• 제목/요약/키워드: N.M.C.

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고강도 $Si_3N_4/SiC$ 구조세라믹스에 관한 연구 (High Strength $Si_3N_4/SiC$ Structural Ceramics)

  • 김병수;김인술;장윤식;박홍채;오기동
    • 한국세라믹학회지
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    • 제30권12호
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    • pp.999-1006
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    • 1993
  • Si3N4(p)-SiC(p) composites were prepared by gas pressure sintering at 190$0^{\circ}C$ for 1 hour. $\alpha$-SiC with average particle size of 0.48${\mu}{\textrm}{m}$ were dispersed from zero to 50vol% in $\alpha$-Si3N4 with average particle size of 0.5${\mu}{\textrm}{m}$. Y2O3-Al2O3 system was used as sintering aids. When 10vol% of SiC was added to Si3N4, optimum mechanical properties were observed; relative density of 98.8%, flextural strength of 930MPa, fracture toughness of 5.9MPa.m1/2 and hardness value of 1429kg/$\textrm{mm}^2$. Grain growth of $\beta$-Si3N4 was inhibited as the amount of added SiC was increased. SiC particles were found inside the $\beta$-Si3N4 intragrains in case of 10, 20 and 30vol%SiC added composites.

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REAL HYPERSURFACES IN A NONFLAT COMPLEX SPACE FORM WITH SPECIAL STRUCTURE TENSOR FIELD

  • Lim, Dong Ho;Kim, Hoonjoo
    • 한국수학교육학회지시리즈B:순수및응용수학
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    • 제28권3호
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    • pp.247-252
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    • 2021
  • Let M be a real hypersurface in a complex space form Mn(c), c ≠ 0. In this paper, we prove that if (∇Xϕ)Y + (∇Yϕ)X = 0 holds on M, then M is a Hopf hypersurface, where ϕ is the tangential projection of the complex structure of Mn(c). We characterize such Hopf hypersurfaces of Mn(c).

1981年 夏季 東海沿岸域의 異常底水溫現象 (On the Abnormal Cooling Phenomenon in the Coastal Areas of East Sea of Korea in Summer,1981)

  • 홍철훈;조규대;양성기
    • 한국해양학회지
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    • 제19권1호
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    • pp.11-17
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    • 1984
  • 1981년 7월 7일~12일 기간중 동해에서의 해양관측 결과와 국립수산진흥원 (1961~1981년) 및 일본 기상청 자료(1975, 1981년)를 분석한 결과, 1981년 하계의 1$0^{\circ}C$ 등온선이 130 E선의 35 30 N 이남 해역에서 약 75m 이심에 나타났으나 이 이북 해역에서부터 20~30m로 급격히 상승했다. 한편, 1966~1981년의 130 E선 에서 35 N~37 30 N의 3정점의 깊이 100m의 수온표준편차는 2~4$^{\circ}C$로서 변동폭이 매우 컸다. 1981년 하계의 수온 편차는 표준 편자의 1.5배 이상이며, 수심 150m 이천은 평년에 비해 5~1$0^{\circ}C$ 낮았다. 특히 1$0^{\circ}C$ 등온선이 평년보다 20~120마일 남하하여 35 N~36 N 해역에 까지 이르렀다. 이상의 결과를 종합해 볼 때 1981년은 약 15년 (1966~1981년) 동안에 처음 있는 이상 저수온년이었다.

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3C-SiC 버퍼층위에 증착된 M/NEMS용 다결정 AlN 박막의 특성 (Characteristics of polycrystalline AlN thin films deposited on 3C-SiC buffer layers for M/NEMS applications)

  • 정귀상;이태원
    • 센서학회지
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    • 제16권6호
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    • pp.462-466
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    • 2007
  • Aluminum nitride (AlN) thin films were deposited on Si substrates by using polycrystalline (poly) 3C-SiC buffer layers, in which the AlN film was grown by pulsed reactive magnetron sputtering. Characteristics of grown AlN films were investigated experimentally by means of FE-SEM, X-ray diffraction, and FT-IR, respectively. The columnar structure of AlN thin films was observed by FE-SEM. X-ray diffraction pattern proved that the grown AlN film on 3C-SiC layers had highly (002) orientation with low value of FWHM (${\Theta}=1.3^{\circ}$) in the rocking curve around (002) reflections. These results were shown that almost free residual stress existed in the grown AlN film on 3C-SiC buffer layers from the infrared absorbance spectrum. Therefore, the presented results showed that AlN thin films grown on 3C-SiC buffer layers can be used for various piezoelectric fields and M/NEMS applications.

