• Journal of the Korean Statistical Society
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• 제11권1호
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• pp.12-24
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• 1982

Selection procedures are proposed for selecting the 'best' industrial process with the smallest fraction defective. For normally distributed industrial processes, this is equivalent to selecting in terms of coefficients of variation. For the case of known vairances, selection procedures by Bechhofer (1954), and Bechhofer and Turnball (1978) are appropriate. We treat this problem for the case of uknown variances with or without reference to a standard. The large sample solutions of design constants are tabulated and the performance of these approximate solutions are investigated.

• 한국소음진동공학회논문집
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• 제13권4호
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• pp.247-257
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• 2003

This paper presents an analytical method to Investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic Journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill's infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.166-174
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• 2002

This paper presents an analytical method to Investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill's infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2002년도 학술발표회 논문집(I)
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• pp.389-393
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• 2002

• Asian-Australasian Journal of Animal Sciences
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• 제3권3호
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• pp.155-159
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• 1990

The growth of lean from nine wholesale cuts in relation to the total lean weight in carcass side were evaluated with three allometric equations for 18 Najdi male camels slaughtered at 8, 16 and 26 months of age. The allometric growth coefficients indicated that as the camels grew, weights of lean form brisket and flank cuts increased relatively more rapidly than the total lean in carcass side (${\beta}$ >1.1) and that weights of lean from wholesale shoulder and rump cuts increased relatively less rapidly (${\beta}$ <.9) than the total lean weight from carcass side. The growth coefficients for the lean in the thoracic limb and pelvic limb showed a dorsoventral rise in the growth impetus, with coefficients for the thoracic limb correspondingly higher than those of pelvic limb. The growth coefficients for the lean from shoulder, rib, flank and leg cuts increased (p<.01) with increased weight of total lean in carcass side, whereas it decreased with increased total lean weight in carcass side for the lean in neck, brisket, plate, loin and rump cuts. At a constant weight of total lean in carcass side, older camels had larger coefficients for lean in neck, brisket, rump, flank and leg cuts, but had smaller coefficients for lean in shoulder, rib, plate and loin cuts.

• 대한기계학회논문집B
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• 제20권12호
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• pp.4027-4035
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• 1996

Accuracy of gas flow measurements using sonic nozzle and factors which influence on the discharge coefficients of sonic nozzle are investigated with high pressure gas flow standard measurement system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle test section, weighing tank, gyroscopic scale and data acquisition system. The experiments are performed at various nozzle throat diameter and inlet pressure. Overall uncertainty of discharge coefficients is estimated to less than .+-.0.2% and most of experimental data fall into this range. Dependence of discharge coefficients on the Reynolds number is good agreement with those suggested in ISO document. The influence of swirl on the discharge coefficients becomes greater as the nozzle throat diameter is enlarged. The discharge coefficient of conical nozzle shows about 4.5% lower discharge coefficients than those of toroidal nozzle, but variation trend with Reynolds number is very similar each other and reproducibility of data is very good.

• Tribology and Lubricants
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• 제25권4호
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• pp.231-235
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• 2009

In this study, the influence of contact pressure on the variation in coefficients of friction between porcine knee joint cartilage and Co-Cr alloy in a repeat pass sliding motion was investigated. Flat-ended cartilage pin specimens(9 mm diameter, 8 mm long) were prepared from porcine(6 months old) knee joints by a drill-type punch. Friction tests were conducted by using a pin-on-disk type friction tester for an hour in PBS lubricated condition under the contact pressures of 0.5, 1 and 2 MPa with 50 mm distance per a cycle at ambient condition. As a result, coefficients of friction increased as the test duration increased for all contact pressures. The maximum coefficients of friction were 0.082, 0.06 and 0.098 for 0.5, 1, and 2 MPa, respectively. It showed that coefficients of friction of porcine knee joint cartilage against Co-Cr alloy depended on the level of contact pressure and related to squeeze film lubrication mechanism.

