Effect of electric field on viscoelastic properties of a disperse system in silicone gel

In the electrorheological (ER) fluids of disperse systems, the poor dispersion stability of particles often limits the development of practical application of the fluids. This key problem can be settled by the chemical gelation of ER fluids. In the present study, a dimethylsilicone oil‐based gel containing the nonaqueous ER particles was newly created. The dynamic properties of viscoelasticity in the sample silicone gel were examined under applied DC electric fields of up to 2.0 kV/mm using a sinusoidal oscillating rheometer with low frequencies of 1 Hz or less. The particle behavior and the shearing deformation in the sample gel were also observed using a microscope, a CCD camera, and a color video monitor. When an electric field was applied to the sample gel, the gap between the electrodes was bridged by the chains of particles arranged in the direction of the electric field. Consequently, it is shown that the electroviscoelastic effect of the gel can be controlled by the electric field. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(2): 1–9, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10098     

The evaluation of a reactivity insertion due to the group motion of FBR core subassemblies beyond Design Basis Ground Motion

The seismic probabilistic safety assessment (PSA) for fast breeder reactors (FBRs) has been carried out to confirm that the seismic safety is equivalent to that of light water reactors (LWRs). The seismic response on the reactor structure of FBRs causes seismic reactivity. The group motion of fuel assemblies is one of a typical seismic response. Therefore, much attention has been paid on the reactivity insertion mechanism due to the group motion of fuel assemblies and its consequence during the earthquake over the Design Basis Ground Motion (DBGM) condition. When the displacement of each subassembly is moving toward the same direction, each gap reduces coherently and the radial core compaction occurs, which results in positive reactivity insertion. We evaluate the gap reduction characteristics at the mid-plane of core by using a correlation coefficient. As a result, the fuel subassemblies are most concentrated when the input seismic motion of about 5 Hz frequency and 40 m/s² acceleration is applied. The amount of reactivity insertion is estimated approximately 1$ that corresponds to prompt criticality.     

Numerical study on sodium–water reaction mechanism in the gas phase using counter-flow reaction region

Sodium water reaction (SWR) is a design basis accident of a sodium-cooled fast reactor (SFR). In a steam generator of the SFR, when a heat transfer tube fails, highly pressurized water and/or water vapor will leak into liquid sodium resulting in a chemical reaction between sodium and water or water vapor. In the previous works, mechanisms of the SWR have been researched on surface reaction and gas-phase reaction. The mechanisms, however, are complicated and have not been fully elucidated. The authors have developed a numerical code in which chemical reaction models of sodium and water vapor are coupled with thermal-hydraulics. Experiments of a counter-flow diffusion flame for the gas-phase reaction have also been carried out. In this article, the authors perform numerical simulations based on the experimental conditions to validate two chemical reaction models, the chemical equilibrium model and the Arrhenius model. With respect to the reaction products, the latter model gives more realistic results. In addition, sensitivity analyses are performed for various hydration numbers and main-flow velocities. It is founded that hydration reaction occurs somewhat in the gas-phase reaction and that influences of the main-flow velocity are not negligible mainly from the viewpoint of the reaction surface location.     

Probabilistic common cause failure modeling for auxiliary feedwater system after the introduction of flood barriers

Causal inference is capable of assessing common cause failure (CCF) events from the viewpoint of causes’ risk significance. Authors proposed the alpha decomposition method for probabilistic CCF analysis, in which the classical alpha factor model and causal inference are integrated to conduct a quantitative assessment of causes’ CCF risk significance. The alpha decomposition method includes a hybrid Bayesian network for revealing the relationship between component failures and potential causes, and a regression model in which CCF parameters (global alpha factors) are expressed by explanatory variables (causes’ occurrence frequencies) and parameters (decomposed alpha factors). This article applies this method and associated databases needed to predict CCF parameters of auxiliary feedwater (AFW) system when defense barriers against internal flood are introduced. There is scarce operation data for functionally modified safety systems and the utilization of generic CCF databases is of unknown uncertainty. The alpha decomposition method has the potential of analyzing the CCF risk of modified AFW system reasonably based on generic CCF databases. Moreover, the sources of uncertainty in parameter estimation can be studied. An example is presented to demonstrate the process of applying Bayesian inference in the alpha decomposition process. The results show that the system-specific posterior distributions for CCF parameters can be predicted.     

