• Polymer(Korea)
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• v.34 no.6
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• pp.534-539
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• 2010

Polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via latex technology and the effect of nanotube length on rheological properties were investigated. Monodisperse PS particle was synthesized by the emulsifier-free emulsion polymerization and two types of MWCNTs were used after surface modification to improve dispersion state and to remove impurities. Final nanocomposites were prepared by the freeze-drying process after dispersing the PS particles and the surface-modified MWCNTs in a ultrasonic bath. The effects of MWCNT content and nanotube length on rheological properties were evaluated by imposing the small-amplitude oscillatory shear flow. The PS/MWCNT nanocomposites showed that rheological properties were enhanced as the amount and length of MWCNT increased. It is speculated that the rheological characteristics of nanocomposites change from liquid-like to solid-like as the MWCNT amount increases, and the critical concentration to achieve network structure decreases as the nanotube length increases.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.54-63
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• 2001

Rapid Prototyping(RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of a part due to layer-by-layer stacking, low build speed caused by point-by-point or line-by-line solidification to build one layer, and additional posts processing to improve surface roughness, so high cost is required to introduce and to maintain the RP apparatus. The objective of this study is to develop a new RP process, Variable Lamination Manufacturing by using expandable polystyrene foam sheet as part material(VLM-S), and to design an apparatus for implementation of the process. So, the process parameters and design criterions of the apparatus were defined and the techniques were proposed to satisfy the design criterion. Based on the results, a knob-shape, pyramid shape. and a solid block were fabricated on the apparatus in which unit shape part(USP) was generated for building each layer.

• Ocean and Polar Research
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• v.29 no.3
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• pp.193-204
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• 2007

In order to find out the annual variations in the marine ecosystem of the East China Sea, temperature, salinity, nutrients, chlorophyll-a, suspended solids, and suspended particulate organic carbon were extensively investigated in the northern East China Sea during the Summer of 2003 and 2006. During the Summer of 2003, the northern East China Sea was not significantly affected by the input of fresh waters from the Changjiang River. During the Summer of 2006, however, fresh waters of the Changjiang River intruded into the western part of the study area where temperature, nitrate, and phosphate in the surface waters were higher than in the other areas, and salinity, silicate, and suspended solids in the surface waters were lower. As a result of the increase in nitrate and phosphate concentrations, concentrations of chlorophyll-a and suspended particulate organic carbon increased in the western part compared with the other areas. However, the depth-integrated chlorophyll-a concentrations measured during the Summer of 2003 were rather similar to those during the Summer of 2006, and not considerably different from those measured in the East China sea during the Summer of 1994 and 1998. Therefore, the depth-integrated chlorophyll-a concentrations have not significantly changed in the East China Sea over the last 12 years. The lower concentrations of silicate and suspended solids in the western part may be related to construction of the Three-Gorges Dam since the concentrations of silicate and suspended solids in fresh waters of the Changjiang River have significantly decreased after construction of the Three-Gorges Dam in June 2003.

• Fashion & Textile Research Journal
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• v.19 no.3
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• pp.312-319
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• 2017

The purpose of this study was to develop a customized wrist brace using 3D scanner and 3D printer. This study included in-depth interviews with people who had wrist pain and ever used wrist braces. The wrist brace has been designed and modeled by the CAD program after 3D scanning the wrist of subjects. Based on the results of the in-depth interviews on wrist brace users and design investigation in the market, a prototype of the wrist brace has been created. The wrist brace does not compress the hand and is easy to put on. In addition, it is adjustable to the wrist of users, allowing them to move his or her wrist without any restrictions. A computer-modeling program produced solid files for the design of the wrist brace after 3D scanning ten subjects' hands. It features a lattice-patterned surface, a velcro adjustment and trimming to smoothen the surface. PLA filaments were used to 3D print the wrist brace. As for the assessment, the wrist brace has been evaluated to be easy to put on and adjust to user's wrist. However, when it comes to appearance and comfortability, it was rated 3.0 or slightly above. This is because 3D printing materials are firm and not flexible compared to other materials such as neoprene or stretchable bands.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.6
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• pp.867-876
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• 2012

The concentration of veterinary antibiotics in aqueous and sediment matrices was measured in agricultural irrigation ditches bordering several animal-feeding operations (AFOs) and then compared to its concentration in the watershed. Analytical determination in aqueous samples was based on solid phase extraction (SPE) and appropriate buffer solutions were used to extract residuals in sediment samples. Separation and detection of extracted veterinary antibiotics were performed with high performance liquid chromatograph tandem mass spectrometry (HPLC/MS/MS). In general, higher concentrations of antibiotic were observed in the aqueous phase of irrigation ditches, with the highest concentration of erythromycin hydrochloride (ETM-$H_2O$) of $0.53{\mu}g\;L^{-1}$, than in aqueous watershed samples. In contrast, higher concentrations were measured in river sediment than in irrigation ditch sediment with the highest concentration of oxytetracycline of $110.9{\mu}g\;kg^{-1}$. There was a high calculated correlation ( > 0.95) between precipitation and measured concentration in aqueous samples from the irrigation ditches for five of the ten targeted veterinary antibiotics, indicating that surface runoff could be an important transport mechanism of veterinary antibiotics from field to environment. Further, environmental loading calculation based on measured concentrations in aqueous samples and flow information clearly showed that irrigation ditches were 18 times greater than river. This result suggests the likelihood that veterinary antibiotics can be transported via irrigation ditches to the watershed. The transport via surface runoff and likely environmental loading via irrigation ditches examined in this study helps identify the pathway of veterinary antibiotics residuals in the environment.

