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Articles 28111 - 28140 of 36710

Full-Text Articles in Physical Sciences and Mathematics

Cross Sections Fall 2003, Department Of Physics And Astronomy Oct 2003

Cross Sections Fall 2003, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

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Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Ya I. Alivov, J. E. Van Nostrand, David C. Look, M. V. Chukichev, B. M. Ataev Oct 2003

Observation Of 430 Nm Electroluminescence From Zno/Gan Heterojunction Light-Emitting Diodes, Ya I. Alivov, J. E. Van Nostrand, David C. Look, M. V. Chukichev, B. M. Ataev

Physics Faculty Publications

In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear …

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Resonant Photoemission In F-Electron Systems: Pu And Gd, James G. Tobin, Brandon W. Chung, Roland K. Schulze, Jeff Russell Terry, John Douglas Farr, David K. Shuh, K. Heinzelman, Eli Rotenberg, George Daniel Waddill, Gerrit V. Van Der Laan Oct 2003

Resonant Photoemission In F-Electron Systems: Pu And Gd, James G. Tobin, Brandon W. Chung, Roland K. Schulze, Jeff Russell Terry, John Douglas Farr, David K. Shuh, K. Heinzelman, Eli Rotenberg, George Daniel Waddill, Gerrit V. Van Der Laan

Physics Faculty Research & Creative Works

Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

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Application Of Interferometric Wave Propagation For Refractive Index Measurements Of Solids, Glen D. Gillen, Shekhar Guha Oct 2003

Application Of Interferometric Wave Propagation For Refractive Index Measurements Of Solids, Glen D. Gillen, Shekhar Guha

Physics

The output signal of a modified Michelson interferometer with a flat-parallel sample, whose normal is oriented at an arbitrary angle with respect to the laser path, placed in one arm is analyzed. The interferometric pattern as a function of angle is calculated, and used to determine the absolute refractive index.

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Microtonal Systems And Guitar Composition, Michael Nielsen Oct 2003

Microtonal Systems And Guitar Composition, Michael Nielsen

Masters

This thesis focuses on the use of microtones in guitar composition. In the course of this study the physical aspects of musical sound (pitch, loudness and quality/timbre), vibrational frequencies of strings, and the theory of musical scales and tuning systems are discussed. Whole-number ratios corresponding to musical intervals within the twelve-note/equal temperament scale are calculated in relation to the overtone series for the purpose of surveying consonance and dissonance within the tempered system. These are compared to the ratios for corresponding intervals within the overtone series. Whole-number ratios are also calculated for intervals involving the microtones referred to in this …

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Materials Characterization At Utah State University: Facilities And Knowledgebase Of Electronic Properties Of Materials Applicable To Spacecraft Charging, John R. Dennison, C. D. Thomson, J. T. Kite, V. V. Zavyalov, Jodie Corbridge Oct 2003

Materials Characterization At Utah State University: Facilities And Knowledgebase Of Electronic Properties Of Materials Applicable To Spacecraft Charging, John R. Dennison, C. D. Thomson, J. T. Kite, V. V. Zavyalov, Jodie Corbridge

All Physics Faculty Publications

In an effort to improve the reliability and versatility of spacecraft charging models designed to assist spacecraft designers in accommodating and mitigating the harmful effects of charging on spacecraft, the NASA Space Environments and Effects (SEE) Program has funded development of facilities at Utah State University for the measurement of the electronic properties of both conducting and insulating spacecraft materials. We present here an overview of our instrumentation and capabilities, which are particularly well suited to study electron emission as related to spacecraft charging. These measurements include electron-induced secondary and backscattered yields, spectra, and angular resolved measurements as a function …

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Utilising Riometry To Observe Gravity Waves In The Sunlit Mesosphere, M. J. Jarvis, R. E. Hibbins, Michael J. Taylor, T. J. Rosenberg Oct 2003

Utilising Riometry To Observe Gravity Waves In The Sunlit Mesosphere, M. J. Jarvis, R. E. Hibbins, Michael J. Taylor, T. J. Rosenberg

All Physics Faculty Publications

The novel use of imaging riometers to observe mesospheric gravity waves is described. Imaging riometers respond to changes in the absorption of cosmic radio noise in the ionospheric D-region which enables them to detect the compression and rarefaction of the atmosphere at 90 km altitude generated by the passage of gravity waves. A considerable advantage of this method is that, unlike conventional techniques which rely on imaging faint optical emissions from the airglow layer at 87 km altitude, riometers remain operative under daylit, moonlit or cloudy conditions. This is particularly important for research into gravity wave forcing of mesospheric temperature …

