• Journal of Power Electronics
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• v.19 no.1
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• pp.288-295
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• 2019

Rectifiers are widely used in industrial applications. Although detailed models of rectifiers are usually used to evaluate their performance, they are complex and time-consuming. Therefore, the Average Value Model (AVM) has been introduced to meet the demand for a simple and accurate model. This type of rectifier modeling can be used to simplify the simulations of large systems. The AVM of diode rectifiers has been an area of interest for many electrical engineers. However, healthy diode rectifiers are only considered for average value modeling. By contrast, faults occur frequently on diodes, which eventually cause the diodes to open-circuit. Therefore, it is essential to model bridge rectifiers under this faulty condition. Indeed, conventional AVMs are not appropriate or accurate for faulty rectifiers. In addition, they are significantly different in modeling. In this paper, a novel application of the parametric average value of a three-phase line-commutated rectifier is proposed in which one diode of the rectifier is considered open-circuited. In order to evaluate the proposed AVM, it is compared with experimental and simulation results for the application of a brushless synchronous generator field. The results clearly demonstrate the accuracy of the proposed model.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.75-84
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• 2023

In this study, we conducted analysis of bubble dynamics and flow of liquid phase change material(PCM) using shadowgraphy and particle image velocimetry(PIV). Characteristics of internal flow varied depending on locations of injection when solid PCM was liquefied from heated vertical wall. When bubbles rose immediately, they exhibited elliptical shape and zigzag trajectory. In contrast, when bubbles rose after merging at the bottom of solid PCM, with equivalent diameter for the inter-wall distance of 0.64 or greater, they showed a jellyfish shape and strong rocking behavior. It was observed by the PIV that the small ellipse bubbles made most strong flow inside the liquid PCM. Furthermore, the flow velocity was highest in the case of front injection, as the directions of temperature gradients and bubble-driven flow were aligned. The results underscore the significant influence of injection location on various characteristics, including bubble size, shape, rising path of bubbles, and internal flow.

• Journal of radiological science and technology
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• v.38 no.1
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• pp.39-49
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• 2015

One of properties which X-ray and Neutron can be applied nondestructive test is penetration into the object with interaction leads to decrease in intensity. X-ray interaction with the matter caused by electrons, Neutron caused by atoms. They share applications in nondestructive test area because of their similarities of interaction mechanism. Grating interferometer is the one of applications produces phase contrast image and dark field image. It is defined by Talbot interferometer and Talbot-Lau interferometer according to Talbot effect and Talbot-Lau effect respectively. Talbot interferometer works with coherence beam like X-ray, and Talbot-Lau has an effect with incoherence beam like Neutron. It is important to expect the interference in grating interferometer compared normal nondestructive system. In this paper, simulation works are conducted according to Talbot and Talbot-Lau interferometer in case of X-ray and Neutron. Variation of interference intensity with X-ray and Neutron based on wave theory is constructed and calculate elements consist the system. Additionally, Talbot and Talbot-Lau interferometer is simulated in different kinds of conditions.

• Korean Journal of Agricultural Science
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• v.39 no.3
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• pp.387-393
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• 2012

In the present study, ${\beta}$-glucanase-assisted extraction of starch from glutinous barley(Hinchal ssalbory) was investigated. ${\beta}$-glucanase was added to a coarse starch suspension obtained after wet milling in the starch extraction process. It was found that in the isolated starch with enzyme treatment, protein content was lower by 0.03%, compared to that with non-enzyme treatment. More importantly it was observed that the extraction yield of starch from enzyme treatment was found to be about 12% higher than the one from non-enzyme treatment (enzyme treated: 90.56%, non-enzyme treated: 78.46%). In order to elucidate this finding, the mass-balance determination of starch in each extraction step was carried out and found that the enzyme treatment might influence on the insoluble residues(R3 and R4 fractions) to hydrolyze ${\beta}$-glucan and other materials (e.g., mucilages etc.), thereby facilitated the separation of starch from it and a next filtration process. With a phase-contrast microscope it was observed that the isolated starch with enzyme treatment contained small starch granules more than the one with non-enzyme treatment and this might result in higher extraction yield observed with the former. In order to confirm this hypothesis, further experiments would be necessary.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.21 no.3
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• pp.231-239
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• 1999

