Hilbert and Chapman-Enskog asymptotic expansion methods for linear evolution equations

The singularly perturbed linear evolution equations of resonance type are considered in a Banach space. The Hilbert and Chapman-Enskog algorithms for generating asymptotic solutions are presented and shown to lead to different results at each finite order of approximation. The asymptotic procedure is applied to the Fokker-Planck equation of the Kramers type. In that case an asymptotic solution of an infinite order can be obtained in a closed form which is identical for both Hilbert and Chapman-Enskog developments and represents an exact solution to the Fokker-Planck equation of the normal type.     

Defect Equilibria and Transport in YBa2Cu3O7-x at Elevated Temperatures: III, Defect Model and Conductivity Mechanism

Based on the measurements of electrical conductivity and thermopower (Seebeck coefficient) as a function of oxygen partial pressure, the defect structure and corresponding conduction mechanisms at elevated temperatures are considered for the Y-Ba-Cu-O (1:2:3) system. It has been postulated that the simple hopping model is not applicable to YBa₂Cu₃O_7-x. A modified conduction hopping mechanism has been proposed and equations describing the mobility of charge carriers in the studied system are derived. The most important advantage of the present model, in comparison to previous models, involves considering interactions between both electrons and electron holes and the resulting effect on their mobility terms. The observed departure of experimental data from the Heikes formula is explained by a very high concentration of defects and resulting substantial interactions between the defects which must be taken into account. The proposed transport model exhibits good agreement with experimental data of nonstoichiometry and the presently determined electrical conductivity and thermopower. It has been argued that the charge transfer mechanism depends substantially on the oxygen partial pressure and resulting oxygen content in the oxide lattice.     

A unified algorithm of reliability estimation of k-out-of-n systems implied by the structure function

A new algebraic form of the structure function of a system will be proposed and its significant properties will be proved. The usefulness of these results in construction of algorithms of reliability estimation will be presented.The general approach to the desig of the algorithms of reliability estimation for both k-out-of-n and consecutive k-out-of-n systems will be presented. The method of the estimation of the lower and/or upper bound of system failure rate will be also discussed.The appropriate program in PASCAL will be given.     

Soft computing and Web intelligence for supporting consensus reaching

A novel idea and architecture of a group decision support system for reaching consensus in a group of individuals (agents) is proposed. The core of the system is the preferences modeling and consensus assessment module, which is based on fuzzy logic. However, the focus is on providing the members of the group with an information- and knowledge-rich environment, and tools to make an effective and efficient use of such an environment. This should help the agent gain proper opinions about the issues and opinions and/or attitudes of other agents, articulate proper testimonies, actively contribute to the discussion, and finally make sound and informed decisions that can help constructively run the consensus reaching process. For this purpose modern Web-based technologies are employed and tightly integrated with the core of the system.     

Influence of the technological conditions of welding using the MIG/MAG method on metal transfer in the welding arc

Results of investigations on the effect of MAG welding technological conditions using filler metals and shielding gases typical for unalloyed and high-alloy steels on metal transfer phenomenon are presented. The course of investigation and the tables including ranges of parameters for specific types of metal transfer are presented for different sets of electrode wires and shielding gases. It is concluded that the test results can be used for the preparation of welding procedure specifications and welding procedure qualification records when the determination of metal transfer type is required.     

Principles for the evaluation of gas cavities in welded joints of steel on the basis of radiographs according to different European standards

During making a weld, many metallurgical reactions resulting from interaction between slag, gas and metal take place. These reactions influence the quality of welded joints. The oxidation, nitriding and hydriding phenomena occurring in welding processes can be a reason for gas void formation. Gas voids, which are the internal imperfections, are detected most often by radiographic methods. The purpose of this paper is to present the principles of assessment of gas cavities in welded joints, specified in different acceptance standards, on the basis of radiographic examination.