• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1139-1146
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• 2000

In this paper, circular-polarized dipole antenna with a novel structure is designed, simulated and fabricated for PCS or IMT-2000 base station at an arbitrary test frequency(1.575 GHz). Its radiation pattern is analyzed by means of physical optics(PO). The designed antenna is made up of a horizontal and a vertical dipole elements at a height of λ/4 above an reflector. One of λ/4 length vertical dipole element is located at a height of λ/8 above an reflector. In this case, circularly polarized radiation pattern is obtained by making impedance difference due to adjusting the length of each element. The characteristic of antenna measured from this study is that return loss is 18.4 dB, -10 dB bandwidth is 360 MHz(22.8%), 2 dB axial ratio bandwidth is 30 MHz, -3 dB beamwidth is 76$^{\circ}$, 2 dB axial ratio beamwidth is 58$^{\circ}$, axial ratio is 1.7 dB at 1.575 GHz. Radiation pattern is in well agreement with the result of PO.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.2
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• pp.115-124
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• 2004

This paper suggested the vibration characteristic improvement by variation mode of ring type ultrasonic motor. Design for the piezoelectric ceramic and elastic body of stator were calculated by the finite element method(FEM) that consider the resonance frequency, vibration mode and coupling efficiency etc. Through the result of vibration analysis from 6 order mode to 8 mode, the 7 order mode was gained very an excellent results that it was the coupling efficient, minimum power loss and bending vibration value. Here over 7 order mode, was acquired that an output current for input voltage was very a large increased results. The result of vibration calculation, from thickness 0.5[mm] to 2[mm], know the fact that the vibration displacement at 0.5[mm] is an high value too. From such analysis result, this paper was manufactured the ultrasonic motor of outer diameter 50[mm], inter 22[mm] having the about 43.86[KHz] resonance frequency. We have gated that a simulation result is 42.2[KHz] and an experiment result is 43.86[KHz]. Then, a propriety of this paper was established the result almost similar to though comparison, investigation of simulation and experiment result.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.581-588
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• 2002

In this paper, we newly propose the optical CDMA routing scheme for the radio access network. At the radio base station (RBS), the received radio signals are multiplied by the PN codes and converted to the CDMA radio signals. In the next optical CDMAS are performed and multiplxed by using the PN codes which are the addresses of the routing mobile switching center (MSC). At the MSC, the CDMA radio signals are routined to another MSC by the CDM receiver at the routing node. In the case MSC is equal to the desired MSC, the radio signal is correlated by the two-layerd spectrum despreading at a time. Finally we theoretically analyze the signal-to-interference and noise power ratio of regenerated signal and the routing error probability and show the availability of proposed scheme.

• Journal of Animal Science and Technology
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• v.51 no.5
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• pp.427-432
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• 2009

This study was undertaken to screen a high xylanase and mannanase producing microbes. In the first experiment, screening was undertaken against 50 samples of microorganisms having xylanase and mannanase activities from soil and fallen leaves. The screening process has focused on picking out fungi having high xylanase and mannanase activities under the solid-state fermentation. The xylanase and mannanase activities of 6 screened microbes were 0.9~1.6 unit/mL and 0.2~0.4 unit/mL, respectively, under the submerged fermentation condition. However, under the solid-state fermentation, xylanase and mannanase activities were 103.7~220.0 unit/g and 20.1~40.3 unit/g, respectively. Finally one microbe (E-3) was selected and its xylanase and mannanase activities were 197.3 unit/g and 39.9 unit/g, respectively. The morphological and molecular biological classification of E-3 showed 99% homology with the Aspergillus niger.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.1
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• pp.127-136
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• 2008

In these days, frequency of constructions on e freeway are increasing according as growing of the importance of e road maintenance and the road management. Work zone on the freeway where vehicles pass with high speed needs control method of lane closure and construction equipment. Because there are seldom researches in domestic study about reflecting characteristics of domestic road, sometimes we have applied for foreign cases to our traffic circumstance but it is not proper to apply for standard of other countries in our cases. foreign nation has different country square, condition of road, and level of people mind. Therefore, this study shows traffic accident characteristics in freeway work zones in Korea. At first, this study collected traffic accident data which include for 3 years $2003{\sim}2005$ in the whole freeway in Korea and then divided the data to five parts - level of the accident, type of the construction work, type of the accident, reason of the accident, according to geometric. According to comparing with non-work zones accident, this study found traffic accident characteristics in freeway work zones in Korea and suggested some alternative ideas for safety of work zones.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.38-44
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• 2007

