• Journal of the Korean Society for Heat Treatment
• /
• v.14 no.4
• /
• pp.235-239
• /
• 2001

급속 표면가열과 기존의 전기로 열처리에서 얻어지는 경화의 가장 중요한 차이점은 전자가 불균질한 오스테나이트를 생성할 수도 있다는 것이다. 즉, 오스테나이트에 미용해 탄화물이 존재할 수도 있고 탄소와 합금원소의 농도 구배가 존재할 수도 있다. 합금강에서, 이러한 탄화물은 합금성분이 비교적 높기 때문에 철 탄화물에 비해서는 좀 더 천천히 기지에 용해된다. 또한 망간, 크롬, 니켈 및 몰리브덴과 같은 치환형 합금원소는 천천히 확산한다. 따라서, 균일한 오스테나이트를 생성하기 위해서는 더 많은 시간과 더 높은 온도가 요구된다. 그러나 표면 구역의 낮은 경화능에도 불구하고 냉각속도가 마르텐사이트의 체적분율이 큰 미세조직을 확보할 만큼 충분히 크기 때문에 경도는 높게 된다.

• Korean Journal of Soil Science and Fertilizer
• /
• v.22 no.1
• /
• pp.61-66
• /
• 1989

Plants were exposed to different sub-optimal growth temperature regimes for hardening or sprayed with abscisic acid (ABA) before being placed at $10^{\circ}C$ for three days. Comparisons were made with non-treated plants for plant survival, photosynthetic activities and fatty acids composition of phospholipids. The level of endogenous ABA of the hardened seedlings was compared with that in control and ABA sprayed-seedlings. The results of the above experiment were summarized as follows: 1. Compared to non-treated plants, the hardening and ABA treatment resulted in higher plant survival rate and better seedling growth following earlier transplanting. The low temperature hardening which gradually increased the duration of the low temperature treatment at 2-day intervals was more effective than the controled temperature hardening which gradually decreased the temperature from $25^{\circ}C$ to $20^{\circ}C$ and $15^{\circ}C$. 2. The photosynthetic activities of rice leaves after 3-day exposure to $10^{\circ}C$ were higher in hardened and ABA sprayed seedlings than in non-treated plants. The root activities after low temperature treatment were also higher in hardened and ABA sprayed seedlings than in control. 3. Fatty acids of phospholipids in rice plants such as stearic acid and oleic acid were decreased and the highly unsaturated fatty acids, linoleic acid and lenolenic acid were increased by hardening or ABA treatments. It is assumed that the increase of cold tolerance in these plants was due to the higher ratio of unsaturated to saturated fatty acids. Respectively, the ratio was 1.86, 1.97 and 1.80 in plants given controled temperature hardening, the low temperature hardening and ABA treatments. While in control plants, it was 1.17. 4. ABA content in rice seedling given the low temperature hardening treatment was 67.2 ng/g F.W which was approximately twice that of non-treated control, which was 33.9 ng/f F. W., in contrast, the ABA content of the ABA treated seedlings was 91.7 ng/g F. W.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1992.10a
• /
• pp.311-315
• /
• 1992

일반적으로 기계구조물에서는 비교적 응력확대계수 K의 해석이 용이한 판 두께를 관통하는 관통크랙보다는 표면에 존재하는 결함에서 발생, 전파하는 표면 크랙이 대부분이다. 표면은 내부보다 소성변형에 대한 저항이 작고, 대기에 직접 접해 있으며, 평활재에 있어서의 인장, 압축이외의 응력은 일반적으로 표면에서 최대가 되는 등의 이유로 내부보다 쉽게 피로재해를 받는다. 침탄질화 열처리를 하는 중요한 목적이 재료 표면에 있어서 경화능과 피로강도의 향상이므로 침탄질화 처리재의 표면 크랙에 관한 연구가 절실히 요구됨은 당연하다.

