Study on the Life Distribution and Reliability of Roller-Based Linear Bearing

A study on the life distribution and reliability for a roller guide with cage was carried out with a total number of 90 test samples in two lots (N _s = 38 and 52), and different fatigue life distribution functions, such as the two and three parameter Weibull distributions, and the log-normal distribution were used for analyzing the test data. The basic dynamic load rating formula standardized by ISO in 2004 was also compared with the life test data in relation to the effect of crowning on both ends of the carriage raceway. This study revealed the following: (1) the best fit for the life test data was achieved by the three-parameter Weibull distribution with the third parameter being the minimum life γ, using a Weibull slope of m = 27/20, and a load life exponent of 10/3. The log-normal distribution came second, and the two-parameter Weibull distribution third. (2) The test data did not fit with the two-parameter Weibull distribution using a Weibull slope of 9/8, which had been used in the ISO linear bearing standard. (3) Fatigue failure on the roller guide was initiated near the starting points of the crowning on both ends of the carriage raceway. Almost 70% of the test specimens were found to have uneven and inclined contact situations with the rollers. (4) The basic dynamic load ratings evaluated theoretically fit well to the life test results, while the λ b _m factors were also observed to fall within a suitable value range.     

Estimation of particle size distribution from cross-sectional particle diameter on the cutting plane

To control highly functional sintered materials, it is necessary to evaluate particle size segregation within materials. In the present study, a new method for estimating particle size distribution is proposed; this method considers the occurrence probability of the cutting diameter. The proper particle size distribution in a particle bed was estimated by calculating a matrix consisting of the occurrence probability and the distribution of particle diameters measured on a cutting plane. The estimated particle size distribution was smoothed using the Phillips–Twomey method. A cavity-filling simulation was carried out to verify the validity of the proposed method using the Distinct Element Method. The particle size distribution estimated by this method correlated well with the actual particle size distribution. The effect of particle size distributions with various geometrical standard deviations on the accuracy of estimated values was also investigated. The accuracy increased as the geometric standard deviation increased, and there was an optimum particle size bin number for a specific particle distribution. It was found that a large bin number and a large number of measured particles were required to obtain a higher accuracy for narrow size distributions.     

First-principles study on quantum-transport properties of single molecule depending on adsorption conditions

We present a first-principles electron-transport simulation within the framework of the density functional theory for a 1,4-benzenedithiol molecule suspended between semi-infinite Au electrodes. The transport properties are demonstrated under the several adsorption conditions. It is found that the conducting electrons have two types of resonant-tunneling transport properties with different responses to changes in adsorption conditions.     

Quantum chemical calculation of electron transfer at metal/polymer interfaces

Calculation of contact charging at metal/polymer interfaces were performed by a quantum chemical method (DV-Xa). In the calculation, model clusters with dangling bonds were used. The model clusters showed surface states in the density of states (DOS), the electron transfer occurred at the contact interfaces between polymer and Al. Then, 0.3 nm was a reasonable value as the contact distance in the present simulation.Contact electrifications between PTFE and six metals, such as Pt, Au, Cu, Al, Pb and Ca were simulated. The charge transferred from the metal to PTFE depended on the work function of the metals, and had a gap in range of 4.25–4.28 eV. According to the gap of metals were classified into two groups. If Fermi level of a metal is lower than the lowest unoccupied molecular orbital (LUMO) level of PTFE, the electrons of the metal transfer to the surface state (interface state). Electrons in the other metals with a higher Fermi level move into the conduction band of PTFE.     

Hydrogen enhanced crack propagation of SCM440H low-alloy steel under long-term varying load

Crack propagation behavior of SCM440H low-alloy steel enhanced by absorbed hydrogen is investigated. Six materials tempered at different temperatures are used. Effects of stress ratio, loading frequency, hold time and material hardness on the crack propagation rate are examined under long-term varying load. Tests have been performed under continuous hydrogen charging, in which the crack tip has been isolated from the electrolyte and kept dry. An acceleration of crack propagation rate about six times compared to the uncharged material is found in all materials. In addition to this, however, an unexpected acceleration of crack propagation up to 1000 times is experienced under certain conditions. In materials with Vickers hardness higher than 280 tested at low frequency, the above marked acceleration is experienced. The crack surface morphology is quasi-cleavage. This critical hardness (HV = 280) is a little lower than the usually accepted critical hardness for delayed failure (HV = 350). In material with Vickers hardness lower than 268, however, such a marked acceleration is not experienced.     

