• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1018-1021
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• 2006

Powdered metal parts and components may be carburized successfully in a vacuum furnace by combining carburizing technology $VacCarb^{TM}$ with a hi-tech control system. This approach is different from traditional carburizing methods, because vacuum carburizing is a non-equilibrium process. It is not possible to set the carbon potential as in a traditional carburizing atmosphere and control its composition in order to obtain a desired carburized case. This paper presents test results that demonstrate that vacuum carburizing system $VacCarb^{TM}$ carburized P.M. materials faster than traditional steel with acceptable results. In the experiments conducted, PM samples with the lowest density and open porosity showed a dramatic increase in the surface carbon content up to 2.5%C and a 3 times deeper case. Currently the boost-diffusion technique is applied to control the surface carbon content and distribution in the case. In the first boost step, the flow of the carburizing gas has to be sufficient to saturate the austenite, while avoiding soot deposition and formation of massive carbides. To accomplish this goal, the proper gas flow rate has to be calculated. In the case of P.M. parts, more carbon can be absorbed by the part's surface because of the additional internal surface area created by pores present in the carburized case. This amount will depend on the density of the part, the densification grade of the surface layer and the stage of the surface. "as machined" or "as sintered". It is believed that enhanced gas diffusion after initial evacuation of the P.M. parts leads to faster carburization from within the pores, especially when pores are open . surface "as sintered" and interconnected . low density. A serious problem with vacuum carburizing is delivery of the carbon in a uniform manner to the work pieces. This led to the development of the different methods of carburizing gas circulation such as the pulse/pump method or the pulse/pause technique applied in SECO/WARWICK's $VacCarb^{TM}$ Technology. In both cases, each pressure change may deliver fresh carburizing atmosphere into the pores and leads to faster carburization from within the pores. Since today's control of vacuum carburizing is based largely on empirical results, presented experiments may lead to better understanding and improved control of the process.

• Bulletin of the Korean Chemical Society
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• v.24 no.12
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• pp.1775-1780
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• 2003

A continuous flow system has been developed to determine trace Cu(II), Mn(II), Ni(II) and Zn(II) in a large volume of water samples by a solvent sublation technique. The mixed solution of 1,10-phenanthroline(phen) and thiocyanate ion was used as ligands for the formation of their ternary complexes. The continuous system was constructed in this laboratory with a peristaltic pump, a mini shaker, three mixing bottles and a flotation cell by connecting each part with a polyethylene tube. The flotation conditions such as the flow rate of sample solution and the injection rates of ligand, buffer and surfactant solutions have been investigated to obtain the best sublation efficiencies. Each solution flowed into the flotation cell through each polyethylene tube by the peristaltic pumps. The ternary complexes were floated and extracted into MIBK in a flotation cell of 2 L by bubbling a nitrogen gas. The absorbances of extracted analytes in MIBK were directly measured by graphite furnace-AAS. The concentrations of 1,10-phenanthroline and thiocyanate ion were $2.6\;{\times}\;10^{-3}$ M and $2.3\;{\times}\;10^{-2}$ M in the mixed solution, respectively. The pH of sample solution was adjusted to 5.0 with a buffer solution and 1%(m/v) sodium lauryl sulphate solution was added as a surfactant to support the effective flotation of the complexes. The $N_2$ gas was bubbled at 30 mL/min for 90 minutes for 20 L of sample. Reproducible results of less than 10% RSD and recoveries of 80-120% could be obtained in real samples.

• Journal of Sensor Science and Technology
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• v.13 no.5
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• pp.329-334
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• 2004

Functional residual capacity (FRC) is an important diagnostic parameter measured using $N_{2}$ analyzer. Since $N_{2}$ analyzer is expensive as well as cumbersome for use of noisy vacuum pump, the FRC measurement becomes possible only in large well-equipped hospitals. The present study introduced a new $TN_{2}$ wash-out technique to measure FRC by $O_{2}/CO_{2}$ analysis, which is relatively cheaper and much simpler to apply. Slower $O_{2}$ response was compensated for high frequency to be coincided with $CO_{2}$ response, thereby enabled indirect, but accurate $N_{2}$ concentration measurement. FRC was estimated by continuous integration of expired $N_{2}$ volume obtained with air flow signal. Experiment with 3 L syringe, a standard calibration device recommended by the American Thoracic Society, demonstrated less than 1% error at 0, 1, and 2 L. Correlation coefficient was almost ideal, guaranteeing linear estimation of FRC. The present technique is inexpensive and simple to apply, thus should he of great convenience.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.1
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• pp.33-41
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• 2014

