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Articles 1 - 17 of 17
Full-Text Articles in Physics
Tidal Decay And Stable Roche-Lobe Overflow Of Short-Period Gaseous Exoplanets, Brian Jackson, Emily Jensen, Sarah Peacock, Phil Arras, Kaloyan Penev
Tidal Decay And Stable Roche-Lobe Overflow Of Short-Period Gaseous Exoplanets, Brian Jackson, Emily Jensen, Sarah Peacock, Phil Arras, Kaloyan Penev
Physics Faculty Publications and Presentations
Many gaseous exoplanets in short-period orbits are on the verge or are in the process of Roche-lobe overflow (RLO). Moreover, orbital stability analysis shows tides can drive many hot Jupiters to spiral inevitably toward their host stars. Thus, the coupled processes of orbital evolution and RLO likely shape the observed distribution of close-in exoplanets and may even be responsible for producing some of the short-period rocky planets. However, the exact outcome for an overflowing planet depends on its internal response to mass loss, and the accompanying orbital evolution can act to enhance or inhibit RLO. In this study, we apply …
Dust Devil Populations And Statistics, Ralph D. Lorenz, Brian K. Jackson
Dust Devil Populations And Statistics, Ralph D. Lorenz, Brian K. Jackson
Physics Faculty Publications and Presentations
The highly-skewed diameter and pressure drop distributions of dust devils on Earth and Mars are noted, and challenges of presenting and comparing different types of observations are discussed. The widely- held view that Martian dust devils are larger than Earth's is critically-assessed: the question is confounded somewhat by different observation techniques, but some indication of a ~3x larger population on Mars is determined. The largest and most intense (in a relative pressure sense) devils recorded are on Mars, although the largest reported number density is on Earth. The difficulties of concepts used in the literature of 'average' diameter, pressure cross …
Hitting The Goalpost: Calculating The Fine Line Between Winning And Losing A Penalty Shootout, Ralf Widenhorn
Hitting The Goalpost: Calculating The Fine Line Between Winning And Losing A Penalty Shootout, Ralf Widenhorn
Physics Faculty Publications and Presentations
The Portland Timbers won their first Major League Soccer (MLS) Cup Championship in December 2015. However, if it had not been for a kind double goalpost miss during a penalty shootout a few weeks earlier, the Timbers would never have been in the finals. On Oct. 30th, after what has been called "the greatest penalty kick shootout in MLS history," featuring a combined 22 penalties that included penalties by both goalkeepers, the Timbers won their first-round playoff against Sporting Kansas City. During the thrilling shootout, which can be watched on the MLS website, Sporting had two potentially game-winning penalties miss …
Förster Resonance Energy Transfer Between Molecules In The Vicinity Of Graphene- Coated Nanoparticles, Tingting Bian, Railing Chang, Pui T. Leung
Förster Resonance Energy Transfer Between Molecules In The Vicinity Of Graphene- Coated Nanoparticles, Tingting Bian, Railing Chang, Pui T. Leung
Physics Faculty Publications and Presentations
The recent demonstration of the plasmonic enhanced Förster resonance energy transfer (FRET) between two molecules in the vicinity of planar graphene monolayers is further investigated using graphene-coated nanoparticles (GNP). Due to the flexibility of these nanostructures in terms of their geometric (size) and dielectric (e.g. core material) properties, greater tunability of the FRET enhancement can be achieved employing the localized surface plasmons. It is found that while the typical characteristic graphene plasmonic enhancements are manifested from using these GNP’s, even higher enhancements can be possible via doping and manipulating the core materials. In addition, the broadband characteristics is further expanded …
The Physics Of Juggling A Spinning Ping-Pong Ball., Ralf Widenhorn
The Physics Of Juggling A Spinning Ping-Pong Ball., Ralf Widenhorn
Physics Faculty Publications and Presentations
