• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.963-966
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• 1998

The KOMAC(KOrea Multi-purpose Accelerator Complex) linac is composed of RFQ(Radio Frequency Quadrupole), CCDTL(Coupled Cavity Drift Tube Linac) and SC(Superconducting)-linac. The required CW output power of RF system is about 25㎿ for 20㎿ proton beam power. Therefore high power RF sources are necessary for cost saving and reliability improvement. The number of klystrons for 0.5 ㎿ at 350MHz and 1 ㎿ at 700MHz are 1 and 31, respectively. In this paper, the design parameters of the klystron system including power supply and energy recovery system are presented.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.957-962
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• 1998

As the first stage accelerator of the Korea Multipurpose Accelerator Complex (KOMAC) 1GeV proton linac, a 350MHZ, cw Radio-Frequency Quadrupole (RFQ) will be built to produce 20㎃ of 3Mev. High current RFQ with cw operation is a major program in the KOMAC project to understand beam dynamics, engineering design, construction, control and diagnostics techniques. The beam dynamics and the engineering design of RFQ are described and the present status of the KOMAC RFQ project is discussed.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.7 s.184
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• pp.30-38
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• 2006

Laser cutting technology is one of flexible rapid manufacturing technologies with various advantageous including a high cutting speed, manufacturing of parts with a complex shape and others. The quality of the cut part and the optimum cutting conditions are highly dependent on the combination of the process parameters. The objective of this research works is to investigate the influence of process parameters, such as power of laser, cutting speed of laser and material thickness, on the surface roughness and the striation formation of the cut section for the case of cutting of CSP 1N sheet using high power Nd:YAG Laser with a continuous wave (CW). In order to find the relationship between process parameters and the surface roughness and the striation formation of the cut section, several experiments are carried out. Through the investigation of the empirical results, it has been shown that the surface roughness is highly related to the striation formation, including the frequency and angle of the striation, of the cut section. From the results of experiments, an optimum cutting speed for each cutting condition has been obtained to improve both the quality of the cut surface and the cutting efficiency.

• Kyungpook Mathematical Journal
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• v.13 no.2
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• pp.235-240
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• 1973

A k-dimensional vector bundle is a bundle ${\xi}=(E,P,B,F^k)$ with fibre $F^k$ satisfying the local triviality, where F is the field of real numbers R or complex numbers C ([1], [2] and [3]). Let $Vect_k(X)$ be the set consisting of all isomorphism classes of k-dimensional vector bundles over the topological space X. Then $Vect_F(X)=\{Vect_k(X)\}_{k=0,1,{\cdots}}$ is a semigroup with Whitney sum (${\S}1$). For a pair (X, A) of topological spaces, a difference isomorphism over (X, A) is a vector bundle morphism ([2], [3]) ${\alpha}:{\xi}_0{\rightarrow}{\xi}_1$ such that the restriction ${\alpha}:{\xi}_0{\mid}A{\longrightarrow}{\xi}_1{\mid}A$ is an isomorphism. Let $S_k(X,A)$ be the set of all difference isomorphism classes over (X, A) of k-dimensional vector bundles over X with fibre $F^k$. Then $S_F(X,A)=\{S_k(X,A)\}_{k=0,1,{\cdots}}$, is a semigroup with Whitney Sum (${\S}2$). In this paper, we shall prove a relation between $Vect_F(X)$ and $S_F(X,A)$ under some conditions (Theorem 2, which is the main theorem of this paper). We shall use the following theorem in the paper. THEOREM 1. Let ${\xi}=(E,P,B)$ be a locally trivial bundle with fibre F, where (B, A) is a relative CW-complex. Then all cross sections S of ${\xi}{\mid}A$ prolong to a cross section $S^*$ of ${\xi}$ under either of the following hypothesis: (H1) The space F is (m-1)-connected for each $m{\leq}dim$ B. (H2) There is a relative CW-complex (Y, X) such that $B=Y{\times}I$ and $A=(X{\times}I)$ ${\cap}(Y{\times}O)$, where I=[0, 1]. (For proof see p.21 [2]).

