Tensile behavior and structure-property relationship of ferritic steels with nano-sized carbide dispersion were invesigated using Ti-added steel and Ti,Mo-added low carbon steels. By austenitizing followed by isothermal heat treatment at 700°C, polygonal ferrites containing very fine carbides of TiC and (Ti,Mo)C were obtained in the Ti-added and the Ti,Mo-added steels, respectively. The size of such carbides was finer in the Ti,Mo-added steel than in the Ti-added steel at the same isothermal holding. The results of tensile tests for these samples showed that the strength is higher as the carbide size is smaller. The structure-based strength calculation led to a good agreement with the experiments, when it was assumed that the Ashby-Orowan mechanism is dominant for precipitation strengthening of nano-sized alloy carbides. It was also suggested that a relatively large tensile ductility is related to enhanced recovery during the tensile deformation, accompanied with promotion of secondary slips or cross slips in a finer scale due to the nano-sized particles.

The first total synthesis of FR-901375, a novel bicyclic depsipeptide isolated from the fermentation broth of Pseudomonas chloroaphis No. 2522, has been achieved. The synthetic approach involves 13 reaction steps and is achieved in 12% overall yield. The key points in the successful synthetic strategy are a concise asymmetric synthesis of the key building block (3R,4E)-3-hydroxy-7-mercapto-4-heptenoic acid, a mild Mitsunobu macrolactonization step, and an I(2)-mediated deprotection with concomitant disulfide-bridge formation.

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We demonstrate suppression of crack generation in GaN epitaxy on Si using cubic SiC as intermediate layers. Crack-free GaN with a thickness of 2μm was obtained. Epilayers of SiC (0–1μm), thin AlN (50nm), and GaN (1–3μm) were prepared on 3in. (111)Si substrates (GaN∕AlN∕SiC∕Si) by metalorganic vapor-phase epitaxy. Cracking of GaN is suppressed with thicker SiC (1μm), whereas cracks are generated in GaN without SiC and with thinner SiC (50nm). Transmission electron microscopy analysis revealed monocrystalline wurzite structure of GaN. Current-voltage measurements showed breakdown voltage exceeding 250V, indicating its potential for high voltage application.

A bstract: The first generation strategies toward the total synthesis of brevetoxin B (1) are presented and the syntheses of the key intermediates 3, 4, 5, 67, 83, and 94-98 required for the projected construction are described. The earliest and most convergent strategy required the application of the hydroxy epoxide cyclization and the intramolecular conjugate addition as key reactions for the construction of the fused tetrahydropyran ring systems (4) [ABC], (7) [FG], and (8 ) [UK], The oxocene ring (H) was formed via a Wittig reaction followed by a hydroxy dithioketal cyclization to produce the hexacyclic fragment [FGHUK] ( 6 -5), The 12-membered dithionolactone 18 was envisioned as the precursor of the dioxepane system of the molecule via a projected bridging reaction, to construct simultaneously both oxepane rings. However, the dithionation of dilactone 17 proved unsuccessful. In a subsequently evolved strategy, a new photolytic approach toward the dioxepane region was developed, starting from the acyclic dithiono progenitor 20 (20 -* 23). Application of this reaction to the brevetoxin B skeleton afforded the desired oxepene (96 -* 97), which after deprotection produced oxepanone 98. A specifically designed reductive hydroxy ketone cyclization (98 -199) was then employed in an attempt to close the remaining ring [E], but, again, without success. The novel rearrangement of hydroxy ketone 87 to the pentacyclic system 89 was observed in a less elaborate skeleton. The scope and generality of these silicon-induced reductive cyclizations are also described.