• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.410-410
• /
• 2010

한TFT-LCD, Solar cell, 반도체 등에 사용되는 Si 박막은 주로 PECVD로 형성한다. 이 때 사용되는 원료 가스로 $SiH_4$가 있으며 대개 $H_2$로 희석해서 사용한다. 저온 증착의 경우 전자 충돌 해리과정을 이용하여 증착이 이루어지며 이 때 중간 생성물로 $SiH_3$, $SiH_2$와 고차유도체($Si_xH_y$)가 생성된다. 고밀도 플라즈마를 이용하는 경우에는 이들의 이온(양, 음)의 비율도 막질 형성에 중요한 요소가 된다. 본 발표에서는 안테나가 외부 및 내부에 있는 경우에 대해서 모델링하였으며 해리된 유도체의 비율은 $SiH_3$ > $SiH_2$의 순서였고 가스 조성비(수소 희석비), U-type 내장형 안테나와 기판 사이의 거리, 챔버 내의 펌핑 포트의 위치 등에 의한 차이가 플라즈마 온도 및 밀도의 균일도에 미치는 영향을 분석하였다. 수치 모델상의 가장 중요한 변수의 하나인 이온, 라디칼의 표면 재결합 상수는 문헌에서 보고된 값을 구하기 어려운 경우에는 가장 실제와 근접한 경향이 나타나는 값을 사용하였다. 이 부분은 분자 동력학 등의 기법을 이용하여 보다 상세한 데이터를 만들어 낼 수 있는 방법의 적용이 필요하다. 기본적인 $SiH_4$의 화학 반응식은 이원기[1]등의 데이터를 이용하였다. 계산 결과 중의 특이한 점의 하나는 고차 유도체인 $Si_2H_4$의 경우 중성보다 오히려 양이온의 밀도가 1 order이상 높았다. 내장형 Y-type 안테나의 경우 전력 흡수 밀도가 $10^7\;W/m^3$ 수준으로 높은 영역이 안테나 주변으로 나타났으며 안테나와 기판 사이의 거리와 압력에 따라서 기판에서의 균일도가 결정 되었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2010.10a
• /
• pp.445-446
• /
• 2010

In Gen-2 Q-algorithm, the initial value of $Q_{fp}$, which is the slot-count parameter, is not defined in the standard. In this case, if we let the initial $Q_{fp}$ be large, the number of empty slot will be large during the initial query round. On the other hand, if the initial $Q_{fp}$ is small, almost all the slots will be collided. As a result, it is anticipated that the performance will be declined because the frame size does not converge to the optimal point quickly during the query round. In this paper, we analyze how the performances of Gen-2 Q-algorithm will be affected by the initial slot-count size.

• Journal of Korean Society of Environmental Engineers
• /
• v.32 no.1
• /
• pp.79-86
• /
• 2010

Effects of operating parameters such as applied voltage, solution conductivity, ferrous ion concentration, electrode material on phenol degradation by pulsed corona discharges were investigated in laboratory scale experiments. The increase of applied voltage enhanced the phenol degradation by generating more energetic electrons. The solution conductivity inversely affected phenol removal rate in the tested ranges because the increase of conductivity decreased the electric field strength through the liquid phase. The addition of ferrous sulfate promoted the phenol degradation through the OH radical production by the Fentonlike reactions between ferrous ion and hydrogen peroxide generated by pulsed corona discharges. Catechol and hydroquinone were detected as primary intermediates of phenol degradation and the decrease of pH and the increase of conductivity were observed probably due to the generation of organic acids. Almost all of the initial phenol was disappeared and 29% of total organic corbon (TOC) was removed in the condition of 0.5 mM of ferrous sulfate after approximately 230 kJ of discharge energy transferred to the reactor.