• Journal of the Korean Society of Clothing and Textiles
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• v.41 no.5
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• pp.939-949
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• 2017

This study uses 3D printing technology to design and fabricate a fall impact protection pad with a spacer fabric structure. The design of the pads consists of hexagonal three-dimensional units connected in a honey-comb shape; in addition, the unit consists of a surface layer and a spacer layer. Protect pads were designed as either a hexagonal type or diamond type according to the surface layer structure; subsequently, a spacer filament was also designed as the most basic I-shape type. Designed pads were printed using four types of flexible filaments to select suitable material for a fall impact protection pad. Impact protection performance and bending stiffness were evaluated for the eight type of pad outputs. As a result of the impact protection performance evaluation, when the force of 6,500N was applied, the force passed through the pad was in the range of 1,370-2,132N. FlexSolid$^{(R)}$ and Skinflex$^{TM}$ showed good protection performance and cubicon flexible filament showed the lowest protection. NinjaFlex$^{(R)}$ was found to be the most flexible in the bending stiffness evaluation.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.177-184
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• 1998

The contact angle on powder hydrophobic polymer PMMA(polymethylmethacrylate), PVC(poly vinyl chloride) and hydrophilic metal aluminium was measured by wicking method on the base of Washburn equation for water, glycerol, formamide, diiodomethane, 1,1,2,2-tetrabromoethane, 1-bromonaphthalene, acetone, chloroform, benzene, ethanol, methanol, and for anionic surfactant SDS(sodium dodecyl sulfate) and cationic surfactant CATB(cetyl trimethylamonium bromide) aqueous solution with concentrations. The values of ${\gamma}_c$ estimated by Zisman plot and adhesion tension plot for contact angle with organic liquids, SDS, and CTAB aqueous solutions were 43.5, 28.3, and $36.2mNm^{-1}$ for PMMA and 44.2, 25.0, and $34.8mNm^{-1}$ for PVC, respectively. From the results, it was considered that wettability and characteristics of solid surface were transformed by adding surfactant. The surface free energy, ${\gamma}_s$ and its components of PMMA, PVC, and aluminium were determined using harmonic equation.

• Journal of Microbiology and Biotechnology
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• v.21 no.12
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• pp.1312-1321
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• 2011

Enzyme extracts of cellulase [filter paper cellulase (FPase) and carboxymethyl cellulase (CMCase)], chitinase, and chitosanase produced by Aspergillus niger NRRL-567 were evaluated. The interactive effects of initial moisture and different inducers for FP cellulase and CMCase production were optimized using response surface methodology. Higher enzyme activities [FPase $79.24{\pm}4.22$ IU/gram fermented substrate (gfs) and CMCase $124.04{\pm}7.78$ IU/gfs] were achieved after 48 h fermentation in solid-state medium containing apple pomace supplemented with rice husk [1% (w/w)] under optimized conditions [pH 4.5, moisture 55% (v/w), and inducers veratryl alcohol (2 mM/kg), copper sulfate (1.5 mM/kg), and lactose 2% (w/w)] (p<0.05). Koji fermentation in trays was carried out and higher enzyme activities (FPase $96.67{\pm}4.18$ IU/gfs and CMCase $146.50{\pm}11.92$ IU/gfs) were achieved. The nonspecific chitinase and chitosanase activities of cellulase enzyme extract were analyzed using chitin and chitosan substrates with different physicochemical characteristics, such as degree of deacetylation, molecular weight, and viscosity. Higher chitinase and chitosanase activities of $70.28{\pm}3.34$ IU/gfs and $60.18{\pm}3.82$ to $64.20{\pm}4.12$ IU/gfs, respectively, were achieved. Moreover, the enzyme was stable and retained 92-94% activity even after one month. Cellulase enzyme extract obtained from A. niger with chitinolytic and chitosanolytic activities could be potentially used for making low-molecular-weight chitin and chitosan oligomers, having promising applications in biomedicine, pharmaceuticals, food, and agricultural industries, and in biocontrol formulations.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.67-74
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• 1999

Problems created by supersonic jet impinging on solid objects or ground arise in a variety of situations. For example multi-stage rocket separation, deep-space docking, V/STOL aircraft, jet-engine exhaust, gas-turbine blade, terrestrial rocket launch, and so on. These impinging jet flows generally contain a complex structures. (mixed subsonic and supersonic regions, interacting shocks and expansion waves, regions of turbulent shear layer) This paper describes experimental works on the phenomena (surface pressure distribution, flow visualization) when underexpanded supersonic jets impinge on the perpendicular, inclined plate using a supersonic cold-(low system. The used supersonic nozzle is convergent-divergent type, exit Mach number 2, The maximum on the plate when it was inclined was much larger than perpendicular plate, owing to high pressure recoveries through multiple shocks. Surface pressure distribution as to underexpanded ratio showed similar patterns together.

• The Journal of the Acoustical Society of Korea
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• v.9 no.4
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• pp.18-32
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• 1990

Deeping on purpose, SAW device may have to function while immersed in a liquid. Those who are familiar with SAW devices would anticipate difficulty since the propagating surface waves will tend to radiate energy into the liquid and hence suffer attenuation. Thus, to design an immerable SAW device, more attention and full information about the wave properites is required to overcome the attenuation and get the highest SAW generation eficiency. Though numerical simulation, the optimal geometry of underwater SAW devices, such as optimal piezoelectric crystal cut, SAW propagation direction and nondimensional wave number(ka) is determined to get the maximum SAW excitation efficiency, the minimum attenuation in propagation and pure mode propagation for all the modes of surface wave propagation. The design technique can be appliedto an arbitrary combination of a piezoelectric layer, a substrate and a liquid medium. In this paper, PZT and PVDF layers and a steel substrate are use for the solid medium. The technique can be easily employed for the design of underwater sensors and actuators for the applications, such as sonar marine antifouling, industrial and medical uses.