Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition

We have studied the electronic structure of bulk single crystals and epitaxial films of magnetite Fe$_3$O$_4$. Fe $2p$ core-level spectra show clear differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra exhibit temperature ($T$)-dependent charge excitations across the Verwey transition at $T_V$=122 K, which is missing in the surface-sensitive spectra. An extended impurity Anderson model full-multiplet analysis reveals roles of the three distinct Fe-species (A-Fe$^{3+}$, B-Fe$^{2+}$, B-Fe$^{3+}$) below $T_V$ for the Fe $2p$ spectra, and its $T-$dependent evolution. The Fe $2p$ HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the magnetically distinct sites associated with the charge excitations. Valence band HAXPES shows finite density of states at $E_F$ for the polaronic metal with remnant order above $T_V$, and a clear gap formation below $T_V$. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B-Fe$^{2+}$ and B-Fe$^{3+}$ electronic states, consistent with resistivity and bulk-sensitive optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter

Microprobe Analyses of the Potassium-Calcium Distribution Relationship in Predentine

Apex regions of continuously growing incisors of Wistar rats were quickly dissected, shock-frozen in liquid nitrogen-cooled propane, freeze-dried at -80 °C and infiltrated with Spurr\u27s resin . 400nm thick dry sections were cut with a diamond knife on an ultramicrotome . Relatively flat sections were transferred with an eye lash onto collodium coated aluminum grids. They were flattened with a glass stick and by placing another collodi um coated aluminum grid just on top of the first one, exerting a uniform pressure . After carbon coating the sections were observed using the backscattered and secondary electron signals in a scanning microscope. The predentine was analyzed for calcium and potassium with an energy dispersive x-ray analysis system. The xray spectra revealed in the predentine regions with beginning dentine formation, near the apex, an uneven K-distribution with very low as well as more prominent x-ray peaks. The K peaks were always lower than those of calcium. In areas with advanced dentine formation, prominent K-peaks were always observed. They were normally higher than the Ca-peaks up to a distance of 5- 10 µ.m from the dentine border. Closer to the dentine border the K concentration decreased while the Ca-peak increased. This might indicate that (besides Na) K is used to balance the negative charges of the macromolecules till K is replaced by Ca at the onset of apatite crystal formation

Effect of Static Extraction TIME on Extraction Efficiencies Using On-line Supercritical Fluid Extraction-High Performance Liquid Chromatography for Lipoquinone Analysis in Activated Sludge

Analysis of microbial community is important for monitoring the performance of biological processes. One of the most simple, quantitative and high reproducible method for analysis of the microbial community is lipoquinone profile method. Lipoquinone is constituent of bacterial plasma membrane that is essential for electron transporter. Lipoquinone could be used as a biomarker to analyze the microbial community because in general one species or genus of bacteria has one dominant type of lipoquinone, thus any changes in the lipoquinone profile would reflect the changes in the microbial community. The method for lipoquinone determination in environmental sample is direct extraction using organic solvent and analysis using chromatography system. Since the method is tedious and uses a large amount of organic solvent, the on-line supercritical fluid extraction-high performance liquid chromatography (on-line SFE-HPLC) has been developed to simplify the method, and was successful determine lipoquinone compounds in activated sludges. The effect of static extraction time on extraction efficiencies of the lipoquinone was investigated in order to eliminate the water pump and methanol pump in the previous system. The CO2 was used as an extraction solvent. The 0.1 g of freeze dried activated sludge was placed into a 1 mL stainless steel extraction vessel and methanol was spiked into the sludge as a modifier. The SFE was connected to HPLC by using trapping column as an interface for collecting lipoquinone extracted from the sludge. The static extraction time was conducted by allowed the matrix to immersed in CO2 and methanol. When the static extraction time finished, the dynamic extraction time was carried out. The extracted and trapped lipoquinone then directly transferred to HPLC system for determination. In this study, the effect of static, dynamic extraction time and volume of spiked methanol were optimized using simplified on-line SFEHPLC for lipoquinone analysis. The best results in terms of extraction yield were obtained at 25 MPa, 45°C, 10 min static extraction time with 500 µL methanol spiked, and 25 min dynamic extraction time with 0.9 mL min-1 CO2 flow rate. It was concluded that the developed method could simplify the online SFE-HPLC system of lipoquinone determination which is useful for a rapid and routine analysis of microbial community in activated sludge