• Microbiology and Biotechnology Letters
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• v.51 no.3
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• pp.257-267
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• 2023

The potential polyhydroxyalkanoates (PHA)-producing bacteria, Bacillus megaterium PP-10, was successfully isolated and studied its feasibility for utilization of pineapple peel waste (PPW) as a cheap carbon substrate. The PPW was pretreated with 1% (v/v) H₂SO₄ under steam sterilization and about 26.4 g/l of total reducing sugar (TRS) in pineapple peel hydrolysate (PPH) was generated and main fermentable sugars were glucose and fructose. A maximum cell growth and PHA concentration of 3.63 ± 0.07 g/l and 1.98 ± 0.09 g/l (about 54.58 ± 2.39%DCW) were received in only 12 h when grown in PPH. Interestingly, PHA productivity and biomass yield (Y_x/s) in PPH was about 4 times and 1.5 times higher than in glucose. To achieve the highest DCW and PHA production, the optimal culture conditions e.g. carbon to nitrogen ratios of 40 mole/mole, incubation temperature at 35℃ and shaking speed of 200 rpm were performed and a maximum DCW up to 4.24 ± 0.04 g/l and PHA concentration of 2.68 ± 0.02 g/l (61% DCW) were obtained. The produced PHA was further examined its monomer composition and found to contain only 3-hydroxybutyrate (3HB). This finding corresponded with the presence of class IV PHA synthase gene. Finally, certain thermal properties of the produced PHA i.e. the melting temperature (T_m) and the glass transition temperature (T_g) were about 176℃ and -4℃, respectively whereas the M_w was about 1.07 KDa ; therefore, the newly isolated B. megaterium PP-10 is a promising bacterial candidate for the efficient conversion of low-cost PPH to PHA.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.619-629
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• 2024

To improve the utilization rate of phosphate tailings (PTs) and widen the sources of subgrade filler, the PTs is employed to modify clay, forming a PTs modified clay, applied in the subgrade. Accordingly, the environmental friendliness of PTs was investigated. Subsequently, an optimal proportion was determined through compaction and California Bearing Ratio (CBR) experiments. Afterward, the stability of mixture with the optimal proportion was further evaluated through the water stability and dry-wet stability experiments. Finally, via the gradation and microstructure experiments, the strength mechanism of PTs modified clay was analyzed. The results show that the PTs were classified in the non-hazardous solid wastes, belonging to Class A building materials. With the increase of PTs content and the decrease of clay content, the optimum water content and the swelling degree gradually decrease, while the maximum dry density and CBR first increase and then decrease, reaching their peak value at 50% PTs content, which is the optimal proportion. The resilient modulus of PTs modified clay at the optimal proportion reaches 110.2 MPa. The water stability coefficient becomes stable after soaking for 4 days, while the dry-wet stability coefficient decreases with the increase of cycles and tends to be stable after 8 cycles. Under the long-term action, the dry-wet change has a greater adverse impact than continuous soaking. The analysis demonstrates that the better strength mainly comes from the skeleton role of PTs and the cementation of clay. The systematic laboratory test results and economic analysis collectively provide data evidence for the advantages of PTs modified clay as a subgrade filler.

• Journal of Science Education
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• v.38 no.2
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• pp.302-316
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• 2014

The purpose of this study is to devise a Small-Scale Chemistry (SSC) lab program for primary school learners and to examine its effects on science learning achievement. In addition, it will be examined whether the type of learning groups affects the achievement or not. The participants in the current study were 173 6th graders from 6 classes of Y elementary school in Changwon city, Gyeongnam. Three classes(86) were assigned to the experimental group and the other three, the comparative group after checking the pre-homogeneity between the two groups through t-test on the scores of the science mid-term exam. We conducted five experimental sessions on the Acid and Base in the science textbook for the sixth graders. The students of one experimental class worked in pairs and another class worked individually, but the students of the comparative classes were divided into groups of six(one group with pair, another group with individual work in the SSC program, and the other group conducting the traditional experiment with groups of six students). The data were analyzed by t-test and ANOVA. The results showed that experimental learning using individual work in the SSC program compared to traditional experimental learning was effective in improving science learning achievement. also it was indicated that the teachers could reduce their burden of preparing for classes and of school hours when they utilized the SSC laboratory learning program. Teachers could also actively support students' experimental activities in employing the program. Based on the results, we suggest that the development of the SSC laboratory learning program is meaningful in the sense that this program can help elementary schoolers to improve science learning achievements more than the existing traditional experimental methods.

