Catalytic graphitization of a phenolic resin carbon by nickel (~100 μm): Selective gasification of three resultant components as studied by SEM

A phenolic resin carbon containing nickel particles, ~100 μm diam., was graphitized to 2773K for 1 h. This treatment created within the specimen three structural components known as graphitic (G), turbostratic (T_s) and matrix (A). The graphitized carbon was oxidized by carbon dioxide, HNO₃-H₂SO₄ mixed acid and Simon's reagent and topographical changes were monitored by SEM. The CO₂ gasified preferentially the T_s-component to produce fissures mainly at the interface with the A- andG-component. The mixed acid reacted preferentially with the G- andT_s-components, the Simon's reagent reacting significantly only with the G-component. The mineral matter of metallurgical coke can act as a graphitization catalyst similar to nickel particles. Hence, the development of structural components within the metallurgical coke followed by gasification by carbon dioxide may cause weakening of the coke at the interfaces of components.     

Development of one pass sea water reverse osmosis module “Hollosep”

CTA hollow fiber membranes with high performance, especially high salt rejection, have been developed for one pass sea water desalination by reverse osmosis.Performances of modules have been studied relating to sea water desalination and are discussed in terms of hollow fiber membrane and module configuration.High salt rejection makes it possible to operate under severe operating conditions of high product water recovery and high salinity sea water.Operating costs are discussed with regard to product water recovery.     

Fabrication of ultrathin and highly uniform silicon on insulator by numerically controlled plasma chemical vaporization machining

Metal-oxide semiconductor field-effect transistors fabricated on a silicon-on-insulator (SOI) wafer operate faster and at a lower power than those fabricated on a bulk silicon wafer. Scaling down, which improves their performances, demands thinner SOI wafers. In this article, improvement on the thinning of SOI wafers by numerically controlled plasma chemical vaporization machining (PCVM) is described. PCVM is a gas-phase chemical etching method in which reactive species generated in atmospheric-pressure plasma are used. Some factors affecting uniformity are investigated and methods for improvements are presented. As a result of thinning a commercial 8 in. SOI wafer, the initial SOI layer thickness of 97.5+/-4.7 nm was successfully thinned and made uniform at 7.5+/-1.5 nm.     

Construction and development of a time-resolved x-ray magnetic circular dichroism-photoelectron emission microscopy system using femtosecond laser pulses at BL25SU SPring-8

A femtosecond pulsed laser system has been installed at the BL25SU soft x-ray beamline at SPring-8 for time-resolved pump-probe experiments with synchronization of the laser pulses to the circularly polarized x-ray pulses. There are four different apparatuses situated at the beamline; for photoemission spectroscopy, two-dimensional display photoelectron diffraction, x-ray magnetic circular dichroism (XMCD) with electromagnetic coils, and photoelectron emission microscopy (PEEM). All four can be used for time-resolved experiments, and preliminary investigations have been carried out using the PEEM apparatus to observe magnetization dynamics in combination with XMCD. In this article, we describe the details of the stroboscopic pump-probe XMCD-PEEM experiment, and present preliminary data. The repetition rate of the laser pulses is set using a pulse selector to match the single bunches of SPring-8's hybrid filling pattern, which consists of several single bunches and a continuous bunch train. Electrons ejected during the bunch train, which do not provide time-resolved signal, are eliminated by periodically reducing the channel plate voltage using a custom-built power supply. The pulsed laser is used to create 300 ps long magnetic field pulses, which cause magnetic excitations in micron-sized magnetic elements which contain magnetic vortex structures. The observed frequency of the motion is consistent with previously reported observations and simulations.     

Evolutionary high-dimensional QoS optimization for safety-critical utility communication networks

This paper proposes and evaluates an evolutionary multiobjective optimization algorithm, called EVOLT, which heuristically optimizes quality of service (QoS) parameters in communication networks. EVOLT uses a population of individuals, each of which represents a set of QoS parameters, and evolves the individuals via genetic operators such as crossover, mutation and selection for satisfying given QoS requirements. For evaluating EVOLT in real-world settings that have high-dimensional parameter and optimization objective spaces, this paper focuses on QoS optimization in safety-critical communication networks for electric power utilities. Simulation results show that EVOLT outperforms a well-known existing evolutionary algorithm for multiobjective optimization and efficiently obtains quality QoS parameters with acceptable computational costs. Moreover, EVOLT visualizes obtained QoS parameters in a self-organizing map in order to aid network administrators to intuitively understand the QoS parameters and the tradeoffs among optimization objectives.     

