• Korean Journal of Materials Research
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• v.8 no.11
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• pp.1011-1019
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• 1998

This work designed Sn-5%Pb-1.5%Ag-x%In solder alloy to develop the solder alloy with low Pb content. This solder alloy doesn't cause environmental pollution. and this study reviewed the probability of replacement of Sn-37%Pb solder as evaluation of melting range, wettability. microstructure, microhardne'ss, tensile strength, drossability of this new solder alloys. The level of international regulation in dissolution amount of Pb ion was 3ppm. But dissolution amount of Pb ion in Sn-5%Pb solder alloy confirmed not to threat the global environmental is 0.46ppm. The melting range of this solder alloy was $183-192^{\circ}C$. Also the range of solidification was very narrow within $5^{\circ}C$. The wettability was similar to Sn-37%Pb solder, and the effect of amount of In addition of wettability couldn't be founded. The probability of replacement in the melting range and wettability is very high. And microhardness of this solder alloy was 1.5 times of conventional type solder. Tensile strength of new solder alloys was a little high than that of conventional type solder. With increasing amount of In% addition, tensile strength was increased, but elongation was decreased. The solder alloy of l%In addition revealed AgSn and Pb on dendrite microstructure boundary, and $Ag_3Sn$, $Ag_3In$ and Pb were revealed on it at the solder alloy of 3% In addition. The drossability was superior to Sn-37%Pb solder alloy and the solder alloys of 2% In addition was not generated for 3hrs.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.493-498
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• 2000

The effects of RRA treatment on the microstructures and mechanical properties of 7050 Al alloy were investigated by differential scanning calolimetry, transmission electron microscopy, microhardness measurement and electrical conductivity. The hardness of 2nd-step aged specimen at $175^{\circ}C$ was decreased to mimimum value and increased to a peak hardness, and then re-decreased with retrogression treatment. It was found that the hardness of 2nd-step aged specimen was further increased by 3rd step aging treatment($120^{\circ}C$x24h). The initial decrease in hardness during 2nd-step aging was due to the partial dissolution of pre-existing GP zone, the major precipitation hardening phase at T6 condition. It was confirmed that the major precipitation hardening phase at 3rd-step aging was GP zone and η' phase. The electrical conductivity increased continually through 2nd-step and 3rd-step aging treatment. It was conclude that the optium 2nd-step aging condition was at $175^{\circ}C$ for 50min by considering the hardness and electrical conductivity.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.5
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• pp.491-495
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• 1985

A series of growth experiment on the effect of phosphate addition to a common carp feed contatining a large amount of soybean meal were conducted at the Fish Culture Experiment Station of the National Fisheries University of Pusan from November 2, 1984 to February 3, 1985. Carp feed containing $40\%$ soybean meal performs very poorly but when supplemented with $2\%$ dibasic sodium phosphate the feed gave a very good performance almost similar to one of the best carp feed commercially available. In this 94 day experiment, phosphate added feed resulted in 1.431 in food coefficient, and 1.619 in daily growth rate for common carp of 73.3g in initial weight, and 1.558 and $1.589\%$ for those of 26.7g, respectively, compared to the performance of the feed without phosphate addition, which resulted in 1.863 in food coefficient and $1.365\%$ in daily growth rate for the large ones, and 1.820 and $1.438\%$ for the small ones, respectively, thus indicating that carp feeds containing a large amount of soybean meal could effectively be used if a proper amount of phosphorus is supplemented.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.117-123
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• 2000

In this study, to fabricate the semi-solid Al alloy, the 3phase-2poles electromagnetic stirring system was adopted. The changes of primary grain size, aspect ratio, standard deviation, hardness and the size morphology of eutectic Si with pouring temperatures and input voltages were investigated. At the same pouring temperature, with increasing input voltage, aspect ratio, standard deviation and primary grain size were decreased. The optimum condition for fabrication of semisolid Al alloys by EMS horizontal continuous casting process was determined that the input voltage was 220V and the pouring temperature was 68$0^{\circ}C$. At this optimum conditions the primary grain size was 54$\mu\textrm{m}$, the aspect ratio was 1.56 and the size of eutectic Si was 0.5$\mu\textrm{m}$. The micro-hardness of the Al alloy was 72.1 Hv. The semi-solid A356 Al alloy which has very low aspect ratio and standard deviation value could be fabricated by adopting the EMS horizontal continuous casting facility that was manufactured for this study.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.6
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• pp.561-567
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• 1987

