• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.87.2-87.2
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• 2012

고출력 반도체 레이저 다이오드는 발진 파장 및 광 출력에 따라 다양한 분야에 응용되고 있으며, 특히 발진파장이 808 nm 및 1470 nm 인 고출력 레이저 다이오드의 경우 재료가공, 펌핑용 광원 (DPSSL, 광섬유 레이저), 의료, 피부미용 (점 제거), 레이저 다이오드 디스플레이 등 가장 다양한 응용분야를 가진 광원 중의 하나라고 할 수 있다. 일례로 재료가공의 경우, 레이저 용접, 레이저 인쇄, 하드디스크의 레이저 텍스쳐링 등 그 응용분야는 무수히 많으며, 최근에는 미래 성장동력 사업의 하나로 중요한 이슈가 되는 태양전지에서 에지 분리 (edge isolation), ID 마킹, 레이저 솔더링 등에서 필수불가결한 광원으로 각광받고 있다. 808 nm 대역 In(Ga)AlAs quantum dots laser diode (QDLD) 성장을 위하여 In(Ga)AlAs QD active 와 In(Ga)AlAs QD LD 성장으로 크게 분류하여 여러 가지 test 실험을 수행하였다. 우선 In(Ga)AlAs QD LD 성장에 앞서 high power LD에 적용 가능한 GaAs/AlGaAs quantum well의 성장 및 전기 측정을 수행하여 그 가능성을 보았다. In(Ga)AlAs QD active layer의 효과적인 실험 조건 조절을 위해 QD layer는 sequential mithod (ex. n x (InGaAlAs t sec + InAs t sec + As 10 sec)를 사용하였다. In(Ga)AlAs QD active layer는 성장 온도, 각 sequence 별 시간, 각 source 양, barrier 두께 조절 및 타입변형, Arsenic flux 등의 조건을 조절하여 실험하였다. 또한 위에서 선택된 몇 가지 active layer 를 이용하여 In(Ga)AlAs QD LD 성장 조건 변화를 시도하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.501-510
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• 2000

Recently, advanced signal analysis which is called "time-frequency analysis" has been used widely in nondestructive evaluation applications. Wavelet transform(WT) and Wigner Distribution are the most advanced techniques for processing signals with time-varying spectra. Wavelet analysis method is an attractive technique for evaluation of material characterization nondestructively. Wavelet transform is applied to the time-frequency analysis of ultrasonic echo waveform obtained by an ultrasonic pulse-echo technique. In this study, the feasibility of noise suppression of ultrasonic flaw signal and frequency-dependent ultrasonic group velocity and attenuation coefficient using wavelet analysis of ultrasonic echo waveform have been verified experimentally. The Gabor function is adopted the analyzing wavelet. The wavelet analysis shows that the variations of ultrasonic group velocity and attenuation coefficient due to the change of material characterization can be evaluated at each frequency. Furthermore, to assure the enhancement of detectability and naw sizing performance, both computer simulated results and experimental measurements using wavelet signal processing are used to demonstrate the effectiveness of the noise suppression of ultrasonic flaw signal obtained from austenitic stainless steel weld including EDM notch.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.110-116
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• 2005

It is very important to reduce the computational processing time for the application of the vision system in real time such as inspection, the determination of object's dimension and welding etc, because the vision system model involves a lot of measurement data acquired by CCD camera. Also, a lot of computation time is required in estimating the parameters in the vision system model if the iterative batch estimation method such as Newton Raphson is used. Thus, the effective computation method such as the Extended Kalman Filtering(EKF) is required to solve the above problems. The EKF has much advantages in that it takes explicitly into account the measurement uncertainties, and is a simple and efficient recursive procedures. Thus, this study is to develop the EKF algorithm to compute the parameters in the vision system model in real time. This vision system model involves the six parameters to account for the cameras inner and outer parameters. Also the EKF is applied to estimate the object's dimension. Finally, practicality of the estimation scheme of the vision system based on the EKF is verified experimently by performing the estimation of object's dimension.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.81-88
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• 2019

