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2013

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Full-Text Articles in Physics

A Model For The Hysteresis Observed In Gating Of Lysenin Channels, Eric Krueger, Radwan Al Faouri, Daniel Fologea, Ralph Henry, David Straub, Greg J. Salamo Dec 2013

A Model For The Hysteresis Observed In Gating Of Lysenin Channels, Eric Krueger, Radwan Al Faouri, Daniel Fologea, Ralph Henry, David Straub, Greg J. Salamo

Physics Faculty Publications and Presentations

The pore-forming toxin lysenin self-inserts to form conductance channels in natural and artificial lipid membranes containing sphingomyelin. The inserted channels exhibit voltage regulation and hysteresis of the macroscopic current during the application of positive periodic voltage stimuli. We explored the bi-stable behavior of lysenin channels and present a theoretical approach for the mechanism of the hysteresis to explain its static and dynamic components. This investigation develops a model to incorporate the role of charge accumulation on the bilayer lipid membrane in influencing the channel conduction state. Our model is supported by experimental results and also provides insight into the temperature ...


Planar Anchoring Strength And Pitch Measurements In Achiral And Chiral Chromonic Liquid Crystals Using 90-Degree Twist Cells, Christine K. Mcginn , '16, Laura I. Laderman , '15, N. Zimmermann, H.-S. Kitzerow, Peter J. Collings Dec 2013

Planar Anchoring Strength And Pitch Measurements In Achiral And Chiral Chromonic Liquid Crystals Using 90-Degree Twist Cells, Christine K. Mcginn , '16, Laura I. Laderman , '15, N. Zimmermann, H.-S. Kitzerow, Peter J. Collings

Physics & Astronomy Faculty Works

Chromonic liquid crystals are formed by molecules that spontaneously assemble into anisotropic structures in water. The ordering unit is therefore a molecular assembly instead of a molecule as in thermotropic liquid crystals. Although it has been known for a long time that certain dyes, drugs, and nucleic acids form chromonic liquid crystals, only recently has enough knowledge been gained on how to control their alignment so that studies of their fundamental liquid crystal properties can be performed. In this article, a simple method for producing planar alignment of the nematic phase in chromonic liquid crystals is described, and this in ...


Evolution Of Magnetism In The Single-Crystal Honeycomb Iridates (Na1−XLiX)2Iro3, Gang Cao, Tongfei Qi, L. Li, Jsaminka Terzic, Vincent Shian Cao, Shujuan Yuan, M. Tovar, Ganpathy Murthy, Ribhu K. Kaul Dec 2013

Evolution Of Magnetism In The Single-Crystal Honeycomb Iridates (Na1−XLiX)2Iro3, Gang Cao, Tongfei Qi, L. Li, Jsaminka Terzic, Vincent Shian Cao, Shujuan Yuan, M. Tovar, Ganpathy Murthy, Ribhu K. Kaul

Physics and Astronomy Faculty Publications

We report the successful synthesis of single crystals of the layered iridate (Na1−xLix)2IrO3, 0 ≤ x ≤ 0.9, and a thorough study of its structural, magnetic, thermal, and transport properties. This compound allows a controlled interpolation between Na2IrO3 and Li2IrO3, while maintaining the quantum magnetism of the honeycomb Ir4+ planes. The measured phase diagram demonstrates a suppression of the Néel temperature TN at an intermediate x, indicating that the magnetic orders in Na2IrO3 and Li2IrO3 are distinct. X-ray data show ...


Spectral Redemption In Clustering Sparse Networks, Florent Krzakala, Cristopher Moore, Elchanan Mossel, Joe Neeman, Allan Sly, Lenka Zdeborová, Pan Zhang Dec 2013

Spectral Redemption In Clustering Sparse Networks, Florent Krzakala, Cristopher Moore, Elchanan Mossel, Joe Neeman, Allan Sly, Lenka Zdeborová, Pan Zhang

Statistics Papers

Spectral algorithms are classic approaches to clustering and community detection in networks. However, for sparse networks the standard versions of these algorithms are suboptimal, in some cases completely failing to detect communities even when other algorithms such as belief propagation can do so. Here, we present a class of spectral algorithms based on a nonbacktracking walk on the directed edges of the graph. The spectrum of this operator is much better-behaved than that of the adjacency matrix or other commonly used matrices, maintaining a strong separation between the bulk eigenvalues and the eigenvalues relevant to community structure even in the ...