Juggling a spinning ball with a ping-pong paddle represents a challenge both in terms of hand-eye coordination and physics concepts. Here, we analyze the ping-pong ball’s motion, and explore how the correct paddle angle relates to the ball’s spin and speed, as it moves vertically up and down. For students, this requires engaging with concepts like momentum, angular momentum, free-body diagrams, and friction. The activities described in this article include high-speed video motion tracking of the ping-pong ball and the investigation of the frictional characteristics of the paddle. They can be done in a physics lab or at home, requiring …
Tunable Magnetism In Metal Adsorbed Fluorinated Nanoporous Graphene, Pankaj Kumar, Vinit Sharma, Fernando A. Reboredo, Li-Ming Yang, Raghani Pushpa
Tunable Magnetism In Metal Adsorbed Fluorinated Nanoporous Graphene, Pankaj Kumar, Vinit Sharma, Fernando A. Reboredo, Li-Ming Yang, Raghani Pushpa
Physics Faculty Publications and Presentations
Developing nanostructures with tunable magnetic states is crucial for designing novel data storage and quantum information devices. Using density functional theory, we investigate the thermodynamic stability and magnetic properties of tungsten adsorbed tri-vacancy fluorinated (TVF) graphene. We demonstrate a strong structure-property relationship and its response to external stimuli via defect engineering in graphene-based materials. Complex interplay between defect states and the chemisorbed atom results in a large magnetic moment of 7 μB along with high in-plane magneto-crystalline anisotropy energy (MAE) of 17 meV. Under the influence of electric field, spin crossover effect accompanied by a change in the MAE …
Identifying The Sources Of Ferromagnetism In Sol-Gel Synthesized Zn1-XCoXO (0 ≤ X ≤ 0.10) Nanoparticles, J. J. Beltrán, C. A. Barrero, A. Punnoose
Identifying The Sources Of Ferromagnetism In Sol-Gel Synthesized Zn1-XCoXO (0 ≤ X ≤ 0.10) Nanoparticles, J. J. Beltrán, C. A. Barrero, A. Punnoose
Physics Faculty Publications and Presentations
We have carefully investigated the structural, optical and electronic properties and related them with the magnetism of sol-gel synthesized Zn1-xCoxO (0 ≤ x ≤ 0.10) nanoparticles. Samples with x ≤ 0.05 were pure and free of spurious phases, whereas ZnCo2O4 was identified as the impurity phase for samples with x ≥ 0.08. Samples with x < 0.05 were found to be true solid solutions with only high spin Co2+ ions into ZnO structure, whereas sample with x = 0.05, exhibited the presence of high spin Co2+ and low spin Co3+. For the impurity-free samples we found that as Co concentration increases, a and …
Defect Driven Magnetism In Doped Sno2 Nanoparticles: Surface Effects, Pushpa Raghani, Pankaj Kumar, Balaji Ramanujam, Alex Punnoose
Defect Driven Magnetism In Doped Sno2 Nanoparticles: Surface Effects, Pushpa Raghani, Pankaj Kumar, Balaji Ramanujam, Alex Punnoose
Physics Faculty Publications and Presentations
Magnetism and energetics of intrinsic and extrinsic defects and defect clusters in bulk and surfaces of SnO2 is investigated using first-principles to understand the role of surfaces in inducing magnetism in Zn doped nanoparticles. We find that Sn vacancies induce the largest magnetic moment in bulk and on surfaces. However, they have very large formation energies in bulk as well as on surfaces. Oxygen vacancies on the other hand are much easier to create than VSn, but neutral and VO+2 vacancies do not induce any magnetism in bulk as well as on surfaces. VO …
Electron Beam Effects In Ge–Se Thin Films And Resistance Change Memory Devices, Kasandra Wolf, Hugh Barnaby, Mahesh S. Ailavajhala, Micahel N. Kozicki, Dmitri A. Tenne, Maria Mitkova
Electron Beam Effects In Ge–Se Thin Films And Resistance Change Memory Devices, Kasandra Wolf, Hugh Barnaby, Mahesh S. Ailavajhala, Micahel N. Kozicki, Dmitri A. Tenne, Maria Mitkova
Physics Faculty Publications and Presentations
