• 한국군사과학기술학회지
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• 제4권2호
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• pp.42-51
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• 2001

The effects of pre-indentation technique are presented for A12024-T3 Alclad alloy using as skin material for aircraft fuselage and wing. Indentations were applied to specimens to be placed on the presumed path of fatigue crack growth before fatigue tests. Tension-tension fatigue tests were conducted on the edge cracked specimens in the L-T orientation. Test results were analyzed to investigate the effectiveness of pre-indentation with the variation of specimen's thickness, position of indentation and applied maximum stress. Fatigue crack retardation by pre-indentation is well recognized in the various conditions.

• 한국안전학회지
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• 제7권1호
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• pp.20-29
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• 1992

Effects of strain hardening exponents on the retardation behavior of fatigue crack propagation are experimentally investigated. The retardation of fatigue crack propagation seems to be induced by the crack closure at crack tip. The phenomenon of crack closure becomes remarkable with the increment of strain hardening exponent and magnitude of percent peak load. The ratio of crack growth increment(a$\_$d//w$\_$d/) is influenced by a single overloading (a$\_$d/) and estimated plastic zone size (W$\_$d/=2r$\_$y/) is increased according with the increasing of strain ha.dening exponents. The number of retarded crack growth cycles were (N$\_$d/) decreased as the baseline stress intensity factor .ange( K$\_$b/) was increased. Within the limitation of these experimental results obtained under the single overload, an empirical relation between crack retardation ratio (Nd/N＊), strain hardening exponent (n) and percent peak load (％PL) has been proposed as; Nd/N＊＝ exp [PL $.$ PL$.$A(n)＋B(n) ] where, A(n)＝${\alpha}$n＋${\beta}$, B(n)＝${\gamma}$n＋$\delta$, PL＝％PL/100 and ${\alpha}$＝0.78, ${\beta}$＝0.54, ${\gamma}$＝0.58 and $\delta$＝-0.01, It is interesting to note that all these constants are identical for materials such as aluminum(A3203), steel(S4SC), steel(SS41) and stainless steel(SUS316) used in this experimental study.

• 대한토목학회논문집
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• 제7권4호
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• pp.103-113
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• 1987

본(本) 연구(硏究)는 단순변동하중하(單純變動荷重下)에서의 피로균열성장거동(疲勞龜裂成長擧動)을 고찰하고 해석방법(解析方法)을 구하고자, 용접구조용강(鎔接構造用鋼) SWS 58을 사용하여 CT 시험편을 제작하고 간단한 하중모델을 설정(設定)하여 피로실험(疲勞實驗)을 행했다. 그 결과 단일과하중작용직후(單一過荷重作用直後)에는 가속효과(加速效果)가 경미(輕微)하게 발생하였으며 그후 상당한 지연효과(遲延效果)가 발생했다. 2단중복하중하(段重復荷重下)에서는 low-high인 경우 약간의 가속효과(加速效果)가 발생하나 high-low인 경우는 상당한 지연효과(遲延效果)가 발생했다. 이러한 하중변화(荷重變化)에 따른 균열성장율(龜裂成長率)(da/dN)은 균열선단(龜裂先端)의 잔류응력(殘留應力)과 소성영역(塑性領域)으로 인한 상호영향(相互影響)때문이며, 이러한 미시적(微視的) 균열성장거동(龜裂成長擧動)은 Elber의 crack closure model로 잘 설명(說明)될 수 있으나 피로균열성장해석방법(疲勞龜裂成長解析方法)으로는 불충분(不充分)하다. 반면 변동하중하(變動荷重下)에서의 피로균열성장해석방법(疲勞龜裂成長解析方法) 중(中) Wheeler의 retardation model은 간편하면서도 적합한 이론임을 알 수 있었다.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1487-1494
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• 2002

In this study, to propose the prediction method of the crack growth under flight-simulation loading, crack growth tests are conducted on 2124-7851 aluminum alloy specimens. The prediction of crack growth under flight-simulation loading is performed by the stochastic crack growth model which was developed in previous study. First of all, to reduce the complex load history into a number of constant amplitude events, rainflow counting is applied to the flight-simulation loading wave. The crack growth, then, is predicted by the stochastic crack growth model that can describe the load interaction effect as well as the variability in crack growth process. The material constants required in this model are obtained from crack growth tests under constant amplitude loading and single tensile overload. The curves predicted by the proposed model well describe the crack growth behavior under flight-simulation loading and agree with experimental data. In addition, this model well predicts the variability of fatigue lives.