Determining The 7li(N,Gamma) Cross Section Via Coulomb Dissociation Of 8li, R. Izsak, A. Horvath, A. Kiss, Z. Seres, A. Galonsky, C. A. Bertulani, Zs Fueloep, T. Baumann, D. Bazin, K. Ieki, C. Bordeanu, N. Carlin, M. Csanád, F. Deák, Paul A. Deyoung, N. Frank, T. Fukuchi, A. Gade, D. Galaviz, C. R. Hoffman, W. A. Peters, H. Schelin, M. Thoennessen, G. I. Veres Dec 2013

Determining The 7li(N,Gamma) Cross Section Via Coulomb Dissociation Of 8li, R. Izsak, A. Horvath, A. Kiss, Z. Seres, A. Galonsky, C. A. Bertulani, Zs Fueloep, T. Baumann, D. Bazin, K. Ieki, C. Bordeanu, N. Carlin, M. Csanád, F. Deák, Paul A. Deyoung, N. Frank, T. Fukuchi, A. Gade, D. Galaviz, C. R. Hoffman, W. A. Peters, H. Schelin, M. Thoennessen, G. I. Veres

Faculty Publications

The applicability of Coulomb dissociation reactions to determine the cross section for the inverse neutron capture reaction was explored using the reaction Li-8(gamma,n)Li-7. A 69.5 MeV/nucleon Li-8 beam was incident on a Pb target, and the outgoing neutron and Li-7 nucleus were measured in coincidence. The deduced (n,gamma) excitation function is consistent with data for the direct capture reaction Li-7(n,gamma) Li-8 and with low-energy effective field theory calculations.


Azimuthal Anisotropy Of Pi(0) And Eta Mesons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Dec 2013

Azimuthal Anisotropy Of Pi(0) And Eta Mesons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The azimuthal anisotropy coefficients v2 and v4 of p 0 and. mesons are measured in Au + Au collisions at root s(NN) = 200 GeV as a function of transverse momentum p(T) (1-14 GeV/c) and centrality. The extracted v(2) coefficients are found to be consistent between the two meson species over the measured p(T) range. The ratio of v(4)/v(2)(2) for pi(0) mesons is found to be independent of p(T) for 1- 9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with p(T ...


Molecular Hydrogen Regulated Star Formation In Cosmological Smoothed Particle Hydrodynamics Simulations, Robert Thompson, Kentaro Nagamine, Jason Jaacks, Jun-Hwan Choi Dec 2013

Molecular Hydrogen Regulated Star Formation In Cosmological Smoothed Particle Hydrodynamics Simulations, Robert Thompson, Kentaro Nagamine, Jason Jaacks, Jun-Hwan Choi

Physics and Astronomy Faculty Publications

Some observations have shown that star formation (SF) correlates tightly with the presence of molecular hydrogen (H2); therefore, it is important to investigate its implication on galaxy formation in a cosmological context. In the present work, we implement a sub-grid model (hereafter H2-SF model) that tracks the H2 mass fraction within our cosmological smoothed particle hydrodynamics code GADGET-3 by using an equilibrium analytic model of Krumholz et al. This model allows us to regulate the SF in our simulation by the local abundance of H2 rather than the total cold gas density, which naturally introduces ...


