Transient behavior of natural circulation for boiling two-phase flow (flow after pump trip)

The idea of a flow diode has been proposed to improve the pump coastdown characteristics of the internal recirculation pumps adopted by the ABWR. In this paper, the transient behavior from forced to natural circulation was experimentally investigated by simulating a pump coastdown condition for the purpose of providing an available source of information that is necessary for designing the flow diode. The results of the study showed that the transient behavior after pump coastdown was influenced by the coastdown period, the trigger velocity and the initial driving force of natural circulation. The potential of each driving factor was governed by the delay time for boiling, which is a very important parameter in natural circulation of boiling two-phase flow. In consequence, a guide for the designing of a flow diode was proposed.     

Imaging of a single atomic column in silicon grain boundary

Atomic resolution high voltage electron microscopy was applied in investigations of the atomic structure of [112] sigma3 CSL grain boundary of silicon. Images of the grain boundary, viewed in the < 110 > direction, showed two types of dark spots. One type was rod shaped, which represented an atomic pair aligned in the < 111 > direction. The other was a small round spot, which represented a single atomic column in the grain boundary. The atomic structure of [112] sigma3 CSL grain boundary was directly shown from the atomic-structure image.     

Improvement of Electrical Contact Between TE Material and Ni Electrode Interfaces by Application of a Buffer Layer

A single ??-structure thermoelectric (TE) module based on p-type NaCo₂O₄, n-type Mg₂Si, and Ni electrode was fabricated by the spark plasma sintering (SPS) method. The NaCo₂O₄ powder was synthesized by using a metal?Ccitric acid complex decomposition method. Bulk Mg₂Si prepared by melt quenching was ground into a powder and sieved to particle size of 75???m or less. To obtain a sintered body of NaCo₂O₄ or Mg₂Si, the powder was sintered using SPS. Pressed Ni powder or mixed powder consisting of Ni and SrRuO₃ powder was inserted between these materials and the Ni electrode in order to connect them, and electrical power was passed through the electrodes from the SPS equipment. The open-circuit voltage (V _OC) values of a single module in which TE materials were connected to the Ni electrodes by using pressed Ni powder was 82.7?mV, and the maximum output current (I _max) and maximum output power (P _max) were 212.4?mA and 6.65?mW at ??T?=?470?K, respectively. On the other hand, V _OC of a single module in which TE materials and an Ni electrode were connected with a mixed powder (Ni:SrRuO₃?=?6:4 volume fraction) was 109?mV, and I _max and P _max were 4034?mA and 109?mW at ??T?=?500?K, respectively. These results indicate that the resistance at the interface between the TE materials and the Ni electrode can be decreased and the output power can be increased by application of a buffer layer consisting of Ni and SrRuO₃.     

Investigation on the effectiveness of various methods of information dissemination aiming at a change of occupant behaviour related to thermal comfort and exergy consumption

These days the number of projects trying to urge a change in the occupant's behaviour towards a sustainable one is increasing. However, still less is known about the effect of such measures. This paper describes the findings of two investigations, a field measurement and an Internet-based survey, both including the dissemination of information about strategies for a high level of comfort without much energy usage. The focus was on the ability to quantify the effect of such measures on the heating and cooling behaviour. As a result, those who participated in a workshop were more likely to change their behaviour than those who received an information brochure only; whether this was due to the method employed or the type of participants could not be ascertained. However, the workshop participants reduced their cooling device usage by up to 16%. The concept of exergy was used to show how this reduction affects the exergy consumption of the cooling device, because it enables us to consider the qualitative aspect of energy as a quantity to be calculated. This showed that the exergy consumed by the workshop group was reduced by up to 20% comparing their behaviour before and after the information dissemination.     

The preparation of copper fine particle paste and its application as the inner electrode material of a multilayered ceramic capacitor

Well size-controlled copper fine particles (diameter: 100-300?nm) were used as the inner electrode material of multilayered ceramic capacitors (MLCCs). The particles were dispersed in terpineol to form a printing paste with 50?wt% copper particles. The MLCC precursor modules prepared by the layer-by-layer printing of copper and BaTiO(3) particles were cosintered. Detailed observation of the particles, paste, and MLCCs before and after sintering was carried out by electron microscopy. The sintering temperature of Cu-MLCC was as low as 960?°C. The permittivity of these MLCCs was successfully measured with the copper inner layers.     

Multi-scale modeling of irradiation effects in spallation neutron source materials

Changes in mechanical property of Ni under irradiation by 3 GeV protons were estimated by multi-scale modeling. The code consisted of four parts. The first part was based on the Particle and Heavy-Ion Transport code System (PHITS) code for nuclear reactions, and modeled the interactions between high energy protons and nuclei in the target. The second part covered atomic collisions by particles without nuclear reactions. Because the energy of the particles was high, subcascade analysis was employed. The direct formation of clusters and the number of mobile defects were estimated using molecular dynamics (MD) and kinetic Monte-Carlo (kMC) methods in each subcascade. The third part considered damage structural evolutions estimated by reaction kinetic analysis. The fourth part involved the estimation of mechanical property change using three-dimensional discrete dislocation dynamics (DDD). Using the above four part code, stress-strain curves for high energy proton irradiated Ni were obtained.     

Excitations bound to a vortex line in layered superconductors

Using Bogoliubov-de Gennes equation, we study quasiparticle excitations in layered superconductors in the presence of a straight vortex line which is parallel to the layers. The lowest bound state is shown to have energy eigenvalue of the order of magnitude , the energy gap, in contrast to the corresponding value ²/E_F when the line is perpendicular to the layers.     

Preparation of spherical fine ZnO particles by the spray pyrolysis method using ultrasonic atomization techniques

An ultrasonic atomizer was used in the spray pyrolysis method to prepare fine, spherical and uniform ZnO particles. Almost spherical particles were obtained successfully which had a mean particle size of 0.15 m and had a very narrow particle size distribution. By using alcohol as the solvent, it was found that the particles do not have hollow shell layers which could usually be observed in the spray pyrolysis process by using water as the solvent. The morphology of the ZnO particles was strongly affected by the concentration of the starting solution.     

Formation of monodispersed Ta2O5 powders

The Ta₂O₅ powders synthesized by the hydrolysis of tantalum pentaethoxide, Ta(OC₂H₅)₅ in alcoholic solution were monodispersed fine oxide particles, which were a uniform, spherical shape, non-agglomerate, and had a narrow size distribution. They grew to 1.2m after ageing for 1 h after hydrolysis. Powder X-ray diffraction and differential thermal analysisthermogravimetric analysis showed the particles were amorphous and hydrated. These particles lost the water at 290° C and gave well-crystalline Ta₂O at 740° C. Throughout these thermal processes, the particle morphology was kept almost the same.