• 대한전자공학회논문지TC
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• 제45권6호
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• pp.34-51
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• 2008

인터넷이 일상생활에서 중요한 위치를 차지함에 따라 인터넷에서 발생되는 트래픽의 특성을 밝히는 것은 매우 중요한 연구과제로 주목을 받고 있다. 그러나 인터넷 트래픽은 대용량이므로 쉽게 다룰 수 없다. 이러한 문제는 인터넷 트래픽 측정 연구에 가장 큰 장애다 많은 연구자들은 다양한 샘플링 기법을 통해 트래픽을 다를 수 있는 양으로 샘플링하여 분석하고 있다. 본 연구에서는 기존의 인터넷 측정 연구에서 사용된 샘플링 기법을 비교 분석하고, 가장 효과적인 샘플링 방안을 제시하고자 한다. 연구에 비교 사용된 샘플링 기법은 규칙적 샘플링, 단순 랜덤 샘플링, 층화 샘플링이며, 샘플링 단위는 1/10, 1/100, 1/1000을 사용하였다. 분석한 항목은 트래픽 크기 분석, 엔트로피 분석, 패킷 크기 분석이다. 단순 랜덤 샘플링은 무난한 결과를 보였고, (간격을 패킷 개수로 설정한) 규칙적 샘플링은 대상과 샘플링 강도에 상관없이 고른 결과를 보였다. 한편, 간격을 시간으로 설정한 규칙적 샘플링은 매우 좋지 않을 결과를 나타내었다. 전송층 프로토콜을 기준으로 층화 샘플링 수행할 경우 더욱 좋은 결과를 얻을 수 있었다. 연구 결과를 통해 샘플링 기법이 시간에 따른 트래픽의 흐름을 얼마나 잘 유지하는가가 샘플링 성능을 좌우함을 알 수 있었다. 또한 엔트로피 분석은 샘플링에 강하고, 이상 트래픽 탐지에 매우 적절함이 확인되었다. 그러나 병목 현상에 의한 트래픽 크기 감소는 잘못된 엔트로피 분석 결과를 유발할 수 있음을 발견하였다. 마지막으로, 패킷 크기 분포는 패킷 샘플링 방식이나 강도에 영향을 받지 않음을 발견하였다.

• 정보처리학회논문지A
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• 제10A권2호
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• pp.157-164
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• 2003

최근 볼륨 그래픽스가 의료 영상의 해석 도구로서 주목을 받아 오고 있다. 볼륨 그래픽스에서는 가시화를 위하여 복셀로 정의된 물체가 필요하다. 이 때문에 기하학적인 방법으로 정의한 다각형 및 곡면을 복셀 기반의 물체로 변환시키는데 이를 복셀화(voxelization)라고 한다. 기하학적인 물체를 복셀화하면 기하학적 물체 데이터를 샘플링 데이터와 함께 단일화된 방법으로 볼륨 렌더링할 수 있다. 본 논문에서는 큐브의 단면을 이용한 복셀화의 한 기법을 제안한다. 그리고 개인용 컴퓨터 환경에서 이 기법을 구현한 후에 단순한 기하학적인 데이터를 이용해서 평가하여 논리적인 타당성을 조사한다. 이 기법은 변환된 복셀로부터 정확한 법선 벡터를 계산할 수 있고 복셀간에 구멍(hole)이 발생하지 않고 다해상도(multi-resolution) 표현이 가능한 특성을 가지고 있다.

• 대한의용생체공학회:의공학회지
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• 제12권2호
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• pp.79-88
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• 1991

Semi-transparent volume rendering technique can provide 3-D visualization well by voxel level Processing and alleviate segmentation arf, ifacts compared wish the surface rendering technique. In this Paper, we consider several new schemes which can improve she Perform ance of volume rendering. A directional interpolation method is proposed to reduce the artifact due to the anisotrophic resolution in X-ray CT data. The computation time for rendering is shortened by using the depth information of the 3-D object. And also, we reduce the quantization artifacts in the rendering by introducing the opacity-dependent sampling interval to sampling in ray-tracing.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1139-1150
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• 1999

The evolution of silica aggregate particles in coflow diffusion flames has been studied experimentally using light scattering and thermophoretic sampling techniques. The measurements of scattering cross section from $90^{\circ}$ light scattering have been utilized to calculate the aggregate number density and volume fraction using with combination of measuring the particle size and morphology through the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh-Debye-Gans and Mie theory for fractal aggregates and spherical particles, respectively. Of particular interests are the effects of flame temperature on the evolution of silica aggregate particles. As the flow rate of $H_2$ increases, the primary particle diameters of silica aggregates have been first decreased, but, further increase of $H_2$ flow rate causes the diameter of primary particles to increase and for sufficiently larger flow rates, the fractal aggregates finally become spherical particles. The variation of primary particle size along the upward jet centerline and the effect of burner configuration have also been studied.