The Roles of the Ge‐Te Core Network and the Sb‐Te Pseudo Network During Rapid Nucleation‐Dominated Crystallization of Amorphous Ge2Sb2Te5

Ge₂Sb₂Te₅ (GST) has demonstrated its outstanding importance among rapid phase‐change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X‐ray scattering data, that germanium and tellurium atoms form a “core” Ge‐Te network with ring formation. It is also suggested that the Ge‐Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb‐Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge‐Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb‐Te pseudo network is responsible for triggering critical nucleation.     

Augmented automatic choosing control of filter type for nonlinear systems and its application to power systems

This paper deals with a feedback control using automatic choosing control and nonlinear filter for nonlinear systems with noise measurement. The state estimation of plants is carried out by the nonlinear filter. The control is designed by piecewise linear controls which are smoothly integrated into a single nonlinear feedback control by the automatic choosing functions. This is called an augmented automatic choosing control of filter type (AACCF) for nonlinear noisy measurement systems. This controller is applied to a transient stability problem of power systems, whose simulation results show that the new controller enables the expansion of the stable region well. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An augmented automatic choosing control of observer type for nonlinear systems with linear measurement and its application to power systems

This paper deals with a feedback control using automatic choosing functions and the observer-control design procedure for nonlinear systems with linear measurement. A constant term which arises from linearization of a nonlinear equation is treated as a coefficient of a stable zero dynamics. A given nonlinear system is linearized piecewise so as to be able to design the linear optimal controllers with the linear observers. By the automatic choosing functions, these controllers are smoothly united into a single nonlinear feedback controller, which is called an augmented automatic choosing control of observer type. This controller is applied to a transient stability of power systems, whose simulation results show that the new controller enables to expand the stable region well. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Selenium and the prevention of prostate and colorectal cancer

Prostate and colorectal cancers are among the most common cancers and identifying modifiable risk factors are important steps to reduce the burden of these severe diseases. Results from several but mostly small observational studies as well as the secondary analysis of an intervention trial provide support for a chemopreventive effect of selenium on prostate and colorectal cancers. Results suggest effect modification by gender and smoking, but this interpretation is limited by the statistical power of previous studies. Several cancer preventive mechanisms have been described and it is likely that selenium acts through multiple pathways. In particular, the anti-oxidative and anti-inflammatory effects mediated through activity of selenoenzymes are discussed, given the relevance of oxidative stress and inflammation in these cancers. Genetic variation in selenoenzymes may modify the potential chemopreventive effect of selenium and need to be further investigated. Additional large observational studies using biomarkers of selenium intake and intervention trials, such as the Selenium and Vitamin E Cancer Prevention Trial, will be important to further evaluate the potential chemopreventive effect of selenium. Furthermore, characterization of functional effects of polymorphisms in selenoenzymes is needed.     

Development of unstructured mesh-based numerical method for sodium–water reaction phenomenon in steam generators of sodium-cooled fast reactors

When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of sodium-cooled fast reactors, a high-velocity and high-temperature jet with sodium–water chemical reaction may cause wastage on the adjacent tubes. For safety assessment of the steam generator, a computational fluid dynamics code called SERAPHIM calculating compressible multicomponent multiphase flow with sodium–water chemical reaction has been developed. The original SERAPHIM code is based on the finite difference method. In this study, unstructured mesh-based numerical method for the SERAPHIM code was developed to advance a numerical accuracy for the complex-shaped domain including multiple heat transfer tubes. Numerical analysis of an underexpanded jet experiment was performed as part of validation of the unstructured mesh-based SERAPHIM code. The calculated pressure profile showed good agreement with the experimental data. To investigate the effect of the introduction of the unstructured mesh and to confirm applicability of the numerical method for the actual situation, water vapor discharging into liquid sodium was analyzed. The calculated behavior of the reacting jet agreed with the previous experimental knowledge. It was demonstrated that the proposed numerical method could be applicable to evaluation of the sodium–water reaction phenomenon.     

An Application of Hydrogen Thermophysical Properties Database “All in One Live CD”

A database for the thermophysical properties of hydrogen that supports a wide range of parameters including high pressures and high temperatures is being developed. The database performance requirements were studied and, in this paper, an application that combines a server–client database and a live CD is proposed. For this, an “All in One Live CD” application has been developed. Web interfaces provide excellent user interfaces for databases. However, there are some disadvantages for web interfaces related to server maintenance and access restrictions. This new application, the “All in One Live CD,” is free of these disadvantages, and provides a database with a property estimation service independent of the computer environment. From a single boot via the “All in One Live CD,” the database becomes accessible on multiple computers so that this feature makes the new application a unique solution as a distribution media.