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1,528 full-text articles. Page 56 of 60.

The Application Of X-Ray Fluorescence To Assess Proportions Of Fresh Concrete, Ezgi Yurdakul, Peter C. Taylor, Halil Ceylan 2012 Iowa State University

The Application Of X-Ray Fluorescence To Assess Proportions Of Fresh Concrete, Ezgi Yurdakul, Peter C. Taylor, Halil Ceylan

Civil, Construction and Environmental Engineering Conference Presentations and Proceedings

Any transportation infrastructure system is concerned with durability and performance issues. The proportioning and uniformity control of concrete mixtures are critical factors that directly affect the longevity and performance of concrete pavements. Currently, the only means available to monitor mix proportions of any batch are to track batch tickets created at the batch plant. This does not take into account potential errors in loading materials into storage silos, calibration errors, and addition of water after dispatch. Therefore, there is a need for a rapid, cost-effective, and reliable field test that estimates the proportions of as delivered concrete mixtures. In addition ...


Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu 2012 University of Tennessee, Knoxville

Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu

Xiaoshan Xu Papers

Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee' - Ee" = 0.7 eV and Ea'1 - Ee' = 0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea'1 > Ee' > Ee" with slightly underestimated values and a bandgap of 1.35 eV.


Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu 2012 University of Tennessee

Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu

Xiaoshan Xu Papers

Agrowth diagram of Lu-Fe-O compounds on MgO (111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe2O4 film and is explained in terms of the effect of the impurity hexagonal LuFeO3 (h-LuFeO3) phase and structural defects.


The Morphotropic Phase Boundary In The (1-X)Pbzro3–X[0.3bi(Zn1/2ti1/2)O3–0.7pbtio3] Perovskite Solid Solution, T. Sareein, W. Hu, Xiaoli Tan, R. Yimnirun 2012 Chiang Mai University

The Morphotropic Phase Boundary In The (1-X)Pbzro3–X[0.3bi(Zn1/2ti1/2)O3–0.7pbtio3] Perovskite Solid Solution, T. Sareein, W. Hu, Xiaoli Tan, R. Yimnirun

Materials Science and Engineering Publications

Ceramics in the (1-x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] solid solution system with 0.48  x  0.56 were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal perovskite phases was identified at x = 0.52. This composition displays the maximum remanent polarization Pr of 40.7 μC/cm2 and the best piezoelectric coefficient d33 of 311 pC/N in the pseudo-binary system. However, the Curie temperature Tc for this MPB composition is 291 °C, much lower than initially expected.


Where Is The Best Place To Sit On A Roller Coaster? Forces, Physics, And Fun At Disneyland, Kelsey Lubetich 2012 Scripps College

Where Is The Best Place To Sit On A Roller Coaster? Forces, Physics, And Fun At Disneyland, Kelsey Lubetich

Scripps Senior Theses

The work presented in this thesis was undertaken to quantitatively determine the best place to sit on a roller coaster. Maximizing the time spent feeling weightless and the highest value of negative Z acceleration were used as criteria for the best seat. Acceleration values were measured on the California Screamin' roller coaster at Disney California Adventure Park using an iPhone and an application to record data from its accelerometers. After analyzing acceleration data, it was determined that the front row had the greatest negative acceleration in the z direction and was therefore the "best place" to sit.


Contamination Effects On Fixed-Bias Langmuir Probes, C.T. Steigies, Aroh Barjatya 2012 Embry-Riddle Aeronautical University

Contamination Effects On Fixed-Bias Langmuir Probes, C.T. Steigies, Aroh Barjatya

Publications

Langmuir probes are standard instruments for plasma density measurements on many sounding rockets. These probes can be operated in swept-bias as well as in fixed-bias modes. In swept-bias Langmuir probes, contamination effects are frequently visible as a hysteresis between consecutive up and down voltage ramps. This hysteresis, if not corrected, leads to poorly determined plasma densities and temperatures. With a properly chosen sweep function, the contamination parameters can be determinedfromthemeasurementsandcorrectplasmaparameterscanthenbedetermined.Inthispaper, we study the contamination effects on fixed-bias Langmuir probes, where no hysteresis type effect is seen in the data. Even though the contamination is not evident from the measurements ...


Multipacting Analysis Of High-Velocity Superconducting Spoke Resonators, C. S. Hopper, J. R. Delayen 2012 Old Dominion University

Multipacting Analysis Of High-Velocity Superconducting Spoke Resonators, C. S. Hopper, J. R. Delayen

Physics Faculty Publications

Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.


