Determination of the glass transition of polymer by the autovibron

The automated Rheovibron (Autovibron) has been useful for determining the glass transition behavior of polymers. The standard (manual Rheovibron viscoelastometer has been used sufficiently small intervals, and so, some accuracy on transition location must be sacrificed when the temperature intervals are taken 5 to 10°C apart. However, the Autovibron can be observed over very small temperature intervals (<1.5°C)), which essentially provide a continous monitoring of the changes in storage modulus, loss modulus, and tan δ. An improved accuracy and sensitivity of the Autovibron are provided by a combination of multiprogrammer, programmable calculator, and lock-in analyzer. The Autovibron are provided by a combination of multiprogrammer, programmable calculator, and lock-in analyzer. The Autovibron shows a good capability for dynamic thermomechanometry. The glass transition bility for dynamic thermomechnometry. The glass transition of polymers can be determined by analyzing the loss tangent peak. The maximum value in loss tangent, peak temperature, and the newly introduced terms, ΔT₁ and ΔT₂ which indicate the widths of tan δ peak, are useful indicators of the glass transition. The ΔT₁ and ΔT₂ show the distribution of the glass transition and are related to order and crystallinity in the structure.     

Three-dimensional reconstruction using homocentric spherical spatiotemporal image analysis

This paper presents a new algorithm for reconstructing a scene of three-dimensional structures from an image sequence. Three-dimensional reconstruction using an image sequence, called the spatiotemporal image method, is robust against image noises. But in this method, camera motion is limited to only one direction translation. Our algorithm makes allowances for camera rotation in spatiotemporal image analysis. With this technique, the whole spatiotemporal image is transformed to spherical projection and three-dimensional structures are determined robustly using the Hough transformation. We call the technique Homocentric Spherical Spatiotemporal Image (HSSI) analysis. With HSSI, it is possible to distinguish objects with a rotating camera from a longer baseline and to measure them with much greater accuracy than previously possible. This algorithm is demonstrated through simulations and experiments with real images from a translating and rotating camera, and the three-dimensional structures in a static scene are reconstructed.     

Buckling induced stresses in martensitic stainless steels for magnetic fusion reactors

Samples of martensitic stainless steel, (Sandvik HT-9) in the form of beams and plates, exhibited a buckling type of structural instability when placed in a uniform magnetic field. Post buckling stresses of up to 497 MPa (72000 psi) were observed for a cantilevered plate placed in a one tesla magnetic field normal to the plate surface. Buckling phenomena were observed for both cantilevered circular rods and flat plates of magnetic stainless steel. The buckling magnetic field was geometry dependent with values as low as 0.25 T for a plate with length to thickness ratio of 90. Above the buckling field the cantilevered structure exhibited two stable equilibrium positions with a tip displacement of as much as 8–10 times the plate thickness.These results suggest that further study be given to the structural design implications of using magnetic steels in magnetic fusion reactors.     

High-Temperature Active Oxidation of Chemically Vapor-Deposited Silicon Carbide in an Ar─O2 Atmosphere

Active oxidation behavior of chemically vapor-deposited silicon carbide in an Ar─O₂ atmosphere at 0.1 MPa was examined in the temperature range between 1840 and 1923 K. The transition from active oxidation (mass loss) to passive oxidation (mass gain) was observed at certain distinct oxygen partial pressures ( P _O2^t). The values of P _O2^t increased with increasing temperature and with decreasing total gas flow rates. This behavior was well explained by Wagner's model and thermodynamic calculations. Active oxidation rates ( k _a) increased with increasing O₂ partial pressures and total gas flow rates. The rate-controlling step of the active oxidation was concluded to be O₂ diffusion through the gaseous boundary layer.     

Optoelectronic matrix switch using heterojunction switching photodiodes

Heterojunction switching photodiodes (InGaAs/InP) were used to construct a 3×3 matrix switch. Isolation and cross-talk losses were better than 63 dB over a frequency range of 10 Hz to 400 MHz and 400 Mbit/s digital signals were switched with switching times shorter than 30 ns.     

Epitaxial growth of AlN on single crystal Mo substrates

We have grown AlN films on single-crystalline Mo(110), (100), and (111) substrates using a low temperature pulsed laser deposition (PLD) growth technique and investigated their structural properties. Although c-axis oriented AlN films grow on Mo(100), the films contain 30° rotated domains due to the difference in the rotational symmetry between AlN(0001) and Mo(100). AlN films with only poor crystalline quality grow on Mo(111) substrates, probably due to the poor surface morphology and high reactivity of the substrates. On the other hand, single crystal AlN films grow epitaxially on Mo(110) substrates with an in-plane relationship of AlN[11-20] // Mo[001]. Reflection high-energy electron diffraction or electron backscattered diffraction analysis has revealed that neither in-plane 30° rotated domains nor cubic phase domains exist in the AlN films. X-ray reflectivity measurements have revealed that the heterointerface between AlN and Mo prepared by PLD at 450 °C is quite abrupt. These results indicate that PLD epitaxial growth of AlN on single crystal Mo substrates is quite promising for the fabrication of future high frequency filter devices.     

Study on the potential inhibition of root dentine wear adjacent to fluoride-containing restorations

The purpose of this in vitro study was to determine whether the vicinity of root dentine that had been restored with fluoride-releasing materials was at reduced risk for erosive/abrasive wear compared to root dentine restored with a non-fluoride-containing material. According to a randomized complete block design, standardized cavities prepared on the surface of 150 bovine root dentine slabs were restored with glass-ionomer cement, resin-modified glass ionomer, polyacid-modified resin composite, fluoride-containing or conventional composite. Specimens were coated with two layers of an acid-resistant nail varnish exposing half of the dentine surface and half of the restoration. Subsequently, specimens were either eroded in an acidic drink or left uneroded, then exposed to artificial saliva and abraded in a toothbrushing machine. Wear depth in the vicinity of restorations was quantified by a stylus profilometer, based on the nonabraded areas surrounding the erosion/abrasion region. Two-way ANOVA did not demonstrate significant interaction between restoratives and eroded-uneroded dentine (p = 0.5549) nor significant difference among restorative materials (p = 0.8639). Tukey’s test ascertained that the wear depth was higher for eroded than for uneroded groups. Fluoride-releasing materials seemed to negligibly inhibit wear in the vicinity of restored root dentine subjected to erosive/abrasive challenges.