• Title/Summary/Keyword: code evolution

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Convergence of Min-Sum Decoding of LDPC codes under a Gaussian Approximation (MIN-SUM 복호화 알고리즘을 이용한 LDPC 오류정정부호의 성능분석)

  • Heo, Jun
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.10C
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    • pp.936-941
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    • 2003
  • Density evolution was developed as a method for computing the capacity of low-density parity-check(LDPC) codes under the sum-product algorithm [1]. Based on the assumption that the passed messages on the belief propagation model can be approximated well by Gaussian random variables, a modified and simplified version of density evolution technique was introduced in [2]. Recently, the min-sum algorithm was applied to the density evolution of LDPC codes as an alternative decoding algorithm in [3]. Next question is how the min-sum algorithm is combined with a Gaussian approximation. In this paper, the capacity of various rate LDPC codes is obtained using the min-sum algorithm combined with the Gaussian approximation, which gives a simplest way of LDPC code analysis. Unlike the sum-product algorithm, the symmetry condition [4] is not maintained in the min-sum algorithm. Therefore, the variance as well as the mean of Gaussian distribution are recursively computed in this analysis. It is also shown that the min-sum threshold under a gaussian approximation is well matched to the simulation results.

Nonlinear evolution of Alfven waves via mode conversion

  • Kim, Kyung-Im;Lee, Dong-Hun;Ryu, Dongsu;Kim, Khan-Hyuk;Lee, Ensang
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.2
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    • pp.119.1-119.1
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    • 2012
  • It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations roughly satisfies the order of ~0.01. In addition, we extended this study for the plasma sheet boundary layer (PSBL) region. We can discuss the maximum disturbances of the Alfven via mode conversion becomes differently saturated through each region.

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Strength characteristics and fracture evolution of rock with different shapes inclusions based on particle flow code

  • Xia, Zhi G.;Chen, Shao J.;Liu, Xing Z.;Sun, Run
    • Geomechanics and Engineering
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    • v.22 no.5
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    • pp.461-473
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    • 2020
  • Natural rock mass contains defects of different shapes, usually filled with inclusions such as clay or gravel. The presence of inclusions affects the failure characteristics and mechanical properties of rock mass. In this study, the strength and failure characteristics of rock with inclusions were studied using the particle flow code under uniaxial compression. The results show that the presence of inclusions not only improves the mechanical properties of rock with defects but also increases the bearing capacity of rock. Circular inclusion has the most obvious effect on improving model strength. The inclusions affect the stress distribution, development of initial crack, change in crack propagation characteristics, and failure mode of rock. In defect models, concentration area of the maximum tensile stress is generated at the top and bottom of defect, and the maximum compressive stress is distributed on the left and right sides of defect. In filled models, the tensile stress and compressive stress are uniformly distributed. Failing mode of defect models is mainly tensile failure, while that of filled models is mainly shear failure.

How does the gas in a disk galaxy affect the evolution of a stellar bar?

  • Seo, Woo-Young;Kim, Woong-Tae
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.2
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    • pp.44.1-44.1
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    • 2017
  • In barred galaxies, gaseous structures such a nuclear ring and dust lanes are formed by a non-axisymmetric stellar bar potential, and the evolution of the stellar bar is influenced by mass inflows to the center and central star formation. To study how the presence of the gas affects the evolution of the stellar bar, we use the mesh-free hydrodynamics code GIZMO and run fully self-consistent three-dimensional simulations. To explore the evolution with differing initial conditions, we vary the fraction of the gas and stability of initial disks. In cases when the initial disk is stable with Q=1.2, the bar strength in the model with 5% gas is weaker than that in the gas-free model, while the bar with 10% gas does not form a bar. This suggests that the gaseous component is unfavorable to the bar formation dynamically. On the other hand, in models with relatively unstable disk with Q=1.0, the presence of gas helps form a bar: the bar forms more rapidly and strongly as the gas fraction increases. This is because the unable disks form stars vigorously, which in turn cools down the stellar disk by adding newly-created stars with low velocity dispersion. However, the central mass concentration also quickly increases as the bar grows in these unstable models, resulting in fast bar dissolution in gas rich models. We will discuss our results in comparison with previous work.

