Fuzzy Complex Ranking Method and its Use for Multi-Criteria Comparison of Alternatives

Cybernetics and Systems Analysis - It is noted that fuzzy methods are widely used to substantiate rational decisions in multi-criteria analysis of complex systems since the operating conditions of...     

Effect of the material of injecting contacts on the CVCs of Pb1 − x Sn x Te:In films

The flowing of the injection current in Pb_{1 ? x} Sn _x Te:In structures (x ≥ 0.3) with various metal contacts at the temperature of helium is considered. The current-voltage characteristics (CVCs) of the structures in the dark and when they are illuminated from the blackbody model are given. It is found that the CVCs depend on the materials of the metal contact. The localized state density distribution over the forbidden band in structures with various contacts is given and the influence of the contact region and localized states on the CVC is discussed. The problems of constructing photodetectors with optimum threshold characteristics are discussed.     

Sol–gel synthesis of 2D and 3D nanostructured YSZ:Yb<Superscript>3+</Superscript> ceramics

This paper presents results of a detailed study of fundamental aspects of the formation of 2D and 3D nanostructured YSZ:Yb³⁺ ceramics with a cubic structure through a key synthesis step in aqueous solutions of zirconium-containing hydroxy nanoparticles (1–2 nm) modified by Y³⁺ and Yb³⁺ ions, with the use of a sol–gel method and subsequent calcination of the resultant xerogels at temperatures above 350°C. As starting chemicals for the synthesis of ceramic powders, we used zirconyl, yttrium, and ytterbium nitrates and chlorides and aqueous ammonia. Using mixed solutions of these salts and a procedure developed by us, we synthesized sols, gels, and xerogels. To examine the effect of temperature on solid-state transformations, the xerogels were calcined according to a predetermined program in a muffle furnace at temperatures in the range from 350 to 1350°C (rarely, up to 1650°C). We focused primarily on ceramic powders close in composition to 0.86ZrO₂ · 0.10Y₂O₃ · 0.04Yb₂O₃. The ceramics were characterized by high-resolution transmission electron microscopy, electron microdiffraction, electronic diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis, and X-ray fluorescence analysis.     

Control of droplet transfer in consumable electrode welding with short circuiting of the arcing gap

We present the results of an experimental programme of fatigue tests carried out on two types of butt joints with thicknesses of 20 and 40 mm respectively, characterized by a significant gap between weld edges, not compliant with the requirements of construction specifications. The tests were conducted on specimens taken from the weld beads of joints typical of those produced at the site (butt joints between web and flanges) and made with the same procedures (welding process, welding position, welding filler, etc.). The test results were elaborated statistically to determine the fatigue resistance category in accordance with the requirements of standard EN 1993-1-9 and IIW recommendations. Calculations took into account both the thickness of the specimens (tests were carried out on both to-scale and true-thickness specimens for the purposes of validation) and also flexural stress components induced by the non-planarity of the specimens.     

Thermochemical and luminescent properties of RbVO<Subscript>3</Subscript>, CsVO<Subscript>3</Subscript>, and Rb<Subscript>0.5</Subscript>Cs<Subscript>0.5</Subscript>VO<Subscript>3</Subscript>

RbVO₃, CsVO₃, and Rb_0.5Cs_0.5VO₃ have been synthesized by the Pechini process. The vanadates have an orthorhombic structure (sp. gr. Pbcm), melt congruently in the range 650–530°C, and undergo a reversible phase transition in the range 520–340°C. We have determined the onset temperatures and end points of the transformations at a temperature scan rate of 3°C/min and their enthalpies, and measured the photo-, roentgeno-, and cathodoluminescence and diffuse reflectance spectra of the vanadates. The luminescence spectra each are well fitted with three pseudo-Voigt functions. CsVO₃ has the highest integrated emission intensity. The emission intensity of the Rb_0.5Cs_0.5VO₃ solid solution is lower than that of the simple vanadates because of the optical absorption around its intrinsic luminescence band. This may be due to the presence of stable vacancy-type structural defects in Rb_0.5Cs_0.5VO₃.     

Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm⁻² at 700 °C in wet H₂/air feeds was demonstrated.