• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1453-1458
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• 2009

This study is to apply the mechanical press joining method to join two kinds of sheet metals with circular holes by mechanical pressing instead of laser beam. Usage of the mechanical pressing avoids the thermal deformation of sheet metals which occurs inevitably in laser joining. A die design has been proposed to make the mechanical press joining applicable with finite element analysis. Five design factors related to the joining force have been selected and applied to the Taguchi method for optimization. Among five factors, 'Forming Depth' and 'Punch Corner Radius' have been revealed to be the most influential ones.

• Journal of the Korean Vacuum Society
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• v.4 no.S2
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• pp.148-155
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• 1995

(1) The metastable crystalline(MX) phases formed by ion mixing are classified into 5 types, i.e. the super-saturated solid solutions and the enlarged HCP-I phases reported earlier, and the newly observed FCC-I phases in hcp-based alloys, The FCC-ll and HCP-ll phases in bcc-based alloys. The growth kinetics of the MX phases is discussed. (2) The interfacial free energy in the multilayered films was found to play an important role in ion beam mixing(IM) induced amorphization. By adding sufficient interfaces, amorphous alloys were obtained even in the systems with rather positive heat of formation. (3) Gibbs free energy diagrams of some representative systems were constructed, by calculating the free energy curves of all the competing phases. Steady-state thermal annealing was conducted and the results confirmed the relevance of the constructed diagrams, which were inturn employed to interpret the MX phase formation as well as the glass forming ability upon IM in the binary metal systems.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.285-287
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• 2008

AAO(Anodic Aluminum Oxidation) method has been known that it is practically useful for the fabrication of nano-structures and makes it possible to fabricate the highly ordered nano masters on large surface and even on the 2.5 or 3D surface at low cost comparing to the expensive e-beam lithography or the conventional silicon processing. In this study, by using the multi-step anodizing and etching processes, highly ordered nano patterned master with concave shapes was fabricated. By varying the processing parameters, such as initial matter and chemical conditions; electrical and thermal conditions; time scheduling; and so on, the size and the pitch of the nano pattern can be controlled. Consequently, various alumina/aluminum nano structures can be easily available in any size and shape by optimized anodic oxidation in various aqueous acids. In order to replicate nano patterned master, the resulting good filled uniform nano molded structure through electro-forming process shows the validity of the fabricated nano pattern masters.

• Journal of the Korean institute of surface engineering
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• v.32 no.4
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• pp.531-537
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• 1999

A copper based leadframe was oxidized in brown-oxide forming solution, then the growth characteristics of brown oxide and the effect of brown-oxide formation on the adhesion strength of leadframe to epoxy molding compound (EMC) were studied by using sandwiched double cantilever beam (SDCB) specimens. The brown oxide is composed of fine acicular CuO, and its thickness increased up to ~150 nm within 2 minutes and saturated. Bare leadframe showed alomost no adhesion to EMC, while once the brown-oxide layer formed on the Surface of leadframe, the adhesion strength increased up to ~80 J/$\m^2$ within 2 minutes. Correlation between oxide thickness, $\delta$ and the adhesion strength in terms of interfacial fracture toughness, $G_{c}$ was linear. Considering the above results, we might conclude that the main adhesion mechanism of brown-oxide treated leadframe to EMC is mechanical interlocking, in which fine acicular CuO plays a major role.e.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.35.3-36
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• 2020

The Time Domain Field is one of the future GTO program fields of JWST(JWST/GTO TDS), surveying about 14' diameter field at the North Eliptical Pole(NEP) with NIRCam/NIRISS. As a part of the multi-wavelength study of the field, we have obtained SCUBA-2 850㎛ mapping which reaches a depth of σrms = 0.9mJy/beam and detect 93 sources at S/N > 3.5 ― which are expected to be highly star-forming (SFR>400M◉/yr) galaxies at z ≳ 1.5-4 and pinpoint the location at <0. " 1 accuracy of 68 sub-mm sources by identifying VLA 3GHz radio counterparts. In this talk, we will introduce the SCUBA-2 JWST/GTO TDS project and the newly discovered sub-mm sources in this field.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.323-335
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• 2022

