Artificial neural network models for the prediction of surface roughness in electrical discharge machining

In the present paper Artificial Neural Networks (ANNs) models are proposed for the prediction of surface roughness in Electrical Discharge Machining (EDM). For this purpose two well-known programs, namely Matlab^® with associated toolboxes, as well as Netlab^®, were emplo- yed. Training of the models was performed with data from an extensive series of EDM experiments on steel grades; the proposed models use the pulse current, the pulse duration, and the processed material as input parameters. The reported results indicate that the proposed ANNs models can satisfactorily predict the surface roughness in EDM. Moreover, they can be considered as valuable tools for the process planning for EDMachining.     

The effect of Fe on the catalytic behavior of model Pd-Rh/CeO2-Al2O3 three-way catalyst

The present work attempts to address the issue whether iron (Fe) which is accumulated on the surface of “three-way” catalysts (TWCs) used in gasoline-driven cars is a true chemical poison of their catalytic activity. This important issue from a scientific and technological point of view is addressed via catalytic activity, temperature-programmed surface reaction (TPSR), and X-ray photoelectron spectroscopy (XPS) measurements over a model TWC (1 wt% Pd–Rh/20 wt% CeO₂–Al₂O₃). It was found that deposition of Fe up to the level of 0.4 wt% (an average concentration found in aged commercial TWCs) on the model TWC does not deteriorate its activity towards CO and C₃H₆ oxidation, and reduction of NO by H₂. Instead it was found that iron improves significantly the T₅₀ parameter in the activity versus temperature profile. Small Fe clusters in contact with the noble metal (Pd and Rh) particles due to the lower work function of Fe compared to Pd and Rh act likely as a source of electron flow towards the noble metals (as evidenced by XPS measurements), thus altering their surface work function and adsorption energetics of reaction intermediates. The latter have increased significantly the activity of the model TWC towards oxidation of CO and propylene, and to a lesser extent the activity towards the reduction of NO by H₂. The presence of Fe on the surface of the model TWC provided and/or created also new active catalytic sites for the reactions investigated. According to previous work from this laboratory, iron up to the level of 0.4 wt% was shown not to deteriorate the oxygen storage capacity (OSC) of the same model TWC used in the present work. Thus, it could be concluded that Fe when deposited on a commercial TWC at least up to the level of 0.4 wt% acts likely as a promoter than a poison of its catalytic activity.     

Network coding-based cooperative ARQ scheme for VANETs

In this paper we introduce a novel Network Coding-based Medium Access Control (MAC) protocol for Vehicular Ad Hoc Networks (VANETs) that use cooperative Automatic Repeat reQuest (ARQ) techniques. Our protocol coordinates the channel access among a set of relays capable of using network coding in order to minimize the number of the total transmissions, thus enhancing the performance of the network in terms of Quality of Service (QoS) metrics. The proposed solution is compared to other cooperative schemes, while analytical and simulation results are provided to evaluate our protocol.     

Survival of faecal coliforms in diluted sewage

Enterobacteria disposed of in natural waters survive for a long time. Environmental engineers need to know their survival kinetics, for the determination of which there are at present various formulae. These, however, are of limited validity: experience has shown that the results of calculations of this type may lack predictive accuracy. A parameter, which has not been adequately taken into account up to now, is the effect of the dilution of sewage on bacterial survival kinetics. The investigation of the effect of dilution forms the object of the present research, with the aim of demonstrating the importance of this parameter to the accuracy of the results of the relevant calculations.     

The remarkable effect of oxygen on the N2 selectivity of water catalytic denitrification by hydrogen

The selective catalytic reduction of nitrates (NO3-) in pure water toward N2 formation by the use of gaseous H2 and in the presence of O2 (air) at 1 atm total pressure and 25 degrees C has been investigated over Pd-Cu supported on various mixed metal oxides, x wt % MO(x(/gamma-Al2O3 (MO(x) = CeO2, SrO, Mn2O3, Cr2O3, Y2O3, and TiO2). It is demonstrated for the firsttime that a remarkable improvement in N2 reaction selectivity (by 80 percentage units) can be achieved when oxygen is present in the reducing feed gas stream. In particular, significantly lower reaction selectivities toward NH4+ and NO2- can be obtained, whereas the rate of NO3- conversion is not significantly affected. Moreover, it was shown thatthe same effect is obtained over the Pd-Cu-supported catalysts irrespective to the chemical composition of support and the initial concentration of nitrates in water used. The Pd-Cu clusters supported on 4.8 wt%TiO2/gamma-Al2O3 resulted in a solid with the best catalytic behavior compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. DRIFTS studies performed following catalytic reduction by H2 of NO3- in water revealed that the presence of TiO2 in the Pd-Cu/TiO2-Al2O3 system enhanced the reactivity of adsorbed bidentate nitrate species toward H2. Nitrosyl species adsorbed on the alumina and titania support surfaces are considered as active intermediate species of the selective catalytic reduction of NO3- by H2 in water. Pd-Cu/TiO2-Al2O3 appears to be the most selective catalyst ever reported in the literature for the reduction of nitrates present in pure water into N2 by a reducing gas mixture of H2/air.     

