• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2188-2197
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• 2022

To ensure the safety margin of a reactor pressure vessel (RPV) under normal operating conditions, it is regulated through the pressure-temperature (P-T) limit curve. The stress intensity factor (SIF) obtained by the internal pressure and thermal load should be obtained through crack analysis of the nozzle corner crack in advance to generate the P-T limit curve for the nozzle. In the ASME code Section XI, Appendix G, the SIF via the internal pressure for the nozzle corner crack is expressed as a function of the cooling or heating rate, and the wall thickness, however, the SIF via the thermal load is presented as a polynomial format based on the stress linearization analysis results. Inevitably, the SIF can only be obtained through finite element (FE) analysis. In this paper, simple prediction equations of the SIF via the thermal load under, cool-down and heat-up conditions are presented. For the Korean standard nuclear power plant, three geometric variables were set and 72 cases of RPV models were made, and then the heat transfer analysis and thermal stress analysis were performed sequentially. Based on the FE results, simple engineering solutions predicting the value of thermal SIF under cool-down and heat-up conditions are suggested.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.5
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• pp.281-288
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• 2002

Recombinant Escherichia coli strain harboring the ${\lambda}$pR-pL promotor and heterologus poly-${\beta}$-hydroxybutyrate (PHB) biosynthesis genes was used to investigate the effect of culture conditions on the efficient PHB production. The expression of phb genes was induced by a temperature upshift from $33^{\circ}C\;to\;38^{\circ}C$. The protein expression levels were measured by using two-dimensional electrophoresis, and the enzyme activities were also measured to understand the effect of culture temperature, carbon sources, and the dissolved oxygen (DO) concentration on the metabolic regulations. AcetylCoA is an important branch point for PHB production. The decrease in DO concentration lowers the citrate synthase activity, thus limit the flux toward the TCA cycle, and increase the flux for PHB production. Since NADPH is required for PHB production, the PHB production does not continue leading the overproduction of acetate and lac-tate. Based on these observations, a new operation was considered where DO concentration was changed periodically, and it was verified its usefulness for the efficient PHB production by experiments.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.180-186
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• 2009

To meet the NOx limit without a penalty of fuel consumption, urea SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal $NH_3$ slip. In this study, as a basic research to develop an algorithm for urea injection control, the characteristics of engine out NOx emission and behavior of NOx reduction during steady-state and transient conditions were investigated using 2L DI diesel engine. Test results show that on increasing the catalyst temperature the variations in the outlet NOx concentration are faster and maximal allowable $NH_3$ storage exponentially decreases. For change from a low to high engine load, it can be seen that a few seconds after load-step is required to reach full NOx conversion and the adsorbed amount of $NH_3$ at lower temperature desorb during the next temperature increase, causing $NH_3$ slip. Engine out NOx emission needs to be corrected because NOx emissions just after step load is lower than that of steay state condition.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3144-3149
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• 2007

A numerical analysis for temperature distribution of four different materials such as iron, silicon, aluminum and PVC has been performed in this study to predict thermal behaviors of combined weapon systems in a large environmental tester. Thus, experimental conditions have been proposed using a calculating software (SolidWorks 2007 COSMOS FloWorks) to prepare for field tests and analyze heat flow inside the environmental tester and temperature distributions of materials. The boundary conditions of the analysis are composed of inlet and outlet conditions of the environmental tester with different pressures and the limit of low temperature of -30$^{\circ}C$. The soaking time of the system in the environmental tester has been calculated by this commercial program in this study to carry out the experiment.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.379-384
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• 2000

We cooled cesium atoms below the Doppler cooling limit by laser cooling. For this deep cooling of atoms, the laser frequency was shifted by using the Zeeman shift of an absorption line of cesium. The stabilization of the laser frequency was maintained while the laser frequency was shifted by 40 MHz within 2 ms. The lowest temperature of the laser-cooled cesium atoms was $2.2\muK$\pm$0.5$\muK$in this experiment. We measured the temperature of the laser-cooled cesium atoms as a function of the frequency detuuing and the intensity of the cooling laser. The results agreed well with the ones calculated by two-photon laser cooling theory.theory.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.1014-1022
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• 2009

