MeMBL: Ring-Opening a Pathway to a Renewable, Chemically Customizable Plastic

The Tower is an official publication of the Georgia Tech Board of Student Publications and is sponsored by the Undergraduate Research Opportunities Program and the Price Gilbert Memorial Library System. This article is from Volume 1, Issue 1.MeMBL (α-methylene-γ-methyl-γ-butyrolactone) is a biomass-derived compound known to be polymerizable to make an acrylic material with a high glass transition temperature. Presence of a lactone ring in the structure of MeMBL can be opened to create a pathway to modification of a MeMBL polymer. This would expand the range of uses for poly(MeMBL) as a plastic. A polymer composed of pure MeMBL and a polymer composed of MeMBL and styrene (the main component of Styrofoam) were prepared, and subjected to reactions with sodium hydroxide in alcohols, water, or dimethyl sulfoxide (DMSO). Evidence of ring-opening was determined either by observation of a change in the polymer’s solubility or by NMR analysis. Both the pure MeMBL polymer and MeMBL/styrene copolymer showed evidence of ring-opening when exposed to sodium hydroxide in water, while no reaction was observed with the same treatment in alcohols. The poly(MeMBL) ring was observed to close over time. Ring-opening was found to be achievable, but ring-opening with hydroxide was found to be an ineffective pathway to further work on the opened ring.Undergraduate Research Opportunities Program ; Price Gilbert Memorial Library System

Emerging Translational Opportunities in Comparative Oncology With Companion Canine Cancers: Radiation Oncology.

It is estimated that more than 6 million pet dogs are diagnosed with cancer annually in the USA. Both primary care and specialist veterinarians are frequently called upon to provide clinical care that improves the quality and/or quantity of life for affected animals. Because these cancers develop spontaneously in animals that often share the same environment as their owners, have intact immune systems and are of similar size to humans, and because the diagnostic tests and treatments for these cancers are similar to those used for management of human cancers, canine cancer provides an opportunity for research that simultaneously helps improve both canine and human health care. This is especially true in the field of radiation oncology, for which there is a rich and continually evolving history of learning from the careful study of pet dogs undergoing various forms of radiotherapy. The purpose of this review article is to inform readers of the potential utility and limitations of using dogs in that manner; the peer-reviewed literature will be critically reviewed, and current research efforts will be discussed. The article concludes with a look toward promising future directions and applications of this pet dog "model.

Relative Income, Redistribution and Well-being

In a model with heterogeneous workers and both intensive and extensive margins of employment, we consider two systems of redistribution: a universal basic income, and a categorical unemployment benefit. Well-being depends on own-consumption relative to average employed workers’ consumption, and concern for relativity is a parameter that affects model outcomes. While labour supply incurs positive marginal disutility, we allow negative welfare effects of unemployment. We also compare Rawlsian and utilitarian welfare in general equilibrium under the polar opposite transfer systems, with varying concern for relativity. Basic income Pareto dominates categorical benefits with moderate concern for relativity in both cases.relative income, redistribution, basic income, unemployment benefits, happiness, well-being

Formation of Ce3+ at the cerium dioxide (110) surface by doping

The formation of Ce3+ ions in CeO2 is key for its applications. We present density functional theory (DFT) studies of doping of the CeO2 (1 1 0) surface with +5 cations, Ta and Nb, as a route to formation of Ce3+. We use DFT corrected for on-site Coulomb interactions (DFT + U, U = 5 eV) and hybrid DFT (HSE06 functional). With both methods we find formation of Ce3+ ions due to the extra electron from the dopant residing on a single Ce site, confirming the DFT + U description of these systems. Doping with Nb and Ta activates the surface to NO2 reduction – there is no interaction with the undoped surface but the Ce3+ ion in the doped surface interacts strongly with NO2

