• 터널과지하공간
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• 제11권3호
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• pp.217-224
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• 2001

암석은 지질학적 생성과정으로 인해 많은 역학적 결함을 포함하고 있으며 이러한 결함 사이에는 암석 브릿지가 존재하게 된다. 이러한 암석 브릿지에서의 균열의 전파 및 결합(coalescence)과정은 사면, 기초, 터널 등의 안정성에 영향을 미치게 된다. 본 연구에서는 단축압축 하에서 균열의 형상변화에 따른 암석 브릿지에서의 균열의 개시, 전파 및 결합거동 변화에 대해 알아보았다. 여산 대리석을 재료로 120$\times$60$\times$25 mm크기의 시료에 균열각도 $\alpha$, 브릿지각도 $\beta$, 균열길이 2c, 브릿지길이 2b를 변화시키면서 2개의 인공균열을 제작하였다. 하중을 가하면서 날개형 균열개시응력, 날개형 균열 전파각도, 균열결합 응력을 측정하였으며 균열결합 유형을 정리하였다. 또한, 정규화된 최대강도(normalized peak strength)를 구하여 Ashby & Hallam 모형 (1986)의 이론해와 비교, 분석 하였다.

• 한국표면공학회지
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• 제41권2호
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• pp.57-62
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• 2008

Electrochemical properties of Ti-30Ta-$(3{\sim}15)$Nb alloys coated by HA/Ti compound layer have been studied by various electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10, and 15 wt% Nb contents were manufactured by the vacuum furnace system. The specimens were homogenized for 24 hrs at $1000^{\circ}C$. The samples were cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The HA/Ti non-coated and coated morphology of Ti alloy were analyzed by x-ray diffractometer(XRD) and filed emission scanning electron microscope(FE-SEM). The corrosion behaviors were investigated using potentiodynamic method in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The homoginazed Ti-30Ta-$(3{\sim}15wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and ${\beta}$ phase peak was predominantly appeared with increasing Nb content. The microstructure of Ti alloy was transformed from needle-like structure to equiaxed structure as Nb content increased. HA/Ti composite surface showed uniform coating layer with 750 nm thickness. The corrosion resistance of HA/Ti composite coated Ti-alloys were higher than those of the non-coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• 한국항공우주학회지
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• 제44권4호
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• pp.373-379
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• 2016

주기적 단속적으로 작동하는 위성부품의 열제어를 위하여 고상-액상 상변화물질(PCM, Phase Change Material)과 열관을 병렬로 결합한 열제어장치를 제안하였으며, 이의 성능을 수치해석을 통하여 검증하였다. 상변화 중 큰 잠열과 일정하게 유지되는 온도에 의하여 작은 방열판 면적에서도 부품의 최고온도를 제어할 수 있으며, 냉각기에는 PCM에 축적된 에너지가 방출됨으로써 보온히터 소모전력을 절약할 수 있다. 동일한 형태의 Al TBM(Thermal Buffer Mass)을 사용하면 비슷한 효과를 기대할 수 있으나, 질량과 보온히터의 소모전력이 증가하므로 PCM에 비하여 비효율적이다. 설계된 PCM 열제어장치는 발열량과 작동시간에 따라 그 양을 최적화할 수 있다.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.17-23
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• 2004

Aeroacoustic characteristics of sirocco fan used in Over-The-Range (OTR) has been analyzed in this paper. A microwave hood combination over the gas range is short for the OTR. The flow phenomena of the double-sided sirocco fan was analyzed numerically and experimentally by using commercial code and three dimensional PIV for flow visualization. Also, microphone array is used in order to understand acoustic characteristics of OTR. Two dimensional unsteady flow and acoustic simulation is tried to qualitatively estimate the effects of tonal noise and broadband noise on the overall sound pressure level. It is found that tonal sound is generated from the strong interaction between the impeller and cutoff while broadband sound is generated from the strong secondary flows along the scroll surface. To reduce the noise level, the V-shape cut-off was applied to improve the sound quality by reducing tonal noise. So the peak noise at BPF (Blade Passing Frequency) was almost reduced. The shape of flow-guide to suppress the secondary flow over the scroll surface was carefully checked. It is found that this affects flow pattern at the fan exit and reduces the broad band noise. Through this numerical and experimental study, the sound pressure level was lowered by 4dBA compared to that of the previous fan at the operating point.

