• Elastomers and Composites
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• v.54 no.2
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• pp.135-141
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• 2019

Polyphenylene sulfide (PPS) was filled with glass fiber (GF), aramid fiber (AF), and solid lubricants to improve the mechanical properties and wear resistance. The addition of GF effectively enhanced the tensile strength, flexural modulus, and impact strength of PPS, while solid lubricants such as polytetrafluoroethylene (PTFE), molybdenum disulfide ($MoS_2$), and tungsten disulfide ($WS_2$) lowered the friction coefficients of the composites to below 0.3. The ball nut and motor pulley of the electric power steering (EPS) were manufactured using the PPS composites, and feasibility was ascertained thereafter by conducting the durability test. The composites filled with GF and AF showed high mechanical strength, but slip occurred at the interface between the pulley and belt while testing above $50^{\circ}C$. When small amounts of lubricants were added, the slip was no longer detected because of the suppression of friction heat. It is realized that the low friction as well as high mechanical properties is important to ensure the reliability of plastic pulleys.

• Elastomers and Composites
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• v.57 no.4
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• pp.157-164
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• 2022

Representative bulletproof materials, such as aramid or ultra-high molecular weight polyethylene(UHMWPE), have excellent strength and modulus in the plane direction but are very vulnerable to forces applied in the thickness direction. This paper reports a study on the effects of reinforcement in the thickness direction when bulletproof composite fabrics are prepared to improve their performance. Aramid and UHMWPE fabrics were combined using the film-bonding, needle-punching, or stitching methods and then subjected to low-velocity projectile and ball-drop impact tests. The results of the low-velocity projectile test indicated that the backface signature(BFS) decreased by up to 29.2% in fabrics obtained via the film-bonding method. However, the weight of the film-bonded fabric increased by approximately 23% compared with that obtained by simple lamination, and the fabric stiffened on account of the binder. Flexibility, light weight for wearability, and excellent bulletproof performance are very important factors in the development of bulletproof materials. When the needle-punching method was used, the BFS increased as the fibers sustained damage by the needle. When the composite fabrics were combined by stitching, no significant difference in weight and thickness was observed, and the BFS showed similar results. When a diagonal stitching pattern was employed, the BFS decreased as the stitching density increased. By contrast, when a diamond stitching pattern was used, the fabric fibers were damaged and the BFS increased as the stitching density increased.

• Journal of Adhesion and Interface
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• v.16 no.1
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• pp.29-34
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• 2015

Hydrocarbon resins, which are defined as low molecular weight, amorphous, and thermoplastic polymers, are widely used as tackifier for various types of adhesives, as processing aids in rubber compounds, and as modifiers for plastics polymers such as isotactic polypropylene. Typically, hydrocarbon resins are non-polar, and thus highly compatible with non-polar rubbers and polymer. However, they are poorly compatible with polar system, such as acrylic copolymer, polyurethanes, and polyamides. Moreover, recently the raw materials of hydrocarbon resin from naphtha cracking had been decreased because of light feed cracking such as gas cracking. To overcome this problem, in this study, novel hydrocarbon resins were designed to have a highly polar chemical structure which material is sustainable. And, it was successfully synthesized by Diels-Alder reaction of dicyclopentadiene monomer and sorbic acid from blueberry as renewable resources. Acrylic resins were formulated with various tackifiers solution including sorbic acid grafted hydrogenated dicyclopentadiene hydrocarbon resins in acrylic adhesive and rolling ball tack, loop tack, $180^{\circ}$ peel adhesion strength, and shear adhesion strength were measured. The properties depend on the softening point and polar content of tackifiers.

• Journal of agricultural medicine and community health
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• v.44 no.3
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• pp.115-123
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• 2019

