• The Korean Journal of Zoology
• /
• v.15 no.3
• /
• pp.133-147
• /
• 1972

Ultrastructures of spermiogeneis in other invertebrates were investigated by several workes (Anderson, et al., 1967; Bloch, et al., 1964; Christen, 1961; Gatenby, et al., 1959; Paik, et al., 1968; Silveira, 1964; Yasuzumi, 1957) but spermiogenesis of dragonfly has not been reported previously. Testes and vass deferentia of the Korean dragonfly, Crocothemis servilia, were used for electron microscopic study of spermiogenesis. Materials were prefixed for 1-2 hours at $3^{\circ}C$ in 1.25% glutaraldehyde buffered to pH 7.2 with 0.2M sodium cacodylate buffer. Fixed tissue was washed twice in 0.2M cacodylate buffer and was subsequently postfixed for 2 hours at $3^{\circ}C$ in 1% osmium tetroxide buffered to pH 7.2 with 0.4M sodium cacodylate buffer solution. Specimens were dehydrated in graded ethyl alcohol, and finally embedded in epoxy Epon resin. Thin sections prepared from all the blocks were doubly stained; first in uranyl acetate and then in lead citrate. All thin sectios were examined with a Hitachi HS-7S electron microscope. The results of this study were summarized as follows. 1. Along the condensation of chromatin in nucleus, the shpae of nucleus was changed from spherical shpae to ellipse and cone cell type. 2. During the elongation of nucleus and the migration of cytoplasm, the nucleus removed to the one side of spermatid and began to invaginate from the posterior portion of nucleus. 3. There are ring centrioles in invaginated portion and axial filaments derived from centriole extend to the tail through the tailward half of spermatid. 4. In the cross sections the axial filament consisted of a central sheath, a central fibril, and 9 peripheral doublets.

• Conservation Science in Museum
• /
• v.1
• /
• pp.37-42
• /
• 1999

Conservation treatment was done for the pottery-stand of Kaya period which was to be exhibited in celebration of the opening of Kimhae National Museum and for the jar of Chinese celadon which was to be exhibited in Korea National Museum's special exhibition "Formation of Ancient States". Through the examinations by naked eyes and under the microscope, condition before treatment, patterns and manufacturing techniques of the objects were observed. According to these examinations, conservation treatments, suitable for each object was finished. As the pottery-stand was damaged severely, the epoxy resin was pasted directly on the broken surface of the pottery to restore the original shape and pattern, color and feeling similar to original state were given to the restored area. Although same restoration material was applied on the celadon, it was not pasted directly on the broken surface of the celadon so that the restored area could be dismantled, and color and feeling were also treated somewhat differently.

• Advances in nano research
• /
• v.15 no.1
• /
• pp.49-57
• /
• 2023

As composite materials are used in many applications, the modern world looks forward to significant progress. An overview of the application of composite fiber materials in sports equipment is provided in this article, focusing primarily on the advantages of these materials when applied to sports equipment, as well as an Analysis of the influence of sports equipment of fiber-reinforced composite material on social sports development. The present study investigated surface morphology and physical and mechanical properties of S-glass fiber epoxy composites containing Al₂O₃ nanofillers (for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%). A mechanical stirrer and ultrasonication combined the Al₂O₃ nanofiller with the matrix in varying amounts. A compression molding method was used to produce sheet composites. A first physical observation is well done, which confirms that nanoparticles are deposited on the fiber, and adhesive bonds are formed. Al₂O₃ nanofiller crystalline structure was investigated by X-ray diffraction, and its surface morphology was examined by scanning electron microscope (SEM). In the experimental test, nanofiller content was added at a rate of 1, 2, and 3% by weight, which caused a gradual decrease in void fraction by 2.851, 2.533, and 1.724%, respectively, an increase from 2.7%. The atomic bonding mechanism shows molecular bonding between nanoparticles and fibers. At temperatures between 60 ℃ and 380 ℃, Thermogravimetric Analysis (TGA) analysis shows that NPs deposition improves the thermal properties of the fibers and causes negligible weight reduction (percentage). Thermal stability of the composites was therefore presented up to 380 ℃. The Fourier Transform Infrared Spectrometer (FTIR) spectrum confirms that nanoparticles have been deposited successfully on the fiber.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.3A
• /
• pp.349-356
• /
• 2008

Recently FRP (Fiber Reinforcement Polymer) is widely used for the strengthening of damaged RC beams. Although many tests were carried out to verify flexural capacity of RC beams strengthened with FRP sheet or plate, the behavior of strengthened RC beams has not yet clearly verified. To investigate the strengthening efficiency of the Near Surface Mounted Reinforcement (NSMR) technique experimentally and analytically, a total of 7 specimens have been tested. The experimental results revealed that specimens strengthened with NSMR improved the flexural capacity of RC beams. Also, while the NSMR specimens utilized CFRP reinforcement efficiently compared to the EBR (Externally Bonded Reinforcement) specimen, the NSMR specimens still have debonding failure between epoxy and concrete interface. This study has proposed the model to predict failure modes and failure loads. Good agreement was obtained between the predicted and the experimental results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2022.10a
• /
• pp.570-573
• /
• 2022

This paper presents the identification of void diameters for a cast-resin transformer using an artificial neural network (ANN) model. A PD signal was measured by the Rogowski coil sensor which has the planar and thin structures fabricated on a printed circuit board (PCB), and the PD electrode system was fabricated to simulate a PD defect by a void. In addition, void samples with different diameters were fabricated by injecting air in a cylindrical aluminum frame using a syringe during the epoxy curing process. To identify the diameter of void defects, PD characteristics such as the discharge magnitude, pulse count, and phase angle were extracted and back propagation algorithm (BPA) was designed using virtual instrument (VI) based on the Labview program. From the experimental results, the BPA algorithm proposed in this paper has over 90% accurate rate to identify the diameter of void defects and is expected to use reference data of maintenance and replacement of insulation for cast-resin transformers in the on-site PD measurement.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.3
• /
• pp.177-183
• /
• 2023

