Statistical analysis of optimum friction welding conditions for 6061 aluminium alloy friction-welded joints

Conferring lightweight and good corrosion resistance, aluminium alloy joints are extensively required in the manufacture of various types of electrical and mechanical components. Research data previously obtained by the authors^{1, 2} show the efficiency of friction-welded joints, regardless of whether produced from similar or dissimilar materials, to be fairly well scattered under identical sets of friction welding conditions and underline the need for statistical analysis of a large number of joints to determine the suitability of any specific set of friction welding conditions. That is to say, joints with a high mean joint efficiency that are friction-welded under optimum friction welding conditions conform to a normal distribution with low scatter during such statistical analysis while simultaneously showing a large Weibull distribution shape parameter and small dispersion. On the other hand, joints with a low mean joint efficiency that are friction-welded under unsuitable friction welding conditions conform to a positively or negatively skewed distribution with heavy scatter while simultaneously having a small Weibull distribution shape parameter and large dispersion.     

Characteristics of VHF excited hydrogen plasmas using a ladder-shaped electrode

A VHF excited hydrogen plasma was produced with a ladder-shaped electrode whose excitation frequency ranged up to 100 MHz for gas pressures of 40–200 mTorr and the plasma parameters were measured with a Langmuir probe. When the excitation frequency was increased, the electron density increased and the electron temperature decreased. The pressure dependence of the electron temperature at excitation frequencies of 65 and 100 MHz was different from the usual relationship: the electron temperature tended to increase with increasing pressure.     

Effect of arrangement of pillar array of aligned carbon nanotube bundles on its field-emission characteristic

We investigated the properties of field emission from a pillar array of aligned carbon nanotube (CNT) bundles, which were fabricated on a Si substrate by thermal chemical vapor deposition. To explore the influence of the pillar arrangement on its field emission, the ratio of interpillar distance (R) to pillar height (H), R/H, was investigated as a function of H by changing H while maintaining R at 100 μm. The most-enhanced field concentration was obtained at R/H ∼ 6, although we previously reported that the optimal configuration of pillars for R = 250 μm was a ratio of R/H = 2. These results show that the optimal R/H for greatest field emission from the CNT pillar array is dependent on R.     

Studies on the structures and antigenic properties of rabies virus glycoprotein analogues produced in yeast cells

We investigated two forms (designated as yGI and yGII) of rabies virus glycoprotein (G) analogues produced in the G cDNA-transfected yeast cells. Molecular weights of yGI and yGII were estimated as 66 and 56 kDa, respectively, according to their relative mobility in SDS-PAGE. Although being produced in large amounts, yGI was present mostly in insoluble forms and hardly extractable with non-ionic detergents. The yGI reacted with polyclonal anti-G antibodies, but did not react with our conformational epitope-specific anti-G monoclonal antibodies (G-MAbs). No protective immunity was induced by yGI in guinea pigs nor in mice. On the other hand, yGII was Triton-soluble, but was only small in amount (at most 1% of total G proteins) and was shown to lack the cytoplasmic domain. The yGII, however, reacted with the G-MAbs and induced protective immunity in guinea pigs as well. When the G-cDNA was expressed in animal cells in culture, a single form (about 66 kDa) of G protein was produced, which displayed similar behaviors as seen in its reactivity with the MAbs and intracellular distribution as seen in the virus-infected cells. These results suggest that most G protein molecules were not processed normally in yeast cells, resulting in abnormal folding and multimer formation, while only a small fraction were occasionally folded normally to have conformational epitopes but were mostly deprived of the C-terminal portion.     

Improvement of Machining Accuracy of 5-Axis Control Ultraprecision Machining by Means of Laminarization and Mirror Surface Finishing

Air bearings are often used in ultraprecision machine tools requiring high accuracy. With increasing the high accuracy for machine tools, it is required to pay attention to microvibration with nanometer order. The fluctuation in compressed air applied to air bearings causes the air turbulence, which results in the microvibration. The study presents the laminarization by the optimal design of piping and air bearing surfaces as well as mirror surface finishing, so that the laminarization can be realized to suppress the microvibration. From experimental results, it is found that the surface roughness of workpieces can be drastically improved by using a revised ultraprecision machining center.     

