Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass

Sliding friction and wear experiments and electron microscopy and diffraction studies were conducted to examine the metallurgical microstructure of a metallic glass surface strained in sliding contact. Friction and wear experiments were conducted with aluminium oxide spheres 3.2 and 6.4 mm in diameter sliding, in reciprocating motion, on a metallic foil with a composition of Fe₆₇Co₁₈B₁₄Si₁ at a sliding velocity of 1.5 mm s^-1 (frictional heating is negligible) with a load of 2.5 N at room temperature and in a laboratory air atmosphere.The results of the investigation indicate that the amorphous alloy (metallic glass) can be crystallized during mechanical contact. Crystallites with a size range of 10–150 nm are produced on the wear surface of the amorphous alloy. A diffused honeycomb-shaped structure formed by dark gray bands is also produced during sliding. Considerable plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminium oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris and/or powdery and whiskery oxide debris. The wear rate of Fe₆₇Co₁₈B₁₄Si₁ was 5 × 10^-9 mm³ N^-1.     

Effect of surface pretreatment by acid pickling on the density of stannate conversion coatings formed on AZ91 D magnesium alloy

Hydrofluoric and hydrochloric acid solutions and a mixture of them were tested as pickling solutions for AZ91 D Mg alloy before application of stannate coatings. Optical microscopy and energy dispersive X-ray spectroscopy (EDX) of the alloy surface after the pickling process showed that the Mg-rich α phase dissolved preferentially rather than the Al-rich β phase in hydrochloric acid solution. On the other hand, in hydrofluoric acid solution, Mg dissolved in a form of pitting corrosion. Pickling pretreatment with a mixture of these acids at an optimal concentration and an optimal pickling time resulted in relatively uniform dissolution of the alloy surface. The potentiodynamic polarization technique was used to investigate the anodic behavior of the uncoated and coated magnesium alloy in borate buffer solution. The morphology of the coatings was observed using a scanning electron microscope (SEM) before and after corrosion tests. The experimental results showed that coating film density and corrosion resistance of stannate-coated samples prepared with pickling pretreatment were improved compared with those of the coated sample without pickling pretreatment.     

Influence of ambient temperatures on performance of a CO2 heat pump water heating system

In residential applications, an air-to-water CO₂ heat pump is used in combination with a domestic hot water storage tank, and the performance of this system is affected significantly not only by instantaneous ambient air and city water temperatures but also by hourly changes of domestic hot water consumption and temperature distribution in the storage tank. In this paper, the performance of a CO₂ heat pump water heating system is analyzed by numerical simulation. A simulation model is created based on thermodynamic equations, and the values of model parameters are estimated based on measured data for existing devices. The calculated performance is compared with the measured one, and the simulation model is validated. The system performance is clarified in consideration of seasonal changes of ambient air and city water temperatures.     

Simple assay method for endocrine disrupters by in vitro quail embryo culture: nonylphenol acts as a weak estrogen in quail embryos

Many chemicals that are not structurally related to estrogen have estrogen-like activity. In this study, we tried to apply a quail embryo culture system for assessing the in vivo effects of such chemicals on the development of quail embryos. Beta-estradiol induced feminization of the gonads of genetically male embryos, which was confirmed by the increase in the size of the left gonad and female-specific aromatase expression, while male-specific SOX9 expression was not affected. Nonylphenol, which has a weak estrogenic activity, reduced the viability and body weight of embryos. Simultaneously, several genetically male embryos were feminized in terms of gonadal size and aromatase expression. These results indicate that the avian embryo culture system was useful for evaluating endocrine disrupters.     

Optimizing service restoration in distribution systems based on scheduling of crews considering priorities of loads

The service restoration to sound sections within a short period as much as possible, performed after the permanent fault occurs in a distribution system, is significant for maintaining power supply reliability. This paper proposes an efficient method to find service restoration procedures based on fault searching and the optimal work scheduling of crews, considering the power supply priorities of loads and the probability of occurrence of faults. The proposed method is composed of two-stage problems to reduce the outage sections efficiently: (i) the problem to find a series of searching procedures for unknown fault locations in the first stage and (ii) the optimization problem of work schedules of crews in the second stage. In the first stage, the order of operation of switches opened for searching for the fault direction is determined, constituting the searching tree. After that, the proposed optimization method can efficiently solve the work scheduling problem by formulating it as a mixed-integer linear programming problem in the second stage. The computational experiments using a large-scale distribution system model with many remote and manual switches show that the proposed method can provide efficient service restoration procedures within a reasonable computational time.