• 한국통신학회논문지
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• 제22권8호
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• pp.1652-1658
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• 1997

본 논문에서는 도심지 마이크로 셀 환경에서의 수신신호에 대한 단구간 페이딩 분포 특성을 분석하였다. 페이딩 특성을 분석하기 위햐어 거리별 페이딩 신호 분포, 전파의 도래 각에 따른 수신 전력 패턴 및 두 수신 안테나사이의 이격 거리에 따른 페이딩 신호의 공간적 상관특성을 보였다. 또한 여러가지 경우에서의 Rician 파라미터 K를 구하여 페이딩 신호의 분포를 비교하였다. 분석 결과, 마이크로 셀에서는 송수신 거리에 따라 페이딩 발생 주기 및 변동폭이 다르게 나타났으며, 가시거리 영역에서 보다 비가시거리 영역에서 페이딩 신호의 발생 주기는 짧아지고 변동폭은 깊게 나타났다. 비교 분석에 이용된 데이터는 전파경로추적 방법(ray tracing technique)에 의한 시뮬레이션을 통하여 얻었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.145-148
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• 2006

The protocrystalline silicon (pc-Si:H) multilayer solar cell is very promising owing to its fast stabilization with low degradation against light irradiation. However, the pc-Si:H multi layers have not extensively been investigated in detail on its material characteristics yet. We present the material characteristics of pc-Si:H multilayer using a transmission electron microscopy(TEM), and Raman spectroscopy. In addition, we present the superior light-soaking behavior of the pc-Si:H mutt i layer solar cell. A TEM micrograph shows that a pc-Si:H multilayer has a repeatedly layered structure and crystalline-like objects in a-Si:H matrix. A Raman spectra introduces improved short-range-order and medium-range-order in pc-Si:H multilayer. As a result the excellent metastability of the pc-Si:H multilayer solar cell is primarily due to the repeatedly layered structure that improves a structural order in absorber layer.

• 한국안전학회지
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• 제9권1호
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• pp.146-154
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• 1994

A series of numerical calculations are performed in order to investigate the dispersion mechanism of toxic gaseous and solid pollutants in extremely short-term and short range. The calculations are carried out in an open space characterized by turbulent boundary layer. The simulation is made by the use of numerical model, in which a control-volume based finite difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling problem. The Reynolds stresses are solved by two-equation, k-$\varepsilon$ model modified for buoyancy. The major parameters consider-ed in this study are temperature, velocity and Injection height of toxic gases, environmental conditions such as temperature and velocity of free stream air, and topographic factor. The results are presented and discussed in detail. The flow field is commonly characterized by the formation of a strong recirculation zone due to the upward motion of the hot toxic gas and ground shear stress. The driving force of the upward motion is explained by the effect of thermal buoyancy of hot gas and the difference of inlet velocity between toxic gas and free stream.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(2)
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• pp.193-196
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• 2002

This paper presents the improvement of the boron penetration and the reverse short channel effect (RSCE) in the 130nm W/WNx/Poly-Si dual gate PMOSFET for a high performance embedded DRAM. In order to suppress the boron penetration, we studied a range in the process heat budget. It has shown that the process heat budget reduction results in suppression of the boron penetration. To suppress the RSCE, we experimented with the halo (large tilt implantation of the same type of impurities as those in the device well) implant condition near the source/drain. It has shown that the low angle of the halo implant results in the suppression of the RSCE. The experiment was supported from two-dimensional(2-D) simulation, TSUPREM4 and MEDICI.

• 대한전자공학회논문지
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• 제3권1호
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• pp.12-17
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• 1966

전자 지연선에 대한 보다 깊은 이론적 해석이 본 논문 속에 제시되었고 n=0 mode 동작시 지연선의 특성을 개량하기 위하여 단락 coil을 사용하므로써 위상이 다른 전류가 상호 자속을 상살시키는 현상을 제거하고 결과적으로 단위 길이당 시간 지연을 증가시킬 수 있음을 이론적으로 입증하고 실험에 의하여 확인하였다. 직경이 3"/8이고 길이가 6"인 전자 지연선을 제작한 후 실험한 결과 10 micro sec/m의 시간 지연을 측정할 수 있었다. 이는 Onoda나 Katz가 얻은 결과보다 월등하게 우수하다고 생각한다. 또한 실제 설계자를 돕기 위하여 설계 공식을 집약하여 알기 쉽게 설명하였다.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.16-23
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• 2001

