Dynamic Response Modeling of High Speed Planing Craft with Enforced Acceleration

Due to the harsh conditions high speed planing crafts must endure, research to further the understanding of high speed vessel response during wave impacts was conducted. The integration of a finite element model and captured sea trial acceleration data was investigated. The research shows that the finite element model sub-model can be used in lieu of a full finite element model with minimum degradation in output, thus allowing for the analysis of local stress concentrations where critical equipment and or personnel may be located. The research effort was completed to develop a method for realizing the stress field and deformation generated following a wave impact. Application of base excitation was investigated and allowed for multiple studies to be completed. Validation of the method was accomplished through comparison of sea trial data with MSC NASTRAN transient response output in the form of acceleration. The method provides insight into the effect that wave impacts have on small vessels at sea, specifically the 11-meter cabin RIB, hull 11MRIB0503

Fractional Chern Insulators from the nth Root of Bandstructure

We provide a parton construction of wavefunctions and effective field theories for fractional Chern insulators. We also analyze a strong coupling expansion in lattice gauge theory that enables us to reliably map the parton gauge theory onto the microsopic Hamiltonian. We show that this strong coupling expansion is useful because of a special hierarchy of energy scales in fractional quantum Hall physics. Our procedure is illustrated using the Hofstadter model and then applied to bosons at 1/2 filling and fermions at 1/3 filling in a checkerboard lattice model recently studied numerically. Because our construction provides a more or less unique mapping from microscopic model to effective parton description, we obtain wavefunctions in the same phase as the observed fractional Chern insulators without tuning any continuous parameters.Comment: 9+3 pages, 6 figures; v2: added refs, amplified discussion of deconfinement, improved discussion of translation invarianc

An Ongoing Shift in Mammalian Nest Predators of Yellow-billed Loons in Arctic Alaska

The Coastal Plain of northern Alaska is an important nesting area for a variety of avian species, where the productivity of ground-nesting species can be strongly influenced by nest predators. Recently, the density of red foxes (Vulpes vulpes) has increased in many areas of the Arctic, likely because of climate warming as well as the availability of anthropogenic food sources during winter. In areas where they occur sympatrically, red foxes can outcompete and kill the smaller Arctic fox (Vulpes lagopus). There is considerable dietary overlap between the fox species, but if the red fox is a more successful nest predator, this ongoing shift in canid species could have important implications for ground-nesting species like the Yellow-billed Loon (Gavia adamsii). We examined time-lapse photographs from 186 nests of Yellow-billed Loons in northern Alaska during the years 2008 – 15 and 2019 for the presence of foxes and other nest predators and quantified nest predation by species. Although both Arctic and red foxes were photographed near nests, we found that all successful predation of Yellow-billed Loon nests by foxes was attributable to red foxes, which were the second most frequent predator of Yellow-billed Loon nests after Glaucous Gulls (Larus hyperboreus). Arctic foxes photographed at Yellow-billed Loon nests were unsuccessful at displacing incubating loons. Several data sources suggest that the prevalence of red foxes has increased in Arctic Alaska over the last three decades, a change that is likely to have negative impacts on the nesting success of Yellow-billed Loons and possibly other large waterbirds. La plaine côtière du nord de l’Alaska est une aire de nidification importante pour une variété d’espèces aviaires, où la productivité des espèces nichant au sol peut être grandement influencée par les prédateurs de nids. Récemment, la densité de renards roux (Vulpes vulpes) a augmenté en maint endroit de l’Arctique, vraisemblablement en raison du réchauffement climatique et de la disponibilité de sources alimentaires anthropiques en hiver. Là où ils se retrouvent de manière sympatrique, les renards roux peuvent l’emporter sur les renards arctiques (Vulpes lagopus) plus petits et réussir à les tuer. Il existe un chevauchement alimentaire considérable entre les espèces de renards, mais si le renard roux est un prédateur de nids plus prolifique, le virage caractérisant les espèces de canidés pourrait avoir d’importantes incidences sur les espèces nichant au sol, comme le plongeon à bec blanc (Gavia adamsii). Nous avons examiné les photographies accélérées de 186 nids de plongeons à bec blanc du nord de l’Alaska prises entre les années 2008 et 2015 ainsi qu’en 2019 afin de repérer la présence de renards et d’autres prédateurs de nids, en plus de quantifier la prédation des nids en fonction des espèces. Même s’il y a des photographies de renards roux et de renards arctiques à proximité de nids, nous avons pu constater que toutes les prédations réussies de nids de plongeons à bec blanc étaient attribuables au renard roux, le deuxième plus grand prédateur de nids de plongeons à bec blanc après le goéland bourgmestre (Larus hyperboreus). Les renards arctiques photographiés aux nids de plongeons à bec blanc n’ont pas réussi à déplacer les plongeons en période d’incubation. Plusieurs sources de données suggèrent que la prédominance des renards roux a augmenté dans l’Arctique alaskien au cours des trois dernières décennies, un changement qui est susceptible d’avoir des incidences négatives sur le succès de la nidification des plongeons à bec blanc, voire d’autres oiseaux aquatiques plus volumineux.

White matter integrity and vulnerability to Alzheimer's disease: Preliminary findings and future directions

AbstractNeuroimaging biomarkers that precede cognitive decline have the potential to aid early diagnosis of Alzheimer's disease (AD). A body of diffusion tensor imaging (DTI) work has demonstrated declines in white matter (WM) microstructure in AD and its typical prodromal state, amnestic mild cognitive impairment. The present review summarizes recent evidence suggesting that WM integrity declines are present in individuals at high AD-risk, prior to cognitive decline. The available data suggest that AD-risk is associated with WM integrity declines in a subset of tracts showing decline in symptomatic AD. Specifically, AD-risk has been associated with WM integrity declines in tracts that connect gray matter structures associated with memory function. These tracts include parahippocampal WM, the cingulum, the inferior fronto-occipital fasciculus, and the splenium of the corpus callosum. Preliminary evidence suggests that some AD-risk declines are characterized by increases of radial diffusivity, raising the possibility that a myelin-related pathology may contribute to AD onset. These findings justify future research aimed at a more complete understanding of the neurobiological bases of DTI-based declines in AD. With continued refinement of imaging methods, DTI holds promise as a method to aid identification of presymptomatic AD. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease