• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.285-293
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• 2001

To improve the vulnerable point and the mechanical property of the existing lightweight foamed concrete, this study was intend to manufacture the lightweight foamed concrete with wasted expanded poly-styrene, examinate and analyze the mechanical property of its. The experiment was being processed with mixing the wasted expanded poly-styrene maximum 40 % by stages and which was mainly basis on the practical mixture. The results of the experiment are following. The flow value is most affected by the mixtured rate of the wasted expanded poly-styrene. The more the mixtured ratio, the less the flow value and the more the more the unit quantity of cement and the W/C, the more the flow value. The apparent specific gravity indicated 0.31∼0.54 and which is seemed to be mainly included in the 0.4 degree and 0.5 degree that are regulated in the KS F 4039. The more the mixtured wasted poly-styrene ratio, the less the apparent specific gravity. The absorbing ratio which was depend on the mixture condition indicated 11 ∼46% and the more the mixtured ratio of the wasted expanded poly-styrene, the less the absorbing ratio remarkably. The compressive strength of the lightweight foamed concrete had a tendency to increase as the mixtured ratio of the wasted poly-styrene, the ratio quantity of cement and the apparent specific gravity increasing but as the ratio of bubble decreasing. The W/C affected little.

• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.9-15
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• 2022

In order to verify the durability of the high-pressure hydrogen tank in the operating pressure range, a hydraulic rupture test should be performed. However, if the bubbles generated by the initial injection process of water are attached to the inner wall of the tank and remain, a sudden pressure change of the bubbles during the rupture of the pressurized tank may cause shock and noise. Therefore, in this study, the flow velocity required to remove the bubbles remaining on the inner wall of the tank was predicted through simplified formulas, and the shape of the injection nozzle to maintain the flow velocity was determined based on the shape of the hydrogen tank for the hydrogen bus. In addition, a numerical model was developed to predict the change in flow velocity according to the inlet pressure, and an experiment was performed through a model tank to prove the validity of the prediction result. As a result of the experiment, the flow velocity near the tank wall was similar to the predicted value of the analysis model, and when the inlet pressure was 1.5 to 5.5 bar, the minimum size of the removable bubble was predicted to be about 2.2 to 4.6 mm.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.3
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• pp.205-211
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• 2011

On board comparison of pH and total alkalinity measurement in seawater was carried out during the JES expedition on R/V Roger Revelle in the East Sea using 550 real seawater samples from the surface to the bottom. Spectrophotometry and potentiometry without liquid junction were compared for pH measurement. The pH values of two methods are generally in a good agreement. Spectrophotometry with a pipette provides higher value compare with the potentiometry in the deep layer, where pH values are lower. However, spectrophotometry without a pipette shows same values with potentiometry within their precision range. The pipetting procedure may remove of $CO_2$ in the sample, which causes increase of pH. Potentiometric titration methods using a closed-cell and an open-cell were compared for the total alkalinity measurement. Values from open cell method are smaller by about 5~10 ${\mu}mol\;kg^{-1}$ than those from closed cell method. This may be caused by the bubble formed in the closed cell during the experiment. Although any analytical method compared in this study for the pH or TA measurement can be applied, special attentions should be paid for satisfactory results.

• Korean Journal of Agricultural Science
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• v.14 no.1
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• pp.81-97
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• 1987

Two nozzles with different size (Figure 2) were particularly designed to supply air through the swirl core into the central part of the liquid stream in the same parallel direction to produce a well-mixed air and water in the whirl chamber as spray liquid in bubble formation. Atomization was attempted to improve by using both the preliminary break-up process with less viscosity and less surface tension in the whirl chamber and the effects of increased frequency of the band of drops with the raised ambient air density in front of the nozzle orifice. The volumetric ratio between spray liquid and air on four levels was used to investigate the effects of air as a component of the mixture on atomization. The results of the experiment were summarized as follows; Droplet size became progressively finer as the operating pressure was increased in the range of $0.70kg/cm^2$ to $6.33kg/cm^2$, which was similar to the previous works. The new atomizing mechanism so-called 'air-center nozzle' gave a narrower range in droplet size distribution with smaller volumetric median diameter (VMD) than that of the existing spray system at a given pressure, which showed the possibility of improvement of atomization in a certain limit. The volumetric median diameter produced by the new atomizing mechanism was decreased from the central region toward the exterior edges across the spray pattern.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.278-285
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• 1991

