• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.11
• /
• pp.980-986
• /
• 2009

In a triple-layered structure of ITO/N,N'-diph enyl-N,N'bis(3-methylphenyl)-1,1' - biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum($Alq_3$)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP)/Al device, we have studied the electrical and optical characteristics of organic light-emitting diodes(OLEDs) depending on the deposition condition of BCP layer. Several different sizes of holes on boat and several different deposition rates were employed in evaporating the organic materials. And then, electrical properties of the organic light-emitting diodes were measured and the performance of the devices was analyzed. It was found that the hole-size of crucible boat and the evaporation rate affect on the surface roughness of BCP layer as well as the performance of the device. When the hole-size of crucible boat and the deposition rate of BCP are 1.2 mm and $1.0\;{\AA}/s$, respectively, average surface roughness of BCP layer is lower and the efficiency of the device is higher than the ones made with other conditions. From the analysis of current density-luminance-voltage characteristics of a triple layered device, we divided the conductive mechanism by four region according to applied voltage. So we have obtained a coefficient of ${\beta}_{ST}$ in schottky region is $3.85{\times}10^{-24}$, a coefficient of ${\beta}_{PF}$ in Poole-Frenkel region is $7.35{\times}10^{-24}$, and a potential barrier of ${\phi}_{FN}$ in Fower-Nordheim region is 0.39 eV.

• The Journal of Pediatrics of Korean Medicine
• /
• v.17 no.2
• /
• pp.161-171
• /
• 2003

This study was to investigate the relationship of headache and back shape using the Moire interferometer and Questionnaire investigations. In this study the subjects consisted of 317 pupils[168 boys(53%), 149girls(47%)] attending S high school in Sungnamsi, Kyoungkido in 2002, and their ages ranged from sixteen to eighteen. The results are following. 1. In questionnaire investigation, we observed that the ratio of headache was more than 70% and the ratio of girls are more than that of boys. The inclination for ages was not shown. 2. In moire topography, the remainder values of scapular region were from 0.5 cm to 1.1 cm in boys, and from 0.45 cm to 1 cm in girls. The remainder values of gluteal region were from 0.2 cm to 0.8 cm in boys, and from 0.4 cm to 0.6 cm in girls. The reminder values of the vertical lines of cervical and buttock region were from 0.71 cm to 1.51 cm in boys, and from 0.96 cm to 1.43 cm in girls. More frequent findings of reminder value of the vertical lines of cervical and buttock region were observed that the vertical lines of cervical region were inclined to left than the vertical lines of buttock 3. Through the Pearson's Correlation analysis of headache and Moire topography, we found the close relationship of headache and the remainder values of scapular region(Pearson correlation coefficient : 0.116, P<0.05) and gluteal region(Pearson correlation coefficient : 0.153, P<0.01). But the relevances to headache and the remainder values of neck lines, sacral lines and neck-sacral lines were not found.

• Journal of Convergence for Information Technology
• /
• v.11 no.5
• /
• pp.9-16
• /
• 2021

In binary-modulation non-orthogonal multiple access (NOMA), there has been rare researches for the 1+1 capacity region to be achieved; how much total power is required and what power allocation is assigned for this total power. In this paper, the average total transmitted power to achieve 1+1 capacity region of binary pulse amplitude modulation (2PAM) NOMA is investigated, with a tolerable loss. Then, based on the sufficient average total transmitted power, we calculate the power allocation coefficient to achieve 1+1 capacity region. Furthermore, it is shown by numerical results that with the tolerable loss less than 0.008, near 1+1 capacity region is achieved. We also calculate numerically the power allocation coefficient for both users to achieve near 1+1 capacity region. As a result, for 2PAM NOMA to operate near 1+1 capacity region, proper total power with appropriate power allocation could be calculated in design of NOMA systems.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.5
• /
• pp.57-65
• /
• 2022

This study investigated the electromechanical response of smart ultra-high performance fiber reinforced concretes (S-UHPFRCs) under flexural loading to evaluate the self-sensing capacity of S-UHPFRCs in both tension and compression region. The electrical resistivity of S-UHPFRCs under flexural continuously changed even after first cracking due to the deflection-hardening behavior of S-UHPFRCs with the appearance of multiple microcracks. As the equivalent bending stress increased, the electrical resistivity of S-UHPFRCs decreased from 976.57 to 514.05 kΩ(47.0%) as the equivalent bending stress increased in compression region, and that did from 979.61 to 682.28 kΩ(30.4%) in tension region. The stress sensitivity coefficient of S-UHPFRCs in compression and tension region was 1.709 and 1.098 %/MPa, respectively. And, the deflection sensitivity coefficient of S-UHPFRCs in compression region(30.06 %/mm) was higher than that in tension region(19.72 %/mm). The initial deflection sensing capacity of S-UHPFRCs was almost 50% of each deflection sensitivity coefficient, and it was confirmed that it has an excellent sensing capacity for the initial deflection. Although both stress- and deflection-sensing capacity of S-UHPFRCs under flexural were higher in compression region than in tension region, S-UHPFRCs are sufficient as a self-sensing material to be applied to the construction field.

