• Nuclear Engineering and Technology
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• v.15 no.4
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• pp.267-279
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• 1983

An analytical system has been established for scrutinizing both uranium- and plutonium-fueled lattices moderated by light water. This system consists of two primary codes. One is a unit cell program called KICC, which has theoretical foundation on the models of GAM and THERMOS incorporated with appropriate approximate treatments for various phenomena, whereas the other is a multi-dimensional diffusion-depletion program entitled KIDD. The adequacy of this system is verified by performing extensive benchmark calculations on a variety of critical experiments. The average value of effective multiplication factors for the selected nineteen UO$_2$ critical experiments of heterogeneous lattice structure is calculated to be 1.0006 with a standard deviation of 0.0039. Power distributions have also been calculated for some critical experiments fueled with both uranium and plutonium of varying concentrations. The maximum percentage difference between the measured and calculated power distributions appears to be less than 5%. This result, together with the previously reported result, illustrates that the KICC/KIDD system is a very effective tool for the analysis of a light water reactor core.

• Journal of Korean Society of Transportation
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• v.25 no.4
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• pp.123-133
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• 2007

This study analyzed whether a transit network with hierarchy is efficient or not, and if transit network hierarchy has cost efficiency, then which condition guarantees the efficiency of the transit network hierarchy. The authors modeled the total cost of the transit network and suggested the conditions in which the transit network hierarchy has cost efficiency through comparing the cost of the transit network with and without hierarchy. The efficiency of transit network hierarchy is guaranteed when the travel cost savings induced by using a higher hierarchy transit network is larger than the increasing non-travel cost, which is the sum of access cost, waiting cost, and operating cost, induced by the introduction of a higher hierarchy transit network. This result is consistent with common sense and with the concept of cost and benefit analysis. If a passenger traveling within the area divided by a higher hierarchy transit network uses only a lower hierarchy transit network and the passenger traveling out of the area divided by the higher hierarchy transit network uses both lower and higher hierarchy transit networks, the travel demand using the higher hierarchy transit network is inversely proportional to the square of the line spacing. This means that the transit network becomes more efficient and small increases of travel demand guarantee the efficiency of the transit network hierarchy as the connectivity of the network becomes higher. This result shows that transit networks have economies of aggregation. This study is the first analytical research on transit network hierarchy and is expected to be a basis for numerical research. However, numerical research should complement this study, since analytical research has some limitations for considering a real network.

• Polymer(Korea)
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• v.34 no.2
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• pp.116-125
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• 2010

The thermotropic liquid crystalline behavior of the homologous series of combined-type liquid crystalline polymers, tri-O-{4-(4'-cyanophenylazo)phenoxy}alkyl celluloses (CACETn, where n, the number of methylene units in the spacer, is 2~10) have been investigated. The CACETn with n of 5 and 7 exhibited enantiotropic nematic phases, while other polymers showed monotropic nematic phases. The isotropic-nematic transition temperature($T_{iN}$) increased when n is increased up to 4, but it decreased with increasing n more than 5. The entropy change at $T_{iN}$ also reaches a minimum at n=5, before it increases again for n=6. The sharp change at n=5 may be attributed to the difference in arrangement in the side groups. The nematic-crystalline transition temperatures, in contrast with $T_{iNS}$, exhibited a distinct odd-even effect, suggesting that the average shape of the side chains in the crystalline phase is different from that in the nematic phase. The mesophase properties of CACETn were significantly different from those reported for tri-O-alkyl celluloses and poly[1-{4-(4'-cyanophenylazo)phenoxyalkyloxy}ethylene]s. The results were discussed in terms of the difference in the chemical structures of the main and side chains and the number of the mesogenic units per repeating unit.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.253-256
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• 2009

This paper describes a core generator (FFT_Core_Gen) which generates Verilog HDL models of 8 different FFT/IFFT cores with $N=64{\times}2^k$($0{\leq}k{\leq}7$ for OFDM-based communication systems. The generated FFT/IFFT cores are based on in-place single memory architecture, and use a hybrid structure of radix-4 and radix-2 DIF algorithm to accommodate various FFT lengths. To achieve both memory reduction and the improved SQNR, a conditional scaling technique is adopted, which conditionally scales the intermediate results of each computational stage, and the internal data and twiddle factor has 14 bits. The generated FFT/IFFT cores have the SQNR of 58-dB for N=8,192 and 63-dB for N=64. The cores synthesized with a $0.35-{\mu}m$ CMOS standard cell library can operate with 75-MHz@3.3-V, and a 8,192-point FFT can be computed in $762.7-{\mu}s$, thus the cores satisfy the specifications of wireless LAN, DMB, and DVB systems.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.665-672
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• 1997

We applied mechanical alloying process by ball milling to produce molybdenum silicides $MoSi_2$ and $Mo_5Si_3$ using a mixture of elemental molybdenum and silicon powders at room temperature. The intermetallic compound MoSi$_3$ have been obtained by ball milling of $Mo_{33}Si_{67}$ mixture powders for 100 h, which is transformed to single $MoSi_2$ phase by subsequent heat treatment up to $725^{\circ}C$. The grain size of the $MoSi_2$ powders thus obtained was 19 nm, being approximately four times smaller than that of the commercial alloy. The intermetallic compound $MoSi_2$ with grain size of 30 nm have been also obtained by ball milling of $Mo_{62}Si_{38}$ mixture powders for 500 h, which is transformed to single $MoSi_2$ phase by heating up to $1000^{\circ}C$. We believe that the retarded ball milling time for the formation of $MoSi_2$ phase is attributed to its complicated crystal structure and large unit cell. The finer grain size in the ball-milled molybdenum silicides powders is expected to improve room-temperature mechanical properties for high-temperature structural materials.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.925-937
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• 1996

