• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.81-84
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• 2005

We suggest flux quantum-based mechanism for force realization in the sub-pico-Newton range. By controlling the number of flux quantum in a superconducting ring, a force can be created as an integer multiple of a constant force step. For a 50 nm-thick Nb ring with the inner and outer radii of $5{\mu}m\;and\;10{\mu}m$, respectively, the force step is estimated to be 165 fN, assuming the magnetic field gradient of 10 T/m. We also estimated a maximum force limit to be $1\sim2$ pN.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• Current Optics and Photonics
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• v.2 no.3
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• pp.233-240
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• 2018

We proposed a two-mode fiber (TMF) design that can effectively reduce the mode overlap between $LP_{01}$ and $LP_{11}$ modes by using a W-shaped index profile core structure, which is a primary concern in uncoupled mode division multiplexing (MDM). TMF has a three-layered core structure; central circular core, inner cladding, and outer ring core. We confirmed that in an optimal structure the $LP_{01}$ mode was highly confined to the central core while the $LP_{11}$ mode was guided along the outer ring core to result in a minimum overlap integral. We used a full-vectorial finite element method to estimate effective index, differential group delay (DGD), confinement loss, chromatic dispersion, and mode overlap controlling the parameters of the W-shaped structure. The optimized W-profile fiber provided optical characteristics within the ITU-T recommended standards over the entire C+L band.

• Journal of the Korean Wood Science and Technology
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• v.44 no.4
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• pp.607-615
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• 2016

The delamination along the annual ring on the cross-section of laminae and the bonding strength according to the tangential angle between laminae were evaluated for the production of 3-ply cross-laminated timber (CLT) using domestic larch. Since there is no standard for CLT in Korea, the production and test of specimens for bonding strength followed the standard procedure of "Structural glued laminated timber" (KS F 3021). The standard specifies to exclude any measurement from the cracks of timbers resulted from drying or knots during delamination test of the glued laminated timbers. However, the failure of cross-sectional tissues along the annual rings was observed near the glue-line of all specimens during the delamination test. Because this phenomenon can generate defects in the CLT that may be exposed to various temperatures and relative humidities after the actual construction, the delamination percentage was measured by including this wood failure. As a result, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed inward was the lowest, which was around 13%, regardless of the annual ring direction of the middle lamina. On the other hand, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed outward was the highest, which was around 26%. Furthermore, end-split occurred in the outer lamina during the drying process of the boiling delamination test, which affected the delamination percentage. Therefore, the soaking delamination test was found to be more appropriate for evaluating the delamination strength of CLT. The block shear strength of larch CLT was $3.9{\pm}0.9$ MPa on average, which was 46% lower than the block shear strength requirement (7.1 MPa) of the standard, but satisfied the criteria of the block shear strength (3.5 MPa) of the European Standard (prEN 16351: 2013).

• Transactions of Materials Processing
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• v.27 no.1
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• pp.37-47
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• 2018

In this paper, a double spot welding process, utilizing electric resistance heating dies, is suggested for the spot welding of dissimilar metal plates for drawing and concurrent spot welding. This double welding process has two heating methods for the fusion welding at the interfacial zone between steel and aluminum plates, such as heating method by thermal conduction of electric resistance by welding current induced to heating dies, and heating method by electric resistance between contacted surfaces of two plates by welding current induced to copper electrode. This double welding process has welding variables such as each current induced in heating dies and in copper electrode, outer diameters of heating dies, and edge shape of copper electrode. Experiments for current conditions in welding process should be demanded in order to get successful welding strength. It was known that the welding strength could be reached to the value demanded on industry fields under such welding conditions as heating dies of outer ring dia.12mm contacted on steel plate, as heating dies of outer ring dia. 14mm contacted on aluminum plate, and as copper electrode of dia. 6.0mm, and as 3 times continuous heating method by $1^{st}$ current of 11 kA(9cycle), $2^{nd}$ current 11 kA(60cycle), $3^{rd}$ current 7 kA(60cycle) applied in steel heating dies and copper electrodes, flat edge of copper electrode, for double spot welding process of dissimilar metal plates of steel and aluminum of 1.0 mm thickness.

