Minimization of torque ripple in SRM drives

The torque pulsations in switched reluctance motors (SRMs) are relatively higher compared to sinusoidal machines due to the doubly salient structure of the motor. The magnetization pattern of the individual phases together with the T-i-&thetas; characteristics of the motor dictate the amount of torque ripple during operation. Both machine design and electronic control approaches have been used to minimize the torque ripple in SRMs. This paper presents an extensive review of the origin of torque ripple and the approaches adopted over the past decade to minimize the torque ripple. A hybrid torque-ripple-minimizing controller that incorporates the attractive features of some of the techniques developed in the past decade is presented along with simulation and experimental results     

Identifying agricultural sites for biomass energy production in Minnesota

This research examines the potential of producing hybrid poplar on location specific marginal agricultural lands in Minnesota. It is assumed that all poplar production would be used to meet biomass energy requirements for two potential 100 MW power plants located in Alexandria and Granite Falls, Minnesota. The delivered fuelwood costs for each power plant are calculated using a cost minimization model. In addition to traditional production and harvesting costs, the model also incorporates landowners opportunity cost of fuelwood production as well as the actual transportation costs associated with supply from each individual analysis area to each power plant. The inclusion of any analysis area as a potential fuelwood supplier is greatly dependent on the interaction and combination of variables such as the opportunity cost, yield rates, and the distance from the power plants. The results show that approximately 40×10³ hectares of land capable of producing about 3.2×10[6] dry Mg of wood would be required to fuel each power plant for a 10 year planning period. The average present value costs of delivered (to the plant gate) fuelwood is about $32 dry Mg⁻¹ for Alexandria and $37 dry Mg⁻¹ for Granite Falls.     

Comparison of the properties of porous silicon films with different back contacts (Ag, Al) for possible photovoltaic applications

In this work, porous silicon (PS) films were prepared by anodization on polished substrates of (1 0 0) Si for a fixed current density (I_d)20 mA cm⁻² and for a fixed anodization time of 30 min using different screen-printed (SP) back contacts, namely Ag and Al. The properties of PS formed using Ag as the back contact were found to be superior compared to the corresponding film using Al as the back contact. The PS formed with Ag-back contact exhibits higher porosity, negligible photoluminescence (PL) decay, better adherence to the substrate and smooth surface morphology compared to that formed with Al as the back contact for the same current density and time of anodization. Fourier transform infrared (FTIR) studies indicated significant presence of Si–O related features at 1050–1150 cm⁻¹ for PS films formed with Al as back contact, which could be responsible for traps and interface (PS–Si) defect densities as compared to corresponding PS films with Ag as the back contact. Measurements of capacitance–voltage (C–V) and current–voltage (I–V) were used for the investigation of the electrical properties of PS films with different back contacts. The frequency-dependent C–V characteristics were analysed to understand the effects of interface states and traps on the properties of PS films. The results have been analysed in terms of eutectic temperature and back surface field (BSF) across the metal–silicon interface.     

Soy isoflavone genistein induces cell death in breast cancer cells through mobilization of endogenous copper ions and generation of reactive oxygen species

Scope: Worldwide geographical variation in cancer incidence indicates a correlation between dietary habits and cancer risk. Epidemiological studies have suggested that populations with high isoflavone intake through soy consumption have lower rates of breast, prostate, and colon cancer. Isoflavone genistein in soybean is considered a potent chemopreventive agent against cancer. Although several mechanisms have been proposed, a clear anticancer action mechanism of genistein is still not known. Methods and results: Here, we show that the cytotoxic action of genistein against breast cancer cells involves mobilization of endogenous copper. Further, whereas the copper specific chelator neocuproine is able to inhibit the apoptotic potential of genistein, the molecules which specifically bind iron (desferroxamine mesylate) and zinc (histidine) are relatively ineffective in causing such inhibition. Also, genistein‐induced apoptosis in these cells is inhibited by scavengers of reactive oxygen species (ROS) implicating ROS as effector elements leading to cell death. Conclusions: As copper levels are known to be considerably elevated in almost all types of cancers, in this proof‐of‐concept study we show that genistein is able to target endogenous copper leading to prooxidant signaling and consequent cell death. We believe that such a mechanism explains the anticancer effect of genistein as also its preferential cytotoxicity towards cancer cells.     

Nonstandard analysis of a converging shock wave in a nonideal gas

The problem of propagation of strong plane and converging shock waves in an unsteady inviscid nonideal gas is studied. A nonstandard analysis is used to derive the jump conditions for both shock waves. It is assumed that the jump occurs on an infinitesimal interval and jump functions in the flow parameters are smooth across this interval. The distribution of the flow parameters across the shock wave is expressed in terms of the Heaviside functions. Numerical computation to study the distribution of the flow parameters is performed.     

Microstructure,optical and dielectric properties of cobalt-doped zinc ferrite nanostructures

Journal of Materials Science: Materials in Electronics - In the present work, we have explored the physical properties of ZnFe2?xCoxO4 (0?≤?x?≤?0.06)...     

Corrosion at the Weld Nugget of the Friction-Stir-Welded Medium Strength Steel: Effect of Microstructure

Metallurgical and Materials Transactions A - In the present investigation, friction stir welding (FSW) was carried out on C-Mn steel using various welding parameters. The microstructural...     

Rapid magnetic cell delivery for large tubular bioengineered constructs

Delivery of cells into tubular tissue constructs with large diameters poses significant spatial and temporal challenges. This study describes preliminary findings for a novel process for rapid and uniform seeding of cells onto the luminal surface of large tubular constructs. Fibroblasts, tagged with superparamagnetic iron oxide nanoparticles (SPION), were directed onto the luminal surface of tubular constructs by a magnetic field generated by a k4-type Halbach cylinder device. The spatial distribution of attached cells, as measured by the mean number of cells, was compared with a conventional, dynamic, rotational cell-delivery technique. Cell loading onto the constructs was measured by microscopy and magnetic resonance imaging. The different seeding techniques employed had a significant effect on the spatial distribution of the cells (p < 0.0001). The number of attached cells at defined positions within the same construct was significantly different for the dynamic rotation technique (p < 0.05). In contrast, no significant differences in the number of cells attached to the luminal surface were found between the defined positions on the construct loaded with the Halbach cylinder. The technique described overcomes limitations associated with existing cell-delivery techniques and is amenable to a variety of tubular organs where rapid loading and uniform distribution of cells for therapeutic applications are required.     

Aspirin improves endothelial dysfunction in atherosclerosis

Archival paraffin-embedded tissue from 5 normal adrenal glands (including 1 from a fetus of 28 weeks' gestation), 6 cases of adrenal cortical hyperplasia, 9 cortical adenomas, 14 cortical carcinomas, and 11 pheochromocytomas were immunostained with monoclonal antibody against bcl-2. Ultrastructural localization of bcl-2 protein was also performed on selected cases. Positive immunostaining for bcl-2 was seen in all of the layers of the normal adrenal cortex, with different staining characteristics. bcl-2 expression was never observed in the normal adrenal medulla. Electron microscopic studies revealed bcl-2 to be localized predominantly to mitochondria, with a small number of labels along the nuclear envelope. Analysis of adrenal neoplasms showed expression of bcl-2 in cortical tumors, but only one positive case in pheochromocytomas. Restriction of bcl-2 expression to adrenal cortex-derived tissue versus adrenal medulla-derived tissue might prove to be helpful for the differential diagnosis between cortical and medullary tumors.