The present thesis describes two experiments performed in the storage ring CELSIUS at The Svedberg Laboratory in Uppsala. In the first experiment the importance of three - nucleon clustering in the six - nucelon system was investigated. The total cross section for the production of the ground state and the 3.56 MeV second excited state of 6Li in the 3He(3He,6Li)π+ reaction has been measured at two beam energies, 261.1 and 262.5 MeV, corresponding to center - of - mass energies 1.2 and 1.9 MeV above the production threshold for the 3.56 MeV state. For the ground state the result was 347 ± 84 ± 42 and 92 ± 84 ± 11 nb respectively. The result for the 3.56 MeV state, 104 ± 23 ± 12 and 56 ± 35 ± 7 nb respectively, is compared to the result of a previous study where the 3.56 MeV state was populated in the d(4He,6Li)π0 reaction. In the second experiment a clean sample of 5×105 eta mesons was prepared by means of the d(p,3He)η reaction. Eta production was tagged by the precise determination of the kinetic energy of the associated 3He ions. In the subsequent decay of eta mesons, channels with lepton - anti - lepton pairs were studied in the WASA detector. In a separate study properties of the WASA deuterium pellet target were investigated and in particular the effects on the beam of the beam - target interactions. In both sets of experiments the fused nuclear system was detected by means of a zero - degree spectrometer with a semiconductor detector telescope. Choosing the detectors to match the rather different requirements, precise information regarding the identity and the momentum of the detected ions could be obtained in both cases.

Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study. A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots. The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.

Les fonctions d'excitation de fusion-évaporation des systèmes 70Zn+150Nd et 86Kr+130,136Xe sont mesurées pour une énergie d'excitation du noyau composé (216,220,222Th) variant de 7 MeV à 70 MeV (soit 4 à 5 MeV par nucléon d'énergie incidente), auprès de l'UNILAC du laboratoire de recherche GSI, Darmstadt (Allemagne). Après désexciation par évaporation (xn, pxn et αxn), les noyaux résiduels sont séparés du faisceau principal et des autres produits de réaction par le filtre de vitesse SHIP et implantés dans un détecteur à localisation. Les énergies caractéristiques des alphas de décroissance de ces noyaux permettent de les identifier et de déduire leur taux de production. Les fonctions d'excitation expériementales de fusion-évaporation sont comparées avec celles menant aux mêmes noyaux composés obtenus par d'autres combinaisons projectile et cible et avec celles calculées par un code développé au GSI. Ce code permet d'évaluer l'évolution des probabilités de fusion avec l'énergie incidente pour chaque système. La variation des sections efficaces et de la probabilité de fusion est étudiée en fonction des variables macroscopiques et microscopiques des noyaux projectiles et cibles. Dans la synthèse de noyaux super-lourds, ces résultats démontrent quantitativement l'intérêt d'utiliser des partenaires de fusion riches en neutrons d'une part et à couche fermée d'autre part (la section efficace de fusion augmente d'un facteur 9 par paire de neutrons supplémentaires). Par contre, la présence d'une couche fermée dans le noyau composé n'influence pas la section efficace de fusion. Il sera moins difficle de synthétiser des noyaux de Z supérieur à 110 à partir de faisceaux secondaires de projectiles enrichis en neutrons, ce qui permettra aussi d'atteindre les isotopes des noyaux super-lourds proches des vallées de stabilité.