• Journal of the Korean Wood Science and Technology
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• 제35권2호
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• pp.29-38
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• 2007

This study was undertaken to investigate the variation of equilibrium moisture content (EMC) in transverse direction and three different directional (longitudinal, radial, and tangential) linear movements, and diffusion coefficients within a tree disc of Korean red pine (pinus densiflora). The EMC gradually increased in heartwood from pith. Therefore, the chemical components might differ even in heartwood and the radial variation in EMC might have a close relationship with the cellulose content within a cross section. The specific gravity increases gradually from pith and the porosity has not direct influence on the variation of EMC within a tree disk. Both the radial and tangential diffusion coefficients exhibited clear trend of increase from pith. The EMC change (${\Delta}EMC$) and tangential diffusion coefficient were close to be axisymmetrical but others were deviated from axisymmetry. The diffusion coefficient decreases with decreasing an activation energy and specific gravity, The diffusion coefficient increased with increasing ${\Delta}EMC$ and hygroscopicity of wood might be inversely proportional to the activation energy, The fJEMC may depend on the chemical constituents of cellulose, hemicellulose and lignin. As the number of sorption sites and sorption capacity of wood increase, therefore, it might be assumed that the hygroscopicity of wood increases while activation energy decreases. Modeling physico-mechanical behavior of wood, the variations should be considered to improve the accuracy.

• 한국작물학회지
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• 제26권4호
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• pp.293-297
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• 1981

맥류시험에 있어서 표본추출 체계를 확립하기 위하여 1979/80년 맥류연구소의 포장에서 실시한 몇가지 소맥재배양식에 대한 표본단위의 크기 및 주어진 정도를 위한 표본수 결정을 시도하였던 바 그 결과를 요약하면 다음과 같다. 1. 소맥의 수수에 대한 변이계수는 휴입광철파를 제외하고는 맥류수량의 평균변이계수와 거의 같았다. 2. 수수의 변이계수와 표본단위의 크기에 대한 회귀계수는 유입광철파를 제외하고 모두 1% 수준에서 유의성을 보였다. 3. 표본단위의 크기는 재배양식에 따라 차이가 크며 변이계수 15%를 허용한다면 협폭파, 관행 및 Drill 파는 각각 0.40, 0.17 및 0.11$m^2$, 로 추정되며 답리작의 유입광철파는 0.55$m^2$, 로 추정되었다. 4. 표본단위간 변이가 심하여 시험오차의 분산성분이 영인 조건하에서 CV=12%를 위해서 2반복인 경우는 구당 2개의 표본단위, 4반복민 경우는 구당 1개의 표본단위로 충분한 것으로 추정되었다.

• 한국작물학회지
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• 제31권2호
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• pp.179-185
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• 1986

구기자 육종의 수량형질에 대한 선발효율을 높이기 위한 기초연구로서 유전력, 표현형 상관, 유전상관, 환경상관 및 경노계수에 대해 연차간 유전통계량을 분석한 결과를 요약하면 다음과 같다. 1. 포기자의 수양형질중 생과중, 건과중 및 생근중의 유전분산이 가장 크고 년차간의 변동이 적었으며 기타의 형질도 유전분산이 환경분산보다는 컸고 연차간변동은 적었다. 2. 3개년간 전품종들을 Pool로 한 분석에서 연차와 품종 및 이들의 교호작용은 건과율 및 건근중률을 제외한 모든 수양형질에서 고도의 유의차가 인정되었으며 연차간변동도 적었다. 3. 광의의 유전력에서는 생과중, 건과중, 생근중, 건근중 및 지골피수량양에서 매우 높았고 연차간변동도 적었다. 4. 유전상관에서는 생과중과 건과중, 생근중과 지골피, 생근중과 지골피비율, 건근중과 지골피간에는 고도의 정의 상관으로 유의성도 높고 연차간의 변동도 적 었다. 5. 경노계수의 연차간변동은 대체로 적었으나 3개년간 모두 지골피수량에 직접, 간접으로 효과를 크게 미치는 형질은 생근중이었다.