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Domain Size And Structure In Exchange Coupled [Co/Pt]/Nio/[Co/Pt] Multilayers, Andrew G. Baruth, Shireen Adenwalla 2011 University of Nebraska-Lincoln

Domain Size And Structure In Exchange Coupled [Co/Pt]/Nio/[Co/Pt] Multilayers, Andrew G. Baruth, Shireen Adenwalla

Shireen Adenwalla Papers

We investigate the competing effects of interlayer exchange coupling and magnetostatic coupling in the magnetic heterostructure ([Co/Pt]/NiO/[Co/Pt]) with perpendicular magnetic anisotropy (PMA). This particular heterostructure is unique among coupled materials with PMA in directly exhibiting both ferromagnetic and antiferromagnetic coupling, oscillating between the two as a function of spacer layer thickness. By systematically tuning the coupling interactions via a wedge-shaped NiO spacer layer, we explore the energetics that dictate magnetic domain formation using high resolution magnetic force microscopy coupled with the magneto-optical Kerr effect. This technique probes the microscopic and macroscopic magnetic behavior as a continuous ...


Assessing Laser Lifetime Test Performance, Joe Weichman, Hamid Hemmati, Malcolm Wright 2011 California State University - Los Angeles

Assessing Laser Lifetime Test Performance, Joe Weichman, Hamid Hemmati, Malcolm Wright

STAR Program Research Presentations

Assessing expected component lifetime is necessary in developing instruments for future space-flight projects to ensure long term operation in the challenging environment. Although semiconductor diode lasers have widespread use in terrestrial applications, their use in space is still an emerging technology that requires on-going testing to demonstrate their capability. The project called for re-establishing the test setup for assessing lifetime performance of 20 continuously running 200mW 830 nm diode lasers. These lasers underwent previous testing based on parameters for NuSTAR’s laser metrology system, and met the six month lifetime project requirements under nominal operating conditions. Laser testing is currently ...


Phase-Field Investigation Of Rod Eutectic Morphologies Under Geometrical Confinement, Melis Şerefoğlu, Ralph E. Napolitano, Mathis Plapp 2011 Iowa State University

Phase-Field Investigation Of Rod Eutectic Morphologies Under Geometrical Confinement, Melis Şerefoğlu, Ralph E. Napolitano, Mathis Plapp

Materials Science and Engineering Publications

Three-dimensional phase-field simulations are employed to investigate rod-type eutectic growth morphologies in confined geometry. Distinct steady-state solutions are found to depend on this confinement effect with the rod array basis vectors and their included angle (α) changing to accommodate the geometrical constraint. Specific morphologies are observed, including rods of circular cross sections, rods of distorted (elliptical) cross sections, rods of peanut-shaped cross-sections, and lamellar structures. The results show that, for a fixed value of α>10∘, the usual (triangular) arrays of circular rods are stable in a broad range of spacings, with a transition to the peanut-shaped cross sectioned rods ...


Efficient Isoparametric Integration Over Arbitrary Space-Filling Voronoi Polyhedra For Electronic Structure Calculations, Aftab Alam, Suffian N. Khan, Brian G. Wilson, Duane D. Johnson 2011 University of Illinois at Urbana-Champaign

Efficient Isoparametric Integration Over Arbitrary Space-Filling Voronoi Polyhedra For Electronic Structure Calculations, Aftab Alam, Suffian N. Khan, Brian G. Wilson, Duane D. Johnson

Ames Laboratory Publications

A numerically efficient, accurate, and easily implemented integration scheme over convex Voronoi polyhedra (VP) is presented for use in ab initio electronic-structure calculations. We combine a weighted Voronoi tessellation with isoparametric integration via Gauss-Legendre quadratures to provide rapidly convergent VP integrals for a variety of integrands, including those with a Coulomb singularity. We showcase the capability of our approach by first applying it to an analytic charge-density model achieving machine-precision accuracy with expected convergence properties in milliseconds. For contrast, we compare our results to those using shape-functions and show our approach is greater than 105 times faster and 107 times ...


