• Geomechanics and Engineering
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• 제12권3호
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• pp.417-439
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• 2017

The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

• Journal of Korean Neurosurgical Society
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• 제59권4호
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• pp.368-373
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• 2016

Objective : Delayed hinge fracture (HF) that develops after cervical open door laminoplasty can be a source of postoperative complications such as axial pain. However, risk factors related to this complication remain unclear. We performed a retrospective clinical series to determine risk factors for delayed HF following plate-only open-door cervical laminoplasty. Methods : Patients who underwent plate-only open-door laminoplasty and had available postoperative computed tomography (CT) scans (80 patients with 270 laminae) were enrolled. Hinge status, hinge gutter location, open location, hinge width, number of screws used, operation level, and open angle were observed in the CT to determine radiographic outcome. Demographic data were collected as well. Radiographic and clinical parameters were analyzed using univariate and multivariate logistic regression analysis to determine the risk factors for HF. Results : Univariate logistic regression analysis results indicated poor initial hinge status, medially placed hinge gutter, double screw fixation on the elevated lamina, upper surgical level, and wide open angle as predictors for HF (p<0.05). Initial hinge status seemed to be the most powerful risk factor for HF (p=0.000) and thus was collinear with other variables. Therefore, multivariate logistic regression analysis was performed excluding initial hinge status, and the results indicated that medially placed hinge gutter, double screw fixation on the elevated lamina, and upper surgical level were risk factors for HF after adjustment for other confounding factors. Conclusion : To prevent HF and to draw a successful postoperative outcome after cervical laminoplasty, surgical and clinical precautions should be considered.

• 한국콘텐츠학회논문지
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• 제6권12호
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• pp.192-200
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• 2006

인터넷의 등장과 웹의 발달로 웹 기반 교육은 언제 어디서나 가상공간에서 학습자 중심의 개별 학습 및 선택 학습을 가능하게 하고 있다. 본 논문에서는 초등학교 4학년 수학과 각도 단원을 중심으로 웹을 활용하는 수업을 위한 학습 활동 중심의 코스웨어를 설계 및 구현하였다. 본 코스웨어는 흥미와 성취도를 향상시키기 위하여 다양한 플래시 애니메이션을 활용한 학습 활동 및 설계 방안을 적용하여 집중적인 학습자 중심의 수업을 할 수 있도록 구현되었다. 개발된 웹코스웨어를 초등학교 4학년 학생들을 대상으로 적용한 결과, 일반적인 수업 방식으로 학습을 한 집단에 비해 학업 성취도가 높게 나타났으며 실험 집단 학생을 대상으로 설문 조사를 실시한 결과 이해도, 흥미도, 편리성, 자기 주도적 학습의 반영 영역에서 긍정적인 응답을 보여 교육적 효과가 높음을 확인하였다.

• Journal of Astronomy and Space Sciences
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• 제26권1호
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• pp.111-126
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• 2009

인공위성 궤도 결정을 위해 한국천문연구원의 0.6m 광시야 망원경을 이용하여 중 고궤도 인공위성과 폐기위성을 관측하였다. 관측 자료는 영상처리 및 좌표 보정을 통해 장착기기에 의한 오차를 보정한다. 위성 관측 사료에서 얻은 좌표 정보는 관측 시스템의 불안정성과 끝점 결정 오차에 의해 13각초의 오차를 가진다. KODAS의 결과로 얻은 시뮬레이션 좌표와 Gauss 방법을 이용해 예비궤도 결정을 수행하고 궤도 결정에 적합한 시간 간격을 찾아보았다. 또한 미분보정을 통한 예비궤도 결정 결과의 향상을 확인하였다. 이들 결과를 평균궤도요소 형대로 변환하여 실제 관측 자료와 비교하여 에비궤도 결정을 통해서 짧은 시간동안 위성의 추적이 가능함을 확인하였으며, 미분보정을 통해 그 결과를 향상시킬 수 있음을 확인하였다.

