A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO₂ phase at 600 °C and Mn₃O₄/Mn₂O₃ and γ‐Al₂O₃ phases at 800 °C. Electron microscopy and N₂ adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ～20 nm and a surface area of >410 m² g^?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals.     

Role of O2/Ar mixing ratio on the performances of IZO thin film transistors fabricated using a two-step deposition process

In this study, a simple method of fabricating a thin-film transistor (TFT) with a double-layered channel using indium–zinc-oxide (IZO) films was proposed. Two IZO films used as channel layers were consecutively deposited via sputtering without stopping the vacuum and only by changing the volumetric fraction of the additive O₂ gas during the deposition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis showed a large difference in the depth profiles of the InO^? and InO₂^? ions between the two IZO layers. Compared to the conventional single-IZO-channel TFT, the double-IZO-channel TFT that was fabricated using the proposed two-step deposition method showed greatly improved electrical characteristics: the on/off-state current ratio was increased from 1.30 × 10⁵ to 1.03 × 10⁶, and the field effect mobility was enhanced from 1.2 to 9.3 cm²/Vs.     

Development of bismuth tellurium selenide nanoparticles for thermoelectric applications via a chemical synthetic process

Bismuth tellurium selenide (Bi₂Te_ySe_3−y) nanoparticles for thermoelectric applications are successfully prepared via a water-based chemical reaction under atmospheric conditions. The nanostructured compound is prepared using a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursor (Bi(NO₃)₃) in water and to favor the reaction with reduced sources of tellurium and selenium. The resulting powder is smaller than ca. 100 nm and has a crystalline structure corresponding to the rhombohedral Bi₂Te_2.7Se_0.3. The nanocrystalline powder is sintered via a spark plasma sintering process to obtain a sintered body composed of nano-sized grains. Important transport properties of the sintered body are measured to calculate its most important characteristic, the thermoelectric performance. The results demonstrate a relationship between the nanostructure of the sintered body and its thermal conductivity.     

Fracture behavior of Cu-cored solder joints

Copper-cored solder can be regarded as the next-generation solder for microelectronic semiconductors exposed to harsh operating conditions owing to its excellent sustainability under extreme thermal conditions, e.g., in microelectronic semiconductors used in transportation systems. Cu-cored solder joints with two different coating layers, Sn–3.0Ag and Sn–1.0In, were compared with the baseline Sn–3.0Ag–0.5Cu solder. The fracture strength and failure mode were examined using the high-speed ball-pull and normal-speed shear tests. The Cu-cored solder joint with the Sn–1.0In plating layer exhibited the highest ball-pull and shear strengths. In addition, it showed a much lower percentage of interface fracture between the Cu-core and plating layer than the interface fracture percentage in the Sn–3.0Ag plating layer due to the improved wettability between the Cu-core and Sn–1.0In plating layer.     

Development of low-noise centrifugal fans for a refrigerator using inclined S-shaped trailing edge

Low-noise centrifugal fans are developed by modifying the linear trailing edge lines of the fan blades into inclined S-shaped lines. The noise reductions achieved by using the inclined S-shaped trailing edges in the existing fans are confirmed by comparing the predicted BPF noise components of the developed fans with those of the existing fan. In addition, the turbulent kinetic energy of the fluid for the inclined S-shaped fans is predicted to be less than that for the existing fan. Finally, experiments using four prototype fans show that the levels of broadband noise from the newly developed fans are less than those of noise from existing fans. An additional experiment performed by using a selected low-noise fan installed in a household refrigerator show that the overall noise from the new fan is reduced by approximately 2.2 dB in comparison with that from the existing fan in the refrigerator.     

Studies on the heating capacity control of a multi-type heat pump system applying a multi-input multi-output (MIMO) method

This paper describes a method to control capacity of a multi-type heat pump system. Because indoor units are interconnected, alteration of the heating or cooling setting of one indoor unit can influence the performance of the other indoor units. Proportional-integral (PI) controllers were used to assess system performance, and the PI controllers’ gain values were optimized by using a genetic algorithm. A system model was established following a system identification optimization process, and a pseudo random binary sequence was selected as the system identification input signal. A multi-input multi-output (MIMO) controller was more effective in reducing such cross-coupling effects than a single-input single-output (SISO) controller. The temperature at the secondary fluid outlet in the condenser and the saturation pressure at the evaporator were selected as the control variables in the MIMO controller. The experimental results showed that an optimized MIMO controller could reduce overshoot by up to 40% compared with the results using a SISO controller.     

Contextualizing the ideas of technology in Korea—Questions of technology and early modern experiences

In the early to mid-2000s, Korea was touted as a strong IT (information technology) nation. But its IT success story has faded into the background less than half a decade’s time. Critiques hold among others the problem of hardware-oriented, commercialistic, and consumerist nature of IT environment including the centralized, statist IT governance responsible for hindering an IT take-off in Korea. This problematic environment of IT is fundamentally a material consequence of particular ideas of technology Korean society maintains—ideas of hardwarism, commercialism, and consumerism. Then the important question is the origin of these ideas. A large body of research argues the national modernization drive of the 1960s as an embryonic momentum in which hardware-centric, commercially oriented, and consumerist ideas of technology were disseminated in earnest. Persuasive as this argument is, the question still remains concerning how such perceptions about technology were embraced by the general populace at that moment with outright enthusiasm. This study argues that they were already gestated during the nation’s initial contact with modernity mostly by way of Japan in the context of the imperialistic world order of the late 19th century. And embedded as a paradigmatic structure, these ideas have been critical in the shaping of the trajectory of technology development and broadly a basic framework of modernization in Korea.     

Synthesis of mesoporous tungsten oxide nanofibers using the electrospinning method

Mesoporous tungsten oxide nanofibers were synthesized via a 500 °C thermal treatment of composite nanofibers prepared by electrospinning an ethanol solution consisting of tungsten ethoxide, P123 triblock copolymer, and polyvinylpyrrolidone. The as-electrospun composites exhibited unwoven nanofibers with an average diameter of 233 nm and a smooth surface morphology. During the calcination process, the composite nanofibers were shrunk to 85 nm in diameter and converted into rough, wormhole-like nanofibers. These were formed by agglomerating polycrystalline WO₃ particles of 10–30 nm along the axial direction. Furthermore, a measured pore-size distribution indicated that this nanofiber mat had different types of meso-sized porosities, which may have resulted from their wormhole-like structures and inter-fiber voids. In addition, it was observed to have the intra-grain porosity with the diameter of about 1.0 nm.