• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.348-353
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the micro scale regime is essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing applications, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse (${\lambda}=248nm,\;FWHM=24\;ns$) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of $0.1{\mu}m\;and\;1\;m/s$, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1140-1147
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the microscale regime are essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing application, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse(λ=248nm, FWHM=24ns) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of 0.1㎛ and 1m/s, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• 천문학논총
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• 제26권1호
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• pp.25-35
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• 2011

A diagnostic tool has been proposed to convert the observed surface distribution of hydrogen recombination line intensities into the radial distributions of the electron temperature and the density in HII regions. The observed line intensity is given by an integral of the volume emission coefficient along the line of sight, which comprises the Abel type integral equation for the volume emission coefficient. As the emission coefficient at a position is determined by the temperature and density of electrons at the position, the local emission coefficient resulted from the solution of the Abel equation gives the radial distribution of the temperature and the density. A test has been done on the feasibility of our diagnostic approach to probing of HII regions. From model calculations of an HII region of pure hydrogen, we have theoretically generated the observed surface brightness of hydrogen recombination line intensities and analyzed them by our diagnostic tool. The resulting temperatures and densities are then compared with the model values. For this case of uniform density, errors in the derived density are not large at all the positions. For the electron temperature, however, the largest errors appear at the central part of the HII region. The errors in the derived temperature decrease with the radial distance, and become negligible in the outer part of the model HII region.

• 한국임상보건과학회지
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• 제8권2호
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• pp.1436-1443
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• 2020

Purpose: The purpose of this study was to differences in the expression rate of Porphyromonas gingivalis according to smoking status, smoking amount and period of smoking. Methods: At the time of investigation, 30 smokers and non-smokers were recruited among patients with periodontitis with a probing pocket depth(PPD) of 4 mm or more. General information was collected using a self-questionnaire, and the average value was used by a dentist to measure the probing pocket depth of three times each for the first or second molar. Plaque collection and analysis were performed by collecting only subgingival plaque using a conventional method, and the expression rate of P. gingivalis was confirmed using polymerase chain reaction (PCR). For statistical analysis, the SPSS Ver 25.0 program was used. Results: Smoking did not have a significant effect on the expression of P. gingivalis, but it did affect the expression of more type II genotypes (p<0.05). In addition, smokers had more slight periodontal pocket, and the amount and duration of smoking did not affect the expression of P. gingivalis. Conclusions: In the future, it is necessary to reinforce the group of smokers and non-smokers with healthy oral conditions, and to investigate the quantitative difference in the expression rate and genotype of P. gingivalis over time of harmful substances in smoking.

• 한국지하수토양환경학회지:지하수토양환경
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• 제27권2호
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• pp.1-23
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• 2022

For its essential importance as a resource, sustainable development of groundwater has been major research interests for many decades. Conventional characterization of aquifer and groundwater has relied on borehole data from observation well. Although borehole data provide useful information on yield and flow of groundwater, it is often difficult and sometimes costly to estimate the spatial distribution of groundwater in entire aquifer. Geophysical probing is an alternative techique that provides such information due to its capability to image subsurface structures as well as to delineate spatial distribution of hydraulic parameters. This study presents various technical information about geophysical probing to estimate main characteristics of aquifer for groundwater exploitation. Subsequently, we analyzed representative cases, in which geophysical methods were applied to identify the location of the groundwater, classify freshwater and brine, derive hydraulic constants, and monitor groundwater.