• 천문학회보
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• 제41권1호
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• pp.48.1-48.1
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• 2016

Polarimetric study of light scattering from cometary dust particles can provide us opportunity to decipher their characteristics, such as sizes, structures, compositions of dust grains, etc. Herein, we present the results of our polarimetric study of long-period comet, C/2013 US10 (Catalina), in optical and near-infrared wavelengths which appeared at large phase angle (52.7 degrees) around the mid-December, 2015. We performed polarimetric and spectroscopic observations with HONIR, attached to the 1.5-m telescope at Higashi-Hiroshima Observatory, on UT 2015 December 17-18 and also obtained optical imaging data sets by the Ishigakijima Astronomical Observatory (IAO) and Okayama Astrophysical Observatory (OAO) taken between 2014-2015. By measuring the intensities of gas emission lines with respect to dust continuum and considering transmittance of each filter, we estimated that the percentages of gas contamination are approximately 10 percents in $R_C$-band and 3 percents in $I_C$-band. With these results, we derive the degree of linear polarization scattered solely from dust components in the coma. At this presentation, we will compare the phase-angle dependence of the degree of linear polarization with those of previous archive data in a wide coverage of wavelengths from $R_C$-band to $K_S$-band. Finally, we are supposed to discuss the spatial variations in polarization within the coma.

• 한국추진공학회지
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• 제5권1호
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• pp.18-25
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• 2001

2차 가스 분사 추력벡터 제어 성능 해석을 위한 체계적인 수치계산을 수행하였다. 분사위치와, 노즐 팽창각이 압력비, 추력비, 비추력비 및 축추력 증대와 같은 전체 성능 파라미터에 미치는 2차 분사의 효과를 고찰하였다. 2차 제트 분사에 의한 복잡한 노즐 배기 유동에 대한 수치 해석은 Baldwin-Lomax 난류 모델을 포함하는 비정상 3차원 레이놀즈 평균 Navier-Stokes 방정식을 이용하여 수행하였고, 팽창 팽착반각이 $9.6^{\cire}$인 로켓 노즐에서의 2차 공기분사에 대해 적용, 실험값과 비교, 검증 하였다. 전체 성능 파라미터에 대한 결과로서 주 노즐의 하류에 2차 분사구를 위치시키는 것이 반사 충격파의 발생을 방지하며, 넓은 적용범위에 대하여 효율적이고 안정한 추력 방향제어에 적합한 것으로 나타났다.

• Macromolecular Research
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• 제12권1호
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• pp.1-10
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• 2004

The structural changes occurring in the isothermal crystallization processes of polyethylene (PE), poly-oxymethylene (POM), and vinylidene fluoridetrifluoroethylene (VDFTrFE) copolymer have been reviewed on the basis of our recent experimental data collected by the time-resolved measurements of synchrotron-sourced wide-angle (WAXS) and small-angle X-ray scatterings (SAXS) and infrared spectra. The temperature jump from the melt to a crystallization temperature could be measured at a cooling rate of 600-1,000 $^{\circ}C$/min, during which we collected the WAXS, SAXS, and infrared spectral data successfully at time intervals of ca. 10 sec. In the case of PE, the infrared spectral data clarified the generation of chain segments of partially disordered trans conformations immediately after the jump. These segments then became transformed into more-regular all-trans-zigzag forms, followed by the formation of an orthorhombic crystal lattice. At this stage, the generation of a stacked lamella structure having an 800-${\AA}$-long period was detected in the SAXS data. This structure was found to transfer successively to a more densely packed lamella structure having a 400-${\AA}$-long period as a result of the secondary crystallization of the amorphous region in-between the original lamellae. As for POM, the formation process of a stacked lamella structure was essentially the same as that mentioned above for PE, as evidenced from the analysis of SAXS and WAXS data. The observation of morphology-sensitive infrared bands revealed the evolution of fully extended helical chains after the generation of lamella having folded chain structures. We speculate that these extended chains exist as taut tie chains passing continuously through the neighboring lamellae. In the isothermal crystallization of VDFTrFE copolymer from the melt, a paraelectric high-temperature phase was detected at first and then it transferred into the ferroelectric low-temperature phase at a later stage. By analyzing the reflection profile of the WAXS data, the structural ordering in the high-temperature phase and the ferroelectric phase transition to the low-temperature phase of the multi-domain structure were traced successfully.

