Numerical Prediction of Dynamically Propagating and Branching Cracks Using Moving Finite Element Method

Phenomena of dynamic crack branching are investigated numerically from a macroscopic point of view. Repetitive branching phenomena, interaction of cracks after bifurcation and their stability, bifurcation into two and three branches were the objectives of this research. For the analysis of dynamic crack branching, recently we developed moving finite element method based on Delaunay automatic triangulation [Nishioka, Furutuka, Tchouikov and Fujimoto (2002)]. In this study this method was extended to be applicable for complicated crack branching phenomena, such as bifurcation of the propagating crack into more than two branches, multiple crack bifurcation and so on. The switching method of the path independent dynamic J integral, which was developed for the case of simple two cracks branching phenomena, demonstrated it's excellent applicability also for the case of complicated crack branching. The simulation results are discussed with consideration to the experimental findings.     

Discrete-time dynamic image segmentation system

A dynamic image segmentation system that consists of a chaotic neural network and a global inhibitor has been developed. this is a discrete-time system and is faster than a locally excitatory globally inhibitory network (LEGION) that is a similar system with continuous-time dynamics. it is demonstrated that the system works well and is faster than the LEGION.     

Short-Span seeking control of hard disk drives with multirate vibration suppression perfect tracking control

In this paper, a novel vibration suppression perfect tracking control (PTC) method is proposed for short-span seeking mode of hard disk drives (HDDs) based on multirate feedforward control. In the proposed method, it is assumed that plant is modeled as the rigid-body and primary vibration modes. By using this model, a feedforward PTC is designed with a modified controllable canonical realization in order to control the transient response of position, velocity, acceleration, and jerk of the proposed virtual plant. Simulations and experiments are carried out to show that the proposed system can suppress the primary vibration mode in short-span seeking control. Finally, the proposed method is applied to a benchmark problem of HDD control which is made by a technical committee of IEE of Japan. The robustness of the proposed feedforward method is examined against the variation of primary vibration frequency. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

On the LiNi0.2Mn0.2Co0.6O2 positive electrode material

Layered LiNi_0.2Mn_0.2Co_0.6O₂ phase, belonging to a solid solution between LiNi_1/2Mn_1/2O₂ and LiCoO₂ most commercialized cathodes, was prepared via the combustion method at 900 °C for a short time (1 h). Structural, electrochemical and magnetic properties of this material were investigated. Rietveld analysis of the XRD pattern shows this compound as having the α-NaFeO₂ type structure (S.G. R-3m; a = 2.8399(2) ?; c = 14.165(1) ?) with almost none of the well-known Li/Ni cation disorder. SQUID measurements clearly indicate that the studied compound consists of Ni²⁺, Co³⁺ and Mn⁴⁺ ions in the crystal structure. X-ray analysis of the chemically delithiated Li_xNi_0.2Mn_0.2Co_0.6O₂ phases reveals that the rhombohedral symmetry was maintained during Li-extraction, confirmed by the monotonous variation of the potential-composition curve of the Li//Li_xNi_0.2Mn_0.2Co_0.6O₂ cell. LiNi_0.2Mn_0.2Co_0.6O₂ cathode has a discharge capacity of ∼160 mAh g⁻¹ in the voltage range 2.7-4.3 V corresponding to the extraction/insertion of 0.6 lithium ion with very low polarization. It exhibits a stable capacity on cycling and good rate capability in the rate range 0.2-2 C. The almost 2D structure of this cathode material, its good electrochemical performances and its relatively low cost comparing to LiCoO₂, make this material very promising for applications.     

Modeling and estimation of deformation behavior of particle-reinforced metal–matrix composite

In order to estimate the characteristic feature of the deformation behavior of materials with a length scale, the strain gradient plasticity theories, corresponding variational principle and a finite element method are given. Then the finite element method is applied to the estimation of the mechanical characteristics of the particle reinforced metal–matrix composites modeled under plane strain conditions. The effects of the volume fraction, size and distribution pattern of the reinforcement particles on the macroscopic mechanical property of the composite are discussed. It has been clarified that the deformation resistance of the composite is substantially increased with decreasing particle size under a constant volume fraction of the reinforcement material. The main cause of the increase of the deformation resistance in the plastic range is the high strain gradient appearing in the matrix material, which increases with the reduction of the distance between particles.     

