• The Korean Journal of Ecology
• /
• 제25권4호
• /
• pp.241-245
• /
• 2002

During the breeding season of 1998, breeding ecology of the Great Reed-Warbler (Acrocephalus arundinaceus orientalis) was studied at Yangsoo-ri and Yongdam-ri of the Yangpyung-gun, Kyunggi province, Korea. Egg-weight (CV: 6.25) was more variable than either length or breadth, and breadth was the least variable of the measures. Significant variations in overall egg-weight occurred between clutches, and that more of the total variation in egg-weight and shape are due to inter-clutch variation as to intra-clutch variation when the data were pooled. The last egg tends to be larger than the remaining eggs in the clutch of the Great Reed-Warbler, suggesting the Great Reed-Warbler may adopt the brood-survival strategy. When method 3 was used, the most common incubation period is 12 days. In the Great Reed-Warbler, the length of the incubation period was related to clutch-size when method 1 (r=0.485, p<0.05) and method 2 (r=0.621, p<0.01) were employed, but not related to egg weight. The averagee number of days of hatching asynchrony was 2.5, raging 0.5~2.5. Asynchronous hatching was related to the clutch size (r=0.66, p<0.01). Hatching sequence was closely related to the laying sequence (r=0.93, p<0.001), suggesting Great Reed-Warblers incubate their eggs before clutch completion. The effect of egg weight on hatching asynchrony was found in Great Reed-Warblers (t-test, p<0.01).

• Journal of Ecology and Environment
• /
• 제31권1호
• /
• pp.75-81
• /
• 2008

Rates of molecular evolution are known to vary widely among taxonomic groups. A number of studies, examining various taxonomic groups, have indicated that body size is negatively and clutch size is positively correlated with the rates of nucleotide substitutions among vertebrate species. Generally, either smaller body mass or larger clutch size is associated with shorter generation times and higher metabolic rates. However, this generality is subject to ongoing debate, and large-scale comparative studies of species below the Order level are lacking. In this study, phylogenetically independent methods were used to test for relationships between rates of the mitochondrial cytochrome b evolution and a range of life history traits, such as body mass and clutch size in the Order Galliformes. This analysis included data from 67 species of Galliformes birds and 2 outgroup species in Anseriformes. In contrast to previous studies, taxa were limited to within-Order level, not to Class or higher. I found no evidence to support an effect of life history traits on the rate of molecular evolution within the Galliformes. These results suggest that such relationship may be too weak to be observed in comparisons of closely related species or may not be a general pattern that is applicable to all nucleotide sequences or all taxonomic groups.

• Journal of Ecology and Environment
• /
• 제29권6호
• /
• pp.545-550
• /
• 2006

2003$\sim$2005년의 쇠제비갈매기 Sterna albifrons의 번식기 동안 충남 홍성군 간월호의 번식군집에서 총 10개의 과산란수의 둥지(nest with supernormal clutch)와 7개의 이종 알 혼합 둥지(nests with mixed species clutch, 쇠제비갈매기와 흰물떼새의 알이 혼합된 둥지)가 관찰되었다. 쇠제비갈매기의 알 회수 행동은 한 배 산란수와 관계없이 두 번째 알 산란 이후 높은 빈도를 보였다. 알 회수 행동은 모든 포란 단계에서 매우 높은 빈도로 나타났다. 쇠제비갈매기는 둥지에서 약 15 cm 떨어진 알에 대하여 높은 알 회수 행동 비율을 보였으나 35$\sim$55 cm의 거리에서 급격히 감소하였고 60 cm 거리에서는 알 회수 행동이 나타나지 않았다. 쇠제비갈매기는 알의 종류 및 크기와 관계없이 둥지 인근에 배치된 알들을 자신의 둥지로 편입시키는 행동을 보였다. 본 조사 결과는 쇠제비갈매기의 알 회수 행동이 과산란수의 둥지 및 이종 혼합 둥지를 생성할 가능성이 있음을 시사한다.

