Nuclear techniques such as perturbed angular correlation (PAC) sample the hyperfine interactions of a large number of probe atoms in specific crystallographic sites. Real crystals contain static defects producing a distribution of electric field gradients (EFGs) that add to the ideal EFG of the crystal at any given probe site. Also, dynamic defects like moving vacancies and interstitial atoms can be present in the crystal and contribute to the distribution of EFGs. The distribution of EFGs leads to line broadening and a change in the observed asymmetry parameter η since the total EFG no longer has the symmetry of the perfect crystal. When both defects are present in a material, obtaining quantitative information from the analysis of PAC spectra is usually very difficult since great care has to be taken to ensure that the source of line broadening is identified correctly. In order to relate the relationship between the static line broadening and changes in the asymmetry parameter η, a uniform random distribution of point charges was used to simulate the static defect EFG. PAC spectra collected on cubic niobium metal, cubic stabilized zirconia and Nb-doped tetragonal zirconia were fitted with this model. Although the quality of the fits is good, more work is needed to clarify the relationship between the new model parameters and the line broadening and asymmetry parameter derived from conventional model fits. The PAC spectra of Nb-doped tetragonal zirconia were fitted with a conventional static model to establish a reliable relationship between line broadening and the asymmetry parameter when only static defects are present in a sample. To account for effects of dynamic defects, a four state stochastic model for vacancy motion was adapted in order to include the line broadening and changes in the asymmetry produced by static defects. As a result, the activation energies corresponding to the rates at which a oxygen vacancy is trapped by, detraps from, and hops among equivalent sites about a PAC probe atom were calculated. The values that were found are physically reasonable, indicating that the dynamics of an oxygen vacancy around a PAC probe atom are satisfactorily described. / Graduation date: 2003

No description available.

Phenotypic plasticity allows some animals to change their behavioural, morphological, performance, and life history traits in response to changes in environmental conditions such as the presence of predators. These changes can enhance survival, but come at a cost. Some of these phenotypic changes are predator and diet specific. I examined the effects of predator diet on the performance, life-history, and morphology of developing Northern Leopard Frog (Lithobates pipiens) tadpoles. Tadpoles were either exposed to cues from fish free water, cues from Brown Bullhead (Ameiurus nebulosus) fed a diet of trout pellets, or cues from A. nebulosus fed a L. pipiens tadpoles diet. Tadpoles exposed to predatory fish cues had smaller bodies, deeper tail fins, slower growth and development rates, and better rotational performance than tadpoles that were not exposed to predatory fish cues. Moreover, tadpoles appeared to differentiate between predatory fish diet and produced diet-specific responses in tail morphology and activity, although the latter effect was only marginally significant. Hatching, metamorphosis rates, and linear performance were not affected by the treatments. These results suggest that A. nebulosus can induce phenotypic changes in L. pipiens tadpoles, with some of these changes being diet specific.

Graduation date: 1992

Twenty-odd years ago, scientists managed to produce several new techniques for manipulating certain properties of laser and microwave radiation. These new properties made it possible for the radiation to contain a lot more information than what was previously known. What they had discovered was that light could be twisted, thereby not only carrying polarization, also known as spin angular momentum (SAM) but also orbital angular momentum (OAM).Radar beams are used by scientists to probe the earth’s ionosphere. By measuring the echo of the radar waves one can deduce a lot of information, such as density and temperature of the plasma. In this thesis we will expand an existing program (iscatspb0.m) which computes the spectrum of plasma fluctuations as seen with an incoherent scatter radar, to having it incorporate radar beams carrying OAM, to see what new information of the plasma can be obtained.The three major findings in this thesis were what magnitude of the integer l is needed in order for the contribution of OAM to equal the contribution for the beam opening angle, how much the radar beam opening angle affected the measurements and in what way the spectrum obtained by a twisted beam is affected by different flows

