• The Pure and Applied Mathematics
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• v.12 no.2 s.28
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• pp.143-152
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• 2005

We present a new block cipher called DyC. It consists of four sets (procedures) having the different $2^2,\;2^2,\;2^4$, and $2^8$ one-to-one correspondence functions as the elements. The round key is used to determine exactly one composite function from the possible $2^{16}$ composite functions. DyC supports 8 $\times$ n bit key size, 16 $\times$ m bit block length, and n rounds. We have confirmed that DyC offers security against other well-known advanced cryptanalytic attacks including the slide attacks and interpolation attacks. In this paper, we show several properties of the key schedule of DyC by mathematical analysis.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.9
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• pp.80-89
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• 1997

Die sinking electrical discharge machining(EDM) was conducted for ceramic composite of 33 weight percent TiC based on AI$_{2}$O$_{3}$ ceramic matrix according to the change of current and duty factor(DF). Material removal rate(MRR) was increased as the current and the duty factor increased, but better surface mor-pholoty was obtained in the region of lower current and duty factor. From the scanning electron microscopy(SEM) photographs and the energy dispersive X-ray spectroscopy(EDX) of the EDMed surface, EDM trace formed by one discharge spark was analyzed. Although the bending strength after EDM was highly decreased, reliability obtained by weibull analysis was increased twice. The bending strength was recovered or more by barrel polishing after EDM. From the FEM analysis of temperature for one spark, the possible melting region of AI$_{2}$O$_{3}$and TiC was obtained.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.131-136
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• 1998

The creep behavior and failure mechanism of the 30 vol% hot-pressed $SiC_t/Si_3N_4$ ceramic composite was experimentally investigated at $1200^{\circ}C$ and at various stress levels in air. The creep threshold stress for zero creep rate after 100 hr was found to be approximately 60 MPa. The stress exponent was estimated to be n~1, which suggests that fiber-reinforcement reduced the stress sensitivity of the HPSN matrix with the stress exponent of 2. The tertiary stage leading to creep rupture was found at 250 MPa but was very short. The microstructure of the crept specimen showed random fiber fracture and no matrix cracking. Interfacial debonding was absent.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.4
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• pp.21-27
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• 1998

In the case of existing in free-edge delaminations of composite laminates which are symmetry with respect to mid-plane in laminates also, in the case of asymmetry and anti-symmetry, the generalized quasi-three dimensional displacement field equations developed from quasi-three dimensional displacement field equations can be applied to solve above cases. We introduce three paramenters in this paper, which have not been used in quasi-three dimensional displacement field equations until now. To the laminate subjected to the axial extension strain $\varepsilon$0(C1) in $\chi$-direction, the bending deformation $\chi$$\chi$(C$_2$) around у-direction, the bending deformation w$\chi$(C$_4$) around z-direction and the twisting deformation $\chi$$\chi$y(C$_3$) around $\chi$-direction .The generalized quasi-three dimensional displacement field equations are able to be analyzed efectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.424-427
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• 2007

A fully differential transconductor using the series composite transistor is proposed. Simulation results show that THD is less than 1.2% for the differential input signal of up to $1.5V_{p-p}$ when the input signal frequency is 10MHz. i he proposed transconductor is used to design a third-order elliptic Gm-C lowpass filter with 138kHz cutoff frequency for ADSL Tx filter. The design procedure is based on signal flow graph(SFG) of a doubly-terminated LC ladder filter by means of fully differential transconductors and capacitors. The filter is fabricated and measured with a $0.35{\mu}m$ CMOS process.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.35-40
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• 2000

The influence of cyclic loading history on the creep behavior of the 30 vol% hot-pressed $SiC_f/Si_3N_4copmposite was experimentally investigated at $1200^{\circ}C$. The duration of loading/unloading had great effects on the creep behaviors. The short term duration cyclic loading history test results showed significant reduction in the primary and steady-state creep rates. For example, 300sec loading/300sec unloading history resulted in 70% lower steady-state creep rate than that of the continuous loading. However the long term duration cyclic loading history test results showed little change in creep rates compared to those of the continuous one. The reason for the significant change in the short term duration cycles was estimated due to the change in the stress redistribution between the fiber and matrix during the creep recovery in the primary stage.

• Proceedings of the KACD Conference
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• 2001.11a
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• pp.584.1-584
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• 2001

The purpose of this study was to evaluate the effects of various cavity configuration on bond strength and micro leakage of composite restoration. The specimens were prepared as followed; For control group(C=1), bovine teeth were wet-ground to expose flat dentin surface and in experimental groups, cylindrical cavities, same all2mm deep and 6mm in diameter(C=2.3), 4mm(C=3.0), and 3mm(C=3.7) were prepared.(omitted)

• Journal of Powder Materials
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• v.4 no.1
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• pp.42-47
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• 1997

It was investigated whether mechanical alloying (MA) processing could be more effective to the formation of metallic composite powder in Cu-C system. Elemental powder mixtures of Cu-70vo1.%C were mechanically alloyed with an attritor in an argon atmosphere and microstructural evolution was examined by X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. It has been found that even with the high volume fraction of immiscible graphite in Cu-C system, the refinement with a few ten nanometer size as well as the highly uniform distribution of copper phases have been achieved by the MA processing.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1061-1062
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• 2006

This paper presents a new approach for analyzing the microstructure of $SiC_p$-reinforced aluminum matrix composites from digital images. Various samples of aluminum matrix composite were fabricated by hot pressing the powder mixtures with certain volume and size combinations of pure Al and SiC particles. Microstructures of the samples were analyzed by computer-based image processing methods. Since the conventional methods are not suitable for separating phases of such complex microstructures, some new algorithms have been developed for the improved recognition and characterization of the particles in the metal matrix composites.

• Carbon letters
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• v.4 no.4
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• pp.163-167
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• 2003

The "Film boiling" Chemical Vapor Infiltration (CVI) process is a rapid densification one developed in particular for the elaboration of carbon/carbon composite materials. In order to optimize this new thermal gradient process, we have carried out several studies, on one hand, about the nature of the complex chemical reactions in a confined medium, and on the other hand, relative to the role of heat and mass transfers inside the preform. We show in this study that the introduction of a permeable sheath around the preform leads to hybrid liquid/gas CVI process which presents the advantages of very high densification rates associated with a moderate input energy.