Performances of Liquid‐Exfoliated Transition Metal Dichalcogenides as Hole Injection Layers in Organic Light‐Emitting Diodes

2D transition metal dichalcogenide (TMD) nanosheets, including MoS₂, WS₂, and TaS₂, are used as hole injection layers (HILs) in organic light‐emitting diodes (OLEDs). MoS₂, WS₂, and TaS₂ nanosheets are prepared using an exfoliation by ultrasonication method. The thicknesses and sizes of the TMD nanosheets are measured to be 3.1–4.3 nm and more than 100 nm, respectively. The work functions of the TMD nanosheets increase from 4.4–4.9 to 4.9–5.1 eV following ultraviolet/ozone (UVO) treatment. The turn‐on voltages at 10 cd m^?2 for UVO‐treated TMD‐based devices decrease from 7.3–12.8 to 4.3–4.4 V and maximum luminance efficiencies increase from 5.74–9.04 to 12.01–12.66 cd A^?1. In addition, this study confirms that the stabilities of the devices in air can be prolonged by using UVO‐treated TMDs as HILs in OLEDs. These results demonstrate the great potential of liquid‐exfoliated TMD nanosheets for use as HILs in OLEDs.     

Production of γ-aminobutyric acid during fermentation of Gastrodia elata Bl. by co-culture of Lactobacillus brevis GABA 100 with Bifidobacterium bifidum BGN4

Gastrodia elata Bl. (GE) is a traditional herbal medicine used for the prevention of cerebrovascular disease and for the regulation of one’s blood pressure. γ-Aminobutyric acid (GABA) is known to be beneficial for preventing neurological disorders and hypertension. The objective of this study was to develop fermented GE products containing high levels of GABA. The optimal medium conditions for the production of GABA during fermentation were as follows: an initial pH of 6.5, 3% (w/v) l-monosodium glutamate, 10% (w/v) freeze-dried GE powder, and 0.5% (w/v) yeast extract. The production of GABA was further enhanced by the co-culture of Lactobacillus brevis GABA 100 with Bifidobacterium bifidum BGN4. During fermentation, high amounts of organic acids and GABA were produced, while gastrodin, the main polyphenol compound of GE, was completely converted to 4-hydroxybenzylalcohol. The fermented GE product with GABA was successfully produced by optimizing the fermentation conditions.     

Bias-stress stability of low-voltage p-channel and n-channel organic thin-film transistors on flexible plastic substrates

The bias-stress stability of low-voltage organic p-channel and n-channel thin-film transistors (TFTs) based on five promising organic semiconductors and fabricated on flexible polyethylene naphthalate (PEN) substrates has been investigated. In particular, it has been studied to which extent the bias-stress-induced decay of the on-state drain current of the TFTs is affected by the choice of the semiconductor and by the gate-source and drain-source voltages applied during bias stress. It has been found that for at least some of the organic p-channel TFTs investigated in this study, the bias-stress stability is comparable to that of a-Si:H and metal-oxide TFTs, despite the fact that the organic TFTs were fabricated at significantly lower process temperatures, which is important in view of the fabrication of these devices on plastic substrates.     

An evaluation of the influence of impurity concentration and composition in concrete on activation and radiation dosein the reactor facility

The content analysis of radioactive waste and radiation dose evaluation is considered as one of the important factors in the reactor facility design.This kind of buildings consists of the concrete for the most part and uses it as the structure and shield of the building.Generally,the concrete has impurities such as cobalt,europium,nickel,and cesium with specific content depending on the production method or manufacturing company.Dominant radioactive nuclides generated from the fundamental compon...     

Modeling alpha-particle-induced accelerated soft error rate in semiconductor memory

This paper presents an analytic integral model for the accelerated soft error rate (ASER). The model took into account the physical and structural parameters as four alpha incident angles and an angular function. Two angles were related to charge collection and another two angles and an angular function were related to measurement configuration and how much alpha flux arrived. The model was verified by measuring ASER in 8 M static RAM. The model could explain ASER characteristics of saturation, exponential dependence, and vanishing with the power supply voltage. The model also reproduced an extraordinary phenomenon that there is a maximum in ASER with respect to the thickness of the capping layer on the static RAM.     

Preparation of stable dispersions of chemically reduced graphene oxide through noncovalent interactions with poly(N-isopropyl acrylamide)-grafted pluronic copolymer

Stable dispersions of chemically reduced graphene oxide (RGO) were prepared by simple noncovalent interaction with poly(N-isopropyl acrylamide) (PNIPAAm)-grafted Pluronic (NGP). Prepared NGP/RGO assembly solutions showed temperature-dependent optical absorbance change below or above their lower critical solution temperature (LCST). Interestingly, LCSTs of NGP/RGO assemblies were unaffected compared with LCSTs of pristine NGPs regardless of the degree of PNIPAAm grafting in NGPs probably because noncovalent anchoring between PNIPAAm chains and RGO plates in NGP/RGO assembly is weak. This supports that PNIPAAm grafting on Pluronic occurred preferentially in hydrophilic PEO segments because hydrophobic PPO segments of NGP must be strongly anchoring on hydrophobic surface of RGO plates while PEO segments will be extended from RGO surface to aqueous medium.     

Measurements of air temperature distribution and optimum cooling condition inside the computer system

Measurements of the temperature distributions of the cooling air flow inside a computer system have been made. An investigation of the optimum cooling condition for the computer system has also been made. Seventy-one K-type (Chromega-Alumega) thermocouples were used to measure distributions of the air flow temperature inside the computer system. They were calibrated against the standard platinum resistance thermometer (PRT) in a constant water circulating bath within an accuracy of ± 0.15 °C. It was found that the number and position of cooling fans as well as their operating condition, whether air intake or air discharge, can greatly influence the cooling effectiveness in the computer system. The results show that the flow rate of intake air should not be higher than that of the discharge air for the most effective cooling. It follows that the optimum cooling has been achieved inside the computer when the three fans are positioned in the inlet front, outlet back, and outlet top in the computer, respectively. Under these conditions, not only is the average temperature inside the computer system maintained at an appropriate level, but the most effective cooling around the central processor (CPU) and graphic card which are responsible for the largest amount of heat dissipation can be accomplished. This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha Dae Hee Lee received a B.S. degree in Mechanical Engineering from Hanyang University in 1984. He then went on to receive his M.S. and Ph.D. degrees from University of California at Davis in 1984 and 1987, respectively. Dr. Lee is currently a Professor at the School of Mechanical Engineering and a Dean of Academic Affairs at Inje University in Korea. Dr. Lee’s research interests are in the area of Convection Heat Transfer, Liquid Crystal Thermography, Co-generation, and Renewable Energy.     

Robust Cognitive‐Radio‐Based OFDM Architecture with Adaptive Traffic Allocation in Time and Frequency

Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference between primary users and CR users, however, becomes a critical problem when they are using adjacent frequency channels with different transmission power levels. In this paper, a robust CR orthogonal frequency division multiplexing (OFDM) architecture, which can effectively suppress interference to nearby primary users and overcome adjacent channel interference (ACI) to the CR user, is proposed. This new approach is characterized by adaptive data repetition for subcarriers under heavy ACI, and adaptive time spreading for subcarriers near the borders of the CR user's spectrum. The data repetition scheme provides extra power gain against the ACI coming from primary users. Time spreading guarantees an acceptable interference level to nearby primary users. By computer simulation, we demonstrate that, under a CR environment, the proposed CR OFDM architecture outperforms conventional OFDM systems in terms of throughput and BER performance.