• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.211-219
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• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.433-439
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• 2016

Several low-cost global navigation satellite system (GNSS) receivers do not support general range-domain correction, and DGNSS-CP (differential GNSS) method had been suggested to solve this problem. It improves its position accuracy by projecting range-domain corrections to the position-domain and then differentiating the stand-alone position by the projected correction. To project the range-domain correction, line-of-sight vectors from the receiver to each satellite should be calculated. The line-of-sight vectors can be obtained from GNSS broadcast ephemeris data or satellite direction information, and this paper shows positioning performance for the two methods. Stand-alone positioning result provided from Septentrio PolaRx4 Pro receiver was used to show the difference. The satellite direction information can reduce the computing load for the DGNSS-CP by 1/15, even though its root mean square(RMS) of position error is bigger than that of ephemeris data by 0.1m.

• Geomechanics and Engineering
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• v.4 no.4
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• pp.281-294
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• 2012

Filtration using granular media such as quarried sand, anthracite and granular activated carbon is a well-known technique used in both water and wastewater treatment. A relatively new pre-filtration method called pebble matrix filtration (PMF) technology has been proved effective in treating high turbidity water during heavy rain periods that occur in many parts of the world. Sand and pebbles are the principal filter media used in PMF laboratory and pilot field trials conducted in the UK, Papua New Guinea and Serbia. However during first full-scale trials at a water treatment plant in Sri Lanka in 2008, problems were encountered in sourcing the required uniform size and shape of pebbles due to cost, scarcity and Government regulations on pebble dredging. As an alternative to pebbles, hand-made clay pebbles (balls) were fired in a kiln and their performance evaluated for the sustainability of the PMF system. These clay balls within a filter bed are subjected to stresses due to self-weight and overburden, therefore, it is important that clay balls should be able to withstand these stresses in water saturated conditions. In this paper, experimentally determined physical properties including compression failure load (Uniaxial Compressive Strength) and tensile strength at failure (theoretical) of hand-made clay balls are described. Hand-made clay balls fired between the kiln temperatures of $875^{\circ}C$ to $960^{\circ}C$ gave failure loads of between 3.0 kN and 7.1 kN. In another test when clay balls were fired to $1250^{\circ}C$ the failure load was 35.0 kN compared to natural Scottish cobbles with an average failure load of 29.5 kN. The uniaxial compressive strength of clay balls obtained by experiment has been presented in terms of the tensile yield stress of clay balls. Based on the effective stress principle in soil mechanics, a method for the estimation of maximum theoretical load on clay balls used as filter media is proposed and compared with experimental failure loads.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.6
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• pp.9-18
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• 2004

This paper proposes a new and simple stereo matching algorithm using the disparity space image (DSI) technique. First of all, we detect some salient feature points on each scan-line of the image pair and set the matching area using those points and define a simple cost matrix. And we take advantage of matching by pixel-by-pixel instead of using the matching window. While the pixel-by-pixel method boost up the speed of matching, because of no using neighbor information, the correctness of the matching may not be better. To cover this point, we expand the matching path using character of disparity-space-image for using neighbor information. In addition, we devise the compensated matching module using the volume of the disparity space image in order to improve the accuracy of the match. Consequently, we can reduce mismatches at the disparity discontinuities and can obtain the more detailed and correct disparity map.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.3
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• pp.74-82
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• 2011

This paper describes a control system for positioning the real-time locations of the autonomous warfare vehicles and infantry, and for avoiding collisions between them. The control system utilizes the low-cost RSSI (Received Signal Strength Indication) for positioning the locations of the wireless devices. The mathematical mean filtering processes are applied to the calculation of the RSS matrix to improve the performance for positioning the wireless devices in the multi-path propagation environment. A fuzzy rule is proposed to recover and replace the broken packets occurring in the wireless communication. The gradient and geometric triangulation algorithms are proposed to trace the real-time locations of wireless devices, based on the distances between them. The estimated location results of the geometric triangulation algorithm are compared with the results of the GPS and the gradient algorithm.

