• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.240-241
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• 2005

비 직선적 정(+) 저항온도계수 특성을 갖는 PTC thermistor는 전이온도(큐리점) 부근에서 온도변화에 대하여 극히 큰 저항 값의 변화를 나타내는 산화물계반도체 저항기(또는 발열체)로써, 일반적으로 반도체의 온도-저항 특성과 같이 상온영역에서 온도의 상승과 함께 부성저항 특성을 나타내다가 온도가 점점 증가하여 큐리점 부근에 도달하면 저항이 급격히 증가하는 독특한 특성을 갖는다. Perovskite 구조의 $BaTiO_3$를 주성분으로 미량의 Dopant를 첨가하여 도전성을 갖게 한 N형 반도체의 일종으로 저항-온도 특성 전류-전압 특성, 전류감쇄 특성 등을 이용하여 과전류 보호회로, 히터, TV 소자회로(degausser), 모터기동회로, 온도센서, 정온발열기기 등으로 널리 사용된다. 본 연구는 큐리점 부근의 급격한 저항변화 현상과 결정입계의 전위장벽 형성 및 그에 따른 정온발열 기능의 상관성으로부터 그 응용성을 조사하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.4
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• pp.373-377
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• 2004

We have investigated the electrical characterization of metal-oxide-semiconductor (MOS) capacitors formed on the inductively coupled plasma (ICP) etch-damaged both n- and p-type 4H-SiC. We found that there was an effect of a sacrificial oxidation treatment on the etch-damaged surfaces. Current-voltage and capacitance-voltage measurements of these MOS capacitors were used and referenced to those of prepared control samples without etch damage. It has been found that a sacrificial oxidation treatment can improve the electrical characteristics of MOS capacitors on etch-damaged 4H-SiC since the effective interface density and fixed oxide charges of etch-damaged samples have been found to increase while the breakdown field strength of the oxide decreased and the barrier height at the SiC-SiO$_2$ interface decreased for MOS capacitors on etch-damaged surfaces.

• Journal of Periodontal and Implant Science
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• v.29 no.3
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• pp.483-509
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• 1999

Biodegradable barrier membrane has been demonstrated to have guided bone regeneration capacity on the animal study. The purpose of this study is to evaluate the effects of cultured calvarial cell inoculated on the biodegradable barrier membrane for the regeneration of the artificial bone defect. In this experiment 35 Sprague-Dawley male rats(mean BW 150gm) were used. 30 rats were divided into 3 groups. In group I, defects were covered periosteum without membrane. In group II, defects were repaired using biodegradable barrier membrane. In group III, the defects were repaired using biodegradable barrier membrane seeded with cultured calvarial cell. Every surgical procedure were performed under the general anesthesia by using with intravenous injection of Pentobarbital sodium(30mg/Kg). After anesthesia, 5 rats were sacrificed by decapitation to obtain the calvaria for bone cell culture. Calvarial cells were cultured with Dulbecco's Modified Essential Medium contained with 10% Fetal Bovine Serum under the conventional conditions. The number of cell inoculated on the membrane were $1{\times}10^6$ Cells/ml. The membrane were inserted on the artificial bone defect after 3 days of culture. A single 3-mm diameter full-thickness artificial calvarial defect was made in each animal by using with bone trephine drill. After the every surgical intervention of animal, all of the animals were sacrificed at 1, 2, 3 weeks after surgery by using of perfusion technique. For obtaining histological section, tissues were fixed in 2.5% Glutaraldehyde (0.1M cacodylate buffer, pH 7.2) and Karnovsky's fixative solution, and decalcified with 0.1M disodium ethylene diaminetetraacetate for 3 weeks. Tissue embeding was performed in paraffin and cut parallel to the surface of calvaria. Section in 7${\mu}m$ thickness of tissue was done and stained with Hematoxylin-Eosin. All the specimens were observed under the light microscopy. The following results were obtained. 1 . During the whole period of experiment, fibrous connective tissue was revealed at 1week after surgery which meant rapid soft tissue recovery. The healing rate of defected area into new bone formation of the test group was observed more rapid tendency than other two groups. 2 . The sequence of healing rate of bone defected area was as follows ； test group, positive control, negative control group. 3 . During the experiment, an osteoclastic cell around preexisted bone was not found. New bone formation was originated from the periphery of the remaing bone wall, and gradually extended into central portion of the bone defect. 4 . The biodegradable barrier membrane was observed favorable biocompatibility during this experimental period without any other noticeable foreign body reaction. And mineralization in the newly formed osteoid tissue revealed relatively more rapid than other group since early stage of the healing process. Conclusively, the cultured bone cell inoculated onto the biodegradable barrier membrane may have an important role of regeneration of artificial bone defects of alveolar bone. This study thus demonstrates a tissue-engineering the approach to the repair of bone defects, which may have clinical applications in clinical fields of the dentistry including periodontics.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.1
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• pp.85-92
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• 2005

