• Journal of Environmental Science International
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• v.7 no.3
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• pp.349-360
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• 1998

Effects of uniform flow on a two-dimensional mesoscale horizontal convection were investigated by using the vorticity and thermodynamic equations. For thins purpose, We simulated properties of a thermal convection m a stably stratified Boussinesq flued caused by partial heating at the center of a lower boundary If we don't consider effects of the uniform flow, the convection takes the form of aidsymmetrlc with respect to the z-alds. But when uniform flow Is strong, velocity field and temperature field consist of a sin91e cell structure which spreads upstream side of the partial heating area. The flow pattern for strong uniform flows takes the form of positive temperatue near the ground and negative temperature perturbation soft over the partial heating area, and downward motion directly over the upwind portion of the partial heating area and upward motion on the downstream side. The downstream edge of the upstream cell Is shifted in the downstream direction with the Increase of uniform flow almost linearly.

• Korean Journal of Veterinary Research
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• v.38 no.3
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• pp.455-460
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• 1998

This study was designed to investigate the distributions of the positive cells in rat spleens by two monoclonal antibodies of MT1 and MB2. The spleens of immature 10 rats (Sprague Duwely, approximately 200gm) were collected and paraffin-embedded sections of spleens were stained with immunohistochemical methods. Higher proportions of MT1-positive cell number in spleens were ordered as marginal zone(8.5~18.1%), red pulp(2.1~8.8%) and periarterial lymphoid sheath(0~1.6%) in white pulp, and those of MB2-positive cell number are ordered as the central area of the periarterial lymphoid sheath(100%), red pulp(29.1~45.0%), marginal zone(15.2~30.4%), and peripheral area of periarterial lymphoid sheath(2.3~3.5%). The positive cells by MB2 are more numerous in number than by MT1. The above results were concluded that the positive cells by above two monoclonal antibodies were scattered throughout the red pulp and marginal zone, but in the central area of the periarterial lymphoid sheath, the MB2-positive cells only were present.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.157-164
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• 2009

An efficient pipeline MDC Radix-4 FFT structure is proposed in this paper. Every stages in pipeline FFT structure consists of delay' commutator and butterfly. Proposed butterflies in front and rear stages utilize CORDIC and Common Sub-expression Sharing(CSS) techniques, respectively. It is shown that proposed butterfly structure can reduce the number of adders through sharing common patterns of CSD type coefficients. The Verilog-HDL modeling and Synopsys logic synthesis results that the proposed structure show 48.2% cell area reduction in the complex multiplication part and 22.1% cell area reduction in overall 256-point FFT structure comparison with those of the conventional structures. Consequently, the proposed FFT structure can be efficiently used in various OFDM systems.

• Journal of the Korean Wood Science and Technology
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• v.45 no.2
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• pp.232-242
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• 2017

The objective of this study was to examine changes in the porosity and internal structure of wood as it goes through the process of saccharification (extraction of fermentable sugars). This study also examined the use of different drying methods to prepare samples for characterization of internal pores, with particular emphasis on the partially disrupted cell wall. Aspen wood flour samples after dilute acid pretreatment followed by enzymatic hydrolysis were examined for nitrogen adsorption. The resulting isotherms were analyzed for surface area, pore size distribution, and total pore volume. Results showed that freeze drying (with sample pre-freezing) maintains the cell wall structure, allowing for examination of saccharification effects. Acid pretreatment (hemicellulose removal) doubled the surface area and tripled the total volume of pores, which were mostly 10-20 nm wide. Subsequent enzymatic hydrolysis (cellulose removal) caused a 5-fold increase in the surface area and a ~ 11-fold increase in the total volume of pores, which ranged from 5 to 100 nm in width. These results indicate that nitrogen adsorption analysis is a feasible technique to examine the internal pore structure of lignocellulosic residues after saccharification. The information on the pore structure will be useful when considering value-adding options for utilizing the solid waste for biofuel production.

• Journal of Chest Surgery
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• v.31 no.4
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• pp.422-426
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• 1998

Progressive dysphagia in a 53 year old man was caused by a giant polypoid tumor in the lower intrathoracic esophagus. Radical transthoracic esophagectomy and esophagogastrostomy were carried out. Microscopic examination of the tumor revealed a true carcinosarcoma, composed of a mixture of basaloid squamous cell carcinoma and chondrosarcoma with multiple cartilagenous productions. Carcinoma metastases were found in the subcarinal and perigastric lymph nodes. Immunohistochemically, squamous area displayed strong positive to cytokeratin, and basaloid area showed positive immunoreaction to high molecular weight cytokeratin (34${\beta}$E12). Spindle cell sarcoma reacted to vimentin and smooth muscle actin. Chondrosarcomatous area reacted to vimentin and S-100 protein. He received postoperative chemotherpy and radiotherapy. He has been free of disease for 11 months.

