• Asian-Australasian Journal of Animal Sciences
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• 제12권8호
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• pp.1316-1323
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• 1999

Extensive emphasis on milk and milk fat yields with no diversion for beef performance increased the yield efficiency of North American dairy cattle. Heavy demand for North American genetics followed national strain comparison trials in Poland, and US and Canadian dairy cattle and germplasm still are an important source of genetics for many countries. Genetic improvement has accelerated in many countries because of the implementation of sampling programs for young bulls and improved evaluation procedures. Rapid access to information and more frequent calculation of genetic information also are having a positive impact on genetic improvement. Traits other than yield should be considered in a breeding program, but those traits mist have a reasonable opportunity for improvement and sufficient economic worth. Because of ever increasing efficiency, the world's milk supply comes from fewer cows each year. However, no decline in the rate of genetic improvement is apparent under current genetic practices; estimates of heritability are increasing, and a decline in yield efficiency is unlikely in the near future. As management improves, especially for subtropical conditions, many of the selection principles used in temperate climates will be adopted for more adverse environmental conditions.

• Safety and Health at Work
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• 제6권3호
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• pp.233-239
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• 2015

Background: The Job Content Questionnaire (JCQ), which is based on the Demand-Control-Support model, is designed to measure the psychosocial characteristics of the respondent's work, and has been identified to predict health and psychological outcomes. The purpose of this study was to investigate the psychometric properties of this instrument and the subsequent adaptation of its scales to the population of Greek health workers. Methods: The Greek version of the JCQ was developed by using forward- and back-translation in accordance with the JCQ policy. The reliability and validity of the measure were investigated in a sample of health workers working in a hospital in Athens, Greece. The internal consistency of the scales was examined based on Cronbach ${\alpha}$ coefficients, and the validity was evaluated subjecting the items of the three main scales of the JCQ (decision latitude, psychological job demands, and social support) to exploratory and confirmatory factor analysis. Results: The reliability of the scales was found to be acceptable for all the scales, except for the skill discretion subscale. Confirmatory factor analysis confirmed a slightly modified version of the original construct including several items to more than one factor. Conclusion: Our findings suggest that the Greek JCQ is reliable and valid for investigating psychosocial job characteristics among Greek health workers.

• Fisheries and Aquatic Sciences
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• 제6권4호
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• pp.194-202
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• 2003

Budgets for water, nitrogen, and chemical oxygen demand (COD) were determined in two 0.012 ha earthy-bottom ponds stocked with Israeli strain common carp at an initial stocking density of $20\;fish/m^3$. Total ammonia nitrogen (TAN) concentrations increased continuously but later decreased in pond A as a consequence of high nitrification. COD concentrations increased during the experimental period due to the accumulation of feed input. Nutrient budgets showed that feed represented $94-95\%$ of nitrogen input and about 99% of organic matter input. Fish harvest accounted for $40\%$ of nitrogen and organic matter input. Seepage and water exchange removed $15-17\%$ of nitrogen input but only $1-2\%$ of organic matter. Draining of the ponds removed $20-26\%$ of input nitrogen, mostly in inorganic forms, but removed only minus organic matter. Fish and water column respiration accounted for $39\%$ of organic matter input, and benthic respiration accounted for $7-12\%$ of organic matter input. No significant change of nitrogen and organic matter in both pond bottoms were found during the three-month growth period. The unrecovered input nitrogen, about $6.3-13\%$, was lost through denitrification and ammonia volatilization. On a dry matter basis, fish growth removed $31\%$ of total feed input and left $69\%$ as metabolic wastes.

• 한국지진공학회논문집
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• 제18권6호
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• pp.291-299
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• 2014

There has been an increasing demand for introducing a base isolation system to secure the seismic safety of a nuclear power plant. However, the design criteria and the safety assessment methodology of a base isolated nuclear facility are still being developed. A performance based design concept for the base isolation system needs to be added to the general seismic design procedures. For the base isolation system, the displacement responses of isolators excited by the extended design basis earthquake are important as well as the design displacement. The possible displacement response by the extended design basis earthquake should be limited less than the failure displacement of the isolator. The failure of isolators were investigated by an experimental test to define the ultimate strain level of rubber bearings. The uncertainty analysis, considering the variations of the mechanical properties of isolators and input ground motions, was performed to estimate the probabilistic distribution of the isolator displacement. The relationship of the displacement response by each ground motion level was compared in view of a period elongation and a reduction of damping. Finally, several examples of isolator parameters are calculated and the considerations for an acceptable isolation design is discussed.

• 한국기계가공학회지
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• 제17권4호
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• pp.9-16
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• 2018

Recently, the demand for eco-friendly parts has increased to reduce materials and parts that use fossil fuels. This has exacerbated the increase of energy prices and the enforcement of regulations by environmental agencies. Currently, polylactic acid (PLA) is a solution, as a common and eco-friendly material. PLA is a biodegradable material that can replace traditional petrochemical polymers. PLA has great advantages since it is resistant to cracking and shrinkage. When it is manufactured, there are few harmful byproducts. Improvement in the brittleness characteristics is another important task to be monitored throughout the production of industrial parts. Improvement in the brittleness property of products lowers the tensile strength and tensile elasticity modulus of the parts. This study focused on the mechanical properties of 3D-printed PLA parts. Tensile tests are performed while varying the infill print parameters to evaluate the applicability of PLA in several industrial areas.

