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Interdiffusion at Interfaces of polymers with Similar Physical Properties
김운천,이창준,심훈구,박형숙,Kim, Un Cheon,Lee, Chang Jun,Sim, Hun Gu,Park, Hyeong Suk Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.6
Interdiffusion process at interfaces of chemically identical polymers (e.g., deuterated-nondeuterated pairs) with different molecular weights or polymers with similar physical properties, is studied here by varying the diffusion time. Considering the vacancy flux ($J_v$) and adopting the Cahn-Hilliard interracial energy in describing this system, we can see that the variation of the interfacial composition profile with time is asymetric and the interface moves towards the polymer with the lower molecular weight as interdiffusion progresses. Furthermore, interface shift $\Delta\chi$, which characterizes the interdiffusion between polymers, agrees well with the behaviors of the existing experimental data. We can also obtain the interface shift factor C, which can be converted into values of $D_s$ (self-diffusion coefficient of the smaller molecules), from the slopes of the linear fits to the data of the interface shift.
이창준,심훈구,김운춘,이송희,박형숙,Lee, Chang Jun,Sim, Hun Gu,Kim, Un Chun,Lee, Song Hui,Park, Hyeong Suk Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.3
Molecular dynamics simulation studies for thermotropic liquid crystalline systems conposed of rodlike molecules with 6 Lennard-Jones interaction sites wre performed in NPT ensemble. Within the range of temperature studied, the system exhibited isotropic and smectic phase. For the characterization of the smectic phase, we examined the structure of the liquid crystalline phase via the radial distribution function, its longitudinal and transverse components to the director, and other orientational correlation function, its longitudinal and transverse components to the director, and other orientational correlation functions. In the smectic A phase, our results showed a large anisotropy in translational motion (i.e.,$D_⊥ >> D_∥$), and the decay of the collective orientational correlation function of rank two became slower than that of the single particle orientational correlation function of rank one. Comments on the spontaneous growth of orientational order directly from the isotropic phase are given.
이창준,심훈구,김운천,이송희,박형숙,Lee, Chang Jun,Sim, Hun Gu,Kim, Un Cheon,Lee, Song Hui,Park, Hyeong Suk Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.4
We present the results of computer simulation for the steady shear flows of rodlike molecules using nonequi-librium molecular dynamics simulation (NEMD) method. The model particle is a rigid rod composed of lin-early connected 6-sites and the Lennard-Jones 12-6 potential governs interactions between sites in different molecules. The system of rodlike molecules exhibits the change of orientational structure, that is, isotropic-nematic transition at high shear rates. We elucidate the nature of the ordered system developed from an isotro-pic phase by steady shear through an analysis of various quantities: orientational order parameters, orientational pair correlation functions, orientational distribution function, and snapshots of configurations. The effects of temperature and density on the shear rate dependence of orientational structure are described.
서울지역 동물보호소 내 유기견의 개 심장사상충 감염 실태조사
김능희 ( Neung Hee Kim ),곽정연 ( Jeong Yeon Kwak ),김혜라 ( Hye Ra Kim ),박형숙 ( Hyeong Suk Park ),김두환 ( Doo Hwan Kim ),이주형 ( Ju Hyung Lee ) 한국동물위생학회 2014 韓國家畜衛生學會誌 Vol.37 No.3
Dirofilaria immitis infection is one of the most important parasitic diseases in dogs and public health. It often elicits nodules in the pulmonary parenchyma and in the subcutaneous tissues of human. In this study, we investigated the prevalence of D. immitis infection among 754 dogs in Seoul area from April to December 2012. The infection rate of 754 dogs was 9.8% (74/754) by the antigen test (canine SNAP 4Dx). The infection rates of D. immitis in dogs at the age of <2, 2∼4, 5∼7, 8∼10, and >10 years were 3.7% (7/189), 12.9% (30/233), 15.0% (19/127), 9.8% (18/184), and 0% (0/21), respectively. The infection rates in the female and male dogs were 9.7% (33/340) and 9.9% (41/414), respectively. The regional infection rates in northern and southern Han river region of Seoul were 10.7% (44/410) and 8.7% (30/344), respectively. In order to confirm D. immitis infection, we performed PCR on serum samples of 74 dogs which tested positive for D. immitis antigen by the antigen test and we detected a specific gene ITS-2 in 59 serum samples. In conclusion, this study suggests that treatment and preventive care on the D. immitis infection should be considered in dogs of Seoul area.