• Clinical and Experimental Pediatrics
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• 제46권6호
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• pp.615-619
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• 2003

시스틴증은 상염색체 열성으로 발생하는 매우 드문 용해소체 축적병으로서, 용해소체 막을 통한 시스틴 운반의 장애로 발생한다. 용해소체 내 시스틴의 축적과 결정화에 의해 전신의 여러 조직에 파괴가 진행되어 성장 장애, Fanconi 증후군, 신부전, 눈의 이상, 내분비 질환 등이 나타난다. 치료제인 cysteamine의 투여가 예후를 향상시킬 수 있으므로 조기 진단과 치료가 중요하다. 저자들은 성장 장애를 주소로 내원한 12세 남아에서 slit-lamp 검사와 혈액 백혈구 시스틴 농도 측정을 통하여 시스틴증을 확진하고 cysteamine 치료를 시행하면서 추적 관찰 중이다.

• BMB Reports
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• 제41권5호
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• pp.363-368
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• 2008

Two genes of temperate mycobacteriophage L5, namely, gp63 and gp64, were hypothesized to be toxic to M. smegmatis. An identical L5 gp64 ortholog (designated hlg1) was cloned from homoimmune mycobacteriophage L1 and characterized at length here. As expected, hlg1 affected the growth of M. smegmatis when overexpressed from a resident plasmid. HLG1 (the protein encoded by hlg1) in fact caused growth retardation of M. smegmatis and the region encompassing its 57-114 C-terminal amino acid residues was found indispensable for its growthretardation activity. Both nucleic acid and protein biosynthesis were severely impaired in M. smegmatis expressing HLG1. Interestingly, HLG1 also affected E. coli almost similarly. This putative delayed early lipoprotein did not participate in the lytic growth of L1.

• 한국환경과학회지
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• 제1권1호
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• pp.13-21
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• 1992

The inhibitory effects of mercury ions on the growth of barley seedlings were studied and the distribution of metal elements in the organs of treated plants was investigated by using synchrotron radiation induced X-ray emission (SRIXE). Although the treatment of mercury ions caused growth inhibition, the mercury-specific increase in variable fluorescence and the abolishment of energy-dependent quenching in broken barley chloroplasts as shown by Moon et at. (1992) were not observed in the leaves of growth-inhibited seedlings. Instead the treatment of mercury decreased Fmax and Fo values. However, Fmax/Fo ratio and photochemical and nonphotochemical quenching coefficients were not affected significantly. By SRIXE analysis of $10\mu\textrm{m}$ mercury chloride treated seedlings, accumulation of mercury in roots was observed after 1 hour of treatment and similar concentration was sustained for 48 hours. Relative contents of mercury was high in roots and underground nodes where seeds were attachedl but was very low in leaves. Iron and zinc were also distributed mainly in the lower parts of the seedlings. However after 72 hours of treatment the contents of these metals in roots decreased and their distribution became more uniform, which may lead to death of the plants. These results suggest that the observed inhibitory effects on barley seedlings upto 48 hours after the treatment is not due to direct damages in the photosynthetic apparatus, but due to its accumulation in roots and the consequent retardation of the growth of barley seedlings. The decrease in Fmax and Fo is probably due to the decrease in chlorophyll and protein contents caused by the retardation of growth. The observed slow expansion of primary leaves could be also explained by the retardation of growth, but the fluorescence induction pattern from the leaves did not show characteristic symptoms of leaves under water stress.