Prediction of gas‐liquid two‐phase mixture flow in a vertical pipe with a sudden expansion in diameter

The principle of gas‐lift pumps is applied to vacuum‐decarburization with the RH (Ruhrstahl Heraeus) process to circulate molten steel. Gas‐lift pumps are also applicable to the transportation of molten iron/steel between different refining processes. This paper treats theoretical analysis of steady‐state flow characteristics of gas‐liquid two‐phase mixtures rising in a vertical pipe with an abrupt expansion of its diameter. The system of governing equations is based upon a one‐dimensional multi‐fluid model. Flow pattern transitions are taken into consideration. A new numerical procedure to predict the flow characteristics at the sudden expansion has been proposed. Experiments have also been performed for several conditions to confirm the applicability as well as the validity of the present numerical model. It has been found that the predictions agree reasonably well with the experimental data. Next, the effect of the sudden expansion of pipe diameter on the pump performance was investigated numerically. As a result, it has been confirmed that the sudden expansion of pipe diameter contributes to improve the pump efficiency.     

Fatal falls among Hispanic construction workers

This study evaluated occupational deaths resulting from fall injuries among Hispanic construction workers using data from the Census of Fatal Occupational Injuries and the Current Population Survey. The demographics and characteristics of fatal falls among Hispanic workers were examined and compared with that of their white, non-Hispanic counterparts. The results show that fatal injuries among Hispanic construction workers were more likely to be caused by a fall than their white, non-Hispanic counterparts (OR = 1.48, 95% CI: 1.05–2.10) after controlling for possible confounders. The rate of fatal falls for foreign-born Hispanic construction workers was 5.5 per 100,000 FTE, which is significantly higher than 4.1 per 100,000 FTE for Hispanic workers who were born in the U.S. (OR = 1.36, 95% CI: 1.08–1.67). The disparities in fatal injuries from falls were found in age groups, job tenure, occupations, and types of construction projects. This study also found that about every two of three fatal falls in construction occurred in establishments with 10 or fewer employees. More prevention, intervention, and training measures must be applied to Hispanic workers, especially those who are new immigrants. OSHA enforcements should target small construction establishments in order to lower overall fatality rates, costs, and unnecessary losses of life.     

Simulation of nanostructure production by electromigration considering specimen's shape

Al nanowires have been successfully formed utilizing electromigration in the passivated Al thin film specimen. A numerical simulation of the nanostructure production method was recently developed based on the governing parameter for electromigration damage. The results of the simulation were verified through experiment. It was shown that this procedure predicted the nanostructure volume formed during lifetime of the specimen, though the nanostructure formation was influenced by the current density and substrate temperature. In this study, the method is applied to Al specimens with various shapes to devote to the theoretical discussion on the efficient production of nanostructure. It is found that volume of the formed nanostructure depends on shape of the specimen. The shape affects distributions of current density, temperature and atomic density in the specimen, so formation speed, lifetime and consequently nanostructure volume during the lifetime are changed. It is clarified that this simulation method will contribute to seeking the optimum specimen's shape for efficient NS production.     

Collaborative investigations on thoron and radon in some rural communities of Balkans

This paper deals with the results of the first-field use in the Balkans, i.e. Serbia and Republic of Srpska (Bosnia and Hercegovina), of a passive polycarbonate Mark II type and poliallyldiglycol carbonate (Cr-39) alpha track detectors sensitive to thoron as well as to radon. Both types of solid state nuclear track detectors were designed and supplied by National Institute of Radiological Sciences (NIRS), Chiba, Japan. The commercial names for these detectors which all have been field tested in Balkan rural communities are known as: UFO and RADUET passive discriminative radon/thoron detectors. No database of thoron and thoron progeny concentrations in dwellings in Serbia or Balkans region exist, and as a result, the level of exposure of the Serbian population to thoron and its progeny is unknown so far.     

Imaging saponin-induced structural changes in neural processes with atomic force microscopy

Temporal changes in the structure of neuronal processes in the presence of saponin were studied by atomic force microscopy in a fluid medium. After saponin treatment, concavities were formed on the surface of some neurites and fibrous structures in other neurites were splayed. The vertical height of these splayed fibrils or fibrillar bundles ranged from 13 to 370 nm, and the horizontal width was less than 500 nm. These findings suggest that formation of concavities and separation of bundled fibrils occurred simultaneously in saponin-treated neurites.