• Journal of Radiation Protection and Research
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• v.45 no.1
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• pp.35-44
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• 2020

Background: Cadmium zinc telluride (CZT) is a promising material because of a high detection efficiency, good energy resolution, and operability at room temperature. However, the cost of CZT dramatically increases as its size increases. In this study, to achieve a large effective volume with relatively low cost, an array structure comprised of individual virtual Frisch-grid CZT detectors was proposed. Materials and Methods: The prototype consisted of 2 × 2 CZTs, a holder, anode and cathode printed circuit boards (PCBs), and an application-specific integrated circuit (ASIC). CZTs were used and the non-contacting shielding electrode method was applied for virtual Frisch-grid effect. An ASIC was used, and the holder and the PCBs were fabricated. In the current system, because the CZTs formed a common cathode, a total of 5 channels were assigned for data processing. Results and Discussion: An experiment using ¹³⁷Cs at room temperature was conducted for 10 minutes. Energy and timing information was acquired and the depth of interaction was calculated by the timing difference between the signals of both electrodes. Based on obtained three-dimensional position information, the energy correction was carried out, and as a result the energy spectra showed the improvements. In addition, a Compton image was reconstructed using the iterative method. Conclusion: The virtual Frisch-grid CZT detector based on the array structure was developed and the energy spectra and the Compton image were successfully acquired.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.413-413
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• 2000

In this paper, we propose a series of calibrations f3r the x-ray three dimensional imaging system. In the developed x-ray system, a three dimensional inner and outer shape of an object can be reconstructed out of two dimensional transmitted x-ray image set, which are acquired by projecting x-ray to the object from different views. To achieve this, a reconstruction algorithm which estimates and updates the three dimensional volume from x-ray images is developed. The algorithm is named as uniform and simultaneous algebraic reconstruction technique(USART) which is an iterative method estimating a 3D volume based on its projected images. In this method, it is assumed that the imaging conditions that are the relative positions between the x-ray sources, object and the image planes are blown. Practically it is not easy to know the three dimensional coordinate of the components of the system, since the x-ray is not visible and the image distortions are present due to the optical components in the system. In this paper, methods of correcting image distortions are present firstly. Then the coordinates of the x-ray systems are calibrated from the x-ray images of the grid pattern. Some experimental results on these calibrations are present and discussed.

• Structural Engineering and Mechanics
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• v.82 no.4
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• pp.477-490
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• 2022

This article investigates the nonlinear behavior of two-directional functionally graded materials (TDFGM) doubly curved panels with porosities for the first time. An improved and effectual approach is established based on the improved first-order shear deformation shell theory (IFSDST) and von Karman's type nonlinearity. The IFSDST considers the effects of shear deformation without the need for a shear correction factor. The composition of TDFGM constitutes four different materials, and the modified power-law function is employed to vary the material properties continuously in both thickness and longitudinal directions. A nonlinear finite element method in conjunction with Hamilton's principle is used to obtain the governing equations. Then, the direct iterative method is incorporated to accomplish the numerical results using the frequency-amplitude, nonlinear central deflection relations. Finally, the influence of volume fraction grading indices, porosity distributions, porosity volume, curvature ratio, thickness ratio, and aspect ratio provides a thorough insight into the linear and nonlinear responses of the porous curved panels. Meanwhile, this study emphasizes the influence of the volume fraction gradation profiles in conjunction with the various material and geometrical parameters on the linear frequency, nonlinear frequency, and deflection of the TDFGM porous shells. The numerical analysis reveals that the frequencies and nonlinear deformations can be significantly regulated by changing the volume fraction gradation profiles in a specified direction with an appropriate combination of materials. Hence, TDFGM panels can overcome the drawbacks of the functionally graded materials with a gradation of properties in a single direction.

• Korean Journal of Remote Sensing
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• v.29 no.2
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• pp.173-182
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• 2013

The early Sea-viewing Wide Field-of-view Sensor(SeaWiFS) atmospheric correction algorithm which is the basis of the atmospheric correction algorithm for Geostationary Ocean Color Imager(GOCI) assumes that water-leaving radiances is negligible at near-infrared(NIR) wavelengths. For this reason, all of the satellite measured radiances at the NIR wavelengths are assigned to aerosol radiances. However that assumption would cause underestimation of water-leaving radiances if it were applied to turbid Case-2 waters. To overcome this problem, Management Unit of the North Sea Mathematical Models(MUMM) atmospheric correction algorithm has been developed for turbid waters. This MUMM algorithm introduces new parameter ${\alpha}$, representing the ratio of water-leaving reflectance at the NIR wavelengths. ${\alpha}$ is calculated by statistical method and is assumed to be constant throughout the study area. Using this algorithm, we can obtain comparatively accurate water-leaving radiances in the moderately turbid waters where the NIR water-leaving reflectance is less than approximately 0.01. However, this algorithm still underestimates the water-leaving radiances at the extremely turbid water since the ratio of water-leaving radiance at two NIR wavelengths, ${\alpha}$ is changed with concentration of suspended particles. In this study, we modified the MUMM algorithm to calculate appropriate value for ${\alpha}$ using an iterative technique. As a result, the accuracy of water-leaving reflectance has been significantly improved. Specifically, the results show that the Root Mean Square Error(RMSE) of the modified MUMM algorithm was 0.002 while that of the MUMM algorithm was 0.0048.