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Examination Of Focused Beam Propagation Through A Finite Non-Reciprocal Planar Chiral Slab Using Complex Fresnel Coefficients And Dual Transforms, Monish Ranjan Chatterjee, Sumit Nema, Partha P. Banerjee Oct 2003

Examination Of Focused Beam Propagation Through A Finite Non-Reciprocal Planar Chiral Slab Using Complex Fresnel Coefficients And Dual Transforms, Monish Ranjan Chatterjee, Sumit Nema, Partha P. Banerjee

Electrical and Computer Engineering Faculty Publications

Recently, uniform plane wave propagation across a nonchiral-chiral interface was examined via the development of appropriate Fresnel coefficients. In this extension, propagation of focused uniform and profiled beams through a finite, planar nonreciprocal chiral slab is investigated using complex Fresnel coefficients via angular plane wave decomposition and dual transforms.

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Toy Models For The Falling Chimney, Gabriele U. Varieschi, Kaoru Kamiya Oct 2003

Toy Models For The Falling Chimney, Gabriele U. Varieschi, Kaoru Kamiya

Physics Faculty Works

In this paper we review the theory of the ‘‘falling chimney,’’ which deals with the breaking in mid-air of tall structures when they fall to the ground. We show that these ruptures can be caused by either shear forces typically developing near the base, or by the bending of the structure which is caused primarily by the internal bending moment. In the latter case the breaking is more likely to occur between one-third and one-half of the height of the chimney. Small scale toy models are used to reproduce the dynamics of the falling chimney. By examining photos taken during …

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Spectral Representation Of The Electrical Properties Of Layered Materials., Anthony Day, A. Mcgurn, D. Bergman, M. Thorpe Sep 2003

Spectral Representation Of The Electrical Properties Of Layered Materials., Anthony Day, A. Mcgurn, D. Bergman, M. Thorpe

Anthony Roy Day

We present a spectral representation for the effective conductivity of two homogeneous layers joined at a rough interface. This spectral representation is closely related to the Bergman-Milton spectral representation for bulk composites, and is easily extended to multilayered materials. By comparing the layered system to a reference layered system that has a flat interface, we form a surface spectral density that captures all the effects of surface structure on the effective conductivity of the layered sample, and is independent of the conductivities of the two layers. Because of the anisotropy of the layered system there are two surface spectral densities, …

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Effect Of Parallel Velocity Shear On The Electrostatic Ion-Cyclotron Instability In Flamentary Current Channels, Erick Agrimson, Su-Hyun Kim, Nicola D'Angelo, Robert L. Merlino Sep 2003

Effect Of Parallel Velocity Shear On The Electrostatic Ion-Cyclotron Instability In Flamentary Current Channels, Erick Agrimson, Su-Hyun Kim, Nicola D'Angelo, Robert L. Merlino

Erick Agrimson

No abstract provided.

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Curvature-Induced Defect Unbinding In Toroidal Geometries, Mark Bowick, David R. Nelson, Alex Travesset Sep 2003

Curvature-Induced Defect Unbinding In Toroidal Geometries, Mark Bowick, David R. Nelson, Alex Travesset

Physics - All Scholarship

Toroidal templates such as vesicles with hexatic bond orientational order are discussed. The total energy including disclination charges is explicitly computed for hexatic order embedded in a toroidal geometry. Related results apply for tilt or nematic order on the torus in the one Frank constant approximation. Although there is no topological necessity for defects in the ground state, we find that excess disclination defects are nevertheless energetically favored for fat torii or moderate vesicle sizes. Some experimental consequences are discussed.