• Journal of the Korean Society of Radiology
• /
• v.2 no.3
• /
• pp.33-35
• /
• 2008

In the neutron capture experiment and calculation, the neutron absorption and scattering are very important. Especially these effects are conspicuous in the resonance energy region and below the thermal energy region. In the present study, we obtained energy dependent neutron absorption ratios of natural rhodium in energy region from 0.003 to 100 eV by MCNP-4B Code. The coefficients for neutron absorption was calculated for several types of thickness. In the lower energy region, neutron absorption is larger than higher region, because of large capture cross section (1/v). Furthermore it seems very different neutron absorption in the large resonance energy region. These results are very useful to decide the thickness of sample and shielding materials.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.2
• /
• pp.101-108
• /
• 2013

This paper is presented an experimental study of flow boiling heat transfer characteristics of ammonia, and is focused on pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal small tube with inner diameter of 3.0 mm and length of 2000 mm. The direct heating method is applied for supplying heat to the refrigerant, where the test tube is uniformly heated by electric current. The local heat transfer coefficients were obtained over a heat flux range of 20 to $80kW/m^2$, a mass flux range of 50 to $500kg/m^2s$, a saturation temperature range of 0 to $10^{\circ}C$, and quality up to 1.0. The pressure drops increase with increasing mass flux and heat flux, and with decreasing saturation temperature. The heat transfer coefficients increase with increasing mass flux and saturation temperature in middle and high quality region. And the local heat transfer coefficient increase with increasing heat flux in low quality region. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coefficient correlation. A new boiling heat transfer coefficient correlation based on the superposition model for ammonia in small tubes is developed average deviation of -0.17% and mean deviation of 10.85%.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.3
• /
• pp.174-186
• /
• 2009

When we apply a propagation model to the ocean with boundaries, we can calculate reflected wave using reflection coefficient suggested by Rayleigh assuming the boundaries are flat. But boundaries in ocean such as sea surface and sea bottom have an irregular rough surface. To calculate the reflection loss for an irregular boundary, it is needed to compute the coherent reflection coefficient based on an experimental formula or scattering theory. In this article, we derive the coherent reflection coefficients for a fluid-fluid interface using perturbation theory, Kirchhoff approximation and small-slope approximation respectively. Based on each formula, we can calculate coherent reflection coefficients for a rough sea surface or sea bottom, and then compare them to the Rayleigh reflection coefficient to analyze the reflection loss for a random rough surface. In general, the coherent reflection coefficient based on small-slope approximation has a wide valid region. Comparing it with the coherent reflection coefficients derived from the Kirchhoff approximation and perturbation theory, we discuss a valid region of them.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.6 no.4
• /
• pp.45-51
• /
• 2003

The reflection and transmission of submerged breakwater with trapezoidal type are computed numerically using boundary element method. The analysis method is based on the wave pressure function with the contlnuit? in the analytical region including fluid and porous structures. Wane motion within the porous structures is simulated by introducing the linear dissipation coefficient and added mass coefficient. The results indicate that transmission and reflection coefficient are determined due to the change of slope of submerged breakwater with trapezoidal type.

• Journal of the Korean institute of surface engineering
• /
• v.46 no.6
• /
• pp.264-270
• /
• 2013

Effects of preoxidation on high temperature wear of piercing plug tool steel sliding against SA210C steel used for production of seamless tube have been studied using a pin-on-disc CETR tribometer, under applied normal load of 20 N at $900^{\circ}C$ in air. It was found in the preoxidized pin specimens of piercing plug tool steel that the coefficient of friction decreased to about 0.4 at an initial stage followed by showing nearly constant value of about 0.4 during high temperature wear testing. On the other hand, it was also found in the pin specimens without preoxidation that the coefficient of friction increased and fluctuated, ranging from about 0.3 to 0.6 during the tests until the running period of about 800 sec. The compact and continuous Fe-oxide layer was formed on the contact surface of the preoxidized pin specimens after high temperature wear testing followed by penetrating along the grain boundaries of coarse ferrite in the decarburized region beneath the oxide layer due to the lower hardness of the region.

• Transactions of Materials Processing
• /
• v.21 no.3
• /
• pp.207-214
• /
• 2012

High temperature deformation behavior of a $Ni_{30}Fe_{53}Co_{17}$ alloy, with its extraordinary low coefficient of thermal expansion less than $10{\times}10^{-6}K^{-1}$ at temperatures ranging from room temperature to 673K, was investigated by conducting a series of compression tests. From an empirical processing map, the appropriate working temperature-strain rate combination for optimum forming was deduced to be in the ~1373K, $10^{-2}s^{-1}$ region. This region has a relatively high power dissipation efficiency, greater than 0.36. Furthermore, open die forging of a 100mm diameter billets was performed to confirm the variation of thermo-physical properties in relation to microstructure. The coefficient of thermal expansion was found to increase considerably with increasing the open die forging temperature and decreasing the cooling rate, which in turn provides a drastic increase in the average grain size.