Spray dispersion in high pressure diesel engines have been simulated experimentally with a special emphasis on the effect of swirl by using a liquid injection technique. A constant volume chamber was designed to be rotatable in order to generate a continuous swirl and to have the flow field closely resembling a solid body rotation. Emulsified fuel was injected into the chamber and the developing process of fuel sprays was visualized. The effect of swirl on the spray dispersion was quantified by calculating non-dimensionalized dispersion area according to the spray tip penetration length. The results show that the effect of swirl on the spray dispersion is different between short and long spray penetrations. For short range of spray tip penetration, the effect of swirl on spray dispersion is quite small. However, as the spray tip is penetrated into longer distance in spray chamber, the effect of swirl on spray dispersion becomes larger. These results can be used as a basic data for designing combustion chamber and injection system of direct injection diesel engine.

• 대한산업공학회지
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• 제15권1호
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• pp.65-75
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• 1989

This study complements the previous studies on workload distribution problems in Flexible Manufacturing Systems. Specifically, we consider the problem in two perspectives, the long-range policy and the short and medium-term planning and control. The long-term loading policy focusses on identifying the optimal loading of the system characterized by either balanced loading or unique unbalanced loading for which a steepest ascent method is developed. These results are then applied to study the optimal medium and short-term planning and control problems, for which a truncated dynamic programming method is developed in order to obtain the optimal allocation of the given operation mix of part types to work stations.

• Journal of Electrical Engineering and Technology
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• 제6권5호
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• pp.693-696
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• 2011

In this work, an exponentially tapered microstrip antenna was implemented using a resistive loading technique in order to suppress the internal reflections. The inductive loading was realized by introducing slits on the antenna to improve radiation efficiency. Compared with a resistive-loaded antenna, the proposed antenna had an average improvement of about 6.2% in radiation efficiency within the range of 2-10.5 GHz. In addition, the highest peak of the radiated short pulse from the proposed antenna became 45% greater than that of an antenna with resistive loading only.

• 한국환경보건학회지
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• 제34권5호
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• pp.361-368
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• 2008

Objective to assess whether exposure to air pollutants is associated with postneonatal infant death, using a timeseries methodology, between 1999 and 2003 in Seoul, Korea.. Methods We investigated the short-term effects of air pollution for 548,725 live births during the study period. The daily count of postneonatal infant deaths from all causes and from SIDS (sudden infant death syndrome) by birth order was analyzed by a Generalized Additive Poisson model, with controlling for the effects of seasonal trends, air temperature, relative humidity, barometric pressure, and day of the week as covariates. Results During the study period, we observed 699 deaths from all causes and 47 deaths from SIDS. We did not find any significant associations between daily mortality and ambient levels of air pollutants except for CO and $NO_2$. The estimated relative risk of postneonatal infant death from all causes was 1.17 (95% CI=1.04-1.32) and 1.16 (95% CI=1.03-1.29) by IQR (interquartile range) for CO and $NO_2$ respectively. Also, we observed no clear trend of the mortality effects of air pollution by birth orders. Conclusion In conclusion, our findings suggest that air pollution, in general, influenced adversely postneonatal infant death from all-cause and SIDS although it was not statistically significant. This study may support that the rationale.

• 한국세라믹학회지
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• 제42권7호
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• pp.449-454
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• 2005

A waveguide method is developed to study the materials with relatively large dielectric constants at microwave range. Basically, the method is similar to the previous waveguide methods represented by short-circuit line and transmission/reflection measurement methods. However, the complex permittivity is not determined by the shift in resonance frequencies, but by numerical analysis of measured scattering parameters. In order to enhance microwave penetration into the specimen with relatively large permittivity, a dielectric plate with lower permittivity is employed for impedance matching. The influences of air gap between the specimen and waveguide wall are evaluated, and the corresponding errors are estimated. The propagation of higher order modes is also considered. Experimental results for several reference ceramics are presented.