Healing of oxygen vacancies on reduced surfaces of gold-doped ceria

As an oxidation-reduction catalyst, ceria can catalyze molecular oxidation and reduction. There has been a focus on understanding and enhancing the vacancy formation process to improve the oxidative power of ceria. However, it is important to also address healing of the surface vacancy. To investigate healing of oxygen vacancies in ceria, we study the interaction of atomic and molecular oxygen and NO2 with oxygen vacancies on gold-doped (110) and (100) surfaces using density functional theory, corrected for on-site Coulomb interactions (DFT+U). For atomic and molecular oxygen, adsorption at the reduced surface is favorable and results in an oxygen atom sitting in an oxygen lattice site, healing the oxygen vacancy. On undoped surfaces, O-2 adsorbs as a peroxo (O(2)2-) species. However, on the doped (110) surface a superoxo (O-2-) species is present. When NO2 adsorbs (exothermically) at a divacancy surface, one oxygen of the molecule sits in the vacancy site and the N-O distances are elongated and an [NO2](-) anion forms, similar to the undoped surface. Vacancy healing of ceria surfaces is favorable, even if vacancy formation is enhanced, justifying the current focus on improving the oxidative power of ceria. We briefly examine a catalytic cycle: the reaction of CO with adsorbed O-2 on the undoped and doped surfaces, and find that the doped (110) surface facilitates CO oxidation

Surface modification of TiO2 with metal oxide nanoclusters: a route to composite photocatalytic materials

Density functional theory simulations show that modifying rutile TiO2 with metal oxide nanoclusters produces composite materials with potential visible light photocatalytic activity

Enhanced oxygen vacancy formation in ceria (111) and (110) surfaces doped with divalent cations

With increasing interest in new catalytic materials based on doping of cerium dioxide with other metal cations, it is necessary to have an atomic level understanding of the factors that impact on the structural and electronic properties of doped ceria as well as its reactivity. We present in this paper simulations of the ceria (111) and (110) surfaces doped with divalent cations Pd and Ni using density functional theory (DFT) corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (using the screened exchange HSE06 functional). Structural distortions due to doping are strong in both surfaces and the most stable structure for both dopants arises through compensation of the dopant + 2 valence through oxygen vacancy formation. Both dopants also lower the formation energy of the active oxygen vacancy in each surface, confirming the potential for these dopants to be used in ceria based materials for catalysis or solid oxide fuel cells, where the oxygen vacancy formation energy is important. When comparing DFT + U and hybrid DFT, although the qualitative descriptions provided by both DFT approaches are similar, we do find that the energetics of oxygen vacancy formation are quantitatively different and the importance of this point is discussed

Charge compensation and Ce3+ formation in trivalent doping of the CeO2(110) surface: The key role of dopant ionic radius

In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is doped with a series of trivalent dopants, namely, Al3+, Sc3+, Y3+, and In 3+. Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized MCe / + O O • (M = the 3+ dopant), O- hole state, confirming the description found with DFT + U. We use DFT + U to investigate the energetics of dopant compensation through formation of the 2MCe ′ +VO ̈ defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al3+, which has the smallest ionic radius, and Sc3+ and In3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the other hand, the Y3+ dopant, with an ionic radius close to that of Ce4+, shows a positive anion vacancy formation energy, as does La3+, which is larger than Ce4+ (J. Phys.: Condens. Matter 2010, 20, 135004). When considering the resulting electronic structure, in Al3+ doping, oxygen hole compensation is found. However, Sc 3+, In3+, and Y3+ show the formation of a reduced Ce3+ cation and an uncompensated oxygen hole, similar to La3+. These results suggest that the ionic radius of trivalent dopants strongly influences the final defect formed when doping ceria with 3+ cations. In light of these findings, experimental investigations of these systems will be welcome

Modifying ceria (111) with a TiO2 nanocluster for enhanced reactivity

Modification of ceria catalysts is of great interest for oxidation reactions such as oxidative dehydrogenation of alcohols. Improving the reactivity of ceria based catalysts for these reactions means that they can be run at lower temperatures and density functional theory (DFT) simulations of new structures and compositions are proving valuable in the development of these catalysts. In this paper, we have used DFT+U (DFT corrected for on-site Coulomb interactions) to examine the reactivity of a novel modification of ceria, namely, modifying with TiO2, using the example of a Ti2O4 species adsorbed on the ceria (111) surface. The oxygen vacancy formation energy in the Ti2O4–CeO2 system is significantly reduced over the bare ceria surfaces, which together with previous work on ceria-titania indicates that the presence of the interface favours oxygen vacancy formation. The energy gain upon hydrogenation of the catalyst, which is the rate determining step in oxidative dehydrogenation, further points to the improved oxidation power of this catalyst structure