• Journal of the Korea Institute of Building Construction
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• v.12 no.4
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• pp.393-400
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• 2012

The effect of ground granulated blast-furnace slag (GGBS) and alkaline activator on the properties of setting, compressive strength, drying shrinkage and resistance of carbonation was assessed to develop high volume slag concrete, the GGBS replacement rate of which was more than 80 percent. The changes in the concrete as the replacement rate of GGBS increases were as follows. Initial and final setting time was delayed by two and a half hours, and the compressive strength development properties of concrete in early and long term age were decreased. Drying shrinkage was satisfactory as below $6{\times}10^{-4}$ in every mixture, and yet showed a tangible trend by replacement rate. Carbonation was materially increased. Setting time and early strength development property, however, were extremely advanced by the addition of the alkaline activator. While drying shrinkage was improved by the alkaline activator, resistance to carbonation was not.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.1032-1040
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• 2010

This paper describes implementation of electonic seal (E-Seal) of a container based on ISO 18185 standard and development of monitoring systems checking E-Seal device and cargo states in the container for secure transportation from departure to destination. For lack of definition on confidentiality support in ISO 18185-4 standard, it is vulnerable to security attack such as sniffing. To cope with this, we developed encryption/decryption functions implementing RC5 and AES-128 standards and compared their performance. Experimental results showed that RC5 outperformed AES-128 in terms of time delay. In addition, RC5 had an advantage under the condition of large sized messages as well as CPUs with low performance. However, the portion of encryption/decryption processing time was less than 1 percent of response time including communication delay between E-Seal tags and readers. Hence, the performance difference between RC5 and AES-128 standards was trivial, which revealed that both specifications were allowable in developed systems.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1432-1436
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• 2007

도시화로 인한 유출량의 증가 및 도달시간의 단축은 도시재해의 한 원인이 되고 있다. 이를 막기 위하여 도시 배수유역내에 저류지를 설치하여 첨두도달시간을 지연시키고 방류량은 하수관거의 통수능 이하로 조절하는 방안을 활용하고 있다. 저류지를 설계 운영함에 있어서 사용되는 수문모형은 일반적으로 계획모형, 설계모형 및 운영모형으로 분류되고 있다. 계획모형과 유사한 형태의 단순화된 설계모형이 있기 때문에 계획모형과 설계모형을 엄밀히 구별하기는 어려우나 일반적으로 저류지 용량 결정시 배수구역에 대한 홍수추적을 실시하여 구하는 경우를 설계모형으로 보고 있다. 본 연구에서는 재해영향평가서 22개소의 기 설계된 저류지를 분석대상으로 하여 여러 가지 저류지 계획모형과 설계모의모형(WinDETPOND 모형, BASINOPT 모형)의 적합성을 검토하고 분석대상 저류지와 비교분석을 실시하였다. 저류지 계획모형의 분석에서 on-line 저류지의 경우는 사다리꼴 형태 설계수문곡선을 채택하고 있는 이종태 등 모형의 결과가 대상 저류지의 실저류량과 가장 유사함을 보였고, off-line 저류지의 경우는 삼각형 형태 설계수문곡선을 채택하고 있는 Abt & Grigg 모형의 결과가 비교적 양호한 결과를 보이는 것으로 나타났다. on-line 실저류지 3개소의 저류지 계획모형과 설계모의모형의 결과를 비교분석결과 도시화 인자 ${\alpha}$의 연관성은 뚜렷이 나타나지는 않았지만, WinDETPOND 모형의 저류량은 BASINOPT 모형에 비해 실저류지와 유사한 결과를 나타내었다.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.105-115
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• 2008

Urbanization results in increased runoff volume and peak flowrate and shortening in time of concentration, which may cause frequent flooding downstream. There are various types of flow retardation methods including detention ponds, retention ponds, and infiltration ponds. In general, hydrologic models to design the detention pond are classified into planning model and design model. This study is comparing and analyzing of planning model to design the detention pond in urban area. Detention ponds data of Disaster Impact Assessment Report on 22 sites were analyzed to investigate proper planning models in this study. From this research, following conclusions are derived, 1) In case of on-line detention pond, Lee model(1991) is the best planning model and similar to real storage volume. 2) In case of off-line detention pond, Abt and Grigg model is much more proper model compared to other models.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.287-287
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• 2011

