Decays of light, pseudoscalar mesons into lepton pairs are one possible way of detecting physics beyond the Standard Model. This thesis will focus on the η' → e+e- decay, because only few experiments have studied this decay. By the use of a basic simulation, the feasibility of conducting a search for the  η' → e+e- decay at DAΦNE, a electron-positron collider in Frascati, Italy, was investigated. The simulation implements an idea from previous experiments, where the η' decay was investigated through the e+e- → η' → X process. The results of the simulation show that experiments at DAΦNE could produce an observable signal of the process when the produced η' decays into one of the most probable decay modes. However, in order to draw a definite conclusion, a more detailed study is needed. / Sönderfallet av lätta, pseudoskalära mesoner till ett par av leptoner är ett möjligt sätt att detektera fysik bortom Standardmodellen. Detta examensarbete fokuserar på η’ → e+e- sönderfallet, på grund av att få experiment har studerat detta sönderfall. Genom att använda en enkel simulering, undersöktes möjligheten att studera η’ → e+e- sönderfallet vid DAΦNE, en elektron-positron accelerator i Frascati, Italien. Simuleringen följde samma genomförande som tidigare experiment, där η’ sönderfallet undersöktes genom e+e- → η’ → X processen. Resultaten av simuleringen visar på att experiment vid DAΦNE kan producera en detekterbar signal av processen då de producerade η’ sönderfaller till de mest troliga sönderfallen. På grund av begränsningarna i den utförda simulationen, behöver dock en mer detaljerad studie göras för att dra definitiva slutsatser.

This thesis describes the experimental study of electron scattering processes from laser-excited barium and ytterbium atoms. These include the electron-impact ionization-excitation from Ba (...6s6p) 1P1 and Ba (...6s5d) 1,3D1,2 to Ba+ (...6p) 2P3/2, the elastic electron scattering from Ba (...6s6p) 1P1 and Ba (...6s5d) 1,3D1,2, and the electron-impact excitation from Yb (...6s6p) 3P1 to Yb (...6s7s) 3S1, Yb (...6s6p) 1P1, and Yb (...6s5d) 3D1,2,3. The experiments utilized electron impact energies in the range of 5 eV to 50 eV. Differential and integral scattering cross sections were determined, and are presented both on absolute and relative scales. By controlling the laser polarization, alignment and orientation parameters characterizing the scattering processes were determined. Additionally, the barium ionization-excitation study observed polarization dependencies of ion line emission fluorescence for radiative decay from Ba+ (...6p) 2P3/2 to Ba+ (...6s) 2S1/2, providing information about the final ionic state composition. Along with experimental measurements of electron-atom collisions, this thesis describes the design and development of a computer-controlled data acquisition system and a laser frequency stabilization system.

The development of a neural network based electron finder designed for the ZEUS calorimeter is described. A study of elastic and inelastic J/ψ meson production in electron-proton collisions at HERA using the ZEUS detector is presented. During the 1993 and 1994 running periods, the ZEUS detector collected ~ 500 nb^-1 and ~ 3 pb^-1 of data respectively. The direct inelastic J/ψ photoproduction cross-section is measured for both running periods and an attempt is made to extract the gluon density inside the proton using the 1994 inelastic J/ψ sample.

This thesis is concerned with non-adiabatic effects in alkali/halogen collision systems. After a general survey of non-adiabatic molecular collision theory, and its application to such systems, calculations have been performed relating to three topics : (i) Vibrational energy distributions resulting from electron transfer collisions between alkali metal atoms and halogen molecules are often treated by the multi-curve crossing approach to the classical path approximation, in the form of two approximations, one valid at high collision energy, the other at low energy; the performance of these is evaluated over a wide energy range by comparison with the results from an "exact" multi-curve crossing approach. (ii) Classical trajectory calculations for reactive alkali / halogen collisions are performed using a simple ionic potential energy surface, developed earlier to model the weakening of the halogen bond by the metal ion immediately after the electron transfer. Detailed comparison is made between the results and those from experiment; good agreement is obtained for K/I₂ and comparison of the results for K/I₂ and Cs/I₂ indicates that this effect is not merely dependent on the charge of the ion. (iii) The population of ground and excited sodium atoms resulting from Na/I charge neutralisation collisions is investigated using the multi-curve crossing approach. Although it has been suggested that population inversions may be produced by such a process, it is shown that this is only possible at extremely high collision energies.

