• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.138-143
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• 2000

In order to maintain the faith and accuracy with precision of machinery, it is recently required the precise comprehension about approach which is appeared in the contact area between two bodies, because approach affects the static stiffness and dynamic characteristic of contact area. This study applied H. Hertz's circle contact area theory as much lower measuring force. It is measured approach influenced by various factors which were concerned with contact errors like material, form of two bodies, using calibration tester. As a result, the following conclusion can be obtained. 1) The approach appears greatly in order of carbon steel(SM20C), aluminum(A601-T6) and high density polyethylene(5305E) 2) The approach appears in order of concave, disc, convex form, in the ration of contact area size by the difference of curvature.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2676-2681
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• 2008

In previous studies, Convex cyclone are proposed to reduce pressure loss which are design cyclone wall with a single continuous curve. Studies about a prediction model for pressure loss and cut-size has focused on conventional cylinder-on-con cyclone. Therefore, the models do not perform well for uncommon design. In this study, a predict model for pressure loss and cut-size depend on cyclone wall curvature are developed. The tangential velocity below vortex-finder is obtained with consideration about friction area and momentum loss on the cyclone wall, and with this the variation of vortex-core and core velocity is obtained. Pressure loss is predicted using a Rankine vortex hypothesis. The prediction results are well agreed with experiments and CFD results.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.352-356
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• 2013

We developed a novel fabrication method of polydimethylsioxane (PDMS) lens, which can easily control the shapes of the lens using soft lithography with common photolithography and water droplet molding. A mold for PDMS lens was prepared by patterning of hydrophobic photoresist on the hydrophilic substrate and dispensing small water droplets onto the predefined hydrophilic patterns. The size of patterns determined the dimension of the lens and the dispensed volume of the water droplet decided the radius of curvature of the PDMS lens independently. The water droplet with photoresist pattern played a robustly fixed mold for lens due to difference in wettability. The radius of curvature could be calculated theoretically because the water droplets could approximate spherical cap on the substrate. Finally, concave and convex PDMS lenses which could reduce or magnify optically were fabricated by curing of PDMS on the prepared mold. The measured radii of the fabricated PDMS lenses were well matched with the estimated values. We believe that our simple and efficient fabrication method can be adopted to PDMS microlens and extended to micro optical device, lab on a chip, and sensor technology.

• Journal for History of Mathematics
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• v.20 no.4
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• pp.49-60
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• 2007

In this article, the concept of rigidity of smooth surfaces in the three dimensional Euclidean space which naturally arises in elementary geometry is introduced, and the natural process of the development of rigidity theory for compact surfaces and its generalizations are investigated.

• Bulletin of the Korean Mathematical Society
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• v.33 no.4
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• pp.537-544
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• 1996

Crofton's formula on Euclidean plane $E^2$ states: Let $\Gamma$ be a rectifiable curve of length L and let G be a straight line. Then $$ \int_{G \cap \Gamma \neq \phi} n dG = 2L $$ where n is the number of the intersection points of G with the curve $\Gamma$.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.758-767
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• 1995

The purpose of this study was to evaluate canal shaping ability after canal preparation by using engine-driven nickel-titanium file and endosonic file in curved canals. 30 mesiobuccal canals of molars extracted within recent 3 months were divided into 3 groups. Group I and group II were prepared by using engine-driven nickel-titanium Gates-Glidden drill type and the engine-driven nickel-titanium file type. Group III prepared by using en do sonic file. The image of preinstrumented canals was taken by X-ray. The image of postinstrumented canal was taken by X-ray in the same condition of preinstrumentation. A magnified X-ray image on magnifier screen was traced and then compared the preinstrumentated canal image with the postinstrumentated canal image by superimposing method. The following results were obtained : 1. In the change of canal curvature, the engine-driven nickel-titanium Gates-Glidden drill type showed the least change and the ultrasonically filing showed the greatest change. 2. In the percentage of canal enlargement, the engine-driven nickel-titanium file type was greatest at all level(p<0.05), the apex of all group was the greatest, the difference of ultrasonically filing group showed greater between apex and cervix. 3. The percentage of canal enlargement on convex side was greater than that of on concave side in apex of each group(p<0.05). In the ultrasonically filing group, both sides of canal enlargement showed sharply difference(p<0.01). 4. The percentage of canal enlargement on convex side was greater than that of on concave side in the third of cervix of the engine-driven nickel-titanium file type and the ultrasonically filling. The percentage of canal enlargement of convex and concave side in the third of middle of the engine-driven nickel-titanium Gates-Glidden drill type show a similar canal enlargement between convex side and concave side. As above result, the engine-driven nickel-titanium file type was greater in canal enlargement than the other instruments. The engine-driven nickel-titanium Gates-Glidden dirll type was efficient endodontic instrument for curved canal preparation because it was least change in canal curvature.

