University of Patras

About: University of Patras is a education organization based out in Pátrai, Greece. It is known for research contribution in the topics: Population & Catalysis. The organization has 13372 authors who have published 31263 publications receiving 677159 citations. The organization is also known as: Panepistímio Patrón.

Mechanistic Study of the Selective Methanation of CO over Ru/TiO2 Catalyst: Identification of Active Surface Species and Reaction Pathways†

Abstract: Selective methanation of CO can be used as the final purification step of re-formate gas for the generation of hydrogen-rich gas streams suitable for PEM fuel cell applications. In the present study, the adsorption/desorption characteristics of reactants, the nature of active sites, and the mechanism of CO/CO2 hydrogenation reactions have been investigated over 5% Ru/TiO2 catalyst with the use of in situ FTIR and temperature-programmed techniques. Results show that adsorption of hydrogen and CO are activated processes. The amount of adsorbed hydrogen increases by a factor of 2 with the increase of adsorption temperature from 25 to 200 °C, mainly due to migration of hydrogen atoms from the metal to the support. Adsorbed CO species evolve during TPD in the form of CO2, which is produced via the Boudouard and water−gas shift (WGS) reactions. Adsorption of CO2 occurs via formation of formate and carbonate species associated with the support whereas in the presence of H2 part of these species are converted to ...

Improving the convergence of the backpropagation algorithm using learning rate adaptation methods

Abstract: This article focuses on gradient-based backpropagation algorithms that use either a common adaptive learning rate for all weights or an individual adaptive learning rate for each weight and apply the Goldstein/Armijo line search. The learning-rate adaptation is based on descent techniques and estimates of the local Lipschitz constant that are obtained without additional error function and gradient evaluations. The proposed algorithms improve the backpropagation training in terms of both convergence rate and convergence characteristics, such as stable learning and robustness to oscillations. Simulations are conducted to compare and evaluate the convergence behavior of these gradient-based training algorithms with several popular training methods.

Active control and global synchronization of the complex chen and Lü systems

Abstract: Chaos synchronization is a very important nonlinear phenomenon, which has been studied to date extensively on dynamical systems described by real variables. There also exist, however, interesting cases of dynamical systems, where the main variables participating in the dynamics are complex, for example, when amplitudes of electromagnetic fields are involved. Another example is when chaos synchronization is used for communications, where doubling the number of variables may be used to increase the content and security of the transmitted information. It is also well-known that similar generalization of the Lorenz system to one with complex ODEs has been introduced to describe and simulate the physics of a detuned laser and thermal convection of liquid flows. In this paper, we study chaos synchronization by applying active control and Lyapunov function analysis to two such systems introduced by Chen and Lu. First we show that, written in terms of complex variables, these systems can have chaotic dynamics and...

Thermal modeling of the material removal rate and surface roughness for die-sinking EDM

Abstract: The die-sinking electrical discharge machining (EDM) process is characterized by slow processing speeds. Research effort has been focused on optimizing the process parameters so as for the productivity of the process to be increased. In this paper a simple, thermal based model has been developed for the determination of the material removal rate and the average surface roughness achieved as a function of the process parameters. The model predicts that the increase of the discharge current, the arc voltage or the spark duration results in higher material removal rates and coarser workpiece surfaces. On the other hand the decrease of the idling time increases the material removal rate with the additional advantage of achieving slightly better surface roughness values. The model’s predictions are compared with experimental results for verifying the approach and present good agreement with them.

Detailed atomistic simulation of a polymer melt/solid interface : Structure, density, and conformation of a thin film of polyethylene melt adsorbed on graphite

Abstract: An atomistic modeling approach is presented for simulating the interface between a polymer melt and a crystalline solid substrate. As a test case, a thin film of polyethylene (PE) melt confined between a semiinfinite graphite phase on the one side and vacuum on the other is considered. The simulation is carried out in the NPT statistical ensemble with an efficient Monte Carlo (MC) algorithm based on state-of-the-art variable connectivity moves. The atomistic simulations are conducted by describing the PE chains with a united atom model, which considers each methylene (CH2) and methyl (CH3) group along the chain backbone as single interaction sites. To calculate the potential energy of interaction between polymer atoms and the semiinfinite graphite substrate, the method designed by Steele was implemented, capable of incorporating the exact crystallographic structure of graphite. The new approach has allowed us to analyze structural and conformational properties on the length scale of just a few angstroms f...