• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.49 no.3
• /
• pp.19-25
• /
• 2012

Underwater sensor networks (UWSNs) employ acoustic channels for communications. One of the main characteristics of the underwater acoustic channel is long propagation delay. Previously proposed MAC (medium access control) protocols for wireless sensor networks cannot be directly used in UWSNs due to the long propagation delay. The long propagation delay and uneven nodes deployments cause spatial fairness in UWSNs. Therefore, a new MAC protocol for UWSNs needs to be developed to provide efficient communications. In this paper, we propose an efficient MAC protocol in order to alleviate the fairness problem. In the proposed scheme, when a node receives a RTS packet, it does not immediately send back but delays a CTS packet. The node collects several RTS packets from source nodes during the delay time. It chooses one of the RTS packets based on the queue status information. And then, it sends a CTS packet to the source node which sent the chosen RTS packet. The performance of the proposed scheme is investigated via simulation. Simulation results show that our scheme is effective and alleviates the fairness problem.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.2
• /
• pp.163-168
• /
• 2015

In order to perform estimations with high reliability, it is necessary to deal with the tail part of the cumulative distribution function (CDF) in greater detail compared to an overall CDF. The use of a generalized Pareto distribution (GPD) to model the tail part of a CDF is receiving more research attention with the goal of performing estimations with high reliability. Current studies on GPDs focus on ways to determine the appropriate number of sample points and their parameters. However, even if a proper estimation is made, it can be inaccurate as a result of an incorrect threshold value. Therefore, in this paper, a GPD based on the Akaike information criterion (AIC) is proposed to improve the accuracy of the tail model. The proposed method determines an accurate threshold value using the AIC with the overall samples before estimating the GPD over the threshold. To validate the accuracy of the method, its reliability is compared with that obtained using a general GPD model with an empirical CDF.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.22 no.4
• /
• pp.279-285
• /
• 2010

In the process of the probabilistic-based design on the coastal structures, the probability density function (pdf) of tidal elevation data is assumed as the normal distribution function. The pdf shape of tidal elevation data, however, is better-fitted to the double-peak normal distribution function and the equivalent mean and standard deviation (SD) estimation process based on the equivalent normal distribution is required. The equivalent mean and SD (equivalent parameters) are different with the mean and SD (normal parameters) estimated in the condition that the pdf of tidal elevation is normal distribution. In this study, the difference, i.e., estimation error, between equivalent parameters and normal parameters is compared and analysed. The difference is increased as the tidal elevation and its range are increased. The mean and SD differences in the condition of the tidal elevation is ${\pm}400cm$ are above 100 cm and about 80~100 cm, respectively, in Incheon station. Whereas, the mean and SD differences in the condition of the tidal elevation is ${\pm}60cm$ are very small values in the range of 2~4 cm, in Pohang station.

• Research in Plant Disease
• /
• v.12 no.3
• /
• pp.254-259
• /
• 2006

Bacillus spp. isolated from mushroom medium wastes were evaluated for their biocontrol potentials on control of Sclerotinia rot of lettuce. The Bacillus isolates were more effectively obtained from waste suspension when directly added into nutrient agar(NA) medium than plating on the agar medium. Totally 42 isolates obtained from the wastes B23 and B42 showed highest antifungal activity against eight fungal pathogens such as Sclerotinia sclerotiorum, Rhizoctonia solani, Pythium ultimum, Phytophthora capsici, Fusarium oxysporum, Colletotrichum gloeosporioides, Cladosporium cucumerinum, and Botrytis cinerea and B23 and B42 were finally selected for further studies. Optimal concentration of the isolates was $10ml(10^7cfu/ml)$ to suppress the Sclerotinia rot of lettuce. Supplements such as starch, glycerol, and egg-yolk successfully maintained the bacterial population for 30 days in vitro and increased bio-control potentials against the disease. The bacterial isolate B23 alone showed 72% control value, furthermore it presented 95% control value when supplemented with 0.2% of starch, glycerol, and egg-yolk. The promising Bacillus isolates B23 and B42 were identified as Brevibacillus brevis and Bacillus stearothermophillus, respectively, based on morphological and physiological characteristics according to API database.

• 한국해양학회지
• /
• v.30 no.5
• /
• pp.442-457
• /
• 1995

The relationships of environmental factors to the distribution patterns of the three species of ophiuroids, Ophiura kinbergi, O. sarsi and ). sarsi vadicola from Yellow Sea southeast seas and East Sea of Korea were studied to characterize their habitual niches. These three species chosen for study illustrated distinct niche and patterns according to their various preferences mainly for bottom water temperature, bottom water salinity and depth from seven environmental variables which were depth, bottom water temperature and salinity, density, bottom water oxygen content, grain size of the surface sediment, and sediment sorting coefficient. The results of habitat niche study mainly dealing with O. sarsi vadicola suggested that the optimum habitat rages were approximately 6$^{\circ}C$∼10$^{\circ}C$ in bottom temperature and 31%∼33.5% in bottom water salinity which also corresponded with the characteristic ranges of Yellow Sea Bottom Cold Water and higher probabilities of occurrence (more than 70%) were found in depth ranging from 100 to 200 m. In addition, the habitats of O. kinbergi and O. sarsi were compared with that of O. sarsi vadicola. Their ranges of habitat niches were found to have different niches in physical space of bottom water temperature, bottom water salinity and depth. Based on the distribution pattern of O. sarsi vadicola in the Yellow Sea, the ecological barrier which confined the distribution of benthic macro-invertebrates in southern Yellow Sea was determined to be the Yellow Sea Warm Current (approximately 34% < and 18$^{\circ}C$ in December) which occurs between 33$^{\circ}$ and 34$^{\circ}$N of southern Yellow Sea in winter time.