• Journal of Korean Society of Forest Science
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• v.108 no.1
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• pp.40-49
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• 2019

Coarse woody debris (CWD), which is a component of the forest ecosystem, plays a major role in forest energy flow and nutrient cycling. In particular, CWD isolates carbon for a long time and is important in terms of slowing the rate of carbon released from the forest to the atmosphere. Therefore, this study measured the physiochemical characteristics and respiration rate ($R_{CWD}$) of CWD for Larix kaempferi and Pinus rigida in temperate forests in central Korea. In summer 2018, CWD samples from decay class (DC) I to IV were collected in the 14 forest stands. $R_{CWD}$ and physiochemical characteristics were measured using a closed chamber with a portable carbon dioxide sensor in the laboratory. In both species, as CWD decomposition progressed, the density ($D_{CWD}$) of the CWD decreased while the water content ($WC_{CWD}$) increased. Furthermore, the carbon concentrations did not significantly differ by DC, whereas the nitrogen concentration significantly increased and the C/N ratio decreased. The respiration rate of L. kaempferi CWD increased significantly up to DC IV, but for P. rigida it increased to DC II and then unchanged for DC II-IV. Accordingly, except for carbon concentration, all the measured characteristics showed a significant correlation with $R_{CWD}$. Multiple linear regression showed that $WC_{CWD}$ was the most influential factor on $R_{CWD}$. $WC_{CWD}$ affects $R_{CWD}$ by increasing microbial activity and is closely related to complex environmental factors such as temperature and light conditions. Therefore, it is necessary to study their correlation and estimate the time-series pattern of CWD moisture.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.E
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• pp.1-17
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• 2000

In this study, the concentrations of particulate organic constituents of environmental tobacco smoke(ETS) were determined using an environmental smog chamber, where ETS is the sole source of target compounds. ETS was generated in a 30 ㎥ environmental chamber by a number of different cigarettes, including the Kentucky 1R4F reference cigarette and eight commercial brands. A total of 12 experimental runs was conducted, and target analytes included a group of ETS markers both in vapor and particulate phase and a class of polycylic aromatic hydrocarbos(PAHs) associated with ETS particles. The mass concentrations of PAH in ETS particles were also determined. The average contents of benzo(a) pyrene and benzo(a) anthracene in ETS particles for the commercial brands were 12.8 and 21.5$\mu\textrm{g}$/g, respectively, There values are all somewhat higher than those determined previously by other studies. Results form the chamber study are further used to estimate the average and variability of cigarette yields for target compounds associated with ETS. Finally, ratios of RSP to the surrogate standards of UVPM, FPM and solanesol were calculated for each sample. The average conversion factors factors for the eight commercial brands were 7.3, 38, and 41 for UVPM, EPM, and solanesol, respectively. The UVPM and FPM factors are in good agreement with the recently published values. Whereas there might be a substantial difference in the solanesol content among cigarettes produced in different countries, the variability is somewhat greater than those of UVPM and FPM, Unfortunately, comparison of the PAH yield data from this study with literature values was complicated by a lack of consistency in cigarette smoke generating methodology. Validation of the PAH yields was also difficult due to a lack of information on the ETS related PAH in the literature. From and engineering viewpoint , however, these data on the cigarette yields of ETS components may still provide useful information to studies on the mathematical modeling of indoor air quality management regarding tobacco smoke as a source of interest, or to studies on the assessment of human exposure to ETS.

• Clinical and Experimental Pediatrics
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• v.50 no.1
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• pp.74-78
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• 2007

Purpose : Systemic lupus erythematosus (SLE) is a chronic multisystemic autoimmune disease with complex clinical manifestations. It probably involves genetic, environmental and immunologic factors. In this study, we investigated the clinical manifestations, laboratory findings and prognosis of pediatric SLE to aid clinical care of pediatric SLE. Methods : The data of 45 patients who were diagnosed as pediatric SLE in Severance Children's Hospital from Jan. 1996 to Dec. 2005 were analysed retrospectively. Results : The mean age at diagnosis was 10.8 (0-15) years old. And the ratio of male to female patients was 1:4. The initial manifestations were facial edema (51.1 percent), malar rash (44.4 percent), and fever (28.9 percent). The ANA (97.8 percent), anti-ds DNA antibody (82.2 percent), lupus nephritis (71.1 percent), malar rash (71.1 percent), and cytopenia (66.7 percent) were the most common findings among the classification criteria by ACR (American College of Rhematology, 1997). Conclusion : Clinical manifestations and prognosis are various in pediatric SLE. Intensive studies of SLE in children should be continued for more effective treatment.