• 대한한방소아과학회지
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• 제24권1호
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• pp.36-45
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• 2010

Objectives The purpose of this study is to evaluate the effect of herbal medicine in children's growth and to report the children's expectation. Methods 171 children visited the department of Pediatrics, Kyung-Hee Oriental Medical Hospital from June 2009 to December 2009 were studied. They were treated more than 6 months and they visited our clinic more than 3 times. Every time when patients visited our hospital, their height, body weight and obesity degree was examined using DS-102(dszenix, Seoul). Also, height percentile of first and the last visit was measured, and those were compared by the Growth Statistics Curve made by the Korean Association of Pediatrics, 2007. Results and Conclusions The mean growth of total children increased by 4.42 percent; the increased percent for boys was 4.17 and that of girls was 5.00. Herbal medical treatment helped growth in children who took medicine for growth retardation problem. Plus, majority of parents who visited the department of Pediatrics, Oriental Medical Hospital satisfied with the service and their children's height. Although thinking genetic factor is important for their height, but they think that herbal medical treatment help the growth with changing eating habit.

• 한국환경보건학회지
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• 제46권4호
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• pp.368-375
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• 2020

Objectives: Some animal studies have reported that methyl mercury causes developmental toxicities such as placental and fetal weight loss, but the mechanism is still unclear. This study aimed to investigate the developmental toxicities of methyl mercury, focusing on placental endocrine function and fetal growth retardation in rats. Methods: Positively same-time-mated female Sprague-Dawley rats were purchased on gestational day (GD) eight and treated with 0, 5, 10 and 20 ppm of methyl mercury (n=5) dissolved in tap water from GD eight through 19. During treatment, the drinking water (methyl mercury) intake and body weight of each pregnant rat was measured daily. On day 19, caesarean sections were performed and blood samples were collected. Developmental data such as placental and fetal weights, fetus numbers, and placental efficiency (fetal weight/placental weight) were also collected. Placental prolactin-growth hormone (PRL-GH) family, such as placental lactogen (PL) -Iv, II, and prolactin-like protein (PLP) -B, levels in serum were analyzed by ELISA. Also, placental tissues were assigned to histochemistry. Results: The mean cumulative methyl mercury exposure for the 5, 10, and 20 ppm groups were 2.37, 4.63, and 9.66 mg, respectively. The mean daily exposure of the 5, 10, and 20 ppm groups were 0.24, 0.47, and 0.97 mg, respectively. Maternal body weight increased in accordance with GD. There was no significant difference in weight gain among the experimental groups. Histopathologic changes were not observed in placental tissues among the experimental groups. However, mean placental and fetal weights were lower in the 10 and 20 ppm exposed groups compared to the control. Placental efficiency was also lower in the 10 and 20 ppm exposed groups compared to the control. Serum PL-Iv and II levels were lower in the 10 and 20 ppm exposed groups than the control, in accordance with the changing pattern of placental and fetal weights and placental efficiency. Conclusion: The inhibitory effects of methyl mercury on the serum levels of placental PRL-GH family such as PL-Iv and II may be secondary leads to the reduction of placental efficiency and fetal growth retardation in rats.

• Asian-Australasian Journal of Animal Sciences
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• 제22권11호
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• pp.1495-1503
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• 2009

This experiment was conducted to determine the effect of dietary supplementation with BCAA (branched-chain amino acids: leucine, isoleucine and valine) on improving the growth of rats in a malnutritional IUGR (Intrauterine Growth Retardation) model, which was established by feeding restriction. In the experimental treatment, rats were fed purified diets supplemented with BCAA (mixed) during the whole gestation period, while arginine and alanine supplementation were set as the positive and negative control group, respectively. The results showed that, compared to the effect of alanine, BCAA reversed IUGR by increasing the fetus weights by 18.4% and placental weights by 18.0% while fetal numbers were statistically increased. Analysis of gene and protein expression revealed that BCAA treatment increased embryonic liver IGF-I expression; the uterus expressed higher levels of estrogen receptor-$\alpha$ (ER-$\alpha$) and progesterone receptor (PR), and the placenta expressed higher levels of IGF-II. Amino acid analysis of dam plasma revealed that BCAA supplementation effectively enhanced the plasma BCAA levels caused by the feed restriction. BCAA also enhanced the embryonic liver gluconeogenesis by augmenting the expression of two key enzymes, namely fructose-1,6-biphosphatase (FBP) and phosphoenolpyruvate carboxykinase (PEPCK). In conclusion, supplementation of BCAA increased litter size, embryonic weight and litter embryonic weight by improving the dam uterus and placental functions as well as increasing gluconeogenesis in the embryonic liver, which further provided energy to enhance the embryonic growth.