Bayesian super-resolution with application to radar target recognition

This thesis is concerned with methods to facilitate automatic target recognition using images generated from a group of associated radar systems. Target recognition algorithms require access to a database of previously recorded or synthesized radar images for the targets of interest, or a database of features based on those images. However, the resolution of a new image acquired under non-ideal conditions may not be as good as that of the images used to generate the database. Therefore it is proposed to use super-resolution techniques to match the resolution of new images with the resolution of database images. A comprehensive review of the literature is given for super-resolution when used either on its own, or in conjunction with target recognition. A new superresolution algorithm is developed that is based on numerical Markov chain Monte Carlo Bayesian statistics. This algorithm allows uncertainty in the superresolved image to be taken into account in the target recognition process. It is shown that the Bayesian approach improves the probability of correct target classification over standard super-resolution techniques. The new super-resolution algorithm is demonstrated using a simple synthetically generated data set and is compared to other similar algorithms. A variety of effects that degrade super-resolution performance, such as defocus, are analyzed and techniques to compensate for these are presented. Performance of the super-resolution algorithm is then tested as part of a Bayesian target recognition framework using measured radar data

Virtually abelian K\"ahler and projective groups

We characterise the virtually abelian groups which are fundamental groups of compact K\"ahler manifolds and of smooth projective varieties. We show that a virtually abelian group is K\"ahler if and only if it is projective. In particular, this allows to describe the K\"ahler condition for such groups in terms of integral symplectic representations

High-spin structure, K isomers, and state mixing in the neutron-rich isotopes 173Tm and 175Tm

High-spin states in the odd-proton thulium isotopes 173Tm and 175Tm have been studied using deep-inelastic reactions and γ-ray spectroscopy. In 173Tm, the low-lying structure has been confirmed and numerous new states have been identified, including a three-quasiparticle Kπ= 19/2- isomer with a lifetime of τ=360(100)ns at 1906keV and a five-quasiparticle Kπ=35/2- isomer with a lifetime of τ= 175(40)ns at 4048keV. The Kπ=35/2- state is interpreted as a t-band configuration that shows anomalously fast decays. In 175Tm, the low-lying structure has been reevaluated, a candidate state for the 9/2-[514] orbital has been identified at 1175keV, and the 7/2-[523] bandhead has been measured to have a lifetime of τ= 460(50)ns. Newly identified high-K structures in 175Tm include a Kπ=15/2- isomer with a lifetime of τ= 64(3)ns at 947keV and a Kπ= 23/2+ isomer with a lifetime of τ= 30(20) μs at 1518keV. The Kπ=15/2- isomer shows relatively enhanced decays to the 7/2-[523] band that can be explained by chance mixing with the 15/2- member of the 7/2- band. Multiquasiparticle calculations have been performed for 173Tm and 175Tm, the results of which compare well with the experimentally observed high-spin states

Multiquasiparticle states in the neutron-rich nucleus 174Tm

Deep inelastic and transfer reactions with an 820-MeV, 136Xe beam and various ytterbium and lutetium targets have been employed to study high-spin structures in the neutron-rich thulium isotopes beyond 171Tm. Results in the doubly odd nucleus, 174Tm, include the identification of numerous new two- and four-quasiparticle intrinsic states including several isomers below 1 MeV, and the observation of the Kπ=4- ground state rotational band populated via direct decay from a τ=153(10)-μs, Kπ=14- isomer at 2092 keV. The 398-keV, M1 transition linking the isomer and ground state band is abnormally fast for a highly forbidden, ΔK=10 decay. This relative enhancement is explained in terms of mixing of the 13- level with the nearby 13- member of a Kπ=8- rotational band, with an interaction strength of V ≈ 1.4 keV. Multiquasiparticle calculations are compared with the observed states

Two-quasiparticle K-isomers and pairing strengths in the neutron-rich isotopes 174Er and 172Er

Isomeric two-quasiparticle states have been identified in the neutron-rich isotopes 172Er and 174Er using multi-nucleon transfer reactions with 136Xe beams incident on various targets, and γ-ray spectroscopy with Gammasphere. A candidate for the Kπ=6+ two-quasineutron state in 172Er is found at 1500 keV. In 174Er, a nuclide whose level scheme was previously unknown, a long-lived isomer is identified at 1112 keV decaying via an inhibited E1 transition and revealing the yrast sequence of 174Er. This isomer is proposed to be a Kπ=8- two-quasineutron state, defining a sequence in the N=106 isotones extending from the well-deformed neutron-rich isotope 174Er to the neutron-deficient isotope 188Pb, where the presence of the isomer signifies a prolate minimum in an otherwise spherical well. Configuration-constrained potential-energy surface calculations are used to predict the excitation energies of the 6+ and 8- intrinsic states and as a basis for extracting the pairing force strength, Gn, in the N=104 and N=106 isotones

