• Title/Summary/Keyword: Stress Components

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A Study of the Failure Distribution and the Failure Difference by the Stress on the K-1 Tracked Vehicle (K-1전차의 고장분포와 부하에 따른 고장률 차이에 대한 연구)

  • Lee, Sang-Jin;Choi, Seok-Yoon
    • Journal of the military operations research society of Korea
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    • v.35 no.2
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    • pp.33-49
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    • 2009
  • The objective of this study is as follows. First, the hazard function on the failure probability density function of the K-1 tracked vehicles can be occurred in the form of the bathtub curve. Second, the failure mode may be different under two different operational situations. The research result shows that the bathtub curve can be fitted in the Weibull distribution, that assumes different shapes according to the specific stage of the system's life cycle. The K-1 tracked vehicle has a relatively high hazard(failure) rate at the time of its first service. The failure rate starts decreasing for a time immediately after it goes into service. After the break-in period, the surviving components have a fairly constant hazard rate. As the K-1 system ages, deterioration of its various parts takes place and the hazard rate starts Increasing. Second, the result shows the failure rate in the harsh operational environment is higher than that in the mild operational environment. In conclusion, the bathtub curve can be logically appropriate in establishing the depot overhaul cycle. Moreover, it is necessary for determining the right time of the depot overhaul to consider not only the age of defense equipment but also the different operational environment.

EFFECTS OF SURFACE ROUGHNESS AND MULTILAYER COATING ON THE CORROSION RESISTANCE OF Ti-6Al-4V ALLOY

  • Ko, Yeong-Mu;Choe, Han-Cheol
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2003.10a
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    • pp.134-135
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    • 2003
  • The dental implant materials required good mechanical properties, such as fatigue strength, combined with a high resistance to corrosion. For increasing fatigue resistance and delaying onset of stress corrosion cracking, shot peening has been used for > 50 years to extend service life of metal components. However, there is no information on the electrochemical behavior of shot peened and hydroxyapatite(HA) coated Ti-6Al-4V alloys. To increase fatigue strength, good corrosion resistance, and biocompatibility, the electrochemical characteristics of Ti/TiN/HA coated and shot peened Ti-6Al-4V alloys by electron beam physical vapor deposition(EB-PVD) have been researched by various electrochemical method in 0.9%NaCl. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. The produced materials were quenched at 1000$^{\circ}C$ under high purity dried Ar atmosphere and were hold at 500$^{\circ}C$ for 2 hrs to achieve the fatigue strength(1140㎫) of materials. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. Shot peening(SP) and sand blasting treatment was carried out for 1, 5, and 10min. On the surface of Ti-6Al-4V alloys using the steel balls of 0.5mm and alumina sand of 40$\mu\textrm{m}$ size. Ti/TiN/HA multilayer coatings were carried out by using electron-beam deposition method(EB-PVD) as shown Fig. 1. Bulk Ti, powder TiN and hydroxyapatite were used as the source of the deposition materials. Electrons were accelerated by high voltage of 4.2kV with 80 - 120mA on the deposition materials at 350$^{\circ}C$ in 2.0 X 10-6 torr vacuum. Ti/TiN/HA multilayer coated surfaces and layers were investigated by SEM and XRD. A saturated calomel electrode as a reference electrode, and high density carbon electrode as a counter electrode, were set according to ASTM GS-87. The potentials were controlled at a scan rate of 100 mV/min. by a potentiostat (EG&G Co.273A) connected to a computer system. Electrochemical tests were used to investigate the electrochemical characteristics of Ti/TiN/HA coated and shot peened materials in 0.9% NaCl solution at 36.5$^{\circ}C$. After each electrochemical measurement, the corrosion surface of each sample was investigated by SEM.

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Establishment of Optimal Fermentation Conditions for Steam-dried Ginseng Berry via Friendly Bacteria and Its Antioxidant Activities (생체친화성 균주에 의한 인삼열매증포 추출물의 최적발효조건 및 항산화활성)

  • Kim, Seung Tae;Kim, Hee Jung;Jang, Su Kil;Lee, Do Ik;Joo, Seong Soo
    • Korean Journal of Food Science and Technology
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    • v.45 no.1
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    • pp.77-83
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    • 2013
  • In this study, we observed optimal conditions and suitable bacteria for the fermentation of steam-dried ginseng berry extracts (SGB) and determined antioxidant effects of the fermented extracts. Five bacteria (Lactobacillus fermentarum, L. plantarum, L. brevis, L. casei, Bacillus subtillis) were examined on their growth activities and viabilities in various culture temperatures ($25-35^{\circ}C$) and concentrations (25-100%). L. plantarum was considered to be the most suitable bacteria for the fermentation in both growth activity and viability. Moreover, the extracts fermented with L. plantarum showed more potent antioxidant efficacy in both 1,1-diphenyl-2-picrylhydrazyl radical and hydroxyl radical scavenging assay. High performance liquid chromatography analysis revealed that fermentation with L. plantarum changed the contents and components of ginsenosides. In conclusion, these data suggest that L. plantarum efficiently ferment SGB and the fermented extracts may have therapeutical values against oxidative stress and be a good candidate in adjuvant therapy where ginsenoside would be the main composition.