In a supersonic turbine, A rotor overlap technique reduced the chance of chocking in the rotor passage, and made the design pressure ratio satisfied. However, the technique also made additional losses, like a pumping loss, expansion loss, etc. Therefore, an approximate optimization technique was appled to find the optimal shape of overlap which maximizes the improvement of the turbine performance. The design variables were shape factors of a rotor overlap. An optimal design for rotor overlap reduces leakage mass flow rate at tip clearance by about 50% and increases about 4% of total-static efficiency compared with the base model. It was found that the most effective design variable is the tip overlap and that the hub overlap size is the lowest.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1889-1896
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• 2003

In the microfluidic applications, viscous-driven pumping mechanism is a promising one since the viscous effect increases significantly as the size of device decreases, relative to the inertial effect. However, there exist a few drawbacks we have to improve such as low efficiency and small volume flow rate. In the present study, an optimum design synthesis is proposed to enhance the performance characteristics of the micropump with single rotating cylinder. First, the unstructured grid CFD method is described and validated by comparing its results to the previous results. Next, an automated optimum design synthesis tool is constructed by combining the aforementioned CFD analysis model with the mathematical optimization model. This technique is used to improve the performance characteristics of newly designed viscous-driven pump. The presented results show that the fluid dynamic optimization tool is robust and may be applied to other microfluidic device design applications.

• Analytical Science and Technology
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• v.26 no.1
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• pp.34-41
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• 2013

Split-flow thin cell (SPLITT) fractionation (SF) is a rapid separation technique capable of separating colloidal particles or macromolecules into two or more fractions. SF allows fractionations in a preparative scale as sample is fed continuously. Generally SF uses a thin ribbon-like channel equipped with two flow stream splitters at the inlet and outlet of the channel. Thus there exist two flow inlets and two flow outlets at the top and bottom of the inlet and outlet of the channel, respectively. There are two operating modes in SF, conventional mode and full-feed mode (FFD). Although the resolution in the FFD mode is lower than that in the conventional mode, FFD mode has some merits. The design of the channel and operation are simpler in the FFD mode, as it does not require the feeding of the solvent. Thus there is no flow stream splitter at the channel inlet, and only one pump is needed, unlike the conventional mode, where two pumps are required for the feedings of the sample and the solvent separately. Also the sample is not diluted in the FFD mode as there is no solvent feeding, which is important for fractionation samples with low colloidal concentrations such as environmental samples. For some of environmental samples, pre-concentration is often required. In this study, a new large-scale splitter-less FFD-SF channel was implemented, where there is no splitter at the outlet as well as at the inlet of the channel. It was possible to build the channel in a much larger dimension than conventional ones, allowing much higher sample throughput (TP). The new channel was tested and optimized with polyurethane (PU) latex beads, and then applied to large-scale separation of Polyacrylate (PA).

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.39-44
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• 2008

The heat exchange between the Borehole Heat Exchanger(BHE) and the surrounding ground depends directly on ground thermal conductivity k at the certain site. The k is thus a key parameter in designing BHE and coupled geothermal heat pump systems. Currently, although a thermal hydraulic response test(TRT) is mostly used in practice, the thermal hydraulic TRT needs additional power and is generally time-consuming. A new, simple wireless P/T probe for a hi-speed k determination was introduced in this paper. This technique using a wireless P/T probe is less time-consuming and requires no external source of energy for measurement and predicts local thermal properties by measuring soil temperatures along the depth. Measured temperature data along the depth was analyzed. In order to verify the new technique for the determination of ground thermal conductivity, ground thermal conductivity k that calculated from the measured temperature data using a wireless P/T probe was compared with one obtained from conventional hydraulic TRT. When comparing the average k of two methods, the relative error was approximately 10%. As a result, the electronic TRT can replace the conventional hydraulic TRT method after carrying out the additional research on a lot of sites.

• Journal of Chest Surgery
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• v.37 no.1
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• pp.11-18
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• 2004