The authors propose to use the slot system in order to improve of the efficiency for the cambered otter boards. The experiment is divided into 2 parts, one is the efficiency model test, and the other is the visualization model test. The hydrodynamic characteristics of the model otter boards were tested by efficiency model test to measure the shearing, drag force of the models and visualization test using hydrogen bubble method to observe the streak-line and time-line of flow around the models, and milk spout method to observe the separation zone in the wake behind the models. This study tested for 5 models such ad without slot, slot position 0.2C, 0.4C, 0.6C and 0.8C. The results obtained are as follows: \circled1 The maximum C sub(L) of model otter board with slot position 0.6C in attack angle 27$^{\circ}$ was the highest of all models, it's value was 1.59. \circled2 In general, the L/D ratio of the one slot otter boards were 16~28% higher than otter board without slot. \circled3 The slot position 0.6C was better than any other slot position, and it's conformed by visiualization. \circled4 As to the model otter board with slot position 0.6C, flow speed of the back side was faster 1.3 to 1.7 times than in the front side. \circled5 The size of the separated zone in case of the model otter board with 0.6C was smaller than that of any other models.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.740-754
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• 2009

Sound in the ocean is scattered by inhomogeneities of many different kinds, such as the sea surface, the sea bottom, or the randomly distributed bubble layer and school of fish. The total sum of the scattered signals from these scatterers is called reverberation. In order to simulate the reverberation signal precisely, combination of a propagation model with proper scattering models, corresponding to each scattering mechanism, is required. In this article, we develop a reverberation model based on the ray theory easily combined with the existing scattering models. Developed reverberation model uses (1) Chapman-Harris empirical formula and APL-UW model/SSA model for the sea surface scattering. For the sea bottom scattering, it uses (2) Lambert's law and APL-UW model/SSA model. To verify our developed reverberation model, we compare our results with those in Ellis' article and 2006 reverberation workshop. This verified reverberation model SNURM is used to simulate reverberation signal for the neighboring seas of South Korea at mid frequency and the results from model are compared with experimental data in time domain. Through comparison between experiment data and model results, the features of reverberation signal dependent on environment of each sea is investigated and this analysis leads us to select an appropriate scattering function for each area of interest.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1
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• pp.10-18
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• 2009

A moving surface vessel generates a ship wake which contains a cloud of micro-bubbles with radii ranging between $8{\sim}200{\mu}m$. Such micro-bubbles can be detected by active sonar system for more than ten minutes depending on the size and speed of the surface vessel. In this paper, a reverberation model for the ship wake is presented. The developed model consists of the acoustic scattering model due to the distribution of the micro-bubbles and the kinematic model for the moving active sonar. The acoustic scattering model is based on the volume integration, where the volume scattering strengths are obtained from the spatial distribution of micro-bubbles. Since the directivity and look-direction of active sonar are important factors for moving active sonar, the kinematic model utilizes the Euler transformation to obtain the relative motion between the global and local coordinates. In order to verify the developed model, a series of sea experiment was executed in September 2007 to obtain the spatial-temporal distribution of a bubble cloud, and analyzed to be compared with the simulation results.

• Journal of the Korean Society of Radiology
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• v.13 no.2
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• pp.261-270
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• 2019

The separation permeation characteristics of $N_2-O_2$ gas in air at cell membrane model of skin which irradiated by high energy electron(linac 6 MeV) were investigated. The cell membrane model of skin used in this experiment was a sulfonated polydimethyl siloxane(PDMS) non-porous membrane. The pressure range of $N_2$ and $O_2$ gas were appeared from $1kg_f/cm^2$ to $6kg_f/cm^2$. In this experiment(temperature $36.5^{\circ}C$), the permeation change of $N_2$ and $O_2$ gas in non-porous membrane by non-irradiation were found to be $1.19{\times}10^{-4}-2.43{\times}10^{-4}$, $1.72{\times}10^{-4}-2.6{\times}10^{-4}cm^3(STP)/cm^2{\cdot}sec{\cdot}cmHg$, respectively. That of $N_2$ and $O_2$ gas in non-porous membrane by irradiation were found to be $0.19{\times}10^{-4}-0.56{\times}10^{-4}$, $0.41{\times}10^{-4}-0.76{\times}10^{-4}cm^3(STP)/cm^2{\cdot}sec{\cdot}cmHg$, respectively. The irradiated membrane was significantly decreased about 4-10 times than membrane which was not irradiated. And ideal separation factor of $N_2$ and $O_2$ gas by non-irradiation was found to be from 1.32 to 0.42 and that of $N_2$ and $O_2$ gas by irradiation was found to be from 0.237 to 0.125. The irradiated membrane was significantly decreased about 4-5 times than membrane which was not irradiated. When the operation change(cut) and pressure ratio(Pr) by non-irradiation were about 0, One was increased to the oxygen enrichment and the other was decreased to the oxygen enrichment. The irradiated membrane was significantly decreased about 4-19 times than membrane which was not irradiated. As the pressure of $N_2$ and $O_2$ gas was increased, the selectivity was decreased. As separation permeation characteristics of $N_2-O_2$ gas in cell membrane model of skin were abnormal, cell damages were appeared at cell.

