Fundamental Studies of Positron Scattering from Atoms and Molecules

This thesis presents measurements of low-energy positron scattering from Argon and C60. Absolute elastic differential cross sections are presented for positron scattering from Argon in the energy range 2 to 50 eV, as well as absolute total elastic and inelastic cross sections up to 20 eV. These results are compared with theoretical calculations using the convergent close-coupling (CCC) and relativistic optical potential (ROP) methods and it was found that generally the measurements were in closer agreement with the CCC method than the ROP method across the energy range, although the ROP method was an excellent description of the total inelastic cross section in this energy range. Argon was also the focus of the first results from the newly developed positron reaction microscope. Experimental techniques were developed to produce measurements of the kinematics of positron-induced single ionisation of Argon. Single ionisation events were detected in coincidence and their momenta reconstructed using data analysis methods detailed in this thesis. Although further work is required to provide total differential cross sections, the initial data presented in this thesis is in alignment with expectations based upon available theory and experiment and provides a promising starting point for future studies using the positron reaction microscope. Finally, a search was conducted for resonant features in the total scattering and Positronium formation cross sections of C60. Motivated by the predictions of Gianturco and Lucchese (1999), which indicated experimentally-accessible resonances, the present data does not show any features. However, the current results in this thesis represent the first preliminary measurements of the total scattering and Positronium formation cross sections for C60 and follow the expected trend for positron-molecule scattering. Additional data to be collected in the future, would allow for confirmation of the presence, or lack thereof, of resonant features with a higher statistical confidence

P1_4 The Importance of Absorption Corrections in Quantitative Transmission Electron Microscopy

This article discusses the effects that absorption has on quantitative transmission electron microscopy and assesses the validity of the assumption that such effects can be neglected if the specimen thickness is below 100nm. Calculations of the absorption correction factor are made for the example case of healthy soft tissue. The threshold thicknesses at which the absorption becomes significant are found to be 150nm and 180nm for Carbon and Nitrogen respectively (with Oxygen as the comparison element). It is concluded that 100nm is an acceptable thickness assumption based upon this evidence, although for other elements the threshold thicknesses will be different. It would also be advisable to consider absorption effects when there is a large level of uncertainty in the thickness, a common occurrence in such experiments

P1_7 Foetal Ultrasound Imaging Safety in Early Pregnancy

This article discusses the temperature increase of foetal soft tissue due to diagnostic ultrasound scans taken during the early stages of pregnancy. It is found that for standard foetal ultrasound frequencies of 3MHz-5MHz, cell development in the foetal tissue is only affected after scans lasting 600-1000s. Transducer motion is considered and it is demonstrated that the time a small piece of foetal tissue will be exposed to ultrasound heating for is unlikely to be this high. Therefore, it is concluded that there is no danger to the foetus due to heating by standard diagnostic foetal ultrasound imaging.Â

P1_3 The Aerodynamics of Pterodactyl Flight

This article discusses the aerodynamic feasibility of pterodactyl flight. The different situations of gliding and flapping are covered, and the perils of a stalling wing introduced. It is concluded that, assuming a similar build to a modern wandering albatross, the pterodactyl could have glided through the air if the wind was strong enough, but would have fallen if required to flap its wings in a gentle wind

P1_8 Turbulence, Atherosclerosis and the Carotid Bruit

This article discusses turbulence in the human carotid artery, its links to narrowing of the artery due to atherosclerosis and the amplitude of the carotid bruit. The Reynolds number at the narrowest part of the artery is found as a function of the degree of stenosis which is then related to the amplitude of the carotid bruit. It is demonstrated that the amplitude of the bruit could be used as an estimate of the degree of stenosis of the artery

P1_5 The Megapixel Limit

This article discusses the megapixel (MP) limit for a camera- the point at which the resolution of the print matches that of the eye. The limit is calculated for normal sight and for the best possible sight. It is found that for print sizes from 6x4â€-18x12†the megapixel limit is 8.61-71.31MP (best sight) and 2.90-23.99MP (normal sight). The variation of the megapixel limit with viewing distance is also addressed; for an 18x12†print the megapixel limit drops below 1MP for viewing distances above 2m. Some factors affecting the visual acuity of an eye are given, and their potential effects on the MP limit mentioned.Â

P1_2 The Deflection of Bullets Using Magnetic Fields

This article demonstrates how low strength magnetic fields can be used to curve the trajectory of a moving particle, requiring a field in the order of 10-9T to loop an electron.  The theory is expanded to investigate whether such an arrangement would curve a bullet at its maximum velocity, in order to investigate the feasibility of using the magnetic field as a form of defence for an object.  It is found that the magnetic field strength required is ~1018T, far too high to have any practical use

P1_9_Powering_Nanobots_with_Body_Heat

This article discusses the feasibility of using variations in the human body temperature to power a medical nanobot. It is found that thermal energy gained from a Carnot cycle process is not sufficient to power a typical nanobot. A typical medical nanobot requires 1x10-9W, the model outlined here finds that the maximum power a nanorobot can gain is 5.7x10-17W. Under normal circumstances the power gain is only 2x1016W. Thus it is concluded that this process is not sufficient to act as the sole power source for such a nanorobot

P1_1 A New Form of Public Transport: The Pneumatic Tube Train

Public transport via a system of pneumatic tubes is discussed and the physical principles surrounding its operation are outlined. The safety considerations inherent in such a design are briefly assessed and initial safe operating parameters are suggested

P1_6 Escaping a Fire Using a Mattress

This article considers the net energy of a body jumping from a first floor window onto a mattress below, comparing it to the energy needed to break a leg bone. It is found that the final energy of the body after landing is 2738.5J, and calculations show that it takes 385.71J to break two legs. Therefore a mattress does not absorb enough energy to avoid injury