• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.1
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• pp.41-46
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• 2011

The artificial aggregates (AAs) composing of 2 wastes, coal bottom ash and dredged soil (7 : 3, weight ratio) were fabricated as a function of red mud contents,0~30 wt% using direct sintering method at $1050{\sim}1250^{\circ}C$ for 10 min, and those physical properties were evaluated. Especially, in order to analyze the red mud addition effect on the bloating phenomenon of AAs manufactured, the specific gravity and water absorption were measured and studied linked with the microstructural observation results. The lightening of AAs was enhanced due to increased bloating with increasing temperature and red mud contents. The AAS sintered at $1050{\sim}1150^{\circ}C$ showed well-developed black-coring structure, but for the specimens containing red mud sintered over $1200^{\circ}C$ generated excessive liquid and gas caused by reduction of $Fe_2O_3$, thus the black-coring part was gradually burst open out of shell of AAs. Particularly, all specimens containing 30 wt% red mud was burst up when sintered over $1100^{\circ}C$. The AAs containing no red mud sintered at $1200^{\circ}C$ had a specific gravity of about 1.2 and those containing 20 wt% had below 1.0 which are characters of lightweight aggregate.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.149-157
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• 2017

As the amount of construction wastes increase, reuse of recycled materials is being considered in research areas. While there are many experimental investigations focusing on development of mortar and concrete using the recycled materials, the studies regarding the fiber-reinforced cement composites (FRCCs) using recycled materials are still limited. In this paper, an experimental attempt has been made to investigate the effect of recycled fine aggregates and fly ash on the mechanical properties of PVA FRCCs. The cement and natural sand were respectively replaced by fly ash and recycled fine aggregates at two content levels, 25% and 50%. Ten types of PVA FRCCs mixes were fabricated and tested to investigate the flexural, compressive and direct tensile behaviors. The test results show that flexural, compressive and direct tensile strength were decreased with increase in fly ash content at all ages. In particular, flexural, compressive and direct tensile strengths of specimens, containing 50% recycled fine aggregates and 50% fly ash, showed the lowest values. The modulus of elasticity of specimens showed similar trend to the 28-day compressive strength. Poisson's ratio was increased with increase in fly ash and recycled fine aggregates content.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.2
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• pp.207-217
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• 2016

Permeability can not be expressed as a function of porosity alone, it depends on the porosity, pore size and distribution, and tortuosity of pore channels in concrete. There has been considerable interest in the relationship between microstructure and transport in cementitious materials, however, it is very rare to deal with the theoretical study on gas permeability coefficient in connection with carbonation of concrete and the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. In this study, fundamental approach to compute gas permeability of (non)carbonated concrete is suggested. For several compositions of cement pastes, the gas permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. For carbonated concrete, reduced porosity was calculated and this was used for calculating the gas permeability coefficeint. As the result of calculation of gas permeability for carbonated concrete, carbonation leaded to the significant reduction of gas permeability coefficient and this was obvious for concrete with high w/c ratio. Meanwhile, the relationship between gas permeability and water permeability has a linear function for cement paste based on Klinkenberg effect, however, which is not effective for concrete. For the evidence of the modeling, YOON's test was accomplished and these results were compared to each other.

• The KIPS Transactions:PartA
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• v.15A no.1
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• pp.53-60
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• 2008

Streaming media has contributed to a significant amount of today's Internet Traffic. Like traditional web objects, rich media objects can benefit from proxy caching, but caching streaming media is more of challenging than caching simple web objects, because the streaming media have features such as huge size and high bandwidth. And to support various bandwidth requirements for the heterogeneous ubiquitous devices, a transcoding proxy is usually necessary to provide not only adapting multimedia streams to the client by transcoding, but also caching them for later use. The traditional proxy considers only a single version of the objects, whether they are to be cached or not. However the transcoding proxy has to evaluate the aggregate effect from caching multiple versions of the same object to determine an optimal set of cache objects. And recent researches about multimedia caching frequently store initial parts of videos on the proxy to reduce playback latency and archive better performance. Also lots of researches manage the contents with segments for efficient storage management. In this paper, we define the 9-events of transcoding proxy using 4-atomic events. According to these events, the transcoding proxy can define the next actions. Then, we also propose the segment-based caching policy for the transcoding proxy system. The performance results show that the proposing policy have a low delayed start time, high byte-hit ratio and less transcoding data.

• Journal of Korean Society of Forest Science
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• v.95 no.3
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• pp.342-349
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• 2006

The survey guideline of forest products statistics suggests a certain type of standard to aggregate production amount of each item such as dry bracken, raw dates, cracked nuts, It does not, however, give any information about transition ratios, which would apply to convert weights of fresh bracken into dry one, or cracked nuts into the non-cracked. This has been one of the main factors which would make the statistics unreliable. The purpose of this study is to examine the aggregation realities and to put forward some proposals to improve forest products statistics with transition ratios. Targets of this study are 10 forest products that are strongly related to the mentioned problems. With the calculated transition ratios and some assumptions the changing rate of the official statistics of 2004 production amounts ranged from -41% to 474% for the 10 subjects. The suggested figures for transitions are based only on one-year analysis results. Therefore more periods are required to improve the accuracy and the reliability, and this study would be a good starting point.

