Transfer function determination of the primary loop of a conceptual nuclear Brayton space powerplant

Transfer functions for primary loop of conceptual nuclear Brayton space power plan

The study of plasmonics in nanohole metallic metamaterials

Plasmonics is the study of light-matter interaction. The interaction of incident light (photons) with surface plasmons present in metamaterials results in unique optical properties. Nanohole arrays are a metamaterial consisting of an array of sub-wavelength holes perforated in an optically thin metallic film which resides upon a dielectric material. The interaction of light with the surface plasmons present in the nanohole array leads to extraordinary optical transmission which produces resonance peaks with a higher intensity than the incident light. By changing the physical parameters of the nanohole array, such as hole size and periodicity, the resonance peaks can be tuned to different locations. This is used in applications such as surface plasmon resonance sensing and surface enhanced Raman spectroscopy studied in this thesis. Previous derivations of transmission and absorption coefficients show that the transmission is only dependent on the periodicity of the nanohole array. However, numerous simulated and experimental results have shown that the periodicity and hole size have an effect on the transmission and absorption of nanohole arrays

Interactions between Bromus tectorum L. (cheatgrass) and native ruderal species in ecological restoration

2012 Fall.Includes bibliographical references.Bromus tectorum L. is an invasive annual grass that dominates much of the rangeland in western North America. It has shown an impressive ability to invade ecosystems, causing substantial changes in the composition and function of native plant and soil communities in ways that promote further exotic invasion through displacement of native plant species and slowing or halting of succession. B. tectorum has several characteristics, including high reproductive rates, affinity for disturbed sites, and the ability to create positive feedback conditions in invaded sites, which make it highly successful at invading new sites, and extremely challenging to remove during revegetation efforts. Traditional control methods including herbicide application, grazing, and burning have largely proven unsuccessful at preventing establishment and spread of B. tectorum. Similarly, restoration seed mixes often consist of native perennial grass species, which tend to be slower growing and less robust in disturbed sites, and therefore provide little competition against B. tectorum and do not promote the reestablishment of native plant communities. In addition, seed mixes are often planted at a fraction of the rate of annual B. tectorum seed production, giving them a distinct disadvantage. Native ruderal species share many traits with B. tectorum and could potentially compete with this invader if used at high, competitive seeding rates in restoration efforts, and may alter site characteristics in ways that promote succession of the native plant community. One key characteristic that may be closely associated with community development is the development and composition of the arbuscular mycorrhizal fungi (AMF) community. AMF are important for resource acquisition by a majority of plant species. They are particularly important for late-seral plant species, which typically exist in low available nutrient conditions. Bromus tectorum causes shifts in the mycorrhizal community that could lead to a loss of AMF species richness and abundance in a very short time period, resulting in conditions that are difficult for late-seral species to colonize, due to a lack of access to resources through host-specific plant-AMF relationships. Utilizing native seed mixes composed of species selected for specific functional and competitive traits, and mycorrhizal status, and creating seeding rates designed to increase interspecific competition with B. tectorum may provide the missing link for successful restoration of B. tectorum-invaded sites. A study was conducted in northern Colorado to determine whether native ruderal species could suppress B. tectorum establishment and persistence in a disturbed site, and how these effects compared to similar effects by sterile wheat. In this study, B. tectorum was seeded with and without a high rate native ruderal seed mix and a sterile wheat species (QuickGuardTM) used in revegetation efforts for erosion control. Bromus tectorum biomass and density data were collected, as well as biomass and density for all seeded native species and sterile wheat. All treatments were seeded in the fall of 2010, and vegetative data collection occurred during the summers of 2011 and 2012. To assess the immediate effects of the establishing plant community on the AMF community, soils were collected from three of the field study treatments after one year of growth: 1) B. tectorum, 2) a mixture of native early-seral species, or 3) B. tectorum plus native early-seral species. Three mycorrhizal host plant species (Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths, Ratibida columnifera (Nutt.) Woot. & Standl., Sorghum bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan) were grown in these soils under greenhouse conditions. Roots were harvested after 30 days and analyzed for AMF colonization. After one growing season, the native ruderal mix significantly reduced B. tectorum biomass in the field. After the second growing season, the effect was no longer detectable in biomass measurements, but was still observed as a reduction in density of B. tectorum in the native ruderal plots. The sterile wheat reduced B. tectorum biomass after one growing season, but to a lesser extent than the native mix, and had a positive effect on density. In 2012, effects on both biomass and density disappeared. Results from the AMF colonization analysis indicated that the presence of the native species had an impact on AMF richness or abundance within the soils and that B. tectorum alters the AMF community in a way that is unique in comparison to weedy native vegetation. Soils from beneath native early-seral plant species had much higher colonization of the host plant species relative to soils from beneath B. tectorum. In addition, the native host R. columnifera had much higher rates of colonization than the non-native host, S. bicolor, indicating that there may be some host-dependent plant-AMF relationships that are more beneficial to the native plant than the non-native plant. The results of these studies could have important practical field applications for restoring invaded sites, particularly when the goal is to create conditions that promote development of late-seral native plant communities. Utilization of native ruderal species in revegetation mixes could provide a critical missing link for facilitation of late-seral, native plant communities through suppression of B. tectorum, as well as rapid facilitation of AMF communities that successfully colonize native late-seral host species. Continued monitoring and assessment of this study site could lend further insight to the long-term dynamics of the native ruderal plant community with B. tectorum and development of a late-seral plant community

