Extending a Hybrid Godunov Method for Radiation Hydrodynamics to Multiple Dimensions

This paper presents a hybrid Godunov method for three-dimensional radiation hydrodynamics. The multidimensional technique outlined in this paper is an extension of the one-dimensional method that was developed by Sekora & Stone 2009, 2010. The earlier one-dimensional technique was shown to preserve certain asymptotic limits and be uniformly well behaved from the photon free streaming (hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and to the strong equilibrium diffusion (hyperbolic) limit. This paper gives the algorithmic details for constructing a multidimensional method. A future paper will present numerical tests that demonstrate the robustness of the computational technique across a wide-range of parameter space.Comment: 25 page

Women of the Wolf

This is a creative thesis that introduces the novel Women of the Wolf and discusses the writer’s influences and research progress. Themes within the novel will include women relationships, cult culture, religious influences, and Native American (mis)representation. The sample included is the first ten pages from the novel. Advisor: Timothy Schaffer

The Use and Abuse of Special-Purpose Entities in Public Finance

States increasingly are raising financing indirectly through special-purpose entities (SPEs), variously referred to as authorities, special authorities, or public authorities. Notwithstanding their long history and increasingly widespread use, relatively little is known or has been written about these entities. This article examines state SPEs and their functions, comparing them to SPEs used in corporate finance. States, even more than corporations, use these entities to reduce financial transparency and avoid public scrutiny, seriously threatening the integrity of public finance. The article analyzes how regulation could be designed in order to control that threat while maintaining the legitimate financing benefits provided by these state entities

Tactic behaviors in bacterial dynamics

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (leaves 89-90).The locomotion of a wide class of motile bacteria can be mathematically described as a biased random walk in three-dimensional space. Fluid mechanics and probability theory are invoked to model the dynamics of bacteria swimming using tactic behaviors (movements or reorientation in response to chemical, physical or environmental stimuli) in flowing, viscous media. Physical descriptions are developed for bacterial chemotaxis (response to chemical agents) near particles exuding attractants, a small-scale process with global-scale implications for the biogeochemistry of the oceans. Three cases were investigated: a stationary particle, a slowly moving particle and a particle that generates a hydrodynamic wake in the form of attached vortices. The key finding of this thesis consists in the discovery of several scenarios in which motile bacteria swimming via random walks put themselves at a disadvantage in their quest for food with respect to non-motile pacteria. Thus, there exist threshold values in nutrient gradients and bacterial chemosensory ability below which bacteria would be better served if they did not swim. In the presence of vortices, it was discovered that bacteria can exploit the recirculating flow field to vastly increase their nutrient supply, but only if they alter their swimming behavior as a function of the concentration field.(cont.) Otherwise, slow bacteria completely miss the hydrodynamic wake (and the high nutrient region) behind a nearby moving particle, while fast bacteria end up colonizing the particle (i.e. clustering around the particle and potentially anchoring themselves to it). These processes are currently under investigation in laboratory experiments using high-speed digital photography, for which software (BacTrackTM) was written that can locate and track multiple bacteria over time, with the aim of providing trajectories and their statistics and ultimately establish the importance of these phenomena for marine ecology and biogeochemistry. Preliminary experiments were conducted with Escherichia coli being exposed to ultraviolet radiation, documenting the known result of E. coli being repelled by UV radiation and providing a successful test bed for the reliability of the tracking software.by Michael David Sekora.S.B

Tunable plasmonic resonances in highly porous nano-bamboo Si-Au superlattice-type thin films

We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. The superlattice-type columns resemble bamboo structures where smaller column sections of gold form junctions sandwiched between larger silicon column sections ("nano-bamboo"). We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous nano-bamboo structures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is observed in the vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like mode frequency within the near-infrared spectral range by varying the geometry of the nano-bamboo structure. In addition, coupled-plasmon-like and inter-band transition-like modes occur in the visible and ultra-violet spectral regions, respectively. We elucidate an example for the potential use of the nano-bamboo structures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water

Determinants of Adoption of Improved Crossbred Cattles: A Case Study of Suba and Laikipia Districts, Kenya

Recognizing that more than 10% of the Kenyan GDP and 50% of agricultural GDP are comprised of sales within the livestock subsector; the purpose of this research is to identify the determinants of adoption of improved crossbred cattle in rural Kenya. This research has important implications for increasing the dairy subsectors’ productivity, improving nutrient intake within rural Kenya and motivating higher rates of foreign direct investment in a sustainable, beneficial sector. We used a publicly available (www.ifpri.org) dataset called "Land Tenure, Agricultural Productivity and the Environment, 2001." A logistical regression analysis is employed to answer our research questions. The results showed that: family members education, having an extra job in addition to farming, and exposure to external market forces (was the farmer a local, or immigrant) all greatly contributed to the likelihood of adoption. This research aims to gnaw away at the ambiguity and lack of research associated with the Kenyan dairy sub-sector and aims to facilitate greater understanding and investment in the sector. Keywords: Adoption, Logistic regression, Kenya, Crossbreed cattl

Optical anisotropy of porous polymer film with inverse slanted nanocolumnar structure revealed via generalized spectroscopic ellipsometry

We use generalized spectroscopic ellipsometry to characterize the biaxial optical properties of porous polymer and slanted nanocolumnar template thin films. The porous polymer with inverse columnar structure was prepared via infiltrating polymer into the voids of the slanted nanocolumnar film and selectively removing the column material (cobalt). The anisotropic Bruggeman effective medium approximation was employed to analyze the ellipsometry data of the porous polymer film and nanocolumnar template. The classification and structure of optical anisotropy are found to be identical for both samples. The interchangeable optical behaviors between two complementary structures are attributed to the equivalency in their anisotropic polarizabilities