This thesis presents a new set of methods to assist the process of ship design for safety with particular reference to collision damage. The study has two principal objectives: " investigations into subdivision aspects of passenger ships to improve their overall survival index " investigations into the subdivision of oil tankers in order to improve the effectiveness against spillage in the event of collision damage. In order to investigate the ship subdivision aspect a damage stability model was needed. A pre-requisite for developing the damage stability software was a robust but flexible method to define the hull and the compartments of subdivision. B-splines have been a popular representationatl ool in computer aided design over the past three decades.T his method, though more complex than other spline techniques such as cubic splines, was adopted with a fourth order basis function in this work. A complete set of spline manipulation libraries and associated numerical solvers were developed for this purpose. In addition to this, a method to define the intersection between the hull and the waterplane in the form of a closed B-spline curve for any given orientation of the vessel in terms of -heel, trim and draught was developed to aid the damage stability calculations. Though the earlier regulations stipulate fixed trim assessments to ease the computational process, it is clearly unsatisfactory and research has confirmed this to be a flawed approach. Free trim calculations on the other hand require an iterative and time consuming process to arrive at the equilibrium trim position for each heel angle. Pawlowski proposed a new method for the stability calculations of a freely floating rig when the unit is arbitrarily orientated to the wind direction. It uses the Euler theorem on the properties of equivolume waterplanes to arrive non-iteratively at the new inclined position. This theory was adapted for use in damage stability calculations and was numerically tested and proved to be sound. Damage stability calculations, though combinatorially large, are also inherently parallel. Parallel Virtual Machines (PVM) is a Message Passing Interface (MPI) developed jointly by ORNL, University of Tennessee, Carnegie Mellon University and the Pittsburgh Supercomputing centre. PVM enables a "virtual configuration" so that a collection of serial, parallel and vector processing machines appear as one large distributed memory computer. PVM was compared with another MPI called Network Linda where the advantage of PVM's user controlled message passing was demonstratedP. VM was used to implement the MJMD Distributed Memory paradigm to exploit this inherent parallelism in damage stability calculations and to obtain speedups. A systematic exploration of the search space for this design problem involves the generation of a large number of internal subdivision configurations. This, coupled with the fact that the design space was multimodal in nature made it suitable to the application of a class of heuristic search algorithms called Genetic Algorithms (GA). A brief description of the mechanisms behind GA is presented along with their mathematical basis in the form of two theorems: the schema theorem and the building block hypothesis. Various techniques for solving constrained optimisation problems with GA was explored. The penalty function method was found to be the most suitable and was finally adopted. The above techniques were applied to the optimisation. of the internal subdivision of passenger ships and cargo ships, oil tankers in particular. For passenger ships, the nature of the 's'-factor formulation on the local index was shown. The multimodal nature of the subdivision problem was highlighted and a GA was used to investigate the optimal subdivision characteristics of the vessel. The 's' factor formulation for cargo ship rules is different to that described by the A. 265 set of regulations for passenger vessels. In addition, the cargo ship rules describe a factor V which accounts for the probabilities of vertical extents of damages. However this formulation does not assign any credit for horizontal subdivision below the waterline. Data on vertical extents and vertical location of damages for cargo ships was collected and analysed in earlier studies done at Newcastle University. This data was used to develop a probability function akin to that developed for the longitudinal extent and longitudinal location so as to give credit for any horizontal subdivisions. The principal objective of this part of the study was to explore the search space for subdivision configurations that would minimize net oil outflow.

No description available.

No description available.

Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2001.

In the last twenty years, electron-atom scattering theory has witnessed significant theoretical developments. One of these advances is the use of the momentum-space convergent closecoupling approach to fully incorporate target atom continua. This theoretical framework is based on the momentum-space Lippmann-Schwinger equation, an integral form of the Schrodinger equation. Although the approach has been highly successful in its application to atomic scattering theory, computing numerical solutions is inherently difficult because the momentum-space LS equation is a singular integral equation. Standard numerical integration techniques are normally employed to solve the problem and as computing power has increased, calculations have improved. However, there remains the problem of the integral's singular nature, which demands complicated methods for selecting integration points, particularly near the energy-dependant singularity. The rotated-contour method uses a conlplex-variable approach that solves the momentum-space LS equation by integrating along a deformed contour in the complex momentum plane away from the singularities. This method has the potential for simplifying the numerical integrations associated with the close-coupling equations. A rotated-contour method is first applied to a simple scattering model - electron scattering from the Yukawa potential. This gives some insight into the difficulties that arise when calculating potential matrix elements for complex momenta. The method is then applied to the s-wave model of the electron-hydrogen scattering problem and finally, the full problem. Existing FORTRAN software written to solve the momentum-space LS equations for electron-hydrogen scattering using standard techniques has been converted to C++. Extensive modification of the code has resulted in a flexible Windows-based program with a graphical user interface that runs on any modern computer using PC architecture. The program can calculate results using either a conventional method (no rotation) or a rotatedcontour method. Using a rotated-contour method to solve the momentum-space LS equations necessitates detailed knowledge of the analytic nature and singularity structure of the coupled channels potentials. This is achieved through the extensive use of the computer symbolic algebra system Maple to compute closed-form solutions for the direct potentials and for a range of partial-wave direct and exchange potentials. It is found that logarithmic branch point singularities are present on the real momentum axis for an extensive class of partial-wave direct-potential matrix elements. The analysis reveals that arotated contour method cannot be applied to the full atomic scattering problem due to these analytic problems which are associated with the long-range nature of the Coulomb potential.

This dissertation work is a study of positronium formation for positron-hydrogen and positron-helium collisions in the Ore gap (the energy region between the threshold for ground-state positronium formation and the first excitation level of the target atom) using variational K-matrices. We have fitted the K-matrices using multichannel effective range theories and using polynomials. Using the variational K-matrices and their fits, we have located zeros in the positronium-formation scattering amplitude and corresponding deep minima in the positronium-formation differential cross section. The zeros are related to the vortices in the extended velocity field associated with the positronium-formation scattering amplitude. For positron-hydrogen collisions, we have found two zeros in the positronium-formation scattering amplitude, and corresponding deep minima in the positronium-formation differential cross section, while we have obtained a zero in the positronium-formation scattering amplitude for positron-helium collisions. We have connected the zeros in the positronium-formation scattering amplitude to vortices in the extended velocity fields. Our work shows that vortices can occur for charge exchange in atomic collisions.