Reconstruction of defect in the anterior part of the maxilla to enable implant placement or prothesis is a complicated treatment due to the anatomical position and lack of soft tissues. Two cases are presented in which autogenous iliac PMCB(particulate marrow and cancellous bone) with titanium mesh were used for premaxilla reconstruction and alveolar bone repair of the anterior maxillas prior to denture and implants fixation respectively. Cancellous bone from the anterior iliac crest was compressed and placed against a titanium mesh fixed to the bone of palate in a patient with severe defect of the anterior maxilla. There were no problem in the healing, and the anterior maxillas of two patients had increased height and width during the initial healing and remodeling. The clinical reports describe the use of titanium mesh for reconstruction of premaxilla. Autogenous bone grafts were harvested from the iliac crest and were loaded on a titanium mesh that were left in the patient's maxilla for 6 months before they were removed respectively. The radiographic analysis demonstrated that a 10mm vertical ridge augmentation had been achieved. In guided bone regeneration, the quantity of bone regenerated under the barrier has been demonstrated to be directly related to the amount of the space under the membrane. This space can diminish as a result of membrane collapse. To avoid this problem which involved the use of a titanium mesh barrier to protect the regenerating tissues and to achieve a rigid fixation of the bone segments, were used in association with autologous bone in 2 cases. The aim of this study was to evaluate the capability of a configured titanium mesh to serve as a mechanical and biologic device for restoring a vertically defected premaxilla.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.1
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• pp.88-93
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• 2024

To evaluate the possibility as a multi-level memory medium for the Ge₂Sb₂Te₅/TiN/W-doped Ge₂Sb₂Te₅ cell structure, the crystallization rate and stabilization characteristics according to voltage (V)- and current (I)- pulse sweeping were investigated. In the cell structures prepared by a magnetron sputtering system on a p-type Si (100) substrate, the Ge₂Sb₂Te₅ and W-doped Ge₂Sb₂Te₅ thin films were separated by a barrier metal, TiN, and the individual thicknesses were varied, but the total thickness was fixed at 200 nm. All cell structures exhibited relatively stable multi-level states of high-middle-low resistance (HR-MR-LR), which guarantee the reliability of the multilevel phase-change random access memory (PRAM). The amorphousto-multilevel crystallization rate was evaluated from a graph of resistance (R) vs. pulse duration (T) obtained by the nanoscaled pulse sweeping at a fixed applied voltage (12 V). For all structures, the phase-change rates of HR→MR and MR→LR were estimated to be approximately t<20 ns and t<40 ns, respectively, and the states were relatively stable. We believe that the doublestack structure of an appropriate Ge-Sb-Te film separated by barrier metal (TiN) can be optimized for high-speed and stable multilevel PRAM.

• Applied Microscopy
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• v.18 no.2
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• pp.177-186
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• 1988

Degeneration of the axon terminals of mamillo-thalamic tract following the electrical coagulation of mamillary body is well known. In this study, the author investigated the ultrastructural alterations of neuropil components, initiated by terminal degenerations. Rats weighing approximately 250 gm were fixed on the stereotaxic instrument(David Kopf Inc., Heavy duty model), and NE 300 active electrode(Rhodes Med. Instr. Inc.) was introduced to the mamillary position of anterior 3.8 mm, lateral 0.5 mm, height 3.8 mm and lateral angle of $23^{\circ}$ according to De Groot's Atlas. Electric current of 20 mA was applied during 1 minute between active and inactive electrodes with Radio Frequency Lesion Generator(RFG 4, Radionics Inc.). Two hours, 2 days, 1 week and 2 weeks following the electrical coagulation of mamillary body, ipsilateral anterior thalamic nucleus was fixed in 1% glutaraldehyde-l% paraformaldehyde and 2% osmium tetroxide, embedded in Araldite mixture, cutted with LKB ultra tome V, stained with uranyl acetate-lead citrate and observed with JEOL 100 CX electron microscope. Observed results were as follows; 1. Degenerated mamillo-thalamic synapses were observed to form asymmetric axospinous or axo-dendritic types. 2. Terminal degeneration was not easily discernible at 2 hours interval after mamillary lesion, but following 2 days the terminal degeneration was apparent. 3. Postsynaptic spines, dendrites and even their cell bodies show edematic changes caused by the degeneration of postsynaptic counterpart. 4. Astrocytic territories, including perivascular processes forming glial limitans of blood-brain barrier, exhibit remarkable expansion. 5. Oligoglia and astroglia are actively engaged in the removal of degenerated elements. 6. Active forms of microglia were increased. 7. The observed results may represent typical ultrastructural alteration pattern within neuropil following the degeneration of certain input axon terminals.

• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.102-109
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• 2023

Following the accident at Fukushima, the true impact of multi-unit accidents came to light. Accordingly, research related to multi-unit accident effect analysis, risk evaluation, and accident prevention/prevention technology has been conducted. Specific examples are mobile/fixed equipment such as multi-barrier accident coping strategy (MACST) and diverse and flexible coping strategies (FLEX), which have been introduced and installed in multi-units for preventing and mitigating multi-unit accidents. These strategies are useful for enhancing the safety of nuclear power plants (NPPs); however, a more efficient strategy is required in terms of the costs of physical and human resources. To effectively and efficiently mitigate an increase in multi-unit accidents, it is necessary to not only to utilize mobile/fixed equipment but to also use crosstie options with resources that already exist at NPPs. Therefore, we analyzed the current international and domestic status of crosstie systems technology and propose a method to evaluate feasibility alongside risk based on a multi-unit probabilistic safety assessment (PSA). To analyze the international and domestic status of crosstie systems technology, actual cases and related research were studied, and a list of potential crosstie safety resources was derived. Additionally, a case study was performed on crosstie cases of two systems within the assumed six units on-site under a multi-unit accident, and a multi-unit PSA-based risk evaluation method is proposed.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.3
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• pp.302-308
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• 2005

Nitrate is one of common contaminants frequently found in the bank filtrate. Biological autotrophic denitrification into permeable reactive barrier(PRB) system to reduce nitrate concentration in bank filtrate was implanted. The objectives of research are to investigate effect of inoculation, to evaluate alternative alkalinity sources, and to determine effect of hydraulic characteristics, such as retention time, flow rate on the performance of semi-pilot PRB system. Semi-pilot scale biological PRB system was installed using elemental sulfur and limestone/oyster shell as reactive materials near Nakdong River in Kyoungnam province, Korea. Nitrate concentration in bank filtrate was reduced by indigenous microorganisms in oyster shell as welt as by inoculating microorganisms isolated from the sludge of an anaerobic digester in a wastewater treatment plant. Oyster shell as well as limestone can be used as an alkalinity source. However, oyster shell resulted in suspended solids of effluent. As the flow rate in the system increased from 66 to 132 mL/min and accordingly the residence time decreased from 15 to 7.5 hours, nitrate concentration in effluent increased and nitrate removal efficiencies decreased from 75 to 58% at the fixed thickness of 80 cm of PRB.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.266-270
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• 2011

This paper suggest tungsten (W)-carbon (C)-nitrogen (N) thin films for diffusion barrier that W is main material and C and N are additives. W-C-N thin films are deposited with fixed rates of W and C but with a variation of $N_2$ gas flow and W-C-N thin films are heated at $600^{\circ}C$. From the experimental results, the variation of elastoplastic region for W-C-N thin film measured by tribological property is larger than that of elastic region with a variation of $N_2$ gas flow. These results show that the $N_2$ gas flow is more directly related with the elastoplastic region of W-C-N thin film. Nanoindenting test executed 16 times consecutively and we got the stress-strain curve graphs and hardness datas at each sample. Through the stress-strain curve graphs, the standard diviation of stress-strain curve for $N_2$ gas flow rate of 2.0 sccm is smaller than that of 0, 0.5, 1.5 sccm. Consequently, the physical stability of W-C-N thin film depends on the flow rate of $N_2$ gas.

• Applied Microscopy
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• v.29 no.1
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• pp.11-23
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• 1999

Ultrastructure of the ependymal cells of X-irradiated rats on their head were studied. Rats weighing $200\sim250gm$ were X-irradiated on their head and neck areas. Total exposures were 3,000 rads or 6,000 rads depending on experimental groups. And irradiated rats were sacrificed on 6 hours, 2 days and 6 days following the radiation exposures. Animals were perfused through the heart with 1% glutaraldehyde-1% paraformaldehyde solution, under ether-anesthesia. The tissues from the wall of lateral ventricles were fixed in the 2% osmium tetroxide solution. The results observed with electron microscope were as follow: 1. In 6 hours group, many ependymal cells were swelled, luminal portions of cytoplasms of some cells protruded into the ventricular lumen, and many cilia were lost or irregularly altered. 2. In 2 days group, ependymal cells were swelled more severely and subependymal edema were pronounced. 3. Protruded cytoplasm contained usually basal bodies of cilia, groups of mitochondria, endoplasmic reticula , etc. 4. Following X-irradiations, some protruded masses contained neural elements including the axon terminals with dense core vesicles. Axons and axon terminals were also found in the enlarged intercellular spaces among ependymal cells. From the above results, the heavy irradiation on the head area of the rat induced alteration of the ependymal cells lining the lateral ventricle. Hence the ependymal functions of selective barrier, protective barrier, and metabolic barrier could be altered following X-irradiation on the head.