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This thesis deals with string theory at finite temperature. String theory has attracted considerable attention in recent years because of its ability to unify the fundamental forces and particles in nature and provide a quantized description of gravity. However, many aspects of this theory remain mysterious, including its behavior at high temperature. One guiding principle for finite temperature string theory is the observation that a quantum theory at finite temperature can be recast as a zero-temperature theory in which a Euclidean time dimension is compactified on a circle. This temperature/radius correspondence holds in quantum mechanics as well as quantum field theory, and is normally assumed to hold in string theory as well. However it was shown recently that this correspondence fails for a class of string theories, called heterotic strings. This motivates a search for an alternate way to restore this correspondence, as well as a reevaluation of the thermodynamic behaviour of other classes of string theories, namely Type~II and Type~I. We find that contrary to the established wisdom, all ten dimensional string theories have a similar behaviour at finite temperature. This also leads us to the conclusion that the Heterotic and Type~I theory behave in a dual way at finite temperature.

<p> A single electron in a quantum cyclotron provides the most precise measurement of the electron magnetic moment, given in units of the Bohr magneton by <i> g</i>/2 = 1.001 159 652 180 73 (28) [0.28 ppt]. The most precise determination of the fine structure constant comes from combining this measurement with Standard Model theory, yielding &alpha;^-1 = 137.035 999 173 (34) [0.25 ppb], limited by the experimental uncertainty of the electron <i> g</i>-value. The most stringent test of CPT symmetry in leptons comes from comparing the electron and positron magnetic moments, limited by the positron uncertainty at 4.2 ppt. A new high-stability apparatus has been built and commissioned for improved measurements of the electron and positron magnetic moments, a greatly improved test of lepton CPT symmetry, and an improved determination of the fine structure constant. These new measurements require robust positron loading from a retractable radioactive source that is small enough to avoid compromising the high-precision environment of our experiment. The design and implementation of such a scheme is a central focus of this work. Robust positron loading at a rate of 1-2 e⁺/min from a 6.5 &mu;Ci ²²Na source has been demonstrated.</p>

Reducing secondary leakage is a common challenge in numerous machines, particularly in steam and gas turbines. Too large leakage in seals produces a substantial loss in efficiency and power delivery with an increase in specific fuel consumption. Various seal types exist, each with unique advantages and disadvantages as per leakage, power loss, and wear. Labyrinth seals are most common due to their simple design and low cost. Their main drawback is a too high leakage due to enlarged (worn) clearances when a rotor vibrates. More complicated seal types, such as brush seals can withstand rotor excursions and ensure lower leakage rates than with labyrinth seals. Brush seals utilize a bristle bed which contacts the rotor and wears out thereby reducing leakage performance. The HALOTM seal, an all-metal seal with flexibly supported shoes, is engineered as a clearance control seal to reduce leakage even more, in particular for operation with high pressure differentials and with high surface rotor speeds. Static leakage tests with hot air at a high temperature (max. 300°C) conducted in a test rig holding a labyrinth seal and a novel all-metal seal (HALOTM seal), both of the same diameter, length and clearance, show the novel seal leaks ~1/5 the flow of a labyrinth seal for pressure ratios (Ps/Pa) > 3.5. The savings in leakage are maximized during operation at high pressure differentials. Leakage measurements with a rotor spinning to a maximum speed of 2,700 rpm (surface speed = 23.6 m/s) produce a slight decrease in leakage with increasing rotor speed. The research product is a reliable leakage data base enabling the application of a state of the art sealing technology that increases system efficiency by reducing leakage and extends maintenance intervals by eliminating wear of components.

The metallic single electron transistor (SET) has been shown to provide charge sensitivity on the order of 10-6 e/(Hz)1/2, when operated as a charge amplifier. This makes it an ideal candidate for low-noise measurement schemes, such as monitoring nano-mechanical oscillations, or reading out the charge state of a quantum bit. The SET operates by exploiting quantum tunneling across an ‘island’ between two insulating tunnel junctions, and can be modulated by a capacitively coupled gate electrode. A metallic SET has been fabricated and characterized at low frequencies. The device was fabricated on a silicon substrate coated with a bi-layer resist, using electron beam lithography. The Al-AlOx¬-Al tunnel junctions were created using double angle evaporation. Samples were tested near 300 mK in a custom helium-3 cryostat system. Results which characterize the SET parameters and conductance behaviour were obtained, in both the superconducting and normal states. This thesis contains a discussion of the fabrication procedures and dc measurement techniques required to produce and test a single electron transistor. Relevant background theory relating to SET operation and cryogenic laboratory techniques is presented. A brief discussion of proposed future experiments using a dual gate radio frequency SET as a more sensitive amplifier is introduced. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2007-08-01 14:07:55.427

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