Permeability measurement of a circular braided preform for resin transfer molding

Permeability of the preform is one of key factors in design of RTM (Resin Transfer Molding) mold, determination of processing conditions, and modeling of flow in the mold. According to previous studies, permeability measured in the unsaturated fiber mats are higher than that in the saturated fiber mats by about 20 % because of the capillary pressure. In this study, permeabilities of several fiber preforms are measured for both saturated and unsaturated flows. A saturated experiment of radial flow has been adopted to measure the permeability of anisotropic fiber preforms with high fiber content, i.e., circular braided preforms. In this method, four pressure transducers are used to measure the pressure distribution. Permeabilities in different directions are determined and the experimental results show a good agreement with the theory. Since permeability is affected by the capillary effect, permeability should be measured in the unsaturated condition for the textile composites to be manufactured under lower pressure as in the Vacuum Assisted Resin Transfer Molding (VARTM).     

Syntheses of new film-forming aromatic poly(amide-imide)s containing isoindoloquinazolinedione unit in the backbone: Poly(biphenylphthalicdianhydride-oxydianiline-4,4′-diamino-3′-carbamoyl-benzanilide) (poly(BPDA-ODA-DACB))

New film forming aromatic poly(amide-imide)s containing isoindoloquinazolinedione (IQ) unit in the backbone chain (polymerXIV) have been successfully synthesized by preparing prepolymers of poly(amic acid-carbonamide), followed by subsequent thermal cyclization of the prepolymers. 4,4′-Diamino-3′-carbamoylbenzanilide (DACB)V has been synthesized by reduction of 3′-carbamoyl-4′-amino-4-nitrobenzanilideIV. The prepolymers of poly(amic-acid-carbonamide) (polymersVII andVIII) which exhibit viscosities ranging from 1.4 to 1.7 dl/g have been prepared by a condensation polymerization of monomers such as BPDA, ODA, and DACB. PolymerXIV has been obtained by thermal cyclization of the polymersVII andVIII. During the thermal cyclization reaction, imide ring structure was first introduced and then transformed to the structure of IQ unit. The thermal degradation rate of the resultant polymers were influenced by the cleavage of amide bond but the final char yield was comparable to that of poly(BPDA-ODA).     

Morphology and properties of polyacrylonitrile/single wall carbon nanotube composite films

Composite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in DMF subsequent to sonication. The SWNTs in the films are well dispersed as ropes with 20–30 nm thickness. Moreover, AFM surface image of the composite film displays an interwoven fibrous structure of nanotubes which may give rise to conductive passways and lead to high conductivity. The polarized Raman spectroscopy is an ideal characterization technique for identification and the orientation study of SWNT. The well-defined G-peak intensity at 1580 cm⁻¹ shows a dependency on the draw ratio under cross-Nicol. The degree of nanotube orientation in the drawn film was measurable from the sine curve obtained by rotating the drawn film on the plane of cross-Nicol of polarized Raman microscope. The threshold loading of SWNT for electrical conductivity in PAN is found to be lower than 1 wt% in the composite film. The electrical conductivity of the SWNT/PAN composite film decreased with increasing of draw ratio due to the collapse of the interwoven fibrous network of the nanotubes with uniaxial orientation.     

Status of bovine mastitis and associated risk factors in subtropical Jeju Island, South Korea

The present investigation was carried out to study the prevalence of mastitis in 136 Holstein cows from a subtropical province of South Korea. Out of 527 milk samples studied, 22.6 % were found positive for mastitis. On animal level, prevalence was estimated at 55.2 %. Late lactating cows were at higher risk for mastitis development as compared to those in early and mid lactations. The study revealed that the risk of an increase in somatic cell count (SSC) and mastitis increased with advanced age and in animals with higher parity. The highest infection rate of 71.4 % was found in the age group >9 years followed by cows with higher than fifth parity (65.5 %). On severity and quarter basis, cows of <3 years of age had higher occurrence (12.5 %) of severe mastitis. From the present study, it may be concluded that a positive relationship exists between increased prevalence of mastitis and high SCC and the advance in age and parity of Holstein cows.     

