• Journal of computational fluids engineering
• /
• v.15 no.2
• /
• pp.86-94
• /
• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation or condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure distribution that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new reconstruction method to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2004.08a
• /
• pp.471-474
• /
• 2004

We investigated field emission (FE) characteristics of multi-walled carbon nanotubes (CNTs) grown on all over patterned cathode electrode lines (CL pattern) and grown on along the central areas of the cathode lines(CL pattern). The CNTs grown on the SL pattern showed a lower threshold voltage and higher emission current than those on the CL pattern, due to the concentration of electric fields at the edges of the cathode lines. For the SL-patterned CNTs, however, the FE gradually spread out to the neighbors with time, and was instantly extinguished in some area and then slowly resumed again. Such areal- spread FE did not occur for the CL-patterned sample, leading to the stable FE together with the instant turn-on capability. It is suggested that the spread FE and instability for the SL-patterned CNTs may be related to the electrical charging on the insulator surface around the cathode line edges.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.10 no.3
• /
• pp.248-256
• /
• 2005

This paper presents the design method of the DC/DC converter using flat transformer which is suitable for midium or large capacity and high density power supply. Flat transformer module is composed and manufactured of multi-transformers in parallel and has a number of parallel single turn secondary windings. Therefore, its leakage inductance is highly decreased and it is more suitable for high frequency operation than conventional one. In this paper, we manufactured and tested 750W AC/DC converter with variable output powers to verify the performance of the flat transformer.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.380-388
• /
• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation of condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new numerical scheme to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the cupid code.

• Journal of Magnetics
• /
• v.17 no.1
• /
• pp.9-12
• /
• 2012

Attempts to dope carbon nanotube (CNT) with impurities in order to control the electronic properties of the CNT is a natural course of action. Boron is known to improve both the structural and electronic properties. In this report, we study the field emission properties of Boron-doped double-walled CNT (DWCNT). Boron-doped DWCNT films were fabricated by catalytic decomposition of tetrahydrofuran and triisopropyl borate over a Fe-Mo/MgO catalyst at $900^{\circ}C$. We measured the field emission current by varying the doping amount of Boron from 0.8 to 1.8 wt%. As the amount of doped boron in the DWCNT increases, the turn-on-field of the DWCNT decreases drastically from 6 V/${\mu}m$ to 2 V/${\mu}m$. The current density of undoped CNT is 0.6 mA/$cm^2$ at 9 V, but a doped-DWCNT sample with 1.8 wt% achieved the same current density only at only 3.8 V. This shows that boron doped DWCNTs are potentially useful in low voltage operative field emitting device such as large area flat panel displays.

• Journal of the Korean Society for Heat Treatment
• /
• v.33 no.6
• /
• pp.303-309
• /
• 2020

A vehicle's differential gear is a device designed to allow the vehicle's outer wheels to turn faster than the inner wheels when turning on a curve. The differential gear case is the main component of the differential gear system, which is composed of ring gear, pinion gear and side gear, and is fastened by pinion shaft pins. The differential gear case rotates when the vehicle is running, so balancing calibration is very important. In this study, a balancing machine that can diagnose and correct the differential gear case and mass imbalance of various rotating bodies was designed. The differential gear case was rotated at high speed to accurately diagnose the location and value of the unbalanced mass, and it was designed to be balanced and corrected by removing the unbalanced mass by drilling. After calibration, it was confirmed that the unbalanced value of all the measured samples was reduced to less than 180g.mm, and the unbalance reduction ratio was improved to 60~70%.

• Progress in Superconductivity and Cryogenics
• /
• v.9 no.2
• /
• pp.35-38
• /
• 2007

A single-stage and two-stage pulse tube refrigerators have been designed for cryopump application. The different diameters of pulse tube and regenerator have been investigated at single-stage pulse tube refrigerator(PTR). Experiments have been performed on single-stage PTR to reach minimum temperature with optimum valve opening at a few frequencies. And the two-stage pulse tube refrigerators have been assembled with tested single-stage pulse tube and tested. When orifice turn is opened to 9 and double inlet is opened to 3 at a single-stage, the lowest temperature of 33.7 K is achieved. The cooling capacity at single-stage is 38 W at temperature of 80 K. A two-stage pulse tube refrigerator has 16.3K at the second stage and 59.7K at the first stage. The cooling capacity achieved is 16.5 W at 80 K, the first stage and 0.6 W at 20 K, the second stage. Some details on the design of pulse tube refrigerator and the experimental apparatus are given.