• Journal of Periodontal and Implant Science
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• v.23 no.1
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• pp.97-108
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• 1993

One of the important initial events required for periodontal regeneration is the attachment and subsequent spreading of periodontal ligament cells on the root surface. The purposes of this study is to investigate the attachment and spreading pattern of human periodontal ligament cell on the surface of glass slides. After establishment of a cell line of the primary cell culture from the periodontal ligament of 1st premolar teeth which were extracted for the purpose of orthodontic treatment, author dispersed the cells at $5{\times}10^3\;cells/ml$ into the each 35mm culture petri-dish containing 2 glass slides. To observe the morphological changes of the cells which attached to the surfaces of glasses at every designed time schedule, author used the inverted phase contrast microscope and scanning electron microscope. During the whole experiment culture condition was at $37^{\circ}C$, 100% Humidity, 5% $CO_2$ gas incubator. The following results were obtained. Periodontal ligament cells showed spherical outline and started to attach to glass surface by basal sytoplasmic extension after 10min in culture. After 30min in culture, periodontal ligament cells were attached to glass surface by well - developed filopodia which protruded from the lamellipodia. The cell surface is covered with bubble-like structures and occasional microvillus can be seen with diffculty among these structures. After 1.5hr in culture, peridontal ligament cells shhowed radially well-spread cytoplasm and the nucleus was centered on its cytoplasm. Unspread central region of the cell was covered with numerous microvilli. The change of cell attachment and spreading pattern was manifest at 6hr in culture. At this time, periodontal ligament cell showed elongated outline and an oval-shaped nucleus. After 12hr in culture, periodontal ligament cells showed more stretched fibroblast-like appearance with polarity. Two long lamellipodia can be seen around the both terminal ends of cells. After 24hr in culture, periodontal ligament cells showed spindle shapes and an oval-shaped nucleus was slanted toward one side of the cell.

• Korean Journal of Environmental Agriculture
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• v.20 no.4
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• pp.203-210
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• 2001

In order to environmentally use wood chips manufactured from low valued forest resources by forest tendering, wood chips were used for the evaluation on chips characteristics, decomposition capability of organic wastes, and field experiment and determination of conditions for decomposer. Bioclusters manufactured by Cryptomeria japonica, commercially available wood chips in Japan, showed higher pore ratio, water reservation and water resistance, and higher cellulose content with lower hot water solubles than domestic wood chips. The useful size of wood chips for swine manure decomposition was 10 (length) ${\times}$ 5 (width) ${\times}$ 2 (thickness) mm, and cellulose contents and alkali solubles of Pinus densiflora and Populus tomentiglandulosa were similar to those of bioclusters. According to the decomposition ratio depending on wood species, it was ordered as Pinus densiflora > Pinus koraiensis > Cryptomeria japonica. The swine manure decomposition ratio depending on treatment hours by Pinus koraiensis was constant with the ratio of 15 to 16 g per hour by 1 kg of chip, indicating of daily swine decomposition amount of 390 kg by 1 ton of chips which was equal to the amount of daily swine manure production by 70 swines. Analyzing by long term used wood chips during 40 days treatment, the treated wood chips characteristically showed stable total nitrogen content, suitable pH, high accumulation of inorganic contents such as calcium, phosphorus, potassium and sodium, and no odor. During winter, the inner temperature of decomposer was kept at $43^{\circ}C$, but air bubble was occurred due to high pH and viscosity of swine manure. The most appropriate mixing ratio between wood chips and swine manure was 1 versus 2 or 3, and at more than ratio 1 versus 3, ammonia gas was caused because of anaerobic fermentation status by high moisture content of wood chips. The mixing interval of decomposer was 3 mins. per hour for the best swine decomposition.