PURPOSES : The objective of this study is to analyze the significance of binder aging in a hot-mix asphalt (HMA) mixture in an insulated camber for a long duration for repair works, where the absolute viscosity level and service life reduction (SLR) are assessed based on the haul time, as well as to suggest a methodology for reducing the aging level. METHODS : Because the HMA mixture is stored in an insulated box carriage at high temperature for repair works, if the binder in the mix is severely oxidized, then the repaired pavement will not exhibit a long service life. Therefore, the 13-mm dense-graded HMA mix with PG64-22 was aged in an oven at 160 °C for 1, 2, 4 and 8 h to evaluate its aging level. Gel-permeation chromatography was performed on the mixture particle without binder recovery to measure the large-molecular size ratio, from which the estimated absolute viscosity (EAV) was computed using a best-fit regression model. The SLR values of aged and repaired mixes were estimated to determine the amount of deterioration in the mixes caused by severe aging. Hydrated lime (HL) was introduced into the mix at a ratio of 1.5 wt% of the total mix. The aging level and SLR were compared with those of the repaired mix without HL. RESULTS : The binder EAV of the HMA mix increases significantly with the mixture aging duration. In particular, the binder EAV level of a 4-h aged mix is similar to the asphalt viscosity level of a pavement with approximately 7 years of service life. The service life expressed based on the aging level is interpreted as the reduced service life of the aged mix, which is already oxidized before it is used. Meanwhile, the binder of an 8-h aged mix without HL aged significantly and its SLR is approximately 11 years. However, its aging level and SLR reduced significantly when HL. is incorporated. CONCLUSIONS : The binder aging level of the repaired mix increases significantly with its storage duration in a hot chamber for carriage. However, since the aging level decreases significantly by the incorporation of HL, the use of HL is highly recommended when preparing new mix for repair works to be performed in a hot-chamber for a long duration.

The aging treatment was applied to Rehmannia glutinosa rhizome (RGR) to improve the digestibility by the enzymatic hydrolysis of undigestible sugars. However, RGR spoils easily during the aging treatment. Thus, the purpose of this study was to investigate the influence of ethanol addition as preservatives on sugars and microbial growth of aged RGR. The RGR was treated with the addition of ethanol (0~10%) at 55℃ for eight days. Reducing, free sugars, and total bacterial counts of RGR with ethanol concentrations were analyzed during the aging periods. The aged RGR with 0-2% ethanol appeared spoiled in appearance, and total bacterial counts of these samples increased from 1.1×105 to 2.2×107 CFU and then decreased again. When treated with 4~10% ethanol, the total bacterial counts of aged RGR decreased by more than 99.9% at eight days. In all samples, reducing and digestible sugars increased, and stachyose decreased by the aging treatment. Sucrose content was highest in the 6% ethanol sample (18.2% at six days). These results indicate that the ethanol addition can be applied to the aging treatment of the RGR for improving qualities (sweetness, digestibility, and microbial growth), and can be considered for the stable production of high quality aged RGR.

In this study, the effect of pre-aging treatment for inhibition of natural aging of Al-4.8Zn-1.3Mg alloy by extrusion process was investigated. Firstly, the as-cast microstructure of Al-4.8Zn-1.3Mg alloy billet and its evolution during homogenization(460℃, 4h + 510℃, 5h) were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), hardness analysis. The as-cast microstructures of Al-4.8Zn-1.3Mg alloy reveal Mg2Zn, Al5Cu, Al3Cu formed between dendrities. After homogenization, MgZn, Al4Cu, Al13Cu phases precipitated into the matrix. In addition, standard deviation of homogenized billet was improved than as-cast billet from 2.62 to 0.99. According to pre-aging(100℃, 1h) Al-4.8Zn-1.3Mg alloy by extrusion process, yield strength and tensile strength deviation improved more than condition by natural aging.

