• Macromolecular Research
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• 제13권1호
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• pp.62-67
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• 2005

This paper investigated the effect of biodegradation behavior on the oxidation of cellulose nanofiber mats. The cellulose mats were produced through electro spinning. The diameter of an electrospun fiber varied from 90 to 240 nm depending on the electrospinning parameters, such as the solution concentration, needle diameter, and rotation speed of a grounded collector. Oxidized cellulose (OC).mats containing different carboxyl contents were prepared using $NO_2$ as an oxidant. The total carboxyl content of the cellulose nanofiber mats obtained after oxidation for 20 h was $20.6\%$. The corresponding carboxyl content was important from a commercial point of view because OC containing $16-24\%$ carboxyl content are used widely in the medical field as a form of powder or knitted fabric. Degradation tests of the OC mats were performed at $37^{\circ}C$ in phosphate-buffered saline (pH 7.4). Microscopy techniques were introduced to study the morphological properties and the degradation behavior of the OC mats. Morphological changes of the mats were visualized using optical microscopy. Within 4 days of exposure to PBS, the weight loss of the OC mats was $>90\%$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 A
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• pp.107-109
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• 1998

This paper presents mechanical analysis of gas turbine generator (113MVA, $3{\phi}$, 2P, 0.9PF, F class, 3600rpm, 60Hz, 13.8kV, 4.72kA, Air-Cooling) field coil deformation. Rotor end coil deformation is only appeared on turbine end but collector end coil is normal. Expansion direction of end coil is tangential not axial. Deformation appears more severe at top turn. Retaining ling is expanded by centrifugal force of coil and itself. In case friction coefficient between coil top surface and retaining ring insulation inner surface is small, coil end length ${\ell}$ does not change. However, in case friction coefficient big condition, coil end is expanded ${\Delta}{\ell}$ due to start and stop. Deformation is assumed about 30mm by watching photograph inner surface of retaining ring is coated by Teflon at manufacturing condition. Usually Teflon coating insulation surface is small friction coefficient. It's value 0.08${\sim}$0.15. However it's value exceeds more than 0.297. Since top turn deformation appears. The distortion and subsequent failure have occurred because of the lack of a sufficient slip-plane between the top field coil conductors and the inside surface of the retaining ring insulation on the turbine end of the field-winding.

• Journal of Electrochemical Science and Technology
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• 제9권4호
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• pp.330-338
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• 2018

The adhesion strength as well as the electrochemical properties of $LiNi_{0.4}Mn_{0.4}Co_{0.2}O_2$ electrodes containing various conductive carbons (CC) such as fiber-like carbon, vapor-grown carbon fiber, carbon nanotubes, particle-like carbon, Super P, and Ketjen black is compared. The morphological properties is investigated using scanning electron microscope to reveal the interaction between the different CC and the active material. The surface and interfacial cutting analysis system is also used to measure the adhesion strength between the aluminum current collector and the composite film, and the adhesion strength between the active material and the CC of the electrodes. The results obtained from the measured adhesion strength points to the fact that the structure and the particle size of CC additives have tremendous influence on the binding property of the composite electrodes, and this in turn affects the electrochemical property of the configured electrodes.

• 한국환경과학회지
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• 제19권11호
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• pp.1407-1421
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• 2010

This study was carried out to elucidate the relation between water quality and structure of the aquatic ecosystem in the agriculture reservoir Otae-ji from January to December in 2009. The proportion of forest was 46.98%, which means that non-point sources are major contributor of water pollution in this area. The annual mean COD(Chemical Oxygen Demand) in Otae-ji was $3.6mgL^{-1}$, indicating, level II of environmental standards and the trophic state was mesotrophic. Although total phosporus concentration in the reservoir was high in August due to large inflow of nutrients from outside the reservoir during monsoon season, there was no break out of significant algal bloom in the summer. The seasonal succession of phytoplankton showed that the dinophyta dominated in the the spring, chlorophyta in the summer, chrysophyta and chlorophyta in the autumn and chrysophyta in the winter. In case of zooplankton, rotifers dominated in the most seasons, but cladoceran(Bosmina longirostris) dominated in June and copepod(Nauplii) in August. The macrophyte plants showed diverse species compositon consisted of 3 varieties, 24 species, 23 genera, 15 families and 14 orders. The macroinvertebrates also showed various FFG(Functional Feeding Groups) such as GC(Gathering-Collector), P(Predator), SH(Shedder), FC(Filter-Collector) and PP(Plant-Piercer). Ecosystem stability analysis using aquatic insects was classified as Group I, which has high resilience and resistance indices. A total of 14 species of fish was collected but exotic species such as Lepomis macrochirus and Micropterus salmoides were not found in Otae-ji. In conclusion, the preservation of healthy food wed in the reservoir ecosystem is closely related to water quality management as well as effective prevention of algal bloom by helping good material circulation in aquatic ecosystems.

