• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.6
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• pp.330-336
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• 2004

In this work, in order to obtain the detailed information about lightning electromagnetic pulses, the electric fields radiated from multiple lightning return strokes were measured and analyzed statistically. The electric field measuring system consists of a hemisphere antenna of 30cm in diameter, integrator and data acquisition device, and its frequency bandwidth ranges from 200Hz to 1.56MHz, and the sensitivity is 0.96㎷/V/m. The electric field signals are digitized every 200ns with the transient signal analyzer having the resolution of 12-bit and the recording length of 5 kilowords and are registered at personal computer. As a result, the electric fields produced by the first return stroke begin with a slow initial part or front, which starts just after or during the last stepped leader. On the average the rise times of the electric fields for the positive first, second and third strokes are 4.21${\mu}\textrm{s}$, 3.94${\mu}\textrm{s}$ and 2.75${\mu}\textrm{s}$, respectively, and those for the negative first, second and third strokes are 3.46${\mu}\textrm{s}$, 3.15${\mu}\textrm{s}$ and 2.79${\mu}\textrm{s}$, respectively. The zero-crossing times of the electric fields for first return strokes range from about 10 to 80${\mu}\textrm{s}$. The mean zero-crossing times for subsequent return strokes are shorter than those for first lightning return strokes.

• Restorative Dentistry and Endodontics
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• v.28 no.5
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• pp.363-368
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• 2003

The purpose of this study is to evaluate the effect of additional enamel etching with phosphoric acid on the microleakage of the adhesion of self-etching primer system. Class V cavity($4mm{\times}3mm{\times}1.5mm$) preparations with all margins in enamel were prepared on buccal surface of 42 extracted human upper central incisor teeth. Prepared teeth were randomly divided into 3 groups. Group 1：no additional pretreatment with 37% phosphoric acid (NE). Group 2：additional pretreatment with 37% phosphoric acid for 10 seconds (E10s). Group 3：additional pretreatment with 37% phosphoric acid for 20 seconds (E20s). The adhesives(Clearfil SE $Bond^{\circledR}$, Kuraray, Osaka, Japan) and composite resins(Clearfil $AP-X^{\circledR}$, Osaka, Kuraray, Japan) were applied following the manufacturer's instructions. All the specimens were finished with the polishing disc(3M dental product, St Paul, MN, USA), thermocycled for 500 cycles between $5^{\circ}C$ and $55^{\circ}C$ and resected apical 3-mm root. 0.028 stainless steel wire was inserted apically into the pulp chamber of each tooth and sealed into position with sticky wax. Surrounding tooth surface was covered with a nail varnish 2 times except areas 1mm far from all the margins. After drying for one day, soaked the samples in the distilled water. Microleakage was assessed by electrochemical method(System 6514, $Electrometer^{\circledR}$), Keithley, USA) in the distilled water. In this study, the microleakage was the lowest in group 1 (NE) and the highest in group 3(E20s)(NE

• Journal of Powder Materials
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• v.15 no.2
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• pp.114-118
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• 2008

Functional nanomaterial is expected to have improved capacities on various fields. Especially, metal nanoparticles dispersed in polymer matrix and metal nanofiber, one of the functional nanomaterials, are able to achieve improvement of property in the electric and other related fields. In this study, the fabrication of metal (Ag) nanoparticle dispersed nanofibers were attempted. The Ag nanoparticle dispersed polymer nanofiber and Ag nanofiber were fabricated by electrospinning method using electric force. First, PVP/$AgNO_3$ nanofibers were synthesized by electrospinning in $18{\sim}22kV$ voltage with the starting materials (Ag-nitrate) added polymer (PVP; poly (vinylpyrrolidone)). Then Ag nanoparticle dispersed polymer nanofibers were fabricated to reduce hydrogen reduction at $150^{\circ}C$ for 3hr. And Ag nanofibers were synthesized by the decomposited of PVP at $300{\sim}500^{\circ}C$ for 3hr. The nanofibers were analyzed by XRD, TGA, FE-SEM and TEM. The experimental results showed that the Ag nanofibers could be applied in many fields as an advanced material.

