• 대한물리의학회지
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• 제6권2호
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• pp.235-246
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• 2011

Purpose: The aim of this study is to compare and assess the effects of lumbar stabilization exercise on the balance ability of young college studets with low back pain after having performed spinal stabilization exercise by using 3-dimensional air-balance system and gym ball. Methods: The subjects of this study were 34 low back patients in their early twenties. They were divided into two groups: 3-dimensional lumbar stabilization exercise group(N=17) and gym ball lumbar stabilization exercise group(N=17). The period of the intervention was for five weeks. VAS(Visual Analogue Scale) for pain test, ODI(Oswestry Disability Index) for ADL limitation test, Tetrax system for static balance test, and Air-balance system 3D for dynamic balance test were used as evaluation tools for this study. Results: Pain showed significant decrease in both groups after having performed the experiment, but ADL limitation of the groups did not show any remarkable difference between before and after the experiment. Dynamic balance ability in the 8-directional angle comparison test significantly increased in all directions except for the backward, left-backward, and right-backward directions. As for dynamic balance ability in the 8-directional postural test, 3D exercise group showed statistically significant reduction in every direction while gym ball exercise group did not(p<.05). However, when it comes to static balance ability in the weight distribution and stability test, there was not significantly change between pre and post test in both groups. Conclusion: This study shows 3-dimensional lumbar stabilization exercise is more effective in the lumbar stabilization of coordinated movement than gym ball exercise, which may imply that 3D air-balance system can be used for the therapeutic treatment of body imbalance for patients with low back pain.

• Korean Chemical Engineering Research
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• 제54권1호
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• pp.16-21
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• 2016

실리콘의 부피팽창과 낮은 전기전도도를 개선하기 위하여 Silicon/Carbon/CNT 복합체를 제조하였다. Silicon/Carbon/CNT 합성물은 SBA-15를 합성한 후, 마그네슘 열 환원 반응으로 Silicon/MgO를 제조하여 Phenolic resin과 CNT를 첨가하여 탄화하는 과정을 통해 합성하였다. 제조된 Silicon/Carbon/CNT 합성물은 XRD, SEM, BET, EDS를 통해 특성을 분석하였다. 본 연구에서는 충방전, 사이클, 순환전압전류, 임피던스 테스트를 통해 CNT 첨가량에 따른 전기화학적 효과를 조사하였다. $LiPF_6$ (EC:DMC:EMC=1 :1 :1 vol%) 전해액에서 Silicon/Carbon/CNT 음극활물질을 사용하여 제조한 코인셀은 CNT 함량이 7 wt% 일 때 1,718 mAh/g으로 높은 용량을 나타내었다. 코인셀의 사이클 성능은 CNT 첨가량이 증가할수록 개선되었다. 11 wt%의 CNT를 첨가한 Silicon/Carbon/CNT 음극은 두 번째 사이클 이후 83%의 높은 용량 보존율을 나타냄을 알 수 있었다.

• 한국농공학회논문집
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• 제57권4호
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• pp.11-19
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• 2015

The important properties of EVA (ethylene vinyl acetate) redispersible polymer was waterproof, densification of internal pore space of concrete and ball bearing and micro filler. Also, the significant role of polypropylene(PP) fiber was crack control and blockade of movement for deterioration factors. The most studies for EVA were limited in the field of mortar and PP fiber reinforced concrete had been studied in the state of being restricted unit water content, rich mix and mixing much of the fiber without considering construction site. Therefore, the control mix design were applied in ready mixed concrete using 10 % fly ash of total cement weight used in batch plant. On the basis of control mix design, EVA contents ranging from 0 % to 10 % of total cement weight and PP fiber contents ranging from 0 % to 0.5 % of EVA concrete volume were used in the mix designs. The results showed the maximum compressive strength value was measured at EVA 5.0 % and PP fiber 0.1 %, the minimum water absorption ratio was at EVA 10 % and PP fiber 0 %, the durability factor for freezing and thawing resistance was at EVA 5.0 % and PP fiber 0.3 % and the minimum weight reduction ratio of resistance to sulfuric acid attack was at EVA 10 % and PP fiber 0.5 % after curing age 42days. Meanwhile, From these results, PP fiber reinforced EVA concrete would be very benefit, if each optimal mix types were used in hydraulic structures, underground utilities and agricultural structures.

