A distributed and adaptive signal processing approach to exploiting correlation in sensor networks

We propose a novel approach to reducing energy consumption in sensor networks using a distributed adaptive signal processing framework and efficient algorithm.¹ While the topic of energy-aware routing to alleviate energy consumption in sensor networks has received attention recently [C. Toh, IEEE Commun. Mag. June (2001) 138; R. Shah, J. Rabaey, Proc. IEEE WCNC, March 2002], in this paper, we propose an orthogonal approach to complement previous methods. Specifically, we propose a distributed way of continuously exploiting existing correlations in sensor data based on adaptive signal processing and distributed source coding principles. Our approach enables sensor nodes to blindly compress their readings with respect to one another without the need for explicit and energy-expensive inter-sensor communication to effect this compression. Furthermore, the distributed algorithm used by each sensor node is extremely low in complexity and easy to implement (i.e., one modulo operation), while an adaptive filtering framework is used at the data gathering unit to continuously learn the relevant correlation structures in the sensor data. Applying the algorithm to testbed data resulted in energy savings of 10–65% for a multitude of sensor modalities.     

A numerical study of a utility boiler tangentially-fired furnace under different operating conditions

For prediction of complex processes in two-phase turbulent reactive flows within large-scale boiler furnaces firing pulverized coal, a comprehensive 3D differential mathematical model and CFD computer code have been developed in-house. The model incorporates trade-offs between submodels sophistication and computational practicality. An easy-to-use interface for introducing input data and grid generation has been build within the code. The main purpose of the paper is to present numerical predictions of processes in the case-study furnace under different operating conditions, obtained by the developed model. The paper also provides information on characteristics and evaluation of the model, with a grid refinement study and comparisons with comprehensive data. The effects of different operating conditions on the processes in the case-study furnace are correctly predicted, demonstrating the ability of the developed model to perform parametric studies.     

Methyl methacrylate and acrylamide crosslinked macroporous copolymers

In this work the synthesis of a crosslinked macroporous copolymer was effected from methyl methacrylate and acrylamide. The synthesis process began with emulsion prepolymerization, followed by sol–gel copolymerization until a hard block was obtained. Determination of the properties of the obtained material was carried out by FTIR, mercury porosimetry, and SEM microscopy. The material was characterized by a porous structure with open pores. The macroporous copolymer obtained can be used for polymer–analog reactions and the transformation of amide and ester groups into acyl azide groups. It can be used as a hard inert support for the immobilization of enzymes, or other proteins, by condensation of acyl azide group on polymer with the free amino group from the base amino acid of enzyme/protein. For the immobilization of microorganisms it can be used by vacuum diffusion of microorganism suspension into the porous structure, without active group transformation reactions. With microorganisms in the polymer pores, microorganism colonies form within the copolymer by microbial fermentation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 387–395, 2004     

On the application of fuzzy-based flow control approach to High Altitude Platform communications

Most of the research effort in the field of HAP communications until now has been invested in the physical layer of the protocol stack, and in the radio related issues in particular. However, the overall system throughput is limited by the performance of the transport layer. Since HAPs will be used in networks with different topological complexity, various kinds of wireless communications links, bit error rates, and various mixtures of multimedia traffic, the control flow in such networks may present itself as a non-linear and stochastic process. Therefore we introduced a fuzzy control of the throughput in the TCP. Our approach is based on the off-line synthesis of the Takagi-Sugeno fuzzy controller based on the simulation data and on-line flow control by the synthesized controller that is built in the conventional TCP. In the paper we present the ns2-based simulation results.     

Self-assembled polyaniline 12-tungstophosphate micro/nanostructures

Polyaniline (PANI) micro/nanostructures were synthesized by the external-template-free oxidative polymerization of aniline in aqueous solution of 12-tungstophosphoric acid (WPA), using ammonium peroxydisulfate (APS) as an oxidant and starting the oxidation of aniline from slightly acidic media (pH 5.4–5.9). The effect of the initial weight ratio of WPA to aniline on molecular structure, morphology, and physicochemical properties of polyaniline 12-tungstophosphate (PANI-WPA) was investigated by FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and conductivity measurements. The morphological change of polymerization products during a single polymerization process, from non-conducting submicro-/microspherical oligoaniline intermediates to semiconducting PANI-WPA consisted of self-assembled nanotubes and/or nanorods co-existing with submicro-/microspheres, has been revealed by SEM and TEM. The average diameter of nanorods in PANI-WPA samples decreased with increasing the initial WPA/aniline weight ratio. The incorporation of 12-tungstophosphate counter-ions into PANI matrix has been proved by FTIR, Raman and ICP-OES spectroscopies, TGA and DTA analysis. Electrical conductivity of PANI-WPA increased in the range (2.5–5.3) × 10^?3 S cm^?1 with the increase of the initial WPA/aniline weight ratio. The presence of branched structures and phenazine units besides the ordinary paramagnetic and diamagnetic emeraldine salt structural features in PANI-WPA was proved by FTIR and Raman spectroscopies.     

