• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.74-80
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• 2012

Past few years have seen the growing importance of micro shock tubes in various engineering applications like micro combution, micro propulsion, particle delivery systems. But in order to efficiently apply Micro Shock Tube to such areas require the detailed knowledge of shock characteristics and flow field inside a micro shock tube. Due to many factors such as boundary layer, low Reynolds number and high Knudsen number shock propagation inside micro shock tubes will be quite different from that of the well established macro shock tubes. In the present study, experimental studies were carried out on micro shock tubes of two diameters to investigate flow characteristics and shock propagation. Pressure values were measured at different locations inside the driven section. From the experimental values other parameters like shock velocity, shock strength were found and shock wave diagram was constructed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4371-4377
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• 2012

In this paper, the structure-fluid coupled analysis is carried out in order to examine the cause of the vibration induced by fluid in the pressure-reducing valves for water. It is confirmed that there is the noise at the area of low frequency of 250Hz by measuring noise at pressure reducing valve. The flow analysis is performed by the commercial software ANSYS/CFX. The flow velocity of about 40 m/s is formed by nozzle effect, and so negative pressure is happened in the pressure reducing valve. The structure analysis is carried out with the load condition of pressure distribution by flow formed in valve. The rubber material at disk is deformed to the extent of closing up flow passage. It is confirmed that the disc deformation which is occurred repeatedly is due to noise and vibration at the pressure reducing valve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.187-192
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• 2013

Thin metallic sandwich plate with pyramidal metallic inner structures is manufactured from a continuous projection welding between face sheets and inner structures. Due to the welding pressure, imperfections of inner structures induced by the deformation of the inner structures occur. The imperfections affect the response of the thin metallic sandwich plate subjected to low-velocity impact loading. The goal of this paper is to obtain a proper dominant imperfection mode of the thin metallic sandwich plate with pyramidal metallic inner structures. The variation of impact responses of the thin metallic sandwich plate for different imperfection modes are investigated by finite element analysis. The results of the FE analysis are compared to those of drop impact experiments. From the results of the comparison, it has been shown that the dominant imperfection mode of the thin metallic sandwich plate with pyramidal metallic inner structures is all type of symmetric imperfection mode with symmetrical imperfections of four struts.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.430-430
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• 2012

The surface recombination velocity of the silicon solar cell could be reduced by passivation with insulating layers such as $SiO_2$, SiNx, $Al_2O_3$, a-Si. Especially, the aluminium oxide has advantages over other materials at rear surface, because negative fixed charge via Al vacancy has an additional back surface field effect (BSF). It can increase the lifetime of the hole carrier in p-type silicon. The aluminium oxide thin film layer is usually deposited by atomic layer deposition (ALD) technique, which is expensive and has low deposition rate. In this study, ICP-assisted reactive magnetron sputtering technique was adopted to overcome drawbacks of ALD technique. In addition, it has been known that by annealing aluminium oxide layer in nitrogen atmosphere, the negative fixed charge effect could be further improved. By using ICP-assisted reactive magnetron sputtering technique, oxygen to nitrogen ratio could be precisely controlled. Fabricated aluminium oxy-nitride (AlON) layer on silicon wafers were analyzed by x-ray photoelectron spectroscopy (XPS) to investigate the atomic concentration ratio and chemical states. The electrical properties of Al/($Al_2O_3$ or $SiO_2/Al_2O_3$)/Si (MIS) devices were characterized by the C-V measurement technique using HP 4284A. The detailed characteristics of the AlON passivation layer will be shown and discussed.

• ETRI Journal
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• v.42 no.4
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• pp.575-584
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• 2020

Electromagnetic (EM) waves used to send signals under seawater are normally restricted to low frequencies (f) because of sudden exponential increases of attenuation (𝛼) at higher f. The mathematics of EM wave propagation in seawater demonstrate dependence on relative permeability (𝜇_r), relative permittivity (𝜀_r), conductivity (𝜎), and f of transmission. Estimation of 𝜀_r and 𝜎 based on the W. Ellison interpolation model was performed for averaged real-time data of temperature (T) and salinity (S) from 1955 to 2012 for all oceans with 41 088 latitude/longitude points and 101 depth points up to 5500 m. Estimation of parameters such as real and imaginary parts of 𝜀_r, 𝜀_r', 𝜀_r", 𝜎, loss tangent (tan 𝛿), propagation velocity (V_p), phase constant (𝛽), and α contributes to absorption loss (L_a) for seawater channels carried out by using normal distribution fit in the 3 GHz-40 GHz f range. We also estimated total path loss (L_PL) in seawater for given transmission power P_t and antenna (dipole) gain. MATLAB is the simulation tool used for analysis.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.235-243
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• 2016

Korea is part of a region of low to moderate seismicity located inside the Eurasian plate with bedrock located at depths less than 30 m. However, the spectral acceleration obtained from site response analyses based on the geologic conditions of inland areas of the Korean peninsula are significantly different from the current Korean seismic code. Therefore, suitable site classification scheme and design response spectra based on local site conditions in the Korean peninsula are required to produce reliable estimates of earthquake ground motion. In this study, site-specific response analyses were performed at more than 300 sites with at least 100 sites at each site categories of $S_C$, $S_D$, and $S_E$ as defined in the current seismic code in Korea. The process of creating a huge database of input parameters - such as shear wave velocity profiles, normalized shear modulus reduction curves, damping curves, and input earthquake motions - for site response analyses were described. The response spectra and site coefficients obtained from site response analyses were compared with those proposed for the site categories in the current code. Problems with the current seismic design code were subsequently discussed, and the development and verifications of new site classification system and corresponding design response spectra are detailed in companion papers (II-development of new site categories and design response spectra and III-Verifications)