• Electronics and Telecommunications Trends
• /
• v.39 no.4
• /
• pp.54-62
• /
• 2024

The emergence and resurgence of novel respiratory infectious diseases since the turn of the millennium, including SARS, H1N1 flu, MERS, and COVID-19, have posed a significant global health threat. Efforts to combat these threats have involved various approaches, however, continued research and development are crucial to prepare for the possibility of emerging viruses and viral variants. Direct detection methods for viral pathogens include molecular diagnostic techniques and immunodiagnostic methods, while indirect diagnostic methods involve detecting changes in the condition of infected patients through imaging diagnostics, gas analysis, and biosignal measurement. Molecular diagnostic techniques, utilizing advanced technologies such as gene editing, are being developed to enable faster detection than traditional PCR methods, and research is underway to improve the efficiency of diagnostic devices. Diagnostic technologies for infectious diseases continue to evolve, and several key trends are expected to emerge in the future. Automation will facilitate widespread adoption of rapid and accurate diagnostics, portable diagnostic devices will enable immediate on-site diagnosis by healthcare professionals, and advancements in AI-based deep learning diagnostic models will enhance diagnostic accuracy.

• Journal of the Korean association of regional geographers
• /
• v.21 no.2
• /
• pp.207-225
• /
• 2015

This study attempts to explore settlement and adaptation status involved in differing urban-to-rural migration types in Gyeongbuk Province and suggests policy implications based on this analysis. The attributes of urban-to-rural migrants in Gyeongbuk Province differ spatio-temporally, and their status of settlement and adaptation is also different depending on urban-to-rural migration types. "U-turn" migrants who are mostly first-generation rural-to-urban migrants with experience in farming and rural community life engage primarily in crop agriculture. "J-turns" and "I-turns," who have no experience in farming or rural community life, migrated for idyllic rural life. The household income of these types is relatively low compared to U-turn type. U-turns' degree of adaptation is relatively lower than the other types, and U-turn migrants mainly rely on family and community assets in order to solve problems. J-turns' and I-turns' degree of satisfaction is relatively high. However they typically have substantial difficulties in adapting due to lack of pre-migration preparation. Policy implications are : 'switching away from general and inclusive policies of support,' 'transition to policies embedded in the attributes of regions and migration types,' 'improvement of policy governance,' 'enhancement of support for pre-migration preparation and customized support based on the needs of migrants,' and 'comprehensive improvements of settlement environment to better integrate migrants with current residents.'.

• Advances in Traditional Medicine
• /
• v.10 no.4
• /
• pp.263-270
• /
• 2010

Scoparia dulcis L. is widely used in the traditional system of medicine for treating liver ailments. In the present study the terpenoids and terpenoid fractions isolated from 1:1:1 petroleum ether, diethyl ether and methanol (PDM) extract of Scoparia dulcis L. were tested for their in vitro 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Selected samples from the assay were further tested for their in vitro hepatoprotective activity against $CCl_4$ induced hepatotoxicity in freshly isolated rat hepatocytes. In the in vitro antioxidant study, fractions 7, 11, 13, 14, and 15 and PDM extract show the DPPH radical scavenging activity. The phytochemical screening of all these fractions show the presence of terpenoids. In the in vitro hepatoprotective study all these fractions and the PDM extract significantly prevent the $CCl_4$ induced changes in the aspartate aspartate amino transferase, alanine amino transferase and alkaline phosphatase levels (p < 0.05). The above results are comparable with the standard, silymarin. The results of the study indicate that, the PDM extract of Scoparia dulcis L. possesses potential hepatoprotective activity and this may be attributed to its free radical scavenging potential, which in turn may be attributed to the presence of terpenoids.