Experimental study on heat transfer and pressure drop in mercury flow system for spallation neutron source

In the design of MW-class spallation target system, using mercury to produce practical neutron applications, keeping the highest level of safety is vitally important. To establish the safety of spallation target system, it is essential to understand the thermal hydraulic properties of mercury. Through thermal hydraulic experiments using a mercury experimental loop, which flows at the rate of 1.2 m³/hr maximum, the following facts were experimentally confirmed. The wall friction factor was relatively larger than the Blasius correlation due to the effects of wall roughness. The heat transfer coefficients agreed well with the Subbotin correlation. Furthermore, for validation of the design analysis code, thermal hydraulic analyses were conducted by using the STAR-CD code under the same conditions as the experiments. Analytical results showed good agreement with the experimental results, using optimized turbulent Prandtl number and mesh size.     

A pilot test plan of the thermochemical water-splitting iodine–sulfur process

Research and development (R&D) of hydrogen production systems using high-temperature gas-cooled reactors (HTGR) are being conducted by the Japan Atomic Research Institute (JAERI). To develop the systems, superior hydrogen production methods are essential. The thermochemical hydrogen production cycle, the IS (iodine–sulfur) process, is a prospective candidate, in which heat supplied by HTGR can be consumed for the thermal driving load. With this attractive feature, JAERI will conduct pilot-scale tests, aiming to establish technical bases for practical plant designs using HTGR. The hydrogen will be produced at a maximum rate of 30 m³/h, continuously using high-temperature helium gas supplied by a helium gas loop, with an electric heater of about 400 kW. The plant will employ an advanced hydroiodic acid-processing device for efficient hydrogen production, and the usefulness of the device was confirmed from mass and heat balance analysis. Through design works and the hydrogen production tests, valuable data for construction and operation will be acquired to evaluate detailed process performance for practical systems. After completing the pilot-scale tests, JAERI will move onto the next R&D step, which will be demonstrations of the IS process to which heat is supplied from a high-temperature engineering test reactor (HTTR).     

Effect of Al contained in polymer-derived SiC crystals on creating stable crystal grain boundaries

Si-Al-C-O materials are well-known as a good precursor material for obtaining a dense, excellent heat-resistant SiC polycrystalline materials. Although it has been found that the aluminum contained in Si-Al-C-O materials plays an important role in obtaining dense SiC materials, its actual behavior during heat-treatment processes has not been investigated. In this study, we investigated the behavior of aluminum contained in the SiC crystals, during the densification of SiC crystals produced from the Si-Al-C-O material. A part of the aluminum contained in the SiC crystals plays an important role in creating a thermodynamically stable grain boundary by the diffusional transportation of aluminum to the SiC grain boundaries at temperatures above 1700°C. Subsequently, most of the aluminum disappeared during the heat treatment at higher temperatures (~1900°C); as a consequence, a dense SiC solid solution with uniformly distributed residual aluminum (0.15wt%) was formed without a secondary phase at the grain boundary.     

An Indolocarbazole‐Based Thermally Activated Delayed Fluorescence Host for Solution‐Processed Phosphorescent Tandem Organic Light‐Emitting Devices Exhibiting Extremely Small Efficiency Roll‐Off

The study reports the development of a solution‐processed phosphorescent tandem organic light‐emitting device (OLED) exhibiting extremely small efficiency roll‐off. The OLED comprises two light‐emitting units (LEUs) connected by an interconnecting unit and employs a thermally activated delayed fluorescence host material. One of the most difficult tasks in the fabrication of OLEDs is to form a multilayer structure without dissolving the underlayer during the coating of the upper layer. The developed host materials exhibit high tolerance to methanol. The upper‐layer adjacent to the light‐emitting layer consists of ZnO nanoparticles, which could be dispersed in methanol by improving the preparation method. This results in the successful fabrication of a solution‐processed phosphorescent tandem OLED comprising two LEUs. The maximum external quantum efficiency (EQE) of the tandem device is 22.8%, and the EQE is 21.9% even at a high luminance of 10 000 cd m^?2. The suppression of efficiency roll‐off is among the best of those previously reported. Moreover, the operational stability of the tandem device is much higher compared with single‐LEU devices.     

Study on laser assisted milling of ferrous based consolidated material

This study deals with the laser beam assisted milling to improve the machinability of a consolidated structure formed by layered manufacturing processes. The laser beam used is a continuous CO₂ laser with a maximum output power of 100 W. The metal powder for layered manufacturing is a ferrous-based mixture. To investigate the influence of laser conditions on the machinability, specific cutting force, tool wear and tool temperature of the flank face are measured. The results showed that the specific cutting force of the consolidated structure was decreased by the effect of energy input on the structure surface. The progress of wear on the flank face assisted by the laser beam was 20% slower due to the softening of the consolidated structure and the melting of the powder which remained on the structure surface. The dimensional accuracy and surface finishing of the consolidated structure were influenced by the rise of the tool temperature on the flank face.     

Structure of beta-amyloid fibrils and its relevance to their neurotoxicity: implications for the pathogenesis of Alzheimer's disease

Alzheimer's disease and cerebral amyloid angiopathy are characterized by the deposition of beta-amyloid fibrils consisting of 40- and 42-mer peptides (A beta 40 and A beta 42). Since the aggregation (fibrilization) of these peptides is closely related to the pathogenesis of these diseases, numerous structural analyses of A beta 40 and A beta 42 fibrils have been carried out. A beta 42 plays a more important role in the pathogenesis of these diseases since its aggregative ability and neurotoxicity are considerably greater than those of A beta 40. This review summarizes mainly our own recent findings from the structural analysis of A beta 42 fibrils and discusses its relevance to their neurotoxicity in vitro.     

A DFT study on benzene adsorption over tungsten sulfides: surface model and adsorption geometries

Benzene adsorption on a WS₂(100) surface was studied by ab initio periodic DFT computations. Benzene adsorption is facile on the bridge site of the bare W edge via η² or η³ coordination. Taking into account the stable configuration at the W edge under typical hydrotreating reaction conditions (623 K, H₂S/H₂ = 0.01), benzene adsorption is found to be difficult, even when defective bridge sites are created.     

Study on tool wear mechanisms in milling laser sintered material

This paper investigates tool wear mechanisms of a ball end mill in cutting laser sintered material. Cutting edge temperature is measured by using a three-color pyrometer with an optical fiber. Bulk carbon steel JIS S55C is selected as the standard steel. Experimental results show that tool life in cutting sintered material is shorter than that in cutting JIS S55C. Observations by SEM show that adhesion of the work material and micro chipping are the main wear mechanisms in cutting sintered material. The corresponding cutting edge temperature shows a continuous increase as wear evolves with cutting time.