Superconducting Spoke Cavities For Electron And High-Velocity Proton Linacs, J. R. Delayen 2012 Old Dominion University

Superconducting Spoke Cavities For Electron And High-Velocity Proton Linacs, J. R. Delayen

Physics Faculty Publications

Spoke resonantors are currently under development for many proton machines but these structures are also considered for high beta electron linacs as well. These structures compare well to traditional elliptical cavities.


Hydrogen Production From Biogas By Oxy-Reforming: Reaction System Analysis, Aleksandra Terlecka, Wojciech M. Budzianowski 2011 Wroclaw University of Technology

Hydrogen Production From Biogas By Oxy-Reforming: Reaction System Analysis, Aleksandra Terlecka, Wojciech M. Budzianowski

Wojciech Budzianowski

Oxy-reforming is emerging as an interesting alternative to conventional methods of hydrogen generation. The current article characterises this process through analysis of individual reactions: SMR (steam methane reforming), WGS (water gas shift) and CPO (catalytic partial oxidation). Analyses relate to optimisation of thermal conditions thus enabling cost-effectivenes of the process.


Characterization And Discrimination Of Large Caliber Gun Blast And Flash Signatures, Bryan J. Steward 2011 Air Force Institute of Technology

Characterization And Discrimination Of Large Caliber Gun Blast And Flash Signatures, Bryan J. Steward

Theses and Dissertations

Two hundred and one firings of three 152 mm howitzer munitions were observed to characterize firing signatures of a large caliber gun. Muzzle blast expansion was observed with high-speed (1600 Hz) optical imagery. The trajectory of the blast front was well approximated by a modified point-blast model described by constant rate of energy deposition. Visible and near-infrared (450 - 850 nm) spectra of secondary combustion were acquired at 0.75 nm spectral resolution and depict strong contaminant emissions including Li, Na, K, Cu, and Ca. The O2 (X-b) absorption band is evident in the blue wing of the potassium D lines ...


Statistical Spectral Parameter Estimation Of Acoustic Signals With Applications To Byzantine Music, Kyriakos Michael Tsiappoutas 2011 University of New Orleans

Statistical Spectral Parameter Estimation Of Acoustic Signals With Applications To Byzantine Music, Kyriakos Michael Tsiappoutas

University of New Orleans Theses and Dissertations

Digitized acoustical signals of Byzantine music performed by Iakovos Nafpliotis are used to extract the fundamental frequency of each note of the diatonic scale. These empirical results are then contrasted to the theoretical suggestions and previous empirical findings. Several parametric and non-parametric spectral parameter estimation methods are implemented. These include: (1) Phase vocoder method, (2) McAulay-Quatieri method, (3) Levinson-Durbin algorithm,(4) YIN, (5) Quinn & Fernandes Estimator, (6) Pisarenko Frequency Estimator, (7) MUltiple SIgnal Characterization (MUSIC) algorithm, (8) Periodogram method, (9) Quinn & Fernandes Filtered Periodogram, (10) Rife & Vincent Estimator, and (11) the Fourier transform. Algorithm performance was very precise. The psychophysical ...


Lectio Praecursoria, Kari Myöhänen 2011 Lappeenranta University of Technology

Lectio Praecursoria, Kari Myöhänen

Kari Myöhänen

Lectio praecursoria: Modelling of combustion and sorbent reactions in three-dimensional flow environment of a circulating fluidized bed furnace


Spatially Resolved Distribution Function And The Medium-Range Order In Metallic Liquid And Glass, X. W. Fang, Cai-Zhuang Wang, S. G. Hao, Matthew J. Kramer, Yongxin Yao, Mikhail I. Mendelev, Z. J. Ding, Ralph E. Napolitano, Kai-Ming Ho 2011 Iowa State University

Spatially Resolved Distribution Function And The Medium-Range Order In Metallic Liquid And Glass, X. W. Fang, Cai-Zhuang Wang, S. G. Hao, Matthew J. Kramer, Yongxin Yao, Mikhail I. Mendelev, Z. J. Ding, Ralph E. Napolitano, Kai-Ming Ho

Materials Science and Engineering Publications

The structural description of disordered systems has been a longstanding challenge in physical science. We propose an atomic cluster alignment method to reveal the development of three-dimensional topological ordering in a metallic liquid as it undercools to form a glass. By analyzing molecular dynamic (MD) simulation trajectories of a Cu64.5Zr35.5 alloy, we show that medium-range order (MRO) develops in the liquid as it approaches the glass transition. Specifically, around Cu sites, we observe “Bergman triacontahedron” packing (icosahedron, dodecahedron and icosahedron) that extends out to the fourth shell, forming an interpenetrating backbone network in the glass. The discovery of ...


