• Bulletin of the Korean Chemical Society
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• v.9 no.3
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• pp.179-182
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• 1988

A simple correlation between cross interaction constants ${\rho}_{ij}$ and bond lengths in the transition state was obtained ; it has been shown that ${\rho}_{ij}$ corresponds to force constant of activation, which in turn is related to bond length by Badger's rule involving only universal constants. A satisfactory correlation between 4-31G ab initio calculated values of bond length and force constant for C-X streching in the transition state of the methyl transfer reaction, $X^-\;+\;CH_3X\;=\;XCH_3\;+\;X^-$, indicated that Badger's rule can be extended to bonds in the transition state. Independence of ${\rho}_{ij}$ values from the variable charge transmission of reaction centers has been demonstrated with nearly constant, experimentally determined I${\rho}$XYI values, and hence similar degree of bond formation, for various $S_N2$ reactions.

• Bulletin of the Korean Chemical Society
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• v.9 no.5
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• pp.280-282
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• 1988

The structural, electrical and magnetic properties were investigated for the high-Tc superconductor $YBa_2Cu_3O_{7-x}$, where x was 0.13. The results of temperature dependence of the resistivity and the magnetization in $YBa_2Cu_3O_{6.87}$ whose structure and phase are confirmed by arialysis of X-ray powder diffraction pattern have been reported. A very sharp superconductivity transition appears at 92K in the specimen whose chemical composition is determined from redox titration, strongly suggesting that this specimen consists of a single-phase superconductor. From the results of X-ray diffraction analysis, magnetization curves, levitation and resistance measurements, it is suggested that the observed superconductivity is bulk property in nature and that the $YBa_2Cu_3O_{6.87}$ phase is responsible for the superconductivity of the present reproducible specimen.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.9
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• pp.749-755
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• 2017

In this paper, a wideband microwave absorber for X-band(8~12 GHz) applications is proposed. The structure of the proposed absorber unit cell consists of a resonator with a slot and slit, a backing ground plate, and a Taconic RF-30(${\varepsilon}_r=3$, $tan{\delta}=0.0014$) substrate with a dimension of $8.5{\times}8.5{\times}0.5mm^3$. The proposed absorber has a dual resonance at 9.83 and 10.37 GHz. To demonstrate the operating principle of the proposed absorber structure at each resonance frequency, the simulated current distributions on the unit cell are analyzed. To verify the performance of the proposed absorber, a prototype absorber was fabricated with a planar array of $20{\times}20$ unit cells. The measured results exhibit two absorptivity peaks stronger than 99 % and full-width at half-maximum(FWHM) bandwidth of 1.1 GHz(9.51~10.61 GHz).

• Communications of the Korean Mathematical Society
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• v.9 no.2
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• pp.411-414
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• 1994

In this paper a flow will be a pair (X, T) where X is a compact Hausdorff space, and T is a homeomorphism of X onto X. We will usually but not always assume that X is a metric space. We sometimes suppress the homeomorphism T notationally, and just denote a flow by X. General references for the preliminary dynamical notations discussed in this section are [5] and [3]. (The latter should be used with care, since transformations are written on the right there.)(omitted)

• International Journal of Contents
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• v.9 no.1
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• pp.38-41
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• 2013

The clamp meter maintains electric safety as a non-invasive method while measuring the absolute value of tube current with it has been recently developed for an X-ray high-tension cable. Especially this can show high accuracy at short X-ray exposure time. Considering such a condition, this study is to evaluate the feasibility of a clamp meter in measuring X-ray tube current by taking the measurements and comparing with those of the Dynalyzer III which has been considered as a standard measuring device. From measuring the tube current accuracy depending on changes in tube voltage and exposure time, the clamp meter showed higher accuracy rate which was -1.3~4.2% difference. Thus clamp meter can be used for clinical radiologists who are not familiar electric circuit to manage X-ray devices easily and correctly in the future.

• Journal of Korean Ophthalmic Optics Society
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• v.3 no.1
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• pp.115-120
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• 1998

The $TiN_x$ thin films were prepared on glass substrate by RF(radio-frequency) magnetron sputtering apparatus from a Ti target in a gaseous mixture of argon and nitrogen. In deposition, a RF power supply was used as a power source with a constant power of 240W, and the substrate was heated to $200^{\circ}C$. The films were obtained at nitrogen flow rates in the range 3-9 seem with a constant argon flow rate of 20 seem. For the films obtained, the chemical binding energy of the films was investigated by XPS (x-ray photoelectron spectroscopy) in order to analyze the chemical nature and composition of the films.