The effect of heat treatment on the microstructure and mechanical properties of cast Ti-6%Al-4%V alloy was investigated. Heat treatment of cast Ti-6Al-4V alloy was conducted by solution treatment at 950 oC for 30 min; this was followed by water quenching and then aging at 550 oC for 1 to 1440 min. The highest hardness of the heat-treated specimens was obtained by solution treatment and subsequent aging for 5 min due to precipitates of fine α that formed from retained β phase. The tensile strength of this alloy increased without dramatic decrease of the ductility due to microstructural refinement resulting from the decomposition of α' martensite into fine α and β phases, and also due to the fine α phase formed from the retained β phase by aging treatment for 5 min. In addition, this strengthening might be caused by the transformation induced plasticity (TRIP) effect, which is a strain-induced martensite transformation from the retained β phase during deformation, and which occurs even after aging treatment at 550 oC for 5 min.

In mammal, unfertilized oocytes remain in the oviduct or under in vitro culture, which is called "oocyte aging". This asynchrony negatively affects fertilization in pre- and post-implantation embryo development. Caffeine a phos-phodiesterase inhibitor is known to rescue oocyte aging in several species. The objective of this study is to determine the cytoskeleton distribution in aged oocytes and the embryo developmental ability of aged oocytes in the present or absence of caffeine during maturation. Caffeine treatment increased the incidence of normal spindle assembly of aged oocytes (treatment, 67.57±4.11% aging, 44.61±6.4%) and no significant differences compared to control group. Fluorescence values were compared using ROS (Reactive oxidation species) stain. Fluorescence values appear of con-trol group intensity rate (51.53.±3.80), aging group (68.10±5.54) and treatment of caffeine (45.04±2.98). Aged oocytes that were derived from addition of caffeine to the IVM (in vitro maturation) medium had significantly increased 2-cell that developed to the blastocyst stage compared to the aging group. Blastocysts, derived from caffeine treatment group, significantly increased the total cell number compare aging (90.44±10.18 VS 67.88±7.72). Apoptotic fragments of genomic DNA were measured in individual embryo using TUNEL assay. Blastocyst derived from caffeine treatment group decreased significantly the apoptotic index compared to blastocyst derived from aging group. In conclusion, we inferred that the caffeine treatment during oocyte aging can improve the developmental rate and quality in bovine embryos developing in vitro

Magnesium alloys are alloyed with rare earth elements (Re, Ca, Sr) due to the limited use of magnesium in high-temperature conditions. In this study, the influences of Zr and Zn on the aging behavior of a Mg-Nd-Y alloy were investigated. magnesium alloys containing R.E elements require aging treatments Specifically, Nd, Y and Zr are commonly used for high-temperature magnesium alloys. Various aging treatments were conducted at temperatures of 200, 250 and 300˚C for 0.5, 1, 3, 6, and 10 hours in order to examine the microstructural changes and mechanical properties at a high temperature (150˚C). Hardness and high-temperature (150˚C) tensile tests were carried out under various aging conditions in order to investigate the effects of an aging treatment on the mechanical properties of a Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy. The maximum hardness was 67Hv; this was achieved after aging at 250˚C for 3 hours. The maximum tensile, yield strength and elongation at 150˚C were 237MPa, 145MPa and 13.6%, respectively, at 250˚C for 3 hours. The strengths of the Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy increased as the aging time increased to 3 hours at 250˚C This is attributed to the precipitation of a Nd-rich phase, a Zr-rich phase and Mg3Y2Zn3.

Ni-20Cr-20Fe-5Nb alloy with or without was manufactured by mechanical alloying process and consolidated by spark plasma sintering (SPS). The grain size of the alloy with was smaller than that of alloy without which results from the effect of suppressing grain growth. The tensile strength at room temperature was increased by the addition of but decreased abruptly at temperature above . It seems to result from the change of deformation mechanism due to fine grain size, that is, grain boundary sliding is predominant at above while internal dislocation movement is predominant at below . After conventional heat treatment process of solution treatment and aging, a small amount of phase was formed in Ni-20Cr-20Fe-5Nb alloy while a large amount of was formed in Inconel 718 in the previous report. This is due to exhaustion of Nb content by the formation of NbC during consolidation.