Accurate And Fast Numerical Solution Of Poisson's Equation For Arbitrary, Space-Filling Voronoi Polyhedra: Near-Field Corrections Revisited, Aftab Alam, Brian G. Wilson, Duane D. Johnson 2011 Ames Laboratory

Accurate And Fast Numerical Solution Of Poisson's Equation For Arbitrary, Space-Filling Voronoi Polyhedra: Near-Field Corrections Revisited, Aftab Alam, Brian G. Wilson, Duane D. Johnson

Ames Laboratory Publications

We present an accurate and rapid solution of Poisson's equation for space-filling, arbitrarily shaped, convex Voronoi polyhedra (VP); the method is O(NVP), where NVP is the number of distinct VP representing the system. In effect, we resolve the long-standing problem of fast but accurate numerical solution of the near-field corrections, contributions to the potential due to near VP—typically those involving multipole-type conditionally convergent sums, or use of fast Fourier transforms. Our method avoids all ill-convergent sums, is simple, accurate, efficient, and works generally, i.e., for periodic solids, molecules, or systems with disorder or imperfections. We demonstrate ...


Chemically Mediated Quantum Criticality In Nbfe2, Aftab Alam, Duane D. Johnson 2011 Ames Laboratory

Chemically Mediated Quantum Criticality In Nbfe2, Aftab Alam, Duane D. Johnson

Ames Laboratory Publications

Laves-phase Nb1+cFe2−c is a rare itinerant intermetallic compound exhibiting magnetic quantum criticality at ccr∼1.5%Nb excess; its origin, and how alloying mediates it, remains an enigma. For NbFe2, we show that an unconventional band critical point above the Fermi level EF explains most observations and that chemical alloying mediates access to this unconventional band critical point by an increase in EF with decreasing electrons (increasing %Nb), counter to rigid-band concepts. We calculate that EF enters the unconventional band critical point region for ccr>1.5%Nb and by 1.74%Nb there is no Nb site-occupation ...


Effect Of Storm Enhanced Densities On Geo-Location Accuracy Over Conus, Lindon H. Steadman 2011 Air Force Institute of Technology

Effect Of Storm Enhanced Densities On Geo-Location Accuracy Over Conus, Lindon H. Steadman

Theses and Dissertations

Storm enhanced densities (SEDs) are ionospheric plasma enhancements that disrupt radio communications in the near-Earth space environment, degrading the Global Positioning System (GPS) and other key technologies. Accurate GPS/total electron content (TEC) correction maps produced by ionosphere models can mitigate degradations from SEDs. An artificial SED was created and ingested via slant TEC measurements into the Global Assimilation of Ionospheric Measurements Gauss-Markov Kalman Filter Model to determine how many ground GPS receivers are needed to produce reliable GPS/TEC correction maps over the continental United States during geomagnetic storming. It was found that 110 well-positioned GPS receivers produced the ...


Synthesis, Field Emission And Associated Degradation Mechanisms Of Tapered Zno Nanorods, Gregory M. Wrobel Mr. 2011 University of Connecticut

Synthesis, Field Emission And Associated Degradation Mechanisms Of Tapered Zno Nanorods, Gregory M. Wrobel Mr.

Master's Theses

Equation 1..... 4

Equation 2..... 4

Equation 3..... 6

Equation 4..... 7

Equation 5..... 9

Equation 6..... 10

Equation 7..... 11

Equation 8..... 12

Equation 9..... 14

Equation 10..... 40

Equation 11..... 51

Synthesis, Field Emission and Associated Degradation Mechanisms of Tapered ZnO Nanorods

Gregory Michael Wrobel, M.S.

University of Connecticut, 2011

Modern development of field emitter arrays (FEA) has been made possible, partly thanks to the synthesis and development of one-dimensional (1D) nanostructures. High aspect ratio 1D nanostructures effectively amplify the electric field at the emitter tips, allowing electrons to be extracted at relatively low electric field. An ...


Ionic Alkalihalides As Pressure Media In Dac Experiments, Julius Monello 2011 Reed College

Ionic Alkalihalides As Pressure Media In Dac Experiments, Julius Monello

Undergraduate Research Opportunities Program (UROP)

In Diamond Anvil Cells (DACs), usually a pressure transmitting medium functions to transform the uniaxial pressure supplied by the opposing diamond anvils into uniform hydrostatic pressure acting on the sample. Conventionally, a 4-1 methanol-ethanol solution, or a 16-3-1 methanol-ethanol-water solution is used as pressure transmitting medium. However, these two solutions transform into a glass with high elastic shear strength at pressures around 12-14 GPa and no longer function as hydrostatic medium. Our goal was to determine if liquid ionic alkalihalide alkanolate complexes will provide more uniform pressure in the cell up to 20 GPa. Ruby (Cr-doped AlP,) produces two Cr ...


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 ...


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