Nonlinear adaptive stabilizing control of an anaerobic digestion model with unknown kinetics

In this paper, we consider a nonlinear model of a biological wastewater treatment process, on the basis of two microbial populations and two substrates. The model, described by a four‐dimensional dynamic system, is known to be practically validated and reliable. We propose a feedback control law for asymptotic stabilization of the closed‐loop system towards a previously chosen operating point. A numerical extremum seeking algorithm is applied to stabilize the dynamics towards an equilibrium point with maximal methane flow rate. Computer simulations are reported to illustrate the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

Adaptive notifications to support knowledge sharing in close-knit virtual communities

Social web-groups where people with common interests and goals communicate, share resources, and construct knowledge, are becoming a major part of today’s organisational practice. Research has shown that appropriate support for effective knowledge sharing tailored to the needs of the community is paramount. This brings a new challenge to user modelling and adaptation, which requires new techniques for gaining sufficient understanding of a virtual community (VC) and identifying areas where the community may need support. The research presented here addresses this challenge presenting a novel computational approach for community-tailored support underpinned by organisational psychology and aimed at facilitating the functioning of the community as a whole (i.e. as an entity). A framework describing how key community processes—transactive memory (TM), shared mental models (SMMs), and cognitive centrality (CCen)—can be utilised to derive knowledge sharing patterns from community log data is described. The framework includes two parts: (i) extraction of a community model that represents the community based on the key processes identified and (ii) identification of knowledge sharing behaviour patterns that are used to generate adaptive notifications. Although the notifications target individual members, they aim to influence individuals’ behaviour in a way that can benefit the functioning of the community as a whole. A validation study has been performed to examine the effect of community-adapted notifications on individual members and on the community as a whole using a close-knit community of researchers sharing references. The study shows that notification messages can improve members’ awareness and perception of how they relate to other members in the community. Interesting observations have been made about the linking between the physical and the VC, and how this may influence members’ awareness and knowledge sharing behaviour. Broader implications for using log data to derive community models based on key community processes and generating community-adapted notifications are discussed.     

Effect of the heat treatment on the morphology and sorption ability to metal ions of metallurgical slag

The effect of the phase composition of metallurgical slag on its ability to adsorb copper ions from aqueous solutions has been investigated. Granulated slag samples, mainly amorphous, have been pre-heated at 400, 600, 800 and 1000°C, then cooled slowly in the absence of moisture. Above 600°C crystallisation of a mineral gehlenite of the melilite group and of calcium silicates of the Ca₂SiO₄ structure type begins. The appearance of crystalline phases facilitates exchange and adsorption and the amount of copper adsorbed per a gram slag increasing about 2–4 times. The important role of the crystalline phases in the slag permits the synthesis of new materials adsorbing heavy metal ions on the basis of controlled liquid slag crystallization.     

Electrical studies of the reactions between ethanol vapours and inversion mode Si-thin SiO2 structures

Processes taking place in Si-thin SiO₂ structures (oxide thickness 135 Å) after exposure to ethanol vapours have been investigated by measurements of the inversion channel I-V characteristics. It has been established that the changes in the Si---SiO₂ structure under the action of ethanol vapours relax with time after their removing and the extent of relaxation depends on the drain voltage duration as well as on the time interval separation of the drain voltage pulses. The I_D(t) dependence obeys two exponents, reflecting the presence of two different processes (one of them being slower than the other one), characterized with different time constants. They appear to be a unique function of the ethanol vapour reaction with the oxide surface. It has been shown that the ethanol vapours action at certain drain voltage leads to the introduction of defects in the Si-thin SiO₂ structure. The defects are a source of electrically active centres. The total value of these charges originating after the interaction of ethanol vapours with the SiO₂ surface is of the order of (1.5–1.7) × 10¹¹ cm⁻². It is proposed that the surface oxide charge is mainly responsible for the ethanol vapours-introduced positive charge in the Si---SiO₂ structure. The paper proposes some concepts for the interpretation of the results obtained. Adsorption of ethanol molecules, surface reaction and desorption of decomposition products are included.     

Carrier mobility in inversion layers of Si–thin Ta2O5 structures

The behaviour of carrier mobility in the inversion channel of gateless p-MOSFETs with thin (7-50 nm) Ta₂O₅ layers, having a dielectric constant of (23-27) and prepared by rf sputtering of Ta in an Ar-O₂ mixture, has been investigated. It is shown that independently of the high dielectric constant of the layers, the transport properties in the channel are strongly affected by defects in Ta₂O₅/Si system in the form of oxide charge and interface states. These defects act as scattering centers and are responsible for the observed minority carrier mobility degradation. Both, the oxide and the interface state charges are virtually independent on the oxygen content (in the range 10-30%) during the sputtering process. A reduction of the oxide charge and the density of interface states with increasing Ta₂O₅ film thickness was found, which results in the observed increase of the inversion channel mobility with thickness. It is assumed that the bond defects (broken or strained Ta-bonds as well as weak Si-O bonds in the transition region between Ta₂O₅ and Si) are much more probable sources of defect centers rather than Ta and O vacancies or impurities.     

Comparison of Water Absorption and Mechanical Behaviors of Polypropene Composites Filled with Rice Husks Ash

Composite materials were obtained by filling polypropene with raw and thermally treated rice husks at filler contents from 1 to 20%. The physicochemical properties were determined. A slight increase was observed in the tensile strength of the composites based on white rice husk ash (WRHA) and aerosil (AR) at degree of filling up to 3%. Young's modulus increased and the elongation at break and energy to break point showed a tendency to decrease for all the composites studied. The thermodynamics and kinetics of water absorption at immersion were studied in the temperature interval 25–90°C. The values of the changes in standard free energy, ΔG°, enthalpy, ΔH°, and entropy, ΔS° of adsorption were calculated. Water absorption was found to be thermodynamically difficult due to the diffusion mechanism of the process and it was accompanied by a decrease in the values of ΔH° and ΔS° with an increase in fillers contents. The effects of the amount of absorbed water, temperature, and treatment time on the composites tensile properties were estimated.     

Reactive synthesis with maximum realizability of linear temporal logic specifications

Acta Informatica - A challenging problem for autonomous systems is to synthesize a reactive controller that conforms to a set of given correctness properties. Linear temporal logic (LTL) provides a...