Using the mathematical model suggested by Bennet et al.(1992), the reflection and transmission coefficients by a circular pile breakwater has been investigated in the framework of potential theory. Flow separation due to sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of exact energy loss coefficient is critical to enhance the reliability of mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code. The energy loss coefficient can be obtained from the pressure difference between upstream and downstream. Energy loss coefficient is the function of porosity and the relation equation between them is suggested throughout the curve fitting processing. To validated the suggested relation, comparison between the analytical results and the experimental results is made for four different porosities with good agreement.

• Journal of Korean Society of Transportation
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• v.21 no.4
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• pp.91-101
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• 2003

This study modeled 4-lane highway in three-dimensional virtual reality in order to overcome difficulties of field experiment. and the research subject was placed in a driving simulator. We survey the driver's cognitive characteristics to the alignment changes in the three-dimensional virtual reality highway. Especially, maximizing the identity of driving movements and virtual scenery on the basis of the data obtained by dynamic analysis module. we minimized simulator sickness for the graphic module of driving simulator. And we carried out cognitive evaluation on the basis of adjective words extracted by dictionary and the opinion of specialist. In this study LISREL model was used to detect the causal relation between geometry and safety in cognitive side, and found that geometric change affects the safety of drivers by static and dynamic road safety model in three-dimensional combined alignments. As the result, for constructing safety road. we consider drivers' cognitive characteristics as human factors in road design, and we think that they are very important factors to improve road safety.

• Journal of Korean Society of Transportation
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• v.22 no.6
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• pp.133-144
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• 2004

A model and a measure which can evaluate the risk of rear end collision are developed. Most traffic accidents involve multiple causes such as the human factor, the vehicle factor, and the highway element at any given time. Thus, these factors should be considered in analyzing the risk of an accident and in developing safety models. Although most risky situations and accidents on the roads result from the poor response of a driver to various stimuli, many researchers have modeled the risk or accident by analyzing only the stimuli without considering the response of a driver. Hence, the reliabilities of those models turned out to be low. Thus in developing the model behaviors of a driver, such as reaction time and deceleration rate, are considered. In the past, most studies tried to analyze the relationships between a risk and an accident directly but they, due to the difficulty of finding out the directional relationships between these factors, developed a model by considering these factors, developed a model by considering indirect factors such as volume, speed, etc. However, if the relationships between risk and accidents are looked into in detail, it can be seen that they are linked by the behaviors of a driver, and depending on drivers the risk as it is on the road-vehicle system may be ignored or call drivers' attention. Therefore, an accident depends on how a driver handles risk, so that the more related risk to and accident occurrence is not the risk itself but the risk responded by a driver. Thus, in this study, the behaviors of a driver are considered in the model and to reflect these behaviors three concepts related to accidents are introduced. And safe stopping distance and accident occurrence probability were used for better understanding and for more reliable modeling of the risk. The index which can represent the risk is also developed based on measures used in evaluating noise level, and for the risk comparison between various situations, the equivalent risk level, considering the intensity and duration time, is developed by means of the weighted average. Validation is performed with field surveys on the expressway of Seoul, and the test vehicle was made to collect the traffic flow data, such as deceleration rate, speed and spacing. Based on this data, the risk by section, lane and traffic flow conditions are evaluated and compared with the accident data and traffic conditions. The evaluated risk level corresponds closely to the patterns of actual traffic conditions and counts of accident. The model and the method developed in this study can be applied to various fields, such as safety test of traffic flow, establishment of operation & management strategy for reliable traffic flow, and the safety test for the control algorithm in the advanced safety vehicles and many others.