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Task 32 Delayed Hydride Cracking Of Spent Fuel Cladding Under Repository Conditions, Ajit K. Roy, Anthony Hechanova, Amy J. Smiecinski Sep 2003

Task 32 Delayed Hydride Cracking Of Spent Fuel Cladding Under Repository Conditions, Ajit K. Roy, Anthony Hechanova, Amy J. Smiecinski

Publications (YM)

The objective of this quality-affecting task is to evaluate the susceptibility of spent nuclear fuel cladding materials (zirconium alloys) to stress corrosion cracking (SCC), delayed hydride cracking (DHC) and localized corrosion (pitting/crevice) in simulated repository environments. During the first year of this project, major efforts were focused on developing the infrastructure for performing the desired testing involving two highly corrosion-resistant alloys namely, zircaloy-2 (Zr-2) and zircaloy-4 (Zr-4) in simulated concentrated acidic water (SAW) and modified SAW (SAWM). Modification of the SAW chemistry was done by adding hydrochloric acid (HC1) to achieve lower pH. The construction of the "Materials Performance Laboratory …

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Kinetics Of Ferroelectric Switching In Ultrathin Films, G. Vizdrik, Stephen Ducharme, V.M. Fridkin, S.G. Yudin Sep 2003

Kinetics Of Ferroelectric Switching In Ultrathin Films, G. Vizdrik, Stephen Ducharme, V.M. Fridkin, S.G. Yudin

Stephen Ducharme Publications

The kinetics of polarization switching in ultrathin ferroelectric polymer films exhibit a critical behavior; there is a pronounced slowing just above the coercive field and just below the critical temperature. The critical slowing is observed in the switching kinetics of ferroelectric Langmuir-Blodgett films of 70% vinylidene-fluoride and 30% trifluoroethylene copolymer with thickness up to 30 ML. Thicker films exhibit an exponential dependence on the field and temperature that is normally associated with extrinsic switching by domain nucleation and growth. We show that the critical behavior arises naturally from the dynamics of homogeneous intrinsic switching in the context of mean-field theory. …

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The Logic Of Peace, Jonathan Schell Sep 2003

The Logic Of Peace, Jonathan Schell

New England Journal of Public Policy

Jonathan Schell’s The Unconquerable World points the way out of the devastation of the twentieth century toward another, more peaceful path. And his investigations into the great nonviolent events of modern times — from Gandhi’s independence movement in India to the explosion of civic activity that brought about the surprising collapse of the Soviet Union — suggest foundations of an entirely new kind on which to construct an enduring peace. As Schell makes clear, all-out war, with its risk of human extinction, must cease to play the role of final arbiter. “The Logic of Peace,” printed here, is the final …

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Search For ΝΜ→ΝE Oscillations In The Nomad Experiment, Nomad Collaboration, P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, S. Buyatov, L. Camilleri, A. Cardini, P. W. Cattaneo, V. Cavasinni, Roberto Petti, Et. Al. Sep 2003

Search For ΝΜ→ΝE Oscillations In The Nomad Experiment, Nomad Collaboration, P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, S. Buyatov, L. Camilleri, A. Cardini, P. W. Cattaneo, V. Cavasinni, Roberto Petti, Et. Al.

Faculty Publications

We present the results of a search for νµ → νe oscillations in the NOMAD experiment at CERN. The experiment looked for the appearance of νe in a predominantly νµ wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are ∆m2 < 0.4 eV2 for maximal mixing and sin2(2θ)−3 for large ∆m2. This result excludes the LSND allowed region of oscillation parameters with ∆m2 ≳∆10 eV2.

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Large Nc And Chiral Dynamics, Joseph Schechter, Masayasu Harada, Francesco Sannino Sep 2003

Large Nc And Chiral Dynamics, Joseph Schechter, Masayasu Harada, Francesco Sannino

Physics - All Scholarship

We study the dependence on the number of colors of the leading pi pi scattering amplitude in chiral dynamics. We demonstrate the existence of a critical number of colors for and above which the low energy pi pi scattering amplitude computed from the simple sum of the current algebra and vector meson terms is crossing symmetric and unitary at leading order in a truncated and regularized 1/Nc expansion. The critical number of colors turns out to be Nc=6 and is insensitive to the explicit breaking of chiral symmetry. Below this critical value, an additional state is needed to enforce the …

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Refrigerator With Phonon Filters: An Application Of The Phonon Deficit Effect In Superconducting Tunnel Junctions, G. G. Melkonyan, Armen Gulian Sep 2003

Refrigerator With Phonon Filters: An Application Of The Phonon Deficit Effect In Superconducting Tunnel Junctions, G. G. Melkonyan, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Nonequilibrium phenomena in thin solid films can result in cooling effects. These types of effects were predicted theoretically a while ago, and only recently were demonstrated experimentally in superconductor-insulator-normal metal (SIN) tunnel junctions. Since then, there is a growing interest in tunneling effects for the purpose to develop on-chip refrigerators. Thin film devices have the advantage of being extremely compact, operate in a continuous mode, dissipate little power, and can easily be integrated in cryogenic detectors. Currently these refrigerators can generate cooling in the order of 100 mK in an environment of 0.3–0.5 K. There are reasons to expect that …

