• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1135-1140
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• 2012

Two-step metallization processes have been proposed to achieve high-efficiency silicon solar cells, where the front-side grids are formed by silver plating after the formation of a nickel seed layer with a mask. Because the conventional mask patterning process is performed by an expensive selective printing method using either UV resist or phase change ink, however, the combination of a simple coating and laser-selective ablation processes is proposed in this study as an alternative means. As a masking material, the solar cell wafer was coated with either inexpensive wax having a low melting temperature or a fluorocarbon solution, and then, an electrode image was patterned by selectively removing the masking material using the laser. It was found that the fluorocarbon coating was not only superior to the wax coating in terms of pattern uniformity but it also increased the efficiency of the solar cell by 0.16%, as confirmed by statistical f and t tests.

• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.374-378
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• 1991

The electrochemical reduction behavior of Bilirubin (BR) in phosphate buffer (pH 7.8) solution was studied by DC polarography, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. In DC polarogram, two reduction waves of BR were found. The half wave potentials of two reduction waves were -1.32 and -1.51 volts vs. Ag/AaCl respectively. The current type of 1st reduction wave was diffusion-controlled and the 2$^{nd}$ reduction wave was diffusion current containing a little kinetic current. The electrochemical reduction process of BR at each reduction step was all irreversible. The prewave appeared at lower concentration than 3.4 ${\times}$ 10$^{-4}$M, this prewave was identified as adsorption prewave. And the number of electron transfered in reduction steps, n$_{app}$ was two for the 1st reduction step and one for the 2$^{nd}$ reduction step.

• Journal of Sensor Science and Technology
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• v.29 no.3
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• pp.187-193
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• 2020

Ultraviolet (UV) sensors are widely applied in industrial and military fields such as environmental monitoring, medicine and astronomy. Zinc oxide (ZnO) is considered as one of the promising materials for UV sensors because of its ease of fabrication, wide bandgap (3.37 eV) and high chemical stability. In this study, we used the hydrothermal growth of ZnO to form two types of ZnO nanostructures (Nanoflower and nanorod) and applied them to a UV sensor. To improve the performance of the UV sensor, the hydrothermal growth was used in a two-step process for fabricating ZnO hierarchical nanostructures. The fabricated ZnO hierarchical nanostructure improved the performance of the UV sensor by increasing the ratio of volume to surface area and the number of nanojunctions compared to one-step hydrothermal grown ZnO nanostructure. The UV sensor based on the ZnO hierarchical nanostructure had a maximum photocurrent of 44 ㎂, which is approximately 3 times higher than that of a single nanostructure. The UV sensor fabrication method presented in this study is simple and based on the hydrothermal solution process, which is advantageous for large-area production and mass production; this provides scope for extensive research in the field of UV sensors.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.16 no.4
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• pp.225-237
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• 2016

In conventional transportation problem (TP), all the parameters are always certain. But, many of the real life situations in industry or organization, the parameters (supply, demand and cost) of the TP are not precise which are imprecise in nature in different factors like the market condition, variations in rates of diesel, traffic jams, weather in hilly areas, capacity of men and machine, long power cut, labourer's over time work, unexpected failures in machine, seasonal changes and many more. To counter these problems, depending on the nature of the parameters, the TP is classified into two categories namely type-2 and type-4 fuzzy transportation problems (FTPs) under uncertain environment and formulates the problem and utilizes the trapezoidal fuzzy number (TrFN) to solve the TP. The existing ranking procedure of Liou and Wang (1992) is used to transform the type-2 and type-4 FTPs into a crisp one so that the conventional method may be applied to solve the TP. Moreover, the solution procedure differs from TP to type-2 and type-4 FTPs in allocation step only. Therefore a simple and efficient method denoted by PSK (P. Senthil Kumar) method is proposed to obtain an optimal solution in terms of TrFNs. From this fuzzy solution, the decision maker (DM) can decide the level of acceptance for the transportation cost or profit. Thus, the major applications of fuzzy set theory are widely used in areas such as inventory control, communication network, aggregate planning, employment scheduling, and personnel assignment and so on.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.688-696
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• 2004

Nonlinear dynamic behavior of diffusive-thermal instability in diluted CH$_4$/O$_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution, which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is net observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.95-101
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• 2004

Dynamic behavior of diffusive-thermal instability in diluted $CH_4/O_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate. transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed Oil the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution. which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is not observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• Journal of the Korean Operations Research and Management Science Society
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• v.30 no.1
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• pp.161-176
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• 2005

