• Advances in nano research
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• v.13 no.4
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• pp.407-416
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• 2022

In this study, the gravitating mechanical stir casting method was used to fabricating the Nb₂O₅/AZ31 magnesium matrix nanocomposites. Niobium pentoxide (Nb₂O₅) used as reinforcement with two different weight percentages (3 wt % and 6 wt %). The influence of Nb₂O₅ on microstructure and mechanical properties has been investigated. The microstructure analysis showed that the composites are mainly composed of the primary α-magnesium phase and phase β-Mg₁₇Al₁₂ secondary phase. The secondary phase was dispersed evenly along the grain boundary of the Mg phase. The Nb₂O₅/AZ31 nanocomposites revealed that the grain size and its lamellar shape (β-Mg₁₇Al₁₂) were gradually refined. Different strengthening mechanisms were assessed in terms of their contributions. Results showed that composite material properties of hardness, yield strength, and fracture study were directly related to Nb₂O₅ as a reinforcement. The maximum values of the mechanical properties were achieved with the addition of 3 wt% Nb₂O₅ on the AZ31 alloy.

• Journal of Korean Foot and Ankle Society
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• v.27 no.4
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• pp.148-153
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• 2023

Traditionally, arthroscopic microfracture and autologous osteochondral autograft transplantation have been the primary surgical treatments for osteochondral lesions of the talus. On the other hand, recent advancements have introduced alternative approaches, such as autologous chondrocyte transplantation, matrix-derived autologous chondrocyte transplantation, intra-articular injection of concentrated bone marrow aspirate concentrate, and the use of fibrin glue to address chondral defects. Furthermore, some studies have explored a combination of bone marrow aspirate and matrix-derived chondrogenesis. In light of these developments, this report presents a case study of a young male patient in his early twenties with a relatively large osteochondral lesion exceeding 1.5 cm² on the medial talar dome. Instead of removing the osteochondral lesion, a surgical approach was employed to retain the lesion while addressing the unstable cartilage in the affected area. This approach involved a combination of bone marrow aspirate concentrate and matrix-derived chondrogenesis. The treatment yielded favorable clinical outcomes and ultimately successfully induced the bony union of osteochondral lesions. This paper reports the author's experience with this innovative approach with a review of the relevant literature.

• Archives of Pharmacal Research
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• v.23 no.6
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• pp.535-547
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• 2000

Recent findings indicate that mechanical strain (deformation) exerted by the extracellular matrix modulates activation of airway smooth muscle cells. Furthermore, cytoskeletal organization in airway smooth muscle appears to be dynamic, and subject to modulation by receptor activation and mechanical strain. Mechanosensitive modulation of crossbridge activation and cytoskeletal organization may represent intracellular feedback mechanisms that limit the shortening of airway smooth muscle during bronchoconstriction. Recent findings suggest that receptor-mediated signal transduction is the primary target of mechanosensitive modulation. Mechanical strain appears to regulate the number of functional G-proteins and/or phospholipase C enzymes in the cell membrane possibly by membrane trafficking and/or protein translocation. Dense plaques, membrane structures analogous to focal adhesions, appear to be the primary target of cytoskeletal regulation. Mechanical strain and receptor-binding appear to regulate the assembly and phosphorylation of dense plaque proteins in airway smooth muscle cells. Understanding these mechanisms may reveal new pharmacological targets for control1ing airway resistance in airway diseases.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.200-204
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• 1994

Low temperature associated damage mechanism is not well known for asphalt concrete. Many studies have related the thermal cracking of pavement in the roadway in cold region with overall shrinkage of the pavement surface under assumption of homogeneous material. This study, however, was intiated based on the assumption that thermal incompatibility of materials (heterogeneous) in asphalt concrete mixture would be the primary cause of the damages. Acoustic emission technique and microscopic obsevation were employed to evaluate damage mechanism of asphalt concrete due to low temperature. The first method showed the sufficient evidence that asphalt concrete could be damaged by lowered temperature only. The second method showed that the damage by temperature resulted in micro-cracks at the interface between asphalt matrix and aggregate particle. It was concluded that these damage mechanisms were the primary cause of major thermal cracking of asphalt pavement in cold region.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1996.10a
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• pp.78-85
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• 1996

The effect of vertical vibration of a beam is significantly influenced by higher modes of vibration. Therefore, a beam can be modeled using several elements must De used to represent a vibrating beam. As a result, analysis of a space framed structure for vertical vibration requires increase number of elements leading to more complicated model with many degree of freedom which requires large amount of computing resources for dynamic analysis. An efficient analysis method for vertical vibration of space framed structures are proposed in this paper which is presented in three method. The first method is to determine minimum nodes that shall be used to obtain dynamic response with the vertical vibration. Secondly, matrix condensation methods are introduced to reduce the computation efforts used to perform dynamic analysis and the selection of primary degree-of-freedom is proposed. The third method is of using the mass participation factor for the selection of primary degree-of-freedom.

