• Communications of the Korean Mathematical Society
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• v.32 no.1
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• pp.147-163
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• 2017

We define de Sitter focal surfaces and hyperbolic focal surfaces of hyperbolic space curves. As an application of the theory of unfoldings of function germs, we investigate the singularities of these surfaces. For characterizing the singularities of these surfaces, we discover a new hyperbolic invariants and investigate the geometric meanings.

• Current Optics and Photonics
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• v.3 no.3
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• pp.227-235
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• 2019

With slimmer, lighter and all-reflective imaging systems in high demand for consumer and military applications, coaxially folded optical image systems are widely considered because they can extend focal length and reduce track length. Most of these systems consist of multiple surfaces, and these surfaces are machined on one element or grouping processing on two elements. In this paper, we report and first experimentally demonstrate an all-aluminum all-reflective optical system which consists of two optical elements, with two high order aspherical surfaces in each element. The coaxially folded system is designed with Seidel aberration theory and advanced optimization with Zemax. The system is made of all-aluminum material processing by single point diamond turning (SPDT). On this basis, we completed the system integration and performed an imaging experiment. The final system has the advantages of short track length and long focal length and broad application prospects in the micro-unmanned aerial vehicle field.

• The Journal of Advanced Prosthodontics
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• v.5 no.3
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• pp.341-350
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• 2013

PURPOSE. To evaluate adherence of human gingival fibroblasts (HGFs) to transmucosal abutment of dental implant with different surface conditions with time and to investigate the roles of focal adhesion linker proteins (FALPs) involved in HGFs adhesion to abutment surfaces. MATERIALS AND METHODS. Morphologies of cultured HGFs on titanium and ceramic discs with different surface were observed by scanning electron microscopy. Biocompatibility and focal adhesion were evaluated by ultrasonic wave application and cell viability assay. FALPs expression levels were assessed by RT-PCR and western blot. RESULTS. There seemed to be little difference in biocompatibility and adhesion strength of HGFs depending on the surface conditions and materials. In all experimental groups, the number of cells remaining on the disc surface after ultrasonic wave application increased more than 2 times at 3 days after seeding compared to 1-day cultured cells and this continued until 7 days of culture. FALPs expression levels, especially of vinculin and paxillin, also increased in 5-day cultured cells compared to 1-day cultured fibroblasts on the disc surface. CONCLUSION. These results might suggest that the strength of adhesion of fibroblasts to transmucosal abutment surfaces increases with time and it seemed to be related to expressions of FALPs.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.266-271
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• 2002

The finite schematic eye based on spherical aberration and Stiles-Crawford effect is designed by an optimization method. It consists of four aspherical surfaces. The radius of curvature, thickness, asphericity, and spherical aberration are used as constraints in the optimization process. Stiles-Crawford effect in the pupil is considered as a weighting value for optimum design. The designed schematic eye has effective focal length of 20.8169 mm, back focal length of 15.4820 mm, front focal length of -13.8528 mm, and image distance of 15.7150 mm. When the pupil diameter is 4 mm, the diameter of entrance pupil and exit pupil are 4.6919 mm and 4.2395 mm, respectively. From the data of 75 measured Korean emmetropic eyes, this finite schematic eye is designed first in Korea.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.12
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• pp.1031-1037
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• 2015

Laser assisted machining (LAM) is an effective method with which to effectively process difficult-to-cut materials. Simple machining processes, such as turning and linear tool paths, have been studied by many researchers. But, there are few research efforts on LAM workpieces using threedimensional shapes because of difficulties controlling the laser heat on workpieces with inclined angles or curved surfaces. Two methods for machining three-dimensional workpieces are proposed in this paper. The first is that the heat source shape and laser focal length are maintained using an index table. Second, a rotary type laser module is controlled using an algorithm to move the laser heat source in all directions. This algorithm was developed to control the rotary type laser module and the machine tool simultaneously. These methods are verified by a CATIA simulation.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.390-396
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• 1993

When a one-dimensional telecentric paraxial holographic kinoform is used as a Fourier transform lens, we analyzed three surface-relief structures, i.e., plano-convex, convex-plano and biconvex shapes, employing exact raytracing method based on Snell's law. For the kinoform of E/8 and focal length of 15 mm, the number of zones, the thickness, and the slope of parabolic surfaces are varied by changing the refractive indicies of kinoform material and surrounding medium. It is found that biconvex shape gives the best results in general, although off-axis performance degrades in all cases as the slope of parabolic surfaces increases.

• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.142-147
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• 2013

In order to deduce the difficulty of fixing the Ritchey-Chretien (R-C) dual reflective optical system and enhance the stability of the secondary mirror, a compact integral structure is presented here composed of two transmitting and two reflective aspheric surfaces. The four surfaces were manufactured from a single germanium lens and integrated together. The two reflective surfaces formed by coating the inner reflecting films were assembled in one lens. It makes the installation of the two mirrors easier and the structure of the secondary mirror more stable. A design of mid-wave infrared (MWIR) compact imaging system is presented with a spectral range chosen as $3.7-4.8{\mu}m$. The effective focal length is f=90 mm. The field of view (FOV) for the lens is $4.88^{\circ}$. It has good imaging capability with Modulation Transfer Function (MTF) of all field of view more than 0.55 close to the diffraction limitation. Outdoor experiments were carried out and it is shown that the integral catadioptric optical system performs well on imaging.

• Korean Journal of Optics and Photonics
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• v.28 no.5
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• pp.241-249
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• 2017

This paper presents the design and evaluation of the optical system for an uncooled thermal-imaging camera. The operating wavelength range of this system is from $7.7{\mu}m$ to $12.8{\mu}m$. Through optimization, we have obtained a LWIR (Long Wave Infrared) optical system with a focal length of 5.44 mm, which consists of four aspheric surfaces and two diffractive surfaces. The f-number of the optical system is F/1.2, and its field of view is $90^{\circ}{\times}67.5^{\circ}$. The hybrid lens was used to balance the higher-order aberrations, and its diffraction properties were evaluated by scalar diffraction theory. We calculated the polychromatic integrated diffraction efficiency, and the MTF drop generated by background noise. We have evaluated the thermal compensation of a LWIR fixed optical system, which is optically passively athermalized to maintain MTF performance in the focal depth. In conclusion, these design results are useful for an uncooled thermal-imaging camera.

• Journal of Biomedical Engineering Research
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• v.40 no.1
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• pp.1-6
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• 2019

Human mesenchymal stem cells (hMSC) are multipotent stromal cells that have great potential to differentiate into a variety of cell types such as osteocytes, chondrocytes, and myocytes. Although there have been many studies on their clinical availability, little is known about how intracellular signals can be modulated by topographic features of the extracellular matrix (ECM). In this study, we investigated whether and how microwavy-patterned extracellular matrix (ECM) could affect the signaling activity of focal adhesion kinase (FAK), a key cellular adhesion protein. The fluorescence resonance energy transfer (FRET)-based FAK biosensor-transfected cells are incubated on microwavy-patterned surfaces and then platelet derived growth factor (PDGF) are treated to trigger FAK signals, followed by monitoring through live-cell FRET imaging in real time. As a result, we report that PDGF-induced FAK was highly activated in cells cultured on microwavy-patterned surface with L or M type, while inhibited by H type-patterned surface. In further studies, PDGF-induced FAK signals are regulated by functional support of actin filaments, microtubules, myosin-related proteins, suggesting that PDGF-induced FAK signals in hMSC upon microwavy surfaces are dependent on cytoskeleton (CSK)-actomyosin networks. Thus, our findings not only provide new insight on molecular mechanisms on how FAK signals can be regulated by distinct topographical cues of the ECM, but also may offer advantages in potential applications for regenerative medicine and tissue engineering.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.183-190
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• 1996

To design three-mirror telescope system (F/8, 120 inch in focal length) for visible and infra-red band imaging, methods for power configuring and correction of the third order aberrations were studied. In the design of the telescope system, a three-mirror system corrected for spherical aberration, coma, and astigmatism was used for infra-red imaging, and the aberrations were corrected by using conic surfaces. For visible imaging, a singlet corrector lens was appended at the front of the focal plane to correct filed curvature. The telescope system has diffraction limited performance for 10 ${\mu}{\textrm}{m}$ in wavelength within 2.4$^{\circ}$ of field-of-view. In the visible band imaging, the rms spot size of the telescope system is less than 25 ${\mu}{\textrm}{m}$ within 3$^{\circ}$ of field-of-view for monochromatic light, and the telescope system satisfies flat field condition for CCD application.