• 한국정밀공학회지
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• 제30권1호
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• pp.120-127
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• 2013

A novel severe plastic deformation process named half channel angular extrusion (HCAE) is proposed in order to produce bulk UFG materials. In HCAE process, equal channel angular extrusion (ECAE) and conventional forward extrusion process is integrated to increase the strain per pass and effectiveness of the SPD process. Three-dimensional finite element analysis was carried out to study the deformation behavior of the materials in the HCAE process. HCAE process was performed experimentally on commercially pure aluminum (AA1050) and micro-Vickers hardness test was used to measure the distribution of hardness on the section of normal to the extrusion direction. The results show that HCAE is able to impose more intensive strains per pass and give rise to higher micro-hardness than ECAE.

• Molecules and Cells
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• 제41권2호
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• pp.119-126
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• 2018

microRNA (miR)-612 shows anticancer activity in several types of cancers, yet its function in melanoma is still unclear. This study was undertaken to investigate the expression of miR-612 and its biological relevance in melanoma cell growth, invasion, and tumorigenesis. The expression and prognostic significance of miR-612 in melanoma were examined. The effects of miR-612 overexpression on cell proliferation, colony formation, tumorigenesis, and invasion were determined. Rescue experiments were conducted to identify the functional target gene(s) of miR-612. miR-612 was significantly downregulated in melanoma tissues compared to adjacent normal tissues. Low miR-612 expression was significantly associated with melanoma thickness, lymph node metastasis, and shorter overall, and disease-free survival of patients. Overexpression of miR-612 significantly decreased cell proliferation, colony formation, and invasion of SK-MEL-28 and A375 melanoma cells. In vivo tumorigenic studies confirmed that miR-612 overexpression retarded the growth of A375 xenograft tumors, which was coupled with a decline in the percentage of Ki-67-positive proliferating cells. Mechanistically, miR-612 targeted Espin in melanoma cells. Overexpression of Espin counteracted the suppressive effects of miR-612 on melanoma cell proliferation, invasion, and tumorigenesis. A significant inverse correlation (r = -0.376, P = 0.018) was observed between miR-612 and Espin protein expression in melanoma tissues. In addition, overexpression of miR-612 and knockdown of Espin significantly increased the sensitivity of melanoma cells to doxorubicin. Collectively, miR-612 suppresses the aggressive phenotype of melanoma cells through downregulation of Espin. Delivery of miR-612 may represent a novel therapeutic strategy against melanoma.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.419-422
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• 2002

A three-dimensional inlet flow structure inside a microfluidic element has been investigated using a micro-PIV(particle image velocimetry) measurement as well as a numerical analysis. The present study employs a state-of-art micro-PIV system which consists of epi-fluorescence microscope, 620nm diameter fluorescent seed particles and an 8-bit megapixel CCD camera. For the numerical analysis, a commercial software CFD-ACE+(V6.6) was employed for comparison with experimental data. Fixed pressure boundary condition and a 39900 structured grid system was used for numerical analysis. Velocity vector fields with a resolution of $6.7{\times}6.7{\mu}m$ has been obtained, and the attention has been paid on the effect of varying measurement conditions of particle diameter and particle concentration on the resulting PIV results. In this study, the microfluidic elements were fabricated on plastic chips by means of MEMS processes and a subsequent melding process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.400-404
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• 2001

A micro-PIV(particle image velocimetry) measurement has been conducted to investigate flow fields in such microfluidic devices as microchannels and micronozzle. The present study employs a state-of-art micro-PIV system which consists of epi-fluorescence microscope, 620nm diameter fluorescent seed particles and an 8-bit megapixel CCD camera. Velocity vector fields with a resolution of $6.7\times6.7{\mu}m$ has been obtained, and the attention has been paid on the effect of varying measurement conditions of particle diameter and particle concentration on the resulting PIV results. In this study, the microfluidic elements were fabricated on plastic chips by means of MEMS processes and a subsequent molding process. Flow fields in a variety of microchannels as well as micronozzle have been investigated.

