• Journal of Korea Foundry Society
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• v.35 no.4
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• pp.80-87
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• 2015

The Al die casting process has been widely used in the manufacturing of automotive parts when the process requires near-net shape casting and a high productive rate. However, porosity arises in the casting process, and this hampers the wider use of this method for the creation of high-durability automotive components. The porosity can be controlled by the shot condition, but, it is critical to set the shot condition in the sleeve, and it remains difficult to optimize the shot condition to avoid air entrapment efficiently. In this study, the 4.5 mm, 2.0 mm plate die castings were fabricated under various shot conditions, such as plunger velocities of 0.7 m/s ~ 3.0 m/s and fast shot set points of the cavity of -25%, 0%, 25%, and 50%. The mold filling behavior of Al melts in the cavity was analyzed by a numerical method. Also, according to the shot conditions, the results of numerical analyses were compared to those of die-casting experiments. The porosity levels of the plate castings were analyzed by X-ray CT images and by density and microstructural analyses. The effects of the porosity on the mechanical properties were analyzed by tensile tests and hardness tests. The simulation results are in good general agreements with the die-casting experimental results. When plunger velocity and fast shot set point are 1.0 m/s and cavity 25% position, castings had optimum condition for good mechanical properties and a low level of porosity.

• Journal of Chest Surgery
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• v.29 no.2
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• pp.239-243
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• 1996

Chest wall reconstruction Is difficult because of the physiological and anatomical functions of thoracic cavity where the thoracic cavity must be stabilized in order to prevent paradoxical motion, and adequate protection must be provided to the mediastinal structures. A 37-year-old male patient with full-thickness defect on the left anterior thoracic cavity due to traffic accident was treated. Emergency operation was performed for debridement and bleeding control, and on postoperative 25 days, chest wall reconstruction was performed as a second-stage operation. Left anterior chest wall was reconstructed with latissimus dorsi myocutaneous flap which had thoracodorsal arterial pedicle, and split-thickness skin grift from the left thigh was done. After chest wall reconstruction, spontaneous self-respiration was possible without ventilatory support. The pulmonary function test performed at postoperative 3 months revealed 80% of predicted values (FVC, FEV1.0). The postoperative result of chest wall reconstruction using latissimus dorsi myocutaneous flap was excellent anatomically, physiologically and aesthetically.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.433-436
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• 2009

This study is concerned with an effect of frictional condition in a forward/backward combined extrusion process. Generally, the material flow of the billet is influenced by the corners of the die cavity, the ratio in reduction in area, and thickness ratio of backward can thickness to forward can thickness. In addition, the frictional condition in contact area between the billet and the punch/die also affect the material flow. This paper investigated the effect of frictional condition for variable friction factors. The FEM simulation has been carried out in order to examine the effect of frictional condition. Deformation patterns and flow characteristics were examined in terms of design parameters such as extruded length ratio etc. Die pressure exerted on the die-workpiece interface is calculated by the simulation results and analyzed for safe tooling. Therefore the numerical simulation works provide a combined extrusion process of stable cold forging process planning to avoid the severe damage on the tool.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.528-533
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• 2008

Cavity in the mold is exposed to high pressure during injection molding operation. Injection molded articles with deep depth are often demanded as design variety increases. Subsequently mold becomes weak and deformation increases as the mold depth increases. Thus the injection molds for deep depth articles should be designed to hold out high pressure or stress concentration and large deformation. Through this study, equation for mold design was examined and suggested novel method to determine equation for mold design with deep depth. Novel equation developed in this study was modified from beam theory considering cantilever and two points bending situation while previous equation was modified from just cantilever bending situation. The validity of novel equation was verified through computer simulations for various mold side and wall thickness.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.1
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• pp.68-75
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• 2009

A major disadvantage of thermal nanoimprint lithography(NIL) is the thermal cycle, that is, heating over glass transition temperature and then cooling below it, which requires a significant amount of processing time and limits the throughput. One of the methods to overcome this disadvantage is to make the processing temperature lower Accordingly, it is necessary to determine the effects on the processing parameters for thermal NIL at reduced temperatures and to optimize the parameters. This starts with a clear understanding of polymer material behavior during the NIL process. In this work, the squeezing and filling of thin polymer films into nanocavities during the low temperature thermal NIL have been investigated based upon a two-dimensional viscoelastic finite element analysis in order to understand how the process conditions affect a pattern quality; Pressure and initial polymer resist thickness dependency of cavity filling behaviors has been investigated.