Evaluations of Si based ternary anode materials by using RF/DC magnetron sputtering for lithium ion batteries

  • Hwang, Chang-Muk;Park, Jong-Wan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.08a
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    • pp.302-303
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    • 2010
  • Generally, the high energy lithium ion batteries depend intimately on the high capacity of electrode materials. For anode materials, the capacity of commercial graphite is unlike to increase much further due to its lower theoretical capacity of 372 mAhg-1. To improve upon graphite-based negative electrode materials for Li-ion rechargeable batteries, alternative anode materials with higher capacity are needed. Therefore, some metal anodes with high theoretic capacity, such as Si, Sn, Ge, Al, and Sb have been studied extensively. This work focuses on ternary Si-M1-M2 composite system, where M1 is Ge that alloys with Li, which has good cyclability and high specific capacity and M2 is Mo that does not alloy with Li. The Si shows the highest gravimetric capacity (up to 4000mAhg-1 for Li21Si5). Although Si is the most promising of the next generation anodes, it undergoes a large volume change during lithium insertion and extraction. It results in pulverization of the Si and loss of electrical contact between the Si and the current collector during the lithiation and delithiation. Thus, its capacity fades rapidly during cycling. Si thin film is more resistant to fracture than bulk Si because the film is firmly attached to the substrate. Thus, Si film could achieve good cycleability as well as high capacity. To improve the cycle performance of Si, Suzuki et al. prepared two components active (Si)-active(Sn, like Ge) elements film by vacuum deposition, where Sn particles dispersed homogeneously in the Si matrix. This film showed excellent rate capability than pure Si thin film. In this work, second element, Ge shows also high capacity (about 2500mAhg-1 for Li21Ge5) and has good cyclability although it undergoes a large volume change likewise Si. But only Ge does not use the anode due to its costs. Therefore, the electrode should be consisted of moderately Ge contents. Third element, Mo is an element that does not alloys with Li such as Co, Cr, Fe, Mn, Ni, V, Zr. In our previous research work, we have fabricated Si-Mo (active-inactive elements) composite negative electrodes by using RF/DC magnetron sputtering method. The electrodes showed excellent cycle characteristics. The Mo-silicide (inert matrix) dispersed homogeneously in the Si matrix and prevents the active material from aggregating. However, the thicker film than $3\;{\mu}m$ with high Mo contents showed poor cycling performance, which was attributed to the internal stress related to thickness. In order to deal with the large volume expansion of Si anode, great efforts were paid on material design. One of the effective ways is to find suitably three-elements (Si-Ge-Mo) contents. In this study, the Si based composites of 45~65 Si at.% and 23~43 Ge at.%, and 12~32 Mo at.% are evaluated the electrochemical characteristics and cycle performances as an anode. Results from six different compositions of Si-Ge-Mo are presented compared to only the Si and Ge negative electrodes.

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Antimicrobial activity and protective effect of Geranium thunbergii against oxidative DNA damage via antioxidant effect (현초의 항산화 활성에 의한 산화적 DNA 손상 보호효과 및 항균활성)

  • Kwon, Tae-Hyung;Lee, Su-Jin;Park, Jae-Ho;Kim, Taewan;Park, Jung-Ja;Park, Nyun-Ho
    • Food Science and Preservation
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    • v.24 no.3
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    • pp.325-333
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    • 2017
  • This study aimed to investigate the various biological activities of Geranium thunbergii such as antimicrobial activity and protective effect against oxidative damage. To evaluate its antioxidant and antimicrobial activities, we first performed methanol extraction; this methanol extract was further partitioned using various solvents. And then, its antioxidant activity was measured using various assays including total phenolic content and protection against oxidative DNA damage, and antimicrobial activities were examined using minimum inhibiting concentration (MIC) test, and paper disc method. In addition, high-performance liquid chromatography was performed to analyze the major chemical components of ethyl acetate fraction. The G. thunbergii fraction with ethyl acetate exhibited higher antioxidant and antimicrobial activities than the other fractions. The results showed that G. thunbergii ethyl acetate fraction at $50{\mu}g/mL$ had strong DPPH and ABTS radical scavenging activities of 80.88% and 80.12%, respectively. In addition, the ethyl acetate fraction protected DNA from the oxidative damage induced by ferrous ion and hydroxyl radicals and showed high antimicrobial activity with diameter of inhibition zones ranging from 13.33 to 15.67 mm. High-performance liquid chromatography analysis revealed the major phenolic compounds of G. thunbergii to be ellagic acid and gallic acid. These results suggest that G. thunbergii might protect DNA against oxidative stress induced by reactive oxygen species and can be utilized as a natural source of antioxidant and antimicrobial agent in the food industry.

