• Proceedings of the KIEE Conference
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• 1996.07c
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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.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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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.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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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).

• Journal of Sensor Science and Technology
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• v.24 no.2
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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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.1
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• pp.1-5
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• 2018

This study analyzed the change of electrical characteristics of a photocoupler when a narrow-band electromagnetic wave was combined with the photocoupler. A magnetron (3 kW, 2.45 GHz) was used as the narrow-band electromagnetic source. The EUT was Photocoupler (6N139) and the input signal was divided into two types: a square pulse and the second signal is 0 V. The malfunction of the photocoupler was confirmed by monitoring the variation in the output voltage of the photocoupler. As a result of the experiment, changes in the malfunctioning was observed as the electric field was increased. There are three types of malfunction modes: delay, output voltage off, and fluctuation. Bit errors were analyzed to verify the electrical characteristics of the photocoupler by narrow-band electromagnetic waves. The result of this study can be used as basic data for the effect analysis of photocoupler protection and impact analysis of high-power electromagnetic waves.

• Journal of the Korean Society of Visualization
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• v.16 no.3
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• pp.8-15
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• 2018

Recently, as the high speed railway becomes more common, new environmental problems such as noise around tunnels are appearing. When a high speed train enters a tunnel, a compression wave in the tunnel is generated and propagated toward the tunnel exit at a sonic speed. When it reaches the tunnel exit, a part of compression wave radiates as a pulse typed impulse wave to the outside of tunnel. The impulse wave has an explosive noise. When the impulse wave is propagated around a village, it induces a serious noise or other problems to the resident. In order to solve these engineering problems, it is important to investigate the radiation characteristics of the impulse wave radiated from the tunnel exit. In this study, the effect of the length and angle of the baffle plate at the tunnel exit on the impulse wave radiated from the tunnel exit was investigated by numerical analysis. As a results, the baffle plate greatly affected the propagation of impulse wave.

• Journal of Advanced Engineering and Technology
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• v.11 no.4
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• pp.245-251
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• 2018

Terahertz waves (T-ray) was extensively studied for the NDE (nondestructive evaluation) of characterization of trailing edges for a use of turbines composed with composite materials. The used NDE system were consisted of both CW(Continuous wave) and TDS (Time domain spectroscopy). The FRP composites were utilized for two kinds of both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS (Time domain spectroscopy) mode resembles almost that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity unlike ultrasound. Also, a method was suggested to obtain the "n" in the materials, which is called the refractive index (n). The data of refractive index (n) could be solved for the trailing edges. The trailing edges were scanned for characterization and inspection. C-scan and B-scan images were obtained and best optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. Especially, it is found that the defect image of T-ray corresponded with defect locations for the trailing edges of wind mill.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1610-1615
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• 2019

Positron emission tomography (PET)/magnetic resonance (MR) scanning has the advantage of less additional exposure to radiation than does PET/computed tomography (CT). In particular, MR based attenuation correction (MR AC) can greatly affect the image quality of PET and is frequently obtained using various MR sequences. Thus, the purpose of the current study was to quantitatively compare the image quality between MR non-AC (MR NAC) and MR AC in PET images with three MR sequences. Percent image uniformity (PIU), percent contrast recovery (PCR), and percent background variability (PBV) were estimated to evaluate the quality of PET images with MR AC. Based on the results of PIU, 15.2% increase in the average quality was observed for PET images with MR AC than for PET images with MR NAC. In addition, 28.6% and 71.1% improvement in the average results of PCR and PBV respectively, was observed for PET images with MR AC compared with that with MR NAC. Moreover, no significant difference was observed among the average values using three MR sequences. In conclusion, the current study demonstrated that PET with MR AC improved the image quality and can be help diagnosis in all MR sequence cases.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.437-441
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• 2022

In this study, we developed a neutron time-of-flight (nTOF) measurement system for a 1.7-MV tandem proton accelerator with a target covered with 300-nm-thick lithium (Li) layer. With implementation of beam chopping module after its ion source, the accelerator is configured to operate in pulsed-beam mode with a pulse width <50 ns at 20-kHz repetition rate. This enables the gamma flash-type nTOF measurement system to identify the neutron generated with 3-MeV proton beam energy. The nTOF system consists of a 30" cylindrical NaI(Tl) and four stilbene scintillation detectors. The NaI(Tl) scintillator is placed 50 cm from the Li target to measure the time of beam irradiation on the target, and the stilbene detectors are placed 2 and 2.4 m away to measure nTOF at each location. The nTOF system successfully measured the generated neutron energy at irradiated proton energies of 2.6 and 3.0 MeV with an average energy resolution of 15%.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.266-272
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• 2021

In the pulsed electron beam generators, such as plasma focus devices and linear induction accelerators whose electron pulse width is in the range of nanosecond and less, as well as in cases where there is no direct access to electron beam, like runaway electrons in Tokamaks, measurement of the electron energy spectrum is a technical challenge. In such cases, the indirect measurement of the electron spectrum by using the bremsstrahlung radiation spectrum associated with it, is an appropriate solution. The problem with this method is that the matrix equation between the two spectrums is an ill-conditioned equation, which results in errors of the measured X-ray spectrum to be propagated with a large coefficient in the estimated electron spectrum. In this study, a method based on the neural network and the MCNP code is presented and evaluated to recover the electron spectrum from the X-ray generated by collision of the electron beam with a target. Multilayer perceptron network showed good accuracy in electron spectrum recovery, so that for the X-ray spectrum with errors of 3% and 10%, the network estimated the electron spectrum with an average standard error of 8% and 11%, on all of the energy intervals.