Structural, Optical and Magnetic Properties of Multiferroic GdMnO3 Nanoparticles

The structural, optical, and magnetic properties of multiferroic GdMnO₃ nanoparticles synthesized by the modified sol–gel route have been investigated. Raman spectroscopy and X-ray diffraction along with Rietveld refinement confirm the pure phase of the GdMnO₃ nanoparticles having an orthorhombic perovskite (space group: Pnma) type structure. The morphology was examined by scanning electron microscopy. Energy dispersive spectroscopy confirms the stoichiometry of the composition. The room temperature UV-visible absorption spectrum using Tauc’s relation gives an optical band gap of ～2.9 eV. A magnetization study of the GdMnO₃ nanoparticles was performed over a temperature range of 2–300 K at an applied field of 0.05 T by using a vibrating sample magnetometer. An effective magnetic moment (μ _eff) of ～9.2μ _B was obtained. The system is paramagnetic at room temperature and shows a ferromagnetic-like nature at 2 K as the applied magnetic field aligns the Gd moments and the contribution of the net moment of Gd spins is larger than that of the anti-ferromagnetically canted state of the Mn spins.     

Electric Pulse Discharge Activated Carbon Supercapacitors for Transportation Application

ScienceTomorrow is developing a high-speed, low-cost process for synthesizing high-porosity electrodes for electrochemical double-layer capacitors. Four types of coal (lignite, subbituminous, bituminous, and anthracite) were used as precursor materials for spark discharge activation with multiscale porous structure. The final porosity and pore distribution depended, among other factors, on precursor type. The high gas content in low-grade carbon resulted in mechanical disintegration, whereas high capacitance was attained in higher-grade coal. The properties, including capacitance, mechanical robustness, and internal conductivity, were excellent when the cost is taken into consideration.     

Microwave processing of electroceramic materials and devices

Microwave synthesis of nano-sized BaTiO₃ and decrystallized titania, and microwave sintering of electroceramics including BaTiO₃, Ba(Zn_1/3Ta_2/3)O₃ (BZT), lead zirconate–titanate (i.e. Pb(Zr _x Ti_1?x )O₃, or PZT), etc., as well as multilayer ceramic capacitors based on X7R, C0G, and ferrite multilayer chip inductors are presented. The results indicate that microwave processing significantly accelerated synthesis and sintering kinetics. As a result, processing time can be saved up to 90%, with the product properties comparable to or better than that of the conventional products.     

Comparison of the Ewald and Wolf methods for modeling electrostatic interactions in nanowires

Ionic compounds pose extra challenges with the appropriate modeling of long‐range coulombic interactions. Here, we study the mechanical properties of zinc oxide (ZnO) nanowires using molecular dynamic simulations with Buckingham potential and determine the suitability of the Ewald (Ann. Phys. 1921; 19) and Wolf (J. Chem. Phys. 1999; 110 (17):8254–8282) summation methods to account for the long‐range Coulombic forces. A comparative study shows that both the summation methods are suitable for modeling bulk structures with periodic boundary conditions imposed on all sides; however, significant differences are observed when nanowires with free surfaces are modeled. As opposed to Wolf's prediction of a linear stress–strain response in the elastic regime, Ewald's method predicts an erroneous behavior. This is attributed to the Ewald method's inability to account for surface effects properly. Additionally, Wolf's method offers highly improved computational performance as the model size is increased. This gain in computational time allows for modeling realistic nanowires, which can be directly compared with the existing experimental results. We conclude that the Wolf summation is a superior technique when modeling non‐periodic structures in terms of both accuracy of the results and computational performance. Copyright © 2010 John Wiley & Sons, Ltd.     

Selection of a pull production control policy under different demand situations for a manufacturing system by AHP-algorithm

A multistage serial production system is considered in the present paper. A generalized model has been developed with the use of probabilistic demand situations for the end product. The demand situations considered are binomial, exponential, lognormal and Poisson. These demand patterns are used as input parameter for various production control policies. The output values for performance parameters are obtained by simulation. The production policies analyzed are Kanban, CONWIP and Hybrid as alternatives for controlling the engineering manufacture. In the presence of several performance measures, it often becomes difficult for the management to select the most appropriate policy. Analytic hierarchy process (AHP) has been implemented for the purpose of selection. Computational results have been reported along with the sensitivity analysis after designing and conducting various experiments.     

Temperature measurements in steady axisymmetric partially premixed flames by use of rainbow schlieren deflectometry

We focus on the utility of rainbow schlieren as a tool for measuring the temperature of axisymmetric partially premixed flames (PPFs). Methane-air PPFs are established on a coannular burner. The flames involve two spatially distinct reaction zones, one in an inner premixed region that has a curved tip and a spatially planar wing portion and another that involves an outer nonpremixed zone in which intermediate species burn in air. Schlieren images are found to visualize clearly these PPF characteristics through light deflection by steep refractive-index gradients in the two reaction zone fronts. The temperature distributions of two flames established at fuel-rich mixture equivalence ratios of phi(r) = 1.5 and 2.0, with bulk-averaged velocities, Vreac = 60 cm s(-1) and Vair = 50 cm s(-1), are inferred from color schlieren images, and a measurement error analysis is performed. Errors arise from two sources. One lies in the process of inferring the temperature from the refractive-index measurement by making assumptions regarding the local composition of the flame. We have shown through simulations that the average temperature deviations due to these assumptions are 1.7% for the phi(r) = 1.5 flame and 2.3% for the phi(r) = 2.0 flame. Another source involves the local uncertainty in the measurement of the transverse ray displacement at the filter plane that is used to determine the refractive index and thereafter the flame temperature. We have ascertained that a maximum error of 4.3% in the temperature determination can be attributed to this local measurement uncertainty. This investigation demonstrates the capability of the schlieren technique for providing not only qualitative displays of the PPFs but also full-field-of-view temperature measurements that are accurate, spatially resolved, and nonintrusive.