Conformation-dependent dynamics of macromolecular ions in the gas phase under an electrostatic field: A molecular dynamics simulation

Highly charged macromolecular ions exhibit various conformations in gas. Intramolecular charge-to-charge interaction induces a transformation from a globular structure into a stretched one. The change in the molecular conformation brings a complex dynamic behavior of ions under an electrostatic field. In the present study, we visualized the movement of a monovalent and multiply charged straight chain macromolecules, polyethylene glycol (PEG), by a molecular dynamics (MD) simulation. The simulation showed that a singly charged PEG ion (899?<?M_W < 4,643) takes a globular conformation. The electrical mobilities of these ions determined from the migration distance under an electric field were compared with the experimental data and those determined by the classical Mason–Schamp theory under an assumption of spherical shape. As a result, we obtained a good agreement between the MD, theoretical, and experimental data for the monovalent ions. We also found that the MD simulation successfully predicts the electrical mobility of the multiply charged stretched PEG ions, but the classical theory fails. We were able to visualize the periodic bending and stretching motion by the MD simulation. This unique motion results from the localization of charges on the PEG molecule and may have a significant effect on the dynamic behavior of macromolecule ions in gas.

Copyright © 2019 American Association for Aerosol Research     

Facile synthesis of tetrapodal ZnO nanoparticles by modified French process and its photoluminescence

Facile synthesis of tetrapodal ZnO nanoparticles was conducted using a modified French process in which oxygen and nitrogen flow rates were controlled. The synthesized ZnO nanoparticles exhibit photoluminescent characteristics depending on the synthesis conditions. Electron microscopic analysis revealed that the tetrapodal nanostructure of ZnO with high crystallinity which was confirmed by XRD analyses could be controlled by a variation of O₂/N₂ feed ratio. Typical photoluminescence with UV and blue emission of the tetrapodal ZnO nanoparticles was influenced by the particle size and crystallinity, which is manipulated by the oxidation condition.     

Generation of uniform tetrapod-shaped zincoxide nanoparticles by gas-phase reaction with using flow restrictor

Tetrapod-shaped ZnO particles are generated via gas-phase reaction of Zn vapor and oxygen in air, where they undergo homogeneous nucleation from supersaturated ZnO vapor and successive growth by surface reaction. It was found that a simple device for flow restrictor is effective in making ZnO particles of terapod-shape by leaving sufficient amounts of unreacted Zn vapor with the embryos of ZnO. In the absence of the flow restrictor, only spherical particles are formed because the oxidation reaction takes place immediately after mixing and unreacted Zn vapor does not remain for the subsequent crystal growth. The Zn vapor concentration distribution, oxygen concentration distribution, temperature, gas velocity and reaction rate in the reactor were analyzed by using a conventional computational fluid dynamic simulation package. The simulation revealed that the flow restrictor does not enhance mixing between Zn vapor and air but suppresses the mixing and reduces the residence time in the reactor so that sufficient amounts of unreacted Zn vapor remain downstream of the flow restrictor, allowing ZnO particles to grow in tetrapod-shape by abnormal crystal growth.     

Adhesion control of fungal spores on solid surfaces using hydrophilic nanoparticles

Mold growth can trigger a variety of serious problems such as allergies and asthma. Designing surfaces that are unfavorable for the adhesion of fungal spores is considered an effective method to prevent fungal growth. In this study, the effect of hydrophilic surface treatment on the adhesion of fungal spores onto substrates was investigated using Aspergillus oryzae as a model fungus. The fungal spores that strongly adhered on the hydrophilic substrates under atmospheric conditions were easily removed by lightly washing by hand in water. These experimental results agreed well with thermodynamic predictions based on contact angle measurements. In addition, the removal ratio of the fungal spores on substrates coated with silica nanoparticles was higher than that on plasma-treated glass. It is believed that the contact area between a spore and substrate depended on the substrate roughness. Atomic force microscopy revealed that there was almost no adhesive force between the spores and glass substrate coated with silica nanoparticles. These results suggest that hydrophilic treatment using hydrophilic silica nanoparticles is more effective than hydrophilic plasma treatment to prevent fungal spore adhesion on glass substrates.