Radiation-induced polymerization of ethylene in pilot plant. III. Heavy-phase recycling process

Radiation-induced polymerization of ethylene using aqueous tert-butyl alcohol as medium was carried out in a large-scale pilot plant with a 50-liter central source-type reactor at a pressure of 105 to 395 kg/cm², temperature of 30° to 80°C, mean dose rate of 4.5 × 10⁴ to 1.9 × 10⁵ rads/hr, ethylene feed rate of 5.5 to 23.5 kg/hr, and medium feed rate of 21 to 102 l./hr. The space–time yield and molecular weight of the polymer were in the range of 4.7 to 16.8 g/l.-hr and 1.3 × 10⁴ to 8.9 × 10⁴, respectively. The space–time yield and molecular weight increased with mean residence time at 30°C, whereas at 80°C they became almost independent of the time. The space–time yield increased with pressure and dose rate, slightly decreased with temperature, and was maximum at ethylene molar fraction of 0.5. The polymer molecular weight increased with pressure and ethylene molar fraction, and decreased with dose rate and temperature. The total amount of deposited polymer on the reactor wall, source case wall, and scraping blades was usually less than 1 kg, which was negligibly small for the analysis of polymerization. Continuous discharge of the polymer slurry and production of fine-powder polyethylene were successfully carried out. In the central source-type reactor, a dose rate of 1.9 × 10⁵ rads/hr was obtained with a ⁶⁰Co source of ca. 12 kCi.     

Temperature Dependence of Young's Modulus and Internal Friction in Alumina, Silicon Nitride, and Partially Stabilized Zirconia Ceramics

The temperature dependence of Young's modulus and internal friction (Q⁻¹)in alumina, silicon nitride, and partially stabilized zirconia (Y-PSZ) ceramics was studied. Little change in Q⁻¹ was found for alumina, whereas Q⁻¹ for silicon nitride ceramics increased above 700°C. The Q⁻¹ of Y-PSZ increased markedly with increasing temperature up to a peak at ∼200°C.     

Catalyst Design of Pt-Modified Ni/Al2O3 Catalyst with Flat Temperature Profile in Methane Reforming with CO2 and O2

Pt(0.3)/Ni(10)/Al₂O₃, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO₂ and O₂ in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al₂O₃ prepared by a coimpregnation method, Ni(10)/Al₂O₃, Pt(0.3)/Al₂O₃, and Pt(10)/Al₂O₃. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility.     

Corrosion of silicon nitride ceramics under hydrothermal conditions

Corrosion behaviour of Si₃N₄ ceramics containing Y₂O₃, Al₂O₃ and AIN as sintering aids was investigated under hydrothermal conditions at 200–300 C and saturated vapour pressures of water for 1–10 days. Hydrothermal corrosion resulted in the dissolution of the Si₃N₄ matrix and the formation of a product layer consisting of the original grain-boundary phases and hydrated silica. The dissolution rate of Si₃N₄ ceramics decreased with decreasing crystallinity of the grain-boundary phase. The dissolution rate could be adequately described by a parabolic plot in the initial stage of the reaction. The apparent activation energies were 83.5–108 kJ mol^–1, and the bending strength of the corroded samples decreased from 600 to 400 MPa in the initial stage of the reaction upto a weight loss of 0.004 g cm^–2, and then was almost constant up to a weight loss of 0.012 g cm^–2.     

Fabrication of large area diffraction grating using LIGA process

X-ray imaging is a very important technology in the fields of medical, biological, inspection, material science, etc. However, it is not enough to get the clear X-ray imaging with low absorbance. We have produced a diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. In this X-ray Talbot interferometer, diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we succeeded to fabricate a high aspect ratio diffraction grating with a pitch of 8 μm and small area using a deep X-ray lithography technique. We discuss that the diffraction gratings having a narrow pitch and an large effective area to obtain imaging size of practical use in medical application. If the pitch of diffraction gratings were narrow, it is expected high resolution imaging for X-ray Talbot interferometer. We succeeded and fabricated the diffraction grating with pitch of 5.3 μm, Au height of 28 μm and an effective area of 60 × 60 mm².     

Nonequilibrium dynamics of a reacting network system

The nonlinear nonequilibrium properties of reacting network systems are studied by computer simulations. It is shown that the fluctuation in the population of each chemical species obeys a log-normal distribution, not the normal Gaussian distribution. The reaction rate shows power-law decay with activation cost (energy), not the Arrhenius-type exponential decay observed in a linear nonequilibrium regime. These two characteristic features will explain the diversity, plasticity, and adaptivity observed in complex biological reaction networks. This work was presented in part at the 13th International Symposium on Artifical Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Multiphase composites of tetragonal zirconia agglomerate dispersed into alumina and alumina-zirconia matrices

Multiphase composites of yttria- and ceria-doped tetragonal zirconia agglomerates (10–50 m) dispersed into an alumina or alumina-zirconia matrix were sintered at 1500–1600 °C in air, followed by post-Hot Isostatic Pressing (HIP) at 1450°C and 150 MPa in an Ar gas atmosphere. The relative density of the recovered composites was above 98% of the theoretical density. By chemically etching on the surface of zirconia agglomerates, the sinterability of composites was apparently improved; and no microcracks nor pores were observed at the interface of agglomerate and matrix. According to scanning electron microscopy (SEM) observation, tetragonal and tetragonal-monoclinic zirconia agglomerates were highly dispersed into the alumina or alumina-zirconia matrix. The multiphase composites containing 10 vol% spherical agglomerates demonstrate the relatively low value of bending strength, < 400 MPa, and a high value of fracture toughness, > 11 MPa m^1/2. The crack propagation introduced by Vickers indentation was efficiently suppressed and deflected by the agglomerates.     

Optimal assignment method for mobile assistive robots using matching theory

Artificial Life and Robotics - The aging population and expectations for nursing care robots increased significantly recently. We focused on mobile assistive robots. When various types of robots...     

Development of an epileptic seizure prediction algorithm using R–R intervals with self-attentive autoencoder

Epilepsy is a neurological disorder that may affect the autonomic nervous system (ANS) from 15 to 20 min before seizure onset, and disturbances of ANS affect R–R intervals (RRI) on an electrocardiogram (ECG). This study aims to develop a machine learning algorithm for predicting focal epileptic seizures by monitoring R–R interval (RRI) data in real time. The developed algorithm adopts a self-attentive autoencoder (SA-AE), which is a neural network for time-series data. The results of applying the developed seizure prediction algorithm to clinical data demonstrated that it functioned well in most patients; however, false positives (FPs) occurred in specific participants. In a future work, we will investigate the causes of FPs and optimize the developing seizure prediction algorithm to further improve performance using newly added clinical data.

     

Numerical simulation of molding-defect formation during resin transfer molding

The present study investigated a numerical simulation of molding-defect formation during resin transfer molding using boundary element method and line dynamics. The proposed method enables to simulate small molding defects by increasing the node for required position during time evolution; thereby, the method computes high-resolution flow front without being affected by the initial mesh geometry. The method was applied to the radial injection RTM with single inlet, and it was confirmed by comparison with theoretical value based on Darcy’s law that the flow advancement was computed with high accuracy. In addition, the method was also applied to the flow advancement for inclusion problem with cylinder, and four-point injection problem. The simulated flow behavior, void formation, and shrinkage agreed with the results in references. Finally, the method was compared with experiments using two-point injection problem. The computed configuration of the flow front and weld line agreed well with the experimental results.