• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.976-983
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• 2004

In high-density hard disk drives, the slider should be made to fly close to the magnetic recording disk to generate better signal resolution and at an increasingly high velocity to achieve better data rate. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation. Contamination particles in the hard disk drive can cause serious problems including slider crash and thermal asperities. We investigated the number and the sizes of particles generated in the hard disk drive, operating at increasing disk rotational speeds, in the CSS mode. CNC (condensation nucleus counter) and PSS (particle size selector) were used for this investigation. In addition, we examined the particle components by using SEM (scanning electron microscopes), AES (auger electron spectroscopy), and TOF-SIMS (time of flight-secondary ions mass spectrometry). The increasing disk rotational speed directly affected the particle generation by slider disk interaction. The number of particles that were generated increased with the disk rotational speed. The particle generation rate increased rapidly at motor speeds above 8000 rpm. This increase may be due to the increased slider disk interaction. Particle sizes ranged from 14 to 200 nm. The particles generated by slider disk interaction came from the lubricant on the disk, coating layer of the disk, and also slider surface.

• Journal of Marine Bioscience and Biotechnology
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• v.12 no.1
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• pp.11-19
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• 2020

This study aims to review the progress of biotechnological applications of sea cucumber and presents fundamental validation data on a range of methods and applications to determine the most promising fields for future exploitation and application. Sea cucumbers from different regions, subjected to numerous industrially applicable drying methods, were evaluated for their biochemical composition. The study highlights the nutritional excellence of Jeju red sea cucumber, particularly the high amino acid and fatty acid composition of its intestinal organs and the possibility of the industrial utilization of these organs. In addition, an efficient extraction method to extract collagen and chondroitin sulfate from red sea cucumber was established. The extracted collagen and chondroitin sulfate can be used as commercially valid biomaterials. Accordingly, the red sea cucumber was confirmed as a valuable source of raw food material of varied functionality and bioactivity. Upon conducting an analysis of patents thus far relating to the sea cucumber, it was found that the associated technology was limited to some parts of primary and secondary industries. Therefore, there is a clear need for the strategic development of technologies to produce specialized functional products from sea cucumber's raw materials, with a view to promote other related industries.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.2
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• pp.168-180
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• 2011

The variation of the physicochemical properties of atmospheric aerosols in coexistence of the heavy Asian Dust and Haze observed from $15^{th}$ to $17^{th}$ March 2009 in Seoul was scrutinized through the mass and ion concentration observations and synoptic weather analysis. Although the ratio of PM1.0/PM10 was constant at 0.3 (which is typical during Asian Dust period in Korea) during the measurement period, both PM10 and PM1.0 mass concentrations were 3~6 times and 2~4 times higher than that of clear days, respectively. Water-soluble ion components accounted for 30~50% of PM10 and 50~70% of PM1.0 mass concentration. One of the secondary pollutants, $NO_3^-$ was found to be associated with $Ca^{2+}$ and $Na^+$ in coarse mode indicating that the aerosol derived from natural source was affected by anthropogenic pollutants. While the acidity of the aerosols increased in fine mode when the stagnation of weather patterns was the strongest (March $16^{th}$), the alkalinity increased in coarse mode when new air masses arrived with a southwestern wind after ending a period of stagnation (March $17^{th}$). In the selected case, SOR (Sulfur Oxidation Ratio, $nSO_4^{2-}/[nSO_4^{2-}+nSO_2]$) and NOR (Nitrogen Oxidation Ratio, $nNO_3^-/[nNO_3^-+nNO_2]$) values of ion components were higher than the general values during Asian Dust period. These results imply that dust aerosols could be mixed with pollutants transported from China even in heavy Asian Dust cases in Korea.

• Journal of Wetlands Research
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• v.13 no.3
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• pp.481-488
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• 2011

Various development activities have lead to the destruction of the ecosystem such as natural wetlands. In order to protect these natural wetlands, the Ministry of Environment (MOE) in Korea enacted the Wetland Conservation Act in 1999 and designated protected areas for wetland conservation. The MOE adapted the use of Best Management Practices (BMP) such as retention ponds and constructed wetlands to treat the polluted water before entering the water system. One of these projects was a free-water surface flow (FWS) constructed wetland built as a secondary treatment unit for piggery wastewater effluent coming from a livestock wastewater treatment facility. Water quality monitoring for the constructed wetland was conducted during rainfall events. The results showed that the average removal efficiencies of TSS, BOD, TN, TP were 86, 60, 45, 70%, respectively. It was observed that the removal efficiency of particulate matter and phosphorus was high compared to nitrogen. Therefore, a longer hydraulic retention time was needed in order to improve the treatment efficiency of nitrogen. The results of this study can contribute to the wetland design, operation and maintenance of constructed wetlands.

