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고무 탄성 이론을 이용한 가교 폴리우레탄의 특성에 관한 연구
허탁 건국대학교 1993 學術誌 Vol.37 No.2
Network formation (branching) theory was used to examine the relations between network structures and their properties. A series of model polyurethane(PU) networks based on poly(oxypropylene glycol), trimethylol propane, and dipheyl methane 4,4'-diisocyanate were prepared and analyzed by EANCs (Elastically Active Network Chains) theory and swelling experiment. The contribution of physical crosslinks to the total crosslinks was found to increase with increasing chemical crosslinks. In addition, with the same chemical crosslinking densities. the effect of physical crosslinks was more significant when the ratio of OH groups belonging to branch units to the total number of OH groups in the mixture (ρ) was larger. Tensile strengths increased with increasing the concentration of EANCs. While elongations at break did not show any trend, the fraction of elastic deformation decreased with increasing the concentration of EANCs. Galss transition temperatures increased with increasing not only the concentration of EANCs but also ρ.
허탁 건국대학교 1994 學術誌 Vol.38 No.2
A crosslinked polyurethane was ground and introduced into the same crosslinked polyurethane matrix as a filler with the variables of size, content, and swelling time in order to investigate the mechanical properties of polyurethane / polyurethane composites. The increase of the filler size decreased the mechanical properties of the composites such as tensile strength, elongation at break, and impact strength. The increase of the filler content from 0 to 20 wt% also deteriorated the properties of the composites. Even though the filler and the matrix showed good adhesion and compatibility (because they are virtually the same), poor mechanical properties was obtained. It may be due to the decrease of the modulus and the interference of the hard-segment phase formation when the filler was incorporated into the matrix. The effect of the swelling time of the polyurethane filler in the presence of poly(propylene glycol), PPG, and trimethylol propane, TMP, was expected to improve the mechanical properties because of the possible interpenetration of PPG and TMP at the filler-matrix interface. However, the decrease of the resulting properties from the increase of the swelling time with 0, 1, 3, 7, 15 days indicates that there was no significant interfacial interpenetration. Instead. the Increase of the swelling time brought about the defects in the network structures and hard-segment phase formation in the polyurethane matrix.
허탁,곽종명 한국공업화학회 2000 응용화학 Vol.4 No.1
In general, petrochemical industries are composed of very complex systems with internally recurring unit processes where the upstream input of a unit process may include the downstream output of the same unit process. Therefore, it is rather difficult to identify and quantify the inputs/outputs for those internally recurring unit processes, respectively. In this study, an objective and consistent calculation method which is applicable to complex systems with internally recurring unit processes are proposed to determine the inputs/outputs associated with each unit process by using simultaneous equations. In this case, unit processes linked another one are considered as variables and materials flows are considered as constants. The LCI results from the above methodology will be analyzed and compared using hypothetical examples.
복수를 동반한 간경변증 환자에서의 혈장 Renin 활성도 및 Aldosterone에 관한 연구
허경,전익섭,채종구,배학연,오금탁,김만우,조건국,양성훈 朝鮮大學校 附設 醫學硏究所 1988 The Medical Journal of Chosun University Vol.13 No.1
Rental circulatory and tubular function impairments are frequent in advanced liver cirrhosis. Renin catalyses the production of angiotensin which promote the secretion of aldosterone. Plasma renin activity is often increased in patients with cirrhosis, particularly those with ascites, but interrelationships between those have not yet been precisely definded. For the purpose of evaluating renin-angiotensin aldosterone axis, 24 hour urine sodium, creatinine clearance, plasma renin activity, and plasma aldosterone by radioimmunoassay kit were measured in patients with liver cirrhosis with ascites and normal control group who were admitted to Chosun University hostpital. The results are summarized as following : 1. The laboratory findings in cirrhotic patients with mild ascites revealed significant reduction of 24 hour urine sodium (81=25mEq)(P<0.01) and increase of PRA, plasma aldosterone levels (3.82±1.75 ng/ml/hour, 157.83±13.27 pg/ml)(P<0.01, P<0.01) as compared to those of normal controls. 2. The levels of 24 hour urine sodium, PRA and plasma aldosterone were 31±15, 6.92±2.32, and 250.61±35.32 respectively in cirrhotic patients with severe ascites. There were significant decrease in 24 hour urine sodium (P<0.005), increase in PRA and plasma aldostorone (P<0.005, P<0.01) as compared to normal controls and cirrhotic patients with mild ascites. 3. PRA was related to plasma aldosterone (r=0.87, P<0.001) but inversely related to creatinine clearance (r=-0.73, P<0.005)