• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.58 no.9
• /
• pp.1757-1763
• /
• 2009

The composites were fabricated by adding 0, 15, 20, 25[vol.%] Zirconium Diboride(hereafter, $ZrB_2$) powders as a second phase to Silicon Carbide(hereafter, SiC) matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by Spark Plasma Sintering(hereafter, SPS) were examined. Reactions between ${\beta}-SiC$ and $ZrB_2$ were not observed in the XRD analysis. The relative density of mono SiC, SiC+15[vol.%]$ZrB_2$, SiC+20[vol.%]$ZrB_2$ and SiC+25[vol.%]$ZrB_2$ composites are 90.93[%], 74.62[%], 74.99[%] and 72.61[%], respectively. The XRD phase analysis of the electroconductive SiC ceramic composites reveals high of SiC and $ZrB_2$ and low of $ZrO_2$ phase. The lowest flexural strength, 108.79[MPa], shown in SiC+15[vol.%] $ZrB_2$ composite and the highest - 220.15[MPa] - in SiC+20[vol.%] $ZrB_2$composite at room temperature. The trend of the mechanical properties of the electroconductive SiC ceramic composites moves in accord with that of the relative density. The electrical resistivities of mono SiC, SiC+15[vol.%]$ZrB_2$, SiC+20[vol.%]$ZrB_2$ and SiC+25[vol.%]$ZrB_2$ composites are 4.57${\times}10^{-1}$, 2.13${\times}10^{-1}$, 1.53${\times}10^{-1}$ and 6.37${\times}10^{-2}$[${\Omega}$ cm] at room temperature, respectively. The electrical resistivity of mono SiC, SiC+15[vol.%]$ZrB_2$. SiC+20[vol.%]$ZrB_2$ and SiC+25[vol.%]$ZrB_2$ are Negative Temperature Coefficient Resistance(hereafter, NTCR) in temperature ranges from 25[$^{\circ}C$] to 100[$^{\circ}C$]. The declination of V-I characteristics of SiC+20[vol.%]$ZrB_2$ composite is 3.72${\times}10^{-1}$. It is convinced that SiC+20[vol.%]$ZrB_2$ composite by SPS can be applied for heater or electrode above 1000[$^{\circ}C$]

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.11
• /
• pp.7555-7563
• /
• 2015

The complex formation from Zn(II) ion and 2-(2-hydroxyethylamino)-2-(hydroxymethyl)-1,3-propanediol (Monotris), Bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane(Bistris) in aqueous solution at $25^{\circ}C$ and at an ionic strength of 0.10 M have been studied potentiometrically. For the Zn(II)-Monotris system, in the Monotris (L) complex $ZnL^{2+}$, one of the hydroxyl oxygen atoms as well as the amine nitrogen of the ligand are coordinated. In basic media, the coordinated hydroxyl group is deprotonated. For the Zn(II)-Bistris system, in the Bistris(L) complex $ZnL^{2+}$, two of the hydroxyl oxygen atoms as well as the amine nitrogen of the ligand are coordinated. In basic media, one of the coordinated hydroxyl groups is deprotonated. In very high basic media, an additional hydroxyl group undergoes deprotonation. The equilibrium constants for the formation of $ZnL^{2+}$, $ZnLH_{-1}{^+}$, $ZnLH_{-2}$, $Zn_2L_2H_{-2}{^{2+}}$ and $Zn_2L_2H_{-3}{^+}$ have been determined.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.3
• /
• pp.121-129
• /
• 2017

In this paper, the shake table test for the masonry infilled reinforced concrete frame with non-seismic details was carried out in order to evaluate its dynamic behaviour and damage under seismic condition. The tested specimens were the RC frame and the masonry infilled RC frame and the dynamic characteristics, such as a resonant period, acceleration response, displacement response and base shear force response, were compared between them. As a result of the shake table test, RC frame specimen had flexural cracks at the top and bottom of the column and shear cracks at the joints. In the case of masonry infilled RC frame, the damage of the frame was relatively minor but the sliding cracks and diagonal shear cracks on the masonry wall were severe at the final excitation. The resonant period of infilled RC frame specimen was shorter than that of the RC frame specimen because the masonry infill contributed to increase the stiffness. The maximum displacement response of the infilled RC frame specimen was decreased by about 20% than the RC frame specimen. It was analyzed that the masonry infill wall applied in this study contributed to increase the lateral strength of the RC frame with non - seismic detail by about 2.2 times and the stiffness by about 1.6 times.

