Swedish Defence Research Agency

About: Swedish Defence Research Agency is a government organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Radar & Laser. The organization has 1413 authors who have published 2731 publications receiving 56083 citations. The organization is also known as: Totalförsvarets forskningsinstitut.

Channel capacity of Middleton's class A interference channel

Abstract: Middleton's class A interference model has properties that make it possible to represent a wide class of interference signals. By choice of model parameters, interference signals ranging from pure Gaussian distributed to pure impulsive interference can be modelled. These properties make the model very useful for a large variety of applications. However, an expression for the channel capacity of the class A interference channel has not yet been published. The channel capacity of this model is derived, and numerical examples are given for some useful sets of model parameters.

Click chemistry for photonic applications: triazole-functionalized platinum(II) acetylides for optical power limiting

Abstract: Three different triazole-containing platinum(II) acetylide compounds were synthesized by click chemistry and evaluated for their use in optical power limiting (OPL) applications. The triazole unit was incorporated at three different positions within, or at the end of, the conjugation path of the chromophore. The aim is to explore the possibilities of using click chemistry to prepare dendronized chromophores, and to evaluate how the triazole structure affects the photophysical properties and the optical power limiting abilities of these acetylide compounds. It is shown that the concept of click chemistry can be used to attach branched monomer units to ethynyl-phenyl arms by Huisgen 1,3-dipolar cycloaddition, forming triazole units within the chromophore. Photophysical characterization of these triazole-containing materials shows an absorption maximum within the UV-A region and emission through both fluorescence and phosphorescence. Bright phosphorescence was emitted from argon purged samples, and decay measurements thereof showed triplet lifetimes of up to 100 µs. The results from the photophysical characterization suggest that the triazole does break the conjugation path, and in order to gain maximum optical limiting the triazole needs to be placed at the end of the conjugation. All three investigated triazole-containing platinum(II) acetylides show good optical power limiting at 532 nm (10 ns pulse, f/5 set-up, 2 mm cells). The most efficient compound, with the triazole positioned at the end of the conjugation, reaches a defined clamping level of 2.5 µJ for a sample with a concentration of 50 mM in THF and a linear transmission above 80% at 532 nm. These data can be compared to the OPL properties of Zn-based porphyrins or derivatized thiophenes, reaching clamping levels of 6–15 µJ.

An experimental and computational study of a multi-swirl gas turbine combustor

Abstract: The turbulent flow and flame dynamics within a lean direct fuel injection (LDI) multi-swirl gas turbine combustor is examined using a combination of state-of-the-art diagnostic methods, including laser doppler velocimetry (LDV), particle imaging velocimetry (PIV) and fine bead thermocouples, and modern computational methods, such as flamelet-based large eddy simulations (LES). The computations provide unsteady field data of any quantity of interest, but are to some extent model dependent, whereas the laboratory studies often can capture only end-results of the real processes with limited details. The combined perspectives can thus provide mutual validation of diagnostics and models, and a more complete understanding of the physical and chemical processes involved, including also interdependencies between processes that are very difficult to characterize in the laboratory. In turn, this provides an improved framework for modification of present gas turbine combustors and for the design of future generations. Good agreement between LES and experimental data is found both for the non-reacting and reacting regimes studied. Both cases were found to be sensitive to the inflow into the swirler, and to the confinement. The non-reacting case is dominated by an annular swirling jet, a central recirculation zone (CRZ) and a weak precessing vortex core, oscillating at ∼250 Hz. For the reacting case the CRZ remains, and dominates the flow in the upstream section of the combustor including the flame and the resulting wall jets. Longitudinal pressure fluctuations at ∼380 Hz (420 Hz in the experiments) are also observed in the reacting case.