• Bulletin of the Korean Mathematical Society
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• v.58 no.6
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• pp.1341-1354
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• 2021

Let r ≥ 2, and let k_i ≥ 2 for 1 ≤ i ≤ r. Mixed van der Waerden's theorem states that there exists a least positive integer w = w(k₁, k₂, k₃, …, k_r; r) such that for any n ≥ w, every r-colouring of [1, n] admits a k_i-term arithmetic progression with colour i for some i ∈ [1, r]. For k ≥ 3 and r ≥ 2, the mixed van der Waerden number w(k, 2, 2, …, 2; r) is denoted by w₂(k; r). B. Landman and A. Robertson [9] showed that for k < r < $\frac{3}{2}$(k - 1) and r ≥ 2k + 2, the inequality w₂(k; r) ≤ r(k - 1) holds. In this note, we establish some results on w₂(k; r) for 2 ≤ r ≤ k.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.1
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• pp.17-20
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• 2020

Developing effective and earth-abundant electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for the commercialization of a water splitting system. In particular, the overpotential of the OER is relatively higher than the HER, and thus, it is considered that one of the important methods to enhance the performance of the electrocatalyst is to reduce the overpotential of the OER. In this work, we present a simple synthetic route for triple perovskite Nd_1.5Ba_1.5CoFeMnO_x with high performance OER and HER activity. This triple perovskite structure which shows high crystallinity through combustion method shows superior bifunctional catalytic performance in alkaline media. We believe that the prepared triple provskite with high performance OER and HER activity can give further feasibility for the commercialization of a water splitting system.

• Communications of the Korean Mathematical Society
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• v.36 no.3
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• pp.401-411
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• 2021

A Diophantine m-tuple is a set {a₁, a₂, …, a_m} of positive integers such that a_ia_j+1 is a perfect square for all 1 ≤ i < j ≤ m. Let E_k be the elliptic curve induced by Diophantine triple {F_2k, 5F_2k+2, 3F_2k + 7F_2k+2}. In this paper, we find the structure of a torsion group of E_k, and find all integer points on E_k under assumption that rank(E_k(ℚ)) = 1 and some further conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.918-922
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• 2006

Chalcogenide Phase change memory has the high performance necessary for next-generation memory, because it is a nonvolatile memory with high programming speed, low programming voltage, high sensing margin, low power consumption and long cycle duration. To minimize the power consumption and the program voltage, the new composition material which shows the better phase-change properties than conventional $Ge_2Sb_2Te_5$ device has to be needed by accurate material engineering. In the present work, we investigate the basic thermal and the electrical properties due to phase-change compared with chalcogenide-based new composition $Ge_1Se_1Te_2$ material thin film and convetional $Ge_2Sb_2Te_5$ PRAM thin film. The fabricated new composition $Ge_1Se_1Te_2$ thin film exhibited a successful switching between an amorphous and a crystalline phase by applying a 950 ns -6.2 V set pulse and a 90 ns -8.2 V reset pulse. It is expected that the new composition $Ge_1Se_1Te_2$ material thin film device will be possible to applicable to overcome the Set/Reset problem for the nonvolatile memory device element of PRAM instead of conventional $Ge_2Sb_2Te_5$ device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.1
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• pp.30-37
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• 2005

The microwave dielectric properties and their related structural characteristics in solid solutions of (1-$\chi$) Ba($Mg_{1/3}$Nb$_{2/3}$) $O_3$-$\chi$La(Mg$_{2/3}$Nb$_{1}$3) $O_3$(BLMN) have been investigated by measuring the dielectric constant($\varepsilon$r), Q value and temperature coefficient of resonant frequency($\tau$f) and by observing the crystal structure using high resolution transmission electron microscopy (HRTEM). Microwave dielectric properties showed characteristic features for specific composition. Dielectric constant($\varepsilon$$_{r}$) showed maximum value at the composition which corresponds to the phase boundary between 1 : 2 ordered and 1 : 1 ordered structure. The increase in $\varepsilon$$_{r}$ may be caused by the rattling of ions by incorporating smaller ions and the disordered structure. The variation of temperature coefficient of resonant frequency($\tau$$_{f}$) was investigated in terms of oxygen octahedra tilting.dra tilting.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.6
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• pp.759-764
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• 2011

Mixed-conducting oxide powders, $BaCe_{0.9}Y_{0.1}O_{2.95}$ (BCY) and $SrCe_{0.9}Y_{0.1}O_{2.95}$ (SCY) powders have been prepared by a solid-state reaction method. Xray diffraction patterns of the prepared powders showed the sharp peaks of the $BaCe_{0.9}Y_{0.1}O_{2.95}$ and $SrCe_{0.9}Y_{0.1}O_{2.95}$ phases. The oxide powders that were prepared by attrition milling showed rather large particles and severe necking between particles in FE-SEM images as well as residual reactant ($BaCO_3$) and secondary phases ($SrCeO_3$ and $CeO_2$) in XRD patterns. The oxide powders prepared using ball milling showed particles under approximately 500 nm and typical XRD patterns of the $BaCe_{0.9}Y_{0.1}O_{2.95}$ and $SrCe_{0.9}Y_{0.1}O_{2.95}$ phases. Ceramic membranes of the $BaCe_{0.9}Y_{0.1}O_{2.95}$ and $SrCe_{0.9}Y_{0.1}O_{2.95}$ phases were fabricated by the aerosol deposition method using the oxide powders synthesized.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.628-633
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• 2011

