• Journal of the Korean Statistical Society
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• 제21권1호
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• pp.14-26
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• 1992

In this paper, asymptotic expansions of the distribution of the likelihood ratio statistic for testing multisample sphericity have been derived in the null and nonnull cases when the alternatives are close to the null hypothesis. These expansions are obtained in the form of series of data distributions.

• 한국유체기계학회 논문집
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• 제5권4호
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• pp.32-39
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• 2002

The purpose of this 3-D numerical simulation is to calculate and examine the complex 3-D stall phenomena on the rotor blade and wake distribution of the wind turbine. The flow characteristics of 500kW Horizontal Axis Wind Turbine (HAWT) are compared with the calculated 3-D stall phenomena and wake distribution. We used the CFX-TASCflow to predict flow and power characteristics of the wind turbine. The CFD results are somewhat consistent with the BEM (Blade Element Momentum) results. And, the rotational speed becomes faster, the 3-D stall region becomes smaller. Moreover, the pressure distribution on the pressure side that directly gets the incoming wind grows high as it goes toward the tip of the blade. The pressure distribution on the blade's suction side tells us that the pressure becomes low in the leading edge of the airfoil as it moves from the hub to the tip. However, we are not able to precisely predict on the power coefficient of the rotor blade at the position of generating complex 3-D stall region.

• Tribology and Lubricants
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• 제4권1호
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• pp.69-73
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• 1988

The effects of journal speed and bearing load on pressure distribution and the temperature distribution of bearing surface are investigated experimentally. The journal bearing which has 219.94mm diameter, length-to-diameter ratio of L/D=0.8 and clearance ratio of 0.004 is used. Journal has a built-in pressure transducer for the measurement of pressure distribution in the mid plane of bearing. Bearing surface temperatures are measured at 60 points. The bearing load is varied from 300 N to 5900 N and journal speed from 300 rpm to 2500 rpm. As the load is increased under constant speed, the location of maximum pressure moves to the site of minimum film thickness, and maximum pressure and absolute value of minimum pressure are increased. The temperature distribution in vicinity of oil inlet shows that heated lubricant's carry-over exists around the oil inlet.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2005년도 공동학술대회 논문집
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• pp.223-226
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• 2005

동일한 파원에서 발생된 P, SH, SV 파를 3성분 지오폰으로 동시에 기록하는 방법을 연구하기 위해서, 94 m의 측선을 따라 2 m 간격으로 설치한 수신점에서 기록된 24채널 자료를 512 ms동안 기록하였다. 원시자료의 수직성분에는 P파가 초동으로 뚜렷하게 나타나며, 측선방향과 수직한 수평성분은 P파가 약화된 반면 S파의 신호/잡음비가 향상된 모습을 보인다. 토모그래피 역산을 통해 계산된 P파 및 S파의 속도 토모그램을 이용하여 동포아송비의 2차원적 분포를 산출한 결과, 동포아송비는 $0.2{\~}0.3$의 범위로 분포하며, 이는 한번의 타격으로 P파 및 S파의 속도분포와 더불어 및 동포아송비의 2차원적 분포까지 획득할 수 있다는데 큰 의의가 있다고 판단된다.

• Journal of the Korean Statistical Society
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• 제13권2호
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• pp.73-80
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• 1984

In this paper, likelihood-ratio test has been derived for testing multisample sphericity in complex multivariate Gaussian populations. The $h^{th}$ moment of the test statistic is given and its exact distribution has been derived using inverse Mellin transform. Asymptotic distribution of the statistic is also given.

• 한국재료학회지
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• 제11권11호
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• pp.972-977
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• 2001

It was investigated the effect of ultrasonic treatment on magnetic property of ultra fine magnetic Fe powders ($\alpha$-Fe) for magnetic tape. The properties were characterized with vibrating sample magnetometer (VSM), particle size analyzer (PSA) and scanning electron microscope (SEM). At 4hours ultrasonic treatment of 70 kHz, magnetic properties such as squareness ratio (S.Q. : 0.8868), orientation ratio (O.R. : 2.45) and switching field distribution (S.F. D. : 0.394) before taping were relatively enhanced. Cumulative particle size distribution of less than 5$\mu\textrm{m}$ fine powder was above 90% below 1 hour leaving time after ultrasonic treatment and it was supposed that ultrasonic treatment prevent aggregation. The magnetic values of S.Q. and S.F.D. of tape manufactured at 70 kHz and 4hour ultrasonic treatment were improved from 0.7747, 0.3818 to 0.8037, 0.3706, respectively. Electro-magnetic property used as in-output signal characteristic was improved, which showed that ultrasonic treatment developed the magnetic properties.