• Journal of Biosystems Engineering
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• v.10 no.1
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• pp.24-38
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• 1985

경사진 밀폐 공간에서 마주 보는 두 벽면의 온도 차로 인하여 발생되는 자연 대류 현상은 여러 공학 분야에서 볼 수 있는 중요한 열전달 현상으로서, 최근 들어 평판형 태양열 집열기를 설계하려는 사람들에게 많은 관심의 대상이 되고 있다. 평판형 태양열 집열기의 경우 덮개판으로 부터의 대류 열손실을 감소시킴으로서 집열 효율을 높일 수 있을 뿐만 아니라 사용목적에 따라 소형 집열기를 제작할 수 있어 경제적으로 유리하게 될 것이다. 밀폐된 공간에서 최초에 정지 상태에 있는 얇은 유체층을 하부에서 가열시켜 주면 열팽창 현상이 일어나고, 이것에 의한 부력이 점도나 열전도도 등의 안정화 요인을 극복할 수 있을 정도로 커지면 System이 불안정하게 되어 자연 대류 현상이 수반되며 이 때문에 열전달율이 급격히 증가하게 된다. 이러한 현상의 지배 방정식은 연립 비선형 편미분 방정식으로 특수한 경계 조건외에는 일반적으로 해석적 해를 구하기가 어렵기 때문에 실험적 연구가 많이 실시되어 왔고 이들 결과의 대부분은 전반적인 열전달 특성치만을 구하는데 집중되어 왔다. 본 연구에서는 수치 해석법의 하나인 유한 차분법을 도입하여 이차원으로 가정한 경사진 평판형 밀폐 공간에서의 자연 대류 현상의 지배 방정식을 유한 차분화시켜, $$2.74{\times}10^3\leq_-Gr\leq_-2.0{\times}10^6$$, Pr=0.73, $$15^{\circ}\leq_-a\leq_-150^{\circ}$$, 종횡비는 1, 2, 3, 5, 9에 대하여 정상 상태에서의 해를 구하면서 수치적으로 실험하였다. 본 연구에서 얻어진 결론을 요약하면 다음과 같다. (1) 해석적으로 구하기 어려운 경사진 밀폐 공간에서 자연대류현상의 지배 방정식을 유한 차분법으로 해결할 수 있으며, 대류항과 확산항을 따로 고려한 유한차분법이 효과적임을 확인하였다. (2) 저온과 고온 벽면에서의 온도를 각각 균일하게 놓고 단변으로 이루어진 벽면은 완전히 절연되어 있는 경우에 대하여 수치해를 구한결과, 이전의 해석적 및 실험적 결과와 일치하였으며, 시간의 경과에 따른 온도 및 유선의 변화를 현상학적으로 관찰할 수 있었다. (3) 평균 열전달 계수에 미치는 경사각의 효과를 살펴본 결과 종횡비가 1 인 경우 경사각이 $45^{\circ}$에서, 종횡비가 2, 3, 5, 9인 경우 경사각이 $60^{\circ}$에서 각각 평균 열전달 계수 최대치가 나타났다. (4) Ra수(Rayleigh number) 가 증가될수록, 경사각에 상관없이 평균 열전달 계수도 증가되었다. 한편 Ra수 및 경사각의 변화에 따라 종횡비가 증가될수록 평균 열전달 계수는 경사각이 $90^{\circ}$인 경우를 제외하고는 감소됨을 볼 수 있었다. 경사각이 $90^{\circ}$인 경우, 평균 열전달 계수는 종횡비가 2 인 곳에서 최대치를 얻을 수 있었으며, 종횡비가 계속 증가될수록 평균 열전달 계수는 점차 감소되어짐을 볼 수 있었다.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.69-77
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• 2004

Investigation of the time-dependent behavior of rock and the associated mechanisms are of key interest in long-term stability analysis of many engineering applications. In this study, creep tests were performed on Daejeon granite samples of 25.4mm diameter under uniaxial compression at varying stress levels. The effect of moisture was investigated by testing both air-dried and fully water-saturated samples. The creep behavior of Daejeon granite exhibited three distinctive stages of primary, secondary and tertiary creep. The ultimate strength of granite under a constant stress decreased considerably with time. Saturation and immersion of the test specimen in water markedly increased the total creep strain as well as the secondary creep rate. The experimental creep curves are fitted to Burger's model as well as two other empirical models suggested by previous researchers. A number of the parameters determined for each model are dependent on stress and influenced by the presence of water. Based on the experimental results, an empirical relation between the applied stress and the time-dependent strain is established separately for each air-dried and fully water-saturated Daejeon granite.