7050 Al합금의 응력부식저항성에 미치는 2단 시효처리의 영향을 미세조직관찰, 전기전도도시험 및 SCF값을 평가함으로써 조사하였다. 최대 경도 이상 과시효에 의해 주 강화상인 η'상이 η상으로 변태되었고, 입내 및 입계에 존재하는 η상의 크기와 간격이 커졌으며 그 결과 응력부식저항성이 증대되었다. 2차 시효시간의 증가에 따라 전기전도도값은 증가되었으나 항복강도의 감소로 인하여 SCF값은 감소되었는데, 이러한 결과는 응력부식저항성의 증가를 의미한다. AMS 4107규격을 기준으로 하였을 때 7050 Al합금 단조재의 적정시효조건은 1차시효가 120˚C에서 6시간, 2차시효는 175˚C에서 12시간이었다.

7050AI합금의 미세조직 및 기계적성질에 미치는 2단시효처리의 영향을 투과전자현미경, 열분석, 경도시험 및 인장 시험을 통하여 조사하였다. 120˚C에서 6시간 1차 시효처리한 후 165˚C와 175˚C에서 2차 시효처리하였을때 165˚C에서는 6시간 시효시 최대경도값 201.3Hv를 나타내었고, 175˚C에서는 3시간 시효처리하였을때 최대경도값 197Hv를 나타내었다.

용탕단조법에 의해 제조된 Mg-6AI-xZn(x=0,1,2)합금의 기계적 성질에 미치는 시효열처리의 영향을 조사하였다. 주조상태에서의 미세조직은 초정 Mg고용체, 과포화된 상태의 Mg상, 응고과정에서 형성된 β(Mg17AI12)화합물 등 3개의 상으로 구성되어 있었다. 용체화처리 수 200˚C및 240˚C에서 시효열처리한 결과 Mg-6AI-xZn(x=0,1,2)합금은 β 석출물에 의한 피크 경도값이 나타났으며, 석출물의 형태는 200˚C에서는 lamella 형태의 불연속 석출물이, 240˚C에서는 미세분산분포된 연속석출물의 형태를 보였다. 용탕단조방법에 의해 제조된Mg-6AI-xZn합금의 기계적 성질은 사형주조법에 비해 인장강도 및 연신율에서 우수한 특성을 보였으며 Zn의 첨가량이 증가함에 따라 Zn의 고용강화 효과에 따라 강도값이 증가되었다.

고역알루미늄합금의 파괴특성에 미치는 시효열처리의 영향에 대하여 검토한 결과는 다음과 같다. 1. 현미경 조직의 관찰결과 190℃, 12hr로 시효열처리한 것이 시효강화된 양호한 조직과 미세한 석출분포를 나타내고 있음을 알 수 있었다. 2. 계단식시효열처리에 의하여 정상시효열처리보다 시효시간을 반정도로 단축시킬 수 있었고, 이들 조직도 유사하였다. 3. 인장파단면의 SEM 전자현미경 사진관찰결과는 190℃, 12hr으로 시효열처리한 것은 딤플형 입계 및 입내연성파괴를 나타내나, 이를 제외한 대부분은 시효열처리 시간과 온도에는 관계없이 입계연성파괴인 것이 관찰되었다.