In this study, the effects of graphene oxide (GO) addition on electromigration (EM) lifetime of Sn-3.0Ag-0.5Cu Pb-free solder joint between a ball grid array (BGA) package and printed circuit board (PCB) were investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of package side finished with electroplated Ni/Au, while $Cu_6Sn_5$ IMC was formed at the interface of OSP-treated PCB side. Mean time to failure of solder joint without GO solder joint under $130^{\circ}C$ with a current density of $1.0{\times}10^3A/cm^2$ was 189.9 hrs and that with GO was 367.1 hrs. EM open failure was occurred at the interface of PCB side with smaller pad diameter than that of package side due to Cu consumption by electrons flow. Meanwhile, we observed that the added GO was distributed at the interface between $Cu_6Sn_5$ IMC and solder. Therefore, we assumed that EM reliability of solder joint with GO was superior to that of without GO by suppressing the Cu diffusion at current crowding regions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.907-913
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• 1994

The design of railroad bridges differs from road bridges because of the interface between track structure and bridge structure. The track generally consists of Continuous Welded Rail(CWR) which is fixed by fasteners to the sleepers embedded in the ballast. The ballast provides the interface between the track structure and the bridge structure. Large longitudinal forces can develop from the temperature variation in rail and bridge structure. These longitudinal forces are specially important for long bridges because the bridge layout for span length, pier dimensions and arrangement and type of bearings can be governed by these forces. This report provides a comparison of longitudinal track forces determined by analysis and actual measured track forces. In recent practice the longitudinal track force for European railways is analyzed using a finite element analysis method. This method is very time-consuming and requires the detail design of the bridge to be complete. Redesign is required if the design criteria for longitudinal track forces are not satisfied. There is a need to develop a simple analysis method considering the large number of bridge structures and a relatively short design time on the Korean High Speed Rail Project. The analysis results presented herein, based on a simplified analysis, show good agreement with those obtained by finite element analysis, as well as with those measured on an actual track. The proposed analysis method is particularly useful for the preliminary design of bridge structures.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.79-87
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• 1978

This is an experimental study on friction welding and heat treatment of engine exhaust valve materials whose welding combination is SCr4 as stem to 21-4N as head and SUH3 to 21-4N. In this study, not only the experiments of friction welding under the selected optimum welding condition and the examination of the mechanical properties were carried out, but also the heat treatment of friction welded specimens under the two selected conditions was taken to obtain the better welding character, eliminating the latent stress and the hardness peak which appeared at the welded zones of heat resisting steel(21-4N, SUH3) and low alloyed steel ($SCr_4$) friction weldments. The results obtained by the experiments and consideration in this study are as follows: I) It was experimentally proved quite reasonable that 'speed=3,OOO rpm, heating pressure Pl=8 kg/ mm2, upsetting pressure p, = 20 kg/mm', heating time $t_1$ = 3 see, upsetting time TEX>$t_2$ = 2.5 sec' was selected as the optimum welding condition for friction-welding the engine exhaust valve materials $SCr_4$ to 21-4 Nand SUH 3 to 21-4 N. 2) The results of the previous study and this one on friction welding of such dissimilar materials as SUH 3-SUH 31, SCr 4-SUH 31, SCr 4-SUH 3, SUH 3-CRK 22, SCr4-21-4 Nand SUH3-21-4 N agreed with each other substantially in the friction welding characteristics at welded interface zones. 3) It was also certified quite satisfactory that '600\ulcornerCX30 min. Xroom air cooling' as an optimum heat treatment condition of the friction welded materials SCr 4-21-4 Nand SUH 3-21-4 N was experimentally determined to eliminate the latent stress and the hardness peak at welded zones. 4) About 20% of the tensile strength before heat treatment of friction welded specimens was decreased after heat treatment 600\ulcornerCX30 min. Xair cooling, but the location of fracture was moved from heat affected zone to parent $SCr_4$ & SUH3. 5) Microscopic examination of the weld joints friction-welded and heat-treated under the above mentioned conditions revealed that the weld zone is very narrow and has a fine grained intermixed structure without any welding defects. 6) The above mentioned conditions can be also utilized as friction welding parameters of the other dissimiar materials for engine valve production.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.14-30
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• 1998

