• 한국해안해양공학회지
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• 제18권3호
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• pp.198-210
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• 2006

본 연구에서 이용한 3차원 유동모델인 POM(Princeton Ocean Model)은 저층수의 거동예측에 유리한 ${\sigma}$ 좌표계를 채용하고 있는 모델로서 범용성이 높고, 해양유동모델로서 개발되었지만 최근에는 연안역에서의 적용 예(박경 등, 1998)도 증가하고 있다. 기존의 POM은 ${\sigma}$좌표계 모델의 좌표변환에 기인한 수치오차에 대한 보정을 실시하지 않은 모델로서, 이러한 수치오차를 축소시키는 것은 저층부근의 유속의 정도향상에 매우 중요하지만 오차의 축소를 시도하지 않고 그대로 적용하고 있는 실정이다. 따라서, 본 연구에서는 $Sl{\Phi}rdal$(1997)이 제안한 방법을 이용하여 오차보정을 통한 3차원 유동모델인 POM의 정도향상을 실시하였다. 구축된 모델을 이용하여 우리나라의 대표적인 기수호중 하나인 영랑호에 적용하여 저층수의 거동을 파악하고 빈산소수괴를 포함한 저층수의 거동 및 형성기구를 명확히 할 수 있는 자료로서 활용하고자 하였다. 적용결과, 기존 POM모델과 비교하여 개량형 POM모델을 이용하였을 경우 수역에서의 저층수의 거동재현에 있어서 더욱 효과가 있음을 볼 수 있었다.

• 대한치과기공학회지
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• 제34권2호
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• pp.135-143
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• 2012

Purpose: The purpose of this in vitro study was to compare the marginal fit of POM restorations with 3 different thickness of metal coping. Methods: 2.0mm Occlusal reduction, 1.0mm preparation of axial wall with 6degree taper, and chamfer margin was prepared a maxillary first premolar on dentiform. Duplicate prepared die and, make 30 individual dies with Ni-Cr metal. Make 3 groups of 30 press ceramic on Metal crown with different thickness of metal coping; 10 of 0.1mm, 10 of 0.3mm, 10 of 0.5mm thickness metal coping. The marginal fit of the crowns was evaluated 50 points per 1 crown, around the crown margin circumference under a optical microscope at original magnification ${\times}100$. A 1-way analysis of variance (ANOVA) was used to compare data. Results: The mean marginal discrepancy for POM with 0.1mm metal copings was $72.56{\mu}m$, $67.83{\mu}m$ for 0.3mm metal coping POMs, and $72.56{\mu}m$ for 0.5mm metal coping POM. The 1-way ANOVA showed significant difference among 3 groups. Conclusion: The marginal fit of pressed-on-metal (POMs) was best with 0.3mm thickness of metal coping, fallowing by 0.1mm, and 0.5mm in the order.

• 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.