Scale transition and enforcement of RVE boundary conditions in second‐order computational homogenization

Formulation of the scale transition equations coupling the microscopic and macroscopic variables in the second‐order computational homogenization of heterogeneous materials and the enforcement of generalized boundary conditions for the representative volume element (RVE) are considered. The proposed formulation builds on current approaches by allowing any type of RVE boundary conditions (e.g. displacement, traction, periodic) and arbitrary shapes of RVE to be applied in a unified manner. The formulation offers a useful geometric interpretation for the assumptions associated with the microstructural displacement fluctuation field within the RVE, which is here extended to second‐order computational homogenization. A unified approach to the enforcement of the boundary conditions has been undertaken using multiple constraint projection matrices. The results of an illustrative shear layer model problem indicate that the displacement and traction RVE boundary conditions provide the upper and lower bounds of the response determined via second‐order computational homogenization, and the solution associated with the periodic RVE boundary conditions lies between them. Copyright © 2007 John Wiley & Sons, Ltd.     

Aminocatalytic Strategy for the Synthesis of Optically Active Benzothiophene Derivatives

A novel approach for the stereoselective synthesis of benzothiophene derivatives with a fused dihydropyran moiety is demonstrated. The reaction of 2‐alkylidenebenzothiophene‐3(2H)‐ones with dienamines derived from α,β‐unsaturated aldehydes and chiral secondary amines proceeds according to the inverse‐electron‐demand hetero‐Diels–Alder pathway. The formation of the aromatic benzothiophene moiety is a driving force for the developed reaction cascade. Target products bearing three adjacent stereogenic centers are obtained in excellent yields and in a highly stereoselective manner.

     

An effect of suint on sheep wool impedance and heat resistance values

ABSTRACT

The phenomenon of impedance finds an application in many areas of science; however, no studies relate to wool. Thus, the aim of the study was an examination of an effect of from the presence of suint layer on sheep wool fibers on impedance and heat resistance values. Electrical characteristics (impedance [Ω]) and heat resistance were compared in terms of wool washing effect. The impedance of wool samples was tested in the frequency range of 10 Hz to 1 MHz. In order to measure electrical characteristics and heat resistance values, five samples of greasy wool were collected from different sheep breeds, standardized by weight. After the analyses, the samples were washed and reexamined. The results showed significant differences in the impedance between the greasy and washed wool samples in each of the tested breed (p > 0.05). The suint layer reduces the impedance level, which was also confirmed by a heat resistance test results demonstrating that absence of suint layer on wool fibers significantly reduced this feature value (p > 0.05). This was also reflected in the weight differences between the examined wool samples before and after their washing.     

Hydrogen Damage in Superaustenitic 904L Stainless Steels

In this work, results on the influence of hydrogen on corrosion resistance and of hydrogen embrittlement of 904L superaustenitic stainless steel were investigated. The cracking behavior was studied by performing a slow strain rate test in synthetic seawater under varying cathodic polarization conditions. The results showed that the steel’s plasticity varied with the applied cathodic current density. Significant reductions in ductility were found, indicating its susceptibility to hydrogen-assisted fracture at current density of 20 mA/cm². Fractographical examinations showed that an increase in hydrogenation current density causes a stepwise decrease in ductility on the fracture surface. The effect of hydrogen on passivity and on pitting corrosion resistance was qualified with the polarization curves registered in synthetic seawater. The conclusion is that hydrogen may affect the passive film stability and thus may decrease the corrosion resistance of the studied steel. The presence of hydrogen increases corrosion current density and decreases the potential of the film breakdown. It was also found that the degree of the susceptibility to hydrogen degradation was dependent on the hydrogen charging conditions.     

The influence of the legal and economical environment and the profile of activities on the optimal design features of a natural-gas-fired combined heat and power plant

The paper deals with the effect of some selected quantities occurring in the legal and economical environment on the optimal values of some selected design quantities of a natural-gas-fired CHP plant. This trend of investigations results from the newly observed legal changes in the legislation concerning new forms of mechanisms supporting the combined production of electricity and heat. Special stress was exerted on changes resulting from the formulation of two directives, viz. 2003/7/EC and 2004/8/EC.For the purpose of realising this task, a reference structure of a CHP plant was selected. For the steam-water part of the plant thirteen quantities were selected, determining the design features of the most essential components of this part of the system. These quantities served as decision variables in processes of optimisation. As the objective function the break-even price of electricity was assumed.The second part of the paper presents the results of sensitivity analyses of the fundamental indices of the energy and economical effectiveness to failures in the adherence of the optimal values of the respective design quantities, as well as the results of investigations on the effect of the operation time of the plant in the course of one year.     