The main idea of the framework is to seamlessly combine a reasonably accurate and fast surrogate model with the importance sampling strategy. Developing a surrogate model for predicting structures' dynamic responses is challenging because it involves high-dimensional inputs and outputs. For this purpose, a novel surrogate model based on cutting-edge deep learning architectures specialized for capturing temporal relationships within time-series data, namely Long-Short term memory layer and Transformer layer, is designed. After being properly trained, the surrogate model could be utilized in place of the finite element method to evaluate structures' responses without requiring any specialized software. On the other hand, the importance sampling is adopted to reduce the number of calculations required when computing the failure probability by drawing more relevant samples near critical areas. Thanks to the portability of the trained surrogate model, one can integrate the latter with the Importance sampling in a straightforward fashion, forming an efficient framework called TTIS, which represents double advantages: less number of calculations is needed, and the computational time of each calculation is significantly reduced. The proposed approach's applicability and efficiency are demonstrated through three examples with increasing complexity, involving a 1D beam, a 2D frame, and a 3D building structure. The results show that compared to the conventional Monte Carlo simulation, the proposed method can provide highly similar reliability results with a reduction of up to four orders of magnitudes in time complexity.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.35-45
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• 2013

The concrete-filled tube column has the excellent structural performance. But it is difficult to connect with column and beam because of closed section. It suggests that pipe should be produced by welding two sides together where two shapes are joined after a channel is pre-welded onto the three sides in order to form an internal diaphragm. The upper diaphragm of the connection used the horizontal plate and the lower diaphragm used the Vertical plate. This research performed 6 monotonic tension experiments describing the connection upside and downside in order to evaluate the structural capability of the offered connection. And the cyclic loading experiment was performed about 2 T-Type column to beam connections. As to the experimental result edge cutting geometry, there was no big effect. An increase in the number of holes of the plate ultimate strength was increased by 5% and The thickness of the plate increases, the maximum strength was increased by 4%. T-Type connections until it reaches the plastic moment showed a stable behavior.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.500-506
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• 1999

We designed and fabricated a bidirectional optical transceiver module for low cost access network. An integrated chip forming a pin-PD on an 1.3 urn FP-LD was assembled by flip-chip bonding on a Si optical bench, a single mode fiber with an angled end facet was aligned passively with the integrated chip on V-groove of Si-optical bench. Gaussian beam theory was applied to evaluate the coupling coefficients as a function of some parameters such as alignment distance, angle of fiber end facet, vertical alignment error. The theory is also used to search the bottle-neck between transmittance and receiving coupling efficiency in the bi-directional optical system. Tn this paper, we confirmed that reduction of coupling efficiency by the vertical alignment error between laser beam and fiber core axis can be compensated by controlling the fiber facet angle. In the fabrication of sub-module, a'||'&'||' we made such that the fiber facet have a corn shape with an angled facet only core part, the reflection of transmitted laser beam from the fiber facet could be minimized below -35 dE in alignment distance of 2: 30 /J.m. In the same condition, transmitted output power of -12.1 dEm and responsivity of 0.2. AIW were obtained.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.623-628
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• 2013

The retrodirective array antenna system is operated faster than existing techniques of beamforming due to its less complexity. Therefore, it is effective for beam tracking in the environment of fast vehicle. On the other hand, it also has difficulty in estimating AOA according to multipath environment or multiuser signals. To improve the certainty of estimating AOA), this article proposes hybrid digital retrodirective array antenna systme combined with MUSIC algorithm. In this paper, the digital retrodirective array antenna system is designed according to the number of antenna array by using only one digital PLL which finds angle of delayed phase. And we evaluate the performance of the digital retrodirective array antenna for the high speed tracking application. Performance is studied by simulink when the speed of mobile is 300km/h and the distance between transmitter and receiver is 100m and then we have to confirm the performance of the system in multi path environment. As a result, the mean of AOA (Angle Of Arrival) error is $4.2^{\circ}$ when SNR is 10dB and it is $1.3^{\circ}$ when SNR is 20dB. Consequently, the digital RDA shows very good performance for high speed tracking due to the simple calculation and realization.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.231-236
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• 2013

We investigated the optical design of a smart headlamp capable of producing various beam patterns through only on/off modulation of light sources. This was implemented by forming a continuous matrix of beams from discontinuous beam patterns by means of a multi-array LED optical system. As one such optical system, the multi-array LED system is a convenient and economical device for implementing beam patterns with the simple on/off modulation of the light sources. A single optical assembly module can be made by combining a multiple-LED array, optical system module, and electronic control with no need for any additional mechanical components. The present optical system was designed to include a secondary lens and a projection lens mounted at the front of each LED in the array to realize accurate lighting patterns as well as the required luminosity at a distance of 25 m in the forward direction. Finally, we identified and analyzed the patterns implemented by the designed optical system that produced satisfactory performance of high beams and adaptive driving beams (ADB).