• Korean Journal of Applied Biomechanics
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• v.17 no.3
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• pp.23-29
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• 2007

The purpose of this study were to investigate the differences between female and male basketball players in knee neuromuscular biomechanical factors during basketball rebound jump. Twelve high school female ($17.9{\pm}0.8years$) and twelve male ($19.0{\pm}1.6years$) basketball players rebound jumped for maximal vertical height to sufficiently stress the anterior cruciate ligament. Kinematic and ground reaction data were collected and combined with inverse dynamics to estimate the knee extensor and abductor torque. The EMG data from the biceps femoris and rectus femoris was used to estimate the ratio of quadriceps muscle activity. Female athletes showed more reduced knee flexion at foot contact, more increased knee abduction, extensor and abductor knee joint torque at foot contact, and quadriceps ratio at stance phase than those of male athletes. In conclusion, Female athletes showed differences in knee neuromuscular biomechanical factors than male athletes during basketball rebound jump.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.119-124
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• 1992

최근들어 고속도로, 고속철도,지하철 등의 건설이 급격히 증가함에 따라 터널의 건설이 늘어나고 있다. 이러한 터널등의 건설에서 필수적으로 따르는 것이 숏크리트의 시공이며 이러한 숏크리트의 시공은 앞으로 더욱 증가할 추세에 있다. 그러나 숏크리트의 광범위한 시공에도 불구하고 현재 여러 가지 문제점을 내포하고 있는 것이 사실이다. 따라서 본 연구에서는 우리나라 현행 숏크리트의 현황과 문제점을 도출하여 성능개선을 위한 최적 배합을 도출하고 고품질의 숏크리트 시공을 위하여 실리카퓸 숏크리트의 개발 및 적용과 인성(Toughness)과 연성(Ductility)을 대폭 증가시키고 시공속도를 빠르게 하여 안전성과 함께 경제성을 확보할 수 있는 강섬유보강 숏크리트의 개발 및 적용에 대한 연구를 집중적을 수행하였다. 본 연구로부터 숏크리트의 최적 배합을 도출하였고 강도와 내구성을 함께 증가시키고 리바운드율을 대폭 감소시킬 수 있는 실리카퓸 숏크리트를 개발하였다. 또한 wiremesh를 대체할 수 있는 강섬유보강 숏크리트를 개발하여 실내시험 및 현장 적용성 시험을 수행하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.402-406
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• 1995

The purpose of this paper is to decrease shotcrete rebound losses and to produce economic effectiveness at the same time in construction. The mechanical properties and quick acceleration of various shoterete mixes were analyzed, which were intuenced by several accelerators and their amouts used. And the application and construction in the felds were evaluated. The shotcrete rebounds relied on the condition of construction rather than on the quality of materials, but it is found that the decreasing of the cost and time in shotcreting under the same condition was based on the rebounds which were affected by the accelerating capability of the accelerators. The application of the accelerator was limited by the condition of tunnel construction ; such as ground water, anti-corrosive, or anti-chemistry. It is important to choose a proper accelerator. Therefore, it is necessary that better accelerators which satisfly mechanical characteristics and economy are developed. Optimal working conditions should be announced to the workers and workers' skill be improved in the shotcrete construction feld as well.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.72-78
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• 2020

The present study developed shotcrete for fiber-net integrated tunnel support system, which consists of fiber-net support materials including netlike fiber and shotcrete and integration technology between support materials. In addition, in order to evaluate the field applicability of the developed tunnel support system and compare with the performance of steel fiber reinforced shotcrete, mock -up test was conducted on the mock -up structure. The test results show that in the case of shotcrete containing coarse aggregate(S20A5RP10-C), the excessive rebound rate occurred as the secondary shotcrete was dropped during construction due to the degradation in bond performance with fiber-net. Also, in the case of steel fiber reinforced shotcrete, the amount of cast shotcrete fell short of target value due to the fiber ball and the degradation of pumpability. On the other hand, the amount of cast mortar shotcrete(S20A5RP10-M) and the installation position of fiber-net were almost close to the target values, and the lower rebound rate occurred compared to the steel fiber reinforced shotcrete.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.4
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• pp.25-32
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• 2010