Variable Renewable Energy In Modeling Climate Change Mitigation Scenarios, Falko Ueckerdt, Robert J. Brecha, Gunnar Luderer, Patrick Sullivan, Eva Schmid, Nico Bauer, Diana Böttger 2011 Potsdam Institute for Climate Impact Research

Variable Renewable Energy In Modeling Climate Change Mitigation Scenarios, Falko Ueckerdt, Robert J. Brecha, Gunnar Luderer, Patrick Sullivan, Eva Schmid, Nico Bauer, Diana Böttger

Physics Faculty Publications

This paper addresses the issue of how to account for short‐term temporal variability of renewable energy sources and power demand in long‐term climate change mitigation scenarios in energy‐economic models. An approach that captures in a stylized way the major challenges to the integration of variable renewable energy sources into power systems has been developed. As a first application this approach has been introduced to REMIND‐D, a hybrid energy‐economy model of Germany. An approximation of the residual load duration curve is implemented. The approximating function endogenously changes depending on the penetration and mix of variable renewable ...


Applications Of Local Fractional Calculus To Engineering In Fractal Time-Space: Local Fractional Differential Equations With Local Fractional Derivative, Yang Xiao-Jun 2011 China University of Mining & Technology

Applications Of Local Fractional Calculus To Engineering In Fractal Time-Space: Local Fractional Differential Equations With Local Fractional Derivative, Yang Xiao-Jun

Xiao-Jun Yang

This paper presents a better approach to model an engineering problem in fractal-time space based on local fractional calculus. Some examples are given to elucidate to establish governing equations with local fractional derivative.


A Short Introduction To Local Fractional Complex Analysis, Yang Xiao-Jun 2011 China University of Mining & Technology

A Short Introduction To Local Fractional Complex Analysis, Yang Xiao-Jun

Xiao-Jun Yang

This paper presents a short introduction to local fractional complex analysis. The generalized local fractional complex integral formulas, Yang-Taylor series and local fractional Laurent’s series of complex functions in complex fractal space, and generalized residue theorems are investigated.


Quantifying Multiple Types Of Damping Acting On Bronze-Wound Guitar Strings, Jonathan Christian 2011 Purdue University

Quantifying Multiple Types Of Damping Acting On Bronze-Wound Guitar Strings, Jonathan Christian

Purdue Polytechnic Masters Theses

The goal of this study was to quantify the contributions of multiple damping types acting on guitar strings for each mode over a wide frequency range so that design variables could be identified to one day create frequency based damping in guitar strings. Structural dynamic testing was used to obtain the time-response of a vibrating string in open air and in a vacuum. From this signal, each harmonic was filtered and the decay envelope was curve-fitted with a function that was a linear summation of decay functions. From the curve-fits, the damping coefficients for aerodynamic, friction, and material damping were ...


Ternary Tetradymite Compounds As Topological Insulators, Lin-Lin Wang, Duane D. Johnson 2011 Ames Laboratory

Ternary Tetradymite Compounds As Topological Insulators, Lin-Lin Wang, Duane D. Johnson

Ames Laboratory Publications

Ternary tetradymites Bi2Te2S, Bi2Te2Se, and Bi2Se2Te are found to be stable, bulk topological insulators via theory, showing band inversion between group V and VI pz orbitals. We identify Bi2Se2Te as a good candidate to study massive Dirac fermions, with a (111) cleavage-surface-derived Dirac point (DP) isolated in the bulk-band gap at the Fermi energy (Ef)-like Bi2Se3 but with a spin texture alterable by layer chemistry. In contrast, Bi2Te2S and Bi2Te2Se (111) behave like Bi2Te3, with a DP below Ef buried in bulk bands. Bi2Te2S offers large bulk resistivity needed for devices.


Fractional Trigonometric Functions In Complex-Valued Space: Applications Of Complex Number To Local Fractional Calculus Of Complex Function, Yang Xiao-Jun 2011 China University of Mining & Technology

Fractional Trigonometric Functions In Complex-Valued Space: Applications Of Complex Number To Local Fractional Calculus Of Complex Function, Yang Xiao-Jun

Xiao-Jun Yang

This paper presents the fractional trigonometric functions in complex-valued space and proposes a short outline of local fractional calculus of complex function in fractal spaces.


