• Journal of Periodontal and Implant Science
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• 제47권6호
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• pp.402-415
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• 2017

Purpose: The aim of this study was to determine the effects of patterned human periodontal ligament stem cell (hPDLSC) sheets fabricated using a thermoresponsive substratum. Methods: In this study, we fabricated patterned hPDLSC sheets using nanotopographical cues to modulate the alignment of the cell sheet. Results: The hPDLSCs showed rapid monolayer formation on various surface pattern widths. Compared to cell sheets grown on flat surfaces, there were no significant differences in cell attachment and growth on the nanopatterned substratum. However, the patterned hPDLSC sheets showed higher periodontal ligamentogenesis-related gene expression in early stages than the unpatterned cell sheets. Conclusions: This experiment confirmed that patterned cell sheets provide flexibility in designing hPDLSC sheets, and that these stem cell sheets may be candidates for application in periodontal regenerative therapy.

• 한국생산제조학회지
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• 제20권6호
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• pp.773-777
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• 2011

Conventional ultrasonic thickness measurement is to be considered as the assumption that the ultrasonic velocity is known. In actual applications the velocity is often not well known and access is often limited to one side. This paper aims at determining the ultrasonic velocity and thickness of plates with parallel or wedged surfaces using contact measurements made on one surface only. For wedged plates the thickness at one point and the wedge angle are determined. Equations are used for determining the ultrasonic velocity, thickness and wedge angle of the plate based on the times-of-flight measured by two contact transducers coupled to one surface. The time-of-flight of the obliquely reflected longitudinal wave echo was measured as a function of the separation between the two transducers. In addition, a simulation was made for comparing the experimental data and a FEM image. Experiments and simulations were performed on flat and wedged plates of aluminium materials; the calculated results for the unknown quantities are generally agreed with them to some degree.

• 대한물리치료과학회지
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• 제19권1호
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• pp.63-69
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• 2012

Background : The purpose of this study was to investigate the frequency domain characteristics of ground reaction forces during quiet standing on inclined surfaces twenty healthy individuals(10 elderly women $68.78{\pm}3.29$ years and 10 young women $20.90{\pm}0.74$ years) participated. Methods : Subjects stood in quiet stance over a force platform positioned in one of three different fixed positions: flat, down and up. Healthy participants completed with eyes open for 120 s trials. Evaluation of postural control were generally based on the interpretation of center of pressure(COP) time series. The COP have been determined using an experimental setup with 3D kinematic and the ground reaction force system. All the data were expressed means and standard deviation by using SAS package program. Results : SEF 50% were not significant in AP and ML direction according to surface slope of both groups. SEF 95% were showed highest frequency in AP direction on down slope of both groups. MEF were not significant all direction according to surface slopes of elderly women. There was no difference between young and elderly women. Conclusion : Elderly women used to ankle strategy during a quiet stance according to COP perturbation of AP direction showed more expanded than ML direction. SEF 95% were showed highest frequency on down slope in elderly women who showed more used ankle strategy for postural control on down slope.

• Tribology and Lubricants
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• 제11권5호
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• pp.71-77
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• 1995

The capacitance technique was used to measure the minimum oil film thickness in engine bearing and the central oil film thickness between cam and tappet. This method is based on the measurement of total capacitance of oil film. For the measurement of the oil film thickness between cam and tappet, two surfaces were assumed to be flat and parallel within the Hertzian region and all the measured capacitance originated from this region. Shear rates from the measured minimum oil film thickness are over 10$^{6}$ sec$^{-1}$ in the greater part in both two cases. The minimum oil film thickness in engine bearing is larger than the surface roughness. Between cam and tappet it is mostly smaller than the surface roughness. In spite of the awkward restriction of the reliability of measured oil film thickness, it was known that the capacitance technique makes it possible to measure the oil film thickness in elastohydrodynamic and mixed lubrication regimes as well as in hydrodynamic regime. Therefore, it is also possible to classify the lubrication regimes based on the oil film thickness.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.809-809
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• 2013

We report a new method for highly controllable local patterning of a hydrogel on microfabricated cantilevers and fabrication of all hydrogel microcantilevers. We constructed a dynamic mask based photolithography setup using a commercial beam projector, a 3-axis microstage and other optical components. Dynamic masks generated from the beam projector controlled the shape, size, and position of hydrogel patterns while the 3-axis microstage mainly controlled the thickness of hydrogel patterns and hydrogel microcantilevers. Using the constructed setup, polyethyleneglycol diacrylate (PEGDA) was patterned on microfabricated cantilevers in a highly controlled manner. Currently, the smallest PEGDA patternable is a 5-${\mu}m$-diameter circle with a thickness of ~$10{\mu}m$. To confirm thicknesses of patterned PEGDAs on silicon microcantilevers, resonance frequencies of microcantilevers were measured before and after each PEGDA patterning. Thicknesses extracted from resonance measurements showed good agreement with measurements using an optical microscope. In addition, PEGDA microcantilevers with various dimensions and thicknesses were fabricated on glass and silicon substrates. Surfaces of fabricated all hydrogel microcantilevers were flat enough to facilitate other post processing and to be used for various sensing applications.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.56-63
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• 2003