• Journal of Embryo Transfer
• /
• v.14 no.2
• /
• pp.99-106
• /
• 1999

핵 이식에 공여되는 수핵난자의 효과적인 동결보존을 위하여 한우 성숙난자를 1.0 M dimethylsulfoxide(DMSO) 또는 1.0 M glycerol이 함유된 동결보호제를 이용하여 처리하거나, 동결보호제 처리 후 완만동결법을 이용한 동결융핼르 시행하여 상기 실험처리로 야기되는 투명대 경화현상을 관찰하였다. 도축장 유래의 난소에서 미성숙난자를 채취한 후 10% 소 태아혈청을 함유한 TCM-199을 이용하여 22∼24 시간 동안 체외성숙배양을 이해하였다. 배양후 작출된 성숙난자를 각각의 동결보호제로 처리, 혹은 처리 후 동격융해한 후 protease를 이용하여 투명 대의 경화현상 발생의 빈도를 조사하였다. 또한 동격란을 동결정액을 이용한 체외수정에 공여한 후 정자 침입농도능을 조사하였다. 동결보호제로 처리한 난자에 있어서 보호제의 종류와 관계없이 투명대 경화현상이 유의적 (P<0.05) 으로 증가하였으나 이후의 동결융해 처리에 의한 추가적인 경화현상의 발생은 증가하지는 않았다. 또한 투명대 경화현상의 발생양상을 동결보호제 처리 후 10분 간격으로 측정한 결과 DMSO의 경우 처리후 10분, glycerol의 경우 처리 후 20분 후부터 유의적으로 차를 발견할 수 없었으며, 수정율 및 난자 1개당 침입한 정자의 수는 동결란에서 유의적으로 증가하지 않았다. 본 연구의 결과 동결난자의 투명대 경화현상은 동결보호제 처리과정에서 이미 일어나지만, 이러한 투명대 경화현상이 난자의 동결보존 후 수정능에는 현자한 영향을 미치지 않는다는 사실이 규명되었다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.8
• /
• pp.961-969
• /
• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Laser Solutions
• /
• v.11 no.4
• /
• pp.7-12
• /
• 2008

Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Composites Research
• /
• v.29 no.6
• /
• pp.395-400
• /
• 2016

Recently, many research groups have studied on the epoxy-based multifunctional electrolyte to develop the structural composite bearing high mechanical properties without sacrificing the ionic conductivity at the same time. The studies on the optimal content and material selection for structural electrolyte have been published, while its curing behavior has not much analyzed yet. In this study, epoxy-based structural electrolyte containing solid electrolyte was prepared by varying the curing temperature and time. In addition, the ionic conductivities and mechanical properties of specimens were measured. We also find out the optimal hardening condition where the epoxy domain enables to be hardened within the range of temperature at which the thermal decomposition of electrolyte does not occur. Finally, we propose the multifunctional structural electrolyte showing achievable electrical and mechanical properties (282 MPa and $9{\times}10^{-6}S/cm@25^{\circ}C$).

• Magazine of the Korea Concrete Institute
• /
• v.6 no.6
• /
• pp.135-142
• /
• 1994

The quality characteristics of concrete using super plasticizer in dornestlc rnarket are evaluat ed in order to put to practical use of high performance concrete with high mobility. high strength ard high durability. For this purpose, rune kmds of super plasticizer are compared and analyzed for the slump, air content. unit weight, water reducing percent and ratios of compressive strength wth admixture content. As a result, the optimum quantity of admixture content were obtained for ordinary and high strength concrete using super plasticizer.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.32 no.6
• /
• pp.899-905
• /
• 2003

The effects of cooked soybean and a traditional fermented soy product, chongkukjang, on blood pressure and lipid metabolism were studied in spontaneously hypertensive rat (SHR). SHRs were divided into 3 groups (n=10, male), and fed casein, powders of cooked soybean, and chongkukjang as dietary protein sources for 6 weeks. Body weight gain was not different among experimental groups, but food efficiency was increased in groups fed cooked soybean and chongkukjang diets compared to control group. Consumption of cooked soybean and chongkukjang for 6 weeks in SHR significantly suppressed blood pressure rise with aging (p<0.05). Feeding of cooked soybean and chongkukjang to SHR decreased plasma triacylglycerols (p<0.05) by 21.6% and 30.2% and LDL-cholesterol by 30.0% and 27.5%, respectively. Addition of cooked soybean and chongkukjang to the diet resulted in reduction of total lipids and triacylglycerols of liver, while consumption of cooked soybean and chongkukjang resulted in the increase of fecal cholesterol and bile acid excretions, respectively (p<0.05). Cooked soybean and chongkukjang diets down-regulated the activity of hepatic HMG-CoA reductase by 56.4% and 94.5%, compared to control, respectively. From the above-mentioned results, it can be concluded that consumption of cooked soybean and chongkukjang might be helpful in preventing cardiovascular disease by suppressing blood pressure rise and hyperlipidemia.

• Journal of Sericultural and Entomological Science
• /
• v.47 no.2
• /
• pp.62-67
• /
• 2005

Much attention has been focused on the activity of the natural antioxidants present in fruits and vegetables, because potentially these components may reduce the level of oxidative stress. Especially, mulberry leaves containing many natural components are considerable resource far natural antioxidants. The antioxidant capacity of mulberry leaves was investigated with minilum L-100 device and ARAW-KIT (anti-radical ability of water-soluble substance), in comparison to the ascorbic acid. The appropriate conditions for pre-treatments of mulberry leaves were 80% MeOH, 30 sec. vortex mixing. The antioxidant capacity of 16 varieties was 3303.4 nmol (ascorbic acid equivalents) at opening stage of five leaves in spring. The highest stage of antioxidant capacity (3708.0 nmol) and yield rate was just before the coloration stare with anthocyanin in fruits, whereas the lowest stage was middle of June (2231.6 nmol) and about two months growing stage after summer pruning (2064.6 nmol). But after summer pruning, the antioxidant capacity of mulberry.