• Progress in Superconductivity
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• 제13권2호
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• pp.111-116
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• 2011

Since superconducting wires have no resistance, electromagnets based on the superconducting wires produce no resistive heating with DC current as long as the current does not exceed the critical current of the wire. However, unlike resistive wires, superconducting wires exhibit AC heat loss. Embedding fine superconducting filaments inside copper matrix can reduce this AC loss to an acceptable level and opens the way to AC-capable superconducting coils. Here, we introduce an easy and accurate method to measure AC heat loss from sample superconducting coils by measuring changes in the rate of gas helium outflow from the liquid helium dewar in which the sample coil is placed. This method provides accurate information on total heat loss of a superconducting coil without any size limit, as long as the coil can fit inside the liquid helium dewar. With this method, we have evaluated AC heat loss of two superconducting solenoids, a 180-turn solid NbTi wire with 0.127 mm diameter (NbTi coil) and a 100-turn filamented wire with 1.4 mm diameter where 7 NbTi filaments were embedded in a copper matrix with copper to NbTi ratio of 6.7:1 (NbTi-Cu coil). Both coils were wound on 15 mm-diameter G-10 epoxy tubes. The AC heat losses of the NbTi and NbTi-Cu coils were evaluated as $53{\pm}4.7\;{\mu}W/A^2Hzcm^3$ and $0.67{\pm}0.16\;{\mu}W/A^2Hzcm^3$, respectively.

• 대한기계학회논문집A
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• 제32권12호
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• pp.1047-1054
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• 2008

In this paper, the molecular dynamics (MD) simulations are performed with single-crystal copper blocks under simple shear and simple tension to investigate the effect of size and crystal orientation. There are many variances to give influences such as deformation path, temperature, specimen size and crystal orientation. Among them, the crystal orientation has a primary influence on the volume averaged stress. The numerical results show that the volume averaged shear stress decreases as the specimen size increases and as the crystal orientation changes from single to octal. Furthermore, the Schmid factor and yield stress for crystal orientation are evaluated by using the MD simulation on the standard triangle of stereographic projection.

• 대한금속재료학회지
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• 제48권8호
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• pp.730-740
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• 2010

Aluminum, magnesium, titanium and high Mn steel are difficult to use in electron backscatter diffraction (EBSD) sample preparation due to the formation of an oxidation layer under conventional polishing. Alcohol-based polishing with colloidal silica suspension was introduced for these delicate samples. A hard particle-embedded sample was analyzed successfully using mechanical polishing. Ion-milling was effective in removing oxidized, deformed and transformed layers after mechanical polishing and was able to reduce artifacts significantly. The microstructure of a cross-section of a thin copper film was evaluated by attachment of a dummy to the film for mechanical polishing.

• 마이크로전자및패키징학회지
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• 제17권4호
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• pp.95-100
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• 2010

LED (Light Emitting Diode)는 인가된 에너지 대비 15%가 빛으로, 나머지 85%가 열로 변환되는 것은 이미 잘 알려져 있다. 최근 LED칩 용량이 증가함에 따라서 LED칩으로부터 방출되는 열은 더욱 증가하게 되고 이는 LED 제품의 성능저하와 수명단축에 직접적인 영향을 미친다. 따라서, 산업계에서는 고출력 LED 칩에서 발생하는 열을 제어하기 위해 제품설계구조 연구가 진행 중에 있으며 또한, 부가적으로, 기존의 알루미늄, 접착제 및 구리를 사용하는 MCL(Metal Clad Laminate)구조에서 저가형 FR4 및 구리를 사용하는 CCL (Copper Clad Laminate)로 변경하여 원가절감을 하고자 하는 대체 소재연구가 진행되고 있다. 본 연구에서는 저가형 CCL에 열방출 극대화를 위하여 열비아(thermal via)를 디자인별로 형성한 후 1 W급 LED 칩을 실장하여 열저항(thermal resistance) 변화를 분석하였으며, 최적의 열방출을 위한 열비아 구조를 제안하고자 하였다.

