Proceedings of the Korean Society of Medical Physics Conference
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2002.09a
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pp.418-421
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2002
Fundamental study on quasi-monochromatic parallel radiography using a polycapillary plate and a plane-focus x-ray tube is described. The x-ray generator consists of a negative high-voltage power supply, a filament (hot cathode) power supply, and an x-ray tube. The negative high-voltage is applied to the cathode electrode, and the transmission type target (anode) is connected to the ground potential. The maximum voltage and current of the power supply were -100 kV (peak value) and 3.0 mA, respectively. In this experiment, the tube voltage was regulated from 20 to 25 kV, and the tube current was regulated by the filament temperature and ranged from 1.0 to 3.0 mA. The exposure time is controlled in order to obtain optimum film density, and the focal spot diameter was about 10 mm. The polycapillary plate is J5022-21 made by Hamamatsu Photonics Inc., and the outside and effective diameters are 87 and 77 mm, respectively. The thickness and the hole diameter of the polycapillary are 1.0 mm and 25 ${\mu}$m, respectively. The x-rays from the tube are formed into parallel beam by the polycapillary, and the radiogram is taken using an industrial x-ray film of Fuji IX 100 without using a screen. In the measurement of image resolution, we employed three brass spacers of 2, 30, and 60 mm in height. By the test chart, the resolution fell according to increases in the spacer height without using a polycapillary. In contrast, the resolution slightly fell with corresponding increases in the height by the polycapillary. In angiography, fine blood vessels of about 100 ${\mu}$m are clearly visible.
Even though the urinary stones are rare in children, careful observation and monitoring are necessary because the incidence has been increasing. This study is aimed to document the characteristics of urinary stones in children including the symptoms, diagnosis, with or without urinary tract infection, other urinary tract anomaly and treatment. 45 patients under the age of 15 years with urinary stones hospitalized during Jan. 1986 to Jun. 1996 at Severance Hospital were reviewed retrospectively. Patients' mean age was 6.5 years and sex ratio (male : female) was 5.4:1. The most common symptom was gross hematuria. Stones accompanied with urinary tract infection was 46.7%, and stones associated with urinary tract anomaly was 35.6%. Extracorporeal shock wave lithotripsy, percutaneous nephrolithotorny, hydration and diuretics were the treatment modality used. Urinary stone were found to be a significant cause of urinary tract obstruction in children, requiring prompt diagnosis and treatment. Although KUB, IVP, and ultrasonography were commonly used to make the diagnosis, many cases were detected only by ultrasonographic study.
The objective of this study is to actualize a statistical model of the 3-detector simplification model, which was proposed to detect outbreak situations by Daganzo in 1997 and to verify the statistical appropriacy thereof. This study presents the calculation process of the 3-detector simplification model and realizes the process using a statistics program. Firstly, the model was applied using data on detector of the main highways on which there is no entrances or exits. Moreover, in order to statistically verify the 3-detector simplification model, accumulative traffics for 30 seconds period, which reflects the dynamic changes of traffics due to shock wave, were estimated for outbreak traffics and steady flow, and the error of acquired data was statistically compared with that of the actual accumulative traffics. As a result, the error ratio between steady and incident cumulative flows has reached its maximum after 2-3 hours from an accident. Moreover, the incident traffic flows by accidents and the stade flows are heterogeneous in terms of their dispersion and means.
Journal of the Computational Structural Engineering Institute of Korea
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v.32
no.5
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pp.287-296
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2019
In this study, the effect of ground boundary conditions on the evaluation of blast resistance performance of precast arch structures was evaluated by a numerical analysis method. Two types of boundary conditions, namely, fixed boundary conditions and a perfectly matched layer (PML) were applied to numerical models. Blast loads that were much higher than the design load of the target structure were applied to compare the effects of the boundary conditions. The distribution and path of the ground explosion pressure, structural displacement, fracture of concrete, stress of concrete, and reinforcing bars were compared according to the ground boundary condition settings. As a result, the reflecting pressure shock wave at the ground boundaries could be effectively eliminated using PML elements; furthermore, the displacement of the foundation was reduced. However, no distinct difference could be observed in the overall structural behavior including the fracture and stress of the concrete and rebar. Therefore, when blast simulations are performed in the design of protective structures, it is rational to apply the fixed boundary condition on the ground boundaries as conservative design results can be achieved with relatively short computation times.
Modern aircraft fighters improve the maneuverability and performance with the RSS (Relaxed Static Stability) concept and therefore these aircrafts are susceptible to abrupt pitch-up in the transonic and moderate Angle-of-Attack (AoA) flight region where the shock wave is formed and the mean aerodynamic center is moved forward during deceleration. Also, the modeling of the aircraft flying in this flight region is very difficult due to complex flow filed and unpredictable dynamic characteristics and the model-based control design technique does not fully cover this problem. In this paper, we analyzed the performance of the TPMC (Transonic Pitching Moment Compensation) control based on the model-based IDI (Incremental Dynamic Inversion) and the Hybrid IDI based on the model and sensor based IDI during the SDT (Slow Down Turn) in transonic region. As the result, the Hybrid IDI had quicker response and the same maximum g suppression performance and provided the predictable flying qualities compared to the TPMC control. The Hybrid IDI improved the performance of the Over-G protection controller in the transonic and moderate AoA region
Journal of the Korea Academia-Industrial cooperation Society
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v.22
no.2
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pp.558-564
/
2021
The water purifier market has increased rapidly in recent years. The welding technology of the evaporator is a key component that determines the level of ice production and the cold water performance of an ice purifier. The finger type evaporator of an ice purifier can remove ice and is divided largely into an instant heat method and a hot gas method. In the hot gas type evaporator, particularly during the production process, the pinhole phenomenon inside the copper pipe and clogging problems occur intermittently when welding high-pressure pipes due to the high-temperature oxygen welding. Its use in a water purifier can cause a problem in that ice and cold water do not form, and repairs cannot be made on site. To solve this problem, in this study, a cap jig was applied to improve the welding defect of the hot gas evaporator. In addition, the oxygen welding flame size was adjusted so that the heat source could be well supplied to the cap jig, and the effectiveness was confirmed through a wave pressure test, a test, and a thermal shock test.