Automated Annotation Of Functional Imaging Experiments Via Multi-Label Classification, Matthew D. Turner, Chayan Chakrabarti, Thomas B. Jones, Jiawei F. Xu, Peter T. Fox, George F. Luger, Angela Laird, Jessica A. Turner Dec 2013

Automated Annotation Of Functional Imaging Experiments Via Multi-Label Classification, Matthew D. Turner, Chayan Chakrabarti, Thomas B. Jones, Jiawei F. Xu, Peter T. Fox, George F. Luger, Angela Laird, Jessica A. Turner

Department of Physics

Identifying the experimental methods in human neuroimaging papers is important for grouping meaningfully similar experiments for meta-analyses. Currently, this can only be done by human readers. We present the performance of common machine learning (text mining) methods applied to the problem of automatically classifying or labeling this literature. Labeling terms are from the Cognitive Paradigm Ontology (CogPO), the text corpora are abstracts of published functional neuroimaging papers, and the methods use the performance of a human expert as training data. We aim to replicate the expert's annotation of multiple labels per abstract identifying the experimental stimuli, cognitive paradigms, response ...


Direct Coupling Of Photonic Modes And Surface Plasmon Polaritons Observed In 2-Photon Peem, Robert Campbell Word, Joseph Fitzgerald, Rolf Könenkamp Dec 2013

Direct Coupling Of Photonic Modes And Surface Plasmon Polaritons Observed In 2-Photon Peem, Robert Campbell Word, Joseph Fitzgerald, Rolf Könenkamp

Physics Faculty Publications and Presentations

We report the direct microscopic observation of optical energy transfer from guided photonic modes in an indium tin oxide (ITO) thin film to surface plasmon polaritons (SPP) at the surfaces of a single crystalline gold platelet. The photonic and SPP modes appear as an interference pattern in the photoelectron emission yield across the surface of the specimen. We explore the momentum match between the photonic and SPP modes in terms of simple waveguide theory and the three-layer slab model for bound SPP modes of thin metal films. We show that because the gold is thin (30- 40 nm), two SPP ...


Physics 2710 – Example Exam Iii, David Peak Dec 2013

Physics 2710 – Example Exam Iii, David Peak

Exams

No abstract provided.


Mid-Latiude Rayleigh-Mie-Raman Lidar For Observations From 15 To 120 Km, Vincent B. Wickwar, Leda Sox, Joshua P. Herron, Matthew T. Emerick Dec 2013

Mid-Latiude Rayleigh-Mie-Raman Lidar For Observations From 15 To 120 Km, Vincent B. Wickwar, Leda Sox, Joshua P. Herron, Matthew T. Emerick

Posters

Rayleigh lidar opened a portion of the atmosphere, from 30 to 90 km, to ground-based observations. Rayleigh-scatter observations were made at the Atmospheric Lidar Observatory (ALO) at Utah State University (USU) from 1993–2004 between 45 and 90 km. The lidar consisted of a 0.44-m diameter mirror, a frequency-doubled Nd:YAG laser opera'ng at 532-nm at 30- Hz at either 18- or 24-W, giving power- aperture products (PAPs) of 2.7- or 3.6- Wm2, respec'vely, and one detector channel. An example of what was accomplished with this system is shown as part of Fig. 1. The ...


Atomic Data For S Ii—Toward Better Diagnostics Of Chemical Evolution In High-Redshift Galaxies, Romas Kisielius, Varsha P. Kulkarni, Gary J. Ferland, Pavel Bogdanovich, Matt L. Lykins Dec 2013

Atomic Data For S Ii—Toward Better Diagnostics Of Chemical Evolution In High-Redshift Galaxies, Romas Kisielius, Varsha P. Kulkarni, Gary J. Ferland, Pavel Bogdanovich, Matt L. Lykins

Physics and Astronomy Faculty Publications

Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA ...


Can Bohmian Mechanics Be Made Relativistic?, Detlef Dürr, Sheldon Goldstein, Travis Norsen, Ward Struyve, Nino Zaghì Dec 2013

Can Bohmian Mechanics Be Made Relativistic?, Detlef Dürr, Sheldon Goldstein, Travis Norsen, Ward Struyve, Nino Zaghì

Physics: Faculty Publications

In relativistic space-time, Bohmian theories can be formulated by introducing a privileged foliation of space-time. The introduction of such a foliation – as extra absolute space-time structure – would seem to imply a clear violation of Lorentz invariance, and thus a conflict with fundamental relativity. Here, we consider the possibility that, instead of positing it as extra structure, the required foliation could be covariantly determined by the wave function. We argue that this allows for the formulation of Bohmian theories that seem to qualify as fundamentally Lorentz invariant. We conclude with some discussion of whether or not they might also qualify as ...