• KSBB Journal
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• 제11권5호
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• pp.606-612
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• 1996

H형 Dowex 50W-X8 강산성 양이온 교환수지 결럼을 이용하여 glutamic acid를 치환전개하면셔 displacer의 농도를 증가시켜 인위적으로 결정화를 유도하였다. Displacer로 사용한 NaOH 놓도를 증 가시킴으로써 glutamic acid가 그 용해도 한계 이상 으로 농축되면서 컬럼내에서 이동도중 결정층이 형 성되었고 생성된 결정은 effluent stream을 따라 fraction collector로 회수되어졌다. 결정충이 이동하는 동안 clogging이나 압력강하의 문제점이 발생 하지 않았으며 1.0 M NaOH를 사용할 때 62% 의 glutamic acid가 결정으로 회수되었다. 수지로부터 치환되 어 나오는 $H^+$에 의한 OH 의 중화작용으로 인해 NaCI 보다는 NaOH가 효과적인 displacer임 을 알 수 있었으며 보다 sharp하고 농축된 band를 얻을 수 있었다 Glutamic acid 결정층의 이동속도 는 displacer 이통속도와 통일하였는데 그 이유는 결정이 이동하는 기작이 고정상의 interstitial fluid를 따라 이통하는 것이 아니라 일정한 두께의 결정층이 형성된 뒤에 앞경계변에셔는 계속 새로운 결정화가, 그리고 뒷경계변에서는 기존결정의 재용해가 일어나 면서 컬럼을 이동하는 것이며 또한 이 결정화 속도 와 재용해 속도가 비슷하게 균형을 이루고 있기 때 문이라고 설명할 수 있다. 이와 같은 이온교환중의 결정화 현상은 수지에 대한 선택도와 함께 용해도라 는 부가적 분리 인자를 통시에 사용함으로써 특정성 분의 분리효율을 높일 수 있으며 이온교환 후 추가 로 거쳐야 할 결정화 콩정의 부담을 줄일 수 있을 것이다. 결정화-재용해가 비슷한 속도로 반복되는 이통결정층이 형성된다는 관찰은 본 실험에서 사용 된 glutamic acid에만 적용할 수 있는 특이한 현상 일 수 있으며 aspartic acid 등 다른 저용해도 아미 노산에도 일반화할 수 있는 현상인지를 밝허가 위해 서는 보충 연구가 펄요하다. 더우기 이러한 결정화 현상은 단순히 용질의 용해도와 displacer 농도뿐만 아니라 pH, ionic strength, 사용하는 수지의 가교 도, mobile phase의 유속, 사용하는 컬럼의 제원에 도 영향을 받을 것이라고 사료되므로 결정회수율을 극대화하기 위한 최적조건의 도출 빛 그 적용범위의 확대에 대한 연구가 필요하다.

• Journal of Ecology and Environment
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• 제31권3호
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• pp.233-241
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• 2008

Functional feeding groups (FFGs) of benthic macroinvertebrates are guilds of invertebrate taxa that obtain food in similar ways, regardless of their taxonomic affinities. They can represent a heterogeneous assemblage of benthic fauna and may indicate disturbances of their habitats. The proportion of different groups can change in response to disturbances that affect the food base of the system, thereby offering a means of assessing disruption of ecosystem functioning. In this study, we used benthic macroinvertebrate communities collected at 650 sites of 23 different water types in the province of Overijssel, The Netherlands. Physical and chemical environmental factors were measured at each sampling site. Each taxon was assigned to its corresponding FFG based on its food resources. A multilayer perceptron (MLP) using a backpropagation algorithm, a supervised artificial neural network, was applied to evaluate the influence of environmental variables to the FFGs of benthic macroinvertebrates through a sensitivity analysis. In the evaluation of input variables, the sensitivity analysis with partial derivatives demonstrates the relative importance of influential environmental variables on the FFG, showing that different variables influence the FFG in various ways. Collector-filterers and shredders were mainly influenced by $Ca^{2+}$ and width of the streams, and scrapers were influenced mostly with $Ca^{2+}$ and depth, and predators were by depth and pH. $Ca^{2+}$ and depth displayed relatively high influence on all four FFGs, while some variables such as pH, %gravel, %silt, and %bank affected specific groups. This approach can help to characterize community structure and to ecologically assess target ecosystems.

• The Korean Journal of Ecology
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• 제19권6호
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• pp.529-541
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• 1996

