• 한국정밀공학회지
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• 제6권3호
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• pp.68-77
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• 1989

The surface rolling for cylindrical surface of a grey cast iron was carried out using a lathe with a simple newly-designed tool system. A surface rolling tool used was steel ball whose diameter was 3/8 inch (9.525mm) The effects of rolling feeds and number of rolling on surface rolling were investigated. The contact pressure between ball and workpiece which was considered as Hertz's contact problem was examined and the track of motion of a ball on the cylindrical surface of a work- piece was measured according to the rolling feed. The results obtained were as follows; 1. The roughness of the machined surface which was originally 5.3 .approx. 28 umRz decreased to 1.2 .approx. 5 umRz according to rolling feeds and numbers of rolling. 2. The hardness increased from Hv 260 to Hv 290 .approx. 310 through 2 .approx. 4 rollings according to the roughness of machined surfaces. 3. The reduction of diameter was found to be proportional to the variations of roughness of previous machined surfaces. About 60% to 90% of reduction in diameter was made during the first rolling process. 4. An equation relating the reduction of diameter and the variation of surface roughness after surface rolling was presented using a geometric surface model. 5. An equation for the calculation of dynamic contact area between pressure ball and workpiece according to the rolling feed was presented.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.910-913
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• 2000

In this research we investigate geometric issues involved while using a particular rapid prototyping system, called Stereolithography(SLA). SLA create prototypes layer by layer, each layer being formed by scanning a laser beam across the x, y surface of a vat of liquid monomer mix. The performance of SLA is influenced by orientation and layer thickness of designed fabrication. The number of layer and the area needed support is influenced by the orientation and layer thickness of designed fabrication. The step influence and volume error is influenced by slice thickness. We minimize the support are, the number of layer and cusp height. These variables of fabrication is minimized using genetic algorithm. The time for genetic algorithm is as little as we can accept. So we calculate support area and cusp height simply.

• 한국정밀공학회지
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• 제19권9호
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• pp.151-156
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• 2002

A new position correction method using four fiducials as reference points was developed and examined. It was aimed to calibrate nonlinear deformation by numerous error sources. A correlation for correction was derived from the geometric relationship between four fiducials and chip position. Compared with three points method, it exhibited more accurate correction, especially for inner area of a quadrilateral composed of four fiducial points. Its accuracy was found to be increased as fiducials moves outwardly within a printed circuit board (PCB) and/or as they form more rectangle-like shape As for arbitrarily nonlinear deformation, this method can be applied using more than five fiducials. In this case, local-area calibration is carried out by sectioning a board area into several rectangular are as.

• Corrosion Science and Technology
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• 제19권5호
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• pp.239-249
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• 2020

The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 ㎛, 10 ㎛, and 30 ㎛ were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 ㎛ and 30 ㎛ was 1.48 and 2.21 times compared to 5 ㎛, respectively.

• Kyungpook Mathematical Journal
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• 제57권4호
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• pp.667-676
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• 2017

We study the positive $C^1$ function z = f(x, y) defined on the plane ${\mathbb{R}}^2$. For a rectangular domain $[a,b]{\times}[c,d]{\subset}{\mathbb{R}}^2$, we consider the volume V and the surface area S of the graph of z = f(x, y) over the domain. We also denote by (${\bar{x}}_V,\;{\bar{y}}_V,\;{\bar{z}}_V$) and (${\bar{x}}_S,\;{\bar{y}}_S,\;{\bar{z}}_S$) the geometric centroid of the volume under the graph of z = f(x, y) and the centroid of the graph itself defined on the rectangular domain, respectively. In this paper, first we show that among nonconstant $C^2$ functions with isolated singularities, S = kV, $k{\in}{\mathbb{R}}$ characterizes the family of catenary rotation surfaces f(x, y) = k cosh(r/k), $r={\mid}(x,y){\mid}$. Next, we show that one of $({\bar{x}}_S,\;{\bar{y}}_S)=({\bar{x}}_V,\;{\bar{y}}_V)$, $({\bar{x}}_S,\;{\bar{z}}_S)=({\bar{x}}_V,\;2{\bar{z}}_V)$ and $({\bar{y}}_S,\;{\bar{z}}_S)=({\bar{y}}_V,\;2{\bar{z}}_V)$ characterizes the family of catenary rotation surfaces among nonconstant $C^2$ functions with isolated singularities.

• 한국환경보건학회지
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• 제32권1호
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• pp.1-7
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• 2006

This study was performed to investigate airborne lead concentration and surface lead contents in preschool facilities. Arithmetic mean of indoor lead concentration in urban area was $44.7\;ng/m^3$ (Geometric mean $32.1\;ng/m^3$) whereas outdoor concentration was $39.5\;ng/m^3$ (GM $22.8\;ng/m^3$). In rural area, airborne lead concentrations were $14.2\;ng/m^3\;(GM\;7.9 ng/m^3),\;12.6\;ng/m^3\;(GM\;5.6 ng/m^3)$, respectively. There is statistical significance of the lead concentrations among the locations of preschool facilities. About $37\%$ of qualitative lead check samples was positive and mainly was found in lead based paint. Though lead concentrations on the floor and window sill were well below the US EPA and HUD standard (floor $40\;{\mu}g/ft^2\;(4.3\;{\mu}g/100\;cm^2)$, window sill $250\;{\mu}g/ft^2\;(26.9\;{\mu}g/100\;cm^2)$, respectively), there were much samples which exceed the standard, i.e., $29\%$ of surface wall, $20\%$ of the desk and chair, $100\%$ of painted wood box of tested samples. In view of our study and hazard of lead to children, we recommended that the contents of lead in preschool facilities should be lowered as possible.