• Restorative Dentistry and Endodontics
• /
• v.31 no.4
• /
• pp.290-299
• /
• 2006

Objectives: The purpose of this study is to evaluate the effect of ethylene glycol analogs on modulus of elasticity and ultimate tensile strength of moist, demineralized dentin matrix. Methods: Dentin disks 0.5 mrn thick were prepared from mid-coronal dentin of extracted. unerupted, human third molars. 'I' beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5M EDTA for 5 days. Ultimate tensile stress (UTS) and low strain modulus of elasticity (E) were determined with specimens immersed for 60 min in distilled water $(H_{2}O)$, ethylene glycol $(HO-CH_{2}-CH_{2}-OH)$, 2-methoxyethanol $(H_{3}CO-CH_{2}-CH_{2}-OH)$, and 1,2-dimethoxyethane $(H_{3}CO-CH_{2}-CH_{3}-OCH_{3})$ prior to testing in those same media. Modulus of elasticity was measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at ${\alpha}\;=\;0.05$. Regression analysis examined the relationship between UTS or E and hoy's solubility parameter for hydrogen bonding $({\delta}_{h})$ of each solvent. Results: The UTS of demineralized dentin in water, ethylene glycol, 2-methoxyethanol, and 1,2-dimethoxyethane was 24 (3), 30 (5), 37 (6), and 45 (6) MPa, ${\times}$ (SD) N = 10. Low strain E for the same media were 16 (13), 23 (14), 52 (24), and 62 (22) MPa. Regression analysis of UTS vs ${\delta}_{h}$ revealed a significant $(p\;<\;0.0001,\;r\;=\;-0.99,\;R^{2}\;=\;0.98)$ inverse, exponential relationship. A similar inverse relationship was obtained between low strain E vs ${\delta}_{h}\;(p\;<\;0.0005,\;r\;=\;-0.93,\;R^{2}\;=\;0.86)$. Significance: The tensile properties of demineralized dentin are dependent upon the hydrogen bonding ability of polar solvents $({\delta}_{h})$. Solvents with low ${\delta}_{h}$ values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high ${\delta}_{h}$ values prevent the development of these new interpeptide H-bonds.

• Journal of Energy Engineering
• /
• v.23 no.2
• /
• pp.42-48
• /
• 2014

Soot and tar which were derived from combustion or pyrolysis processes in Puverized Coal(PC) furnace or boiler have been significantly dealing in a radiative heat transfer and an additional source of NOx. Furthermore, the increasing for the use of a coal with low caloric value gives rise to a lot of tar-soot yield and LOI in a recycled ash for using cement materials. So, the ash with higher tar-soot yield and LOI can not recycle due to decreased strength of concrete. In this study, tar-soot yields and flame structures were investigated using the LFR for a blending combustion with bituminous coal and sub-bituminous coal. Also, The investigation were conducted as each single coals and blending ratio. The coals are used in a doestic power plant. In the experimental results, sub-bituminous coal with high volatile contents shows longer soot cloud length than bituminous coal, but overall flame length was shorter than bituminous coal. Tar-soot yields of sub-bituminous coal is lower than those of bituminous coal. Combustion characteristics are different between single coal and blended coal. Therefore, finding an optimal coal blending ratio according to coal rank effects on tar-soot yields.

• The Journal of Engineering Geology
• /
• v.18 no.4
• /
• pp.459-470
• /
• 2008

Types of slope failure related to cut slope stability are interpreted through case analyses, and also factors affecting structurally controlled instability investigated, which are developed by geologic structures along a national road No. 25 across the Cheongwon and Boeun-Guns, Chungbuk. Engineering properties such as orientation, persistence, roughness and uniaxial compressive strength of joints are analyzed by square-inventory method in three areas with well-preserved outcrops. The study area is located in Ogcheon folded bet, and are composed of quartz-schist and quartzite in the Midongsan Formation and phyllite in the Ungyori Formation. Flexural beds by folding, schistosity and cleavage besides joints are developed due to slight metamorphism. Various types of joints developed by folding are formed such as strike-parallel, strike-perpendicular, wedge and wrench joint sets by both initially regional and later superposed folding. Factors of slope instability are created by crossing the orientations of joint, cleavage, bedding and slope one another. In the case that the orientation of a slope is coincident with one of beds, factors causing large-scale failure including plane failure are increased greatly. Also in the region that orientations of the slope and bed are crossed each other at high angle, only local and minor failures are shown in the slope.

