Electron-Phonon Driven Spin Frustration in Multi-Band Hubbard Models: MX Chains and Oxide Superconductors

We discuss the consequences of both electron-phonon and electron-electron couplings in 1D and 2D multi-band (Peierls-Hubbard) models. After briefly discussing various analytic limits, we focus on (Hartree-Fock and exact) numerical studies in the intermediate regime for both couplings, where unusual spin-Peierls as well as long-period, frustrated ground states are found. Doping into such phases or near the phase boundaries can lead to further interesting phenomena such as separation of spin and charge, a dopant-induced phase transition of the global (parent) phase, or real-space (``bipolaronic'') pairing. We discuss possible experimentally observable consequences of this rich phase diagram for halogen-bridged, transition metal, linear chain complexes (MX chains) in 1D and the oxide superconductors in 2D.Comment: 6 pages, four postscript figures (appended), in regular Te

Niobrara National Scenic River, 1985-2000: Old arguments, new compromises

In May 1991, President George H. Bush signed into law the Niobrara Scenic River Designation Act, which gave federal scenic-river designation to a 70-mile stretch of this northern-Nebraska river. The successful effort to protect this river was a protracted, often acrimonious battle, pitting Nebraska neighbors against each other. Interested parties found themselves on opposing sides of a seemingly insurmountable divide, either believing that this river resource should be given federal protection to preserve it unimpaired for future generations, or arguing that the local people should be allowed to determine the fate of “their” river without federal interference. The twentieth century West has seen this same battle waged many times before the Niobrara case. From Hetch-Hetchy to Echo Park to Glen Canyon; from Buffalo River to Auburn Dam to the Sagebrush Rebellion, the debate has been much the same. Those who favor federal protective legislation contend that only the federal government has the wherewithal and the power to assure that these fragile resources are protected from development and short-sighted exploitation. Those opposed to federal designation argue that any such preservation actions would compromise their freedoms and property rights. The impetus for federal designation came from a group of landowners along the river, who first organized in 1980 and lobbied U.S. Senator J. James Exon to introduce federal legislation protecting the river. He did so in 1985. This initiated a six-year process of meetings, discussions, editorializing, angry rhetoric, and finally compromise, involving Nebraska’s entire Congressional delegation, three governors, countless local officials, and a number of the state’s newspapers. This thesis will consider the federal, state and local efforts that led to the designation of the Niobrara as a federal scenic river, and the efforts at managing the park in its first decade of existence

New record of the pavement ant, Tetramorium immigrans (Hymenoptera: Formicidae), in South Dakota with notes on its thermal tolerance and geographic distribution

The pavement ant, Tetramorium immigrans, is an abundant and widespread species across large portions of the United States. Yet despite its current distribution in Northeastern, Midwestern, Pacific, and Western states, there is a surprising lack of records from the Great Plains. Here we present an updated county list of T. immigrans from museum collections and research grade observations (459 counties; ~15% of US counties), highlighting the first records from one Great Plains state—South Dakota. Observations on community science platforms since 2006 have undoubtedly increased the awareness of T. immigrans (+329 counties; ~72% of all county records), however we posit that such platforms may also highlight the dispersal limitations of this species into the less urban, colder Northern Great Plains states of Montana, Nebraska, North Dakota, South Dakota, and Wyoming (~5% of 291 counties). As such, we offer novel information on T. immigrans’ thermal biology including measurements of critical thermal limits, knock-down resistance, and chill coma recovery. While T. immigrans can likely tolerate the warm summer temperatures found in South Dakota due to its heat tolerance hovering around 46°C, its lower ability to tolerate cold winter conditions may be a possible mechanism for its limited dispersal

Fluid Delivery System for a Cell Culture on a Microfluidic Chip

This project report provides a description of the progress made in the development of a fluid delivery system for a microfluidic cell culture on a chip. The system is intended to be used in a humidified incubator in a university laboratory and the fluid delivery system is required to exist and operate within that incubator for extended periods of time. Therefore, the system will be gravity-driven and contain no electronic components. The key specification of the system is to provide fluid flow at a constant velocity. After manufacturing and testing the device, all specifications were met except for the fluid velocity remaining constant over extended periods of time. This report will go into detail on the results of the tests that passed and why this specification was not met during testing, as well as future recommendations for this system