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.

Suppression of Clutter in Multichannel SAR GMTI

Abstract: In this paper, the results of moving-target detection in multichannel UHF-band synthetic aperture radar (SAR) data are shown. The clutter suppression is done using finite-impulse response (FIR) filtering of multichannel SAR in combination with a two-stage fast-backprojection algorithm to focus the moving target using relative speed. The FIR filter coefficients are chosen with the use of space-time adaptive processing filtering. Two parameters are used for target focusing, target speed in range and in azimuth. When the target is focused, both speed parameters of the target are found. In the experimental results, two channels were used in order to suppress clutter. In the resulting SAR images, it is obvious that very strong scatterers and the forest areas have been suppressed in comparison to the moving target in the image scene. The gain obtained can be measured using signal-to-clutter-and-noise-ratio gain, which is about 19 dB. Another way to measure the signal processing gain is the ability to suppress the strongest reflecting object in the SAR scene. The gain of the target in relation to this object is 25 dB. This shows that using UHF-band SAR ground moving target indication (GMTI) for suppressing forest and increasing the target signal can work.

Application of a line-implicit scheme on stretched unstructured grids

Abstract: A line-implicit Runge-Kutta time stepping scheme is derived, implemented and applied. It is applied to fluid flow problems governed by the Navier-Stokes equations on stretched unstructured grids. The flow equations are integrated implicitly in time along structured lines in regions where the grid is stretched, typically in the boundary layer, and explicitly elsewhere. The integration technique is introduced for steady state problems with the intention to speed up the rate of convergence. It is extended to unsteady problems by a dual time stepping approach. The paper focuses on the implementation of the line-implicit scheme starting from an explicit multigrid flow solver and on the application of it. Numerical results are presented for test cases in two and three dimensions for inviscid and viscous flow problems. The line-implicit time integration convergence rates are compared to pure explicit convergence rates and the gain is quantified in terms of reduction of iterations and CPU time. All presented test cases show improved convergence rates. The gain is highest for the three dimensional test cases for which reductions of up to 75% of the computing time is obtained.

Comparative Analysis of Type III Effector Translocation by Yersinia pseudotuberculosis Expressing Native LcrV or PcrV from Pseudomonas aeruginosa

Abstract: The homologues LcrV of Yersinia species and PcrV of Pseudomonas aeruginosa are pore-forming components. When expressed in a Yersinia lcrV background, PcrV formed smaller pores in infected erythrocyte membranes, correlating to a lowered translocation of Yersinia effectors. To understand this phenomenon, cytotoxins exoenzyme S of P. aeruginosa and YopE of Yersinia were introduced into a Yersinia background without Yop effectors but expressing LcrV or PcrV. Comparable translocation of each substrate indicated that substrate recognition by LcrV/PcrV is not a regulator of translocation. Yersinia harboring pcrV coexpressed with its native operon efficiently translocated effectors into HeLa cell monolayers and formed large LcrV-like pores in erythrocyte membranes. Thus, a PcrV complex with native P. aeruginosa translocon components is required to form fully functional pores for complete complementation of effector translocation in Yersinia.