• Economic and Environmental Geology
• /
• v.41 no.4
• /
• pp.453-464
• /
• 2008

This study is to examine a relation between coal mining subsidence occurrence at abandoned underground coal mines and underground goaf with respect to surface geology, subsurface structure, depth and thickness of coal beds and the distribution of drifts. A study is carried out at the site where susceptibility of coal mining subsidence was proven high in a previous study. In that previous study, the susceptibility of coal mining subsidence was spatially analyzed by GIS using digitized geological maps, investigation reports, digitized mining tunnel maps without consideration of subsurface structure and the multi-level arrangement of drifts. Here we analyze geological characteristics around the goaf and the distribution of coal seam based upon digitized geological maps and investigation reports on the study area. And digitized mining tunnel maps are also used to analyze the depth and multi-level arrangement of drifts. The results show that weakened surface rock strength, relatively shallow depth and large thickness of coal seam below the surface are closely related to the coal mining subsidence occurrence. Complicatedly inter-connected drifts, shallow depth of drifts and surface rock fractures are revealed as additional control factors affecting coal mining subsidence. These factors examined in this study as well as original factors should be taken into account for the quantitative estimation of coal mining subsidence occurrence at abandoned underground coal mine.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.24 no.1
• /
• pp.67-73
• /
• 2016

The application of titanium has been gradually rising because the utilizing ranges for low weight and high strength are rapidly increased by the need for improving the fuel economy in production industries such as the aviation and automotive in recent. The purpose in this study is to investigate the appropriate cutting conditions on the life of flat and round end mills by measuring the maximum cutting temperature relative to the machining time, and calculating the wear rates of cutting tool with the spindle speed and feed rate of vertical machining center as a parameter in the titanium roughing cut machining which is widely used in critical parts of aircraft, cars, etc. When the wetted roughing cut machining of titanium with a soluble cutting oil is conducted by the flat and round end mills, the maximum cutting temperatures for a variety of spindle speed and feed rate are measured at ten-minute intervals during 60 minutes by an infrared thermometer, and the wear rates of cutting tool are calculated by the weight ratios based on tool wear before and after the experiment. It is found that the maximum cutting temperature and the wear rates of cutting tool are raised as the cutting amount per tool edge is increased with the rise of feed rate, in this experimental range, and as the frictional area due to the rise of contacting friction numbers between tool and specimen is increased with the rises of cutting time and spindle speed. In addition, the increasing rate of maximum cutting temperature in the flat and round end mills are the highest for the cutting time from 50 to 60 minutes, and the wear rate of cutting tool in the flat end mill is 1.14 to 1.55 times higher than that in the round end mill for all experimental conditions.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.10 no.6
• /
• pp.487-495
• /
• 2017

The thermal characteristics of the electrodeless lamp are one of the main factors that determine the design and performance of the lamp. The coupler changes the impedance characteristic by heat and its use temperature is usually within about $150^{\circ}C$. In this study, we observed the phenomenon when the coupler was exposed at a temperature of $150^{\circ}C$ or higher, which has not been discussed so far. Two types of coupler A and coupler B with different spacing between the inner tube and the coupler were analyzed for electrical, thermal and optical properties and deterioration characteristics with different heat and heat shielding conditions. First, the impedance of the system is obtained and used as a criterion for analyzing the electrical characteristics through it. The diameters of the two types of couplers are 1 mm, and the experimental result shows that the coupler diameter is 1 mm, which can cancel out the loss of the magnetic field strength. Therefore, based on these results, when the coupler is exposed to high temperature of about $200^{\circ}C$, the efficient design method corresponding thereto is proposed.

• Journal of Navigation and Port Research
• /
• v.44 no.3
• /
• pp.244-252
• /
• 2020

The 2008 global financial crisis was triggered by the Lehman Brothers crisis caused by the sub-prime mortgage crisis in the United States This crisis has had an impact on the globe's dry bulk shipping market by reducing dry bulk cargo volume. An oversupply of dry bulk carriers caused a serious recession in the globe's dry-bulk shipping industry and shipbuilding industry. In this situation, the Korean dry-bulk shipping companies were victims of the quagmire of a long recession since the global financial crisis and could not overcome this crisis. This condition forced them into severe financial risk Thus, it caused many shipping companies to file for bankruptcy. In this study, we classified Korean ocean-going dry-bulk shipping companies into two groups, that is, the solvent group and the insolvent group. We also separated the research period before and after the 2008 global financial crisis. Then we investigated the differences in the major financial ratios of the two groups by t-test and found that some financial ratios such as profitability ratios and growth ratios showed the difference between the two groups with statistical significance. The significance of this study is as follow. First, the shipping company management is also crucial for the systematic management of financial strength and business strategy, it is crucial to manage cargo which a high profitable freight. Second, the shipping company should be managed as a company with continued growth through efficient operation and management of ships.