• Composites Research
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• v.31 no.1
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• pp.23-29
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• 2018

The RFI process can be applied to very thick structures without limiting the resin viscosity. When the proper thickness of the resin film cannot be set, the resin film creates either the non-impregnated section or the excessive resin contents and this leads to the deterioration of mechanical properties. Therefore, this study proposed a method for setting the resin film thickness in the RFI process. The fiber compaction behavior test was proposed by setting the proper resin film thickness and the properties of composites were evaluated through short beam shear strength test, compression test and porosity measurement to verify the proposed method. The evaluation of physical properties of composites was conducted and an appropriate level of resin film thickness was found based on the results of fiber compaction behavior test.

• Fisheries and Aquatic Sciences
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• v.17 no.3
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• pp.361-367
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• 2014

Cuttlefish Sepia esculenta are commercially important in Korea. Assessments of their biomass currently depend on fishery-landings data, which may be biased. Towards fishery-independent acoustic surveys of cuttlefish, target strength (TS) measurements at 70 and 120 kHz were made of 23 live cuttlefish, in early May 2010. The fish were caught by traps in the inshore waters around Geojedo, Korea. The TS were measured using split-beam echosounders (Simrad ES60 and EY500, respectively). The cuttlefish mantle lengths (L) ranged from 15.6 to 23.5 cm (mean L=17.8 cm) and their masses (W) ranged from 335 to 1020 g (mean W=556.1 g). Their mean TS values at 70 and 120 kHz were -33.01 dB (std=1.39 dB) and -31.76 dB (std=2.15 dB), respectively. The mean TS at 70 kHz was 0.17 dB higher than the TS-length relationship resulting from a least-squares fit to the data ($TS=24.67{\log}_{10}L(cm)-64.03$, $r^2$ = 0.52, N=23). The mean TS at 120 kHz was 0.45 dB higher than the fitted TS-length relationship ($TS=40.59{\log}_{10}L(cm)-82.96$, $r^2$ = 0.58, N=23). The differences between the mean TS values and an equation regressed from all of the TS measurements at both frequencies ($TS=24.92{\log}_{10}L(cm)-4.92{\log}_{10}{\lambda}(m)-22.82$, $r^2$ = 0.86, N=46) was 0.22 dB at 70 kHz and 0.31 dB at 120 kHz, respectively.

• Laser Solutions
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• v.9 no.2
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• pp.23-30
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• 2006

Silicon Nitride $(Si_3N_4)$, which is widely used in a variety of applications, is hard-to-machine due to its high hardness. At high temperature (e.g. above $1000^{\circ}C)$, however, the machinability can be greatly improved. In this work, we used a $CO_2$ laser with a high absorptivity to $Si_3N_4$ of 0.9 to locally heat the surface of a rotating $Si_3N_4$ rod on a lathe. In order to examine the effects of the laser-assisted heating on hardness, an $Si_3N_4$ rod is heated to temperatures from 900 to $1800^{\circ}C$ and is rotated at speeds from 440-900 rpm in experiments. When the rod is naturally cooled to room temperature, we measured the Vickers hardness (Hv); and observed the surface of HAZ using a scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used for ingredient analysis. Results showed that when heated at $1600^{\circ}C$, the hardness of $Si_3N_4$ decreased from 1500 Hv to 1000 Hv. Also, in order to predict the depth of HAZ, we numerically analyzed the laser-assisted heating of $Si_3N_4$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.12
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• pp.1655-1662
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• 2011

We have conducted a study on stainless steel laser-welding materials by using a laser beam for the evaluation. Stainless steel used in a rust and excellent thermal deformation has a variety of application. In this study, to improve the mechanical properties of stainless steel, a 50 W laser thermal source is used and magnetic fields are applied, on the basis of suggestions. The mechanical properties and performance are evaluated by performing a numerical analysis, tensile test, and shape, microstructure, and hardness test. The results show that the mechanical properties of improve increased speed the melting pool, tensile strength of 16 kPa rise, run into the melting zone and hardness 7 Hv.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.426-426
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• 2012

본 연구에서는 GaAs p-i-n 접합 구조에 InAs 양자점을 삽입한 양자점 태양전지(Quantum Dot Solar Cell; QDSC)의 내부 전기장(internal electric field)을 조사하기 위하여 Photoreflectance (PR) 방법을 이용하였다. QDSC 구조는 GaAs p-i-n 구조의 공핍층 내에 8주기의 InAs 양자점 층을 삽입하였으며 각 양자점 층은 40 nm 두께의 i-GaAs로 분리하였다. InAs/GaAs QDSC는 분자선박막 성장장치(molecular beam epitaxy; MBE)를 이용하여 성장하였다. 이 때 양자점의 형성은 InAs 2.0 ML(monolayer)를 기판온도 $470^{\circ}C$에서 증착하였다. QDSC 구조에서 여기광원의 세기에 따른 전기장의 변화를 조사하였다. 아울러 양자점 층 사이의 i-GaAs 층 내에 6.0 nm의 AlGaAs 퍼텐셜 장벽(potential barrier)을 삽입하여 퍼텐셜 장벽 유무에 따른 전기장 변화를 조사하였다. PR 측정에서 여기광원으로는 633 nm의 He-Ne 레이저를 이용하였으며 여기광의 세기는 $2mW/cm^2$에서 $90mW/cm^2$까지 변화를 주어 여기광세기 의존성실험을 수행하였다. 여기광의 세기가 증가할수록 photovoltaic effect에 의한 내부 전기장의 변화를 관측할 수 있었다. PR 결과로부터 p-i-n 구조의 p-i 영역과 i-n 접합 계면의 junction field를 검출하였다. p-i-n의 i-영역에 양자점을 삽입한 경우 PR 신호에서 Franz-Keldysh oscillation (FKO)의 주파수가 p-i-n 구조와 비교하여 변조됨을 관측하였다. 이러한 FKO 주파수성분은 fast Fourier transform (FFT)을 이용하여 검출하였다. FKO의 주파수 성분들은 고전기장하에서 electron-heavyhole (e-hh)과 electron-lighthole (e-lh) 전이에 의해 나타나는 성분으로 확인되었다.