Three types of mordenites treated by steaming($SM_{6.5}$), HF solution for $SM_{6.5}(FM_a)$ and HF solutlon+steaming for $SM_{6.5}(FM_b)$ were prepared and used as cracking catalysts of vacuum gas oil. These samples were analysed by XRF and XPS for average and surface Si/Al atomic ratio, XRD for unit cell constants, nitrogen adsorption/desorption for porosity, pyridine-IR for acidic properties. In comparison with three type samples, $SM_{6.5}$ had a lot of acid amount and showed micropore volume mostly(>85% to total volume). Dealuminated $FM_a$, compared with $SM_{6.5}$, was decreased a little in acid amount and improved for porosity. Also, $FM_b$ was decreased further in acid amount and developed in mesopore dramatically. The catalytic activity and the yield of gasoline, kerosine+diesel and branched aromatic over the modified mordenites which have developed mesopore were improved. This is due to limited access of diffusion of large molecules within pore of the modified mordenites.

• Journal of the Korean Association of Geographic Information Studies
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• v.11 no.3
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• pp.23-33
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• 2008

This study was performed to determine the central place hierarchy in Daejeon metropolitan city by examining its central place systems for the existing central place analyses through formation of urban spatial structure and GIS method. The central place structure and hierarch for the year of 2000 and 2005 were analyzed by using the model of W. K Davis modified, in which $1km{\times}1km$ GRID was applied. The analysis results showed the establishment of one CBD(existing center of Eunghaeng-dong and Sunhwa-dong) and two Subcenters (tourist resort of Yusung-dong and administrative center of Dunsan-dong) in Daejeon metropolitan city for the year of 2000. For the year of 2005, established were two CBD(existing center of Eunghaeng-dong and Sunhwa-dong and administrative center of Dunsan-dong) and two Subcenters (tourist resort of Yusung-dong and bus-terminal of Yongjeon) in Daejeon metropolitan city. The analysis results are expected to play a pivotal role in supporting the urban spatial policies in near future.

• Journal of the Korean Chemical Society
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• v.40 no.3
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• pp.161-166
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• 1996

6-ethyl-5,6-dihydrouracil($C_6H_10N_2O_2$) is monoclinic, space group $$P2_{1}c}$$ with a=10.302(2), b=10.419(3), $c=7.095(1)\AA$, $\beta=106.6(0)$, Z=4, $V=729.7(3)\AA$^3$$, $D_c=1.29 g/cm^3,\;{\lambda}(MoK\alpha)=0.71073\AA$, $\mu=0.010cm^{-1}$, F(000)=304, and R=0.054 for 1070 unique observed reflection with F>4.0 $\sigma(F).$ The structure was solved by direct methods and refined by full-matrix least-squares refinement with the fixed C-H bond length at $0.96\AA.$ The hydrouracil molecule makes an envelope conformation with the ethyl substituent oriented to an axial position attainable to a varying degree of steric strain. There are two intermolecular hydrogen-bondings via N-H---O interactions, being nearly parallel to the 100 plane. The shortest distance between molecules is $3.187\AA$ of C(4) and O(8) (-x,-y, 1-z).

• Journal of the Korean Chemical Society
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• v.40 no.5
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• pp.295-301
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• 1996

A series of solid solutions of the $CaGa_1-xFexO_3-y$ system with the compositions of x=0.25, 0.50, 0.75, and 1.00 has been prepared at $1150^{\circ}C$ under an atmospheric air pressure. The structure, nonstoichiometric chemical formula, and the distribution of cations for the solid solutions are determined by X-ray diffraction analysis, Mohr salt titration, Mossbauer spectroscopic analysis. Their physical properties are discussed with electrical conductivity and magnetic measurements. The crystal system of all the compositions is a brownmillerite orthorhombic system from the X-ray diffraction analysis and the reduced lattice volume increases linearly with x value except that of the composition of x=0.25. All the solid solutions do not contain $Fe^{4+}$ ion and the mole number of oxygen vacancies or y value is 0.50 from Mohr salt analysis. The oxidation state of Fe ion, the coordination state, the structure change in the Brownmillerite-type structure, and the distribution of $Ga^{3+}$ and $Fe^{3+}$ ions are discussed with Mossbauer spectroscopic analysis. The electrical conductivity increases and activation energy decreases, as x value increases. The traditional semiconducting property of this system is described in terms of band theory. The compositions of x=0.50∼1.00 show a thermal magnetic hysteresis in the magnetic measurement with the cooling conditions, which is discussed in terms of the space group and Dzyaloshinsky-Moriya interaction.

• Journal of Broadcast Engineering
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• v.24 no.6
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• pp.919-927
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• 2019

In this paper, we propose an accurate camera calibration method for acquiring multiview stereoscopic images. Generally, camera calibration is performed by using checkerboard structured patterns. The checkerboard pattern simplifies feature point extraction process and utilizes previously recognized lattice structure, which results in the accurate estimation of relations between the point on 2-dimensional image and the point on 3-dimensional space. Since estimation accuracy of camera parameters is dependent on feature matching, accurate detection of checkerboard corner is crucial. Therefore, in this paper, we propose the method that performs accurate camera calibration method through accurate detection of checkerboard corners. Proposed method detects checkerboard corner candidates by utilizing 1-dimensional gaussian filters with succeeding corner refinement process to remove outliers from corner candidates and accurately detect checkerboard corners in sub-pixel unit. In order to verify the proposed method, we check reprojection errors and camera location estimation results to confirm camera intrinsic parameters and extrinsic parameters estimation accuracy.