• Journal of Marine Bioscience and Biotechnology
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• v.9 no.1
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• pp.14-21
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• 2017

The purpose of this study was to inhibit biofouling on a selectively permeable membrane (SPM) and increase biomass productivity in marine photobioreactors (PBRs) for microalgal cultivation by chemical treatment. Surfaces of a SPM, composed of polyethylene terephthalate (PET), was sulfonated to decrease hydrophobicity through attaching negatively charged sulfonic groups. Reaction time of sulfonation was varied from 0 min to 60 min. As the reaction time increased, the water contact angle value of SPM surface was decreased from $75.5^{\circ}$ to $44.5^{\circ}$, indicating decrease of surface hydrophobicity. Furthermore, the water permeability of sulfonated SPM was increased from $5.42mL/m^2/s$ to $10.58mL/m^2/s$, which reflects higher nutrients transfer rates through the membranes, due to decreased hydrophobicity. When cultivating Tetraselmis sp. using 100-mL floating PBRs with sulfonated SPMs, biomass productivity was improved by 34% compared with the control group (non-reacted SPMs). In addition, scanning electron microscopic observation of SPMs used for cultivation clearly revealed lower degree of cell attachment on the sulfonated SPMs. These results suggest that sulfornation of a PET SPM could improve microalgal biomass productivity by increasing nutrients transfer rates and inhibiting biofouling by algal cells.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.3
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• pp.275-281
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• 2004

Socket weldment used to change the flow direction of fluid nay have flaws such as lack of fusion and cracks. Liquid penetrant testing or Radiography testing have been applied as NDT methods for flaw detection of the socket weldment. But it is difficult to detect the flaw inside of the socket weldment with these methods. In order to inspect the flaws inside the socket weldment, a ultrasonic testing method is established and a ultrasonic transducer and automated ultrasonic testing system are developed for the inspection. The automated ultrasonic testing system is based on the portable personal computer and operated by the program based Windows 98 or 2000. The system has a pulser/receiver, 100MHz high speed A/D board, and basic functions of ultrasonic flaw detector using the program. For the automated testing, motion controller board of ISA interface type is developed to control the 4-axis scanner and a real time iC-scan image of the automated testing is displayed on the monitor. A flaws with the size of less than 1mm in depth are evaluated smaller than its actual site in the testing, but the flaws larger than 1mm appear larger than its actual size on the contrary. This tendency is shown to be increasing as the flaw size increases. h reliable and objective testing results are obtained with the developed system, so that it is expected that it can contribute to safety management and detection of repair position of pipe lines of nuclear power plants and chemical plants.

• Journal of Korean Dental Science
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• v.10 no.1
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• pp.10-21
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• 2017

Purpose: The purpose of this study was to investigate the electrochemical characteristics of nanotubular Ti-25Nb-xZr ternary alloys for dental implant materials. Materials and Methods: Ti-25Nb-xZr alloys with different Zr contents (0, 3, 7, and 15 wt.%) were manufactured using commercially pure titanium (CP-Ti), niobium (Nb), and zirconium (Zr) (99.95 wt.% purity). The alloys were prepared by arc melting in argon (Ar) atmosphere. The Ti-25Nb-xZr alloys were homogenized in Ar atmosphere at $1,000^{\circ}C$ for 12 hours followed by quenching into ice water. The microstructure of the Ti-25Nb-xZr alloys was examined by a field emission scanning electron microscope. The phases in the alloys were identified by an X-ray diffractometer. The chemical composition of the nanotube-formed surfaces was determined by energy-dispersive X-ray spectroscopy. Self-organized $TiO_2$ was prepared by electrochemical oxidation of the samples in a $1.0M\;H_3PO_4+0.8wt.%$ NaF electrolyte. The anodization potential was 30 V and time was 1 hour by DC supplier. Surface wettability was evaluated for both the metallographically polished and nanotube-formed surfaces using a contact-angle goniometer. The corrosion properties of the specimens were investigated using a 0.9 wt.% aqueous solution of NaCl at $36^{\circ}C{\pm}5^{\circ}C$ using a potentiodynamic polarization test. Result: Needle-like structure of Ti-25Nb-xZr alloys was transform to equiaxed structure as Zr content increased. Nanotube formed on Ti-25Nb-xZr alloys show two sizes of nanotube structure. The diameters of the large tubes decreased and small tubes increased as Zr content increased. The lower contact angles for nanotube formed Ti-25NbxZr alloys surfaces showed compare to non-nanotube formed surface. The corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface showed longer the passive regions compared to non-treatment surface. Conclusion: It is confirmed that corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface has longer passive region compared to without treatment surface.