The solution of coupled neutronic/thermal hydraulic nuclear reactor calculations requires the treatment of the nonlinear feedback induced by the thermal hydraulic dependence of the neutron cross sections. As a result of these nonlinearities, current solution techniques often diverge during the iteration process. These instabilities arise due to the low level of coupling achieved by these methods between the neutronic and thermal hydraulic components. In this work, this solution method is labeled the Decoupled Iteration (DI) method, and this technique is examined in an effort to improve its efficiency and stability. An examination of the DI method also serves to provide insight into the development of more highly coupled iteration methods. After the examination of several possible iteration procedures, two techniques are developed which achieve both a higher degree of coupling and stability. One such procedure is the Outer Iteration Coupling (OIC) method, which combines the outer iteration of the multigroup diffusion calculation with the controlling iteration of the thermal hydraulic calculations. The OIC method appears to be stable for all cases, while maintaining a high level of efficiency. Another iteration procedure developed is the Modified Axial Coupling (MAC) procedure, which couples the neutronic and thermal hydraulic components at the level of the axial position within the coolant channel. While the MAC method does achieve the highest level of coupling and stability, the efficiency of this technique is less than that of the other methods examined. Several characteristics of these coupled calculation methods are examined during the investigation. All methods are shown to be relatively insensitive to thermal hydraulic operating conditions, while the dependence upon convergence criteria is quite significant. It is demonstrated that the DI method does not converge for arbitrarily small convergence criteria, which is a result of a non-asymptotic solution approximation by the DI method. This asymptotic quality is achieved in the coupled methods. Thus, not only do the OIC and MAC techniques converge for small values of the relevant convergence criteria, but the computational expense of these methods is a predictable function of these criteria. The degree of stability of the iterative techniques is enhanced by a higher level of coupling, but the efficiency of these methods tends to decrease as a higher degree of coupling is achieved. This is apparent in the diminished efficiency of the MAC procedure. Seeking an optimum balance of efficiency and stability, the OIC technique is demonstrated to be the optimum method for coupled neutronic/thermal hydraulic reactor calculations. / Graduation date: 1994

Aim: The primary aim of this study was to find if there is any correlation between the corneal radius of curvature and its eccentricity. Method: 45 subjects participated in this study, 24 emmetropes, 18 myopes and three hyperopes. All subjects were free of ocular abnormalities and had no media opacities. All the subjects had normal ocular health and good visual acuity of 1.0 or better for both distance and near. The values for eccentricity and corneal radius of curvature were obtained by using a Topcon CA-100F Corneal Analyzer. Results: For the 4.5 mm zone the only significant correlation between corneal radius of curvature and eccentricity was obtained for the mean of the meridian (p = 0.007). On the other hand, we found no significant correlation for the average of two meridians or for meridian 1 and meridian 2 separately in the 8.0 mm zone. Conclusions: We found no correlation between the corneal radius of curvature and the eccentricity for both zones. In addition, no correlation could be found between the spherical equivalent of the refractive errors and the corneal eccentricity. The reason for not finding any significant correlation between the two entities could be due to factors such as smaller sample size and poor distribution of refractive errors in the sample. Moreover, there may be other factors that could influence the overall corneal shape like eye shape, axial length and corneal diameter, which was not evaluated in this study.

The main aim of this research is to survey the general colour scheme for private dwellings inVisby, built 1860–1930. During this period the visual appearance of the town of Visby changedsubstantially, since the increased local production of lime led to the plastering of many woodenbuildings. Which colour schemes were chosen for the different building types of the historic centreof Visby, and which colours came to dominate the time period? The methods used for answeringthese questions have partly been field studies on site and sampling of selected buildings, andpartly critical reading and observation of iconographic material (paintings, drawings, aquarelles,postcards and photographs). The field study includes about 45 objects, in which a number ofsamples are taken from each building element (mouldings, plaster, windows and doors). Thesamples were first analysed ocularly as cross sections. A selection of cross sections have then beenanalysed by means of scanning electron microscopy analysis. The results show a unitary colourscheme, based on earth pigment and carbon black. The dwellings erected during the 19th centuryin Visby, represent a significant part of its building stock, and the lack of scientifically groundedresearches makes implementation of adequate maintenance difficult. It also appears that a largenumber of these dwellings have recently been (or are soon to be) restored, causing a serious lossof primary source of information, as well as affecting town and streetscape with new colourings.

In this paper, we study sections of a Calabi-Yau threefold fibered over a curve by K3 surfaces. We show that there exist infinitely many isolated sections on certain K3 fibered Calabi-Yau threefolds and the subgroup of the N´eron-Severi group generated by these sections is not finitely generated. This also gives examples of K3 surfaces over the function field F of a complex curve with Zariski dense F-rational points, whose geometric models are Calabi-Yau. Furthermore, we also generalize our results to the cases of families of higher dimensional Calabi-Yau varieties with Calabi-Yau ambient spaces.

