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 & Synthetic aperture radar. The organization has 1413 authors who have published 2731 publications receiving 56083 citations. The organization is also known as: Totalförsvarets forskningsinstitut.

Transmission of tularemia from a water source by transstadial maintenance in a mosquito vector

Abstract: Mosquitoes are thought to function as mechanical vectors of Francisella tularensis subspecies holarctica (F. t. holarctica) causing tularemia in humans. We investigated the clinical relevance of transstadially maintained F. t. holarctica in mosquitoes. Aedes egypti larvae exposed to a fully virulent F. t. holarctica strain for 24 hours, were allowed to develop into adults when they were individually homogenized. Approximately 24% of the homogenates tested positive for F. t. DNA in PCR. Mice injected with the mosquito homogenates acquired tularemia within 5 days. This novel finding demonstrates the possibility of transmission of bacteria by adult mosquitoes having acquired the pathogen from their aquatic larval habitats.

Investigations of microwave stimulation of a turbulent low-swirl flame

Abstract: Irradiating a flame by microwave radiation is one of several plasma-assisted combustion (PAC) technologies that can be used to modify the combustion chemical kinetics in order to improve flame-stability and to delay lean blow-out. One practical implication is that engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. In addition, this technology may assist in reducing thermoacoustic instabilities that may severely damage the engine and increase emission production. To examine microwave-assisted combustion a combined experimental and computational study of microwave-assisted combustion is performed for a lean, turbulent, swirl-stabilized, stratified flame at atmospheric conditions. The objectives are to demonstrate that the technology increases both the laminar and turbulent flame speeds, and modifies the chemical kinetics, enhancing the flame-stability at lean mixtures. The study combines experimental investigations using hydroxyl (OH) and formaldehyde (CH2O) Planar Laser-Induced Fluorescence (PLIF) and numerical simulations using finite rate chemistry Large Eddy Simulations (LES). The reaction mechanism is based on a methane (CH4)–air skeletal mechanism expanded with sub-mechanisms for ozone, singlet oxygen, chemionization, electron impact dissociation, ionization and attachment. The experimental and computational results show similar trends, and are used to demonstrate and explain some significant aspects of microwave-enhanced combustion. Both simulation and experimental studies are performed close to lean blow off conditions. In the simulations, the flame is gradually subjected to increasing reduced electric field strengths, resulting in a wider flame that stabilizes nearer to the burner nozzle. Experiments are performed at two equivalence ratios, where the leaner case absorbs up to more than 5% of the total flame power. Data from experiments reveal trends similar to simulated results with increased microwave absorption.

Determination of vapor pressure of low-volatility compounds using a method to obtain saturated vapor with coated capillary columns.

Abstract: The vapor pressures of O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX), O-isobutyl S-2-diethylaminoethyl methylphosphonothiolate (RVX), and 2,4-dinitrotoluene (2,4-DNT) were determined with the gas saturation method in temperatures ranging from -12 to 103 degrees C The saturated vapor was generated using a fused-silica column coated with the compound This column was placed in a gas chromatograph, and the vapor pressure was determined directly from the detector signal or by sampling on Tenax tubes that were subsequently analyzed From the linear relationships obtained by plotting log P vs 1/T, the enthalpies of vaporization (deltaHvap) and the vapor pressures at selected temperatures were determined The vapor pressure of VX at 25 degrees C was 0110 Pa and the deltaHvap 779 kJ x mol(-1) The corresponding results for RVX were 0082 Pa and 766 kJ x mol(-1) The vapor pressure of 2,4-DNT at 72 degrees C (melting point) was determined to 60 Pa, and the enthalpies of the solid and the liquid state were 942 and 753 kJ x mol(-1), respectively Using capillary columns to generate saturated vapors has three major advantages: short equilibrium time, low consumption of sample, and safe handling of toxic compounds

Implicit and Explicit Subgrid Modeling in LES Applied to a Marine Propeller

Abstract: The flow around a four-bladed marine propeller in homogeneous inflow and in non-cavitating conditions is investigated using Large Eddy Simulation, LES. Explicit, using a k-equation eddy viscosity model, and implicit subgrid modeling are compared for both the standard LES formulation as well as a mixed formulation containing the, so called, scale similarity term. A wall-modeled approach is used on a relatively coarse grid, containing 5.5 million cells, for the full propeller in order to mimic a future applied computation including the ship hull. The implicit modeling is of particular interest in cavitation simulation, where the interaction between an explicit subgrid model and the liquid-vapor interface may cause numerical and modeling problems. All simulations yield fairly similar results, although the implicit LES gives better prediction of the global performance of the propeller. The agreement with experimental data is good close to the propeller, but the simulated flow structures diffuses quickly at the present grid resolution.