• Journal of Adhesion and Interface
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• v.9 no.1
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• pp.3-8
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• 2008

Self-sensing was evaluated for carbon nanofiber (CNF)/epoxy composites with two different aspect ratios via electro-micromechanical technique and wettability test. Volumetric electrical resistance was measured to evaluate the comparative dispersion degree indirectly and it decreased due to the increase of electric contacts with increasing CNF concentration. The dispersion degree was evaluated indirectly by calculating coefficient of variation (COV) of volumetric electrical resistance. The CNF type A with a high aspect ratio showed better self-sensing than the case of CNF type B with a short aspect ratio. The CNF type B/epoxy composite showed little self-sensing at a concentration higher than 2 vol% probably due to poor dispersion. The apparent modulus of CNF type B was higher than that of CNF type A due to the orientation effect and the high surface area. The thermodynamic work of adhesion was consistent with the result of apparent modulus.

• Journal of Adhesion and Interface
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• v.12 no.3
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• pp.88-93
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• 2011

Optimal dispersion and fabrication conditions of carbon nanotube (CNT) embedded in phenolic resin were determined by electrical resistance measurement; and interfacial property was investigated between plasma treated carbon fiber and CNT-phenolic composites by electro-micromechanical techniques. Wettability of carbon fiber was improved significantly after plasma treatment. Surface energies of carbon fiber and CNT-phenolic nanocomposites were measured using Wilhelmy plate technique. Since surface activation of carbon fiber, the advancing contact angle decreased from $65^{\circ}$ to $28^{\circ}$ after plasma treatment. It was consistent with static contact angle results of carbon fiber. Work of adhesion between plasma treated carbon fiber and CNT-phenolic nanocomposites was higher than that without modification. The interfacial shear strength (IFSS) and apparent modulus also increased with plasma treatment of carbon fiber.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.37-43
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• 2019

This study investigated electrical conductivity, electromagnetic shielding effectiveness, and mechanical property to improve electromagnetic shielding performance of high performance fiber reinforced cementitious composites (HPFRCC). Steel fiber, steel slag and carbon black as a conductive material were incorporated into the HPFRCC mixes. In addition, 2% CNT solution which was produced by dispersing multi-wall carbon nanotube (MWCNT) into water was used as a conductive material. In the test results, electrical conductivity of HPFRCC specimens was very low except for the specimen incorporating 1% carbon black. Micro structure of cement matrix was changed as the curing time increased, which negatively affected the conductive network of HPFRCC. In case of HC1 specimen showing a conductive network (0.083 S/cm), the electrical conductivity of the specimen after being dried at $60^{\circ}C$ for 72 hours to exclude the effect of water on electrical conductivity was significantly reduced to 0.0003 S/cm. The most important parameter of electromagnetic shielding effect was found to be a steel fiber while the effect of carbon black and steel slag was very few. The correlation between electrical conductivity and electromagnetic shielding effect does not seem to be clear.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.4
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• pp.215-226
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• 2022

Significant efforts have been devoted to developing high-performance composite materials by emulating the structure of biological creatures with superior mechanical characteristics. Nacre has been one of the most sought-after natural structures due to its exceptional fracture toughness compared with the constituent materials. However, the effect of manipulating the nacre-like geometry on the impact performance has not been fully investigated thus far. In this study, composites of randomly manipulated nacreous geometry are numerically developed and the impact performance is analyzed. We develop an algorithm by which the planar area of platelets in the nacre-like design is randomly resized. Thereafter, the numerical models of nonuniform nacre-patterned multi-layer structures are developed and the drop-weight impact simulation is performed. The impact behaviors of the model are evaluated by using the ratio of absorbed energy, the von Mises stress distribution, and the impact force-time curve. Therefore, the effect of the geometric irregularity on the nacre-patterned design is elucidated. This insight can be efficiently utilized in establishing the optimum design of the nacre-patterned structure.

• Journal of Adhesion and Interface
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• v.23 no.4
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• pp.122-129
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• 2022

In this study, the hydrophilicity of the metal fiber is improved by introducing an oxygen-containing functional group to the fiber surface after treatment of the metal fiber using the oxygen plasma treatment time as an experimental variable. For the surface modification of metal fibers, changes in surface properties before and after plasma treatment were observed using SEM and x-ray photoelectron spectroscopy (XPS). In order to observe the effect of the plasma treatment time on the surface of the metal fiber, the change in contact angle of the metal fiber with respect to a polar solvent and a non-polar solvent was measured. After calculating the change in surface free energy using the measured contact angle, the contact angle and the surface free energy for metal fibers before and after oxygen plasma treatment were compared, and the correlation with the adhesion work was also considered. The microdroplet specimens were prepared to investigate the effect of surface changes of these metal fibers on the improvement of shear strength at the interface when combined with other materials and the interfacial shear strength was measured, and the correlation with the adhesion work was also identified. Therefore, the oxygen plasma treatment of the metal fiber results in an increase in the physical surface area on the fiber surface and a change in contact angle and surface energy according to the introduction of the oxygen-containing functional group on the surface. This surface hydrophilization resulted in improving the interfacial shear strength with the polymer resin.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.150-168
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• 2023

