On perturbative field theory and twistor string theory

It is well-known that perturbative calculations in field theory can lead to far simpler answers than the Feynman diagram approach might suggest. In some cases scattering amplitudes can be constructed for processes with any desired number of external legs yielding compact expressions which are inaccessible from the point of view of conventional perturbation theory. In this thesis we discuss some attempts to address the nature of this underlying simplicity and then use the results to calculate some previously unknown amplitudes of interest. Witten's twistor string theory is introduced and the CSW rules at tree-level and one-loop are described. We use these techniques to calculate the one-loop gluonic MHV amplitudes in N=1 super-Yang-Mills as a verification of their validity and then proceed to evaluate the general MHV amplitudes in pure Yang-Mills with a scalar running in the loop. This latter amplitude is a new result in QCD. In addition to this, we review some recent on-shell recursion relations for tree-level amplitudes in gauge theory and apply them to gravity. As a result we present a new compact form for the n-graviton MHV amplitudes in general relativity. The techniques and results discussed are relevant to the understanding of the structure of field theory and gravity and the non-supersymmetric Yang-Mills amplitudes in-particular are pertinent to background processes at the LHC. The gravitational recursion relations provide new techniques for perturbative gravity and have some bearing on the ultraviolet properties of Einstein gravity.Comment: 123+56 pages, 29 figures, uses axodraw.sty; PhD thesis. v3: Reference added, appendix update

Demographic change and employment in the Central North Island, 1986-1996

This paper examines some dimensions of demographic and economic change in a region which is generally considered to be one of the most productive and affluent parts of New Zealand’s “heartland”. The paper highlights considerable demographic and economic diversity within the Central North Island. This is a complex region in terms of its population composition, its mix of rural and urban places and industries, and its linkages to other parts of New Zealand’s society and economy. The consistently poorer performance found in a wide range of indices of social and economic change in this part of New Zealand is very sobering

Flexible magazine operation and cellular techniques in automation systems

There is a strong current trend in automation towards These often systems that can handle small to medium batch sizes are also often associated with In prototyping situations. Batch numbers High complexity the application described Is for British Airways Heathrow Airport where the number of variations pattern of their meal trays Is large. The batch size the assembly variations Is also extremely variable. Catering at in assembly of each of This thesis describes the justification and design of anautomatic system to assemble these trays whilst retaining the flexibility Inherent In the current manual assembly arrangement.The work examines system layouts. Considering each possibility particularly from the flexibility and potential reliabilityaspects. This leads to the consideration of Industrial robots because of their Inherent flexibility. Consequently the variousconfigurations of robots are examined to assess the suitability of each In a cell arrangement the system which was chosen forIts potential reliability. The work continues by developing the Ideas and techniques of parts feeding to realise the maximumbenefits from a robotic cell system." The thesis describes novel magazining arrangements for handling each of the Items which make. up the tray assembly. Two major developments are described. one for the handling of stackable Items and the other for handling small discrete parts from bulk. Both systems are flexible to accomodate variations In part dimensions and possess ability to be quickly re-configured - to handle completely different parts. The equipment designed and constructed for British Airwaysuses Ideas that could also find use In many similar applications where the components have the same characteristics

The evaluation of hollow core, sliced, and solid large round hay bales

Three bale-package types, hollow core, solid, and sliced large round hay bales, were evaluated. An experiment was conducted to determine differences among package types for temperature buildup during curing and nutritional losses during storage. Also, the amount of energy required to tub grind each bale type was measured. Third-cutting alfalfa hay was baled at two moisture content levels into the three bale types and was left outside for 36 days immediately after baling for curing. After curing, most bales were moved inside for the remaining six months of storage; however, five bales were left outside for comparison of differences in nutrient losses for inside and outside storage. Temperature buildup during curing was minimal in the 15% moisture treatment. The hollow core bales had significantly lower temperature than other bales (p\u3c0.05). In the 20% moisture treatment, no differences were found (pKO.05). The bale temperatures of the 20% moisture treatment were significantly higher than the ones of the 15% moisture treatment. Moisture content and density of bales in the 15% moisture treatment were different from that of bales in the 20% moisture treatment. Hollow core bales packaged at 15% moisture content exhibited lower moisture contents and densities than any other bale packages or moisture treatments. Nutritional losses of the 20% moisture content treatment bales stored inside and of outside stored bales were significantly greater than those of the 15% moisture bales stored inside (p\u3c0.05). There were no differences in nutritional losses among bale packages. Bales stored outside lost the greatest amount of nutritional value iv (p\u3c0.05). There were no statistical differences of nutritional losses among bale package types at any moisture level or storage treatment. The number of bales available for grinding was too few to show any significance in the amount of energy required to grind each bale type (p\u3c0.05)

Neuro-electromagnetic imaging of the human visual cortex

Methods of solving the neuro-electromagnetic inverse problem are examined and developed, with specific reference to the human visual cortex. The anatomy, physiology and function of the human visual system are first reviewed. Mechanisms by which the visual cortex gives rise to external electric and magnetic fields are then discussed, and the forward problem is described mathematically for the case of an isotropic, piecewise homogeneous volume conductor, and then for an anisotropic, concentric, spherical volume conductor. Methods of solving the inverse problem are reviewed, before a new technique is presented. This technique combines prior anatomical information gained from stereotaxic studies, with a probabilistic distributed-source algorithm to yield accurate, realistic inverse solutions. The solution accuracy is enhanced by using both visual evoked electric and magnetic responses simultaneously. The numerical algorithm is then modified to perform equivalent current dipole fitting and minimum norm estimation, and these three techniques are implemented on a transputer array for fast computation. Due to the linear nature of the techniques, they can be executed on up to 22 transputers with close to linear speedup. The latter part of the thesis describes the application of the inverse methods to the analysis of visual evoked electric and magnetic responses. The CIIm peak of the pattern onset evoked magnetic response is deduced to be a product of current flowing away from the surface areas 17, 18 and 19, while the pattern reversal P100m response originates in the same areas, but from oppositely directed current. Cortical retinotopy is examined using sectorial stimuli, the CI and CIm ;peaks of the pattern onset electric and magnetic responses are found to originate from areas V1 and V2 simultaneously, and they therefore do not conform to a simple cruciform model of primary visual cortex

Ruppeiner theory of black hole thermodynamics

The Ruppeiner metric as determined by the Hessian of the Gibbs surface provides a geometric description of thermodynamic systems in equilibrium. An interesting example is a black hole in equilibrium with its own Hawking radiation. In this article, we present results from the Ruppeiner study of various black hole families from different gravity theories e.g. 2D dilaton gravity, BTZ, general relativity and higher-dimensional Einstein-Maxwell gravity.Comment: 10 pages, 1 figure. Talk given by N Pidokrajt at ERE2006 in Palma de Mallorca, Spai