Work function and surface stability of tungsten-based thermionic electron emission cathodes

Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W-Ba-O is the canonical materials system that functions as the thermionic electron emitter used commercially in a range of high power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W-Ba-O system using Density Functional Theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba-O species with compositions in the range of Ba0.125O to Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis, and thus may exhibit surface orientation fractions well-described by the calculated Wulff construction

“We’re Out Here Talking About Life and Death”: Reparations for Human Rights Violations in Vieques, Puerto Rico

From 1941-2003, the U.S. Navy used the island of Vieques, which is inhabited by close to 10,000 U.S. citizens, for war games, bombing exercises, and simulated aquatic landings. During those six decades, the bombardment of Vieques with both conventional and chemical weapons devastated the environment and created a massive health crisis. The health crisis is exacerbated by the extreme poverty on the island, much of which is also traceable to Navy policy there. Since 2003, several petitions and attempts for reparations for Vieques’ residents have been made to the Navy specifically and the US government generally, most notably a class action lawsuit in which more than three-quarters of Viequenses were named plaintiffs. Since that lawsuit’s dismissal in 2013, the question of reparations has again come to the foreground of Viequenses politics. The Navy, while conceding the facts of both the toxicity of their bombing exercises and the heightened health problems faced by Viequenses, consistently denies that there is a connection between the two. This thesis places that denial in the context of the Navy’s long-running obfuscation of its responsibilities to the Viequense people and, drawing on relevant human rights norms as well as other sources of reparation theory, argues that the Navy and US Government have a moral and legal obligation to provide comprehensive reparations to the people of Vieques

Arizona Oil and Gas Update

In Murphy Farrell, the court\u27s holding concerned, inter alia, the effect of an acreage discrepancy in an agreement for the sale of certain surface mineral rights (i.e., the right to mine certain decorative boulders for use in landscaping) and determining the applicability of the doctrine of after-acquired title as well as the enforceability of a right of first refusal to purchase a quarry

Reexamining the Desert: A Study of Place-Based Food Insecurity

Food Deserts are areas where individuals lack access to healthy and affordable food. Since 1995, the United States Department of Agriculture has been one of the leading organizations studying the phenomenon of food deserts. However, issues relating to the scale of their analysis limit their ability to gain a nuanced understanding of food insecurity. In the past decade, an increased emphasis has been placed on the importance of local factors that contribute to food insecurity and complicate the large-scale study of the phenomenon. This research explores the various place-based factors shaping food insecurity in Lincoln, Nebraska, by readapting Penchansky and Thomas’ (1981) new definition and taxonomy of “Access.” Using contemporary literature, this paper expands traditional food “Access” determination metrics to incorporate place-based factors of food insecurity. Observational data, collected at each of Lincoln’s 52 grocery stores, is analyzed to determine the place-based characteristics that consumers experience while shopping. A quantitative analysis highlights specific instances of low Access across the City of Lincoln. Quantitative study findings are then compared to the USDA’s large-scale food insecurity study to unpack the differences between varying scales of analysis. Lastly, this research concludes with a framework analysis that connects the common threads of low Accessibility grocery stores across the city and identifies commonalities that increase a consumer’s risk of food insecurity. Advisor: Robert Shepar

Marshall University Music Department Presents a Junior Recital, Ryan Morgan, double bass

https://mds.marshall.edu/music_perf/1290/thumbnail.jp