Micro/nano adhesion and friction properties of mixed self-assembled monolayer (SAM) with different chain length for MEMS application were experimentally studied. Many kinds of SAM having different spacer chains(C6, C10 and C18) and their mixtures (1:1) were deposited onto Si-wafer, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and micro scale applied load were measured using ball-on-flat type micro-tribotester. Surface roughness and water wetting angles were measured with SPM (scanning probe microscope) and contact anglemeter. Results showed that wetting angles of mixed SAMs showed the similar value of pure SAMs. The coating surface morphology was increased as mixing of SAM. Nano adhesion and nano friction decreased as increasing of the spacer chain length and mixing of SAM. Micro friction was decreased as increasing of the spacer chain, but micro friction of mixed SAM showed the value between pure SAMs. Nano adhesion and friction mechanism of mixed SAM was proposed in a view of stiffness of spacer chain modified chemically and topographically.

• 대한수의학회지
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• 제24권2호
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• pp.195-199
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• 1984

The present observations were focussed mainly on the macroscopic and histopathological observation to polyps encountered on the stomach of 4-month-old pig, small intestine of 3-month-old pig and cecum of 9-month-old dog. The results were summarized as follows; 1. The polyps were gray or pink hemispherical shapes attached by the broad base to the gastrointestinal walls and were 3 to 8 mm in diameter and diffuse appearance. The surfaces of polyps were flat or indented and were ulcerated in some large polyps. 2. In histopathological findings, the polyps were nodules composed of lymphoid follicles, which were characterized by the differentiation and proliferation of the lymphoid cells in the lamina propria or submucosa of the gastrointestinal tract. The lymphoid nodules have the thin septa and thick capsules of the connective tissues, also comprised more numerous and larger sinus-like-blood vessels and more diffuse lymphoid cells in the peripheral zones than those in the central zones of nodules. In addition, the external surface of the polyps bulged toward the intestinal lumen were covered with the abnormal epithelium, or the degenerative and necrotic lymphocyte aggregates. 3. These polyps were considered as lymphoid polyps caused by the hyperplasia of the lymhoid follicles.

• 한국분말재료학회지
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• 제22권6호
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• pp.391-395
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• 2015

We report on the successful fabrication of ZnO nanorod (NR)/polystyrene (PS) nanosphere hybrid nanostructure by combining drop coating and hydrothermal methods. Especially, by adopting an atomic layer deposition method for seed layer formation, very uniform ZnO NR structure is grown on the complicated PS surfaces. By using zinc nitrate hexahydrate $[Zn(NO_3)_2{\cdot}6H_2O]$ and hexamine $[(CH_2)_6N_4]$ as sources for Zn and O in hydrothermal process, hexagonal shaped single crystal ZnO NRs are synthesized without dissolution of PS in hydrothermal solution. X-ray diffraction results show that the ZnO NRs are grown along c-axis with single crystalline structure and there is no trace of impurities or unintentionally formed intermetallic compounds. Photoluminescence spectrum measured at room temperature for the ZnO NRs on flat Si and PS show typical two emission bands, which are corresponding to the band-edge and deep level emissions in ZnO crystal. Based on these structural and optical investigations, we confirm that the ZnO NRs can be grown well even on the complicated PS surface morphology to form the chestnut-shaped hybrid nanostructures for the energy generation and storage applications.

• 한국산업융합학회 논문집
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• 제16권3호
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• pp.85-93
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• 2013

The MCT has been most extensively used in the machining. In particular, the ball endmill has been mainly adopted for finishing on the free- form surface. The advancement of CAD/CAM software has made it possible to develop various cutting pattern methods and to create diverse tool routes. Therefore, the current research made an attempt to find the optimal cutting pattern among the seven cutting patterns (i.e., Follow Periphery, Zig, Zig Zag, Concentric Zig, Concentric Zig Zag, Radial Zig, Radial Zig Zag) when aluminium 6000 series were machined by the ball endmill. The optimal pattern was found by comparing different shapes and surface roughness produced by the seven patterns. The current research found that each cutting pattern produced its own unique geometric features on the machined surface. It was found that the Radial Zig cutting pattern produced the lowest roughness on the flat surfaces. The Radial Zig Zag cutting pattern was found to produce the most accurate free-form surface. Finally, the most efficient cutting pattern in terms of machining time turned out to be the Follow Periphery.

• Transactions on Electrical and Electronic Materials
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• 제16권4호
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• pp.206-211
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• 2015

We investigated the formation of a nanopyramidal structure and fabricated nanotextured Si solar cells using an Ag metal-assisted chemical etching process. The nanopyramidal structure was formed on a Si flat surface and the nanotexturing process was performed on the p-type microtextured Si surface. The nanostructural formation shows a transition from nanopits and nanopores to nanowires with etching time. The nanotextured surfaces also showed the photoluminescence spectra with an enhanced intensity in the wavelength range of 1,100~1,250 nm. The photoreflectance of the nanotextured Si solar cells was strongly reduced in the wavelength range of 337~596 nm. However, the quantum efficiency is decreased in the nanotextured samples due to the increased nanosurface recombination. The nanotexturing process provides a better p-n junction impedance of the nanotextured cells, resulting in an enhanced shunt resistance and fill factor which in turn renders the possibility of the increased conversion efficiency.