• 한국추진공학회지
• /
• 제24권2호
• /
• pp.1-13
• /
• 2020

Zr을 원료로하는 점화제와 ZrNi를 원료로 하는 지연제로 구성된 파이로테크닉스의 노화현상을 열적/화학적/광학적으로 분석하였다. 열적 분석에는 Differential Scanning Calorimetry (DSC) 와 Thermogravimetry Analysis(TGA)를 통해 열 기반의 반응식을 규명했다. DSC의 결과로 수행한 픽 분석기법 (peak deconvolution)을 통해 각 연료의 노화에 따른 열적 변화를 분석하였다. 화학종 변화 분석에는 Laser Induced Breakdown Spectroscopy (LIBS)와 X-ray Photoelectron Spectroscopy (XPS)를 사용하였다. 수분에 의한 산화제의 분해가 연료의 노화에 크게 영향을 미쳤으며, 열에너지 감소의 원인은 연료 표면의 산화막 형성과 산화금속의 형성으로 나타났다.

• 한국주조공학회지
• /
• 제38권4호
• /
• pp.75-81
• /
• 2018

This study examined the effect of the CaMgSn ternary phase on the aging response of the Mg-Sn-Zn alloy. The results revealed that the CaMgSn ternary phase formed in rod-like or needle-like shapes in Mg-3Zn-0.3Ca-xSn (x=1.5, 3, and 5 wt%) alloys and its size decreased as the Sn content increased from 1.5 wt% to 5 wt%. The Mg-3Zn-0.3Ca-5Sn alloy with a relatively fine CaMgSn phase was subjected to solution heat treatment and an aging process. Both the Mg-5Sn-3Zn-0.3Ca and Mg-5Sn-3Zn (base alloy) alloys had similar peak hardness values throughout all aging temperatures but the time-to-peak hardness in the Mg-5Sn-3Zn-0.3Ca alloy was 24-36 hours-earlier than that in the base alloy. Precipitates in the Mg-5Sn-3Zn-0.3Ca alloy were more refined than those in the Mg-5Sn-3Zn alloy and were mostly formed on basal planes. The $Mg_2Sn$ phase formed in either plate-like or rod-like shapes in the Mg-5Sn-3Zn alloy, whereas block-shaped $Mg_2Sn$ particles also formed in the Mg-5Sn-3Zn-0.3Ca alloy.

• 한국재료학회지
• /
• 제8권4호
• /
• pp.354-358
• /
• 1998

Inconel 719 선재의 경도에 미치는 냉간신선가공량과 시효시간의 영향을 경도측정과 전자현미경을 사용하여 조사하였다. 고용화처리된 재료의 경도는 245Hzv이었으나 50% 냉간신선가공으로 450Hv까지 증가했다. 경도값은 시효시간이 증가함에 따라 초기에 증가하다 감소하는 것으로 나타났으며, 시효 초기 경도증가는 $\gamma^{"}$과 $\gamma^{'}$ 상의 석출에 의한 것이며, 최고경도 이후의 경도감소는$\gamma^{'}$상이 $\delta$상으로 변태되었기 때문이다. 냉간가공도가 증가함에 따라 최고경도에 이르는 시간은 감소되어 0, 30, 50%가공재들에 대해 각각 30, 10, 5분으로 나타났다. 이는 냉간가공으로 인해 $\gamma^{'}$ / $\gamma^{'}$ 상의 석출이 촉진되었기 때문이다. 50%가공재의 경우 1116K에서 5분 시효로$\Upsilon^{'}$ 및 $\Upsilon^{'}$상들이 석출되었다. 또한 50%가공재에서는 초기경도 이하로 경도값이 감소되었는데, 이와 같은 경도값의 큰 감소는 재결정이 일어났기 때문이다.

