Thermal stability of low-oxygen SiC fibers fired under different conditions

To fabricate the low-oxygen SiC fibers with excellent thermal stability, electron-beam irradiation polycarbosilane fibers were fired for holding time of 3.6, 18 and 36 ks at each temperature of 1273 to 1573 K, and subsequently the high-temperature exposure test was carried out at 1873 K. As-fired fibers and exposed fibers were characterized by thermogravimetry, chemical analysis, Auger electron spectroscopy, resistivity measurement and tensile test. The strength of both as-fired fibers and fibers exposed to 1873 K increased with prolonging the holding time of firing treatment below 1473 K. On the contrary, a long time firing treatment at 1573 K was no longer effective for the strengthening of the low-oxygen SiC fiber.     

Thermal Stability of Low-SiC Fiber (Hi-Nicalon) Treated in a Hot Isostatic Press

The low-oxygen SiC fiber fabricated by the electron-beam irradiation curing method, Hi-Nicalon, was heated at 1773 to 2273 K in a hot isostatic press (800 MPa of argon) and was subsequently reheated at 1873 K at 1 atm (101 kPa) of argon. The hot isostatic press treatment delayed the onset of fiber deterioration to higher temperature. The fiber strength remained almost unchanged by subsequent reheating at 1873 K in 101 kPa of argon. The thermal stability of Hi-Nicalon, as a consequence of the permanent change in surface structure, can be greatly improved by treating in the hot isostatic press.     

Modeling the forces of cutting with scissors

Modeling forces applied to scissors during cutting of biological materials is useful for surgical simulation. Previous approaches to haptic display of scissor cutting are based on recording and replaying measured data. This paper presents an analytical model based on the concepts of contact mechanics and fracture mechanics to calculate forces applied to scissors during cutting of a slab of material. The model considers the process of cutting as a sequence of deformation and fracture phases. During deformation phases, forces applied to the scissors are calculated from a torque-angle response model synthesized from measurement data multiplied by a ratio that depends on the position of the cutting crack edge and the curve of the blades. Using the principle of conservation of energy, the forces of fracture are related to the fracture toughness of the material and the geometry of the blades of the scissors. The forces applied to scissors generally include high-frequency fluctuations. We show that the analytical model accurately predicts the average applied force. The cutting model is computationally efficient, so it can be used for real-time computations such as haptic rendering. Experimental results from cutting samples of paper, plastic, cloth, and chicken skin confirm the model, and the model is rendered in a haptic virtual environment.     

Transparent biosensor with micro channel array for optical and electrophysiological detection of luciferin–luciferase reaction

This paper describes a transparent biosensor that was designed to detect both the optical and electrophysiological signals of the luciferin–luciferase reaction. By using microelectromechanical system (MEMS) technologies, we have studied and developed a ‘Micro Channel Array’ (MCA) integrated with suction holes and electrodes as planar patch‐clamp biosensors. A transparent biosensor was developed as an advanced MCA. The developed transparent biosensor employs an SU‐8‐based MCA structure for simultaneous multipoint sensing of optical and electrophysiological signals. In this study, we tested the newly developed biosensor using the mPer1‐luc slice culture, which has circadian rhythms and is a typical example of cells in which a luciferin–luciferase reaction occurs. We could measure the optical and electrophysiological signals of the mPer1‐luc slice culture. Here we describe the experimental results of this study, and describe the design and fabrication of the transparent biosensor with MCA. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Oxidation behavior of Si-M-C-O fibers under wide range of oxygen partial pressures

The active-to-passive oxidation transition for three types of Si-M-C-O fibers (Lox M, ZMI and SA) was examined at 1773 K and p _O2 = 1–25000 Pa through TG, XRD analysis, SEM observation and tensile tests. The p _O2 value of the active-to-passive oxidation transition for Lox M and ZMI fibers was between 100–250 Pa. While the strength of Lox M and ZMI fibers was considerably retained after passive-oxidation, it was markedly degraded after active-oxidation ( = 0 Gpa). For SA fibers, the passive-oxidation occurred even at p _O2 = 1 Pa, producing a very large decrease in the tensile strength.     

Oxidation behavior and thermal stability of Si-C-O fibers (Nicalon) in carbon dioxide

The oxidation behavior and thermal stability of Si-C-O fibers (Nicalon) in CO₂ gas were examined at 1273 to 1773 K through mass change determination, XRD analysis, resistivity measurement, SEM observation and tensile test. Large mass gains and SiO₂ film formation show that Nicalon fibers are passively oxidized in CO₂, as well as Si-C fibers (Hi-Nicalon). The grain growth of -SiC, the drop of resistivity and the crystallization of SiO₂ film were observed above 1573 K. On being oxidized at high temperature, the thermal decomposition of SiC _X O _Y and the formation of imperfections in SiO₂ film caused the degradation of the room-temperature tensile strength of both the as-oxidized fibers and unoxidized cores. It became evident that the oxygen partial pressure for the active-to-passive oxidation transition of Nicalon fibers is between 1.00 × 10² and 1.78 × 10² Pa at 1773 K.     

