UHF Antenna Design for AFIT Random Noise Radar

The design of a small ultra-high frequency (UHF) antenna for an ultra-wideband (UWB) random noise radar (RNR) system was undertaken to improve system bandwidth and reduce overall system size. The Vivaldi dipole antenna class showed the greatest potential for high performance in this specific application. After extensive computer simulation, three designs were built using two printed circuit board antenna construction methods. The antipodal chopped Vivaldi dipole antenna, built with a milling machine, achieved a wider bandwidth and more uniform spectral performance characteristics. Though current results show improvement over the current log-periodic antenna (LPA) used on the system, greater performance could possibly be achieved with higher fidelity construction methods. The chopped Vivaldi dipole antenna can be classified as a highly efficient, electrically small antenna optimized for UWB applications, due to the combination of small size as well as a nearly uniform frequency response and low dispersion in the UHF bandwidth. Though designed for AFIT\u27s Noise Network (NoNET) system, a UHF UWB RNR, the antenna could be applied to a variety of UHF systems looking to optimize the trade-off between size and power budgets

The Design of a Paper Launching Device

The American Society of Mechanical Engineers has challenged us to create a machine that forms a projectile from a single sheet of paper, and then launches that projectile. The success of the device will be measured by how far the projectile is effectively propelled, how straight the projectile is propelled, and how much volume the device takes up when packaged

Interaction effects on 2D fermions with random hopping

We study the effects of generic short-ranged interactions on a system of 2D Dirac fermions subject to a special kind of static disorder, often referred to as ``chiral.'' The non-interacting system is a member of the disorder class BDI [M. R. Zirnbauer, J. Math. Phys. 37, 4986 (1996)]. It emerges, for example, as a low-energy description of a time-reversal invariant tight-binding model of spinless fermions on a honeycomb lattice, subject to random hopping, and possessing particle-hole symmetry. It is known that, in the absence of interactions, this disordered system is special in that it does not localize in 2D, but possesses extended states and a finite conductivity at zero energy, as well as a strongly divergent low-energy density of states. In the context of the hopping model, the short-range interactions that we consider are particle-hole symmetric density-density interactions. Using a perturbative one-loop renormalization group analysis, we show that the same mechanism responsible for the divergence of the density of states in the non-interacting system leads to an instability, in which the interactions are driven strongly relevant by the disorder. This result should be contrasted with the limit of clean Dirac fermions in 2D, which is stable against the inclusion of weak short-ranged interactions. Our work suggests a novel mechanism wherein a clean system, initially insensitive to interaction effects, can be made unstable to interactions upon the inclusion of weak static disorder.Comment: 16 pages, 10 figures; References added, figures enlarged; to be published in Phys. Rev.

Systematics of Desmognathus monticola

Undergraduate Basi

Nonalcoholic fatty liver disease is a risk factor for thiopurine hepatotoxicity in Crohn\u27s disease

BACKGROUND: Patients with Crohn\u27s disease (CD) are predisposed to nonalcoholic fatty liver disease (NAFLD). CD management often includes thiopurines which can promote hepatotoxicity. We aimed to identify the role of NAFLD on the risk of developing liver injury from thiopurines in CD. METHODS: In this prospective cohort analysis, CD patients at a single center were recruited 6/2017-5/2018. Patients with alternative liver diseases were excluded. The primary outcome was time to elevation of liver enzymes. Patients underwent MRI with assessment of proton density fat fraction (PDFF) on enrollment, where NAFLD was defined as PDFF \u3e5.5%. Statistical analysis was performed using a Cox-proportional hazards model. RESULTS: Of the 311 CD patients studied, 116 (37%) were treated with thiopurines, 54 (47%) of which were found to have NAFLD. At follow-up, there were 44 total cases of elevated liver enzymes in those treated with thiopurines. Multivariable analysis demonstrated that NAFLD was a predictor of elevated liver enzymes in patients with CD treated with thiopurines (HR 3.0, 95% CI 1.2-7.3, CONCLUSIONS: NAFLD at baseline is a risk factor for thiopurine-induced hepatotoxicity in patients with CD. The degree of liver fat positively correlated with the degree of ALT elevation. These data suggest that evaluation for hepatic steatosis be considered in patients with liver enzyme elevations with thiopurine therapy

