• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.1
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• pp.85-95
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• 1998

The broadband ultrasonic transducers have been designed to use in obtaining the broadband echo signals from fish schools in relation to the identification of fish species. The broadening of bandwidth was achieved by attaching double acoustic matching layers on the front face of a Tonpilz transducer consisted of an aluminum head, a piezoelectric ring, a brass tail and to evaluate the performance characteristics, such as the transmitting voltage response(TVR) of transducers. The constructed transducers were tested experimentally and numerically by changing the parameters such as impedances and thicknesses of the head, tail and matching layers, in the water tank. Also, the developed transducer was excited by a chirp signal and the received chirp waveforms were analyzed. According to the measured TVR results, the available 3 dB bandwidth of the transducer with double matching layers of an $Al_O_3/epoxy$ composite of 7 mm thick and a polyurethane window of 18 mm thick was 7.3 kHz with a center frequency of 38.8 kHz, and the maximum and the minimum values of the TVR in this frequency region were 135.7 dB and 132.7 dB re $1\;{\mu}Pa/V$ at 1 m, respectively. Also, the available 3 dB bandwidth of the transducer with double matching layers of an $Al_O_3/epoxy$ composite of 11 mm thick and a polyurethane window of 15 mm thick was 6.2 kHz with a center frequency of 38.6 kHz, and the maximum TVR value in the frequency region was 136.3 dB re $1\;{\mu}Pa/V$ at 1 m. Reasonable agreement between the experimental results and the numerical results for the TVR of the developed transducers was achieved. The frequency dependant characteristics of experimentally observed chirp signals closely matched to the measured TVR results. These results suggest that there is potential for increasing the bandwidth by varying other parameters in the transducer design and the material of the acoustic matching layers.

• Korean Journal of Food Science and Technology
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• v.38 no.6
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• pp.742-750
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• 2006

This study was carried out to investigate the efficacy of two kinds of electrolyzed water with added 0.5% (v/v) citron juice, SAEW-CJ[Strong Acidic Electrolyzed Water with added Citron Juice, pH 2.57, ORP (oxidation-reduction potential) 1,122 mV, HClO 23.05ppm] and LAEW-CJ (Low Alkaline Electrolyzed Water with added Citron Juice, pH 4.67, ORP 997mV, HClO 42.55mV) as storing liquid for peeled taro. During storage at $5^{\circ}C$ until 30 days, SAEW-CJ and LAEW-CJ inhibited the growth of microorganisms more effectively than 0.2% (w/v) APS (aluminium potassium sulfate) and 0.85% (w/v) NaCl did. Total phenolic contents, PRO (polyphenol oxidase) activity, color differences value (${\Delta}E$) and vitamin C contents of peeled taro stored in SAEW-CJ and LAEW-CJ were lower than those stored in 0.2% APS and 0.85% NaCl. The hardness decrement of peeled taro stored in LAEW-CJ was lower than that of the others. In addition, the contents of moisture, crude protein, crude ash, total sugars, and reducing sugars were gradually decreased during storage. However, no difference by peeling methods or immersion liquid was found.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.375-378
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• 2015

In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, $(Pb_{0.88}La_{0.08})(Zr_{0.65}Ti_{0.35})O_3$ ceramics were fabricated by the conventional solid-state method. Electrocaloric effects of $(Pb_{0.88}La_{0.08})(Zr_{0.65}Ti_{0.35})O_3$ ferroelectric ceramics were investigated and discussed using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to $220^{\circ}C$. The temperature change ${\Delta}T$ due to the electrocaloric effect was calculated by Maxwell's relations, and reached the maximum of ~0.19 at $190^{\circ}C$ under applied electric field of 30 kV/cm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.14-14
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• 2009

In this study, we investigated the effects of Cr dopant on the bulk trap level and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) using dielectric functions such as $Z^*$, $Y^*$, $M^*$, ${\varepsilon}^*$, and $tan{\delta}$. More than two bulk traps of $Zn_i$ and $V_o$ probably in different ionization states could be identified in ZBCr($ZnO-Bi_2O_3-Cr_2O_3$). The grain boundaries of ZBCr could be electrochemically divided into two types: sensitive to ambient oxygen and thus electrically active one and oxygen-insensitive and thus electrically inactive one.

• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.1
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• pp.40-49
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• 2001

We have developed a repeatable process of forming uniform, small-size and high-density self-assembled Si nano-crystals. The Si nano-crystals were fabricated in a conventional LPCVD (low pressure chemical vapor deposition) reactor at $620^{\circ}c$ for 15 sec. The nano-crystals were spherical shaped with about 4.5 nm in diameter and density of $5{\times}l0^{11}/$\textrm{cm}^2$. More uniform dots were fabricated on nitride film than on oxide film. To take advantage of the above-mentioned characteristics of nitride film while keeping the high interface quality between the tunneling dielectrics and the Si substrate, nitride-oxide tunneling dielectrics is proposed in n-channel device. For the first time, the single electron effect at room temperature, which shows a saturation of threshold voltage in a range of gate voltages with a periodicity of ${\Delta}Ｖ_{GS}\;{\approx}\;1.7{\;}V$, corresponding to single and multiple electron storage is reported. The feasibility of p-channel nano-crystal memory with thin oxide in direct tunneling regime is demonstrated. The programming mechanisms of p-channel nano-crystal memory were investigated by charge separation technique. For small gate programming voltage, hole tunneling component from inversion layer is dominant. However, valence band electron tunneling component from the valence band in the nano-crystal becomes dominant for large gate voltage. Finally, the comparison of retention between programmed holes and electrons shows that holes have longer retention time.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.604-609
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• 2014