• 디지털융복합연구
• /
• 제10권1호
• /
• pp.185-194
• /
• 2012

한국에서의 고령화는 아직 걱정할 단계는 아니지만 고령화의 속도가 지나치게 빠르게 진행된다는데 문제가 있다. 인구의 절대규모는 2030년의 52,160 천명에서 정점을 이루다가 감소하여 2050년에는 2005년 수준인 48,121천명으로 감소하며, 핵심근로계층인 25-54세의 인구는 저출산과 고령화로 인하여 이미 2012년부터 감소하는 것으로 예측되었다. 고령화는 불가피하게 노동력의 부족을 초래하게 되며, 이는 한 번도 경험해보지 못한 상황에서 정책 수단들을 세워나가야 한다. 본 논문에서는 몇 가지의 대안을 제시하였다. 첫째, 인구규모 자체의 감소를 예방하기 위한 것으로 국가 지원의 보육체계를 포함하는 출산장려정책을 제시하였으며, 둘째, 노동력 절대규모의 감소라는 현실적 상황에서 고용률로 측정된 노동시장의 참여를 증대시킬 수 있는 방안을 제시하였다. 먼저 정년 연장형의 임금피크제를 포함하는 고령자 및 출산의 기회비용을 낮추어 여성의 노동시장 참여를 촉진하는 방안을 제시하였다. 결론적으로 고령화는 피할 수 없는 상황이며, 지속가능한 균형성장이라는 틀에서 문제해결에 접근해야 한다.

• 운동영양학회지
• /
• 제25권1호
• /
• pp.16-22
• /
• 2021

[Purpose] Aerobic exercise training (AT) reverses aging-induced deterioration of arterial stiffness via increased arterial nitric oxide (NO) production. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, was decreased by AT. However, whether AT-induced changes in ADMA levels are related to changes in nitrite/nitrate (NOx) levels remains unclear. Accordingly, we aimed to clarify whether the relationship between plasma ADMA and NOx levels afected the AT-induced reduction of arterial stifness in middle-aged and older adults. [Methods] Thirty-one healthy middle-aged and older male and female subjects (66.4 ± 1.3 years) were randomly divided into two groups: exercise intervention and sedentary controls. Subjects in the training group completed an 8-week AT (60%-70% peak oxygen uptake [${\dot{V}}O_{2peak}$] for 45 min, 3 days/week). [Results] AT signifcantly increased ${\dot{V}}O_{2peak}$ (P < 0.05) and decreased carotid β-stifness (P < 0.01). Moreover, plasma ADMA levels were significantly decreased while plasma NOx levels and NOx/ADMA ratio were significantly increased by AT (P < 0.01). Additionally, no sex diferences in AT-induced changes of circulating ADMA and NOx levels, NOx/ADMA ratio, and carotid β-stifness were observed. Furthermore, the AT-induced increase in circulating ADMA levels was negatively correlated with an increase in circulating NOx levels (r = -0.414, P < 0.05), and the AT-induced increase in NOx/ADMA ratio was negatively correlated with a decrease in carotid β-stifness (r = -0.514, P < 0.01). [Conclusion] These results suggest that the increase in circulating NOx with reduction of ADMA elicited by AT is associated with a decrease in arterial stiffness regardless of sex in middle-aged and older adults.

• 한국세라믹학회지
• /
• 제39권2호
• /
• pp.109-112
• /
• 2002

The structural and optical features of Porous Silicon(PS) were investigated; the porous silicon was prepared by electrochemical etching of silicon wafers in HF solution. The morphologies and Photoluminescece(PL) features of the PS were investigated in terms of etching time, current density and aging conditions. The average pore diameter and pore depth were determined by current density and etching time, respectively. As-prepared PS exhibited the maximum PL peak at the wavelength of ∼ 450 nm. The degree of deviation from as-prepared PS during aging treatment seemed to depend on the microstructure as well as morphology of the PS. It is found that etching current density played an important role on the microstructural features of the PS.

• 열처리공학회지
• /
• 제35권5호
• /
• pp.255-261
• /
• 2022

In this work, the strain-amplitude independent and strain-amplitude dependent damping capacities of Mg-5%Sn alloy have been investigated as a function of its age-hardening response. The hardness increased with an increase in aging time, reached a peak value after 48 h, and then it gradually decreased. The damping capacities of the Mg-5%Sn alloy exhibited a decreasing tendency in the order of solution-treated, under-aged, peakaged, and over-aged states in the strain-amplitude dependent region, whereas they increased continuously with aging time in the strain-amplitude independent region. The microstructural examination during aging revealed that the lower concentration of Sn solutes in the α-(Mg) matrix and the lower density of the Mg₂Sn precipitate particles may well be the crucial factors for better damping values in the strain-amplitude independent and strain-amplitude dependent regions, respectively.