During the period of December 1992 (winter-spring) and from February 1995 (winter-spring), the leaf processing rates of oak (Quercus serrata) and tulip (Liriodendron tulipifera) tree was investigated in the headwater streams in southeastern part of Korea in conjunction with the distribution pattern of macroinvertebrate fauna. Using two types of bags ($10\times30cm$ with 5 g of dry leaves; open bag with holes, closed bag without holes), decomposition rates of oak and tulip tree by shredder and/or microbiota at a reatively undisturbed 2nd-order stream were compared, Regardless of leaf type, leaves in the open bage decomposed slightly faster than those in the closed bags. In the 1992 experiment, osk leaves decomposed much slower than tulip leaves (after 138 degree days, osk : closed, 0.006% loss/day ; open, 0.008 ; tulip: closed, 0.021 ; open, 0.023; n=2). The of the first experiment using oak leaves in 1995 were similar to those of the first experiment (after 151 degree days, oak: closed, 0.005% loss / day; open, 0.006; n=6). Over 50% of invertebrates from 122 leaf pack samples collected from 12 streams during the winter period of 1994 were identified as shredders (shredder, 56.2; collector, 32.7; scraper, 8.65; predator, 2.45%). Among shredders, Gammarus sp. and Tipula sp. were dominant species in terms of number and biomass (8.2 ind./g, 1.0 ind./g AFDW of leaves). Among many physico-chemical parameters, the width of stream channel was found to be the most influential factor in the distribution of Gammarus and Tipula (Gammarus: r=-0.34, P<0.001;Tipula:r=0.40, P<0.001). Considering the fact that oak is one the dominant riparian vegetation in the southeastern part of korea, the patterns of oak processing and shredder distribution shown in theis study may well represent some of the important characteristics of headwater steams in southeastern Korea.

• 한국산업보건학회지
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• 제27권4호
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• pp.324-332
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• 2017

Objectives: Much scientific evidence indicate a positive association between moldy environments and respiratory illnesses and/or symptoms. However, few comprehensive assessments of mold have been performed for such settings. Spore counts or microscopic enumeration only may not be sufficient for evaluating fungal exposure. Recently, Mold Specific QPCR technology developed by the US EPA (Environmental Relative Moldiness Index, ERMI) has been widely used worldwide and great performance for assessing fungal exposure has been shown. Methods: We aimed to develop a Korean version of ERMI suitable for the distribution of fungal flora in Korea. Thirty dwellings in the Seoul and Incheon area were selected for sampling, and each was classified as 'Flooded, 'Water-damaged' or 'Non-water-damaged'. Results: Dust on the floor and airborne sampling were collected using an MAS100 and a 'Dustream' collector. Samples were analyzed by quantitative polymerase chain reaction(QPCR) for the 36 molds belonging to ERMI. Student t-test and ANOVA tests were carried out using SAS software. The median ERMI values of flooded, water damaged, and non-water damaged dwellings were 8.24(range: -5.6 to 27.9), 5.47(-25. 4 to 32.7), and -15.30(-24.6 to 14.8), respectively. Significant differences were observed between flooded and non-water damaged dwellings (P=0.001) and between water-damaged and non-water damaged dwellings (P=0.032). Conclusion: Our findings indicate that ERMI values attributed to dust samples in Korea could be applicable for the identification of flooded or water damaged buildings. However, much data is needed for continuously developing the Korean version of ERMI values.

• 한국수산과학회지
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• 제43권3호
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• pp.223-230
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• 2010

To compare seed collection and the growth of Anadara subcrenata in Suncheon and Boseong Bays, environmental factors and the growth of larvae and spats were investigated from August 2008 to July 2009 in commercial farming sites in both bays. The variation in water temperature in both bays was similar, but the salinity was lower in Suncheon Bay than in Boseong Bay. The chlorophyll-a content was higher in Suncheon Bay due to the large inflow of freshwater. The density and shell length of A. subcrenata larvae did not differ significantly between the two bays. However, the relative growth of shell height to shell length was significantly higher in Suncheon Bay (P<0.05). The growth of A. subcrenata spats attached to a collector was significantly faster in Suncheon Bay (P<0.05). The spats in Suncheon and Boseong Bays grew to 24.3 and 21.0 mm in shell length, respectively, within 1 year after spawning, and the shell length reached 35.6 and 34.8 mm, respectively, within 2 years of spawning. The initial spats density was higher in Boseong Bay, but the growth of spats was better in Suncheon Bay. The faster growth of A. subcrenata in Suncheon Bay can be explained by the high chlorophyll-a content in this bay. Based on the low survival (%) and slower growth rate of spats in Boseong Bay, the commercial culture density of A. subcrenata in Boseong Bay should be reduced to the optimum level of the carrying capacity.

• 자원리싸이클링
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• 제1권1호
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• pp.69-77
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• 1992

본 연구는 충주 동양 골석광산에서 사분 및 수선처리하고 버려지는 저온위의 백운암질 골석정광을 회수할 목적으로, 이 광산에서 산출되는 비교적 순수한 골석과 백운석에 대한 부선특성을 조사하고, 이를 기초로 상기 골석광미 시과에 대한 Batch 부선실험을 행하였다. 그 결과를 요약하면 다음과 같다. 1) 비교적 순수한 골석 부선시에는 여러가지 기포제 중에서 Dowfroth 250을 사용하는 것이 가장 효과적이었으며, 그 사용성은 본 실험조건에서 50mg/l(200g/t)정도이다. 2) 골석 부선시 기포제로서 Dowfroth 250을 사용하는 경과, 적당한 광액의 pH는 pH6~pH9의 범위이다. 3) 저온위의 백운암질 골석광미로 부터 골석을 부선 할 경과 본 실험의 조건 하에서 회수 가능한 골석정광의 품위는 CaO 1,.40%, 백색도 84.5 로서 이때의 실수율은 53% 정도였다.