• 대한화학회지
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• 제29권3호
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• pp.220-225
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• 1985

불꽃 원자 흡수 분광법의 Micro Sampling Technique을 이용하여 염의 농도가 높고, 양이 제한된 시료중에 미량으로 함유된 Cu, Zn 및 Fe의 분석을 시도하였다. 최적기간 및 분석조건을 조사한 결과 측정시간 0.3초, 시료부피 100${\mu}l$, 시료의 흡입속도 7.5ml/min, 연료와 산화기체의 혼합비 2.0 및 버어너 높이는 Cu일때 6.0mm, Zn 및 Fe는 8.0mm이었다. 이 방법을 일반적인 불꽃 방법과 비교하여 보면 시료의 전처리 과정이 필요없이 간단하고, 비교적 정밀성과 정확성이 있으며, 특히 100${\mu}l$정도로 양이 제한된 시료와 약 20% 정도로 염의 농도가 높은 시료의 경우도 버어너 틈새가 막히지 않고 안정한 불꽃에서 분석이 가능하였다.

• 한국산업보건학회지
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• 제3권1호
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• pp.22-36
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• 1993

This study was conducted to evaluate the charcoal tube sampling method for carbon disulfide in the air. Breakthrough was investigated according to flow rate, sampling time and air volume. Also the storage stability by storage method and time was investigated. The results are summarized as follows. 1. The samples stored at room temperature($28.2^{\circ}C$), refrigerator($3.8^{\circ}C$) and freezer($-15.6^{\circ}C$) were analyzed every week to five weeks. At one week storage at room temperature, 3.5% of $CS_2$ in the front section of the charcoal tube migrated into the back section and 57.7% at five weeks. The amount of $CS_2$ in the back section of the charcoal increased continuously by storage time. Migration of $CS_2$ was slow at refrigerator, and stopped occur at freezer. Recovery rate $CS_2$ was 52-82% at room temperature and 92-101% at refrigerator, based on the amount at freezer as a reference value. Thus loss was observed at room temperature. 2. When 6-48 L of fresh air were passed through tubes with spiked amounts of 0.379 and 0.759mg sample, the amounts of $CS_2$ in the back section of charcoal were 5.7-132.4 and 0-92% of the amount in the front section, respectively. The total recovery rates of$CS_2$ from 0.379 and 0.759mg spiked sample were 35.7-101.0% and 9l.3-100.1%, respectively. $CS_2$ loss was observed in 0.379mg spiked sample, but not in 0.759mg spiked sample. In the spiked samples, the amount of $CS_2$ in the back section of charcoal was not affected by flow rate when the air volume was controlled. The amount of $CS_2$ in the back section of charcoal increased over sampling time. And the faster the flow rate, the more the migration amount when the sampling time was the same. 3. A known concentration, 10 ppm of $CS_2$, was produced in a 200 L Tedlar bag. When the air volume was 24, 36, 48 L, breakthrough was 5.8, 16.9, 47.4%, respectively. The sampling flow rate of 0.05, 0.1, 0.2 Lpm did not change the breakthrough rate. Breakthrough increased over sampling time. And the faster the flow rate, the more the breakthrough, when the sampling time was the same.

• 한국산림과학회지
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• 제46권1호
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• pp.29-43
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• 1980

본조사지역(本調査地域)에 적용(適用)된 표본조사법(標本調査法)은 임분구성상태(林分構成狀態)를 고려(考慮)하여 단순무작위추출법(單純無作爲抽出法), 계순적추출법(系純的抽出法) 및 부차추출법(副次抽出法) 등(等)이었다. 표본점수(標本點數)의 산출(算出)을 위(爲)하여 변이계수(變異係數)는 40%를 적용(適用)하였으며 그 결과(結果) 단순무작위추출법(單純無作爲抽出法) 및 계순적추출법(系純的抽出法)에서는 공(共)히 57개소(個所)의 표본점수(標本點數)를 산출(算出)하였다. 그러나 부차추출법(副次抽出法)에서는 전림(全林)에서 1차(次)로 5개소(個所)의 Block unit, 2차(次)로 4개소(個所)의 Major unit, 3차(次) 2개소(個所)의 Minor unit를 추출(抽出)하여 소요(所要) 표본점수(標本點數)를 40개소(個所)로 하였다. 전림추정재적(全林推定材積) 및 전림실측재적(全林實測材積)을 구(求)하여 비교검토(比較檢討)한 결과(結果)는 다음과 같다. 1. 표본조사방법별(標本調査方法別)로 추정오차율(推定誤差率)을 비교(比較)한 결과(結果) 단순무작위추출법(單純無作爲抽出法)이 9.24%, 계통적(系統的) 추출법(抽出法)이 8.36%, 부차추출법(副次抽出法)이 7.54%의 순(順)으로서 부차추출법(副次抽出法)이 가장 높은 정도(精度)를 나타냈다. 2. 전림실측재적(全林實測材積)과 각(各) 표본조사법(標本調査法)에 의(依)한 전림추정재적(全林推定材積)과의 오차율(誤差率)을 비교(比較)한 결과(結果) 단순무작위추출법(單純無作爲抽出法)이 7.92%, 계통적추출법(系統的抽出法)이 4.18%, 부차추출법(副次抽出法)이 0.39%의 순(順)으로서 이때에도 역시(亦是) 부차추출법(副次抽出法)이 가장 높은 정도(精度)를 나타냈다. 3. 이상(以上)과 같은 여러가지 결과(結果)를 종합적(綜合的)으로 통계분석(統計分析)하여 비교검토(比較檢討) 해볼 때 본(本) 조사지역(調査地域)에서는 부차추출법(副次抽出法)이 가장 정도(精度)가 높은 결과(結果)를 얻었으며 표본점(標本點)의 추출(抽出) 개소수(個所數)도 가장 적게 이용(利用)되었으므로 시간(時間), 노력(努力) 및 조사경비(調査經費)가 타방법(他方法)에 비(比)하여 절감(節減)될 수 있는 기초적(基礎的)인 결과(結果)가 나타났다고 사료(思料)되며 삼림조사법(森林調査法)으로는 부차추출법(副次抽出法)이 가장 이상적(理想的)인 방법(方法)으로 구명(究明)되었다.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1151-1162
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• 1999

