• Journal of Chest Surgery
• /
• v.31 no.6
• /
• pp.586-590
• /
• 1998

Background: The regression of the left ventricular hypertrophy after prosthetic valve replacement in patients with aortic valvular stenosis is an important factor to determine the appropriateness of the replaced prosthetic valvular size. Methods: To assess the regression of myocardial hypertrophy, a retrospective analysis of Doppler echocardiographic and electrocardiographic data was undertaken before, soon after(7.5$\pm$2.1 day), and late after(10.7$\pm$1.8 months) surgery in 36 patients(22 males, 14 female, mean age 54$\pm$12.1 years, mean BSA 1.61$\pm$0.15m2) with predominant aortic valvular stenosis. The patients underwent St. Jude Medical aortic valve replacement. By the size of the valves used, the patients were divided into three groups(19, 21 and 23+). Results: The mean body surface area(1.48$\pm$0.13) in the patients with the 19 mm valve was smaller than that in the other groups(1.63$\pm$0.12)(p<0.05). No significant changes of ejection fraction were detected in all groups over time. Left ventricular muscle mass index(gm/m2) was reduced significantly in the 21 and 23+ groups over time(p<0.05), but there were no significant changes in the 19 mm valve group. The electric voltage height on EKG at the period of late after surgery was reduced significantly in all groups(p<0.05). Conclusion: Despite clinical improvement, the LVH was not reduced significantly in 19 mm valve group. Thus we suggest that more attention and additional procedures such as annular enlargement should be taken in patients who will undergo the replacement of 19 mm prosthetic valve.

• Journal of Korea Foundry Society
• /
• v.25 no.4
• /
• pp.168-172
• /
• 2005

In this study, the effects of chill layers occurred in shot sleeve on the molten metal filling were analyzed through computer simulation and the behavior of chill layers with temperature variation of shot sleeve set from 200 to $280^{\circ}C$ was also investigated. The simulation results showed the chill layers set in the in-gates during the injection process change the main filling direction and cause turbulent flow pattern, resulting in porosities inside the castings. The amount of chill layers with the increasing temperature of shot sleeve was considerably reduced. And particularly, at the setting temperature of $280^{\circ}C$ by heat control unit, the big reduction in chill layers, excellent trimmed surface and the highest densification were achieved, suggesting that as the optimal sleeve condition in diecasting, especially for the highly complex parts like valve body.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.7 s.250
• /
• pp.707-714
• /
• 2006

A numerical analysis study has performed in terms of fluid dynamics to identify the wall thinning generated in the main feedwater isolation valve body of a nuclear power plant. To review the relations between flow characteristics and the wall thinning induced by flow accelerated corrosion (FAC), numerical analysis using FLUENT code and ultrasonic tests (UT) were performed. The local velocities according to the analysis results were compared with the distribution of the measured wall thickness by ultrasonic tests. The comparison results show that the local velocity in the x-direction had no correlation with the wall thinning but the local velocity in the y-direction and turbulence intensity had a great influence on that. These results provide a good match to those of the previous studies - locations colliding vertically against components undergo severe wall thinning. These results may be utilized to the design modification and the wall thinning management for main feedwater isolation valves for preventing the wall thinning degradation.

• The Journal of Korea Robotics Society
• /
• v.2 no.1
• /
• pp.1-8
• /
• 2007

This paper presents a PID automatic gain-tuning algorithm for the electronic throttle valve which is driven by wire. Since the system characteristics of position control for electronic throttle valve are so complicated that both the real time robustness and the manufacturing cost must be considered for mass production. To resolve this paradox, a kind of algorithm called RLS (Recursive Least Square) is adopted for the control of the ETB (Electronic Throttle Body). Using this algorithm, the PID gains can be adjusted automatically with the estimated system parameters. Furthermore, a pre-filter is supplemented for the sake of the robustness against the friction and loads. From the industrial requests for the system, the design specifications are decided as follows: the settling time should be less than 1sec and the overshoot should be kept below 3%. The results of the experiments based on this approach show that the high robustness can be achieved while the system stability is satisfied steadily. A parameter estimation scheme and a gain-tuning algorithm have been properly combined and utilized in this research and the effectiveness is verified through the real experiments.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.174-179
• /
• 2005

In the super slow speed die casting process, the casting defects due to melt flow should be controlled in order to obtain sound casting products. The casting defects that are caused by molten metal were cold shut formation, entrapment of air, gas, and inclusion. But the control of casting defects has been based on the experience of the foundry engineers. The calculation of simulation can produce very useful and important results. The calculation data of die casting process condition from the computer simulation by the Z-CAST is made to insure that the liquid metal is injected at the right velocity range and that the filling time is small enough to prevent premature solidification. The parameters of runner shape that affected on the optimized conditions that was calculated with simple equation were investigated. These die casting process control techniques of automobile valve body mid-plate have achieved good agreement with the experimental data of tensile strength, hardness test, and material structure photographies satisfactory results.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.279-284
• /
• 2005

The casting defects that are caused by molten metal were cold shut formation, entrapment of air, gas, and inclusion. But the control of casting defects has been based on the experience of the foundry engineers. In this thesis, the computer simulation analyzed the flow of molten metal. The quantitative analyses which proposed the effective mold design was executed Flow patterns of 0.15-0.16m/s molten metal in 15 mm thin plate casting were investigated in order to optimize die-casting process. As increasing ingate velocity in thin plate casting, cold shot was decreased. The parameters of runner shape that affected on the optimized conditions that was calculated with simple equation were investigated. These die casting process control techniques of automobile valve body mid-plate have achieved good agreement with the experimental data of tensile strength, hardness test, and material structure photographies satisfactory results.