• JOURNAL OF ELECTRICAL WORLD
• /
• s.349
• /
• pp.90-94
• /
• 2006

“해마다늘어만가는지구촌곳곳의기상이변, 특히세계유전지대의혹독한풍수해가지난해와마찬가지로일시에밀어닥친다면올해도국제유가의고공행진은하늘을찌를것이다.” 고유가가대세로점쳐지고있는가운데 2 0 0 6년새해를맞아유가의고공행진에대한극단적인우려감이높다. 지난해지구촌이 겪은미국발 허리케인의공포가채 가시지 않은 탓이다. 고유가의정착으로 인해고통을감내한 세계각국은올해초 국제유가의향방을대부분부정적으로내다보고있다. 고유가의원인으로는수요급증에따른수급불균형을우선꼽으면서도고공행진의유가를촉발할여러가지변수도다각도로진단하고있다. 지난해40% 가까이급등한국제유가는올한해에도고공비행을계속할것으로보고있는가운데일부언론은유가 6 0달러시대는이제기정사실화됐다고보도하기도했다. 만약부정적인상황이온다면“WTI 가격은최고 8 0달러, 두바이유가격은최고 6 7달러수준까지상승한다”는전망이나오는가하면“미국과이란의정치적충돌로페르시아만폐쇄사태라도터진다면유가가배럴당 1 0 0달러까지도치솟을수있다”는 경고도 나오고 있다. 우려는 하되 긍정적인 시각도 있다. 고유가가 올해 인플레에 미칠 영향에 대해 경제협력개발기구( O E C D ) 의코엔빈센트수석애널리스트가바로이경우다. 그는최근의고유가는지난 7 0년대와 8 0년대초의석유파동때와는성격이다르다고전제하면서다음과같이진단했다. “당시는공급쪽의충격이컸으나이제는수요급증으로발생하는것”이라고지적하며“선진권경제의석유의존도가크게떨어진점도고유가의파고가큰우려가되지않는다”고밝히고있다. 국내 전문가들도중동정세가 안정되고 미국 경기가 크게 둔화돼 석유수요가감소할경우에도 O P E C의 적극적 감산이예상돼유가가 4 0달러대밑으로내려가기는어려울것으로내다보고있다. 케임브리지에너지연구소( C E R A ) 의경우브렌트유기준으로 지난 연말 배럴당 5 5 . 4달러에서 올해는 5 3 . 5달러로되레떨어질것으로내다봤다. 2006년미국과중국의석유수요가대폭둔화될경우배럴당 4 1 . 3달러까지하락할수도있다는전망을내놨다. 그러나주요산유국의공급차질로인한비관 적인상황이도래할경우엔배럴당7 6달러까지도급등할것이라는경고도덧붙였다. 하여튼 2 0 0 6년유가의향방은고공추세에다주변변수가어떻게잘마무리되느냐, 나아가돌발풍수해에따라선‘껑충’거릴수밖에없다는진단이우세하다. 새해를맞아최근의국제유가동향과나아가유가의향방및변수를진단해봤다.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.5
• /
• pp.557-565
• /
• 2021

Path-following control is considered as one of the most fundamental skills to realize autonomous navigation of marine vessels in the ocean. This study addresses with the path-following control for a ship in which there are environmental disturbances in the directions of the surge, sway, and yaw motions. The guiding principle and back-stepping method was utilized to solve the ship's tracking problem on the reference path generated by a virtual ship. For path-following control, error dynamics is one of the most important skills, and it extends to the research fields of automatic collision avoidance and automatic berthing control. The algorithms for the guiding principles and error variables have been verified by numerical simulation. As a result, most error variables converged to zero values with the controller except for the yaw angle error. One of the most interesting results is that the tracking errors of path-following control between two ships are smaller than the existing safe passing distances considering interaction forces from near passing ships. Moreover, a trade-off between tracking performance and the ship's safety should be considered for determining the proper control parameters to prevent the destructive failure of actuators such as propellers, fins, and rudders during the path-following of marine vessels.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.1
• /
• pp.187-192
• /
• 2015

In general, design of urban intersections are fundamentally different from rural intersections, but current urban intersection design has been appled to rural standards. This study has suggested the design standard for urban intersection grades based on the existing literature, field investigating and comparative analysis. Moreover, this study analyzes and compares the differences between urban and rural intersections, and intersections have been derived by appropriate design standards after reviewing the domestic and international grades design criteria. Site survey was performed to validate the derived design criteria by analyzing statistically to establish the design standards. Results were produced for the intersection portion grade standards by comparing the number of instructions which produced appropriate slope degree from 2.5% to 3% in normal condition and slope can be extended to 5% in some critical cases. In-situ investigation was performed to validate the produced data where slope was found from 0.0~8.6%. Additional data of accident analysis were also collected for the validation of the suggested data and correlation analysis was performed using the SPSS tool. Data were analyzed statistically using 95% significance level for vehicle-to-vehicle collided, head-on collision accident rates, where accident rates significantly correlated with the grade. Therefore, appropriate grade at the intersection should be designed and applied in order to reduce the number of accidents at the intersection. Finally, appropriate grades for urban intersections are suggested from 1-3% for normal cases and grades could extend up to 5% for unavoidable cases where extra care must be taken when designing.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.11
• /
• pp.25-36
• /
• 2019