Si-Cr계 내열강 SUH3와 Cr-Ni계 stainless강 SUS 303 및 이들이 마찰용접재 SUH3-SUS303을 1,060℃에서 용체화처리하고 다시 700℃에서 10, 100시간 시효열처리한 각 시험편의 고온 피로강도에 대한 시효열처리의 효과를 알기 위하여 700℃에서 고온 회전굽힘 피로시험을 하고 파약거동을 미시적으로 관찰하여 다음과 같은 결과를 얻었다. 1) SUH3재와 SUS303재의 최적마찰용접조건은 회전수 2420rpm, 마찰가압력 8kg/mm2, 전 upset량 7mm(마찰가압시간 3sec, upset시간 2sec)이었다. 2) 700℃ 고온에서 장시간 이루어지는 고온피로시험에 있어, 용체화처리재의 S-N 곡선 경사부의 기울기가 가장 급하게 나타났다. 3) SUH3-SUS303 마찰용접재는 1,060℃에서 1시간용체화 처리하고, 700℃에서 시효처리하는 경우 최적시효시간은 10시간이었다. 4) 10시간 시료재의 고온피로한도는 모재보다 SUH3은 75.4%, SUS303은 28.5% 높았으며, 용접재 SUH3-SUS303은 44.2% 정도 높았다. 100시간 시효재는 모재보다 SUH3은 64.91% SUS303은 30.4% 높았으며, SUH3-SUS303은 30.4% 높았으며, SUH3-SUS303은 36.6% 높았다. 5) 마찰용접재의 상온 및 고온의 피로파단은 모두 SUS303의 모재측에 발생하였으며, 용접면에서의 파단은 전혀 없었다. 6) SUS303재와 마찰용접재 SUH3-SUS303재의 크랙은 입내파양형이었으나 SUH3은 입계크랙의 전파로 파양한다.

Background : Ginseng seeds are one of short-lived seeds species which loose their viability easily in the condition of conventional storage. Cryopreservation using liquid nitrogen (LN) has been recommended as a alternative storage for this kind of germplasm short lived or dessiccation-sensitive. This study was performed to find out whether cryopreservation could assure initial viability not only for seeds with high germination rate but also for seeds with low germination rate (in aging process). Methods and Results : In this work, 3 cultivars of dehisced ginseng seeds were artificial aged in the condition of 40℃, 95% RH during 6 hours with 3 hours-interval. The germination rate of ginseng seeds was decreased to the range of 71 - 94% of initial viability by artificial aging treatment. After 24 hours of vapor-LN exposure on both of artificial aged and non treated seeds as a cryopreservation, germination rate for each cultivar was decreased with the range of 76 - 95% of initial viability. While the decreasing patterns of germination rate for each cultivar showed similar curves between before and after vapor-LN exposure, the aging effects could be slightly little by cryopreservation for 3 cultivars of ginseng seeds. Conclusion : From the above results, we may suggest that cryopreservation could be recommened for storage tool of dehisced ginseng seeds even with low viability also and expected to make slower seed aging process during preservation period through further study.

미숙과의 가공법 제안 및 기능성 규명을 위한 기초 연구 의 일환으로 반시 미숙과를 7 step으로 나누어 열처리 숙성 하면서 이화학적 특성 및 항산화 활성의 변화를 분석하였 다. 반시 미숙과는 숙성됨에 따라 수분함량과 pH는 점차 감소하고, 산도는 증가하는 경향이었다. 숙성이 진행됨에 따라 갈변이 유도되면서 step 3까지 적색도는 급격히 증가 하였으며, 황색도는 큰 폭으로 감소하였다. 반시의 탄력성, 씹힘성과 점착성의 경우에는 step 2~3에서 변화한 후에는 유의적인 차이를 보이지 않았다. 숙성 중 반시 미숙과의 fructose의 함량은 감소한데 반해 glucose 함량은 미량 증가 하였다. 페놀성 화합물은 gallic acid와 homogentisic acid, 2종이 검출되었는데 이들 화합물은 step 2까지는 검출되지 않았으나, step 3부터 숙성단계가 지남에 따라 함량이 증가 하였다. 이와 상반되게 탄닌 함량은 step 1에서 가장 높게 측정되었고 step 2에서 급감하였다. 숙성 단계별 반시 미숙 과 물 추출물의 DPPH와 ABTS 라디칼 소거능 및 FRAP법 에 따른 항산화 활성은 시료의 농도에 비례하여 유의적으로 증가하였으나, 숙성이 진행될수록 오히려 낮아졌다.