Allometric equations for estimating the aboveground volume of five common urban street tree species in Daegu,Korea

Quantifying urban tree biomass and carbon (C) storage by using allometric equations is required for various studies such as assessing the inventory, modelling, and measuring ecosystem services of urban trees. However, the lack of urban-specific allometric equations leads to uncertainty when estimating urban tree biomass and C storage. Therefore, we followed a nondestructive approach and developed allometric equations specifically for Acer buergerianum Miq., Ginkgo biloba L., Platanus orientalis L., Prunus yedoensis Matsum., and Zelkova serrata (Thunb.) Makino in Daegu, Korea. Diameter at breast height (DBH)-based and DBH-and-height-based allometric equations were highly accurate at estimating the aboveground volume (R² > 0.92), while the allometric equations for P. orientalis and Z. serrata developed for traditional forests overestimated volume by 68% and 427%, respectively. The addition of a height variable into the DBH-based allometric equations did not increase the reliability of the allometric equations at a local level. The mean aboveground C storage of urban street trees was 24.9 Mg C/ha except for P. orientalis with a mean of 69.7 Mg C/ha, and the total aboveground C storage of urban street trees in Daegu was 10.6 Gg C. Alternatively, a generalized allometric equation which compiled species-specific equations can be applied for large-scale estimation. The generalized equations developed in this study and those found in the literature may suggest a constant value (～2.3–2.4) for the scaling exponent in the generalized equations. Allometric equations developed from natural or artificial stands may overestimate the volume of urban street trees; therefore, estimating urban tree biomass and C storage requires urban-specific allometric equations.     

Mechanical properties of denim fabric reinforced poly(lactic acid)

Denim, a twilled cotton fabric, was used to enhance the mechanical and thermal properties of poly(lactic acid) (PLA). The denim fabric reinforced composites with different numbers of denim layers were fabricated by using a hand layup method. The impact, tensile, and dynamic mechanical properties of the composites were observed with increasing denim layers to examine the reinforcing effect of denim fabrics. Numerical analysis was carried out to model the elastic modulus of the composite by using a commercial software. Three-dimensional geometry of the denim fabric reinforced PLA composite was generated through a CAD program, and the elastic modulus was calculated by applying uniform deformation on one surface. The impact strength, tensile strength, and thermal properties of the composites were improved by piling denim fabrics. The denim fabric reinforced composites exhibited outstanding impact strength due to the retarded crack propagation as well as large energy dissipation. The 3 layer denim reinforced composite showed best results among all specimens, and its impact strength, tensile strength, and tensile modulus were measured to be 82 J/m, 75.76 MPa, and 4.65 GPa, respectively. The PLA/denim composites have good mechanical properties and can substitute traditional composites such as glass fiber or carbon fiber reinforced composites.     

Optimal Conditions for Long-distance Transportation of Live Black Rockfish (Sebastes schlegeli) and Changes in their Characteristics during Transport

Optimal transport conditions for the live black rockfish and changes in their characteristics during long-distance transport were investigated. Oxygen consumption by black rockfish was lowest at 4°C and increased as the water temperature increased up to a maximum at 10°C. At a water temperature of 8°C and 10°C, the plasma glucose concentration of the fish was 36.2 and 38.2 mg/dL, respectively. The mean weight of the fish reduced to approximately 2.8% of initial weight after 16 days of storage at 8°C. The fish did not feed, and the survival rate of fish stored for 16 days at 8°C was 98.4%. The longer the live fish were stored in the container, the quicker the onset of rigor mortis after the slaughter was reached. Compared with fillets from control fish, the chewiness of fillets was somewhat lower (17.3%) after storage of fish for 16 days, but the softness of the fillets was slightly higher (21.6%). From these results, it was suggested that the optimum temperature for long-distance transport of the live fish was 8°C and that the long transport period of live fishes decreased their fillet quality more rapidly after fish death.     