Rather than emitting pulses, passive radar systems rely on illuminators of opportunity, such as TV and FM radio, to illuminate potential targets. These systems are attractive since they allow receivers to operate without emitting energy, rendering them covert. Until recently, most of the research regarding passive radar has focused on detecting and tracking targets. This dissertation focuses on extending the capabilities of passive radar systems to include automatic target recognition. The target recognition algorithm described in this dissertation uses the radar cross section (RCS) of potential targets, collected over a short period of time, as the key information for target recognition. To make the simulated RCS as accurate as possible, the received signal model accounts for aircraft position and orientation, propagation losses, and antenna gain patterns. An extended Kalman filter (EKF) estimates the target's orientation (and uncertainty in the estimate) from velocity measurements obtained from the passive radar tracker. Coupling the aircraft orientation and state with the known antenna locations permits computation of the incident and observed azimuth and elevation angles. The Fast Illinois Solver Code (FISC) simulates the RCS of potential target classes as a function of these angles. Thus, the approximated incident and observed angles allow the appropriate RCS to be extracted from a database of FISC results. Using this process, the RCS of each aircraft in the target class is simulated as though each is executing the same maneuver as the target detected by the system. Two additional scaling processes are required to transform the RCS into a power profile (magnitude only) simulating the signal in the receiver. First, the RCS is scaled by the Advanced Refractive Effects Prediction System (AREPS) code to account for propagation losses that occur as functions of altitude and range. Then, the Numerical Electromagnetic Code (NEC2) computes the antenna gain pattern, further scaling the RCS. A Rician likelihood model compares the scaled RCS of the illuminated aircraft with those of the potential targets. To improve the robustness of the result, the algorithm jointly optimizes over feasible orientation profiles and target types via dynamic programming.

An accurate and computationally fast method to generate nodal cross sections for the Pebble Bed Reactor (PBR) was presented. In this method, named Spectral History Correction (SHC), a set of fine group microscopic cross section libraries, pre-computed at specified depletion and moderation states, was coupled with the nodal nuclide densities and group bucklings to compute the new fine group spectrum for each node. The relevant fine group cross-section library was then recollapsed to the local broad group cross-section structure with this new fine group spectrum. This library set was tracked in terms of fuel isotopic densities. Fine group modulation factors (to correct the homogeneous flux for heterogeneous effects) and fission spectra were also stored with the cross section library. As the PBR simulation converges to a steady state fuel cycle, the initial nodal cross section library becomes inaccurate due to the burnup of the fuel and the neutron leakage into and out of the node. Because of the recirculation of discharged fuel pebbles with fresh fuel pebbles, a node can consist of a collection of pebbles at various burnup stages. To account for the nodal burnup, the microscopic cross sections were combined with nodal averaged atom densities to approximate the fine group macroscopic cross-sections for that node. These constructed, homogeneous macroscopic cross sections within the node were used to calculate a numerical solution for the fine group spectrum with B1 theory. This new fine spectrum was used to collapse the pre-computed microscopic cross section library to the broad group structure employed by the fuel cycle code. This SHC technique was developed and practically implemented as a subroutine within the PBR fuel cycle code PEBBED. The SHC subroutine was called to recalculate the broad group cross sections during the code convergence. The result was a fast method that compared favorably to the benchmark scheme of cross section calculation with the lattice cross-section generator for two PBR reactor designs.

Cost effective maintenance of pavement sections requires timely preventive maintenance and planned rehabilitation treatments. Knowledge of the increase in condition due to application of treatment and the loss of condition after treatment are essential when deciding the maintenance and rehabilitation treatments. Any error in formulating these values can cause significant changes in recommendations provided. Many researchers have developed pavement performance prediction models; however, less research has been done on the impact of treatment actions on the condition of a pavement section after treatments. The objective of the research is to develop equations, using deterministic empirical method, that predict the increase in pavement condition and rate of decrease in pavement condition after treatment actions with respect to pavement condition just before the treatment. The equations are developed for different treatments and different functional class, and surface type combination to quantify the impact of the treatment for the use in pavement management system. These equations can be used to quantify the effects of different treatments for the use in pavement management system. Numerical illustration is presented using the data from the Metropolitan Transportation Commission-Pavement Management System software developed by the Metropolitan Transportation Commission (MTC) located in Oakland, California. A relation is observed between increase in pavement condition and pavement condition just before treatment for different treatments and different functional class and surface type combination. Hence the equations to determine the trend in increase in pavement condition for different treatments and different functional class and surface type combination are developed. For rate of decrease in pavement condition, due to large variability in the data the loss of pavement condition per year could not be related to pavement condition just before treatment. Hence the equations to determine the trend in loss in pavement condition after treatment could not be developed. The developed equations can be efficiently used to predict increase in pavement condition due to application of the treatment and the loss of pavement condition after treatment.