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The Evolution of the Mass-Metallicity Relation at 0.20 < z < 0.35

  • Chung, Jiwon;Rey, Soo-Chang;Sung, Eon-Chang
    • Journal of Astronomy and Space Sciences
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    • v.30 no.1
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    • pp.59-67
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    • 2013
  • We present a spectroscopic study of 343 blue compact galaxies (BCGs) at 0.20 < z < 0.35 from the Sloan Digital Sky Survey (SDSS) DR7 data. We derive gas phase oxygen abundance using the empirical and direct method. Stellar masses of galaxies are derived from the STARLIGHT code. We also derive star formation rates of galaxies based on $H{\alpha}$ emission line from the SDSS as well as far-ultraviolet (FUV) flux from the Galaxy Evolution Explorer GR6 data. Evolution of the luminosity-metallicity and mass-metallicity (M-Z) relations with redshift is observed. At a given luminosity and mass, galaxies at higher redshifts appear to be biased to low metallicities relative to the lower redshift counterparts. Furthermore, low mass galaxies show higher specific star formation rates (SSFRs) than more massive ones and galaxies at higher redshifts are biased to higher SSFRs compared to the lower redshift sample. By visual inspection of the SDSS images, we classify galaxy morphology into disturbed or undisturbed. In the M-Z relation, we find a hint that morphologically disturbed BCGs appear to exhibit low metallicities and high SSFRs compared to undisturbed counterparts. We suggest that our results support downsizing galaxy formation scenario and star formation histories of BCGs are closely related with their morphologies.

A Good Puncturing Scheme for Rate Compatible Low-Density Parity-Check Codes

  • Choi, Sung-Hoon;Yoon, Sung-Roh;Sung, Won-Jin;Kwon, Hong-Kyu;Heo, Jun
    • Journal of Communications and Networks
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    • v.11 no.5
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    • pp.455-463
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    • 2009
  • We consider the challenges of finding good puncturing patterns for rate-compatible low-density parity-check code (LDPC) codes over additive white Gaussian noise (AWGN) channels. Puncturing is a scheme to obtain a series of higher rate codes from a lower rate mother code. It is widely used in channel coding but it causes performance is lost compared to non-punctured LDPC codes at the same rate. Previous work, considered the role of survived check nodes in puncturing patterns. Limitations, such as single survived check node assumption and simulation-based verification, were examined. This paper analyzes the performance according to the role of multiple survived check nodes and multiple dead check nodes. Based on these analyses, we propose new algorithm to find a good puncturing pattern for LDPC codes over AWGN channels.

An Isothermal Mganetohydrodynamic Code and Its Application to the Parker Instability

  • KIM JONGSOO;RYU DONGSU;JONES T. W.;HONG S. S.
    • Journal of The Korean Astronomical Society
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    • v.34 no.4
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    • pp.281-283
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    • 2001
  • As a companion to an adiabatic version developed by Ryu and his coworkers, we have built an isothermal magnetohydrodynamic code for astrophysical flows. It is suited for the dynamical simulations of flows where cooling timescale is much shorter than dynamical timescale, as well as for turbulence and dynamo simulations in which detailed energetics are unimportant. Since a simple isothermal equation of state substitutes the energy conservation equation, the numerical schemes for isothermal flows are simpler (no contact discontinuity) than those for adiabatic flows and the resulting code is faster. Tests for shock tubes and Alfven wave decay have shown that our isothermal code has not only a good shock capturing ability, but also numerical dissipation smaller than its adiabatic analogue. As a real astrophysical application of the code, we have simulated the nonlinear three-dimensional evolution of the Parker instability. A factor of two enhancement in vertical column density has been achieved at most, and the main structures formed are sheet-like and aligned with the mean field direction. We conclude that the Parker instability alone is not a viable formation mechanism of the giant molecular clouds.