• Toxicological Research
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• v.26 no.1
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• pp.61-66
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• 2010

Retinoids have many beneficial effects on dermatological applications. But, retinoids cause skin irritation. In this study, the safety of retinoids was clarified via both primary skin irritation test in rabbits and sensitization study using an integrated model for the differentiation of chemical-induced allergic and irritant skin reaction (IMDS), an alternative method to sensitization test. The effects of retinoids on the change of ultraviolet A (UVA)-induced matrix metalloproteinase-1 (MMP-1) in human skin fibroblasts and the modulation of type-1 pN collagen synthesis in hairless mice were examined to clarify the anti-wrinkle effects. Alltrans retinol (t-ROL) and its derivative, all-trans retinoic acid (t-RA), showed mild skin irritation but did not induce the sensitization. t-ROL and t-RA exerted anti-wrinkle effects by inhibiting the UVA-induced MMP-1 in human skin fibroblasts and increasing the type-1 pN collagen synthesis in hairless mice. These findings suggest that retinoids do not induce the allergy, and show anti-wrinkle effects by decreasing MMP-1 activation and increasing collagen synthesis.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.35-40
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• 2000

The influence of cyclic loading history on the creep behavior of the 30 vol% hot-pressed $SiC_f/Si_3N_4copmposite was experimentally investigated at $1200^{\circ}C$. The duration of loading/unloading had great effects on the creep behaviors. The short term duration cyclic loading history test results showed significant reduction in the primary and steady-state creep rates. For example, 300sec loading/300sec unloading history resulted in 70% lower steady-state creep rate than that of the continuous loading. However the long term duration cyclic loading history test results showed little change in creep rates compared to those of the continuous one. The reason for the significant change in the short term duration cycles was estimated due to the change in the stress redistribution between the fiber and matrix during the creep recovery in the primary stage.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.06a
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• pp.183-195
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• 1997

The micorstructural characteristics, particularly $\alpha$-halo formation, in semi-solid state processed hypereutectic Al-Si alloy was investigated. The microstructural changes during reheating of wedge type mold cast ingot, hot-rolled sheet, and Si particulate reinforced Al composite was compared with those occurred during stirring of semi-solid state hypereutectic alloy. In the case of semi-solid state reheating of wedge type ingot and hot-rolled sheet, fine particles of Si as well as $\alpha$-halo formed after heat treatment. Although there seemed to be no coarsening with variations of holding time, the region of $\alpha$-halo decreased due to homogenization. Nucleation and recrystallization was accelerated with the addition of alloying elements during hot rolling resulting in primary Si particle size decrease and $\alpha$-halo formation. In the case of extruded specimens, very little morphological change of reinforcing Si particles was observed. Almost no $\alpha$-halo formed during reheating because of the oxide film formed on the reinforcing Si particles which acted as a diffusion barrier between the matrix and the primary Si particles.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.557-558
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• 2006

In all conventional sintered PM products, the pores present are of two types, primary and secondary. Primary pores forming during compaction and latter during sintering, due to penetration of formed liquid through the matrix grain boundary. Effect of carbon addition on diffusion of Cu in SH737-2Cu system was investigated. After compaction and transient liquid phase sintering at $1120^{\circ}C$ and $1180^{\circ}C$, samples were characterized for densification, showing rise in sintering density and reduction in swelling on carbon addition. Quantitative microstructural characterization (shape factor and pore size) revealed bimodal distribution for 0% carbon, more rounded pores for 0.9% carbon and higher sintering temperature, and pore coarsening at higher sintering temperature.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.4
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• pp.179-184
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• 2021

Two types of secondary hardening martensitic steels, 10Co-14Ni and 6Co-5Ni, were produced by vacuum induction melting to investigate the effect of ausforming process on mechanical properties. According to the results of present study, the alloy samples ausformed at low temperature indicated a rather low hardness level in overall aging time despite the refinement of martensite lath width. As the result can closely be related with the presence of primary carbides precipitated within the initial austenite matrix, we confirmed that, in ultrahigh strength secondary hardening martensitic alloy steels, the ausforming process can rather limit the degree of secondary hardening during the subsequent aging treatment.