Generation and Progress Behavior of Strain-Induced Abnormally Large Grains in Superalloy 718

Metallurgical and Materials Transactions A - Herein, the behavior associated with strain-induced abnormally large grains in superalloy 718 was investigated using compression testing and subsequent...     

Heat and mass transfer during in-flight nitridation of molybdenum disilicide powder in an induction plasma reactor

The present study reveals some of the important parameters which control the in-flight nitridation of molybdenum disilicide (MoSi₂) powders when carried out in an induction thermal plasma reactor. Initially, gradients of temperature, velocity and concentration were evaluated, using an enthalpy probe system, for the plasma flow without injection of MoSi₂ powders. Radial profiles were then measured at the torch exit to examine the mass and energy transfer mechanisms occurring under different nitridation conditions. These measurements were performed using an induction plasma torch connected to a 50 kW radio-frequency (r.f.) power supply, the torch being attached to a water cooled cylindrical reactor. The process operating conditions studied were plasma plate power, chamber pressure, sheath gas composition, composition and flow rate of quench gas. The effect of last named parameter on the nitridation of the powders was found to be the most important parameter in the nitridation process. The results show that there is an optimum flow rate value for each type of quench gas and the temperature and concentration mapping demonstrates that the combination of high temperatures and high concentrations of N₂ are necessary to reach maximum nitridation levels in MoSi₂.     

Recent advances in nanofibrous assemblies based on β‐sheet‐forming peptides for biomedical applications

Amyloid fibrils are supramolecular polymers with β‐sheet‐rich structures formed by polymerization of protein/peptide with intermolecular interaction. Amyloid fibrils have been miscast as toxic villains since they have historically been studied as pathogens associated with serious diseases, including Alzheimer's and Parkinson's disease. However, recent studies on their toxicity and formation mechanism and discovery of their functionality in nature correct the misconception and strongly facilitate the possible use of β‐sheet‐forming peptides in designing novel nanomaterials. Self‐assembly based on β‐sheet‐forming peptides can provide highly ordered nanostructures under certain conditions. Therefore, ingenious design of the building block peptides allows the construction of nano‐assemblies, which contain large quantities of bio‐functional molecules, including drugs and bioactive peptides, and exhibit unique properties, such as assembly or disassembly in response to external stimulus or specific molecules. These properties provide a novel strategy for the creation of innovative nanomaterials, especially for biomedical applications. Here, we describe recent progress in the biomedical application of fibrous assemblies based on β‐sheet‐forming peptides, such as the suppression of aberrant protein aggregation, controlled release, tissue engineering and other applications. This review focuses not only on the function of the nanofibrous assemblies but also on the functions of component molecules, namely amyloidogenic peptides. © 2016 Society of Chemical Industry     

Molecular dynamics studies on the structures of polymer electrolyte membranes and diffusion mechanism of protons and small molecules

We performed a series of molecular dynamics (MD) simulations on Nafion^® membranes containing various quantities of H₂O and CH₃OH. The simulations afforded diverse nanoscale phase-separated structures, such as clusters, channels, and cluster–channels. The calculated cluster–channel structure qualitatively agrees with the experimental results of X-ray diffraction studies. We also investigated the diffusion mechanisms for H₂O, protons, CH₃OH, H₂, and O₂ in these membranes. To reproduce the hopping transfer of protons, we employed a semi-classical MD approach using the empirical valence bond method. The estimated diffusion coefficients of H₂O and proton in the membranes significantly depended on the H₂O content, and these values showed qualitatively good agreement with the experimental results. The diffusion coefficient of proton in H₂O-rich membranes was much larger than that of H₂O, and the proton mainly formed H₅O₂⁺ complex. Furthermore, the simulation results indicate that the majority of CH₃OH permeates through the H₂O clusters, and the majority of H₂ and O₂ permeates through the hydrophobic region of the membrane.     