• Clinical and Experimental Reproductive Medicine
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• v.25 no.2
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• pp.153-160
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• 1998

The objective of this retrospective study was to evaluate whether the transvaginal ultrasonographic analysis of endometrial pattern and thickness could predict the stage of menstrual cycle. Endometrial pattern and thickness were observed in those patients receiving infertility work up from April, 1994 to July, 1998 at Seoul National University Hospital. The study group was 185 patients with normal regular menstrual cycles. Among them, 44 patients received endometrial biopsy, and the date of endometrium was compared with the observed endometrial pattern and thickness. The observed endometrial pattern was presence or absence of central cavity echogenicity, triple line sign, endometrial hypoechogenicity, ring sign, endometrial hyperechogenicity and posterior acoustic sonic enhancement. The results were as follows; Central cavity echogenicity was seen throughout menstrual cycle. Triple line sign was observed in 81.1% of patients during early secretory phase. However, in mid to late secretory phase, triple line sign was appeared in only 6.8%. The percentage of positive endometrial hypoechogenicity was highest in early secretory phase. In contrast to hypoechogenicity, positive endometrial hyperechogenicty was highest in mid to late secretory phase. Ring sign was observed in 73.5% of the patients during early secretory phase with peak incidence. Posterior acoustic enhancement was seen in 72.7% of the patients during late secretory phase. The sensitivity and specificity of being a secretory phase if the patients showed hyperechogenic endometrium, were 84.2%, 83.3% respectively. The sensitivity and specificity of being a secretory phase if the patients showed posterior acoustic enhancement were 93.8%, 58.3% respectively. Endometrial thickness was not correlated with endometrial dating. In conclusion, transvaginal ultrasonographical delineation of the endometrial pattern might be useful tool in predicting endometrial status during normal menstrual cycle. But, endometrial thickness could not predict the endometrial dating.

• Journal of Chest Surgery
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• v.9 no.2
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• pp.175-186
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• 1976

The cellular change of the pulmonary tuberculous lesions may be divided into two groups,exudative and proliferative form by their course and fate. In the most cases, the patients usually have very much complex type of cellular changes. Therefore, the shadows of the chest films in pulmonary tuberculosis are also much variable in nature. And Daniel said that knowledge of the pathology of tuberculosis and an appreciation of the method of progression and healing are essential to proper interpretation of the films. Author, having reviewed 33 cases of resected tuberculous lung obtained in N.M.T.H. for one year from Oct. '75 to Sep. '76 by surgical managements, classified the Pathological findings such as: 1) caseation only, 2) tuberculoma, 3) atelectatic lung 4) cavitary lesion and 5) atelectasis with cavity, and examined the relationship between the roentgenological characteristics of the chest films and the pathological process of tuberculous lesions of the resected lungs, The result were obtained as follows. (1) Tuberculoma was commonly appeared in $S_2$ segment in right and $S_6$ segment in left. (2) Atelectasis and destroyed lung were more commonly appeared in left lung than right, and their containing rate of cavity was 82%. (3) Cavities were mostly appeared in $S_1$ and $S_2$ segments of both lung and the appearance-rate of cavity on $S_6$ segment was higher in left than right. And among the cavitary lesions of the resected lung, cavity was not seen in the preoperative chest films in 22%. (4) The configuration, thickness and sharpness of the walls of cavities, which revealed the cavitary shadows in the preoperative chest films, were mostly depended on the degree of increased collagenous fiber of the wall, existence of perifocalitis, and more or less of the caseous masses on the inner surface of the cavity wall.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.532-540
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• 2004

