A Long-Term Variability Study of Dying Low and Intermediate Mass Stars

We are studying the long-term light variation of dying stars (similar to the sun). These stars pulsate, causing them to vary in light. Our purpose is to better understand the internal structure of these objects though light curve and period analysis. These dying stars are in the proto-planetary nebula (PPN) phase, which lasts only a few thousand years between the red giant phase and the planetary nebula phase. First discovered with the Infrared Astronomical Satellite Survey in 1983, PPN emit strongly in the region, but the central stars of PPN can be studied in visible light. This summer we have observed 20 nights from the Valparaiso University Observatory gathering data for 26 stars. We also have data from collaborators using the SARA-North and SARA-South telescopes located at Kitt Peak, Arizona and Cerro Tololo, Chile, respectively. Our project has two main parts: (1) to continue the long-term observations of PPNs, which started in 1994, and (2) to combine the data from several CCD cameras to enlarge the sample and to better determine the light curves of PPN. We are analyzing a subset of 12 PPN to determine their pulsation periods and amplitudes in order to understand their long-term variability. About the authors: Allyse (Allie) Appel is currently a standing junior as a physics major. Her long-term goal is to go to graduate school, possibly receiving a PhD in Particle Physics or Astrophysics as well as to participate in research for the United States. Justin Reed is currently a sophomore physics major, unsure of future career plans. Both students are first year astronomy research students working with Dr. Bruce Hrivnak

Surface-Dependence of Interfacial Binding Strength between Zinc Oxide and Graphene Investigated from First Principles

There is an increasing interest in hybridized materials for applications such as improving the structural integrity of known and commonly used materials. Recent experiments have suggested that the adhesion of zinc oxide (ZnO) nanowires with carbon fibers can significantly improve the interfacial shear strength of fiber-reinforced composites. We have carried out a systematic study of the interaction between ZnO and graphene based on density functional theory, with a focus on the effect of the surface orientation and termination of ZnO. The most thermodynamically stable hexagonal phase of ZnO is modeled by a cluster with (001), (100), and (110) facets, and the (001) surface is constructed to have both Zn-rich and O-rich terminations. The interaction has been explored through varying both the orientation and the binding sites of the interacting surfaces. The interfacial binding strength is calculated by scanning the potential energy surface while bringing the ZnO cluster incrementally closer to graphene. Results from these energy scans will be presented and discussed along with simple physical arguments to rationalize the observed behavior

Surface-dependence of Interfacial Binding Strength Between Zinc Oxide and Graphene

There is an increasing interest in hybrid materials with impacts such as improving structural integrity of known and commonly used materials. Recent experiments have suggested that the adhesion of zinc oxide (ZnO) nanowires with carbon fibers can significantly improve interfacial shear and tensile strength of fiber reinforced polymer composites. We have carried out a systematic study of the interaction between ZnO and graphene based on density functional theory, with a focus on the effect of the surface orientation and termination of ZnO. The interaction has been explored through varying both the orientation and binding sites of the interacting surfaces. The calculated binding strength shows a strong dependence on the surface orientation and termination of ZnO, which can be explained from the difference in electronegativity of Zn and O, and the induced charge redistribution owing to the in-plane and out-of-plane dipole moment of the oxide surface

Surface-dependence of interfacial binding strength between zinc oxide and graphene

© The Royal Society of Chemistry. There is an increasing interest in hybrid materials with impacts such as improving structural integrity of known and commonly used materials. Recent experiments have suggested that the adhesion of zinc oxide (ZnO) nanowires with carbon fibers can significantly improve interfacial shear and tensile strength of fiber reinforced polymer composites. We have carried out a systematic study of the interaction between ZnO and graphene based on density functional theory, with a focus on the effect of the surface orientation and termination of ZnO. The interaction has been explored through varying both the orientation and binding sites of the interacting surfaces. The calculated binding strength shows a strong dependence on the surface orientation and termination of ZnO, which can be explained from the difference in electronegativity of Zn and O, and the induced charge redistribution owing to the in-plane and out-of-plane dipole moment of the oxide surface