• Journal of Hydrogen and New Energy
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• v.26 no.3
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• pp.212-220
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• 2015

The engineering plastic of sulfonated polyether ether ketone (SPEEK) as a polymer matrix has been developed in this lab to replace Nafion, solid polymer electrolytes of perfluorosulfonic acid membrane which has several flaws such as high cost, and limited operational temperature above $80^{\circ}C$. The SPEEK was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstosilicic acid (Cs-TSiA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TSiA/ceria 1% membrane showed the optimum results such as 0.1882 S/cm of proton conductivity at $80^{\circ}C$, and 99.61 MPa of tensile strength which were better than Nafion 117 membrane.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.4
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• pp.621-628
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• 2017

The efficiency of implementation of the arithmetic operations in finite fields depends on the choice representation of elements of the field. It seems that from this point of view normal bases are the most appropriate, since raising to the power 2 in $GF(2^n)$ of characteristic 2 is reduced in these bases to a cyclic shift of the coordinates. We, in this paper, introduce our algorithm to transform fastly the conventional bases to normal bases and present the result of H/W implementation using the algorithm. We also propose our algorithm to calculate the multiplication and inverse of elements with respect to normal bases in $GF(2^n)$ and present the programs and the results of H/W implementations using the algorithm.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.12
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• pp.761-767
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• 1999

Poly-Si TFTs(polycrystalline silicon thin film transistors) fabricated on a low cost glass substrate have attracted a considerable amount of attention for pixel elements and peripheral driving circuits in AMLCS(active matrix liquid crystal display). In order to apply poly-Si TFTs for high resolution AMLCD, a high operating frequency and reliable circuit performances are desired. A new poly-Si TFT with CLBT(counter doped lateral body terminal) is proposed and fabricated to suppress kink effects and to improve the device stability. And this proposed device with BC(buried channel) is fabricated to increase ON-current and operating frequency. Although the troublesome LDD structure is not used in the proposed device, a low OFF-current is successfully obtained by removing the minority carrier through the CLBT. We have measured the dynamic properties of the poly-Si TFT device and its circuit. The reliability of the TFTs and their circuits after AC stress are also discussed in our paper. Our experimental results show that the BC enables the device to have high mobility and switching frequency (33MHz at $V_{DD}$ = 15 V). The minority carrier elimination of the CLBT suppresses kink effects and makes for superb dynamic reliability of the CMOS circuit. We have analyzed the mechanism in order to see why the ring oscillators do not operate by analyzing AC stressed device characteristics.

• Korean journal of applied entomology
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• v.48 no.1
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• pp.45-51
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• 2009

This paper presents sequential sampling plans for evaluating the pest density based on complete counts from probe in a rice storage warehouse. Both maize weevil and Indian meal moth population showed negative binomial dispersion patterns in brown rice storage. For cost-effective monitoring and action decision making system, sequential sampling plans by using the sequential probability ratio test (SPRT) were developed for the maize weevil and Indian meal moth in warehouses with 0.8 M/T storage bags. The action threshold for the two insect pests was estimated to 5 insects per kg, which was projected by a matrix model. The results show that, using SPRT methods, managers can make decisions using only 20 probe with a minimum risk of incorrect assessment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1644-1652
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• 2003

The monitor product is packed by cushioning materials because the monitor can be broken during transportation. However, the addition of the cushioning material increased the volume of the product. Therefore, it is required that the usage of cushioning material be minimized. In practice, design engineers have followed the ad hoc design with experiences of predecessors. Automation of the design process is very important for the reduction of engineering cost, and can be achieved by an excellent design process and software development. According to Axiomatic design, a design flow is defined and a software system is developed for automated design. At first, a basic model is defined. A user can modify the model from menus and design is carried out according to the input from the user. Finite element models are automatically generated based on the design. A nonlinear finite element analysis program called LS/DYNA3D is linked for the impact analysis. The process of Design of Experiments using orthogonal array is installed to minimize the maximum acceleration in drop test. Therefore, a new design can be proposed by the system. The program is designed according to the Independence Axiom of Axiomatic design. FRs and DPs of the software system are defined and decomposed by zigzagging process. Independent modules can be generated by analysis of the full design matrix and each module is coded as class in Object Oriented Programming (OOP). Design results are discussed.