• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.497-500
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• 2004

Recently, the use of structure compound waterproof agent (hereinafter referred to as 'SCWA') that is used when manufacturing concrete for concrete structures, increases in quantity. However, while it is expected that the SCWA that is mixed in the concrete inside can significantly affect the change of physical properties that lift the internal force of a structure. This study has been conducted through an experiment for the effects of cement hardener on the formation of microscopic texture, and newly generated hydrates from that result were not confirmed in the present experiment. It was found that at the hydrate reaction it has the property that can be hardened within the limit of pore diameterar a specific size rather than there is the internal gap filling capacity due to generating other hydrates.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.797-800
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• 2004

Some test results indicated that the current ASTM grip adapter of GFRP rebar was not successful in developing the design tensile strength of GFRP rebar with reasonable accuracy. It is because the current ASTM grip adapter of GFRP rebar does not take into account the various geometric characteristics of GFRP rebar such as surface treatment, shape of bar cross section, bar deformation as well as physical characteristics such as poisson effect, elastic modulus in the transverse direction and so on. The research reported in this paper is to provide how to proportion an adequate grip adapter to develop design tensile properties of GFRP rebar. The proposed grip adapter is derived from the equilibrium or compatibility equations. From the preliminary test results for rounded GFRP rebar, it was found that the grip adapter with specific size proportioned by proposed method shows the highest tensile strength among them.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.663-666
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• 2004

An analysis of the annual frequency of collapse(AF) is performed for each bridge pier exposed to ship collision. AF is computed for each bridge component and vessel classification. The summation of AFs computed over all of the vessel classification intervals for a specific component should equal the annual frequency of collapse of the component. The designer should use judgment in developing a distribution of the vessel frequency data based on discrete groupings or categories of vessel size by DWT. In the present study the effect of vessel classification on the annual frequency of collapse in the ship collision risk assessment is investigated by illustrative numerical examples based on the vessel frequency data of the domestic harbor. The DWT interval for larger vessels has more effect on the ship collision risk. Therefore the expert judgement in determining the larger DWT interval is required because the design impact lateral resistances of bridge components depend on the ship collision risk.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.595-602
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• 2004

In this study, the roughness of fracture surfaces in cementitious material has been characterized by roughness number (RN). A systematic experimental investigation was carried out to examine the dependency of fracture parameters on the aggregate sizes as well as the loading rates. Three aggregate sizes (0.1875 in, 0.5 in, and 0.75 in) and two loading rates (slow and fast loading rate) were used. A total of 52 compression tests and 53 tension tests were performed. All fracture parameters exhibited an increase, to varying degrees, when aggregates were added to the mortar matrix. The fracture surfaces of the specimens were digitized and analyzed. Fracture roughness was monotonically increased as maximum aggregate sizes increase.

• Journal of the Korean Institute of Educational Facilities
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• v.12 no.5
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• pp.35-46
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• 2005

It has been almost 20 years since Korea has started the research of school facilities, but there has not been any form of organized information or studies done about such a trend of the research. In this respect, this research places its focus on categorizing 44 policy studies initiated and proceeded by different organizations for last twenty years(1983-2004) and 186 volumes of the research about education facility plans and projects released by journal of Architectural Institute of Korea and journal of Korean Institute of Educational Facilities in 17 subjects of this study. It also concentrates on organizing data based on different levels of schools and periods of time as well as understanding the trend. The result of this research is followings. Considering every volume of the paper and the subjects that have previously been treated in those papers, the trend of this study is divided into the first stage of research period(1983-1993), the second stage of research period(1994-2001), and the third stage of research period(2002-present). Of all the papers, there has been the most number of papers objecting elementary schools(110 volumes, 56.1%), and most of them focused on space formation, size, and the present situation of utilization of each classroom in elementary schools. In the meantime, the studies about educational information, application of the media, space formation and size under teachers'consent, two-dimension types, a design of outdoor space(including gardens), the present situation of utilization, remodeling of school facilities, an evaluation of space and recognition-awareness analysis have been mainly done since 1995. Such a result mentioned above provides a sense of understanding about a level of studies about education facilities in our country, and as a basic source for future guidelines of studies and contents, in my personal opinion, it contains a high level of application.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.168-174
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• 2004