The anisotropic behavior of rocks is primarily attributed to the directional arrangement of rock-forming minerals and the distribution characteristics of microcracks. Notably, sedimentary and metamorphic rocks often exhibit distinct transverse isotropy in terms of their strength and deformation characteristics. Consequently, it is crucial to gain accurate insights into the deformation and failure characteristics of transversely isotropic rocks during rock mechanics design processes. The deformation of such rocks is described by five independent elastic constants, which are determined through laboratory testing. In this study, the characteristics of the directional variation of apparent elastic constants in transversely isotropic rocks were investigated using experimental data reported in the literature. To achieve this, the constitutive equation proposed by Mehrabadi & Cowin was introduced to calculate the apparent elastic constants more efficiently and systematically in a rotated Cartesian coordinate system. Four transversely isotropic rock types from the literature were selected, and the influence of changes in the orientation of the weak plane on the variations of the apparent elastic modulus, apparent shear modulus, and apparent Poisson's ratio was analyzed. Based on the investigation, a new constraint on the elastic constants has been proposed. If the proposed constraint is satisfied, the directional variation of the apparent elastic constants in transversely isotropic rocks aligns with intuitive predictions of their tendencies.

• Journal of Korea Water Resources Association
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• v.56 no.spc1
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• pp.1059-1069
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• 2023

Dam-break flow occurs when an elevated dam suddenly collapses, resulting in the catastrophic release of rapid and uncontrolled impounded water. This study compares laminar and turbulent closure models for simulating three-dimensional dam-break flows using OpenFOAM. The Reynolds-Averaged Navier-Stokes (RANS) model, specifically the k-ε model, is employed to capture turbulent dissipation. Two scenarios are evaluated based on a laboratory experiment and a modified multi-layered block obstacle scenario. Both models effectively represent dam-break flows, with the turbulent closure model reducing oscillations. However, excessive dissipation in turbulent models can underestimate water surface profiles. Improving numerical schemes and grid resolution enhances flow recreation, particularly near structures and during turbulence. Model stability is more significantly influenced by numerical schemes and grid refinement than the use of turbulence closure. The k-ε model's reliance on time-averaging processes poses challenges in representing dam-break profiles with pronounced discontinuities and unsteadiness. While simulating turbulence models requires extensive computational efforts, the performance improvement compared to laminar models is marginal. To achieve better representation, more advanced turbulence models like Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) are recommended, necessitating small spatial and time scales. This research provides insights into the applicability of different modeling approaches for simulating dam-break flows, emphasizing the importance of accurate representation near structures and during turbulence.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1982.05a
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• pp.10.1-10
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• 1982

The use of phonosurgery in the recent development of laryngomicrosurgery has enabled the restoration of a normal voice in respect to functional laryngeal surgery which in Korea in the past limited to simple removal of benign laryngeal tumor such as laryngeal polyp or nodules and cordal injection of $Teflon^{{\circledR}}$ for the treatment of recurrent nerve paralysis under the vision of suspension laryngoscopy. Performance of phonosurgery for the treatment of cord paralysis, mutational dysphonia, vocal cord atrophy, hyperkinetic dysphonia and sulcus vocalis is a happy event in the view point of development of phonosurgery in Korea. In this aspect thyroplasty to change the position and physical characteristics of the cord outside the glottis instead of the direct handling of the vocal cord through direct endoscopy is popular. Among the 4 types of thyroplasty, classified by Insshiki(1974), type I thyroplasty(1ateral compression of vocal cord) and type IV thyroplasty(lengthening of vocal cord) were effective in the treatment of unilateral vocal cord paralysis. Advantages of this operation are the fine adjustment of the degree of lateral compression under local anesthesia according to the phonation of the patient during operation and avoidance of dyspnea and intralaryngeal hemorrhage due to the manipulation outside the internal perichondrium of the thyroid cartilage. We did 7 cases of thyroplasty for the treatment of unilateral vocal cord paralysis in the 7 months from September 1981 to March 1982. Before the operation aerodynamic study, psychoacoustical evaluation, stroboscopy and sound spectrographic analysis were done. Two months after the operation the above procedures were performed again. Results of preoperative and postoperative examination were compared and the following results were obtained. 1) In the aerodynamic study, maximum phonation time increased to 158% of the preoperative value and the phonation quotient and the mean flow rate decreased to 58% and 54% of preoperative values. 2) The degree of hoarseness improved in the psychoacoustical evaluation and the glottic chink during phonation was decreased in the stroboscopic examiantion. 3) In the sound spectrographic analysis, periodicity was much restored and noise distribution decreased especially in the high frequency area.

