• Design & Manufacturing
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• v.12 no.1
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• pp.52-57
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• 2018

With the recent strengthening of environmental regulations and the need for cost reduction, excavators, a type of construction equipment, are being miniaturized while components are being developed in consideration of stability. In the case of excavator press parts, mainly high-strength steel sheets are being used to enhance stability and reduce weight. However, in the case of high-strength materials, there is a need to research product forming methods to reduce Springback in defects arising in parts assembly due to Springback that result from the internal residual stress that occurs in press forming being released after product forming. Accordingly, regarding the tank cover, an excavator press-forming part, this study selected a method to reduce distortion through analysis of the Springback occurrence rate and Springback causes through a forming analysis. A forming analysis was conducted for the Springback of the tank cover. Deformations of 13.714 mm in the upper part and 6.244 mm in the inner part of the product occurred, while wrinkles occurred on the sides of the product due to uneven thickness. A forming analysis was conducted for the major shapes of the product to investigate the causes of Springback. Distortion deformation due to the bead in the center of the product was confirmed to be a large factor. A Springback reduction method of correcting uneven thickness in the product sides, a Springback reduction method of removing the bead, and a correction method of restriking after the final forming were used in a forming analysis to determine the degree of Springback reduction. For the forming method to correct uneven thickness in the sides, deformation was reduced by 12% in the upper side compared to the existing model, but deformation in the inner side increased by 1%. For the restriking forming method, deformation decreased by 25% in the upper side and 13% in the inner side. For the bead removal method, deformation decreased by 28% in the upper side and 13% in the inner side, the largest Springback correction results. This indicates that the bead has a large affect on Springback.

• The Journal of Korean Physical Therapy
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• v.12 no.1
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• pp.101-112
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• 2000

The aim of this study is to compared the cerebral palsy children with normal children in the exercise and cardio vascular ability after this study as the fundamental data fer mating programs for the cerebral palsy children. The test of this study is about twenty girls, the control group of the normal children(n=10) and the experiment group of cerebral palsy children(n=10). They were studied in four aspects which were the anthropometry, the medical check in the rest, the physical fitness or exercise roads test and the change of the target heart rate during exercise. The result were as follows : 1. The characteristic of the physical type : The control group is higher than the experiment group in the standing height and the body weight but their's little difference between them (p<0.05). The control group is lower than the experiment group in the body fat. 2. The characteristic of the medical check in the rest : The control group is higher than the experiment group in the vital capacity and flood expiratoryvolume one second. The control group is higher that the experiment group in the blood pressure of systolic and Diastolic. There's little difference between them(p<0.01). The control is lower than the experiment group in the heart pulse rate. There's little difference between them(p<0.005). 3. The characteristic of basic physical strength evaluation : The experiment group is the lowest dynamic muscular endurance, balance, agility and endurance which need to move the body with weight. The control group is much higher than the experiment group in the flexibility and muscle strength(Back strength). There's no difference between them(p<0.05). 4. The characteristics of the exercise stress last : The control group is higher than the experiment group in the endurance, the maximum of oxygen intake, endurance level and the out take of calory. There's little difference between them(p<0.01). 5. The characteristic of the change of the target heart rate during exercise : The control group is lower than the experiment group exchange of target heart rate, There's no difference them.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1677-1685
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• 2014

Short discrete fibers compounded with concrete can enhance the tensile resistance and ductility of concrete. Recently, the effectiveness of the reinforcement has increased according to the increasing length of steel fiber. However, the lengthening of steel fiber requires reducing the ratio of the fiber content to remain the workability and quality of concrete. Thus, the present study evaluated the flexural performance of fiber reinforced concrete with less than l.0% fiber volume ratios of steel fiber, 30mm and 60mm long, and polypropylene fiber, being evaluated as a good reinforcing material with chemical stability, long-term durability, and cost effectiveness. Concrete with more than 0.25% steel and 0.5% polypropylene fibers improved the brittle failure of concrete after reaching cracking strength. Concrete reinforced with polypropylene exhibited deflection-softening behavior, but that with more than 0.5% polypropylene delayed stress reduction and recovered flexural strength by 60 to 80% after cracking strength. In conclusion, concrete reinforced with more than 0.75% polypropylene could improve structural flexural performance. In particular, energy absorption capacity of reinforced concrete with 1.0% polypropylene fiber was similar to that with 0.5% and 0.7% steel fibers.

• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.169-179
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• 2010

The aim of this study was to investigate occupational and individual risk factors and working conditions in relation to musculoskeletal symptoms in street cleaners. Investigation was conducted through a survey of 395 male street cleaners employed by the government office in Seoul, Gyeonggi and Chung-Nam from July to August of 2009. The control group was comprised of 143 male drivers and security guards. Risk factors for musculoskeletal symptoms in street cleaners were investigated by multiple logistic regression analysis and also evaluated ergonomic risk factors by assessing working conditions of 4 street cleaners. As a result of symptom questionnaires, all of the prevalent rates of musculoskeletal symptoms in street cleaners had significantly higher results than those of the control group(p<0.05). On binary logistic regression analysis of musculoskeletal symptoms, street cleaners showed significant higher odds ratio as 18.84(95%CI: 6.56-54.12) in the arm/elbow, 10.49(95%CI: 4.29-25.65) in the hand/wrist compared to the control group. Both absence of rest breaks and exposure to ergonomic risk factors showed to be important internal risk factors of musculoskeletal symptoms among street cleaners. The exposure levels of QEC(Quick exposures checklist) in street cleaners were revealed to be higher on the shoulder/arm, wrist/hand, and neck than back, or from stress. The findings appear to show that street cleaners were high-risk group of work-related musculoskeletal disorders. Therefore street cleaners require a holistic interventional strategy, including adequate arrangement of rest breaks, improvement of working tools and control of individual risk factors such as obesity and smoking.

• Resources Recycling
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• v.29 no.3
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• pp.11-23
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• 2020

This study aims to investigate breakage and liberation characteristics of iron ore from Shinyemi mine, Jeongseon by ball mill. Parameters of breakage functions for three grade samples of iron ore were obtained using single-sized-feed breakage test and back-calculation based on nonlinear programming. The results showed that with the increase in the grade of iron ore, the breakage rate factor decrease whereas the particle size sensitivity decreases. This results from retardation of microcrack-propagation by magnetite grain in the ore. Breakage distribution analysis showed that the breakage mechanism appear to be impact fracture dominant with the increase of grade owing to the stress distribution effect by magnetite grain. Degree of liberation (DOL) increased with the increase in grade and decrease in particle size, respectively. Using the breakage function and size-DOL relationship, a model that can predict time-dependent-DOL is established. When scale-up factors from operating condition are available, the model is expected to be capable of predicting size and DOL with time in actual mining process.

• Journal of the Korean Vacuum Society
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• v.22 no.4
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• pp.188-192
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• 2013

Many studies have been conducted for preventing from diffusion between silicon wafer and metallic thin film due to a decrease of line-width and multi-layer thin film for miniaturization and high integration of semiconductor. This paper has focused on the nano-mechanical property of diffusion barrier which sample is prepared for various gas flow rate of nitrogen with tungsten (W) base from 2.5 to 10 sccm. The deposition rate, resistivity and crystallographic properties were measured by a ${\beta}$-ray back-scattering spectroscopy, 4-point probe and x-ray diffraction (XRD), respectively. We also has investigated the nano-mechanical property using the nano-indenter. As a result, the surface hardness of W-N thin film was increased rapidly from 10.07 to 15.55 GPa when the nitrogen gas flow was increased from 2.5 to 5 sccm. And the surface hardness of W-N thin film had 12.65 and 12.77 GPa at the nitrogen gas flow of 7.5 and 10 sccm respectively. These results were decreased by the comparison with the W-N thin film at nitrogen gas flow of 5 sccm. It was inferred that these severe changes were caused by the stoichiometric difference between the crystalline and amorphous state in W-N thin film. In addition, these results were caused by increased compressive stress.