The purpose of this study was to find out the removal capacity of harmful ammonia by different filter media in the submerged biological filters in a given space of chamber. Four materials, pile cloth, corrugated skylight roofing plate, embossed plastic plate, and gravel, were used as the experimental filter media. Each filter medium was placed in two aquariums, each aquarium measuring $90cm\times60cm\times60cm\;(depth)$. Under the normal operating condition, the average of mean ammonia removal rates during the first and second functioning periods by each filter material which occupied tile space in the filter chamber (aquarium) was as follows: 1. Pile cloth: $8.381\;g{\cdot}m^{-3}.\;day^{-1}$ 2. Corrugated skylight roofing plate: $7.834\;g{\cdot}m^{-3}.\;day^{-1}$ 3. Embossed plastic plate: $7.797\;g{\cdot}m^{-3}.\;day^{-1}$ 4. Gravel: $7.051\;g{\cdot}m^{-3}.\;day^{-1}$ Thus, there were no significant differences between the media, but at the time of practical application of these materials, some other factors such as investment cost, easiness for the removal of excess detritus accumulated in tile interstices of filter media, etc. should be fallen into consideration. When large units are required, in particular, removal of excess detritus from tile gravel bed is extremely difficult, and in case of pile cloth filters the installation work is much complicated and a problem in supporting the structure when drained also exists. In these respects, corrugated skylight roofing plate and embossed plastic plate seem to be more optimal, but again in practice the local situation for the availability and the price of the materials should be rechecked and the fitness of tile materials in the particular filter chambers under use or under consideration for construction must be taken into account.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.14 no.4
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• pp.233-238
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• 1981

A recirculating water system without filter bed was used for a high density experimental rearing of common carp, Cyprinus carpio, during the summer of 1981. Of the water system, 3 tanks were used for stocking each tank with 10,000, 20,000 and 30,000 common carp fingerlings which averaged 0.6 g. The water in the system was maintained in dark green colour by heavy growth of phytoplankton during the most period of the experiment. In this experiment, the best daily growth rate, $3.7\%$, was obtained from the 10,000 fish group followed by $2.8\%\;and\;3.0\%$ from the 20,000 and 30,000 fish groups respectively. Thus there was no significant difference between the latter two groups. Especially, notably high concentration of total ammonia, $5\sim7$ ppm ammonia-N, in the culture water appeared during the most experimental period, but this did not seem to have affected feeding and growth of the fish when the water was kept at heavy bloom. It was also obvious that the outbreak of columnaris disease was effectively depressed in this green water recirculating system compared to that in clarified recirculating system. One tank ($7m^2$) of this system was stocked with 446 common carp of intermediate size averaging 352.2 g and after 40 day rearing they grew to 486.3 g in average with a daily growth rate of $0.8\%$. This result was a little inferior to that reared in a tank of the clarified water system as control which showed $1.0\%$ daily growth rate. Therefore, before an initiation of the commercial production of fish in this method, further studies concerning the amount of ammonium with its effect on the fish under rearing in this system and the columnaris disease problem should be carried out.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.3 no.1
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• pp.65-70
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• 1970

This report is a part of the studies of the lower part of the Naktong River. The temperature and quality of the river water were investigated from May 1967 to June 1968. Except for Hadan which is a point located at the mouth of the river and much Influenced by sea water the average water temperature is generally below $10^{\circ}C$ up to the end of March, 10 to $20^{\circ}C$ from the beginning of April to the 1st-2nd ten days of May, and thereafter becomes above $20^{\circ}C$ which is adequate for the growth of warm-water fishes. The water again becomes below $20^{\circ}C$ at the beginning of October and becomes below $10^{\circ}C$ in December The difference of water temperature between at 7.00 a.m. and 4.00 p.m. is considerably great at Hadan, the mouth of the river, where the water is relatively stagnant. It shows an average monthly difference of 2.6 to $6.8^{\circ}C$ with a total average difference of $4.6^{\circ}C$. At the Kupo and Samrangjin stations the difference is very small For the basic data In the management of rivers, the water temperature should be measured twice a day at its highest and lowest temperatures, and the long term fluctuation of temperature should be investigated.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.19 no.6
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• pp.581-585
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• 1986

