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.     

Implicit Formulation for SPH‐based Viscous Fluids

We propose a stable and efficient particle‐based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second‐ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.     

An architecture framework for an adaptive extensible processor

To improve the performance of embedded processors, an effective technique is collapsing critical computation subgraphs as application-specific instruction set extensions and executing them on custom functional units. The problem with this approach is the immense cost and the long times required to design a new processor for each application. As a solution to this issue, we propose an adaptive extensible processor in which custom instructions (CIs) are generated and added after chip-fabrication. To support this feature, custom functional units are replaced by a reconfigurable matrix of functional units (FUs). A systematic quantitative approach is used for determining the appropriate structure of the reconfigurable functional unit (RFU). We also introduce an integrated framework for generating mappable CIs on the RFU. Using this architecture, performance is improved by up to 1.33, with an average improvement of 1.16, compared to a 4-issue in-order RISC processor. By partitioning the configuration memory, detecting similar/subset CIs and merging small CIs, the size of the configuration memory is reduced by 40%.     

High aspect ratio fabrication method using O2 RIE and electroplating

A polyimide-based process for the fabrication of vertical structures with high aspect ratio has been developed. O₂ reactive ion etching (O₂ RIE) has been employed in the polyimide processing. Achieved etching characteristics of the O₂ RIE system are: 4.0 m/min etching rate, 15 aspect ratio, 75 m etching depth. Polyimide has excellent chemical and thermal properties which makes it a good building material for micromachines. Polyimide could be also used as molds for electroplating. Electroplated copper structures were formed in the polyimide molds and metal gears were fabricated by these fabrication technologies. New possibilities for micromachining were opened by the use of O₂ RIE and electroplating.This work was supported by Japanese ministry of Education Science and Culture under a grant-in-Aid No. 03102001.     

Frequency Stability Improvement of a Two-Mode Stabilized 633-nm He-Ne Laser

The red side (lower-frequency) mode of a two-mode stabilized 633-nm He-Ne laser has been locked to the hyperfine structure of the P() line of (127)I(2) by means of frequency modulation spectroscopy enhanced by an external optical cavity. Both the red side and blue side (higher-frequency) modes of the laser exhibit a frequency stability of 2.3 x 10(-11) tau(-1/2). In addition, the frequency fluctuations of the blue side mode are detected by a Fabry-Perot cavity and compensated through an acousto-optic frequency shifter. The short-term stability of better than 3 x 10(-11) is attained for integration times of between 2 x 10(-3) and 2 x 10(-1) s.     

Visual simulation of mixed-motion avalanches with interactions between snow layers

In the field of computer graphics, simulation of fluids, including avalanches, is an important research topic. In this paper, we propose a method to simulate a kind of avalanche, mixed-motion avalanche, which is usually large and travels down the slope fast, often resulting in impressive visual effects. The mixed-motion avalanche consists of snow smokes and liquefied snow which form an upper suspension layer and a lower dense-flow layer, respectively. The mixed-motion avalanche travels down the surface of the snow-covered mountain, which is called accumulated snow layer. We simulate a mixed-motion avalanche taking into account these three snow layers. We simulate the suspension layer using a grid-based approach, the dense-flow and accumulated snow layer using a particle-based approach. An important contribution of our method is an interaction model between these snow layers that enables us to obtain the characteristic motions of avalanches, such as the generation of the snow smoke from the head of the avalanche.     

Effects of plastic strain amplitudes on non-proportional cyclic plasticity

Summary A series of plastic strain controlled cyclic tests was performed to facilitate the modelling of cyclic plasticity under general multiaxial loading conditions. The tests were carried out by applying combined axial force and torque to thin-walled tubular specimens of type 316 stainless steel at room temperature. Torsional and circular cycles of the equivalent plastic strain amplitude (von Mises type) ofe ^p /2=0.1, 0.2 and 0.4% were specified.The results showed that the cyclic hardening under the circular cycles is 1.5–1.8 times as large as that under the torsional cycles of the same value ofe ^p /2 in the saturated state. It was also observed that, in the case of torsional cycles, these saturated values are not affected by the sequence of plastic strain cycles in the past, while in the case of circular cycles, they are affected by the cycles of larger amplitudes. Furthermore, it was elucidated that this memory effect depends only on the cycles of the largest amplitude in the past.With 12 Figures