The aim of this study is to investigate the effect of process conditions on the microstructual changes and mechanical properties of large 7175 aluminum die forgings. The cast billets of 370 and 720 mm in diameter were homogenized and die forged after direct chill casting. The size and volume fraction of second phase particles in 720 mm billet were larger than those of 370 mm billet. The interdendritic sites containing the second phase particles was considered to be a crack initiation region in the process of cold upsetting. The tensile and yield strength of die forged specimens of 720 mm billet in the direction of Land L T were higher than those of 370 mm billet. However, the tensile strength of these specimens were 5 to 10% lower than that of American military specification. The plane strain fracture toughness of die forged specimens of 370 mm cast billet showed almost the same level of 720 mm billet, which was die forged after free forging.

• The KIPS Transactions:PartD
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• v.11D no.1
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• pp.95-104
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• 2004

This paper proposes an efficient remote video evaluation system that is matched well with personalized characteristics of students using information filtering based on user profile. For making a question in forms of video, a key frame extraction method based on coordinate, size and color information is proposed. And Question-mating intervals are extracted using gray-level histogram difference and time window. Also, question-making method that combined category-based system with keyword-based system is used for efficient evaluation. Therefore, students can enhance their study achievement through both supplementing their inferior area and preserving their interest area.

• Transactions on Electrical and Electronic Materials
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• v.5 no.3
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• pp.109-112
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• 2004

In this study, in order to develop the low temperature sintering ceramics for ultrasonic vibrator, Pb(Sb$\_$$\frac{1}{2}$/Nb$\_$$\frac{1}{2}$/) O$_3$-Pb(Ni$\_$1/3/Nb$\_$2/3/)O$_3$-Pb(Zr$\_$0.48/Ti$\_$0.52/)O$_3$ ceramics were manufactured as a function of the amount of CuO addition, and their dielectric and piezoelectric characteristics were investigated. With increasing CuO addition, the grain size and density increased up to 0.3 wt% CuO addition. Taking into consideration electromechanical coupling factor(k$\_$p/) of 0.53, mechanical quality factor(Q$\_$m/) of 423, dielectric constant($\varepsilon$$\_$r/) of 1,759 and piezoelectric constant(d$\_$33/) of 362pC/N, it could be concluded that 0.5 wt% CuO added composition ceramic sintered at 920$^{\circ}C$ was suitable for ultrasonic vibrator application.

• Journal of Labour Economics
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• v.39 no.4
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• pp.1-29
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• 2016

This study examines the effects of the "youth unemployment bonus" program implemented in 2004. We view this program through the lenz of search-matching models and apply a quasi-experimental approach to an administrative unemployment insurance database of Korea. This episode is particularly useful because the program aims at long-term unemployed youths and the size of public assistance is large enough to subsidize employers for a year with a monthly subsidy of about $600. The main effects are found to be as follows: (i) the search period gets shortened by 18 days, (ii) the subsequent wage has increased by about three percents, and (iii) a conservative benefit-cost analysis reveals the validity of this program. We interpret these results in the context of general equilibrium models.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.358-362
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• 2004

$Si_3$$N_4$ ceramics have been identified as one of the promising structural ceramics. This study has been carried out to investigate of the synthetic behaviors of $Si_3$$N_4$ derived from domestic silica-stone by direct nitriding method. The silicon nitridation reaction has been studied in the temperature range of $1300～1550^{\circ}C$. Below the $1400^{\circ}C$, the nitriding rate was measured to be 16%. For the temperatures higher than the $1400^{\circ}C$, $\beta$-$Si_3$$N_4$ phase was formed mainly, and the nitriding rate showed above 98%. With the increasing of sample weight of silicon powder, the nitriding rate and $\beta$-$Si_3$$N_4$ phase increased at $1400^{\circ}C$ for 2 hours. The shape and particle size of$ Si_3$$N_4$ powder synthesized at $1400^{\circ}C$ for 2 hours showed the irregular angular-type and 10 $\mu\textrm{m}$, respectively.