Computerized inspection of gear tooth surfaces

An approach is proposed that uses coordinate measurements of the real surface of spiral bevel gears to determine the actual machine tool setting applied during the gear manufacturing process. The deviations of the real surface from the theoretical one are also determined. Adjustments are then applied by machine tool corrections to minimize these surface deviations. This is accomplished by representing the real surface analytically in the same Gaussian coordinates as the theoretical surface

Navigating the Middle Grades: Evidence from New York City

Educators have long asserted that the middle grade years (typically, grades six through eight) are a time of both great importance and vulnerability in students' K-12 schooling. Anecdotal and empirical evidence suggest that students encounter new social and emotional challenges, increased academic demands, and major developmental transitions during the middle grade years. In this study, we investigate whether and how students' achievement and attendance change between grade four and eight and identified moments during this period when students' achievement and attendance suggest that they will struggle to graduate from high school within four years

On a zero speed sensitive cellular automaton

Using an unusual, yet natural invariant measure we show that there exists a sensitive cellular automaton whose perturbations propagate at asymptotically null speed for almost all configurations. More specifically, we prove that Lyapunov Exponents measuring pointwise or average linear speeds of the faster perturbations are equal to zero. We show that this implies the nullity of the measurable entropy. The measure m we consider gives the m-expansiveness property to the automaton. It is constructed with respect to a factor dynamical system based on simple "counter dynamics". As a counterpart, we prove that in the case of positively expansive automata, the perturbations move at positive linear speed over all the configurations

Multiscale imaging of HIV-1 transmission in humanized mice

HIV transmission within lymphoid tissues remains incompletely characterized at the level of individual cells and virions. Here we visually describe our approach to understanding HIV-1 dissemination at different levels of volume and resolution within lymphoid tissues from HIV-1-infected humanized mice. We combined tissue clearing techniques, immunostaining, and light sheet fluorescence microscopy to visualize large-volumes of intact tissue with single-cell resolution from HIV-1-infected humanized mice. In parallel, we imaged adjacent regions of tissue using electron microscopy and electron tomography to gain 3D ultrastructural information about the same tissue samples. This approach can provide spatial information about the density and distribution of target cells, HIV-1-infected cells, and individual budding and free-virions within lymphoid tissues. Multiscale imaging of HIV-1 infected tissues from humanized mice can provide insight into the biological mechanisms of HIV-1 transmission through the correlation of global pathology with structural details and these methods are directly translatable to other animal models and human clinical samples