Chalcogenide glasses are the advanced materials of choice for the emerging nanoionic memory devices – conductive bridge random access memory (CBRAM). To understand the nature of the effects occurring in these devices under influence of electron-beam radiation, the interaction of blanked chalcogenide films and nanostructured films containing chalcogenide glass and silver (Ag) source are studied. Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction are used for establishing the structural and compositional effects occurring under radiation. They have strong compositional dependence with the stoichiometric compositions being most stable showing less structural changes after radiation. These effects are associated with the availability …
Selective-Area Growth Of Heavily N–Doped Gaas Nanostubs On Si(001) By Molecular Beam Epitaxy, Yoon Jung Chang, Paul J. Simmonds, Brett Beekley, Mark S. Goorsky, Jason C.S. Woo
Selective-Area Growth Of Heavily N–Doped Gaas Nanostubs On Si(001) By Molecular Beam Epitaxy, Yoon Jung Chang, Paul J. Simmonds, Brett Beekley, Mark S. Goorsky, Jason C.S. Woo
Physics Faculty Publications and Presentations
Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth(SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growthparameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAsgrowth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grownGaAs …
On The Visible Size And Geometry Of Aggressively Expanding Civilizations At Cosmological Distances, S. Jay Olson
On The Visible Size And Geometry Of Aggressively Expanding Civilizations At Cosmological Distances, S. Jay Olson
Physics Faculty Publications and Presentations
If a subset of advanced civilizations in the universe choose to rapidly expand into unoccupied space, these civilizations would have the opportunity to grow to a cosmological scale over the course of billions of years. If such life also makes observable changes to the galaxies they inhabit, then it is possible that vast domains of life-saturated galaxies could be visible from the Earth. Here, we describe the shape and angular size of these domains as viewed from the Earth, and calculate median visible sizes for a variety of scenarios. We also calculate the total fraction of the sky that should …
Intramembrane Congestion Effects On Lysenin Channel Voltage-Induced Gating, Eric Krueger, Sheenah Bryant, Nisha Shrestha, Tyler Clark, Charles Hanna, David Pink, Daniel Fologea
Intramembrane Congestion Effects On Lysenin Channel Voltage-Induced Gating, Eric Krueger, Sheenah Bryant, Nisha Shrestha, Tyler Clark, Charles Hanna, David Pink, Daniel Fologea
Physics Faculty Publications and Presentations
All cell membranes are packed with proteins. The ability to investigate the regulatory mechanisms of protein channels in experimental conditions mimicking their congested native environment is crucial for understanding the environmental physicochemical cues that may fundamentally contribute to their functionality in natural membranes. Here we report on investigations of the voltage-induced gating of lysenin channels in congested conditions experimentally achieved by increasing the number of channels inserted into planar lipid membranes. Typical electrophysiology measurements reveal congestion-induced changes to the voltage-induced gating, manifested as a significant reduction of the response to external voltage stimuli. Furthermore, we demonstrate a similar diminished voltage …
Mechanisms Of Methane Transport Through Populus Trichocarpa, Ellynne Marie Kutschera, M. A. K. Khalil, Andrew Rice, Todd Rosenstiel
Mechanisms Of Methane Transport Through Populus Trichocarpa, Ellynne Marie Kutschera, M. A. K. Khalil, Andrew Rice, Todd Rosenstiel
Physics Faculty Publications and Presentations
Although the dynamics of methane (CH4) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global CH4 emission and the mechanisms of tree transport are relatively unknown. CH4 emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to CH4 enriched water and canopy emissions of CH4 were measured. The average flux for 34 trials (at temperatures ranging from 17 to 25 °C) was 2.8 ± 2.2 …
Determination Of The Goos-Hänchen Shift In Dielectric Waveguides Via Photo Emission Electron Microscopy In The Visible Spectrum, Theodore Stedmark, Robert Campbell Word, Rolf Kӧnenkamp