• Progress in Medical Physics
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• v.17 no.4
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• pp.192-200
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• 2006

We evaluated the positional accuracy of the delivered beams to the target in a phantom by simulating the whole process of the radiation treatments Including CT scanning, planning and beam exposures with MLCs. For this purpose, a phantom was made to calibrate the alignment between the CT and the attached laser system. A new, convenient method was also devised to align the setup lasers in the treatment room. Film was used for the Identification of the delivered beam and analyzed with a homemade computer program. The positional differences between the target and the beam centers varied with the couch rotations. The accelerator we used showed a maximum discrepancy of 2.0 mm at the table angle of $295^{\circ}$. The same measurements based on the new isocenter from the Winston-Lutz test resulted in the maximum of 1.35 mm for all rotation angles. The evaluation of the differences between the target and the beam centers is useful for the treatment planning.

• Polymer(Korea)
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• v.24 no.6
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• pp.737-743
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• 2000

Polyquinonediimines (PQDI) which have stable structure on heat and contains mono-azobenzene in the side chain were synthesized by means of condensation polymerization under TiCl$_4$. The synthesized monomers and polymers were identified by FT-IR, $^1$H-NMR, and elementary analysis. Especially, PQDI was comfirmed by the double-bonding peak of >C=N appeared near 1625 $cm^{-1}$ / by means of FT-IR spectrum. PQDI containing mono-azobenzene group in both side chains wat not soluble in non-polar solvents at all but partially soluble in the polar solvents having small dielectric constant, and dissolved in the strong acid such as sulfuric acid and $CH_3$SO$_3$H. Molecular weight distribution of PQDI measured by GPC showed 1.74. It was confirmed through X-ray diffraction analysis that the polymer was partially crystalline at the low angle region, but amorphous after heat treatment at 1$25^{\circ}C$. The glass transition temperature (T$_{g}$ ) of synthesized polymer was measured as 1$25^{\circ}C$ by differential scanning calorimetry. The SHG value for $\chi$$^{(2)}$ after poling at 1$25^{\circ}C$ was 8.6 pm/V (λ=1.542 ${\mu}{\textrm}{m}$). The SHG value slowly decreased with time from the start but appeared temporal stability after 100 hours.

• Membrane Journal
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• v.21 no.3
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• pp.222-228
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• 2011

Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer was synthesized via atom transfer radical polymerization (ATRP) and used as an electrolyte for electrochromic device. Plasticized polymer electrolytes were prepared by the introduction of propylene carbonate (PC)/ethylene carbonate (EC) mixture as a plasticizer. The effect of salt was systematically investigated using lithium tetrafluoroborate ($LiBF_4$), lithium perchlorate ($LiClO_4$), lithium iodide (LiI) and lithium bistrifluoromethanesulfonimide (LiTFSI). Wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) measurements showed that the structure and glass transition temperature ($T_g$) of polymer electrolytes were changed due to the coordinative interactions between the ether oxygens of POEM and the lithium salts, as supported by FT-IR spectroscopy. Transmission electron microscopy (TEM) showed that the microphase-separated structure of PVC-g-POEM was not greatly disrupted by the introduction of PC/EC and lithium salt. The plasticized polymer electrolyte was applied to the electrochromic device employing poly(3-hexylthiophene) (P3HT) conducting polymer.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.26 no.3
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• pp.350-366
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• 2016