An assessment view to evaluate whether Spatial Data Infrastructures meet their goals

The motives for constructing Spatial Data Infrastructures (SDIs) are often based on their anticipated benefits for society, economy, and environment. According to those widely articulated but rarely proven benefits, SDI coordinators have been defining more specific objectives to be achieved by their SDIs. However, there is a limited number of assessment approaches that are able to demonstrate whether SDIs indeed realize the intended goals. In this article we develop, apply and evaluate an assessment view for evaluating the extent to which SDIs realize their goals. The assessment view has been developed stepwise using the Multi-view SDI assessment framework as a guideline. The application of the proposed view in the Dutch SDI demonstrates its potential. In addition, the evaluation of the proposed view by the potential users confirms to a certain extent its usability. The results also show that the ease of determining assessment indicators depends on the precision with which the SDI goals are formulated.     

Selection of a representative value function in robust multiple criteria sorting

We introduce the concept of a representative value function in robust ordinal regression applied to multiple criteria sorting problems. The proposed approach can be seen as an extension of UTADIS^GMS, a new multiple criteria sorting method that aims at assigning actions to p pre-defined and ordered classes. The preference information supplied by the decision maker (DM) is composed of desired assignments of some reference actions to one or several contiguous classes—they are called assignment examples. The robust ordinal regression builds a set of general additive value functions compatible with the assignment examples and results in two assignments: necessary and possible. The necessary assignment specifies the range of classes to which the action can be assigned considering all compatible value functions simultaneously. The possible assignment specifies, in turn, the range of classes to which the action can be assigned considering any compatible value function individually. In this paper, we propose a way of selecting a representative value function among the set of compatible ones. We identify a few targets which build on results of the robust ordinal regression and could be attained by a representative value function. They concern enhancement of differences between possible assignments of two actions. In this way, the selected function highlights the most stable part of the robust sorting, and can be perceived as representative in the sense of robustness preoccupation. We envisage two possible uses of the representative value function in decision support systems. The first one is an explicit exhibition of the function along with the results of the UTADIS^GMS method, in order to help the DM to understand the robust sorting. The other is an autonomous use, in order to supply the DM with sorting obtained by an example-based procedure driven by the chosen function. Three case studies illustrating the use of a representative value function in real-world decision problems are presented. One of those studies is devoted to the comparison of the introduced concept of representativeness with alternative procedures for determining a single value function, which we adapted to sorting problems, because they were originally proposed for ranking problems.     

Adsorption and reduction of platinum(IV) chloride complex ions on activated carbon

The adsorption kinetics of platinum(IV) chloride complex ions on the activated carbon Norit GF40 was investigated. Experiments were carried out at different initial concentrations of Pt(IV) chloride complex ions, temperature, rate of mixing and pH. It was found that the value of activation energy of the studied process is equal to 19.7 kJ/mol. From the ICP MS analysis it was confirmed that platinum ions (Pt(IV) and Pt(II)) are removed from the solution due to the adsorption and are further reduced to the metallic state. Such mechanism was confirmed by XPS analysis which showed that on the carbon surface three forms of platinum species, i.e. Pt(0), Pt(II) and Pt(IV), exist. The presence of platinum in the solution at different oxidation states was also confirmed spectrophotometrically by identification of their characteristic absorption bands. The metallic form of Pt present on the surface of activated carbon was observed in the form of small spherical islands with the diameter not exceeding 500 nm. Those islands consist of smaller, flake-shape particles with a thickness of about 35 nm.     

The influence of economic parameters on the optimal values of the design variables of a combined cycle plant

This paper presents the analysis of the influence of fuel price variation on the optimal values of the design variables of the steam part of a combined cycle plant. The investigated system was a power plant with a triple-pressure heat recovery steam generator and extraction-condensation steam turbine. Fourteen design variables for the steam part were identified. The variables that were optimised were the pressure levels of the working medium in the steam part of the system, and characteristic differences of temperatures in the heat recovery steam generator. Thanks to the development of an optimising programme, based on the genetic algorithms theory, it was possible to find an optimal solution. The indices of economic efficiency, in the form of the break-even price of electricity, were chosen as the objective function in the optimisations. The results of economic optimisations were compared with the results of the optimisation, where the electric efficiency was the objective function. This paper includes an analysis of the sensitivity of the economic objective function to failures in the adherence of the optimal values of decision variables. This analysis allowed the selection of variables such that a failure results in the highest increase of the break-even price of electricity.     

Non-linear diode ladder network

The analysis and synthesis are presented of a non-linear ladder network with diodes incorporated in the series branches. An explicit form of solution is proposed and then applied to the synthesis of piecewise-linear characteristics. An illustrative example is given.