• 한국생산제조학회지
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• 제21권2호
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• pp.252-258
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• 2012

A study of terahertz waves was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The terahertz systems were consisted of time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both non-conducting polymeric composites and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. The CFRP (Carbon fiber reinforced plastics) laminates were utilized for confirming the experimentation in the terahertz NDE. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field direction of the terahertz waves and the intervening fiber directions. A refractive index (n) was defined as one of mechanical properties; so a method was obtained in order solve the "n" in the material with non-conductivity. The usefulness and limitations of terahertz radiation are investigated for the NDE of FRP composites.

• 한국정밀공학회지
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• 제21권12호
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• pp.13-20
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• 2004

Manufacturing process for the microfluidic device can include such sequential steps as master fabrication, electroforming, and injection molding. The laser ablation using masks has been applied to the fabrication of channels in microfluidic devices. In this study, manufacturing of polymer master and mold insert for micro injection molding was investigated. Ablation of PET (polyethylene terephthalate) by the excimer laser radiation could be used successfully to make three dimensional master fur nickel mold insert. The mechanism fur ablative decomposition of PET with KrF excimer laser $({\lambda}: 248 nm, pulse duration: 5 ns)$ was explained by photochemical process, while ablation mechanism of PMMA (polymethyl methacrylate) is dominated by photothermal process, the .eaction between PC (polycarbonate) and KrF excimer laser beam generate too much su.face debris. Thus, PET was adopted in polymer master for nickel mold insert. Nickel electroforming using laser ablated PET master was preferable for replication method. Finally, it was shown that excimer laser ablation can substitute for X-ray lithography of LIGA process in microstructuring.

• 분석과학
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• 제5권4호
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• pp.367-372
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• 1992

방사선 중성자 선원의 에너지 스펙트럼을 측정하기 위하여 액체 섬광 검출기(NE213)와 펄스모형 분리장치를 감마선 선원과 중성자 선원을 이용하여 그 감응 특성을 분석하였다. Am-Be 선원을 이용하여 이 장치에 대한 "Figure of Merit"을 측정한 결과 1.13 이었다. 이 값은 단색 에너지 중성자 선원인 $^{12}C(d,\;n)^{13}N$에서의 1.3 과 상당히 유사한 값을 보여 준다. NE213-PSD 장치의 성능 시험을 위한 이 실험결과는 중성자-감마 혼합 방사선장에서 스펙트럼의 측정과 중성자 에너지 스펙트럼과 속밀도 측정표준을 확립하는 데 기술적으로 유용하게 쓰일 것이다.

• Journal of Astronomy and Space Sciences
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• 제33권2호
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• pp.75-92
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• 2016

It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.

• 한국전자파학회논문지
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• 제7권3호
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• pp.211-218
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• 1996

1.9GHz On-Glass 안테나의 이론 및 실험적 연구를 수행하였다. 본 논문에서 설계된 On-Glass안테나의 구조는 페이징 코일에 의해 분리된 5/8 $\lambda$ 상부 요소와 1/4$\lambda$ 하부 요소로 구성된다. On-Glass 안테나는 안테나와 직렬로 적절하게 배치된 페이징 코일을 이용하여 공진시킬 수 있다. 이와 같은 공진 구조는 안테나 효율에 있어 향상을 가져오고, 차량과 같이 한정된 공간에서 이용되는 경우 설치하는데 매우 유용하다. 해석 방법은 펄스 함수를 갖는 콜로케이션법에 근거한다. 수치 해석법에 의해 얻어진 결과를 제시하고 측정 결과와 비교하였다. 이러한 결과로 부터 On-Glass 안테나의 VSWR, 이득, 복사패턴, 대역폭 등이 해석되었다.