Obesity, Obstructive Sleep Apnea, and Metabolic Dysfunction (비만, 폐쇄성 수면무호흡증과 대사장애)

  • Kim, Jinkwan;Pyo, Sang Shin;Yoon, Dae Wui
    • Korean Journal of Clinical Laboratory Science
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    • v.53 no.4
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    • pp.285-295
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    • 2021
  • Sleep plays an important role in maintaining overall human health. There is increasing interest regarding the impact of sleep related disorders on metabolic diseases. Obstructive sleep apnea (OSA) is a common health problem, and in the last decade, the emergence of increasing obesity rates has further led to a remarkable increase in the prevalence of OSA, along with more prominent metabolic diseases. Obesity is the strongest risk factor for OSA. However, OSA is also known to cause obesity, suggesting an interaction between OSA and obesity. Although the underlying mechanisms leading to OSA-induced metabolic diseases are probably multi-factorial and are yet to be fully elucidated, the activation of inflammation and oxidative stress and the dysregulation of appetite-regulating hormones have emerged as important pathophysiological components of metabolic dysfunction and obesity observed in patients with OSA. Here, we will review the current state of research regarding the association of OSA with metabolic diseases and the possible pathophysiological mechanisms by which OSA could lead to such diseases. This will enhance our understanding of the potential interactions between OSA and obesity and between OSA and metabolic dysfunction.

Effect of a Hot Water Extract of Sparasis Crispa on the Expression of Tight Junction-Associated Genes in HaCaT Cells (꽃송이버섯 열수추출물이 HaCaT의 세포 연접 관련 유전자의 발현에 대한 영향)

  • Han, Hyo-Sang
    • Journal of The Korean Society of Integrative Medicine
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    • v.9 no.2
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    • pp.83-92
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    • 2021
  • Purpose : Keratinocytes are the main cellular components involved in wound healing during re-epithelization and inflammation. Dysfunction of tight junction (TJ) adhesions is a major feature in the pathogenesis of various diseases. The purpose of this study was to identify the various effects of a Sparassis crispa water extract (SC) on HaCaT cells and to investigate whether these effects might be applicable to human skin. Methods : We investigated the effectiveness of SC on cell HaCaT viability using MTS. The antioxidant effect of SC was analyzed by comparing the effectiveness of ABTS to that of the well-known antioxidant resveratrol. Reverse-transcription quantitative polymerase chain reaction (qRT-PCR) is the most widely applied method Quantitative RT-PCR analysis has shown that SC in HaCaT cells affects mRNA expression of tight-junction genes associated with skin moisturization. In addition, Wound healing is one of the most complex processes in the human body. It involves the spatial and temporal synchronization of a variety of cell types with distinct roles in the phases of hemostasis, inflammation, growth, re-epithelialization, and remodeling. wound healing analysis demonstrated altered cell migration in SC-treated HaCaT cells. Results : MTS analysis in HaCaT cells was found to be more cytotoxic in SC at a concentration of 0.5 mg/㎖. Compared to 100 µM resveratrol, 4 mg/㎖ SC exhibited similar or superior antioxidant effects. SC treatment in HaCaT cells reduced levels of claudin 1, claudin 3, claudin 4, claudin 6, claudin 7, claudin 8, ZO-1, ZO-2, JAM-A, occludin, and Tricellulin mRNA expression by about 1.13 times. Wound healing analysis demonstrated altered cell migration in SC-treated HaCaT cells and HaCaT cell migration was also reduced to 73.2 % by SC treatment. Conclusion : SC, which acts as an antioxidant, reduces oxidative stress and prevents aging of the skin. Further research is needed to address the effects of SC on human skin given the observed alteration of mRNA expression of tight-junction genes and the decreased the cell migration of HaCaT cells.