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.149-156
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• 1999

An experimental simulation on the flow in Czochralski melt using a cold model was carried out to obtain the velocities of fluid flow which affects the oxygen concentration of Czochralski crystal growing system. Low melting point Woods metal with similar Pr number to the silicon melt was adopted as a working fluid. Local flow velocities at numerous positions in the melt were simulataneously measured in three dimension using incorporated magnet probe. The measured velocity field showed a non-axisymmetric pattern dominated by natural convection. The analysis on the correlation between data set of temperatures simultaneously measured at two melt positions showed that the values of correlation coefficients were smaller than those of previous study on the small size of silicon melt and these phenomena are believed to occur because turbulent behavior becomes stronger in large size of the melt.

• Transactions on Electrical and Electronic Materials
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• v.17 no.6
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• pp.375-379
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• 2016

Increasing fat tissue of obese people, increases the rate of cardiovascular disease, diabetes, metabolic syndromes and dyslipidemia. An increase in the focal tissue of pancreas is a known risk factor of these diseases. Although there exists sufficient research on the diagnosis and treatment of pancreatic cancer, studies have been done on fatty pancreas. In this study, based on ultrasound imaging and using a texture characteristic of GLCM, fatty pancreas was divided into three categories: mild, moderate and severe. We compared and analyzed the three groups was by Pancreatic ultrasonography and body characteristics, serological tests, pressure and the degree of arteriosclerosis, against normal control group. The following parameters of control and test groups were measured: WC (waist circumference),BMI (body mass index), TC (total cholesterol), TG (triglyceride), HDL-C (High-density lipoprotein cholesterol) and LDL-C (Low-density lipoprotein cholesterol), SBP (systolic blood pressure), BST (Blood Sugar Test) and aortic PWV (pulse wave velocity). We observed the values correspondingly increasing fat deposition. However, ABI (Ankle Brachial pressure index) stenosis and HDL-C levels decreased with increasing fat deposit (p <0.05); a drop in these parameters are known to be harmful to the human body. The difference in texture characteristics between normal control group and pancreatic fatty group (mild, moderate, and severe) was statistically confirmed. Ultrasound imaging of pancreatic steatosis categorized the disease as mild, moderate and severe based on the characteristic texture. In conclusion, we observed on increase in metabolic syndrome, dyslipidemia, and arteriosclerosis, proportional to the degree of pancreatic fat deposition. The escalation of these diseases was confirmed and was directly related with predictors of cardiovascular diseases.

• Journal of Biomedical Engineering Research
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• v.41 no.2
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• pp.84-93
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• 2020

Despite of a lot of studies about proprioception tests, there are little study results to investigate the relationship between the functional movement and proprioception level. In this study, we tried to perform quantitative analysis for the effect of ankle joint proprioception level on the one leg standing postural control ability. Nine healthy people volunteered for this study. Force and position aspects of proprioception were evaluated using the electromyography system (EMG) and mobile clinometer application, respectively. The center of pressure (COP) trajectories, measured by a pressure mat sensor, were used for quantitative analysis of balance for each subject. We computed indices and errors of force and position aspects of proprioception from the EMG and ankle angle. Mean velocity of total and anterior-posterior direction (Vm and Vm_ap), root mean squared distance in anterior-posterior direction (RDap), travel length (L), and area (A) of COP trajectories were also calculated as indices of postural control ability of subjects. Two aspects of proprioception showed the low correlation from each other as previous studies. However, the EMG error of gastrocnemius lateral activation showed a high correlation coefficient with COP variables such as Vm (ρ=0.817, p=0.007), Vm_ap (ρ=0.883, p=0.002), RDap (ρ=0.854, p=0.003), L (ρ=0.817, 0.007) and A (ρ=0.700, p=0.036). Within our knowledge, this is almost the first study that investigated the relationship between proprioception level and functional movement. These study results could support that the ankle joint proprioception facilitation exercise would have positive effects on functional balance rehabilitation interventions.

• Journal of the Korean Geotechnical Society
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• v.32 no.7
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• pp.15-24
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• 2016

To investigate the unsaturated characteristics of the Boeun granite weathered soil, matric suction and volumetric water content were measured in both drying and wetting paths using Automated Soil-Water Characteristics Curve Apparatus. Based on the measured results, Soil-Water Characteristics Curve was estimated by van Genuchten (1980) model. The relationship between effective degree of saturation and matric suction showed the non-linear curve with S-shape and the hysteresis phenomenon occurred during drying and wetting paths. Suction Stress Characteristics Curve was estimated by the Lu and Likos (2006) model. The suction stress in drying path was constantly maintained and that in wetting path tended to increase when the effective degree of saturation was low. But the suction stress in drying path was larger than that in wetting path at the same degree of saturation when the effective degree of saturation became larger. Meanwhile, Hydraulic Conductivity Function was evaluated by the van Genuchten (1980) model which is one of the parameter estimation methods. The unsaturated hydraulic conductivity decreased with increasing the matric suction, and the decreasing velocity regarding to the matric suction in drying path was larger than that in wetting path.