<p>Reconstructing locomotor patterns from fossils is crucial for understanding the origins of primates and important transitions in various primate clades. Recent studies suggest that the semicircular canals of the inner ear provide evidence about locomotion. The canals sense rotational head accelerations and drive reflexes essential for normal movement. Because bony aspects of canal morphology influence canal sensitivity, this system can be studied in osteologic specimens and fossils. Variation in canal morphology in living and, by inference, extinct primates has been attributed to interspecific differences in locomotor behavior. However, the manner in which movement selects for canal morphology is debated, alternative scenarios are plausible, and no relevant measurements are available documenting head movements in primates.</p><p>To refine proposed links between canal morphology and locomotor function, and to resolve conflicting functional interpretations, this study examines head rotations in lemurs and lorises exhibiting diverse locomotor behaviors. Three-dimensional kinematic analyses were used to characterize angular velocities of the head during locomotion. These data are used to test hypotheses concerning intraspecific, interspecific, and body-size dependent variation in head rotations. Cranial CT scans are used to model canal sensitivity to rotations in different directions. Observed patterns of head rotation are compared to predicted patterns of sensitivity to test hypotheses about the relationship between locomotor behavior and canal design.</p><p>Evaluation of existing locomotor inferences reveals that brain size exerts a significant effect on canal size and that the prevailing equations for predicting agility from body and canal size are highly inaccurate. Intraspecific comparisons between maps of observed angular velocity and predicted sensitivity allow identification of map types associated with different general locomotor modes and do not support existing hypotheses about the primary selective forces acting on canal morphology. The new data are used to formulate and test a novel "fast-accurate hypothesis" to explain why all vertebrates are more sensitive to rotations about some axes than others. The fast-accurate hypothesis stipulates that angular velocities presented about axes of mean sensitivity are most accurately interpreted by the brain, and that selection aligns axes of mean sensitivity with axes of habitually fast rotation because accurate perception of rapid rotations confers survival benefit. The fast-accurate hypothesis was used to predict which features of the canals should be correlated with high mean angular velocities of head movement. Novel equations that predict behavior from these newly identified canal morphologies were generated and found to outperform existing equations when tested on the original sample of 11 strepsirrhine species.</p> / Dissertation

Spinning targets are usually observed in videos. The targets may sometimes appear as mobile targets at the same time. The targets become mobile spinning targets. Tracking a single point on a target is easier than tracking the whole target. We use a characteristic point on the target to estimate the interested parameters, such as angular velocity, virtual rotation center and moving velocity. Among these parameters, virtual rotation center does not spin, therefore it can be used to represent the position of the target. Traditionally, extended Kalman filter (EKF), unscented Kalman filter (UKF) and particle filter (PF) are choices for solving the nonlinear problems, but some problems exist. Linearization errors cause that EKF cannot accurately estimate the angular velocity. UKF and PF have high computational complexity. In the thesis, we give angular velocity an initial value. So we can establish a linear dynamic system model to displace the nonlinear model. Then, a new structure is proposed to avoid errors caused by initial value of angular velocity. In the structure, angular velocity is estimated individually and used to correct the initial value by feedback. We try to use fast Fourier transform to estimate angular velocity. But the convergence time of this method is affected by the value of angular velocity, and the direction of angular velocity can not be estimated directly. Therefore, Kalman filter (KF) with pseudo measurement is proposed to estimate the value of angular velocity. The estimator is accurate and has low computational complexity. Once angular velocity is estimated, we can easily predict the virtual rotation center from geometric relationship. In video system, measurements may be quantized and targets may sometimes be obstacled. We fix the measurement equation and use KF to mitigate quantization error. When measurements for the target is missing, the previous state is used to predict the current state. Finally, computer simulations are conducted to verify the effectiveless of the proposed method. The method can work in environments where measurement noise or quantization error exists. The methods can also be applied to different kinds of mobile spinning targets.

The protein structure prediction problem consists of determining a protein’s three-dimensional structure from the underlying sequence of amino acids. A standard approach for predicting such structures is to conduct a stochastic search of conformation space in an attempt to find a conformation that optimizes a scoring function. For one subclass of prediction protocols, called template-based modeling, a new protein is suspected to be structurally similar to other proteins with known structure. The solved related proteins may be used to guide the search of protein structure space. There are many potential applications for statistics in this area, ranging from the development of structure scores to improving search algorithms. This dissertation focuses on strategies for improving structure predictions by incorporating information about closely related “template” protein structures into searches of protein conformation space. This is accomplished by generating density estimates on conformation space via various simplifications of structure models. By concentrating a search for good structure conformations in areas that are inhabited by similar proteins, we improve the efficiency of our search and increase the chances of finding a low-energy structure. In the course of addressing this structural biology problem, we present a number of advances to the field of Bayesian nonparametric density estimation. We first develop a method for density estimation with bivariate angular data that has applications to characterizing protein backbone conformation space. We then extend this model to account for multiple angle pairs, thereby addressing the problem of modeling protein regions instead of single sequence positions. In the course of this analysis we incorporate an informative prior into our nonparametric density estimate and find that this significantly improves performance for protein loop prediction. The final piece of our structure prediction strategy is to connect side-chain locations to our torsion angle representation of the protein backbone. We accomplish this by using a Bayesian nonparametric model for dependence that can link together two or more multivariate marginals distributions. In addition to its application for our angular-linear data distribution, this dependence model can serve as an alternative to nonparametric copula methods.

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