• Korean Journal of Ecology and Environment
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• v.36 no.4 s.105
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• pp.403-412
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• 2003

Temporal and spatial variations of size-structured phytoplankton (chlorophyll a) were investigated over an annual cycle (February-October, 2003) to elucidate phytoplankton dynamics in the Juam Reservoir, Chonnam. Physical properties were also measured to investigate the relationship between the properties and temporal and spatial variations of size structured phytoplankton using simple linear regression. Phytoplankton (chlorophyll a) were grouped into three size classes: micro-size(> 20 ${\mu}m$), nano-size (3-20 ${\mu}m$) and pico-size (< 3 ${\mu}m$) in this study. Physical properties included water temperature, light attenuation coefficients, PAR (photosynthetically active radiation) and turbidity. Maximum chlorophyll a was observed in April, 2003 in the lower region whereas a peak of chlorophyll a developed in October, 2003 in the upper region. Large cell-sized phytoplankton (micro-size class)were dominant in the events of the chlorophyll a peaks. Potential mechanisms in the physical properties affecting the size-structured phytoplankton dynamics in the Juam Reservoir were discussed.

• Journal of Digital Convergence
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• v.12 no.8
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• pp.1-18
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• 2014

Recently, many of the mobile network operators or telcos are introducing the LTE service in order to effectively cope with an explosive increasing mobile traffics due to an expansion of the use of smart phones. The 1.8GHz, 2.6GHz, and 800MHz band classes are most widely used for LTE. In particular, the 1.8GHz band class is the most useful one in terms of the reusability of the existing (2G) network, global harmonization, bandwidth, eco-system of equipments and devices, and so on. In recent years, major countries in the world have allocated the 1.8GHz band spectrum in a wide bandwidth unit suitable for the upcoming LTE-Advanced service. This paper surveyed the 1.8GHz band spectrum allocation policies of the 12 OECD countries, including Republic of Korea. From the survey, we have found that they rebuilt or refarmed the existing holders' bands, recovered the public (i.e., military)-use bands, and allocated the bands in a wide bandwidth and in an equal or similar size.

• Journal of Internet Computing and Services
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• v.16 no.4
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• pp.61-70
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• 2015

This paper presents a web-based Java applet for understanding the concepts in digital logic circuits and student satisfaction survey was carried out in order to show its educational validity. Through our educational Java applet, the learners will be capable of learning the concepts and principles related to digital logic circuit experiments and how to operate virtual experimental equipments and virtual bread board. The proposed educational Java applet is composed of five important components: Principle Classroom to explain the concepts and principles for digital logic circuit operations, Simulation Classroom to provide a web-based simulator to the learners, Virtual Experiment Classroom to provide interactive Java applet about the syllabus of off-line laboratory class, Assessment Classroom, and Management System. With the aid of the Management System every classroom is organically tied together collaborating to achieve maximum learning efficiency. Finally, we have obtained several affirmative effects such as high learning standard, reducing the total experimental hours and the damage rate for experimental equipments.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.120-127
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• 1998

This study was performed to produce basic data for developing prediction techniques of desalinization through analyzing soil properties of reclaimed tidal lands, using soil samples collected in 11 units of tidal land reclamation projects. The average apparent specific gravity (bulk density), real specific gravity (particle density), porosity, and saturation percentage were measured to be 1.33, 2.64, 49.6%, and 56.3%, respectively. It was estimated that the soil texture class of reclaimed tidal lands would be silt or silt loam. The electrical conductivity and exchangeable sodium percentage were estimated to be $20{\sim}40dS\;m^{-1}$ and 30~50% in the beginning of tidal land reclamation, and the value of pH was measured to be 6.5~7.9. In conclusion, the soil properties of reclaimed tidal lands could be descrived to be saline-sodic soils with the high electrical conductivity and exchangeable sodium percentage.