• 한국공작기계학회논문집
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• 제13권4호
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• pp.95-99
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• 2004

In this study, the leak detection technique of pressure vessel by using acoustic emission(AE) signal is suggested experimentally. The leak of pressure vessel is located at the welding line due to welding defects. we measured the AE signal using Rl5I sensor, and examined the AE parameters in leak condition. It is investigated that the mean value of AE signal is dependent on leak source location. So the absolute mean value of AE signal is adopted as dominant AE parameter. We proposed leak detection algorithm using AE signal mean value for monitoring the leak source location.

• 대한의용생체공학회:의공학회지
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• 제11권2호
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• pp.195-202
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• 1990

The hypothesis of asymmetric resistance to explain the phenomenon of lung hyperinflation (LHI) during hlgh frequency ventilation (HFV) was quantitatively studied. LHI was predicted by modeling the ism-volume pressure-flow (IVPF) data from 5 human subjects using the empirical Rohrer's equation. Non-steadiness during HFV was compensated by em- ploying recently proposed volume-frequency diagram. Tidal volume and ventilation frequency were 100 ml and 20 Hz, respectively. Airflow pattern was a symmetric sinusoid. The predic- tion results of mean pressure drop across the airways were averaged for those 5 subjects, and compared with zero by one-sided student's t-test. A marginally significant (P<0.1) increase in mean pressure drop was observed during HFV at low lung volumes (below FRC) , which could increase mean lung volume up to one liter When the lung volume was above FRC, no significant LHI (P >0.25) was resulted. LHI seemed to be inversely related to the lung volume. These results recommend to clinically apply HFV only at lung volumes above FRC.

• 한국정밀공학회지
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• 제11권4호
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• pp.13-25
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• 1994

In order to design and improve a new machine tool, there is a need for a better understanding of the cutting force. In this paper, the computer programs were developed to predict not only the mean specific cutting pressure but also the cutting force. The simulated cutting forces in X, Y, Z directions resulted form the developed cutting force model were compared with the measured cutting forces in the time and frequency domains. The simulated cutting forces resulted from the new cutting force model have a good agreement with the measured force in comparison with these resulted from the existing cutting force model.

• 한국표면공학회지
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• 제34권5호
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• pp.367-377
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• 2001

Plasma is generated by electrical discharge. Most plasma generation has been carried out at low-pressure gas typically less than one millionth of atmospheric pressure. Plasmas are in general generated from impact ionization of neutral gas molecules by accelerated electrons. The energy gain of electrons accelerated in an electrical field is proportional to the mean free path. Electrons gain more energy at low-pressure gas and generate plasma easily by ionization of neutrals, because the mean free path is longer. For this reason conventional plasma generation is carried out at low pressures. However, many practical applications require plasmas at high-pressure. In order to avoid the requirement for vacuum pumps, researchers in Korea start to develop plasmas in high-pressure chambers where the pressure is 1 atmosphere or greater. Material processing, environmental protection/restoration and improved energy production efficiency using plasmas are only possible for inexpensive bulk plasmas. We thus generate plasmas by new methods and plan to set foundations for new plasma technologies for $21^{st}$ / century industries. This technological research will play a central role in material processing, environmental and energy production industries.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.201-208
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• 2000

In this study, the behavior of saturated sandy soils under dynamic loads - pore water pressure and effective stress - was investigated using Disturbed State Concept(DSC) model. The model parameters are evaluated from laboratory test data. During the process of loading and reverse loading, DSC model is utilized to trace strain-hardening and cyclic softening behavior. The procedure of back prediction proposed in this study are verified by comparing with laboratory test results. From the back prediction of pore water pressure and effective mean pressure under cyclic loading, excess pore water pressure increases up to initial effective confining pressure and effective mean pressure decrease close to zero in good greement with laboratory test results. Those results represent the liquefaction of saturated sandy soils under dynamic loads. The number of cycles at initial liquefaction using the model prediction is in good agreement with laboratory test results. Therefore, the results of this study state that the liquefaction of saturated sandy soils can be explained by the effective tress analysis.

• 한국운동역학회지
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• 제17권4호
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• pp.191-200
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• 2007

The purpose of this study was to analyze the foot-pressure distribution of trekking boots for assessing their functionality. Subjects participated in this study included 10 university male students who had no injury experience in lower limbs and a normal gait pattern. The size of all subjects was 270mm. Five models of trekking boots, most popular in Korea (A, B, C, D & E company), were selected for the test. Using the PEDAR-X system and PEDAR-X insoles, 5 different walking stages were analyzed for the foot-pressure distribution: (a) straight gait; (b) $45^{\circ}$ turn gait; (c) $25^{\circ}$ uphill gait; and (d) $25^{\circ}$ downhill gait. Results of the foot-pressure distribution and functionality on each stage were as follow; 1. Straight gait - In case of Max ground reaction force, mean plantar pressure and Max plantar pressure, there was not a distinct tendency; however, products manufactured by E and A company showed relatively lower pressure distribution. 2. $45^{\circ}$ turn gait - In Max ground reaction force, mean plantar pressure and Max plantar pressure, there wasn't a distinct tendency; however, products manufactured by E and A company showed relatively lower pressure distribution. Results also revealed that the products manufactured by E and A company were superior to those by other companies in terms of functionality. 3. $25^{\circ}$ uphill gait - In Max ground reaction force, mean plantar pressure and Max plantar pressure, there wasn't a distinct tendency; however, products manufactured by E and C company showed relatively lower pressure distribution. Results also revealed that the products manufactured by E and C company were superior to those by other companies in terms of functionality. 4. $25^{\circ}$ downhill gait - In Max ground reaction force, Mean plantar pressure and Max plantar pressure, there wasn't a distinct tendency; however, products manufactured by E company showed relatively lower pressure distribution. Results also revealed that the products manufactured by E company were superior to those by other companies in terms of functionality. Overall, five pairs of trekking shoes selected in this study showed the excellent performance in several conditions. The findings above may provide us with the important criteria for choosing trekking boots.

