• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Annals of Clinical Neurophysiology
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• v.11 no.2
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• pp.41-47
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• 2009

Background: Discogenic pain can develop into chronic low back pain that is very difficult to treat effectively, because the pathogenesis of the disease still remains controversial. To clarify the pathogenesis, numerous animal models of intervertebral disc degeneration have been proposed in the literature, each with attendant advantages and disadvantages. The aim of this study was to determine the most efficacious method and dose of complete Freund's adjuvant (CFA) injection into intervertebral disc to develop a discogenic pain in a rat. Methods: CFA was injected into the L5-L6 or L4-L5 disc of male Sprague-Dawley rats in various conditions including a dose of CFA (10, 20, or 50 uL), drilling, injection site sealing using cyanoacrylate, and injection velocity. Sham animals were subjected to the same procedure, except for the CFA injection. Mechanical and heat allodynia were serially measured at both hindpaws until 8 weeks post-operatively. Serial MRI analyses were performed to observe degenerative changes of the discs. In addition, CGRP & Substance P-immunoreactivities (ir) in the superficial dorsal horn were evaluated at 4 weeks using immunohistochemistry. Results: Each condition provoked various problems such as development of hindpaw paralysis, CFA leakage, and no pain development. Mid-sagittal T2 MRI revealed no significant degenerative changes in the CFA injected disc. The CGRP-ir of the bilateral superficial dorsal horns at the level of L5-L6 was significantly increased in the CFA group. Conclusions: A total of 10 uL CFA injection into L5-L6 disc for a period of 10 minutes using a 26-gauge needle without drilling was the most efficacious way to develop discogenic pain animal model.

• Journal of Conservation Science
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• v.32 no.3
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• pp.425-436
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• 2016

The Yakhyeon catholic church (Historic Site No. 252 in Korea) that was constructed in 1892 has been the first western brick structure to ever have existed and one of the most important historical materials in the Korean modern architecture. After a fire had broken out at the catholic church in 1998, the stained glass on the back wall, the slab glass (dalle de verre) introduced by Lee Nam Guy in 1974, was repaired in 1999 because of singe scorch and water leakage. An analysis of the coloration elements showed that yellow, red and green included Zn, K and Cd, respectively. The glass of red contained Se, dark green contained Mn and Cr, and blue contained Pb and S. According to material analysis, the masonry joint was identified dolomite ($CaMg(CO_3)_2$) and calcite ($CaCO_3$), which was observed plate, columnar, rhombic and square of crystalline particles. Meanwhile, ultrasonic velocity in the stained glass recorded low speed in the middle and lower right of the window (an average of 4,130 m/s). And the joint was measured the lowest physical properties of the top left and middle of the window (an average of 2,053 m/s). This study have showed that extensive physical damage was founded to the left and middle rather than the right side. In this respect, more research in needed to conserve the correlation between color and physical properties.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.339-345
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• 2012

RMembrane LNG storage tanks have been recently investigated to replace full-containment LNG storage tanks because of safety and cost aspects. Quantitative Risk Analysis (QRA) and Finite Element Method (FEM) were used to evaluate safety of membrane LNG storage tanks. In this study, structural safety evaluation results via FEM analysis showed that both membrane type and full-containment type cryogenic LNG storage tanks with 140,000 $m^3$ capacity were equivalently safe in terms of strength safety and leakage safety of a storage tank system. Also, Fault Tree Analysis (FTA) was used to improve the safety of membrane LNG storage tanks and membrane LNG tanks were modified by adding three safety equipments: impact absorber structure for the low part of the membrane, the secondary barrier to diminish the thermal stress of the corner part of the outer tank, and a pump catcher in case of falling of a pump. Consequently, the safety of the modified membrane LNG storage tanks were proved to be equivalent to that of full-containment LNG storage tanks.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.13 no.1
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• pp.57-68
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• 2010

