• Journal of Advanced Marine Engineering and Technology
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• v.30 no.5
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• pp.636-644
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• 2006

Recently, there were some successful examples that the laser welding was introduced into production line. However, the spread of laser welding is not sufficient in many industries. There are several reasons why it is difficult to penetrate the laser welding into production lines. Because it is different from reflection, absorption and permeation of laser beam according to material and surface condition. Moreover, there are significant problems in processing such as absorption and scattering of beam by the induced plasma or plume. Therefore, understanding of mechanism on formation of weld defect in laser welding of the laminated core for motor is very important. In this paper, it was analyzed in terms of materials which was source of defect in laser welding and conventional arc welding. As a results of analysis, insulation coating film of the laminated core was judged to main factor of weld defect. it could be well aware as tracing carbon volume, and it was deduced that weld defect by insulation coating film was caused by difference of mechanism between the two heat sources.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.710-719
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• 1996

Laser applied combustion diagnostic techniques-laser induced fluorescence (LIF) and coherent anti-Stokes Ramann spectroscopy (CARS)-are demonstrated. The profiles of hydroxyl radical (OH) and temperature in the counterflow burner are measured and compared with the numerical results. OH radical is excited on the Q$_1$(6) line of the $A^2$$\sum^+$$\leftarrow$$X^2{\prod}$(1, 0) band transition (281.1 nm) and LIF signal is measured at the the bands of (0, 0) and (1, 1) transition (306~326 nm). Absolute OH radical is obtained by using the laser absorption technique. The quenching effects are considered. Temperature is measured using broadband CARS system. Two dimensional OH radical profile is also obtained. The profiles of OH radical and temperature are found to agree well with those of numerical calculation.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.6
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• pp.309-313
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• 2002

In this paper, we have studied minimization of the kerf-width and surface burning, which occurred after the conventional singulation process of the multi-layer BGA board with copper, polyethylene and epoxy glass fiber. The high thermal energy of a pulsed Nd:YAG laser is used to cut the multi-layer board. The most considerable matter in the laser cutting of the multi-layer BGA boards is their different absorption coefficient to the laser beam and their different heat conductivity. The cut mechanism of a multi-layer BGA board using a 2$^{nd}$ harmonic Nd:YAG laser is the thermal vaporization by high temperature rise based on the Gaussian profile and copper melting point. In this experiment, we found that the sacrifice layer and Na blowing are effective in minimizing the surface burning by the reaction between oxygen in the air and the laser beam. In addition, N2 blowing reduces laser energy loss by debris and suppresses surface oxidation. Also, the beam incidence on the epoxy layer compared to polyimide was much more suitable to reduce damage to polyimide with copper wire for the multi layer BGA singulation. When the polyester double-sided tape is used as a sacrifice layer, surface carbonization becomes less. The SEM, non-contact 3D inspector and high-resolution microscope are used to measure cut line-width and surface morphology.

• Journal of Sensor Science and Technology
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• v.16 no.5
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• pp.349-354
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• 2007

This paper presents characteristics of surface acoustic wave (SAW) gas sensor for detecting volatile gases such as ethanol gas by measuring the phase shift of output signal. A delay-line with a center frequency of 400 MHz was fabricated on $128^{\circ}$ Y-Z $LiNbO_{3}$ substrates. Experimental results, which showed the phase change of the output signal under the absorption of volatile gas on sensor surface, were presented. The sensitivities of SAW delay lines coated with polyurethane films were greatly increased compared to those for uncoated devices. This SAW gas sensor system may be well suited for a high sensitivity electronic nose system.

• Journal of the Korean Society of Costume
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• v.57 no.8
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• pp.24-36
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• 2007

This study was performed for 235 caddies of 5 membership golf clubs in Jeonnam area to find out their attitude and usage, satisfaction and preference on uniforms $1^{st}\;to\;15^{th}$ February 2007. The result of the study could be summarized as fellows. First, 69.7% of them affirm in the inquiry of 'to feel belong' and 'to tell from others', but they showed low affirmation in other inquiries. In the case of satisfaction of wearing uniforms, they show low satisfaction in most categories such as design, color, materials, activity, and symbol. Second, the most favored color coordination is the two color coordination in the upper and bottom uniform, and the fevered design pattern is the no-pattern one with single color. The favored uniform constitutes a jacket and a trouser in spring through fall, and a parka long enough to hip line, a polo neck, a vest, and a trouser in winter Third, activity is the most important considering factor in the choice of uniform and is also the most improve-wanted factor in the presently wearing uniform. The most important factor in the characteristic of material is absorption of sweat, but there is especially high dissatisfaction in absorption. It shows that there are demands of functional design considering caddies' working environment and activities. Differentiated from other normal uniforms, the uniform should be improved for caddies to develop their specialty and to feel wearing satisfaction.

• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.187-193
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• 2014

Recent cosmological observations indicate that the reionized universe may have started at around z = 6, where a significant suppression around $Ly{\alpha}$ has been observed from the neutral intergalactic medium. The associated neutral hydrogen column density is expected to exceed $10^{21}cm^{-2}$, where it is very important to use the accurate scattering cross section known as the Kramers-Heisenberg formula that is obtained from the fully quantum mechanical time-dependent second order perturbation theory. We present the Kramers-Heisenberg formula and compare it with the formula introduced in a heuristic way by Peebles (1993) considering the hydrogen atom as a two-level atom, from which we find a deviation by a factor of two in the red wing region far from the line center. Adopting a representative set of cosmological parameters, we compute the Gunn-Peterson optical depths and absorption profiles. Our results are quantitatively compared with previous work by Madau & Rees (2000), who adopted the Peebles approximation in their radiative transfer problems. We find deviations up to 5 per cent in the Gunn-Peterson transmission coefficient for an accelerated expanding universe in the red off-resonance wing part with the rest wavelength ${\Delta}{\lambda}{\sim}10{\AA}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.364-364
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• 2007

This paper presents characteristics of surface acoustic wave (SAW) gas sensor for detecting volatile gases such as ethanol gas by measuring phase shift of output signal. A delay-line with a center frequency of 400MHz was fabricated on 128o Y-Z $LiNbO_3$ substrates. Experimental results, which show the phase change of output signal under the absorption of volatile gas on sensor surface, were presented. The sensitivities of SAW delay lines coated with polyurethane films are greatly increased compared to those for uncoated devices. This SAW gas sensor system may be well suited for a high sensitivity electronic nose system.

• Progress in Superconductivity
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• v.14 no.2
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• pp.99-101
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• 2012

Fluorescent yield X-ray absorption fine structure (XAFS) spectroscopy is useful for analyzing local structure of specific elements in matrices. We developed an XAFS apparatus with a 100-pixel superconducting tunnel junction (STJ) detector array with a high sensitivity and a high resolution for light-element dopants in wide-gap semiconductors. An STJ detector has a pixel size of $100{\mu}m$ square, and an asymmetric layer structure of Nb(300 nm)-Al(70 nm)/AlOx/Al(70 nm)-Nb(50 nm). The 100-pixel STJ array has an effective area of $1mm^2$. The XAFS apparatus with the STJ array detector was installed in BL-11A of High Energy Accelerator Research Organization, Photon Factory (KEK PF). Fluorescent X-ray spectrum for boron nitride showed that the average energy resolution of the 100-pixels is 12 eV in full width half maximum for the N-K line, and The C-K and N-K lines are separated without peak tail overlap. We analyzed the N dopant atoms implanted into 4H-SiC substrates at a dose of 300 ppm in a 200 nm-thick surface layer. From a comparison between measured X-ray Absorption Near Edge Structure (XANES) spectra and ab initio FEFF calculations, it has been revealed that the N atoms substitute for the C site of the SiC lattice.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.164-175
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• 2009

CFD is used to analyze gas flow characteristics, power absorption, electron temperature, electron density and chemical species profile of an internal antenna type inductively coupled plasma system. An optimized grid generation technology is used for a complex real-scale models for industry. A bare metal antenna shows concentrated power absorption around rf a feeding line. Skin depth of power absorption for a system is modeled to 50 mm, which is reported 53 mm by experiments. For an application of bipolar plates for hydrogen fuel cells, multi-sheet loading ICP nitriding system is proposed using an internal ICP antenna. It shows higher atomic nitrogen density than reported simple pulsed dc nitriding systems. Minimum gap between sheets for uniform nitriding is modeled to be 39 mm.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.56-60
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• 2005

We studied fire properties of MOF(Metering Out Fit) insulation cover and field condition of 22.9kV power receiving system. $49.5\%$ of formal equipments were installed indoors, whereas $40.8\%$ of informal equipments were installed as H-type. Insulation treatment was not done at a $22.4\%$ ratio of main line($27.7\%$ of transformer, $70.2\%$ of COS, $10.4\%$ of MOF). Fire pattern analysis showed that the fire started at the secondary part of OC wire. In the result of DTA(Differential Thermal Analysis), normal cover showed exothermic reactions at $310^{\circ}C,\;399^{\circ}C\;and\;510^{\circ}C$ (endothermic reactions at $382^{\circ}C$). Whereas damaged cover showed exothermic reactions at $412^{\circ}C$(endothermic reactions at $389^{\circ}C$). In the result of TGA(Thermo Gravimetric Analysis), the thermal weight change of normal cover was similar compared to damaged cover. In the result of FT-IR analysis, normal cover showed absorption peaks at $3,024cm^{-l},\;2,921cm^{-l},\;1,600cm^{-1},\;1,492cm^{-1},\;1,451cm^{-1},\;1,154cm^{-l},\;1,027cm^{-1},\;906cm^{-1}$. Whereas, in case of tracked cover, the absorption peaks that were shown in normal cover disappeared and different absorption peak was shown at $966cm^{-1}$.