• Communications of the Korean Mathematical Society
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• v.23 no.3
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• pp.357-369
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• 2008

We obtain the superstability of a generalized exponential functional equation f(x+y)=E(x,y)g(x)f(y) and investigate the stability in the sense of R. Ger [4] of this equation in the following setting: $$|\frac{f(x+y)}{(E(x,y)g(x)f(y)}-1|{\leq}{\varphi}(x,y)$$ where E(x, y) is a pseudo exponential function. From these results, we have superstabilities of exponential functional equation and Cauchy's gamma-beta functional equation.

• Journal of applied mathematics & informatics
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• v.35 no.5_6
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• pp.565-586
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• 2017

In this paper we continue to investigate the Super Vertex Mean behaviour of all graphs up to order 5 and all regular graphs up to order 7. Let G(V,E) be a graph with p vertices and q edges. Let f be an injection from E to the set {1,2,3,${\cdots}$,p+q} that induces for each vertex v the label defined by the rule $f^v(v)=Round\;\left({\frac{{\Sigma}_{e{\in}E_v}\;f(e)}{d(v)}}\right)$, where $E_v$ denotes the set of edges in G that are incident at the vertex v, such that the set of all edge labels and the induced vertex labels is {1,2,3,${\cdots}$,p+q}. Such an injective function f is called a super vertex mean labeling of a graph G and G is called a Super Vertex Mean Graph.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.35-41
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• 2002

In this paper, we generalize the family of binary bent sequences introduced by Olsen, Scholtz and Welch [2] to obtain the generalized binary bent sequences with optimal correlation and balance properties. The modified trace transform is introduced and it enables us to use linear function from ${F_{2^n}}$ to the intermediate field ${F_{2^e}}$, where e|n. If we choose e=1, our method becomes the conventional binary bent sequence case. Also, some examples are given which show that our construction gives the family of simple binary sequences with optimal correlation and balance properties.

• Korean Journal of Veterinary Service
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• v.39 no.2
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• pp.87-92
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• 2016

Porcine edema disease (ED) is a communicable disease of pigs caused by infection with Shiga toxin (Stx)-producing Escherichia coli (STEC) which expresses F18 fimbriae and/or Stx type 2e (Stx2e). While STEC causes a severe illness including hemorrhagic colitis and hemolytic-uremic syndrome in humans, it induces damage to the vascular endothelium, which results in edema, hemorrhage, and microthrombosis, leading in high mortality in pigs. In the present study, we cultured Stx2e-producing E. coli field isolates from conventional pig farms that experienced sudden deaths previously with symptoms similar to porcine edema disease, which were further investigated with Shiga toxin profiles. A total of 43 strains were identified from the collected samples by F18 or Stx2e specific PCR. Based on the PCR, 42 isolates out of 43 isolates were proved to carry one of F18 or Stx2e genes and 14 isolates to carry both F18 and Stx2e genes. All of the 30 isolates that harbored Stx2e gene induced the cytopathic effect (CPE) in vero cells and especially, the isolate 150229 produced the highest level of Shiga toxin. Therefore, we identified the virulence genes (F18 and Stx2e) and demonstrated Shiga toxin-producing abilities from porcine edema disease causing E. coli filed isolates. These results suggested that one of the isolates could be a vaccine antigen candidate against STEC through further investigating to elicit an immune response.

• Phonetics and Speech Sciences
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• v.2 no.3
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• pp.23-27
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• 2010

The purpose of this study was to find how English vowels /a, e, i, o, u/ affect the production of English labials /p, b, f, v/ by Korean learners of English. Sixty syllables were composed by five vowels and four labials in the syllable types CV, VC, and VCV. The nonsense syllables were produced three times by nine subjects. The major results show that (1) in inter-vocalic position, the subjects had higher scores in producing /v/ composed with /a, e, o/ and /u/, while subjects had lower scores in producing /p/ with /i/ and /o/, (2) in post-vocalic position, the subjects had higher scores in producing /v/ and /f/ with /a, e/, and /o/, while subjects had lower scores in producing /b/ with /e/ and /i/, and (3) in pre-vocalic position, the subjects had higher scores in producing /v/ with /e, o, u/ and /f/ with /u/, while subjects had lower scores in producing /b/ with /e/, /i/ and /u/. The results suggest that on the whole, Korean learners of English have much difficulty in producing /p/ with /i/ in inter-vocalic condition and /b/ with /i, /e/ in pre-vocalic position.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.1
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• pp.1-8
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• 1996

Recently, much attention has been paid to problems which is concerned with voltage instability phenomena and much works on these phenomena have been made. In this paper, by substituting d $P_{k}$ d $e_{k}$ ( $v^{\rarw}$= e +j f) for $P_{k}$ in conventional load flow, direct method for finging the limit of voltage stability is proposed. Here, by using the fact that taylor se- ries expansion in .DELTA. $P_{k}$ and .DELTA. $Q_{k}$ is terminated at the second-order terms, constraint equation (d $P_{k}$ d $e_{k}$ =0) and power flow equations are formulated with new variables .DSLTA. e and .DELTA.f, so partial differentiations for constraint equation are precisely calculated. The fact that iteratively calculated equations are reformulated with new variables .DELTA.e and .DELTA.f means that limit of voltage stability can be traced precisely through recalculation of jacobian matrix at e+.DELTA.e and f+.DELTA.f state. Then, during iterative process divergence may be avoid. Also, as elements of Hessian mat rix are constant, its computations are required only once during iterative process. Results of application of the proposed method to sample systems are presented. (author). 13 refs., 11 figs., 4 tab.