Mass screening for neuroblastoma at 6 months of age: difficult to justify

BACKGROUND/PURPOSE: A statistical analysis of the mass screening for neuroblastoma in Japan based on a population study rarely has been reported. This study aims to evaluate retrospectively the effectiveness of mass screening at 6 months of age using the available population data. METHODS: The data on the neuroblastoma cases registered by the Committee for Pediatric Solid Malignant Tumors in the Kyushu area were analyzed based on both screened and unscreened populations in the Kyushu area. RESULTS: From 1988 to 1992, the cumulative incidence of neuroblastoma in children less than 5 years of age was 82 in 484,599 for screened children, and 11 in 92,966 for unscreened children, respectively. Fourteen of the 82 screened patients had negative findings at 6 months of age (MS-negative cases). No significant difference was observed in the cumulative mortality rates from neuroblastoma in children younger than 5 years of age between the screened children and the unscreened children. Six of seven patients who died among the screened children were MS-negative cases with stage III or IV disease. In addition, no significant difference was found in the cumulative mortality rates from the neuroblastoma cases in patients less than 5 years of age between the children screened from 1988 to 1992 (7 of 484,599) and all children from 1980 to 1984 (14 of 668,084). CONCLUSIONS:These findings suggests that the majority of the patients detected by mass screening had a favorable prognosis, and, mass screening in Japan for children less than 6 months of age was not observed to reduce the incidence and mortality from neuroblastoma. Therefore, mass screening at 6 months of age was not found to improve substantially the prognosis of patients with unfavorable neuroblastoma identified over 1 year of age, which is the primary purpose of such mass screening for neuroblastoma.     

In vitro expansion of hematopoietic progenitor cells induces functional expression of Fas antigen (CD95)

Fas antigen (Fas Ag; CD95) is a cell surface molecule that can mediate apoptosis. Bcl-2 is a cytoplasmic molecule that prolongs cellular survival by inhibiting apoptosis. To investigate the role of both molecules in hematopoiesis, we evaluated the expression of Fas Ag and Bcl-2 on CD34+ hematopoietic progenitor cells expanded in vitro. CD34+ cells isolated from bone marrow were cultured in iscove's modified Dulbecco's medium supplemented with 10% fetal calf serum, 1% bovine serum albumin, 50 ng/mL stem cell factor, 50 ng/mL interleukin-3 (IL-3), 50 ng/mL IL-6, 100 ng/mL granulocyte colony-stimulating factor, and 3 U/mL erythropoietin for 7 days. Colony-forming unit of granulocytes/macrophages (CFU-GM) and burst-forming unit of erythroids (BFU-E) were expanded 6.9-fold and 8.8-fold in number at day 5 of culture, respectively. Freshly isolated CD34+ cells did not express Fas Ag, whereas approximately half of them expressed Bcl-2. CD34+ cells cultured with hematopoietic growth factors gradually became positive for Fas Ag and rapidly lost Bcl-2 expression. Furthermore, apoptosis was induced in the cultured CD34+ population when anti-Fan antibody (IgM; 1 microgram/mL) was added, as shown by significant decrease in the number of viable cells, morphologic changes, induction of DNA fragmentation, and significant decrease in the number of clonogenic progenitor cells including CFU. GM and BFU-E. These results indicate that functional expression of Fas Ag is induced on CD34+ cells expanded in vitro in the presence of hematopoietic growth factors. Induction of Fas Ag and downregulation of Bcl-2 may be expressed as part of the differentiation program of hematopoietic cells and may be involved in the regulation of hematopoiesis.     

Fiber-optic magnetic gradiometer utilizing the magnetictranslational force

A fiberoptic AC/DC magnetic gradiometer utilizing magnetic translational force is proposed, and its working principle is verified. The minimum gradient of an AC magnetic field of 4×10^-2 is detected with 100 mm of Sm-Co-coated sensor fiber built into an interferometer. This gradiometer is intrinsically insensitive to spatially uniform magnetic fields but is sensitive to their gradients. Therefore, the dynamic range and S/N ratio of measurements with the proposed sensor are not restricted by the magnitude of background magnetic field, including the geologic magnetic field. Spatial resolution is <1 mm     

Fibre-optic magnetic sensor utilising metal-coated fibre

A metal-coated fibre was injected with an electric current into its jacket for magnetic field detection using a Lorentzian force. AC and DC field detection sensitivities of 25rad/Gs and 15-7rad/Gs and linearity over four decades have been obtained with a 100 mm sensing fibre. This configuration can also be extended to multiplexed DC magnetic sensors.