In this paper, interference analysis is carried out to obtain the operating criterion and coexistence condition between digital television devices and cognitive radio-based mobile wimax devices in the UHF (Ultra High Frequency) broadcasting frequency bands. To this end, an efficient interfering calculation tool known as SEAMCAT (Spectrum Engineering Advanced Monte-Carlo Analysis Tool) is employed to acquire the coexistence criterions between heterogeneous radio links operating in the same portion of spectrum. As a result, these criterions will be used to achieve interference temperature limit level applied to interference temperature model for analyzing the capacity of cognitive radio receivers accurately.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.483-489
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• 2009

A CFD code was developed to investigate the inception of cavitation around impeller blades of centrifugal fuel pump using two dimensional cascade modeling. With the verification test for numerical validity of the developed code, the prediction of the onset of cavitation was made for the configuration of a newly designed KHP fuel pump. The calculation results show impeller design was free of cavitation if the pump operates within the operational temperature and rotational speed range. However, the cavitation would be relatively easy to occur at off design region of fuel pump where the rotational speed is higher than design limit. Specially, the onset of cavitation is sensitively dependent on the increase in fuel temperature while the decrease in temperature will reduce the possibility of cavitation inception in the pump.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.51.3-51.3
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• 2010

Due to the recent public awareness of global warming and sustainable economic growth, there has been a growing interest in alternative clean energy sources. Hydrogen is considered as a clean fuel for the next generation. One of the technical challenges related to the use of hydrogen is safe monitoring of the hydrogen leak during separation, purification and transportation. For detecting various gases, chemiresistor-type gas sensors have been widely studied and used due to their well-established detection scheme and low cost. However, it is known that many of them have the limited sensitivity and slow response time, when used at low temperature conditions. In our work, a sensor based on Schottky barriers at the electrode/sensing material interface showed promising results that can be utilized for developing fast and highly sensitive gas sensors. Our hydrogen sensor was designed and fabricated based on indium oxide (In2O3)-doped tin oxide (SnO2) semiconductor nanoparticles with platinum (Pt) nanoclusters in combination with interdigitated electrodes. The sensor showed the sensitivity as high as $10^7%$ (Rair/Rgas) and the detection limit as low as 30 ppm. The sensor characteristics could be obtained via optimized materials synthesis route and sensor electrode design. Not only the contribution of electrical resistance from the film itself but also the interfacial effect was identified as an important factor that contribute significantly to the overall sensor characteristics. This promises the applicability of the developed sensor for monitoring hydrogen leak at room temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.338-346
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• 2000

Although the net-shape molding of composites is generally recommended, molded composites are frequently required cutting or grinding due to the dimensional inaccuracy for precision machine elements . During the composite machining operations such as cutting and grinding, the temperature at the cutting point may increase beyond the allowed limit due to the low thermal conductivity of composites, which might degrade the matrix of composite. Therefore, in this work, the temperature at the cutting point during cut-off grinding of carbon fiber epoxy composites was measured. The cutting force and surface roughness were also measured to investigate the cut-off grinding characteristics of the composites. The experiments were performed both under dry and wet grinding conditions with respect to cutting speed and feed rate. From the experimental investigation, the optimal conditions for the composite cut-off grinding were suggested.

• Journal of Biomedical Engineering Research
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• v.16 no.1
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• pp.67-76
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• 1995

Explosive evaporative removal process of biological tissue by absorption of a CW laser has been simulated by using gelatin and a multimode Nd: YAG laser. Because the point of maximun temperature of laser-irradiated gelatin exists below the surface due to surface cooling, evaporation at the boiling temperature is made explosively from below the surface. The important parameters of this process are the conduction loss to laser power absorption (defined as the conduction-to-laser power parameter, Nk), the convection heat transfer at the surface to conduction loss (defined as Bi), dimensionless extinction coefficient (defined as BrJ, and dimensionless irradiation time (defined as Fo). Dependence of Fo on Nk and Bi has been observed by experiment, and the results have been compared with the numerical results obtained by solving a 2-dimensional conduction equation. Fo and explosion depth (from the surface to the point of maximun temperature) are increased when Nk and Bi are increased. To find out the minimum laser power for explosive evaporative removal process, steady state analysis has been also made. The limit of Nk to induce evaporative removal, which is proportional to the inverse of the laser power, has been obtained.