Objectives: No 3D anthropometric analyses have been conducted for Korean children's faces for the purpose of designing respiratory protective devices. The aim of this study was to develop masks against yellow dust and fine particulates, particularly for children in Korea. Methods: This study utilized a 3D scanning method to obtain 16 facial anthropometric data from children, ages of 5 to 13 years old. A total of 144 boys and girls were recruited from the kindergarten, elementary schools and middle schools in Seoul. With facial dimensions obtained, cluster analysis was performed to categorize them into similar facial groups. For each cluster, an optimal mask was designed and manufactured using a 3D printer. In addition, lung function data were obtained from 62 subjects and compared with those of normal adults. The pulmonary physiological results were subsequently used to suggest a test method for mask certification. Results: Facial shapes were classified into tree clusters: small, medium, and large. The face width and length for the first group were small with high nosal protrusion. The face width and length for the second group were the largest among the three clusters. The third group had the largest angle of nose root - gnathion(n-prn-gn). Age was the most significant variable in the facial dimensions. Children's pulmonary physiological capacity was about 60% of adults' capacity. The results of fit test using the prototype masks developed showed very good fits for children. Conclusions: For Korean children, three mask sizes will be sufficient and practical for providing protection against yellow dust and fine particulates. Anthropometric data obtained using digitalized 3D face analysis can be very effective for designing respiratory devices. 3D images can be accurate and easily measured for multiple dimensions, particularly for curved areas of the face. It is imperative to adopt different test methods for certifying respiratory protective devices for children, since their pulmonary physiological capacity is inferior compared with that of adults.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.45-53
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• 2000

To analyze the photodegradation mechanism of materials for fisheries facilities which stand for considerable time immediately under or even partly above the water surface, such as cage collar, cage net, stationary fishing gear, egc. after 900 hours exposure, weathering experiments on 3 kinds of netting twines like dyed polyethylene(PE) and nylon, and non-treated high strength PE(Hi-PE) were carried out by using xenon light source. The results obtained are as follows : It was observed by scanning electron micrograph(SEM) that a good protection by pigments was obtained in PE and nylon specimen, while crack was rapidly progressed at the surface of Hi-PE one owing to etching by UVR. There was a little increase in density resulting from reorientation of polymer chain, chain scission, etc. in Hi-PE specimen. A wide angle X-ray diffraction showed that 3 kinds of specimens had no fundamental changes in polymer crystalline structure considering each 2$\theta$ of diffraction peak. Remaining tenacity of netting twines was in order of PE, nylon, and Hi-PE after having been exposed to the effect of 900 hours. PE and nylon treated with stuffs were shown to be more resilient than non-treated Hi-PE as confirmed by SEM.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.313-319
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• 2012

In this work, the electroplating of copper was introduced on PAN-based carbon fibers for the enhancement of mechanical interfacial strength of carbon fibers-reinforced composites. The surface properties of carbon fibers were determined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and contact angle measurements. Its mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). From the results, it was found that the mechanical interfacial properties of Cu-plated carbon fibers-reinforced composites (Cu-CFRPs) enhanced with increasing the Cu plating time, Cu content and COOH group up to Cu-CFRP-30. However, the mechanical interfacial properties of the Cu-CFRPs decreased dramatically in the excessively Cu-plated CFRPs sample. In conclusion, the presence of Cu particles on carbon fiber surfaces can be a key factor to determine the mechanical interfacial properties of the Cu-CFRPs, but the excessive Cu content can lead the failure due to the interfacial separation between fibers and matrices in this system.

• Fibers and Polymers
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• v.6 no.1
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• pp.19-27
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• 2005

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight poly­mers, HM s-PS and LM s-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2-3 km/min. The crystal modification was a-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (OSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LM s-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HM s-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-duc­tile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a uni­versal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached -0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.