Most Popular Books by Andrew Davidson

The extraordinary story of a young doctor who in 1914 illegally took his camera to war. This book shows his remarkable photographs for the first time and offers an unusually intimate portrait of life among a band of brothers. It also examines just how ill-prepared Army doctors were for the carnage they faced, and asks, how did they cope?

2000 all-action, Dino Supersaur stickers for hours of stickering fun! This book is packed with scenes to fill with stickers, as well as sticker-and-doodle pictures to complete and inventive puzzles and activities. Children will love using the cartoon sound effects and speech bubble stickers to complete the comic strips and make the superpowered dinosaur goodies and baddies burst into life.

Theory predicts that when prey can reach a size refuge from predation, prey vulnerability to predation is a function of hatchling size, growth rate, and the handling limitations of its predator, which collectively influence the amount of time prey spend vulnerable. I examined the mechanistic role of prey size for the predator-prey interaction between predatory crayfish (Procambarus fallax) and apple snail prey (Pomacea paludosa and P. maculata) and found that crayfish feeding rates decreased with snail size, such that smaller hatchling P. maculata were more than twenty times more vulnerable than hatchling P. paludosa. Experimental manipulations of productivity increased apple snail growth rates, reducing the effects of predatory crayfish on P. maculata survivorship, but not P. paludosa survivorship. My results indicate that when prey can reach a size refuge from predation, increased system productivity decreases predator limitation of that prey.

The studies described here coalesce around the application of using nanomaterials as X-ray sensitizers for the treatment of cancers and elucidate several important principles regarding this topic. Specifically in this work the interaction of X-rays with nanomaterials is explored through simulations and experiments to better characterize the potential applications of nanomaterials as radiosensitizers. The thesis has four major components. First, the mechanism by which nanomaterials can absorb X-rays and deposit energy in water is described by Monte Carlo simulations. Electrons emitted from a gold nanoparticle under X-ray radiation are followed and their energy deposition mapped. The dose enhancement factor by various gold nanomaterials, their shape, and arrangement are determined. These simulations demonstrate two types of physical dose enhancement in relation to the location of the nanoparticle, remote T1PE and local T2PE. Secondly, these theoretical studies are supported by experiments employing silica coated gold nanoparticles and a fluorescent probe to determine the amount of hydroxyl radicals produced in water, a main radical product of X-ray radiolysis. T1PE was measured for a range of gold concentrations and broadband X-ray spectra. The results were compared with simulations and a strong agreement is shown. Similarly, small bare gold nanoparticles at concentrations lower than predicted are shown to exhibit a new type of radiosensitization mechanism known as chemical enhancement. This chemical enhancement mechanism is found to arise from catalytic conversion of radical species on the surface of gold nanoparticles and is quantified under various chemical conditions. Employment of nanomaterial radiosensitizers for chemical reactions is demonstrated with the polymerization of aniline and measured with a surface enhanced Raman spectroscopy. Because of these enhancement schemes, it is possible to employ these nanomaterials to treat targets such as tumors in the body. The third part of this thesis deals with instrumentation to treat, detect and image nanomaterials. Methods to enhance the dose of X-rays at a target location are explored through Monte Carlo simulations. X-ray beam delivery geometries were simulated and the dosage at the isocenter was compared with that at the surface of the interaction medium. The developed simulation code is also used to study detection and imaging of nanomaterials which have been delivered to a volume of interest. X-ray fluorescence imaging is simulated to understand the feasibility of such a system to detect and image small areas with added nanomaterials. The final part of this thesis presents the results of investigating the toxicity of the nanomaterials and its implications into their future success as radiosensitizers. X-ray absorption spectroscopy is employed to analyze the state of silver nanoparticles inhaled in the lungs of rats. This is a first of its kind study to attempt to determine the fate of silver nanoparticles in animals and better understand mechanisms of toxicity.