• Journal of the Korean Society of Safety
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• v.37 no.6
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• pp.158-165
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• 2022

Eco-friendly policies proposed by the government of The Republic of Korea have encouraged the use of eco-friendly vehicles. Hydrogen vehicles have exhibited the highest growth rate, although the current number of registered vehicles is low. In hydrogen vehicles, a thermally activated pressure relief device (TPRD) is installed to prevent explosions in the hydrogen gas cylinder. When discharged due to low ignition energy, hydrogen gas readily forms a jet flame. The risks induced by such jet flames were analyzed through a numerical analysis. Jet flames can activate TPRDs installed in nearby hydrogen gas cylinders. As a result, high-voltage cables exposed in the lower area of a vehicle can ignite within seconds. There was a 9.5-kW/m2 area around the vehicle (which can result in casualties) at a distance of ~5 m from the hydrogen gas cylinder, and a 37.5-kW/m2 area (which can cause significant damage) in the form of an inverted triangle toward the lower section of the vehicle. We believe that the risk factors analyzed herein should be considered for addressing accidents in hydrogen vehicles.

• Transactions of Materials Processing
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• v.33 no.4
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• pp.248-254
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• 2024

The triply periodic minimal surface (TPMS) structure is characterized by a high surface-to-volume (S/V) ratio and the separated internal structure for flow. Combining the different TPMS structures can provide unique flow and strength characteristics. This paper investigates the effects of dimension, density and arrangement of the unit cell of the TPMS on contact and flow areas of combined TPMS structures. Several representative TPMS structures, including primitive, gyroid and diamond structures, are adopted to design gradient and heterogeneous types TPMS structures. The estimation method of contact and flow areas using an image processing technique is proposed. Python software is used to predict contact and flow area. The influence of the combination method of TPMS on contact and flow areas in the contact surface of combined TPMS structures with different shapes is investigated. Based on the results of the investigation, an appropriate combination method of TPMS structures is discussed.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.326-329
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• 2005

Proton exchange membrane (PEM) should be sufficiently hydrated with proper water management to maintain a good ionic conductivity and performance of a PEM fuel cell. However. cathode flooding resulting from excess water can impede the transport of reactants and hence deteriorate the fuel cell performance. For the PEM fuel cell to be commercially viable as vehicle or portable applications, the flooding on the cathode side should be minimized during the fuel cell operation. In this study, visualization technique was applied to understand the cathode flooding phenomena on the cathode side of a PEM fuel cell. To this end. a transparent PEM unit fuel cell wi th an act ive area of $25cm^2$ was designed and manufactured to allow for the visualization of cathode channel with performance characteristics. Two-phase flow resulting from the electro-chemical reaction of fuel cell was investigated experimentally. The images photographed by CCD camera with cell operating temperatures $(30\~50^{\circ}C)$ were presented. Results indicated that the flooding on the cathode side first occurs near the exit of cathode channel. As the operating temperature of fuel cell increases. it was found that liquid water droplets tend to evaporate easily and it can have an influence on lowering the flooding level. It is expected that this study can effectively contribute to the detailed researches on modeling water transport of an operating PEM fuel cell including two-phase flow phenomena.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.6
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• pp.620-627
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• 2004

As h-bridge multilevel inverter is connected with series of single phase power cell, so it obtain high voltage using low voltage power semi-conductor and output voltage similar to sine wave. In this topology, the number of power cell increases in proportion to the output voltage level. Therefore, there are drawbacks that are responsibility against operating ability of main controller and signal wire increase. However, we can overcome this problems by the substitution of serial communication for the PWM signal in power cell control. Additionally, it has merits of reliability and maintenance. This paper deals with the synchronization and phase-shift method of power cell PWM using CAN(Controller Area Network) communication interrupt in H-bridge multilevel inverter. The advantages of proposed method are signal-line simplification using serial communication between main controller and cell controller, burden reduction in main controller, modularization of power cell, easy protection of each power cell, expandability improvement and reliability increase of control signal and power cell. This paper establishes propriety and reliability of proposed method through experiment of 13-level H-bridge multilevel inverter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10A
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• pp.1461-1472
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• 2000

Recently, the mobile users seem to be rapidly increasing and then the capacity limit will be reached at close hand. In these situations, to provide them with good quality of service in the coming future, newly planned cell design is needed. In the next generation mobile communication systems, namely IMT-2000, good quality services will be possible only by designing the cell structure hierarchically with the help of appropriate cell planning. In the research process, the standardization reports on the future mobile cellular IMT-2000 system (3GPP) are investigated and the parameters, that are essential to cell planning, are also researched. Modeling of IMT-2000 radio link and the numerical analysis on that make it possible to calculate the forward/reverse link budget, system capacity call blocking probability Erlang capacity and cell coverage. In planning the cell of IMT-2000 system, various parameters are considered, such as hierarchical cell structure, number of users, data service forms and propagation area environments. From the results, efficient cell planning methods are proposed. Through this thesis efficient cell planning and maximum capacity will be achieved in the beginning of commercial IMT-2000 service.