• Journal of the Korean Data and Information Science Society
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• v.14 no.4
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• pp.1007-1012
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• 2003

A recursive procedure for finding the Cholesky root of the inverse of sample covariance matrix, leading to a direct solution for the inverse of a positive definite matrix, is developed using the likelihood equation for the maximum likelihood estimation of the Cholesky root under normality assumptions. An example of the Hilbert matrix is considered for an illustration of the procedure.

• Kyungpook Mathematical Journal
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• v.47 no.4
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• pp.549-568
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• 2007

In this paper we obtain a decomposition of certain factors of the signed Brauer algebra into a direct sum of simple algebras and we obtain the structure of the factor algebra.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1215-1230
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• 2000

Parallel Approaches using Cray T3E which is NIPP (Massively Parallel Processors) machine are presented for the efficient computation of the finite element analysis of 3-D shape rolling processes. D omain decomposition method coupled with parallel linear equation solver is used. Domain decomposition is applied for obtaining element tangent stifffiess matrices and residual vectors. Direct and iterative parallel algorithms are used for solving the linear equations. Direct algorithm is_parallel version of direct banded matrix solver. For iterative algorithms, the well-known preconditioned conjugate gradient solver with Jacobi preconditioner is also employed. Moreover a new effective iterative scheme with block inverse matrix preconditioner, which is named by present authors, is presented and its results are compared with the one using Jacobi preconditioner. PVM and MPI are used for message passing and synchronization between processors. The performance and efficiency of each algorithm is discussed and comparisons are made among different algorithms.

• Bulletin of the Korean Chemical Society
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• v.21 no.10
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• pp.959-968
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• 2000

Direct reaction of elemental silicon with a mixture of (dichloromethyl)silanes 1 $[Cl_3-nMenSiCHCl_2:$ n = 0 (a), n = 1(b), n = 2(c), n = 3(d)] and hydrogen chloride has been studied in the presence of copper catalyst using a stirred bed reactor equ ipped with a spiral band agitator at various temperatures from $240^{\circ}C$ to $340^{\circ}C.$ Tris(si-lyl) methanes with Si-H bonds, 3a-d $[Cl_3-nMenSiCH(SiHCl_2)_2]$, and 4a-d $[Cl_3-nMenSiCH(SiHCl_2)(SiCl_3)]$, were obtained as the major products and tris(silyl)methanes having no Si-H bond, 5a-d $[Cl_3-nMenSiCH(SiCl_3)_2]$, as the minor product along with byproducts of bis(chlorosilyl)methanes, derived from the reaction of silicon with chloromethylsilane formed by the decomposition of 1. In addition to those products, trichlorosilane and tetra-chlorosilane were produced by the reaction of elemental silicon with hydrogen chloride. The decomposition of 1 was suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to 1. Cad-mium was a good promoter for and the optimum temperature for this direct synthesis was $280^{\circ}C$.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.413-420
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• 2013

Effect of inherent volatile matters in fuels on electrochemical reactions of anode was investigated for a single direct carbon fuel cell (DCFC). Raw coals used as power source in the DCFC release light gases into the atmosphere under the operating temperature of DCFC ($700^{\circ}C$) by thermal decomposition and only char remained. These exhausted gases change the gas composition around anode and affect the electrochemical oxidation reaction of system. To investigate the effect of produced gases, comparative study was conducted between Indonesian sub-bituminous coal and its char obtained through thermal treatment, carbonizing. Maximum power density of raw coal ($52mW/cm^2$) was appeared higher than that of char ($37mW/cm^2$) because the gases produced from the raw coal during thermal decomposition gave additional positive results to electrochemical reaction of the system. The produced gases from coals were analyzed using TGA and FT-IR. The influence of volatile matters on anodic electrolyteelectrode interface was observed by the equivalent circuit induced from fitting of impedance spectroscopy data.

• Journal of Ecology and Environment
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• v.44 no.2
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• pp.81-89
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• 2020

In the forest ecosystems, litterfall is an important component of the nutrient cycle that regulates the accumulation of soil organic matter (SOM), the input and output of the nutrients, nutrient replenishment, biodiversity conservation, and other ecosystem functions. Therefore, a profound understanding of the major processes (litterfall production and its decomposition rate) in the cycle is vital for sustainable forest management (SFM). Despite these facts, there is still a limited knowledge in tropical forest ecosystems, and further researches are highly needed. This shortfall of research-based knowledge, especially in tropical forest ecosystems, may be a contributing factor to the lack of understanding of the role of plant litter in the forest ecosystem function for sustainable forest management, particularly in the tropical forest landscapes. Therefore, in this paper, I review the role of plant litter in tropical forest ecosystems with the aims of assessing the importance of plant litter in forest ecosystems for the biogeochemical cycle. Then, the major factors that affect the plant litter production and decomposition were identified, which could direct and contribute to future research. The small set of studies reviewed in this paper demonstrated the potential of plant litter to improve the biogeochemical cycle and nutrients in the forest ecosystems. However, further researches are needed particularly on the effect of species, forest structures, seasons, and climate factors on the plant litter production and decomposition in various types of forest ecosystems.