• Wind and Structures
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• 제31권5호
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• pp.431-443
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• 2020

The modern tall buildings are often constructed as an unconventional plan and as twin buildings. Wind load on the tall building is significantly influenced by the presence of another building in the near vicinity. So, it is imperative to study wind forces on an unconventional plan shaped tall building. Mean wind pressure coefficients of a square and 'H' plan shape tall buildings are investigated using wind tunnel experiments. The experiments were carried out for various wind directions from 00 to 900 at an interval of 300 and various locations of the identical interfering building. The experimental results are presented at the windward face from the viewpoint of effects on cladding design. To quantify the interference effects, interference factors (I.F) are calculated. Mean pressure coefficients of both models are compared for isolated and interference conditions. The results show that pressure reduces with an increase in wind angle till 600 wind direction. The interfering building at full blockage interference condition generates more suction than the other two conditions. The interference factor for both models is less than unity. H-plan building model is subjected to a higher pressure than the square model.

• 설비공학논문집
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• 제9권4호
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• pp.561-571
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• 1997

In this paper, the fundamental equations are developed for the pulsatile laminar flow generated by changing the oscillatory flow with $0{\leq}f{\leq}48Hz$ into a steady one with $0{\leq}Re{\leq}2500$ in a rigid circular pipe. Analytical solutions for the wave propagation factor k, the axial distributions of cross-sectional mean velocity $u_m$ and pressure p are schematically derived and confirmed experimentally. The axial distributions of centerline velocity and pressure were measured by using Pitot-static tubes and strain gauge type pressure transducers, respectively. The cross-sectional mean velocity was calculated from the centerline velocity by applying the parabolic distribution of the laminar flow and it was confirmed by using the ultrasonic flowmeter. It was found that the axial distributions of cross-sectional mean velocity and pressure agree well with theoretical ones and depend only on the Reynolds number Re and angular velocity $\omega$.

• 한국임상보건과학회지
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• 제11권1호
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• pp.1632-1638
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• 2023

Purpose: The aim of this study was to determine the distribution of the cornea thickness and intra ocular pressure Korean adult of 20 to 24 year old using the Pentacam and tonometer. Methods: The subjects of this study were 43 Korean adults with healthy eyes. Corneal thickness was measured with Pentacam device. The intra ocular pressure was measured with tonometer. Data was analyzed by means of the Pearson's correlation cofficient. P-values<0.001 were considered statistically significant. Results: Mean age of subjects was 20.41±0.86 years. The mean +/- intra ocular pressure of the right eye and left eye were 16.236±2.523mmHg and 16.971±1.992mmHg, respectively. The mean central corneal thickness of the right eye and left eye was 545.324±38.682㎛ and 547.442±33.778㎛, respectively. No significant difference in central corneal thickness was found between the right and left eyes. But, there was a statistically significant difference between central cornea thickness and peripheral cornea thickness around 4 mm of central cornea(p<0.001, Pearson's correlation). However there was no statistically significant difference between central cornea thickness and intra ocular pressure. Conclusion: The results of this study could be used as a clinical reference data for diagnosis and treatment of cornea in Korean adult.

• Journal of Korean Neurosurgical Society
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• 제60권1호
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• pp.1-7
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• 2017

Objective : The diagnosis of shunt malfunction can be challenging since neuroimaging results are not always correlated with clinical outcomes. The purpose of this study was to evaluate the efficacy of a simple, minimally invasive cerebrospinal fluid (CSF) lumbar tapping test that predicts shunt under-drainage in hydrocephalus patients. Methods : We retrospectively reviewed the clinical and radiological features of 48 patients who underwent routine CSF lumbar tapping after ventriculoperitoneal shunt (VPS) operation using a programmable shunting device. We compared shunt valve opening pressure and CSF lumbar tapping pressure to check under-drainage. Results : The mean pressure difference between valve opening pressure and CSF lumbar tapping pressure of all patients were $2.21{\pm}24.57mmH_2O$. The frequency of CSF lumbar tapping was $2.06{\pm}1.26times$. Eighty five times lumbar tapping of 41 patients showed that their VPS function was normal which was consistent with clinical improvement and decreased ventricle size on computed tomography scan. The mean pressure difference in these patients was $-3.69{\pm}19.20mmH_2O$. The mean frequency of CSF lumbar tapping was $2.07{\pm}1.25times$. Fourteen cases of 10 patients revealed suspected VPS malfunction which were consistent with radiological results and clinical symptoms, defined as changes in ventricle size and no clinical improvement. The mean pressure difference was $38.07{\pm}23.58mmH_2O$. The mean frequency of CSF lumbar tapping was $1.44{\pm}1.01times$. Pressure difference greater than $35mmH_2O$ was shown in 2.35% of the normal VPS function group (2 of 85) whereas it was shown in 64.29% of the suspected VPS malfunction group (9 of 14). The difference was statistically significant (p=0.000001). Among 10 patients with under-drainage, 5 patients underwent shunt revision. The causes of the shunt malfunction included 3 cases of proximal occlusion and 2 cases of distal obstruction and valve malfunction. Conclusion : Under-drainage of CSF should be suspected if CSF lumbar tapping pressure is $35mmH_2O$ higher than the valve opening pressure and shunt malfunction evaluation or adjustment of the valve opening pressure should be made.