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Articles 1 - 19 of 19
Full-Text Articles in Physics
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 …
Puddle Jumping: Spontaneous Ejection Of Large Liquid Droplets From Hydrophobic Surfaces During Drop Tower Tests, Babek Attari, Mark M. Weislogel, Andrew Paul Wollman, Yongkang Chen, Trevor Snyder
Puddle Jumping: Spontaneous Ejection Of Large Liquid Droplets From Hydrophobic Surfaces During Drop Tower Tests, Babek Attari, Mark M. Weislogel, Andrew Paul Wollman, Yongkang Chen, Trevor Snyder
Mechanical and Materials Engineering Faculty Publications and Presentations
Large droplets and puddles jump spontaneously from sufficiently hydrophobicsurfaces during routine drop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamic droplet phenomena for drops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed in drop tower tests including relationships to predict droplet ejection durations and velocities as functions of drop volume, surface texture, surface contour, wettability pattern, and fluid properties including contact angle. The latter is determined via profile image comparisons with numerical …
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 …
Communication: Visualization And Spectroscopy Of Defects Induced By Dehydrogenation In Individual Silicon Nanocrystals, Dmitry A. Kislitsyn, Jon M. Mills, Vancho Kocevski, Sheng-Kuei Chiu, William J.I. Debenedetti, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Communication: Visualization And Spectroscopy Of Defects Induced By Dehydrogenation In Individual Silicon Nanocrystals, Dmitry A. Kislitsyn, Jon M. Mills, Vancho Kocevski, Sheng-Kuei Chiu, William J.I. Debenedetti, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Chemistry Faculty Publications and Presentations
We present results of a scanning tunneling spectroscopy (STS) study of the impact of dehydrogenation on the electronic structures of hydrogen-passivated silicon nanocrystals (SiNCs) supported on the Au(111)surface. Gradual dehydrogenation is achieved by injecting high-energy electrons into individual SiNCs, which results, initially, in reduction of the electronic bandgap, and eventually produces midgap electronic states. We use theoretical calculations to show that the STS spectra of midgap states are consistent with the presence of silicon dangling bonds, which are found in different charge states. Our calculations also suggest that the observed initial reduction of the electronic bandgap is attributable to the …
Large Length Scale Capillary Fluidics: From Jumping Bubbles To Drinking In Space, Andrew Paul Wollman
Large Length Scale Capillary Fluidics: From Jumping Bubbles To Drinking In Space, Andrew Paul Wollman
Dissertations and Theses
In orbit, finding the "bottom" of your coffee cup is a non-trivial task. Subtle forces often masked by gravity influence the containment and transport of fluids aboard spacecraft, often in surprising non-intuitive ways. Terrestrial experience with capillary forces is typically relegated to the micro-scale, but engineering community exposure to large length scale capillary fluidics critical to spacecraft fluid management design is low indeed. Low-cost drop towers and fast-to-flight International Space Station (ISS) experiments are increasing designer exposure to this fresh field of study. This work first provides a wide variety of drop tower tests that demonstrate fundamental and applied capillary …
Photoemission Electron Microscopy For Analysis Of Dielectric Structures And The Goos-Hänchen Shift, Theodore Axel Stenmark
Photoemission Electron Microscopy For Analysis Of Dielectric Structures And The Goos-Hänchen Shift, Theodore Axel Stenmark
Dissertations and Theses
Photoemission Electron Microscopy (PEEM) is a versatile tool that relies on the photoelectric effect to produce high-resolution electron images. Ultrafast pulse lasers allow for multi-photon PEEM where multiple visible or IR photons excite a single electron in a nonlinear process. The photoelectron yield in both cases is related to the near-field region of electromagnetic fields at the surface of the sample. We use this ability here to analyze wave propagation in a linear dielectric waveguide with wavelengths of 410 nm and 780 nm. The propagation constant of the waveguide can be extracted from interference patterns created by light propagating in …
Physics-Based Imaging Methods For Terahertz Nondestructive Evaluation Applications, Gabriel Paul Kniffin
Physics-Based Imaging Methods For Terahertz Nondestructive Evaluation Applications, Gabriel Paul Kniffin
Dissertations and Theses
Lying between the microwave and far infrared (IR) regions, the "terahertz gap" is a relatively unexplored frequency band in the electromagnetic spectrum that exhibits a unique combination of properties from its neighbors. Like in IR, many materials have characteristic absorption spectra in the terahertz (THz) band, facilitating the spectroscopic "fingerprinting" of compounds such as drugs and explosives. In addition, non-polar dielectric materials such as clothing, paper, and plastic are transparent to THz, just as they are to microwaves and millimeter waves. These factors, combined with sub-millimeter wavelengths and non-ionizing energy levels, makes sensing in the THz band uniquely suited for …
On The Variability Of Pacific Ocean Tides At Seasonal To Decadal Time Scales: Observed Vs Modelled, Adam Thomas Devlin
On The Variability Of Pacific Ocean Tides At Seasonal To Decadal Time Scales: Observed Vs Modelled, Adam Thomas Devlin
Dissertations and Theses
Ocean tides worldwide have exhibited secular changes in the past century, simultaneous with a global secular rise in mean sea level (MSL). The combination of these two factors contributes to higher water levels, and may increase threats to coastal regions and populations over the next century. Equally as important as these long-term changes are the short-term fluctuations in sea levels and tidal properties. These fluctuations may interact to yield locally extreme water level events, especially when combined with storm surge. This study, presented in three parts, examines the relationships between tidal anomalies and MSL anomalies on yearly and monthly timescales, …