Conceptual eco-hydrological model reflecting the interaction of climate-soil-vegetation-groundwater table in humid regions (습윤 지역의 기후-토양-식생-지하수위 상호작용을 반영한 개념적인 생태 수문 모형)

  • Choi, Jeonghyeon;Kim, Sangdan
    • Journal of Korea Water Resources Association
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    • v.54 no.9
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    • pp.681-692
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    • 2021
  • Vegetation processes have a significant impact on rainfall runoff processes through evapotranspiration control, but are rarely considered in the conceptual lumped hydrological model. This study evaluated the model performance of the Hapcheon Dam watershed by integrating the ecological module expressing the leaf area index data sensed remotely from the satellite into the hydrological partition module. The proposed eco-hydrological model has three main features to better represent the eco-hydrological process in humid regions. 1) The growth rate of vegetation is constrained by water shortage stress in the watershed. 2) The maximum growth of vegetation is limited by the energy of the watershed climate. 3) The interaction of vegetation and aquifers is reflected. The proposed model simultaneously simulates hydrologic components and vegetation dynamics of watershed scale. The following findings were found from the validation results using the model parameters estimated by the SCEM algorithm. 1) Estimating the parameters of the eco-hydrological model using the leaf area index and streamflow data can predict the streamflow with similar accuracy and robustness to the hydrological model without the ecological module. 2) Using the remotely sensed leaf area index without filtering as input data is not helpful in estimating streamflow. 3) The integrated eco-hydrological model can provide an excellent estimate of the seasonal variability of the leaf area index.

Policy Compliance and Smoking related Behavior Change in a Smoke-free Apartment (금연 공동주택 주민들의 정책 순응도와 흡연 관련 행태 변화)

  • Cho, Hoosun;Kim, Eunsu;Nam, Hae-Sung
    • Journal of agricultural medicine and community health
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    • v.45 no.4
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    • pp.221-234
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    • 2020
  • Objectives: The purpose of this study is to identify the policy compliance according to the socio-demographic characteristics, stress, satisfaction of relationship, Health Belief Model and characteristics of smoking behaviors and knowledge related smoking of the residents living in the Smoke-free apartment and to investigate the change of the smoking related behavior before and after the implementation of the policy. Methods: The subjects of the survey were 293 residents aged 19 or older who reside in apartments six months after the designation of Smoke-free apartment located in Daejeon. All collected data were analyzed using T-test, ANOVA and Hierarchical multiple regression of SPSS for windows(ver 24.0) program. Results: The policy compliance was higher in women and those who lived for less than two years, and non-smokers were significantly higher. The policy compliance of the whole subjects was related to satisfaction with the surrounding relationship, perceived disability about smoking cessation, frequency of smoking and the amount of smoking. The policy compliance of the whole subjects was related to the satisfaction of the surrounding relationship, the perceived disability about smoking cessation, and the amount of smoking. In addition, after the implementation of the gold research station designation policy, it had a positive impact on smoker's smoking behavior and resulted in reducing the frequency of secondhand smoke among residents. Conclusions: In order to increase the compliance of the non-smoking policy It is necessary to continuously expand the indoor smoking cessation zone policy, develop policies and supplement the health belief model components.

Structural Design Optimization of Gageocho Jacket Structure Considering Unity Check (가거초 자켓 구조물의 허용응력비를 고려한 구조 최적설계)

  • Kim, Byungmo;Ha, Seung-Hyun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.34 no.4
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    • pp.205-212
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    • 2021
  • Offshore jacket structures generally comprise steel members, and the safety standard for jacket structures typically focuses on the steel components. However, large amounts of concrete grouting is filled in the legs of the Gageocho jacket structure to aid in the recovery from typhoon damage. This paper proposes a safe and lightweight design for the Gageocho ocean research station comprising steel members instead of large amounts of concrete reinforcement in the legs. Based on the actual design, the structural members are grouped according to their functional roles, and the inner diameter of the cross-section in each design group is defined as a design variable. Structural optimization is carried out using a genetic algorithm to minimize the total weight of the structure. To satisfy the conservative safety standards in the offshore field, both the maximum stress and the unity check criteria are considered as design constraints during optimization. For enhanced safety confidence, extreme environmental conditions are assumed. The maximum marine attachment thickness and the section erosion in the splash zone are applied. Additionally, the design load is defined as the force induced by extreme waves, winds, and currents aligned in the same direction. All the loading directions surrounding the structure are considered to design the structure in a balanced and safe manner. As a result, compared with the current structure, the proposed structure features a 45% lighter design, satisfying the strict offshore safety criteria.