• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1304-1317
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• 2020

The tubes in a heat exchanger, such as a steam generator (SG), are subjected to crossflow, and interaction between tubes and supports can happen, which can cause fretting wear of tubes. Although many experiments and models have been established, some detailed mechanisms are still not sufficiently clear. In this work, more attention is paid to obtain the regulation of impact and sliding in the complex process and many factors, such as excitation forces and clearances. The responses and contact forces were analyzed to obtain clear understanding of the influences of these factors. Room temperature tests in the air were established. The results show that the effect of clearance on the normal work rate is not monotonous and instead has two peaks. The force ratio can influence the normal work rate by changing the distribution of contact angles, which can result in higher sliding in the contact process. Fretting wear tests are conducted, and the wear surfaces are analyzed by a scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX). The results of this work can serve as a reference for impactsliding contact analysis between AVBs and tubes in steam generators.

• Journal of the Korean Chemical Society
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• v.36 no.5
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• pp.720-726
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• 1992

Multivariate analysis such as factor analysis was applied to interpret multivariate data, which were obtained from the overlapped X-ray fluorescence spectra. X-ray fluorescence spectra of 11 reference samples were obtained by the wavelength dispersive spectrometer at a specified range of angle such as $33.50∼34.50^{\circ}$. The data matrix was made from the spectra of 8 samples. The results of abstract factor analysis gave three factors. By the target testing with 8 elements contained in the reference samples, the three factors were found to be Pb, As and Cu. The concentration of these elements in the test samples was determined by target transformation factor analysis regardless overlapping individual peaks.

• Korean Membrane Journal
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• v.2 no.1
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• pp.36-47
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• 2000

This paper deals with the separation of MTBE-methanol mixtures using crosslinked Poly(vinyl alcohol)(PVA) membranes with sulfur-succinic acid(SSA) as a crosslinking agent by pervaporation and vapor permeation technique. The operating temperatures, methanol concentration in feed mixtures, and SSA concentrations in PVA membranes were varied to investigate the separation performance of PVA/SSA membranes and the optimum separation characteristics by pervaporation and vapor permeation. And also, for PVA/SSA membranes, the swelling measurements were carried out to study the transport phenomena. The swelling measurements were carried out for pure MTBE and methanol, and MTBE/methanol=90/10, 80/20 mixtures using PVA/SSA membranes with varying SSA compositions. There are two factors of the membrane network and the hydrogen bonding. In pervaporation separation was also carried out for MTBE/methanol=90/10, 80/20 mixtures at various temperatures. The sulfuric acid group in SSA took an important role in the membrane performance. The crosslinking effect might be over the hydrogen bonding effect due to the sulfuric acid group at 3 and 5% SSA membranes, and this two factors act vice versa on 7% SSA membrane. In this case, the 5% SSA membrane shows the highest separation factor of 2,095 with the flux of 12.79g/㎡$.$hr for MTBE/methanol=80/20 mixtures at 30$^{\circ}C$ which this mixtures show near the azeotopic composition. Compared to pervaporation, vapor permeation showed less flux and similar separation factor. In this case, the flux decreased significantly because of compact structure and the effect of hydrogen bonding. In vapor permeation, density or concentration of methanol in vaporous feed is lower than that of methanol in liquid feed, as a result, the hydrogen bonding portion between the solvent and the hydroxyl group in PVA is reduced in vapor permeation. In this case, the 7% SSA membranes shows the highest separation factor of 2,187 with the flux of 4.84g/㎡$.$hr for MTBE/methanol=80/20 mixtures at 30$^{\circ}C$.