• Journal of Photoscience
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• 제9권2호
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• pp.430-432
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• 2002

The changes in expression of copper-zinc superoxide dismutase (CuZn-SOD), manganese superoxide dismutase (Mn-SOD) and glutathione peroxidase (GPX) in light-damaged rat retinas were examined. Sprague-Dawley rats (male, 6-weeks-old) were maintained on a cyclic photoperiod (12 hours light and 12 hours darkness) for 2 weeks. The illumination intensity during the light period was 80 lux. To induce light damage to the retina, a high-intensity illumination (3000-lux) was applied to the animals for 24 hours. After light exposure, the animals were returned to cyclic lighting. Eyes were enucleated 12 and 24 hours after light exposure started or 1,3, and 7 days after light exposure ended. Eyes were fixed and embedded in paraffin wax. Tissues were cut into 4${\mu}{\textrm}{m}$-thick sections. Sections were immunostained using antibody against CuZn-SOD, Mn-SOD, GPX and 8-hydroxy-deoxyguanocine (8-OHdG) as oxidative stress marker. 8-OHdG was observed in the outer nuclear layer (ONL) and retinal pigment epithelium (RPE) during light exposure. In light-damaged retinas CuZn-SOD labeling was up regulated in the ONL and RPE. Mn-SOD labeling was up regulated in rod inner segments (RIS) during light exposure and that in the RPE was up regulated after exposure. GPX labeling was observed in rod outer segments (ROS) during light exposure. GPX labeling was also observed in the RPE during and after light exposure. All three enzymes were observed in the outer retina, which suffered light damage, but occurred in defferent layers except within the RPE, in which case all three were expressed. These enzymes may play complementary roles as protective factors in light-damaged retinas.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.421-421
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• 2008

Generally, the polymer thick-film resistors for embedded organic or hybrid substrate are patterned by screen printing so that the accuracy of resistor pattern is not good and the tolerance of resistance is too high(${\pm}$20~30%). To reform these demerits, a method using Fodel$^{(R)}$ technology, which is the patterning method using a photosensitive resin to be developable by aqueous alkali-solution as a base polymer for thick-film pastes, was recently incorporated for the patterning of thermosetting thick-film resistor paste. Alkali-solution developable photosensitive resin system has a merit that the precise patterns can be obtained by UV exposure and aqueous development, so the essential point is to get the composition similar to PSR(photo solder resist) used for PCB process. In present research, we made the photopatternable resistor pastes using 8 kinds of epoxy acrylates and a conductive carbonblack (CDX-7055 Ultra), evaluated their developing performance, and then measured the resistance after final curing. To become developable by alkali-solution, epoxy acrylate oligomers with carboxyl group were prepared. Test coupons were fabricated by patterning copper foil on FR-4 CCL board, plating Ni/Au on the patterned copper electrode, applying the resistor paste on the board, exposing the applied paste to UV through Cr mask with resistor patterns, developing the exposed paste with aqueous alkali-solution (1wt% $Na_2CO_3$), drying the patterned paste at $80^{\circ}C$ oven, and then curing it at $200^{\circ}C$ during 1 hour. As a result, some test compositions couldn't be developed according to the kind of oligomer and, in the developed compositions, the measured resistance showed different results depending on the paste compositions though they had the same amount of carbonblack.

• 한국재료학회지
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• 제28권1호
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• pp.32-37
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• 2018

We report on the efficient detection of NO gas by an all-oxide semiconductor p-n heterojunction diode structure comprised of n-type zinc oxide (ZnO) nanorods embedded in p-type copper oxide (CuO) thin film. The CuO thin film/ZnO nanorod heterostructure was fabricated by directly sputtering CuO thin film onto a vertically aligned ZnO nanorod array synthesized via a hydrothemal method. The transport behavior and NO gas sensing properties of the fabricated CuO thin film/ZnO nanorod heterostructure were charcterized and revealed that the oxide semiconductor heterojunction exhibited a definite rectifying diode-like behavior at various temperatures ranging from room temperature to $250^{\circ}C$. The NO gas sensing experiment indicated that the CuO thin film/ZnO nanorod heterostructure had a good sensing performance for the efficient detection of NO gas in the range of 2-14 ppm under the conditions of an applied bias of 2 V and a comparatively low operating temperature of $150^{\circ}C$. The NO gas sensing process in the CuO/ZnO p-n heterostructure is discussed in terms of the electronic band structure.