• Macromolecular Research
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• 제11권5호
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• pp.375-381
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• 2003

Silver salt complex membranes with glassy poly(methyl methacrylate) (PMMA) unexpectedly showed higher propylene permeance than those with rubbery poly(butyl methacrylate) (PBMA) where as neat PMMA is much less permeable to propylene than that of neat PBMA. Such unusual facilitated olefin transport has been systematically investigated by changing the side chain length of polymethacrylates (PMAs) from methyl, ethyl to butyl. The ab initio calculation showed almost the same electron densities of the carbonyl oxygens in the three PMAs, expecting very similar intensity of the interaction between carbonyl oxygen and silver ion. However, the interaction intensity decreases with the length of the alkyl side chain: PMMA > PEMA > PBMA according to wide angle X-ray scattering and FT-Raman spectroscopy. The difference in the interaction intensity may arise from the difference in the hydrophilicity of the three PMAs, as confirmed by the contact angle of water, which determines the concentrations of the ionic constituents of silver salts: free ion, contact ion pair and higher order ionic aggregate. However, propylene solubilities and facilitated propylene transport vary with the side chain length significantly even at the same concentration of the free ion, the most active olefin carrier, suggesting possible difference in the prohibition of the molecular access of propylene to silver ion by the side chains: the steric hindrance. Therefore, it may be concluded that both the hydrophilicity and the steric hindrance associated with the side chain length in the three PMAs are of pivotal importance in determining facilitated olefin transport through polymer/silver salt complex membranes.

• Physical Therapy Rehabilitation Science
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• 제6권1호
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• pp.7-13
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• 2017

Objective: The aim of this study was to investigate the inter-rater and intra-rater reliability of rehabilitative ultrasound imaging (RUSI) for measurement of muscle thickness with changes in angles of the gluteus maximus (GM) at rest and during contraction. Design: Cross-sectional study. Methods: Twenty-two healthy men volunteered for this study. GM muscle images were obtained in the resting position and during prone hip extension with knee flexion at hip abduction angles of $0^{\circ}$ and $30^{\circ}$, respectively. Two examiners randomly measured the thickness of the GM twice in three different positions. The first position was a comfortable prone position. The second position was prone hip extension with knee flexion (PHEKF) to $90^{\circ}$. The third position was achieved by hanging a 1-kg weight on the ankle of the lifted leg during PHEKF with the angle of the lifted leg the same as the second position. Intra-class correlation coefficients (ICCs), standard error measurements, and minimal detectable changes were used to estimate reliability. Results: The intra-rater reliability ICCs (95% confidence interval) of the GM were >0.870, indicating good reliability. Inter-rater reliability ICCs ranged from 0.668 to 0.913. The reliability of measurements of muscle thickness at each position was similar to the reliability of the angle change. Differences in muscle thickness and ratios for each position with $0^{\circ}$ and $30^{\circ}$ of hip abduction were not statistically significant. Conclusions: In the present study, the intra-rater reliability of muscle thickness measurements of the GM was good, and the inter-rater reliability was moderate to good. Reliable RUSI measurements of wide and large muscles, such as the GM muscle at rest and during contraction, are feasible. Further investigation is required to establish the reproducibility of the protocols presented in this study.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1698-1700
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• 2003

The electrostatic precipitator(ESP) is a device for removing particulate pollutants in the form of either a solid (dust or fumes) or a liquid (mist) from a gas using an electrostatic force, Electrostatic precipitation has been widely used for cleaning gas from almost all industrial processes with a medium to large gas volume(>2,000 $m^3/min$), including utility boilers, blast furnaces, and cement kilns. ESP is also in wide use for air cleaning in living environments (home, offices, hospitals, etc.) ESP has large advantages over other particulate control device : a low operating cost, a high collection performance, and ease of maintenance. The purpose of this study is to investigate the characteristics of the smoke removal of an air cleaner by adjusting variable frequency and monitoring of turbidity three results of this research are as follows ;the first is the best efficient switching frequency which is 60Hz, the second is the smoke removal time which is obtained to 9 seconds, third is that the best efficient firing angle is $90^{\circ}$ As a result, the switching trigger frequency and SCR gate firing angle is very important factor to predict the best collection efficiency.