• Journal of Energy Engineering
• /
• v.11 no.1
• /
• pp.26-33
• /
• 2002

In this paper, incompressible and compressible flow characteristics around the butterfly valve have been investigated. In order to simplify the problem, a flat disk valve with various valve disk angles and pressure ratios is considered in the present calculations. It was found that as the disk angle increases, the stagnation point on the front surface of the disk moves to the center of the surface and the inflow velocity decreases. The maximum flow velocity occurs at the downstream of throat because of the formation of vents contracta. As the pressure ratio decreases, compressibility effects increase and the jet formed between the throttle body wall and the disk edge becomes supersonic. This flow also builds up as a shock cell structure. The increase of disk angle and pressure ratio makes the mass flow at the inlet decrease, while the increase of disk angle and the decrease of pressure ratio make the pressure loss coefficient increase.

• Journal of the Korean Institute of Gas
• /
• v.10 no.4 s.33
• /
• pp.23-28
• /
• 2006

This paper presents the strength safety and the weight reduction analysis of nine gas valve models for a LPG cylinder using a finite element analysis program, MARC and Taguchi's experimental method. The maximum Von Mises stress of a gas valve body represents a safety of a brass valve structure for the given gas pressure of $91kg/cm^2$, which considered a safety factor of a LPG gas cylinder. The weight reduction analysis is very important for reducing a gas flow friction loss and a manufacturing cost as a design parameter. The calculated results present an design model 9 as an optimized design data with 10mm radius of a lower part gas flow pipe A, 6mm radius of an upper part gas flow pipe B and a connecting length 2 mm of tapered pipe D between lower and upper pipes.

• Journal of Chest Surgery
• /
• v.53 no.1
• /
• pp.1-7
• /
• 2020

Background: The aim of this study was to evaluate the short-term and long-term results of surgical treatment for native valve endocarditis (NVE) and to investigate the risk factors associated with mortality. Methods: Data including patients' characteristics, operative findings, postoperative results, and survival indices were retrospectively obtained from Hallym University Sacred Heart Hospital. Results: A total of 29 patients underwent surgery for NVE (affecting the mitral valve in 20 patients and the aortic valve in 9) between 2003 and 2017. During the follow-up period (median, 46.9 months; interquartile range, 19.1-107.0 months), the 5-year survival rate was 77.2%. In logistic regression analysis, body mass index (p=0.031; odds ratio [OR], 0.574; 95% confidence interval [CI], 0.346-0.951), end-stage renal disease (ESRD) (p=0.026; OR, 24.0; 95% CI, 1.459-394.8), and urgent surgery (p=0.010; OR, 34.5; 95% CI, 2.353-505.7) were significantly associated with in-hospital mortality. Based on Cox proportional hazard regression analysis, the statistically significant predictors of long-term outcomes were hypertension, ESRD, and urgent surgery. Conclusion: Surgical treatment for NVE is associated with considerable mortality. The in-hospital mortality and 5-year survival rates of this study were 13.8% and 77.2%, respectively. Underlying conditions, including hypertension and ESRD, and urgent surgery were independent risk factors for unfavorable outcomes.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.32 no.4
• /
• pp.435-448
• /
• 2022

Objectives: As the time spent wearing masks has increased with spread of COVID-19, various research related to masks have been reported. However, there are still few experiments on the physiological response of the body to wearing industrial dust masks in South Korea. Considering the actual working hours at the work site, it is necessary to investigate the comfort of industrial dust masks. Therefore, this study aims to confirm the change in subjective discomfort level according to the wearing time for industrial dust masks in South Korea that have been certified for safety by KCS. Methods: This study evaluated subjective discomfort level over four hours. The experimental conditions were five types: not worn (control group), special grade, first grade, second grade (with valve), and second grade (without valve). The subjective discomfort levels were classified for breathing, warmth (body and face) and wetness (body and face). Subjects recorded their discomfort level on a checklist every one hour. Results: In special grade and second grade (without valve), the discomfort level in terms of breathing, warmth (face), and wetness (face) was significantly higher than that of the control group. However, the effects of all kinds of industrial dust masks on the discomfort level in the body were low. Conclusions: Since this study was conducted on subjects working in an office with a comfortable working environment, it is difficult to apply it to workers at actual industrial sites. However, it is considered meaningful as the first clinical study to evaluate the subjective level of discomfort over a long time for domestic industrial dust masks that have been certified for safety by KCS.