Background: We tested the effect of indomethacine and total spinal anesthesia on the improvement of placental flow during cardiopulmonary bypass on fetal lamb. Material and Method: Twenty fetuses at 120 to 150 days of gestation were subjected to bypass via trans-sternal approach with a 12 G pulmonary arterial cannula and 14 to 18 F venous cannula for 30 minutes. All ewes received general anesthesia with ketamine. In all the fetuses, no anesthetic agents were used except muscle relaxant. Ten served as a control group in which placenta was worked as an oxygenator during bypass (Control group). The remainder worked as an experimental group in which pretreatment with indomethacine and total spinal anesthesia was performed before bypass with the same extracorporeal circulation technique as control group (Experimental group). Observations were made every 10 minutes during a 30-minute bypass and 30-minute post bypass period. Result: Weights of the fetuses ranged from 2.2 to 5.2 kg. In Control group, means of arterial pressure decreased from 44.7 to 14.4 mmHg and means of Pa$CO_2$ increased from 61.9 to 129.6 mmHg at each time points during bypass. Flow rate was suboptimal (74.3 to 97.0 $m\ell$/kg/min) during bypass. All hearts fibrillated immediately after the discontinuation of bypass. On the contrary, in Experimental group, means of arterial pressure reamined higher (45.8 to 30 mmHg) during bypass (p<0.05). Means of Pa$CO_2$ were less ranging from 59.8 to 79.4 mmHg during bypass (P<0.05). Flow rates were higher (78.8 to 120.2 $m\ell$/kg/min) during bypass (p<0.05). There were slower deterioration of cardiac function after cessation of bypass. Conclusion: In this study, we demonstrated that the placental flow was increased during fetal cardiopulmonary bypass in the group pretreated with indomethacine and total spinal anesthesia. However, further studies with modifications of the bypass including a creation of more concise bypass circuit, and a use of axial pump are mandatory for the clinical application.

• Journal of Chest Surgery
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• v.24 no.2
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• pp.123-134
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• 1991

Twenty eight patients had undergone repair of an isolated complete atrioventricular septal defect between April 1986 and September 1990 in Seoul National University Children`s Hospital. The group comprised 13 male and 15 female patients. They ranged in age from 2 months to 8 years[mean 18.6months] and in weight from 3. 4kg to 23kg[mean 9.0$\pm$4.6kg]. They were analysed as Rastelli type A in 17 patients, Rastelli type B in 2 patients, and Rastelli type C in 9 patients. Seven patients had concomitant Down`s syndrome. All patients had large left-to-right shunt[mean pulmonary to systemic flow ratio 3.5 $\pm$2.2 ranging from 0.68 to 10.0] and high pulmonary systolic pressure[mean 74$\pm$18.8mmHg, ranging from 35 to 110]. In 11 patients, one patch technique was used to close the atrial and ventricular septal defect and 16 patients were undergone by two patch technique. We urgently managed only one patient by pulmonary artery banding whose anatomy was Rastelli type C and severe mitral regurgitation was identified. Postoperative complete A - V block was noted in 3 patients, two of whom were dead in operating room due to combined LVOTO and myocardial failure, and one patient with Rastelli type C was undergone by VVI type permanent pacemaker insertion 1wk later after two patch technique, but we had to manage him by modified Konno operation and total correction due to LVOTO and VSD leakage and severe mitral regurgitation 3 years later. Another two reoperation cases due to severe mitral regurgitation after two patch technique were undergone, one of whom we managed by mitral annuloplasty 3 months later but aggravated mitral regurgitation made us to control him by MVR 3 months later. Another one case of VSD leakage and tricuspid regurgitation was managed by total correction but she died of respiratory insufficiency 14 days later. We experienced pulmonary hypertensive crisis in 3 patients, who were dead in two cases comparing with one control case. So operative mortality is 9/27[33.6%], in one patch group of 3/11[29.2%] comparing with two patch group of 6/16[37.5%]. In summary, causes of death were pump weaning failure, myocardial failure and low cardiac output syndrome and pulmonary hypertensive crisis, resp. failure, complete AV block. Mean follow up period is 15.8$\pm$10.7 months[ranging from 3months to 37 months]

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.2
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• pp.153-170
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• 2022

Waterjet has been comprehensively used in urban areas owing to a suitable technique for cutting concrete and rock, and low noise and vibration. Recently, the abrasive waterjet technique has been adopted and applied by the Korea Atomic Energy Research Institute to demolish concrete plugging without disturbing and damaging In-situ Demonstration of Engineered Barrier System in the disposal research tunnel. In this study, the use of abrasive waterjet in the tunnel was evaluated for practical applicability and the existing cutting model was compared with the experimental results. As a variable for waterjet cutting, multi-cutting, water flow rate, abrasive flow rate, and standoff distance were selected for the diversity of analysis. As regarding the practical application, the waterjet facilitated path selection for cutting the concrete plugging and prevented additional disturbances in the periphery. The pump's noise at idling was 64.9 dB which is satisfied with the noise regulatory standard, but it exceeded the standard at ejection to air and target concrete because the experiment was performed in the tunnel space. The experimental result showed that the error between the predicted and measured cutting volume was 12~13% for the first cut and 16% for second cut. The standoff distance had a significant influence on the cutting depth and width, and the error tended to decrease with decrement of standoff distance.