Effects of Instant Coffee Consumption on Oxidative DNA Damage, DNA Repair, and Redox System in Mouse Liver

ABSTRACT:  To examine the effects of instant coffee consumption on cancer risk, we analyzed the oxidative DNA damage levels and the DNA repair and redox systems in the livers of coffee-fed mice. Three-week-old male ICR mice were fed with/without 0.1% (w/v) instant coffee solution. At 2, 4, and 8 mo, the levels of 8-hydroxydeoxyguanosine (8-OH-dG), a major form of oxidative DNA damage, and the expression of mouse 8-OH-dG repair-associated genes and redox system-associated genes, the SOD activity, and the LPO level were analyzed. Simultaneously, half of the mice were fed a low vitamin (LV) diet (autoclaved diet) to disturb the defense system against oxidative stresses. As a result, the 8-OH-dG level was increased in the livers of LV diet (+ water)-fed mice for 8 mo, in comparison to those of the 0 M control mice and normal diet (+ water)-fed mice. However, no significant differences between water drinking and coffee drinking were observed, in terms of the 8-OH-dG level. In addition, the 8-OH-dG repair-associated gene expression, the SOD activity, and the LPO level also showed no significant differences between water drinking and coffee drinking in all mouse groups. On the other hand, among the redox system-associated genes, only the expression of  GPx1  was changed. These results suggest that instant coffee consumption has little, if any, effect on the risk of liver cancer due to oxidative stresses.     

Microbial community analysis of food-spoilage bacteria in commercial custard creams using culture-dependent and independent methods

Custard cream is made from highly nutritive raw materials such as milk and sugar and is easily spoiled by the multiplication of specific microbial contaminants or residents. However, this spoilage microbial community has not been studied. We determined the spoilage microbiota in commercial custard creams using culture-dependent and independent methods. Using the culture-dependent analysis with various agar media, 185 bacterial colonies and 43 eukaryal colonies were isolated from 7 commercial custard cream products. All bacterial isolates were morphologically, physiologically, and genetically identified as bacilli, staphylococci, lactic acid bacteria, and psychrotrophic gram-negative rods. Using culture-independent molecular analysis, the PCR-denaturing gradient gel electrophoresis technique, spoilage of the commercial custard creams was found to be caused by bacilli, staphylococci, lactic acid bacteria, psychrotrophic gram-negative rods, Anoxybacillus sp., Caurobacter sp., and Streptococcus sp. bacteria. The detected spoilage bacteria were the same species as previously detected in spoiled milk products and shown in other reports, suggesting that spoilage bacteria in a raw material easily grow in processed foods made from milk. We determined the spoilage microbial communities in commercial custard creams, and these are the first data concerning spoilage microbiota in nonfermented processed foods using a culture-independent analysis. Our study will be useful for the manufacture and safe preservation of dairy products because the first step toward safe food preservation by food manufacturers is to understand the spoilage microbiota in a target food to select optimal preservatives and to reduce the use of food additives.     

Experimental study on titanium heat exchanger used in a gas fired water heater for latent heat recovery

In general, latent heat recovery is usually accompanied by the corrosion of the heat exchanger, which is caused by the strongly acidic condensate when the temperature of the flue gas is lowered below the acid dew point. The present study has been conducted to investigate the heat and mass transfer characteristics in a titanium heat exchanger with excellent corrosion resistance used for waste heat recovery with the condensation arranged in a gas fired water heater. In addition, the thermal efficiency of the gas fired water heater was evaluated based on the net calorific value at the maximum rated output during latent heat recovery from the exhaust flue gas. Parametric studies were conducted for the flue gas flow rate, inlet temperature and mass flow rate of the supplied water, respectively. Different arrangements of the tubes of the heat exchanger including in-line and staggered configurations were investigated. The experimental results indicate that the thermal efficiency of the gas fired water heater with a latent heat recovery (LHR) heat exchanger was enhanced by about 10% compared with conventional instantaneous water heaters, i.e., water heaters without heat recovery. In addition, in terms of the Nusselt number and the Sherwood number, the heat and mass transfer performance of the staggered tube bank type were approximately 50% and 10% higher than that on the in-line tube bank type when the Reynolds number of the flue gas was 10³.