Circuit realisation of negative-impedance convertor at v.h.f.

A circuit realisation of a v.h.f. negative-impedance convertor (n.i.c.) is presented. Using simultaneous multiple negative feedback, a stable operation is obtained to approximately 15% of fT. Using transistors with an fT of 1.1 GHz, the realised n.i.c. circuit operates to 160 MHz.     

Fiber of poly(vinyl alcohol) derived from vinyl trifluroacetate. III. Production and properties of fibers

The direct wet-spinning of syndiotacticity-rich poly(vinyl alcohol) from ammonolysis solutions of poly(vinyl trifluoroacetate) was carried out. The high draft in spinning could not be accomplished at lower and higher polymer concentration, but it was accomplished at a certain middle polymer concentration. The drawn fibers with high draft have not always high strength. The fibers with high strength were obtained from fibers wound at moderate draft in spinning and then drawn at higher times without solvent. The strength was independent on the degree of polymerization (in a range from DP = 1870 to DP = 5580), but it became higher in the case of thinner fibers obtained from the solutions of lower polymer concentration. Here, the highest Young's modulus and strength at break were 13.8 GPa and 12 gr/denier, respectively.     

Highly stabilized amorphous 3-bis(4-methoxyphenyl)methylene-2-indolinone (TAS-301) in melt-adsorbed products with silicate compounds

3-Bis(4-Methoxyphenyl)methylene-2-indolinone (TAS-301) is a poorly water-soluble drug showing low oral bioavailability in rats and dogs. Previously, we reported that when a physical mixture of TAS-301 and a porous calcium silicate, Florite® RE (FLR), was heated at high temperature (250°C), the drug melted and was adsorbed by the FLR in an amorphous state, and that the preparation (melt-adsorbed product) showed a significantly increased solubility and dissolution rate, and a significantly enhanced oral bioavailability of the drug. The aim of the present study was to elucidate important factors for preparing a melt-adsorbed product showing greater stability of drug in an amorphous state. We examined the effects of the kind of adsorbent, drug/adsorbent ratio, heating conditions, and drug particle size on converting drug crystal into an amorphous state, the stability of amorphous state, and chemical stability of the drug in the melt-adsorbed products under a high temperature and high humidity condition (60°C/80% RH, open). FLR, light anhydrous silicic acid and two types of hydrated silicon dioxides were tested as adsorbents. For the batch method, TAS-301 was converted into an amorphous state by heating TAS-301/adsorbents physical mixtures above the melting point of TAS-301 for more than 2 min. The amorphous state was most stabilized when FLR was used as an adsorbent and drug/FLR ratio was 1:0.5 and more. For the continuous method using the twin screw extruder that enables significantly larger scale manufacturing than batch method, TAS-301 melt-adsorbed products were able to produce when only FLR was used as adsorbent. The heating temperature was needed to be set above the melting point of TAS-301 to convert it into an amorphous state as well as batch method. The amorphous state was stabilized when drug/FLR ratio was 1:2 and more. The micronization of the drug decreased the stability of the amorphous state. These results indicate the importance of optimizing the above factors in the preparation of melt-adsorbed product.     

Technical application of fracture mechanics to thin-walled structures

This paper reviews recent developments in the application of fracture mechanics to such structures as welded steel tanks, ships, and thin-wall pressure vessels, with particular attention to Japanese work. It describes methods for estimating critical crack size and safe working conditions, taking into account such fabrication variables as angular distortion, welding residual stress, prestrain, plate curvature and stress concentration. Whilst most of the paper is devoted to a consideration of the conditions for crack instability, it also discusses crack arrest and gives experimental results for the effect of thickness on both initiation and arrest.     

Dielectric dispersion in a disordered nitrite compound: AgNo2·NH3

A pronounced dielectric dispersion was observed along the a- and c-axes in a disordered nitrite compound of AgNO₂·NH3. The activation energy of 0.32 eV was found for the dielectric relaxation time both along the a-axis and along the c-axis. Phase transition was not observed down to liquid helium temperature.     

A note on brittle crack deceleration in a structural steel

The deceleration of a brittle crack in a steel is attributed to plastic deformation developed around the crack. The investigation shows that a ductile fibrous crack stops suddenly, but a brittle cleavage crack does sluggishly.

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Résumé La décélération d'une fissure fragile dans un acier est attribuée à la déformation plastique qui se développe autour de cette fissure.L'étude montre qu'une fissure fibreuse et ductile s'arrête brutalement tandis qu'une fissure fragile et de clivage s'arrête lentement.