In oral and maxillofacial surgery, there are many cases requiring the graft of epidermal tissues such as maxillectomy, and vestibuloplasty. There have been so many challenges for the culture of the epidermal tissue. Observing the ultrastructure of the cultured human oral kertinocytes, we could compare this findings with that of in vivo ones. With that, we could find the differencies and similarities between cultured cells and in vivo ones, and evaluate the clinical applications of cultured tissue. Human gingiva was obtained and the specimen was explanted on 24-well plate. Two types of culture media were used in this culture system. One was for the growth of the keratinocytes (Media I), and the other was for the stratification (Media II). Media I had special ingredients for the epidermal growth. Those were 0.5% dimethyl sulfoxide (DMSO), 30ng/ml of epidermal growth factor (EGF), 30ng/ml of cholera toxin, and $5{\mu}g/ml$ of transferrin. We cultured the oral keratinocytes for 3 weeks, and at that time the cultured keratinocytes were processed to prepare the specimen for the TEM study. The results were as follows.; 1. In the phase contrast micrograph, epidermal outgrowth firstly appeared on the 3rd day after explantation, and the growing keratinocytes were activley mitotic, and had polygonal shape and increased N/C ratio. 2. In the phase contrast micrograph, the outer most cells exhibited areas where broad cytoplasmic processes extended out onto the culture subtratum(fan-like appaearance). 3. In the TEM micrographs, the cultured keratinocytes showed stratification. The cells were in elongated form, and there were no morphologic differencies among the layers usually found in the in vivo gingiva. 4. Most of cellular organelles underwent lysis, and keratohyaline granules were seen. Tonofibrils were dispersed in the cytoplasm. 5. The cells were interconnected by desmosomes, and their frequency of distribution was considered to be lower than that of in vivo keratinocytes. 6. We could conclude the cultured oral keratinocytes exhibited signs of terminal differentiation.

• Atmosphere
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• v.24 no.3
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• pp.403-417
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• 2014

Future changes in seasonal mean temperature and precipitation over East Asia under anthropogenic global warming are investigated by comparing the historical run for 1979~2005 and the Representative Concentration Pathway (RCP) 4.5 run for 2006~2100 with 20 coupled models which participated in the phase five of Coupled Model Inter-comparison Project (CMIP5). Although an increase in future temperature over the East Asian monsoon region has been commonly accepted, the prediction of future precipitation under global warming still has considerable uncertainties with a large inter-model spread. Thus, we select best five models, based on the evaluation of models' performance in present climate for boreal summer and winter seasons, to reduce uncertainties in future projection. Overall, the CMIP5 models better simulate climatological temperature and precipitation over East Asia than the phase 3 of CMIP and the five best models' multi-model ensemble (B5MME) has better performance than all 20 models' multi-model ensemble (MME). Under anthropogenic global warming, significant increases are expected in both temperature and land-ocean thermal contrast over the entire East Asia region during both seasons for near and long term future. The contrast of future precipitation in winter between land and ocean will decrease over East Asia whereas that in summer particularly over the Korean Peninsula, associated with the Changma, will increase. Taking into account model validation and uncertainty estimation, this study has made an effort on providing a more reliable range of future change for temperature and precipitation particularly over the Korean Peninsula than previous studies.

• Journal of Microbiology and Biotechnology
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• v.19 no.8
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• pp.749-759
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• 2009

A survey of Bacillus thuringiensis (Berliner) strains isolated from Spanish citrus orchards has been performed, and the strains were tested for insecticidal activity against the Mediterranean fruit fly Ceratitis capitata (Wiedemann), a key citrus pest in Spain. From a total of 150 environmental samples, 376 isolates were selected, recording a total B. thuringiensis index of 0.52. The collection was characterized by means of phase-contrast microscopy, SDS-PAGE, and PCR analysis with primer pairs detecting toxin genes cry1, cry2, cry3, cry4, cry5, cry7, cry8, cry9, cry10, cry11, cry12, cry14, cry17, cry19, cry21, cry27, cry39, cry44, cyt1, and cyt2. Diverse crystal inclusion morphologies were identified: bipyramidal (45%), round (40%), adhered to the spore (7%), small (5%), and irregular (3%). SDS-PAGE of spore-crystal preparations revealed 39 different electrophoresis patterns. All primer pairs used in PCR tests gave positive amplifications in strains of our collection, except for primers for detection of cry3, cry19, cry39, or cry44 genes. Strains containing cry1, cry2, cry4, and cry27 genes were the most abundant (48.7%, 46%, 11.2%, and 8.2% of the strains, respectively). Ten different genetic profiles were found, although a total of 109 strains did not amplify with the set of primers used. Screening for toxicity against C. capitata adults was performed using both spore-crystal and soluble fractions. Mortality levels were less than 30%. We have developed a large and diverse B. thuringiensis strain collection with huge potential to control several agricultural pests; however, further research is needed to find out Bt strains active against C. capitata.