Structure of three-quasiparticle isomers in Ho169 and Tm171

A three-quasiparticle isomer with τ=170(8) μs and Kπ= (19/2 +) has been identified in the neutron-rich isotope Ho169. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2-[523] proton configuration, whose structure is characterized through analysis of the in-band γ-ray branching ratios. In the isotone Tm171, the rotational band based on the known 19/2+, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in Ho169 are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in Tm171

Isomers and excitation modes in the gamma-soft nucleus 192Os

New spectroscopic results for high-spin states in 192Os populated in deep-inelastic reactions include the identification of a 2-ns, 12+ isomeric state at 2865 keV and a 295-ns, 20+ state at 4580 keV and their associated δJ=2 sequences. The structures are interpreted as manifestations of maximal rotation alignment within the neutron i13/2 and proton h11/2 shells at oblate deformation. Rotational band members based on the long-lived, Kπ=10- isomer are also identified for the first time. Configuration-constrained, potential-energy-surface calculations predict that other prolate multi-quasiparticle high-K states should exist at low energy

Deep inelastic reactions and isomers in neutron-rich nuclei across the perimeter of the A = 180-190 deformed region

Recent results on high-spin isomers populated in deep-inelastic reactions in the transitional tungsten-osmium region are outlined with a focus on 190Os, 192Os and 194Os. As well as the characterization of several two-quasinutron isomers, the 12+ and 20+ isomers in 192Os are interpreted as manifestations of maximal rotation alignment within the neutron i13/2 and possibly proton h11/2 shells at oblate deformation

Decay properties of high-spin isomers and other structures in Sb121 and Sb123

High-spin states populated in the decay of microsecond isomers in the transitional nuclei Sb121 and Sb123 have been investigated in detail in several experiments using γ-ray and electron spectroscopy. The nuclei were formed using multinucleon transfer and fusion-fission reactions with Xe136 beams and also using the Sn120(Li7,α2n)Sb121 and Sn122(Li7,α2n)Sb123 incomplete-fusion reactions. Isomeric half-lives ranging from several nanoseconds to a few hundred microseconds were determined by means of conventional decay curve analyses, whereas very short-lived isomers (T1/2~1 ns) were identified using the generalized centroid-shift method. A number of new transitions were observed, including a branch through spherical states from the 19/2+ member of the 9/2+ deformed band in Sb121, in competition with the main decay path through the rotational band. This is attributed to mixing between the 19/2+ band member and a 19/2+ spherical state. Both levels are predicted to coincide approximately in energy in Sb121. The fact that a 25/2+ isomer occurs for A=121 and the lighter isotopes, while a 23/2+ isomer is observed for A=123-131 is explained through a multistate mixing calculation, taking into account the gradual shift of the 2d5/2 and 1g7/2 proton orbitals and the change in proton-neutron effective interactions from an attractive particle-particle type in the lower part of the shell to a repulsive particle-hole type with increasing the neutron number toward the N=82 shell closure. The observed enhancement of the B(E2;19/2-→15/2-) values in Sb121 and Sb123 over the B(E2;7-→5-) values in the corresponding Sn cores is discussed in terms of configuration mixing between spherical and deformed states

Decay of a Kπ=21/2-, 17-ms isomer in Ta185

High-spin states in the neutron-rich nucleus Ta185, populated in the decay of a long-lived, three-quasiparticle state, have been studied using deep-inelastic reactions with Xe136 ions and a W186 target. The lifetime of the isomer has been measured as 17(2) ms and the spin and parity determined to be Kπ=21/2-, leading to a π7/2+[404]ν3/2-[512]11/2+[615] configuration assignment. The isomer decays into the rotational band built upon the π9/2-[514] intrinsic state via K-forbidden transitions with reduced hindrances of 52 and 71. The π9/2-[514] state is itself an isomer with a lifetime of 17(3) ns. It decays via K-allowed E1 transitions to states in the π7/2+[404] band with strengths that are similar to equivalent transitions in the lighter tantalum isotopes