• 한국전문물리치료학회지
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• 제22권2호
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• pp.70-80
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• 2015

The spinal cord is highly complex, consisting of a specialized neural network that comprised both neuronal and non-neuronal cells. Any kind of injury and/or insult to the spinal cord leads to a series of damaging events resulting in motor and/or sensory deficits below the level of injury. As a result, muscle paralysis (or paresis) leading to muscle atrophy or shrinking of the muscle along with changes in muscle fiber type, and contractile properties have been observed. Traditionally, histology had been used as a gold standard to characterize spinal cord injury (SCI)-induced adaptation in spinal cord and skeletal muscle. However, histology measurements is invasive and cannot be used for longitudinal analysis. Therefore, the use of conventional magnetic resonance imaging (MRI) is promoted to be used as an alternative non-invasive method, which allows the repeated measurements over time and secures the safety against radiation by using radiofrequency pulse. Currently, many of pathological changes and adaptations occurring after SCI can be measured by MRI methods, specifically 3-dimensional MRI with the advanced diffusion tensor imaging technique. Both techniques have shown to be sensitive in measuring morphological and structural changes in skeletal muscle and the spinal cord.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1523-1525
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• 1996

Partial discharges(PD) in air insulated electric power systems cause power loss, produce interfering electromagnetic radiation, and can indicate incipient failure. An understanding of PD in air gap is clearly important. The Wavelet transformation is an extended method of fourier transformation. The fourier method is a powerful tool for signal analysis, but it can't include informations for time. However tile wavelet transformation analysis can include on the informations of time and frequency at the same time. In this paper we apply the wavelet transformation to the PD signals in needle-plane air gap for tile purpose of analysis of developing aspects of PD. We can analyze the developing aspects of PD, namely, PD current, repetition rates, width of pulse distribution region, pulseless region and frequencies distribution of PD pulses.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.3-3
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• 2002

Many studies on crystal growth mechanisms of the hen egg-white lysozyme protein crystals have mainly performed by optical microscopy and atomic force microscopy (AFM). As results, two types of growth mechanisms, which are a two-dimensional nucleation mechanism and a spiral growth mechanism, were identified. However, there was no direct evidence of grown-in screw dislocations at the spiral sites. We first observed the screw dislocations in tetragonal lysozyme crystals using synchrotron X-ray topography. In addition, to confirm the characteristics of dislocations, we have observed some elastic constants in lysozyme crystals in terms of the sound velocity measurement by pulse echo methods. Tetragonal hen egg-white lysozyme crystals were grown by the concentration gradient method. The crystals were grown in test tubes, with an inner diameter of 8 ㎜ and 80 ㎜ in length, held vertically. The test tubes were kept at 23C for 2 weeks. The maximum size of crystals were 3×3×4 ㎟. The high quality crystals were examined by Laue topography with a water filter using synchrotron radiation. Figure is a X-ray topograph. Several straight screw dislocations were observed. We also determined Burgers vector to be a [110] direction. The measurement of sound velocity was performed by the digital signal processing method. the crystals were placed in stainless steel vessel, which was filled with lysozyme solution used for crystal growth. We observed the longitudinal sound velocity along the [110] direction in the tetragonal is obtained to be 1817 ㎧. Therefore, Young modulus and shear modulus were evaluated to be 2.70 Gpa and 1.02 Gpa, respectively, if we assumed Poisson ratio is 0.33. These results will be discussed at the meeting.

• 한국생산제조학회지
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• 제21권1호
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• pp.102-108
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• 2012

A study of terahertz waves (T-ray) was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The to-be-used systems were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both turbine blades of wind energy (non-conducting polymeric composites) and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. This was demonstrated in CFRP (Carbon fiber reinforced plastics) laminates. Refractive index (n) was defined as one of mechanical properties; so a method was solved in order solve the "n" in the material with the cut parts of the turbine blades of wind energy. The defects and anomalies investigated by terahertz radiation were foreign material inclusions and simulated disband. Especially, it is found that the T-ray went through the turbine blade with greater thickness (about 90mm).

• 센서학회지
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• 제24권2호
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• pp.101-106
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• 2015

We designed, developed and characterized a multi-segmented tissue equivalent proportional (TEPC) counter for microdosimetry. The energy resolution of the multi-segmented TEPC was about 12% for $^{241}Am$ 5.45 MeV alpha particles. The resolution was better than 33% for a single un-segmented TEPC. A compact and low power consumption TEPC could be made by using digital pulse processor (DPP). We also successfully calibrated the TEPC by using $^{252}Cf$ standard neutron source in Korea Research Institute of Standards and Science (KRISS). According to the results, the TEPC is useful for several application of radiation monitoring such as a neutron monitor, air crew monitor and space dosimeter.