• 전자공학회논문지 IE
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• v.43 no.4
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• pp.115-121
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• 2006

In this paper, we proposed about data error check and correction on channel transmission in the communication system. LDPC codes are used for minimizing channel errors by modeling AWGN Channel as a VDSL system. Because LDPC Codes use low density parity bit, mathematical complexity is low and relating processing time becomes shorten. Also the performance of LDPC code is better than that of turbo code in long code word on iterative decoding algorithm. This algorithm is better than conventional algorithms to correct errors, the proposed algorithm assigns weights for errors concerning parity bits. The proposed weighted Bit-flipping algorithm is better than the conventional Bit-flipping algorithm and we are recognized improve gain rate of 1 dB.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.39-48
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• 2004

Turbo codes, whose performance in bit error rate is close to the Shannon limit, have been adopted as a part of standard for the third-generation high-speed wireless data services. Iterative Turbo decoding results in decoding delay and high power consumption. As wireless communication systems can only use limited power supply, low power design techniques are essential for mobile device implementation. This paper proposes new effective criteria for stopping the iteration process in turbo decoding to reduce power consumption. By setting two stopping criteria, decodable threshold and undecodable threshold, we can effectively reduce the number of decoding iterations with only negligible error-correcting performance degradation. Simulation results show that the number of unsuccessful error-correction can be reduced by 89% and the number of decoding iterations can be reduced by 29% on the average among 12500 simulations when compared with those of an existing typical method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.185-192
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• 2011

In this paper, we simulate and analyze performance of iterative coding scheme, double binary turbo code, for high speed power line communication (PLC) systems. PLC system has hostile environment for high speed data transmission, so error correction method is necessary to compensate effects of PLC channel. We employ the PLC model proposed by M. Zimmerman and Middleton Class A interference model, and system performance is evaluated in terms of bit error rate (BER). From the simulation results, we confirm double binary turbo code provides considerable coding gains to PLC system and BER performance is significantly improved as the number of iteration increase. It is also confirmed that BER performance increases as code rate is lager, while it decreases as the code rate is smaller.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.6
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• pp.66-74
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• 2010

Recently distributed video coding (DVC) is spotlighted for the environment which has restriction in computing resource at encoder. Wyner-Ziv (WZ) coding is a representative scheme of DVC. The WZ encoder independently encodes key frame and WZ frame respectively by conventional intra coding and channel code. WZ decoder generates side information from reconstructed two key frames (t-1, t+1) based on temporal correlation. The side information is regarded as a noisy version of original WZ frame. Virtual channel noise can be removed by channel decoding process. So the performance of WZ coding greatly depends on the performance of channel code. Among existing channel codes, Turbo code and LDPC code have the most powerful error correction capability. These channel codes use stochastically iterative decoding process. However the iterative decoding process is quite time-consuming, so complexity of WZ decoder is considerably increased. Analysis of the complexity of LPDCA with real video data shows that the portion of complexity of LDPCA decoding is higher than 60% in total WZ decoding complexity. Using the HDA (Hard Decision Aided) method proposed in channel code area, channel decoding complexity can be much reduced. But considerable RD performance loss is possible according to different thresholds and its proper value is different for each sequence. In this paper, we propose an adaptive HDA method which sets up a proper threshold according to sequence. The proposed method shows about 62% and 32% of time saving, respectively in LDPCA and WZ decoding process, while RD performance is not that decreased.

• ETRI Journal
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• v.27 no.5
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• pp.525-532
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• 2005

In this paper, we propose and present implementation results of a high-speed turbo decoding algorithm. The latency caused by (de)interleaving and iterative decoding in a conventional maximum a posteriori turbo decoder can be dramatically reduced with the proposed design. The source of the latency reduction is from the combination of the radix-4, center to top, parallel decoding, and early-stop algorithms. This reduced latency enables the use of the turbo decoder as a forward error correction scheme in real-time wireless communication services. The proposed scheme results in a slight degradation in bit error rate performance for large block sizes because the effective interleaver size in a radix-4 implementation is reduced to half, relative to the conventional method. To prove the latency reduction, we implemented the proposed scheme on a field-programmable gate array and compared its decoding speed with that of a conventional decoder. The results show an improvement of at least five fold for a single iteration of turbo decoding.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.562-571
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• 2010

Forward error correction (FEC) coding schemes using iterative soft decision detection (SDD) information are mandatory in most of the next generation wireless communication system, in order to combat inevitable channel imparirnents. At the same time, space-time block coding (STBC) schemes are used for the diversity gain. Therefore, SDD information has to be fed into FEC decoder. In this paper, we propose efficient SDD methods for turbo-coded STBC system using high order modulation such as QAM. We present simulation results of various SDD schemes for turbo-coded STBC systems, and show that the proposed methods can provide almost approximating performance to maximum likelihood detection with much less computational load.