• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.69-70
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• 2023

The development of advanced 3D printing technologies has opened up new opportunities for customized digital designs in the construction industry. Using nano- and micro-scale additives is expected to improve the performance of cement-based materials in 3D printing. TiO₂ particles have been widely used as reinforcing additives in cement-based materials. Therefore, this study aims to investigate the application of cement-based materials containing multi-size TiO₂ particles in binder jet 3D printing and the effect of different-size TiO₂ particles on the performance of printed samples. TiO₂ particles exhibit an excellent filling effect, which increases the density of the printed samples and promotes hydration, thereby improving the compressive strength of the samples. In addition, larger TiO₂ particles exert more pronounced filling and photocatalytic effects on the resulting samples.

• Archives of Pharmacal Research
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• v.17 no.4
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• pp.278-280
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• 1994

1,5-diketones(3) undewent cyclization to 4H-pyrano[3,2-d]pyrazoles (4a-d),4H-piperidino[3, 2-d]pyrazole (5) and pyrazolo[5,4-d]thiopyran (6) upon treatment with P/sub 2/O/sub 5/, CH/sub 3/COONH/sub 4/ and /or P/sub 2/S/sub 5/. Moreover, treatment of (4) with CH/sub 3/COONH/sub 4/ and/or P/sub 2/S/sub 5/ afforded (5) and (6). The structures of the hitherto unknown ring systems have been confirmed by analytical and spectral data.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.188-189
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• 2022

With the development of nano-reinforcement technology, TiO₂ nanomaterials have received widespread attention as one of the additives without pozzolanic reaction, which can be used to improve the mechanical properties of cement-based materials. Meanwhile, with the development of additive manufacturing technology or known as 3D printing technology, its application in the construction field has also got noticed. Therefore, in this work, the effect of three sizes of TiO₂ on the compressive strength of hardened cement-based materials fabricated by binder jetting 3d printing was evaluated. According to the results, the TiO₂ particles with larger sizes can provide better reinforcement to the hardened cement due to its more significant filling effect.

• Journal of Powder Materials
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• v.30 no.4
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• pp.318-323
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• 2023

The thermoelectric effect, which converts waste heat into electricity, holds promise as a renewable energy technology. Recently, bismuth telluride (Bi2Te3)-based alloys are being recognized as important materials for practical applications in the temperature range from room temperature to 500 K. However, conventional sintering processes impose limitations on shape-changeable and tailorable Bi₂Te₃ materials. To overcome these issues, three-dimensional (3D) printing (additive manufacturing) is being adopted. Although some research results have been reported, relatively few studies on 3D printed thermoelectric materials are being carried out. In this study, we utilize extrusion 3D printing to manufacture n-type Bi_1.7Sb_0.3Te₃ (N-BST). The ink is produced without using organic binders, which could negatively influence its thermoelectric properties. Furthermore, we introduce graphene oxide (GO) at the crystal interface to enhance the electrical properties. The formed N-BST composites exhibit significantly improved electrical conductivity and a higher Seebeck coefficient as the GO content increases. Therefore, we propose that the combination of the extrusion 3D printing process (Direct Ink Writing, DIW) and the incorporation of GO into N-BST offers a convenient and effective approach for achieving higher thermoelectric efficiency.

• Journal of Powder Materials
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• v.30 no.2
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• pp.123-129
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• 2023

High-temperature and high-pressure post-processing applied to sintered thermoelectric materials can create nanoscale defects, thereby enhancing their thermoelectric performance. Here, we investigate the effect of hot isostatic pressing (HIP) as a post-processing treatment on the thermoelectric properties of p-type Bi_0.5Sb_1.5Te_3.0 compounds sintered via spark plasma sintering. The sample post-processed via HIP maintains its electronic transport properties despite the reduced microstructural texturing. Moreover, lattice thermal conductivity is significantly reduced owing to activated phonon scattering, which can be attributed to the nanoscale defects created during HIP, resulting in an ~18% increase in peak zT value, which reaches ~1.43 at 100℃. This study validates that HIP enhances the thermoelectric performance by controlling the thermal transport without having any detrimental effects on the electronic transport properties of thermoelectric materials.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.230-236
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• 2021

