National Technical University of Athens

About: National Technical University of Athens is a education organization based out in Athens, Attiki, Greece. It is known for research contribution in the topics: Large Hadron Collider & Nonlinear system. The organization has 13445 authors who have published 31259 publications receiving 723504 citations. The organization is also known as: Athens Polytechnic & NTUA.

Metolachlor photocatalytic degradation using TiO2 photocatalysts

Abstract: The photocatalytic degradation of the herbicide metolachlor is studied, using TiO 2 photocatalysts. Apart from the titania aqueous dispersions, immobilized semiconductor thin films were used in order to evaluate their effectiveness. The films exhibit a rough, nanocrystalline configuration, ideal for heterogeneous processes. Additionally the thin films were silver modified to determine if noble metal nanoclusters affect the photocatalytic efficiency. The kinetics obtained demonstrated that powder titania ( t 1/2 =21 min) was more efficient for the photocatalytic decomposition of metolachlor compared to pure titania thin film catalysts ( t 1/2 =52 min), while the presence of silver ions in TiO 2 particles modification did not prove to promote the solar photocatalytic process. Intermediate products from the slurry system were isolated and identified by means of solid-phase extraction (SPE) coupled to gas chromatography–mass spectroscopy techniques (GC–MS). A proposed degradation pathway of metolachlor is presented, involving mainly hydroxylation and dealkylation reactions. In addition, toxicity studies based on the luminescence of the bacteria Vibrio fischeri before and after the photocatalytic treatment were performed. The results demonstrated that the transient intermediates formed were more toxic compared to parent compound. At low photocatalyst loads, the toxicity of the irradiated solution remains relatively high even though 88% of metolachlor is decomposed.

Targeted energy transfers in vibro-impact oscillators for seismic mitigation

Abstract: In the field of seismic protection of structures, it is crucial to be able to diminish ‘as much as possible’ and dissipate ‘as fast as possible’ the load induced by seismic (vibration-shock) energy imparted to a structure by an earthquake. In this context, the concept of passive nonlinear energy pumping appears to be natural for application to seismic mitigation. Hence, the overall problem discussed in this paper can be formulated as follows: Design a set of nonlinear energy sinks (NESs) that are locally attached to a main structure, with the purpose of passively absorbing a significant part of the applied seismic energy, locally confining it and then dissipating it in the smallest possible time. Alternatively, the overall goal will be to demonstrate that it is feasible to passively divert the applied seismic energy from the main structure (to be protected) to a set of preferential nonlinear substructures (the set of NESs), where this energy is locally dissipated at a time scale fast enough to be of practical use for seismic mitigation. It is the aim of this work to show that the concept of nonlinear energy pumping is feasible for seismic mitigation. We consider a two degree-of-freedom (DOF) primary linear system (the structure to be protected) and study seismic-induced vibration control through the use of Vibro-Impact NESs (VI NESs). Also, we account for the possibility of attaching to the primary structure additional alternative NES configurations possessing essential but smooth nonlinearities (e.g., with no discontinuities). We study the performance of the NESs through a set of evaluation criteria. The damped nonlinear transitions that occur during the operation of the VI NESs are then studied by superimposing wavelet spectra of the nonlinear responses to appropriately defined frequency – energy plots (FEPs) of branches of periodic orbits of underlying Conservative systems.