• 한국식품조리과학회지
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• 제33권3호
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• pp.292-299
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• 2017

Purpose: The present study explored cookie making performance using Jeju magma seawater to elucidate the effects of minerals in water on quality of baked goods. Methods: Seven water samples were analyzed for their mineral content, pH and water hardness. Starch pasting properties of flour in water samples was analyzed using RVA, and cookie making performance using water samples was evaluated with the AACCI wire-cut cookie baking method. Quality of cookies was measured by weight loss during baking, cookie geometry, color, and firmness. Results: Hardness of water samples ranged from 0-4200, and mineral content was in the order of magma seawater > 100% ED mineral water > 50% ED mineral water > 10% ED mineral water > tap water > Samdasoo > distilled water. RVA results showed that water hardness exhibited significant relationships with pasting temperature (p<0.05, R=0.863), peak viscosity (p<0.001, R=0.944), final viscosity (p<0.05, R=0.861), and setback (p<0.05, R=0.782). Cookie baking results showed that cookie diameter increased in the order of magma seawater < 100% ED mineral water < 50% ED mineral water < 10% ED mineral water $\approx$ tap water < Samdasoo < distilled water. Conclusion: As mineral content in water increased, flour pasting temperature and viscosity increased, whereas cookie diameter decreased with color fading. However, cookies formulated with 50% ED mineral water showed similar cookie geometry and texture to those with tap water. Therefore, controlling the mineral content of water can be successfully applied to produce mineral-enriched cookies.

• 한국조경학회지
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• 제32권4호
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• pp.28-38
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• 2004

Korean goral (Nemorhaedus caudatus raddeanus) is one of the endangered species in Korea, and the rugged terrain of the Soraksan National Park (373㎢) is a critical habitat for the species. But the goral population is threatened by habitat fragmentation caused by roads and hiking trails. The objective of this study was to develop a potential habitat suitability model for Korean goral in the park, and the model was based on the concepts of fuzzy set theory and multi-criteria evaluation. The process of the suitability modeling could be divided into three steps. First, data for the modeling was collected by using field work and a literature survey. Collected data included 204 points of GPS data obtained through a goral trace survey and through the number of daily visitors to each hiking trail during the peak season of the park. Second, fuzzy set theory was employed for building a GIS data base related to environmental factors affecting the suitability of the goral habitat. Finally, a multiple-criteria evaluation was performed as the final step towards a goral habitat suitability model. The results of the study were as follows. First, characteristics of suitable habitats were the proximity to rock cliffs, scattered pine (Pinus densiflora) patches, ridges, the elevation of 700∼800m, and the aspect of south and southeast. Second, the habitat suitability model had a high classification accuracy of 93.9％ for the analysis site, and 95.7％ for the validation site at a cut off value of 0.5. Finally, 11.7％ of habitatwith more than 0.5 of habitat suitability index was affected by roads and hiking trails in the park.

• 한국통신학회논문지
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• 제30권4A호
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• pp.288-295
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• 2005

OFDM(orthogonal frequency division multiplexing) 통신 시스템은 고속 무선 데이터 전송에 적합한 방식으로 널리 알려져 있지만, 높은 PAPR(peak-to-average power ratio)로 인하여 HPA(high power amplifier)에서 큰 비선형 왜곡을 겪는 문제점을 갖는다. 본 논문에서는 이러한 높은 PAPR을 저감하는 방법으로 더미 시퀀스(dummy sequence)를 삽입하는 새로운 SLM (selective mapping)방식을 제안하며, 이를 DSI-SLM기법이라 하기로 한다. 제안된DSI-SLM 기법은 각 브랜치(branch)에서 일정비율의 부반송파에 각기 다른 더미 시퀀스를 인가하고 IFFT(inverse Fourier transform) 후 가장 낮은 PAPR을 갖는 브랜치의 데이터를 전송한다. 이 방식에 사용된 더미 시퀀스는 송신단에서 PAPR 저감만을 위해 사용될 뿐 수신단에서의 데이터 복원 과정에는 필요로 하지 않으므로, 기존의 SLM및 PTS에서 나타나는 부가정보 전송의 필수성과 같은 단점을 해결하면서 실시간 데이터 처리를 가능케 한다.

• 대한금속재료학회지
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• 제46권10호
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• pp.691-699
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• 2008

Electrochemical characteristics of Ti-30Ta-xZr alloys coated with HA/TiN by using magnetron sputtering method were studied. The Ti-30Ta containing Zr(3, 7, 10 and 15wt%) were 10 times melted to improve chemical homogeneity by using a vacuum furnace and then homogenized for 24hrs at $1000^{\circ}C$. The specimens were cut and polished for corrosion test and coating, and then coated with HA/TiN, respectively, by using DC and RF-magnetron sputtering method. The analyses of coated surface and coated layer were carried out by using optical microscope(OM), field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). The electrochemical characteristics were examined using potentiodynamic (-1,500 mV~ + 2,000 mV) and A.C. impedance spectroscopy(100 kHz ~ 10 mHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The microstructure of homogenized Ti-30Ta-xZr alloys showed needle-like structure. In case of homogenized Ti-30Ta-xZr alloys, a-peak was increased with increasing Zr content. The thickness of TiN and HA coated layer showed 400 nm and 100 nm, respectively. The corrosion resistance of HA/TiN-coated Ti-30Ta-xZr alloys were higher than that of the non-coated Ti-30TaxZr alloys, whic hindicate better protective effect. The polarization resistance($R_p$) value of HA/TiN coated Ti-30Ta-xZr alloys showed $8.40{\times}10^5{\Omega}cm^2$ which was higher than that of non-coated Ti-30Ta-xZr alloys.

