Effect of armature reaction of a permanent-magnet claw pole SMC motor

The finite-element method enables an accurate analysis for the study on effects of armature reaction in electromagnetic devices, particularly those with complex structures and three-dimensional (3-D) magnetic flux paths. This paper investigates the effects of armature reaction on the parameters and performance of a permanent-magnet (PM) claw pole motor with soft magnetic composite (SMC) core, based on the magnetic field analysis using the 3-D nonlinear time-stepping finite-element method. The current in the stator winding produces a magnetic field, which interacts with the air gap field generated by the rotor magnets. Consequently, the air gap flux density profile against the rotor position produced by the rotor magnets deviates, and so does the back electromotive force. Since the stator field also changes the local saturation level of the magnetic core, the winding inductance varies with both the rotor position and stator currents. The inclusion of these effects in terms of parameter variations in the motor model is important for accurate performance analysis. On the other hand, the pattern of inductance against the rotor position and stator currents can be employed to effectively predict the rotor position at standstill and low speeds for robust sensorless control. The parameter computations are verified by experimental results on the PM claw pole SMC motor prototype. © 2007 IEEE

Visualization of vortex motion in FeAs-based BaFe<inf>1.9</inf>Ni <inf>0.1</inf>As<inf>2</inf> single crystal by means of magneto-optical imaging

Superconductivity has been found in newly discovered iron-based compounds. This paper studies the motion of magnetic vortices in BaFe1.9Ni 0.1As2 single crystal by means of the magneto-optical imaging technique. A series of magneto-optical images reflecting magnetic flux distribution at the crystal surface were taken when the crystal was zero-field cooled to 10 K. The behavior of the vortices, including penetration into and expulsion from the single crystal with increasing and decreasing external fields, respectively, is discussed. The motion behavior is similar to that observed in high-Tc superconducting cuprates with strong vortex pinning; however, the flux-front is irregular due to randomly distributed defects in the crystal. © 2011 American Institute of Physics

Thermal Contraction of Electrodeposited Bi/BiSb Superlattice Nanowires

The lattice parameter of Bi/BiSb superlattice nanowire (SLNW) has been measured using in situ high-temperature X-ray diffraction method. The single crystalline Bi/BiSb SLNW arrays with different bilayer thicknesses have been fabricated within the porous anodic alumina membranes (AAMs) by a charge-controlled pulse electrodeposition. Different temperature dependences of the lattice parameter and thermal expansion coefficient were found for the SLNWs. It was found that the thermal expansion coefficient of the SLNWs with a large bilayer thickness has weak temperature dependence, and the interface stress and defect are the main factors responsible for the thermal contraction of the SLNWs

Flux distribution in Fe-based superconducting materials by magneto-optical imaging

This paper presents the magnetic flux distributions in Fe-based superconducting materials including single crystal of Ba(Fe 1.9Ni 0.1)As 2 and Ba(Fe 1.8Co 0.2)As 2, as well as polycrystalline SmFeO 0.75F 0.2As by means of magneto-optical imaging (MOI) technique. The single crystals were grown out of FeAs flux while polycrystalline sample was grown by hot-press. A MOI film with in-plan magnetization was used to visualize flux distributions at the sample surface. A series of magneto-optical images was taken when the samples were zero-field cooled and field cooled. The flux behavior, including penetration into and expelling from the samples, as well as pinning properties were studied. When external fields increase, flux is completely shielded from the crystals, then, gradually penetrates toward the crystal center from the edge. For polycrystalline sample, Meissner state was observed at very low field. With increasing the field further, flux penetrates into the sample easily along grain boundary, then into grain. Compared with high-T c cuprates, it is found that the flux distributions in Fe-based superconducting materials are very similar to that in high-T c cuprates with strong pinning strength. © 2012 American Institute of Physics

Heavy metal in surface sediments of the Liaodong Bay, Bohai Sea: distribution, contamination, and sources

In an effort to assess the potential contamination and determine the environmental risks associated with heavy metals, the surface sediments in Liaodong Bay, northeast China, were systematically sampled and analyzed for the concentrations of Cu, Pb, Zn, Cr, Ni, As, and Hg. The metal enrichment factor (EF) and geoaccumulation index (I (geo)) were calculated to assess the anthropogenic contamination in the region. Results showed that heavy metal concentrations in the sediments generally met the criteria of China Marine Sediment Quality (GB18668-2002); however, both EF and I (geo) values suggested the elevation of Pb concentration in the region. Based on the effect-range classification (TEL-PEL SQGs), Cu, Pb, Ni, and As were likely to pose environment risks, and the toxic units decreased in the order: Ni &gt; Pb &gt; Cr &gt; Zn &gt; As &gt; Cu &gt; Hg. The spatial distribution of ecotoxicological index (mean-ERM-quotient) suggested that most of the surface sediments were &quot;low-medium&quot; priority zone. Multivariate analysis indicated that the sources of Cr, Ni, Zn, Cu, and Hg resulted primarily from parent rocks, and Pb or As were mainly attributed to anthropogenic sources. The results of this study would provide a useful aid for sustainable marine management in the region.</p

Active and passive biomonitoring comparison: a good choose to understand the complexity of a transition environment

A lectin, Craniella australiensis (CAL), was isolated from sponge C. australiensis by ion-exchange on DEAE-Sephacel and purified by gel filtration on Sephadex G-150 and HPLC on DEAF-5PW. The purified lectin was a trimeric protein as revealed by SDS-PAGE and MALDI-TOF analysis. SDS-PAGE showed that the CAL protein had a molecular mass of 54 kDa, and consisted of three 18 kDa subunits. Gel filtration of purified lectin on Sephadex G-200 indicates that it exists as a 54 kDa protein in its native state. The amino acid composition was rich in Thr and Glx. CAL was found to agglutinate native and trypsinized human A, B erythrocytes, and agglutinate native erythrocytes of mouse, sheep, rabbit and chicken, and trypsinized erythrocytes of sheep and rabbit. The hemagglutination activity was inhibited by glycoproteins such as PSM and asialo-PSM, but not by any of the monosaccharides tested. The activity was stable between 20 and 70 C. Significant CAL activity was observed between pH 5 and 8. The lectin reaction is independent of the presence of divalent cations Ca2+ and Mg2+. The sequence of N-terminal residues of CAL was determined as TSSCQSIVVE. The lectin showed a potent mitogenic response towards BALB/c splenocytes. (c) 2005 Elsevier Inc. All rights reserved