• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.8
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• pp.34-42
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• 2001

The 1${\times}$2, 1${\times}$4 and 1${\times}$8 multimode interference(MMI) optical power splitters are fabricated by using $Ag^+-Na^+$ ion exchange on BK7 glass. Before fabricating the MMI optical power splitters, we find the refractive index of the channel waveguide and calculate the multimode section length and width. The multimode section lengths and widths are 887${\mu}m$, 1666${\mu}m$ and 1834${\mu}m$ and 40${\mu}m$, 80${\mu}m$ and 120${\mu}m$ for 1${\times}$2, 1${\times}$4 and 1${\times}$8 MMI optical power splitters respectively. The measured properties of the fabricated MMI optical power splitters show that the unbalance ratios of the 1${\times}$2, 1${\times}$4 and 1${\times}$8 MMI optical power splitters are 1.4[dB], 1.7[dB] and 2.0[dB] and the excess losses of those sre 0.96[dB], 2.26[dB] and 1.67[dB]. respectively.

• Journal of Biosystems Engineering
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• v.26 no.4
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• pp.323-330
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• 2001

The regular maintenance and repair status of major farm machinery such as power tiller, farm tractor, rice transplanter and combine harvester etc., were surveyed and analyzed for the full-time farmers in order to get basic information for promoting farm machinery productivity. The survey was carried out through 209 farmers from 9 provinces. The results of this study can be summarized as follows; 1. The regular maintenance of farm machinery was conducted at repair shop(49.5%) or dealer agency(12.0%), and also conducted by farmers at their house(34.9%). 2. For the status on the cleanness or exchange times of engine oil, fuel filter and air cleaner, most farmers conducted fewer times than the necessary times. And, 5.3%, 7.7%, and 2.9% of surveyed farmers experienced breakdowns due to the insufficient cleanness or exchange oil, fuel filer, and air cleaner, respectively. 3. Most farmers(76.1%) recognized the necessity of farm machinery training or education, and they preferred one week for the training period, simple or easy maintenance for the training level, agricultural technical center or farm machinery manufacturer for the training agency. 4. Complete recognition of operation manual and sufficient maintenance before-, during-, and after-operation for the farm machinery can minimize the breakdowns, enlarge the endurance prevent the safety accidents, and promote productivity of farm machinery. And, these can be accomplished by the thorough training or education for agricultural machinery.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.24-29
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• 2002

It was observed that exchange bias field was increased with smooth surface and better ${\gamma}$-FeMn formation. Sputtering conditions were varied for the control of the surface roughness and ${\gamma}$-FeMn formation. From the results of Cu deposition as underlayer, it was found that ${\gamma}$-FeMn formation was closely related with the thickness of underlayer. After heat treatment, exchange bias field was increased over three times. This improvement was likely that the crystallites of ${\gamma}$-FeMn were well formed. In Co/Cu/Co/FeMn spin valve structure, magnetoresistance was increased over 1.4 times through the heat treatment. This was due to the disappearance of Co/Cu intermixed dead layer and removal of defect, and this was examined by AES analysis.

• Journal of the Korean Home Economics Association
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• v.17 no.1
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• pp.22-28
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• 1979

The phyio-chemical properties of Ion exchange salt, crude salt, particaly refined salt, and Isoized salt were determined. The basic amount of salt used in cooking were standardized . Acceptabilities as to the taste and saltiness of food prepared with the standard amounts of various kinds of salt were compared. Whereupon, the following conclusion was obtained. 1) Crude salt showed 12.23 per cent water content, the highest among the kinds of salt examined, while particaly refined salt had 2.53% water content. Refined salt, Ion exchange salt, and Iodized salt showed 0.36%, and 0.28%, respectively. 2) Where the same amount of salt was dissolved in the same amount of water, crude salt and partialy refined salt were dissolved twice as Ion exchange salt of fine-grain form, refined salt, and Iodized salt. In actual cooking, Ion exchanges salt and refined salt are used only half as much as raw salt, and it can be said that the time required for dissolving salt is the same. 3) The comparison between content and weight of various kinds of salt showed that the weights of Ion exchange salt, Iodized salt, and refined salt were two times as heavy as crude salt and partialy refined condition of same content. 40 The threshold concentration of salt is the sensed degree of saltiness. Different concentrations were recorded for various for various kinds of salt, the threshold concentration of Ion exchanges salt showed the lowest degree of 0.05, while that of partialy refined salt was 0.09 equivalent to 1.8 times that of the former. 5) Experimental cooking involving various kinds of salt indicated that where salt was used accurately, soup, vegetables, kimchi, and soybean sauce which were prepared with Ion exchanges salt showed the best acceptability , but no statistical differences could be noted among sarious kinds of salt used in preparing those foods.

