Computing solenoidal fields in micromagnetic simulations

In finite-difference micromagnetic simulations, the electric field originated from time variations of magnetic induction is evaluated by means of a discrete version of Faraday's law. The electric field can be then calculated as the convolution of a tensor and the time derivative of the magnetic induction. This paper presents an analytical expression for the tensor. The paper also reports on a quantitative test of the tensor that simulates the electric field of an oscillating magnetic point dipole.     

Effect of magnetic hysteresis on rotational losses in heteropolar magnetic bearings

This paper extends a method for predicting rotational losses for laminated rotors of heteropolar magnetic bearings by using an eddy-current model to include the effect of magnetic hysteresis in the rotor material. It compares the modeling results to the experimental data that were used earlier to assess the loss model neglecting hysteresis. The correction to the total electromagnetic loss in the rotor due to the hysteresis is significant at rotational speeds below 6000 revolutions per minute (RPM), where the model including hysteresis effects provides much better agreement with existing experimental data.     

Variable-domain-size theory of spin ferromagnetism

A physically based hysteresis theory incorporating a domain size that depends on the Weiss effective field explains the observed ranges of reversible and irreversible magnetization in the initial-magnetization curve and exterior loop of ferromagnetic materials. The theory applies to materials exhibiting both normal and wasp-waisted exterior loops and agrees well with measured data. It also provides close linkages between magnetization at the quantum scale, domain properties at the mesoscopic scale, and measurements at the macroscopic scale.     

Filtration efficiency and the percolation phenomenon in a grooved-plate Separator

We present here the results of a study of the separation process in the extraction matrix of a novel high-intensity magnetic separator (HIMS). The matrix uses an ordered array of grooved plates (replacing conventional collectors, which are generally made of wires). Only experimental results are available for grooved plates in the literature, but here we propose a new theoretical approach. We report on the particles' behavior, the existence of a percolation phenomenon, and the filtration efficiency, in order to analyze and compare the performance of matrix structures (Lenoir's and Jones'). We discuss the causes of the percolation phenomenon and its effect on filtration efficiency. Correspondence between the theory and the experiments is good. We suggest appropriate uses of each matrix structure according to the property of the processed particles.     

Composition, Structure, and Thermal Expansion of Ca3Fe4S3O6 and CaFeSO

The iron calcium oxysulfides Ca₃Fe₄S₃O₆ and CaFeSO are synthesized by reacting mixtures of CaO and FeS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by x-ray microanalysis and x-ray diffraction. From the temperature-dependent lattice parameters of the oxysulfides (measured up to 1020 K), their thermal expansion coefficients are evaluated.     

Synthesis and Sintering of Bi2Ti4O11

The conditions of Bi₂Ti₄O₁₁ formation are studied. It is shown that the process is diffusion-controlled and depends significantly on the heating rate. The optimal conditions for producing Bi₂Ti₄O₁₁ ceramics are determined. Cold pressing of Bi₂Ti₄O₁₁ ceramic powder at high pressures is shown to influence the unit-cell parameters and volume, positional parameters of Bi and Ti, and bond distances in the ferroelectric ceramics produced by subsequent sintering. The ferroelectric transition temperature decreases steadily with increasing densification pressure.     

Synthesis and Study of Ion Adsorption and Fluorescent Properties of Silica-Grafted Bis(crownazo)methine

A ketocyanine ligand containing two N-aza-15-crown-5 residues has been synthesized and covalently anchored to a silica substrate through an azomethine link. The ligand formation and molecular structure have been determined by combining spectral data and molecular simulations. Preferential adsorption of rare-earth metals from aqueous solutions to the modified surface has been noticed. In the case of lanthanum, the adsorption is accompanied by significant fluorescence enhancement, which allows this system to be used as a sensor for La³⁺ ion.     

Nonadditivity of Properties and the Possibility of Formation of Ensembles of Incommensurate Structures in the GaSe–Ga2Se3 System

The GaSe–Ga₂Se₃ system is studied by x-ray diffraction, electron microscopy, and differential scanning calorimetry. The results demonstrate that the nonadditivity of heat capacity observed near the eutectic composition after quenching is similar to the nonadditivity of properties in misfit layer compounds, which contain incommensurate structural components. The origin of this similarity is discussed in terms of the self-organization of interacting incommensurate elements in the melt and the formation of unstable suprastructural ensembles.     

A direct stiffness analysis of a composite beam with partial interaction

The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd.     

Numerical analysis of Augmented Lagrangian algorithms in complementary elastoplasticity

The main subject of the paper is the investigation of Augmented Lagrangian algorithms and update formulas in the solution of elastoplastic problems. A stress rate formulation for elastoplastic models with internal variables and its finite increment form is employed to state the mechanical problem. In this formulation the Augmented Lagrangian is used to enforce the constraint of plastic admissibility directly on the stresses and thermodynamic forces. This is not a limitation of the Augmented Lagrangian approach, and the same framework can be built on more classical displacement formulations as well. The meaning and the derivation of various first and second order Lagrangian multipliers update formulas and iterative schemes is shown. A new diagonal iteration algorithm and the introduction of a scale factor for the Augmented Lagrangian term are proposed. Numerical examples compare the efficiency of several forms of Augmented Lagrangian algorithms and illustrate the influence of the scale factor and of the penalty parameter. Copyright © 2004 John Wiley & Sons, Ltd.