heat transfer experiments, the transitional Reynolds number for a pseudoplastic fluid was smaller than that for a Newtonian fluid, and heat transfer augmentation in the transitional region was larger in a pseudoplastic fluid than in a Newtonian fluid. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res 25(4): 254–266, 1996     

Glucose Stimulates Glial Cell Line-Derived Neurotrophic Factor Gene Expression in Microglia through a GLUT5-Independent Mechanism

Feeding-regulating neurotrophic factors are expressed in both neurons and glial cells. However, nutritional regulation of anorexigenic glial cell line-derived neurotrophic factor (GDNF) and orexigenic mesencephalic astrocyte-derived neurotrophic factor (MANF) expression in specific cell types remains poorly understood. Hypothalamic glucose sensing plays a critical role in the regulation of food intake. It has been theorized that local glucose concentration modulates microglial activity partially via glucose transporter 5 (GLUT5). We hypothesized that an increased local glucose concentration stimulates GDNF expression while inhibiting MANF expression in the hypothalamus and microglia via GLUT5. The present study investigated the effect of glucose on Gdnf and Manf mRNA expression in the mouse hypothalamus and murine microglial cell line SIM-A9. Intracerebroventricular glucose treatment significantly increased Gdnf mRNA levels in the hypothalamus without altering Manf mRNA levels. Exposure to high glucose caused a significant increase in Gdnf mRNA expression and a time-dependent change in Manf mRNA expression in SIM-A9 cells. GLUT5 inhibitor treatment did not block glucose-induced Gdnf mRNA expression in these cells. These findings suggest that microglia are responsive to changes in the local glucose concentration and increased local glucose availability stimulates the expression of microglial GNDF through a GLUT5-independent mechanism, contributing to glucose-induced feeding suppression.     

Electrical and Optical Properties of Conducting Polymer - Fullerene and Conducting Polymer - Carbon Nanotube Composites

Various novel photo-physical properties such as a drastic photoluminescence quenching and photoconductivity enhancement and a photo-induced enhancement of low-field microwave absorption due to a highly effective photo-induced electron transfer have been observed in various conducting polymers doped with fullerenes and also acceptor-type molecules and conducting polymers. New types of junction devices utilizing effective charge separation at the interface of conducting polymer/C₆₀, C₆₀-doped conducting polymer/C₆₀ and acceptor type conducting polymer / donor type conducting polymer have been proposed and their novel characteristics have been demonstrated. Novel concepts such as an interpenetrating network, a condensed interface and the effect of introduction of photo-harvesting antenna molecule at the interface have been discussed. Nano-composite films of carbon nanotube (NT) and conducting polymer were prepared. With increasing the volume fraction of NT in conducting polymer the conductivity increases drastically at relatively low concentration of NT, which can be explained in terms of conduction by percolation process. Enhancement of photoconductivity of composite films has been found at near percolation threshold. Heterojunctions made of carbon NT and conducting polymer have also been found to be photosensitive.     

Superplasticity of Hot Isostatically Pressed Hydroxyapatite

Dense and translucent hydroxyapatite polycrystals (Ca₁₀(PO₄)₆(OH)₂ with a grain size of 0.64 μMm) were obtained by hot isostatic pressing at 203 MPa and 1000°C for 2 h in argon. The material exhibited superplastic elongation (>150%) in a tension test at temperatures from 1000° to 1100°C and at strain rates from 7.2×10⁻⁵ to 3.6 × 10⁻⁴ s⁻¹. Extensive strain hardening was observed. The stress exponent of the yield stress was larger than 3.     

Application of channel flow double electrode to the study on platinum dissolution during potential cycling in sulfuric acid solution

The applicability of a channel flow double electrode (CFDE) as an in situ monitoring method of Pt dissolution during potential cycling in 0.5 M H₂SO₄ solution at 25 °C was investigated. In the CFDE, Pt ions (Ptⁿ⁺) dissolved from a platinum working electrode were detected by reducing them to Pt on a gold collector electrode which was placed at the downstream. The detection of the Pt dissolution by the collector current was confirmed by EPMA analysis of the collector electrode surface. In anodic scan, a rise of the collector current above 1.05 V clearly indicated the platinum dissolution. The collector current showed two different rates of dissolution, i.e. a lower rate from 1.05 to 1.3 V where only one layer of oxide (PtO) is formed and the higher rate from 1.3 to 1.46 V where two layers of oxides (probably PtO/PtO₂) are formed. The collector current, in the cathodic scan, clearly showed two different reduction peaks due to the Pt deposition, which was confirmed by EPMA analysis. On the basis of collector current, the rate and potential range of the Pt dissolution are discussed.     

纯铬钝化膜的电化学性能

本文用交流阻抗技术,通过对钝化铬在中性H₃BO₃+Na₂B₄O₇溶液中添加了K₃Fe₂(CN)₆/K₄Fe(CN)₆氧化还原对溶液中的极化性能及交流阻抗特性的研究,讨论了铬的钝化膜的电路模型。