A new approach for kinetic modeling and optimization of rubber molding

Although extensive research has been carried out on the understanding of the complex vulcanization process, the influence of reversion through exposure time and temperature on the vulcanization degree remains unclear. Therefore, the main aim of this study was a novel optimization approach that can help the industrial practitioners to select the optimal operating parameters, exposure time, and molding temperature, to achieve desired vulcanization degree of selected product. Spheres of four different diameters (2.5, 5, 10, and 20 cm) were selected as test geometry for simulation and optimization of rubber molding. Obtained vulcanization rheometer data for commercially available rubber blend (NR/SBR) were fitted by a new modeling approach, dividing vulcanization curve into two fitting sets: curing and reversion. The heat transfer equations for chosen geometry were coupled with proposed kinetic model. A new temperature-dependent kinetic parameter x, as the maximal reversion degree, was introduced, enabling determination of the lowest operating molding temperature (T_min = 132.36 °C), preventing high reversion and overheating of the rubber product. The final optimization goal was assessment of the optimal temperature and vulcanization time dependence on the rubber products dimensions. Proposed models have precise prediction with R² values greater than 0.8328 and MAPE less than 2.3099%.     

The effect of extraction techniques on yield,extraction kinetics,and antioxidant activity of aqueous-methanolic extracts from nettle (Urtica dioica L.) leaves

Five extraction techniques, maceration, reflux, Soxhlet, Tillepape, and ultrasonic extraction, were used to obtain the extractive matter from nettle leaves. The antioxidant activity of extracts was assessed by DPPH, FRAP, and H₂O₂ test, while the total phenolic and total flavonoid content was determined according to the Folin–Ciocalteu and aluminium chloride methods, respectively. Model Ponomarev and a non-stationary diffusion model through the plant material were used for modelling extraction process. The extract obtained by Soxhlet extraction, containing higher amounts of extractive matter as well as phenolic and flavonoid compounds, showed better antioxidant activity than those obtained by other extraction techniques.     

Moisture absorption capacity of polyamide 6,6 fabrics surface functionalised by chitosan-based hydrogel finishes

The present study aims at investigating the moisture absorption capacity of polyamide 6,6 fabrics when their surface is functionalised by chitosan-based hydrogels. For the finishing procedure, bulk hydrogels of chitosan (CS) with different contents of embedded thermosensitive microparticles of poly(N-isopropylacrylamide-co-acrylic acid) (PNIAA) were used. In practice, hydrogel incorporation into the fabric surface layer was achieved by crosslinking primary amine groups of chitosan with the end amine groups of polyamide, using the natural crosslinker genipin. Among other analytical techniques, Scanning Electron Microscopy (SEM) was used to characterize the surface morphology of both hydrogel and fabric samples, Differential Scanning Calorimetry (DSC) to determine the Lower Critical Solution Temperature (LCST) of PNIAA, and X-ray Photoelectron Spectroscopy (XPS) to analyse the fabric surface chemical composition. The fabric moisture contents were determined by weight measurements at different temperatures and relative humidity values (RH). Liquid porosimetry, water vapour transmission (WVT) and dynamic wetting measurements were also performed to assess the fabric pore volume distribution, permeability and wetting times, respectively. It was found that the moisture absorbed by the functionalised polyamide fabrics can be regulated at different conditions of temperature and relative humidity according to the PNIAA/CS ratio in the hydrogel. For example, at 40 °C (i.e. above the PNIAA LCST) and even at high RH (85%), the higher the PNIAA/CS ratio was in the incorporated hydrogel, the lower were the moisture contents of the functionalised fabrics, compared to the reference. In all cases, the presence of CS increased significantly the polyamide fabric wetting times.     

Effect of the chain extender and selective catalyst on thermooxidative stability of aqueous polyurethane dispersions

Polyurethane aqueous dispersion based on poly(propylene glycol) (PPG), dimethylol propionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG). The polyurethane dispersions were characterized using thermogravimetric dynamic method. In the dynamic method, heating rates of 0.5, 1, 2 and 10 °C/min were used in the range of 30–500 °C, and degradations of 0.025, 0.05, and 0.10 were considered. From the Arrhenius plots, activation energies were evaluated ranging between 23 and 117 kJ/mol at α ≥ 0.05 for polyurethane aqueous dispersion depending on the temperature interval, selectivity of catalyst, type of chain extender and degree of degradation. The polyurethane aqueous dispersion based on ethylene glycol as the chain extender, with the more selective catalyst shows higher thermal stability. The dynamic method offered evidence for the presence of different degradation processes and was suitable for the evaluation of kinetics parameters at higher degrees of degradation.     

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.