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A Study on KAN Code ID for Promoting Distribution Information or Agricultural Products (농산물 유통 정보화 촉진을 위한 KAN코드 사용 확대에 관한 연구)

  • Ahn, Seung-Yong;Kang, Kyung-Sik
    • Journal of the Korea Safety Management & Science
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    • v.8 no.5
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    • pp.99-117
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    • 2006
  • Consumers keep demanding for diversified high quality products, valuable services and safety. With this in mind, Distribution Industry is being updated rapidly to accomodate this demand. Meanwhile, Distribution Information Technology of agricultural products has been in slow progress with little in-depth studies. In this study, it has been analyzed the usage of Bar code which is the key element for agricultural Distribution Information Technology. The analysis was conducted through a survey utilizing questionnaire covering 5 Hypermarkets(Super-centers) including big 3 companies. Also, Japanese market trends have been studied to visit a Japan Government Organization concerned, GS1 Japan, an Agricultural Cooperative, an Agricultural Wholesale Market, and a Retail Company. If we could use KAN code for all agricultural products, we could collect and analyze the information of price and trade quantity of them. It opens a new era to understand the agricultural products supply and demand easily. This will certainly make a great contribution to the evolution of agricultural products distribution. From this research, it is suggested that collective efforts by suppliers, wholesalers, retailers and Government Officers are needed to make large scale mutual marketing Organizations, which specialize in sending out agricultural products. The Organization is recommended to standardize and pack every final agricultural products, to promote the use of KAN code.

FLY-BY ENCOUNTERS BETWEEN DARK MATTER HALOS IN COSMOLOGICAL SIMULATIONS

  • AN, SUNG-HO;KIM, JEONGHWAN H.;YUN, KIYUN;KIM, JUHAN;YOON, SUK-JIN
    • Publications of The Korean Astronomical Society
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    • v.30 no.2
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    • pp.331-333
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    • 2015
  • Gravitational interactions - mergers and fly-by encounters - between galaxies play a key role as the drivers of their evolution. Here we perform a cosmological N-body simulation using the tree-particle-mesh code GOTPM, and attempt to separate out the effects of mergers and fly-bys between dark matter halos. Once close pair halos are identified by the halo finding algorithm PSB, they are classified into mergers ($E_{12}$ < 0) and fly-by encounters ($E_{12}$ > 0) based on the total energy ($E_{12}$) between two halos. The fly-by and merger fractions as functions of redshift, halo masses, and ambient environments are calculated and the result shows the following.(1) Among Milky-way sized halos ($0.33-2.0{\times}10^{12}h^{-1}M{\odot}$), $5.37{\pm}0.03%$ have experienced major fly-bys and $7.98{\pm}0.04%$ have undergone major mergers since z ~ 1; (2) Among dwarf halos ($0.1-0.33{\times}10^{12}h^{-1}M{\odot}$), $6.42{\pm}0.02%$ went through major fly-bys and $9.51{\pm}0.03%$ experienced major mergers since z ~ 1; (3) Milky-way sized halos in the cluster environment experienced fly-bys (mergers) 4-11(1.5-1.7) times more frequently than those in the field since z ~ 1; and (4) Approaching z = 0, the fly-by fraction decreases sharply with the merger fraction remaining constant, implying that the empirical pair/merger fractions (that decrease from z ~ 1) are in fact driven by the fly-bys, not by the mergers themselves.

APPLICATION OF UNCERTAINTY ANALYSIS TO MAAP4 ANALYSES FOR LEVEL 2 PRA PARAMETER IMPORTANCE DETERMINATION

  • Roberts, Kevin;Sanders, Robert
    • Nuclear Engineering and Technology
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    • v.45 no.6
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    • pp.767-790
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    • 2013
  • MAAP4 is a computer code that can simulate the response of a light water reactor power plant during severe accident sequences, including actions taken as part of accident management. The code quantitatively predicts the evolution of a severe accident starting from full power conditions given a set of system faults and initiating events through events such as core melt, reactor vessel failure, and containment failure. Furthermore, models are included in the code to represent the actions that could mitigate the accident by in-vessel cooling, external cooling of the reactor pressure vessel, or cooling the debris in containment. A key element tied to using a code like MAAP4 is an uncertainty analysis. The purpose of this paper is to present a MAAP4 based analysis to examine the sensitivity of a key parameter, in this case hydrogen production, to a set of model parameters that are related to a Level 2 PRA analysis. The Level 2 analysis examines those sequences that result in core melting and subsequent reactor pressure vessel failure and its impact on the containment. This paper identifies individual contributors and MAAP4 model parameters that statistically influence hydrogen production. Hydrogen generation was chosen because of its direct relationship to oxidation. With greater oxidation, more heat is added to the core region and relocation (core slump) should occur faster. This, in theory, would lead to shorter failure times and subsequent "hotter" debris pool on the containment floor.