• Korean Security Journal
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• no.58
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• pp.177-194
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• 2019

Last year, the Moon Jae-In administration made an attempt to abolish the presidential security office overseeing the presidential security and to transfer the work to the presidential security service under the National Police Agency. Currently, all of the G7 nations maintain a security system spearheaded by the police, so the policy of transferring the presidential security to the National Police Agency may be discussed. However, it is necessary to focus on the following reality. First, the current presidential security system is consisted of the overlapping security organizations classified into (1) inner ring of the presidential security agency, (2) middle ring of the police agency, and (3) outer ring of the capital defense command. If the presidential security agency is abolished, a vacuum will result as per the principle of class. Second, for the efficient security guard of the President, currently, the presidential security agency at the Presidential Security Safety Measure Committee plays the role of coordinating the tasks. If the National Police Agency becomes the control tower of the presidential security, whether command will be available for the military and diplomatic aspects of the presidential security work should also be considered. Third, Korea is currently in a truce with North Korea, so there is a big difference in terms of the security environment with such G7 nations as the UK, Germany, France, and Japan.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.537-545
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• 2013

The elastic recovery of a metal seal is a factor that can be used to assess its sealing performance. In this study, a compliant mechanism topology optimization has been performed to find a structure of a metal O-ring seal that can maintain excellent sealing performance with a maximized elastic recovery over extended operation. An evolutionary structural optimization (ESO) was used as a topology optimization algorithm with two different types of objective functions considering both flexibility and stiffness. In particular, a circular design domain was adopted to consider the outer shape of the metal O-ring seal. The elastic recovery of the optimal topology was calculated and compared to that of a commercial product.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.342-346
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• 2006

A polymeric ring resonator with electrically variable extinction ratio at resonant wavelengths has been proposed and demonstrated. It consists of a ring waveguide coupled to a straight bus waveguide and a modulating electrode, which is formed in the outer cladding region outside of the ring. When electrical power is applied to the electrode, the refractive index of the polymers underneath the electrode is lowered to strengthen the confinement of the guided mode of the ring and thus the equivalent effective refractive index felt by the mode is decreased. Therefore, the propagation loss of the guided mode is reduced with the applied electrical power Consequently the extinction ratio at resonant wavelengths is varied by the electrical power. For the achieved results, the extinction ratio was changed by about 9 dB for the electrical power of 12 mW, when the propagation loss of the ring was reduced by 80 dB/cm.

• Journal of Astronomy and Space Sciences
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• v.34 no.1
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• pp.45-54
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• 2017

This study examines the scale unique instruments used for astronomical observation during the Joseon dynasty. The Small Simplified Armillary Sphere (小簡儀, So-ganui) and the Sun-and-Stars Time-Determining Instrument (日星定時儀, Ilseong-jeongsi-ui) are minimized astronomical instruments, which can be characterized, respectively, as an observational instrument and a clock, and were influenced by the Simplified Armilla (簡儀, Jianyi) of the Yuan dynasty. These two instruments were equipped with several rings, and the rings of one were similar both in size and in scale to those of the other. Using the classic method of drawing the scale on the circumference of a ring, we analyze the scales of the Small Simplified Armillary Sphere and the Sun-and-Stars Time-Determining Instrument. Like the scale feature of the Simplified Armilla, we find that these two instruments selected the specific circumference which can be drawn by two kinds of scales. If Joseon's astronomical instruments is applied by the dual scale drawing on one circumference, we suggest that 3.14 was used as the ratio of the circumference of circle, not 3 like China, when the ring's size was calculated in that time. From the size of Hundred-interval disk of the extant Simplified Sundial in Korea, we make a conclusion that the three rings' diameter of the Sun-and-Stars Time-Determining Instrument described in the Sejiong Sillok (世宗實錄, Veritable Records of the King Sejong) refers to that of the middle circle of every ring, not the outer circle. As analyzing the degree of 28 lunar lodges (lunar mansions) in the equator written by Chiljeongsan-naepyeon (七政算內篇, the Inner Volume of Calculation of the Motions of the Seven Celestial Determinants), we also obtain the result that the scale of the Celestial-circumference-degree in the Small Simplified Armillary Sphere was made with a scale error about 0.1 du in root mean square (RMS).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.475-485
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• 2010

This paper proposes a novel concept for a microstrip resonator that can function as a filter and as an antenna at the same time. The proposed structure consists of an outer ring, an open loop-type inner ring, a circular patch, and three ports. The frequencies where the proposed structure works as a filter and as an antenna, respectively, are determined primarily by the radius of the inner ring and the circular patch. The measured results show that, when the microstrip resonator operates as a filtering device, this filter has about 15.1 % bandwidth at the center frequency of 0.63 GHz and a minimum insertion loss of 1.5 dB within passband. There are three transmission zeros at 0.52 GHz, 1.14 GHz, and 2.22 GHz. In the upper stopband, cross coupling - taking place at the stub of the outer ring - and the open loop-type inner ring produce one transmission zero each. The circular patch generates the dual-mode property of the filter and another transmission zero, whose location can be easily adjusted by altering the size of the circular patch. The proposed structure works as an antenna at 2.7 GHz, showing a gain of 3.8 dBi. Compared to a conventional patch antenna, the proposed structure has a similar antenna gain. At the resonant frequencies of the filter and the antenna, high isolation(less than -25 dB) between the filter port and the antenna port can be obtained.