Developing a Measure of Safety Data Culture

Safety is a critical concern for many organizations, especially those in construction and manufacturing. A newer approach to improving an organization’s decision making involves the use of data analytics. In regard to safety, the use of data analytics would allow for detecting and tracking risk factors such as behaviors, environmental contingencies, production, procedures, and hazards that are associated with workplace injuries. However, many organizations do not have a culture involving the use and measurement of relevant variables on an ongoing basis. Accordingly, the purpose of the study is to develop a measure of safety culture with a specific emphasis on the extent to which data is being utilized for management of safety in an organization. This measure of safety culture and analytics will assist in determining the extent to which an organization is ready to utilize data analytics into their safety program

Neural Priming for Sample-Efficient Adaptation

We propose Neural Priming, a technique for adapting large pretrained models to distribution shifts and downstream tasks given few or no labeled examples. Presented with class names or unlabeled test samples, Neural Priming enables the model to recall and conditions its parameters on relevant data seen throughout pretraining, thereby priming it for the test distribution. Neural Priming can be performed at test time in even for pretraining datasets as large as LAION-2B. Performing lightweight updates on the recalled data significantly improves accuracy across a variety of distribution shift and transfer learning benchmarks. Concretely, in the zero-shot setting, we see a 2.45 improvement in accuracy on ImageNet and 3.81 accuracy improvement on average across standard transfer learning benchmarks. Further, using our test time inference scheme, we see a 1.41 accuracy improvement on ImageNetV2. These results demonstrate the effectiveness of Neural Priming in addressing the common challenge of limited labeled data and changing distributions. Code is available at github.com/RAIVNLab/neural-priming.Comment: 18 pages, 8 figures, 9 table

Metal-insulator transition from combined disorder and interaction effects in Hubbard-like electronic lattice models with random hopping

We uncover a disorder-driven instability in the diffusive Fermi liquid phase of a class of many-fermion systems, indicative of a metal-insulator transition of first order type, which arises solely from the competition between quenched disorder and interparticle interactions. Our result is expected to be relevant for sufficiently strong disorder in d = 3 spatial dimensions. Specifically, we study a class of half-filled, Hubbard-like models for spinless fermions with (complex) random hopping and short-ranged interactions on bipartite lattices, in d > 1. In a given realization, the hopping disorder breaks time reversal invariance, but preserves the special ``nesting'' symmetry responsible for the charge density wave instability of the ballistic Fermi liquid. This disorder may arise, e.g., from the application of a random magnetic field to the otherwise clean model. We derive a low energy effective field theory description for this class of disordered, interacting fermion systems, which takes the form of a Finkel'stein non-linear sigma model [A. M. Finkel'stein, Zh. Eksp. Teor. Fiz. 84, 168 (1983), Sov. Phys. JETP 57, 97 (1983)]. We analyze the Finkel'stein sigma model using a perturbative, one-loop renormalization group analysis controlled via an epsilon-expansion in d = 2 + epsilon dimensions. We find that, in d = 2 dimensions, the interactions destabilize the conducting phase known to exist in the disordered, non-interacting system. The metal-insulator transition that we identify in d > 2 dimensions occurs for disorder strengths of order epsilon, and is therefore perturbatively accessible for epsilon << 1. We emphasize that the disordered system has no localized phase in the absence of interactions, so that a localized phase, and the transition into it, can only appear due to the presence of the interactions.Comment: 47 pages, 25 figures; submitted to Phys. Rev. B. Long version of arXiv:cond-mat/060757