Bae, Jong In;Lee, Haeng Bok;Kim, Jeong Won;Lee, Kyung Mook;Kim, Myung-Whun
Korean Journal of Optics and Photonics
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v.33
no.2
/
pp.74-83
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2022
The entire process, from the raw material to the final system qualification test, has been developed to fabricate a large-diameter, lightweight reflective-telescope system for a satellite observation. The telescope with 3 anastigmatic mirrors has an aperture of 700 mm and a total mass of 66 kg. We baked a silicon carbide substrate body from a carbon preform using a reaction sintering method, and tested the structural and chemical properties, surface conditions, and crystal structure of the body. We developed the polishing and coating methods considering the mechanical and chemical properties of the silicon carbide (SiC) body, and we utilized a chemical-vapor-deposition method to deposit a dense SiC thin film more than 170 ㎛ thick on the mirror's surface, to preserve a highly reflective surface with excellent optical performance. After we made the SiC mirrors, we measured the wave-front error for various optical fields by assembling and aligning three mirrors and support structures. We conducted major space-environment tests for the components and final assembly by temperature-cycling tests and vibration-shock tests, in accordance with the qualifications for the space and launch environment. We confirmed that the final telescope achieves all of the target performance criteria.
The hydroxyl radical (·OH) and superoxide anion radical (·O2- ) generated by the shock wave generated during ultrasonic cavitation collapse in TiO2 suspension are highly useful because they can sterilize and disinfect. For practical use as a sterilization method without any chemicals, in this study, we proposed a method for evaluating the generation of radicals generated by high-intensity ultrasound emitted to titanium dioxide suspension. In the proposed method, the sonoluminescence phenomenon, which emits light by ultrasonic cavitation decay energy, was utilized, and the degree of radical generation was evaluated through the amount of light energy by sonoluminescence. As a result, even at a low concentration of titanium dioxide of 0.02 wt%, light energy 5 times higher than in the absence of titanium dioxide was received. After that, as the concentration increased by 0.1 wt%, the luminous intensity of sonoluminescence increased linearly by about 14.8 × 10-12 lm. Therefore, it was confirmed that the radicals generated by radiating high-intensity ultrasound to the titanium dioxide suspension increased linearly as the concentration of titanium dioxide increased within a given concentration range.
Some reports have shown a decreased effectiveness of extracorporeal shock wave lithotripsy(ESWL) with newer lithotriptors. We compared the treatment results of ESWL with a second generation Northgate SD-3 and a third generation Modulith SLX device. A total of 2,000 patients underwent ESWL treatments for single urinary calculus between September, 1988 and July, 1998. 1,241 patients were treated with Northgate SD-3 between September, 1988 and December, 1995. And 759 patients were treated with Modulith SLX between January, 1996 and July 1998. The treatment results were compared using chi-square test to determine statistical significance. The overall success rate, success rate according to the location and size, the mean number of sessions, complication rate and retreatment rate were calculated, according to lithotriptor. The overall success rate was 90.6% with Northgate SD-3 and 89.1% with Modulith SLX. With Northgate SD-3 and Modulith SLX, the success rate according to the location was 91.0%(579/636) and 88.1%(236/268) in kidney: 93.2%(517/555) and 89.9%(258/287) in upper ureter: 83.3%10/12) and 94.4%167/177) in middle and lower ureter: 47.4%(18/38) and 55. 6%(15/27) in staghorn stone, respectively. The success rate according to the size of stone with Northgate SD-3 and Modulith SLX for stones with the size under 10mm was 96.1%(612/637) and 93.1%(470/505); from 11mm to 20mm was 87.3%(421/482) and 86.4%(165/191); from 21mm to 30mm, 77.5%(62/80) and 67.5%(23/34): and for stones larger than 31mm was 69%(29/42) and 62.1%(18/29), respectively. Mean number of sessions for successful fragmentation was 1.21 and 1.69, respectively with Northgate SD-3 and Modulith SLX. Retreatment rate was 16.7% and 17.5%, respectively. The complications after treatment were severe pain(6.2% with Northgate SD-3 vs. 2.0% with Modulith SLX), steinstrasse(3.4% vs. 1.9%), fever(1.2% vs. 0.5%) and perirenal hematoma(0.2% vs. 0%) in order of frequency. There was no significant difference in the effectiveness of Northgate SD-3 and Modulith SLX. However, a statistically significant difference was observed between the two lithotriptors. We concluded that ESWL with Modulith SLX is more safe compared to Northgate SD-3.
Proceedings of the Korean Society of Propulsion Engineers Conference
/
2003.05a
/
pp.91-93
/
2003
A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.
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