Physics Commons^™

The Development Of Computational Tools For Halo Analysis And Study Of Halo Growth In The Spallation Neutron Source Linear Accelerator, Dirk A. Bartkoski

Masters Theses

The Spallation Neutron Source (SNS), being built at the Oak Ridge National Laboratory, utilizes a high intensity particle accelerator for neutron production. One of the challenges in SNS, as with all high intensity accelerators, is to minimize the amount of beam lost. High beam losses can cause costly damage and lead to residual activation of accelerator components, which complicates routine maintenance.

One of the key components in beam loss at SNS is the development and propagation of beam halo. Halo particles are those driven to large amplitudes by space charge forces between the beam particles or by mismatch between the …

Applications Of Genetic Algorithms To A Variety Of Problems In Physics And Astronomy, Kevin Richard Williams

Masters Theses

Genetic algorithms are search techniques that borrow ideas from the biological process of evolution. By means of natural selection, genetic algorithms can be employed as robust numerical optimizers on problems that would normally be extremely problematic due to ill-behaved search spaces. The genetic algorithm has an advantage in that it is a global optimization strategy, as opposed to more conventional methods, which will often terminate at local maxima.

The success and resourcefulness of genetic algorithms as problem-solving strategies are quickly gaining recognition among researchers of diverse areas of study. In this thesis I elaborate on applications of a genetic algorithm …

Effect Of Surface Morphology On Adsorption-Induced Bending Of Microcantilevers, Ramya Desikan

Masters Theses

Microcantilevers undergo bending due to molecular adsorption when adsorption is confined to a single surface. The origin of the adsorption-induced force is assumed to be surface stress variation due to molecular adsorption. Single crystal silicon cantilevers were etched for a series of different time periods using two different types of Potassium Hydroxide solutions in order to obtain a rough and a smooth finish on the cantilever surface. Cantilevers that approximately had the same resonance frequency in the rough and smooth etched categories were chosen for comparison in the experiment. Liquid phase adsorption of 1-Do-decan-thiol on the cantilevers having a thin …

Ametropic Eye Modeling, Bo Tan

Masters Theses

Using a commercial optical design software, a general ametropic eye model was constructed based on the measured data of 69 young adults. The experiment data was obtained from 2 published literatures. The correlation between refractive errors of the eyes and their axial lengths, cornea curvatures and intraocular powers was investigated and adopted into the modeling for the first time. The optical performance of the new model eye was evaluated and compared with published aberration data from human eyes. The comparison was performed on both on-axis and periphery vision. High-order wavefront aberrations that include the asymmetric properties of eyes and the …

Investigating Keratoconus Using Optical Eye Modeling, Kevin Charles Baker

Masters Theses

Keratoconus (KC) is a corneal atrophy which causes a conical extrusion (cone). It is often misdiagnosed as optical defocus with astigmatism. In this thesis, computer KC eye models for various conditions are constructed. Using the KC eye model the influence on visual performance including the consequent refractive errors and the higher-order aberrations of KC eyes was investigated. The affects of cone shape, dimension (volume), and location on visual performance are also discussed. The modeled KC eyes are additionally used to evaluate the performance of a common eye vision-screening instrument. The simple photorefraction (PR) technique uses only one small light source …

A Stark-Effect Modulator For Co2 Laser Free-Space Communications, Ryan Lane Holloman

Masters Theses

A Stark-effect modulator prototype has been designed and constructed to transmit an RF signal upon an infrared carrier wave produced by a CO₂ laser. The anticipated future use of this prototype will be to integrate it into an all-weather long-wavelength infrared (LWIR) free-space communication link. This communication system is expected to be capable of operation at 2.5 Gbits/sec over a range of >6 kilometers. The Stark-effect modulator prototype is ideal to replace existing microwave and radio communication links used currently. Also, the Stark-effect modulator is a better choice than electro-optic crystal modulators and acousto-optic Bragg cell modulators because it …

Raman Under Ln2: A Simple Approach To Low Temperature Raman Spectroscopy, E. Darren Ellis

Masters Theses

Conventional low temperature Raman Spectroscopy techniques utilize expensive equipment to cool a sample to 77˚ K. In this work, a new technique for performing Raman Spectroscopy at liquid nitrogen temperatures is presented. This technique of taking data with the sample placed under liquid nitrogen provides a low cost alternative to conventional methods, and can be utilized by any lab with a Raman spectrometer without the purchase of additional equipment. Representative spectra for CCl₄, C₆₀, and Single Wall Carbon Nanotubes at room temperature and under liquid nitrogen are shown and compared as validation of the utility of …