Bilayers In Nanoparticle-Doped Polar Mesogens, Alexander Lorenz, Dena Mae Agra-Kooijman, Natalie Zimmermann, Heinz-S. Kitzerow, Dean R. Evans Dec 2013

Bilayers In Nanoparticle-Doped Polar Mesogens, Alexander Lorenz, Dena Mae Agra-Kooijman, Natalie Zimmermann, Heinz-S. Kitzerow, Dean R. Evans

Physics Publications

Structures of the mesophases of five members of the 4-n-alkyl-4′-cyanobiphenyl homologous series (4-n-butyl-4′-cyanobiphenyl to 4-n-octyl-4′-cyanobiphenyl) doped with milled BaTiO3 nanoparticles were investigated by x-ray scattering. Clear solutions of each of the 4-n-alkyl-4′-cyanobiphenyls were first prepared in n-heptane and then doped with an n-heptane/nanoparticle dispersion, which led to gelation. The nanogels were found to be one-dimensional, multilayered, smectic nanostructures in each case. Surprisingly, a characteristic layer spacing of 4.5 nm was observed in all five homologues. Synchrotron x-ray scattering study of the multilayer structures of doped 4-n-pentyl-4′-cyanobiphenyl and 4-n-octyl-4′-cyanobiphenyl revealed nine orders ...


Capillary Channel Flow Experiments Aboard The International Space Station, Michael Conrath, P. J. Canfield, P. M. Bronowicki, Michael E. Dreyer, Mark M. Weislogel, A. Grah Dec 2013

Capillary Channel Flow Experiments Aboard The International Space Station, Michael Conrath, P. J. Canfield, P. M. Bronowicki, Michael E. Dreyer, Mark M. Weislogel, A. Grah

Mechanical and Materials Engineering Faculty Publications and Presentations

In the near-weightless environment of orbiting spacecraft capillary forces dominate interfacial flow phenomena over unearthly large length scales. In current experiments aboard the International Space Station, partially open channels are being investigated to determine critical flow rate-limiting conditions above which the free surface collapses ingesting bubbles. Without the natural passive phase separating qualities of buoyancy, such ingested bubbles can in turn wreak havoc on the fluid transport systems of spacecraft. The flow channels under investigation represent geometric families of conduits with applications to liquid propellant acquisition, thermal fluids circulation, and water processing for life support. Present and near future experiments ...


Universal Quantum Fluctuations Of A Cavity Mode Driven By A Josephson Junction, A. D. Armour, M. P. Blencowe, E. Brahimi, A. J. Rimberg Dec 2013

Universal Quantum Fluctuations Of A Cavity Mode Driven By A Josephson Junction, A. D. Armour, M. P. Blencowe, E. Brahimi, A. J. Rimberg

Open Dartmouth: Faculty Open Access Scholarship

We analyze the quantum dynamics of a superconducting cavity coupled to a voltage-biased Josephson junction. The cavity is strongly excited at resonances where the voltage energy lost by a Cooper pair traversing the circuit is a multiple of the cavity photon energy. We find that the resonances are accompanied by substantial squeezing of the quantum fluctuations of the cavity over a broad range of parameters and are able to identify regimes where the fluctuations in the system take on universal values.


Precision Spectroscopy Of Polarized Molecules In An Ion Trap, Huanqian Loh, Kevin C. Cossel, Matt Grau, Kang-Kuen Ni, Edmund R. Meyer, John L. Bohn, Jun Ye, Eric A. Cornell Dec 2013

Precision Spectroscopy Of Polarized Molecules In An Ion Trap, Huanqian Loh, Kevin C. Cossel, Matt Grau, Kang-Kuen Ni, Edmund R. Meyer, John L. Bohn, Jun Ye, Eric A. Cornell

Physics Faculty Contributions

Polar molecules are desirable systems for quantum simulations and cold chemistry. Molecular ions are easily trapped, but a bias electric field applied to polarize them tends to accelerate them out of the trap. We present a general solution to this issue by rotating the bias field slowly enough for the molecular polarization axis to follow but rapidly enough for the ions to stay trapped. We demonstrate Ramsey spectroscopy between Stark-Zeeman sublevels in 180Hf19F+ with a coherence time of 100 ms. Frequency shifts arising from well-controlled topological (Berry) phases are used to determine magnetic g-factors. The rotating-bias-field technique ...


