Comparative study of apatite formation on CaSiO<Subscript>3</Subscript> ceramics in simulated body fluids with different carbonate concentrations

Apatite formation on CaSiO₃ ceramics was investigated using two different simulated body fluids (SBF) proposed by Kokubo (1990) and Tas (2000) and three sample/SBF (S/S) ratios (1.0, 2.5 and 8.3 mg/ml) at 36.5°C for 1–25 days. The CaSiO₃ ceramic was prepared by firing coprecipitated gel with Ca/Si = 0.91 at 1400°C. The bulk density was 2.14 g/cm³ and the relative density about 76%. The two SBF solutions contain different concentrations of HCO₃^– and Cl^– ions, the concentrations of which are closer to human blood plasma in the Tas SBF formulation than in the Kokubo formulation. The pH values in the former solution are also more realistic. The CaSiO₃ ceramics show apatite formation in SBF (Kokubo) after soaking for only 1 day at all S/S ratios whereas different phases were formed at each S/S ratio in SBF (Tas). The crystalline phases formed were mainly apatite at S/S = 1.0 mg/ml, carbonate-type apatite at 2.5 mg/ml and calcite at 8.3 mg/ml. At higher S/S ratios the increase in the Ca concentration became higher while the P concentration became lower in the reacted SBF. These changes in SBF concentrations and increasing pH occurred at higher S/S ratios, producing more favorable conditions in the SBF for the formation of carbonate bearing phases, finally leading to the formation of calcite instead of apatite in the higher HCO₃^– ion concentration SBF (Tas). Apatite is, however, formed in the lower HCO₃^– ion concentration SBF (Kokubo) even though the Ca and P concentrations change in a similar manner to SBF (Tas).     

Effect of solid/solution ratio on apatite formation from CaSiO<Subscript>3</Subscript> ceramics in simulated body fluid

The effect of the solid/solution (S/S) ratio on apatite formation from CaSiO₃ ceramics in simulated body fluid (SBF) was investigated. CaSiO₃ ceramics with a Ca/Si ratio of 0.91 were prepared by sintering CaSiO₃ powder coprecipitated from ethanol solutions of Ca(NO₃)₂⋅4H₂O and Si(OC₂H₅)₄ using NH₄OH as the precipitant. These ceramics were reacted with SBF at S/S ratios of 1.0, 2.5 and 8.3 mg/ml at 36.5 ^∘C for various times. Formation of apatite was observed at all the S/S ratios after soaking for 1 day. The amount and microstructure of the apatite obtained at a S/S ratio of 8.3 mg/ml, however, differed largely from the product formed at the other two S/S ratios. The apatite formed at S/S = 8.3 mg/ml was of smaller particle size, formed in smaller amount and with less preferred orientation of the (00l) of apatite crystals compared with those formed at S/S = 1.0 and 2.5 mg/ml. An increase of Ca and decrease of the P components occurred in the soaked SBF at S/S = 8.3 mg/ml, the changes being much more marked than with the other two S/S ratios. These differences in the concentration changes in SBF at different S/S ratios are attributed to the difference in the apatite formation from the CaSiO₃ ceramics.     

Compensation for harmonic currents and reactive power in wind power generation system using PWM inverter

In recent years, awareness of environmental problems is growing, and the price of electric power purchased by electric companies has been expensive for power plants utilizing natural energy. Thus, the introduction of wind power generation is being promoted in Japan. Generally, squirrel‐cage induction machines are widely used as generators in wind power generation systems because of their small size, light weight, and low cost. However, the induction machines do not have a source of excitation. Thus, inrush currents and instantaneous voltage drops occur when the generator is directly connected to a power grid. To reduce the inrush currents, an AC power regulator is used. Wind power generators are frequently connected to and disconnected from the power grid. However, when the inrush currents are reduced, harmonic currents are caused by phase control of the AC power regulator. And the phase control of the AC power regulator cannot control the power factor. Therefore, we propose the use of the AC power regulator to compensate for the harmonic currents and reactive power in a wind power generation system, and demonstrate the validity of this system by simulated and experimental results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(2): 58–67, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20254     

A natural soil and mechanism of removal

Nitrogen compounds in natural soils are studied in relation to their effect on the soil removal mechanism in detergency. Nitrogen compounds in various forms and in fairly large amts are found in natural soils, and more than 24% of these nitrogen compounds are presumed to be high mol wt nitrogen compounds or proteins. These high mol wt nitrogen compounds which cannot be removed by water can be removed by the detergent action of sodium dodecyl benzene sulfonate (DBS). When the detergency of DBS was compared with nonyl phenol-polyoxyethylene adduct, the detergency for artificial soil cloths did not coincide with results obtained with naturally soiled cloths. These data suggest that some interaction between DBS and nitrogen compounds might have contributed to the detergent action. If proteins were added to the present artificial soil formulation, better correlation might be expected between artificial and natural soil detergency results in DBS evaluation.     