Various failure modes occur in the concrete beams reinforced with GFRP(Glass Fiber Reinforced Plastic) under initial condition and repairing patterns. In this study, the failure behaviors of concrete beams restrengthened with GFRP sheet with slightly higher elastic modulus than concrete were investigated. For the tests, concrete beams with 24 MPa were manufactured, and the effects of initial notch, overlapping, end-strip reinforcement, and fiber anchors were analyzed on failure load. The cases of GFRP overlap around notch and the initial notch showed increasing failure loads similar to those of normal restrengthened case since the epoxy of the saturated GFRP sufficiently repaired the notch area. Compared to the control case without restrengthening of GFRP, the concrete with initial notch showed 0.78 of loading ratio and normal restrengthening showed 4.43~5.61 times of increasing ratio of failure loading, where interface-debonding from flexural crack were mainly observed. The most ideal failure behavior, break of GFRP, was observed when end-strip over 1/3 height from bottom and fiber anchor were installed, which showed increasing failure load over 150 % to normal restrengthening.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.4
• /
• pp.458-466
• /
• 2023

Structures in our surroundings deteriorate over time due to environmental and chemical factors, resulting in a decrease in their performance. The primary causes of degradation in concrete structures are carbonation, salt damage, and freeze-thaw cycles. Various maintenance methods exist to address these degradation issues. However, research and technological development for existing maintenance methods have been ongoing, but the accuracy and effectiveness of repair materials and techniques have not been extensively validated. Therefore, in this study, we conducted a material performance evaluation of various manufacturers' repair materials. Based on this evaluation, we applied corrosion inhibitors and epoxy, which are the methods most closely related to crack repair, to assess the durability performance against carbonation, salt damage, and freeze-thaw cycles. The results show approximately a two-fold performance improvement against carbonation and salt damage, and a 5% enhancement in repair performance against freeze-thaw cycles. Thus, it is considered effective in preventing rebar corrosion when appropriate maintenance is carried out according to environmental and chemical factors during structural repairs.

• Membrane Journal
• /
• v.33 no.6
• /
• pp.416-426
• /
• 2023

In this study, hindered amine-grafted graphene oxide (HA-GO) with antioxidant properties was prepared and incorporated into Nafion-based composite membranes as an effective filler material for polymer electrolyte membrane fuel cell applications. HA-GO was synthesized via a ring-opening reaction between amine groups in 4-amino-2, 2, 6, 6-tetramethyl piperidine and epoxy groups on the surface of GO. Nafion-based composite membranes containing different weight contents of HA-GO were fabricated to compare the polymer electrolyte membrane properties with those of the pure Nafion membrane. The composite membranes with HA-GO were found to have better mechanical properties, chemical stability, and proton conductivity than the pure Nafion membrane. In particular, the conductivity retention behavior confirmed by the decrease in proton conductivity after Fenton's test of the composite membranes was better than that of the pure Nafion membrane due to the incorporation of HA-GO with effective antioxidant properties.

• Imaging Science in Dentistry
• /
• v.53 no.4
• /
• pp.345-353
• /
• 2023

Purpose: The objective of this study was to propose a method for developing a clinical phantom to reproduce various diseases that are clinically prevalent in the field of dentistry. This could facilitate diverse clinical research without unnecessarily exposing patients to radiation. Materials and Methods: This study utilized a single dry skull, which was visually and radiographically examined to evaluate its condition. Existing lesions on the dry skull were preserved, and other relevant lesions were artificially created as necessary. These lesions were then documented using intraoral radiography and cone-beam computed tomography. Once all pre-existing and reproduced lesions were confirmed by the consensus of 2 oral and maxillofacial radiologists, the skull was embedded in a soft tissue substitute. To validate the process, cone-beam computed tomography scans and panoramic radiographs were obtained of the fabricated phantom. All acquired images were subsequently evaluated. Results: Most lesions could be identified on panoramic radiographs, although some sialoliths and cracked teeth were confirmed only through cone-beam computed tomographic images. A small gap was observed between the epoxy resin and the bone structures. However, 2 oral and maxillofacial radiologists agreed that this space did not meaningfully impact the interpretation process. Conclusion: The newly developed phantom has potential for use as a standardized phantom within the dental field. It may be utilized for a variety of imaging studies, not only for optimization purposes, but also for addressing other experimental issues related to both 2- and 3-dimensional diagnostic radiography.

• ETRI Journal
• /
• v.46 no.2
• /
• pp.347-359
• /
• 2024

A simultaneous transfer and bonding (SITRAB) process using areal laser irradiation is introduced for high-yield and cost-effective production of mini- or micro-light-emitting diode (LED) display panels. SITRAB materials are special epoxy-based solvent-free pastes. Three types of pot life are studied to obtain a convenient SITRAB process: Room temperature pot life (RPL), stage pot life (SPL), and laser pot life (LPL). In this study, the RPL was found to be 1.2 times the starting viscosity at 25℃, and the SPL was defined as the time the solder can be wetted by the SITRAB paste at given stage temperatures of 80℃, 90℃, and 100℃. The LPL, on the other hand, was referred to as the number of areal laser irradiations for the tiling process for red, green, and blue LEDs at the given stage temperatures. The process windows of SPL and LPL were identified based on their critical time and conversion requirements for good solder wetting. The measured RPL and SPL at the stage temperature of 80℃ were 6 days and 8 h, respectively, and the LPL was more than six at these stage temperatures.