Determination Of The Top-Quark Pole Mass And Strong Coupling Constant From The T T-Bar Production Cross Section In Pp Collisions At Sqrt(S) = 7 Tev, Cms Collaboration, Vanessa Gaultney, Samantha Hewamanage, Stephan Linn, Pete E. Markowitz, German Martinez, Jorge Luis Rodriguez Dec 2013

Determination Of The Top-Quark Pole Mass And Strong Coupling Constant From The T T-Bar Production Cross Section In Pp Collisions At Sqrt(S) = 7 Tev, Cms Collaboration, Vanessa Gaultney, Samantha Hewamanage, Stephan Linn, Pete E. Markowitz, German Martinez, Jorge Luis Rodriguez

Department of Physics

The inclusive cross section for top-quark pair production measured by the CMS experiment in proton–proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, m[pole over t], or the strong coupling constant, α[subscript S]. With the parton distribution function set NNPDF2.3, a pole mass of 176.7[+3.8 over −3.4] GeV is obtained when constraining α[subscript S] at the scale of the Z boson mass, m[subscript Z], to the current world average. Alternatively ...


Optically-Pumped Spin-Exchange Polarized Electron Source, Munir Pirbhai Dec 2013

Optically-Pumped Spin-Exchange Polarized Electron Source, Munir Pirbhai

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Polarized electron beams are an indispensable probe of spin-dependent phenomena in fields of atomic and molecular physics, magnetism and biophysics. While their uses have become widespread, the standard source based on negative electron affinity gallium arsenide (GaAs) remains technically complicated. This has hindered progress on many experiments involving spin-polarized electrons, especially those using target gas loads, which tend to adversely affect the performance of GaAs sources. A robust system based on an alternative way to make polarized electron beams has been devised in this study, which builds on previous work done in our lab. It involves spin-exchange collisions between free ...


The Progenitors Of The Compact Early-Type Galaxies At High Redshift, Christina C. Williams, Mauro Giavalisco, Paolo Cassata, Elena Tundo, Tommy Wiklind, Yicheng Guo, Bomee Lee, Guillermo Barro, Stijn Wuyts, Eric F. Bell, Christopher J. Conselice, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Norman A. Grogin, Nimish Hathi, Kuang-Han Huang, Dalibor D. Kocevski, Anton M. Koekemoer, David C. Koo, Swara Ravindranath, Sarah Salimbeni Dec 2013

The Progenitors Of The Compact Early-Type Galaxies At High Redshift, Christina C. Williams, Mauro Giavalisco, Paolo Cassata, Elena Tundo, Tommy Wiklind, Yicheng Guo, Bomee Lee, Guillermo Barro, Stijn Wuyts, Eric F. Bell, Christopher J. Conselice, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Norman A. Grogin, Nimish Hathi, Kuang-Han Huang, Dalibor D. Kocevski, Anton M. Koekemoer, David C. Koo, Swara Ravindranath, Sarah Salimbeni

Physics and Astronomy Faculty Publications

We use GOODS and CANDELS images to identify progenitors of massive (M > 1010 M ) compact early-type galaxies (ETGs) at z ~ 1.6. Because merging and accretion increase the size of the stellar component of galaxies, if the progenitors are among known star-forming galaxies, these must be compact themselves. We select candidate progenitors among compact Lyman-break galaxies at z ~ 3 on the basis of their mass, star-formation rate (SFR), and central stellar density, and we find that these account for a large fraction of, and possibly all, compact ETGs at z ~ 1.6. We find that the average far-UV spectral ...


