Phenomenological analysis of random telegraph noise in amorphous TiOx-based bipolar resistive switching random access memory devices

As dimensions of resistive random access memories (RRAMs) devices continue to shrink, the low-frequency noise of nanoscale devices has become increasingly important in evaluating the device reliability. Thus, we investigated random telegraph noise (RTN) caused by capture and emission of an electron at traps. We physically analyzed capture and emission processes through systematic measurements of amorphous TiOx (alpha-TiOx)-based bipolar RRAMs. RTNs were observed during high-resistance state (HRS) in most devices. However, discrete switching behavior was scarcely observed in low-resistance state (LRS) as most of traps in the alpha-TiOx were filled with mobile ions such as O2- in LRS. The capture and emission processes of an electron at traps are largely divided into two groups: (1) both capture and emission processes are mainly affected by electric field; and (2) one of the capture and emission processes is only influenced by the thermal process. This paper provides fundamental physics required to understand the mechanism of RTNs in alpha-TiOx-based bipolar RRAMs.     

Control of particle size and shape of precursors for ceria using ammonium carbonate as a precipitant

Spherical nanocrystalline precursors of ceria (CeO₂) and CeO₂ powder with different size distributions were prepared by a reflux method using cerium nitrate hexahydrate (CN) as the cerium source and ammonium carbonate (AC) as the precipitant. The crystalline phases of the synthesized CeO₂ precursors were identified as orthorhombic Ce₂O(CO₃)₂·H₂O and hexagonal CeCO₃OH. The particle size and shape could be easily controlled by the CN concentration and the ratio of [AC]/[CN]. The CeO₂ precursors were calcined at 400-700 °C to obtain CeO₂. The particle size distribution and morphology of the synthesized CeO₂ powders were unaffected by the calcination. The specific surface area of the CeO₂ powders was increased by the release of CO₂ and H₂O during the calcination. The calcination temperature is an important factor for the preparation of CeO₂ powder with a high surface area.     

Cold Oxygen Plasma Treatments for the Improvement of the Physicochemical and Biodegradable Properties of Polylactic Acid Films for Food Packaging

The effects of cold plasma (CP) treatment on the physicochemical and biodegradable properties of polylactic acid (PLA) films were studied. The PLA films were exposed to CP for 40 min at 900 W and 667 Pa using oxygen as the plasma‐forming gas. The tensile, optical, and dynamic mechanical thermal properties, surface morphology, printability, water contact angle, chemical structure, weight change, and biodegradability properties of the films were evaluated during storage for up to 56 d. The tensile and optical properties of the PLA films were not significantly affected by CP treatment (CPT; P > 0.05). The surface roughness and water contact angle of PLA films increased by CPT and further increased during storage for 56 d. The printability of the PLA films increased following CPT and remained stable throughout the storage period. CP‐induced hydrophilicity was also sustained during the storage period. The PLA films lost 1.9% of their weight after CPT, but recovered 99.5% of this loss after 14 d in storage. Photodegradation, thermal, and microbial biodegradable properties of the films were significantly improved by CPT (P < 0.05). Accelerated biodegradation of CP‐treated PLA sachets with and without cheese was observed in compost. These results demonstrate the potential of CPT for modifying the stiffness, water contact angle, and chemical structure of PLA films and improving the printability and biodegradability of the films for food packaging.     

Differentiated influences of benefit and risk perceptions on nuclear power acceptance according to acceptance levels: evidence from Korea

The perceived benefit and risk of nuclear power generation have received considerable attention as determinants of the public's nuclear power acceptance. However, the contingency of the relative importance of these benefit and risk has been less explored. Using Korea as an example, this study explores the possibility that the relative importance of perceived benefit and risk on nuclear power acceptance depends on acceptance levels. Our results from latent class analysis and multinomial probit show that, in determining whether an individual shows a moderate level of nuclear power acceptance rather than a low level, perceived risk plays a dominant role compared to perceived benefit; however, regarding whether he/she shows a high level of nuclear power acceptance rather than a moderate level, this relative importance is reversed. These results carry practical implications for risk governance of nuclear power, particularly with regard to communication with the public.     