• Journal of Surface Science and Engineering
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• v.49 no.3
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• pp.307-315
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• 2016

The properties of AlTiN films by a cathodic arc deposition process have been studied. Oblique angle deposition has been applied to deposit AlTiN films. AlTiN films have been deposited on stainless steel (SUS304) and cemented carbide (WC) at a substrate temperature of $500^{\circ}C$. AlTiN films were analyzed by scanning electron microscopy, glow-discharge light spectroscopy, micro-vickers hardness, and nanoindenter. When applying a current of 50 A to the cathodic arc source, it showed that the density of macroparticle of AlTiN films was 5 lower than other deposition conditions. With the increase of the bias voltage applied to the substrate up to -150 V, the density of macroparticle was decreased. The change of the $N_2$ flow rate during coating process made no influence on the film properties. For the multi-layered films, the film prepared at oblique angle of $60^{\circ}$ showed the highest hardness of 28 GPa and $H^3/E^2$ index of 0.18. AlTiN films have been shown a good oxidation resistance up to $800^{\circ}C$.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.127-134
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• 2009

This study was performed to establish the process mean which is statistically satisfying the critical limit of deformation strength $(S_D)$, which is found to reflect rutting characteristics of asphalt mixture relatively well. The process means were determined using the critical $S_D$ values (3MPa for local highway and 4MPa for arterial highways), which were obtained from correlation analysis of APA and $S_D$ test data of actual highway projects, and coefficient of variation of 32 combinations of domestic mixtures. The process means of 3.2 MPa for local highway and 4.25 MPa for arterial highways were suggested when using 3 specimens (diameter of 100mm). However, since these values are based on the loading speed of 30mm/min, the higher values, 3.5 MPa for local highway and 4.5 MPa for arterial highways, were suggested, respectively, if the loading speed of 50mm/min is applied using the old Marshall machine, which should give higher test values.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.126-132
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• 2014

The P-T characteristics of mixed refrigerant in thermostatic expansion valve sensing bulb were studied using R-134a and R-410A refrigerant. The characteristics of mixed refrigerant were investigated according to pressure variation and the variation of composition ratio of R-134A and R-410A in the temperature range of $-15^{\circ}C{\sim}15^{\circ}C$. The Thermodynamic characteristic values of the mixed refrigerants were identified using the characteristic value analysis program of mixed refrigerant(Refrop v9.0, NIST). The P-T characteristics in the case of the mixing ratio of 90:10 for R-410A and R-134A were the same result as R-22. And the physical properties showed similar results with R-22. The Maximum operating pressure(MOP) of mixed refrigerant showed a tendency to decrease with decreasing the mixing ratio of additive gases($N_2$ or He) gases. The characteristics in the case of the mixing ratio of 80:1 for mixed refrigerant and additive gases were the similar result as Reference refrigerant.(R-22 MOP, Sporlan company) In addition $N_2$ and He, both showed the same results. It was able to confirm that a MOP on the thermostatic expansion valve sensing bulb can be maintained by adjusting the mixing ratio of mixed refrigerant gases and additive gases.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.449-449
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• 2010