SEMI-INVARIANT MINIMAL SUBMANIFOLDS OF CONDIMENSION 3 IN A COMPLEX SPACE FORM

  • Lee, Seong-Cheol;Han, Seung-Gook;Ki, U-Hang
    • 대한수학회논문집
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    • 제15권4호
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    • pp.649-668
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    • 2000
  • In this paper we prove the following : Let M be a real (2n-1)-dimensional compact minimal semi-invariant submanifold in a complex projective space P(sub)n+1C. If the scalar curvature $\geq$2(n-1)(2n+1), then m is a homogeneous type $A_1$ or $A_2$. Next suppose that the third fundamental form n satisfies dn = 2$\theta\omega$ for a certain scalar $\theta$$\neq$c/2 and $\theta$$\neq$c/4 (4n-1)/(2n-1), where $\omega$(X,Y) = g(X,øY) for any vectors X and Y on a semi-invariant submanifold of codimension 3 in a complex space form M(sub)n+1 (c). Then we prove that M has constant principal curvatures corresponding the shape operator in the direction of the distingusihed normal and the structure vector ξ is an eigenvector of A if and only if M is locally congruent to a homogeneous minimal real hypersurface of M(sub)n (c).

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N-아실 아미노산계 계면활성제에 관한 연구(제9보) -Sodium N-Lauroyl-N-methyl-taurate의 미셀형성에 대한 온도 및 전해질의 영향- (Studies on the Surfactants of the N-Acyl Amino Acid(part 9) -The Effect of Temperature and Electrolytes on the Micellization of Sodium N-Lauroyl-N-Methyl-Taurate-)

  • 김진현;김태영;주명종;남기대
    • 공업화학
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    • 제7권3호
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    • pp.401-409
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    • 1996
  • Sodium N-lauroyl-N-methyl taurate의 cmc에 대한 온도효과를 검토하였다. cmc값들은 처음 $20^{\circ}C{\sim}40^{\circ}C$의 온도 범위에서는 감소하다가 더욱 온도가 증가되면 다시 증가하는 경향이었다. cmc에 대한 온도의 의존성으로부터 여러가지 열역학적 파라미터들(${\Delta}H_m$, ${\Delta}G_m$, ${\Delta}S_m$)을 산출하였다. Sodium N-lauroyl-N-methyl taurate의 cmc에 대한 여러 전해질들의 첨가효과를 또한 검토하였고, 소수성결합 형성에너지 및 미셀의 해리도를 log cmc와 log conc.의 곡선으로부터 산출하였다. ${\Delta}H_m$값들은 온도가 증가함에 따라 감소하였고, $40^{\circ}C{\sim}50^{\circ}C$의 온도범위에서 부호가 양에서 음으로 변하였다. ${\Delta}G_m$값들은 전해질 농도 및 온도가 증가할수록 감소하였다.

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CONVOLUTION SUMS OF ODD AND EVEN DIVISOR FUNCTIONS

  • Kim, Daeyeoul
    • 호남수학학술지
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    • 제35권3호
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    • pp.445-506
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    • 2013
  • Let ${\sigma}_s(N)$ denote the sum of the s-th power of the positive divisors of N and ${\sigma}_{s,r}(N;m)={\sum_{d{\mid}N\\d{\equiv}r\;mod\;m}}\;d^s$ with $N,m,r,s,d{\in}\mathbb{Z}$, $d,s$ > 0 and $r{\geq}0$. In a celebrated paper [33], Ramanuja proved $\sum_{k=1}^{N-1}{\sigma}_1(k){\sigma}_1(N-k)=\frac{5}{12}{\sigma}_3(N)+\frac{1}{12}{\sigma}_1(N)-\frac{6}{12}N{\sigma}_1(N)$ using elementary arguments. The coefficients' relation in this identity ($\frac{5}{12}+\frac{1}{12}-\frac{6}{12}=0$) motivated us to write this article. In this article, we found the convolution sums $\sum_{k<N/m}{\sigma}_{1,i}(dk;2){\sigma}_{1,j}(N-mk;2)$ for odd and even divisor functions with $i,j=0,1$, $m=1,2,4$, and $d{\mid}m$. If N is an odd positive integer, $i,j=0,1$, $m=1,2,4$, $s=0,1,2$, and $d{\mid}m{\mid}2^s$, then there exist $u,a,b,c{\in}\mathbb{Z}$ satisfying $\sum_{k& lt;2^sN/m}{\sigma}_{1,i}(dk;2){\sigma}_{1,j}(2^sN-mk;2)=\frac{1}{u}[a{\sigma}_3(N)+bN{\sigma}_1(N)+c{\sigma}_1(N)]$ with $a+b+c=0$ and ($u,a,b,c$) = 1(Theorem 1.1). We also give an elementary problem (O) and solve special cases of them in (O) (Corollary 3.27).