• Journal of Korean Neurosurgical Society
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• 제51권2호
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• pp.120-123
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• 2012

Objective : Percutaneous vertebroplasty (PVP) is usually carried out under three-dimensional (2D) fluoroscopic guidance. However, operative complications or bone cement distribution might be difficult to assess on the basis of only 2D radiographic projection images. We evaluated the feasibility of performing an intraoperative and postoperative examination in patients undergoing PVP by using three-dimensional (3D) reconstructive C-arm. Methods : Standard PVP procedures were performed on 14 consecutive patients by using a Siremobil Iso-$C^{3D}$ and a multidetector computed tomography machine. Post-processing of acquired volumetric datasets included multiplanar reconstruction (MPR) and surface shaded display (SSD). We analyzed intraoperative and immediate postoperative evaluation of the needle trajectory and bone cement distribution. Results : The male : female ratio was 2 : 12; mean age of patients, 70 (range, 77-54) years; and mean T score, -3.4. The mean operation time was 52.14 min, but the time required to perform and post-process the rotational acquisitions was 7.76 min. The detection of bone cement distribution and leakage after PVP by using MPR and SSD was possible in all patients. However, detection of the safe trajectory for needle insertion was not possible. Conclusion : 3D rotational image acquisition can enable intra- or post-procedural assessment of vertebroplasty procedures for the detection of bone cement distribution and leakage. However, it is difficult to assess the safe trajectory for needle insertion.

• 한국지반공학회논문집
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• 제35권1호
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• pp.17-30
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• 2019

본 연구는 3차원 수치해석을 통해 기존말뚝과 보강말뚝의 하중분담율(Load Distribution Ratio)과 근사적 해석 기법으로 보강말뚝의 축방향 강성(Axial Stiffness)을 산정하였다. 시공단계를 고려하여 말뚝기초의 LDR에 영향을 미치는 인자를 파악하기 위해서 1) 말뚝기초의 강성, 2) 말뚝기초의 선단지지조건, 3) 기초판 접촉효과, 4) 보강말뚝의 설치위치에 따라 해석을 수행하여 기존말뚝과 신설말뚝의 하중분담율 거동을 확인하였다. 또한 5) 기존말뚝의 축방향 강성($K_{ve}$)를 사용하여 말뚝지지 전면기초의 3차원 근사적 해석기법(YSPR)으로 보강말뚝의 직경에 따른 강성($K_{vr}$)을 산정하고, 장기간 사용으로 인한 경화를 고려하여 $K_{ve}$를 3단계로 나누어 감소시켜 보강말뚝의 강성 변화의 경향을 살펴보고, 신설 말뚝의 강성 산정방법을 제시하였다.

• 한국재료학회지
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• 제30권5호
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• pp.223-230
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• 2020

As a case study on aspect ratio behavior, Kaolin, zeolite, TiO₂, pozzolan and diatomaceous earth minerals are investigated using wet milling with 0.3 mm media. The grinding process using small media of 0.3 pai is suitable for current work processing applications. Primary particles with average particle size distribution D₅₀, ~6 ㎛ are shifted to submicron size, D₅₀ ~0.6 ㎛ after grinding. Grinding of particles is characterized by various size parameters such as sphericity as geometric shape, equivalent diameter, and average particle size distribution. Herein, we systematically provide an overview of factors affecting the primary particle size reduction. Energy consumption for grinding is determined using classical grinding laws, including Rittinger's and Kick's laws. Submicron size is obtained at maximum frictional shear stress. Alterations in properties of wettability, heat resistance, thermal conductivity, and adhesion increase with increasing particle surface area. In the comparison of the aspect ratio of the submicron powder, the air heat conductivity and the total heat release amount increase 68 % and 2 times, respectively.

• International Journal of Automotive Technology
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• 제2권3호
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• pp.93-101
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• 2001

Distribution of fuel-air mixture has a strong influence on performance and emissions of a compressed natural gas (CNG) engine. In this paper, parametric study is performed by KIVA-3V to investigate fuel-air mixture with respect to injection timing, cycle equivalence ratio and engine speed. With open-valve injection intensive mixing during intake and compression stroke results in relatively homogeneous mixture in the cylinder. Sequential induction of fuel-air mixture and fresh air results in stratification in the cylinder among the test cases at closed-valve injection. There is close similarity in the calculated distributions of the mixture in the cylinder with different cycle equivalence ratios and engine speeds. The results are compared against pressure traces and flame images obtained in a single cylinder engine converted from a 11L six-cylinder heavy duty diesel engine.