• 공업화학
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• 제10권6호
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• pp.902-906
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• 1999

메틸셀루로스를 호스트고분자로 하고 copper(II) percolate를 산화제로 사용하여 기상상태에서 직접중합방법으로 전도성 복합필름을 합성하였다. 필름으로서 우수한 성형성과 기계강도를 갖고 있는 메틸셀루로즈는 PVA와 키토산과는 달리 피롤에 대하여 높은 친화성을 나타내어서 기상중합시 호스트고분자로 적합하였다. 기상중합법으로 합성된 폴리피롤은 복합재료 내에서 전도성네트워크를 형성하여 전도성 복합필름의 전기전도도는 $10^{-1}-10^{-7}S/cm$를 나타내었다. 피롤이 호스트고분자 내에서의 폴리피롤로 중합이 되는 정도를 UV-vis분광계로 확인하였다. 전도성 복합필름의 전기전도도와 기계강도는 산화제의 농도와 합성시간에 크게 의존하였다. TGA분석결과는 호스트고분자 내에 형성된 폴리피롤은 복합재료의 열적 안정성에 영향을 미치지 않는다. 전자현미경 분석결과 폴리피롤이 복합재료 내에 균일하게 침투하여 분산되어 있음을 나타내었다. DMA를 사용하여 폴리피롤과 호스트고분자와의 상용성을 조사하였으며 dynamic mechanical analysis(DMA) 분석결과 복합재료 내에서 폴리피롤의 함량이 증가되면서 상용성이 점진적으로 저하되었다.

• 한국주조공학회지
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• 제24권5호
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• pp.281-289
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• 2004

The present study focused on the estimation of the interfacial heat transfer coefficient as a function of the surface temperature of the aluminum casting at the mold/casting interface to investigate the effects of superheat and coating layer. The casting experiments of aluminum into a cylindrical copper mold were systematically conducted to obtain the thermal history during solidification. The thermal history recorded by four thermocouples embedded both in the mold and the casting was used to solve the inverse heat conduction problem using Beck's method. The effects of superheat and coating on the interfacial heat transfer coefficient in the liquid state, during the solidification, and in the solid state were comparatively discussed. In the liquid state, the interfacial heat transfer coefficient is thought to be affected by the roughness of the mold, the wettability of the casting on the mold surface, and the thermophysical properties of the coating layer. When the solidification begins, the air gap forms between the casting and the mold, and the interfacial heat transfer coefficient becomes a function of the air gap as well as surface roughness and the superheat. In the solid phase, it depends only upon the thermal conductivity and the thickness of the air gap. The coating layer reduces seriously the interfacial heat transfer coefficient in the liquid state and during the solidification.

• Membrane and Water Treatment
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• 제9권2호
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• pp.95-104
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• 2018

Copper pollution around the world has caused serious public health problems recently. The heavy metal adsorption on traditional membranes from wastewater is limited by material properties. Different adsorptive materials are embedded in the membrane matrix and act as the adsorbent for the heavy metal. The carbonized leaf powder has been proven as an effective adsorbent material in removing aqueous Cu(II) because of its relative high specific surface area and inherent beneficial groups such as amine, carboxyl and phosphate after carbonization process. Factors affecting the adsorption of Cu(II) include: adsorbent dosage, initial Cu(II) concentration, solution pH, temperature and duration. The kinetics data fit well with the pseudo-first order kinetics and the pseudo-second order kinetics model. The thermodynamic behavior reveals the endothermic and spontaneous nature of the adsorption. The adsorption isotherm curve fits Sips model well, and the adsorption capacity was determined at 61.77 mg/g. Based on D-R model, the adsorption was predominated by the form of physical adsorption under lower temperatures, while the increased temperature motivated the form of chemical adsorption such as ion-exchange reaction. According to the analysis towards the mechanism, the chemical adsorption process occurs mainly among amine, carbonate, phosphate and copper ions or other surface adsorption. This hypothesis is confirmed by FT-IR test and XRD spectra as well as the predicted parameters calculated based on D-R model.