Polarization-Coupled Transport Behavior In Ultrathin Ferroelectric Heterostructures, Haidong Lu Dec 2013

Polarization-Coupled Transport Behavior In Ultrathin Ferroelectric Heterostructures, Haidong Lu

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Ferroelectric polarization-coupled resistive switching behavior in ferroelectric tunnel junctions (FTJs), the tunneling electroresistance (TER) effect, is a recently predicted new phenomenon, which attracts interest due to potential application in the next generation non-volatile ferroelectric random access memories (FeRAMs). In this dissertation, we demonstrate the TER effect in FTJ devices by means of scanning probe microscopy (SPM) techniques. We have investigated several device configurations for enhancement of polarization stability and for demonstration of the resistive switching behavior: (i) using the SPM probe as a top electrode; (ii) using heterostructures with engineered interfacial atomic terminations; (iii) using metal electrodes; (iv) adding an ...


Structure And Coarsening At The Surface Of A Dry Three-Dimensional Aqueous Foam, R. E. Roth, B. G. Chen, Douglas J. Durian Dec 2013

Structure And Coarsening At The Surface Of A Dry Three-Dimensional Aqueous Foam, R. E. Roth, B. G. Chen, Douglas J. Durian

Department of Physics Papers

We utilize total-internal reflection to isolate the two-dimensional surface foam formed at the planar boundary of a three-dimensional sample. The resulting images of surface Plateau borders are consistent with Plateau's laws for a truly two-dimensional foam. Samples are allowed to coarsen into a self-similar scaling state where statistical distributions appear independent of time, except for an overall scale factor. There we find that statistical measures of side number distributions, size-topology correlations, and bubble shapes are all very similar to those for two-dimensional foams. However, the size number distribution is slightly broader, and the shapes are slightly more elongated. A ...


Asymptotic Multi-Layer Analysis Of Wind Over Unsteady Monochromatic Surface Waves, Shahrdad Sajjadi, Julian Hunt, Frederique Drullion Dec 2013

Asymptotic Multi-Layer Analysis Of Wind Over Unsteady Monochromatic Surface Waves, Shahrdad Sajjadi, Julian Hunt, Frederique Drullion

Publications

Asymptotic multi-layer analyses and computation of solutions for turbulent flows over steady and unsteady monochromatic surface wave are reviewed, in the limits of low turbulent stresses and small wave amplitude. The structure of the flow is defined in terms of asymptotically-matched thin-layers, namely the surface layer and a critical layer, whether it is ‘elevated’ or ‘immersed’, corresponding to its location above or within the surface layer. The results particularly demonstrate the physical importance of the singular flow features and physical implications of the elevated critical layer in the limit of the unsteadiness tending to zero. These agree with the variational ...


Electron-Impact Vibrational Excitation Of Vibrationally Excited H2 Molecules Involving The Resonant 2(Sigma)G+ Rydberg-Excited Electronic State, R Celiberto, R. K. Janev, V Laporta, J Tennyson, J. M. Wadehra Dec 2013

Electron-Impact Vibrational Excitation Of Vibrationally Excited H2 Molecules Involving The Resonant 2(Sigma)G+ Rydberg-Excited Electronic State, R Celiberto, R. K. Janev, V Laporta, J Tennyson, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Electron-impact theoretical cross sections and rate coefficients for vibrational excitation of vibrationally excited H2 molecules, occurring through the H−2 resonant species in the 2Σ+g Rydberg-excited electronic state, are presented. The cross sections are calculated as functions of the incident electron energy by adopting the local-complex-potential model for resonant collisions and by using ab initio calculated molecular potentials and resonance widths. The calculations have been extended to all possible vibrational transitions linking all 15 vibrational levels of the electronic ground state of the H2 molecule. The corresponding rate coefficients are also obtained as a function of the electron temperature ...