유기발광소자(organic light-emitting diodes, OLEDs)는 저공정비용, 경량화, 가용성 및 대면적화 등의 장점으로 조명 분야와 디스플레이 분야로의 응용 가능성으로 인해 크게 주목을 받아 왔다. 이러한 OLED 소자의 고효율, 고휘도 및 저소비전력 등을 구현하기 위해서는 전극으로부터 전하 주입 층으로 효율적인 전하 주입이 요구된다. 즉, 각 전극의 폐르미 준위로부터 전하 전도준위대로의 전하주입 장벽이 없어야 한다. 본 연구에서는 홀 주입장벽이 없는 정공주입 층으로 $MoO_x$(molybdenum oxide)가 도핑된 NPB(N, N'-diphenyl-N, N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine) 층을 사용하여 hole-only 소자를 제작하고 전류-전압 특성을 통해 양극으로부터 홀주입 층으로의 hole-ohmic 특성을 고찰했다. 또한, 전자 주입장벽이 없는 전자주입 층으로 $C_{60}$(fullerene)/LiF(lithum fluoride)의 이종 층을 사용하여 electron-only 소자를 제작하고 음극으로부터 전자주입 층으로의 전자 ohmic 특성을 조사했다. 또한, 전극으로부터 전하주입 층으로 ohmic 특성을 더 자세히 이해하기 위하여 전하주입 층의 자외선 광방출 스펙트럼(ultraviolet photoemission spectra)을 조사했다. 한편, glass/ITO/$MoO_x$-doped NPB (x%: x=0,25, 50 및 75; 5nm)/NPB (63nm)/$Alq_3$ (37nm)/$C_{60}$ (5nm)/LiF (1nm)/Al (100nm)로 구성된 all-ohmic OLED 소자의 발광특성은 $MoO_x$의 도핑 농도가 25%이상일 때 최적의 특성을 보여줬다. 이러한 현상은 정공주입 층에서 p형 도핑 농도의 증가에 따른 정공 농도의 증가에 기인한다. 또한 $MoO_x$의 도핑 농도의 증가에 따라 정공주입 층의 new gap state와 전극의 페르미 준위의 pinning에 기인한다. 25%의 $MoO_x$을 가진 OLED소자는 7.2V의 낮은 전압에서 $58300 cd/m^2$의 높은 휘도를 보여줬다.

• Korean Journal of Food Science and Technology
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• v.50 no.1
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• pp.37-43
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• 2018

Optimization of the lactic acid fermentation process was carried out to produce an old antler extract fortified with ${\gamma}$-aminobutyric acid (GABA). An old antler extract (OAE; 5%, w/v) obtained using a herbal extractor showed the highest contents of solids (1.75%) and proteins ($980{\mu}g/mL$). It also showed the highest total amino acid contents of $13,659{\mu}g/mL$, with glycine, proline, and glutamine concentrations of 1,945, 3,405, and $1,641{\mu}g/mL$, respectively. For the over-production of GABA, OAE was fermented with Lactobacillus plantarum EJ2014 in the presence of 0.5%, 1.5% glucose, and 3.5% MSG at $30^{\circ}C$ for 7 days. The fermented OAE showed high viable cell count of $2.0{\times}10^8CFU/mL$, pH of 6.56 and 0.77% acidity after 7 days. In particular, the acidity was greatly decreased by fermentation for 3 days, and 1.4% GABA was produced by the efficient conversion of the substrate, mono sodium glutamate.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.1
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• pp.127-131
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• 1998

The effect of extraction temperature ($60\~100^{\circ}C$) and pH ($2.0\~13.5$) on the yield and chemical compositions of crude porphyran from Porphyra Yezoensis was investigated. The yield and chemical compositions of crude porphyran were greatly affected by extraction pH and temperature. Yield was highest between pH $3\~4$ at all temperature ranges. Crude porphyran extracted in acidic conditions showed more sulfate and less protein content than extracted in neutral conditions, but molecular weights was decreased. Crude porphyran extracted in alkaline conditions showed low sulfate and high protein content. For high yield and low molecular weight, acidic condition, particulary pH $3\~4$, was effective. But in order to avoid molecular weight degradation, neutral conditions were effective.

• Food Science and Preservation
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• v.12 no.4
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• pp.305-309
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• 2005

To investigate the effects of cinnamon extracts pretreatment and packaging on the quality of dried persimmon. Dried persimmon were storaged during 100 days at room temperature($15^{\circ}C$) after dipping in cinnamon extracts and then packaging with LDPE(low density polyethylene) and Nylon/LDPE pouch Weight loss of dried persimmon treated with K-V was maintained $20.2\%$ lower than control. Firmness was $87\%$, browning was $56\%$ lower. Skin color change was 0.80 point, which was the lowest changes comparing with others. As a result, dipping in cinnamon extracts and packaging Nylon/LDPE film were good for maintaining dried qualities.