• Clean Technology
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• v.18 no.3
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• pp.295-300
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• 2012

Synthesis of well-defined particle with tunable size, shape, and functionalities is strongly emphasized for various applications such as chemistry, biology, material science, chemical engineering, medicine, and biotechnology. This study presents micromolding method for the fabrication of anisotropic particles with elegant control of curvature of covex roof. For the demostration of rapid fabrication of the particles, we have applied polydimethylsiloxane (PDMS) micromold as structure guiding template and wetting fluid to control curvature of roof of the particles. Based on this approach, we can control the radius of curvature from $20{\mu}m$ to $70{\mu}m$ with different aspect ratio of mold. In addition, wetting fluids with different wetting properties can also modulate the height and radius of curvature of the particles. We envision that this methodology is promising tool for precise control of particle shape in 3-dimensional space and new synthetic route for anisotropic particles with cost effective, simple, easy, and fast procedure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1473-1480
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• 1999

In the case of Impingement of plane moving shock wave over concave or convex double wedges (pseudo-stationary flow) and cylindrical walls (truly non-stationary flow), it Is expected that there are transitions from regular reflection to Mach reflection or vice versa In shock wave reflections. In these connections, it is necessary to verify the various of reflection process and transition angle for the reflection problems In double wedges, and to verify the transition angle, effects of curvature radius and initial wall angle on it for the reflection problems In cylindrical walls. Especially, we focused our attention to confirm the existence of hysteresis phenomenon induced by the different transition processes, and Neumann paradox, which is a small discrepancy between theoretical and experimental transition angles. Experiments were carried out by using the shock tube of $6{\times}6cm^2$, and high speed photographic technique consisted of delay unit, triggering system, light source of Xe lamp and so on was used for flow visualization.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2575-2580
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• 2013

An intake port for Range Extender engine has been developed using CFD technique. Three dimensional intake port model has been built and computational analysis has been performed. Computed non-dimensional flow coefficient, swirl ratio and swirl number have been compared with the experimental result. Convex and concave curvature of the intake port have been optimized to reduce recirculation flow and flow resistance. Finally, the mean flow coefficient is 0.383 and the mean swirl number is 1.544. The intake port shows relatively excellent performance compared with those of general 2 valve engine system intake ports.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.236-242
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• 2012

In general, such methods as interferometers or wavefront sensors are commonly used for testing of an optical system and optical components. In these cases, the surrounding environments are unlikely to affect the measurements. On the other hand, intraocular lenses of hydrophilic materials with special properties experience a certain difficulty in testing the optical properties. An intraocular lens is dried in the air, which causes deformation and changes the optical characteristics such as index of refraction and thickness. Thus, it is hard to measure the optical characteristics of an intraocular lens by using common methods. In this study, a special structure is used for measuring of the transmission wavefront aberration and effective focal length of an intraocular lens of hydrophilic materials by using a Shark-Hartmann sensor among the various measuring methods. As an application of this measuring method, this study shows a simple method to measure the index of refraction of unknown liquids with a plano-convex lens with a well known index of refraction. Also, this method is used to measure the optical properties of a plano-convex such as index of refraction and curvature by using a liquid with a well known index of refraction.