• Bulletin of the Korean Mathematical Society
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• v.33 no.2
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• pp.253-258
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• 1996

Let X be a finite connected CW-complex, $\Gamma = \pi_1(X)$ its fundamental group, $\tilde{X}$ its universal covering space. Then $\Gamma$ acts on $\tilde{X}$ by covering transformations and on the homology group $H_*(\tilde{X})$. In this note we establish the following vanishing result for the Euler characteristic $x(X)$ of X.

• Communications of the Korean Mathematical Society
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• v.25 no.1
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• pp.111-117
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• 2010

For a based, 1-connected, finite CW-complex X, we denote by $\varepsilon(X)$ the group of homotopy classes of self-homotopy equivalences of X and by $\varepsilon_#\;^{dim+r}(X)$ the subgroup of homotopy classes which induce the identity on the homotopy groups of X in dimensions $\leq$ dim X+r. In this paper, we calculate the subgroups $\varepsilon_#\;^{dim+r}(X)$ when X is a wedge of two Moore spaces determined by cyclic groups and in consecutive dimensions.

• Bulletin of the Korean Mathematical Society
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• v.58 no.2
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• pp.445-449
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• 2021

We define the relative self-closeness number N��(g) of a map g : X → Y, which is a generalization of the self-closeness number N��(X) of a connected CW complex X defined by Choi and Lee [1]. Then we compare N��(p) with N��(X) for a fibration $X{\rightarrow}E{\rightarrow\limits^p}Y$. Furthermore we obtain its rationalized result.

• Communications of the Korean Mathematical Society
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• v.21 no.1
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• pp.185-191
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• 2006

This paper observes that the induced homomorphisms on cohomology groups by a cyclic map are trivial. For a CW-complex X, we use the fact to obtain some conditions of X so that the n-th Gottlieb group $G_n(X)$ is trivial for an even positive integer n. As corollaries, for any positive integer m, we obtain $G_{2m}(S^{2m})\;=\;0\;and\;G_2(CP^m)\;=\;0$ which are due to D. H. Gottlieb and G. Lang respectively, where $S^{2m}$ is the 2m- dimensional sphere and $CP^m$ is the complex projective m-space. Moreover, we show that $G_4(HP^m)\;=\;0\;and\;G_8(II)\;=\;0,\;where\;HP^m$ is the quaternionic projective m-space for any positive integer m and II is the Cayley projective space.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.285-289
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• 2018

In this paper, we demonstrate electromagnetic wave focusing and rectification based on time reversal as a smart method for far-field wireless power transfer. Time reversal in a complex propagation environment allows for transmission of high peak power pulses by focusing the electromagnetic waves selectively regardless of the receiver position. We demonstrate wave focusing and radio frequency (RF) to direct current (DC) rectification via numerical simulation of a complex propagation environment. The results reveal that time reversal can ensure peak power up to 12 dB greater compared to a narrowband continuous wave signal, thereby enhancing the rectified DC voltage with better efficiency.

• Phonetics and Speech Sciences
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• v.4 no.3
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• pp.13-23
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• 2012

The sound /w/ has been traditionally regarded as an independent segment in Korean regardless of the phonological contexts in which it occurs. There have been, however, some questions regarding whether it is an independent phoneme in /CwV/ context (cf. Kang 2006). The present pilot study examined how Korean /w/ is realized in $/S^*wV/$ context by performing some perception tests. Our assumption was that if Korean /w/ is a part of the preceding complex consonant like $/C^w/$, it should be more or less uniformly articulated and perceived as such. If /w/ is an independent segment, it will be realized with speaker variability. Experiments I and II examined the identification rates as "labialized" of the spliced original stimuli of $/S^*-V/$ and $/S^{w*}-^wV/$, and the cross-spliced stimuli $/S^{w*}-V/$ and $/S^*-^wV/$. The results showed that round qualities of /w/ are perceived at significantly different temporal point with speaker and context variability. We therefore conclude that /w/ in $/S^*wV/$ context is an independent segment, not a part of the preceding segment. Full-scale examination of the production test in the future should be performed to verify the conclusion we suggested in this paper.