Improvement of numerical instabilities in topology optimization using the SLP method

In this paper, we present a method for preventing numerical instabilities such as checkerboards, mesh-dependencies and local minima occurring in the topology optimization which is formulated by the homogenization design method and in which the SLP method is used as optimizer. In the present method, a function based on the concept of gravity (which we named “the gravity control function”) is added to the objective function. The density distribution of the topology is concentrated by maximizing this function, and as a result, checkerboards and intermediate densities are eliminated. Some techniques are introduced in the optimization procedure for preventing the local minima. The validity of the present method is demonstrated by numerical examples of both the short cantilever beam and the MBB beam. Received February 23, 1999     

Elastic Properties of Titanium Monoboride Measured by Nanoindentation

In order to measure the elastic properties of titanium monoboride (TiB), which are not well known, a Ti/TiB composite with 95% volume fraction of TiB was fabricated by the powder metallurgy route. After compacting mixed Ti+TiB₂ powders by a hot unidirectional pressure (1200°C, 25 MPa, 60 min, <10⁻² Pa), annealing at 1200°C was performed for 48 h, after which the main phase in the material was TiB. The elastic properties of TiB were directly measured by using the nanoindentation technique. The polycrystalline modulus and hardness of the TiB were 450 and 27.5 GPa, respectively.     

Topology optimization of switched reluctance motors for the desired torque profile

This paper presents the design optimization of switched reluctance motors (SRMs). The design goals are high average torque, low torque ripple and low mass under the constrained phase current of SRMs. To achieve these goals, we design not only the geometries of SRMs using topology optimization, but also voltage on–off angles. The performance analysis of SRMs is carried out to predict the torque profile. Fourier series expansion is used to obtain the explicit expression of inductance curves, which allows us to perform the analytical design sensitivity analysis of the torque profile. The optimization problem is solved using the sequential linear programming (SLP) method. In the optimized geometry, the arc lengths of poles are increased with the notched shape near airgap, and the holes inside the rotor are created. In addition, the mechanical characteristics of the optimized SRM are investigated using the modal and thermal analysis by MSC/NASTRAN.     

Enhancement of the Photocatalytic Activity Under Visible-Light Irradiation over N-doped TiO2 Modified by Platinum Chloride

N-doped TiO₂ adsorbed platinum chloride (PtCl _x /N-TiO₂, x being an unidentified number) was found to show much higher photocatalytic activity than either N-TiO₂ or PtCl _x /TiO₂ for the decomposition of acetic acid into CO₂ and H₂O under Visible-light irradiation, while neither PtCl _x /SiO₂, PtCl _x /Al₂O₃ nor an aqueous solution of H₂PtCl₆ was active. An enhancement of the photo-activity on PtCl _x /N-TiO₂ has been proposed as a Z-scheme mechanism.     

Optical compensation for hologram distortion using wavefront interpolation in angle-multiplexed holograms

Distortion of the hologram may occur when the photopolymer material used in the medium shrinks or expands. We analyzed interference fringe distortion for plane waves and a reference beam with an angular gap between recording and reproducing for the purpose of compensating for the distortion. We found that the wavefronts that could compensate for the distortion could approximately be obtained by linear interpolation of such angle-multiplexed holograms. We recorded 80 data pages with the angle-multiplexing method and obtained an optimized wavefront to compensate for hologram distortion on the first, fortieth, and eightieth data pages using adaptive optics with genetic algorithms and linear interpolated wavefronts at the other data pages. The calculation time for 80 wavefronts to compensate for distortion fell to 3/80th of that of having to calculate optimizations for all pages. The bit error rates were lower than 1.0?×?10^?2 on all data pages reproduced using these wavefronts.     

Characteristics of pure-titanium and low carbon steel friction-welded joint with post-weld heat-treatment

The characteristics of friction-welded joint between commercially pure-titanium (CP-Ti) and low carbon steel, of which was subjected to post-weld heat-treatment (PWHT), was investigated. When the joint was made with friction speed of 25?s^?1, friction pressure of 200?MPa, friction time of 2.5?s and forge pressure of 250?MPa, it had the same tensile strength as that of the CP-Ti base metal. The joint had no intermediate layer consisting of intermetallic compound (IMC interlayer) at the weld interface. The joint efficiency of the joint subjected to PWHT decreased with increasing heating temperature and its holding time, and the joint fractured at the weld interface although it had no IMC interlayer. The void was generated on the weld interface of the joint during PWHT process.     