• Composites Research
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• 제12권5호
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• pp.87-97
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• 1999

층상복합재료란 이종재료들을 적층하여 계면에서 확산에 의하여 새로운 금속조직을 제어하는 것으로 정의한다. 기계적 성질이 다른 금속이 결합하여 서로의 단점을 보완·개선함으로써 재료의 기계적 성질을 한층 더 향상시킬 뿐만 아니라, 동시에 전기적 성질도 향상시킬 수 있는 재료로 그 종류는 다양하며 용도도 광범위하다. 본 연구에서는 Al/Cu 피복이종복합재료를 직·간적압출하는데 필요한 성형 조건을 도출하기 위하여 유한요소 상용 package인 DEFORM을 이용하여 이종복합재료의 거동해석을 수행하였다. 압출해석에 필요한 물성치를 구하기 위하여 본 연구에서 제조한 재료를 이용하여 압축실험을 수행하였으며, 압출방법, 압출온도, 피복재의 두께 등의 변화에 다른 이종복합재료의 거동을 파악하였다. 또한 해석결과를 바탕으로 이종복합재료의 열간압출실험의 결과와 비교·검토하였다.

• 한국인터넷방송통신학회논문지
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• 제15권3호
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• pp.219-224
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• 2015

현재 에너지 절감에 대한 사회적 요구가 높다. 이번 기회에 IGBT 딤머시스템이 기존 SSR,SCR 딤머시스템과 비교하여 얼마만큼의 효율성을 갖는 것에 대한 목적을 가지고 연구를 하였다. 방법은 2가지로 첫째는 디머시스템의 조광시 출력에 따른 정현파 변형의 비교실험으로 전력손실이 얼마나 나타나는지에 대하여 오슬로스코프로 비교 측정 실험을 진행하였고, 둘째는 조광시 장비가 갖는 소리에 대한 데시벨 크기를 측정하여 장비 배치에 대한 소음에 대하여 데시벨 측정기로 실험을 진행하였다. 결과는 전력손실에 따른 효율성과 공간에 따른 소음이 많은 SSR, SCR 딤머보다 IGBT 딤머가 효율적이라는 것을 확인 하였다.

• 한국지진공학회논문집
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• 제16권6호
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• pp.21-28
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• 2012

Welded Unreinforced Flange-Welded Web (WUF-W) connection is one of Special Moment Frame (SMF) specified in ANSI/AISC-358. From the experimental test of WUF-W connection specimens conducted by the previous study, fracture occurred in the beam flange before achieving total inter-story drift angle of 0.04radian required for Special Moment Frames (SMF) system even though the specimens satisfied the design and detailing requirement specified in ANSI/AISC-358. These results are estimated as problem of the access hole geometry. In this study, a full-scale WUF-W connection specimen was made with a modified access hole geometry, and tested with the same test setting and loading as the previous test. From test results, the deformation capacity of the tested WUF-W connection specimen exceeded 4%, which is required for connections in SMF system. Comparing with the WUF-W specimens of the previous study, the strain demand of the beam flange in the tested specimen was decreased and energy dissipation capacity of the specimen was improved.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1017-1024
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• 2009

In the past few decades, the rockfill embankment dam, which has superior workability and economy, has become a major trend. In Korea, most of the embankment dams are rockfill dams, but recently, in response to the demand for sustainable development and environmentally-friendly water resource development, the sand and gravel in streams has become a major construction material for dams, rather than the non-economic rockfill, and its application examples have also increased. In this study, a large triaxial test was performed, with construction samples of different maximum sizes, in parallel with the grading method at the 'B Dam' construction site in Korea, and the effects of the different maximum sizes on the strain of the dam construction material and on the shear strength characteristics were analyzed to provide the basic data for determining the strength characteristics of the coarse-grained materials by the maximum size.

• Steel and Composite Structures
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• 제20권1호
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• pp.1-20
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• 2016

The strength and stiffness of the steel beams to concrete-filled tubular columns connections are significantly reduced if the thick-walled components are used. However, the thick-walled tubes used for columns can largely reduce the demand for space and increase the strength-to-weight ratio. This paper describes the cyclic performance of extended through-diaphragm connections between steel beams and thick-walled concrete-filled tubular columns improved with fillets around the diaphragm corners. Test on one full-scale connection was conducted to assess the seismic behavior of the connection in terms of strength, stiffness, ductility, deformation, energy dissipation, and strain distribution. It is shown that the fillets and extended through-diaphragm can alleviate the stress concentration in the connection and thus improve the seismic performance. The test results demonstrate that the through-diaphragm connections with thick-walled concrete-filled tubular columns can offer sufficient energy dissipation capacity and ductility appropriate for its potential application in seismic design.