High performance shotcrete has been recently researched partly as a result of high consensus on high strength and durability. However, they are very initial step compared from the advanced countries. For instance, they has been mainly on high strength or durability without any consideration on pumpability and shootability which are very crucial on workability. The purpose of this dissertation was to make a high performance wet-mix shotcrete (high workability) which would solve the general problems of wet-mix process in Korea. For this, the main experimental variables were selected to be silica fume(0.0, 4.5, 9%), air entrained agent(0.0, 0.005%). Rheology with IBB rheometer was measured for evaluating pumpability and shootability as well as pump pressure, rebound rate and build-up thickness. The conclusions from a series of experiments were as follow: The results of analyzing the effects of AE agent and silica fume on rheology indicated that AE agent reduced both of flow resistance(G) and torque viscosity(H) and silica fume increased flow resistance (G) and reduced torque viscosity(H). An increase in the value of torque viscosity(H) produces an increase in the requried pumping pressure. These result indicated that the reduction of torque would work better at improving pumpability. And an increase flow resistance(G) improved shootability(increase build-up thickness and reduce rebound).

• Journal of IKEEE
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• v.21 no.4
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• pp.416-419
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• 2017

In this paper, we propose a new digital delay-locked loop (DLL) for high-speed DDR3/DDR4 SDRAMs. The proposed digital DLL adopts a fine delay line using phase interpolation to eliminate the jitter increase problem due to the boundary switching problem. In addition, the proposed digital DLL utilizes a new gradual search algorithm to eliminate the harmonic lock problem. The proposed digital DLL is designed with a 1.1 V, 38-nm CMOS DRAM process and has a frequency operating range of 0.25-2.0 GHz. It has a peak-to-peak jitter of 1.1 ps at 2.0 GHz and has a power consumption of about 13 mW.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.131-140
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• 1994

Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcreting is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcreting practice. The purpose of the present study is, therefore, to explore the problems in the current shotcreting practice, to derive an optimum mix for efficient shotcreting, To this end, extensive experimental study has been conducted. Optimum mixes with high quality and economy were derived. The present study provides a firm bast: in our country to apply high-quality shotcrete in tunnel construction.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.235-242
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• 2005

This study is on the evaluation of performance of polymer cement mortar which is used for pre-wetting spray method. Pre-wetting spray method is an epoch-making method to repair concrete structures damaged, which is added a small quantity water preciously to dry mortar to reduce dust and rebound and spray mortar mixed with fixed quantity water at nozzle before spray. The result showed that physical performance such like compressive, flexural and adhesive strength of polymer cement mortar, TS 100 used for pre-wetting spray method was superior to other repair mortar. Also durable performance such as resistance on permeability of chloride ion, carbonation, chemical and freezing-thawing was excellent.

• Geotechnical Engineering
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• v.13 no.2
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• pp.155-168
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• 1997

Lattice girder is a new steel support developed in Europe for the replacement of an existing H-shaped steel set, which is installed after tunnel excavation. Lattice girder has the following several advantages : 1. Lattice girder minimizes the amount of shotcrete shadow which happens to occur behind a steel support. 2. A triangular shape of lattice girder makes shotcrete placed efficiently. 3. Lattice girder provides a good bond strength for shotcrete, which makes the composite structure of lattice girder and shotcrete behave monolithic, and therefore, the rock load can be supported effectively by the lattice girder system, This paper presents the results from a model wall test, a strength test for shotcrete shot on the model wall and a strength test for the bond between lattice girder and shotcrete. These tests proved that lattice-girder system is superior to H-shaped steel-set system concerning the shotcrete rebound rate, the developed shotcrete strength and the adhesion characteristics.

• International Area Studies Review
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• v.22 no.1
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• pp.41-60
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• 2018

It is widely known that the increased productivity lead to a decrease in energy consumption. The policy for reducing energy consumption is also focusing on the improvement of firm's productivity. However, the issue of productivity dilemma phenomenon is recently raised in various fields. It is phenomenon that the increased productivity rather lead to a increased in energy consumption through a rise in output. This paper analyzed the presence of productivity dilemma in korean firm using Tang et al(2015)'s theoretical model. To closely analyze, I performed the analysis using 715 firms during 2011-2015 and estimated the model using system GMM to minimize the endogeneity. The results show that total effect of productivity had a significantly negative coefficient. It is implies that the increased productivity doesn't increase energy consumption. In other word, this paper could not identified productivity dilemma and so did in overseas investment firm and national firm cases.