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In high performance liquid chromatography (HPLC) column development, the bonded-phase silica is often only investigated to determine the suitability of a packed column for a particular separation class and not [...]

Poly(L-lactic acid) (PLLA) is quite promising for use as biodegradable and non-petroleum derived plastics. In this study we developed an innovative two-step polycondensation process so as to produce economically PLLA with high molecular weight. The process is composed of both melt polycondensation under the lactide-re ux and solid-phase polycondensation. First we studied a direct polycondensation of L-lactic acid with a small amount of solvent, using a mixture of L-lactic acid as raw material, diphenyl ether as solvent, Tin (II) chloride dihydrate as catalyst, and p-toluene sulfonic acid as a discoloration prevention agent. After the dehydrative oligomerization of L-lactic acid, the polycondensation of the oligocondensates and solid-phase post-polycondensation, PLLA of Mw= 266,000 could be obtained. Then, we carried out direct bulk polycondensation tests from L-lactic acid without any solvent added. After optimization of the reaction conditions, PLLA with Mw= 134,000 was successfully produced by the melt-poly-condensation of L-lactic acid accompanied by solid-phase post-poly-condensation. In both systems, the lactide-re ux was indispensable for promoting dehydration/water removal. The re uent lactide was taken into the polymer-chain by trans-esterification reaction during the melt-poly-condesation. Furthermore, the catalyst was allowed to deactivate and stabilize during the solid-phase polymerization to cause the Mwgrowth.

Scanning and transmission electron microscopy has been used to examine the fracture surface topography and the dislocation structure of 70:30 brass and copper in order to study the mechanisms of Stage II fatigue crack growth. In the early period of Stage II growth the fracture surfaces lay mainly in crystallographic planes, the crystallographic features in fractographs being more pronounced in brass than in copper. Beneath the fracture surfaces, there were observed dislocation arrays densely packed in the slip planes in brass and the well developed cells in copper. In the late period of Stage II growth, however, fine contrast of indistinct shape was observed just beneath the striations on fracture surfaces in both the metal and the alloy. Outside such regions, however, numerous twin bands were observed in brass and in the elongated cells in copper. It appears that in the later period of Stage II cracks grow by means of an opening and closing behaviour which is unaffected by their crystallographic orientations.

Fast valving could cause second swing instability in a relatively weak system, though it is effective on first swing stability. This paper presents the proposed control methods for fast valving which are concerned with a practical way to control turbine power according to a fault severity and demonstrates their effectiveness by detailed digital simulations performed on a multimachine system.

Abstract: Observations of dislocation structures around the fatigue cracks in the early stage in polycrystalline copper were made through an ultrahigh voltage electron microscope operating at 2000 kV. Ladder like structures and initial cracks within them were fre-quently observed. These dislocation structures were formed prior to the crack initia-tion, and the crack was initiated and propagated within these structures accompanied by no appreciable dislocation entanglements in the earliest stage. On the other hand, cell structures were observed around the cracks which appeared to have grown into the sub-sequent stage (the stage between Stages I and II). Cell size ahead of the crack tip was not so small, and it seemed that the crack was able to propagate across the cells. On the basis of these observations, the mechanisms of fatigue crack initiation and propagation in the early stage in copper bulk-specimens are briefly discussed.

Total cavopulmonary connection with use of an autogenous intraatrial tunnel to create a straight tube between the inferior vena cava and the pulmonary artery was attempted in several types of cardiac anomaly in eight consecutive candidates for the Fontan operation. A small right atrium with an extraordinary location of the inferior vena cava and a short superior vena cava prevented the use of this procedure in two cases. By preserving the crista terminalis and the sinus node and its arteries we prevented the development of postoperative atrial arrhythmias in the short follow-up period, and the P trigger-signal averaged P waves were not different from those of other cardiac anomalies. The proximal stump of the superior vena cava was not incised in any case to enlarge the anastomosis, even when size mismatch between the superior and inferior venae cavae existed, as in a case of bilateral superior venae cavae. Stretching the vessels by approximately 150% was possible and permitted an adequate anastomosis. Cavopulmonary connections via the intraatrial tunnel ensured smooth, nonturbulent, somewhat pulsatile flow without a pressure gradient. We concluded that the creation of an autogenous intraatrial tunnel was possible in many cases without serious complications and that this procedure has potential benefit for the pulmonary circulation in the aspect of pulsatility. (J THORAC CARDIOVASC SURG 1995;110: 625-32)

Biodegradable plastics have been quickly accepted as one of the key solutions for today's waste plastics problems in Japan. Particularly, poly(lactic acid) is looked forward to as the most promising biodegradable plastics because of its high quality in optical and physical properties as well as chemical recyclability and compostability. Furthermore, lactic acid as a raw material of this polymer can be produced from agricultural starch wastes. However, one of the greatest issues in biodegradable plastics including poly(lactic acid) and lactic acid-based copolymers lays in their extremely high price when compared to typical commodity plastics on the market. Regarding poly(lactic acid), a polymer with high molecular weight of more than Mw = 100 000 is conventionally obtained only by a ring-opening polymerization process from lactide, i.e., dimer of lactic acid, which is very expensive.

Fast valving by momentary closing of turbine intercept valves will effectively improve transient stability. However, momentary closing of intercept valves may cause a disturbance in the boiler, turbine, and control systems. The effects on these systems should be considered in the application of fast valving Digital simulation using a model which represented a large fossil-fired unit in a multimachine system was performed, and the effects on the unit were analyzed and provisions for application of fast valving were considered. The results of studies indicate that no problems 'are expected in the application of fast valving on the large unit, and only minor modification is necessary to implement fast valving.

We report here two rare surgical cases of tetralogy of Fallot with portal venous atresia. Both patients, previously diagnosed with tetralogy of Fallot, developed portal hypertension and showed hematemesis and/or melena. One patient needed endoscopic sclerotherapy. Intracardiac repair was performed under cardiopulmonary bypass (CPB) with moderate hypothermia. After surgery, one of the patients developed cardiogenic shock due to cardiac tamponade with accumulated chyle in the pericardial sac in the ninth postoperative day, and showed deteriorated liver function, suggesting that liver might have been vulnerable because of the absence of portal blood.