Novel Mg2+ fluorescent molecular probes (KMG-20-AM and KMG-27-AM; where AM is an acetoxymethyl group) based on a coumarin possessing a charged beta-diketone structure were designed and synthesized. These fluorescent probes produced a red shift from 425 to 445 nm in the absorption spectra after formation of a complex with Mg2+. The fluorescence spectra of these probes also showed a red shift from 485 to 495 nm and an increasing fluorescence intensity after formation of a complex with Mg2+. The optimum experimental conditions were excitation wavelength of 445 nm and a monitored wavelength of 500 nm, where these probes functioned as an indicator showing an image of increasing fluorescence in the presence of Mg2+. These probes showed a "seesaw-type" fluorescent spectral change with the isosbestic point at 480 nm due to the light excitation at 445 nm, which indicates that ratiometry can be used for the measurement. The molecular probes formed a 1:1 complex with Mg2+ and the dissociation constant (Kd) was 10.0 mM for KMG-20. The association constants of the probes with Mg2- were approximately 3 times higher than that with Ca2+, which showed that the selectivity of Mg2+ versus Ca2+ for these probes was over 200 times higher than that for commercially available Mg2+ fluorescent molecular probes such as mag-fura-2, Magnesium Green. As an application of these probes, intracellular fluorescent imaging of Mg2+ was demonstrated using a fluorescent microscope. After the addition of KMG-20-AM and KMG-27-AM into PC12 cells, a strong fluorescence was observed in the cytoplasm and a weak fluorescence in the nuclei region. After treatment with a high-K+ medium, the fluorescence intensity increased due to increasing intracellular Mg2+. The real image of Mg2+ release from the magnesium store was successfully observed with these Mg2+ fluorescent probes.
Nanometer-scale differences in mechanical and structural properties between the molybdenum- dithiocarbamate/zinc-dialkylsithiophosphate (MoDTC/ZDDP) tribofilm and ZDDP tribofilm were successfully evaluated by using atomic force microscopic phase-image techniques, Auger electron spectroscopy and X-ray photo spectroscopy. It is well known that the MoDTC/ZDDP tribofilm exhibits markedly lower friction behavior than the ZDDP tribofilm. To elucidate the mechanism of friction reduction originating from the MoDTC additive, attention was focused on property differences in the surface area in particular, from the uppermost surface to an underlying region of less than 10 nm in depth. It was found that the friction reduction due to the MoDTC/ZDDP additives originates from an inner skin layer formed by MoS2 nanostrips just below the surface. The MoS2 nanostrips were oriented in the sliding direction, had low yield strength and acted as a solid lubricant in lowering the friction coefficient of the MoDTC/ZDDP tribofilm.
Nitriding phenomena that occur on the surfaces of pure Fe and Fe-Cr alloy (16 wt% Cr) samples were investigated. An Ar + N 2 mixture-gas glow-discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar + ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasmanitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N 2 + ) and nitrogen molecule from the glow-discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle-resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N x -Fe y -O, NO + , and NO 2 − . In the Fe-Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided.
The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow-discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N 2 * ) or nitrogen molecule ions (N 2 + ). The optical emission spectra suggested that the formation of N 2 * -rich or N 2 + -rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N 2 + -rich plasma had a much higher nitrogen concentration than that by a N 2 * -rich plasma, likely due to the larger chemical activity of the N 2 + species as well as the N 2 + sputtering bombardment to the cathode surface. The strong reactivity of the N 2 + species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N 2 + -rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N 2 * -rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination.
In order to integrate a five-phase inverter system into the limited space of an in-wheel motor, a high temperature low stray inductance SiC half-bridge power module with a volume of about 5 ml was designed, fabricated and tested. The stray inductance in the module was calculated by an electromagnetic simulator and confirmed by measurements to be 4.4 nH. Double-pulse switching tests were conducted at temperatures up to 200°C. Thermal resistance, including that of the substrate, was calculated to be 0.153 °C/W. Fast switching capability was accomplished with an external gate resistance of 1 Ω.
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