Ultrasonic Dispersion of TiO2 Nanoparticles in Aqueous Suspension

Aggregation and dispersion behavior of nanometer and submicrometer scale TiO₂ particles in aqueous suspension were investigated using three kinds of mechanical dispersion methods: ultrasonic irradiation, milling with 5-mm-diameter balls, and milling with 50 μm beads. Polyacrylic acids with molecular weights ranging from 1200 to 30 000 g/mol were used as a dispersant, and the molecular weight for each dispersion condition was optimized. Viscosities and aggregate sizes of the submicrometer powder suspensions were not appreciably changed in the ultrasonic irradiation and 5-mm-ball milling trials. In contrast, in the trials in which nanoparticle suspension was used, ultrasonic irradiation produced better results than 5-mm-ball milling. Use of ultrasonication enabled dispersion of aggregates to primary particle sizes, which was determined based on the specific surface area of the starting TiO₂ powders, even for relatively high solid content suspensions of up to 15 vol%. Fifty-micrometer-bead milling was also able to disperse aggregates to the same sizes as the ultrasonic irradiation method, but 50-μm-bead milling can be used only in relatively low solid content suspensions. It was concluded that the ultrasonic dispersion method was a useful way to prepare concentrated and highly dispersed nanoparticle suspensions.     

Excess Adsorption of Helium in Extremely Narrow Slit Pores

Wave functions of quantum helium in narrow slit pores are strongly restricted; as such, quantum helium condensed in narrow slit pores displays different behaviors from that in bulk. Herein, we report the densities of helium adsorbed on carbon surfaces and in carbon slit pores with average pore widths of 0.7, 0.9, and 1.1 nm at 2–5 K. The density of adsorbed quantum helium in the 0.7-nm slit pores was significantly higher than those in the larger slit pores and bulk. The average layer density of helium in the 0.7-nm pores was also significantly higher than those in the larger slit pores, suggesting solid-like structure formation even under helium vapor condition. The highly dense state of helium in narrow slit pores is due to strong attractive potential effects in such slit pores.     

Relationship between Rice Flour Particle Sizes and Expansion Ratio of Pure Rice Bread

We examined a method to produce bread from crystalline rice flour without using thickening agents such as gluten, polysaccharide thickening, and amorphous rice flour. Rice grains were pulverized by a jet mill to produce flour. Samples of rice flours of various particle size distributions were prepared by using a size shifter. The degree of starch damage and the dynamic viscoelasticity of rice batter were measured in this work. We also baked bread of the flour of each size distribution to study processability for making bread. The batter made by the pulverized flour of rice particle size ranging from 75 to 106 μm had the highest expansion ratio and a good processability for baking breads compared to other particle size batters. The rice bread with high expansion ratio was produced by controlling particle size of crystalline rice flour without using thickening agents.     

Performance analysis of CSMA/CD‐DRC system

Multimedia communication systems must handle two types of messages, one is data type and the other is voice type. Data type messages can tolerate longer delay but voice type ones cannot. Though communication systems with huge capacity by optical fibers and ATM switches have little problem for multimedia communication, most of the present LANs cannot handle messages, especially voice type ones, satisfactorily because of their poor capacity. In this paper we propose a new protocol for LANs, CSMA/CD‐DRC (Carrier Sense Multiple Access with Collision Detection and Dynamic Retransmission Control). This protocol is for the multimedia communication systems which must handle those two types of messages but do not have enough channel capacity, and controls retransmission rates dynamically to achieve higher throughput and shorter delay for voice type message. Moreover, we analyze the protocol in order to confirm its performance. In analysis we derive Laplace–Stieltjes transform (LST) of the probability distribution function (PDF) of the performance measures. Through LSTs, we can calculate not only averages but also higher moments of performance measures as well as coefficients of variation. We also present some numerical results, from which we find the proposed protocol can improve the system performance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Electrochemical oxidation of cholesterol in acetonitrile leads to the formation of cholesta-4,6-dien-3-one

Cholesterol was shown to be oxidized at the glassy carbon electrode in an acetonitrile–2-propanol mixture and this oxidation reaction was applied to the determination of serum total cholesterol by high-performance liquid chromatography with electrochemical detection (K. Hojo, H. Hakamata, A. Ito, A. Kotani, C. Furukawa, Y.Y. Hosokawa, F. Kusu, J. Chromatogr. A 1166 (2007) 135–141). To gain insight into the detection mechanisms of cholesterol, an electrolytic product of cholesterol was collected and characterized by infrared spectroscopy, one- and two-dimensional nuclear magnetic resonance, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The three techniques, together with comparisons of literature spectral data, confirmed the formation of cholesta-4,6-dien-3-one. The conversion of cholesterol to cholesta-4,6-dien-3-one, a four-electron, four-proton electrochemical process, has been proposed as an electrochemical oxidation mechanism of cholesterol in acetonitrile.