• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 추계종합학술대회
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• pp.319-322
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• 2001

본 논문에서는 단거리 M/W 전송장비에서 사용 가능한 10Mbps 급 OFDM/QPSK 시스템을 제안하였다. OFDM 변조 신호는 two-ray 다중경로 페이딩의 영향을 받는다. 채널 모델은 Rummler가 제안한 마이크로파 대역의 two-ray 채널 모델을 사용하였다. 수신단에서는 다중 경로 채널에 따른 성능 왜곽을 보상하기 위해 여분의 Training Sequence 또는 Pilot 심볼 없이 등화를 행할 수 있는 Blind 적응 등화기를 채택하였다. OFDM 시스템에 따른 두 가지의 등화기, Pre-FFT 적응 등화기와 주파수 적응 등화기 및 두 개의 등화기를 결합한 병행 적응 등화기를 각각 시스템에 도입하여 성좌도와 SER 성능 곡선을 통해 성능 개선 정도를 분석하였다. 분서결과로부터 주파수 적응 등화기와 Pre-FFT 적응 등화기의 각각의 특성을 확인할 수 있었으며, 또한 병행 적응 등화기의 도입에 따른 시스템 개선 정도를 확인할 수 있었다.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.153-158
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• 2007

The present study covers numerical analysis of a thermionic scanning electron microscope(SEM) column. The SEM column contains an electron optical system in which electrons are emitted and moved to form a focused beam, and this generates secondary electrons from the specimen surfaces, eventually making an image. The electron optical system mainly consists of a thermionic electron gun as the beam source, the lens system, the electron control unit, and the vacuum unit. For a systematic design of the electron optical system, the beam trajectories are investigated through numerical analyses by tracing the ray path of the electron beams, and the quality of resulting image is evaluated from the analysis results.

• 한국정밀공학회지
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• 제21권5호
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• pp.158-165
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• 2004

Up to now, many crack repair techniques have been developed for inhibiting crack growth in structural components. However, the simplest way for inhibiting crack growth is to apply a indentation at the crack tip or at some distance ahead of the expected crack growth path so as to produce residual compressive stresses that can reduce the effective stresses around the crack tip. In spite of its importance to the aerospace industry, little attention has been devoted to evaluation of the indentation residual stress effect on the fatigue crack initiation life quantitatively. Therefore, in the present work, the magnitude and distribution of the indentation residual stresses were investigated in order to estimate the beneficial effect on fatigue crack initiation by using finite element method. Furthermore, to examine the validity of finite element analysis results, residual stress distribution in the indented specimen was measured by using X-ray diffraction technique, and fatigue crack behavior at fastener hole in aluminum alloy 7075-T6 before and after indentation processes was investigated.

• ETRI Journal
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• 제45권4호
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• pp.557-569
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• 2023

Traditional deterministic channel modeling is accurate in prediction, but due to its complexity, improving computational efficiency remains a challenge. In an alternative approach, we investigated a multilayer artificial neural network (ANN) to predict large-scale and small-scale channel characteristics in metro tunnels. Simulated high-precision training datasets were obtained by combining measurement campaign with a ray tracing (RT) method in a metro tunnel. Performance on the training data was used to determine the number of hidden layers and neurons of the multilayer ANN. The proposed multilayer ANN performed efficiently (10 s for training; 0.19 ms for prediction), and accurately, with better approximation of the RT data than the single-layer ANN. The root mean square errors (RMSE) of path loss (2.82 dB), root mean square delay spread (0.61 ns), azimuth angle spread (3.06°), and elevation angle spread (1.22°) were impressive. These results demonstrate the superior computing efficiency and model complexity of ANNs.

• 전기학회논문지
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• 제58권7호
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• pp.1450-1455
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• 2009

Assumed that an IPTV camera system is to be used as an ad-hoc sensor for the surveillance and diagnostics of safety-critical equipments installed in the in-containment building of the nuclear power plant, an major problem is the presence of high dose-rate gamma irradiation fields inside the one. In order to uses an IPTV camera in such intense gamma radiation environment of the in-containment building, the radiation-weakened devices including a CCD imaging sensor, FPGA, ASIC and microprocessors are to be properly shielded from high dose-rate gamma radiation using the high-density material, lead or tungsten. But the passive elements such as mirror, lens and window, which are placed in the optical path of the CCD imaging sensor, are exposed to a high dose-rate gamma ray source directly. So, the gamma-ray irradiation characteristics of the passive elements, is needed to test. A CCD camera lens, made of glass material, have been gamma irradiated at the dose rate of 4.2 kGy/h during an hour up to a total dose of 4 kGy. The radiation induced color-center in the glass lens is observed. The degradation performance of the gamma irradiated lens is explained using an color component analysis.

