The formation of a molecular beam using a miniature supersonic nozzle source is discussed. The results of operation at room, liquid nitrogen and liquid helium temperatures of a supersonic nozzle system designed for use in a polarized helium³ ion source are presented. It is shown that helium⁴ beam intensities at 4.2ºK are approximately 1/8 of those at 300ºK. Factors upon which the beam intensity depend have been investigated experimentally and it is found that at room temperature and a distance of 16cm from the skimmer a heliun⁴ beam intensity of 3x10¹⁶ molecules/cm²/sec is attainable under certain circumstances. This beam intensity is an improvement by a factor of 10 over the original performance of the nozzle source. Assuming a 40% transmission through the magnet and a 0.25% ionization efficiency an ion current of 0.02 microamperes is estimated for the polarized helium³ ion source. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is to determine the shear capacity of a reinforced concrete beam column connection at zero moment. The joint under study is formed by casting the beam against a smooth column face with the top and bottom reinforcing bars projecting through the joint and no key or surface roughening provided. The variables considered are the size of reinforcing bars and the distance to the first beam stirrup. The strength of the joint is broken down into components of a) top dowels b) bottom dowels and c) interface bond and friction. The components and the entire joint strength are investigated theoretically and experimentally. Comparisons of both theoretical and experimental results are compared and show that the strength of the joint can be predicted from the sum of the top and bottom dowel strengths. The strength of this beam column connection is shown to provide adequate strength and a method is suggested for calculating the shear capacity of the joint. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A comparison is made between the experimental and theoretical behaviour of the H" beam in the TRIUMF central region cyclotron. The axial injection process and the first six accelerated turns are studied in detail. In order to optimize the cyclotron performance the phase space emittance of the beam at the injection line exit must be matched to the central region acceptances. To this end,a theoretical study was made of the ion optical properties of the injection elements: the magnet bore, the spiral electrostatic inflector, the electrostatic deflector and the first radio-frequency accelerating gap. In many cases these results were confirmed by experimental observations. It was also shown theoretically that by a suitable choice of the accelerating gap, under optimum conditions, 10% of the injected beam can be directed within the radial acceptance and 30% within the vertical acceptances. The effects of a chopper and buncher in the injection line were also measured. A minimum pulse length of approximately 2.5 nsec was obtained with a bunching factor of 3-0. To accelerate a beam to full radius, vertical steering had at first to be provided by means of asymmetrically-powered trim coils and electrostatic deflection plates for each turn. The steering required is known to be consistent with the effects of magnetic field asymmetries and dee misalignments measured later. The size and shape of the vertical beam envelopes were found to be consistent with theory. The vertical tune vz was estimated to be 0.17 ± 0.03 for 20 deg phase ions. This agreed with the predicted value of 0.17- The transition phase which separates the vertically-focused and defocused phases was estimated to be -3 ± 3 deg, while the predicted value was 0 deg. The radial beam diagnostic techniques used for determining proper centring and isochronous operating conditions are discussed. With these techniques it was possible to centre a 30 deg phase interval to within 0.15 in., which was the approximate uncertainty in our measurements. A simplified treatment of radia 1 - longitudinal coupling is given and used to explain qualitatively the behaviour of a small emittance beam. The effects of space charge on the first six accelerated turns are calculated. For a beam occupying a phase width of 30 deg, these effects are predicted to be negligible for average accelerated currents below 100 uA. The experimental observations made on high-current beams are described.; prior to the shutdown of the cyclotron beams of up to 1^0 uA average current were accelerated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The purpose of this investigation was to compare the behaviour of real prestressed concrete columns to the predictions of a mathematical model. A previously developed computer programme, based on the mathematical model, had suggested several problems which needed examination. The programme indicated that, in some circumstances, an unstable equilibrium configuration could occur. The existence of this unstable loading path meant that a snap-through type of buckling was a possibility. To check these hypotheses, six T-shaped prestressed concrete columns were constructed and tested at the University of British Columbia. In most instances, experimental observations closely matched the predictions of the mathematical model. The computed and observed peak loads compared well and the presence of an unstable equilibrium path was confirmed. Unfortunately, attempts to measure curvatures and to compare them with mathematically obtained values were unsuccessful. No satisfactory explanation for this problem was found. Having established the validity of the mathematical model through the experimental programme, an examination of snap- — through buckling was made. It was concluded that prestressed concrete columns are not prone to snap-through buckling, although sufficient additional energy applied to a column might result in a jump from a stable equilibrium configuration to an unstable one. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Skin collimation in electron therapy ensures sharper penumbra and maximal protection to adjacent critical structures. It also provides a better clinical dose to the target and avoids recurrences at the periphery. The thickness of the electron skin collimation must be adequate for shielding purposes, not too thick to cause discomfort to the patient and be conformal to the skin. This study assessed the clinical potential of machined brass skin collimation with variable thickness. Brass transmission factors for 6, 9, and 12 MeV electron beams were measured and used to determine the skin collimation clinically acceptable thickness. Dosimetric performance of the variable thickness skin collimation was evaluated for 9 MeV electrons within a rectilinear water-equivalent phantom and a water-filled head phantom. Results showed the variable thickness skin collimation is dosimetrically equivalent to the uniform thickness collimation. Favorable dosimetric advantages for brass skin collimation for small electron fields were achieved. / Includes bibliography. / Thesis (PMS)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Much of the work done on active and passive constrained layer beams is done with mathematical models proposed by Kerwin and extended by DiTaranto, Mead and Markus, and others. The mathematics proposed by these early researchers was tailored to fit the damping treatments in use at that time: thin foil damping tapes applied to panels for noise reduction. A key assumption was that all layers had identical transverse displacements. While these assumptions are reasonable when the core layer, normally a soft viscoelastic material(VEM), is thin and the constraining layer is weak in bending, there are many situations in industry and in the literature where the ``Mead and Markus'' (MM) assumptions should be questioned. An important consequence of the MM modeling assumptions is that the strain energy in the VEM core is dominated by shear strain, and this in turn means that only the shear modulus is of primary importance. This is fortunate since only the shear modulus is available to engineers for viscoelastic materials used for layered damping treatments. It is a common practice in industry and academia to simply make an educated guess of the value of Poisson's ratio. It is shown in the dissertation that this can result in erroneous predictions of damping, particularly in partial-coverage configurations. Finite element analysis is used to model both the MM assumptions and a less-restrictive approach commonly used in industry. Predictions of damping from these models are compared against models with elements from C0 elements and a C1-capable element that matches tractions at material interfaces. It is shown that the time-honored modal strain energy method is a good indicator of modeling accuracy. To assess the effects of the MM assumptions on an active PZT used as a constraining layer, closed-loop damping versus gain is determined using both the MM and higher order elements. For these analyses, the time-dependent properties of the viscoelastic material are represented by a Maxwell model using internal variables. Finally, the basic MM premise that all layers share the same transverse displacement is disproved by experiment. / Ph. D.

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