The purpose of this study is to analyze the characteristics of environment-friendliness of waterproof materials based on comprehensive experiments on waterproofness in terms of coefficients of permeability, harmfulness of waterproof materials and fish toxicity of Oryzias latipes mortality to verify eco-toxicity of each method of construction and waterproof material, which are to be applied by taking eco-toxicity into account when building ecological flows in upper areas on natural and artificial grounds. As a result, the following conclusions have been reached in this study: 1. In regard of the harmfulness analyzed, each material showed a different result of analytical value in each lab tank. Compared to input water, pH, COD, SS, T-P, and T-N values increased a little, but DO value decreased. The value of turbidity analyzed independent of the water quality standard of aquatic ecosystem set forth by the Ministry of Environment increased a little compared to the value in input water. 2. In the experiment of fish toxicity, compacted quicklime, cement fluid waterproof material, cement mortar waterproof material and bentonite powder were found to have 100% of fish mortality, respectively, and membrane waterproof material showed 83.3% of mortality, indicating strong fish toxicity. Improved asphalt sheet (63.3%) and synthetic rubber sheet (53.3%) were analyzed to have medium fish toxicity, while bentonite sheet (6.7%), Hwang-toh (6.7%) and clay (3.3%) showed relatively lower mortality and fish toxicity. 3. Regarding the analysis on waterproofness in terms of the coefficient of permeability of each waterproof material, improved asphalt sheet, synthetic rubber sheet, membrane waterproof material, cement fluid and mortar waterproof material and bentonite sheet were found impervious in case no leakage takes place in construction. Bentonite powder was found practically impervious based on the analytical results from the experiment done in compliance with weight ratios. So were the clay and Hwang-toh from the experimental results. To sum up such results as found in the experiment mentioned so far, the values of harmfulness and waterproofness analyzed were different in each lab tank, but there was absolutely little correlation with the mortality gained from the experiment on fish toxicity. In the experiment of fish toxicity, environment-friendly waterproof materials were analyzed, and it was found that clay, Hwang-toh and bentonite sheet are highly environment-friendly. In contrast, synthetic rubber and improved asphalt sheets were found to have medium-level environment-friendliness. Also, membrane water-proof materials, compacted quicklime, cement fluid and mortar waterproof material and bentonite powder were analyzed to have low environment-friendliness.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.14-18
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• 2018

Generally. the Ohmic's law is an important factor to increase the conductivity in a micro device. So it is also known that the Ohmic contact in a semiconductor device is import. The PN junction as a structure of semiconductor involves the depletion layer, and this depletion layer induces the non linear electrical properties and also makes the Schottky contact as an intrinsic characteristics of semiconductor. To research the conduction effect of insulators in the semiconductor device, $SiO_2$ thin film and $V_2O_5/SiO_2$ thin film were researched by using the current-voltage system. In the nano electro-magnetic system, the $SiO_2$ thin film as a insulator had the non linear Schottky contact, and the as deposited $V_2O_5$ thin film had the linear Ohmic contact owing to the $SiO_2$ thin film with superior insulator's properties, which decreases the leakage current. In the positive voltage, the capacitance of $SiO_2$ thin film was very low, but that of $V_2O_5$ thin film increased with increasing the voltage. In the normal electric field system, it was confirmed that the conductivity of $V_2O_5$ thin film was increased by the effect of $SiO_2$ thin film. It was confirmed that the Schottky contact of semiconductors enhanced the performance of electrical properties to increased the conductivity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.222-227
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• 2020

Pb(Zr,Ti)O₃(denoted as PZT) in the perovskite phase is used as a dielectric, piezoelectric, and super appetizer material owing to its ferroelectric properties. A PZT film was formed by an RF magnetron sputtering process by preparing a target composed of Pb_1.3(Zr_0.52Ti_0.48)O₃. The PZT film was formed by dividing the material into a mono-layer PZT produced continuously with the same sputtering power and a bi-layer PZT produced with two-stage sputtering power. The bi-layer PZT consisted of a lower layer produced under low-power sputtering conditions and an upper layer produced under the same conditions as the mono-layer PZT. XRD revealed small amounts of pyrochlore phase in the mono-layer PZT, but only the perovskite phase was detected in the bi-layer PZT. SEM and AFM revealed the upper part of the bi-layer PZT to be more compact and smooth. Moreover, the bi-layered PZT showed superior symmetry polarization and a significantly reduced leakage current of less than 1×10-5 A/cm². This phenomenon observed in bi-layer PZT was attributed to the induction of growth into a pure perovskite phase by suppressing the formation of a pyrochlore phase in the upper PZT layer where the densely formed lower PZT layer was produced sequentially.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.1-7
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• 2018

