• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.53-64
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• 2011

The present study considers multi-level approach for the analysis of parametric roll phenomena. Three kinds of computation method, GM variation, impulse response function (IRF), and Rankine panel method, are applied for the multi-level approach. IRF and Rankine panel method are based on the weakly nonlinear formulation which includes nonlinear Froude-Krylov and restoring forces. In the computation result of parametric roll occurrence test in regular waves, IRF and Rankine panel method show similar tendency. Although the GM variation approach predicts the occurrence of parametric roll at twice roll natural frequency, its frequency criteria shows a little difference. Nonlinear roll motion in bichromatic wave is also considered in this study. To prove the unstable roll motion in bichromatic waves, theoretical and numerical approaches are applied. The occurrence of parametric roll is theoretically examined by introducing the quasi-periodic Mathieu equation. Instability criteria are well predicted from stability analysis in theoretical approach. From the Fourier analysis, it has been verified that difference-frequency effects create the unstable roll motion. The occurrence of unstable roll motion in bichromatic wave is also observed in the experiment.

• 공업화학
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• 제19권4호
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• pp.452-456
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• 2008

메조포러스 실리케이트 물질은 넓은 비표면적과 규칙적인 나노 기공구조를 가지고 있어 흡착제로 활용도가 높다. 본 연구에서는 대표적인 메조포러스 실리케이트인 MCM-41, SBA-15을 흡착제로 활용하여 휘발성 유기화합물의 하나인 벤젠의 기상 흡착 실험을 수행하였다. 벤젠의 파과곡선(Breakthrough curves)을 통하여 각 물질의 벤젠 흡착량을 비교한 결과, 본 실험의 조건에서는 기공구조가 큰 SBA-15이 더 높은 벤젠 흡착량을 보여주었다. 특히 다른 분자체 물질인 제올라이트 X보다도 약 2.7배 높은 흡착력을 보여주었다. SBA-15를 이용하여 흡착온도와 벤젠 주입속도를 달리하며 벤젠 기상 흡착을 수행한 결과, 온도가 증가할수록 벤젠의 흡착량은 급속히 감소하였다. 이러한 결과는 SBA-15에 흡착하는 벤젠의 결합이 약하다는 것을 보여준다.

• Journal of Preventive Medicine and Public Health
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• 제42권6호
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• pp.386-391
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• 2009

Objectives : This cross-sectional study was performed to examine if the serum gamma-glutamyltransferase (GGT) level that is within its normal range is associated with the risk of type 2 diabetes and if the association between the waist hip ratio (WHR) and type 2 diabetes is different depending on the serum GGT levels. Methods : The study subjects were 23,436 persons aged 40 years or older and who participated in regular health check-ups at 11 hospitals (males: 5,821, females: 17,615). The gender-specific quintiles of the serum GGT and WHR were used to examine the associations with type 2 diabetes. Results : The serum GGT levels within their normal range were positively associated with type 2 diabetes only in women. The adjusted odds ratios (ORs) were 1.0, 1.0, 1.4, 2.1, and 2.5 according to the quintiles of the serum GGT ($p_{trend}$<0.01). The WHR was more strongly associated with the prevalence of diabetes among the women with a high-normal serum GGT level as compared with those with a low-normal serum GGT level (p for interaction=0.02). For example, the adjusted ORs for women with a low normal serum GGT level were 1.0, 1.2, 1.5, 2.2, and 2.4 according to the quintiles of the WHR, while those figures were 1.0, 2.4, 3.6, 5.0, and 8.3 among the women with a high normal serum GGT level. However, in men, the serum GGT was very weakly associated with type 2 diabetes and the association between the WHR and type 2 diabetes was not different depending on the serum GGT level. Conclusions : Serum GGT within its normal range was positively associated with type 2 diabetes, and central obesity was more strongly associated with the prevalence of type 2 diabetes when the serum GGT level was highnormal. However, these associations were observed only in women, which is different from the previous findings. The stronger relation between central obesity and type 2 diabetes among women with a high-normal serum GGT level can be useful for selecting a group that is at high risk for type 2 diabetes irregardless of whatever the underlying mechanism is.