• Asian Spine Journal
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• v.12 no.6
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• pp.1060-1068
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• 2018

Study Design: Retrospective study. Purpose: Lumbar intervertebral disc degeneration is an important cause of low back pain. Overview of Literature: Spinal fusion is often reported to have a good course for adolescent idiopathic scoliosis (AIS). However, many studies have reported that adjacent segment degeneration is accelerated after lumbar spinal fusion. Radiography is a simple method used to evaluate the orientation of the vertebral column. magnetic resonance imaging (MRI) is the method most often used to specifically evaluate intervertebral disc degeneration. The Pfirrmann classification is a well-known method used to evaluate degenerative lumbar disease. After spinal fusion, an increase in stress, excess mobility, increased intra-disc pressure, and posterior displacement of the axis of motion have been observed in the adjacent segments. Methods: we retrospectively secured and analyzed the data of 15 patients (four boys and 11 girls) with AIS who underwent a spinal fusion surgery. We studied the full-length view of the spine (anterior-posterior and lateral) from the X-ray and MRI obtained from all patients before surgery. Postoperatively, another full-length spine X-ray and lumbosacral MRI were obtained from all participants. Then, pelvic tilt, sacral slope, curve correction, and fused and free segments before and after surgery were calculated based on X-ray studies. MRI images were used to estimate the degree to which intervertebral discs were degenerated using Pfirrmann grading system. Pfirrmann grade before and after surgery were compared with Wilcoxon signed rank test. While analyzing the contribution of potential risk factors for the post-spinal fusion Pfirrmann grade of disc degeneration, we used generalized linear models with robust standard error estimates to account for intraclass correlation that may have been present between discs of the same patient. Results: The mean age of the participant was 14 years, and the mean curvature before and after surgery were 67.8 and 23.8, respectively (p<0.05). During the median follow-up of 5 years, the mean degree of the disc degeneration significantly increased in all patients after surgery (p<0.05) with a Pfirrmann grade of 1 and 2.8 in the L2-L3 before and after surgery, respectively. The corresponding figures at L3-L4, L4-L5, and L5-S1 levels were 1.28 and 2.43, 1.07 and 2.35, and 1 and 2.33, respectively. The lower was the number of free discs below the fusion level, the higher was the Pfirrmann grade of degeneration (p<0.001). Conversely, the higher was the number of the discs fused together, the higher was the Pfirrmann grade. Conclusions: we observed that the disc degeneration aggravated after spinal fusion for scoliosis. While the degree of degeneration as measured by Pfirrmann grade was directly correlated by the number of fused segments, it was negatively correlated with the number of discs that remained free below the lowermost level of the fusion.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.2
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• pp.377-384
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• 2022

Vortex-induced vibration (VIV) occurs owing to the vortex generated from the back side of the appendages of ships and submarines during operation. Recently, the importance of high-order modes (HOMs) vibration and fatigue failure has become increasingly emphasized by increasing the speed of ships and the size of structures. In addition, predicting the vibration of HOMs is significantly necessary as the VIV becomes stronger in the fast flow speed condition than in the low flow speed condition. This study introduces a methodology according to HOMs hybrid Fluid Structure Interaction (FSI) for predicting the HOMs VIV on the hydrofoils. The HOMs FSI system is verified by comparing the VIV results from the FSI simulation with the experimental results. Finally, the effectiveness of the HOMs FSI is determined by applying the maximum von-Mises stress obtained from the VIV on the hydrofoil to the S-N curve released from Det Norske Veritas (DNV). VIV results from the HOMs FSI include the lock-in characteristics as well as a significant increase of more than 10 times compared with that of low-order modes (LOMs) FSI. In the future works, advanced studies will be required for improving cantilever boundary conditions and the shape of hydrofoils.

• Asia Marketing Journal
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• v.15 no.3
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• pp.15-29
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• 2013

