• Laser Solutions
• /
• v.3 no.3
• /
• pp.39-45
• /
• 2000

The volume and depth of the craters produced on silicon samples during high power laser ablation show a strong nonlinear change as the laser irradiance increases across a threshold value, approximately 2.2$\times$10$\^$10/ W/㎠. Time-resolved shadowgraph images of the ablation plume reveal the ejection of large particulates from the sample for laser irradiance above the threshold, with a time delay of about 300-400 ㎱. The numerically estimated thickness of the superheated liquid layer, considering the transformation of liquid metal into liquid dielectric near the critical state, agrees with the measured agrees with crater depths. It is suggested that a phase explosion of the deep superheated liquid layer near the critical state is responsible for the measured sudden increase of crater volume and the ejection of large particulates.

• Proceedings of the KSR Conference
• /
• 2009.05a
• /
• pp.1351-1359
• /
• 2009

The purpose of this article is to find out and analyze the diverse factors that are incurring stress to the railway safety-critical employees. To attain this purpose, the authors made the questionnaires based on in-depth interview, and analyzed statistically the factors of stressors in terms of job categories. And the effective ways of managing and overcoming the stressors were suggested.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.1045-1051
• /
• 2005

For critical structures and application, where a given reliability must be met, it is necessary to account for uncertainties and variability in material properties, structural parameters affecting the corrosion process, in addition to the statistical and decision uncertainties. This paper presents an approach to the fuzzy arithmetic based modeling of the chloride-induced corrosion of reinforcement in concrete structures that takes into account the uncertainties in the physical models of chloride penetration into concrete and corrosion of steel reinforcement, as well as the uncertainties in the governing parameters, including concrete diffusivity, concrete cover depth, surface chloride concentration and critical chloride level for corrosion initiation. The parameters of the models are regarded as fuzzy numbers with proper membership function adapted to statistical data of the governing parameters and the fuzziness of the corrosion time is determined by the fuzzy arithmetic of interval arithmetic and extension principle

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.10a
• /
• pp.1157-1166
• /
• 2008

Critical surcharge value of silt ground polluted with garbage leachate to the dyes $q_{cr}=3.73c_u$ and ultimate bearing capacity value $q_{ult}=8.60c_u$. Lateral flow pressure at polluted silt ground was about $P_{max}$/3 and depth of maximum lateral flow pressure was found at that of H/3 of soft layer thickness(H). Expression of polluted silt ground of fracture baseline at stability control charge by Matsuo Kawamura is $S_v=3.56\exp\{0.51(Y_m/S_v)\}$.

• Biotechnology and Bioprocess Engineering:BBE
• /
• v.7 no.6
• /
• pp.362-366
• /
• 2002

A mathematical model has been developed for describing the oxygen concentration during the exponential growth of microorganisms, in a static solid substrate bed supported on a tray fermentor. The model equations comprise of one partial differential equation for mass transfer and an ordinary differential equation of growth. After nondimensionlisation, analytical solution tn the model has been obtained by the method of Laplace transforms. An expression for critical thickness of bed is deduced from the model equation. The significance of the model in the design of tray fermentors is discussed. The validity of the discussion is verified by taking an illustration from the literature.

• International Journal of Ocean System Engineering
• /
• v.3 no.3
• /
• pp.136-141
• /
• 2013

The present research was aimed at comparing performance of metallic and polymer composite shells of a typical underwater vessel of length and inner diameter of 1650 mm and 350 mm respectively, based on the critical buckling pressure for operating depth of 1000 m using ANSYS. High strength steel, aluminium alloy, titanium alloy, glass / epoxy and carbon / epoxy materials were examined. The results indicated weight savings of 46 % in carbon/epoxy and 31 % in glass / epoxy when compared with high strength steel, based on the thickness of the shell for sustaining 10 MPa buckling pressure.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.901-904
• /
• 2002

The cutting thickness of ultra-precision machining is generally very small, only a few micrometer or even down to the order of a flew manometer. In such case, a basic understanding of the mechanism on the micro-machining process is necessary to produce a high quality surface. When machining at very small depths of cut, metal flow near a rounded tool edge become important. In this paper a finite element analysis is presented to calculate the stagnation point on the tool edge or critical depth of cut below which no cutting occurs. From the simulation, the effects of the cutting speed on the critical depths of cut were calculated and discussed. Also the transition of the stagnation point according to the increase of the depths of cut was observed.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.12
• /
• pp.167-173
• /
• 2004

Recently, it has been reported that frictional behavior at nanometer scale can be different from that at macro scale. In this article, friction and wear tests were conducted using an AFM to investigate the effect of real contact area on the coefficient of friction and wear property. SiO$_2$, Hica, and SiGe were used in friction test and the AFM tip was Si$_3$N$_4$. The real contact area between an AFM tip and flat surface was calculated by the Johnson-Kendall-Roberts (JKR) theory. Wear specimen was Mica, and the diamond tip was used. We found that the coefficient of friction is constant below a critical area, but it is degraded over the area. Moreover, it is found that wear depth increased rapidly from a certain load and was degraded as a function of the number of the scanning cycles. Also, the range of scanning velocity used in this study had little effect on the wear depth.

• Steel and Composite Structures
• /
• v.6 no.1
• /
• pp.15-31
• /
• 2006

Beams with web openings are an attractive system for multi-storey buildings where it is always desirable to have long spans. The openings in the web of steel beams enable building services to be integrated within the constructional depth of a floor, thus reducing the total floor depth. At the same time, the increased beam depth can give high bending moment capacity, thus allowing long spans. However, almost all of the research studies on web openings have been concentrated on beam behaviour at ambient temperature. In this paper, a preliminary numerical analysis using ABAQUS is conducted to develop a general understanding of the effect of the presence of web opening on the behaviour of steel beams at elevated temperatures. It is concluded that the presence of web openings will have substantial influence on the failure temperatures of axially unrestrained beams and the opening size at the critical position in the beam is the most important factor. For axially restrained beams, the effect of web openings on the beam's large deflection behaviour and catenary force is smaller and it is the maximum opening size that will affect the beam's response at very high temperatures. However, it is possible that catenary action develops in beams with web openings at temperatures much lower than the failure temperatures of the same beam without axial restraint that are often used as the basis of current design.

• The Journal of the Korea Contents Association
• /
• v.16 no.3
• /
• pp.43-51
• /
• 2016

This paper presents the concept of "interactive teleprompter", which provides the user with interaction with oneself or other users for live television broadcasts or smart mirrors. In such interactive applications, eye contacts between the user and the regenerated image or between the user and other persons are important in handling psychological processes or non-verbal communications. Unfortunately, it is not straightforward to address the eye contact issues with conventional combination of normal display and video camera. To address this problem, we propose an "interactive" teleprompter enhanced from conventional teleprompter devices. Our interactive teleprompter can recognize the user's gestures by applying infra-red (IR) depth sensor. This paper also presents test results for a beam splitter which plays a critical role for teleprompter and is designed to handle both visual light for RGB camera and IR for Depth sensor effectively.