• Polymer(Korea)
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• v.35 no.5
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• pp.385-389
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• 2011

In rubbing process, process factors, the properties of alignment layer and the physical properties of rubbing cloth have acted as important variables. These factors affect the orientation properties of the alignment layer by rubbed extent that is determined by rubbing density and rubbing force. In this work, we studied the effects of rubbing cloths with different pile density and rigidity on rubbing density(length) and rubbing force. As the pile density and rigidity of rubbing cloths increased, the birefringence and the surface roughness of the rubbed alignment layers became bigger, but the characteristics of rubbing-effect had differed each other. The pile density of rubbing cloths which was related with the number of pile, affected the rubbing density(length). On the other hand, the pile rigidity of rubbing was closely related to rubbing force rather than the rubbing density(length).

• Membrane Journal
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• v.30 no.1
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• pp.21-29
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• 2020

In this study, we have established the optimum design condition of pore-filled anion-exchange membrane for all-vanadium redox flow battery (VRFB). From the experimental results, it was proven that the membrane design factors that have the greatest influence on the charge-discharge performance of VRFB are the ion exchange capacity, the porosity of substrate film, and the crosslinking degree. That is, the ohmic loss and the crossover of active materials in VRFB were shown to be determined by the above factors. In addition, two methods, i.e. reducing the ion exchange capacity at low crosslinking degree and increasing the crosslinking degree at high ion exchange capacity, were investigated in the preparation of pore-filled anion-exchange membranes. As a result, it was found that optimizing the crosslinking degree at sufficiently high ion exchange capacity is more desirable to achieving high VRFB charge-discharge performances.

• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.496-502
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• 2015

Polyketide secondary metabolites share common precursor pools, acyl-CoA. Thus, the effects of engineering strategies for heterologous and native secondary metabolite production are often determined by the measurement of pikromycin in Streptomyces venezuelae. It is hard to compare the effectiveness of engineering targets among published data owing to the different pikromycin production media used from one study to the other. To determine the most important nutritional factor and establish optimal culture conditions, medium optimization of pikromycin from Streptomyces venezuelae ATCC 15439 was studied with a statistical method, Plackett-Burman design. Nine variables (glucose, sucrose, peptone, (NH₄)₂SO₄, K₂HPO₄, KH₂PO₄, NaCl, MgSO₄·7H₂O, and CaCO₃) were analyzed for their effects on a response, pikromycin. Glucose, K₂HPO₄, and CaCO₃ were determined to be the most significant factors. The path of the steepest ascent and response surface methodology about the three selected components were performed to study interactions among the three factors, and the fine-tune concentrations for maximized product yields. The significant variables and optimal concentrations were 139 g/1 sucrose, 5.29 g/l K₂HPO₄, and 0.081 g/l CaCO₃, with the maximal pikromycin yield of 35.5 mg/l. Increases of the antibiotics production by 1.45-fold, 1.3-fold, and 1.98-fold, compared with unoptimized medium and two other pikromycin production media SCM and SGGP, respectively, were achieved.

• Korean Journal of Occupational Health Nursing
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• v.15 no.2
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• pp.94-103
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• 2006

Purpose: This study was to understand foreign workers' experiences exposed hazard chemical materials in korean industry. Method: The research subjects were 92 foreign workers worked in seoul, namyangju, ansan, suwon, pocheon, incheon, jincheon, and daejeon. It was that grounded theory method as qualitative approach was applied with in-depth interview, recording and dictation, and collected data was analysed line-by-line by research teams. The analysis process of in depth interview data was three phase. Results: The first phase was that find out meaningful data and confronted data for meaningful data was 53 meaningful items. The second phase was coding process of meaningful data, total coding items were 9, difficulty of new environment, existence of health hazard factors originated in work, performance of basic health management, management of hazard materials in work-site, self care of hazard materials in work-site, discrimination of disaster-compensation originated in work, perception of work stress, motivation of leaving position, satisfaction for present life. The third phase was 5 adaptation process, copying phase for new environment, management phase for health hazard factors, health change phase, life change phase, illegal stay phase. Conclusion: In summary, as a results it was concluded that foreign workers was experienced new environment and then has various problems in working site. But these evidences were not different from korean workers basically, undoubtedly reality of a korean small and medium enterprise. And foreign workers with long time stay have had many health problems probably, but they have want to long stay and so reach an unexpected result, illegal long stay. Therefore, we should make efforts for adequate foreign workers' health management at work-site and overall life in governmental and industrial nursing level.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.2
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• pp.73-80
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• 2015

