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Mun, Hueong-Tae,Namgung, Jeong,Namgung, Jeong-Hee-Namgung The Ecological Society of Korea 2000 Journal of Ecology and Environment Vol.23 No.2
Mass loss and changes of mineral nutrients during decomposition of Phragmites communis for 13 months from November 1998 to December 1999, were investigated at the fringe of stream at Boryeong, Chungnam Province in Korea. Plant materials, which were collected in November 1998. were divided into leaves, culms and rhizomes. Litterbags, 15${\times}$15 cm, were made of nylon mesh with 2-mm$^2$ holes. At 13 months after installation, remaining mass of leaves, culms and rhizomes was 29.0%, 57.4%, 20.6%, respectively. Mass loss rate of the culms was significantly lower than those of the leaves and rhizomes. The decay rate of leaves, culms and rhizomes was 1.21. 0.42 and 1.48 per year, respectively. Initial concentration of N, P, K, Ca and Mg of leaves. culms and rhizomes was 22.5, 9.0, 15.5 mg/g for N, 0.34. 0.10, 0.33 mg/g for P, 15.0, 12.5. 12.3 mg/g for K, 2.84. 0.80, 0.03 mg/g for Ca. 1.94. 0.97, 0.40 mg/g for Mg, respectively. Concentrations of nutrients were higher in leaves than in culms and rhizomes. Except for N and Mg in rhizomes, there was no immobilization period during the decomposition. In the case of remaining K and Ca, most are lost during the first 3 months. Without any suitable method for removal of dead part, eutrophication of freshwater may be accelerated by dead macrophytes.
Namgung, Bumseok,Ong, Peng Kai,Wong, Yun Hui,Lim, Dohyung,Chun, Keyoung Jin,Kim, Sangho IOP Pub 2010 PHYSIOLOGICAL MEASUREMENT Vol.31 No.9
<P>We have recently proposed a computer-based method utilizing a thresholding algorithm (the Otsu method) to provide a convenient way of measuring the cell-free layer width <I>in vivo</I> and <I>in vitro</I>. However, this method does not seem to be a universal method that can be applied to all microvascular studies. Thus, we examined four different histogram-based thresholding algorithms (Otsu, intermode, minimum and second peak) to provide a technical suggestion on the selection of a suitable thresholding algorithm for the cell-free layer measurement. All the measurements were taken in microvascular flows in the rat cremaster muscle recorded with a high-speed camera. The width of the cell-free layer manually measured was compared with that determined by the automated method utilizing the four thresholding algorithms. With our experimental system, results showed that the cell-free layer width determined by the minimum algorithm was in best accordance with the manual measurement. We concluded that the accuracy of the automated methods for determination of the cell-free layer width would depend on the image quality, in particular on the contrast between the red blood cell core and background, which might differ due to the different microscopic setup. Therefore, one may need to examine several appropriate thresholding methods when selecting the best suitable algorithm for the experimental conditions.</P>
Investigation of Burst Pressures in PWR Primary Pressure Boundary Components
Namgung, Ihn,Giang, Nguyen Hoang Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.1
In a reactor coolant system of a nuclear power plant (NPP), an overpressure protection system keeps pressure in the loop within 110% of design pressure. However if the system does not work properly, pressure in the loop could elevate hugely in a short time. It would be seriously disastrous if a weak point in the pressure boundary component bursts and releases radioactive material within the containment; and it may lead to a leak outside the containment. In this study, a gross deformation that leads to a burst of pressure boundary components was investigated. Major components in the primary pressure boundary that is structurally important were selected based on structural mechanics, then, they were used to study the burst pressure of components by finite element method (FEM) analysis and by number of closed forms of theoretical relations. The burst pressure was also used as a metric of design optimization. It revealed which component was the weakest and which component had the highest margin to bursting failure. This information is valuable in severe accident progression prediction. The burst pressures of APR-1400, AP1000 and VVER-1000 reactor coolant systems were evaluated and compared to give relative margins of safety.
Cr(OH)<sub>3</sub>(s) Oxidation Induced by Surface Catalyzed Mn(II) Oxidation
Namgung, Seonyi,Kwon, Man Jae,Qafoku, Nikolla P.,Lee, Giehyeon American Chemical Society 2014 Environmental science & technology Vol.48 No.18
<P>We examined the feasibility of Cr(OH)<SUB>3</SUB>(s) oxidation mediated by surface catalyzed Mn(II) oxidation under common groundwater pH conditions as a potential pathway of natural Cr(VI) contaminations. Dissolved Mn(II) (50 μM) was reacted with or without synthesized Cr(OH)<SUB>3</SUB>(s) (1.0 g/L) at pH 7.0–9.0 under oxic or anoxic conditions. Homogeneous Mn(II) oxidation by dissolved O<SUB>2</SUB> was not observed at pH ≤ 8.0 for 50 days. At pH 9.0, by contrast, dissolved Mn(II) was completely removed within 8 days and precipitated as hausmannite. When Cr(OH)<SUB>3</SUB>(s) was present, this solid was oxidized and released substantial amounts of Cr(VI) as dissolved Mn(II) was added into the suspension at pH ≥ 8.0 under oxic conditions. Production of Cr(VI) was attributed to Cr(OH)<SUB>3</SUB>(s) oxidation by a newly formed Mn oxide via Mn(II) oxidation catalyzed on Cr(OH)<SUB>3</SUB>(s) surface. XANES results indicated that this surface-catalyzed Mn(II) oxidation produced a mixed valence Mn(III/IV) solid phase. Our results suggest that toxic Cr(VI) can be naturally produced via Cr(OH)<SUB>3</SUB>(s) oxidation coupled with the oxidation of dissolved Mn(II). In addition, this study evokes the potential environmental hazard of sparingly soluble Cr(OH)<SUB>3</SUB>(s), which has been considered the most common and a stable remediation product of Cr(VI) contamination.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2014/esthag.2014.48.issue-18/es503018u/production/images/medium/es-2014-03018u_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es503018u'>ACS Electronic Supporting Info</A></P>
Namgung, Ho,Kim, Choongho,Kim, Yujun,Kim, Jongho,Lee, Taek Seung American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.8
<P>We report the synthesis of a fluorescent polymer containing the rhodamine 6G (Rh6G) derivative as a side chain. The rhodamine (Rh) moiety in the polymer had a ligand interaction with Al3+, which allowed the polymer to be used for detection of Al3+. The Rh moiety (in closed form) was non-fluorescent and colorless, whereas the open form of the Rh derivative showed strong fluorescence. Upon exposure to Al3+, the green-emitting polymer backbone had a spectral overlap with the absorption of the open form of Rh in the side chain, leading to an energy transfer from the polymer backbone to the Rh moiety. Upon addition of Al3+ to the polymer solution, the emission of the polymer backbone (green) has gradually decreased and, concomitantly, the red emission of Rh has increased via Forster resonance energy transfer (FRET). As the fluorescence of the polymer varied in the presence of Al3+ ions, the polymer could be used as a FRET-based sensor for detecting Al3+.</P>