• 한국동물학회:학술대회논문집
• /
• 한국동물학회 1994년도 한국생물과학협회 학술발표대회
• /
• pp.105.1-105
• /
• 1994

No Abstract, See Full Text

• Tribology and Lubricants
• /
• 제30권6호
• /
• pp.337-342
• /
• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• 한국기계가공학회지
• /
• 제8권1호
• /
• pp.57-63
• /
• 2009

Magneto-Rheological(MR) fluid composes of a base fluid and ferromagnetic particles less than tens of micrometer size dispersed in the fluid. It is called as a smart material because its rheological properties are changable by a magnetic field. Its important applications are active devices such as controllable dampers and controllable clutches. The merit of those products is that their functional characteristics are controllable such that they enable active control strategies. This paper proposes an idea for machine tool applications of the MR fluid clutch as a safety device for power transmission. FEM has been used for magnetic field analyses and the results are compared with some former experiments. Some design syntheses of the MR clutches are suggested and hopefully considered that it may be an effective safety device for power transmission of machine tools.

• 한국환경생태학회지
• /
• 제24권4호
• /
• pp.345-350
• /
• 2010

1988년부터 2007년 사이에 수행된 붉은머리오목눈이(Paradoxornis webbianus)의 생태연구 과정에서 종내탁란으로 추정되는 현상은 4개 둥지(0.38%, n=1,062)에서 관찰되었다. 첫 번째는 1995년 경기도 양평군 부용리에서 붉은머리오목눈이의 한배산란수의 범위를 초과하는 9개의 알이 있는 둥지가 관찰되었다. 두 번째와 세 번째는 2001년과 2005년, 경기도 안산시 사동에서 하루 사이에 2개의 알이 산란된 둥지가 각각 관찰되었다. 마지막은 2007년 부용리에서 어미새의 산란 전에 어미새의 알과는 색이 다른 알이 하나 산란된 둥지가 발견되었다. 이러한 결과는 비록 낮은 빈도이지만 붉은머리오목눈이에서 종내탁란 현상이 나타나고 있음을 보여준다.

• 한국동물학회:학술대회논문집
• /
• 한국동물학회 1995년도 제16회 생물과학 심포지움 강연록
• /
• pp.68-73
• /
• 1995

Most female Great Tits lay one egg each day until the clutch is complete. However, some exceptions are found. “Pause day/s” most frequently occur after the 1st egg is laid. In general, egg-size increase with laying sequence, but there is year-to-year variation. The relationship between egg size and laying sequence is found more significantly in relatively larger clutches than in smaller ones. Great Tits tend to advance the hatching of their chicks by starting to incubate earlier in relation to clutch completion as the breeding season progresses. hatching asynchrony affects chick´s growth rate, but when the effect of laying date on hatching asynchrony is controlled, the effect of hatching asynchrony on growth rate is not found. These findings support the ´hurry-up´ hypothesis.

• 대한기계학회논문집A
• /
• 제31권2호
• /
• pp.269-276
• /
• 2007

Optimal thickness and shape of the pedal arm of an automotive clutch is determined, using the numerical optimization technique, by solving the size and shape optimization problems to minimize its weight. For the optimization problems, two cases of stress and displacement constraints are considered: one from the vertical, and the other from the transverse stiffness test condition. The result of the transverse case is shown to be more conservative than that from the vertical case, being determined as the final optimum.

• Animal cells and systems
• /
• 제15권1호
• /
• pp.85-90
• /
• 2011

In 2001, we conducted a study to assess the effects of differential arrival times and nest-site selection on reproductive performance in a mixed-species heronry consisting of six species in Taeseong-ri, Chungbuk, Korea. We recorded the arrival dates, nest heights, clutch sizes, and brood sizes after 15-20 days of the age of the birds' chicks. The grey herons and cattle egrets arrived first and last, respectively, on the colony site. In the homogenous vegetation structure of the breeding site, the pitch pine trees (Pinus rigida) were mainly used for building nests on 48 of the 50 pine trees (96%). The breeding species vertically stratifies the nest sites according to their body size, except for the cattle egrets and black-crowned night herons that nested at sites higher than those predicted from their body size. The mean nest success rates of the six species under study were positively correlated with the mean nest heights. Our findings suggest that aggressive interspecific interactions among neighbors influence nest-site selection to enhance breeding success.