Determination Of The Goos-Hänchen Shift In Dielectric Waveguides Via Photo Emission Electron Microscopy In The Visible Spectrum, Theodore Stedmark, Robert Campbell Word, Rolf Kӧnenkamp
Physics Faculty Publications and Presentations
Photoemission Electron Microscopy (PEEM) is a versatile tool that relies on the photoelectric effect to produce high-resolution images. Pulse lasers allow for multi-photon PEEM where multiple photons are required excite a single electron. This non-linear process can directly image the near field region of electromagnetic fields in materials. We use this ability here to analyze wave propagation in a linear dielectric waveguide with wavelengths of 410nm and 780nm. The propagation constant of the waveguide can be extracted from the interference pattern created by the coupled and incident light and shows distinct polarization dependence. The electromagnetic field interaction at the boundaries …
Interface-Induced Spin Polarization In Graphene On Chromia, Renu Choudhary, Pankaj Kumar, Priyanka Manchanda, David J. Sellmyer, Peter A. Dowben, Arti Kashyap, Ralph Skomski
Interface-Induced Spin Polarization In Graphene On Chromia, Renu Choudhary, Pankaj Kumar, Priyanka Manchanda, David J. Sellmyer, Peter A. Dowben, Arti Kashyap, Ralph Skomski
Physics Faculty Publications and Presentations
The induced spin polarization of graphene on Cr2O3 (001) is investigated using density-functional theory (DFT) and model calculations. The magnetic moment in graphene is a proximity effect and can be regarded as a second-order Stoner scenario, and similar mechanisms are likely realized for all graphene systems with an insulating magnetic substrate. In the absence of charge transfer, the magnetic moment would be quadratic in the exchange field, as contrasted to the usually encountered approximately linear dependence. The net magnetization of the graphene is small, of the order of 0.01 μB per atom, but the energy-dependent spin …
Theoretical Estimates Of Spherical And Chromatic Aberration In Photoemission Electron Microscopy, Joseph P. S. Fitzgerald, Robert Campbell Word, Rolf Kӧnenkamp
Theoretical Estimates Of Spherical And Chromatic Aberration In Photoemission Electron Microscopy, Joseph P. S. Fitzgerald, Robert Campbell Word, Rolf Kӧnenkamp
Physics Faculty Publications and Presentations
We present theoretical estimates of the mean coefficients of spherical and chromatic aberration for low energy photoemission electron microscopy (PEEM). Using simple analytic models, we find that the aberration coefficients depend primarily on the difference between the photon energy and the photoemission threshold, as expected. However, the shape of the photoelectron spectral distribution impacts the coefficients by up to 30%. These estimates should allow more precise correction of aberration in PEEM in experimental situations where the aberration coefficients and precise electron energy distribution cannot be readily measured.
Atmospheric Methane Isotopic Record Favors Fossil Sources Flat In 1980s And 1990s With Recent Increase, Andrew L. Rice, Christopher Butenhoff, Doaa Galal Mohammed Teama, Florian H. Roger, M. A. K. Khalil, R. A. Rasmussen
Atmospheric Methane Isotopic Record Favors Fossil Sources Flat In 1980s And 1990s With Recent Increase, Andrew L. Rice, Christopher Butenhoff, Doaa Galal Mohammed Teama, Florian H. Roger, M. A. K. Khalil, R. A. Rasmussen
Physics Faculty Publications and Presentations
Observations of atmospheric methane (CH4) since the late 1970s and measurements of CH4 trapped in ice and snow reveal a meteoric rise in concentration during much of the twentieth century. Since 1750, levels of atmospheric CH4 have more than doubled to current globally averaged concentration near 1,800 ppb. During the late 1980s and 1990s, the CH4 growth rate slowed substantially and was near or at zero between 1999 and 2006. There is no scientific consensus on the drivers of this slowdown. Here, we report measurements of the stable isotopic composition of atmospheric CH4 (13C/12C and D/H) from a rare air …