• 한국콘텐츠학회논문지
• /
• 제19권1호
• /
• pp.174-186
• /
• 2019

본 연구는 고령인력 증가가 다른 영역보다 빨리 진행되며, 인적자원관리가 쉽지 않은 공기업 임금피크 근로자의 인구 경제 조직적 특성과 임금피크제 및 퇴직 간 관계에 대해 살펴보고자 하였다. 연구대상은 임금피크제 실시 공기업 19개사에 종사하는 임금피크 근로자 211명이었다. 연구결과에 따르면 인구 경제적 특성에 있어서, 교육수준, 가계총수입, 퇴직 후 생활비, 퇴직대비저축과 투자금액은 임금피크만족도, 임금피크수용도, 퇴직준비와 퇴직태도에 영향을 미치는 것으로 나타났다. 조직적 특성에서는 직급과 직군, 근무기간과 정년퇴직잔여기간, 퇴직준비프로그램 참여 그리고 임금피크 적용 여부에 따라 각각 차이가 나타났다. 연구 결과를 바탕으로 고령사회를 위한 실효성 있는 임금피크제 시행을 위해서는 복지지원, 교육훈련, 전직지원과 같은 고령친화인사제도의 직군, 직급, 경제수준 및 교육수준 별 시행의 필요성을 시사함과 동시에 후속 연구를 위한 제언을 논의하였다.

• 열처리공학회지
• /
• 제10권1호
• /
• pp.63-70
• /
• 1997

A study was performed to examine the aging behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry and transmission electron microscopy. DSC measurements were conducted over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $5^{\circ}C$/min. for the specimens aged at 130, 160, $190^{\circ}C$ and $220^{\circ}C$ for various times after solution treatment at $540^{\circ}C$ for 30 minutes. The peaks due to the formation of G.P.zone were not detected in the specimens aged at 130 and $160^{\circ}C$, but those at 190 and $220^{\circ}C$ appeared in DSC curves. The heat absorption due to the dissolution of ${\delta}^{\prime}$ phase was increased with increasing aging time at $130^{\circ}C$ aging. In contrast, those values for the specimens aged at 160 and $190^{\circ}C$ were initially increased and inversely decreased at the transition time of 72 and 1 hour, respectively. The heat evolution due to the formation of $T_1$ phase was nearly unchanged at $130^{\circ}C$ aging, but at $160^{\circ}C$ and $190^{\circ}C$ aging, drastically decreased after the transition time. It can be considered that the increase of $T_1$ phase results in the decrease of ${\delta}^{\prime}$ phase when aging time is longer than the transition time. The hardness of the specimen aged at $190^{\circ}C$ is initially higher compared with that at $160^{\circ}C$, however, the peak hardness shows the lower value than that at $160^{\circ}C$.

• Nuclear Engineering and Technology
• /
• 제46권5호
• /
• pp.605-618
• /
• 2014

The effects of variability of the mechanical properties of lead rubber bearings on the response of a seismic isolation system are investigated. Material variability in manufacturing, aging, and operation temperature is assumed, and two variation models of an isolation system are considered. To evaluate the effect of ground motion characteristics on the response, 27 earthquake record sets with different peak A/V ratios were selected, and three components of ground motions were used for a seismic response analysis. The response in an isolation system and a superstructure increases significantly for ground motions with low A/V ratios. The variation in the mechanical properties of isolators results in a significant influence on the shear strains of the isolators and the acceleration response of the superstructure. The variation provisions in the ASCE-4 are reasonable, but more strict variation limits should be given to isolation systems subjected to ground motions having low A/V ratios. For application of seismic isolation systems to safety-related nuclear structures, the variation in the material and mechanical properties of the isolation system should be properly controlled during the manufacturing and aging processes. In addition, special consideration should be given to minimize the accidental torsion caused by the dissimilarity in the stiffness variations of the isolators.