모니터링 자료의 부족으로 인하여 다양한 토지이용에서 발생하는 비점오염물질의 관리에 어려움을 겪고 있는 실정이다. 현재 환경부에서는 현행 토지계의 원단위를 세부적으로 분류하여 재산정하기 위하여 지목별로 장기 모니터링이 수행되고 있다. 특히, 산림 지역의 경우 도시 및 축산지역에 비하여 강우유출수의 농도는 낮더라도 유량적인 측면에 보았을 때 전체 수계에 대한 부하량 기여도는 매우 높다고 볼 수 있다. 따라서 본 연구는 장기모니터링의 일환으로 산림지역에 대한 비점오염물질 유출 특성을 파악하기 위하여 모니터링 및 분석을 실시하였으며, 이러한 결과는 향후 비점오염원 평가기반을 마련하고자 한다. 본 연구는 활엽수지역을 대상으로 2010년 4월부터 10월까지 총 16회에 걸쳐 모니터링이 수행되었으며, 시료의 성분 변화를 막기 위해 냉장기능이 있는 자동채수기를 이용하여 시료를 채취하였다. 수질분석항목은 BOD, COD, DOC, SS, T-N, $NO_3$-N, $NH_3$-N, T-P, $PO_4$-P로 총 9가지 항목을 분석하였다. 강우사상에 대한 모니터링 결과, 총강우량은 7.0~76.5mm, 강우지속시간은 1~30hr, 평균 강우강도는 0.88~18.50mm/hr의 범위를 보이고 있으며, EMC(Event Mean Concentration, 유량가중평균농도)결과 BOD는 0.4~2.4mg/L, T-N은 1.156~14.777mg/L, T-P는 0.009~0.562mg/L인 것으로 나타났으며, SS는 1.8~71.9mg/L 로 비교적 높은 값을 나타내는 것으로 분석되었다. 농도 변화 및 유출경향의 패턴을 볼 때, 유량이 증가함에 따라 농도도 점점 증가하여 첨두유량이 발생된 후 감소하는 경향을 나타내는 것으로 분석되었다. 또한 우리나라의 경우, 시험유역을 대개 산지 소유역에 설치하는 경우가 많아서 일반적으로 지연시간이 짧은 경우가 많기 때문에 이 지역 역시 강우가 내린 후 계류유출량의 증가에 영향을 주는 강우의 유출속도는 비교적 빠른 것으로 나타났다. 그리고 단기 수문곡선상에서 강우량이 많을 시 유출이 빠르게 일어나 첨두 유량에 도달하는 시간이 짧고, 강우량이 적을 시에는 첨두 유량의 출현시간이 늦어지는 것을 볼 수 있었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.3
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• pp.292-303
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• 2002

This paper presents experimental results for early-age properties of concrete such as the setting time and strength, evaluated via the ultrasonic pulse velocity (UPV). Developing and using an automatically-recording monitoring system, the UPV's of mortar and concrete with various water to binder ratios (W/B) were measured during the first 24 hours. In addition, probe penetration and compression tests were conducted to measure the setting time and compressive strength, respectively. It was observed that the UPV's of mortar with high W/B remained constant during the first 6.5 hours and then abruptly began to increase at constant rates. On the other hand, the UPV of mortar with low W/B increased relatively slowly and gradually due to the setting retardation caused by the use of high range water reducing agent (HRWR). It was found that setting of concrete occurs when the UPV reaches a certain value. Moreover, it was concluded that the estimation formulas should incorporate the effects of W/B to more accurately estimate the early-age strength of concrete from the UPV.

• Journal of Internet Computing and Services
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• v.9 no.5
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• pp.153-163
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• 2008

Almost literature has so far proposed the modifications to IEEE 802.11 DCF MAC protocol to improve system throughput and average delay. Jitter(variance in packet delays) is, however, considered as an important QoS parameter for real-time streaming service which is popularized increasingly. Unfortunately, legacy access protocol for WLAN can't support the jitter. This paper proposes two schemes modifying the DCF MAC protocol to reduce the average value of jitter for multimedia frames arrived at received nodes. The one scheme, referred to as DCW-DCF(Decreasing Contention Window-DCF), reduces CW(Contention Window) size by half whenever a transmitted frame collided against other frames and back-off happens. Also, it increase initial CW size according as the link utilization and the collision probability increase. The other scheme, referred to as D-DIFS(Differential-DIFS), assigns different values to DIFS. That is, the DIFS interval is deceased as the number of back-off for a frame increases. In this paper, the two schemes are evaluated through simulation using ns2 and simulation results show that the proposed schemes are effective for improving the jitter property of standard WLAN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.7
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• pp.1044-1049
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• 1993

In this paper, it is shown that B-CDMA systems inherently reduce the effects of Multi Path fading phenomena which causes to degrade the performance of mobile communication systems. B-COMA systems use PN codes of high chip rates ( > 10 Mbps) and evaluate autocorrelation with the same code in the receiver. Therefore, it is possible that multipath signals, whose delay time is longer than one chip duration compared to the first signal, are removed. We model the wideband fading channel as a suitable linear filter, and perform computer simulation of signal transmission and reception. Graphic comparison of eye diagrams between the narrowband and wideband systems is shown.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.2
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• pp.146-153
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• 2013

The IR-UWB radar system radiates a pulse whose width is several hundred pico sec at Tx antenna and check the time to receive the pulse that reflected from target to measure the TOA. In this paper, we present a new algorithm which supplement the conventional ranging algorithm for more accurate estimation. We get received signal data using IR-UWB Radar module which equipped a NVA6000 UWB Transceiver and analysis the data of multi-path. Consequently, we found the property of UWB multi-path signal, which best fit a Gamma distribution. so we present a algorithm using Gamma-distribution and compared a performance with conventional ranging algorithm.

• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.454-460
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• 2007

In this paper, we implemented a ray-tracing simulator with a ray-launching technique and generated the propagation path of each ray in an multiple-wall indoor environment. In this simulator, we adopted two dimension ray-tracing techniques considering the reflection and penetration were dominant propagation factor in the indoor channel. From the result, we verified that this ray-tracing simulator shows the similar pattern and delay distribution with the experiment results of the previous research.