形变Z因子与动态再结晶晶粒尺寸间的理论模型

以晶界迁移机制进行再结晶的材料，其稳定动态昌粒尺寸Ｄ取决于形变Ｚｅｎｅｒ－ｈｏｌｌｏｍｏｎ参数（Ｚ因子）。作建立了反映Ｄ－Ｚ间关系的理论模型，进行了Ｓｔ４１钢平面应变热变形动态再结晶实验，探讨了动态再结晶晶粒细化的机理。该理论模型为Ｓｅｌｌａｒｓ的经验公式提供了物理基础。研究结果表明，提高形变储存能是动态再结晶晶粒的重要途径。     

Enchanced high-temperature performances of SiC/SiC composites by high densification and crystalline structure

We report the enchanced in situ performances of tensile strength and thermal conductivity at elevated temperatures of the PCS-free SiC/SiC composite with a high fiber volume fraction above 50% fabricated by NITE process for nuclear applications. The composite was fabricated by the optimized combination of the fiber coating, the matrix slurry and the pressure-sintering conditions, based on our previous composites’ study history. The composite showed the excellent tensile strength up to 1500 °C, that it retained approximately 88% of the room-temperature strength. Also, the thermal conductivity of the composites represented over 20 W/m K up to 1500 °C, which was enough high to take the advantage of the assumed design value for nuclear applications. Microstructural observation indicated that the excellent high-temperature performances regarding tensile strength and thermal conductivity up to 1500 °C were the contribution to the high densification and crystalline structure in matrix.     

Impact of NOx reduction on long-term ozone trends in an urban atmosphere

We investigated the relationships between ambient O(3) concentrations and the concentrations of its precursors, NO(x) and NMHC, in Osaka, Japan. The levels of O(x)' (where [O(x)']=[O(3)]+[NO(2)]-0.1x[NO(x)] where the last term accounts for primary emissions of NO(2)) were uniform within the city even in the photochemically active season. We suggested that NO oxidation by peroxy radicals was a minor contributor, and that oxidation of locally emitted NO by background O(3) in the city was the primary control on NO(2) concentrations. Ozone concentrations increased linearly from 1985 to 2002 at a rate of 0.6 ppbv/yr, even though O(x)' concentrations remained constant after the mid 1990s. The trend for O(x)' concentrations could not be explained in terms of an increase in local O(3) production, and the trend was found to reflect background O(3) concentrations in Japan. There was a clear relationship between the NO(2)/O(x)' ratio and NO(x) concentration: the ratio decreased with decreasing NO(x) concentration. As a consequence, O(3) increased with decreasing NO(x) concentration. The reduction of NO(x) emissions was deemed to be an important factor for the recent trend of increasing O(3) concentrations in Osaka City.     

Purified Canola Lutein Selectively Inhibits Specific Isoforms of Mammalian DNA Polymerases and Reduces Inflammatory Response

In the screening of DNA polymerase (pol) inhibitor, we isolated lutein, a carotenoid, from the crude (unrefined) pressed oil of canola (low erucic acid rapeseed, Brassica napus L.). Commercially prepared carotenoids such as lutein (1), zeaxanthin (2), β-cryptoxanthin (3), astaxanthin (4), canthaxanthin (5), β-carotene (6), lycopene (7), capsanthin (8), fucoxanthin (9) and fucoxanthinol (10), were investigated for the inhibitory activities of pols. Compounds 1, 2 and 8 exhibited strong inhibition of the activities of mammalian pols β and λ, which are DNA repair- and/or recombination-related pols. On the other hand, all carotenoids tested had no influence on the activity of a mammalian pol α, which is a DNA replicative pol. Lutein (1) was the strongest pol inhibitor of mammalian pols β and λ in the prepared ten carotenoids tested, but did not influence of the activities of mammalian pols α, γ, δ and ε. The tendency for pols β and λ inhibition by these carotenoids showed a positive correlation with the suppression of TPA (12-O-tetradecanoylphorbol-13-acetate)-induced inflammation. These results suggest that cold pressed unrefined canola/rapeseed oil, or other oils with high levels of lutein and other carotenoids, may be useful for their anti-inflammatory properties.