Effects Of External Radiation Fields On Line Emission—Application To Star-Forming Regions, Marios Chatzikos, Gary J. Ferland, R. J. R. Williams, Ryan Porter, P. A. M. Vanhoof Dec 2013

Effects Of External Radiation Fields On Line Emission—Application To Star-Forming Regions, Marios Chatzikos, Gary J. Ferland, R. J. R. Williams, Ryan Porter, P. A. M. Vanhoof

Physics and Astronomy Faculty Publications

A variety of astronomical environments contain clouds irradiated by a combination of isotropic and beamed radiation fields. For example, molecular clouds may be irradiated by the isotropic cosmic microwave background, as well as by a nearby active galactic nucleus. These radiation fields excite atoms and molecules and produce emission in different ways. We revisit the escape probability theorem and derive a novel expression that accounts for the presence of external radiation fields. We show that when the field is isotropic the escape probability is reduced relative to that in the absence of external radiation. This is in agreement with previous ...


Electron Tunneling Characteristics Of A Cubic Quantum Dot, (Pbs)32, Sanjeev K. Gupta, Haiying He, Douglas Banyai, Anil K. Kandalam, Ravindra Pandey Dec 2013

Electron Tunneling Characteristics Of A Cubic Quantum Dot, (Pbs)32, Sanjeev K. Gupta, Haiying He, Douglas Banyai, Anil K. Kandalam, Ravindra Pandey

Physics

No abstract provided.


Infrared Skin Damage Thresholds From 1319-Nm Continous-Wave Laser Exposures, Gavin D. Buffington, Clifton D. Clark Dec 2013

Infrared Skin Damage Thresholds From 1319-Nm Continous-Wave Laser Exposures, Gavin D. Buffington, Clifton D. Clark

Physics Faculty Publications

A series of experiments were conducted in vivo using Yucatan miniature pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1319-nm continuous-wave Nd:YAG laser irradiation. Experiments employed exposure durations of 0.25, 1.0, 2.5, and 10 s and beam diameters of ∼0.6 and 1 cm. Thermal imagery data provided a time-dependent surface temperature response from the laser. A damage endpoint of fifty percent probability of a minimally visible effect was used to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a ...


Magneto-Transport Characteristics Of A 2d Electron System Driven To Negative Magneto-Conductivity By Microwave Photoexcitation, Ramesh G. Mani, Annika Kriisa Dec 2013

Magneto-Transport Characteristics Of A 2d Electron System Driven To Negative Magneto-Conductivity By Microwave Photoexcitation, Ramesh G. Mani, Annika Kriisa

Physics and Astronomy Faculty Publications

Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking-property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/ resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly ...


Hydrogen Evolution Reaction Measurements Of Dealloyed Porous Nicu, Kyla Koboski, Evan Nelsen, Jennifer R. Hampton Dec 2013

Hydrogen Evolution Reaction Measurements Of Dealloyed Porous Nicu, Kyla Koboski, Evan Nelsen, Jennifer R. Hampton

Faculty Publications

Porous metals are of interest for their high surface area and potential for enhanced catalytic behavior. Electrodeposited NiCu thin films with a range of compositions were electrochemically dealloyed to selectively remove the Cu component. The film structure, composition, and reactivity of these samples were characterized both before and after the dealloying step using scanning electron microscopy, energy-dispersive spectroscopy, and electrochemical measurements. The catalytic behavior of the dealloyed porous Ni samples towards the hydrogen evolution reaction was measured and compared to that of the as-deposited samples. The dealloyed samples were generally more reactive than their as-deposited counterparts at low overpotentials, making ...


Magnetic Anisotropy And Exchange In (001) Textured Fept-Based Nanostructures, Tom George Dec 2013

Magnetic Anisotropy And Exchange In (001) Textured Fept-Based Nanostructures, Tom George

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Hard-magnetic L10 phase FePt has been demonstrated as a promising candidate for future nanomagnetic applications, especially magnetic recording at areal densities approaching 10 Tb/in2. Realization of FePt’s potential in recording media requires control of grain size and intergranular exchange interactions in films with high degrees of L10 order and (001) crystalline texture, including high perpendicular magnetic anisotropy. Furthermore, a write-assist mechanism must be employed to overcome the high coercivity of L10 FePt nanograins. The research described in this dissertation examines potential solutions to the aforementioned problems. Specifically, a nonepitaxial method of fabricating highly (001 ...