Stereocomplex formation between enantiomeric poly(lactic acid). VIII. Complex fibers spun from mixed solution of poly(D-lactic acid) and poly(L-lactic acid)

To obtain poly(lactic acid) (PLA) complex fibers, spinning was performed by wet and dry methods from 5–10 g/dL chloroform solutions of poly(D-lactic acid) (PDLA) and poly(L-lactic), both with a viscosity-average molecular weight of 3 × 10⁵. The dope was extruded from a monohole nozzle into coagulation baths from ethanol and chloroform for wet spinning and into a drying column kept at 60°C for dry spinning. Scanning electron microscopic observation of the as-spun fibers showed that the surface of the wet-spun fiber had large basins with diameters of 50–100 μm and many pores with diameters from sub μm to 10 μm, whereas the surface of dry-spun fiber had a microporous structure with the pore diameter of 1–3 μm. The tensile strength of the wet-spun complex fiber was very low and could not be drawn at high temperatures, in contrast to the dry-spun fiber. The tensile strength of dry-spun complex fiber increased upon hot drawing and showed the tensile strength of 94 kg/mm² by drawing at 160°C to the draw ratio of 13. Differential scanning calorimetry revealed that the complex fibers contained both the stereocomplex crystallites (racemic crystallites) and the crystallites of the single polymers, PDLA and PLLA, regardless of the spinning methods. The ratio of the racemic crystallites to the single-polymer crystallites increased with the draw ratio of the complex fiber. © 1994 John Wiley & Sons, Inc.     

The influence of drawing,twisting, heat setting and untwisting on the structure and mechanical properties of melt spun polypropylene filament

The changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was noted.     

Usefulness of Permanent Power Fuse in Control Centers with Molded Case Circuit Breakers

The increase in electric power consumption in industry has led to the development of modern distribution systems such as control centers having high kVA ratings and high prospective fault current. In such a situation, the improvement of the system usefulness such as reliability and cost effectiveness is the essential requirement. An index is presented to evaluate the system usefulness using the cost effectiveness for fault protection in a system of given bank kVA. The index is estimated on four different system structures of control centers, including one which utilizes Permanent Power Fuses (PPF). It is presented that the PPF combined with molded case circuit breaker in main circuit effectively improves the cost effectiveness in control centers with high fault current. Operating principles of the PPF and the control center utilizing the PPF are briefly outlined.     

Theoretical studies on VPI-5. 3. The MS-Q force field for aluminophosphate zeolites

Aluminophosphate zeolite is an artificial material which shows strange hydrophilicity. We have been investigating the reason by quantum mechanics, and found that the hydrophilicity of this zeolite depended on the local geometric deformation, and speculated that the site-specific hydrophilicity might be explained by differences in the stiffness of the local deformation determined by the location with the pore structure. In order to test these ideas, we construct a reliable force field based on the new MS-Q approach developed by Demiralp, Cagin, and Goddard. Our force field well reproduces the experimental structure of VPI-5.     

Effect of dehydroepiandrosterone sulfate on fetal middle cerebral artery flow velocity waveforms in term pregnancy

OBJECTIVE: To investigate whether bolus injection of dehydroepiandrosterone sulfate (DHAS) is associated with changes in fetal middle cerebral artery flow velocity waveforms in term pregnancy. METHODS: Ten normal full-term pregnant women received the administration of a 200-mg intravenous dose of DHAS in 20 ml of 5% dextrose. Ten normal full term pregnant women received 20 ml 5% dextrose as controls. Color Doppler flow imaging and pulsed Doppler ultrasonographic assessments were made on fetuses in each group before and 10 min, 30 min, 60 min, 90 min. and 120 min after DHAS or dextrose administration. The pulsatility index (PI) values for the middle cerebral artery, and umbilical artery, and fetal heart rate were recorded. RESULTS: In the DHAS group, middle cerebral artery PI decreased from baseline by 24% (p<.05) after 10 min, and the mean reduction was 22% (p<.05) after 30 min. The PI returned to the baseline value 60 min later. In the control group, there was no change in middle cerebral artery PI. No change was found in umbilical artery PI or fetal heart rate in the control or DHAS group. CONCLUSION: DHAS induces a significant decrease in the fetal middle cerebral artery PI, which suggests a possible decrease in fetal cerebral vascular impedance in term pregnancy.     

Dopamine D3 receptor gene polymorphism and the psychiatric symptoms seen in first-break schizophrenic patients

Cycads, the most primitive of the living gymnosperms, have been used and continue to be used for food and medicinal purposes by many cultures, although toxins must be removed before ingestion. In our quest to identify tropical plants that contain inhibitors of the cytochrome P-450 aromatase and thus may be efficacious in treating estrogen-dependent tumors, we have screened extracts from 5 species of cycad folia encompassing 3 genera: Cycas cairnsiana F. Muell., Cycas revoluta Thunb., Cycas rumphii Miq., Dioon spinulosum Dyer and Encephalartos ferox Bertol. All extracts were found to contain inhibitors of the human enzyme.     

The effect of substituent groups in bis(dithiobenzil) nickel compounds on their absorption spectra,reduction potential and singlet oxygen quenching efficiency

The influence of substituents on the longest wavelength (Λ_max) of absorption maxima and the reduction potential of bis(p-substituted dithiobenzil) nickel compounds has been evaluated by the classical Hammett equation. A good linear relationship between Λ_max or reduction potential and σ_p or σ_p⁺ shows that at least one phenyl ring is conjugated with the five-membered nickel chelate ring, although neither of the phenyl rings is actually coplanar to the chelate ring. The amount of singlet oxygen quenched by bis(p-substituted dithiobenzil) nickel has been conveniently measured by means of a gas chromatograph using a capillary column.     

Mechanism of the Photofading of Stilbene–fluorescent Dyes. Contribution of Singlet Oxygen to the Photofading of 4, 4‘–Bisacetamidostilbene

Self—sensitized and Rose Bengal—sensitized photo—oxidation of 4, 4′-bisacetamidostilbene (BAAS) in solution gives p—acetamidobenzaldehyde and p—acetamidobenzoic acid via the reaction of singlet oxygen with the trans isomer (la). The rate of the photo—oxidation is retarded in the presence of effective singlet oxygen quenchers. On the other hand, cls—BAAS (lb) is more stable to visible light under the conditions of Rose Bengal—sensitized photo—oxidation than trans—stilbene.     

Multiresidue determination of quinolones in animal and fishery products by HPLC

A simple and rapid multiresidue method was developed for the determination of twelve quinolones (ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, ofloxacin, orbifloxacin, oxolinic acid and sarafloxacin) in muscle, liver, chicken eggs, milk, prawn and rainbow trout.The quinolones were extracted from a sample with acetonitrile-water (95 : 5). A fifth part of the filtered extract was diluted with water to keep the acetonitrile ratio at ca. 60%, and passed through a C18 mini-column. The eluate was evaporated to dryness, and the residues were dissolved in methanol-water (30 : 70) for HPLC analysis.The quinolones were separated on a Inertsil ODS-3V column (4.6 mm i.d.x250 mm) with a gradient system of 0.1% phosphoric acid-acetonitrile as the mobile phase, with fluorescence detection.No interfering peak was found on the chromatograms of animal and fishery products, except for milk. The recoveries of the quinolones were over 60% from the animal and fishery products fortified at 0.1 microg/g, and the quantification limits of the quinolones were 0.005 microg/g. This proposed method was found to be effective and suitable for the screening of the quinolones in animal and fishery products.