NUMERICAL SIMULATION OF NATURAL CONVECTION WITH DENSITY INVERSION IN A SQUARE CAVITY

Water has its density maximum at 4^oC, and natural convection around the temperature is complicated. In this study, natural convection with density inversion in a two-dimensional vertical square cavity is investigated numerically. To express the average Nusselt number nondimensionally, some parameters are chosen by observing the calculated flow-temperature fields. Then a simple expression of heat transfer correlation as a function of Galilei number, wall temperature ratio, and density function is proposed. The present correlation has a deviation of about 10%.     

Comparative study of the estimation of creep crack growth behaviour of TiAI by using a precrack and a notch CT specimens

The fatigue crack growth behaviour of Ti-48.2%A1 intermetallics (full lamellar structure) strongly depends on the microstructure, that is lamellar alignment, and it grows along the lamellar direction. Therefore, it is difficult to introduce a straight fatigue precrack in a CT specimen to provide a standardized specimen for the estimation of the crack growth rate. Concerning high temperature creep brittle materials, since notch opening displacement at the time of creep crack initiation is small, a sharp notched specimen can keep similar stress singularity as a fatigue precracked specimen. In this paper, comparative research on the characteristics of creep deformation and crack extension was performed by using a fatigue precracked and a sharp notched CT specimens. Based on this result, a mechanical model was constructed and finite element stress analyses on the creep deformation for both specimens were performed. By these analytical results, the different behaviour of the characteristics of creep deformation and crack extension between a precrack and a sharp notch specimens were verified mechanically. Furthermore, the validity of using a sharped notched CT specimen to estimate creep crack growth rate was assured for creep brittle materials.     

Nationwide survey of salmonella prevalence in environmental dust from layer farms in Japan

A nationwide survey was conducted to determine Salmonella prevalence in airborne dust from layer farms. Of the 4,090 layer farms in Japan, 203 were surveyed and 48 (23.6%) of these were positive for Salmonella. Salmonella isolation rates were higher in the eastern (24.3%), central (25.6%), western (23.9%), and southern (27.5%) prefectures than they were in the northern (13.3%) prefecture. We recovered 380 Salmonella isolates and identified 34 different Salmonella serovars. Salmonella Infantis was the most prevalent serovar (42 [11.1%] of 380), followed by Salmonella Agona (39 [10.3%] of 380), Salmonella Mbandaka (37 [9.7%] of 380), Salmonella Cerro (32 [8.4%] of 380), Salmonella Thompson (29 [7.6%] of 380), and Salmonella Braenderup (27 [7.1%] of 380). Of the 380 isolates, 273 (71.8%) were resistant to more than one antibiotic. Salmonella Infantis (41 [97.6%] of 42), Salmonella Agona (38 [97.4%] of 39), and Salmonella Mbandaka (34 [91.9%] of 37) showed the highest resistance rates. We found 18 different resistance patterns and the most common (179 [47.1%] of 273) was resistant to dihydrostreptomycin. One of the 13 Salmonella Hadar isolates was resistant to eight antibiotics. To investigate characteristics of Salmonella Agona, Salmonella Infantis, and Salmonella Mbandaka isolates across different prefectures, we performed pulsed-field gel electrophoresis by using XbaI and BlnI. The Salmonella Agona and Salmonella Mbandaka dendrograms were grouped into seven clusters, with 80 and 70% similarity, respectively. Because the Salmonella Infantis dendrogram showed low similarity, there is a possibility of genetic diffusion of this serovar across Japan. This report is the first to describe Salmonella contamination in airborne dust from layer farms in Japan. Our findings should be useful for future Salmonella infection monitoring and control.     

Molecular Evolution of Fern Squalene Cyclases

Triterpenes, a diverse group of natural products comprising six isoprene units, are distributed across various organisms from bacteria to higher plants. Ferns are sporophytes that produce triterpenes and are lower on the evolutionary scale than higher plants. Among ferns that produce triterpenes analogous to bacterial hopanoids, Polypodiodes niponica produces migrated dammaranes and oleananes, which are also widely found in higher plants. Because the study of terpene‐producing ferns could help us to understand the molecular basis of triterpene biosynthesis, cDNA cloning of squalene cyclases (SCs) from P. niponica was carried out. Two SCs (PNT and PNG) were obtained. The heterologously expressed PNT produces tirucalla‐7,21‐diene (67 % major), and PNG produces germanicene (69 %). Phylogenetic analysis revealed that PNT and PNG, which produce higher‐plant‐type migrated dammaranes and oleananes, are closely related to bacterial‐type SCs. Furthermore, analysis of the minor products indicated that fern SCs gained the ability to directly form dammarenyl cations, which are key intermediates in oleanane formation during molecular evolution.