• Bulletin of the Korean Chemical Society
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• v.9 no.5
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• pp.289-291
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• 1988

The ratio of trivalent to divalent copper has been determined by the redox titration for two superconducting phases of $YBa_2Cu^{3+}_{2x}Cu^{2+}_{3-2x}O_{6.5+x}$ with the onset temp. of 60K (x = 0.23 ${\pm}$ 0.01) and 90K (x = 0.35 ${\pm}$ 0.02), and for the insulating one (x ${\cong}$ 0) which was kept in an ambient atmosphere for 72 hrs. It is found that $T_c$, and the ratio of $Cu^{3+}/Cu^{2+}$ depend strongly on the annealing temperature and time. A typical orthorhombic phase can easily be obtained by a slow cooling or stepwise cooling at $PO_2$ = 1 atm, and shows a high Tc (ca. 90K) superconductivity.

• Bulletin of the Korean Mathematical Society
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• v.33 no.3
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• pp.419-425
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• 1996

Let ${X, X_n, n \geq 1}$ be a sequence of independent and identically distributed(i.i.d) random variables with EX = 0 and $E$\mid$X$\mid$^p < \infty$ for some $p \geq 1$. Let ${a_{ni}, 1 \leq i \leq n, n \geq 1}$ be a triangular arrary of constants. The almost sure(a.s) convergence of weighted sums $\sum_{i=1}^{n} a_{ni}X_i$ can be founded in Choi and Sung[1], Chow[2], Chow and Lai[3], Li et al. [4], Stout[6], Sung[8], Teicher[9], and Thrum[10].

• Proceedings of the KAIS Fall Conference
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• 2000.10a
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• pp.27-29
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• 2000

다공성 세라믹 기질에 제올라이트의 코팅은 기체 분리용 membrane으로 매우 효과적이다. 수열합성법으로 NaX 제올라이트를 다공성 cordierite와 cordierite, mullite 복합기질의 표면에 코팅하는 과정에서 H₂O/Al₂O₃ 몰비를 500, 1000으로 증가시키면서 코팅 특성의 변화와 코팅 속도를 측정한 결과 몰비가 감소할수록 코팅층에 NaA 제올라이트의 존재비가 증가하였으며, 코팅층의 형성 속도는 증가하였다. H₂O/Al₂O₃ 1000 몰에서는 반응 9일에 매우 치밀하고 균일한 NaX 제올라이트 코팅층을 얻을 수 있었으며, H₂O/Al₂O₃ 1000 몰에서는 반응3일에서 1000 몰의 9일과 같은 결과를 얻을 수 있었다.

• Journal of the Korean Magnetics Society
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• v.3 no.2
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• pp.130-134
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• 1993

The magnetic properties of the amorphous $Fe_{73.5-X}Co_{X}Cu_{1}Nb_{3}Si_{13.5}B_{9}(x=2,\;4)$ alloys, fabricated by a single roll rapid quenching technique and annealed at $400~650^{\circ}C$, have been investigated. The optimum annealing temperature is $550^{\circ}C$ for the amorphous $Fe_{71.5}Co_{2}Cu_{1}Nb_{3}Si_{13.5}B_{9}$ alloy. The properties of the nanocrystalline $Fe_{71.5}Co_{2}Cu_{1}Nb_{3}Si_{13.5}B_{9}$ alloy show the relative permeability of $1.1{\times}10^{4}$ and the coercive force of 0.22 Oe at 1 kHz. When annealed at $600^{\circ}C$, the nanocrystalline $Fe_{69.5}Co_{4}Cu_{1}Nb_{3}Si_{13.5)B_{9}$ alloy shows the relative permeability of $1.0{\times}10^{4}$ and the coercive force of 0.19 Oe at 1 kHz. From the X-ray measurement, it is found that the remarkably improved soft magnetic properties are the effect of the formation of $\alpha$-Fe(Si) grain. By the results of FMR exper-imeIlt, the optimum annealing condition is just below temperature which the peak-to-peak line width of FMR spectrum increase rapidly.