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Visar resultat 1 - 5 av 19 avhandlingar som matchar ovanstående sökkriterier.

  1. 1. Inverse Problems in Tomography and Fast Methods for Singular Convolutions

    Författare :Fredrik Andersson; Matematik LTH; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Mathematics; Matematik; Unequally spaced FFT; Integral transforms; Singular integrals; Lippmann?Schwinger equation; Helmholtz equation; Inverse problems; Fast Gauss transform; Fast summation; Convolution; Radon transform; Tomography;

    Sammanfattning : There are two, partially interlaced, themes treated in this thesis; inverse problems of tomographic type and fast and accurate methods for the application of convolution operators. Regarding the first theme, the inverse problem of Doppler tomography is considered and the Doppler moment transform is introduced for that purpose. LÄS MER

  3. 2. Fast Radon Transforms and Reconstruction Techniques in Seismology

    Författare :Viktor Nikitin; Matematik LTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; Fourier transform FFT ; Radon transforms; GPU;

    Sammanfattning : The measurements conducted in tomography and seismology typically yield large multidimensional data sets. This in combination with the fact that the data may have an irregular structure makes it computationally prohibitive to use simple reconstruction methods directly. LÄS MER

  4. 3. Domain Decomposition and Preconditioned Iterative Methods for the Helmholtz Equation

    Författare :Elisabeth Larsson; Kurt Otto; Bengt Fornberg; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Helmholtz equation; domain decomposition; preconditioned iterative method; fast transforms; parallelization; Numerical Analysis; Numerisk analys;

    Sammanfattning : New preconditioned iterative solution methods for the Helmholtz equation are constructed. To evaluate the performance of the methods, two-dimensional problems with a waveguide geometry are used as model problems. Second- and fourth-order accurate finite difference discretizations are used. LÄS MER

  5. 4. Some results on fast correlation attacks

    Författare :Fredrik Jönsson; Institutionen för elektro- och informationsteknik; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Technological sciences; stream ciphers; linear feedback shift registers; cryptology; correlation attacks; cryptanalysis; Teknik; Informatics; systems theory; Informatik; systemteori;

    Sammanfattning : This thesis presents new results on fast correlation attacks on stream ciphers. In particular, fast correlation attacks on stream ciphers containing linear shift registers with an arbitrary number of taps, are considered. A general introduction to stream ciphers and correlation attacks is given. LÄS MER

  7. 5. Application of fast backprojection techniques for some inverse problems of integral geometry

    Författare :Stefan Nilsson; Frank Natterer; Linköpings universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES;

    Sammanfattning : In this thesis we study some mathematical inverse problems concerning the determination of a function from circular averages, which appear in certain radar applications, and the determination of a function from its line integrals, which appear in the well known problem of computerized tomographic imaging (CT). The thesis is divided into three parts. LÄS MER