• Journal of Welding and Joining
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• 제7권4호
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• pp.38-45
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• 1989

In this study, in order to evaluate the shape and the size of the plastic zone at the notch tip before stable crack growth, a newly developed technique for plastic strain measurement, that is, the recrystallization-etching technique was applied to observe the intense strain zone at the notch tip of weld HAZ. 1) The recrystallized specimens showed that the amount of the intense strain zone, more than 20% plastic zone, was quantitatively observed as the plane strain state during the growth of the plastic zone. 2) The behavior of plastic deformation at midsection are different for parent and weld HAZ. In addition, the micro crack initiation occurs at midsection, parent and weld HAZ when the crack opening displacement(COD) value is .delta.$_{t}$=0.4mm. 3) The plastic zone for parent proceeds in the forward direction at notch tip and for weld HAZ in the right and left direction at the notch tip. 4) The relation between plastic strain energy(Wp) and COD(.delta.$_{t}$) depended on yield stress, gradient and plastic strain size.ize.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.209-212
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• 2001

It is known that the mim forming processes show somewhat different phenomena compared with the conventional metal forming processes, namely, the size effect, enhanced friction effect and etc. Such typical phenomena, however, are not predicted by the conventional finite element analysis, which has been an efficient numerical tool to predict the metal forming processes. It is due to the fact that the constitutive relations used does not describe the microstructural characteristics of the materials. In the present investigation, the finite element formulation using the rate-dependent rigid plastic crystal plasticity model of the face-centered cubic materials is conducted to predict the micro mechanical behaviors during the mim forming processes. The finite element analysis, however, provides mesh-dependent solutions for the intragranular deformations. Therefore, the couple stress energy is additionally introduced into the variational principle and formulated within the framework of the rigid plastic finite element method to obtain mesh-independent solutions. Micro deformations of single crystal and bicrystal with various orientations are calculated to show the potential of the developed formulation.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
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• pp.352-355
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• 2007

We have developed tight bonding of plastic LCD with new rigid spacer. For tight bonding of two plastic substrates, we designed structures to collect UV or thermal epoxy placed on the top of rigid spacer spontaneously by capillary effect. We confirmed that tight bonded plastic LCD has a good adhesion without induced defects and a high mechanical stability against the various external deformations. This method can be applicable to the fabrication of large plastic LCDs using stamping process.

• Medical Lasers
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• 제9권1호
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• pp.39-43
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• 2020

Background and Objectives Breast reconstruction has the advantage of reducing the loss of the body image of patients after mastectomy surgery, and also improving the quality of the social and sexual life of breast cancer patients. However, in surprising and unfortunate number of patients, acute postoperative pain persists beyond the normal course of postsurgical recovery. We set out to investigate the effect of local dynamical micro-massage (LDM) treatment for achieving pain relief and reducing other postoperative complications. Materials and Methods We performed a retrospective analysis on 58 patients who underwent LDM treatment for postoperative pain management at Soonchunhyang University Bucheon Hospital between February 2017 and June 2019. Those patients who complained of persistent postoperative pain, which was uncontrollable with medication, were treated with LDM. The degree of pain and discomfort with contracture were recorded using numerical rating scale (NRS) scoring system with numbers from 0 to 10 ('none' to 'worst'). Results The median NRS score of pain was reduced by 62.3% from the start to the end of LDM treatment (p<0.001). Further, the NRS score of discomfort with contracture was reduced 66.0% (p<0.001). There was no complication related to the LDM treatment. Conclusion Dual-frequency ultrasound LDM can be an effective therapeutic option for persisting pain after breast reconstruction surgery. It was also effective in improvement of discomfort with contracture and erythema of the surgical wound.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.702-705
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• 2005

Burr is an undesirable projection as result of plastic deformation. Burr minimization and effective deburring process are required strongly to reduce the cost of the parts. In doing these efforts, the precise burr measurement must be provided for the efficient process. For this purpose the conoscopic holography sensors are selected before. However, it has been very difficult to measure micro burrs less than $10{\mu}m$ due to their tiny and sharp geometries as well as the effect of ambient vibration during scanning. A new micro burr measurement system using high precision. Conoprobe sensor and XY table can measure the micro burrs which is less than $10{\mu}m$. Experiments were carried out showing that micro burr around $10{\mu}m$ was successfully measured and analyzed.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.159-162
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• 2007

Recently, Pb-free solder ball technology, which is getting more significant in miniaturization of electronic equipment, and resolution of recent environmental problems, is necessary to be developed. A plastic-core solder ball is much promising in those considerations. Plastic-core solder balls have the tendency to replace the usual metal-core solder ball from low material cost and superior mechanical properties. The thermal effects, however, are important in manufacturing process, such as deposing micro-sized metal thin film on the spherical polymer surface. Furthermore plastic-core solder balls are easy to be broken due to CTE and elastic coefficient of material property from heat transfer. We propose technical computational investigations for the manufacturing design and the reliability of plastic-core solder ball from thermal stress analysis.