• 대한기계학회논문집B
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• 제23권8호
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• pp.997-1009
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• 1999

Silica particle formation and growth process including chemical reaction, coagulation and sintering was studied in a counterflow diffusion flame burner. The counterflow geometry provides a one dimensional flow field, along the stagnation point streamline, which greatly simplifies interpretation of the particle growth characteristics. $SiCl_4$ has been used as the source of silicon in hydrogen/oxygen/argon flames. The temperature profiles obtained by calculation showed a good agreement with experiment data. Using one and two dimensional sectional method, aerosol dynamics equation in a flame was solved, and these two results were compared. The two dimensional section method can consider sintering effect and growth of primary particle during synthesis, thus it showed evolution of morphology of non-spherical particles (aggregates) using surface fractal dimension. The effects of flame temperature and chemical loading on particle dynamics were studied. Geometric mean diameter based on surface area and total number concentration followed the trend of experiment results, especially, the change of diameters showed the sintering effect in high temperature environment.

• 약학회지
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• 제29권4호
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• pp.176-182
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• 1985

As a part of the studies on adsorptive properties of Korean halloysite clays, Hadong white clays of premium grade were examined for geometric pore structured by mercury porosimetry and for specific surface areas by nitrogen adsorption according to the BET procedure. Three size fractions of the native clay sample were derived from passage BS #100, #200 and #325 meshes, respectively. Several parameters lhus observed in relation to the pore structures are shown below: 1. The size fraction of BS #100, #200 and #325 show internal pore volumes of 25.3, 30.2 and $35.0m^2g^{-1}$, respectively. 2. In the distribution curves of the cumulative pore volume against pore diameter, it has been shown that the larticle sizes, the steeper the distribution over the larger ranges of pore diameters. The converse is true the smaller particles. 3. Internal pore areas increase with decrease in pore sizes. It follows that the pores having diameters of $\leq$0.1$\mu\textrm{m}$ are responsible for more than 90% of the total pore area. 4. The behaviour of nitrogen adsorption can be best described by BET type IV isotherm. Further, the hysteresis loops of the adsorptiondesorption curves become narrower with decresing particle sizes. 5. The specific surface areas observed for the fractions of BS #100, BS #200 and BS #325 are 34.6, 35.4 and 43.2m $^2g^{-1}$, respectively. and the calcined clay of BS #325 has a specific surface area near $30.4m^2g^{-1}$.

• 대한원격탐사학회지
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• 제29권3호
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• pp.307-314
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• 2013

The Bidirectional Reflectance Distribution (BRD) effect is critical to interpret the surface information using remotely sensed data. This effect was caused by geometric relationship between sensor, target and solar that is inevitable effect for data of optical sensor. To remove the BRD effect, semi-empirical BRDF models are widely used. It is faster to calculate than physical models and demanded less observation than empirical models. In this study, Ross-Li kernel and Roujean kernel were used respectively in National Aeronautics and Space Administration (NASA) and European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) that are used to compare each other. The semi-empirical model consists of three parts which are isotropic, geometric and volumetric scattering. Each part contained physical kernel and empirical coefficients that were calculated by statistical method. Red and NIR channel of SPOT/VEGETATION product were used to compute Nadir BRDF Adjusted Reflectance (NBAR) over East Asia area from January 2009 to December 2009. S1 product was provided by VITO that was conducted atmospheric correction using Simplified Method of Atmospheric Correction (SMAC). NBAR was calculated using corrected reflectance of red and NIR. Previous study has revealed that Roujean geometric kernel had unphysical values in large zenith angles. We extracted empirical coefficients in three parts and normalized reflectance to compare both BRDF models. Two points located forest in Korea peninsular and bare land in Gobi desert were selected for comparison. As results of time series analysis, both models showed similar reflectance change pattern and reasonable values. Whereas in case of empirical coefficients comparison, different changes pattern of values were showed in isotropic coefficients.

• 한국도로학회논문집
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• 제13권2호
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• pp.95-102
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• 2011

융설액 분사 시스템은 강설이 예상되거나 진행 중인 상황에서 즉시 대응이 가능하며, 강설 초기에 효율적인 처리로 강설로 인해 발생 가능한 교통사고와 교통 지정체를 감소시킬 수 있는 장점을 가지고 있다. 그러나 시스템의 설치비용이 고가이고, 설치되는 장비의 종류에 따라 운영 및 유지관리 비용이 지속적으로 소요되기 때문에 모든 도로 구간에 설치하는 것은 현실적으로 불가능하다. 최근 국내에서는 결빙 위험 구간을 파악할 수 있는 프로그램들이 개발되어 턴키 및 대안 설계에 활용되고 있다. 그러나 프로그램 개발 업체들마다 분석 방식이 상이하고 객관적인 기준이 없는 실정이다. 이에 따라 융설시스템 적용구간에 대한 기준 마련도 시급하다고 볼 수 있다. 본 연구에서는 선형, 기상조건, 일조조건 등을 다양한 도로 조건을 정량화하여 어떤 구간에 우선적으로 융설시스템을 적용하여야 하는지 판단할 수 있는 기준을 제시한다. 이를 위해 국내 지역별 기상 조사, 지형지물에 의해 음지 발생 여부 분석, 선형과 미끄럼 저항성을 고려한 차량 시뮬레이션 등을 수행하고 이론적 검토를 통해 설치 기준 방법론을 정립하는데 중점을 둔다.