• 대한조선학회논문집
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• 제51권4호
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• pp.274-282
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• 2014

Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

• 대한토목학회논문집
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• 제14권6호
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• pp.1375-1383
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• 1994

관수로시스템 문제는 수리학적 및 시스템운영 제약조건아래서 시스템의 전체비용을 최소비용으로 구하는 것이다. 관수로시스템 문제는 수많은 국지해(local minimum)을 갖는 비볼록(nonconvex) 이므로 종래의 최적화 기법은 임의의 국지해만을 구할 수 있다. 따라서 본 연구에서는 좀더 나은 국지해를 구하기 위해 외부탐사 및 내부최적화 단계 즉 2 단계 분해기법을 제안하였다. 외부탐사 단계에서는 관로들의 최적유량을 찾기 위해 여러 국지해 사이를 이동하면서 좀더 나은 국지해를 찾는 방법인 추계학적탐사방법(stochastic probing method)을 이용 하였고 내부최적화 단계(local minimizer)에서는 외부탐사 단계에서 구한 국지해를 증진시킨다. 이 제안한 방법은 신설 관수로시스템 설계와 기존 관수로시스템의 확장에 적용할 수 있으며, 제안한 방법의 효율성을 검증하기 위해 어느 관수로시스템을 표본으로 채택하여 제안한 방법을 적용한 결과 먼저 발표된 연구자들의 결과보다 적은 비용으로 설계할 수 있었다.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 제14회 정기총회 및 03년 동계학술발표회
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• pp.22-23
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• 2003

The new method of x-ray photon correlation spectroscopy (XPCS) [1] is developed recently for probing the dynamics of surface height fluctuations as a function of lateral length scale. Measurements were performed on supported polystyrene (PS) films of thicknesses varying from 84 to 333 nm at temperatures above the PS glass transition temperature. Within a range of wave vectors spanning $10^{-3}$ to $10^{-2}$ $nm^{-1}$, good agreement is found between the measured surface dynamics and the theory of overdamped thermal capillary waves on thin films. Quantitatively, the data can be accounted for using the viscosity of bulk PS. (omitted)

• 한국콘텐츠학회논문지
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• 제7권8호
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• pp.59-65
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• 2007

오버레이 멀티캐스트는 하드웨어적인 인프라 구축 없이도 시스템의 자원과 네트워크 대역폭을 효율적으로 사용할 수 있는 기법이며 중간 노드의 이탈이 발생하게 될 경우 멀티캐스트 트리를 재구성한다. 그러나 빈번한 멀티캐스트 트리의 재구성은 심각한 성능 저하를 가져오게 된다. 본 논문에서는 이러한 성능저하를 보완하기 위해 각 자식 노드들로부터 소스 노드에게 주기적으로 피드백 되어오는 정보(RTCP-probing)를 기반으로 트리 성능 최적화 알고리즘을 제안한다. 제안된 모델은 서비스하는 부모노드가 트리의 성능을 저하시키는 원인으로 판단되어질 때 수행하는 메커니즘이다. 메커니즘을 수행하여 성능 최적화 트리를 구성함으로써 전체적인 서비스 트리의 성능을 향상시켰다. 시뮬레이션 결과를 통해 제안된 모델뿐만이 아니라 기존의 기법들에 적용하였을 때도 효과적인 방안임을 보여주고 있다.

• Journal of Periodontal and Implant Science
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• 제41권3호
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• pp.117-122
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• 2011

Purpose: The purpose of the present randomized controlled clinical study was to evaluate the short-term outcomes of micro-current electrical neuromuscular stimulation (MENS) as an adjunct method to nonsurgical periodontal therapy. Methods: Twenty patients with moderate to severe chronic periodontitis were recruited into the study and randomly treated with either nonsurgical periodontal therapy followed by 5 MENS treatments with a micro current device or by nonsurgical periodontal therapy alone. Periodontal parameters were measured at baseline and 6 weeks following therapy, and included the plaque index, bleeding on probing, probing depth, and clinical attachment level (CAL). Results: All measured values were reduced at the time of re-evaluation. The amount of inflammation was significantly reduced in both the test (P=0.002) and control group (P=0.015). The test group demonstrated a significant CAL gain at 6 weeks following therapy, including non-molar (P=0.009) and molar teeth (P=0.028). In comparison with the control group, the test group showed statistically significant differences in the CAL on both molar (P=0.027) and non-molar teeth (P=0.031). Conclusions: In conclusion, the short-term results of the study indicate that MENS could be a suitable adjunctive method in the treatment of chronic periodontitis.