• Korean Journal of Materials Research
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• v.4 no.8
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• pp.847-854
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• 1994

An amorphous single phase and coexistent amorphous and hcp-Mg phases in Mg-Zn-Ce system were found to form in the composition ranges of 20 to 40% Zn, 0 to 10% Ce and 5 to 20% Zn, 0 to 5% Ce, respectively. A $Mg_{85}Zn_{12}Ce_{3}$ amorphous alloy containing nanoscale hcp-Mg particles was found to form either by melt spinning or by heat treatment of melt -spun ribbon. The particle size of the hcp-Mg phase can be controlled in the range of 4 to 20 nm. The mixed phase alloy prepared thus has a good bending ductility and exhibits high ultimate tensile strength($\sigma_{B}$) ranging from 670 to 930 MPa and fracture elongation($\varepsilon_{f}$) of 5.2 to 2.0%. The highest specific strength($\sigma_{B}$/density =$\sigma_{s}$)$3.6 \times 10^5N \cdot m/kg$. It should be noted that the highest values of flB, US and ？1 are considerably higher than those (690MPa,$2.5 \times 10^5N \cdot m/kg$and 2.5%) for amorphous Mg-Zn-Ce alloys. The increase of the mechanical strengths by the formation of the mixed phase structure is presumably due to a dispersion hardening of the hcp supersaturated solution which has the hardness higher than that of the amorphous phase with the same composition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.487-495
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• 2012

In order to prevent the high velocity bullet from penetration, aluminum alloy and RHA(Rolled Homogeneous Armour) steel, which have a high tensile and compressive strength, are usually used as the bullet-proof armor material. Although these materials have a good bullet proof performance, but not an area density which is a weight increasing factor of bullet-proof armor. Therefore, Mg(magnesium) alloy is a promising substitute for the traditional bullet-proof armor material due to the relatively low areal density. The spatial efficiency of Mg alloy, however, is inferior to the traditional material's, which is a volume(thickness) increasing factor of bullet-proof armor. In this study, we select the multi-layered hybrid armor which consist of Ceramic, with a high strength; Mg alloy, with a low areal density; Kevlar, with a high tensile strength-to-weight ratio; in order to make up for the poor spatial efficiency of Mg alloy. By predicting V50 of the multi-layered armor against 9mm FMJ(Full Metal Jarket). we show that the multi-layered armor have the capability in improving bullet-proof performance in the respect of the areal density, but also the spatial efficiency.

• Journal of the Korean Geosynthetics Society
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• v.7 no.3
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• pp.41-49
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• 2008

This study was carried out the model experiment in laboratory to evaluate the bearing capacity improvement of soft ground as altered constraint condition of reinforcements according to geotextile, georid, steel bar. As a results, the value of BCR was increased linearly as improvement of the stiffness of reinforcements, and the factor governed the increasement of BCR was the increasement of frictions between reinforcement and clay as far as the constrain conditions increased until T=85.6kg. Moreover, An angle of inclination, ${\theta}$, between reinforcement and horizontal surface was distributed from $38^{\circ}$ to $50^{\circ}$ for Geotextile, from $45^{\circ}$ to $50^{\circ}$ for Geogrid and from $14^{\circ}$ to $16^{\circ}$ for steel bar. A radius of heaving, r, of clay ground by vertical weight at side was distributed from 0.6m to 0.7m for Geotextile, from 0.5m to 0.8m for Geogrid, and from 2.4m to 3.0m for steel bar. In case of steel bar, r was 4 times that of Geotextile.