The effects of radial heat and $H_2O$ diffusion on the evolution of silica particles in coflow diffusion flames have been studied experimentally. The evolution of silica aggregate particles in coflow diffusion flames has been measured experimentally using light scattering and thermophoretic sampling techniques. The measurements of scattering cross section from $90^{\circ}$ light scattering have been utilized to calculate the aggregate number density and volume fraction using with combination of measuring the particle size and morphology through the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh-Debye-Gans and Mie theory for fractal aggregates and spherical particles, respectively. Flame temperatures and volumetric differential scattering cross sections have been measured for different flame conditions such as inert gas species, $H_2$ flow rates, and burner injection configurations to examine the relation between the formation of particles and radial $H_2O$ diffusion. The comparisons of oxidation and flame hydrolysis have also been made for various $H_2$ flow rates using $N_2$ or $O_2$ as a carrier gas. Results indicate that the role of oxidation becomes dominant as both carrier gas($O_2$) and $H_2$ flow rates increases since the radial heat diffusion precedes $H_2O$ diffusion in coflow flames used in this study. The effect of carrier gas flow rates on the evolution of silica particles have also been studied. When using $N_2$ as a carrier gas, the particle volume fraction has a maximum at a certain carrier gas flow rate and as the flow rate is further increased, the hydrolysis reaction Is delayed and the spherical particles finally evolves into fractal aggregates due to decreased flame temperature and residence time.

• 한국대기환경학회지
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• 제18권4호
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• pp.285-295
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• 2002

In this study, several types of gravimetric methods (such as high, medium, low, and ultra low volume sampling methods) were applied to determine suspended particulate matter concentrations in both ambient and indoor environments. Comparative evaluations were undertaken with SPM data obtained using a variety of samplers (TSP, PM10, and PM4.0) at different sampling flow rates. Correlation coefficients between TSP and PM10 concentrations measured at different flow rates fell in the range of 0.73∼0.94 (n=40). In addition, correlation coefficients for PM concentrations measured by different TSP samplers were in the range of 0.90∼0.95 (n=36 or n=38), while 0.77∼0.91 (n=38) for PM10 samplers. Correlation analysis was also conducted on indoor monitoring data that were measured using ultra-low-volume samplers at both different or identical flow rates. The correlation coefficients were in the range of 0.98∼0.99 (n=38) between TSP and TSP and 0.92∼0.94 (n=38) between TSP and PM10. The mean ratio for high volume PM10 to TSP concentration that was monitored at identical flow rates in the ambient air appeared to be 0.72. The mean ratios of PM10 to TSP and PM4.0 to TSP observed with identical flow rates at indoor environments were 0.47 and 0.40. The results of this study may provide empirical information concerning the compatability of aerosol data obtained by gravimetric sampling methods at different flow rates.

• 한국환경보건학회지
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• 제35권4호
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• pp.322-333
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• 2009

In this study, a measurement method was evaluated for the determination of polycyclic aromatic hydrocarbons (PAHs) in the ambient atmosphere. PAHs were sampled by high-volume samplers, and were then analysed with a GC/MS system. Particulate PAHs were collected on $8"{\times}10"$ quartz fiber filter, while vapor phase PAHs were adsorbed on polyurethane foam (PUF). Target compounds included a total of 36 PAHs, which are known to be frequently detected in the urban atmosphere. It was not necessary to clean-up samples before samples were analyzed using GC/MS, and the overall performance of the method was tested by a variety of quality control and quality assurance schemes. It is generally known that the clean-up procedure can negatively affect the recovery of samples. Precision and accuracy was evaluated using SRM provided by US NIST, and the results were generally satisfactory and reliable. However, the GC/MS method appeared not to be adequate for 6-rings PAHs, such as coronene, due to its lower sensitivity. In addition, collection efficiencies for low molecular compounds, such as 2-rings PAHs, were poor because of the lower retention volume of the PUF adsorbent. As a result, it was concluded that the method based on high-volume sampling and GC/MS analysis can give very reliable data by simultaneous sampling of both particulate and vapor phases for 3-rings to 5-rings PAHs of environmental concern.