Flow instability due to cryogenic cavitation in the downstream of orifice

Flow instability in LRE (liquid rocket engine) occurs due to various reasons such as flow interactions with valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of mass and pressure oscillations because of the cyclic formation and depletion of cavitation. Meanwhile, the main propellant in a liquid rocket engine is the cryogenic fluid, which properties are very sensitive to temperature variation. And the change of propellant properties to temperature variation by thermodynamic effect needs to be properly taken into account in the flow analysis in order to understand basic mechanisms for cryogenic cavitation. The present study focuses on the formation of cryogenic cavitation by using the IDM model suggested by Shyy and coworkers. The flow instability was also numerically investigated in the downstream of orifice with a developed numerical code. Calculation results show that cryogenic cavitation can be a primary source of flow instability, leading to mass fluctuations accompanied by pressure oscillations. The prediction of cavitation in cryogenic fluid is of vital importance in designing a feeding system of an LRE. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park Changjin Lee received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1983 and 1985. He then went on to receive his Ph.D. degree from University of Illinois at Urbana- Champaign in 1992. Dr. Lee is currently a Professor at the department of Aerospace Engineering at Konkuk University in SEOUL, Korea. His research interests are in the area of combustion instabilities of hybrid, liquid rocket and jet propulsions. Tae-Seong Roh received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1984 and 1986. He then went on to receive his Ph.D. degree from Pennsylvania State University in 1995. Dr. Roh is currently a Professor at the department of Aerospace Engineering at Inha University in Incheon, Korea. His research interests are in the area of combustion instabilities, rocket and jet propulsions, interior ballistics, and gas turbine engine defect diagnostics.     

Effects of formaldehyde/urea mole ratio and melamine content on the hydrolytic stability of cured urea-melamine-formaldehyde resin

The influence of formaldehyde/urea (F/U) mole ratio and melamine content on the hydrolytic stability of urea-melamine-formaldehyde (UMF) resin was investigated. The hydrolytic stability of cured UMF resin was determined by measuring the mass loss and the liberated formaldehyde concentration after acid hydrolysis. A higher F/U mole ratio and greater melamine content of UMF resins resulted in lower hydrolytic stability. These results indicated that higher F/U mole ratio and greater melamine content resulted in more branched network structure, which subsequently increases the susceptibility of cured UMF resin toward acid hydrolysis.     

A block transportation scheduling system considering a minimisation of travel distance without loading of and interference between multiple transporters

Material transportation scheduling problems concerning scheduling optimisation have been extensively investigated by researchers in such fields as industrial engineering and management science. Various algorithms have been proposed to solve such problems. However, the majority of these algorithms cannot be applied to a block transportation problem when a shipyard that uses a transporter, a large vehicle employed for moving weight, is considered. In this study, a hybrid optimisation algorithm is proposed for solving a block transportation problem when multiple transporters are used. With regards to the transporters, a minimisation of the travel distance without loading of and interference between the transporters is considered. A block transportation scheduling system is then developed based on the proposed algorithm. The developed system is applied to an actual block transportation scheduling problem of a shipyard. From the attained results, we demonstrate that the proposed algorithm has the ability to effectively solve the block transportation scheduling problems of a shipyard.     

Selective Production of H2 from Ethanol at Low Temperatures over Rh/ZrO2–CeO2 Catalysts

A series of Rh catalysts on various supports (Al₂O₃, MgAl₂O₄, ZrO₂, and ZrO₂–CeO₂) have been applied to H₂ production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO₂–CeO₂ > Rh/Al₂O₃ > Rh/MgAl₂O₄ > Rh/ZrO₂. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO₂–CeO₂ catalyst exhibits the highest CO₂ selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO₂–CeO₂ catalyst exhibited the highest H₂ yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO₂–CeO₂ resulting in efficient transfer of mobile oxygen species from the H₂O molecule to the reaction intermediate.     

Comparative Study on Nano-Sized 1 wt% Pt/Ce<Subscript>0.8</Subscript>Zr<Subscript>0.2</Subscript>O<Subscript>2</Subscript> and 1 wt% Pt/Ce<Subscript>0.2</Subscript>Zr<Subscript>0.8</Subscript>O<Subscript>2</Subscript> Catalysts for a Single Stage Water Gas Shift Reaction

Abstract  

A comparative study on nano-sized Pt/Ce_0.8Zr_0.2O₂ and Pt/Ce_0.2Zr_0.8O₂ catalysts in a single stage water gas shift (WGS) reaction was carried out. These catalysts were prepared by impregnating 1 wt% Pt on nano-sized cubic (Ce_0.8Zr_0.2O₂) and tetragonal (Ce_0.2Zr_0.8O₂) supports. Both catalysts have been applied to WGS under identical conditions to understand beneficial effect of cubic/tetragonal phases of Ce_(1 − x)Zr_(x)O₂. 1 wt% Pt/Ce_0.8Zr_0.2O₂ exhibited higher CO conversion than 1 wt% Pt/Ce_0.2Zr_0.8O₂. In addition, 1 wt% Pt/Ce_0.8Zr_0.2O₂ catalyst showed relatively stable activity with time on stream. The high activity/stability of 1 wt% Pt/Ce_0.8Zr_0.2O₂ catalyst was correlated to its higher Pt dispersion and easier reducibility.