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Plants modulate their growth and development according to the prevailing light conditions. To detect light signals plants have an array of photoreceptors including the phytochromes which monitor the red and far-red light regions of the light spectrum. Phytochromes regulate gene expression in response to light in part by physically interacting with nuclear-localized bHLH transcription factors called PHYTOCHROME INTERACTING FACTORS (PIFs). PIFs are known to function as negative regulators of photomorphogenesis. Here we show that PIF1, the PIF family member with the highest affinity for phys, is degraded after pulses or continuous red, far-red or blue light in a phytochrome dependent manner. In etiolated seedlings, phyA plays a dominant role in regulating the degradation of PIF1 after a pulse of red, far-red or blue light; while phyB, phyD and other phys also influence PIF1 degradation after prolonged illumination. PIF1 interacted with phyA and phyB in a blue light-dependent manner, and the interactions with phys are necessary for the light-induced degradation of PIF1. In response to red, far-red or blue light treatments PIF1 is rapidly phosphorylated, poly-ubiquitinated and degraded via the ubiquitin/26S proteasomal pathway. In addition, we show that PIF1 negatively regulates photomorphogenesis at the seedling stage. The overexpression of a light-stable truncated form of PIF1 causes constitutively photomorphogenic phenotypes in the dark. pif1 seedlings displayed more open cotyledons and slightly reduced hypocotyl length compared to wild type under diurnal (12h light/12h dark) blue light conditions. Double mutant analyses demonstrated that pif1phyA, pif1phyB, pif1cry1 and pif1cry2 have enhanced cotyledon opening compared to the single photoreceptor mutants under diurnal blue light conditions. Taken together, these data suggest that PIF1 functions as a negative regulator of photomorphogenesis and that light-activated phys induce the degradation of PIF1 through the ubi/26S proteasomal pathway to promote photomorphogenesis. / text

Phenomenological models have long been employed by nuclear physicists to explain systematic trends in data. The Geometrical Model of Bohr, Mottelson and Rainwater (GM) and the Interacting Boson Model (IBM) are two such models that have been used to study the spectra of even-even nuclei. The IBM differs from previous boson models in that the total number of bosons is conserved and finite. In the GM the bosons of lowest angular momentum have ℓ = 2 and are taken to represent quadrupole shape vibrations, whereas in the IBM the bosons are generally taken to have ℓ = 0, 2 and can be interpreted as correlated pairs of fermions. These models have been extended to handle the neighboring odd-even nuclei by considering the interaction of a fermion with the bosonic space. If the fermionic space consists of the single-particle angular momenta j₁, j₂, ..., then the largest group describing this mixed system of bosons and fermions is the product group Uᴮ(5) x Uᶠ(m(j)) (GM) or Uᴮ(6) x Uᶠ(m(j)) (IBM), where m(j) = Σ(2jᵢ + 1). If one of the subgroups of Uᴮ(5) or Uᴮ(6) is isomorphic to one of the subgroups of Uᶠ(m(j)), then we can combine the two group chains into a common bose-fermi group chain. These combined bose-fermi groups have been used extensively in the Interacting Boson-Fermion Model (IBFM) to study odd-even nuclei and have been claimed as evidence for the existence of supersymmetries; however, the superalgebras associated with these supersymmetries were never identified. We have identified, for the first time, the superalgebras that are associated with some of these combined bose-fermi symmetries. This superalgebra, the non-compact orthosymplectic superalgebra Osp(4s+2/2,R), is fundamentally different than those previously used in the IBFM, where the product algebra was simply embedded into the superalgebra U(6/m(j)). The U(6/m(j)) superalgebras do not imply any particular coupling scheme, and hence cannot be associated with any particular one of the combined bose-fermi algebras. The last few chapters are devoted to a study of coherent states for the non-compact orthosymplectic supergroups Osp(1/2N,R) and Osp(2/2N,R), although the results generalize rather easily to the compact versions of these supergroups. These coherent states, besides being of mathematical interest, form the basis for a study of Osp(M/2N,R) coherent states. (Abstract shortened with permission of author.)

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In modern systems for air surveillance, it is important to have a high quality situationassessment. SAAB has a system for air surveillance, and in this thesis possibleimprovements of the tracking performance of this system are explored. The focushas been on improving the tracking of highly maneuverable targets observed withlow sampling rate. To evaluate improvements of the tracking performance, a componentthat is similar to the one used in SAAB’s present tracker was implementedin an Interacting Multiple Model (IMM) structure. The use of an Auxiliary ParticleFilter for improving the tracking performance is explored, and a way to fita particle filter into SAAB’s existing IMM framework is proposed. The differentfilters were implemented in Matlab, and evaluation was done by the meansof Monte Carlo simulations. The results from Monte Carlo simulations show significantimprovement when tracking in two dimensions. However, the results inthree dimensions do not display any substantial overall improvement when usingthe particle filter compared to using SAAB’s present filter. It is therefore notworthwhile to switch the filter used in SAAB’s present tracker for a particle filter,at least not under the high SNR circumstances presented in this thesis. However,further studies within this area are recommended before any final decisions aremade.