• Journal of Power Electronics
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• v.11 no.2
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1399-1404
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• 2015

This paper analyzed the phenomenon of drain induced barrier lowering(DIBL) for the ratio of channel length vs. thickness of asymmetric double gate(DG) MOSFET. DIBL, the important secondary effect, is occurred for short channel MOSFET in which drain voltage influences on potential barrier height of source, and significantly affects on transistor characteristics such as threshold voltage movement. The series potential distribution is derived from Poisson's equation to analyze DIBL, and threshold voltage is defined by top gate voltage of asymmetric DGMOSFET in case the off current is 10^-7 A/m. Since asymmetric DGMOSFET has the advantage that channel length and channel thickness can significantly minimize, and short channel effects reduce, DIBL is investigated for the ratio of channel length vs. thickness in this study. As a results, DIBL is greatly influenced by the ratio of channel length vs. thickness. We also know DIBL is greatly changed for bottom gate voltage, top/bottom gate oxide thickness and channel doping concentration.

• Atmosphere
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• v.29 no.4
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• pp.429-438
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• 2019

Organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured with Sunset Laboratory Model-5 Semi-Continuous OC/EC Field Analyzer by NIOSH/TOT method at Anmyeondo Global Atmosphere Watch (GAW) Regional Station (37°32'N, 127°19'E) in July and August, 2017. The mean values of OC and EC were 3.7 ㎍ m^-3 and 0.7 ㎍ m^-3, respectively. During the study period, the concentrations of reactive gases and aerosol compositions were evidently lower than those of other seasons. It is mostly due to meteorological setting of the northeast Asia, where the influence of continental outflow is at its minimum during this season under southwesterly wind. While the diurnal variation of OC and EC were not clear, the concentrations of O₃, CO, NOx, EC, and OC were evidently enhanced under easterly wind at night from 20:00 to 8:00. However, the high concentration of EC was observed concurrently with CO and NOx under northerly wind during 20:00~24:00. It indicates the influence of thermal power plant and industrial facilities, which was recognized as a major emission source during KORUS-AQ campaign. The diurnal variations of pollutants clearly showed the influence of land-sea breeze, in which OC showed good correlation between EC and O₃ in seabreeze. It is estimated to be the recirculation of pollutants in land-sea breeze cycle. This study suggests that in general, Anmyeondo station serves well as a background monitoring station. However, the variation in meteorological condition is so dynamic that it is primary factor to determine the concentrations of secondary species as well as primary pollutants at Anmyeondo station.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.151-158
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• 1990

Various factors may contribute on the mixing processes in the surf zone formed by irregular waves. The turbulence motion driven by wave breaking may be one of the major causes, the effect due to spatial variation on current velocity be a secondary one, and the additional process may result from the irregular superposition of radiation stresses or wave breaking dissipation incurred by random breaking waves in a broadened surf zone. In the present study a numerical model of spectral waves and induced currents was developed using a superposition technique with ${\kappa}-{\varepsilon}$ closure for mixing process and applied to a field situation of longshore current generated by spectral waves on a uniform beach. It was found from the application that the surf-zone mixing processes formed by irregular waves can be well described by using ${\kappa}-{\varepsilon}$ equations if the source of ${\kappa}$ is properly represented. The nonlinear energy transfer was also found to have some influence on the velocity profile of longshore current particularly in very shallow water region near coast.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.360-367
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• 2009

The acoustic emission(AE) behavior of reinforced concrete slab under flexural loading was investigated to assess the integrity. This study was aimed at identifying the characteristics of AE response associated with damage development. By applying cyclic loading in various load steps, it was able to differentiate each AE source such as distributed micro crack initiation, friction, flexural crack and localized diagonal tension crack. The secondary peak and the change of AE hit rate gave valuable criteria fur assessment. From the analysis of the felicity ratio, furthermore, it was shown that this values can be used for evaluating the degree of concrete damage. Based on the experimental results, this approach for practical AE application may provide a promising method for estimating the level of damage and distress in concrete structures.

• Archives of Plastic Surgery
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• v.33 no.6
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• pp.715-722
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• 2006

Purpose: The main advantages of the perforator flap are minimal donor site morbidity, preservation of any main source artery and its thin characteristics. Most perforator flaps for hand reconstruction need primary and secondary procedures such as a flap debulkiness and liposuction etc. However, flap thickness of calf area is thinner than any other perforator flaps. Methods: We performed an anatomical study and clinical application of medial sural artery perforator flap. We found that there are two or more medial sural perforators located on a straight line drawn from the mid-point of popliteal crease to the mid-point of medial malleolus. Most pathway of medial sural artery comes along with this line. It is possible to observe the first perforators almost exactly 8 cm from midpoint of popliteal crease in a distal half circle drawn with a radius of 2 cm. Results: We report 12 cases in 11 patients of hand reconstruction with medial sural perforator free flap from Febrary 2003 to Febrary 2006. Complete healing was possible in 11 cases. Total flap loss for venous insufficiency was in 1 patient. During the follow-up, good contour and full range of motion was observed on hand reconstruction with medial sural perforator free flap. Conclusion: In the authors' experience, this anatomical study made it possible to prepare a diagram of the exact location of the medial sural perforators. This flap can be used to achieve acceptable functional and aesthetic results for hand reconstruction because of its thin characteristics.