• Journal of Veterinary Clinics
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• v.31 no.3
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• pp.194-198
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• 2014

Methicillin-resistant staphylococci (MRS) are emerging as important pathogens in humans and animals worldwide. The aim of this study was to investigate the prevalence of MRS in the racehorse population and in horse-related personnel in Korea. A total of 195 horses and 18 humans (eight veterinarians, three veterinary hospital staff, and seven horse-handlers) from racehorse farms in Korea were included in the study. The samples were collected from nasal cavities using bacterial transport medium and were cultivated on tryptic soy agar with 5% sheep blood for 3 days at $37^{\circ}C$ to confirm the presence of Staphylococcus spp. Presumptive Staphylococcus spp. isolates were identified by 16S ribosomal RNA gene analysis. The coagulase test and oxacillin susceptibility tests were performed using the tube dilution and disk diffusion methods, respectively. The presence of the mecA gene was determined using a polymerase chain reaction assay. Of the 195 horses, 29 (15.6%) yielded 29 MRS isolates. Twelve (66.7%) of the 18 horse-related personnel yielded 12 MRS isolates. All of the MRS isolates from horses or horse-related personnel were identified as methicillin-resistant coagulase-negative staphylococci (MRCNS). The result of this study suggest that the prevalence of MRS increased with the duration of antibiotic use (p = 0.002). This study also provides evidence for the zoonotic transmission of MRCNS between horses and humans, although further investigations are needed.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.2
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• pp.235-242
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• 2017

Marsupialization and decompression constitute a well-established procedure for treating cavitary bone lesions of the jaw. The technique can be a primary treatment option, especially for pediatric patients with large cysts or lesions involving vital anatomical structures, such as a developing tooth germ. In this procedure, a decompression stent, such as a customized acrylic obturator or space-maintaining appliance, silicone tube, or nasal cannula, is inserted to maintain the patency of the cyst. However, this may cause clinical problems, such as irritation or trauma to the adjacent tissues, as well as discomfort to the patient, or failure of the stent due to cyst shrinkage. It can also be a reason for patient noncompliance. In the cases described here, a minimally invasive marsupialization technique using a metal tube made from a 16-gauge needle was used for odontogenic cysts in pediatric patients associated with unerupted teeth. Through this method, the lesions were removed, with patient cooperation, and the cyst-associated teeth erupted spontaneously.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.9
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• pp.418-424
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• 2017

Magnesium has a higher specific strength than other metals and is widely used industry wide due to its excellent vibration absorption ability and electromagnetic wave shielding property.For example, it is used for automobile parts such as car seat frames and cylinder heads, and is widely used in electronic products such as notebook cases and mobile phone cases. In addition, it is in the spotlight as a bone-implant material used to assist in the treatment of damaged bones when the bones are cracked or broken. Currently, Ti alloy, stainless steel and Co-Cr-Mo alloy are used as the implant material, and the Mg alloy remains in research stage. The current problem with bone implant implants is that the patients must undergo reoperation to remove the implants after joint surgery. Magnesium, however, can achieve sufficient strength compared to current materials. In addition, since it is self-decomposed after the recovery, reoperation is not necessary. In this paper, Mg alloys were designed by adding harmless Ca and Zn to the human body. In order to improve the strength and corrosion resistance, the final alloy was designed by adding a small amount of Sr as a grain refiner. The radioactive elements of Sr are harmful to the human body, but other naturally occurring Sr elements are harmless. Microstructure analysis of the alloys was performed by optical microscopy and scanning electron microscopy. The mechanical properties and corrosion characteristics were evaluated by tensile test, potentiodynamic test and immersion test.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.275-282
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• 2006

Recently, Fiber Reinforced Polymers(FRP) has been emerged as an alternative material to solve the corrosion of steel reinforcement in reinforced concrete structures. FRP exhibits higher specific strength and lower weight compared to steel reinforcement. Moreover, good resistance to corrosion of the FRP may be useful in aggressive environments causing deterioration such as chloride environment. However, causes for higher initial cost of FRP than that of steel, little information on the long-term behavior of FRP, and brittle failure make the efforts to apply FRP in civil structures slow. Glass fiber among the fibers used to manufacture FRP can be seen as the most beneficial material with regard to initial costs. But its low elastic modulus, which attains barely a quarter of steel, nay thus lead to excessive deflections when used as reinforcement for flexural members. This research was carried out on the tensile properties of hybrid rods made with glass and carbon fibers to improve those of FRP rod made with glass fiber. Parameters were resin type and the arrangement of glass and carbon fibers. The tensile properties of hybrid rods were compared with those of rods manufactured with only glass or carbon fibers. The results indicated that the tensile properties of hybrid rod were good when the carbon fiber was arranged in the core.