• 한국산업보건학회지
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• 제16권2호
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• pp.110-122
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• 2006

Objective : This study was conducted to quantify chronic lead exposure from various media(ie. working environment, food, ambient air), and to certify the usefulness of exposure assessment using Monte-Carlo simulation in the fields of occupational health. Methods : Data were obtained from Korean Industrial Health Association, Korea Food and Drug Administration, and the Ministry of Environment. Then lead worker's exposure was estimated indirectly from various media and parameters (ie. volume inhaled, body weight, dietary intake, etc.). Uncertainty was analyzed by Monte Carlo simulation with Crystal Ball software. Exposure doses and hazard indices were simulated with various hypothetical scenarios including weekly working hours and respiratory protective equipment. Results : Without respiratory protective equipment, the total exposure dose per kilogram of body weight of lead workers was estimated as $5.45{\times}10^{-3}mg/kg/day$, and hazard index was estimated as 2.26, and exposure contributions were calculated as follows : working environment(82.42 %); foods(17.57 %); and ambient air(0.01 %). But, if working condition has changed - reduction of working hours and using respiratory protective equipment, the total exposure dose per kilogram of body weight was estimated between $1.34{\times}10^{-3}-1.49{\times}10^{-3}mg/kg/day$, and hazard index was estimated between 0.56 - 0.62. Conclusions : This study suggested that occurrence of hazardous impact(ie. increased blood pressure) through lifetime lead exposure would be expected, and that the Monte-Carlo simulation was useful for the fields of occupational health.

• Journal of Welding and Joining
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• 제18권5호
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• pp.98-104
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• 2000

Aluminum alloys are being employed in automobile parts as strive to reduce overall vehicle weight to meet demands for improved fuel economy and reduction in vehicle emissions. Al-based composites reinforced with ceramic ($Al_2O_3,\;SiC,\;TiC\;and\;B_4C$) applications in a variety of components in automotive engines, such as liners, where the tribological properties of the material are important. In this study, Al-base composites reinforced with TiC particle powders has been developed for producing plasma spray coatings. The composite plasma spray powders were prepared Al-13Si-3Mg(wt%) alloy with TiC(40, 60 and 80wt%) particles ($0.2~5{\mu}textrm{m}$) by drum type ball milling. The composite powders ($36~76{\mu}textrm{m}$) were sprayed with plasma torch. Plasma sprayed coatings were heat-treated at $500^{\circ}C$ for 3 hours. The wear resistances of the plasma sprayed coatings were found to decrease with increasing TiC content and improved with heat treatment. AlSiMg-40% TiC heat-treated coatings were showed the best wear resistance in this study.

• 한국음향학회지
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• 제43권1호
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• pp.60-71
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• 2024

본 연구는 일반적인 평평한 에틸렌 비닐 아세테이트(Ethylen Vinyl Acetate, EVA) 완충재의 형상을 변화시켜 다양한 차음소재와 조합하여 복합구조의 바닥충격음 변화를 조사하는 데에 목적이 있다. 바닥충격음 저감에 효과적인 완충재를 선정하기 위해 Flat, Deck, Cavity type의 EVA, EPS, PET 흡음재, PP판넬, 고무발판 등 다양한 완충재를 조합하여 뱅머신을 이용한 1차 실험을 진행하였다. 1차 실험 데이터에 대해 통계분석한 결과 완충재 두께가 40 mm에 가까울수록 바닥충격음 저감효과가 증가하였으며 PET 흡음재, PP시트, 고무발판 등을 조합한 복합완충재에서 바닥충격음 효과가 증가하는 것을 알 수 있었다. 이에따라 2차 실험에서 모든 복합완충재의 두께는 40 mm로 통일하였으며, 1차 실험에 사용된 Flat, Deck, Cavity type 및 EVA를 발판형태로 가공한 Mount type 등 4가지 형태의 복합완충재를 설계하였다. 또한, Mount type을 제외한 3가지 기본 형태에서 각각 PET 흡음재(7 mm)를 추가했을 시 바닥충격음 변화를 살펴보았으며, Mount type의 경우 EVA발판 개수에 따른 바닥충격음 변화에 대해 고무공 충격원을 이용한 2차 실험을 진행하였다. 모든 실험은 공인인증시험기관의 목업실험실에서 진행하였다. 실험 결과, 기본형태의 Flat, Deck, Cavity type에서 PET를 추가할 경우 통계적으로 경량 5 dB ~ 9 dB, 중량 1 dB ~ 5 dB의 저감효과가 나타난 것을 알 수 있었다. 특히, Mount type의 경우 발판 수가 36개 이상일 때 경량 및 중량충격음에서 우수한 것으로 나타났다. 또한, 4가지 기본형태에 따라 동탄성계수가 높아질수록 바닥충격음의 저감이 증가하는 것으로 나타났다.

• 한국건설순환자원학회논문집
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• 제9권4호
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• pp.642-649
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• 2021

건축물의 에너지 절약기준이 강화되면서 외단열 공법의 적용과 단열재 두께가 증가하고 있다. 유기계 단열재는 시공성, 경제성 등 시공비용 절감 효과와 뛰어난 단열성능을 가지고 있다. 하지만, 유기계 단열재 특성상 열에 매우 취약하므로 화재 발생 시 급격한 화재확산과 유독가스 발생으로 심각한 피해가 발생한다. 무기계 단열재는 기본적으로 불연성능을 가지나 무겁고 유기계 단열재에 비해 단열성능이 떨어진다. 글라스 버블은 소다 라임 보로실리케이트 유리로 밀도가 매우 낮고, 내부가 비어 있는 구형의 입자로 볼베어링 효과로 유동성이 개선된다. 또한, 무기계 단열재에 혼입하여 사용할 경우 밀도와 단열성능이 개선된다. 본 연구는 시멘트계 재료와 글라스 버블을 혼합하여 무기 단열재를 제조하였고 단열, 난연 및 불연성능을 평가하였다. 연구 결과, 글라스 버블의 혼입률이 증가할수록 열린 기공을 형성하고 있으나, 기공 및 셀 벽에 분포됨에 따라 충분한 단열성능을 보인다. 또한, 글라스 버블의 혼입률은 10% 이하로 사용하는 것이 바람직하다.