• Wind and Structures
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• v.36 no.1
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• pp.61-73
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• 2023

In this article, a novel structural modal parameters identification methodology is developed to determine the natural frequencies and damping ratios of civil structures based on the symplectic geometry mode decomposition (SGMD) approach. The SGMD approach is a new decomposition algorithm that can decompose the complex response signals with better decomposition performance and robustness. The novel method firstly decomposes the measured structural vibration response signals into individual mode components using the SGMD approach. The natural excitation technique (NExT) method is then used to obtain the free vibration response of each individual mode component. Finally, modal natural frequencies and damping ratios are identified using the direct interpolating (DI) method and a curve fitting function. The effectiveness of the proposed method is demonstrated based on numerical simulation and field measurement. The structural modal parameters are identified utilizing the simulated non-stationary responses of a frame structure and the field measured non-stationary responses of a supertall building during a typhoon. The results demonstrate that the developed method can identify the natural frequencies and damping ratios of civil structures efficiently and accurately.

• Archives of Metallurgy and Materials
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• v.64 no.2
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• pp.695-700
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• 2019

Mordenite-zeolite supported Ca-Cu and Ba-Cu catalysts (Ca-Cu/MOR and Ba-Cu MOR) were successfully fabricated for direct decomposition of both NF₃ and N₂O gases contained in waste gas stream of (semiconductor) electronics industry. N₂O conversion rates of Ca-Cu and Ba-Cu catalysts were 79 and 86%, respectively, at 700℃ and 1 atm under space velocity of 5000 h^-1. The Ca-Cu catalyst was especially noteworthy in that its capability of converting N₂O could be maintained even after its exposure to co-feeding NF₃ gas constituent in the waste gas stream. Compositional and surface morphological analyses of the Ca-Cu and Ba-Cu catalysts were made before and after exposure to the waste gas stream to examine any noticeable degradation or change of the catalysts. Unlike Ba-Cu catalyst, SiO₂ constituent of the Ca-Cu catalyst was found to remain immune to the NF₃-cofeeding waste gas stream, casting a positive prospect for superior and steady N₂O decomposition performance via maintenance of its structural integrity.

• Carbon letters
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• v.6 no.1
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• pp.41-46
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• 2005

Plasma carbon blacks of 20~30 nm diameter were synthesized by direct decomposition of natural gas using a hybrid plasma torch system with 50 kW direct current and 4 MHz of radio frequency. The insulating rector which inside diameter of 400 mm and length of 1500 mm, respectively was kept at 300~$400^{\circ}C$ during the preparation. The ultimate analysis of plasma carbon blacks reveals that the raw plasma carbon blacks contains a large quantity of volatile which is mainly consist of hydrogen. Therefore devolatilization of raw plasma carbon blacks were carried out at $900^{\circ}C$ for one hour under nitrogen atmosphere. The devolatilization leads to the decrease in electrical resistivity and surface oxygen functional groups of plasma carbon black significantly. In order to investigate the plasma carbon as a catalyst support, devolatilized plasma black at $900^{\circ}C$ (DPB) supported PtAu catalyst was synthesized by sodium boronhydride reduction method. Electrochemical measurements and direct formic acid fuel cell test indicated that catalytic activity of DPB supported PtAu catalyst for formic acid oxidation was similar to that of Vulcan XC-72 of commercial carbon black supported one.

• Solar Energy
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• v.20 no.1
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• pp.45-54
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• 2000

Five direct/diffuse decomposition models were validated using the eight years data set of direct normal beam insolation measured in Seoul. The comparison has been performed In terms of the widely used statistical indicators such as MBE, RMSE, CV(RMSE), t-Statistic and Degree of Agreement. Result indicates that most of the correlations exhibit a tendency to underestimate the direct normal beam insolation except Bouguer's model. Most of big discrepancies between the measured and the predicted values was mainly shown in near the sunrising and the sunset period. Even though the investigated five models showed fairly large disagreement for the measured values by 34%$\sim$48% of CV(RMSE), Udagawa's correlation which includes the effect of solar altitude variation appears to performs always better in every statistical error tests.