Athanasios Konstandopoulos PhD

A two-step thermo-chemical cycle process for solar hydrogen production from water has been developed. By using mixed iron-oxide-based redox systems at moderate temperatures the cycle offers promising properties concerning thermodynamics and efficiency and affords pure ...

... Auteur(s) / Author(s). KONSTANDOPOULOS Athanasios G. ; Résumé / Abstract. In the present work a practice for conducting experiments and analyzing the fundamental descriptors of DieselParticulate Filter (DPF) flow resistance behavior is described. ...

Nanoparticles (NPs), due to their increased application and production, are being released into the environment with unpredictable impact on the physiology of marine organisms, as well as on entire ecosystems and upcoming effects on human health. The aim of the present study was to evaluate and compare the oxidative responses of the mussel Mytilus galloprovincialis after exposure to iron oxide NPs and to iron oxide NPs incorporated into zeolite for 1, 3 and 7 days. Our results showed that both effectors induced changes on animal physiology by causing oxidative stress in hemocytes of exposed mussels compared to control animals. This was shown by the significant increase in reactive oxygen species (ROS) production, protein carbonylation, lipid peroxidation, ubiquitin conjugates and DNA damage. In addition an increase in prooxidant levels as measured by the prooxidant-antioxidant balance (PAB) assay was observed in exposed mussels' hemolymph. The results show that ROS, DNA damage, protein and lipid oxidation, ubiquitin conjugates and PAB could constitute, after further investigation, reliable biomarkers for the evaluation of pollution or other environmental stressors. In addition, more studies are needed in order to ensure the safety of these NPs on various biomedical applications, since it is critical to design NPs that they meet the demands of application without causing cellular toxicity.

The axonal translocation of two commonly used nanoparticles in medicine, namely CeO2 and SiO2, is investigated. The study was conducted on frog sciatic nerve fibers in an ex vivo preparation. Nanoparticles were applied at the proximal end of the excised nerve. A nerve stimulation protocol was followed for over 35 hours. Nerve vitality curve comparison between control and exposed nerves showed that CeO2 has no neurotoxic effect at the concentrations tested. After exposure, specimens were fixed and then screen scanned every 1 mm along their length for nanoparticle presence by means of Fourier transform infrared microscopy. We demonstrated that both nanoparticles translocate within the nerve by formation of narrow bands in the Fourier transform infrared spectrum. For the CeO2, we also demonstrated that the translocation depends on both axonal integrity and electrical activity. The speed of translocation for the two species was estimated in the range of 0.45-0.58 mm/h, close to slow axonal transportation rate. Transmission electron microscopy provided direct evidence for the presence of SiO2 in the treated nerves.

The use of Diesel Particulate Filters (DPFs) has become unavoidable for particulate matter reduction; however, DPFs need to be periodically or continuously cleaned (regenerated) in order to achieve efficient and safe operation of the vehicle. The regeneration method selected has to take into account the current state of the filter and the engine operating conditions. This fact introduces the need

ABSTRACT The present work is an investigation of the redox performance of several cobalt oxide based compositions, as candidate materials for energy storage in future concentrated solar power plants. To this respect, various commercial and in-house synthesized grades were evaluated in the form of small structured perforated monolithic bodies (flow-through pellets) and assessed in terms of their capability to perform reversible cyclic reduction–oxidation reactions under air flow in the temperature range of 800–1000 °C. The compositions studied involved pure cobalt oxide as well as composites of cobalt oxide with ceria, zirconia, alumina, iron oxide, silicon carbide and manganese oxide. The main criterion for the evaluation of compositions considered was a combination of high redox reaction extent with good thermo-mechanical stability of fabricated structured bodies. Among the materials studied and based on this criterion, the most promising ones were the cobalt oxide–alumina and cobalt oxide–iron oxide composites. Although pure cobalt oxide, and especially one grade synthesized in the lab, exhibited the highest redox performance, the respective shaped structures did not manage to retain their macro-structural integrity in the course of 10 redox cycles. Moreover, it was found that, under certain conditions, the addition of ceria improved redox reaction kinetics, while total performance of cobalt oxide was not affected. However, the structural stability of cobalt oxide–ceria pellets was also problematic. It was also demonstrated that by varying the second oxide, the start-of-reduction/oxidation temperatures of cobalt oxide can be significantly altered. A preliminary simplified kinetic model was developed and its good agreement with pure cobalt oxide redox experimental data was also demonstrated. Post-characterization of used structured bodies confirmed the experimental findings of redox performance measurements and, to some extent, provided explanations regarding the main phenomena involved upon cyclic operation of different compositions employed.

Abstract: It is a big challenge how to satisfy both the purification of exhaust gas and the decrease of fuel penalty, that is, carbon-dioxide emission. Regarding the Diesel Particulate Filter (DPF) applied in the diesel after-treatment system, it must be effective for lowering the fuel ...