• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.57-58
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}Na_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}Na_{1/2}TiO_3$. $Bi_{1/2}Na_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_{1/2}Na_{1/2}TiO_3$, $BaCO_3$, $TiO_2$ and $Y_2O_3$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.

• The Journal of the Acoustical Society of Korea
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• v.36 no.4
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• pp.254-260
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• 2017

The purpose of this study is to evaluate the sound absorption characteristics of a human body according to the amount of clothing worn by using reverberation method measurement method for developing standard test dummy, which can be used for testing absorption of occupied audience chair. Test method was based on the previous study (Conti et al., 2004), each experiment is conducted in the reverberation room and a subject wearing clothes is standing in that chamber. In this experiment, the sound absorption area of each frequency band according to the wearing of various material clothing was measured. As a result of measurements, the average sound absorption area of the whole frequency band was $0.25m^2-0.48m^2$ in case of a subject not wearing outer clothes, and $0.38m^2-0.98m^2$ in case of wearing of outerwear. Polyester tops by showing the maximum value, the highest characteristics in the 800 Hz to 1 kHz band among the rest of fiber materials. The outer jacket made of the wool and cotton materials show a higher absorption area as the frequency increases to the higher frequency band. The change of the sound absorption area according to the clothing amount was divided by the thermal resistance (clo) of the worn clothes and the weight per body surface area.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.249-263
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• 2017

The expansion behavior of inflatable steel pipe rockbolt shows geometric nonlinearity due to its ${\Omega}-shaped$ section. Previous studies on the anchoring behavior of inflatable steel pipe rockbolt were mainly performed using theoretical method. However, those studies oversimplified the actual behavior by assuming isotropic expansion of inflatable steel pipe rockbolt. In this study, the anchoring behavior of the inflatable steel pipe rockbolt were investigated by the numerical method considering the irregularity of pipe expansion and other influencing factors. The expansion of inflatable steel pipe rockbolt, the contact stress distribution and the change of the average contact stress and the contact area during installation were analyzed. The contact stresses were developed differently depending on the constitutive behavior of rocks. Small contact stresses occurred in steel pipes installed in elasto-plastic rock compared to steel pipes installed in elastic rock. Also, the anchoring behaviors of the inflatable steel pipe rockbolt were different according to the stiffness of the rock. The steel pipe was completely unfolded in the case of the stiffness smaller than 0.5 GPa, but it was not fully unfolded in the case of the stiffness larger than 0.5 GPa for the given analysis condition. When the steel pipe is completely unfolded, the contact stress increases as the rock stiffness increases. However, the contact stress decreases as the rock stiffness increases when the steel pipe is not fully expanded.

• Clean Technology
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• v.22 no.4
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• pp.308-315
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• 2016

$SiO_x/ZnO$ composites were prepared from sol-gel method for excellent cycle life characteristics. The composites were coated by PVC as a carbon precursor. ZnO removal to create a void space therein was able to buffer the volume change during charge and discharge. To determine the crystal structure and the shape of the synthesized composite, XRD, SEM, TEM analysis was performed. The carbon contents in the composites were confirmed by TGA. The pore structure and pore size distribution of the composite was measured with the BET specific surface area analysis and BJH pore size distribution. Enhanced electric conductivity by carbon addition was determined from powder resistance measurement. Electrochemical properties were measured with the AC impedance and the charge and discharge cycle life characteristics. When carbon was coated on the $SiO_x/ZnO$ sample, the electrical conductivity and the discharge capacity were increased. After removal of ZnO with HCl the surface area of the sample was increased, but the discharge capacity was decreased. $SiO_x/ZnO$ sample without acarbon coating showed very low discharge capacity, and after carbon coating the sample showed high discharge capacity. For cycle life characteristics, $C-SiO_x/ZnO$ composite (Zn : Si : C = 1 : 1 : 8) with a capacity of $815mAh\;g^{-1}$ at 50 cycle and 0.2 C has higher capacity than existing graphite-based anode materials.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.2
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• pp.143-166
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• 1999

The success of porcelain laminate veneer depends on the bond strength between tooth structure and ceramic restoration and the design of tooth preparation. In particular, incisal coverage and incisal finish line are the two most important factors in long-term fracture resistance. Although the majority of clinicians are practicing incisal coverage and there are various opinions on the geo-metrical ratio between the clinical crown length of the remaining tooth structure and the length of incisal extension in porcelain laminate veneer and the optimal incisal finish lines. scientific evidence still loaves much to be desired. The purpose of this study was to determine the effects of the amounts of incisal coverage and the types of incisal finish line on the stress distribution in maxillary anterior porcelain laminate veneers under two different loading conditions. Three-dimensional finite element models of a maxillary anterior porcelain veneer with differ-ent amounts of incisal coverage ; 0, 1, 2, and 3mm and different incisal finish lines feathered edge, incisal bevel, reverse bevel and lingual chamfer with various amounts of lingual extension were developed. 300N force was applied at the point 0.5mm cervical of the linguoincisal edge in two loading conditions ; A) 125 degrees, B) 132 degrees. Tensile and compressive stress in ceramic and shear stress in the resin cement layer were analyzed using three-dimensional finite element method. The results were as follows : 1. The types of incisal finish line had more influence on the stress distribution in porcelain laminate veneer than the amounts of incisal coverage. 2. In case of no incisal coverage, incisal beveled laminate exhibited more evenly distributed tensile stress than feathered edged laminate. And in case of incisal coverage, reverse beveled laminate and lingual chamfered laminate with 1mm lingual extension exhibited more evenly distributed tensile stress than lingual chamfered laminates with 2mm and 3mm lingual extension. 3. As long as the lingual chamfer goes, less tensile stress was found at the incisal edge, while much more tensile stress was found at the lingual margin area in proportion to the length of lingual extension. 4. Under 125 degree load, tensile stress in porcelain laminate veneer had increased compared with that under 132 degree load and the difference exhibited by the change of the amount of tooth support was larger. 5. The types of incisal finish line and the distance from the incisal finish line to the loading point had more influence on the shear stress distribution in the resin cement layer than the amounts of incisal coverage. In contrast loading condition had little influence.

