• Journal of radiological science and technology
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• v.18 no.1
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• pp.97-110
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• 1995

This study was undertaken to investigate ultrastructural changes according to the radiosensitivity in the spermatogenic cells and Sertoli cell of the seminiferous tubules in Korean native pheasants. During spermatogenetic period, testes were collected from male adult Korean native pheasant and they were used as experimental and control birds. The experimental group was divided into a single-dose whole body irradiation group (400, 600, 800 and 1,000 rads) and a split-dose whole body irradiation groups(400/2, 600/2, 800/2 and 1,000/2 rads). The experimental birds were sacrificed at 24 and 72 hrs after irradiation and the control pheasants were sacrificed at the same time. Ultrastructural changes of Sertoli cells and spermatogonia were investigated by ultrathin section with electron microscope. The results obtained are summarized as follows; 1. The apoptosis was observed after 72 hrs group of the single-dose irradiation of 400 rads. 2. The cytoplasmic organelles of spermatogonia were severely damaged more than that of sertoli cell in 72 hours group of split-dose irradiation of 800 rads. 3. The cytoplasmic organelles of Sertoli cell were severely damaged except the nuclear membrane of Sertoli cells in 72 hrs group of split-dose irradiation of 1,000 rads.

• Journal of Power Electronics
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• v.9 no.4
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• pp.535-543
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• 2009

In this paper, pulse-width modulation (PWM) control strategy of various topologies of matrix converters is presented, which is based on direct duty ratio PWM (DDPWM). Because the DDPWM method has the characteristics of the inherent per-phase modular structure, it can be effectively applied to single-phase, two-phase and three-phase four-leg matrix converters as well as the common three-phase to three-phase matrix converter. Also, this paper treats command generation method in each matrix converter. The feasibility and validity of the proposed method are verified by experimental results.

• Food Science and Biotechnology
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• v.16 no.6
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• pp.879-883
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• 2007

This study examined whether dietary supplementation with sea tangle alters the intestinal morphology of streptozotocin-induced diabetic rats and affects the glucose absorption rate. Forty male Sprague-Dawley rats were divided into 2 groups and fed either a control (AIN76-based) diet or a sea tangle-supplemented diet. After 3 weeks, 10 rats in each group received an intramuscular injection of streptozotocin (45 mg/kg BW), and feeding was continued for 3 additional weeks. Dietary supplementation with sea tangle resulted in a lower fasting plasma glucose level compared with the control diet in diabetic rats. Scanning electron micrographs revealed serious damage to the jejunal villi of diabetic rats fed the control diet, whereas supplementation with sea tangle alleviated the damage. In a separate experiment, 20 male Sprague-Dawley rats were divided into 2 groups and fed either a control diet or a sea tangle-supplemented diet for 5 weeks, and fasted rats were subjected to in situ single-pass perfusion. The glucose absorption rate determined in the absence of digesta was decreased by 34% in the jejunum of rats fed a sea tangle diet compared with those fed a control diet. In conclusion, sea tangle supplementation lowered glucose absorption rate, altered intestinal morphology, and appeared to protect villi from damage caused by diabetes mellitus.

• Journal of the Korean Vacuum Society
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• v.12 no.2
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• pp.144-149
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• 2003

Carbon tips were grown on Si cantilevers by applying an electron beam to them directly with Scanning Electron Microscope. A carbon tip was fabricated by aligning the electron beam directly down the vertical axis of Si cantilever and then irradiating a single spot on the cantilever for a proper time in the dominant atmosphere of residual gases generated by the oil of the diffusion pump. A number of control parameters for SEM, including exposure time, acceleration voltage, emission current, and beam probe current, were allowed to make various aspect ratio feature. The growth of carbon tips was not affected by the surface morphology of substrates. We could acquired the tip whose effective length is 0.5 $\mu\textrm{m}$, bottom diameter is 90 nm and cone half angle $3.5^{\circ}$ The growth technique of the high aspect ratio carbon tips on the tip-free cantilevers is available to reduce the complexities of fabricating sub-micron scale tips on the PZT thin film actuator integrated AFM cantilevers.

• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.258-264
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• 2014

Objectives: This in vitro study aimed to investigate the ability of Candida albicans (C. albicans) and Enterococcus faecalis (E. faecalis) to penetrate dentinal tubules of instrumented and retreated root canal surface of split human teeth. Materials and Methods: Sixty intact extracted human single-rooted teeth were divided into 4 groups, negative control, positive control without canal instrumentation, instrumented, and retreated. Root canals in the instrumented group were enlarged with endodontic instruments, while root canals in the retreated group were enlarged, filled, and then removed the canal filling materials. The teeth were split longitudinally after canal preparation in 3 groups except the negative control group. The teeth were inoculated with both microorganisms separately and in combination. Teeth specimens were examined by scanning electron microscopy (SEM), and the depth of penetration into the dentinal tubules was assessed using the SMILE view software (JEOL Ltd). Results: Penetration of C. albicans and E. faecalis into the dentinal tubules was observed in all 3 groups, although penetration was partially restricted by dentin debris of tubules in the instrumented group and remnants of canal filling materials in the retreated group. In all 3 groups, E. faecalis penetrated deeper into the dentinal tubules by way of cell division than C. albicans which built colonies and penetrated by means of hyphae. Conclusions: Microorganisms can easily penetrate dentinal tubules of root canals with different appearance based on the microorganism size and status of dentinal tubules.

• Archives of Plastic Surgery
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• v.33 no.1
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• pp.31-38
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• 2006

The effect of melatonin on morphological changes after ischemia-reperfusion injury was investigated in rat skeletal muscle. Dimethyl-sulfoxide(DMSO) was also tested for comparison. Muscle injury was evaluated in 4 groups as a single laparotomy group(control), ischemia-reperfusion group, DMSO group, melatonin group. Left hind limb ischemia was induced for 4 hours by vascular clamping of the common femoral artery and followed by 24 hours of reperfusion. The midportion of gastrocnemius muscle was taken for histological evaluation. In light microscopic study, ischemia-reperfusion group showed severe neutrophil infiltration, interstitial edema, and partial loss or degeneration of muscle fibers. The muscle tissue of melatonin group showed relatively normal architecture with mild inflammatory cell infiltration. In electron microscopic study, dilated cisternae of sarcoplasmic reticulum, dilated mitochondria with electron loose matrix and dilated cristae, disordered or loss of myofilament, indistinct A-band and I-band, intracytoplasmic vacuoles, and markedly decreased glycogen granules were observed in ischemia-reperfusion group. But relatively well maintained A-band, I-band, Z-line, M-line, and mildly dilated mitochondria with well preserved cristae were observed in melatonin group. The DMSO group showed intermediately attenuated ultrastructural changes. The results show that melatonin improves morphologically ischemia-reperfusion injury more effectively than DMSO. In conclusion, melatonin seems to be a promising agent that can salvage the skeletal muscle from severe ischemia-reperfusion injury.

• Journal of Microbiology and Biotechnology
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• v.15 no.6
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• pp.1229-1239
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• 2005

Human immunodeficiency virus-like particles (HIVVLPs) with native conformations similar to that of the wild-type virion could be valid candidates for vaccine development. To this end, we used a Semliki Forest Virus (SFV) expression system to produce HIV- VLPs containing high quantities of native envelope proteins. Here, we described a single SFV replicon containing the HIV gagpol and env genes under the control of separate subgenomic promoters. Mature VLPs incorporating the Gag and Env proteins were detected in the supernatant of replicon-expressing cells by Western blot analysis. The HIV-VLPs showed the expected molecular density (1.14-1.18 g/ml) on a $20-60\%$ sucrose gradient; the particles were 100-120 nm in diameter and Env proteins were observed on their surfaces by immunogold electron microscopy. RT-PCR analysis of VLP-associated RNAs in mature HIV-VLPs revealed two SF V-derived RNA species (full-length and subgenomic). Immunization studies in Balb/c mice showed that these HIV-VLPs were capable of inducing both HIV-specific antibodies and cell-mediated immune responses. Taken together, our results indicate that the SFV replicon system is useful for the production of HIV-VLPs, which may be valuable candidates for an HIV vaccine.