Microtuberization of Potato (Solanum tuberosum L.) as Influenced by Supplementary Nutrients, Plant Growth Regulators, and In Vitro Culture Conditions

Five experiments with in vitro-grown plantlets of potato cvs ‘Superior,’ ‘Early Valley,’ ‘Golden Valley,’ and ‘Winter Valley’ were carried out to investigate in a stepwise approach the potential for enhancing microtuber production of (1) adding supplementary nutrients (SN) including KNO₃, NH₄H₂PO₄, Ca(NO₃)₂.4H₂O, and MgSO₄ in full- or half-strength Murashige and Skoog (MS) medium, (2) adding a pretested combination of plant growth regulators (PGRs), i.e., 10 mg l⁻¹ 6-benzyl aminopurine plus 200 mg l⁻¹ succinic acid 2,2-dimethylhydrazide, (3) varying the timing of the supplemental applications, and (4) varying the replenishment of the medium. Plantlets of ‘Superior’ for microtuberization were grown from two-node explants for 75 days under environmental conditions consisting of 22 ± 2 °C and a 16-h photoperiod on a solid basal medium consisting of half-strength MS (1/2 MS) medium containing 6 % sucrose and a moderate concentration of supplementary nutrients, SN-2 (KNO₃, 1.22 g l⁻¹; NH₄H₂PO₄, 1.41 g l⁻¹; Ca(NO₃)₂4H₂O, 0.23 g l⁻¹; and MgSO₄, 0.74 g l⁻¹). Thereafter, plantlets were grown for 60 days under dark conditions. Liquid media containing different combinations of MS, SN, and PGR levels plus 8 % sucrose were added as a supplement and were evaluated for their ability to increase tuberization compared to the control composition of the supplement (MS with 8 % sucrose). In the first experiment, addition of 1/2 MS liquid medium containing 8 % sucrose and SN-2 before dark incubation induced the highest total number of microtubers (on average 1.4 per plantlet), a significantly higher weight and size than the control, and the highest percentage (50 %) of large-sized (>500 mg) microtubers. In the second experiment, addition of 1/2 MS liquid medium containing 8 % sucrose, SN-2, and PGRs produced the highest number (on average 1.5 per plantlet) and total yield (on average 971 mg per plantlet) of microtubers, and significantly the highest percentage (66 %) of large-sized (>500 mg) microtubers. The size of the microtubers was higher than for the treatment without growth regulators. The optimum time for addition of supplemental medium containing 8 % sucrose, SN-2, and PGRs was shown in experiment 3 to be latest 1 week before dark incubation. This timing resulted in both the highest microtuber number (on average 1.6 per plantlet) and yield (on average 1208 mg per plantlet), and the highest percentage (64 %) of large-sized microtubers. Finally, it was found that a second supplemental treatment consisting of 50 % replacement of the liquid medium (by volume) 2 weeks after transfer to dark conditions gave rise to the highest number (on average 1.9 per plantlet), yield (on average 1346 mg per plant), and also significantly the highest percentage (25 %) of large-sized microtubers (>1000 mg) as compared to replacement of a greater or smaller proportion of the medium. Four potato cultivars, ‘Superior,’ ‘Early Valley,’ ‘Golden Valley,’ and ‘Winter Valley’ produced acceptable numbers and yield of microtubers of relatively large-sized tubers using a process that included supplemental liquid medium with 1/2 MS, 8 % sucrose, moderate concentration (SN-2) of SNs and PGRs, followed by a 50 % replacement of the same medium.     

Preparation and characterization of iptycene polymer/SWCNT nanocomposites

To enhance the strength while retaining the ductility of triptycene polyester, triptycene polyester/SWCNT nanocomposites were prepared. First, two different types of triptycene polyesters containing triptycenes that differ in size were synthesized and their mechanical and thermal characteristics were studied. Thermal analysis showed that the polyester containing the larger triptycene posed as a bigger hindrance factor to polymer chain-packing, resulting in lower crystallinity. Although the presence of triptycene interfered the packing of polymer chains, the increased size and amount of triptycene enhanced the thermal stability of the polymer. For the smaller sized triptycene-polyester/SWCNT composites, higher SWCNT content increased the stiffness and strength of the composite, but at the expense of the ductility. The increase in SWCNT content in the larger-sized triptycene polyester/SWCNT composites somewhat decreased the stiffness as well as the ductility of the polymer.