n-Type Copolymers with Fluorene and 1,3,4-Heterodiazole Moieties

The successful realization of n-channel field-effect transistors requires the application of semiconducting polymers with high electron mobility (n-type). However, reports on n-type polymers are rather scarce in the literature. Therefore, the development of polymers with suitable electron transport properties is particularly challenging for the synthetic chemistry. Main chain polymers with strong acceptor units, such as 1,3,4-heterodiazoles, are potential candidates for electron transport materials in electronic devices. The fluorene unit is another ring system with interesting physical and chemical properties, which is often used in rigid-rod, main chain polymers. The present work introduces the synthesis of organo-soluble copolymers consisting of alternating fluorene-, 1,3,4-heterodiazole, and, in some cases, additional 2,5-dialkoxyphenylene units in the main chain. The reported synthesis involves modified classical polycondensation as well as the tetrazole route. We demonstrate the possibility of exchanging oxygen in the heteroaromatic ring with sulfur using Lawesson's reagent during the ring closure reaction. An alternative structure of the heterocyclic ring with N-phenyl in the oxygen position is feasible using the tetrazole synthetic route. The chemical and electrochemical properties of the copolyfluorenes are investigated in detail. Some of the synthesized copolyfluorenes have also been used for the preparation of electron-only devices enabling the calculation of the electron mobilities. Further, an organic field-effect transistor (OFET) characteristic was shown

Wing Shape Improvement in the Presence of an Over-the-Wing Mounted UHBR Engine for a Short Range Transport Aircraft

The aerodynamic benefit of over-the-wing mounted engines for commercial aircraft withSTOL capabilities in cruise flight conditions is explored. Favorable aerodynamic installation effects and less space constraints, like landing gear length for under-the-wing mounted engines, offer a promising potential for future transport aircraft configurations in combination with ultra-high bypass ratio engines. Nevertheless, the aerodynamic interaction between wing and engine, located at the wing upper side close to the trailing edge, is crucial and involves a design challenge to exploit the full aerodynamic performance potential. Especially the aerodynamics of the wing experiences a significant alteration due to the installation of the engine, which differs from engines mounted under a wing. The shock position and topology changes significantly and, consequently, also the spanwise load distribution is significantly changed. Therefore, the wing shape has to be adapted to the presence of the engine to meet the performance requirements and utilize potentially positive engine installation effects. Targeting on a low noise aircraft with short take-off and landing capabilities, two optimization steps were accomplished. As a first step, the wing-twist of a wing/body/engine/pylon (WBEP) configuration was adapted to improve the spanwise load distribution followed by a shape optimization. For this purpose, a surrogate-based optimization approach was applied

Newton-Krylov algorithm with a loosely coupled turbulence model for aerodynamic flows

A fast Newton–Krylov algorithm is presented that solves the turbulent Navier–Stokes equations on unstructured 2-D grids. The model of Spalart and Allmaras provides the turbulent viscosity and is loosely coupled to the mean-flow equations. It is often assumed that the turbulence model must be fully coupled to obtain the full benefit of an inexact Newton algorithm. We demonstrate that a loosely coupled algorithm is effective and has some advantages, such as reduced storage requirements and smoother transient oscillations. A transonic single-element case converges to 1 1012 in 90 s on recent commodity hardware, whereas the lift coefficient is converged to three figures in one quarter of that time