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.

The variational approximation for Bayesian inference

Abstract: The influence of this Thomas Bayes' work was immense. It was from here that "Bayesian" ideas first spread through the mathematical world, as Bayes's own article was ignored until 1780 and played no important role in scientific debate until the 20th century. It was also this article of Laplace's that introduced the mathematical techniques for the asymptotic analysis of posterior distributions that are still employed today. And it was here that the earliest example of optimum estimation can be found, the derivation and characterization of an estimator that minimized a particular measure of posterior expected loss. After more than two centuries, we mathematicians, statisticians cannot only recognize our roots in this masterpiece of our science, we can still learn from it.

Hydrogen sulfide is an endogenous stimulator of angiogenesis

Abstract: The goal of the current study was to investigate the role of exogenous and endogenous hydrogen sulfide (H2S) on neovascularization and wound healing in vitro and in vivo Incubation of endothelial cells (ECs) with H2S enhanced their angiogenic potential, evidenced by accelerated cell growth, migration, and capillary morphogenesis on Matrigel Treatment of chicken chorioallantoic membranes (CAMS) with H2S increased vascular length Exposure of ECs to H2S resulted in increased phosphorylation of Akt, ERK, and p38 The KATP channel blocker glibenclamide or the p38 inhibitor SB203580 abolished H2S-induced EC motility Since glibenclamide inhibited H2S-triggered p38 phosphorylation, we propose that KATP channels lay upstream of p38 in this process When CAMs were treated with H2S biosynthesis inhibitors dl-propylargylglycine or beta-cyano-L-alanine, a reduction in vessel length and branching was observed, indicating that H2S serves as an endogenous stimulator of the angiogenic response Stimulation of ECs with vascular endothelial growth factor (VEGF) increased H2S release, while pharmacological inhibition of H2S production or KATP channels or silencing of cystathionine gamma-lyase (CSE) attenuated VEGF signaling and migration of ECs These results implicate endothelial H2S synthesis in the pro-angiogenic action of VEGF Aortic rings isolated from CSE knockout mice exhibited markedly reduced microvessel formation in response to VEGF when compared to wild-type littermates Finally, in vivo, topical administration of H2S enhanced wound healing in a rat model, while wound healing was delayed in CSE−/− mice We conclude that endogenous and exogenous H2S stimulates EC-related angiogenic properties through a KATP channel/MAPK pathway

The CSP method for simplifying kinetics

Abstract: The Computational Singular Perturbation (CSP) method of simplified kinetics modeling is presented with emphasis on its comparative merits versus conventional methodologies. A new “refinement” procedure for the basis vectors spanning the fast reaction subspace is presented. A simple example is first worked through using the conventional partial-equilibrium and quasi-steady approximations, and is then treated in some detail using CSP.

Elastic Bandwidth Allocation in Flexible OFDM-Based Optical Networks

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has recently been proposed as a modulation technique for optical networks, because of its good spectral efficiency, flexibility, and tolerance to impairments. We consider the planning problem of an OFDM optical network, where we are given a traffic matrix that includes the requested transmission rates of the connections to be served. Connections are provisioned for their requested rate by elastically allocating spectrum using a variable number of OFDM subcarriers and choosing an appropriate modulation level, taking into account the transmission distance. We introduce the Routing, Modulation Level and Spectrum Allocation (RMLSA) problem, as opposed to the typical Routing and Wavelength Assignment (RWA) problem of traditional WDM networks, prove that is also NP-complete and present various algorithms to solve it. We start by presenting an optimal ILP RMLSA algorithm that minimizes the spectrum used to serve the traffic matrix, and also present a decomposition method that breaks RMLSA into its two substituent subproblems, namely 1) routing and modulation level and 2) spectrum allocation (RML+SA), and solves them sequentially. We also propose a heuristic algorithm that serves connections one-by-one and use it to solve the planning problem by sequentially serving all the connections in the traffic matrix. In the sequential algorithm, we investigate two policies for defining the order in which connections are considered. We also use a simulated annealing meta-heuristic to obtain even better orderings. We examine the performance of the proposed algorithms through simulation experiments and evaluate the spectrum utilization benefits that can be obtained by utilizing OFDM elastic bandwidth allocation, when compared to a traditional WDM network.