• Korean Journal of Food Science and Technology
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• v.35 no.2
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• pp.217-221
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• 2003

Effect of direct addition of $CaCl_2$ into sodium alginate film-making solution and immersion of alginate films into $CaCl_2$ solutions on tensile strength (TS), percentage elongation at break (E), water vapor permeability (WVP), and water solubility (WS) of the films were investigated. TS of alginate films prepared by both methods increased. E of $CaCl_2-added$ films did not change significantly (P>0.05), whereas that of $CaCl_2-immersion$ films decreased significantly (p<0.05). WVP of films prepared by both methods decreased significantly, but the effect was more significant in the $CaCl_2-immersion$ films. Water resistance was not changed in the $CaCl_2-added$ films, whreras increased significantly in $CaCl_2-immersion$ films (p<0.05). Properties of alginate films depend on the concentration of $CaCl_2$ treatments in both methods, and they also depend on treatment time in the immersion method.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.587-594
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• 2005

The purpose of seismic design is to ensure the serviceability of buildings against earthquake, which might be occurred during the service life of buildings, and to minimize the loss of life by preventing their failure under strong earthquake. The lack resistance of walls resulting from a tendency toward high-rise apartment buildings with shear walls and use of piloti would lead to a concentration of inelastic behaviors in their weak story. In this study, the seismic performance of reinforced concrete shear wall buildings haying piloti was analyzed by using the evaluation techniques which was proposed by FEMA 273 and ATC-40. The results from comparison with these two techniques are summarized as follows.; The results of elastic analysis method for seismic performance evaluation show that the effect of piloti and building height decrease performance index. In case of shear wall building, the state of insufficient shear stress governs their overall performance and it becomes evident in the case of the buildings with more than 25 stories. For the buildings of piloti, the change of mass, weak story, as well as insufficient shear stress, decrease the performance index rapidly compared with the performance index of the buildings without piloti. The results, obtained from the nonlinear static analysis using capacity spectrum method, indicate that the performance Point increases for the structure having Piloti and high story. Also, deformation limits of buildings satisfy the allowable criteria at the life safety level, but the immediate occupancy level is exceeded in buildings which have more than 25 stories.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.9-14
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• 2016

This study evaluated a digital locking device design using detection distance of 13.4mm of a human body sensing type magnetic field coil. In contrast to digital locking devices that are used nowadays, the existing serial number entering buttons, lighting, number cover, corresponding pcb, exterior case, and data delivery cables have been deleted and are only composed of control ON/OFF power switches and emergency terminals. When the magnetic field coil substrates installed inside the inner case detects the electric resistance delivered from the opposite side of the 12mm interval exterior contacting the glass body part, the corresponding induced current flows. At this time, the magnetic field coil takes the role as a sensor when coil frequency of the circular coil is transformed. The magnetic coil as a sensor detects a change in the oscillation frequency output before and after the body is detected. This is then amplified to larger than 2,000%, transformed into digital signals, and delivered to exclusive software to compare and search for embedded data. The detection time followed by the touch area of the body standard to a $12.8{\emptyset}$ magnetic field coil was 30% contrast at 0.08sec and 80% contrast at 0.03sec, in which the detection distance was 13.4mm, showing the best level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.94-104
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• 2013

Experiments were divided into two parts; one part is to understand the basic properties of high flowable VA/VeoVa-modified cement mortar with different polymer cement ratio (P/C) and the weight ratio of fine aggregate to cement (C:F) and the other part is to investigate the effect of surface water spread on the concrete substrate on adhesion in tension. To understand the basic performance, the specimens were prepared with proportionally mixing VA/VeoVa redispersible powder, ordinary portland cement, silica sand, superplasticizer and viscosity enhancing agent. Here, P/C were 10, 20, 30, 50 and 75% and C:F were 1:1 and 1:3. As the change of P/C and C:F unit weight, flow test, crack resistance and adhesion in tension were measured. Three specimens with good adhesion properties were selected among specimens with different P/C and C:F. The effect of surface water evenly sprayed on concrete substrate on adhesive strength is investigated. The results show that surface water on concrete substrate increases the adhesion in tension of high flowable VA/VeoVa-modified cement mortar and additionally improves the flowability compared to the non-sprayed case.

• Journal of Energy Engineering
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• v.25 no.2
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• pp.52-64
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• 2016

The production of nuclear energy from thorium which is non-fissile material was a main issue until the middle of 1970's, because of the thorium's abundance as energy resources, its capability of breeding fissile material U233, and the reduction of long-lived actinides. However, to use thorium as nuclear fuel, some obstacles such as the necessities of external neutron source and long-term neutron irradiation for effective breeding, and the production of high radioactive isotopes in the course of thorium breeding cycle should be overcome. The difficulties to resolve these cons of thorium cycle became the reason of interruption of the related researches in the middle of 1970's. But in the 21st century, the change of societal perspective regarding nuclear energy and the appearance of accelerator-driven nuclear reactor shift those cons into pros and rehabilitate the study of thorium. The high activity of thorium cycle turned out to be a good option as higher resistance and easier detectibility of nuclear proliferation and the employment of subcritical accelerator-driven reactor as external neutron sources is considered to enhance the nuclear safety. In this study we compare the thorium cycle with the currently-used uranium cycle and analyze the technical status and perspective of thorium researches which use accelerator-driven reactors.