A New Viewpoint To The Discrete Approximation: Discrete Yang-Fourier Transforms Of Discrete-Time Fractal Signal, Yang Xiao-Jun 2011 China University of Mining & Technology

A New Viewpoint To The Discrete Approximation: Discrete Yang-Fourier Transforms Of Discrete-Time Fractal Signal, Yang Xiao-Jun

Xiao-Jun Yang

It is suggest that a new fractal model for the Yang-Fourier transforms of discrete approximation based on local fractional calculus and the Discrete Yang-Fourier transforms are investigated in detail.


Logistic Curves, Extraction Costs And The Effective Size Of Oil Resources, Robert J. Brecha 2011 University of Dayton

Logistic Curves, Extraction Costs And The Effective Size Of Oil Resources, Robert J. Brecha

Physics Faculty Publications

The size of potential fossil fuel resources is an issue of perennial interest and controversy. Fundamentally, there appears to be a conflict in interpretation of available data for both past and future extraction histories. As fossil-fuel prices rose dramatically over the past several years, the question of resources once again became acute. In this paper we concentrate on conventional and non-conventional oil resources and make four main points, with the overarching theme that one can determine an effective oil resource that represents significantly less availability for consumption than usually posited by tallying resources in place.

First, looking at oil production ...


Ferrofluids, James Patt 2011 California Polytechnic State University - San Luis Obispo

Ferrofluids, James Patt

Physics

Ferrofluids are truly fascinating. Technologically savvy artists have been able to capture the human imagination with little but a judicious application of a magnetic field. The substance seems to defy gravity, flowing and shaping itself seemingly like magic (see Figure 1). The true magic, however, is the vast range of properties that this intrinsically simple substance can exhibit. It can vary its viscosity given the strength of the magnetic field. It can draw heat away from an over worked mechanical component. It can even split a beam of light in two. It’s hard to imagine what kind of strange ...


Fabry-Perot Observations Of Midlatitude Neutral Winds And Atmospheric Gravity Wave Activity, Marjory Anne Katon 2011 Embry-Riddle Aeronautical University - Daytona Beach

Fabry-Perot Observations Of Midlatitude Neutral Winds And Atmospheric Gravity Wave Activity, Marjory Anne Katon

PhD Dissertations and Master's Theses

The mesosphere and lower thermosphere displays a wide range of dynamical phenomena resulting in a complex and variable regions. Governed primarily by fluid dynamics, the motion of the upper atmosphere is modulated by a number of atmospheric waves propagating upward from various sources in the lower atmosphere. Among these are atmospheric gravity waves which have been recognized as a major source of momentum and energy in the mesosphere and lower thermosphere as well as a major factor in the dynamic coupling between the troposphere and lower thermosphere. A Fabry-Perot interferometer possessed by the Space Physics Research Laboratory at the Embry-Riddle ...


Prioritizing Investment In Residential Energy Efficiency And Renewable Energy: A Case Study For The U.S. Midwest, Robert J. Brecha, Austin Mitchell, Kevin P. Hallinan, J. Kelly Kissock 2011 University of Dayton

Prioritizing Investment In Residential Energy Efficiency And Renewable Energy: A Case Study For The U.S. Midwest, Robert J. Brecha, Austin Mitchell, Kevin P. Hallinan, J. Kelly Kissock

Physics Faculty Publications

Residential building energy use is an important contributor to greenhouse gas emissions and in the United States represents about 20% of total energy consumption. A number of previous macro-scale studies of residential energy consumption and energy-efficiency improvements are mainly concerned with national or international aggregate potential savings. In this paper we look into the details of how a collection of specific homes in one region might reduce energy consumption and carbon emissions, with particular attention given to some practical limits to what can be achieved by upgrading the existing residential building stock. Using a simple model of residential, single-family home ...


Computational Study Of Carbon Nanotubes Under Strain, Jeremy Feliciano, William Wolfs 2011 University of Nevada, Las Vegas

Computational Study Of Carbon Nanotubes Under Strain, Jeremy Feliciano, William Wolfs

Festival of Communities: UG Symposium (Posters)

We perform computational studies of carbon nanotubes (CNTs) using molecular dynamics simulations to examine the behavior of single-walled (SW) and multiwalled (MW) CNTs under large compressive and bending strains. We study the effects of defects, heating and chirality on their properties. Research on CNTs holds great promise for developing new advanced materials in applications ranging from high-strength composites to next-generation electronics.