The safety barrier is installed on road embankment to prevent vehicles from falling into road side slope. Among the safety barrier, flexible guardrails are usually installed. The flexible guardrail generally consists of a protection cross-beam and supporting in-line piles. These guardrail piles are installed nearby slope edge of road embankment because the side area of the road is much narrow. The protection cross-beam absorbs impact energy caused by vehicle collision. The pile-soil interaction also absorbs the rest of the impact energy and then, finally, the flexible guardrail system resists the impact load. This paper aims to investigate the pile-soil interaction subjected to impact load using centrifuge model tests. In this study, a single pile was installed in compacted residual soil and loaded under lateral impact load. An impact loading system was designed and developed available on centrifuge tests. Using this loading system, a parametric study was performed and the parameters include types of loading and ground. Finally, the ultimate bearing capacity of supporting pile under impact load was analyzed using load-displacement curve and soil reaction pressure distributions at ultimate were evaluated and compared with previous studies.

• Journal of Korean Society of Transportation
• /
• v.33 no.4
• /
• pp.323-336
• /
• 2015

Estimating the risks on the roadway using surrogate safety measures (SSM) has an advantage in that it focuses on the vehicle trajectory directly involved in conflicts. On the other hand, there is a restriction on estimating the risks of continuous segments due to the limited data collected from a location. To overcome the restriction, this study presents the scheme of acquiring the vehicular trajectory using real time kinematics-differential global positioning system (RTK-DGPS) and develops a methodology which contains the considerations of the problems to calculate the SSM such as time-to-collision (TTC), deceleration rate to avoid collision (DRAC) and acceleration noise (AN). By using the methodology, this study shows a result from an experiment executed in a section where the variation of vehicular movement can be observed from several continuous flow roadway sections near Seoul and Gyeonggi Province in Korea. The result illustrated the risks on the roadway by the SSM metrics in certain situations like merging and diverging, stop-and-go, and weaving. This study would be applied to relate the dangers with characteristics of drivers and roadway sections, and prevenst accidents or conflicts by detecting dangerous roadway sections and drivers' behaviors. This study contributes to improving roadway safety and reducing car-accidents.

• Journal of the Korea Concrete Institute
• /
• v.27 no.2
• /
• pp.103-113
• /
• 2015

This paper studies impact performance of wire-mesh and steel fiber-reinforced concrete based on high-velocity impact experiments using hard spherical balls. In this experimental study, panel specimens were tested with various parameters such as steel fiber volume fraction, presence/absence of wire mesh, panel thickness, impact velocity, and aggregate size for the comparison of impact resistance performance for each specimen. While improvement of the impact resistance for reducing the penetration depth is barely affected with steel fiber volume fraction, the impact resistance to scabbing and perforation is improved substantially. This was due to the fact that the steel fiber had bridging effects in concrete matrix. The wire mesh helped minimizing the crater diameter of front and back face and enhanced the impact resistance to scabbing and perforation; however, the wire mesh did not affect the penetration depth. The wire mesh also reduced the bending deformation of the specimen with wire mesh, though some specimens had splitting bond failure on the rear face. Additionally, use of 20 mm aggregates is superior to 8 mm aggregates in terms of penetration depth, but for reducing the crater diameter on front and back faces, the use of 8 mm aggregates would be more efficient.

• Journal of Korean Society of Transportation
• /
• v.20 no.7
• /
• pp.107-116
• /
• 2002

Crash Cushion is a kind of safety facilities on roadside which acts the role of absorbing impact energy when vehicles are driven out of normal route such as Gore area of freeway off ramp. Criteria for severity index considering accident occurrence possibility are needed to have strong effect on installing the facilities. However, present criteria for establishing crash cushion design do not include such processes. Therefore, the paper presents two kinds of study to develop criteria for severity index. First of all, development of accident forecasting model on freeway off ramp is presented. The module is a relationship between accidents and road environment by negative binomial distribution (NB) which is called to reflect very well quality of accidents at Gore of crash cushion installed freeway Secondly, freeway exiting behavior model is developed because the human factor is the most important one. However, many literatures have shown between road environment and accidents which are more quantitative than human factor. The study supposed advanced process steps on actual freeway and analysed correlation between variables and accidents. The criteria for severity index is presented to determine whether to install or not by benefit cost analysis for each module. The standard for severity index will help to determine whether to install the crash cushion or not and to estimate severity for freeway and off ramp.