Characterization of Porous ß-Type Tricalcium Phosphate Ceramics Formed via Physical Foaming with Freeze-Drying.

Porous ß-tricalcium phosphate (Ca3(PO4)2; ß-TCP) was prepared via freeze-drying and the effects of this process on pore shapes and sizes were investigated. Various samples were prepared by freezing ß-TCP slurries above a liquid nitrogen surface at -180 °C with subsequent immersion in liquid nitrogen at -196 °C. These materials were then dried under reduced pressure in a freeze-dryer, after which they were sintered with heating. Compared with conventional heat-based drying, the resulting pores were more spherical, which increased both the mechanical strength and porosity of the ß-TCP. These materials had a wide range of pore sizes from 50 to 200 µm, with the mean and median values both approximately 100 µm regardless of the freeze-drying conditions. Mercury porosimetry data showed that the samples contained small, interconnected pores with sizes of 1.24 ± 0.25 µm and macroscopic, interconnected pores of 25.8 ± 4.7 µm in size. The effects of nonionic surfactants having different hydrophilic/lipophilic balance (HLB) values on foaming and pore size were also investigated. Materials made with surfactants having lower HLB values exhibited smaller pores and lower porosity, whereas higher HLB surfactants gave higher porosity and slightly larger macropores. Even so, the pore diameter could not be readily controlled solely by adjusting the HLB value. The findings of this work indicated that high porosity (>75%) and good compressive strength (>2 MPa) can both be obtained in the same porous material and that foaming agents with HLB values between 12.0 and 13.5 were optimal.

Detection and in situ switching of unreversed interfacial antiferromagnetic spins in a perpendicular-exchange-biased system.

By using the perpendicular-exchange-biased Pt/Co/α-Cr(2)O(3) system, we provide experimental evidence that the unreversed uncompensated Cr spins exist at the Co/α-Cr(2)O(3) interface. The unreversed uncompensated Cr spin manifests itself in both the vertical shift of an element-specific magnetization curve and the relative peak intensity of soft-x-ray magnetic circular dichroism spectrum. We also demonstrate an in situ switching of the interfacial Cr spins and correspondingly a reversal of the exchange bias without interfacial atomic diffusion. Such switching shows the direct relationship between the interfacial antiferromagnetic spins and origin of the exchange bias. The demonstrated switching of exchange bias would likely offer a new design of advanced spintronics devices, using the perpendicular-exchange-biased system, with low power consumption and ultrafast operation.

[A case of gastric mucosal bridge with Behçet's disease].

A 69-year-old man visiting our hospital with an epigastralgia and tarry stool was diagnosed as having Behçet's disease on the basis of repetitious aphthous stomatitis, erythema nodosum and arthralgia in 1991. The next year, he suffered from double active ulcers in the antrum of the stomach, and he had been operated on for intestinal perforation. In 1994, endoscopic examination revealed the gastric mucosal bridge between the double ulcers. The double ulcer healed after an eradication therapy of H. pylori, but the gastric mucosal bridge has remained there on the gastrointestinal endoscopy. The gastric mucosal bridge with Behçet's disease has not been reported in Japan, being considered to be very rare.