Shopping is considered a 'must-do' activity for most people on travel. One of the major parts of tourist shopping is the purchasing of souvenirs. Souvenirs are universally associated with tourism as a commercially produced and purchased object to remind the purchaser of the experience. Recently, Korea becomes one of the most popular destinations that many Asian tourists like to visit. Among those Asian tourists, the number of Thai tourists bound for Korea shows an incredible rapid growth. Thai people pick Korea and Seoul as their favorite country and city to visit for three consecutive years since 2009. One of the major reasons why Thais are choosing to tour Korea is the enthusiasm for Korean pop culture. That is, 'Hallyu' has influenced Thais' decision to visit Korea and purchase Korean products. The primary objective of the current research is to explore the shopping experiences of Thai tourists, specifically their souvenir shopping. It adopts a reflexive interpretive approach to bring light to the various meanings Thai tourists attach to the souvenirs they purchase in Korea. In order to accomplish the objective, the individual interviews were conducted. A total of 12 Thais who have experienced traveling in Korea participated in the study. Four themes were identified through interview text analysis. First, the research participants almost always purchase souvenirs in Korea because the souvenirs represent their identities as tourists. Especially, they purchase the souvenirs as gifts for others, including family members, friends, and colleagues. The souvenirs as gifts show love and thanks to others, and they cement the social relationship. However, purchasing souvenirs for others is more like the moral obligations which evoke the psychological stress. Secondly, the research participants feel closer to Korea while shopping souvenirs around. Thirdly, they obtain imaginative experiences and pleasure through souvenirs related to the Korean pop culture. Souvenirs provide them to visually extraordinary experiences. Lastly, souvenirs purchased in Korea act as visible status marker when they go back to Thailand. They show the socioeconomic status and lifestyles. Tourists themselves and others place special value to souvenirs that were purchased out of Thailand. The findings of this study are of both academic and practical importance. Souvenirs are among the most pervasive elements of the travel experience. However, souvenir shopping is the complicated consumer behavior within tourism both from business and social science perspectives. Along the same line, it needs strategic approaches in order to maximize the economy effects. It concludes by suggesting how further research could offer unique insights into how the souvenirs are positioned both in the context of tourism academics and industry.

• Journal of Korean Dental Hygiene Science
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• v.1 no.2
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• pp.41-52
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• 2018

The purpose of this study was to examine the state of oral prophylaxis practice among dental hygiene students and their awareness of musculoskeletal diseases in an effort to provide some information on how to strengthen education on treatment posture to manage musculoskeletal diseases and how to raise awareness of musculoskeletal diseases. From November 2 to 13, 2016, a self-administered survey was conducted on 653 sophomores, juniors and seniors with an experience of oral prophylaxis practice. SPSS version 20.0 for Windows was employed to analyze the collected data. The findings of the study were as follows: 1. The largest group that accounted for 37.4% responded that the total number of students undergoing oral prophylaxis practice during a semester was four to six. The biggest group that represented 65.4% answered that the required practice time per student was one to fewer than three hours. 76.0% continued to be in the repeated same posture. 2. As for the posture of patients, supine position was most common for the maxillary sinus, which accounted for 82.2%. And semi-upright position was most common for the mandibular sinus, which represented 49.6%. 3. In regard to the burden of oral prophylaxis practice, 33.9% considered the required for the practice appropriate. 42.3% took the repeated long-lasting posture, and 53.5% were under physical pressure. 55.4% suffered from mental pressure and stress. 4. The most dominant musculoskeletal area that they experienced pain after oral prophylaxis practice was neck with 52.5%; waist with 48.2, shoulders/wrists/hands with 45.5, back with 10.3, buttocks with 4.1, elbows with 2.3, legs with 2.1, ankles/feet with 0.8 and knees with 0.6%. 5. Concerning the maintenance of repeated treatment postures and pain experience, the students who continued to be in the repeated same position underwent more pain than the others who didn't on the shoulders(2.92±1.05), in the waist(3.02±1.01), buttocks(1.75±0.92), elbows(1.55±0.79) and ankles/foot(2.52±1.25). The differences were statistically significant(p<.05, p<.01). 6. As to educational experience on treatment posture and musculoskeletal diseases, 88.8% received education on treatment posture; 87.9%, on what position should be taken in times of cooperation; 46.9%, on musculoskeletal diseases; 51.9%, on carpal tunnel syndrome; 42.3%, on varicose vein. The students who replied education on occupational diseases was necessary accounted for 89.6%. 7. The students who experienced treatment posture education were better aware of the causes of musculoskeletal diseases(3.23±3.00), ways for preventing the diseases(3.33±.834) and how to stretch the body(3.63±.858). The differences were statistically significant(p<.05, p<.001). 8. The students who experienced education on occupational diseases heard more about musculoskeletal diseases(3.27±.965), were better cognizant of the causes of the diseases(3.45±.847), were better aware of how to prevent them(3.55±.805) and found themselves to know how to stretch to prevent the diseases (3.73±.826). The differences were statistically significant(p<.001).