Ionic conduction mechanism of Mg-Al layered double hydroxides (LDHs) intercalated with CO₃^2- (Mg-Al CO₃^2- LDH) was studied. The electromotive force for the water vapor concentration cell using Mg-Al CO₃^2- LDH as electrolyte showed water vapor partial pressure dependence and obeyed the Nernst equation, indicating that the hydroxide ion transport number of Mg-Al CO₃^2- LDH is almost unity. The ionic conductivity of Mg(OH)₂, MgCO₃ and Al₂(CO₃)₃ was also examined. Only Al₂(CO₃)₃ showed high hydroxide ion conductivity of the order of 10^-4 S cm^-1 under 80% relative humidity, suggesting that Al₂(CO₃)₃ is an ion conducting material and related to the generation of carrier by interaction with water. To discuss the ionic conduction mechanism, Mg-Al CO₃^2- LDH having deuterium water as interlayer water (Mg-Al CO₃^2- LDH(D₂O)) was prepared. After the adsorbed water molecules on the surface of Mg-Al CO₃^2- LDH(D₂O) were removed by drying, DC polarization test for dried Mg-Al CO₃^2- LDH(D₂O) was examined. The absorbance attributed to O-D-stretching band for Mg-Al CO₃^2- LDH(D₂O) powder at around the positively charged electrode is larger than that before polarization, indicating that the interlayer in Mg-Al CO₃^2- LDH is a hydroxide ion conduction channel.

• Journal of IKEEE
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• v.26 no.2
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• pp.329-332
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• 2022

In this paper, retention characteristics of lateral charge migration according to parameters of 3D NAND flash memory to which ferroelectric (HfO₂) structure is applied and ∆V_th were analyzed. The larger the P_s, the greater maximum polarization possible in ferroelectric during Programming. Therefore, the initial V_th increases by about 1.04V difference at P_s 70µC/cm² than at P_s 25µC/cm². Also, electrons trapped after the Program operation causes lateral charge migration over time. Since ferroelectric maintains polarization without applying voltage to the gate after Programming, regardless of P_s value, polarization increases as P_r increases and the ∆V_th due to lateral charge migration becomes smaller by about 1.54V difference at P_r 50µC/cm² than P_r 5µC/cm².

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10A
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• pp.958-964
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• 2005

In this thesis, the matching network at the local oscillator port of the sub-harmonic mixer is optimized for reducing the conversion loss. A downconverter for point to point system applications is designed and fabricated using the such sub-harmonic mixer. The sub-harmonic mixer achieved the conversion loss of 11.8 dB at the 12 dBm input power of the local oscillator and the isolation of less than -40 dB. The downconverter achieved the IF output power flatness of 2 dB and the total noise figure of 5.9 dB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.6
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• pp.2649-2669
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• 2020

In this paper, we analyze the secrecy performance of single-input multiple-output (SIMO) relay systems over κ-μ shadowed fading channels. Based on considering relay model employing decode-and-forward (DF) protocol, two security evaluation metrics, namely, secure outage probability (SOP) and probability of strictly positive secrecy capacity (SPSC) are studied, for which closed-form analytical expressions are derived. In addition, Monte Carlo results prove the validity of the theoretical derivation. The simulation results confirm that the factors that enhance the security include large ratio of (μ_D, μ_E), (m_D, m_E), (L_D, L_E) and small ratio of (k_D, k_E) under the high signal-to-noise ratio regime.

• The Pure and Applied Mathematics
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• v.30 no.3
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• pp.337-345
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• 2023

Different versions of the boundary Schwarz lemma for the 𝒩 (𝜌) class are discussed in this study. Also, for the function g(z) = z+b₂z²+b₃z³+... defined in the unit disc D such that g ∈ 𝒩 (𝜌), we estimate a modulus of the angular derivative of g(z) function at the boundary point 1 ∈ 𝜕D with g'(1) = 1 + 𝜎 (1 - 𝜌), where ${\rho}={\frac{1}{n}}{\sum\limits_{i=1}^{n}}g(c_i)={\frac{g^{\prime}(c_1)+g^{\prime}(c_2)+{\ldots}+g^{\prime}(c_n)}{n}}{\in}g^{\prime}(D)$ and 𝜌≠1, 𝜎 > 1 and c₁, c₂, ..., c_n ∈ 𝜕D. That is, we shall give an estimate below |g"(1)| according to the first nonzero Taylor coefficient of about two zeros, namely z = 0 and z ≠ 0. Estimating is made by using the arithmetic average of n different derivatives g'(c₁), g'(c₂), ..., g'(c_n).