• Fisheries and Aquatic Sciences
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• v.19 no.2
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• pp.8.1-8.11
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• 2016

To quantitatively estimate the influence of cuttlebone on the target strength (TS) of golden cuttlefish, the cuttlebone was carefully extracted from 19 live cuttlefish caught using traps in the inshore waters around Geojedo, Korea, in early May 2010 and the TS was measured using split-beam echosounders (Simrad ES60 and EY500). The TS-length relationships for the cuttlefish (before the extraction of cuttlebone, Fish Aquat Sci. 17:361-7, 2014) and the corresponding cuttlebone were compared. The cuttlebone length ($L_b$) ranged from 151 to 195 mm (mean $L_b$ = 168.3 mm) and the mass ($W_b$) ranged from 29.3 to 53.2 g (mean $W_b$ = 38.8 g). The mean TS values at 70 and 120 kHz were -33.60 dB (std = 1.12 dB) and -32.24 dB (std = 1.87 dB), respectively. The mean TS values of cuttlebone were 0.19 dB and 0.04 dB lower than those of cuttlefish at 70 and 120 kHz, respectively. For 70 and 120 kHz combined, the mean TS value of cuttlebone was -32.87 dB, 0.11 dB lower than that of cuttlefish (-32.76 dB). On the other hand, the mean TS value of cuttlebone predicted by the regression ($TS_b$ = 24.86 $log_{10}$ $L_b$ - 4.86 $log_{10}$ ${\lambda}$ - 22.58, $r^2$ = 0.85, N = 38, P < 0.01) was -33.10 dB, 0.04 dB lower than that of cuttlefish predicted by the regression ($TS_c$ = 24.62 $log_{10}$ $L_c$ - 4.62 $log_{10}$ ${\lambda}$ - 22.64, $r^2$ = 0.85, N = 38, P < 0.01). That is, the contribution of cuttlebone to the cuttlefish TS determined by the measured results was slightly greater than that by the predicted results. These results suggest that cuttlebone is responsible for the TS of cuttlefish, and the contribution is estimated to be at least 99 % of the total echo strength.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.117-118
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• 2000

The secondary electron emission coefficient ${\gamma}$ of MgO single crystals according to the gas mixture ratio of Xe to Ne have been investigated by ${\gamma}-focused$ ion beam system. It is found that the MgO single crystals of (111) crystallinity has the highest ${\gamma}$ from 0.09(0.03) up to 0.16(0.04), while from 0.07(0.02) to 0.15(0.03) for (200) and from 0.06(0.01) to 0.13(0.02) for (220) crystallinity for operating Ne (Xe) ions ranging from 50eV to 200eV throughout this experiment. And it is found that the ${\gamma}$ ranged from 0.03 up to 0.06 for Ne-Xe mixtures are much smaller than those of 0.09 up to 0.16 for pure Ne ions under accelerating voltage ranged from 50V to 200V.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.113-114
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• 2000

The secondary electron emission coefficient(${\gamma}$) of vacuum annealed MgO films has been investigated by ${\gamma}-focused$ ion beam(${\gamma}-FIB$) system. The vacuum annealed MgO films have been found to have higher ${\gamma}$ values from 0.053 up to 0.121 than those for as-deposited MgO films from 0.026 up to 0.062 for $Ne^+$ ion energies ranged from 50eV to 200eV. Also it is found that ${\gamma}$ for air hold of vacuum annealed MgO layers for 24-hours is similar to that for vacuum annealed MgO films without any air-hold.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1354-1362
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• 2015

Heterogeneous network technology is expected to be a core technology for 5G mobile communications. 5G mobile network would be composed of many base stations even have mobility, then the operator should connect base stations through the wireless backhaul technology. This paper presents Ultra Wide Area Wireless Backhaul Network System with massive array antenna. We conducted link budget analysis for Ultra Wide Area Wireless Backhaul Network and performance analysis of massive array antenna system through the transmission simulator based on beamforming technology. In wide area ($10km^2$) wireless backhaul system composed of massive antenna, we achieved 5 bps/Hz average spectral efficiency with 1 W transmission power per beam.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2204-2206
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• 1999

Pulsed Nd:YAC laser is used widely for materials processing and instrumentation. It is very important to control the laser energy density in materials processing by a pulsed Nd:YAG laser. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this study, the alternating charge-discharge system was designed to adjust a pulse repetition rate. This system is controlled by one chip microprocessor and allows to replace an expensive condenser for high frequency to a cheap condenser for low frequency. In addition. we have investigated the current pulse shape of flashlamp and the operating characteristics of a pulsed Nd:YAG laser. As a result, it is found that the laser output of the power supply using the alternating charge-discharge system is not less than that of typical power supply. As the pulse repetition rate rises from 30pps to 120pps by the step of 30pps at 1200V, it is found that the laser efficiency decreases but the laser output power increases about 6W at each step.