• 공업화학
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• 제26권5호
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• pp.543-548
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• 2015

리튬이온 전지용 음극소재의 용량 및 사이클 성능을 향상시키기 위해서 Si/C/CNF 합성물의 특성이 조사되었다. 제조과정으로는 SBA-15를 합성하고 볼밀링을 이용한 마그네슘환원을 통해 Si/MgO를 얻은 다음, Phenolic resin과 CNF를 이용해 탄화과정을 거쳐 최종적으로 산처리하여 Si/C/CNF 활물질을 합성하였다. 합성된 Si/C/CNF는 BET, XRD, FE-SEM 그리고 TGA를 이용하여 분석하였다. $50^{\circ}C{\sim}70^{\circ}C$까지 온도에 따라 SBA-15를 합성한 결과 $60^{\circ}C$에서 가장 큰 비표면적을 갖는 결과를 얻었다. 또한 LiPF6 (EC : DMC : EMC = 1 : 1 : 1 vol%) 전해질을 사용하여, 충방전, 사이클, CV와 임피던스 등과 같은 전기화학적 테스트를 수행하여 Si/C/CNF 전극의 이차전지 음극활물질로서 성능을 조사하였다. Si/C/CNF (Si : CNF = 97 : 3 중량비)를 이용한 전지의 용량은 1,947 mAh/g으로 다른 합성물보다 우수한 결과를 보였다. CNF 첨가량이 3 wt%에서 11 wt%로 증가함에 따라 용량 보존율이 84~77%로 안정성이 감소되었다. Si/C/CNF 합성소재 전극이 이차전지의 사이클 성능과 전기전도도를 개선할 수 있다는 것을 알 수 있었다.

• Tribology and Lubricants
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• 제36권4호
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• pp.244-252
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• 2020

Materials manufactured by powder metallurgy (PM) are widely used in various applications such as water pump, shock absorber, and airplane components due to the reduction in the cost and weight. In this study, tribological properties of carbon steel subjected by surface treatment were investigated. The main purpose is to increase the strength and improve the tribological properties by reducing pores that formed by PM. Moreover, the surface treatment was carried out at room and high temperatures (RT and HT). The surface roughness of the untreated (NON) and treated (AFTER) samples was measured. It was found that the surface roughness was reduced after both the RT AFTER and HT AFTER compared to RT NON sample. The tribological properties of the samples were performed against bearing steel ball under dry conditions. The friction coefficient of the RT NON samples was reduced by 22% and 56% RT AFTER and HT AFTER, respectively. The wear volume of the RT NON sample was also reduced by 43% and 87% RT AFTER and HT AFTER, respectively. Tribocorrosion tests were also performed and it was found that the surface of the RT AFTER, HT AFTER samples was less corroded compared to RT NON sample. The HT AFTER sample demonstrated a relatively higher corrosion potential in comparison with the RT AFTER samples. Hence, it was confirmed that after surface modification the surface roughness and hardness of the samples were significantly improved resulting in improvement in tribological and tribocorrosion behaviors of PM carbon steel.

• 한국재료학회지
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• 제26권9호
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• pp.468-471
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• 2016

$SnO_2:CNT$ thick films for gas sensors were fabricated by screen printing method on alumina substrates and were annealed at $300^{\circ}C$ in air. The nano $SnO_2$ powders were prepared by solution reduction method using tin chloride ($SnCl_2.2H_2O$), hydrazine ($N_2H_4$) and NaOH. Nano $SnO_2:CNT$ sensing materials were prepared by ball-milling for 24h. The weight range of CNT addition on the $SnO_2$ surface was from 0 to 10 %. The structural and morphological properties of these sensing material were investigated using X-ray diffraction and scanning electron microscopy and transmission electron microscope. The structural properties of the $SnO_2:CNT$ sensing materials showed a tetragonal phase with (110), (101), and (211) dominant orientations. No XRD peaks corresponding to CNT were observed in the $SnO_2:CNT$ powders. The particle size of the $SnO_2:CNT$ sensing materials was about 5~10 nm. The sensing characteristics of the $SnO_2:CNT$ thick films for 5 ppm $H_2S$ gas were investigated by comparing the electrical resistance in air with that in the target gases of each sensor in a test box. The results showed that the maximum sensitivity of the $SnO_2:CNT$ gas sensors at room temperature was observed when the CNT concentration was 8wt%.