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Transition Probabilities In Kr Ii And Kr Iii Spectra, Stevan Djenize, Vladimir Milosavljevic, Milan S. Dimitrijevic Sep 2003

Transition Probabilities In Kr Ii And Kr Iii Spectra, Stevan Djenize, Vladimir Milosavljevic, Milan S. Dimitrijevic

Articles

On the basis of the relative line intensity ratio (RLIR) method, transition probability values of the spontaneous emission (Einstein's A values) of 14 transitions in the singly (Kr II) and 7 transitions in doubly (Kr III) ionized krypton spectra have been obtained relatively to the reference A values related to the 435.548 nm Kr II and 324.569 nm Kr III, the most intensive transitions in the Kr II and Kr III spectra. Our Kr III transition probability values are the first data obtained experimentally using the RLIR method. A linear, low–pressure, pulsed arc operated in krypton discharge was used as …

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Complex Multiplication Symmetry Of Black Hole Attractors, Monika Lynker, Vipul Periwal, Rolf Schimmrigk Sep 2003

Complex Multiplication Symmetry Of Black Hole Attractors, Monika Lynker, Vipul Periwal, Rolf Schimmrigk

Faculty Articles

We show how Moore’s observation, in the context of toroidal compactifications in type IIB string theory, concerning the complex multiplication structure of black hole attractor varieties, can be generalized to Calabi-Yau compactifications with finite fundamental groups. This generalization leads to an alternative general framework in terms of motives associated to a Calabi-Yau variety in which it is possible to address the arithmetic nature of the attractor varieties in a universal way via Deligne’s period conjecture.

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Percolation Of Satisfiability In Finite Dimensions, Alan Middleton, J. M. Schwarz Sep 2003

Percolation Of Satisfiability In Finite Dimensions, Alan Middleton, J. M. Schwarz

Physics - All Scholarship

The satisfiability and optimization of finite-dimensional Boolean formulas are studied using percolation theory, rare region arguments, and boundary effects. In contrast with mean-field results, there is no satisfiability transition, though there is a logical connectivity transition. In part of the disconnected phase, rare regions lead to a divergent running time for optimization algorithms. The thermodynamic ground state for the NP-hard two-dimensional maximum-satisfiability problem is typically unique. These results have implications for the computational study of disordered materials.

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Exact Lattice Supersymmetry From Topological Field Theory, Simon Catterall Sep 2003

Exact Lattice Supersymmetry From Topological Field Theory, Simon Catterall

Physics - All Scholarship

We discuss the connection between supersymmetric field theories and topological field theories and show how this connection may be used to construct local lattice field theories which maintain an exact supersymmetry. It is shown how metric independence of the continuum topological field theory allows us to derive the lattice theory by blocking out of the continuum in a deformed geometry. This, in turn, allows us to prove the cut-off independence of certain supersymmetric Ward identities.

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Stabilization Of Extra Dimensions At Tree Level, Scott Watson, Robert H. Brandenberger Sep 2003

Stabilization Of Extra Dimensions At Tree Level, Scott Watson, Robert H. Brandenberger

Physics - All Scholarship

By considering the effects of string winding and momentum modes on a time dependent background, we find a method by which six compact dimensions become stabilized naturally at the self-dual radius while three dimensions grow large.

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Nanocomposite (Nd,Dy)(Fe,Co,Nb,B) 5.5/Α-Fe Multilayer Magnets With High Performance, W. Liu, Z.D. Zhang, J. Ping Liu Sep 2003

Nanocomposite (Nd,Dy)(Fe,Co,Nb,B) 5.5/Α-Fe Multilayer Magnets With High Performance, W. Liu, Z.D. Zhang, J. Ping Liu

David Sellmyer Publications

The structural and magnetic properties of rare-earth nanocomposite magnets of a (Nd,Dy)(Fe,Co,Nb,B) 5.5 single layer and a (Nd,Dy)(Fe,Co,Nb,B) 5.5/α-Fe multilayer prepared by sputtering and heat treatment have been investigated. Incomplete exchange coupling behaviour is observed in the Ti-buffered NdDyFeCoNbB + 40 wt%Fe single layer magnet. After annealing, the laminated nanostructure consisting of mutually dispersed soft and hard phases results in remanence enhancement. The optimum magnetic properties of Jr= 1.11 T, μ0i Hc = 0.88 T and (BH)max = 192 kJ m-3 are achieved in the multilayer magnet annealed at 550°C for 30 min. …