• Membrane Journal
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• v.20 no.3
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• pp.217-221
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• 2010

In order to overcome the drawback of proton exchange membrane fuel cells (PEMFCs), solid alkalime membrane fuel cells (SAMFCs) have been studied. In this report, we synthesized new sulfonated polybenzimidazole derivatives for SAMFCs. The polyimidazole derivatives were doped by KOH, and base-doped polybenzimidazoles showed high hydroxy ion conductivity and excellent mechanical properties. Especially, sPBI-co-PBI (75 : 25 for molar ratio of sulfonated and non-sulfonated moiety) showed good possibility for the anion exchange membrane. It has $2.98{\times}10^{-2}\;S/cm$ at $90^{\circ}C$ under 100% relative humidity.

• Membrane Journal
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• v.20 no.4
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• pp.335-341
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• 2010

This study focuses on the investigation of the anion exchange membrane through blending poly(ethylenimine) (PEI) and poly(vinyl alcohol) (PVA) varying the mixing ratio. To characterize the resulting membranes, the water content, contact angle, FT-IR, thermal gravimetric analysis, ion exchange capacity, ion conductivity and elastic modulus were measured. The PVA / PEI = 90 / 10 membrane showed the ion conductivity, $5.16{\times}10^{-2}S/cm$ and simultaneously the contact angle, $78.3^{\circ}$. According to TGA measurement, the resulting membranes seemed durable at room temperature. Through the modulus test, the mechanical properties increased with increasing PVA content and apparently the membranes looked very robust.

• Journal of The Korean Astronomical Society
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• v.10 no.1
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• pp.23-30
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• 1977

We have collected times of minimum light available in the literature for WZ Andromedae and analyzed the nature of the period variations. The O-C diagram of WZ And clearly shows that two abrupt changes near JD 2418000 and JD 2435000 are deduced by dp/p=$+4.24{\timesa}10^{-6}$ and dp/p=$-2.46{\times}10^{-6}$, respectively. For these period changes, we have introduced the equations which represent mass exchange in the close binery systems given by Biermann and Hall (1973), and the computation yieleled a mass flow of $7.42{\times}10^{-5}M$. from the hotter component to the cooler one. Due to the amount of mass flow, the period decrease may also be calculated. The theoritical new period after JD 2435000 became 0.69565858 days, which is in good agreement with the value 0.69566034 days found in the O-C diagram. In this computation, the mass ratio of WZ And suggested that the hotter star is the filling its Rochclooe, and thus WZ And is in Paczynski's stage II.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.21-24
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• 2008

Proton Exchange Membrane Fuel Cell (PEMFC) is an attractive candidate for residential power generator due to fast start-up and stop, high efficiency, low emission, and high power density. In this study, we employ short module stack to understand the performance of the unit cell of the stack in terms of operating temperatures. To simulate the practical fuel cell stack of residential power generator, the structure and active area of the short module stack is kept the same as that of the practical fuel cell. The results shows that the electric potential of short module stack is different from the number of cells times the potential of unit cell because of cell-to-cell variation.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1993.04a
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• pp.343-352
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• 1993

In this study, a modified algorithm for the exchange heuristic is developed and applied to a resource-constrained scheduling problem. The problem involves multiple projects and multiple resource categories and allows flexible resource allocation to each activity. The objective is to minimize the maximum completion time. The exchange heuristkc is a multiple pass algorithm which makes improvements upon a given initial feasible schedule. Four different modified algorithms are proposed. The original algorithm and the new algorithms were compared through an experimental investigation. All the proposed algorithms reduce the maximum completion time much more effectively than the original algorithm. Especially, one of four proposed algorithms obviously outperforms the other three algorithms. The algorithm of the best performance produces significantly shorter schedules than the original algorithm, though it requires up to three times more computation time. However, in most situations, a reduction in schedule length means a significant reduction in the total cost.

• Macromolecular Research
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• v.15 no.4
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• pp.379-384
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• 2007

Sulfonation of polyetheretherketones (PEEK) was carried out in order to fabricate commercial perfluorosulfonic acid membrane alternatives, which were characterized in terms of their ion exchange capacity, ionic conductivity, water swelling, methanol crossover and electrochemical performance in their direct application as a methanol fuel cell. A high ion exchange capacity, 1.88, was achieved with a sulfonation reaction time of 8 h, with a significantly low methanol crossover low compared to that of Nafion. However, the morphological stability was found to deteriorate for membranes with sulfonation reaction times exceeding 8 h. Electrochemical cell tests suggested that the fabrication parameters of the membrane electrode assembly based on the sulfonated PEEK membranes should be optimized with respect to the physicochemical properties of the newly prepared membranes.