Substrate Specificity of the Highly Thermostable Esterase EstDZ3

Esterases are among the most studied enzymes, and their applications expand into several branches of industrial biotechnology. Yet, despite the fact that information on their substrate specificity is crucial for selecting or designing the best fitted biocatalyst for the desired application, it cannot be predicted from their amino acid sequence. In this work, we studied the substrate scope of the newly discovered hydrolytic extremozyme, EstDZ3, against a library of esters with variable carbon chain lengths in an effort to understand the crucial amino acids for the substrate selectivity of this enzyme. EstDZ3 appears to be active against a wide range of esters with high selectivity towards medium- to long-carbon chain vinyl esters. In-silico studies of its 3D structure revealed that the selectivity might arise from the mainly hydrophobic nature of the active site's environment.     

Design and Implementation of an Integrated High Resolution Imaging Ground Penetrating Radar for Water Pipeline Rehabilitation

Accurate and timely detection of leaks in water supply pipes is a significant environmental issue. Development of efficient non-invasive methods would lead into significant water saving and prevention of health hazards introduced by water leakage. This paper shows the ability to use a high resolution ground penetrating imaging radar (GPIR), to be used as an instrument for water pipeline rehabilitation situations, parallel to the existing industrial equipment. In the framework of the European research initiative WATERPIPE, a decision support system (DSS) for the rehabilitation management of the underground water pipelines has been developed, parallel to the implementation of the GPIR.     

Structure reinforcement of porous hydroxyapatite pellets using sodium carbonate as sintering aid: Microstructure,secondary phases and mechanical properties

Porous HAP pellets suitable for loading therapeutic agents were prepared using microcrystalline cellulose (MCC) as pore former and sodium carbonate as sintering aid (SAID). The effect of sintering temperature on the microstructure, mechanical properties and disintegration of pellets prepared at different SAID content was studied. Pellets were characterized by SEM, image analysis, porosimetry and surface area. Secondary phases were identified by PXRD, ATR-FTIR and Raman spectroscopy. Increasing the sintering temperature decreased the diameter, porosity, surface area and friability of the pellets but increased the pore size, tensile strength and disintegration time. The effect of SAID was dependent on sintering temperature. With 5% SAID, a secondary β-tricalcium phosphate (β-TCP) phase was formed, indicated by FTIR peak at 980 cm^?1 and characteristic PXRD reflections, whereas with 10%, a secondary B-type carbonated hydroxyapatite phase (CHA) formed, indicated by FTIR peaks at 878 and 1450 cm^?1, a broad Raman peak in the region 1020 to 1050 cm^?1 and PXRD reflections. Pellets prepared with SAID showed high strength and also porosity. The biphasic HAP/β-TCP pellets exhibited remarkably great strength (4.39 MPa) at the high sintering temperature, while still retaining 43.9% porosity. Relationships were established between the mechanical properties or disintegration time of the porous pellets and the microstructural parameters.     

The effect of raw glycerol concentration on the production of 1,3‐propanediol by Clostridium butyricum

Raw glycerol, the main by‐product of the bio‐diesel production process, was converted to 1,3‐propanediol by Clostridium butyricum F2b. In batch cultures, 47.1 g dm^?3 of 1,3‐propanediol were produced. Continuous cultures were conducted at a constant dilution rate (= 0.04 h^?1) and various inlet glycerol concentrations with 1,3‐propanediol produced at levels up to 44.0 g dm^?3. At increasing glycerol concentrations in the inlet medium, biomass yield decreased. This decrease was attributed to the microbial metabolism being directed towards the biosynthesis of organic acids (and hence carbon losses as CO₂) instead of biochemical anabolic reactions. An autonomous analytical model was developed, and quantified the effect of inlet glycerol concentration on the production of biomass and metabolites. Indeed, high inlet substrate concentrations positively affected the biosynthesis, principally of butyric acid and to a lesser extent that of acetic acid. In contrast, at increased glycerol concentrations, the relative increase of 1,3‐propanediol production per unit of substrate consumed was lower as compared with that of acetic and, mainly, butyric acid. This could be explained by the fact that the butyric acid pathway represents an alternative and competitive one to that of 1,3‐propanediol for re‐generation of NADH₂ equivalents in the microbial cell. Copyright © 2004 Society of Chemical Industry