Listening To Lasers: Photoacoustic Gas Sensing, Michael Hopkins
Listening To Lasers: Photoacoustic Gas Sensing, Michael Hopkins
Student Research Symposium
Herein lies the makings of a sensor for gaseous materials due to the technique known as photo-acoustic spectroscopy. Whereby a gas filled metallic tube of known resonance has an impingement to its open aspect a beam of photons of known colour and at a specified rate such that the rate of incoming light corpuscles matches the natural standing wave frequency for the column of gas within said tube, to wit resonance. Through foresight of the molecular orbital theory and historic datums on the subject of infrared spectroscopy one naturally comes to the employment of absorbance transfiguring energy to kinetic motions …
A Chemistry Neutral Flow Battery Performance Model Development, Validation, And Application, Alasdair James Crawford
A Chemistry Neutral Flow Battery Performance Model Development, Validation, And Application, Alasdair James Crawford
Dissertations and Theses
A physical model for redox flow batteries is developed to estimate performance for any chemistry using parameters such as electrolyte conductivity and kinetic rate constants. The model returns the performance as a function of flow rate, current density, and state of charge. Two different models are developed to estimate the current density distribution throughout the electrode in order to evaluate physical performance of the battery. This is done using electrochemical parameters such as conductivity and kinetic rate constant. The models are analytical in order to produce a computationally cheap algorithm that can be used in optimization routines. This allows for …
More Investigations In Capillary Fluidics Using A Drop Tower, Andrew Paul Wollman, Mark M. Weislogel, Brentley M. Wiles, Donald Pettit, Trevor Snyder
More Investigations In Capillary Fluidics Using A Drop Tower, Andrew Paul Wollman, Mark M. Weislogel, Brentley M. Wiles, Donald Pettit, Trevor Snyder
Mechanical and Materials Engineering Faculty Publications and Presentations
A variety of contemplative demonstrations concerning intermediate-to-large length scale capillary fluidic phenomena were made possible by the brief weightless environment of a drop tower (Wollman and Weislogel in Exp Fluids 54(4):1, 2013). In that work, capillarity-driven flows leading to unique spontaneous droplet ejections, bubble ingestions, and multiphase flows were introduced and discussed. Such efforts are continued herein. The spontaneous droplet ejection phenomena (auto-ejection) is reviewed and demonstrated on earth as well as aboard the International Space Station. This technique is then applied to novel low-g droplet combustion where soot tube structures are created in the wakes of burning drops. …
A Novel Methodology For Spatial Damage Detection And Imaging Using A Distributed Carbon Nanotube-Based Composite Sensor Combined With Electrical Impedance Tomography, Hongbo Dai, Gerard J. Gallo, Thomas Schumacher, Erik T. Thostenson
A Novel Methodology For Spatial Damage Detection And Imaging Using A Distributed Carbon Nanotube-Based Composite Sensor Combined With Electrical Impedance Tomography, Hongbo Dai, Gerard J. Gallo, Thomas Schumacher, Erik T. Thostenson
Civil and Environmental Engineering Faculty Publications and Presentations
This paper describes a novel non-destructive evaluation methodology for imaging of damage in composite materials using the electrical impedance tomography (EIT) technique applied to a distributed carbon nanotube-based sensor. The sensor consists of a nonwoven aramid fabric, which was first coated with nanotubes using a solution casting approach and then infused with epoxy resin through the vacuum assisted resin transfer molding technique. Finally, this composite sensor is cured to become a mechanically-robust, electromechanically-sensitive, and highly customizable distributed two-dimensional sensor which can be adhered to virtually any substrate. By assuming that damage on the sensor directly affects its conductivity, a difference …
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 …
Mapping Of Defects In Individual Silicon Nanocrystals Using Real- Space Spectroscopy, Dmitry A. Kislitsyn, Vancho Kocevski, Jon M. Mills, Sheng-Kuei Chiu, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Mapping Of Defects In Individual Silicon Nanocrystals Using Real- Space Spectroscopy, Dmitry A. Kislitsyn, Vancho Kocevski, Jon M. Mills, Sheng-Kuei Chiu, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Chemistry Faculty Publications and Presentations
The photophysical properties of silicon semiconductor nanocrystals (SiNCs) are extremely sensitive to the presence of surface chemical defects, many of which are easily produced by oxidation under ambient conditions. The diversity of chemical structures of such defects and the lack of tools capable of probing individual defects continue to impede understanding of the roles of these defects in SiNC photophysics. We use scanning tunneling spectroscopy to study the impact of surface defects on the electronic structures of hydrogen-passivated SiNCs supported on the Au(111) surface. Spatial maps of the local electronic density of states (LDOS) produced by our measurements allowed us …
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 …
Complex Capillary Fluidic Phenomena For Passive Control Of Liquids In Low-Gravity Environments, Logan Torres
Complex Capillary Fluidic Phenomena For Passive Control Of Liquids In Low-Gravity Environments, Logan Torres
Undergraduate Research & Mentoring Program
In an effort to further apply the recent results of puddle jumping research, we seek to expand the oblique droplet impact studies of others by exploiting large liquid droplets in the near weightless environment of a drop tower. By using the spontaneous puddle jump mechanism, droplets of volumes 1 mL ≤ V ≤ 3 mL with corresponding Weber numbers of We ≈ 1 are impinged on surfaces inclined in the range 40° ≤ α ≤ 80° (measured from the horizontal plane). Impact surface wetting characteristics exhibit static contact angles θstatic = 165 ± 5°. All impacts result in complete rebound. …
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 …