• The korean journal of orthodontics
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• v.33 no.2 s.97
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• pp.73-84
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• 2003

This study was performed to find out how much projection errors in the cephalometric measurements were made by vertical head rotation in taking posteroanterior cephalograms. 25 adults without any apparent facial asymmetry or severe sagittal skeletal discrepancy were selected and the posteroanterior cephalograms were taken with the head rotated $5^{\circ},\;10^{\circ}$ superior and inferior each to the reference $position(0^{\circ})$. The 7 height, 5 width and 6 angular measurements were taken at each 5 positions. Through the statistical analysis of all measurements taken at each rotated position, folowing results were obtained.1. The projection errors of height measurements were remarkably target than those of width or angular measure nents. f. Among the height measurements, the farther to the rotation axis the measurements were, the larger the projection errors were. 3. Among the width measurements, mandibular width and mandibular width of mandibular first molars showed significant differences between the values taken at each rotated position, while nasal width, maxillary width and intermolar width of maxillary first molars did not. 4. Among the angular measurements, the angle between horizontal reference line and the line that is connected to crista galli and antegonion or maxillare showed significant differences between the values taken at each rotated Position. The above results suggest that it is needed to the effort to keep constant head position for taking the useful posteroanterior cephalogra, because projection errors are caused by vertical head rotation.

• The korean journal of orthodontics
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• v.40 no.2
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• pp.66-76
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• 2010

Objective: Obstructive sleep apnea (OSA) is a common disorder which is characterized by a recurrence of entire or partial collapse of the pharyngeal airway during sleep. A given tidal volume must traverse the soft tissue tube structure of the upper airway, so the tendency for airway obstruction is influenced by the geometries of the duct and characteristics of the airflow in respect to fluid dynamics. Methods: Individualized 3D FEA models were reconstructed from pretreatment computerized tomogram images of three patients with obstructive sleep apnea. 3D computational fluid dynamics analysis was used to observe the effect of airway geometry on the flow velocity, negative pressure and pressure drop in the upper airway at an inspiration flow rate of 170, 200, and 230 ml/s per nostril. Results: In all 3 models, large airflow velocity and negative pressure were observed around the section of minimum area (SMA), the region which narrows around the velopharynx and oropharynx. The bigger the Out-A (outlet area)/ SMA-A (SMA area) ratio, the greater was the change in airflow velocity and negative pressure. Conclusions: Pressure drop meaning the difference between highest pressure at nostril and lowest pressure at SMA, is a good indicator for upper airway resistance which increased more as the airflow volume was increased.

• Radiation Oncology Journal
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• v.9 no.1
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• pp.111-116
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• 1991

From 1979 to 1987, 33 patients with polymorphic reticulosis (PMR) limited in the upper airway were treated with primary radiation therapy and the analysis of treatment results was undertaken. Systemic symptoms such as fever, night sweats, and weight ioss were noted in $48\%$. The nasal cavity was most frequently involved $(85\%)$, although involvement of PNS $(33\%)$ and palate $(30\%)$ was not uncommon. The 5 and 10 year actuarial survival rates were $47\%\;and\;40\%$, respectively. The difference in NSD between patients with in-field failure and those without it was significant statistically. Also, field size was significantly smaller in patients with marginal failure than those without it. During the follow-up period, systemic failure was found in S patients (diffuse histiocytic Iymphoma in 4, histiocytic medullary reticulosis in 1). In this study, we can suggest that total radiation dose of at least 4500 cGy with generous treatment volume should be delivered to achieve better local control and that the developement of an effective systemic chemotherapeutic regimen is required to improve the survival after systemic relapse.