• 전기학회논문지
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• 제56권3호
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• pp.556-560
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• 2007

In this study, both structural and microwave dielectric properties of the $Mg_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1400^{\circ}C{\sim}1500^{\circ}C$. The bulk density and quality factor of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were increased with increasing sinterning temperature in the range of $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased the sintering temperature of above $1450^{\circ}C$. The dielectric constant of the $Mg_5Ta_4O_{15}$ ceramics was increased continuously with increasing sintering temperature. And the dielectric constant of the $Mg_5Nb_4O_{15}$ ceramics was increased in as the sintering temperature increasesfrom $1400^{\circ}C{\sim}1450^{\circ}C$ but was decreased at the temperatures above $1475^{\circ}C$. In the case of the $Mg_5Ta_4O_{15}\;and\;Mg_5Nb_4O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, $-10.91ppm/^{\circ}C$ and 14, 37,350 GHz, $-52.3ppm/^{\circ}C$, respectively.

• BMB Reports
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• 제29권1호
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• pp.1-10
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• 1996

The binding interaction of ethidium to a series of synthetic deoxyoligonucleotides containing a B-Z junction between left-handed Z-DNA and right-handed B-DNA, was studied. The series of deoxyoligonucleotides was designed so as to vary a dinucleotide step immediately adjacent to a B-Z junction region. Ethidium binds to the right-handed DNA forms and hybrid B-Z forms which contain a B-Z junction, in a highly cooperative manner. In a series of deoxyoligonucleotides, the binding affinity of ethidium with DNA forms which were initially hybrid B-Z forms shows over an order of magnitude higher than that with any other DNA forms, which were entirely in B-form DNA The cooperativity of binding isotherms were described by an allosteric binding model and by a neighbor exclusion model. The binding data were statistically compared for two models. The conformation of allosterically converted DNA forms under binding with ethidium is found to be different from that of the initial B-form DNA as examined by CD spectra. The ratio of the binding constant was interestingly correlated to the free energy of base unstacking and the conformational conversion of the dinucleotide. The more the base stacking of the dinucleotide is unstable, or the harder the conversion of B to A conformation, the higher the ratio of the binding constant of ethidium with the allosterically converted DNA forms and with the initial B-Z hybrid forms. DNA sequence around a B-Z junction region affects the binding affinity of ethidium. The results in this study demonstrate that ethidium could preferentially interact with unusual DNA structures.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제19권4호
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• pp.327-335
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• 2012

We study half lightlike submanifolds M of semi-Riemannian manifolds $\widetilde{M}$ of quasi-constant curvatures. The main result is a characterization theorem for screen homothetic Einstein half lightlike submanifolds of a Lorentzian manifold of quasi-constant curvature subject to the conditions; (1) the curvature vector field of $\widetilde{M}$ is tangent to M, and (2) the co-screen distribution is a conformal Killing one.

• 대한수학회보
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• 제54권6호
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• pp.2053-2063
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• 2017

In this paper we prove a condition under which a hyperbolic starshaped set has a center of hyperbolic symmetry. We also give the definition of isometric diameters for a hyperbolic convex set, which behave similar to affine diameters for Euclidean convex sets. Using this concept, we give a definition of constant hyperbolic width and we prove that the only hyperbolic sets with constant hyperbolic width and with a hyperbolic center of symmetry are hyperbolic discs.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제17권3호
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• pp.211-229
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• 2010

Various types of predator-prey systems are studied in terms of the stabilities of their steady-states. Necessary conditions for the existences of non-negative constant steady-states for those systems are obtained. The linearized stabilities of the non-negative constant steady-states for the predator-prey system with monotone response functions are analyzed. The predator-prey system with non-monotone response functions are also investigated for the linearized stabilities of the positive constant steady-states.

• 대한화학회지
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• 제65권3호
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• pp.179-184
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• 2021

본 연구에서는 용매 특성에 따른 인지질 내 글리세롤 골격 구조 변화를 알아보기 위해서 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) 단분자에 대한 분자동역학 시뮬레이션을 용매 특성을 변화시켜가며 진행하였다. DOPC 골격구조는 인지질 내 글리세롤 C1-C2 결합의 비틀림각에 따라 A(θ3 = trans, θ4 = gauche), B(θ3 = gauche, θ4 = gauche-), C(θ3 = gauche-, θ4 = trans) 세가지 형태로 구분된다. 용매의 유전상수와 표면장력을 변수로 하여 DOPC의 골격 구조 변화를 살펴본 결과, 유전상수가 증가할수록, 표면장력이 클수록 B 구조의 빈도가 증가하였으며 그 이유는 B 구조의 solvation 에너지가 A에 비해서 더 크고, 표면적이 A에 비해서 작기 때문이다. 이러한 연구 결과는 추후 인지질 구조 연구에 활용될 것으로 기대된다.