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Analysis Of Resonance Structure In The Above-Threshold Ionization Photoelectron Spectra Of Magnesium, Glen D. Gillen, L D. Van Woerkom Sep 2003

Analysis Of Resonance Structure In The Above-Threshold Ionization Photoelectron Spectra Of Magnesium, Glen D. Gillen, L D. Van Woerkom

Physics

Using high-resolution photoelectron spectroscopy and 120-fs, 800-nm Ti:sapphire laser pulses, we observe and analyze intensity-dependent resonant population of specific intermediate excited states of neutral magnesium atoms and their subsequent photoionization in the laser field. Various participating states are identified using angular-momentum selection rules, partial yields, and angular distributions. Several unexpected results are observed and discussed, including peaks that do not correspond to expected resonant processes, and order-to-order variations in the photoelectron spectra.

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Driven Depinning Of Strongly Disordered Media And Anisotropic Mean-Field Limits, M. Christina Marchetti, A. Alan Middleton, Karl Saunders, J. M. Schwarz Sep 2003

Driven Depinning Of Strongly Disordered Media And Anisotropic Mean-Field Limits, M. Christina Marchetti, A. Alan Middleton, Karl Saunders, J. M. Schwarz

Physics

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the drive and slip along at least one of the directions transverse to the motion. In the limit of infinite-range elastic and viscous coupling this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special cases of the generic model.

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Scale Invariance Without Inflation?, Christian Armendariz-Picon, Eugene A. Lim Sep 2003

Scale Invariance Without Inflation?, Christian Armendariz-Picon, Eugene A. Lim

Physics - All Scholarship

We propose a new alternative mechanism to seed a scale invariant spectrum of primordial density perturbations that does not rely on inflation. In our scenario, a perfect fluid dominates the early stages of an expanding, non-inflating universe. Because the speed of sound of the fluid decays, perturbations are left frozen behind the sound horizon, with a spectral index that depends on the fluid equation of state. We explore here a toy model that realizes this idea. Although the model can explain an adiabatic, Gaussian, scale invariant spectrum of primordial perturbations, it turns out that in its simplest form it cannot …

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Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel Sep 2003

Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel

Chemistry Faculty Publications and Presentations

The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above …

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Low-Energy Operators In Effective Theories, C Felline, Nirav P. Mehta, J Piekarewicz, James R. Shepard Sep 2003

Low-Energy Operators In Effective Theories, C Felline, Nirav P. Mehta, J Piekarewicz, James R. Shepard

Physics and Astronomy Faculty Research

Modern effective-theory techniques are applied to the nuclear many-body problem. A novel approach is proposed for the renormalization of operators in a manner consistent with the construction of the effective potential. To test this approach, a one-dimensional, yet realistic, nucleon-nucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective-range expansion and a variety of bare operators are renormalized in a fashion compatible with this construction. Predictions for the expectation values of these effective operators in the ground state reproduce the results of the exact theory with remarkable accuracy (at the 0.5% …

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High Resolution, High Sensitivity Imaging Of The Galactic Center At 330 Mhz, Michael E. Nord, Crystal L. Brogan, Scott D. Hyman, T. Joseph W. Lazio, Namir E. Kassim, Ted N. Larosa, K. Anantharamaiah, Nebojsa Duric Sep 2003

High Resolution, High Sensitivity Imaging Of The Galactic Center At 330 Mhz, Michael E. Nord, Crystal L. Brogan, Scott D. Hyman, T. Joseph W. Lazio, Namir E. Kassim, Ted N. Larosa, K. Anantharamaiah, Nebojsa Duric

Faculty Articles

We present results derived from a wide field, sub-arcminute resolution VLA image of the Galactic Center region at 330 MHz (λ = 90 cm). With a resolution of ∼7″ × 12″ and an rms noise of 1.6 mJy beam−1, this image represents a significant increase in resolution and sensitivity over the previously published VLA image at this frequency (eg. LaRosa et al. 2000). The improvement in sensitivity has significantly increased the census of small diameter sources in the region, resulted in the detection of two new Non-Thermal Filaments (NTFs) and 18 new NTF candidates, and resulted in …

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