Performance and maximum load capacity of uninterruptible power system using double‐layer capacitor

Power service interruptions cause problems in various facilities. Even an instantaneous voltage drop may give rise to serious problems in computer systems or electronic equipment. The uninterruptible power system (UPS) has been used to compensate for the power service interruptions. Also, the instantaneous voltage drop compensator using the electrolytic capacitor has been developed for the instantaneous voltage drop. Recently, the double‐layer capacitor has been considered as a new energy storage element. This capacitor has many advantages such as no maintenance, long lifetime, and quick charge/discharge characteristics with large current and it has higher energy density than the electrolytic capacitor. Therefore, we developed the UPS using the double‐layer capacitor. In this paper, the performance of the UPS using the double‐layer capacitor is shown by simulated and experimental results. Furthermore, the discharge characteristics of the double‐layer capacitors are investigated on the basis of the equivalent circuit including the capacitors and a voltage booster. Finally, the maximum load capacity to compensate is clarified for the system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 73–81, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20190     

Approaches to suppressing shaft voltage in brushless DC motor driven by PWM inverter

This paper describes the approaches to suppressing the shaft voltage and bearing current by electrostatically shielding the stator end windings of the brushless DC motor driven by PWM inverter. At first, measured shaft voltage and bearing current are compared with those calculated waveforms to verify the common mode equivalent circuit of the brushless DC motor. Next, the relationship between shaft voltage and stator winding to rotor capacitance is calculated using the common mode equivalent circuit. Finally, the electrostatic shielding of the stator end windings is evaluated to reduce the shaft voltage by experiments and calculations. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 73–79, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20701     

Strain‐induced crystallization behavior of phenolic resin crosslinked natural rubber/clay nanocomposites

Nanocomposites of natural rubber (NR) and unmodified clay were prepared by latex compounding method. Phenolic resin (PhOH) was used to crosslink NR. Crosslinked neat NR was also prepared for comparison. The structure–property relationship of uncrosslinked and crosslinked NR/clay nanocomposites was examined to verify the reinforcement mechanism. Microstructure of NR/clay nanocomposites was studied by using transmission electron microscopic (TEM), X‐ray diffraction (XRD), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering (SAXS) analyses. The results showed the evidence of intercalated clay together with clay tactoids for the nanocomposite samples. The highest tensile strength was achieved for the crosslinked NR/clay nanocomposite. The onset strain of deformation induced the crystallization of NR for nanocomposites was found at almost the same strain, and furthermore their crystallization was developed at lower strain than that of the crosslinked neat NR because of the clay orientation and alignment. However, at high strain region, the collaborative crystallization process related to the clay dispersion and conventional crosslink points in the NR was responsible to considerably high tensile strength of the crosslinked NR/clay nanocomposite. Based on these analyses, a mechanistic model for the strain‐induced crystallization and orientational evolution of a network structure of PhOH‐crosslinked NR/clay nanocomposite was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42580.     

Interaction between carbon nanotubes and human cell

Carbon nanotubes (CNTs) have been attracting increasing attention for the possibilities of their widespread applications and many studies have been conducted for their development. On the other hand, the research on the influence of CNTs on human organisms is still scarce and some show concerns about genotoxicity or cytotoxicity. Therefore, in this research, we are proposing a new way of biocompatibility evaluation for CNTs by examining the relation between biocompatibility and structure of CNTs. In our cytotoxicity tests, neither chromosome abnormality nor cell cycle dysregulation occurred, evaluated by fluorescence activated cell sorting (FACS) analysis. However, significances were assessed for cell proliferation and viability for semiconducting CNTs by the paired t-test. It is also clear that CNTs showed adherence to cell, since efficiency of cell ablation by trypsin decreased dramatically in CNTs dishes; this phenomenon was observed especially in semiconducting CNTs. Since semiconducting CNTs do not include armchair CNTs while metallic CNTs do, it indicates that armchair CNTs have high possibility of affection toward biocompatibility. It is expected that armchair CNTs change the behavior of cells such as proliferation and viability.