• 공업화학
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• 제10권6호
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• pp.885-888
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• 1999

본 연구에서는 $Na_2B_4O_7{\cdot}10H_2O/Na_2B_4O_7{\cdot}5H_2O$ 반응계의 열분해 탈수반응에 의한 반응속도상수를 결정하고 반응계의 재현성 및 화학축열재의 반복사용에 따른 내구성을 검토하였다. 반응계의 열분해 탈수반응의 차수는 1차이었고, 열분해 탈수 반응속도는 수증기의 분압차에 정비례하였다. 반응계의 반응속도상수는 약 0.27이었고, 반응속도상수와 반응차수에 대한 반응의 재현성이 우수하였다. 또한 화학축열재의 내구성은 연속적으로 반복 사용하여도 활성변화는 ${\pm}5%$ 범위 내에 있었다.

• 한국결정성장학회지
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• 제13권2호
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• pp.88-92
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• 2003

본 연구에서는, Mn-Co-Ni 산화물계 NTC 써미스터의 열처리 조건에 따른 전기적 특성간의 상호관계에 대하여 고찰하였으며, 이를 위해 XRD. 소결체 밀도측정 및 B정수, 저항 열방산정수 등의 전기적 특성치를 조사하였다. NTC 써미스터의 열처리 과정은 Mn-Co-Ni 산화물 시험편의 소결특성에 큰 영향을 미치고있었으며, 본 연구의 조성하에서는 $1250^{\circ}C$, 2시간 동안 열처리한 경우 가장 높은 밀도치를 얻을 수 있었다. 이 조건하에서 미세구조 관찰결과 치밀화과정이 거의 완전하게 이뤄짐을 확인하였다. 제조된 NTC 써미스터는 소결 온도가 상승함에 따라 저항값 및 B 정수값이 커지는 것을 확인하였으며, 연료 액위의 변화에 다른 출력전압의 거동을 측정한 결과 선형 감소 거동을 나타내었다. 따라서, 본 연구에서 제조된 Mn-Co-Ni 산화물계 NTC 써미스터의 전기적 특성은 열처리 조건과 밀접한 연관성이 존재하는 것으로 사료되며, 향후 자동차용 연료액위센서로의 응용성이 가능할 것으로 기대된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.386-389
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• 2001

In this study, development of a new LTCC material using non-glassy system was attempted with repsect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. However, presence of liquid phases usually decrease dielectric properties, especially the quality factor. Therefore, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, $ZnWO_4$ was turned out the suitable LTCC material. $ZnWO_4$ can be sintered up to 98% of full density at $1050^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 15.5, 74380GHz, and $-70ppm/^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, $B_{2}O_{3}$ and $V_{2}O_{5}$ were added to $ZnWO_4$. 40 mol% $B_{2}O_{3}$ addition reduced the dielectric constant from 15.5 to 12. And the temperature coefficient of resonant frequency was improved from -70 to $-7.6ppm/^{\circ}C$. However, sintering temperature did not change due to either lack of liquid phase or high viscosity of liquid phase. Incorporation of small amount of $V_{2}O_{5}$ in $ZnWO_{4}-B_{2}O_{3}$ system enhanced liquid phase sintering. 0.1 wt% $V_{2}O_{5}$ addition to the $0.6ZnWO_{4}-0.4B_{2}O_{3}$ system, reduced the sintering temperature down to $950^{\circ}C$. Dielectric constant, quality factor, and temperature coefficient of resonant frequency were 9.5, 16737GHz, and $-21.6ppm/^{\circ}C$, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.386-389
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• 2001

In this study, development of a new LTCC material using non-glassy system was attempted with respect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. However, presence of liquid phases usually decrease dielectric properties, especially the quality factor. Therefore, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, ZnWO$_4$ was turned out the suitable LTCC material. ZnWO$_4$ can be sintered up to 98% of full density at 105$0^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 15.5, 74380GHz, and -70ppm/$^{\circ}C$, respectively In order to modify the dielectric properties and densification temperature, B$_2$O$_3$ and V$_2$O$_{5}$ were added to ZnWO$_4$. 40 mol% B$_2$O$_3$ addition reduced the dielectric constant from 15.5 to 12. And the temperature coefficient of resonant frequency was improved from -70 to -7.6ppm/$^{\circ}C$. However, sintering temperature did not change due to either lack of liquid phase or high viscosity of liquid phase. Incorporation of small amount of V$_2$O$_{5}$ in ZnWO$_4$-B$_2$O$_3$ system enhanced liquid phase sintering. 0.lwt% V$_2$O$_{5}$ addition to the 0.6ZnWO$_4$-0.4B$_2$O$_3$ system, reduced the sintering temperature down to 95$0^{\circ}C$ Dielectric constant, quality factor, and temperature coefficient of resonant frequency were 9.5, 16737GHz, and -21.6ppm/$^{\circ}C$ respectively.ively.