Objective: This study was conducted to examine the effects of a health promotion program on the health condition of rural elderly women implemented at primary health care posts using Korean Frailty Index. Methods: The research was designed a nonequivalent control group pretest-posttest setting. The participants in this study were 50 residents (intervention group: 25, control group: 25) selected from 4 villages 2 primary health care posts in J city Gyeongsangnam-do. The health promotion program was conducted at the primary health care posts twice a week for 12 weeks. This program consisted of basic exercises(Gukseondo + Theraband muscle strength training) and additional activities(including modified Theraband activity, rubber ball exercise, ball massage, nutrition class, singing class). Collected data were analyzed by descriptive statistics, paired t-test, and repeated measures ANOVA with SPSS 21.0. Results: Results of the health promotion program showed that the health conditions(measured by perceived health status, frailty score, upper/lower flexibility, maximum grip strength, dynamic balance test Timed Up and Go) of the experimental group(25) all statistical significantly improved. Conclusion: Study findings indicate that the health promotion program implemented at primary health care posts on rural elderly women is effective and can contribute to a developed health promotion program for local residents in the future.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.24 no.1
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• pp.115-124
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• 1994

The purpose of this study was to examine the differences in representation of a globular radiopaque mass on the pantomograms and Waters' views and to compare the efficacy of periapical radiograms, pantomograms and Waters' views in detection of defects on the internal walls of the maxillary sinus. This study was performed with dried human skull. For the study of difference of radiopaque mass shadow in the two views, rubber ball with a diameter of 10㎜ was used as the experimental lesion. It was placed successively on the internal wall of the anterior, posterior, medial, lateral walls and floor of the maxillary sinus. To examine the detectability of defects for radiographic techniques, defects were formed in the anterior, posterior, medial, lateral walls, and floor of the maxillary sinus. They were formed with 0.5㎜, 0.75㎜, 1.0㎜, 2.0㎜ and 3.0㎜ sized steel round burs with a slow speed dental handpiece. By subsequently plugging the holes with zinc oxide eugenol paste, radiopaque defects were produced. After that the periapical radiograms, the pantomograms and the Waters' views were taken each and every defect. The obtained results were as follows: 1. Rubber balls placed on each internal wall of the maxillary sinus were correctly depicted on the posterior wall and the floor in case of the pantomogram, and on the anterior wall and the medial wall in case of the Waters' view. 2. On the detectability of defects for each radiographic technique, radiolucent defects were detected in different places for each technique. Periapical radiogram could detect 1.0㎜ defect on the floor of the maxillary sinus, pantomogram could detect 2.0㎜ defect on every internal wall of the maxillary sinus, and Waters' view could detect 3.0㎜ defect on the anterior wall of the maxillary sinus. 3. On the detectability of defects for each radiographic technique, radiopaque defects were detected in different places for each technique. Periapical radiogram could clearly detect 0.5㎜ defect on the floor of the maxillary sinus, pantomogram could detect 0.5㎜ defect on every internal wall of the maxillary sinus, and finally Waters' view could detect 0.5㎜defect on the anterior wall of the maxillary sinus but 0.75㎜ defect on the anterior wall, lateral wall and floor of the maxillary sinus. As the result, the periapical radiogram is the most simple and satisfactory method for investigating in the maxillary sinus. The pantomogram is suitable method for screening of changes in the maxillary sinus. And the Waters' view is available for detect of lesion in the anterior wall of the maxillary sinus. For the purpose of accurate diagnosis and evaluation of lesion in the maxillary sinus, these techniques supplement each other.

• Tribology and Lubricants
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• v.31 no.5
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• pp.195-204
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• 2015

Several researches are focused on improving the value of fine chemicals based on biomass resources due to environmental and other concerns associated with the use of petroleum-based products. Therefore, the synthesis and application of estolides derived from plant-based waste oil materials and their application as lubricants and as processing oil for butyl rubber products have been studied. Four kinds of estolide were prepared with conversions of 71~92% over 24h using various vegetable oils, as determined by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. FT-IR spectroscopy determines the esterification of estolides using 2-ethylhexyl alcohol. The estolides have iodine values of 35~90, α-ester/α-acid ratios of 0.45~0.55, and total acid number of 114~134 mg KOH g^–1. Four ball wear tests show that the wear scar diameters (WSDs) of estolides as base oil significantly decreased to 0.328~0.494 mm, compared to WSDs of 0.735 and 0.810 mm of WSD for 150N and Yubase 6, respectively, as general base oil. Thus, the estolides have better wear resistance and satisfying design objectives for the engineering of a variety of lubricant base oils.