• 한국정밀공학회지
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• 제26권11호
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• pp.92-98
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• 2009

The scanning electron microscope (SEM) contains an electron optical system in which electrons are emitted and moved to form a focused beam, and generates secondary electrons from the specimen surfaces, eventually making an image. The electron optical system usually contains two condenser lenses and an objective lens. The condenser lenses generate a magnetic field that forces the electron beams to form crossovers at desired locations. The objective lens then focuses the electron beams on the specimen. The present study covers the design and analysis of an objective lens for a thermionic SEM. A finite element (FE) analysis for the objective lens is performed to analyze its magnetic characteristics for various lens designs. Relevant beam trajectories are also investigated by tracing the ray path of the electron beams under the magnetic fields inside the objective lens.

• Applied Science and Convergence Technology
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• 제23권6호
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• pp.317-327
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• 2014

In order to develop nano-devices with much lower power consumption for beyond-CMOS applications, the fundamental understanding and precise control of the electronic properties of ultrathin transition metal oxide (TMO) films are strongly required. The metal-insulator transition (MIT) is not only an important issue in solid state physics, but also a useful phenomenon for device applications like switching or memory devices. For potential use in such application, the electronic structures of MIT, observed for TMO nano-structures, have been investigated using a synchrotron radiation angle-resolved photoelectron spectroscopy system combined with a laser molecular beam epitaxy chamber and a scanning photoelectron microscopy system with 70 nm spatial resolution. In this review article, electronic structures revealed by soft X-ray nano-spectroscopy are presented for i) polarity-dependent MIT and thickness-dependent MIT of TMO ultrathin films of $LaAlO_3/SrTiO_3$ and $SrVO_3/SrTiO_3$, respectively, and ii) electric field-induced MIT of TMO nano-structures showing resistance switching behaviors due to interfacial redox reactions and/or filamentary path formation. These electronic structures have been successfully correlated with the electrical properties of nano-structured films and nano-devices.

• Journal of Radiation Protection and Research
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• 제42권1호
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• pp.26-32
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• 2017

Background: Ionizing radiation is known to be harmful to human health. The shielding of ionizing radiation depends on the attenuation which can be achieved by three main rules, i.e. time, distance and absorbing material. Materials and Methods: The mass attenuation coefficient, linear attenuation coefficient, Half Value Layer (HVL) and Tenth Value Layer (TVL) of X-rays (32 keV, 74 keV) and gamma rays (662 keV) are measured in Barium compounds. Results and Discussion: The measured values agree well with the theory. The effective atomic numbers ($Z_{eff}$) and electron density (Ne) of Barium compounds have been computed in the wide energy region 1 keV to 100 GeV using an accurate database of photon-interaction cross sections and the WinXCom program. Conclusion: The mass attenuation coefficient and linear attenuation coefficient for $BaCO_3$ is higher than the $BaCl_2$, $Ba(No_3)_2$ and BaSO4. HVL, TVL and mean free path are lower for $BaCO_3$ than the $BaCl_2$, $Ba(No_3)_2$ and $BaSO_4$. Among the studied barium compounds, $BaCO_3$ is best material for x-ray and gamma shielding.

• 한국정보통신학회논문지
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• 제11권1호
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• pp.40-45
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• 2007

본 논문에서는 무선공중망을 이용하여 재택 혹은 원거리에서도 환자의 상태를 확인하고 감시함으로써 의료서비스의 이동성을 제공하기 위한 의료정보 무선전송 시스템을 제안하고, 시뮬레이션 하였다. 제안한 방법은 응급상황 발생시 의료정보를 디지털 데이터로 변환하여 PDA와 같은 이동형 단말에 전송함으로써 신속한 응급처치 등이 가능토록 한다. 시뮬레이션은 이동 무선채널환경에서 신뢰성 있는 의료정보의 전송을 위하여 IEEE 802.11a에 근거한 OFDM 전송방식을 사용하였고, AWGN과 3-ray 이동 다중경로 페이딩 환경에서 신뢰성 있는 정보전송을 위하여 콘볼루션 코딩을 적용하여 시스템 성능을 분석하였다.

• 반도체디스플레이기술학회지
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• 제16권4호
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• pp.36-40
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• 2017

With an attempt to enhance the visibility of laser beam, we have investigated a black matrix with scattering particles by ray tracing simulations. As the scattering particle density is increased, the detected power by the receiver is increased, thereby enhancing the visibility. In reality, the visibility is reduced with increasing incident angle (away from the normal incidence) of laser beam, a phenomenon also observed by ray tracing simulations. It is due to the fact that the mean path is increased within a highly absorptive BM layer or a smaller number of rays hit the BM area when the incident angle is high. Embedding a number of scattering particles into BM may bring in crosstalk among pixels. However, it is negligible because scattered rays inside highly absorptive BM are re-scattered due to the high scattering particle density, decreasing the power of scattered rays into the active areas.