• Korean Journal of Remote Sensing
• /
• v.36 no.5_2
• /
• pp.975-988
• /
• 2020

Change detection is the process of identifying changes by observing the multi-temporal images at different times, and it is an important technique in remote sensing using satellite images. Among the change detection methods, the unsupervised change detection technique has the advantage of extracting rapidly the change area as a binary image. However, it is difficult to understand the changing pattern of land cover in binary images. This study used grid points generated from seamless digital map to evaluate the satellite image change detection results. The land cover change results were extracted using multi-temporal KOMPSAT-3A (K3A) data taken by Gimje Free Trade Zone and change detection algorithm used Spectral Angle Mapper (SAM). Change detection results were presented as binary images using the methods Otsu, Kittler, Kapur, and Tsai among the automated threshold selection algorithms. To consider the seasonal change of vegetation in the change detection process, we used the threshold of Differenced Normalized Difference Vegetation Index (dNDVI) through the probability density function. The experimental results showed the accuracy of the Otsu and Kapur was the highest at 58.16%, and the accuracy improved to 85.47% when the seasonal effects were removed through dNDVI. The algorithm generated based on this research is considered to be an effective method for accuracy assessment and identifying changes pattern when applied to unsupervised change detection.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.24 no.2
• /
• pp.120-127
• /
• 2012

Exploratory data analysis was carried out by using the long-term wave climate data in Sokcho coastal zone. The main features found in this study are as follows. The coefficient of variations on the wave height and period are about 0.11 and 0.02, respectively. It also shows that the annual components of the wave height and period are dominant and their amplitudes are 0.24 m and 0.56 seconds, respectively. The amount of intra-annual variation range is about two times greater than that of the inter-annual variation range. The distribution shapes of the wave data are very similar to the log-normal and GEV(generalized extreme value) functions. However, the goodness-of-fit tests based on the KS test show as "rejected" for all suggested density functions. Then, the structure of the timeseries wave height data is roughly estimated as AR(3) model. Based on the wave duration results, it is clearly shown that the continuous and maximum duration is decreased as a power function shape and the total duration is exponentially decreased. Meanwhile, the environment of the Sokcho coastal zone is classified as a wave-dominated environment.

• Journal of the Korea Concrete Institute
• /
• v.21 no.5
• /
• pp.573-580
• /
• 2009

This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.6C
• /
• pp.429-437
• /
• 2008

Multiple-input multiple-output (MIMO) techniques can be used for the spectral efficiency enhancement of the cellular systems, which can be categorized into spatial multiplexing (SM) and spatial diversity schemes. MIMO systems suffer a severe performance degradation due to the intercell interference from the adjacent cells as the mobile terminal moves toward the cell boundary. Therefore for the spectral efficiency enhancement, an appropriate transmission scheme for the given channel environment and reception scheme which can mitigate the intercell interference are required. In this paper, we propose an adaptive signal transmission/reception scheme for the spectral efficiency improvement of $M_R{\times}M_T$ MIMO systems, present the decision criteria for the adaptive operation of the proposed scheme, and demonstrate the performance gain. The proposed scheme performs adaptive transmission using spatial multiplexing and spatial diversity, and adaptive reception using maximal ratio combining (MRC) and intercell spatial demultiplexing (ISD) when the spatial diversity transmission is used at the transmitter. Spatial multiplexing/demultiplexing is performed at the high signal-to-interference ratio (SIR) range, and the transmit diversity in conjunction with the adaptive reception uses either conventional MRC or ISD which can mitigate the $M_R-1$ interference signals, based on the mobile location. For the performance evaluation of the proposed adaptive scheme, the probability density function (pdf) of the effective SIR for the transmission/reception methods in consideration are derived for $M_R{\times}M_T$ MIMO systems. Using the results, the average effective SIR and spectral efficiency are presented and compared with simulation results.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.2
• /
• pp.125-130
• /
• 2011

Since conventional optimization that is classified as a deterministic method does not consider the uncertainty involved in a modeling or manufacturing process, an optimum design is often determined to be on the boundaries of the feasible region of constraints. Reliability-based design optimization is a method for obtaining a solution by minimizing the objective function while satisfying the reliability constraints. This method includes an optimization process and a reliability analysis that facilitates the quantization of the uncertainties related to design variables. Moment-based reliability analysis is a method for calculating the reliability of a system on the basis of statistical moments. In general, on the basis of these statistical moments, the Pearson system estimates seven types of distributions and determines the reliability of the system. However, it is technically difficult to practically consider the Pearson Type IV distribution. In this study, we propose an enhanced Pearson Type IV distribution based on a kriging model and validate the accuracy of the enhanced Pearson Type IV distribution by comparing it with a Monte Carlo simulation. Finally, reliability-based design optimization is performed for a system with type IV distribution by using the proposed method.