The aim of this study was to measure the cusp deflection during composite restoration for MOD cavity in premolar and to examine the influence of cavity dimension, C-factor and restoration method on the cusp deflection. Thirty extracted maxillary premolar were prepared to four different sizes of MOD cavity and divided into six groups. The width and depth of the cavity were as follows. Group 1; $1.5{\;}{\times}{\;}1{\;}mm$, Group 2; $1.5{\;}{\times}{\;}2{\;}mm$, Group 3; $3{\;}{\times}{\;}1{\;}mm$, and Group 4-6; $3{\;}{\times}{\;}2{\;}mm$ respectively. Group 1-4 were restored using bulk filling method with Z-250 composite. However, Group 5 was restored incrementally, and Group 6 was restored with an indirect resin inlay. The cusp deflection was recorded at the buccal and lingual cusp tips using LVDT probe for 10,000 seconds. The measured cusp deflections were compared between groups, and the relationship between the cube of the length of cavity wall/the cube of the thickness of cavity wall ($L^3/T^3$). C-factor and cusp deflection or % flexure ($100{\;}{\times}$ cuspal deflection / cavity width) was analyzed. The cusp deflection of Group 1-4 were $12.1{\;}\mu\textrm{m},{\;}17.2{\;}\mu\textrm{m},{\;}16.2{\;}\mu\textrm{m}{\;}and{\;}26.4{\;}\mu\textrm{m}$ respectively. The C-factor was related to the % flexure rather than the cusp deflection. There was a strong positive correlationship between the $L^3/T^3$ and the cusp deflection. The cusp deflection of Group 5 and 6 were $17.4{\;}\mu\textrm{m}{\;}and{\;}17.9{\;}\mu\textrm{m}$ respectively, which are much lower value than that of Group 4.

• Journal of electromagnetic engineering and science
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• v.17 no.4
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• pp.202-207
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• 2017

This paper presents the performance of a planar, low-profile, and wide-gain-bandwidth leaky-wave slit antenna in different thickness values of high-permittivity gallium arsenide substrates at terahertz frequencies. The proposed antenna designs consisted of a periodic array of $5{\times}5$ metallic square patches and a planar feeding structure. The patch array was printed on the top side of the substrate, and the feeding structure, which is an open-ended leaky-wave slot line, was etched on the bottom side of the substrate. The antenna performed as a Fabry-Perot cavity antenna at high thickness levels ($H=160{\mu}m$ and $H=80{\mu}m$), thus exhibiting high gain but a narrow gain bandwidth. At low thickness levels ($H=40{\mu}m$ and $H=20{\mu}m$), it performed as a metasurface antenna and showed wide-gain-bandwidth characteristics with a low gain value. Aside from the advantage of achieving useful characteristics for different antennas by just changing the substrate thickness, the proposed antenna design exhibited a low profile, easy integration into circuit boards, and excellent low-cost mass production suitability.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1E
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• pp.9-15
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• 2009

In this paper, FSTL (Field Sound Transmission Loss) measured in a mock-up simulating ship cabins is studied. A mock-up is built by using 6 mm steel plate, and two identical cabins are made where 25 mm or 50 mm sandwich panel is used to construct wall and ceiling inside the steel structure. Various wall panels and ceilings are tested, where effects of wall and ceiling panel thickness, and presence of a unit toilet on FSTL are investigated. It is found that the effect of unit toilet on FSTL is at most 1 dB. From the comparison of FSTL for panels of the same thickness of 50 mm, it is observed that panel having inside air cavity of 10 mm shows higher STL than that of the panel without air cavity. Comparison of FSTL for panels of 50 mm and 25 mm thickness shows that dependency on surface density predicted by mass law is not observed. The sandwich panels act as a mass-spring system, which shows a resonant mode that cannot be explained by the mass law. It is also found that STL from laboratory test is higher than FSTL by 5- 10 dB, which can be explained by flanking structure-borne noise transmission path such as ceiling, floor and corridor-facing wall.