A growth experiment of the Israeli strain of common carp (Cyprinus carpio) under varying dissolved oxygen levels in the recirculating water system was conducted at the Fish Culture Experiment Station of the National Fisheries University of Pusan from August 28, 1985 to September 17, 1985. Five tanks with a capacity of $5m^3$ of water each were used under the same condition of water parameters except for dissolved oxygen levels which were designed to maintain at 2.0, 2.5, 3.0, 3.5 and 4.0 mg/l ranges. The weight of fish in the beginning was about 300g and each tank was stocked with 200kg of fish. DO level of 3.5mg/l was found to be the best level with a feed coefficient of 1.57 and a daily growth rate of $1.411\%$ whereas 4.mg/l showed a slightly decreased performance of 1.63 and $1.365\%$ respectively. The amounts of feed consumed in 3.5 and 4.0mg/l DO levels were almost the same. Below 3.0mg/l DO levels the growth rate markedly decreased. Furthermore, in 2.0 and 2.5 mg/l groups, the fish did not accept feed vigorously and after feeding the fish usually concentrated around the inflow point showing oxygen deficiency response, The experiment indicates that the DO range of 3.5 to 4.0mg/l is the optimum level for the best growth at $27.5^{\circ}C$. DO concentration above these levels is considered a waste of energy resulting in uneconomical performance, and on the other hand, below these levels, the carp certainly shows a poor growth performance.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.161-172
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• 2003

This study has evaluated the stream gauge network with the main emphasis on if the current stream gauge network can catch the runoff characteristics of the basin. As the evaluation of the stream gauge network in this study does not consider a special purpose of a stream gauge, nor the effect from a hydraulic structure, it becomes an optimization of current stream gauge network under the condition that each stream gauge measures the natural runoff volume. This study has been applied to the Nam-Han River Basin for the optimization of total 31 stream gauge stations using the entropy concept. Summarizing the results are as follows. (1) The unit hydrograph representing the basin response from rainfall can be transferred into a probability density function for the application of the entropy concept to optimize the stream gauge network. (2) Accurate derivation of unit hydrographs representing stream gauge sites was found the most important part for the evaluation of stream gauge network, which was assured in this research by comparing the measured and derived unit hydrographs. (3) The Nam-Han River Basin was found to need at least 28 stream gauge stations, which was derived by considering both the shape of the unit hydrograph and the runoff volume. If considering only the shape of the unit hydrograph, the number of stream gauges required decreases to 23.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.173-181
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• 2003

This study has evaluated the raingauge network of Nam-Han River Basin by assuming that the rainfall field is homogeneous in space and its spatial correlation structure is exponential. The results of the study was compared with the standard of WMO. Summarizing the results are as follows: (1) The Nam-Han River Basin is not the mountain area, nor the plain area of the WMO standard. However, the correlation length of the downstream part is longer than that of the upstream part, enough to differentiate the rainfall fields in both areas. (2) It seems that the standard for the evaluation of the raingauge network of Nam-Han River Basin should be decided to represent upper 50% of correlations derived, when the maximum intervals between neighboring gauges are estimated to be 18.2km for the upstream area and 21.1km for the downstream area. Simply evaluating the raingauge density, the Nam-Han River Basin has enough raingauges exceeding the WMO standard for the mountain area in the temperate region. (3) Evaluation of the spatial distribution of raingauges in the Nam-Han River Basin shows that its spatial distribution Is not in a proper level, especially when applying the WMO standard for the mountain area in the temperate region. However, when applying the new standard proposed in this study, only five to six more raingauges are required to be added.