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.     

Relaxor Behavior of Ge-Doped TlInS2

The dielectric and pyroelectric properties of Ge-doped (0.1 mol %) TlInS₂ crystals are studied. The results demonstrate that TlInS₂ is a ferroelectric relaxor. The experimental data are used to evaluate, using the Vogel–Fulcher relation, the activation energy (0.045 eV), preexponential factor (f ₀ = 2 × 10¹³ Hz), and the dipole-freezing temperature (T _F = 142 K) and to determine the temperature range of the stable relaxor (nanodomain) state and the temperature of the transition to the ferroelectric (macrodomain) state, accompanied by an anomaly in the temperature-dependent pyroelectric coefficient.     

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.     

Electrosprayed and selenized Cu/In metal particle films

Nano-particulate copper and indium metal layers of 1-2 μm have been deposited by non-vacuum techniques such as doctor blade, screen printing and electrospray using alcoholic suspension pastes. Electrospray showed a high efficiency of material usage and yielded the most uniform morphology. The metal precursor layers were subjected to a thermal treatment (500-600 °C) in selenium vapor to convert the porous metal layers into CuInSe₂ compound layers. The chemical conversion, investigated by X-ray diffraction, showed the presence of the In₂O₃ impurity phase in the precursor as well as in the selenized layers.     

Accuracy Investigations of Boundary Element Methods for the Solution of Laplace Equations

Boundary element methods (BEMs) are approved methods for an efficient numerical solution of problems, which are based on a Laplace equation. Here, the solution of electrostatic field problems, steady current flow field problems, and magnetostatic field problems is considered. Focus of this paper is on investigations of accuracy of direct formulations, which are based on Green's theorem. Different types of coupling of computational domains are examined with respect to accuracy and convergence behavior of iterative solvers of the linear system of equations. Furthermore, the influence of singular and nearly singular integrals and the influence of matrix compression techniques to the accuracy of the solution are observed     

Preparation and properties of heavy-metal halide glasses

We have studied the effect of In³⁺, Pb²⁺, Gd³⁺, and Cl (heavier ions) substitutions for Al³⁺, Ba²⁺, La³⁺, and F^? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF₄-BaF₂-LaF₃-AlF₃-NaF system). We obtained stable glasses containing InF₃ and BaCl₂ instead of AlF₃ and BaF₂, respectively, and offering increased IR transmission. The presence of CCl₄ in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs.     

Analysis of operating conditions of ground-fault protection schemes for generator stator winding

This paper presents results of simulation studies of the influence of methods of grounding the stator winding of the unit-connected generator neutral on the operating conditions of a 100-percent ground-fault protection excited by the third-harmonic voltage ratio in the generator neutral and at its terminals. The analysis was performed for a generator with the neutral grounded through a ground-fault neutralizer, a third-harmonic stop filter, a resistor, and a capacitive voltage divider. The influence of the parameters of the particular elements of the grounding circuits on the voltage-feeding measuring element of the protection was determined. The capacitance to ground of the generator breakers was taken into account. The simulations were run for 1110-MVA unit-connected generator at ground faults along the whole length of the generator stator winding. It has been found that the method of grounding the generator neutral and the parameter of the grounding elements significantly influences the operating conditions of this protection. It is shown that through the proper selection of these parameters, the ground-fault protection of whole stator winding, counting from the generator neutral to the terminals is ensured.     

Design of a wideband microstrip antenna and the use of artificial neural networks in parameter calculation

This paper deals with the design of a multi-slot hole-coupled microstrip antenna on a substrate of 2 mm thickness that gives multi-frequency (wideband) characteristics. The Method of Moments (MoM)-based IE3D software was used to simulate the results for return loss, VSWR, the Smith chart, and the radiation patterns. A tunnel-based artificial neural network (ANN) was also developed to calculate the radiation patterns of the antenna. The radiation patterns were measured experimentally at 10.5 GHz and 12 GHz. The experimental results were in good agreement with the simulated results from IE3D and those of the artificial neural network. A new method of using a genetic algorithm (GA) in an artificial neural network is also discussed. This new method was used to calculate the resonant frequency of a single-shorting-post microstrip antenna. The resonant frequency calculated using the genetic-algorithm-coupled artificial neural network was compared with the analytical and experimental results. The results obtained were in very good agreement with the experimental results.     

Terahertz characterisation of building materials

To obtain realistic models for propagation channels in future pico-cellular indoor terahertz communication systems it is necessary to know the reflective properties of building materials found in a typical office environment. The angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations. This approach is more efficient than a set of measurements in reflection geometry for different angles. Verification of the method with a set of such reflection measurements shows an excellent agreement.