Studies on lead-free piezoelectrics have been attractive as means of meeting environmental requirements. We synthesized lead-free piezoelectric $(Bi_{1/2}Na_{1/2})TiO_3-Ba(Cu_{1/3}Nb_{2/3})O_3$ (BNT-BCN) ceramics, and their dielectric, piezoelectric, and strain behavior were characterized. As BCN with a tetragonal phase was incorporated into the rhombohedral BNT lattice, the lattice constant increased. A small amount of BCN increased the density and dielectric constant forming the complete solid solution with BNT. However, BCN above 10 mol% was precipitated into a separate phase, and which was detected with XRD. In addition, EDX measurement revealed that Cu in BCN was not distributed homogeneously but was accumulated in a certain area. A lower density with a large amount of BCN was attributed to the nonsinterable property of BCN with large tetragonaliy. The dielectric constant vs the temperature change and the strain vs the electric field indicated that the ferroelectric property of BNT was diminished and paraelectric behavior was enhanced with the BCN addition. BNT-7.5BCN showed a 0.11% unimorph strain with a 9.0 kV/mm electric field with little hysteresis.

• Biomolecules & Therapeutics
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• v.31 no.2
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• pp.168-175
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• 2023

Tramadol is an opioid analog used to treat chronic and acute pain. Intradermal injections of tramadol at hundreds of millimoles have been shown to produce a local anesthetic effect. We used the whole-cell patch-clamp technique in this study to investigate whether tramadol blocks the sodium current in HEK293 cells, which stably express the pain threshold sodium channel Na_v1.7 or the cardiac sodium channel Na_v1.5. The half-maximal inhibitory concentration of tramadol was 0.73 mM for Na_v1.7 and 0.43 mM for Na_v1.5 at a holding potential of -100 mV. The blocking effects of tramadol were completely reversible. Tramadol shifted the steady-state inactivation curves of Na_v1.7 and Na_v1.5 toward hyperpolarization. Tramadol also slowed the recovery rate from the inactivation of Na_v1.7 and Na_v1.5 and induced stronger use-dependent inhibition. Because the mean plasma concentration of tramadol upon oral administration is lower than its mean blocking concentration of sodium channels in this study, it is unlikely that tramadol in plasma will have an analgesic effect by blocking Na_v1.7 or show cardiotoxicity by blocking Na_v1.5. However, tramadol could act as a local anesthetic when used at a concentration of several hundred millimoles by intradermal injection and as an antiarrhythmic when injected intravenously at a similar dose, as does lidocaine.

• Bulletin of the Korean Mathematical Society
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• v.57 no.6
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• pp.1491-1499
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• 2020

We give a strong fundamental domain for the quotient of PGL₂(𝔽_q((t^-1))) by PGL₂(𝔽_q[t]) as a subset of distinct ordered triple points of ℙ¹(𝔽_q((t^-1))).

• Korean Journal of Mineralogy and Petrology
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• v.34 no.3
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• pp.169-176
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• 2021

This study aimed to fundamentally understand structural changes of zeolite under pressure and in the presence of different pressure-transmitting media (PTM) for application studies such as immobilization of heavy metal cation or CO₂ storage using pressure. High-pressure X-ray powder diffraction study was conducted on the zeolite-W (K_6.4Al_6.5Si_25.8O₆₄× 15.3H₂O, K-MER) to understand linear compressibility and the bulk moduli in different PTM conditions. Zeolite-w is a synthetic material having the same framework as natural zeolite merlinoite ((K, Ca_0.5, Ba_0.5, Na)₁₀ Al₁₀Si₂₂O₆₄× 22H₂O). The space group of the sample was identified as I4/mmm belonging to the tetragonal crystal system. Water, carbon dioxide, and silicone-oil were used as pressure-transmitting media. The mixture of sample and each PTM was mounted in a diamond anvil cell (DAC) and then pressurized up to 3 GPa with an increment of ca. 0.5 GPa. Pressure-induced changes of powder diffraction patterns were measured using a synchrotron X-ray light source. Lattice constants, and bulk moduli were calculated using the Le-Bail method and the Birch-Murnaghan equation. In all PTM conditions, linear compressibility of c-axis (𝛽^c) was 0.006(1) GPa^-1 or 0.007(1) GPa^-1. On the other hand, the linear compressibility of a(b)-axis (𝛽^a) was 0.013(1) GPa^-1 in silicone-oil run, which is twice more compressible than the a(b)-axis in water and carbon dioxide runs, 𝛽^a = 0.006(1) GPa^-1. The bulk moduli were measured as 50(3) GPa, 52(3) GPa, and 29(2) GPa in water, carbon dioxide, and silicone-oil run, respectively. The orthorhombicities of ac-plane in the water, and carbon dioxide runs were comparatively constant, near 0.350~0.353, whereas the value decreased abruptly in the silicone-oil run following formula, y = -0.005(1)x + 0.351(1) by non-penetrating pressure fluid condition.