Aspect Ratio Dependent Buckling Mode Transition In Single-Walled Carbon Nanotubes Under Compression, Jeremy Feliciano 2011 University of Nevada, Las Vegas

Aspect Ratio Dependent Buckling Mode Transition In Single-Walled Carbon Nanotubes Under Compression, Jeremy Feliciano

Festival of Communities: UG Symposium (Posters)

Using molecular dynamics simulations, we study axial compressive behavior of single-walled carbon nanotubes (SWCNTs) with a wide range of aspect ratios (length to diameter ratio). It is shown that the difference in aspect ratio leads to distinct buckling modes in SWCNTs. Small-aspect-ratio SWCNTs primarily exhibit shell buckling; they switch to column buckling mode with increasing aspect ratio. Further compression of the already column buckled large-aspect-ratio SWCNTs results in a shell buckling. This shell buckling mode is distinct from that of small-aspect-ratio SWCNTs in that it originates from the column buckling induced bending deformation.


Topologically Correct Phase Boundaries And Transition Temperatures For Ising Hamiltonians Via Self-Consistent Coarse-Grained Cluster-Lattice Models, Teck L. Tan, Duane D. Johnson 2011 University of Illinois at Urbana-Champaign

Topologically Correct Phase Boundaries And Transition Temperatures For Ising Hamiltonians Via Self-Consistent Coarse-Grained Cluster-Lattice Models, Teck L. Tan, Duane D. Johnson

Ames Laboratory Publications

We derive a cluster mean-field theory for an Ising Hamiltonian using a cluster-lattice Fourier transform with a cluster of size Nc and a coarse-grained (CG) lattice into cells of size Ncell. We explore forms with Ncell⩾Nc, including a non-CG (NCG) version with Ncell→∞. For Nc=Ncell, the set of static, self-consistent equations relating cluster and CG lattice correlations is analogous to that in dynamical cluster approximation and cellular dynamical mean-field theory used in correlated electron physics. A variational Nc-site cluster grand potential based on Nc=Ncell CG lattice maintains thermodynamic consistency and improves predictions, recovering Monte Carlo and series ...


Sensitivity Analysis Of Empirical Parameters In The Ionosphere-Plasmasphere Model, Janelle V. Jenniges 2011 Air Force Institute of Technology

Sensitivity Analysis Of Empirical Parameters In The Ionosphere-Plasmasphere Model, Janelle V. Jenniges

Theses and Dissertations

A sensitivity analysis of empirical parameters used in physics-based models was completed in this study to determine their effect on electron densities and total electron content (TEC) in the ionosphere. The model used was the Ionosphere-Plasmasphere Model (IPM) developed by Utah State University. The empirical parameters studied include the O+/O collision frequency, zonal wind, secondary electron production, nighttime ExB drifts, and tidal structure. The sensitivity analysis was completed by comparing a default run of the IPM to a run with the parameter adjusted for three geophysical cases. Many of the comparisons resulted in nonlinear changes to the model output ...


Integration Of A Worldwide Atmospheric Based Model With A Live Virtual Constructive Simulation Environment, David B. Simmons 2011 Air Force Institute of Technology

Integration Of A Worldwide Atmospheric Based Model With A Live Virtual Constructive Simulation Environment, David B. Simmons

Theses and Dissertations

Yearly DoD spends millions of dollars on Modeling and Simulation tools in order to accomplish two fundamental tasks: make better decisions and develop better skills. Simulators that are based on realistic models enable the USAF to properly train, educate, and employ military forces. LEEDR is an atmospheric model based on worldwide historic weather data that is able to predict the extinction, absorption, and scattering of radiation across a broad range of the electromagnetic spectrum. Through this study LEEDR models the propagation of 1.0642 micron laser radiation at worldwide locations and through various environmental conditions. This modeled laser transmission output ...


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