Decorating surface charge of graphite nanoplate using an electrostatic coupling agent for 3-dimensional polymer nanocomposite

Here, we report a facile approach to electrostatically couple the surface charges of graphite nanoplate (GNP) fillers and poly(methyl methacrylate) (PMMA) polymer particles using ethylene maleic anhydride (EMA) copolymer as an electrostatic coupling agent. Our strategy involved switching the intrinsic repulsive electrostatic interactions between the directly exfoliated GNPs fillers and the PMMA particles to attractive electrostatic surface interactions for preparing core(PMMA)-shell (GNP) precursor in order to optimizing 3-dimensionally dispersed polymer nanocomposite. As a result, the electrical conductivity of the composites dramatically increased by a factor of 16.7 in the EMA-coupled GNP/PMMA composites compared with that of the EMA-free GNP/PMMA composites. In addition, the percolation threshold was also notably reduced from 0.32 to 0.159 vol% after electrostatic coupling of the GNPs fillers and PMMA particles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48390.     

Pressureless sintering and characterization of cordierite/ZrO2 composites

Cordierite/ZrO₂ composites with 5 to 25 wt% ZrO₂ were fabricated by conventional powder mixing and pressureless sintering method. Their densification behavior, microstructure, mechanical and thermal properties were studied. By dispersing 25 wt% (9.57 vol%) ZrO₂, densified cordierite/ZrO₂ composite with a relative density of 98.5% was obtained at an optimum sintering condition of 1440 °C and 2 h. ZrO₂ particles were homogenously dispersed within matrix grains and at the grain boundaries. The intragranular particles were finer than 100 nm and the intergranular particles were coarser. Both fracture strength and toughness could be enhanced more than two times higher, compare to those of monolithic cordierite, by dispersing 25 wt% ZrO₂ into the cordierite matrix. The toughening mechanism in the present composites was mainly attributed to martensitic transformation due to ZrO₂ dispersion. Electronic Publication     

Nitrogen removal using recycled polystyrene bottles as biofilm media

The performance of an attached growth wastewater treatment process was investigated in an effort to improve nitrogen removal efficiency. Recycled Yakult (lactic acid fermentation drink) bottles made of polystyrene were used as a biofilm media. The use of Yakult bottles as a biofilm media has been attempted by numerous researchers in Japan for the removal of solids and organics. However, these studies focused only on the removal of solids and organics. This study extended their application to the removal of nitrogen for domestic sewage treatment. Yakult media was placed in a reactor with 70% apparent reactor volume in a conventional A/O process. The bottom of the Yakult media was removed, and randomly filled Yakult media were effectively able to reduce the flow in tanks, resulting in an increase in the contact time between pollutants and microorganisms. With higher HRT, the nitrogen removal efficiency was increased by up to 83% with 12 hr of HRT. Nitrification appeared to be the limiting factor of nitrogen removal at an HRT that is less than 12 hr, indicating that the Yakult process requires more retention time to achieve nitrification compared to other biofilm processes. The removal efficiencies of organics and solids were high regardless of the change of operational parameters. This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24–27, 2003.     

mVoIP for P2P service based authentication system using AA authentication server

VoIP (Voice over Internet Protocol), which provides voice calls as well as additional services at cheaper prices than PSTN (Public Switched Telephone Network), is gaining ground over the latter, which had been the dominant telephone network in the past. This kind of a VoIP service is evolving into a dedicated mVoIP service for the smartphone which allows calls to be made at cheap prices using a WiFi network, as the number of smartphone users is skyrocketing as of late. While an increase in the user base is expected for mVoIP, a packet network is an open network which means anyone can easily gain access and so there can be various problems. To mitigate this, in this paper an authentication system is designed which has an AA (Attribute Authority) server added to VoIP in order to increase security and discriminate user access. In this paper a system for addressing security vulnerabilities from the increase in the use of VoIP services and providing differentiated services according to user access privileges is designed. This paper is organized as follows: Chapter 1 gives the introduction; Chapter 2 is on related research; Chapter 3 describes the proposed technique and system; Chapter 4 implements the system and analyzes its the performance; and Chapter 5 gives the conclusions.     

Strain improvement of Aspergillus sojae for increased l-leucine aminopeptidase and protease production

Food Science and Biotechnology - Conventional random mutagenesis was implemented to improve l-leucine aminopeptidase (LAP) and protease production in Aspergillus sojae. Through successive...     

Bi and Te thin films synthesized by galvanic displacement from acidic nitric baths

Bismuth (Bi) and tellurium (Te) thin films were formed by galvanic displacement of different sacrificial iron group thin films [i.e. nickel (Ni), cobalt (Co) and iron (Fe)] where the formation was systematically investigated by monitoring the change of open circuit potential (OCP), surface morphology and microstructure. The surface morphologies and crystal structures of galvanically displaced Bi or Te thin films strongly depended on the type and thickness of the sacrificial materials. Continuous Bi thin films were successfully deposited with the sacrificial Co. However, dendrites and nanoplatelets were formed from the Ni and Fe thin films. Te thin films were synthesized with all the three sacrificial thin films. Chemical dissolution rate of the sacrificial thin films and mixed potential strongly influenced formation of Bi or Te thin films.     

Reaction characteristics of the Au-Sn solder with under-bump metallurgy layers in optoelectronic packages

The reaction characteristics of molten Au/Sn eutectic solder with potential diffusion-barrier materials of optoelectronic packages were investigated. The characteristics were studied by reflowing the solder on Pt, Ni, and Co plates, respectively, and by measuring the thickness of the reaction product. In addition, the dissolution rate of Pt into the solder was measured. The results indicated that Pt, which is commonly used as the diffusion-barrier layer in the under-bump metallurgy (UBM) of optoelectronic packages, reacts readily with the molten solder, resulting in discontinuous reaction products at the solder/Pt interface. Cobalt, on the other hand, reacted with the solder at an order of magnitude slower rate than that of Pt and provided an effective barrier against the reaction with the solder.     

Radioecological studies in Korea atomic energy research institute, KAERI

Regarding the assessment of the terrestrial food chain dose to man, radioecology may be the field that is focused on the transfer of radionuclides from environmental media to food crops. In Korea, the environmental transfer of radionuclides to staple food crops have been investigated at Korea Atomic Energy Research Institute (KAERI) for the last 25 y mainly through radiotracer experiments in greenhouses. As a result, several hundreds of parameter values for the prediction of the radionuclide transfer have been produced. Many of them appear in two recent publications of International Atomic Energy Agency. This paper outlines the KAERI's past radioecological work and introduces the ongoing research and future plans.     

An improved sensorless driving method for SRM using a phase-shift circuit technique

This paper presents an improved sensorless driving method for switched reluctance motor (SRM) using a phase-shift circuit technique. The conventional method consists of impressing short voltage pulses during unenergized phases, measuring the phase current pulses, and finding the correlation between the filtered current signals and rotor position. However, the filtering process causes a signal phase delay which varies with motor speed. This delay must be compensated for in providing the sensorless signal which is proper to the rotor position. A solution for this phase delay compensation, based on a simple analog and digital circuit, is proposed in this paper.