• Journal of Preventive Medicine and Public Health
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• v.33 no.2
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• pp.150-156
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• 2000

Objective : To analyze the factors affecting the participation rate in the health screening program of medical insurance. Method : We investigated the factors associated with the participation rate in the health screening program in Korea. Data were collected at the aggregate level from 145 employee health insurance societies and 227 self-employed health insurance societies from 1995 to 1997 Data were also collected at the individual level from four health insurance societies. This study hypothesized that the participation rate of the health screening program was related to 1) the characteristics of its members and the size of the health insurance society; 2) the specifications of the health screening program; 3) the venue of the health screening institution and the interests of individuals in the health screening program; and 4) the activities of the health insurance society. We used bivariate and multiple regression models to examine the factors on the participation rate of the health screening program. Results : First, in the case of dependents of on employee health insurance society, the ratio of dependents 40 years old and over, the average monthly contribution per household, the interest and satisfaction level of individuals in health screening, and the level of refunds for over-payment were all associated with the participation rate in the health screening program, accounting for 54.4% of the participation rate. Second, in case of those insured by the self-employed health insurance society, the interest and satisfaction level of individuals in health screening, the level of refunds for over-payment, and the performance level of on-the-spot health screening were statistically significant, accounting for 40.1% of the participation rate. Conclusion : The factors concerning the participation rate in the health screening program of medical insurance, in both a health insurance society and for individuals, were closely related to the age and gender of individuals and household contributions.

• International Journal of Highway Engineering
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• v.8 no.4 s.30
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• pp.135-143
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• 2006

This study evaluated the fatigue resistance characteristics of hot-mix recycled asphalt mixtures which were prepared by a new blending method. Since the binder of RAP shows higher viscosity without being rejuvenated in the ordinary recycled mixture, this new(modified) blending method was developed for obtaining more uniform level of binder viscosity in the recycled mixture. Cold-planned RAP was collected and mix design was performed using 15% RAP content for two virgin aggregate, gneiss and granite. Penetration grade of 60-80 asphalt was used in mixing recycled mixture together with a polymer modifier, LDPE. Indirect tensile fatigue tests were carried out to evaluate characteristics of fatigue resistance of performance of recycled asphalt mixtures. The recycled mixtures with LDPE 6% showed higher repeated loading fatigue life. Fatigue life ratio of new(N) mixing method mixtures was approximately 0.6-0.7 before aging and 0.8-1.0 after aging treatment of ordinary(O) mixing method mixture. This means the N mixture becomes stronger with aging process increase. If further aging is treated, N mixture may be showing stronger resistance than O mixture.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.2
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• pp.98-102
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• 2009

Various physical properties of soils were investigated in the areas where organic farming had been practiced widely, for upland fields. The investigations were also conducted in the nearby fields under conventional to find out the influence of organic farming on the physical properties of soils. The investigated properties involved bulk density, hardness, shearing resistance, friction resistance, sinking depth of small rectangular board, water stable aggregates and the depth of soil available to plants. By and large, the practice of organic farming tended to improve all of the physical properties soils, investigated in upland soils. However, in case of water stable soil aggregates in upland soils, the reverse was previous data; in those soils water stable soil aggregates were less under organic farming. It was suspected that this might be due to intensive application of the organic materials with high C/N ratio like wood chips and wood bark. The contents of OM, Av. P2O5, and Ex. cations were higher in organic farming than those of nearby fields under conventional, due to heavy organic matter application. From the results, It could be concluded that soils under organic farming were looser and softer than those under conventional as shown by lower bulk density and hardness, but that the effect of organic farming on water stable aggregates were low.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5636-5645
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• 2015

Physical characteristics of aggregates affect the workability and strength of mortar and concrete, which include their fineness ratio, particle size distribution and water absorption. The workability of construction materials decreases if the incorporated fine aggregates show improper size distribution of their particles. This study shows the particle size effect on the rheological behavior of mortar and provides basic information for evaluating its workability. A mini-slump flow test was adopted to evaluate the workability of mortar. In addition, its plastic viscosity and yield stress were measured using a rheometer for building materials. The sand samples were prepared by sieving river sand and sorting out with their particle sizes. As a result, it was observed that the fines less than 0.7 mm increases the yield stress and plastic viscosity of the mortar samples. If the fines are less than 0.34 mm, the water absorption of the fines dominates change on the workability.

• Journal of The Korean Astronomical Society
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• v.41 no.3
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• pp.65-76
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• 2008

We have investigated the optical properties of the global haze on Titan from spectra recorded between 7100 and $9200{\AA}$, where $CH_4$ absorption bands of various intensities occur. The Titan spectra were obtained on Feb. 23, 2005 (UT), near the times of the Cassini T3 flyby and Huygens probe, using an optical echelle spectrograph (BOES) on the 1.8-m telescope at Bohyunsan Observatory in Korea. In order to derive the optical properties of the haze as a function of altitude, we developed an inversion radiative-transfer program using an atmospheric model of Titan and laboratory $CH_4$ absorption coefficients available from the literature. The derived extinction coefficients of the haze increase toward the surface, and the coefficients at shorter wavelengths are greater than those at longer wavelengths for the 30 - 120 km altitude range, indicating that the Titanian haze becomes optically thin toward the longer wavelength range. Total optical depths of the haze are estimated to be 1.4 and 1.2 for the 7270 - $7360{\AA}$ and 8940 - $9150{\AA}$ ranges, respectively. Based on the Huygens/DISR data set, Tomasko et al. (2005) reported total optical depths of 2.5 - 3.5 at $8290{\AA}$, depending on the assumed fractal aggregate particle model. The total optical depths based on our results are smaller than those of Tomasko et al., but they partially overlap with their results if we consider a large uncertainty from possible variations of the $CH_4$ mixing ratio over Titan's disk. We also derived the single scattering albedo of the haze particles as a function of altitude: it is less than 0.5 at altitudes higher than ${\sim}150\;km$, and approaches 1.0 toward the surface. This behavior suggests that, at altitudes above ${\sim}150\;km$, the average particle radius is smaller than the wavelengths, whereas near the surface, it becomes comparable or greater.