The gases emitted from internal combustion engines using fossil fuels are causing many social problems, such as environmental pollution, global warming, and adverse health effects on the human body. In recent years, the demand for renewable energy has increased, and government policy support and research and development are also active. In the collecting part of a solar energy system, which is widely used at home, propylene glycol (PG) (anti-freeze), as a heating medium, is mixed with water at a fixed value of 50%, and the heat is transferred to the collecting part at subzero temperatures. On the other hand, when leakage occurs in the heat medium in the heat collecting part, supplemental water is supplied to the solar heat collecting part due to the characteristics of the solar heat system, so that the concentration of antifreeze in the replenishing water becomes low. As a result, the temperature of the solar heat collecting part is lowered resulting in a frost wave, which causes economic damage. The purpose of this study was to develop a device capable of controlling the antifreeze concentration automatically in response to a temperature drop to prevent freezing of the heat collecting part generated in the solar energy system. The electrical conductivity of the H2O component was larger than that of PG, and the resistance increased with decreasing temperature. The PG concentration control values of 40, 50, and 60% should be controlled through calibration with a PG concentration of 39.6, 50.7, and 60.1%.

• Korean Journal of Bronchoesophagology
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• v.5 no.2
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• pp.130-137
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• 1999

Background and Objectives : Provox, a recently developed tracheoesophageal prosthesis, had been widely used for voice rehabilitation after total laryngectomy for its low resistance and easiness of speech ability. But, long-term use of Provox resulted in many complications and resulted in cessation of Provox as a primary method of vocal rehabilitation. The aim of this study is to report Provox-related problems and the long-term results of Provox voice prosthesis. Materials and Methods : Medical records from patients who had undergone total laryngectomy with Provox insertion at seoul National University Hospital between January 1993 and December 1998 were reviewed retrospectively. Results : 36 patients had used 79 Provox voice prostheses during the observed period. The most common complication causing prosthesis change or removal was leakage and/or aspiration, followed by granulation formation, crusting and/or obstruction, and non-function. Median in situ lifetime of Provox was 274 days and 1-year-in situ rate was 31.0% Among 36 patients, 17 patients had undergone tracheoesophageal shunt closure at the last follow-up visit. 10 patients had complications but got along without further treatments, and 1 patient changed to Blom-Singer voice prosthesis. Only 8 patients experienced no complication, and 5 out of whom had several times of Provox change. Conclusion : long-term use of Provox resulted in discontinuation of its use due to complications in many cases. A better voice prosthesis with lower complication rate and longer in situ lifetime is needed.

• Polymer(Korea)
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• v.25 no.3
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• pp.399-405
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• 2001

Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]s were synthesized in 2:1, 1:1, and 1:2 mole ratios, and organic electroluminescent devices were fabricated using the copolymers. The opto-electrical properties of the copolymers were studied by PL, EL spectra, I-V, and V-L curves of the organic electroluminescent devices in conjunction with the energy band diagrams which were obtained from the cyclic voltammogram and the electronic absorption spectra. The LUMO energy level of P(OT/FPT)(1:1) is the lowest as -3.35 eV. In the copolymers P(OT/FPT)(2:1) and P(OT/FPT)(1:1) the ${\lambada}_{max}$ in the PL and EL spectra red-shifted as the mole ratio of fluorophenyl group increased while in P(OT/FPT)(1:2) it showed a blue-shift. This indicates that the backbone chain is twisted due to the steric hinderance of the fluorophenyl group leading to shorter ${\pi}$-conjugation length. P(OT/FPT)(1:1) showed the highest EL intensity and the highest power efficiency among the three copolymers. In P(OT/FPT)(1:2) the roughness of the film surface causes unusually high local leakage current leading to the low efficiency of electroluminescence.