• Journal of Powder Materials
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• v.15 no.3
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• pp.239-243
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• 2008

Ni-W(1-5 at.%) alloy rods were made by powder metallurgy process including powder mixing, compacting and subsequent sintering. Ni and W powder of appropriate compositions were mixed by a ball milling and isostatically pressed in a rubber mold into a rod. The compacted rods were sintered at $1000^{\circ}C-1150^{\circ}C$ at a reduced atmosphere for densification. The lattice parameters of Ni-W alloys were estimated by a high resolution neutron powder diffractometer. All sintered rods were found to have a face centered cubic structure without any impurity phase, but the diffraction peak locations were linearly shifted with increasing W content. The lattice parameter of a pure Ni rod was $3.5238{\AA}$ which is consistent with the value reported in JCPDS data. The lattice parameter of N-W alloy rods increased by $0.004{\AA}$ for 1 atomic % of W, which indicates the formation of a Ni-W solid solution due to the substitution of nickel atoms by tungsten atoms of larger size.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.88-95
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• 2003

The auditory experiments based on subjective responses were undertaken for the standard heavy and light weight impact noise and rubber ball impact noise, jumping noise to investigate relations between floor Impact noise levels and subjective responses and to establish the upper/lower limits of floor impact noises. As a result, it was shown that relations between floor Impact noise levels and subjective responses was linear and the lower limit of heavy-weight impact noise was L/sub i, Fmax, AW/=46㏈ and the lower limit of light-weight impact noise was L'/sub n,AW/=56㏈. Finally the 3 subjective classes of floor impact noises were established.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.23 no.2
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• pp.277-285
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• 1993

This study was performed to evaluate the role of Waters' view and panoramic view for the interpretation of mucosal cyst of the maxillary sinus and to determine the radiographic features of that according to the sites and sizes. For this study, clinically 25 cases of mucosal cyst of the maxillary sinus were used, and experimentally with two dry skulls, rubber ball of 15mm in diameter for marked radiopacity, and two jelly balls of 8 and 20㎜ in diameter for the similar radiopacity to cyst were used. The 25 cases with 25 panoramic views and 15 Waters' views were first analyzed, and secondly, the radiographic features of artificial lesions attached to the each wall of the antrum on Waters' view and panoramic view were analyzed. The obtained results were as follows: At clinical analysis, 1. 4 cases of 13-14㎜, 4 cases of 15-19mm, 14 cases of 20-25㎜, 3 cases of over 30㎜ in dia- meter were found on panoramic views. And 24 cases of 25 cases showed no relationship with teeth, and only 1 case was associated with advanced periodontal disease 2. The majority of mucosal cysts appeared to arise the posterior portion of the floor of the sinus and were superimposed with the inominate line of zygoma and the horizontally linear image of hard palate on panoramic view. 3. Only 2 cases of 15 cases were identified on both films. At experimental analysis, 4. On Waters' view, the images of the artificial lesion of the anterior portion and midportion of the floor of the sinus were lessend in diameter compared with the real size. On panoramic views, the images of the lesion were more radiolucent with lessened diameter than images on Water' view. 5. The images of the lesion of the posterior wall and the posterior portion of the floor of sinus on panoramic view were well detected by the preeducated group but not or poorly detected by the non-preeducated observer group. 6. On Waters' view, both observer groups recognized that the cystic images of the posterior portion of the floor of the maxillary sinus were superimposed with the petrous portion of the skull.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.607-614
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• 2021

Research on elevator noise has mainly focused on the cause of its occurrence and measures to reduce it. There is still insufficient research on how to accurately measure and evaluate elevator noise. There is a measurement method established as an international standard for the measurement method, but it is also difficult to apply to high-rise apartments, and there are many cases that do not closely reflect the characteristics of elevator noise. In order to solve this problem, a study was conducted to improve the elevator noise measurement method in the current standard. In this study, the characteristics of elevator noise were closely identified. Through frequency analysis of the elevator noise and other equipment, it was verified that the elevator noise is noise with different characteristics from other equipment. Elevator noise was compared with heavy floor impact noise, which is a representative structural transmission noise, as structural transmission noise. Elevator noise was compared with heavy floor impact noise, which is a representative structural transmission noise, as structural transmission noise. The correlation between bang machine and rubber ball was found to be very high at 0.9 level. As a result, it was verified that the mid-low frequency band of the elevator noise is the main structural transmission noise and cannot be evaluated together with other equipment.