Manganese is an essential element in the body. It is mainly deposited in the liver and to a lesser degree in the basal ganglia of the brain and eliminated through the bile duct. Rapid turnover of managanese in the body makes it difficult to evaluate the manganese exposure in workers, esecially in those with irregular or intermittent exposure, like welders. Therefore, conventional biomarkers, including blood and urine manganese can provide only a limited information about the long-tern or cumulative exposure to manganese. Introduction of magnetic resonance imaging (MRI) made a progress in the assessment of manganese exposure in the medical conditions related to manganese accumulation, e. g. hepatic failure and long-term total parenteral nutrition. Manganese shortens spin-lattice(T1) relaxation time on MRI due to its paramagnetic property, resulting in high signal intensity (HSI) on T1-weighted image(T1W1) of MRI. Manganese deposition in the brain, therefore, can be visualizedas an HSI in the globus pallidus, the substantia nigra, the putamen and the pituitary. clinical and epidemiologic studies regarding the MRI findings in the cases of occupational and non-occupational manganese exposure were reviewed. relationships between HSI on T1W1 of MRI and age, gender, occupational manganese exposure, and neurological dysfunction were analysed. Relationships betwen biological exposure indices and HSI on MRE werealso reviewed. Literatures were reviewed to establish the relationships between HSI, Manganese deposition in the brain, pathologic findings, and neurological dysfunction. HSI on T1W1 of MRI reflects regional manganese deposition in the brain. This relationship enables an estimation of regional manganese deposition in the brain by analysing MR signal intensity. Manganese deposition in the brain can induce a neuronal loss in the basal ganglia but functional abnormality is supposed to be related to the cumulative exposure of manganese in the brain, use of brain MRI for the assessment of exposure in a group of workers seems to be hardly rationalized, while ti can be a useful adjunct for the evaluation of manganese exposure int he cases with suspected manganese-related health problems.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.685-698
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• 1995

This study was conducted to the effect of temporary cement on the adhesiveness of dentin bonding agent to dentin surface. One hundred freshly extracted bovine mandibular incisors were grinded to expose flat labial dentin surface. The dentin surfaces were temporarized with either eugenol-containing temporary cement(TemBond and Zinc Oxide Eugenol cement) or non-eugenol temporary cement(Nogenol and TempBond NE) for 7days, and then the temporarization was removed with surgical currette and the exposed dentin surfaces were water-rinsed. Bonding specimens were made by use of All-Bond 2 and Super-Bond C&B dentin bonding agent, and stored in $37^{\circ}C$ distilled water for 24hours. The tensile bond strenth and the cohesive failure rate were measured, and then the pretreated dentin surfaces which the temporary cement had been applied to and removed from and the fractured dentin surfaces after bonding test were examined under scanning electron microscope. The results were as follows : In case of bonding with All-Bond 2, tensile bond strength of each experimental group was lower than that of the control group(p<0.05), but there was no significant difference between the bond strengths of the control group and each experimental group in case of bonding with Super-Bond C&B(p>0.05). No significant difference between tensile bond strength of experimental group, whether temporary cement contains eugenol or not, was seen(p>0.05). In case of bonding with All-Bond 2, the control group showed cohesive-adhesive mixed failure mode and the experimental groups mainly showed adhesive failure mode, but in case of bonding with Super-Bond C&B, almost of the control and the experimental groups mainly showed cohesive failure mode. On SEM examination, all of the dentin specimens pretreated with either 10 % phosphoric acid or 10% citric acid after application of the temporary cements demonstrated remnants of temporary cement attached to dentin surface.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.48 no.3
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• pp.189-196
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• 2022

Plasma refers to an ionized gas that is often referred to as "the fourth phase of matter", following solid, liquid, and gas. Plasma has traditionally been utilized for industrial applications such as welding and neon signs, but its promise in biomedical fields such as cancer treatment and dermatology has lately been recognized. Indeed, due to its beneficial effects in promoting collagen production, improving skin tone, and eliminating harmful bacteria in the skin, plasma treatment constitutes an important target for dermatological research. In this study, a plasma device for cosmetic manufacturing based on nitrogen, the main component of the atmosphere, was designed and assembled. Moreover, nitric oxide (NO) was selected since is easier to follow and evaluate than other nitrogen plasma active species, and its contents were measured to perform a quantitative and qualitative evaluation of plasma. First, an injection method, using different proximities labeled "sinking" and "non sinking" treatments, was performed to test the most efficient plasma treatment method. As a result, it was observed that the formulation obtained by a non sinking treatment was more effective. Furthermore, toner and ampoule were selected as cosmetics formulations, and the characteristics of the formulation and changes in the injected plasma state were observed. In both formulations, the successful injection of NO plasma was 2 times higher in toner formulation than ampoule formulation, and it gradually decreased with time, having dissipated after a week. It was confirmed that the nitrogen plasma used did not affect the stability of the toner and ampoule formulations at low temperature (4 ℃), room temperature (25 ℃), and high temperature (37 ℃ and 50 ℃) conditions. The results of this study demonstrate the potential of plasma cosmetics and highlight the importance of securing the stability of the injected plasma.