Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

High-performance ternary organic solar cells with thick active layer exceeding 11% efficiency

Abstract: We present a novel ternary organic solar cell with an uncommonly thick active layer (∼300 nm), featuring thickness invariant charge carrier recombination and delivering 11% power conversion efficiency (PCE). A ternary blend was used to demonstrate photovoltaic modules of high technological relevance both on glass and flexible substrates, yielding 8.2% and 6.8% PCE, respectively.

Thermal stability and oxidation resistance of laser clad TiVCrAlSi high entropy alloy coatings on Ti–6Al–4V alloy

Abstract: TiVCrAlSi high entropy alloy coatings were deposited on Ti–6Al–4V alloy by laser cladding. SEM, XRD and EDS analyses show that, the as-clad coating is composed of (Ti,V) 5 Si 3 and a BCC solid solution. After annealing at 800 °C for 24 h under vacuum, the coating is composed of (Ti,V) 5 Si 3 , Al 8 (V,Cr) 5 , and a BCC solid solution. The temperature-dependent phase equilibrium for the coating material calculated by using the CALPHAD method, indicates that above 880 °C the stable phases existing in the coating material are a BCC solid-solution and (Ti,V) 5 Si 3 . When the temperature is below 880 °C, the stable phases are (Ti,V) 5 Si 3 , Al 8 (V,Cr) 5 , and a BCC solid solution. In order to validate the calculation results, they were compared with TiVCrAlSi alloy samples prepared by arc melting, encapsulated in quartz tubes under vacuum, annealed at 400–1100 °C for 3 days and water-quenched. XRD analysis shows that the experimental phase composition agrees with the thermodynamic calculations. After vacuum annealing, there is a small increase of hardness for the laser clad TiVCrAlSi coating, which is due to the formation of Al 8 (V,Cr) 5 . The oxidation tests show that the TiVCrAlSi coating effectively improves the oxidation resistance of Ti–6Al–4V at 800 °C in air. The formation of a dense and adherent scale consisting of SiO 2 , Cr 2 O 3 , TiO 2 , Al 2 O 3 and a small amount of V 2 O 5 is supposed to be responsible for the observed improvement of the oxidation resistance.

The Resurgence of Instantons in String Theory

Abstract: Nonperturbative eects in string theory are usually associated to D{branes. In many cases it can be explicitly shown that D{brane instantons control the large{order behavior of string perturbation theory, leading to the well{known (2g)! growth of the genus expansion. This paper presents a detailed treatment of nonperturbative solutions in string theory, and their relation to the large{order behavior of perturbation theory, making use of transseries and resurgent analysis. These are powerful techniques addressing general nonperturbative contributions within non{linear systems, which are developed at length herein as they apply to string theory. The cases of topological strings, the Painlev e I equation describing 2d quantum gravity, and the quartic matrix model, are explicitly addressed. These results generalize to minimal strings and general matrix models. It is shown that, in order to completely understand string theory at a fully nonperturbative level, new sectors are required beyond the standard D{brane sector.