Arsenic which is found in several different chemical forms and oxidation states and causes acute and chronic adverse health effects is a toxic trace element widely distributed in soils and aquifers from both geologic and anthropogenic sources. Arsenic which has a mysterious ability to change color, behavior, reactivity, and toxicity has diverse chemical behavior in the natural environment. Arsenic which has stronger ability to readily change oxidation state than nitrogen and phosphorus due to a consequence of the electronic configuration of its valence orbitals with partially filled states capable of both electron donation and acceptance although the electronegativity of arsenic is greater than that of nitrogen and similar to that of phosphorus. Arsenate (V) is the thermodynamically stable form of As under aerobic condition and interacts strongly with solid matrix. However, it has been known that adsorption and oxidation reactions of arsenite (III) which is more soluble and mobile than As(V) in soils are two important factors affecting the fate and transport of arsenic in the environment. That is, the movement of As in soils and aquifers is highly dependent on the adsorption-desorption reactions in the solid phase. This article, however, focuses primarily on understanding the fate and speciation of As in soils and what fate arsenic will have after it is incorporated into soils.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.5-12
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• 2015

The construction of waste landfill sites has been increased due to recent expansion of various waste. Geotextiles are widely used for the purpose of reinforcement and protection of waste inside the landfill. Geotextile affects the shear behavior of waste landfill which forms the contact surface with soil. In this study, the effect of acidic and alkaline components in leachate has been analyzed through the laboratory experiment on the shear stress reduction of the contact surface of ground-geotextile under the cyclic load. For this purpose, a dynamic contact surface shear tester has been manufactured, and cyclic simple shear tests have been performed using geotextile and soil specimen which were immersed in chemical solutions for 60 and 840 days, respectively. Based on the Disturbed State Concept, the characteristics of shear stress on the contact surface of ground-geotextile due to chemical factors have been identified by the disturbance function.

• Journal of Preventive Medicine and Public Health
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• v.55 no.4
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• pp.321-333
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• 2022

Objectives: Extensive evidence links low vitamin D status and comorbidities with coronavirus disease 2019 (COVID-19) outcomes, but the results of published studies are contradictory. Therefore, we investigated the association of lower levels of vitamin D and comorbidities with the risk of COVID-19 infection. Methods: We searched MEDLINE (via PubMed), Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov for articles published until August 20, 2021. Sixteen eligible studies were identified (386 631 patients, of whom 181 114 were male). We included observational cohort and case-control studies that evaluated serum levels of vitamin D in COVID-19-positive and COVID-19-negative patients. Mean differences (MDs) with 95% confidence intervals (CIs) were calculated. Results: Significantly lower vitamin D levels were found in COVID-19-positive patients (MD, -1.70; 95% CI, -2.74 to -0.66; p=0.001), but with variation by study design (case-control: -4.04; 95% CI, -5.98 to -2.10; p<0.001; cohort: -0.39; 95% CI, -1.62 to 0.84; p=0.538). This relationship was more prominent in female patients (MD, -2.18; 95% CI, -4.08 to -0.28; p=0.024) than in male patients (MD, -1.74; 95% CI, -3.79 to 0.31; p=0.096). Male patients showed higher odds of having low vitamin D levels (odds ratio [OR], 2.09; 95% CI, 1.38 to 3.17; p<0.001) than female patients (OR, 1.17; 95% CI, 0.74 to 1.86; p=0.477). Comorbidities showed inconsistent, but generally nonsignificant, associations with COVID-19 infection. Conclusions: Low serum vitamin-D levels were significantly associated with the risk of COVID-19 infection. This relationship was stronger in female than in male COVID-19 patients. Limited evidence was found for the relationships between comorbidities and COVID-19 infection, warranting large population-based studies to clarify these associations.