In a situation that ordinal preferences on multiattribute weights are captured, we present two solution approaches: an exact approach and an approximate method. The former, an exact solution approach via interaction with a decision-maker, pursues the progressive reduction of a set of non-dominated alternatives by narrowing down the feasible attribute weights region. Subsequent interactive questions and responses, however, sometimes may not guarantee the best alternative or a complete rank order of a set of alternatives that the decision-maker desires to have. Approximate solution approaches, on the other hand, can be divided into three categories including surrogate weights methods, dominance value-based decision rules, and three classical decision rules. Their efficacies are evaluated in terms of choice accuracy via a simulation analysis. The simulation results indicate that a proposed hybrid approach, intended to combine an exact solution approach through interaction and a dominance value-based approach, is recommendable for aiding a decision making in a case that a final choice is seldom made at single step under attribute weights that are imprecisely specified beyond ordinal descriptions.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.5
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• pp.395-401
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• 2018

Recently, most of mobile devices are equipped with GNSS (Global Navigation Satellite System). When the GNSS signal is available, it is easy to obtain position information. However, GNSS is not suitable solution for indoor localization, since the signals are normally not reachable inside buildings. A wide varieties of technology have been developed as a solution for indoor localization such as Wi-Fi, beacons, and inertial sensor. With the increased sensor combinations in mobile devices, mobile devices also became feasible to provide a solution, which based on PDR (Pedestrian Dead Reckoning) method. In this study, we utilized the combination of three sensors equipped in mobile devices including accelerometer, digital compass, and gyroscope and applied three representative PDR methods. The proposed methods are done in three stages; step detection, step length estimation, and heading determination and the final indoor localization result was evaluated with terrestrial LiDAR (Light Detection And Ranging) data obtained in the same test site. By using terrestrial LiDAR data as reference ground truth for PDR in two differently designed experiments, the inaccuracy of PDR methods that could not be found by existing evaluation method could be revealed. The firstexperiment included extreme direction change and combined with similar pace size. Second experiment included smooth direction change and irregular step length. In using existing evaluation method which only checks traveled distance, The results of two experiments showed the mean percentage error of traveled distance estimation resulted from three different algorithms ranging from 0.028 % to 2.825% in the first experiment and 0.035% to 2.282% in second experiment, which makes it to be seen accurately estimated. However, by using the evaluation method utilizing terrestrial LiDAR data, the performance of PDR methods emerged to be inaccurate. In the firstexperiment, the RMSEs (Root Mean Square Errors) of x direction and y direction were 0.48 m and 0.41 m with combination of the best available algorithm. However, the RMSEs of x direction and y direction were 1.29 m and 3.13 m in the second experiment. The new evaluation result reveals that the PDR methods were not effective enough to find out exact pedestrian position information opposed to the result from existing evaluation method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.397-406
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• 1999

A new solution procedure for approximate reanalysis, using the staged hybrid methods with substructuring, is proposed in this study. Displacements are calculated with two step mixed procedures. First step is to introduce the conservative approximation, which is a hybrid form of the linear and reciprocal approximation, as local approximation. In the next step, it is combined with the global approximation by reduced basis approach. Stresses are evaluated from the displacements by matrix transformation. The quality of reanalyzed quantities can be greatly improved through these staged hybrid approximations, specially for large changes in the design. Overall procedures are based on substructuring scheme. Several numerical examples illustrate the validity and effectiveness of the proposed methods.

• Journal of the Korean Applied Science and Technology
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• v.17 no.3
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• pp.149-157
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• 2000

The synthesis of N-methyl glucamine was performed in two step reaction. The first step involves the amination between methylamine and glucose in methane. The N-methyl glucamine was obtained by the reduction of using Ni catalyst under the high pressure. The second step was glucamide anionic derivatives synthesis from N-methyl glucamine, maleic anhydride, lauryl alcohol and laurylamine by Schotten Banmann reaction respectively. Their molecular structures of N-methyl glucamine and glucamide (EG-MAS and AC-MAS) were investigated by IR and $^{1}H-NMR$. Basic physical properties and biodegradability of there glucamide anionic surfactant was investigated. The range of cmc values determined by measurements of surface tention was $10^{-5}{\sim}10^{-4}mol/l$ and the surface tension of the aqueous solution revealed in the range $28{\sim}30$ dyne/cm and their biodegradability was very good in the pH $5{\sim}10$.