성형 압력변화에 따른 고온초전도체 $Y_1Ba_2Cu_3O_7-\delta$ (Structural and electrical property studies dependent on the molding pressure in high-Tc superconductor $Y_1Ba_2Cu_3O_7-\delta$)

  • 김채옥;박정수;이교운
    • E2M - 전기 전자와 첨단 소재
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    • 제9권1호
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    • pp.18-23
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    • 1996
  • The molding pressure is also one of the important parameters in the preparation of HTSC materials by the solid state reaction method. In the present study, changes in structural, electrical and microstructural proper-ties with the molding pressure in YiB $a_{2}$C $u_{3}$ $O_{70{\delta}}$ superconductors have been performed. The investigated molding pressures were 0.5*10$^{3}$ N/c $m^{2}$, 1*10$^{3}$ N/c $m^{2}$, 2*10$^{3}$ n/c $m^{2}$ and 4*10$^{3}$ N/c $m^{2}$. As the molding pressure increased, the anisotropy of the crystal structure decreased and the grains have been grown preferentially in a c-axis direction. Since the size of the grain becomes larger with the decrease of the porosity, denser textures are formed. The results indicated that the critical current density is improved resulting from the enhanced densification due to higher molding pressure. When the molding pressure was between 1*10$^{3}$ N/c $m^{2}$ and 2*10$^{3}$ N/c $m^{2}$, while it did not affect the oxygen deficiency and Tc, the increase of the molding pressure affects remarkably on grain size and densification of the $Y_{1}$B $a_{2}$C $u_{3}$ $O_{7-{\delta}}$. When the molding pressure is larger than 2*10$^{3}$ N/c $m^{2}$, electrical proper-ties are independent on the molding pressure..

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C32-CONSTRUCTION ON Mn(κ)

  • Song, Youngkwon
    • Korean Journal of Mathematics
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    • 제12권1호
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    • pp.23-32
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    • 2004
  • Let (B, $m_B$, ${\kappa}$) be a maximal commutative ${\kappa}$-subalgebra of a matrix algebra $M_n(\kappa)$. We will construct a maximal commutative ${\kappa}$-subalgebra (R, $m$, ${\kappa}$) of $M_n+3(\kappa)$ from the algebra B such that the algebra R has dimension greater than the dimension of B by 3. Moreover, we will show a $C_i$-construction doesn't imply a $C^3_2$-construction for $i=1,2$.

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p-Dimethylaminobenzaldehyde 4-(p-Ethoxyphenyl) Thiosemicarbazone구조의 정밀화 (Refinement of the Structure of p-Dimethylaminobenzaldehyde 4-(p-Ethoxyphenyl) Thiosemicarbazone)

  • 서일환;서추명;박영자
    • 한국결정학회지
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    • 제2권1호
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    • pp.12-16
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    • 1991
  • p-dimethylaminobenzaldehyde 4-(p-ethoxyphenyl) thiosemicarbazone, C18H22N4OS의, 단위포상수는 단사정계 a=11.802(2), b=31.962(2), c=9.829(2)A, β=100.12(1)˚, V=3694.8A3이며 F(000)=1472, Mr=342.47, 공간군은 P2₁/c, Z=8, Dx=1.246 Mg m-3, Dm=1.17Mg m-3, μ=0.15mm-1이다. T=294 K에서 Mo Ka(λ=0.71073 A)을 사용하여 최종 R값은 0.0856이다. 비대칭단위내의 두개 분자간의 구조상의 큰차이는 C(9)-N(1)-C(6)-C(7)의 비틀림각이 각각 58.8(8)˚와 1(1)˚인것으로, 각 분자는 길이가 각각 2.613(7)과 2.566(7) A인 N(1)-H(10)'N(3) 분자내 수고결합을 하고 있으며 각 분자는 N(2)원자를 정점으로 하여 V-모양을 하고 있다. 독립적인 두 분자는 두개의 분자간 수소 결합 N(2)-H(11)'S'=3.367(5) A과 N(2')-H(11')'S=3.421(4)A으로 연결되어 이중체(dimer)를 형성하고 있으며 그 이중체들은 van der Waals력으로 결합되어 있다.

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