• 운동영양학회지
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• 제25권3호
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• pp.16-22
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• 2021

[Purpose] Exercise-associated hyponatremia (EAH) is a well-known condition among endurance athletes at low altitudes. The incidence of EAH during ultramarathons at high altitudes warrants further investigation. This prospective observational study was conducted on the participants of the Leadville Trail 100 run, a 161-km race held at a high altitude (2,800 m-3,840 m). [Methods] Venous blood samples were collected before and immediately after the race. The participants completed an electronic survey after the race. Our main outcome measure was the post-race serum sodium ([Na⁺]) level. [Results] Of the 672 athletes who started the race, 351 (52%) successfully completed the event within the 30-hour cut-off. Post-race blood samples were collected from 84 runners (66 finishers). Both pre- and post-race blood samples were collected from 37 participants. Twenty percent of the post-race participants had EAH. Only one post-race participant had a [Na⁺] level of <130 mmol/L. All participants with EAH were asymptomatic. One participant had an abnormal pre-race [Na⁺] level (134 mmol/L). Female participants had a significantly higher rate of EAH than male participants (40% vs. 16%; p=0.039). Age, body mass index, weight changes, race completion status, nonsteroidal anti-inflammatory drug use, and urine specific gravity were not associated with the development of EAH. Lower postrace [Na⁺] levels were associated with higher serum creatine kinase values (R²=0.1, p<0.005). [Conclusion] High altitude (3,840 m peak) does not appear to enhance the incidence of EAH after an ultramarathon footrace. This suggests that ambient temperature (low temperatures reduce risk), sex (female predilection), endurance running, and overhydration are more prominent risk factors for EAH than high altitude.

• 한국응용곤충학회지
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• 제48권4호
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• pp.527-533
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• 2009

본 연구에서는 소나무재선충병 매개충의 소나무재선충 보유 정도와 산란 및 섭식행동을 통한 전파에 대하여 조사하였다. 첫째, 세 가지 종류의 벌채목으로부터 우화 탈출하는 솔수염하늘소의 소나무재선충 보유 정도를 조사하였다. (가)의 경우는 건전한 소나무를 벌채하여 감염림 내에 방치한 것이고, (나)의 경우는 감염목에서 우화 탈출한 솔수염하늘소를 건전한 벌채목에 산란시켰을 경우이며, (다)의 경우는 솔수염하늘소는 서식하고 있으나 소나무재선충은 보유하지 않은 소나무를 벌채하고 소나무재선충을 인공적으로 접종한 경우이다. 세 경우 모두 이듬해에 벌채목으로부터 우화탈출하는 솔수염하늘소의 소나무재선충 보유율과 보유수를 조사하였다. (가)와 (나)의 경우 소나무재선충 보유율은 각각 18.3%와 15.6%이었고, 보유한 소나무재선충 수는 각각 $5,713.1{\pm}9,248.3$마리와 $2,034.1{\pm}4,746.8$마리로서 차이가 없었다. 그러나 인공적으로 소나무재선충을 접종한 (다)의 경우에는 소나무재선충 보유율과 보유수가 각각 38.3%와 $20,083.1{\pm}32,188.3$마리로서 다른 두 경우에 비해 높은 경향이었다. 한편, 소나무재선충 보유수를 조사한 세 경우 전체 52마리의 솔수염하늘소 중에서 20마리(38.5%)가 5,000마리 이상의 소나무재선충을 보유하고 있었고, 이들 20마리가 보유한 소나무 재선충이 전체 소나무재선충의 97.9%를 차지하였다. 둘째, 야외의 소나무재선충 감염림에서 채취한 소나무로부터 우화한 솔수염하늘소와 북방수염하늘소의 섭식 과정 중에 이들로부터 이탈하는 소나무재선충의 수를 조사하였다. 소나무재선충이 솔수염하늘소와 북방수염하늘소 몸으로부터 이탈한 일수는 각각 $34.9{\pm}12.4$일과 $23.9{\pm}16.2$일이었고, 우화 후 2주째에 가장 많이 탈출하였다. 우화 후 2주 이내에 탈출한 소나무재선충의 비율은 솔수염하늘소의 경우는 44.5%, 북방수염하늘소의 경우에는 47.2%이었으며, 매개충 한 마리당 이탈하는 소나무재선충의 수는 각각 $3,570.6{\pm}5,189.2$ 마리와 $1,556.2{\pm}1,710.3$ 마리이었다.