• Journal of applied mathematics & informatics
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• v.19 no.1_2
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• pp.127-133
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• 2005

An f-coloring of a graph G = (V, E) is a coloring of edge set E such that each color appears at each vertex v $\in$ V at most f(v) times. The minimum number of colors needed to f-color G is called the f-chromatic index $\chi'_f(G)$ of G. Any graph G has f-chromatic index equal to ${\Delta}_f(G)\;or\;{\Delta}_f(G)+1,\;where\;{\Delta}_f(G)\;=\;max\{{\lceil}\frac{d(v)}{f(v)}{\rceil}\}$. If $\chi'_f(G)$= ${\Delta}$f(G), then G is of $C_f$ 1 ; otherwise G is of $C_f$ 2. In this paper, the classification problem of complete graphs on f-coloring is solved completely.

• Korean Journal of Materials Research
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• v.2 no.6
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• pp.428-435
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• 1992

AISI 4600 Iron powder was mixed with 0~1.0% phosphor as F$e_2$P powder and/or 0~0.8% carbon as graphite powder in rotating mixer. Mixed powder was pressed 800MPa in double-punch mould. Compacts were sintered at 115$0^{\circ}C$for 30 min. in vacuum or mixed hydrogen and nitrogen gas. Sintered compacts were ground and polished, and etched by 2% nital etchant. The microstructure was observed by image analyzer and optical microscope. Density and microhardness were tested by ASTM B3l2 and Microvickers hardness tester. The results obtained were as follows : (1) As the amount of F$e_2$P powder increased, sintered microstructure showed more densified effect and the grain size was larger. (2) The shape of pore was rounded and the number of pore was decreased by F$e_2$P addition. But mean pore size was larger with F$e_2$P content. (3) Simultaneous alloying addition of F$e_2$P and graphite brought about larger grain growth than respective addition. (4) Sintering atmosphere did not affect the microstructure. (5) Hardness of sintered compact increased with phosphrous and carbon content.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.58-62
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• 2001

The L $i_{0.5}$F $e_{2.5-x}$A $l_{x}$ $O_4$ systems (x=0, 0.3, 0.6, 0.9, 1.2, 1.5) were investigated by X-ray diffraction and Mossbauer spectroscopy. The structure of all the samples is cubic spinel type and lattice constant decrease with increasing Al content x. The Moissbauer spectra reveal two sextet for 0$\leq$x$\leq$0.6, two sextet and a doublet for 0.9$\leq$x$\leq$1.2, and a doublet for x=1.5. The cation distribution of the samples is (L $i_{1-a}$$^{+}$F $e_{a}$ $^{3+}$)$^{A}$[L $i_{a-0.5}$$^{+}$A $l_{2.5-a-x}$$^{+}$F $e_{2.5-a-x}$$^{3+}$]$^{B}$ $O_4$$^{2-}$ and substituted $Al^{3+}$ ions decrease the covalency of F $e^{3+}$- $O^{2-}$ bond in B-sites and A-B super-exchange interactions.tions.s.tions.ons.s.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1023-1029
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• 2001

Hexagonal ferrite $Co_2$Z(B $a_3$ $Co_2$F $e_{24}$ $O_{41}$ ) was prepared by various coprecipitation-oxidation methods. The formation of $Co_2$Z was studied in order to determine the optimal method. The $Co_2$Z composition hydroxides were prepared with the different oxidation and precipitation from the aqueous solution of $Ba^{2+}$, $Co^{2+}$ and F $e^{2+}$ chloride mixture. The coprecipitates were heat-treated at various temperatures, and their formation phases and microstructures were investigated from the analyses of DTA/TGA, powder XRD and SEM. The $Co_2$Z phase was observed in the case where the precursor will have the amorphous like oxyhydoxide($\delta$-FeOOH), and formed from $Ba_3$F $e_{32}$ $O_{51}$ , BaF $e_{12}$ $O_{19}$ (M-type) and $Ba_2$ $Co_2$F $e_{12}$ $O_{22}$ (Y-type). The $Co_2$Z was synthesized by the heat-treatment of the coprecipitate, which was prepared from the precipitation after oxidizing the chloride mixed solution, above 110$0^{\circ}C$.EX>.