• Journal of Chest Surgery
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• v.32 no.12
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• pp.1093-1099
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• 1999

배경 : 류마티스성 승모판막 폐쇄부전증과 퇴행성 승모판막 폐쇄부전증에서 승모판막 성형술의 결과와 비교하여 류마티스성 승모판막 폐쇄부전증에서도 승모팍막성형술이 적합한 치료방법이 될 수 있는지를 알아보았다. 대상 및 방법 : 95년 1월부터 98년 12월 까지 승모판막 성형술을 시행받은 184명의 환자중에서 류마티스성 승모판막 폐쇄부전증 49례(1군)의 퇴행성 승모판막 폐쇄부전증 78례(2군)를 대상으로 하였다. 평균연령은 1군이 36.3$\pm$14.6(16-74세) 2군은 52.5$\pm$13.4(14-77)세였다 총 추적 관찰기간은 1군이 72.2인년 2군이77.2인년이었다 두군에서 수술후와 수술후 6개월 1년 및 이후 1년 단위로 주기적인 심초음파를 시행하였고 이를 통계적 검정하였다. 결과 : 두 군간에 수술전 혈류역학적인 차이를 보이지 않았고 수술전 평균 승모판막 폐쇄 부전의 정도는 1군이 3.0$\pm$0.4, 2군이 3.9$\pm$0.3였으나 수술후 추적 관찰에서 각각 0.9$\pm$0.9와 0.8$\pm$0.7정도의 양호한 판막 성형술의 결과를 보였고 승모판막 면적의 변화나 승모판막에서의 평균압력차이 등 혈류역학적인 결과에도 차이를 보이고 있지 않았다 수술조기 사망과 후기 사망은 없었으며 재수술율은 1군이 인년대비 1.4% 2군이 인년대비 2.6%였고 색전발생율은 1군이 인년대비 2.8% 2군이 1.3%였다. 심내막염발생은 1군에서만 1례있었으며 상기 결과들에서 두군간에 의미있는 차이를 보이고 있지는 않았다 결론 : 향후 장기적인 추적 관찰이 필요하나 중기 성적에서 승모판막 성형술이 류마티스성 승모판막 폐쇄 부전증에서도 효과적인 치료방법임을 알수 있었다.다 출생후 폐포막의 FN의 활성은 출생후 5일 및 7일에 최고주에 달했다. 출생직후 1-2일경에 혈관의 조직내 FN의 활성이 양성을 나타내지만 3일이후 활성이감소되었다. 폐포대식세포내 FN의 활성은 출생후 증가되었다. 폐조직내 소기관지의 FN의 활성은 출생후 완만하게 상승되었다. 큰 폐포세포는 출생 1-3일에 일정량의 FN 반응이 세포질과 미세융모내에 관찰되었다. 결론 : 이상과 같은 결과로 흰쥐의 폐포의 분화과정이 계속되는 출생후 폐에서 FN의 분비는 7일이내에 성숙흰쥐의 폐포내 반응과 비슷한 반응으르 보이며 이때 폐의 실질조직은 분화가 거의 완료되었을 것으로 사료되었고 큰 폐포세포에서도 FN이 분비되는 것으로 결론지울수 있다.X>에서 $1,332.75{\mu}g/mL$으로 최 대값을 나타내었으며, 추출시간 4.24시간 및 시료에 대한 용매비 9.71 mL/g에서 가장 높게 나타났다. 추출온도가 높고, 추출시간이 증가할수록 총 polyphenol 함량이 증가하는 경향을 나타내었다. Gallic acid 함량은 $65.84^{\circ}C$에서 $30.51{\mu}g/mL$으로 최대값을 나타내 었으며, 추출시간 1.65시간 및 시료에 대한 용매비 17.17mL/g에서 가장 높은 추출율을 보였다. Gallic acid 함량에 대한 추출조건의 영향은 추출시간과 용매비에 영향을 받는 것으로 나타났으며, 설정된 범위 내에서 온도에 대한 영향은 거의 나타나지 않는 것으로 나타났다. 실험연구가 더 필요하리라 본다. 혈액학적 변화를 유도하고 환자의 연령, 혈소판 수, 대동맥 차단 시간, 체외 순환 시간, 술후 PT 및 aPTT와 같은 다인적 상황들이 술후 출혈에 영향을 미친다는 점들을 시사하고

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.6 no.2
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• pp.120-128
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• 2003

Purpose: Recently, while the authors were experiencing that the epidemic period of rotaviral infection happened more in the early spring, we tried to find out how the outbreaks of rotaviral infection are changing in detail depending on the weather condition since it has something to do with the climate factors and PM10. Methods: Fourteen hundreds seventy nine patients who were proved to be positive to rotavirus were chosen among children less than 5 years old from January 1995 to June 2003. Among various climate factors, monthly average temperature, humidity, rainfall and PM10 were selected. Results: Rotaviral infection was most active in 2002 as 309 (20.9%) patients. It has been the spring that is the most active period of rotaviral infection since 2000. The temperature (RR=0.9423, CI=0.933424~0.951163), rainfall (RR=1.0024, CI=1.001523~1.003228) and PM10 (RR=1.0123, CI=1.009385~1.015248) were significantly associated with the monthly distribution of rotaviral infection. Conclusion: Through this study we determined that the epidemic period of rotaviral infection is changed to spring, which is different from the usual seasonal periods such as late fall or winter as reported in previous articles. As increased PM10 which could give serious influence to the human body, and changing pattern of climate factors such as monthly average temperature and rainfall have something to do with the rotaviral infection, we suppose that further study concerning this result is required in the aspects of epidemiology, biology and atmospheric science.