The thermoelectric power and dc conductivity of $La_{2/3+x}TiO_{3-{\delta}}$ (x = 0, 0.13) were investigated. The thermoelectric power was negative between 80K and 300K. The measured thermoelectric power of x = 0.13 increased linearly with increased temperatures and was represented by $S_0+BT$. The x = 0 sample exhibited insulating behavior, while the x = 0.13 sample showed metallic behavior. The electric resistivity of x = 0.13 had a linear temperature dependence at high temperatures and a T3/2 dependence below about 100K. On the other hand, the electric resistivity of x = 0 has a linear relation between $ln{\rho}/T$ and 1/T in the range of 200 to 300K, and the activation energy for small polaron hopping was 0.23 eV. The temperature dependence of thermoelectric power and the resistivity of x = 0 suggests that the charge carriers responsible for conduction are strongly localized. This temperature dependence indicates that the charge carrier (x = 0) is an adiabatic small polaron. These experimental results are interpreted in terms of spin (x = 0.13) and small polaron (x = 0) hopping of almost localized Ti 3d electrons.

• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.355-358
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• 2001

Selection of optima] nutrient sources and cultural methods for liquid spawn culture of Flammulina velutipes were carried out. The optimal temperature and pH for mycelial growth of F. velutipes were $20^{\circ}C$ and 6.0 to 7.5. respectively. In the 250ml ${Delta}$-flask culture. the amount of inoculum and culture period for the optimal mycelial growth of F. velutipes were 3 mycelial disks(diametcr 6mm) and 6 days, respectively. For the mass production of submerged culture. the optimal inoculum amount and aeration rate of F. velutipes were 5%(inoculum vol/medium vol.) and l.0vvm(vol of air/vol. of medium/min), respectively.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.639-643
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• 2001

Recently, photovoltaic system has been studied widely as a renewable energy system, because it does not produce environmental pollution and it has infinity energy source from the sun. A study on photovoltaic system has a lot of problems like as reappearance and repetition of some situation in the laboratory experiment for development of MPPT algorithm and islanding detection algorithm, because output characteristics of solar cell are varied by irradiation and surface temperature of solar cell. And this system is consisted a lot of solar cell unit. Therefore, the assistant equipment which emulates the solar cell characteristics which can be controlled arbitrarily by researcher is require to the researchers for reliable experimental data. In this paper, the virtual implement of solar cell (VISC) system is proposed to solve these problems and to achieve reliable experimental result on photovoltaic system. VISC system emulates the solar cell output characteristics, and this system can substitute solar cell in laboratory experiment system. To realize the VISC, mathematical model of solar cell is studied for driving converter and the DC/DC converters are compared in viewpoint of tracking error using computer simulation. And then analysis of parallel and series characteristics was done for combination of VISC model.

• Journal of The Korean Astronomical Society
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• v.35 no.4
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• pp.175-185
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• 2002

Almost half of primeval galaxies show P-Cygni type profiles in the Ly$\alpha$ emission line. The main underlying mechanism for the profile formation in these systems is thought to be the frequency re-distribution of the line photons in expanding scattering media surrounding the emission source. A Monte Carlo code is developed to investigate the Ly$\alpha$ line transfer in an optically thick and moving medium with a careful consideration of the scattering in the damping wings. Typical column densities and expansion velocities of neutral hydrogen investigated in this study are $N_{H1}{\~}10^{17-20}\;cm^{-2}$ and ${\Delta}V{\~} 100 km\;s^{-1}$. We investigate the dependence of the emergent profiles on the kinematics and on the column density. Our numerical results are applied to show that the damped Ly$\alpha$ absorbers may possess an expanding H I supershell with bulk flow of ${\~}200 km\;s^{-l}$ and H I column density $N_{H1}{\~}10^{19}\;cm^{-2}$. We briefly discuss the observational implications.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.70.2-70.2
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• 2013

We present collections of optical photometry for a pre-main sequence star HBC 722. It showed large amplitude optical outburst (${\Delta}V=4.7$ mag) in 2010 and classified as a FU Orionis type object. We have been observing HBC 722 from 2011 April to 2013 May, using Camera for QUasars in EArly uNiverse (CQUEAN) attached to the 2.1 m Otto Struve telescope at the McDonald Observatory. Time-series monitoring data (minute-scale interval) were obtained in SDSS r, i and z bands to see short-scale behaviors as well as trace the long-term brightness changes after the eruption in 2010. Interestingly, it started to brighten from 2011 early summer and became brighter than the first outburst peak in our 2013 May observation. We expect that the recovering phase would result from re-increase of disk accretion rate, might attribute to distinctive short-scale color features. In this presentation, we report long- and short-timescale optical behaviors of HBC 722 in the post-outburst phase.