• Tribology and Lubricants
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• v.30 no.4
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• pp.218-223
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• 2014

This paper presents a method of controlling the stiffness of a tungsten probe for an atomic force microscope (AFM) in order to provide high-quality phase contrast images in accordance with sample characteristics. While inducing sufficient deformation on sample surfaces with commercial Si or $Si_3N_4$ probes is difficult because of their low stiffness, a tungsten probe fabricated by electrochemical etching with appropriately high stiffness can generate relatively large elastic deformation without damaging sample surfaces. The fabrication of the tungsten probe involves two separate procedures. The first procedure involves immersing a tungsten wire with both ends bent parallel to the surface of an electrolyte and controlling the stiffness of the tungsten cantilever by decreasing its diameter using electrochemical etching in the direction of the central axis. The second procedure involves immersing the end of the etched tungsten cantilever in the direction perpendicular to the surface of the electrolyte and fabricating a tungsten tip with a tip radius of 20-50 nm via the necking phenomenon. The latter etching process applies pulse waves every 0.25 seconds to the manufactured tip to improve its yield. Finite element analysis (FEA) of the stiffness of the tungsten probe as a function of its diameter showed that the stiffness of the tungsten probes greatly varies from 56 N/m to 3501 N/m according to the cantilever diameters from $30{\mu}m$ to $100{\mu}m$, respectively. Thus, the proposed etching method is effective for producing a tungsten probe having specific stiffness for optimal use with an AFM and certain samples.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.1 no.2
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• pp.144-153
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• 1991

This study was conducted to evaluate worker exposure to airborne asbestos fibers by industry, and to evaluate polarized-light microscopy for determining airborne asbestos fibers. A total of 11 plants including asbestos textile, brake-lining manufacturing, slate manufacturing, and automobile maintenance shops were investigated. Rsults of the study are summarized as follows. 1. Worker exposure levels to airborne asbestos fibers were the highest in asbestos textile industry, followed by brake-lining manufacturing, slate manufacturing, and automobile maintenance shops, in order. In asbestos textile industry, large variation of asbestos levels was found by plants. The worst plant indicated airborne fiber concentrations in excess of 10 fibers/cc, however, the best plant showed concentrations within 0.50 fibers/cc. 2. Characterization of airborne fibers by industry indicated that fibers from asbestos textile industry were the longest with the largest aspect ratio. Fibers from automobile maintenance shops were the shortest with the smallest aspect ratio. Based on characteristics of fibers and the highest levels of concentrations, it is concluded that workers in the asbestos textile industry are exposed to the highest risk of producing asbestosis, lung cancer, and mesothelioma. 3. Result s obtained using polarized-light microscopy were $43.7{\pm}12.3%$ of the results obtained using phase contrast microscopy. This may be resulted from the worse resolution of polarized-light microscopy than that of phase contrast microscopy. Based on the results, it is recommended that polarized-light microscopy be used for mainly bulk sample analyses and further study be performed to improve the method for determining airborne samples. However, polarized-light microscopy can be used for determining thick fibers.

• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.568-573
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• 2016

We explore the crystalline structure and phase transition of lithium thiophosphate ($Li_7P_3S_{11}$) solid electrolyte using electron microscopy and X-ray diffraction. The glass-like $Li_7P_3S_{11}$ powder is prepared by the high-energy mechanical milling process. According to the energy dispersive X-ray spectroscopy (EDS) and selected area diffraction (SAD) analysis, the glass powder shows chemical homogeneity without noticeable contrast variation at any specific spot in the specimen and amorphous SAD ring patterns. Upon heating up to $260^{\circ}C$ the glass $Li_7P_3S_{11}$ powder becomes crystallized, clearly representing crystal plane diffraction contrast in the high-resolution transmission electron microscopy image. We further confirm that each diffraction spot precisely corresponds to the diffraction from a particular $Li_7P_3S_{11}$ crystallographic structure, which is also in good agreement with the previous X-ray diffraction results. We expect that the microscopic analysis with EDS and SAD patterns would permit a new approach to study in the atomic scale of other lithium ion conducting sulfides.