A stochastic realization algorithm via block LQ decomposition in Hilbert space

A stochastic realization problem of a stationary stochastic process is re-visited, and a new stochastically balanced realization algorithm is derived in a Hilbert space generated by second-order stationary processes. The present algorithm computes a stochastically balanced realization by means of the singular value decomposition of a weighted block Hankel matrix derived by a “block LQ decomposition”. Extension to a stochastic subspace identification method explains how the proposed abstract algorithm is implemented in system identification.     

Pressureless sintering and characterization of cordierite/ZrO2 composites

Cordierite/ZrO₂ composites with 5 to 25 wt% ZrO₂ were fabricated by conventional powder mixing and pressureless sintering method. Their densification behavior, microstructure, mechanical and thermal properties were studied. By dispersing 25 wt% (9.57 vol%) ZrO₂, densified cordierite/ZrO₂ composite with a relative density of 98.5% was obtained at an optimum sintering condition of 1440 °C and 2 h. ZrO₂ particles were homogenously dispersed within matrix grains and at the grain boundaries. The intragranular particles were finer than 100 nm and the intergranular particles were coarser. Both fracture strength and toughness could be enhanced more than two times higher, compare to those of monolithic cordierite, by dispersing 25 wt% ZrO₂ into the cordierite matrix. The toughening mechanism in the present composites was mainly attributed to martensitic transformation due to ZrO₂ dispersion. Electronic Publication     

Damage tolerance of glass mat/epoxy laminates hybridized with flexible resin under static and impact loading

This study deals with the impact property and damage tolerance of matrix hybrid composite laminates with different laminate constitution. The matrix hybrid composite laminates consisted of the laminae with a conventional epoxy resin and the laminae with a flexible epoxy resin modified from the conventional resin to avoid the interlaminar delamination. The impact energy absorption ratio greatly depended on the matrix resin placed at the impact face. The energy absorption was almost constant if the conventional resin was placed at the impact surface layer, while it increased exponentially with the increasing fraction of the flexible resin if the flexible resin was placed at the impact face. The impact energy was absorbed by the damage development and propagation in the laminate with conventional resin laminae as the impacted face, while it was absorbed by both the recoverable deformation of the flexible resin and the damage propagation in the laminate with flexible resin laminae as the impacted face.     

Quasi-optical waveguide-mode converters using a pair of phase correction mirrors

This paper describes a quasi-optical method for the conversion of modes transmitted through highly oversized circular waveguides. A waveguide-mode is radiated once from a waveguide cut in the form of a radiation beam, which is then properly shaped by two curved mirrors and directed back into the waveguide. The curved mirror shapes are iteratively and automatically determined for given propagation distances using the design technique for phase correction mirrors. The proposed method gives favorable results in designing a waveguide expander/reducer, a TE₀₁-TE₀₂ mode converter, and a TE₀₁-HE₁₁ mode converter.     

Effect of grain size on creep of Ti-53.4mol%Al intermetallics at 1100 K

Constant stress creep under compression stress, 100 to 316 MPa, at 1100 K was investigated on single-phase TiAl intermetallics. The material was ingot-cast, isothermally forged, and then annealed to produce stable equi-axed grain structures, whose average grain diameters were 25, 42 and 70m. Creep curves were very similar among the three specimens with different grain diameters and the creep rates at a given strain, as well as the minimum creep rates, depended little on grain size. Two regimes were observed on the stress dependence of the minimum creep rate. The stress exponent under high stresses was about 4.5, independent of grain size. Under stresses lower than about 150 MPa it became about 8.     

Bending of ionic polymer gel caused by swelling under sinusoidally varying electric fields

Deformation of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel (PVA–PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending–straightening motion of the PVA–PAA gel rods of about 1 mm in diameter have been observed in Na₂CO₃ aqueous solutions under the fields. The PVA–PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect. © 1993 John Wiley & Sons, Inc.     

Melt viscosity and flow birefringence of polycarbonate

Melt viscosity and flow birefringence of bisphenol A-type polycarbonate were measured and analyzed by the application of rubber-like photoelastic theory. The melt viscosity in the Newtonian flow region increased with the molecular weight to the power of 3.4. In polycarbonate, the shear stress of the Newtonian flow region was to 10⁶ dyn/cm², whereas in PMMA it was at most 3 = 10⁵ dyn/cm². The flow birefringence δn has a linear relation with shear stress S, that is δn = 5.7 × 10^?10 S. The principal polarization difference of flow unit α₁ – α₂ was 1.62 × 10^?23 cm³, which was obtained by the application of the rubber-like elastic theory. In PMMA, it was 3.9 = 10^?25 cm³; about 1/40 of that was polycarbonate. The anisotropy of polarizability of the flow unit of polycarbonate was also about 40 times larger than that of PMMA. So the anisotropy reflected the large flow birefringence of the polycarbonate.     

An Application of Silica‐Based Monolithic Membrane Emulsification Technique for Easy and Efficient Preparation of Uniformly Sized Polymer Particles

Summary: Uniformly sized polymer particles were prepared by an emulsification and polymerization technique utilizing a silica monolithic membrane, namely the “silica monolithic membrane emulsification technique”. In this paper, we utilized silica monolithic membrane as a device for the preparation of uniformly sized polymer particles. A mixture of monomers, diluents and oil‐soluble initiator was emulsified into a continuous medium through the silica monolithic membrane and polymerized. The particles obtained had a higher size uniformity than that of particles prepared by previously reported membrane emulsification techniques, such as the Shirasu Porous Glass (SPG) emulsification technique. Through the silica monolithic membrane emulsification technique, we could prepare particles having availability as a possible packing material for solid‐phase extraction (SPE) and high performance liquid chromatography (HPLC).

SEM photograph of silica particles prepared through capillary plate membrane.     

Differences between corrosion products formed on copper exposed in Tokyo in summer and winter

We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu₂O and posnjakite Cu₄SO₄(OH)₆·H₂O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate.