The development of the microstructural and electrical characteristics of NTC thick-film thermistors during firing

One kohm/sq. thick-film NTC thermistors (4993, EMCA Remex) with high, non-linear and negative temperature coefficients of resistivity were fired at different temperatures. The development of the resistors’ conductive phase and microstructure was investigated by X-ray diffraction analysis and by scanning electron microscopy. Sheet resistivities, beta factors and noise indices were measured as a function of the firing temperature. In the fired layers of the thermistors the X-ray analyses showed mainly spinel phase and RuO₂, which is added to the thick-film NTC materials to decrease the specific resistance and to improve the stability and the current noise. Higher firing temperatures led to more densely sintered microstructures, to increased resistivities and to higher beta factors. The higher resistivities were attributed to the partial exchange of ions on the “B” sites of the spinel structure with aluminium ions.     

2-local 5/4-competitive algorithm for multicoloring triangle-free hexagonal graphs

An important optimization problem in the design of cellular networks is to assign sets of frequencies to transmitters to avoid unacceptable interference. A cellular network is generally modeled as a subgraph of the infinite triangular lattice. The distributed frequency assignment problem can be abstracted as a multicoloring problem on a weighted hexagonal graph, where the weight vector represents the number of calls to be assigned at vertices. In this paper we present a 2-local distributed algorithm for multicoloring triangle-free hexagonal graphs using only the local clique numbers ω₁(v) and ω₂(v) at each vertex v of the given hexagonal graph, which can be computed from local information available at the vertex. We prove that the algorithm uses no more than colors for any triangle-free hexagonal graph G, without explicitly computing the global clique number ω(G). Hence the competitive ratio of the algorithm is 5/4.     

The use of EAF dust in cement composites: Assessment of environmental impact

Electric arc filter dust (EAF dust) is a waste by-product which occurs in the production of steel. Instead of being disposed of, it can be used in cement composites for civil engineering, and for balances in washing machines. To estimate the environmental impact of the use of EAF dust in cement composites leachability tests based on diffusion were performed using water and salt water as leaching agents. Compact and ground cement composites, and cement composites with addition of 1.5% of EAF dust by mass were studied. The concentrations of total Cr and Cr(VI) were determined in leachates over a time period of 175 days. At the end of the experiment the concentrations of some other metals were also determined in leachates. The results indicated that Cr in leachates was present almost solely in its hexavalent form. No leaching of Cr(VI) was observed in aqueous leachates from compact cement composites and compact cement composites to which different quantities of EAF dust have been added. In ground cement composites and in ground cement composites with addition of EAF dust, Cr(VI) was leached with water in very low concentrations up to 5 μg L⁻¹. Cr(VI) concentrations were higher in salt water leachates. In compact and ground cement composites with addition of EAF dust Cr(VI) concentrations were 40 and 100 μg L⁻¹, respectively. It was experimentally found that addition of EAF dust had almost no influence on leaching of Cr(VI) from cement composites. Leaching of Cr(VI) originated primarily from cement. Leaching of other metals from composites investigated did not represent an environmental burden. From the physico-mechanical and environmental aspects EAF dust can be used as a component in cement mixtures.     

Catalytic wet-air oxidation processes: A review

Environmental catalysis usually refers to end-of-the-pipe treatment processes that reduce the emissions of hazardous pollutants. Abatement of pollutants in aqueous streams by means of heterogeneous catalysts is an example of such process. This paper reviews the developments in the field of catalytic wet-air oxidation (CWAO). Catalysts are reviewed first, followed by mechanistic speculations and kinetics that have been proposed for the CWAO process. The process is discussed more in detail only in those cases where it is already commercialised or at least foreseen to be in the near future. Particular attention was given to the heterogeneously catalyzed wet-air oxidation of real industrial wastewaters (such as Kraft bleach plant effluents) in batch and continuous-flow oxidation reactors. Finally, the considerable potential of the CWAO process to ultimately destroy organic pollutants in industrial effluents and detoxify them by using novel titania-supported Ru catalysts is presented.     

Morphology and Crystallization Behavior of Sol-Gel-Derived Titania

TiO₂ sols were prepared by hydrolysis of titanium ethoxide. The sols were exposed for several days at room temperature to atmospheres of different humidity in order to study its influence during aging of sols on rutile formation, morphology, and crystal structure. Exposure of sols to high relative humidity resulted in nonagglomerated TiO₂ powders with a rutile structure. TiO₂ gels obtained from sols aged at low relative humidity were composed of gel fragments with a poorly crystallized anatase structure.     

Concurrent engineering in small companies

In 1991, attainment of independence in Slovenia caused a drastic decrease in the domestic market for Slovenian companies. The companies which did not adapt to the new market conditions were destined for ruin. In this time several smaller companies were established which could adapt to new market conditions more easily. When these companies entered the world market they encountered several difficulties such as excessive flow times for development of new products. After a survey of available literature had been made it was found that those problems could be solved by transforming sequential engineering to concurrent engineering. The article presents the principles of sequential and concurrent product development processes. The market forces small Slovenian companies to a transition from sequential to concurrent engineering and as team work is the basic element of the concurrent engineering, special attention has been paid to workgroups forming in the loops of concurrent product development process in small companies.A survey of published works in the field of planning teams in big companies has revealed that a three-level team structure is recommended in big companies. Analysis of the three-level structure has led us to the conclusion that a two-level team structure and matrix organisation should be preferred in small companies.Presented are the results of planning a two-level team structure and matrix organisation of a small Slovenian company which produces mini-loaders.     

Optimization of displacement-measuring quadrature interferometers considering the real properties of optical components

We present the influence of alignment and the real properties of optical components on the performance of a two-detector homodyne displacement-measuring quadrature laser interferometer. An experimental method, based on the optimization of visibility and sensitivity, was established and theoretically described to assess the performance and stability of the interferometer. We show that the optimal performance of such interferometers is achieved with the iterative alignment procedure described.