• Restorative Dentistry and Endodontics
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• v.45 no.3
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• pp.36.1-36.10
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• 2020

Objectives: This study aims to assess the effect of universal adhesives pretreatment on the bond strength of resin-modified glass ionomer cement to dentin. Materials and Methods: Fifty caries-free human third molars were employed. The teeth were randomly assigned into five groups (n = 10) based on dentin surface pretreatments: Single Bond Universal (3M Oral Care), Gluma Bond Universal (Heraeus Kulzer), Prime&Bond Elect (Dentsply), Cavity Conditioner (GC) and control (no surface treatment). After Fuji II LC (GC) was bonded to the dentin surfaces, the specimens were stored for 7 days at 37℃. The specimens were segmented into microspecimens, and the microspecimens were subjugated to microtensile bond strength testing (1.0 mm/min). The modes of failure analyzed using a stereomicroscope and scanning electron microscopy. Data were statistically analyzed with one-way analysis of variance and Duncan tests (p = 0.05). Results: The surface pretreatments with the universal adhesives and conditioner increased the bond strength of Fuji II LC to dentin (p < 0.05). Single Bond Universal and Gluma Bond Universal provided higher bond strength to Fuji II LC than Cavity Conditioner (p < 0.05). The bond strengths obtained from Prime&Bond Elect and Cavity Conditioner were not statistically different (p > 0.05). Conclusions: The universal adhesives and polyacrylic acid conditioner could increase the bond strength of resin-modified glass ionomer cement (RMGIC) to dentin. The use of universal adhesives before the application of RMGIC may be more beneficial in improving bond strength.

• Transactions on Electrical and Electronic Materials
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• v.3 no.1
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• pp.30-37
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• 2002

A focusing grating coupler (FGC) was not fabricated by the 'Continuous Path Control'writing strategy but by an electron-beam lithography system of more general exposure mode, which matches not only the address grid with the grating period but also an integer multiple of the address grid resolution (5 nm). To more simplify the fabrication, we are able to reduce a process step without large decrease of pattern quality by excluding a conducting material or layer such as metal (Al, Cr, Au), which are deposited on top or bottom of an e-beam resist to prevent charge build-up during e-beam exposure. A grating pitch period and an aperture feature size of the FGC designed and fabricated by e-beam lithography and reactive ion etching were ranged over 384.3 nm to 448.2 nm, and 0.5 $\times$ 0.5 mm$^2$area, respectively. This fabrication method presented will reduce processing time and improve the grating quality by means of a consideration of the address grid resolution, grating direction, pitch size and shapes when exposing. Here our investigations concentrate on the design and efficient fabrication results of the FGC for coupling from slab waveguide to a spot in free space.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.31-32
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• 2010

In our previous reports [1-3], electron transport for the switching and memory devices using alkyl thiol-tethered Ru-terpyridine complex compounds with metal-insulator-metal crossbar structure has been presented. On the other hand, among organic memory devices, a memory based on the OFET is attractive because of its nondestructive readout and single transistor applications. Several attempts at nonvolatile organic memories involve electrets, which are chargeable dielectrics. However, these devices still do not sufficiently satisfy the criteria demanded in order to compete with other types of memory devices, and the electrets are generally limited to polymer materials. Until now, there is no report on nonvolatile organic electrets using nano-interfaced organic monomer layer as a dielectric material even though the use of organic monomer materials become important for the development of molecularly interfaced memory and logic elements. Furthermore, to increase a retention time for the nonvolatile organic memory device as well as to understand an intrinsic memory property, a molecular design of the organic materials is also getting important issue. In this presentation, we report on the OFET memory device built on a silicon wafer and based on films of pentacene and a SiO2 gate insulator that are separated by organic molecules which act as a gate dielectric. We proposed push-pull organic molecules (PPOM) containing triarylamine asan electron donating group (EDG), thiophene as a spacer, and malononitrile as an electron withdrawing group (EWG). The PPOM were designed to control charge transport by differences of the dihedral angles induced by a steric hindrance effect of side chainswithin the molecules. Therefore, we expect that these PPOM with potential energy barrier can save the charges which are transported to the nano-interface between the semiconductor and organic molecules used as the dielectrics. Finally, we also expect that the charges can be contributed to the memory capacity of the memory OFET device.[4]